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EX_03_RS_Storm Retrofit Study
Page 1 MEMORANDUM TO: Ken Srilofung, PE, CIP Project Manager FROM: Mike Giseburt, PE, WSP Project Manager SUBJECT: Stormwater Facility Retrofit Study – Existing Conditions Summary DATE: February 12, 2021 INTRODUCTION AND BACKGROUND The City of Renton (City) owns and maintains over 400 stormwater facilities constructed as far back as the 1970s to mitigate for the stormwater impacts of urbanization. Between the 1970s and early 1990s, stormwater facilities were primarily focused on providing stormwater storage (i.e., detention). Since the 1990s, design standards have advanced so that today’s stormwater facilities provide better water quality treatment to mitigate the detrimental impacts of stormwater pollutants on stream water quality and aquatic habitat. These newer stormwater treatment systems target the removal of suspended solids, dissolved heavy metals, nutrients, and petroleum hydrocarbons. Typically, stormwater facilities owned by City connect to the municipal storm sewer system and drain to the closest water body. Taken as a whole, the older facilities in the City’s system are much less effective at protecting stream resources and water quality from pollutants than if the facilities included features required by today’s standards. The City received a grant from the Washington State Department of Ecology (WSDOE) to perform a study of many of the existing flow control facilities that have little or no water quality treatment features. The overarching goal is to improve the water quality in multiple creeks within the City that are part of the Cedar River/Lake Washington and Duwamish/Green watersheds. The study entails a series of six sequential analytical tasks to be undertaken to prioritize the sites with the greatest potential to improve water quality. The first task, Task 1, was to select the existing facilities for evaluation: • Existing Facilities Selection (Task 1) –City staff selected forty-nine (49) existing flow control facilities for this study primarily based on their understanding that these particular existing facilities provide minimal water quality treatment (see Figure 1). The second task, Task 2, is this memorandum prepared by the WSP Team which includes: • Existing Conditions Summary (Task 2) -- This effort included collecting information about the 49 selected existing facilities. The summarized data includes: BMP type (stormwater best management practices are often referred to as “BMPs” in this memorandum), size, and age; tributary area characteristics; drainage basin information; and tracking of other information, which helps characterize existing facility information Entire Document Available Upon Request RECEIVED 02/08/2022 JDing PLANNING DIVISION DocuSign Envelope ID: AA732A77-1AE9-4064-B9A8-5210DA54C2A0 Stormwater Facility Retrofit Study – Existing Conditions Summary Page 2 and can be used in future tasks to evaluate stormwater treatment performance and site-specific opportunities. Figure 1. Site Map Stormwater Facility Retrofit Study – Existing Conditions Summary Page 3 These next tasks that are part of the study and will each be documented in subsequent technical memoranda include: • Treatment Gap Analysis (Task 3) -- This effort will identify deficiencies (gaps) in the treatment of stormwater at the facilities. This analysis will consider the needed treatment in comparison with treatment that would be provided using today’s stormwater design standards. • Retrofit Type and Opportunity Identification (Task 4) – This effort will build upon the treatment gap analysis to assess the types of opportunities available and the feasibility of retrofitting facilities to improve treatment performance. This develop a preliminary suite of BMP types and sizes for each site. • Retrofit Opportunity Scoring and Prioritization (Task 5) – This effort will include develop a method to screen retrofit opportunities to create a ranked list that focuses on the (a) highest benefit of water quality improvement and (b) most effective opportunities. • Conceptual Design of Highest Priority Sites (Task 6) – This effort will include the development of concept designs and cost estimates for the top three prioritized retrofit sites. EXISTING CONDITIONS CHARACTERIZATION PROCEDURE A procedure was developed to assess what data was available and what important information the study would require in order to analyze and compare the 49 City selected facilities. The initial steps to characterize existing conditions included: • WSP obtained City GIS spatial, attribute, and metadata files on the existing facilities. • Where available, City as-builts and Technical Information Report (TIRs) on the existing facilities were obtained. TIRs are the technical engineering reports that project proponents submit to the City for approvals, such as a land development approval, and they typically provide the basis of design for a site’s stormwater facilities. • This information was reviewed to confirm that GIS data and City’s As-builts/TIRs were reasonably consistent, and then a two-part assessment was conducted: − First, the tributary basin associated with each facility was delineated, largely based on as-built and TIR data and supplemented by the storm sewer/ditch network in the City GIS data. − Once delineated, GIS data was analyzed at each of the individual tributary basin to characterize land cover, land use, natural resources, and sensitive areas associated with the basin. Existing BMP Characterization A tracking worksheet was developed with both information obtained from as-builts, TIRs and other data provided by the City (see Attachment A). Table 1 summarizes the key information on the tracking worksheet including a brief description of why the data is relevant to identify the sites with the greatest relative water quality treatment needs and opportunities. Stormwater Facility Retrofit Study – Existing Conditions Summary Page 4 Table 1. Key Existing Flow Control Facility Attributes Data Group Data Relevance of Data Facility Features Type of flow control facility (detention vault, tank, or pond) Live storage volume (ft3) – from City data and/or checked with as-builts Can be used (a) to estimate flow control standard used, (b) to calculate storage volume per acre, and (c) to estimate relative drainage basin (in conjunction with delineated basin areas) Water quality BMP (Y/N) and type Presence or absence of existing water quality BMP & if present, type of BMP Pond liner (Y/N) Indicates potential issue with infiltration at site such as (a) groundwater protection requirements, (b) native soils with too rapid of an infiltration rate, or (c) relatively high groundwater level Approximate year of construction An indication of what design standard likely was used Opportunity Screening Adjacent open (non-developed) land to BMP Adjacent land available affords possible opportunities for BMPs for retrofitting Infiltration capacity of site soils – if available from TIR then design infiltration rate may be useful (otherwise, study to rely on soils mapping data) Information relevant to applicability of low impact development (LID) or infiltration BMPs for retrofitting Property ownership or agreements related to parcel with BMP (e.g., City street ROW vs property easement vs other ownership) Possible constraints or opportunities due to shared ownership or other signed agreements Natural Resource Context Stream basin Understanding of other stormwater issues such as flooding, water quality, and other activities in the basin such as through the City’s Comprehensive Stormwater Plan currently under development Receiving body Identifying the segment of the named receiving body to which the facility discharges to be able to investigate impairments known by WSDOE or City. Tributary Basin Delineation A key step in reviewing and assimilating the existing data was to delineate the tributary drainage basin/catchment for each of the 49 facilities. This delineation allows for spatial analysis to determine the total basin acreage and characterize the composition of each basin. Geo-processing tools can then spatially assess overlapping characteristics within a basin (for instance, grassy steep slopes overlying Type C soils for hydrologic modeling) as well as identify any critical or other regulated areas (for instance, does the basin area intersect with wellhead protection or steep slope areas). The existing data sources (TIRs, as-builts, and GIS) were used to develop a GIS data layer that contained the tributary drainage basin to each of the existing flow control facilities. The following outlines the general process and assumptions of the delineation work: • For each existing facility, the tributary basin within the area of the development was defined based on as- builts. The TIRs, where available, provided additional references on the basin size which helped to refine Stormwater Facility Retrofit Study – Existing Conditions Summary Page 5 and confirm the delineation. All 49 facilities had drainage as-builts and 9 facilities also had associated TIRs. • Tributary basins extending beyond the area covered by the as-built drawings were adjusted using a combination of 2-foot contour data, GIS drainage features from the City’s database (storm sewers and ditches), and roadway limits. • Unless there was a clear break in grade, full parcel (i.e., all of the property within a parcel boundary including impervious and pervious areas) was included in the delineation when plans showed the property had a connection to the storm sewer draining to the facilities. Engineering judgement was used as needed to resolve information inconsistencies. For example, in some cases, GIS pipe data conflicted with the existing project records. In other cases, new construction since the installation of the flow control facility appeared to have altered flow paths shown in a TIR basin map. Digital tools, such as Google Street View, along with documentation from WSP’s prior project work in Renton were used to resolve conflicts or discrepancies. The details associated with these discrepancies are discussed in the Data Gap Resolution section of this memorandum. Tributary Basin Characteristics The following spatial data layers were manipulated to evaluate tributary basin information in a useful format for decision-making and later analyses: Soils by hydrologic soil group (HSG): This is a USDA based soil classification that is used in Washington State for hydrologic stormwater modeling. For this study, soils were assigned to one of seven groups (A, B, C, D, A/D, B/D, and C/D). Soils identified as Type A or Type B were categorized as highly feasible for infiltration. All other soils groups were assumed to have limited infiltration potential. The characteristics of these groups are described as follows: • Group A. Soils having a high infiltration rate (low runoff potential) when thoroughly wet. These consist mainly of deep, well drained to excessively drained sands or gravelly sands. These soils have a high rate of water transmission/infiltration. • Group B. Soils having a moderate infiltration rate when thoroughly wet. These consist chiefly of moderately deep or deep, moderately well drained or well drained soils that have moderately fine texture to moderately coarse texture. These soils have a moderate rate of water transmission/infiltration. • Group C. Soils having a slow infiltration rate when thoroughly wet. These consist chiefly of soils having a layer that impedes the downward movement of water or soils of moderately fine texture or fine texture. These soils have a slow rate of water transmission/infiltration. • Group D. Soils having a very slow infiltration rate (high runoff potential) when thoroughly wet. These consist chiefly of clays that have a high shrink-swell potential, soils that have a high water table, soils that have a claypan or clay layer at or near the surface, and soils that are shallow over nearly impervious material. These soils have a very slow rate of water transmission/infiltration. Stormwater Facility Retrofit Study – Existing Conditions Summary Page 6 If a soil is assigned to a dual hydrologic group (A/D, B/D, or C/D), the first letter is for drained areas and the second is for undrained areas. Only the soils that in their natural (undrained) condition are in group D are assigned to dual classes. Land Slopes in Excess of 15%: This layer was developed from the digital elevation model information available for the study area. It compares reasonably well to the City’s critical area mapping for steep slopes. The “15% land slope” threshold was selected based on the City’s critical area regulations which define: • Slopes of 15% or less as a low landslide hazard. • Slopes of 15% or less as a low erosion hazard area. • Slope of 25% or less as non-sensitive slopes. Wellhead Protection Areas: The current City maps available at the time of this study, included wellhead protection areas and wellfield capture zones. It was recommended by the City that the wellhead protection area zones be used for initial site screening sites. The zones are designated as Zone 1, Zone 1 Modified, and Zone 2. Zone 1 Modified and Zone 2 allow stormwater infiltration whereas for Zone 1 stormwater infiltration is not permitted without a project-specific hydro-geologic study and City approval on a case-by-case basis. Therefore, retrofitting an existing facility in Zone 1 with infiltration will not be considered in this study. Other groundwater resources such as Cedar Valley Sole Source Aquifer and other aquifers or private well systems were not investigated at this time. Stream Basin & Receiving Water Body Status: The Washington State Department of Ecology (WSDOE) Water Quality Assessment data, provided in their Water Quality Atlas map tool, was used to investigate whether receiving bodies for discharges from the flow control facilities had any known impairments. For this screening, the following protocols were followed: • Using GIS storm pipe, roadway, and topographic data, the flow path downstream of each facility was followed until it appeared that the network discharged into a stream layer. This is where an outfall from the City’s municipal separate storm sewer system was assumed to be present. • Impairments in the stream (or lake) at the stormwater outfall, or within one-quarter mile downstream, were identified. • Only impairments identified as Category 4 or Category 5 in the WSDOE map tool were recorded. Category 4 impairments cover those that are not on the 303(d) list for a variety of reasons but there is a well- documented impairment. According to WSDOE, a segment of a water body is designated as Category 5 impairment “when data indicates that water quality criteria are not persistently attained, or when well- documented narrative evidence indicates impairment of a designated use by a pollutant”. The Category 5 impairment is on the State’s 303(d) list and, according to WSDOE, requires “a TMDL, pollution control program, or other action(s) to bring the water into compliance with the water quality standards.” Other Data: The City has additional information and maps which may be reviewed at later study stages to see if certain land uses, existing or proposed infrastructure, or sensitive area designations could either constrain or enhance Stormwater Facility Retrofit Study – Existing Conditions Summary Page 7 stormwater retrofit options at certain existing facilities. These data could include: coal mine hazards, known contaminated soils, major utility conflicts, stream or wetland typing, and proximity to the Renton airport and flight paths. There also may be opportunities to leverage stormwater retrofit work at certain sites with proposed private or public developments. Table 2: Basin Screening Attributes for Stormwater Retrofit Constraints Basin Attribute Relevance to Study Hydrologic soil group Used to compare basins in terms of relative (a) infiltrative capacity of pervious areas and (b) feasibility of utilizing LID/infiltration BMPs for retrofitting. Also, will be incorporated into hydrologic modeling work. Steep slopes Can be used to compare basins in terms of relative runoff as is it will be incorporated into hydrologic modeling work. Areas downstream of BMP not assessed at this time but steep slopes, erosion hazard, and landslide hazard areas could preclude LID/infiltration BMPs for retrofitting Wellhead protection In general, any facilities within Zone 1 of a Wellhead Protection Area will preclude use of LID/infiltration BMPs for retrofitting Receiving water body status This is useful to evaluate whether receiving body is on the 303(d) list or has an established TMDL (or similar approved action) for any pollutants. It is assumed that all receiving bodies are potentially fish- bearing (streams or lake) so stream typing was not used for screening. Land Use: The City has three different GIS data sets that capture citywide land use information. These are: (1) present use parcel data, (2) current City zoning, and (3) land use designations from the City’s Comprehensive Plan. Each of these data sets contain relevant information on both current and future development patterns—factors that often correlate with stormwater quality. The present use parcel level data was selected to categorize land use areas because it has much finer resolution than the other two data sets and the present day land use was deemed most relevant for this study. The rationale is that, while future development could be more intensive in a basin of interest (for example, where zoning would allow the conversion of an existing farm to a dense residential sub- division), any future development would need to meet today’s more stringent stormwater requirements. Land use was primarily of interest in this study to establish potential pollution source hotspots (relative to other areas). With that goal in mind, the ninety-seven (97) parcel land use types which the City tracks were grouped into seven (7) land categories initially as shown in Table 3. Stormwater Facility Retrofit Study – Existing Conditions Summary Page 8 Table 3. Land Use Categories in Study Land Use Categories Types of Parcels Included Single Family Residential (SFR) All single-family residential parcels except vacant ones Multi-Family Residential (MFR) All multi-family residential parcels except vacant ones Industrial Heavy and light industrial sites, rail and airfield sites, quarries Institutional/Offices Schools, government campuses, office parks, office buildings Commercial 1 Gas stations, nurseries, car wash, car repair & dealerships, lube shops, surface parking lots, bus terminal, warehouse (potential higher pollutant source parcels Commercial 2 All other commercial/retail parcels. This category was for lower pollutant source parcels Open Space Parks, cemetery, timberland, greenbelt, utility sites, easements, wilderness reserves Vacant Vacant parcel of any land use. Water Open water, streams, tidelands Golf Golf course areas including fairways and surrounding wooded area Road Right-of-Way See discussion From a land use perspective, roadways were further separated into two basic groups based solely on the City’s GIS road classifications: • Low use: local and private roads • High use: collectors, arterials, and freeway/highway The impervious cover associated with roadways and sidewalks was calculated separately as discussed in the following section. As the present use parcel data did not distinguish between different development densities for Single Family Residential (SFR) areas (all parcels in the data set were in a single SFR category), the parcel size data was then used to develop an SFR Density layer (see Table 4). This layer can be used in later work to more accurately identify potential pollutant hotspots (due to higher pavement densities) when comparing tributary basins composed mainly of SFR parcels. Note that while these designations were broken down along typical SFR zoning categories, to be consistent with the study’s approach of evaluating sites based on current conditions, SFR density categorizations were based on current parcel size alone. Table 4. Single Family Residential Designations in Study SFR Zoning SFR Density Designation Approximate range of parcel size (sf) Unspecified Low SFR Density1 >87,120 R1-Residential (1 du/ac) Low SFR Density 43,560 to 87,120 R4-Residential (4 du/ac) Med SFR Density 10,890 to 43,560 R6-Residential (6 du/ac) High SFR Density 7,260 to 10,890 R8-Residential (8 du/ac) 5,445 to 7,260 R10-Residential (10 du/ac) 4,356 to 5,445 R14-Residential (14 du/ac) 3,111 to 4,356 Unspecified <3,111 1A “Rural” category for single-family residential parcels could be considered in future work for screening Stormwater Facility Retrofit Study – Existing Conditions Summary Page 9 Land use may be used to screen likely non-point pollution sources. As the work unfolded, it became apparent that many of the tributary basins contained little land use that was anything other than single-family residential developments and associated roadways. However, there were a few basins with significant non-SFR land use development, and several tributary areas had high-use roadways. To capture this information, a map was developed that places any current use multi-family residential, industrial, institutional, commercial 1, or commercial 2 parcel in a single land use category. This map also highlights any high use roadway as described above. This map efficiently identifies tributary basins with relatively higher likelihood of non-point pollution sources. Land Cover: In addition to land use information, it was essential to develop basin-specific, spatially distributed information on land cover in order to support the different analyses required for this study. These analyses will include: (1) identifying areas where retrofits would not be likely due to protected or native growth land cover (wetlands and forested land); (2) determining the amount of impervious cover within each basin for need-based screening of basins with most pollution-generating impervious surface; (3) estimating the amount of managed pervious cover in each basin for need-based screening of basins with most pollution-generating pervious surface (such as golf courses or even high density SFR areas with high fertilizer and pesticide use) and (4) allowing for future hydrologic modeling in each basin in latter study stages. Effective impervious cover ratios were not used at this stage of work but may be useful in future analyses depending on the project’s analytical modeling approach. Quantifying the land cover acreage by basin required the following general steps: • Wetlands were from the City’s delineated wetland GIS layer • Forest land cover polygons were developed by the project team based on land use and aerial imagery. Forest land cover was generally not delineated on any developed single-family parcel under the assumption of possible, near-term clearing and generally the isolated nature of the tree-covered area • Impervious cover relied on multiple data sets: o Rooftop areas were derived directly from the City’s building footprint layer. According to the City’s meta-data, this layer is “dynamic and in a constant state of maintenance, correction, and update”. Very few locations were found where building footprints had to be manually deleted or added based on inspection of the aerial imagery. o Driveway coverage was based on spot inspection of around five (5) residential parcels in each tributary basin, developing an average area per driveway, and multiplying by the number of single-family residential parcels in each basin. o Discrete polygons for large parking lots associated with multi-family residential/commercial sites in the majority of the basins were delineated by the project team (as a GIS shapefile for these paved areas was not available). There were only about four total locations where this was required. However, the two largest basins (111421 and 11422) had significant multi-family, institutional, commercial, and industrial areas. For these parcel types in these two basins, it was assumed that outside of the building footprint, 80% of the land cover was impervious and the remaining 20% was grass cover. Stormwater Facility Retrofit Study – Existing Conditions Summary Page 10 o A road cover layer was developed for this project as data based on the City’s impervious data layer (raster data from 2009) was not of adequate quality for the basins in the study. More detail on this work is provided below. • Open water encompassed streams, lakes, or ponds delineated within the GIS data sets. • There were no large managed grass/landscape areas associated with golf courses, schools, or parks in the basins other than possibly in the two largest basins (111421 and 11422). • All remaining land cover was defined as grass land cover. This included the following: − Land on single-family residential parcels not defined as roof or driveway − All vacant parcels were classified as 100% grass except areas already classified as forest or wetland. Based on inspection of the aerial map and/or Google Earth, it was confirmed that this was appropriate for these parcels in all basins. − All open space areas and parcels were classified as 100% grass except areas classified as forest or wetland. Based on inspection of the aerial map and/or Google Earth, it was confirmed that this was appropriate for these parcels in all basins. Current impervious cover was initially evaluated using the City’s impervious cover data set. This data set was developed in 2000 originally and then updated in 2009. This data was not used for the following reasons: • Missing roads and building footprints developed since 2009. • Did capture well impervious areas such as driveways and sidewalks and also defined many non- impervious areas as impervious (see orange shaded areas in top image of Figure 2). Therefore, to develop a roadway impervious layer for this study the following steps were required: • The roadway impervious area layer was first generated based on the null space between parcel lines. This approach captured the roadway, driveway aprons, and sidewalks as part of this roadway layer. • Planted center medians and circles were delineated separately as open areas (grass) where required. • Each basin was reviewed against the aerial imagery to ensure identify road areas that were missed or needed to be added to the layer. A minor disadvantage of this approach is any roadside planting strips within the public right-of-way was counted in the impervious roadway layer. Stormwater Facility Retrofit Study – Existing Conditions Summary Page 11 Figure 2. Impervious Cover Data Quality Comparison (top image: 2009 raster data; bottom image: 2021 project data layer) DATA GAP RESOLUTION There were several instances where basins draining to the flow control facility of interest could not be defined due to gaps or uncertainty in the project as-builts, project TIRs, and City GIS data. These specific cases and subsequent assumptions made are described below. It is recommended that the City review these facilities to determine whether additional investigation is needed. It is noted that 15 site visits were originally planned to support the existing data analysis phase. However, it was concluded that site visits would be more useful for addressing gaps in data when assessing opportunities for BMP retrofits. These site visits can also be used to help resolve some of these data gaps particularly in terms of tributary basin delineation. Ripley Lane (#111421) – The facility was identified as a stormwater vault in the initial information provided by the City. From a review of the as-built drawings, it appears that the vault does not function as a flow control facility, but rather a “flow equalization” vault that allows multiple pipe connections to convey drainage from the east side of Ripley Lane under a large 84-inch diameter sanitary sewer. The vault did not appear to provide any “restrictor” or other type of discharge control. The vault’s inlets and outlets are all flat and confined in terms of available space. A retrofit opportunity at the vault appears unlikely; the only potential opportunity might be on the east Stormwater Facility Retrofit Study – Existing Conditions Summary Page 12 side of Ripley Lane where a series of log weirs were constructed (likely to reduce erosion). The City should review this site and assess whether the facility should be included in future study efforts. Renton Village (#111422) - The facility was identified as a vault in the initial information provided by the City. From a review of the as-builts, it appears that the original system included a long run of both 60-inch diameter pipe followed by 72-inch diameter pipe that then was reduced in size at the downstream end to 42-inch diameter. Thus, the pipe downsizing appeared to act as a flow control restriction. However, based on subsequent information provided by the City, it was determined that the downstream system was replaced with a larger 4-foot by 6-foot box culvert constructed in 2007. As a result, there is no control structure and the entire system functions as a simple conveyance network. The City should review this site and assess whether continuing to include it in future study efforts is desirable. Denny’s (#111391) - The outlet of the Denny’s facility may combine with the Ripley Lane drainage (or possibly connect during high flow conditions). For the purpose of the preliminary assessment, the tributary area to the Denny’s facility was kept separate from the Ripley drainage. This can be confirmed in the next phase of the study. Davis Ave S One Valley Place (#145398) - The tributary area delineation for the Davis Facility should be reviewed in the next step of the planning study. A large area directly up-slope from the pond of interest (South of Davis Ave S One Valley Place and East of the pond) would appear to drain to the pond based on topography data alone. However, the provided as-builts show that a culvert from this neighboring development crosses the main storm pipe that conveys the Davis Ave S One Valley Place surface runoff to the pond. The assumption was made that runoff from the neighboring development bypasses the facility, and therefore the basin delineation for this facility excluded the area in question. This delineation can be reviewed prior to the next step in the planning process. SUMMARY OF EXISTING CONDITIONS The findings confirmed what was anticipated due to the age of the existing facilities--many of these facilities solely provided flow control without any documented water quality treatment features and were constructed to detain runoff from roadways and parcels within single family residential areas. Table 5 below provides a summary of each existing flow control facility and delineated tributary basin. Key summary data include: • The 49 individual detention facilities consisted of 32 tanks, 4 vaults, and 13 ponds. • The average unit storage volume for each detention facility was 2,600 ft3/acre (about 3/4” of an inch per acre) however there was a huge range in these values. • Only 6 of the flow control facilities (111369, 117931, 117938, 117947, 166609, and 200049) have any associated water quality BMPs to treat detained flows. All of these existing BMPs are of the “basic” treatment type. The sufficiency of sizing for each may be determined later in the study if necessary, for evaluating retrofit options. • Installation dates are only known for about half of the facilities in the study. For those with known dates, all facilities were installed between 1976 and 2001 (except asset # 200049 Nantucket Short Plat installed in 2016). • For those facilities that discharge directly to an impaired water body (via the City’s municipal separate storm sewer system), the following impairments exist: Stormwater Facility Retrofit Study – Existing Conditions Summary Page 13 − Bioassessment (12 sites), temperature (10 sites), dissolved oxygen (6 sites), bacteria (9 sites), sediment bioassay (2 sites associated with Lake Washington), and pH (1 site associated with the Cedar River mainstem). Bioassessment impairments are based on poor benthic invertebrate health that are lower than the 10-percentile of reference site scores (based on B-IBI or RIVPACS scoring criteria). Bacteria refers to high levels of fecal coliform, E. coli, and/or enterococci organisms exceeding standards for recreational use (fresh and marine waters) or shellfish harvesting (marine waters). Attachment A provides a table of the data for each flow control facility collected as part of the as-built and TIR review as well as certain key data that was provided by the City in November 2020 at the outset of the study. Attachment B is a set of two maps showing the named stream and lake basins that each flow control facility/tributary basin falls within. Attachment C is a set of two maps developed to (1) identify tributary basins with natural features like to contribute to relatively high unit runoff rates and (2) preliminarily identify existing detention where infiltration is likely to be less feasible and/or less desirable. Attachment C depicts areas within each tributary basin that have: • Land slopes > 15% • Hydrologic soil group types other than type A or type B soils • Areas within the different wellhead protection zones • Mapped wetlands Attachment D is a set of two maps that was developed to summarize known data that will be useful to evaluate the relative need of a tributary basin for water quality treatment. Attachment D depicts areas within each tributary basin: • With parcels with current uses of industrial, multi-family residential, or commercial • Roadways identified as freeway, highway, major arterial, minor arterial, or collector in the City’s road class data set. • There is also a color-coded icon associated with each flow control site which characterizes the following about each site: − Type of flow control BMP and whether it is associated with a dedicated water quality treatment BMP − Level of existing impervious cover in the tributary basin (calculated as percent of land area with impervious cover) − If nearest receiving water body has a known water quality or sediment-related impairment Stormwater Facility Retrofit Study – Existing Conditions Summary Page 14 Table 5. Summary of Stormwater Detention Facility Data Site Number (City Asset ID) Development Project Name Receiving Water Body Year Constructed (if known) Detention Structure Type Water Quality Treatment Type Tributary Basin Acreage Percent Impervious 111332 SUMMERWIND DIV I II III Greenes Creek Pond None 20.2 54% 111342 WINSPER (LIBERTY VIEW I&II) Panther Creek 1991 Pond None 1.2 55% 111354 SPRINGBROOK TERRACE Upper Springbrook Creek 1985 Pond None 5.2 51% 111361 HIDDEN CEDARS DIV II Soos Creek Main Pond None 5.2 48% 111369 PANTHER MEADOW Panther Creek Pond Bio-swale 2.9 44% 111391 DENNYS RESTAURANT Lake Washington - East Pond None 20.2 35% 111393 CASTLEWOOD RANCHETTES Maplewood Creek 1981 Pond None 6.0 32% 111394 CASTLEWOOD RANCHETTES Maplewood Creek 1981 Pond None 13.2 24% 111408 BERGSMA SHORT PLAT Upper Springbrook Creek Pond None 3.1 26% 111421 RIPLEY LN STORM IMPROVEMENT PR Lake Washington - East Vault None 401.6 39% 111422 RENTON VILLAGE INTERCEPTOR Thunder Hills Creek Vault None 736.4 50% 117894 SWAN MEADOWS I Johns Creek 1989 Tank None 1.7 52% 117900 MEADOW AV N & N 24TH ST South Kennydale Tank None 2.7 45% 117902 TIFFANY PARK DIV 4 Cedar Main Urban 1979 Tank None 10.2 59% 117912 ARMSTRONG AND SANDELIUS Soos Creek Main Tank None 2.2 28% 117915 KNUDSON Soos Creek Main Tank None 0.2 94% 117916 PARKWOOD SOUTH DIV I Thunder Hills Creek 1976 Tank None 5.5 55% 117917 WINDSOR HEIGHTS Panther Creek Tank None 0.3 100% 117918 BENSON WOODS Panther Creek 1994 Tank None 1.8 30% 117921 SWAN MEADOWS II Johns Creek 1993 Tank None 0.8 77% 117929 BOB BURKE? Upper Springbrook Creek Tank None 2.1 34% 117931 BENSON GLEN Panther Creek Tank Bio-swale 1.7 52% 117936 FERNWOOD EAST Maplewood Creek 1980 Tank None 9.4 47% 117938 CHINQUAPIN RIDGE Panther Creek Tank Bio-swale 0.6 66% 117940 VALLEY VUE ESTATES Panther Creek 1998 Tank None 1.0 55% Stormwater Facility Retrofit Study – Existing Conditions Summary Page 15 Site Number (City Asset ID) Development Project Name Receiving Water Body Year Constructed (if known) Detention Structure Type Water Quality Treatment Type Tributary Basin Acreage Percent Impervious 117941 WEATHERWOOD II Lower May Creek Tank None 12.0 50% 117945 HIDDEN CEDARS DIV II Soos Creek Main Tank None 1.4 45% 117947 BENSON GLEN Soos Creek Main Tank Bio-swale 4.6 44% 117952 CHINQUAPIN RIDGE Panther Creek Tank None 2.2 63% 145336 PETETT MEADOWS SHORT PLAT Honey Creek Pond None 1.5 60% 145398 DAVIS AV S ONE VALLEY PLACE Upper Springbrook Creek Pond None 11.3 57% 145407 VICTORIA HILLS Rolling Hills Creek 1981 Pond None 44.6 40% 145785 ELIZABETH PLACE Johns Creek 2001 Tank None 0.9 94% 145824 RUDDELLS 2ND ADDITION Johns Creek 1979 Tank None 3.2 27% 145827 PARKWOOD Thunder Hills Creek Tank None 7.5 46% 145832 SOUTH KNOLL WATER EXTENSION South Renton Tank None 8.4 29% 145834 POLLOS ESTATES Lower May Creek 1992 Tank None 2.2 48% 145836 HIGHBURY PARK Johns Creek 1980 Tank None 14.2 41% 145851 YOUNG ADDITION Honey Creek 1992 Tank None 1.1 87% 145864 RIDGEVIEW ESTATES May Creek 1988 Tank None 6.8 52% 145869 YOUNG ADDITION Honey Creek 1992 Tank None 1.6 47% 146790 LUND SHORT PLAT Thunder Hills Creek Pond None 0.5 28% 166609 SUNSET BLVD/DUVALL AVE NE INT Honey Creek Vault Wet vault 0.3 100% 167768 ORCHARD PARK Panther Creek Tank None 4.4 47% 168953 VILLAGE ON UNION Cedar Main Urban 1995 Tank None 16.5 52% 200040 KELSEY LANE Panther Creek 1981 Tank None 2.0 61% 200041 KELSEY LANE Panther Creek 1981 Tank None 0.2 100% 200049 NANTUCKET SHORT PLAT South Kennydale 2016 Vault Wet vault 5.4 37% 200096 PARKWOOD SOUTH DIV III Thunder Hills Creek Tank None 1.3 22% Stormwater Facility Retrofit Study – Existing Conditions Summary Page 16 NEXT STEPS The next task in this study (Treatment Gap Analysis--Task 3) is to evaluate each tributary basin to the existing flow control facilities in the study in terms of (a) existing water quality treatment and (b) what type of treatment would be required for the basin to comply with current water quality treatment requirements if it were to be re- developed. The following task (Retrofit Type and Opportunity Identification --Task 4), will use the soil, slope, land cover, and land use existing conditions data in each tributary basin in order to then conduct hydrologic modeling to evaluate the types and sizes of water quality treatment BMPs appropriate for fully retrofitting each existing tributary basin. It is expected that from Task 4 onward input from various City stakeholders will be key to ensuring the study prioritizes sites and develops retrofit solutions that best meet the objectives of the study. ATTACHMENTS: A: Storm Water Detention Facilities Data Worksheet B: Drainage Sub-Basins Maps C: Infiltration Constraints Maps D: Existing Conditions Maps Stormwater Facility Retrofit Study – Existing Conditions Summary Page 17 Attachment A: Storm Water Detention Facilities Data Worksheet ASSET ID PROJECT NAME INFILTRATION (YES/NO) CONTROL TYPE DETENTION TYPE RESIDENTIAL (YES/NO)LOCATION TIR AVAILABLE AS-BUILTS AVAILABLE APPROX. LIVE VOLUME (CF) PIPE/VAULT/POND DIMENSIONS WQ FEATURE POND LINER TRIBUTARY AREA FROM TIR (ACRES)ADDRESS WTR_NAME 111332 SUMMERWIND DIV I II III NO FLOW POND YES TRACT YES YES 23,217 NONE NONE 18.3 Unnamed 111342 WINSPER (LIBERTY VIEW I&II)NO FLOW POND YES TRACT YES YES 3078.95 NONE NONE 1.36 10006 S 32nd Pl, Renton, 98055 Unnamed Panther Creek Tributary 111354 SPRINGBROOK TERRACE NO FLOW POND YES TRACT NO YES 3786 ~2.62 FT X 1445 SF NONE NONE N/A Unnamed 111361 HIDDEN CEDARS DIV II NO FLOW POND YES TRACT NO YES 13263 ~2.17 FT x 6112 SF NONE NONE N/A 18005 124th Ave SE, Renton, 98058 Big Soos Creek 111369 PANTHER MEADOW YES NONE POND YES TRACT NO YES 11488.62 ~3.09 FT X 3718 SF BIO-SWALE NONE N/A Unnamed Panther Creek Tributary 111391 DENNYS RESTAURANT NO NONE POND NO RIGHT OF WAY YES YES 97968 NONE NONE 236.07 4774 Lake Washington Blvd NE, Renton, 98056 Newport Hills Creek 111393 CASTLEWOOD RANCHETTES NO NONE POND YES TRACT NO YES 5985 ~2.45 FT x 2443 SF N/A NONE N/A 800 Duvall Ave NE, Renton, 98059 Honey Creek 111394 CASTLEWOOD RANCHETTES FLOW POND YES PUBLIC LAND NO YES 8907 ~0.5 FT x 17,813 SF N/A NONE N/A 4782 NE 9th St, Renton, 98059 Honey Creek 111408 BERGSMA SHORT PLAT NO FLOW POND YES TRACT NO YES 605 ~0.75 FT X 807 SF N/A NONE N/A 18851 103rd Ct SE, Renton, 98055 Unnamed Panther Creek Tributary 145336 PETETT MEADOWS SHORT PLAT NO FLOW POND YES TRACT YES YES 11588 NONE NONE 1.4 3879 NE 21st St, Renton, 98056 Newport Hills Creek 145398 DAVIS AV S ONE VALLEY PLACE NO FLOW POND NO EASEMENT NO YES 50450 N/A NONE N/A Unnamed Panther Creek Tributary 145407 VICTORIA HILLS YES FLOW POND YES TRACT YES YES 41000 NONE NONE 68.14 1102 S 23rd St, Renton, 98055 Panther Creek 146790 LUND SHORT PLAT NO FLOW POND YES TRACT YES YES 7806 NONE NONE 0.91 16345 114th Ave SE, Renton, 98055 Big Soos Creek 117894 SWAN MEADOWS I FLOW TANK YES RIGHT OF WAY NO YES 1624 140 LF x 58" X 36" SEMIELLIPTICAL PIPE N/A N/A N/A 1325 Camas Ave NE, Renton, 98056 Johns Creek 117900 MEADOW AV N & N 24TH ST FLOW TANK YES EASEMENT NO YES 653 52 LF X 48" DIA N/A N/A N/A 2435 Garden Ct N, Renton, 98056 Johns Creek 117902 TIFFANY PARK DIV 4 FLOW TANK YES EASEMENT NO YES 13598 85" x 54" PIPE ARCH x 110 LF, 85" x 54" PIPE ARCH x 124 LF, 85" x 54" PIPE ARCH x 113 LF, 85" x 54" PIPE ARCH x 176 LF N/A N/A N/A 1409 Olympia Ave SE, Renton, 98058 Unnamed 117912 ARMSTRONG AND SANDELIUS FLOW TANK YES EASEMENT NO YES 516 73 LF X 36" DIA N/A N/A N/A 16592 111th Ave SE, Renton, 98055 Unnamed Panther Creek Tributary 117915 KNUDSON NO FLOW TANK YES RIGHT OF WAY NO YES 127 18 LF X 36" DIA N/A N/A N/A 18012 124th Ave SE, Renton, 98058 Big Soos Creek 117916 PARKWOOD SOUTH DIV 1 FLOW TANK YES RIGHT OF WAY NO YES 884 125 LF X 36" DIA N/A N/A N/A 2104 Jones Pl SE, Renton, 98055 Unnamed 117917 WINDSOR HEIGHTS NO FLOW TANK YES RIGHT OF WAY NO YES 551 78 LF X 36" DIA N/A N/A N/A 18475 Main Ave S, Renton, 98055 Unnamed Panther Creek Tributary 117918 BENSON WOODS NO FLOW TANK YES TRACT NO YES 1276 96 LF X 42"x29" CMP, 100 LF of 42"x29" CMP N/A N/A N/A 18949 111th Pl SE, Renton, 98055 Panther Creek 117921 SWAN MEADOWS II NO FLOW TANK YES RIGHT OF WAY NO YES 1445 115 LF X 48" DIA N/A N/A N/A 1277 Blaine Ave NE, Renton, 98056 Johns Creek 117929 BOB BURKE?NO TANK YES TRACT NO YES 2513 200 LF X 48" DIA N/A N/A N/A 19600 92nd Ave S, Renton, 98055 Unnamed 117931 BENSON GLEN NO FLOW TANK YES RIGHT OF WAY NO YES 3393 270 X 48" DIA BIOFILTRATION SWALE N/A N/A 10900 SE 170th St, Renton, 98055 Unnamed Panther Creek Tributary 117936 FERNWOOD EAST FLOW TANK YES TRACT YES YES 6707 NONE N/A 10.66 130 Bremerton Ave SE, Renton, 98059 Maplewood Creek 117938 CHINQUAPIN RIDGE NO FLOW TANK YES RIGHT OF WAY NO YES 905 72 LF X 48" DIA BIO-SWALE N/A N/A 11205 SE 190th Pl, Renton, 98055 Panther Creek 117940 VALLEY VUE ESTATES NO FLOW TANK YES RIGHT OF WAY NO YES 1276 65 LF X 60" DIA N/A N/A N/A 310 S 22nd Pl, Renton, 98055 Panther Creek 117941 WEATHERWOOD II FLOW TANK YES RIGHT OF WAY NO YES 5459 278 LF X 60" DIA N/A N/A N/A 2571 NE 23rd Pl, Renton, 98056 Johns Creek 117945 HIDDEN CEDARS DIV II NO FLOW TANK YES TRACT NO YES 3958 140 LF X 72" DIA N/A N/A N/A Big Soos Creek 117947 BENSON GLEN NO TANK YES TRACT NO YES 5089 180 LF X 72" DIA BIOFILTRATION SWALE N/A N/A 17032 110th Pl SE, Renton, 98055 Big Soos Creek 117952 CHINQUAPIN RIDGE NO FLOW TANK YES RIGHT OF WAY NO YES 8042 160 LF X 96" DIA N/A N/A N/A 11214 SE 188th Pl, Renton, 98055 Unnamed Panther Creek Tributary 145785 ELIZABETH PLACE NO FLOW TANK YES TRACT NO YES 13410 3 PIPES, 60 LF X 142" X 91" PIPE ARCH N/A N/A N/A 2412 NE 12th St, Renton, 98056 Johns Creek 145824 RUDDELLS 2ND ADDITION FLOW TANK YES EASEMENT NO YES 1770 184 LF x 42" DIA N/A N/A N/A 3344 NE 10th St, Renton, 98056 Honey Creek 145827 PARKWOOD FLOW TANK YES RIGHT OF WAY NO YES 2237 178 LF X 48" DIA N/A N/A N/A 2101 Aberdeen Ct SE, Renton, 98055 Unnamed 145832 SOUTH KNOLL WATER EXTENSION FLOW TANK YES EASEMENT NO YES 2262 180 LF X 48" DIA N/A N/A N/A 250 Oakesdale Ave SW, Renton, 98057 Black River 145834 POLLOS ESTATES NO FLOW TANK YES RIGHT OF WAY NO YES 3967 3 PIPES, 105.24 LF X 48" DIA N/A N/A N/A 2099 Aberdeen Pl NE, Renton, 98056 Johns Creek 145836 HIGHBURY PARK FLOW TANK YES RIGHT OF WAY NO YES 10304 300 LF x 48" DIA + 130LF x 96" DIA (UPSTREAM OF FACILITY)N/A N/A N/A 448 Edmonds Ave NE, Renton, 98056 Johns Creek 145851 YOUNG ADDITION FLOW TANK YES EASEMENT NO YES 1610 82 LF X 60" DIA N/A N/A N/A 1636 Shelton Ave NE, Renton, 98056 Honey Creek 145864 RIDGEVIEW ESTATES NO FLOW TANK YES EASEMENT YES YES 3817 135 LF x 72" DIA N/A N/A N/A 2624 Anacortes Ave NE, Renton, 98059 Unnamed 145869 YOUNG ADDITION FLOW TANK YES EASEMENT NO YES 7549 267 LF X 72" DIA N/A N/A N/A 4067 NE 17th St, Renton, 98056 Honey Creek 167768 ORCHARD PARK NO FLOW TANK YES RIGHT OF WAY NO YES 2513 50 LF X 96" DIA NONE N/A N/A 17944 112th Ave SE, Renton, 98055 Unnamed Panther Creek Tributary 168953 VILLAGE ON UNION YES TANK YES TRACT NO YES 7314 3 PIPES, 194 LF X 48" DIA N/A YES N/A 501 Shelton Ct NE, Renton, 98056 Maplewood Creek 200040 KELSEY LANE NO FLOW TANK YES EASEMENT NO YES 2802 223 LF X 48" DIA N/A N/A N/A Unnamed Panther Creek Tributary 200041 KELSEY LANE NO FLOW TANK NO RIGHT OF WAY NO YES 1060 54 LF X 60" DIA N/A N/A N/A 10821 SE 172nd St, Renton, 98055 Unnamed Panther Creek Tributary 200096 PARKWOOD SOUTH DIV III NO FLOW TANK RIGHT OF WAY NO YES 2011 160 LF X 48" DIA N/A N/A N/A 2089 Edmonds Dr SE, Renton, 98055 Unnamed 111421 RIPLEY LN STORM IMPROVEMENT PR VAULT EASEMENT YES YES 3994 2 PIPES: 187 LF X 36", 1 PIPE: 191 LF X 36" DIA NONE N/A 406.68 4618 Seahawks Way, Renton, 98056 Gypsy Creek 111422 RENTON VILLAGE INTERCEPTOR ST*VAULT NO YES 2513 732.83 LF X 72" DIA N/A N/A N/A 653 S Renton Village Pl, Renton, 98057 166609 SUNSET BLVD/DUVALL AVE NE INT*NO FLOW VAULT NO RIGHT OF WAY NO YES 7105 WET VAULT N/A N/A 4442 NE Sunset Blvd, Renton, 98059 Honey Creek 200049 NANTUCKET SHORT PLAT NO VAULT YES TRACT NO YES 2250 WET VAULT N/A N/A 2826 Park Ave N, Renton, 98056 Johns Creek DATA FROM AS-BUILTs AND TIRs Stormwater Facility Retrofit Study – Existing Conditions Summary Page 18 Attachment B: Drainage Sub-Basins Maps §¨¦405LakeWashingtonBlvd NE Sunset BlvdWest Hill Johns Creek May Creek Maplewood Creek Cedar Main Urban South Renton Honey Creek Gypsy Lower May Creek Lake Washington East South Kennydale West Kennydale Greenes Creek NE 4th StRent o n AveS Rainier Ave S Duvall Ave NEPark Ave NEMercerWayCo al Creek P k wySESEMayValleyRd N E 3 rd S tW MercerWay LoganAveNN 3rd St Newcastle GolfClubRd Rai ni er Ave NForestDr SE S 132nd St N 4th St 156th Ave SES 133rd St Airport Way NESunse tB lvd 68th Ave SNSouthportD r Houser W ay SS 1 2 4thStFactory Pl N Rainier Ave SM ay Creek H o n e y C re ekCedar River CoalCreek 0276ABorenCreekGy p s y Cree k 0276J oh ns Creek Newpo rt Hills C reek Kennyd a l e Cr e e kMapl e w oo d C reek0275O268E LongMarshCre e k O268D 111421 111394 200049 145785 145834 117894117921 145832 145851 145869 117900 145824 168953 166609 111393 111391 117936 117941 145836 145864 145336 111332 Legend Storm Water Detention Facility Approx. Tributary Area To Facility £ 0 2,000 4,0001,000 Feet SUBBASINS - NORTH CITY OF RENTON STORM WATERFACILITY RETROFIT STUDY ProjectName ASSETIDSUMMERWIND DIV I II III 111332DENNYS RESTAURANT 111391CASTLEWOOD RANCHETTES 111393CASTLEWOOD RANCHETTES 111394RIPLEY LN STORM IMPROVEMENT PR 111421SWAN MEADOWS I 117894MEADOW AV N & N 24TH ST 117900SWAN MEADOWS II 117921WEATHERWOOD II 117941PETETT MEADOWS SHORT PLAT 145336ELIZABETH PLACE 145785RUDDELLS 2ND ADDITION 145824POLLOS ESTATES 145834HIGHBURY PARK 145836YOUNG ADDITI ON 145851RIDGEVIEW ESTATES 145864YOUNG ADDITI ON 145869SUNSET BLVD/DUVALL AVE NE INT*166609VILLAGE ON UNION 168953NANTUCKET SHORT PLAT 200049 note: for clarity, only stream basins with storm water detention facilities studied are shown. §¨¦405 Soos Creek Main Garrison Creek South Renton West Hill Panther Creek Maplewood CreekCedar Main Urban South Renton Ginger Creek Rolling Hills Creek Upper Springbrook Creek Thunder Hills Creek SE 192nd St140th Ave SESE P etrovitsky Rd Oakesdale Ave SWS 180th St SW 43rd St S W G r a d y W a y I n t e r u r b a n Av e SN E 3 rd S tSouthcenterPkwy84th Ave SN 3rd St S 132nd St E Valley HwyS E CarrRdS 133rd St 140thWaySE 124th Ave SERentonAveS Tukwila Pkwy 148th Ave SESouthcent e r B lvdMo nsterRdSW S G ra d y W ayAirport Way Park Ave N68thAveSS178thSt S C arrRdRainier Ave SHouser Way SCedar River GreenRiverPanthe r CreekSpringbrookCreekBigSoos C r e e kMillCreekMola ssesCreekGinger C r eekBl ac k R i v e rM aplewoo d C reekDuwamishRiver RollingHillsCreekT h u n der HillsCreek MadsenCreekRol l i ng Hi l l s Creek111422 200096 200041 200040 145827 117952 117929 117931 117947 145832 117902 117912 117915167768 117938 145398 146790 117918111408 117936 117945 117917 117940 117916 111369 111361 111354 145407 111342 Legend Storm Water Detention Facility Approx. Tributary Area To Facility £ 0 2,000 4,0001,000 Feet SUBBASINS - SOUTH CITY OF RENTON STORM WATERFACILITY RETROFIT STUDY ProjectName AS SETIDWINSPER (LIBERTY VIEW I&II)111342SPRINGBROOK TERRACE 111354HIDDEN CEDARS DIV II 111361PANTHER MEADOW 111369BERGSMA SHORT PLAT 111408RENTON VILLAGE INTERCEPTOR ST 111422TIFFANY PARK DIV 4 117902ARMSTRONG AND SANDELIUS 117912KNUDSON117915PARKWOOD SOUTH DI V 1 117916WINDSOR HEIGHTS 117917BENSON WOODS 117918BOB BURKE 117929BENSON GLEN 117931FERNWOOD EAST 117936CHINQUAPIN RIDGE 117938VALLEY VUE ESTATES 117940HIDDEN CEDARS DIV II 117945BENSON GLEN 117947CHINQUAPIN RIDGE 117952DAVIS AV S ONE VALLEY PLACE 145398VICTORIA HILLS 145407PARKWOOD145827SOUTH KNOLL WATER EXTENSI ON 145832LUND SHORT PL AT 146790ORCHARD PARK 167768KELSEY LANE 200040KELSEY LANE 2 200041PARKWOOD SOUTH DI V.I II 200096 note: for clarity, only stream basins with storm water detention facilities studied are shown. Stormwater Facility Retrofit Study – Existing Conditions Summary Page 19 Attachment C: Infiltration Constraints Maps §¨¦405LakeWashingtonBlvd NE Sunset BlvdNE 4th StRent o n AveS Rainier Ave S Duvall Ave NEPark Ave NEMercerWayCo al Creek P k wySESEMayValleyRd N E 3 rd S tW MercerWay LoganAveNN 3rd St Newcastle GolfClubRd Rai ni er Ave NForestDr SE S 132nd St N 4th St 156th Ave SES 133rd St Airport Way NESunse tB lvd 68th Ave SNSouthportD r Houser W ay SS 1 2 4thStFactory Pl N Rainier Ave SM ay Creek H o n e y C re ekCedar River CoalCreek 0276ABorenCreekG ypsyC reek0276J oh ns Creek Newpo rt Hills C reek Kennyd a l e Cr e e kMapl e w oo d C reek0275O268E LongMarshCre e k O268D 111421 111394 200049 145785 145834 117894117921 145832 145851 145869 117900 145824 168953 166609 111393 111391 117936 117941 145836 145864 145336 111332 £ 0 2,000 4,0001,000 Feet INFILTRATION CONSTRAINTS - NORTH CITY OF RENTON STORM WATERFACILITY RETROFIT STUDY ProjectName ASSETIDSUMMERWIND DIV I II III 111332DENNYS RESTAURANT 111391CASTLEWOOD RANCHETTES 111393CASTLEWOOD RANCHETTES 111394RIPLEY LN STORM IMPROVEMENT PR 111421SWAN MEADOWS I 117894MEADOW AV N & N 24TH ST 117900SWAN MEADOWS II 117921WEATHERWOOD II 117941PETETT MEADOWS SHORT PLAT 145336ELIZABETH PLACE 145785RUDDELLS 2ND ADDITION 145824POLLOS ESTATES 145834HIGHBURY PARK 145836YOUNG ADDITI ON 145851RIDGEVIEW ESTATES 145864YOUNG ADDITI ON 145869SUNSET BLVD/DUVALL AVE NE INT*166609VILLAGE ON UNION 168953NANTUCKET SHORT PLAT 200049 Legend Storm Water Detention Facility Approx. Tributary Area To Facility Wetland Slope >15% Low Infiltration Soils/High Ground Water Wellfield Capture Zones §¨¦405 SE 192nd St140th Ave SESE Petrovi tsky R d Oakesdale Ave SWS 180th St SW 43rd St S W G r a d y W a y N E 3 rd S tI n t e r u r b a n Av e S84th Ave SN 3rd St S 132nd St E Valley HwyS E CarrRdS 133rd St RentonAveS 140thWaySE 124th Ave SE148th Ave SETukwila Pkwy Southcent e r B lvdMo nsterRdSW S G r a d y W ayAirport Way Park Ave N68thAveSS C arrRdRainier Ave SHouser W ay S61st Ave SCedar River GreenRiverP anther Creek SpringbrookCreekBigSoosC r eekMill CreekMolassesCreekGinger C r eekB l ac k R i v e r M aplewoo d C reekDuwamishRiver RollingHillsCreekMa d s e n C reek T h u n der HillsCreek Madsen CreekRol l i ng Hi l l s CreekMadsenCreek111422 200096 200041 200040 145827 117952 117929 117931 117947 145832 117902 117912 117915167768 117938 145398 146790 117918111408 117936 117945 117917 117940 117916 111369 111361 111354 145407 111342 £ 0 2,000 4,0001,000 Feet INFILTRATION CONSTRAINTS - SOUTH CITY OF RENTON STORM WATERFACILITY RETROFIT STUDY ProjectName ASSETIDWINSPER (LIBERTY VIEW I&II)111342SPRINGBROOK TERRACE 111354HIDDEN CEDARS DI V II 111361PANTHER MEADOW 111369BERGSMA SHORT PLAT 111408RENTON VILLAGE INTERCEPTOR ST 111422TIFFANY PARK DIV 4 117902ARMSTRONG AND SANDELIUS 117912KNUDSON117915PARKWOOD SOUTH DIV 1 117916WINDSOR HEIGHTS 117917BENSON WOODS 117918BOB BURKE 117929BENSON GLEN 117931FERNWOOD EAST 117936CHINQUAPIN RIDGE 117938VALLEY VUE ESTATES 117940HIDDEN CEDARS DI V II 117945BENSON GLEN 117947CHINQUAPIN RIDGE 117952DAVIS AV S ONE VALLEY PLACE 145398VICTORIA HILLS 145407PARKWOOD145827SOUTH KNOLL WATER EXTENSION 145832LUND SHORT PLAT 146790ORCHARD PARK 167768KELSEY LANE 200040KELSEY LANE 2 200041PARKWOOD SOUTH DIV.III 200096 Legend Storm Water Detention Facility Approx. Tributary Area To Facility Wetland Slope >15% Low Infiltration Soils/High Ground Water Wellfield Capture Zones Stormwater Facility Retrofit Study – Existing Conditions Summary Page 20 Attachment D: Existing Conditions Maps §¨¦405LakeWashingtonBlvd NE Sunset BlvdNE 4th StRent o n AveS Rainier Ave S Duvall Ave NEPark Ave NEMercerWayCo al Creek P k wySESEMayValleyRd N E 3 rd S tW MercerWay LoganAveNN 3rd St Newcastle GolfClubRd Rai ni er Ave NForestDr SE S 132nd St N 4th St 156th Ave SES 133rd St Airport Way NESunse tB lvd 68th Ave SNSouthportD r Houser W ay SS 1 2 4thStFactory Pl N Rainier Ave SM ay Creek H o n e y C re ekCedar River CoalCreek 0276ABorenCreekG ypsyC reek0276J oh ns Creek Newpo rt Hills C reek Kennyd a l e Cr e e kMapl e w oo d C reek0275O268E LongMarshCre e k O268D 111421 111394 200049 145785 145834 117894117921 145832 145851 145869 117900 145824 168953 166609 111393 111391 117936 117941 145836 145864 145336 111332 £ 0 2,000 4,0001,000 Feet EXISTING CONDITIONS - NORTH CITY OF RENTON STORM WATERFACILITY RETROFIT STUDY ProjectName ASSETIDSUMMERWIND DIV I II III 111332DENNYS RESTAURANT 111391CASTLEWOOD RANCHETTES 111393CASTLEWOOD RANCHETTES 111394RIPLEY LN STORM IMPROVEMENT PR 111421SWAN MEADOWS I 117894MEADOW AV N & N 24TH ST 117900SWAN MEADOWS II 117921WEATHERWOOD II 117941PETETT MEADOWS SHORT PLAT 145336ELIZABETH PLACE 145785RUDDELLS 2ND ADDITION 145824POLLOS ESTATES 145834HIGHBURY PARK 145836YOUNG ADDITI ON 145851RIDGEVIEW ESTATES 145864YOUNG ADDITI ON 145869SUNSET BLVD/DUVALL AVE NE INT*166609VILLAGE ON UNION 168953NANTUCKET SHORT PLAT 200049 Legend Storm Water Detention Facility Approx. Tributary Area To Facility High Use Roadway Industrial, Institutional, Commercial or Multi-Family Land Use Existing Facility Type (Top Square) Pond (No Treatment) Vault/Tank (No Treatment) Basin Imperviousness (Middle Square) <40% 40% to 70% >70% Receiving Water Impairment (Bottom Square) No Known Impairment Impairment Pond/Vault/Tank with Treatment Facility Icon Key §¨¦405 SE 192nd St140th Ave SESE Petr ovits ky Rd Oakesdale Ave SWI n t e r u r b a n Av e SS 180th St SW 43rd St S W G r a d y W a y 84th Ave SSouthcenterPkwySouthcenter Blvd S 132nd St 124th Ave SEE Valley Hwy148th Ave SES E CarrRdS 133rd St 140thWaySETukwilaPkwy NE 3 rd S tMo nsterRdSW S G r a d y W ayS178thSt Airport Way Renton Ave S Kli c ki tatDr SE204thWay68thAveSParkAveNS C arrRdRainier Ave SHouser W ay SGreenRi v erCedarRive r Big S oos C r e e kSpringbrookCreekMill CreekMolassesCreekGinger C r eekP anther Creek Bl ac k R i v e r DuwamishRiver RollingHillsCreekT h u n der HillsCreek M aplewoodC reekUnnamedSoosetteTributaryRol l i ng Hi l l s Creek111422 200096 200041 200040 145827 117952 117929 117931 117947 145832 117902 117912 117915167768 117938 145398 146790 117918111408 117936 117945 117917 117940 117916 111369 111361 111354 145407 111342 £ 0 2,000 4,0001,000 Feet EXISTING CONDITIONS - SOUTH CITY OF RENTON STORM WATERFACILITY RETROFIT STUDY ProjectName ASSETIDWINSPER (LIBERTY VI EW I&I I )111342SPRINGBROOK TERRACE 111354HIDDEN CEDARS DIV II 111361PANTHER MEADOW 111369BERGSMA SHORT PLAT 111408RENTON VI LLAGE INTERCEPTOR ST 111422TIFFANY PARK DIV 4 117902ARMSTRONG AND SANDELIU S 117912KNUDSON117915PARKWOOD SOUTH DIV 1 117916WINDSOR HEIGHTS 117917BENSON WOODS 117918BOB BURKE 117929BENSON GLEN 117931FERNWOOD EAST 117936CHINQUAPIN RIDGE 117938VALLEY VUE ESTATES 117940HIDDEN CEDARS DIV II 117945BENSON GLEN 117947CHINQUAPIN RIDGE 117952DAVIS AV S ONE VALL EY PLACE 145398VICTORIA HILLS 145407PARKWOOD145827SOUTH KNOLL WATER EXTENSION 145832LUND SHORT PLAT 146790ORCHARD PARK 167768KELSEY LANE 200040KELSEY LANE 2 200041PARKWOOD SOUTH DIV.I I I 200096 Legend Storm Water Detention Facility Approx. Tributary Area To Facility High Use Roadway Industrial, Institutional, Commercial or Multi-Family Land Use Existing Facility Type (Top Square) Pond (No Treatment) Vault/Tank (No Treatment) Basin Imperviousness (Middle Square) <40% 40% to 70% >70% Receiving Water Impairment (Bottom Square) No Known Impairment Impairment Pond/Vault/Tank with Treatment Facility Icon Key Page 1 MEMORANDUM TO:Ken Srilofung, PE, CIP Project Manager FROM:Mike Giseburt, PE, WSP Project Manager SUBJECT: Stormwater Facility Retrofit Study – Treatment Gap Analysis DATE:April 2, 2021 INTRODUCTION AND BACKGROUND The City of Renton (City) owns and maintains over 400 stormwater facilities constructed as far back as the 1970s to mitigate for the stormwater impacts of urbanization. Between the 1970s and early 1990s, stormwater facilities were primarily focused on providing stormwater storage (i.e., detention). Since the early 1990s, design standards have advanced so that today’s stormwater facilities provide better water quality treatment to mitigate the detrimental impacts of stormwater pollutants on stream water quality and aquatic habitat. These newer stormwater treatment systems target the removal of suspended solids, dissolved heavy metals, nutrients, and petroleum hydrocarbons. Typically, stormwater facilities owned by the City connect to the municipal storm sewer system and drain to the closest water body. The older facilities in the City’s system primarily included stormwater detention without a specific water quality treatment component, and thus are less effective at protecting stream resources from pollutants than the stormwater detention facilities with water quality treatment designed by today’s standards. The City received a grant from the Washington State Department of Ecology (WSDOE) to perform a study of many of the existing flow control facilities that have little or no water quality treatment features. The overarching goal is to improve the water quality in multiple streams within the City that are part of the Cedar River/Lake Washington and Duwamish/Green watersheds. The study entails a series of six sequential tasks to be undertaken to prioritize the sites with the greatest potential to improve water quality. The first tasks, Task 1 and Task 2, entailed selecting the existing facilities for evaluation and then preparing an existing conditions summary: ·Existing Facilities Selection (Task 1) — City staff selected forty-nine (49) existing flow control facilities for this study primarily based on their understanding that these particular existing facilities provide minimal water quality treatment (see Figure 1). ·Existing Conditions Summary (Task 2) — This effort is complete and included collecting information and evaluating site conditions of the 49 selected existing facilities. The summarized data includes: BMP type (stormwater best management practices are often referred to as “BMPs” in this memorandum), size, and age; tributary area characteristics; drainage basin information; and other information, all which helps characterize the existing facilities and can be used in future tasks to evaluate stormwater treatment performance and site-specific water quality retrofit opportunities. WSP submitted the Existing Conditions Summary (Task 2) memorandum to the city on February 12, 2021. Page 2 Figure 1. Site Map Page 3 The next task, Task 3, is the work of this memorandum. ·Gap Analysis (Task 3) — This effort identifies deficiencies (gaps) in the treatment of stormwater at the selected facilities. This analysis considers the comparison of the existing amount of runoff treatment in the drainage basins to the amount of runoff treatment needed to meet current water quality treatment standards (per the 2017 City of Renton Surface Water Design Manual). The next three tasks will be completed as a part of future study efforts. ·Identifying Stormwater Retrofit Locations (Task 4) —This effort will build upon the treatment gap analysis to identify existing flow control facilities to retrofit with additional runoff treatment benefits. This task will develop a preliminary suite of BMP types and sizes for each site. ·Prioritizing and Scoring Sites for Stormwater Retrofit Opportunities (Task 5) —This effort will develop a method to screen retrofit locations identified in Task 4 to create a ranked list that focuses on the (a) highest benefit of water quality improvement and (b) most effective opportunities. ·Project Selection, Conceptual Design and Costs (Task 6) —This effort will include the development of concept designs and cost estimates for the top three prioritized retrofit locations. SUMMARY OF EXISTING CONDITIONS CHARACTERIZATION The Task 2 effort summarized existing conditions of the stormwater facilities. The treatment gap analysis uses the key information obtained from the Task 2 existing conditions summary listed below: ·Tributary area ·Tributary area land use, land cover, slope, and soil characteristics ·Facility information including whether water quality treatment is provided Due to the age of the existing facilities, many of these stormwater facilities only provide flow control without any documented water quality treatment features and were constructed to detain runoff from roadways and parcels within single family residential areas. Some key findings of the facility review include: ·The 49 individual detention facilities consisted of 32 tanks, 4 vaults, 13 ponds. One of the detention tanks (168953) is an underground infiltration system (preceded by a treatment swale). ·The average unit storage volume for each detention facility was 2,600 ft3/acre (about 3/4” of an inch per acre) however there was a wide range in these values. ·Only a handful of the flow control facilities have any associated water quality BMPs to treat detained flows. All of the existing BMPs are of the “basic” treatment type, where facility choices are designed to remove 80 percent of total suspended solids ·Installation dates were noted for some of the facilities based on information from their Stormwater Technical Information Reports (TIR) and were updated for this memorandum based on the design/as-built drawing dates. Some of the installation dates are approximate, because if only design drawings were available, facilities could have been constructed later. ·Some facilities discharge within a quarter mile of an impaired water body (via the City’s municipal separate storm sewer system), as described below: Page 4 o Bioassessment (12 sites): Bioassessment impairments are based on poor benthic invertebrate health that are lower than the 10-percentile of reference site scores (based on B-IBI or RIVPACS scoring criteria), o Temperature (10 sites), o Dissolved oxygen (6 sites), o Bacteria (9 sites): Bacteria refers to high levels of fecal coliform, E. coli, and/or enterococci organisms exceeding standards for recreational use (fresh and marine waters) or shellfish harvesting (marine waters), and o Sediment bioassay (2 sites associated with Lake Washington) Attachment A includes a map displaying which facilities being assessed drain to an impaired water body. TREATMENT GAP ANALYSIS APPROACH STEP 1: SUPPLEMENTAL EXISTING INFORMATION TO ASSESS CURRENT WATER QUALITY TREATMENT The gap analysis started by reviewing the context of the selected detention facilities to better understand the level of treatment that may be occurring within each tributary basin. This step entailed: ·Review of prior design manuals:A review of stormwater standards at the time of the design was used as a preliminary screening tool to identify detention facilities where treatment would be expected based simply on the age of the facility. A general history of the manuals and key standards is described below. ·Additional existing water quality treatment BMPs: GIS data was used to determine if any other existing treatment facilities were present. These treatment facilities, while not associated with the detention facility of interest, could be located within or immediately downstream of the detention facility’s tributary basin and treating some or all of the runoff in the detention facility’s tributary basin. STEP 2: WATER QUALITY TREATMENT GAP AT DETENTION FACILITY SITES The water quality treatment needs for each facility was evaluated to prioritize potential retrofit opportunities. This analysis identifies the deficiency (gap) in the stormwater treatment at the selected facilities by: ·Determining the required level of water quality treatment: The tributary basin for all detention facilities were evaluated to identify the level of water quality treatment that would be required under current standards. ·Assessing the efficacy facilities with treatment BMPs:As-built drawings and existing data were used to model the existing detention facility and the facility’s tributary basin. The existing treatment BMP could then be compared to a treatment BMP sized under the current requirements. ·Calculating the design treatment runoff volume for facilities without treatment BMPs:A per acre unit rate for the required water quality volume and flow rates of each land type was developed and then scaled to model the tributary basin for those existing detention facilities without any associated treatment BMP. The treatment requirements calculated for each tributary basin represent the treatment “gap” for these facilities; while sedimentation deposition and removal of suspended solids can occur in a stand-alone detention facility, the water quality benefit was considered negligible for the purpose of this study. Page 5 Review of prior design manuals The City’s drainage design standards have evolved over the last 40 years, over time enforcing stricter detention/treatment standards as well as prioritizing infiltration. A general history of the manuals and key standards that relate to stormwater quality treatment are described below. While the dates of adoption are approximate and therefore the application to the stormwater facilities in the study should be loosely applied, a general understanding of the design standard progression can suggest or confirm a deficiency (gap) of water quality treatment in existing facilities. o Prior to approximately 1990-1992, the City adopted the King County’s Storm Drainage Control Requirements (1979). The manual primarily applied the “Rational Method” (Q = c I A) for conveyance sizing. The Manual required the Rational Method, but also applied the Yrjanainen & Warren (Y&W) method to size stormwater detention on many projects. The intent of the stormwater detention was to match a project’s predevelopment runoff rates; however, this simplistic method tended to over predict a project’s pre-development runoff and also did not provide adequate storage. This manual did not typically require water quality treatment BMPs, and dead storage was not required below the live storage volume in detention facilities. o Between about 1992 and about 1997, the City adopted the 1990 King County Surface Water Design Manual (KCSWDM). This manual modified the detention storage sizing method from the Y&W method to a TR- 55/SBUH hydrograph method and required that projects provide detention to match the 2-year storm peak flow to ½ of the predevelopment 2-year storm peak flow and match predevelopment peak flow rates for the 25-year and 100-year storms. The manual added a water quality treatment component to either provide a bioswale or water quality wetpool storage equivalent to the 6-month, 24-hour storm, with a priority to infiltrate as much of the water quality design storm as possible. The manual included several water quality treatment best management practices (BMP) options. o Between about 1998 and 2000, the City adopted the 1998 KCSWDM – This manual reflected a substantial change in the methodology for hydrologic analysis, which required matching durations of flow and resulted in greater storage. The water quality design standard was also increased to target 80% TSS removal for basic treatment. o City of Renton 2010 Amendments to the 2009 KCSWDM - This manual is the first manual to require flow duration control to forested conditions using continuous hydrologic modeling for much of the City. This resulted in larger stormwater detention facilities. These amendments also increased the levels of treatment required by source control and water quality treatment BMPs, and enhanced the requirements for on-site stormwater management and associated low impact development (LID) techniques. o 2017 City of Renton Stormwater Design Manual (SWDM) – This is the current manual and incorporates most the design criteria in the prior manual. The manual placed more emphasis on low impact development BMPs and refined their design standards. Based on the work in this task, it was found that no water quality treatment BMPs were installed with a detention facility prior to 1989. Interestingly though, some facilities designed after 1989 had water quality treatment BMPs installed while many others did not. There are many possible reasons for this, but further research will not be relevant for the opportunity analysis. Page 6 Additional Existing Water Quality Treatment BMPs The City maintains a spatial database of existing water quality treatment BMPs. This data was combined with the tributary basin mapping conducted during the Existing Conditions task to determine if any upstream or downstream treatment facilities are present that are not associated with the detention facilities in this study or were not documented in the as-built drawings and TIRs that were reviewed. Explicitly estimating the level of treatment that occurs within each of these additional BMPs was beyond the scope of this study. However, recognizing where there is a treatment facility within or immediately downstream of a detention facility’s basin can be a factor used to prioritize potential retrofit opportunities. Therefore, water quality BMPs, when occurring within a tributary basin to a detention facility, were documented and presented in Attachment B. Level of Water Quality Treatment The detention facility sites were reviewed to determine whether any tributary basin if redeveloped would trigger a level of treatment beyond "Basic Water Quality" under the City's current SWDM. The following checks were conducted for this: ·CHECK #1: 50% or more of the basin runoff comes from commercial, industrial, or multi-family land use or roadways exceeding ADT counts of 7,500 vehicles, requiring Enhanced Basic Water Quality treatment BMPs o The following facilities have significant tributary areas with these land uses: 111391, 111421, 111422, and 145398. o While none of these basins has these land uses exceeding 50% of basin land coverage, additional modeling would be required to determine if the "50% or more of basin runoff" threshold is crossed. ·CHECK #2: The detention site falls within areas required Sensitive Lake or Sphagnum Bog Protections BMPs, Per Section 1.2.8.1 of the City's SWDM o The City does not have any drainage areas requiring Sensitive Lake or Sphagnum Bog Protection BMPs. ·CHECK #3: The tributary basin includes a High-Use Area, per the Definitions Section of City’s SWDM o No detention facility sites appear to trigger requirements associated with High-Use Areas at the detention site. o Smaller areas within certain tributary basins could trigger this under a re-development scenario, and this check will be applied when evaluating retrofit opportunities ·CHECK #4: The detention facility is located within the City’s Aquifer Protection Areas o Four (4) facility tributary basins overlap with Zones 1 and 2 of the City's Aquifer Protection Areas: 111422, 117900, 145834, and 200049. o Retrofit opportunities at the detention facilities within the Aquifer Protection Area might have restricted infiltration options and require facility lining. This information will be incorporated into the retrofit evaluation work to be conducted in latter tasks. Facilities with Treatment BMPs. Based on the as-built review conducted as part of the Existing Conditions task, six (6) of the forty-nine (49) detention facilities in the study were found to have an associated water quality BMP treating the detained flows. Upon evaluating the GIS data documenting all existing water quality facilities in the City of Renton, four (4) additional detention facilities were found to have an associated water quality BMP. These ten (10) detention Page 7 facilities associated with a water quality BMP are summarized in the table below. All of the existing BMPs are of the “basic” treatment type consisting either of wetpools or bio-filtration swales. Site Number (City Asset ID)Development Project Name Year Constructed Detention Structure Type Water Quality Treatment Type Tributary Basin Acreage Basin Percent Impervious 111369 PANTHER MEADOW 1 1989 Pond Bio-swale 2.9 44% 117931 BENSON GLEN 1992 Tank Bio-swale 1.7 52% 117947 BENSON GLEN 1992 Tank Bio-swale 4.6 44% 117938 CHINQUAPIN RIDGE 1990 Tank Bio-swale 0.6 66% 166609 SUNSET BLVD/DUVALL AVE NE INT 2009 Vault Wet vault 0.3 100% 200049 NANTUCKET SHORT PLAT 2016 Vault Wet vault 5.4 37% 117940 VALLEY VUE ESTATES 1997 Tank Bio-swale 1.0 55% 168953 VILLAGE ON UNION 2 1995 Tank Infiltration 16.5 52% 117918 BENSON WOODS 3 1989 Tank Wetland 1.8 30% 117929 BOB BURKE 4 1991 Tank Bio-swale 2.1 34% 1. The bio-swale treats less than a 1/3 of the detention facility’s tributary basin, therefore the treatment is considered inadequate without the need for additional modeling. 2. The detention facility at Village on Union infiltrates all of the runoff, therefore the treatment swale preceding the infiltration storage tank was not modeled separately. 3. The stormwater wetland treatment facility downstream of the detention facility at Benson Woods will require site investigation and/or additional record drawings, as the facility lies outside of the as-builts provided for the existing conditions work (Task 2). 4. GIS data from Renton shows a bio-swale within the development next to the detention facility, however the as-builts for the site do not show the existence of a water quality BMP. The site will require field investigation and/or additional record drawings to confirm the BMP both exists and impacts the tributary basin. In order to evaluate the effectiveness of those existing water quality treatment BMPs associated with a detention facility in the study, the existing water quality treatment BMPs were modeled under current stormwater management standards using the basin characteristics calculated during the existing condition assessment (Task 2). Wet Vaults For facilities with wetpools, the water quality volume calculated by WWHM can be compared with the facility’s wetpool volume to determine the extent to which the facility meets current water quality standards. 166609 – Sunset Blvd/Duvall Ave NE Int The existing wetpool volume is 1,772 cubic feet, and the required water quality volume is 2,130 cubic feet. The existing wetpool is 358 cubic feet smaller than required under current standards. 200049 – Nantucket Short Plat The existing wetpool volume is 2,000 cubic feet, and the required water quality volume is 16,422 cubic feet. The existing wetpool is 14,422 cubic feet smaller than required under current standards. Bio-swales The existing hydraulic features of the detention facility (such as storage volume and outlet control orifices) were modeled in Western Washington Hydrologic Model (WWHM 2012) to determine the 2-year flow rate out of the detention facility. The 2-year flow rate from the detention tank provided the water quality design flow rate to size Page 8 a bioswale under current City standards. This modeled bioswale serves as a point of reference for evaluating the efficacy of the existing bioswale. Design assumptions: ·Precipitation depth for the 24-hour storm with a 6-month return frequency = 1.5 inches ·The soil and vegetation cover for the bio-swale was a grass-legume mix on lightly compacted soil, to more closely match the existing conditions (Manning’s n=0.22). ·Maximum design flow depth at the water quality flow rate = 0.33 feet (4 inches) 117931 - Benson Glen The flow depth in the existing bioswale is below the maximum allowed depth of 4 inches; however, the length of the bioswale needs to be extended approximately 45 feet to meet current City standards. Alternatively, the width of the swale could be widened to 6 feet. 117947 - Benson Glen The flow depth in the existing bioswale is just over 10 inches, which exceeds the maximum allowable depth of 4 inches. If the existing bioswale’s cross-sectional dimensions are maintained and the flow depth requirement ignored, the length would still need to be extended at least 24 feet to provide sufficient treatment. In order to meet the flow depth requirements, the width of the facility would need to be approximately 20 feet. 117938 - Chinquapin Ridge The flow depth in the existing bioswale is less than the maximum allowed depth and the length of the existing facility is sufficient for treatment. 117940 - Valley Vue Estates The flow depth in the existing bioswale is about 4.5 inches, which exceeds the maximum allowable depth of 4 inches. If the existing bioswale’s cross-sectional dimensions are maintained and the flow depth requirement relaxed, the length would need to be extended approximately 27 feet to provide sufficient treatment. The as-built drawings indicate that additional flow from a neighboring development combines with the outflow of the Valley Vue detention facility upstream of the water quality BMP, therefore the bioswale is likely even more undersized. A site investigation or additional as-built drawings can be reviewed in following tasks efforts to determine what additional treatment is needed. As expected from the installation dates, the existing water quality treatment BMPs for the all of the existing detention facilities, except for Chinquapin Ridge, are significantly undersized relative to current standards. Therefore, it is recommended that the nine undersized water quality facilities still be considered for retrofit when conducting the analysis work to identify potential retrofit opportunities (in Tasks 4 and 5). Refer to Attachment E for the modeling documentation of bioswales. Facilities without Treatment BMPs. The water quality volume (the simulated daily volume that accounts for 91% of the entire runoff volume) and the water quality flow rates (the flow rate at or below which 91% of the total estimated runoff volume from a continuous runoff model will be treated) were estimated for each facility’s tributary basins to compare the relative water quality needs amongst those tributary basins that have no treatment BMP. This data will be used to Page 9 identify potential retrofit opportunities in the subsequent study task by providing rates for preliminary sizing of retrofit treatment BMPs. A per-acre unit rate for water quality volume (acre-ft), the online water quality flow rate (cfs), and the offline water quality flow rate (cfs), was selected for each land cover, soil group and slope combination. The per-acre rates could then be scaled according to the GIS data collected on each facility’s tributary basin (Task 2). The offline flow rate applies when a flow-splitter is upstream of the facility and can regulate the flow entering the water quality BMP. The online flow rate applies when the water quality BMP does not use a flow splitter, and instead receives all the stormwater runoff from the contributing basin. The per acre rates came from basin models run through WWHM 2012 (Version 4.2.16) with a 15-minute time step. The rainfall data pulled from the Seatac rain gauge with a scaling factor of 1.167, as this was the most conservative scaling factor for any of the facilities. No HSPF PERLNDS or IMPERLNDS were modified and surface runoff included surface and interflow. Basin models of a single land type were reviewed at various acreages to confirm that increasing the total acreage resulted in a linear increase of the water quality volumes and flow rates. The analyses also showed which combination of land characteristics when modeled produced similar water quality rates and did not need to be modeled discretely, such as flat and moderate slopes with pervious land and type C soil. Once the unit rates had been selected, the water quality volume and flow rates from WWWH models of basins with mixed land types were compared with the water quality volume and flow rates based on the per-acre unit rates. Interestingly, all of the WWHM models for mixed land use basins matched the per-acre rate method, except if the mixed basin contained any lawn. Since the per-acre unit rate method yielded more conservative water quality volumes and rates in these mixed basins with lawn, the unit rate method was selected for the purpose of this study. The per-acre quantities used to calculate the water quality volume and flow rates in each basin are listed in the following table. The tributary basin land use breakdown and calculated water quality rates for each detention facility is included in Attachment C. LAND USE TYPE (ACRE)SLOPE1 SOIL TYPE2 24 HOUR WQ VOLUME (AC-FT/ACRE) WQ ONLINE FLOW RATE (CFS/ACRE) WQ OFFLINE FLOW RATE (CFS/ACRE) Road Mod N/A 0.14189 0.1911 0.1080 Road Steep N/A 0.13831 0.2222 0.1250 Lawn Mod A/B 0.02824 0.1441 0.0678 Lawn Steep A/B 0.02950 0.1589 0.0730 Lawn Mod C 0.06545 0.0362 0.0203 Lawn Steep C 0.08397 0.0502 0.0277 Forest Mod A/B 0.00033 0.0008 0.0006 Forest Steep A/B 0.00042 0.0013 0.0007 Forest Mod C 0.02550 0.1210 0.0585 Forest Steep C 0.02750 0.1445 0.0675 Wetland Mod N/A 0.06486 0.0937 0.0464 Wetland Steep N/A 0.07551 0.1257 0.0656 1.Flat/Mod = 0% to 15% ground slope; Steep = >15% ground slope 2.Type A and B hydrologic soil groups = A/B soil; Type C, D, A/D, B/D, and C/D hydrologic soil groups = C soil Attachment D provides a more detailed summary on the various analyses used to determine whether a per-acre unit rate to model each basin would be an appropriate and conservative method for estimating the WQ volumes and flow rates for the purposes of the treatment gap analysis, as well as for preliminary sizing of different BMPs for retrofitting as part of the opportunity screening work to be conducted in later tasks. Page 10 TREATMENT GAP FINDINGS The following table summarizes the water quality volumes and flow rates required of potential BMPs to provide full runoff treatment for each basin based on existing land cover. Based on this analysis, the following was found: ·The age of detention facility (as estimated based on drawing sets provided by the City) is not a reliable predictor of presence or absence of treatment BMPs at the detention facility. ·Except for one facility, the detention facilities with existing water quality treatment BMPs should be considered for retrofit as these existing BMPs do not meet current design standards at all but one detention facility site. ·A wide range of design volumes and flow rates exist between the delineated detention facility basins such that the size of retrofits will vary substantially between basins and will be a key part of identifying retrofit opportunities and constraints in later tasks Site Number (City Asset ID)Development Project Name Year Constructed Tributary Basin Acreage Percent Impervious Detention Structure Type WQ VOLUME (ACRE-FT) WQ ONLINE FLOW RATE (CFS) WQ OFFLINE FLOW RATE (CFS) 111332 SUMMERWIND DIV I II III 6/28/86 20.2 54%Pond 1.813 3.446 1.817 111342 WINSPER (LIBERTY VIEW I&II)2/1/88 1.2 55%Pond 0.110 0.208 0.110 111354 SPRINGBROOK TERRACE 9/30/83 5.2 51%Pond 0.439 0.947 0.492 111361 HIDDEN CEDARS DIV II 7/10/89 5.2 48%Pond 0.428 0.863 0.451 111391 DENNYS RESTAURANT 1/5/82 20.2 35%Pond 1.705 2.603 1.385 111393 CASTLEWOOD RANCHETTES 5/1/81 6.0 32%Pond 0.394 0.971 0.491 111394 CASTLEWOOD RANCHETTES 5/1/81 13.2 24%Pond 0.631 1.456 0.743 111408 BERGSMA SHORT PLAT 4/1/80 3.1 26%Pond 0.199 0.490 0.248 111421 RIPLEY LN STORM IMPROVEMENT PR 3/19/08 401.6 35%Vault 30.830 61.870 32.156 111422 RENTON VILLAGE INTERCEPTOR 8/23/82 736.4 31%Vault 53.743 122.320 62.615 117894 SWAN MEADOWS I 2/20/89 1.7 52%Tank 0.152 0.294 0.154 117900 MEADOW AV N & N 24TH ST 7/1/95 2.7 45%Tank 0.221 0.457 0.238 117902 TIFFANY PARK DIV 4 5/7/79 10.2 59%Tank 1.059 1.787 0.963 117912 ARMSTRONG AND SANDELIUS 10/9/85 2.2 28%Tank 0.132 0.358 0.178 117915 KNUDSON 3/25/92 0.2 94%Tank 0.027 0.037 0.021 117916 PARKWOOD SOUTH DIV I 9/15/77 5.5 55%Tank 0.497 0.934 0.493 117917 WINDSOR HEIGHTS 8/16/94 0.3 100%Tank 0.036 0.048 0.027 117921 SWAN MEADOWS II 2/20/89 0.8 77%Tank 0.094 0.146 0.080 117936 FERNWOOD EAST 5/22/79 9.4 47%Tank 0.762 1.560 0.812 117941 WEATHERWOOD II 4/18/79 12.0 50%Tank 1.021 2.033 1.064 117945 HIDDEN CEDARS DIV II 7/10/89 1.4 45%Tank 0.110 0.230 0.120 117952 CHINQUAPIN RIDGE 8/14/90 2.2 63%Tank 0.223 0.388 0.208 145336 PETETT MEADOWS SHORT PLAT 7/20/05 1.5 60%Pond 0.146 0.262 0.140 145398 DAVIS AV S ONE VALLEY PLACE 3/31/82 11.3 57%Pond 1.132 1.818 0.990 145407 VICTORIA HILLS 11/1/78 44.6 40%Pond 3.302 7.654 3.911 145785 ELIZABETH PLACE 5/2/00 0.9 94%Tank 0.115 0.177 0.099 145824 RUDDELLS 2ND ADDITION 4/14/77 3.2 27%Tank 0.188 0.502 0.252 145827 PARKWOOD 9/15/77 7.5 46%Tank 0.562 1.051 0.556 145832 SOUTH KNOLL WATER EXTENSION 4/1/85 8.4 29%Tank 0.787 0.756 0.424 145834 POLLOS ESTATES 5/5/90 2.2 48%Tank 0.179 0.367 0.191 145836 HIGHBURY PARK 9/28/78 14.2 41%Tank 1.054 2.369 1.213 145851 YOUNG ADDITION 2/21/91 1.1 87%Tank 0.145 0.213 0.118 145864 RIDGEVIEW ESTATES 8/11/88 6.8 52%Tank 0.589 1.144 0.601 145869 YOUNG ADDITION 2/21/91 1.6 47%Tank 0.129 0.261 0.136 146790 LUND SHORT PLAT 6/9/05 0.5 28%Pond 0.036 0.083 0.042 167768 ORCHARD PARK 10/10/91 4.4 47%Tank 0.354 0.725 0.378 200040 KELSEY LANE 6/25/81 2.0 61%Tank 0.193 0.341 0.182 200041 KELSEY LANE 6/25/81 0.2 100%Tank 0.024 0.033 0.019 200096 PARKWOOD SOUTH DIV III 9/15/77 1.3 22%Tank 0.052 0.114 0.059 Page 11 NEXT STEPS The next effort under this study is to identify potential locations for water quality retrofit, determine what treatment BMPs are feasible at these locations, and size the potential treatment facilities under current water quality standards (Task 4). The facility locations will be presented in both narrative and map form. This effort will build upon the gap analysis to assess the types of opportunities available and the feasibility of retrofitting facilities to improve treatment performance. This will rely on a preliminary suite of BMP types along with site specific conditions including space, topography, conveyance, infiltration potential, and other site conditions. It is expected that this task will include input from various City stakeholders to ensure the study prioritizes sites and develops retrofit solutions that best meet City objectives. ATTACHMENTS: A: Detention Facilities Outfalling Near an Impaired Water Body B: Existing WQ Treatment BMPs Associated with Detention Facility Tributary Basins C: Water Quality Volume and Flow Rates for Tributary Basins Without Water Quality Facilities D: WWHM Modeling for Unit Sizing Water Quality Volumes and Flow Rates E: WWHM Modeling Reports and Bioswale Sizing of Existing Water Quality Facilities Page 12 ATTACHMENT A: DETENTION FACILITIES OUTFALLING NEAR AN IMPAIRED WATER BODY §¨¦405LakeWashingtonBlvd NE Sunset Blvd17110012001475 171 1 0012000024 17110 0 1 2 0 0 023917110012000228 171100 1 2001528 47122F2A0 47122F2D0_SE NE 4th StRent o n AveS Rainier Ave S Duvall Ave NEPark Ave NEMercerWayCo al Creek P k wySESEMayValleyRd N E 3 rd S tW MercerWay LoganAveNN 3rd St Newcastle GolfClubRd Rai ni er Ave NForestDr SE S 132nd St N 4th St 156th Ave SES 133rd St Airport Way NESunse tB lvd 68th Ave SHouser W ay SS 1 2 4thStFactory Pl N Rainier Ave SM ay Creek H o n e y C re ekCedar Ri verCoalCreek 0276ABorenCreekG ypsyC reek0276J ohns Creek Newpo rt Hills C reek Kennyd a l e Cr e e kMapl e w oo d C reek0275O268E LongMarshCre e k O268D 111421 111394 200049 145785 145834 117894117921 145832 145851 145869 117900 145824 168953 166609 111393 111391 117936 117941 145836 145864 145336 111332 £ 0 2,000 4,0001,000 Feet IMPAIRED WATER BODIES - NORTH CITY OF RENTON STORM WATERFACILITY RETROFIT STUDY ProjectName ASSETIDSUMMERWIND DIV I II III 111332DENNYS RESTAURANT 111391CASTLEWOOD RANCHETTES 111393CASTLEWOOD RANCHETTES 111394RIPLEY LN STORM IMPROVEMENT PR 111421SWAN MEADOWS I 117894MEADOW AV N & N 24TH ST 117900SWAN MEADOWS II 117921WEATHERWOOD II 117941PETETT MEADOWS SHORT PLAT 145336ELIZABETH PLACE 145785RUDDELLS 2ND ADDITION 145824POLLOS ESTATES 145834HIGHBURY PARK 145836YOUNG ADDITI ON 145851RIDGEVIEW ESTATES 145864YOUNG ADDITI ON 145869SUNSET BLVD/DUVALL AVE NE INT*166609VILLAGE ON UNION 168953NANTUCKET SHORT PLAT 200049 Legend Storm Water Detention Facility Approx. Tributary Area To Facility Water Quality Assessment Unit Catagories 4 & 5 17110012000228 (Bioassessment,Termperature, Bacteria) 17110012000239 (Temperature) 17110012001475 (Temperature, Bacteria) 17110012001528 (Temperature, Bacteria, Dissolved Oxygen) 47122F2A0 (Bacteria) 47122F2D0_SE (Sediment Bioassay) §¨¦405 Milit a r y Rd S42nd Ave SSE 192nd St I n t e r u r b a n Av e SOakesdale Ave SWSouthcenter Blvd S 180th St SW 43rd St S W G r a d y W a y SE Petrovi tsky Rd OrilliaRdS84th Ave SN E 3 rd S tSouthcenterPkwyS 188th StTukwila Intl Blvd51st Ave SS 178thSt M a c a d a m RdSS 132nd St N 3rd St E Valley HwyS E CarrRdS 176th St 124th Ave SES 133rd St Klickit a t Dr Tukwila Pkwy RentonAve S Mo nsterRdSW S G r a d y W ay40thAveSAirport Way Park Ave N68thAveSS C arrRdRainier Ave SHouser W ay SGreenRiverPanthe r CreekCedar River SpringbrookCreekBig S o osCreekMillCreekGinger C r eekBl ac k R i v e r D u w a mish River RollingHillsCreekT h u n der HillsCreekRol l i ng Hi l l s Creek111422 200096 200041 200040 145827 117952 117929 117931 145832 117902 117912 117915167768 117938 145398 146790 111408 117945 117917 117940 117916 111369111354 145407 111342 £ 0 2,000 4,0001,000 Feet IMPAIRED WATER BODIES - SOUTH CITY OF RENTON STORM WATERFACILITY RETROFIT STUDY ProjectName AS SETIDWINSPER (LIBERTY VIEW I&II)111342SPRINGBROOK TERRACE 111354HIDDEN CEDARS DIV II 111361PANTHER MEADOW 111369BERGSMA SHORT PLAT 111408RENTON VILLAGE INTERCEPTOR ST 111422TIFFANY PARK DIV 4 117902ARMSTRONG AND SANDELIUS 117912KNUDSON117915PARKWOOD SOUTH DI V 1 117916WINDSOR HEIGHTS 117917BENSON WOODS 117918BOB BURKE 117929BENSON GLEN 117931FERNWOOD EAST 117936CHINQUAPIN RIDGE 117938VALLEY VUE ESTATES 117940HIDDEN CEDARS DIV II 117945BENSON GLEN 117947CHINQUAPIN RIDGE 117952DAVIS AV S ONE VALLEY PLACE 145398VICTORIA HILLS 145407PARKWOOD145827SOUTH KNOLL WATER EXTENSI ON 145832LUND SHORT PL AT 146790ORCHARD PARK 167768KELSEY LANE 200040KELSEY LANE 2 200041PARKWOOD SOUTH DI V.I II 200096 Legend Storm Water Detention Facility Water Quality Assessment Unit Catagories 4 & 5 Approx. Tributary Area To Facility 17110013000129 (Bioassessment) 17110013000134 (Bioassessment) 17110013007619 (Bioassessment) 17110013007648 (Bioassessment) 17110013007714 (Bioassessment) Page 13 ATTACHMENT B: EXISTING WQ TREATMENT BMPS ASSOCIATED WITH DETENTION FACILITY TRIBUTARY BASINS "6 §¨¦405LakeWashingtonBlvd NE Sunset Blvd"6 !H 111421 111394 200049 145785 145834 117894117921 145832 145851 145869 117900 145824 168953 111393 111391 117936 117941 145836 145864 145336 111332 NE 4th StRent o n AveS Rainier Ave S Duvall Ave NEPark Ave NEMercerWayCo al Creek P k wySESEMayValleyRd N E 3 rd S tW MercerWay LoganAveNN 3rd St Newcastle GolfClubRd Rai ni er Ave NForestDr SE S 132nd St N 4th St 156th Ave SES 133rd St Airport Way NESunse tB lvd 68th Ave SNSouthportD r Houser W ay SS 1 2 4thStFactory Pl N Rainier Ave SM ay Creek H o n e y C re ekCedar River CoalCreek 0276ABorenCreekG ypsyC reek0276J oh ns Creek Newpo rt Hills C reek 0275O268ELongMarshCre e k O268D £ 0 2,000 4,0001,000 Feet WATER QUALITY - NORTH CITY OF RENTON STORM WATERFACILITY RETROFIT STUDY ProjectName ASSETIDSUMMERWIND DIV I II III 111332DENNYS RESTAURANT 111391CASTLEWOOD RANCHETTES 111393CASTLEWOOD RANCHETTES 111394RIPLEY LN STORM IMPROVEMENT PR 111421SWAN MEADOWS I 117894MEADOW AV N & N 24TH ST 117900SWAN MEADOWS II 117921WEATHERWOOD II 117941PETETT MEADOWS SHORT PLAT 145336ELIZABETH PLACE 145785RUDDELLS 2ND ADDITION 145824POLLOS ESTATES 145834HIGHBURY PARK 145836YOUNG ADDITI ON 145851RIDGEVIEW ESTATES 145864YOUNG ADDITI ON 145869SUNSET BLVD/DUVALL AVE NE I NT*166609VILLAGE ON UNION 168953NANTUCKET SHORT PLAT 200049 Legend Approx. Tributary Area To Facility Existing WQ Treatment BMPs Associated with Detention Facility's Tributary Basin Structure Type !H Bioswale Media Filter Drain #0 Modified Media Filter Drain Stormfilter - Contech 'Stormwater Wetland 'Wet Pond "6 Wet Vault Storm Water Detention Facility 166609166609166609 Tributary Basins !H !H !H !H #0 #0 ' ' §¨¦405 !H 111422 111342 145407 111354 111361 111369 117916 117940 117917 117945 117936 111408 117918 146790 145398 117938 167768 117915 117912 117902 145832 117947 117952 145827 200040 200041 200096RollingHill s Cr eekMolassesCreekBig Soos C r eek P a n t her Cr e e k T h u n derHillsCreekRollingHillsCreek Pa nther Creek Maplewo o dCr e e kSpringbrookCreekMaplew oodCreekG inger Cre e k B l a c k R i ver B86-DITCHPanther Creek M olass e s Creek Soosette CreekTrib utaryG re e n Ri verUnnamedSoosetteTributaryLowe rGarrisonCreekMil l CreekDuwamish Riv e r C eda r River G r e enRiver S 202ndSt E Valley Hwy84thAveSKli ckitatDr S 132nd St Tukwila P kwy S 3rdSt S 2nd St InterurbanAveS 124thAveSERainierAveSHouserW aySOakesdaleAve S WSE P etrov its ky RdSouthcenter PkwySW 43rd St S E Carr R dRentonAveExtS G r a d y W a y ParkAveNS 43rdSt 148th Ave SESE 192nd St SouthcenterBlvd S 180th St66 t h Av e SAirport Way S178thSt S W G r a d y W a y Renton A v e S SE 204thW ay61stAve SM onster Rd SW NE 3 rd S t1 4 0 th A veSES CarrRd140thWaySEHouserWayN68thAveSS 133rd St £ 0 2,000 4,0001,000 Feet WATER QUALITY - SOUTH CITY OF RENTON STORM WATERFACILITY RETROFIT STUDY ProjectName AS SETIDWINSPER (LIBERTY VIEW I&II)111342SPRINGBROOK TERRACE 111354HIDDEN CEDARS DIV II 111361PANTHER MEADOW 111369BERGSMA SHORT PLAT 111408RENTON VILLAGE INTERCEPTOR ST 111422TIFFANY PARK DIV 4 117902ARMSTRONG AND SANDELIUS 117912KNUDSON117915PARKWOOD SOUTH DI V 1 117916WINDSOR HEIGHTS 117917BENSON WOODS 117918BOB BURKE 117929BENSON GLEN 117931FERNWOOD EAST 117936CHINQUAPIN RIDGE 117938VALLEY VUE ESTATES 117940HIDDEN CEDARS DIV II 117945BENSON GLEN 117947CHINQUAPIN RIDGE 117952DAVIS AV S ON E VALL EY PLACE 145398VICTORIA HILLS 145407PARKWOOD145827SOUTH KNOLL WATER EXTENSI ON 145832LUND SHORT PLAT 146790ORCHARD PARK 167768KELSEY LANE 200040KELSEY LANE 2 200041PARKWOOD SOUTH DI V.III 200096 Legend Existing WQ Treatment BMPs Associated with Detention Facility's Tributary Basin Approx. Tributary Area To Facility Structure Type !H Bioswale Media Filter Drain #0 Modified Media Filter Drain Stormfilter - Contech 'Stormwater Wetland 'Wet Pond "6 Wet Vault Storm Water Detention Facility Tributary Basins Page 14 ATTACHMENT C: WATER QUALITY VOLUME AND FLOW RATES FOR TRIBUTARY BASINS WITHOUT WATER QUALITY FACILITIES Road, Mod, N/A Road, Steep, N/A Lawn, Mod, A/B Lawn, Steep, A/B Lawn, Mod, C Lawn, Steep, C Forest, Mod, A/B Forest, Steep, A/B Forest, Mod, C Forest, Steep, C Wetlands, Mod, A/B Wetlands, Steep, A/B Wetlands, Mod, C Wetland, Steep, C ASSET ID PROJECT NAME 1 2 3 4 5 6 7 8 9 10 11 12 13 14 WQ VOLUME (ACRE-FT) WQ ONLINE FLOW RATE (CFS) WQ OFFLINE FLOW RATE (CFS) 111332 SUMMERWIND DIV I II III 10.685 0.246 8.107 1.138 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 1.813 3.446 1.817 111342 WINSPER (LIBERTY VIEW I&II)0.667 0.000 0.551 0.005 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.110 0.208 0.110 111354 SPRINGBROOK TERRACE 1.213 1.368 0.566 2.077 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.439 0.947 0.492 111361 HIDDEN CEDARS DIV II 2.465 0.018 2.497 0.177 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.428 0.863 0.451 111391 DENNYS RESTAURANT 4.120 2.976 0.969 0.846 3.464 3.825 0.000 0.000 0.673 3.330 0.000 0.000 0.000 0.000 1.705 2.603 1.385 111393 CASTLEWOOD RANCHETTES 1.895 0.073 3.298 0.737 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.394 0.971 0.491 111394 CASTLEWOOD RANCHETTES 3.063 0.128 4.702 0.834 0.000 0.000 3.157 1.008 0.000 0.000 0.305 0.000 0.000 0.000 0.631 1.456 0.743 111408 BERGSMA SHORT PLAT 0.986 0.000 2.092 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.199 0.490 0.248 111421 RIPLEY LN STORM IMPROVEMENT PR 111.245 47.725 115.749 59.007 14.931 11.097 8.783 18.912 1.055 4.250 13.512 6.114 0.480 0.026 30.830 61.870 32.156 111422 RENTON VILLAGE INTERCEPTOR ST*211.670 69.049 304.451 136.061 5.053 12.703 3.894 0.256 0.000 0.000 2.079 0.161 0.000 0.026 53.743 122.320 62.615 117894 SWAN MEADOWS I 0.901 0.000 0.808 0.032 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.152 0.294 0.154 117900 MEADOW AV N & N 24TH ST 1.094 0.184 1.172 0.242 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.221 0.457 0.238 117902 TIFFANY PARK DIV 4 6.749 0.044 3.299 0.073 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 1.059 1.787 0.963 117912 ARMSTRONG AND SANDELIUS 0.552 0.059 1.005 0.592 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.132 0.358 0.178 117915 KNUDSON 0.186 0.000 0.012 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.027 0.037 0.021 117916 PARKWOOD SOUTH DIV 1 2.942 0.073 2.207 0.233 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.497 0.934 0.493 117917 WINDSOR HEIGHTS 0.250 0.002 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.036 0.048 0.027 117921 SWAN MEADOWS II 0.625 0.000 0.181 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.094 0.146 0.080 117936 FERNWOOD EAST 4.332 0.048 4.682 0.292 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.762 1.560 0.812 117941 WEATHERWOOD II 5.624 0.387 4.842 1.100 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 1.021 2.033 1.064 117945 HIDDEN CEDARS DIV II 0.623 0.000 0.772 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.110 0.230 0.120 117952 CHINQUAPIN RIDGE 1.411 0.000 0.799 0.022 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.223 0.388 0.208 145336 PETETT MEADOWS SHORT PLAT 0.911 0.000 0.606 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.146 0.262 0.140 145398 DAVIS AV S ONE VALLEY PLACE 7.279 0.164 2.241 0.420 0.000 0.000 0.932 0.252 0.000 0.000 0.000 0.000 0.000 0.000 1.132 1.818 0.990 145407 VICTORIA HILLS 11.871 5.943 11.571 14.994 0.360 0.040 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 3.302 7.654 3.911 145785 ELIZABETH PLACE 0.352 0.462 0.035 0.015 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.115 0.177 0.099 145824 RUDDELLS 2ND ADDITION 0.819 0.039 2.302 0.034 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.188 0.502 0.252 145827 PARKWOOD 3.397 0.008 2.731 0.032 0.000 0.000 1.187 0.116 0.000 0.000 0.000 0.000 0.000 0.000 0.562 1.051 0.556 145832 SOUTH KNOLL WATER EXTENSION 1.791 0.750 0.000 0.000 3.290 2.543 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.787 0.756 0.424 145834 POLLOS ESTATES 0.994 0.042 0.656 0.464 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.179 0.367 0.191 145836 HIGHBURY PARK 5.319 0.420 5.300 3.115 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 1.054 2.369 1.213 145851 YOUNG ADDITION 0.963 0.030 0.076 0.074 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.145 0.213 0.118 145864 RIDGEVIEW ESTATES 3.491 0.001 3.054 0.230 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.589 1.144 0.601 145869 YOUNG ADDITION 0.741 0.000 0.798 0.029 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.129 0.261 0.136 146790 LUND SHORT PLAT 0.186 0.000 0.279 0.046 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.036 0.083 0.042 167768 ORCHARD PARK 2.020 0.011 2.181 0.141 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.354 0.725 0.378 200040 KELSEY LANE 1.184 0.025 0.758 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.193 0.341 0.182 200041 KELSEY LANE 0.170 0.001 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.024 0.033 0.019 200096 PARKWOOD SOUTH DIV III 0.281 0.000 0.416 0.000 0.000 0.000 0.582 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.052 0.114 0.059 Page 15 ATTACHMENT D: WWHM MODELING FOR UNIT SIZING WATER QUALITY VOLUMES AND FLOW RATES The following analyses were completed to assess the validity of using a unit-scaled approach to estimate the required minimum WQ volumes and flow rates for site-specific treatment BMP sizing. 1.The WWHM location shown in the figure below was used for all basin modeling. The precipitation factors range from 1 to 1.167, therefore the more conservative precipitation factor was selected for the gap analysis. 2.All impervious types were classified as “road” in WWHM 2012, as the following impervious land use types all generated identical water quality volume and flow results. LAND TYPE PERV/ IMPV SOIL SLOPE ACRE 24 HOUR WQ VOLUME (ACRE-FT) WQ ONLINE (CFS) WQ OFFLINE (CFS) Roads Impervious N/A Flat 1 0.1418 0.191 0.1079 Roof Tops Impervious N/A Flat 1 0.1418 0.191 0.1079 Driveways Impervious N/A Flat 1 0.1418 0.191 0.1079 Sidewalks Impervious N/A Flat 1 0.1418 0.191 0.1079 Parking Impervious N/A Flat 1 0.1418 0.191 0.1079 3.Confirmed linear relationship between the size of the basin and the WQ volume and WQ online and offline flow rates. 4.Slope sensitivity: o C soils had nearly identical WQ volumes and flow rates for flat and moderate slopes LAND TYPE PERV/ IMPV SOIL SLOPE ACRE 24 HOUR WQ VOLUME (AC-FT) WQ ONLINE (CFS) WQ OFFLINE (CFS) Forest Pervious C Flat 10 0.5436 0.2963 0.1623 Forest Pervious C Mod 10 0.5438 0.2967 0.1625 Forest Pervious C Steep 10 0.7678 0.4279 0.2296 Lawn Pervious C Flat 10 0.6522 0.3579 0.2014 Lawn Pervious C Mod 10 0.6545 0.3617 0.2032 Lawn Pervious C Steep 10 0.8397 0.5023 0.2771 o The water quality volumes and flow rates for A/B soil with a moderate slope fell in between A/B soil with flat slopes and A/B soil with steep slopes. LAND TYPE PERV/ IMPV SOIL SLOPE ACRE 24 HOUR WQ VOLUME (AC-FT) WQ ONLINE (CFS) WQ OFFLINE (CFS) Forest Pervious A/B Flat 1 0.0002 0.0007 0.0005 Forest Pervious A/B Mod 1 0.0003 0.0007 0.0006 0 0.5 1 1.5 2 2.5 0 2 4 6 8 10 12WQNeed Basin Area (acres) Road, Flat WQ Volume (ac-ft)WQ Online (cfs)WQ Offline (cfs) 0 0.5 1 1.5 0 2 4 6 8 10 12WQNeed Basin Area (acres) Lawn, A/B, Flat WQ Volume (ac-ft)WQ Online (cfs)WQ Offline (cfs) Forest Pervious A/B Steep 1 0.004 0.0013 0.0006 Lawn Pervious A/B Flat 1 0.0258 0.1213 0.0585 Lawn Pervious A/B Mod 1 0.0279 0.1448 0.0677 Lawn Pervious A/B Steep 1 0.0295 0.1588 0.0729 Pasture Pervious A/B Flat 1 0.0011 0.0066 0.0026 Pasture Pervious A/B Mod 1 0.0022 0.0132 0.0055 Pasture Pervious A/B Steep 1 0.0032 0.0187 0.0078 o The water quality volumes and flow rates for road with a moderate slope was very similar to road with a flat slope. LAND TYPE PERV/ IMPV SOIL SLOPE ACRE 24 HOUR WQ VOLUME (AC-FT) WQ ONLINE (CFS) WQ OFFLINE (CFS) Roads Impervious N/A Flat 10 1.4189 1.9113 1.0797 Roads Impervious N/A Mod 10 1.4029 2.1341 1.2021 Roads Impervious N/A Steep 10 1.3831 2.2216 1.2496 o CONCLUSION:The moderate data was selected to represent the rates for both flat and moderate slopes due to minimal differences and the more conservative of the two options. The steep slopes had separate water quality volumes and flow rates. 5.Checked to confirm that calculating the water quality volumes and flow rates for a basin using unit volumes and flow rates (calculated as the summation of acreage of each land type x unit rate of that land type) produced comparable volumes and flow rates to a basin modeled explicitly in WWHM 2012. o When lawn pervious type was used in combination with other land covers, the combined basin model produced much lower rates than when per acre unit rates were summed. o All combined models resulted in lower total WQ volumes and flow rates, therefore the per acre assumption was considered the more conservative approach for calculating design water quality volumes and flow rates and adequate for prioritization purposes. LAND TYPE PERV/ IMPV SOIL SLOPE ACRE 24 HOUR WQ VOLUME (AC-FT) WQ ONLINE WQ OFFLINE Forest Pervious A/B Flat 1 0.0002 0.0007 0.0005 Roads Impervious N/A Flat 1 0.1418 0.191 0.1079 Roads Impervious N/A Flat 1 0.1418 0.191 0.1079 TOTAL SUM 0.2838 0.3827 0.2163 1 Forest + 2 Road Combo A/B Flat 3 0.2838 0.3824 0.216 Lawn Pervious A/B Flat 1 0.0258 0.1213 0.0585 Roads Impervious N/A Flat 1 0.1418 0.191 0.1079 Roads Impervious N/A Flat 1 0.1418 0.191 0.1079 TOTAL SUM 0.3094 0.5033 0.2743 Lawn + 2 Road Combo A/B Flat 3 0.2847 0.3858 0.2178 Lawn Pervious A/B Flat 1 0.0258 0.1213 0.0585 Lawn Pervious A/B Flat 1 0.0258 0.1213 0.0585 Lawn Pervious A/B Flat 1 0.0258 0.1213 0.0585 Roads Impervious N/A Flat 1 0.1418 0.191 0.1079 Roads Impervious N/A Flat 1 0.1418 0.191 0.1079 TOTAL SUM 0.361 0.7459 0.3913 3 Lawn + 2 Road Combo A/B Flat 5 0.2907 0.3929 0.2219 Forest Pervious A/B Flat 1 0.0002 0.0007 0.0005 Forest Pervious A/B Flat 1 0.0002 0.0007 0.0005 Forest Pervious A/B Flat 1 0.0002 0.0007 0.0005 Roads Impervious N/A Flat 1 0.1418 0.191 0.1079 Roads Impervious N/A Flat 1 0.1418 0.191 0.1079 TOTAL SUM 0.2842 0.3841 0.2173 3 Forest + 2 Road Combo A/B Flat 5 0.284 0.3827 0.2162 Lawn Pervious A/B Flat 1 0.0258 0.1213 0.0585 Lawn Pervious A/B Flat 1 0.0258 0.1213 0.0585 Lawn Pervious A/B Flat 1 0.0258 0.1213 0.0585 Forest Pervious A/B Flat 1 0.0002 0.0007 0.0005 Forest Pervious A/B Flat 1 0.0002 0.0007 0.0005 TOTAL SUM 0.0778 0.3653 0.1765 3 Lawn + 2 Forest Combo A/B Flat 5 0.0697 0.3456 0.1633 6.A higher percentage of lawn in a given basin resulted in much lower water quality volumes and flow rates than that calculated using per acre unit rates. Most of the basins have a high percentage of impervious surfaces, therefore the discrepancy will be minimized, and the unit rates, while conservative, will be reasonably close to rates calculated if each basin was explicitly modeled. WQ VOLUME (ACRE-FT)WQ ONLINE FLOW RATE (CFS)WQ OFFLINE FLOW RATE (CFS) % ACRES OF LAWN PER 10 ACRES Slope, Soil PER ACRE ASSUMPTION COMPLETE BASIN MODEL PER ACRE ASSUMPTION COMPLETE BASIN MODEL PER ACRE ASSUMPTION COMPLETE BASIN MODEL 0%Flat, A/B 1.42 1.42 1.91 1.91 1.08 1.08 10%Flat, A/B 1.30 1.28 1.84 1.72 1.03 0.97 20%Flat, A/B 1.19 1.14 1.77 1.54 0.98 0.87 30%Flat, A/B 1.07 1.00 1.70 1.35 0.93 0.76 40%Flat, A/B 0.95 0.86 1.63 1.16 0.88 0.66 50%Flat, A/B 0.84 0.72 1.56 0.97 0.83 0.55 60%Flat, A/B 0.72 0.58 1.49 0.79 0.78 0.44 70%Flat, A/B 0.61 0.44 1.42 0.60 0.73 0.34 80%Flat, A/B 0.49 0.31 1.35 0.41 0.68 0.23 90%Flat, A/B 0.37 0.17 1.28 0.23 0.63 0.13 100%Flat, A/B 0.26 0.26 1.21 1.21 0.59 0.59 7.Pasture was not evaluated fully since that land cover was not part of the basins in this study but confirmed that falls between lawn and forest, and slightly closer to forest. LAND TYPE PERV/ IMPV SOIL SLOPE ACRE 24 HOUR WQ VOLUME (AC-FT) WQ ONLINE (CFS) WQ OFFLINE (CFS) Forest Pervious C Flat 1 0.0543 0.0296 0.0162 Pasture Pervious C Flat 1 0.0584 0.0316 0.0174 Lawn Pervious C Flat 1 0.0652 0.0357 0.0201 Page 16 ATTACHMENT E: WWHM MODELING REPORTS AND BIOSWALE SIZING OF EXISTING WATER QUALITY FACILITIES WWHM2012 PROJECT REPORT ___________________________________________________________________ Project Name: Renton Retrofit Site Name: Asset ID 117947 Benson Glen Site Address: 17032 110th Pl SE City : Renton Report Date: 3/18/2021 Gage : Seatac Data Start : 1948/10/01 Data End : 2009/09/30 Precip Scale: 1.00 Version Date: 2019/09/13 Version : 4.2.17 ___________________________________________________________________ Low Flow Threshold for POC 1 : 50 Percent of the 2 Year ___________________________________________________________________ High Flow Threshold for POC 1: 50 year ___________________________________________________________________ PREDEVELOPED LAND USE Name : Dummy Basin Bypass: No GroundWater: No Pervious Land Use acre A B, Forest, Flat 4.633 Pervious Total 4.633 Impervious Land Use acre Impervious Total 0 Basin Total 4.633 ___________________________________________________________________ Element Flows To: Surface Interflow Groundwater ___________________________________________________________________ MITIGATED LAND USE Name : Basin 1 Bypass: No GroundWater: No ASSET ID 117947 BENSON GLEN Pervious Land Use acre A B, Lawn, Mod 2.418 A B, Lawn, Steep .105 Pervious Total 2.523 Impervious Land Use acre ROADS MOD 2.11 Impervious Total 2.11 Basin Total 4.633 ___________________________________________________________________ Element Flows To: Surface Interflow Groundwater Tank 1 Tank 1 ___________________________________________________________________ Name : Tank 1 Tank Name: Tank 1 Dimensions Depth: 6 ft. Tank Type : Circular Diameter : 6 ft. Length : 180 ft. Discharge Structure Riser Height: 5.5 ft. Riser Diameter: 18 in. Orifice 1 Diameter: 3 in. Elevation: 0 ft. Orifice 2 Diameter: 3 in. Elevation: 3.1 ft. Element Flows To: Outlet 1 Outlet 2 ___________________________________________________________________ ANALYSIS RESULTS Stream Protection Duration ___________________________________________________________________ Predeveloped Landuse Totals for POC #1 Total Pervious Area:4.633 Total Impervious Area:0 ___________________________________________________________________ Mitigated Landuse Totals for POC #1 Total Pervious Area:2.523 Total Impervious Area:2.11 ___________________________________________________________________ CONTROL STRUCTURE SIZES BASED ON AS-BUILTS Flow Frequency Return Periods for Predeveloped. POC #1 Return Period Flow(cfs) 2 year 0.003931 5 year 0.00595 10 year 0.007593 25 year 0.01006 50 year 0.01221 100 year 0.014654 Flow Frequency Return Periods for Mitigated. POC #1 Return Period Flow(cfs) 2 year 0.415971 5 year 0.543402 10 year 0.6378 25 year 0.768908 50 year 0.875515 100 year 0.9901 ___________________________________________________________________ 2 YEAR FLOW RATE FROM DETENTION TANK USED AS WATER QUALITY FLOW RATE IN SWALE DESIGN SPREADSHEET RT.05 - Wet Biofiltration Swale Project: Renton RetroFit Designed By: Mark Bodnar Description: Asset ID 117947 Benson Glen Checked By: WET BIOSWALE SPREADSHEET VERSION 2.1 Design Steps D-1 Determine runoff treatment design flow rate Qwq Qwq 0.416 Runoff treatment design flow rate from MGS Flood OR SBUH; MGSFlood reports an online and offline flow rate, please enter the applicable design flow rate D-2 Determine the wet biofiltration design flow rate (Qbiofil) Is the wet bioswale in eastern WA? No 1.50 Wet biofiltration swales are offline -------> offline Qbiofil 1.551 runoff treatment design flow rate D-3 Determine the longitudinal slope of the proposed wet biofiltration swale (ft/ft) s 0.005 ft/ft D-4 Select a soil and vegetation cover suitable for the wet biofiltration swale soil/veg <--Use pull down box Manning's n=0.22 D-5 Select the design depth of flow y (see HRM Table 5-4) y 0.33 (ft) design depth of flow; wet biofiltration swales depth of flow = 4" (0.33 ft) for WQ event D-6 Select a trapezoidal swale cross-sectional shape. D-7 <--manning's changed HRM Chapter 5 Equation E-11 Use Excel Solver D-7a Qbiofil 1.551 cfs - runoff treatment design flow rate A 7.013 ft2 - wetted area R 0.314 ft - hydraulic radius s 0.005 ft/ft longitudinal slope of swale n 0.22 Manning's coefficient b 20.26 ft; wet bioswale bottom width zforeslope 3.00 horizontal number of bioswale slope i.e. 1V:3H, z=3 in this instance zbackslope 3.00 horizontal number of bioswale slope i.e. 1V:3H, z=3 in this instance y 0.330 ft - design depth flow = maximum depth of flow Qbiofil 1.551 Wet bioswales with bottom witdths between 10 to 25 feet must maintain a 5:1 length to width ratio D-7b If the swale calculations above give a swale width less than 2 feet wide, re-run calculations with 2 foot wide swale, solve for depth y Or if redesigning swale with different dimensions, use below calculator and use Excel Goal Seek to determine new depth of flow. Qbiofil 1.551 cfs - runoff treatment design flow rate A 4.741 ft2 - wetted area R 0.565 ft - hydraulic radius s 0.005 ft/ft longitudinal slope of swale n 0.22 Manning's coefficient b 3.00 ft - enter new wet bioswale bottom width if applicable (2 foot is minimum) zforeslope 3.00 horizontal number of bioswale slope i.e. 1V:3H, z=3 in this instance zbackslope 3.00 horizontal number of bioswale slope i.e. 1V:3H, z=3 in this instance y 0.853 ft - design depth flow Qbiofil 1.551 6-month 24 hr precip depth (in) Grass-legume mix on lightly compacted topsoil From HRM Table 5-3 Use Manning's Eq and first approximations relating hydraulic radius and dimensions to get width for trapezoidal cross section cfs - use goal seek under "What-If Analysis" in the "DATA" menu to set this cell equal to Qbiofil above changing the "b" value cfs - use goal seek under "What-If Analysis" in the "DATA" menu to set this cell equal to Q above n sARQbiofil 2 1 3 2 49.1= 5.0 67. 49.1 s nQ AR biofil= CABS Size Benson Glen 1.xls 3/19/2021 2:08 PM Version 2.1 D-8 Enter Final Bioswale Dimensions from the calculations in Step D-7a or D-7b Enter Final Swale Area 4.741 ft2 - Wetted Area Enter Final Swale R 0.565 ft - hydraulic radius Enter Final Swale slope s 0.005 ft/ft longitudinal slope of swale Enter Final Swale n 0.22 Manning's coefficient Enter Final Swale bottom width b 3.00 ft - swale bottom width Enter Final Swale zforeslope 3.00 horizontal number of bioswale slope i.e. 1V:3H, z=3 in this instance Enter Final Swale zbackslope 3.00 horizontal number of bioswale slope i.e. 1V:3H, z=3 in this instance Enter Final Swale flow depth y 0.853 ft - design depth flow D-9 Computer the flow velocity at Qbiofil HRM Chapter 5 Equation E-12 Vbiofil 0.33 ft/sec - flow velocity; 1 ft/sec maximum Flow veloicty is OK since it is less than 1 ft/sec D-10 Compute Swale Length L (ft) t 540 seconds - 9 minutes (540 seconds) for CABS, Basic, and Wet bioswale L 176.64 ft - required length of bioswale; If swale is less than 100 feet, make swale have narrower bottom width (2 foot minimum) and repeat Steps D-7 - D-10 and recalculate to get length over 100 feet or keep swale bottom width make swale length 100 feet minimum D-11 Extended Wet Season Adjustment for Western Washington designs only Is the wet bioswale downstream of a detention pond? Enter the wet bioswale length (ft) --------------> wet bioswale bottom treatment area x 2 = Adjust the wet bioswale length and/or bottom width to provide an equivalent bottom treatment area; maintaining a 5:1 length to width ratio and depth of flow of 4 inches D-12 Revise Wet Bioswale Dimensions to meet minimums and for construction Is the wet bioswale length at least 100 feet? If not, increase swale length to 100 feet. Is the wet bioswale bottom width a constructible width? Do no recalculate the wet bioswale depth of flow or velocity if the wet bioswale has the extended wet season adjustment. Enter Final Adjusted Wet Bioswale Dimensions Enter Final Swale bottom width b 3.00 ft - swale bottom width Enter Final Swale length 177.00 ft - swale bottom length ERROR; wet bioswale treatment area needs to be increased for the extended wet season adjustment critria above. 177.00 ft 3.0 ft 0.005 ft/ft 3.0 3.0 0.85 ft 0.85 ft "DATA" menu to set this cell equal to Qbiofil above changing the "y" value Yes But does not apply Final Wet Bioswale Dimensions Swale Depth = WQ Depth for offline swales Wet Bioswale Length Wet Bioswale Bottom Width Swale Longitudinal Slope zforeslope zbackslope WQ Depth A Q V biofil biofil = tVLbiofil´= CABS Size Benson Glen 1.xls 3/19/2021 2:08 PM Version 2.1 WWHM2012 PROJECT REPORT ___________________________________________________________________ Project Name: Renton Retrofit Site Name: Asset ID 117931 Benson Glen Site Address: 10900 SE 170th St City : Renton Report Date: 3/18/2021 Gage : Seatac Data Start : 1948/10/01 Data End : 2009/09/30 Precip Scale: 1.00 Version Date: 2019/09/13 Version : 4.2.17 ___________________________________________________________________ Low Flow Threshold for POC 1 : 50 Percent of the 2 Year ___________________________________________________________________ High Flow Threshold for POC 1: 50 year ___________________________________________________________________ PREDEVELOPED LAND USE Name : Dummy Basin Bypass: No GroundWater: No Pervious Land Use acre A B, Forest, Flat 1.704 Pervious Total 1.704 Impervious Land Use acre Impervious Total 0 Basin Total 1.704 ___________________________________________________________________ Element Flows To: Surface Interflow Groundwater ___________________________________________________________________ MITIGATED LAND USE Name : Mitigated Bypass: No GroundWater: No ASSET ID 117931 BENSON GLEN Pervious Land Use acre A B, Lawn, Mod .742 A B, Lawn, Steep .001 Pervious Total 0.743 Impervious Land Use acre ROADS MOD 0.961 Impervious Total 0.961 Basin Total 1.704 ___________________________________________________________________ Element Flows To: Surface Interflow Groundwater Tank 1 Tank 1 ___________________________________________________________________ Name : Tank 1 Tank Name: Tank 1 Dimensions Depth: 4 ft. Tank Type : Circular Diameter : 4 ft. Length : 330 ft. Discharge Structure Riser Height: 3.5 ft. Riser Diameter: 12 in. Orifice 1 Diameter: 1.73 in. Elevation: 0 ft. Orifice 2 Diameter: 1.91 in. Elevation: 2.15 ft. Element Flows To: Outlet 1 Outlet 2 ___________________________________________________________________ ANALYSIS RESULTS Stream Protection Duration ___________________________________________________________________ Predeveloped Landuse Totals for POC #1 Total Pervious Area:1.704 Total Impervious Area:0 ___________________________________________________________________ Mitigated Landuse Totals for POC #1 Total Pervious Area:0.743 Total Impervious Area:0.961 ___________________________________________________________________ CONTROL STRUCTURE SIZES BASED ON AS-BUILTS Flow Frequency Return Periods for Predeveloped. POC #1 Return Period Flow(cfs) 2 year 0.001446 5 year 0.002188 10 year 0.002793 25 year 0.0037 50 year 0.004491 100 year 0.00539 Flow Frequency Return Periods for Mitigated. POC #1 Return Period Flow(cfs) 2 year 0.128118 5 year 0.186891 10 year 0.234354 25 year 0.305199 50 year 0.366652 100 year 0.436238 ___________________________________________________________________ 2 YEAR FLOW RATE FROM DETENTION TANK USED AS WATER QUALITY FLOW RATE IN SWALE DESIGN SPREADSHEET RT.05 - Wet Biofiltration Swale Project: Renton RetroFit Designed By: MPB Description: Asset ID 117931 Benson Glen Checked By: WET BIOSWALE SPREADSHEET VERSION 2.1 Design Steps D-1 Determine runoff treatment design flow rate Qwq Qwq 0.128 Runoff treatment design flow rate from MGS Flood OR SBUH; MGSFlood reports an online and offline flow rate, please enter the applicable design flow rate D-2 Determine the wet biofiltration design flow rate (Qbiofil) Is the wet bioswale in eastern WA? No 1.50 Wet biofiltration swales are offline -------> offline Qbiofil 0.478 runoff treatment design flow rate D-3 Determine the longitudinal slope of the proposed wet biofiltration swale (ft/ft) s 0.005 ft/ft D-4 Select a soil and vegetation cover suitable for the wet biofiltration swale soil/veg <--Use pull down box Manning's n=0.22 D-5 Select the design depth of flow y (see HRM Table 5-4) y 0.33 (ft) design depth of flow; wet biofiltration swales depth of flow = 4" (0.33 ft) for WQ event D-6 Select a trapezoidal swale cross-sectional shape. D-7 <--manning's changed HRM Chapter 5 Equation E-11 Use Excel Solver D-7a Qbiofil 0.478 cfs - runoff treatment design flow rate A 2.304 ft2 - wetted area R 0.285 ft - hydraulic radius s 0.005 ft/ft longitudinal slope of swale n 0.22 Manning's coefficient b 5.99 ft; wet bioswale bottom width zforeslope 3.00 horizontal number of bioswale slope i.e. 1V:3H, z=3 in this instance zbackslope 3.00 horizontal number of bioswale slope i.e. 1V:3H, z=3 in this instance y 0.330 ft - design depth flow = maximum depth of flow Qbiofil 0.478 D-7b If the swale calculations above give a swale width less than 2 feet wide, re-run calculations with 2 foot wide swale, solve for depth y Or if redesigning swale with different dimensions, use below calculator and use Excel Goal Seek to determine new depth of flow. Qbiofil 0.478 cfs - runoff treatment design flow rate A 2.489 ft2 - wetted area R 0.255 ft - hydraulic radius s 0.005 ft/ft longitudinal slope of swale n 0.22 Manning's coefficient b 8.00 ft - enter new wet bioswale bottom width if applicable (2 foot is minimum) zforeslope 3.00 horizontal number of bioswale slope i.e. 1V:3H, z=3 in this instance zbackslope 3.00 horizontal number of bioswale slope i.e. 1V:3H, z=3 in this instance y 0.281 ft - design depth flow Qbiofil 0.479 cfs - use goal seek under "What-If Analysis" in the "DATA" menu to set this cell equal to Qbiofil above changing the "y" value 6-month 24 hr precip depth (in) Grass-legume mix on lightly compacted topsoil From HRM Table 5-3 Use Manning's Eq and first approximations relating hydraulic radius and dimensions to get width for trapezoidal cross section cfs - use goal seek under "What-If Analysis" in the "DATA" menu to set this cell equal to Qbiofil above changing the "b" value n sARQbiofil 2 1 3 2 49.1= 5.0 67. 49.1 s nQ AR biofil= CABS Size Benson Glen 2.xls 3/19/2021 2:09 PM Version 2.1 D-8 Enter Final Bioswale Dimensions from the calculations in Step D-7a or D-7b Enter Final Swale Area 2.489 ft2 - Wetted Area Enter Final Swale R 0.255 ft - hydraulic radius Enter Final Swale slope s 0.005 ft/ft longitudinal slope of swale Enter Final Swale n 0.22 Manning's coefficient Enter Final Swale bottom width b 8.00 ft - swale bottom width Enter Final Swale zforeslope 3.00 horizontal number of bioswale slope i.e. 1V:3H, z=3 in this instance Enter Final Swale zbackslope 3.00 horizontal number of bioswale slope i.e. 1V:3H, z=3 in this instance Enter Final Swale flow depth y 0.281 ft - design depth flow D-9 Computer the flow velocity at Qbiofil HRM Chapter 5 Equation E-12 Vbiofil 0.19 ft/sec - flow velocity; 1 ft/sec maximum Flow veloicty is OK since it is less than 1 ft/sec D-10 Compute Swale Length L (ft) t 540 seconds - 9 minutes (540 seconds) for CABS, Basic, and Wet bioswale L 103.61 ft - required length of bioswale; If swale is less than 100 feet, make swale have narrower bottom width (2 foot minimum) and repeat Steps D-7 - D-10 and recalculate to get length over 100 feet or keep swale bottom width make swale length 100 feet minimum D-11 Extended Wet Season Adjustment for Western Washington designs only Is the wet bioswale downstream of a detention pond? Enter the wet bioswale length (ft) --------------> wet bioswale bottom treatment area x 2 = Adjust the wet bioswale length and/or bottom width to provide an equivalent bottom treatment area; maintaining a 5:1 length to width ratio and depth of flow of 4 inches D-12 Revise Wet Bioswale Dimensions to meet minimums and for construction Is the wet bioswale length at least 100 feet? If not, increase swale length to 100 feet. Is the wet bioswale bottom width a constructible width? Do no recalculate the wet bioswale depth of flow or velocity if the wet bioswale has the extended wet season adjustment. Enter Final Adjusted Wet Bioswale Dimensions Enter Final Swale bottom width b 8.00 ft - swale bottom width Enter Final Swale length 104.00 ft - swale bottom length ERROR; wet bioswale treatment area needs to be increased for the extended wet season adjustment critria above. 104.00 ft 8.0 ft 0.005 ft/ft 3.0 3.0 0.28 ft 0.28 ftSwale Depth = WQ Depth for offline swales Wet Bioswale Length Wet Bioswale Bottom Width Swale Longitudinal Slope zforeslope zbackslope WQ Depth changing the "y" value Yes Does not apply Final Wet Bioswale Dimensions A Q V biofil biofil = tVLbiofil´= CABS Size Benson Glen 2.xls 3/19/2021 2:09 PM Version 2.1 WWHM2012 PROJECT REPORT ___________________________________________________________________ Project Name: Renton Retrofit Site Name: Asset ID 117938 Chinquapin Ridge Site Address: 11205 SE 190th Pl City : Renton Report Date: 3/17/2021 Gage : Seatac Data Start : 1948/10/01 Data End : 2009/09/30 Precip Scale: 1.00 Version Date: 2019/09/13 Version : 4.2.17 ___________________________________________________________________ Low Flow Threshold for POC 1 : 50 Percent of the 2 Year ___________________________________________________________________ High Flow Threshold for POC 1: 50 year ___________________________________________________________________ PREDEVELOPED LAND USE Name : Dummy Basin Bypass: No GroundWater: No Pervious Land Use acre A B, Forest, Flat .549 Pervious Total 0.549 Impervious Land Use acre Impervious Total 0 Basin Total 0.549 ___________________________________________________________________ Element Flows To: Surface Interflow Groundwater ___________________________________________________________________ MITIGATED LAND USE Name : Mitigated Bypass: No GroundWater: No ASSET ID 117938 CHINQUAPIN RIDGE Pervious Land Use acre A B, Lawn, Mod .133 A B, Lawn, Steep .053 Pervious Total 0.186 Impervious Land Use acre ROADS MOD 0.352 ROADS STEEP 0.011 Impervious Total 0.363 Basin Total 0.549 ___________________________________________________________________ Element Flows To: Surface Interflow Groundwater Tank 1 Tank 1 ___________________________________________________________________ Name : Tank 1 Tank Name: Tank 1 Dimensions Depth: 4 ft. Tank Type : Circular Diameter : 4 ft. Length : 72 ft. Discharge Structure Riser Height: 3.5 ft. Riser Diameter: 12 in. Orifice 1 Diameter: 1.625 in. Elevation: 0 ft. Orifice 2 Diameter: 1.625 in. Elevation: 1.9 ft. Element Flows To: Outlet 1 Outlet 2 ___________________________________________________________________ ANALYSIS RESULTS Stream Protection Duration ___________________________________________________________________ Predeveloped Landuse Totals for POC #1 Total Pervious Area:0.549 Total Impervious Area:0 ___________________________________________________________________ Mitigated Landuse Totals for POC #1 Total Pervious Area:0.186 Total Impervious Area:0.363 ___________________________________________________________________ CONTROL STRUCTURE SIZES BASED ON AS-BUILTS Flow Frequency Return Periods for Predeveloped. POC #1 Return Period Flow(cfs) 2 year 0.000466 5 year 0.000705 10 year 0.0009 25 year 0.001192 50 year 0.001447 100 year 0.001737 Flow Frequency Return Periods for Mitigated. POC #1 Return Period Flow(cfs) 2 year 0.081835 5 year 0.101626 10 year 0.115989 25 year 0.135569 50 year 0.151217 100 year 0.167798 ___________________________________________________________________ 2 YEAR FLOW RATE FROM DETENTION TANK USED AS WATER QUALITY FLOW RATE IN SWALE DESIGN SPREADSHEET RT.05 - Wet Biofiltration Swale Project: Renton RetroFit Designed By: MPB Description: Asset ID 117938 Chinquapin Ridge Checked By: WET BIOSWALE SPREADSHEET VERSION 2.1 Design Steps D-1 Determine runoff treatment design flow rate Qwq Qwq 0.082 Runoff treatment design flow rate from MGS Flood OR SBUH; MGSFlood reports an online and offline flow rate, please enter the applicable design flow rate D-2 Determine the wet biofiltration design flow rate (Qbiofil) Is the wet bioswale in eastern WA? No 1.50 Wet biofiltration swales are offline -------> offline Qbiofil 0.305 runoff treatment design flow rate D-3 Determine the longitudinal slope of the proposed wet biofiltration swale (ft/ft) s 0.005 ft/ft D-4 Select a soil and vegetation cover suitable for the wet biofiltration swale soil/veg <--Use pull down box Manning's n=0.22 D-5 Select the design depth of flow y (see HRM Table 5-4) y 0.33 (ft) design depth of flow; wet biofiltration swales depth of flow = 4" (0.33 ft) for WQ event D-6 Select a trapezoidal swale cross-sectional shape. D-7 <--manning's changed HRM Chapter 5 Equation E-11 Use Excel Solver D-7a Qbiofil 0.305 cfs - runoff treatment design flow rate A 1.536 ft2 - wetted area R 0.267 ft - hydraulic radius s 0.005 ft/ft longitudinal slope of swale n 0.22 Manning's coefficient b 3.67 ft; wet bioswale bottom width zforeslope 3.00 horizontal number of bioswale slope i.e. 1V:3H, z=3 in this instance zbackslope 3.00 horizontal number of bioswale slope i.e. 1V:3H, z=3 in this instance y 0.330 ft - design depth flow = maximum depth of flow Qbiofil 0.305 D-7b If the swale calculations above give a swale width less than 2 feet wide, re-run calculations with 2 foot wide swale, solve for depth y Or if redesigning swale with different dimensions, use below calculator and use Excel Goal Seek to determine new depth of flow. Qbiofil 0.305 cfs - runoff treatment design flow rate A 1.563 ft2 - wetted area R 0.261 ft - hydraulic radius s 0.005 ft/ft longitudinal slope of swale n 0.22 Manning's coefficient b 4.00 ft - enter new wet bioswale bottom width if applicable (2 foot is minimum) zforeslope 3.00 horizontal number of bioswale slope i.e. 1V:3H, z=3 in this instance zbackslope 3.00 horizontal number of bioswale slope i.e. 1V:3H, z=3 in this instance y 0.316 ft - design depth flow Qbiofil 0.305 6-month 24 hr precip depth (in) Grass-legume mix on lightly compacted topsoil From HRM Table 5-3 Use Manning's Eq and first approximations relating hydraulic radius and dimensions to get width for trapezoidal cross section cfs - use goal seek under "What-If Analysis" in the "DATA" menu to set this cell equal to Qbiofil above changing the "b" value cfs - use goal seek under "What-If Analysis" in the "DATA" menu to set this cell equal to Qbiofil above changing the "y" value n sARQbiofil 2 1 3 2 49.1= 5.0 67. 49.1 s nQ AR biofil= CABS Chinquapin Ridge.xls 3/19/2021 2:07 PM Version 2.1 D-8 Enter Final Bioswale Dimensions from the calculations in Step D-7a or D-7b Enter Final Swale Area 1.563 ft2 - Wetted Area Enter Final Swale R 0.261 ft - hydraulic radius Enter Final Swale slope s 0.005 ft/ft longitudinal slope of swale Enter Final Swale n 0.22 Manning's coefficient Enter Final Swale bottom width b 4.00 ft - swale bottom width Enter Final Swale zforeslope 3.00 horizontal number of bioswale slope i.e. 1V:3H, z=3 in this instance Enter Final Swale zbackslope 3.00 horizontal number of bioswale slope i.e. 1V:3H, z=3 in this instance Enter Final Swale flow depth y 0.316 ft - design depth flow D-9 Computer the flow velocity at Qbiofil HRM Chapter 5 Equation E-12 Vbiofil 0.20 ft/sec - flow velocity; 1 ft/sec maximum Flow veloicty is OK since it is less than 1 ft/sec D-10 Compute Swale Length L (ft) t 540 seconds - 9 minutes (540 seconds) for CABS, Basic, and Wet bioswale L 105.36 ft - required length of bioswale; If swale is less than 100 feet, make swale have narrower bottom width (2 foot minimum) and repeat Steps D-7 - D-10 and recalculate to get length over 100 feet or keep swale bottom width make swale length 100 feet minimum D-11 Extended Wet Season Adjustment for Western Washington designs only Is the wet bioswale downstream of a detention pond? Enter the wet bioswale length (ft) --------------> wet bioswale bottom treatment area x 2 = Adjust the wet bioswale length and/or bottom width to provide an equivalent bottom treatment area; maintaining a 5:1 length to width ratio and depth of flow of 4 inches D-12 Revise Wet Bioswale Dimensions to meet minimums and for construction Is the wet bioswale length at least 100 feet? If not, increase swale length to 100 feet. Is the wet bioswale bottom width a constructible width? Do no recalculate the wet bioswale depth of flow or velocity if the wet bioswale has the extended wet season adjustment. Enter Final Adjusted Wet Bioswale Dimensions Enter Final Swale bottom width b 4.00 ft - swale bottom width Enter Final Swale length 106.00 ft - swale bottom length ERROR; wet bioswale treatment area needs to be increased for the extended wet season adjustment critria above. 106.00 ft 4.0 ft 0.005 ft/ft 3.0 3.0 0.32 ft 0.32 ft changing the "y" value Yes But does not apply Final Wet Bioswale Dimensions Swale Depth = WQ Depth for offline swales Wet Bioswale Length Wet Bioswale Bottom Width Swale Longitudinal Slope zforeslope zbackslope WQ Depth A Q V biofil biofil = tVLbiofil´= CABS Chinquapin Ridge.xls 3/19/2021 2:07 PM Version 2.1 WWHM2012 PROJECT REPORT ___________________________________________________________________ Project Name: Renton Retrofit Site Name: Asset ID 117940 Valley View Estates Site Address: 310 S 22nd Pl City : Renton Report Date: 3/17/2021 Gage : Seatac Data Start : 1948/10/01 Data End : 2009/09/30 Precip Scale: 1.00 Version Date: 2019/09/13 Version : 4.2.17 ___________________________________________________________________ Low Flow Threshold for POC 1 : 50 Percent of the 2 Year ___________________________________________________________________ High Flow Threshold for POC 1: 50 year ___________________________________________________________________ PREDEVELOPED LAND USE Name : Dummy Basin Bypass: No GroundWater: No Pervious Land Use acre A B, Forest, Flat 1.034 Pervious Total 1.034 Impervious Land Use acre Impervious Total 0 Basin Total 1.034 ___________________________________________________________________ Element Flows To: Surface Interflow Groundwater ___________________________________________________________________ MITIGATED LAND USE Name : Mitigated Bypass: No GroundWater: No ASSET ID 117940 VALLEY VIEW ESTATES Pervious Land Use acre A B, Lawn, Mod .387 A B, Lawn, Steep .023 Pervious Total 0.41 Impervious Land Use acre ROADS MOD 0.569 ROADS STEEP 0.055 Impervious Total 0.624 Basin Total 1.034 ___________________________________________________________________ Element Flows To: Surface Interflow Groundwater Tank 1 Tank 1 ___________________________________________________________________ Name : Tank 1 Tank Name: Tank 1 Dimensions Depth: 5 ft. Tank Type : Circular Diameter : 5 ft. Length : 65 ft. Discharge Structure Riser Height: 4.5 ft. Riser Diameter: 12 in. Orifice 1 Diameter: 1.25 in. Elevation: 0 ft. Orifice 2 Diameter: 2.3 in. Elevation: 0 ft. Element Flows To: Outlet 1 Outlet 2 ___________________________________________________________________ ANALYSIS RESULTS Stream Protection Duration ___________________________________________________________________ Predeveloped Landuse Totals for POC #1 Total Pervious Area:1.034 Total Impervious Area:0 ___________________________________________________________________ Mitigated Landuse Totals for POC #1 Total Pervious Area:0.41 Total Impervious Area:0.624 ___________________________________________________________________ CONTROL STRUCTURE SIZES BASED ON AS-BUILTS Flow Frequency Return Periods for Predeveloped. POC #1 Return Period Flow(cfs) 2 year 0.000877 5 year 0.001328 10 year 0.001695 25 year 0.002245 50 year 0.002725 100 year 0.003271 Flow Frequency Return Periods for Mitigated. POC #1 Return Period Flow(cfs) 2 year 0.190746 5 year 0.223128 10 year 0.244278 25 year 0.270859 50 year 0.290637 100 year 0.31045 ___________________________________________________________________ 2 YEAR FLOW RATE FROM DETENTION TANK USED AS WATER QUALITY FLOW RATE IN SWALE DESIGN SPREADSHEET RT.05 - Wet Biofiltration Swale Project: Renton RetroFit Designed By: MPB Description: Asset ID 117940 Valley View Checked By: WET BIOSWALE SPREADSHEET VERSION 2.1 Design Steps D-1 Determine runoff treatment design flow rate Qwq Qwq 0.191 Runoff treatment design flow rate from MGS Flood OR SBUH; MGSFlood reports an online and offline flow rate, please enter the applicable design flow rate D-2 Determine the wet biofiltration design flow rate (Qbiofil) Is the wet bioswale in eastern WA? No 1.50 Wet biofiltration swales are offline -------> offline Qbiofil 0.711 runoff treatment design flow rate D-3 Determine the longitudinal slope of the proposed wet biofiltration swale (ft/ft) s 0.020 ft/ft D-4 Select a soil and vegetation cover suitable for the wet biofiltration swale soil/veg <--Use pull down box Manning's n=0.22 D-5 Select the design depth of flow y (see HRM Table 5-4) y 0.33 (ft) design depth of flow; wet biofiltration swales depth of flow = 4" (0.33 ft) for WQ event D-6 Select a trapezoidal swale cross-sectional shape. D-7 <--manning's changed HRM Chapter 5 Equation E-11 Use Excel Solver D-7a Qbiofil 0.711 cfs - runoff treatment design flow rate A 1.761 ft2 - wetted area R 0.274 ft - hydraulic radius s 0.020 ft/ft longitudinal slope of swale n 0.22 Manning's coefficient b 4.35 ft; wet bioswale bottom width zforeslope 3.00 horizontal number of bioswale slope i.e. 1V:3H, z=3 in this instance zbackslope 3.00 horizontal number of bioswale slope i.e. 1V:3H, z=3 in this instance y 0.330 ft - design depth flow = maximum depth of flow Qbiofil 0.711 D-7b If the swale calculations above give a swale width less than 2 feet wide, re-run calculations with 2 foot wide swale, solve for depth y Or if redesigning swale with different dimensions, use below calculator and use Excel Goal Seek to determine new depth of flow. Qbiofil 0.711 cfs - runoff treatment design flow rate A 1.692 ft2 - wetted area R 0.291 ft - hydraulic radius s 0.020 ft/ft longitudinal slope of swale n 0.22 Manning's coefficient b 3.50 ft - enter new wet bioswale bottom width if applicable (2 foot is minimum) zforeslope 3.00 horizontal number of bioswale slope i.e. 1V:3H, z=3 in this instance zbackslope 3.00 horizontal number of bioswale slope i.e. 1V:3H, z=3 in this instance y 0.368 ft - design depth flow Qbiofil 0.711 cfs - use goal seek under "What-If Analysis" in the "DATA" menu to set this cell equal to Qbiofil above changing the "y" value 6-month 24 hr precip depth (in) Grass-legume mix on lightly compacted topsoil From HRM Table 5-3 Use Manning's Eq and first approximations relating hydraulic radius and dimensions to get width for trapezoidal cross section cfs - use goal seek under "What-If Analysis" in the "DATA" menu to set this cell equal to Qbiofil above changing the "b" value n sARQbiofil 2 1 3 2 49.1= 5.0 67. 49.1 s nQ AR biofil= CABS Valley View.xls 3/19/2021 2:09 PM Version 2.1 D-8 Enter Final Bioswale Dimensions from the calculations in Step D-7a or D-7b Enter Final Swale Area 1.692 ft2 - Wetted Area Enter Final Swale R 0.291 ft - hydraulic radius Enter Final Swale slope s 0.020 ft/ft longitudinal slope of swale Enter Final Swale n 0.22 Manning's coefficient Enter Final Swale bottom width b 3.50 ft - swale bottom width Enter Final Swale zforeslope 3.00 horizontal number of bioswale slope i.e. 1V:3H, z=3 in this instance Enter Final Swale zbackslope 3.00 horizontal number of bioswale slope i.e. 1V:3H, z=3 in this instance Enter Final Swale flow depth y 0.368 ft - design depth flow D-9 Computer the flow velocity at Qbiofil HRM Chapter 5 Equation E-12 Vbiofil 0.42 ft/sec - flow velocity; 1 ft/sec maximum Flow veloicty is OK since it is less than 1 ft/sec D-10 Compute Swale Length L (ft) t 540 seconds - 9 minutes (540 seconds) for CABS, Basic, and Wet bioswale L 226.89 ft - required length of bioswale; If swale is less than 100 feet, make swale have narrower bottom width (2 foot minimum) and repeat Steps D-7 - D-10 and recalculate to get length over 100 feet or keep swale bottom width make swale length 100 feet minimum D-11 Extended Wet Season Adjustment for Western Washington designs only Is the wet bioswale downstream of a detention pond? Enter the wet bioswale length (ft) --------------> wet bioswale bottom treatment area x 2 = Adjust the wet bioswale length and/or bottom width to provide an equivalent bottom treatment area; maintaining a 5:1 length to width ratio and depth of flow of 4 inches D-12 Revise Wet Bioswale Dimensions to meet minimums and for construction Is the wet bioswale length at least 100 feet? If not, increase swale length to 100 feet. Is the wet bioswale bottom width a constructible width? Do no recalculate the wet bioswale depth of flow or velocity if the wet bioswale has the extended wet season adjustment. Enter Final Adjusted Wet Bioswale Dimensions Enter Final Swale bottom width b 3.50 ft - swale bottom width Enter Final Swale length 227.00 ft - swale bottom length ERROR; wet bioswale treatment area needs to be increased for the extended wet season adjustment critria above. 227.00 ft 3.5 ft 0.020 ft/ft 3.0 3.0 0.37 ft 0.37 ftSwale Depth = WQ Depth for offline swales Wet Bioswale Length Wet Bioswale Bottom Width Swale Longitudinal Slope zforeslope zbackslope WQ Depth changing the "y" value Yes But not applicable Final Wet Bioswale Dimensions A Q V biofil biofil = tVLbiofil´= CABS Valley View.xls 3/19/2021 2:09 PM Version 2.1 Page 1 MEMORANDUM DATE: June 29, 2021 (updated September 14, 2021) TO: Ken Srilofung, PE, CIP Project Manager FROM: Mike Giseburt, PE, WSP Project Manager SUBJECT: Stormwater Facility Retrofit Study – Identify Stormwater Retrofit Locations (Task 4 Effort) 1. INTRODUCTION AND BACKGROUND The City of Renton (City) owns and maintains over 400 stormwater facilities constructed as far back as the 1970s to mitigate for the stormwater impacts of urbanization. Between the 1970s and early 1990s, stormwater facilities were primarily focused on providing stormwater storage (i.e., detention). Since the early 1990s, design standards have advanced so that today’s stormwater facilities provide better water quality treatment to mitigate the detrimental impacts of stormwater pollutants on stream water quality and aquatic habitat. Today’s newer stormwater treatment systems target the removal of suspended solids, dissolved heavy metals, nutrients, and petroleum hydrocarbons. Typically, stormwater facilities owned by the City connect to the municipal storm sewer system and drain to the closest water body. The older stormwater detention facilities in the City’s system typically do not include a specific water quality treatment component, and thus are less effective at protecting stream resources from pollutants than the stormwater detention facilities with water quality treatment designed using today’s standards. The City received a grant from the Washington State Department of Ecology (Ecology) to perform a study of many of the existing flow control facilities that have little or no water quality treatment features. The overarching goal is to improve the water quality in multiple streams within the City that are part of the Cedar River/Lake Washington and Duwamish/Green watersheds. The study entails a series of six sequential tasks to be undertaken to prioritize the sites with the greatest potential to improve water quality. The first three tasks, Tasks 1 through 3, are complete and include: Existing Facilities Selection (Task 1) — City staff selected 49 existing flow control facilities for this study primarily based on their understanding that these particular existing facilities provide minimal water quality treatment (see Figure 1). Existing Conditions Summary (Task 2) — This effort is complete and included collecting information and evaluating site conditions of the 49 selected existing facilities. The summarized data includes stormwater best management practice (BMP) type, size, and age; tributary area characteristics; drainage basin information; and other information, all which help characterize the existing facilities and can be used in future tasks to evaluate stormwater treatment performance and site-specific water quality retrofit opportunities. Page 2 Figure 1. Site Map Page 3 Gap Analysis (Task 3) — This effort identified deficiencies (gaps) in the treatment of stormwater at the selected facilities. The analysis compared the existing amount of runoff treatment in the drainage basins to the amount of runoff treatment needed to meet current water quality treatment standards (per the 2017 City of Renton Surface Water Design Manual [SWDM]). It is noted that the City of Renton water quality treatment standards is deemed equivalent to Ecology Standards for development and redevelopment. The next task, Task 4, is the work of this memorandum. Identifying Stormwater Retrofit Locations (Task 4) — This effort builds upon the treatment gap analysis to identify existing flow control facilities to retrofit with additional runoff treatment benefits. This task will develop a preliminary suite of BMP types and sizes for each site while considering site-specific conditions, such as space, topography, conveyance, infiltration potential, and other considerations. The next two tasks will be completed as a part of future study efforts. Prioritizing and Scoring Sites for Stormwater Retrofit Opportunities (Task 5) — This effort will develop a method to screen retrofit locations identified in Task 4 to create a ranked list that focuses on the (a) highest benefit of water quality improvement and (b) most effective opportunities. Project Selection, Conceptual Design, and Costs (Task 6) — This effort will include the development of concept designs and cost estimates for the top three prioritized retrofit locations. 2. LEVEL OF WATER QUALITY TREATMENT The Task 3 memorandum evaluated the level of treatment required. Forty-six of the 49 detention facilities under review for potential water quality retrofit would require basic treatment under current City standards: “80% TSS removal level is reasonably attainable using properly designed, constructed and maintained structural stormwater BMPs”. Enhanced treatment is required for one of these 49 sites because (1) more than 50% of the runoff that drains to the facility is from land uses that include commercial, industrial, or multifamily land uses. Sites that receive drainage from roadways having an average daily traffic count greater than 7,500 vehicles would also require enhanced treatment, but none were identified. The site requiring enhanced treatment is No. 145398 (Davis Avenue One Valley). Enhanced treatment is intended to remove more metals than basic treatment because these land uses typically have higher metal pollutant concentrations. Lower metal concentrations, such as copper and zinc, reduce the risk to fish from exposure to both chronic and acute toxic concentrations. Enhanced treatment is designed to achieve > 30% dissolved copper removal and > 60% dissolved zinc removal and 80% TSS removal. Three of the sites within the basic treatment requirements category, sites 111391 (Denny’s Restaurant), 111421 (Ripley Lane Storm Improvement Site), and 111422 (Renton Village Interceptor Site), had modest portions of their tributary basin made up by commercial, industrial, or multifamily land uses. On a preliminary review of their basin maps, it appeared that none of these three basins had these land uses exceeding 50% of basin land coverage. Thus, for this effort, they were included in the basic treatment category. Additional modeling would be required to determine if the "50% or more of basin runoff" threshold from commercial, industrial, or multifamily land uses is crossed. Should one of these facilities be considered a higher priority for retrofitting, additional detailed analysis is recommended to review whether enhanced treatment should be considered. Another criterion to determine if special treatment is needed is whether the site drains to a sphagnum bog wetland. The two detention facilities that discharge to a sphagnum bog area are Hidden Cedars Div II (111361) and Knudson (117915). A sphagnum bog wetland is defined as a wetland dominated by sphagnum moss and which has an associated acid-loving plant community. A sphagnum bog wetland requires a specific treatment train of two or Page 4 three facilities, in order to include the control of nutrients, alkalinity, and pH (total phosphorus reduction of 50%, nitrate + nitrate reduction of 40%, pH below 6.5, and alkalinity below 10 mg CaCO3/L). In the 2017 City of Renton SWDM, it states that no sphagnum bogs were identified (Section 1.2.8.1) but recognizes they may exist. At the same time, two sphagnum bog wetlands were identified through the City’s GIS mapping. Under the current water quality requirements for new development discharging to a sphagnum bog area, water quality facilities would need to use an infiltration system preceded by facilities from the Basic Water Quality (WQ) menu. If infiltration is not feasible, then the selection of water quality BMPs are guided by the Sphagnum Bog Protection menu. This menu relies up two or three train treatment systems. The following entails more detail about these sites. Knudson sits within 50 feet of a seismic hazard zone, so infiltration is not feasible, and the site would require two or three facilities in series, unless an exemption applies (see excerpt from Renton Manual below). Hidden Cedars Div II is also very close to a seismic hazard zone, somewhere between 50 and 100 feet. Because it is so close, the same requirements as Knudson were assumed. 3. REGULATED SITE RESTRICTIONS AFFECTING POTENTIAL BMP OPTIONS The City’s Stormwater Manual restricts the use of certain types of stormwater facilities based on a number of natural physical settings and regulated zones. The following site characteristics were evaluated to identify potential BMP retrofit options and BMP retrofit restrictions for each stormwater detention facility: Setbacks from steep slopes or landslide hazard areas Setbacks from other water resources Infiltration requirements and limitations of use within the City’s Aquifer Protection Area (APA) and groundwater recharge areas Setbacks from Steep Slopes, Landslide Hazard Areas, and Water Recourses Graphical analysis of the setbacks from steep slopes and landslide hazard areas were performed using the City’s GIS information, which are included in Appendix A for each site. An example is provided on the following page as Figure 2 (specific to Facility 117894, Swan Meadows Div. 1). Pri vate RdCamas Pl NENE 13th Pl Dayton Ave NECamas Ave NEBlaine Ave NE117921 117894 £ 0 100 20050 Feet CITY OF RENTON STORM WATER FACILITY RETROFIT STUDY Legend315 2 8 0 310290 3 0 5 2 8 5 295 117921 117894 50'50'100'100'200'200'Slope >15% & <=25% Slope >25% Seismic Hazard Areas Landslide Hazard Wellfield Capture Zones Wetlands Open Water Stormwater Pipe Approx. Tributary Area To Facility 117894 Low Infiltration Soils/ High Ground Water Stormwater Detention Facility Estimated Offset Ranges From Existing Facitly Note - 1. Offset ranges may determine the feasible retrofit BMP type. e.g. steep slopes, wetland etc. SWAN MEADOWS I FIGURE 2 Page 6 For each site, split views include an aerial photo showing the drainage system, and a second view showing topography, site location, tributary area, low infiltration soils in the area, steep slopes, aquifer protection wellfield capture zones, landslide/seismic hazard areas, and open waters. The graphic also provides “offset distances ranges from the facility measure at 50 and 100 feet” (these distances are used because the City’s manual uses both 50-foot and 100-foot required setbacks from certain features). These are described in the following table. Table 1. Stormwater Facility Setbacks SETBACK REQUIREMENTS FOR INFILTRATION AND OPEN FACILITIES > 5-FT SETBACK FROM TRACT LINE > 50 FT FROM SLOPE >15% > 50 FT (LINED ONLY) OR > 100 FT (INFILTRATION) FROM SEPTIC TANK > 200 FT FROM A LANDSLIDE OR STEEP SLOPE HAZARD AREA SETBACK REQUIREMENTS FOR ALL WATER QUALITY FACILITIES > 100 FT FROM OPEN WATER > 100 FT FROM WELLS > 100 FT FROM DRAIN FIELDS > 200 FT FROM SPRINGS USED FOR POTABLE WATER Infiltration Requirements The City’s stormwater manual includes requirements limiting stormwater infiltration BMPs. Certain general requirements apply unless they are superseded for locations within its APA. The City also has requirements for groundwater protection areas. These requirements and restrictions are described below. General Infiltration Requirements Infiltration must be outside critical areas and applicable buffers. Critical areas and applicable buffers include aquatic areas, wetlands, flood hazard areas, erosion hazard areas, landslide hazard areas, steep slope hazard areas, and critical aquifer recharge areas. General soil requirements. The first 2 feet or more of soil has either a measured infiltration rate less than or equal to 9 inches per hour or is logged as one of the classes from the USDA Textural Triangle, excluding sand and loamy sand, OR composed of less than 25% gravel by weight with at least 75% of the soil passing the #4 sieve (and some additional gradations… per Section 5.2.1 of SWDM) In addition, soils must have a cation exchange capacity greater than 5, and organic content of 1% or greater. Aquifer Protection Area APAs are classified in three different zones as referenced in Section 15-B in the City Stormwater Manual (and RMC 4-3-050). The restrictions for each zone are described below: Zone 1 Infiltration trench prohibited Open facilities (ponds, stormwater wetlands, infiltration facilities) are prohibited Open conveyance (ditches and channels) are prohibited Page 7 Zone 1 Modified Infiltration is allowed and may require a liner and the Zone 1 open conveyance restrictions do not apply Infiltration Zone 2 Open facilities might require a liner Ditches and channels might require a liner None of the selected detention facilities fall within the APA Zone 1. The four facilities identified in Table 2 lie within the APA Zone 1 Modified or APA Zone 2. Table 2. Facilities within Aquifer Protection Areas APA Zone 1 Modified APA Zone 2 117900 - Meadow Av N & 24th St 117941 - Weatherwood II 145834 - Pollos Estates 200049 - Nantucket Short Plat Groundwater Wellhead Protection Areas The City also identifies a groundwater wellhead protection area, which is made up of three geographical components, including the Cedar Valley Sole Source Aquifer Project Review Area designated by the federal Environmental Protection Agency, the Wellfield Capture Zones as mapped by the Washington State Department of Health, and the APAs (described above). The groundwater wellhead protection area defines zones for 1-, 5-, and 10-year time of travel zones associated with municipal wells. The soil properties required within the groundwater wellhead protection area specify that: The first 2 feet or more of soil has a measured infiltration rate less than or equal to 2.4 inches per hour, OR is logged as one of the classes from the USDA Textural Triangle, excluding sand, loamy sand and sandy loam, OR has a measured infiltration rate less than or equal to 9 inches per hour, and composed of less than 25% gravel by weight with at least 75% of the soil passing the #4 sieve (and some additional gradations… per Section 5.2.1 of SWDM) Summary of Site Limitations on BMP Options Appendix A provides the basis of information used to assess limitations on BMP options at each site. The following table (Table 3) summarizes the water quality BMP facility restrictions and infiltration opportunities at each detention facility under review. Table 3 provides a brief summary of the information that identifies where infiltration is possible, where the BMP must be a vault-type BMP versus and open water type of facility, and where a geotechnical report is required or likely required based on area slopes and landslide/seismic hazards. See the footnotes in Table 3 for an explanation of each of the criteria used. Its noted in Table 3, that while infiltration may be allowed based on soils and proximately to the APA (as noted in the sixth column), infiltration may still be prohibited if the site is within 50 feet of a landslide/seismic hazard area (as noted in the 7th column) where a vault type of facility is required. Appendix B includes a more detailed table of the input for various site characteristics that were used to form these summary results. Page 8 Table 3. Summary of BMP Facility Restrictions and Infiltration Opportunities 4. TYPES AND SIZING OF WATER QUALITY BMPs This section provides a discussion of the types and sizing of water quality retrofit BMPs considered for retrofits during this study. Future phases of this study, Tasks 5 and 6, will then further evaluate opportunities and develop a scoring system to prioritize retrofit sites that result in the greatest water quality benefit. Site Number (City Asset ID)Development Project Name Receiving Water Body Infiltration Potential (APA Zone and Soil/ Groundwater) (1) Lining Maybe Required (BMP in APA 2 Zone) (2) Infiltration WQ BMP Not Allowed (In APA Zone 1 or Within 100ft of Open Water) (3)(4) Only Vault Allowed (Landslide and Seismic Hazard: <50=No, <200=Geotech approval required)(5) Within Distance Equal to Total Vertical Height of Slope >15% (6) 111332 SUMMERWIND DIV I II III Greenes Creek Yes No Allowed Yes Likely 111342 WINSPER (LIBERTY VIEW I&II) Panther Creek Yes No Allowed No Likely 111354 SPRINGBROOK TERRACE Upper Springbrook Creek Yes No Allowed No Likely 111361 HIDDEN CEDARS DIV II Soos Creek Main Yes No Allowed Geotech Approval Required Unlikely 111369 PANTHER MEADOW Panther Creek Yes No Allowed No Unlikely 111391 DENNYS RESTAURANT Lake Washington - East No No Allowed Yes Likely 111393 CASTLEWOOD RANCHETTES Maplewood Creek Yes No Allowed No Likely 111394 CASTLEWOOD RANCHETTES Maplewood Creek Yes No Allowed No Unlikely 111408 BERGSMA SHORT PLAT Upper Springbrook Creek Yes No Not Allowed No Unlikely 111421 RIPLEY LN STORM IMPROVEMENT PR Lake Washington - East Yes No Allowed Yes Likely 111422 RENTON VILLAGE INTERCEPTOR Thunder Hills Creek No No Allowed Geotech Approval Required Unlikely 117894 SWAN MEADOWS I Johns Creek Yes No Allowed Geotech Approval Required Unlikely 117900 MEADOW AV N & N 24TH ST South Kennydale Yes No Not Allowed Geotech Approval Required Likely 117902 TIFFANY PARK DIV 4 Cedar Main Urban Yes No Allowed Geotech Approval Required Unlikely 117912 ARMSTRONG AND SANDELIUS Soos Creek Main Yes No Not Allowed No Unlikely 117915 KNUDSON Soos Creek Main Yes No Allowed Yes Unlikely 117916 PARKWOOD SOUTH DIV I Thunder Hills Creek Yes No Allowed Yes Likely 117917 WINDSOR HEIGHTS Panther Creek Yes No Not Allowed No Likely 117918 BENSON WOODS Panther Creek Yes No Allowed No Unlikely 117921 SWAN MEADOWS II Johns Creek Yes No Allowed No Unlikely 117929 BOB BURKE Upper Springbrook Creek Yes No Allowed No Unlikely 117931 BENSON GLEN Panther Creek Yes No Allowed No Likely 117936 FERNWOOD EAST Maplewood Creek Yes No Not Allowed Geotech Approval Required Likely 117938 CHINQUAPIN RIDGE Panther Creek Yes No Allowed No Likely 117940 VALLEY VUE ESTATES Panther Creek No No Allowed Yes Likely 117941 WEATHERWOOD II Lower May Creek Yes Yes Allowed No Unlikely 117945 HIDDEN CEDARS DIV II Soos Creek Main Yes No Allowed No Unlikely 117947 BENSON GLEN Panther Creek Yes No Allowed No Likely 117952 CHINQUAPIN RIDGE Panther Creek Yes No Allowed No Unlikely 145336 PETETT MEADOWS SHORT PLAT Honey Creek Yes No Allowed No Unlikely 145398 DAVIS AV S ONE VALLEY PLACE Upper Springbrook Creek Yes No Allowed Yes Likely 145407 VICTORIA HILLS Rolling Hills Creek Yes No Not Allowed Yes Likely 145785 ELIZABETH PLACE Johns Creek Yes No Allowed Yes Likely 145824 RUDDELLS 2ND ADDITION Johns Creek Yes No Allowed No Likely 145827 PARKWOOD Thunder Hills Creek Yes No Allowed No Unlikely 145832 SOUTH KNOLL WATER EXTENSION South Renton Yes No Allowed Geotech Approval Required Likely 145834 POLLOS ESTATES Lower May Creek Yes Yes Allowed Geotech Approval Required Unlikely 145836 HIGHBURY PARK Johns Creek Yes No Allowed Yes Unlikely 145851 YOUNG ADDITION Honey Creek Yes No Allowed No Likely 145864 RIDGEVIEW ESTATES May Creek Yes No Allowed No Unlikely 145869 YOUNG ADDITION Honey Creek Yes No Allowed No Unlikely 146790 LUND SHORT PLAT Thunder Hills Creek Yes No Allowed No Unlikely 166609 SUNSET BLVD/DUVALL AVE NE INT Honey Creek Yes No Allowed No Unlikely 167768 ORCHARD PARK Panther Creek Yes No Allowed No Likely 168953 VILLAGE ON UNION Cedar Main Urban Yes No Not Allowed Yes Likely 200040 KELSEY LANE Panther Creek Yes No Allowed No Unlikely 200041 KELSEY LANE Panther Creek Yes No Allowed No Likely 200049 NANTUCKET SHORT PLAT South Kennydale Yes Yes Allowed Yes Unlikely 200096 PARKWOOD SOUTH DIV III Thunder Hills Creek Yes No Allowed No Unlikely Notes: 1 Identifies whether infiltration is feasible and may be considered. Sites within APA Zone 1 or within type C/D soils asssumed disqualify infiltration as potential retrofit. 2 Indicates whether pond impemiable or soil liner may be required for infiltraiton retrofit. Sites within APA Zone 2 may require liner. 3 Identifies whether infiltration is feasible and may be considered. Sites within APA Zone 1 or within 100 feet of open water disqualify infiltration as potential retrofit. 4 Note that while infiltration may be allowed based on location outside of APA Zone and underlying soils, it is precluded when a vault is required as noted in Column 7. 5 Only Vault type BMP is allowed when site is in or within a landslide or siesmic hazard area. Also identifies when geotechnical report is required to landslide hazard if within 200 feet of site. 6 Identifies whether it is likely or unlikely that the a site is within a threshold distance to require a geotechnical report. This threshold is defined as a setback from the top of a slope that exceeds 15%, where the setback distance is defined as the height of the slope. Page 9 Types of BMPs These types of BMPs considered during this study were selected with input from the City to (1) capture the range of different types of BMPs, (2) ensure the analysis only considered BMPs that the City would use, and (3) limit the scope of effort to a reasonable number. As such, not all water quality BMPs in either the Renton Stormwater Manual or Ecology manual were considered. The water quality BMPs evaluated are organized into general types and include: Infiltrative Type BMPs Bioretention Swales and Cells Media Filter Drains Settling Type BMPs Wetpond/Constructed Stormwater Wetland (e.g., within a footprint of a detention pond where ponds exist) Wetvault Filtration/Other Type BMPs Sand Filter Vault Proprietary Filter Media Vault (e.g., StormFilter) Basic Bioswale (with or without compost amendment) Vegetated Filter Strip (with or without compost amendment) Infiltrative Type Water Quality BMPS This study evaluated the available data to identify sites where infiltration type BMPs (bioretention swales and cells, media filter drains) may be feasible. For new development projects, these infiltrative type BMPs are now required by the City where feasible. Infiltrative type BMPs are expected to best simulate the pre-development hydrologic response of the landscape to provide stream-protection flow control. The infiltrative type BMPs also tend to remove a better range and amount of pollutants relative to non-infiltrative type BMPs. In locations where infiltrated runoff returns as interflow to the nearby channel, these return flows are typically cooler or at least more closely match the temperature regime of the stream flows than the characteristics of detained or undetained surface runoff. Stand-alone infiltration BMPs (infiltration trenches and infiltration basins) were not specifically considered for each site due to uncertainties of infiltration rates, the ability to reliably meet current City of Renton standards with the data available at the time of this study, such as groundwater depth data (which was not available for most sites) and soil infiltration rate potential. Rather, the approach for this phase of the study was to consider infiltrative type BMPs (bioretention swales and cells, and media filter drains) at each site where infiltration was determined feasible to capitalize on some level of infiltration where physical conditions allow. Then, in future phases of the study, further assess infiltrative type BMPs for specific sites selected for the prioritization process. Settling Water Quality BMPs Settling type BMPs are typically stormwater ponds (wetponds/constructed wetlands) that maintain a pool of water for most of the year and capture solids through the gravity settling of particles during the relatively long residence time. Stormwater wetlands typically perform better pollutant removal than just wetponds through Page 10 biological uptake. A common BMP retrofit is to convert an existing detention pond that provides quantity control to a combined detention pond/wetpond configuration that then provides both quantity and quality control. One concern about open ponds is a potential increase in temperature to receiving waters. Filtration/Other Type BMPs Filtration type BMPs remove pollutants primarily by physical filtration. As stormwater passes through a media layer, pollutants are trapped in the small void spaces or adhere to the media. Two examples of filtration type BMPs include a sand filter vault and proprietary type filter media vault (e.g., StormFilter). Basic bioswale (with or without compost amendment) and vegetated filter strip are included in this category because they offer at least partial filtration as runoff passes through dense vegetation at very shallow levels. Filtration type BMPs may require pre-settling as void capacity may be lost over time. Requirements for pre- settling are discussed in the individual BMP descriptions below. While manufactured filter systems can provide better removals than wetponds or bioretention BMPs, in most cases these systems do very little to mimic natural hydrology or moderate runoff temperatures. Typical drawing sections for the BMPs from the City’s Stormwater Manual are highlighted in the following sections, as well as some comments/considerations of their use and restrictions when considering their use for retrofitting. Sizing methodologies and associated assumptions are discussed at the end of this section. BIORETENTION CELL (ALSO SWALES AND PLANTERS) Bioretention cells are shallow depressions with a designed planting soil mix and a variety of plant material, including trees, shrubs, grasses, and/or other herbaceous plants. Bioretention cells capture, treat, and largely infiltrate most of the runoff volume over time. Bioretention swales are similar in that they include shallow depressions, planting bioretention soil mix and plants, however they can be designed as part of a conveyance system. Bioretention planters are similar to cells, but they are usually contained in vertically walled sides, usually constructed of concrete. The designs for bioretention (cells, swales, and planters) in the Renton SWDM follow the design criteria in Ecology’s 2019 Stormwater Management Manual for Western Washington (SMMWW Manual) (BMP T7.30). Some additional considerations for the bioretention cells include: Requires the existing system to be relatively shallow to avoid deep/excessive excavations. Takes up relatively large space requirements compared with other BMPs. Page 11 MEDIA FILTER DRAIN A media filter drain is typically designed for treating runoff from flat surfaces (i.e., pavement) that captures runoff in a depression that contains treatment media. Some additional considerations for a media filter drain include: Because most of the retrofits would reflect an end-of-pipe (or concentrated) flow, the configuration of a filter strip would have to include directing flow to a flat level spreader that then spills out over the media filter drain. Requires the existing system to be relatively shallow to avoid deep/excessive excavations. WETPOND The wetpond is placed below the flow line of the drainage system forming a closed depression of volume to capture sediments. Some additional considerations for a wetpond include: Can sometimes be an efficient retrofit especially if it can be constructed below the bottom of an existing detention pond. Can require undesirable deep excavations where the existing storm drain system is already deep. Page 12 Advantage is that it does not require any head and all volume is be located below the hydraulic grade line. A disadvantage is the potential to increase runoff temperatures. May require safety fencing. In most cases, a constructed wetland could be substituted for the wetpond. Volume sizing is same as for a constructed wetland. WETVAULT Some additional considerations for a wetvault include: Lower space required than some BMPs, but more than StormFilter. Can be located under roads. Dead storage should be below hydraulic grade line. Page 13 SAND FILTER VAULT Some additional considerations for a sand filter vault include: Lower space required than some BMPs, but more than StormFilter. Can be located under roads. Requires minimum of about 3 feet of head. PROPRIETARY MEDIA FILTER OR MEMBRANE FILTER SYSTEM: STORMFILTER VAULT The StormFilter vault with ZPG (ziolite/perlite/granular activated carbon) has been selected for sizing a media filter option, as King County DNRP has approved the facility for the Basic WQ treatment requirements. For this analysis, it was assumed that pretreatment/pre-settling could be omitted at this stage and further considered on a case-by-case basis if a site proceeds to design and construction. This is due in part because of the large space that would be required and that some of the facilities could be located downstream of a detention facility, lessening the need for pretreatment. Section 6.5.1 in the Renton Stormwater Manual Reference 14-A provide discussions of pretreatment. Reference 14-A indicates that pretreatment be required when heavy grit loads are anticipated. Page 14 Some additional considerations for the StormFilter vault include: Small space required. Requires minimum of 1.8 feet of head for low head filter. Higher maintenance costs than most BMPs. Can be located under roads. BASIC BIOSWALE Some additional considerations for a basic bioswale include: May not be appropriate where existing system is deep because basic bioswale would require lots of space and/or walls. The basic bioswale is different than at bioretention swale in that it would include positive sloping drainage for conveyance (i.e., no depression) and it would not include the bioretention soil mix. The design criteria for the basic bioswale in the Renton SWDM follows Ecology’s 2019 SWMMWW design criteria for the basic biofiltration swale (BMP T9.10). VEGETATED FILTER STRIP Some additional considerations for a filter strip include: Because most of the retrofits would reflect an end-of-pipe (or concentrated) flow, the configuration of a filter strip would have to include directing flow to a flat level spreader that then spills out over the filter strip. Sizing BMPs Page 15 Sizing for each BMP site and type of BMP listed above was completed using a simplified sizing calculator included in Appendix C. The calculator considers inputs, such as water quality design flow and water quality volume. This allowed for a streamlined approach to sizing. General assumptions and inputs used for the sizing of BMPs include: Facilities are sized to be online and do not bypass the water quality design flow to the BMP. Facilities were generally sized to meet City of Renton requirements. Typical minimum slopes and other features are specified in the detailed sizing spreadsheets in Appendix C. Pre-settling is not needed for proprietary media filter BMPs; however, this would need to be confirmed for each site. No retaining walls assumed when sizing open features to generate a more conservative footprint for initial analysis. All proposed water quality facilities considered upstream of a detention system regardless of its location relative to the existing detention facility, as the existing detention facilities do not necessarily meet current detention standards. Further analysis could always be done to assess reducing the size of a BMP when downstream of a facility during future planning/design efforts. Infiltration BMPs are not sized to have an underdrain or lining for initial sizing. 5. IDENTIFY FEASIBLE WATER QUALITY OPTIONS FOR POTENTIAL RETROFIT SITES Once limitations on BMP types were reviewed and preliminary sizing was completed, this information was used to further assess applying the various BMP types to each site. Some general siting considerations for this assessment are provided in Table 4. Table 4. BMP Requirements Summary BMP SPECIFIC DESIGN REQUIREMENTS BIOSWALE / CABS (Basic and Wet Bioswales) MEDIA FILTER DRAIN / COMPOST AMENDED FILTER STRIP STANDARD FILTER STRIP WETPOND / STORMWATER WETLAND COMBINED DETENTION POND & WETPOND FACILITY BIORETENTION CELL WETVAULT SAND FILTER VAULT STORMFILTER VAULT W/ ZPG MEDIA SITE GEOMETRY COMPATIBILITY CHANNEL / LINEAR SIDE SLOPE SIDE SLOPE OPEN POND OPEN POND OPEN POND WITHIN ROADWAY WITHIN ROADWAY WITHIN ROADWAY TRIBUTARY AREA < 5 ACRES N/A FLOWPATH < 150 LF N/A N/A <5,000 SF per cell <10 acres***** N/A N/A APPROX. MIN. FOOTPRINT: WIDTH (ft) x LENGTH (ft) 6 x 100 14* x N/A 5* x N/A 16 x 48 16 x 48 ~7.5 x 9*** 4 x 12 N/A 6x12**** APPROX. MAX. FOOTPRINT: WIDTH (ft) x LENGTH (ft) 20 X N/A N/A N/A N/A N/A ~1300 SF*** N/A N/A 8x24**** MIN. SLOPE (%) 1.5% Longitudinal N/A Filter Strip: 1% in flow direction N/A N/A N/A N/A N/A N/A MAX. SLOPE (%) 6% Longitudinal 12.5% or flatter in flow direction Filter Strip: 15% in direction of flow, 2% in direction of flow spreader N/A N/A 6% N/A N/A N/A APPROX MIN. HEAD DROP ACROSS BMP (ft) 2.17 3.5 (for min. footprint) <.2 0 0 0 0 4 2.3 (or 1.8 for low drop) *Length refers to the measurement of the BMP side running perpendicular to the roadway **Refers to slope of contributing drainage area parallel to direction of the flow ***Assumes 6" depth and 6" freeboard with 3:1 side slopes ****Limits on size only apply to precast off-the-shelf vaults from Contech *****Based on cost-effectiveness, per SWDM 2017 Each of the sites has a unique physical setting and system configuration. Some of the general consideration when assessing each site that helped determined the preferred BMP retrofits are described below: Consideration of any of the set-back requirements described in Section 2. For example, several sites were limited to vault type BMPs when they were located too close to a landslide hazard area. Space available for BMP retrofit. Typically, where the size of the BMP was large in order to meet City of Renton standards, there was often not enough available space. Preference for a BMP retrofit to be located either on public property or an existing easement. It was also recognized the only portions of the road right-of-way could be used. Even with underground vault systems, much of the right-of-way is taken up with other utilities such as water, sewer, and private utilities. Keeping aware of the slopes of the detention system’s upstream and downstream conveyance system. Typically, where the system was very flat, it eliminated any type of BMP that requires elevation head such as a media filter. Where there was elevation drops, there was typically an opportunity for media filter. Preference for lower cost BMPs based on engineering knowledge and sizes. For example, where there was an existing open pond, the first approach was to add wetpond storage within the pond’s footprint. Page 16 Preference for infiltration type BMPs. As noted previously, stand-alone infiltration BMPs (infiltration trenches and infiltration basin) were not assessed for each site due to uncertainties of both infiltration rates and the ability to fully meet current Renton standards. For this phase, infiltrative-type BMPs (bioretention swales and cells, and Media Filter Drains) were considered. Keeping aware of the depth of the existing system. Deeper systems are more difficult and costly (e.g., when considering such BMPs as wetvault, sand filter vault, and basic bioswale). In some locations, existing detention facilities consisted of “back-up” type ponds or vaults. “Back-up” type systems are configured with the main inflow directly connected to a control structure that also has a riser control and outlet pipe. The control manhole also has a pipe that connects to the “storage”. The control manhole restricts flow that causes water to back up into the storage facility. These types of facilities do not provide the water quality benefit of the flow passing through the facility. Whenever these were noted, it was recommended to convert the facility to a “flow-through” facility. The results of the analysis are presented in site exhibits in Appendix D. Figure 3 (specific to Facility 117894 (Swan Meadows Div I) on the following page presents the format for these exhibits. Each exhibit includes: Existing detention system type Tributary area (ac) Tributary basin impervious percentage (%) Water quality volume Online water quality flow rate (cfs) Offline water quality flow rate (cfs) Site vicinity map (showing existing pipe layout, contours, right-of-way/parcel boundaries and aerial images Street view graphic (with location and direction of photo) Listing of BMPs not previously eliminated, including Size to meet current standards Observations and site notes Miscellaneous notes Generally indicated site influencing factors, preferences Preliminary conclusion about best BMP(s) Screen scopes of key as-built information, including plan and profile 117894: SWAN MEADOWS I BMP EVALUATION EXISTING DETENTION SYSTEM TYPE Tank AREA OF TRIBUTARY BASIN (ACRES)1.7 TRIBUTARY BASIN IMPERVIOUS PERCENTAGE (%)52% WATER QUALITY VOLUME (ACRE-FT)0.152 ONLINE WQ FLOW RATE (CFS)0.31 OFFLINE WQ FLOW RATE (CFS)0.17 BMP OPTION DIMENSIONS SITE NOTES & OBSERVATION WET POND 42’X80’Insufficient space within dense residential area. WET VAULTs Vault size – 13’X60’Sufficient space but likely utility conflicts. SANDFILTER VAULT Presettling vault – 10’X30’ Vault size – (1) 40’X80’ Probably sufficient space and head drop. PROPRIETARY MEDIA FILTER VAULT, 18” CARTRIDGES WITH ZPG MEDIA(STORMFILTER VAULTS) 19 cartridges, ~ (1) 8’X11’ vault Sufficient space in roadway and head drop. BIOSWALE 11’X210’Insufficient space available. FILTER STRIP 20’X190’Insufficient space available. BIORETENTION 11’X260’Insufficient space available. MEDIA FILTER DRAIN 14’X600’Insufficient space available. MISCALLANEOUS NOTES: -Site is within 200’ of landslide area and geotechnical approval may be required for non-vault BMPs. Site is also within a groundwater protection area. -Stormfilter vault appears to be best option based on available head and likely being more cost effective than wetvault. FIGURE 3 117894: SWAN MEADOWS I AS-BUILT DRAWING SUMMARY PLAN VIEW PROFILE DATE OF AS-BUILT DRAWINGS 02/20/89 TIR PROVIDED No ADDRESS 1325 Camas Ave NE, Renton, 98056 FIGURE 3 (CON'T) Page 18 Summary of Recommended BMP Retrofits In terms of overall results, it was often challenging to identify a workable option that met City of Renton standards without taking up an unreasonable portion of the right-of-way or acquisition of property through new or expanded easements. Due to these challenges and site constraints, the StormFilter vault was recommended more frequently than other BMPs, largely due to its small footprint, and ability to meet City of Renton standards. For some sites, a preliminary recommended option is noted for a retrofit that would not fully meet Renton standards but could still provide a meaningful water quality benefit. For example, converting an existing detention pond to a combined wetpond/detention pond is very economical and results in significant benefit while not fully meeting Renton standards. Table 5 presents a summary of the number and type of recommended preferred retrofits. Table 5. Summary of Retrofit BMP Types RETROFIT BMP TYPE NUMBER StormFilter BMP 24 Adding Wetpond Storage to Existing Detention Pond 7 Basic Bioswale/Bioretention 5 Wetvault 4 Converting “back-up” type facility to a “flow-through” type 1 No recommendation was given for nine sites because either it would be too costly, would not be feasible, and in one case the site was considered to meet current City of Renton standards. One observation in performing this assessment is that there are a wide variety of approaches to BMP selection, layout, extent of existing system modifications, and bias towards the range of considerations, such as different designers would often come to different conclusions about the best concept. We want to recognize this and the City’s experience in managing and maintaining the facilities and the City is encouraged to leverage its own experience when providing input on BMP preferences. 6. NEXT STEPS The identified preferred BMP retrofit opportunities will be scored and prioritized sites for stormwater retrofit opportunities. This effort will develop a method to screen retrofit locations identified during this effort to create a ranked list that focuses on the (a) highest benefit of water quality improvement and (b) most effective opportunities. 7. APPENDICES Appendix A. GIS Mapping Exhibits of Site Restrictions and Buffer Setbacks Appendix B. BMP Site Opportunities and Limitations Detail Summary Appendix C. Updated Water Quality Volume and Flow Rate and BMP Sizing Calculators Appendix D. Site Retrofit BMP Assessments APPENDIX A: GIS MAPPING EXHIBITS OF SITE RESTRICTIONS AND BUFFER SETBACKS NE 24th Ct N E 2 3 rd C tNE 23rd St NE 24th St NE 21st St Ilwaco Ave NE111332 £ 0 100 20050Feet CITY OF RENTON STORM WATER FACILITY RETROFIT STUDY Legend 3 5 5 4 4 5 3 6 0 3 6 5 440 3 7 0 435 3 8 0 3 8 5 4 3 0 3 9 0 3 9 5 4 0 5 4 1 0 420 415 111332 50'100'200'Slope >15% & <=25% Slope >25% Seismic Hazard Areas Landslide Hazard Wellfield Capture Zones Wetlands Open Water Stormwater Pipe Approx. Tributary Area To Facility 111332 Low Infiltration Soils/ High Ground Water Stormwater Detention Facility Estimated Offset Ranges From Existing Facitly Note - 1. Offset ranges may determine the feasible retrofit BMP type. e.g. steep slopes, wetland etc. SUMMERWIND DIV I II III Wells Ave SMorris Ave SS 32nd Pl S 31st CtS 31st St S 32nd St 111342 £ 0 100 20050Feet CITY OF RENTON STORM WATER FACILITY RETROFIT STUDY Legend 1902651952602 0 5 2552452402 3 523022021521011134250'100'200'Slope >15% & <=25% Slope >25% Seismic Hazard Areas Landslide Hazard Wellfield Capture Zones Wetlands Open Water Stormwater Pipe Approx. Tributary Area To Facility 111342 Low Infiltration Soils/ High Ground Water Stormwater Detention Facility Estimated Offset Ranges From Existing Facitly Note - 1. Offset ranges may determine the feasible retrofit BMP type. e.g. steep slopes, wetland etc. WINSPER (LIBERTY VIEW I&II) S 1 9 4 th S t98th Pl S S 55th St 98thAve S111354 £ 0 100 20050Feet CITY OF RENTON STORM WATER FACILITY RETROFIT STUDY Legend 1 4 0 1 4 5 260255245240155235230160220215210205195190185180170165111354 50'100'2 0 0 ' Slope >15% & <=25% Slope >25% Seismic Hazard Areas Landslide Hazard Wellfield Capture Zones Wetlands Open Water Stormwater Pipe Approx. Tributary Area To Facility 111354 Low Infiltration Soils/ High Ground Water Stormwater Detention Facility Estimated Offset Ranges From Existing Facitly Note - 1. Offset ranges may determine the feasible retrofit BMP type. e.g. steep slopes, wetland etc. SPRINGBROOK TERRACE 123rdCt SESE 179th Pl SE 181st St 123rd Pl SE124th Ave SE111361 117915 £ 0 100 20050Feet CITY OF RENTON STORM WATER FACILITY RETROFIT STUDY Legend 4103803953903 8 5 405111361 11791550'50'100'200'200' Slope >15% & <=25% Slope >25% Seismic Hazard Areas Landslide Hazard Wellfield Capture Zones Wetlands Open Water Stormwater Pipe Approx. Tributary Area To Facility 111361 Low Infiltration Soils/ High Ground Water Stormwater Detention Facility Estimated Offset Ranges From Existing Facitly Note - 1. Offset ranges may determine the feasible retrofit BMP type. e.g. steep slopes, wetland etc. HIDDEN CEDARS DIV II Private Rd103rd Ct SE103rd Pl SESE 190th Pl 104thPl SESE 190th St SE 192nd St 111369 £ 0 100 20050Feet CITY OF RENTON STORM WATER FACILITY RETROFIT STUDY Legend 41542011136950'100'200'200'Slope >15% & <=25% Slope >25% Seismic Hazard Areas Landslide Hazard Wellfield Capture Zones Wetlands Open Water Stormwater Pipe Approx. Tributary Area To Facility 111369 Low Infiltration Soils/ High Ground Water Stormwater Detention Facility Estimated Offset Ranges From Existing Facitly Note - 1. Offset ranges may determine the feasible retrofit BMP type. e.g. steep slopes, wetland etc. PANTHER MEADOW S/B I-405 RampNE 48th StSeahawks WayLake Washington Blvd NEI-405 FWY111391 £ 0 100 20050Feet CITY OF RENTON STORM WATER FACILITY RETROFIT STUDY Legend35706560 5545 40 111391 50' 100' 2 0 0 ' Slope >15% & <=25% Slope >25% Seismic Hazard Areas Landslide Hazard Wellfield Capture Zones Wetlands Open Water Stormwater Pipe Approx. Tributary Area To Facility 111391 Low Infiltration Soils/ High Ground Water Stormwater Detention Facility Estimated Offset Ranges From Existing Facitly Note - 1. Offset ranges may determine the feasible retrofit BMP type. e.g. steep slopes, wetland etc. DENNYS RESTAURANT NE 8th St Duvall Pl NEN E 7th PlChelan Pl NEDuvall Ave NE111393Duvall Ave NE£ 0 100 20050Feet CITY OF RENTON STORM WATER FACILITY RETROFIT STUDY Legend 4 0 5 440410435430415420111393 5 0 '100'200'Slope >15% & <=25% Slope >25% Seismic Hazard Areas Landslide Hazard Wellfield Capture Zones Wetlands Open Water Stormwater Pipe Approx. Tributary Area To Facility 111393 Low Infiltration Soils/ High Ground Water Stormwater Detention Facility Estimated Offset Ranges From Existing Facitly Note - 1. Offset ranges may determine the feasible retrofit BMP type. e.g. steep slopes, wetland etc. CASTLEWOOD RANCHETTES Pedestrian WalkNE 10th St NE 9th St DuvallPl NEDuvall Ave NE111394 DuvallAveNE£ 0 100 20050Feet CITY OF RENTON STORM WATER FACILITY RETROFIT STUDY Legend 4 2046043045543 5 4 4 5 440 111394 50'100'200'Slope >15% & <=25% Slope >25% Seismic Hazard Areas Landslide Hazard Wellfield Capture Zones Wetlands Open Water Stormwater Pipe Approx. Tributary Area To Facility 111394 Low Infiltration Soils/ High Ground Water Stormwater Detention Facility Estimated Offset Ranges From Existing Facitly Note - 1. Offset ranges may determine the feasible retrofit BMP type. e.g. steep slopes, wetland etc. CASTLEWOOD RANCHETTES SE 190th Pl S 52nd St SE 188 th St 103rd Ct SE103rd Pl SESE 190th St102nd Ave SE111408PantherCreek £ 0 100 20050Feet CITY OF RENTON STORM WATER FACILITY RETROFIT STUDY Legend 410420415111408 PantherCreek5 0 '100'200'2 0 0 ' Slope >15% & <=25% Slope >25% Seismic Hazard Areas Landslide Hazard Wellfield Capture Zones Wetlands Open Water Stormwater Pipe Approx. Tributary Area To Facility 111408 Low Infiltration Soils/ High Ground Water Stormwater Detention Facility Estimated Offset Ranges From Existing Facitly Note - 1. Offset ranges may determine the feasible retrofit BMP type. e.g. steep slopes, wetland etc. BERGSMA SHORT PLAT I-405 FWYS/B I-405 RampSeahawks Way111421 £ 0 100 20050Feet CITY OF RENTON STORM WATER FACILITY RETROFIT STUDY Legend20 3530111421 50'100'2 0 0 ' Slope >15% & <=25% Slope >25% Seismic Hazard Areas Landslide Hazard Wellfield Capture Zones Wetlands Open Water Stormwater Pipe Approx. Tributary Area To Facility 111421 Low Infiltration Soils/ High Ground Water Stormwater Detention Facility Estimated Offset Ranges From Existing Facitly Note - 1. Offset ranges may determine the feasible retrofit BMP type. e.g. steep slopes, wetland etc. RIPLEY LN STORM IMPROVEMENT PR I-405 FW YTalbot Rd SS /B I-405 R am pS a m 's C l u b A c R d S Renton Village Pl Access Rd 111422 RollingHillsCreekRolling HillsCreek TributaryRolling Hills Creek £ 0 100 20050Feet CITY OF RENTON STORM WATER FACILITY RETROFIT STUDY Legend 45403530111422 RollingHillsCreekRolling Hills Creek Rolling HillsCreek Tributary50'100'200' Slope >15% & <=25% Slope >25% Seismic Hazard Areas Landslide Hazard Wellfield Capture Zones Wetlands Open Water Stormwater Pipe Approx. Tributary Area To Facility 111422 Low Infiltration Soils/ High Ground Water Stormwater Detention Facility Estimated Offset Ranges From Existing Facitly Note - 1. Offset ranges may determine the feasible retrofit BMP type. e.g. steep slopes, wetland etc. RENTON VILLAGE INTERCEPTOR ST Pri vat e RdCamas Pl NENE 13th Pl Dayton Ave NECamas Ave NEBlaine Ave NE117921 117894 £ 0 100 20050Feet CITY OF RENTON STORM WATER FACILITY RETROFIT STUDY Legend315 2 8 0 31029 0 305 2 8 5 295 117921 117894 50'50'100'100'200'200'Slope >15% & <=25% Slope >25% Seismic Hazard Areas Landslide Hazard Wellfield Capture Zones Wetlands Open Water Stormwater Pipe Approx. Tributary Area To Facility 117894 Low Infiltration Soils/ High Ground Water Stormwater Detention Facility Estimated Offset Ranges From Existing Facitly Note - 1. Offset ranges may determine the feasible retrofit BMP type. e.g. steep slopes, wetland etc. SWAN MEADOWS I N 24th StGardenCt NPark Pl NAccess RdN 26th St 117900 £ 0 100 20050Feet CITY OF RENTON STORM WATER FACILITY RETROFIT STUDY Legend 95105110115245120130135140145240155160235230220215210205195190185180170165117900 50' 100'200'Slope >15% & <=25% Slope >25% Seismic Hazard Areas Landslide Hazard Wellfield Capture Zones Wetlands Open Water Stormwater Pipe Approx. Tributary Area To Facility 117900 Low Infiltration Soils/ High Ground Water Stormwater Detention Facility Estimated Offset Ranges From Existing Facitly Note - 1. Offset ranges may determine the feasible retrofit BMP type. e.g. steep slopes, wetland etc. MEADOW AV N & N 24TH ST Pierce Ave SENewpor t Ct SESerene Cir SE SE 1 6t h P l SE 17th St S E R o y a l H ills D rOlympia Ave SE117902 £ 0 100 20050Feet CITY OF RENTON STORM WATER FACILITY RETROFIT STUDY Legend 260 415265 270 280285290295 410305 320 330 335 340 345 355 360 365 315 37 0 380 385 390 310 395 4 0 5 117902 50'100'200'Slope >15% & <=25% Slope >25% Seismic Hazard Areas Landslide Hazard Wellfield Capture Zones Wetlands Open Water Stormwater Pipe Approx. Tributary Area To Facility 117902 Low Infiltration Soils/ High Ground Water Stormwater Detention Facility Estimated Offset Ranges From Existing Facitly Note - 1. Offset ranges may determine the feasible retrofit BMP type. e.g. steep slopes, wetland etc. TIFFANY PARK DIV 4 SE 166th Pl111th Ave SE117912 Big S o os Creek £ 0 100 20050Feet CITY OF RENTON STORM WATER FACILITY RETROFIT STUDY Legend 445435440430117912 Bi g S o o s Creek 50' 100' 2 0 0 ' Slope >15% & <=25% Slope >25% Seismic Hazard Areas Landslide Hazard Wellfield Capture Zones Wetlands Open Water Stormwater Pipe Approx. Tributary Area To Facility 117912 Low Infiltration Soils/ High Ground Water Stormwater Detention Facility Estimated Offset Ranges From Existing Facitly Note - 1. Offset ranges may determine the feasible retrofit BMP type. e.g. steep slopes, wetland etc. ARMSTRONG AND SANDELIUS 123rdCt SESE 179th Pl SE 181st St123rd Pl SE124th Ave SE111361 117915 £ 0 100 20050Feet CITY OF RENTON STORM WATER FACILITY RETROFIT STUDY Legend 395390385405380111361 11791550'50'100'200'Slope >15% & <=25% Slope >25% Seismic Hazard Areas Landslide Hazard Wellfield Capture Zones Wetlands Open Water Stormwater Pipe Approx. Tributary Area To Facility 117915 Low Infiltration Soils/ High Ground Water Stormwater Detention Facility Estimated Offset Ranges From Existing Facitly Note - 1. Offset ranges may determine the feasible retrofit BMP type. e.g. steep slopes, wetland etc. KNUDSON J o n e sCt S E J one s Ci r SERolling Hills Condo AcRdS E 2 1 s t P lPug e t D r SE Gateway Pointe Apt AcRd JonesPl SES Puget Dr Rolling Hills Ave SE117916 £ 0 100 20050Feet CITY OF RENTON STORM WATER FACILITY RETROFIT STUDY Legend370 440380385435390430395420405415410117916 50'100'200'Slope >15% & <=25% Slope >25% Seismic Hazard Areas Landslide Hazard Wellfield Capture Zones Wetlands Open Water Stormwater Pipe Approx. Tributary Area To Facility 117916 Low Infiltration Soils/ High Ground Water Stormwater Detention Facility Estimated Offset Ranges From Existing Facitly Note - 1. Offset ranges may determine the feasible retrofit BMP type. e.g. steep slopes, wetland etc. PARKWOOD SOUTH DIV 1 102ndAve SEMain Ave SS 4 7th Pl SE 185th Pl S 49th St SE 186th St S 4 8t h St S 47th St Private Rd 117917 PantherCreek £ 0 100 20050Feet CITY OF RENTON STORM WATER FACILITY RETROFIT STUDY Legend 380 3 8 5 415390395410405117917 Pa nther Creek50'100'200'Slope >15% & <=25% Slope >25% Seismic Hazard Areas Landslide Hazard Wellfield Capture Zones Wetlands Open Water Stormwater Pipe Approx. Tributary Area To Facility 117917 Low Infiltration Soils/ High Ground Water Stormwater Detention Facility Estimated Offset Ranges From Existing Facitly Note - 1. Offset ranges may determine the feasible retrofit BMP type. e.g. steep slopes, wetland etc. WINDSOR HEIGHTS SE 190th St SE 189th Pl 110th Pl SE110th Ct SESE 189th St 111thPl SE112th Ave SE117918 117938 £ 0 100 20050Feet CITY OF RENTON STORM WATER FACILITY RETROFIT STUDY Legend 470 485480117918 117938 50'50'100'100'200'200'Slope >15% & <=25% Slope >25% Seismic Hazard Areas Landslide Hazard Wellfield Capture Zones Wetlands Open Water Stormwater Pipe Approx. Tributary Area To Facility 117918 Low Infiltration Soils/ High Ground Water Stormwater Detention Facility Estimated Offset Ranges From Existing Facitly Note - 1. Offset ranges may determine the feasible retrofit BMP type. e.g. steep slopes, wetland etc. BENSON WOODS Access RdPri vate RdNE 13th Pl NE 12th St Camas Ave NEBlaine Ave NE117921 117894 £ 0 100 20050Feet CITY OF RENTON STORM WATER FACILITY RETROFIT STUDY Legend 295 2 9 0 2 8 0 2 8 5 117921 117894 50'50'100'100'200'Slope >15% & <=25% Slope >25% Seismic Hazard Areas Landslide Hazard Wellfield Capture Zones Wetlands Open Water Stormwater Pipe Approx. Tributary Area To Facility 117921 Low Infiltration Soils/ High Ground Water Stormwater Detention Facility Estimated Offset Ranges From Existing Facitly Note - 1. Offset ranges may determine the feasible retrofit BMP type. e.g. steep slopes, wetland etc. SWAN MEADOWS II S 197th St 92ndAve S117929 £ 0 100 20050Feet CITY OF RENTON STORM WATER FACILITY RETROFIT STUDY Legend1 0 5 110 145 140 120 115 1351 3 0 117929 50'100'200'Slope >15% & <=25% Slope >25% Seismic Hazard Areas Landslide Hazard Wellfield Capture Zones Wetlands Open Water Stormwater Pipe Approx. Tributary Area To Facility 117929 Low Infiltration Soils/ High Ground Water Stormwater Detention Facility Estimated Offset Ranges From Existing Facitly Note - 1. Offset ranges may determine the feasible retrofit BMP type. e.g. steep slopes, wetland etc. BOB BURKE 109thPl SESE 169th Pl SE 170th St Private Rd 117931 £ 0 100 20050Feet CITY OF RENTON STORM WATER FACILITY RETROFIT STUDY Legend 4304 3 5 430 11793150'100'200'200'Slope >15% & <=25% Slope >25% Seismic Hazard Areas Landslide Hazard Wellfield Capture Zones Wetlands Open Water Stormwater Pipe Approx. Tributary Area To Facility 117931 Low Infiltration Soils/ High Ground Water Stormwater Detention Facility Estimated Offset Ranges From Existing Facitly Note - 1. Offset ranges may determine the feasible retrofit BMP type. e.g. steep slopes, wetland etc. BENSON GLEN SE 2nd StBremertonPl SENE 1st St Vashon Ave SE NE 1st Pl Bremerton Ave NEBremerton Pl NEBremerton Ave SE117936 Maplewood Creek £ 0 100 20050Feet CITY OF RENTON STORM WATER FACILITY RETROFIT STUDY Legend 4 0 5 3953 9 5 3 9 0 3553 8 5 3 8 03 60365370117936 MaplewoodCreek 50'100'200'Slope >15% & <=25% Slope >25% Seismic Hazard Areas Landslide Hazard Wellfield Capture Zones Wetlands Open Water Stormwater Pipe Approx. Tributary Area To Facility 117936 Low Infiltration Soils/ High Ground Water Stormwater Detention Facility Estimated Offset Ranges From Existing Facitly Note - 1. Offset ranges may determine the feasible retrofit BMP type. e.g. steep slopes, wetland etc. FERNWOOD EAST SE 190th PlSE 192nd St 113th Way SESE 189th Pl 112th Pl SE112th Ave SE117918 117938 SE 192nd St £ 0 100 20050Feet CITY OF RENTON STORM WATER FACILITY RETROFIT STUDY Legend 4 6 0 4 6 5 4954 7 0 490485480117918 11793850'50'100'100'200'200'Slope >15% & <=25% Slope >25% Seismic Hazard Areas Landslide Hazard Wellfield Capture Zones Wetlands Open Water Stormwater Pipe Approx. Tributary Area To Facility 117938 Low Infiltration Soils/ High Ground Water Stormwater Detention Facility Estimated Offset Ranges From Existing Facitly Note - 1. Offset ranges may determine the feasible retrofit BMP type. e.g. steep slopes, wetland etc. CHINQUAPIN RIDGE ShattuckAve SS 21st St Shattuck Pl ST a lb o t C r e s t D r S S 22nd P l S 22nd CtDavisAve S117940 £ 0 100 20050Feet CITY OF RENTON STORM WATER FACILITY RETROFIT STUDY Legend 3 0 1903 5 4 045 55606570808590951051101151 8 0 1201851 7 0 130135140145155165160117940 50'100'200'Slope >15% & <=25% Slope >25% Seismic Hazard Areas Landslide Hazard Wellfield Capture Zones Wetlands Open Water Stormwater Pipe Approx. Tributary Area To Facility 117940 Low Infiltration Soils/ High Ground Water Stormwater Detention Facility Estimated Offset Ranges From Existing Facitly Note - 1. Offset ranges may determine the feasible retrofit BMP type. e.g. steep slopes, wetland etc. VALLEY VUE ESTATES NE 24th Ct Edmonds Ave NENE 24th Pl NE 24th St NE 23rd St NE 23rd Pl NE 22nd St 117941 £ 0 100 20050Feet CITY OF RENTON STORM WATER FACILITY RETROFIT STUDY Legend315 330320117941 50' 1 0 0 '200'Slope >15% & <=25% Slope >25% Seismic Hazard Areas Landslide Hazard Wellfield Capture Zones Wetlands Open Water Stormwater Pipe Approx. Tributary Area To Facility 117941 Low Infiltration Soils/ High Ground Water Stormwater Detention Facility Estimated Offset Ranges From Existing Facitly Note - 1. Offset ranges may determine the feasible retrofit BMP type. e.g. steep slopes, wetland etc. WEATHERWOOD II 123rdCt SE122ndCt SES E 1 7 9 t h P l S E 1 7 8 t h S t 117945 £ 0 100 20050Feet CITY OF RENTON STORM WATER FACILITY RETROFIT STUDY Legend 4 1 040511794550'100'200'200'Slope >15% & <=25% Slope >25% Seismic Hazard Areas Landslide Hazard Wellfield Capture Zones Wetlands Open Water Stormwater Pipe Approx. Tributary Area To Facility 117945 Low Infiltration Soils/ High Ground Water Stormwater Detention Facility Estimated Offset Ranges From Existing Facitly Note - 1. Offset ranges may determine the feasible retrofit BMP type. e.g. steep slopes, wetland etc. HIDDEN CEDARS DIV II 110th Pl SESE 170th St SE 169th Pl 117947 £ 0 100 20050Feet CITY OF RENTON STORM WATER FACILITY RETROFIT STUDY Legend 43041542011794750'100'200'200'Slope >15% & <=25% Slope >25% Seismic Hazard Areas Landslide Hazard Wellfield Capture Zones Wetlands Open Water Stormwater Pipe Approx. Tributary Area To Facility 117947 Low Infiltration Soils/ High Ground Water Stormwater Detention Facility Estimated Offset Ranges From Existing Facitly Note - 1. Offset ranges may determine the feasible retrofit BMP type. e.g. steep slopes, wetland etc. BENSON GLEN 112th Pl SESE 189th Pl SE 189th Ct S E 1 8 8 t h P l117952 £ 0 100 20050Feet CITY OF RENTON STORM WATER FACILITY RETROFIT STUDY Legend 5104 8 0 4 8 5 505495490117952 50' 1 0 0 '200'Slope >15% & <=25% Slope >25% Seismic Hazard Areas Landslide Hazard Wellfield Capture Zones Wetlands Open Water Stormwater Pipe Approx. Tributary Area To Facility 117952 Low Infiltration Soils/ High Ground Water Stormwater Detention Facility Estimated Offset Ranges From Existing Facitly Note - 1. Offset ranges may determine the feasible retrofit BMP type. e.g. steep slopes, wetland etc. CHINQUAPIN RIDGE SheltonCt NENE 22nd St NE 21st St 145336 £ 0 100 20050Feet CITY OF RENTON STORM WATER FACILITY RETROFIT STUDY Legend440 435430 145336 50'100'200'Slope >15% & <=25% Slope >25% Seismic Hazard Areas Landslide Hazard Wellfield Capture Zones Wetlands Open Water Stormwater Pipe Approx. Tributary Area To Facility 145336 Low Infiltration Soils/ High Ground Water Stormwater Detention Facility Estimated Offset Ranges From Existing Facitly Note - 1. Offset ranges may determine the feasible retrofit BMP type. e.g. steep slopes, wetland etc. PETETT MEADOWS SHORT PLAT Copper Ridge Apt AcRdLake Pl SSR 167 RampSR 167145398 £ 0 100 20050Feet CITY OF RENTON STORM WATER FACILITY RETROFIT STUDY Legend 959085304045556035657080145398 50'100'200'Slope >15% & <=25% Slope >25% Seismic Hazard Areas Landslide Hazard Wellfield Capture Zones Wetlands Open Water Stormwater Pipe Approx. Tributary Area To Facility 145398 Low Infiltration Soils/ High Ground Water Stormwater Detention Facility Estimated Offset Ranges From Existing Facitly Note - 1. Offset ranges may determine the feasible retrofit BMP type. e.g. steep slopes, wetland etc. DAVIS AV S ONE VALLEY PLACE Main Ct SS 22nd Ct S 23rd StHillsideVillageApt AcRd145407 Rolling HillsCreek RollingHillsCreek£ 0 100 20050Feet CITY OF RENTON STORM WATER FACILITY RETROFIT STUDY Legend 305295160 290285280165 2701 7 0 265260255180185190195205210215220230235240245145407 RollingHillsCree k RollingHillsCreek50'100'200'Slope >15% & <=25% Slope >25% Seismic Hazard Areas Landslide Hazard Wellfield Capture Zones Wetlands Open Water Stormwater Pipe Approx. Tributary Area To Facility 145407 Low Infiltration Soils/ High Ground Water Stormwater Detention Facility Estimated Offset Ranges From Existing Facitly Note - 1. Offset ranges may determine the feasible retrofit BMP type. e.g. steep slopes, wetland etc. VICTORIA HILLS NE 11th Ct NE 13th Pl NE SunsetBlvd NE 14th StDaytonPl NENE 13th St NE 12th StDayton Ave NEEdmonds Ave NEEdmonds Pl NE145785 NE Sunset Blvd £ 0 100 20050Feet CITY OF RENTON STORM WATER FACILITY RETROFIT STUDY Legend345 2 6 5 270 3403353302 8 0 285320290315310305295145785 50'100'200'200'Slope >15% & <=25% Slope >25% Seismic Hazard Areas Landslide Hazard Wellfield Capture Zones Wetlands Open Water Stormwater Pipe Approx. Tributary Area To Facility 145785 Low Infiltration Soils/ High Ground Water Stormwater Detention Facility Estimated Offset Ranges From Existing Facitly Note - 1. Offset ranges may determine the feasible retrofit BMP type. e.g. steep slopes, wetland etc. ELIZABETH PLACE Newport Ct NENE 10th St NE 9th StMonroe Ave NE145824 £ 0 100 20050Feet CITY OF RENTON STORM WATER FACILITY RETROFIT STUDY Legend 415 410 380 405 385 390 3 9 5 145824 50'100'200'Slope >15% & <=25% Slope >25% Seismic Hazard Areas Landslide Hazard Wellfield Capture Zones Wetlands Open Water Stormwater Pipe Approx. Tributary Area To Facility 145824 Low Infiltration Soils/ High Ground Water Stormwater Detention Facility Estimated Offset Ranges From Existing Facitly Note - 1. Offset ranges may determine the feasible retrofit BMP type. e.g. steep slopes, wetland etc. RUDDELLS 2ND ADDITION S E 2 0 th C tMonterey Ct SESE 21st Ct AberdeenCt SEAberdeen Ave SESE 22nd Pl SE 160th StAberdeen Pl SE145827 £ 0 100 20050Feet CITY OF RENTON STORM WATER FACILITY RETROFIT STUDY Legend 4704 3 0 435 440 455 445 465460145827 50'100'200'Slope >15% & <=25% Slope >25% Seismic Hazard Areas Landslide Hazard Wellfield Capture Zones Wetlands Open Water Stormwater Pipe Approx. Tributary Area To Facility 145827 Low Infiltration Soils/ High Ground Water Stormwater Detention Facility Estimated Offset Ranges From Existing Facitly Note - 1. Offset ranges may determine the feasible retrofit BMP type. e.g. steep slopes, wetland etc. PARKWOOD S W S u n s et Blv d SW 3rd Pl Powell Ave SWOakesdaleAve SW145832 £ 0 100 20050Feet CITY OF RENTON STORM WATER FACILITY RETROFIT STUDY Legend245 1 4 0 2401 4 5 235 1 5 5 1 6 0 230 165170220215210205180195190185145832 50'100'200'Slope >15% & <=25% Slope >25% Seismic Hazard Areas Landslide Hazard Wellfield Capture Zones Wetlands Open Water Stormwater Pipe Approx. Tributary Area To Facility 145832 Low Infiltration Soils/ High Ground Water Stormwater Detention Facility Estimated Offset Ranges From Existing Facitly Note - 1. Offset ranges may determine the feasible retrofit BMP type. e.g. steep slopes, wetland etc. SOUTH KNOLL WATER EXTENSION NE 21st St NE 2 3r d St A b e r d e e n P l N E NE 20th StAberdeen Ave NE145834 £ 0 100 20050Feet CITY OF RENTON STORM WATER FACILITY RETROFIT STUDY Legend285 320315310305295285290145834 50' 100' 200'Slope >15% & <=25% Slope >25% Seismic Hazard Areas Landslide Hazard Wellfield Capture Zones Wetlands Open Water Stormwater Pipe Approx. Tributary Area To Facility 145834 Low Infiltration Soils/ High Ground Water Stormwater Detention Facility Estimated Offset Ranges From Existing Facitly Note - 1. Offset ranges may determine the feasible retrofit BMP type. e.g. steep slopes, wetland etc. POLLOS ESTATES NE 4 th St Windsor W ay N EWindsor Pl NEFerndale Ave NEEdmonds Ave NEEdmonds Ct NE 145836 £ 0 100 20050Feet CITY OF RENTON STORM WATER FACILITY RETROFIT STUDY Legend 1802 9 5 2 9 02852801852701902651952602552052352102302402152202 4 5 145836 50'100'200'Slope >15% & <=25% Slope >25% Seismic Hazard Areas Landslide Hazard Wellfield Capture Zones Wetlands Open Water Stormwater Pipe Approx. Tributary Area To Facility 145836 Low Infiltration Soils/ High Ground Water Stormwater Detention Facility Estimated Offset Ranges From Existing Facitly Note - 1. Offset ranges may determine the feasible retrofit BMP type. e.g. steep slopes, wetland etc. HIGHBURY PARK Creekside on Sunset AcRd NE 18th St NE 17th StSheltonAve NERedmond Ct NEAccess R d 145869 145851 Honey Creek £ 0 100 20050Feet CITY OF RENTON STORM WATER FACILITY RETROFIT STUDY Legend 380 385 390 420 410 405 415 395 145869 145851 HoneyCreek 50' 50'100'1 0 0 '200'Slope >15% & <=25% Slope >25% Seismic Hazard Areas Landslide Hazard Wellfield Capture Zones Wetlands Open Water Stormwater Pipe Approx. Tributary Area To Facility 145851 Low Infiltration Soils/ High Ground Water Stormwater Detention Facility Estimated Offset Ranges From Existing Facitly Note - 1. Offset ranges may determine the feasible retrofit BMP type. e.g. steep slopes, wetland etc. YOUNG ADDITION NE 2 6th Ct SE 95th Way NE 25th Ct Anacortes Ave NEDu v a ll Av e NE145864 D u v a ll A v e N E £ 0 100 20050Feet CITY OF RENTON STORM WATER FACILITY RETROFIT STUDY Legend 355 435360 365 370 380 385 390 395 405 41 0 41 5 42 0 4 3 0 145864 5 0 '100' 2 0 0 ' Slope >15% & <=25% Slope >25% Seismic Hazard Areas Landslide Hazard Wellfield Capture Zones Wetlands Open Water Stormwater Pipe Approx. Tributary Area To Facility 145864 Low Infiltration Soils/ High Ground Water Stormwater Detention Facility Estimated Offset Ranges From Existing Facitly Note - 1. Offset ranges may determine the feasible retrofit BMP type. e.g. steep slopes, wetland etc. RIDGEVIEW ESTATES NE 15th StAccess RdUnion Ave NENE 18th St NE 17th St 145869 145851 £ 0 100 20050Feet CITY OF RENTON STORM WATER FACILITY RETROFIT STUDY Legend 385 390 3 9 5 430 420 4 1 5 4 1 0 4 0 5 145869 145851 50'50' 1 0 0 ' 100'200'Slope >15% & <=25% Slope >25% Seismic Hazard Areas Landslide Hazard Wellfield Capture Zones Wetlands Open Water Stormwater Pipe Approx. Tributary Area To Facility 145869 Low Infiltration Soils/ High Ground Water Stormwater Detention Facility Estimated Offset Ranges From Existing Facitly Note - 1. Offset ranges may determine the feasible retrofit BMP type. e.g. steep slopes, wetland etc. YOUNG ADDITION Pr i vat e RdSE 164th St 113th Ave SESE 162nd St 114thAve SE146790 £ 0 100 20050Feet CITY OF RENTON STORM WATER FACILITY RETROFIT STUDY Legend 4554 8 0 460465470146790 50'100'2 0 0 ' Slope >15% & <=25% Slope >25% Seismic Hazard Areas Landslide Hazard Wellfield Capture Zones Wetlands Open Water Stormwater Pipe Approx. Tributary Area To Facility 146790 Low Infiltration Soils/ High Ground Water Stormwater Detention Facility Estimated Offset Ranges From Existing Facitly Note - 1. Offset ranges may determine the feasible retrofit BMP type. e.g. steep slopes, wetland etc. LUND SHORT PLAT Anacortes Ave NEN E S u n s e t B lv d Access Rd 166609 H o n e y C r e e k £ 0 100 20050Feet CITY OF RENTON STORM WATER FACILITY RETROFIT STUDY Legend415 4 0 5 4 1 0 166609 H o n e y C r e e k50'100'200'Slope >15% & <=25% Slope >25% Seismic Hazard Areas Landslide Hazard Wellfield Capture Zones Wetlands Open Water Stormwater Pipe Approx. Tributary Area To Facility 166609 Low Infiltration Soils/ High Ground Water Stormwater Detention Facility Estimated Offset Ranges From Existing Facitly Note - 1. Offset ranges may determine the feasible retrofit BMP type. e.g. steep slopes, wetland etc. SUNSET BLVD/DUVALL AVE NE INT S E 1 8 0 t h P l 113th Ave SESE 180th St SE 179th St SE 181st St112thAv e SE111th Ave SE167768 £ 0 100 20050Feet CITY OF RENTON STORM WATER FACILITY RETROFIT STUDY Legend435 445470465460455440167768 50'100'200'Slope >15% & <=25% Slope >25% Seismic Hazard Areas Landslide Hazard Wellfield Capture Zones Wetlands Open Water Stormwater Pipe Approx. Tributary Area To Facility 167768 Low Infiltration Soils/ High Ground Water Stormwater Detention Facility Estimated Offset Ranges From Existing Facitly Note - 1. Offset ranges may determine the feasible retrofit BMP type. e.g. steep slopes, wetland etc. ORCHARD PARK NE 4th Ct NE 4th Cir Tacoma Pl NEShelton Ct NENE 5th Pl NE 5th Aly RedmondPl NENE 5th St Crown PointeApartments AcRdShelton Pl NE168953 £ 0 100 20050Feet CITY OF RENTON STORM WATER FACILITY RETROFIT STUDY Legend 405 395 3553 8 0 390 3603 8 5 365370168953 50'100'200'Slope >15% & <=25% Slope >25% Seismic Hazard Areas Landslide Hazard Wellfield Capture Zones Wetlands Open Water Stormwater Pipe Approx. Tributary Area To Facility 168953 Low Infiltration Soils/ High Ground Water Stormwater Detention Facility Estimated Offset Ranges From Existing Facitly Note - 1. Offset ranges may determine the feasible retrofit BMP type. e.g. steep slopes, wetland etc. VILLAGE ON UNION Be n s o nDr SBenson Rd SSE 172nd St Access Rd108th Ave SESE 173rd St 200040 200041 £ 0 100 20050Feet CITY OF RENTON STORM WATER FACILITY RETROFIT STUDY Legend 3903954054104154 2 0 200040 200041 50'50'100'100'200'Slope >15% & <=25% Slope >25% Seismic Hazard Areas Landslide Hazard Wellfield Capture Zones Wetlands Open Water Stormwater Pipe Approx. Tributary Area To Facility 200040 Low Infiltration Soils/ High Ground Water Stormwater Detention Facility Estimated Offset Ranges From Existing Facitly Note - 1. Offset ranges may determine the feasible retrofit BMP type. e.g. steep slopes, wetland etc. KELSEY LANE Benson Rd SSE 172nd St Access Rd108th Ave SEPrivate Rd SE 173rd St 200040 200041 £ 0 100 20050Feet CITY OF RENTON STORM WATER FACILITY RETROFIT STUDY Legend 390395405410415420200040 200041 50'50'100'100'200'Slope >15% & <=25% Slope >25% Seismic Hazard Areas Landslide Hazard Wellfield Capture Zones Wetlands Open Water Stormwater Pipe Approx. Tributary Area To Facility 200041 Low Infiltration Soils/ High Ground Water Stormwater Detention Facility Estimated Offset Ranges From Existing Facitly Note - 1. Offset ranges may determine the feasible retrofit BMP type. e.g. steep slopes, wetland etc. KELSEY LANE Meadow Pl NPrivate RdN 2 7 t h C t Access Rdwy N 27th Pl Park Ave NN 28th Pl N 29th St N 28th Aly N 28th St 200049 K enn yda le Creek £ 0 100 20050Feet CITY OF RENTON STORM WATER FACILITY RETROFIT STUDY Legend 2152101601651701 8 0 1 8 5 2 0 5 1 9 0 1 9 5 200049 Ken nyd ale Creek 50'100'200'Slope >15% & <=25% Slope >25% Seismic Hazard Areas Landslide Hazard Wellfield Capture Zones Wetlands Open Water Stormwater Pipe Approx. Tributary Area To Facility 200049 Low Infiltration Soils/ High Ground Water Stormwater Detention Facility Estimated Offset Ranges From Existing Facitly Note - 1. Offset ranges may determine the feasible retrofit BMP type. e.g. steep slopes, wetland etc. NANTUCKET SHORT PLAT SE 160th StDaytonDr SESE 20th Pl Dayton Ct SEEdmonds Dr SESE 19th St SE 21st St 116th Ave SE200096 £ 0 100 20050Feet CITY OF RENTON STORM WATER FACILITY RETROFIT STUDY Legend 4 7 0 440 445 465 4 6 0 455 200096 50'100'200'Slope >15% & <=25% Slope >25% Seismic Hazard Areas Landslide Hazard Wellfield Capture Zones Wetlands Open Water Stormwater Pipe Approx. Tributary Area To Facility 200096 Low Infiltration Soils/ High Ground Water Stormwater Detention Facility Estimated Offset Ranges From Existing Facitly Note - 1. Offset ranges may determine the feasible retrofit BMP type. e.g. steep slopes, wetland etc. PARKWOOD SOUTH DIV III APPENDIX B: BMP SITE OPPORTUNITIES AND LIMITATIONS DETAIL SUMMARY Detention Site WQ NeedsSite Number (City Asset ID)Development Project Name111332 SUMMERWIND DIV I II III111342 WINSPER (LIBERTY VIEW I&II)111354 SPRINGBROOK TERRACE111361 HIDDEN CEDARS DIV II111369 PANTHER MEADOW111391 DENNYS RESTAURANT111393 CASTLEWOOD RANCHETTES111394 CASTLEWOOD RANCHETTES111408 BERGSMA SHORT PLAT111421 RIPLEY LN STORM IMPROVEMENT PR111422 RENTON VILLAGE INTERCEPTOR117894 SWAN MEADOWS I117900 MEADOW AV N & N 24TH ST117902 TIFFANY PARK DIV 4117912 ARMSTRONG AND SANDELIUS117915 KNUDSON117916 PARKWOOD SOUTH DIV I117917 WINDSOR HEIGHTS117918 BENSON WOODS117921 SWAN MEADOWS II117929 BOB BURKE117931 BENSON GLEN117936 FERNWOOD EAST117938 CHINQUAPIN RIDGE117940 VALLEY VUE ESTATES117941 WEATHERWOOD II117945 HIDDEN CEDARS DIV II117947 BENSON GLEN117952 CHINQUAPIN RIDGE145336 PETETT MEADOWS SHORT PLAT145398 DAVIS AV S ONE VALLEY PLACE145407 VICTORIA HILLS145785 ELIZABETH PLACE145824 RUDDELLS 2ND ADDITION145827 PARKWOOD145832 SOUTH KNOLL WATER EXTENSION145834 POLLOS ESTATES145836 HIGHBURY PARK145851 YOUNG ADDITION145864 RIDGEVIEW ESTATES145869 YOUNG ADDITION146790 LUND SHORT PLAT166609 SUNSET BLVD/DUVALL AVE NE INT167768 ORCHARD PARK168953 VILLAGE ON UNION200040 KELSEY LANE200041 KELSEY LANE200049 NANTUCKET SHORT PLAT200096PARKWOOD SOUTH DIV IIISpaghnum Water Quality15% Slope (within 50ft)Landslide Hazard Area NotesLandslide Hazard AreaSeismic Hazard AreaAquifer Protection Area 1Aquifer Protection Area 1 - ModifiedAquifer Protection Area 2Groundwater Protection AreaWellfield Capture ZoneOpen Water (within 100ft)Low Infiltration Soils/High Ground WaterNo YesYes<50 No No No No Maybe No No NoNo YesNoNo No No No No No No No NoNo YesNoNo No No No No No No No NoYes NoNoNo >50 No No No No No No NoNo NoNoNo No No No No No No No NoNo YesNoNo <50 No No No No No No YesNo YesNoNo No No No No Yes No No NoNo NoNoNo No No No No Yes No No NoNo NoNoNo No No No No No No Yes NoNo YesNoNo <50 No No No No No No NoNo NoNoNo >50 No No No Yes No No YesNo NoYes - within 200ft, Moderate>50 No No No No Yes No No NoNo YesYes, within 100ft, Moderate>50 No No Yes No Yes Yes No NoNo NoYes - within 200ft, Moderate>50 No No No No Yes No No NoNo NoNoNo No No No No No No Yes NoYes NoNoNo <50 No No No No No No NoNo YesYes - within 100ft, Moderate<50 No No No No No No No NoNo YesNoNo No No No No No No Yes NoNo NoNoNo No No No No No No No NoNo NoNoNo No No No No Yes No No NoNo NoNoNo No No No No No No No NoNo YesNoNo No No No No No No No NoNo YesYes - within 100ft, Moderate>50 No No No No Yes No Yes NoNo YesNoNo No No No No No No No NoNo YesYes - at site, High<50 No No No No No No No YesNo NoNoNo No No No Yes Yes No No NoNo NoNoNo No No No No No No No NoNo YesNoNo No No No No No No No NoNo NoNoNo No No No No No No No NoNo NoNoNo No No No No Yes No No NoNo YesYes - within 50ft, Moderate and High<50 <50 No No No No No No NoNo YesYes - at site, High<50 No No No No No No Yes NoNo YesYes - within 50 ft, Moderate<50 No No No No Yes No No NoNo YesNoNo No No No No Yes No No NoNo NoNoNo No No No No No No No NoNo YesYes - within 100ft, Moderate>50 No No No No No No No NoNo NoYes - within 100ft, Moderate>50 No No No Yes Yes Yes No NoNo NoYes - at site, High<50 No No No No Yes No No NoNo YesNoNo No No No No Yes No No NoNo NoNoNo No No No No Yes No No NoNo NoNoNo No No No No Yes No No NoNo NoNoNo No No No No No No No NoNo NoNoNo No No No No Yes No No NoNo YesNoNo No No No No No No No NoNo YesYes - within 50ft, Moderate<50 No No No No Yes No Yes NoNo NoNoNo No No No No No No No NoNo YesNoNo No No No No No No No NoNo NoYes - within 200ft, Moderate<50 No No No Yes Yes Yes No NoNoNoNoNoNoNoNoNoYesNoNoNoAppendix B: BMP Site Opportunities and LImitations Detail Summary Detention Site WQ NeedsSite Number (City Asset ID)Development Project Name111332 SUMMERWIND DIV I II III111342 WINSPER (LIBERTY VIEW I&II)111354 SPRINGBROOK TERRACE111361 HIDDEN CEDARS DIV II111369 PANTHER MEADOW111391 DENNYS RESTAURANT111393 CASTLEWOOD RANCHETTES111394 CASTLEWOOD RANCHETTES111408 BERGSMA SHORT PLAT111421 RIPLEY LN STORM IMPROVEMENT PR111422 RENTON VILLAGE INTERCEPTOR117894 SWAN MEADOWS I117900 MEADOW AV N & N 24TH ST117902 TIFFANY PARK DIV 4117912 ARMSTRONG AND SANDELIUS117915 KNUDSON117916 PARKWOOD SOUTH DIV I117917 WINDSOR HEIGHTS117918 BENSON WOODS117921 SWAN MEADOWS II117929 BOB BURKE117931 BENSON GLEN117936 FERNWOOD EAST117938 CHINQUAPIN RIDGE117940 VALLEY VUE ESTATES117941 WEATHERWOOD II117945 HIDDEN CEDARS DIV II117947 BENSON GLEN117952 CHINQUAPIN RIDGE145336 PETETT MEADOWS SHORT PLAT145398 DAVIS AV S ONE VALLEY PLACE145407 VICTORIA HILLS145785 ELIZABETH PLACE145824 RUDDELLS 2ND ADDITION145827 PARKWOOD145832 SOUTH KNOLL WATER EXTENSION145834 POLLOS ESTATES145836 HIGHBURY PARK145851 YOUNG ADDITION145864 RIDGEVIEW ESTATES145869 YOUNG ADDITION146790 LUND SHORT PLAT166609 SUNSET BLVD/DUVALL AVE NE INT167768 ORCHARD PARK168953 VILLAGE ON UNION200040 KELSEY LANE200041 KELSEY LANE200049 NANTUCKET SHORT PLAT200096PARKWOOD SOUTH DIV IIIInfiltration Potential(APA Zone and Soil/Groundwater)Lining Maybe Required (BMP in APA 2 Zone)Infiltration WQ BMP Not Allowed (In APA Zone 1 or Within 100ft of Open Water)Only Vault Allowed(Landslide and Seismic Hazard: <50=No, <200=Geotech approval required)Within Distance Equal to Total Vertical Height of Slope >15% (for determining if a geotechnical report is required to assess landslide hazard)Yes No Allowed Yes LikelyYes No Allowed No LikelyYes No Allowed No LikelyYes No Allowed Geotech Approval Required UnlikelyYes No Allowed No UnlikelyNo No Allowed Yes LikelyYes No Allowed No LikelyYes No Allowed No UnlikelyYes No Not Allowed No UnlikelyYes No Allowed Yes LikelyNo No Allowed Geotech Approval Required UnlikelyYes No Allowed Geotech Approval Required UnlikelyYes No Not Allowed Geotech Approval Required LikelyYes No Allowed Geotech Approval Required UnlikelyYes No Not Allowed No UnlikelyYes No Allowed Yes UnlikelyYes No Allowed Yes LikelyYes No Not Allowed No LikelyYes No Allowed No UnlikelyYes No Allowed No UnlikelyYes No Allowed No UnlikelyYes No Allowed No LikelyYes No Not Allowed Geotech Approval Required LikelyYes No Allowed No LikelyNo No Allowed Yes LikelyYes Yes Allowed No UnlikelyYes No Allowed No UnlikelyYes No Allowed No LikelyYes No Allowed No UnlikelyYes No Allowed No UnlikelyYes No Allowed Yes LikelyYes No Not Allowed Yes LikelyYes No Allowed Yes LikelyYes No Allowed No LikelyYes No Allowed No UnlikelyYes No Allowed Geotech Approval Required LikelyYes Yes Allowed Geotech Approval Required UnlikelyYes No Allowed Yes UnlikelyYes No Allowed No LikelyYes No Allowed No UnlikelyYes No Allowed No UnlikelyYes No Allowed No UnlikelyYes No Allowed No UnlikelyYes No Allowed No LikelyYes No Not Allowed Yes LikelyYes No Allowed No UnlikelyYes No Allowed No LikelyYes Yes Allowed Yes UnlikelyYesNoAllowedNoUnlikelyAppendix B: BMP Site Opportunities and LImitations Detail Summary (Con't) APPENDIX C: UPDATED WATER QUALITY VOLUME AND FLOW RATE AND BMP SIZING CALCULATORS Detention Site WQ NeedsSite Number (City Asset ID)Development Project NameReceiving Water BodyYear Constructed Tributary Basin AcreagePercent ImperviousDetention Structure TypeWater Quality Treatment TypeWQ VOLUME(ACRE-FT)WQ VOLUME(CF)WQ ONLINE FLOW RATE(CFS)WQ OFFLINE FLOW RATE(CFS)111332 SUMMERWIND DIV I II IIIGreenes Creek6/28/8620.2 54% Pond None 1.8127 78962 3.6837 1.9478111342 WINSPER (LIBERTY VIEW I&II)Panther Creek2/1/881.2 55%PondNone 0.1104 4808 0.2225 0.1179111354 SPRINGBROOK TERRACEUpper Springbrook Creek9/30/835.2 51%PondNone 0.4387 19108 0.9745 0.5067111361 HIDDEN CEDARS DIV IISoos Creek Main7/10/895.2 48% Pond None 0.4281 18646 0.9179 0.4808111369 PANTHER MEADOWPanther Creek4/6/892.9 44% Pond Bio-swale 0.2312 10069 0.5147 0.2680111391 DENNYS RESTAURANTLake Washington - East1/5/8220.2 35% Pond None 1.8886 82268 2.2942 1.2583111393 CASTLEWOOD RANCHETTESMaplewood Creek5/1/816.0 32% Pond None 0.3939 17159 1.0129 0.5143111394 CASTLEWOOD RANCHETTESMaplewood Creek5/1/8113.2 24% Pond None 0.6309 27483 1.5243 0.7805111408 BERGSMA SHORT PLATUpper Springbrook Creek4/1/803.1 26% Pond None 0.1990 8668 0.5118 0.2604111421 RIPLEY LN STORM IMPROVEMENT PRLake Washington - East3/19/08401.6 35%VaultNone 31.6360 1378066 62.2778 32.6103111422 RENTON VILLAGE INTERCEPTORThunder Hills Creek8/23/82736.4 31%VaultNone 54.4123 2370200 125.1760 64.3906117894 SWAN MEADOWS IJohns Creek2/20/891.7 52% Tank None 0.1515 6601 0.3137 0.1654117900 MEADOW AV N & N 24TH STSouth Kennydale7/1/952.7 45% Tank None 0.2209 9624 0.4817 0.2516117902 TIFFANY PARK DIV 4Cedar Main Urban5/7/7910.2 59% Tank None 1.0590 46131 1.9368 1.0457117912 ARMSTRONG AND SANDELIUSSoos Creek Main10/9/852.2 28% Tank None 0.1323 5764 0.3698 0.1851117915 KNUDSONSoos Creek Main3/25/920.2 94% Tank None 0.0268 1166 0.0415 0.0232117916 PARKWOOD SOUTH DIV IThunder Hills Creek9/15/775.5 55% Tank None 0.4968 21640 0.9991 0.5294117917 WINDSOR HEIGHTSPanther Creek8/16/940.3 100%TankNone 0.0358 1559 0.0538 0.0303117918 BENSON WOODSPanther Creek9/10/891.8 30% Tank Stormwater Wetland 0.1235 5380 0.2866 0.1482117921 SWAN MEADOWS IIJohns Creek2/20/890.8 77% Tank None 0.0938 4088 0.1595 0.0874117929 BOB BURKEUpper Springbrook Creek7/2/912.1 34% Tank Bio-swale 0.1418 6178 0.3544 0.1811117931 BENSON GLENPanther Creek8/21/921.7 52% Tank Bio-swale 0.1574 6855 0.3122 0.1659117936 FERNWOOD EASTMaplewood Creek5/22/799.4 47% Tank None 0.7621 33198 1.6560 0.8654117938 CHINQUAPIN RIDGEPanther Creek8/14/900.6 66% Tank Bio-swale 0.0569 2479 0.1054 0.0567117940 VALLEY VUE ESTATESPanther Creek2/27/971.0 55% Tank Bio-swale 0.1157 5039 0.1489 0.0838117941 WEATHERWOOD IILower May Creek4/18/7912.0 50%TankNone 1.0207 44461 2.1585 1.1329117945 HIDDEN CEDARS DIV IISoos Creek Main7/10/891.4 45% Tank None 0.1103 4803 0.2442 0.1272117947 BENSON GLENPanther Creek8/21/924.6 44% Tank Bio-swale 0.3708 16153 0.8154 0.4253117952 CHINQUAPIN RIDGEPanther Creek8/14/902.2 63% Tank None 0.2235 9735 0.4198 0.2254145336 PETETT MEADOWS SHORT PLATHoney Creek7/20/051.5 60%PondNone 0.1464 6379 0.2818 0.1507145398 DAVIS AV S ONE VALLEY PLACEUpper Springbrook Creek3/31/8221.5 46% Pond None 1.6974 73937 3.6367 1.9060145407 VICTORIA HILLSRolling Hills Creek11/1/7844.6 40% Pond None 3.3024 143853 7.9186 4.0565145785 ELIZABETH PLACEJohns Creek5/2/000.9 94% Tank None 0.1153 5021 0.1852 0.1035145824 RUDDELLS 2ND ADDITIONJohns Creek4/14/773.2 27% Tank None 0.2798 12190 0.2545 0.1449145827 PARKWOODThunder Hills Creek9/15/777.5 46% Tank None 0.5617 24467 1.1264 0.5977145832 SOUTH KNOLL WATER EXTENSIONSouth Renton4/1/858.4 29% Tank None 0.7867 34268 0.7955 0.4463145834 POLLOS ESTATESLower May Creek5/5/902.2 48%TankNone 0.1790 7798 0.3896 0.2030145836 HIGHBURY PARKJohns Creek9/28/7814.2 41% Tank None 1.0544 45929 2.4870 1.2784145851 YOUNG ADDITIONHoney Creek2/21/911.1 87% Tank None 0.1451 6321 0.2348 0.1300145864 RIDGEVIEW ESTATESMay Creek8/11/886.8 52% Tank None 0.5886 25639 1.2218 0.6436145869 YOUNG ADDITIONHoney Creek2/21/911.6 47%TankNone 0.1286 5600 0.2778 0.1453146790 LUND SHORT PLATThunder Hills Creek6/9/050.5 28% Pond None 0.0356 1550 0.0871 0.0446166609 SUNSET BLVD/DUVALL AVE NE INTHoney Creek6/3/090.3 100% Vault Wet Vault 0.0494 2152 0.0743 0.0418167768 ORCHARD PARKPanther Creek10/10/914.4 47% Tank None 0.3539 15417 0.7701 0.4023168953 VILLAGE ON UNIONCedar Main Urban1/30/9516.5 52%Tank Infiltration1.5440 67259 2.7019 1.4479200040 KELSEY LANEPanther Creek6/25/812.0 61% Tank None 0.2066 9001 0.3272 0.1791200041 KELSEY LANEPanther Creek6/25/810.2 100% Tank None 0.0243 1061 0.0366 0.0206200049 NANTUCKET SHORT PLATSouth Kennydale7/1/155.4 37% Vault Wet Vault 0.3772 16430 0.9153 0.4698200096PARKWOOD SOUTH DIV IIIThunder Hills Creek9/15/771.322%TankNone0.051822540.12030.0623 BASIC WETPOND INPUTS OUTPUTS ASSUMPTIONS INPUT WQ Volume (acre-ft)0.978 Depth h (both cells) (ft)4 L:W ratio 4 :1 CALCULATIONS Side slope 3 :1 Vb (cf)42580 a=8 b= 120 c= -20713.95 x= 43.93 Bottom width of wetpool Bottom Width (FT) 43.93 Botom Length (FT) 175.7 Bottom Area (SF) 7721 WQ Surface Wdith (ft) 68 WQ Surface Length (ft) 200 WQ Design Surface Area (SF) 13569 REFERENCE EQUATIONS OUTPUTS Facility Width (FT)74 Facility Length (FT)206 BASIC WETVAULT INPUTS OUTPUTS ASSUMPTIONS INPUT WQ Volume (acre-ft)0.978 WQ Design Depth (FT)8 WQ Volume (CF))42580 L:W ratio*5 :1 Sediment depth** (FT)1.00 Baffle / Oil Separater No OUTPUT WIDTH (top area, ft)32.63 LENGTH (top area, ft)163.13 *If L:W ratio is 5:1 or great, the baffle or wall may be ommitted and vault may be one-celled S SAND FILTER VAULT ASSUMPTIONS Sand Filter Cell INPUT Hydraulic Conductivity 2.32E-05 fps Online WQ Flow Rate (cfs)1.470 cfs Max Storage Depth Above Filter 6.00 ft Average Depth of Water above Filter (max depth / 2)3.00 ft OUTPUT Thickness of Sand Media 1.50 ft Surface Area 12700 sf L:W ratio*2 :1 Width of Sand Filter 80 ft Sediment depth (FT)1.00 Length of Sand Filter 159 ft Baffle / Oil Separater No Pre-Settling Tank WQ Design Depth (FT)6 L:W ratio*3 :1 Sediment depth (FT)1.00 INPUTS Baffle / Oil Separater No Basin WQ Volume (acre-ft)0.978 OUTPUTS Presettling Volume (cf)10645 *25% OF WQ VOLUME Presettling Cell Width 24 1 acre of impervious = 0.2134 Presettling Cell Length 73 SAND FILTER CELL PRESETTLING CELL STORMFILTER VAULT INPUTS OUTPUTS ASSUMPTIONS STORMFILTER VAULT 12" Cartridges 18" Cartridges 27" Cartridgse WQ Online Flow Rate (cfs)1.47 PRE-CAST VAULT WIDTH FROM CONTECH CATALOGUE 8 8 8 12" Cartridge 18" Cartridge 27" Cartridge ADDITIONAL DESIGN REQUIREMENTS Flow Rate/Cartridge (GPM)5 7.5 11.25 Flow Rate/Cartridge (CFS) 0.0111 0.0167 0.0251 Max # Cartridges for StormFilter Pre-cast Vault 61 *Assuming a 8ft x 24ft precast vault MAX PEAK FLOW RATE (CFS)1.8 Vault Sizes If # Cartridges > Than Vault Length (ft)Standard Vault Size 12" Cartridges 18" Cartridges 27" Cartridgse 1 7 8'X6' Max Flow Rates for a Basin 0.6795 1.0193 1.5290 12 12 8'X11' Minimum Head Drop 1.8 2.3 3.05 26 15 8'X14' 34 17 8'X16' 39 19 8'X18' 44 21 8'X20' 51 23 8'X22' 56 25 8'X24' 12" Cartridge 18" Cartridge 27" Cartridge # OF CARTRIDGES 132 88 59 VAULT LENGTH 25 25 25 VAULT SIZE 8'X24'8'X24'8'X24' IF >61 CARTRIDGES, EQUIV # OF 8'X24' VAULTS 3.00 2.00 N/A STORMFILTER VAULT BASIC BIOSWALE INPUT Online WQ Flow Rate (cfs)1.47 ft3/s Design Flow Depth 4 in Longitudinal slope 0.02 ft/ft GIVENS Side slopes (H:V)3 :1 6-MONTH, 24-HR PRECIPITATION (IN)*1.32 Depth of swale 1.333333 ft Ratio, k, to modfy the WQ flow rate** 1.7588 Max bottom width (without dividers) 10 ft Mannings Roughness Co. for Shallow Flow 0.2 CALCULATED COMPOST-AMENDED BIO-SWALE y (Design flow depth)0.33 inches if use same n then same as Basic Bio-Swale b (Bottom Width of Swale) 15.4 ft Awq (Cross-sectional area of flow at design depth) 5.456 ft2 WQ Design Velocity 0.47 ft/sec Minimum Swale Length 255.9 ft CHECKS Velocity < 1 ft/sec?Velocity Good Bottom Width of Swale >2ft and <10ft?Too wide ft OUTPUTS Swale Length***256 ft Top Width of Swale 23.37 ft *For Seatac Gauge. ** Equation to interpolate the adjustment factor, k: Y=1.44x-.142 ***Swale length increased to 100 LF if design length is less than minimum allowed ASSUMPTIONS STANDARD FILTER STRIP INPUTS Media depth 12 in On-line WQ flow rate 1.47 = Q ft3/s Design Depth of Flow 0.083 ft Longitudinal Slope 0.02 :1 GIVENS Length of Filter Strip (contributing length of pavement)500 ft 6-MONTH, 24-HR PRECIPITATION (IN)*1.32 Width of Gravel Spreader*1.5 ft Ratio, k, to modfy the WQ flow rate**1.7588 n (Manning's roughness coefficient) 0.35 *Allows for contributing path up to 50 ft **usually 1.0 but increased to account for conceptual level flows & possible high sediment/poor maintenance CHECKS Design Flow Depth 0.05533 =[(Q*k*n)/(1.49 * W * s^0.5 )]^0.6 Design Flow Depth < 1 Depth Good Design Flow Velocity (ft/sec)0.0934 =(Q*k)/(Width * depth of flow) Velocity < 0.5 ft/sec? Velocity Good OUTPUTS Length of Filter Strip (ft)50.46 Total Length of MFD Facility (ft)51.96 Total Width of Filter Strip (ft)501.50 *For Seatac Gauge. ** Equation to interpolate the adjustment factor, k: Y=1.44x-.142 ASSUMPTIONS BIORETENTION CELLS INPUTS WQ Volume (acre-ft)0.5 WQ Volume for Scaling # of Bioretention Cells WQ Volume (CF)21780 WQ Volume for 1 acre of Road w/ Moderate Slope 0.14189 acre WQ Volume for 5000 SF Road w/ Moderate Slope 0.01628673 acre-ft SIZING OF CELL FOR 5000 SF IMPERVIOUS FROM MGSFLOOD MODEL Bottom Widgth 2 ft MGSFlood Modeling Assumptions to size a single bioretention cell Bottom Length 21 ft Impervious Tributary Area**5000 sf Climate region Puget East 48 in MAP CALCULATIONS FOR FOOTPRINT OF SINGLE CELL (5000 SF IMPERVOUS) Underdrain (Y/N)No Depth from Roadway to Bottom of Bioretention Cell 1.5 ft Ponding Depth 0.5 ft Top Width 11 ft Presettling Catch Basin Top Length 30 Side Slopes 3 :1 Required width of facility from edge of road to far edge of bioretention cell 13 ft Bioretention Soil Mix Depth 1.5 ft Footprint of Bioretention Cell 390 sf Bioretention Soil Infiltration Rate***12 in/hr Native Soil Infiltration Rate 0.3 in/hr Bioretention Soil Porosity***52 %OUTPUTS Ponding Depth****0.5 ft # OF BIORETENTION CELLS 31 Free Board 0.5 ft TOTAL LENGTH OF ALL CELLS 801 ft Free board elevation below roadway elevation 0.5 ft TOP WIDTH OF BIORETENTION CELL 11 ft Offset of biotention cell from road 2 ft *Minimum subgrade infiltration allowed for bioretention without an underdrain **Max tributary area to a single cell ***Based on WWHM bioretention soil characteristic properties ****Assume sites in ROW areas with high pedestrian traffic ADDITIONAL DESIGN REQUIREMENTS Max Drawdown Time 24 hrs Min elevation of bioretetion soil above seasonal high groundwater elevation 3 ft ASSUMPTIONS MEDIA FILTER DRAIN (MFD) TYPE 4/5 (note Type 6/7 uses two-year release from u/s detention facility for the sizing flow rate) INPUTS Media depth 12 in On-line WQ flow rate 0.03 cfs Media Filter Drain Mix Width*4 ft Grass Strip Width 3 ft GIVENS Gravel Strip Width 1 ft 6-MONTH, 24-HR PRECIPITATION (IN)*1.32 Edge of BMP to Center of Ditch 6 ft Ratio, k, to modfy the WQ flow rate**1.7588 MFD Infiltration Rate**10 in/hr Modified WQ Flow Rate 0.052764 cfs MFD Infiltration Rate**0.0002 ft/sec *Allows for contributing path up >35 ft OUTPUTS **Accounts for siltation over time and a factor of safety per Renton SWDM Length of Filter Strip (ft)57 Total Length of MFD Facility (ft)61 Total Width of MFD Facility (ft)14 *For Seatac Gauge. ** Equation to interpolate the adjustment factor, k: Y=1.44x-.142 Q (design online WQ flow rate) * k = Length Media x Width Media x Infiltration Rate (Q * k )/(L x infiltration)= W ASSUMPTIONS APPENDIX D: SITE RETROFIT BMP ASSESSMENTS Appendix D Notes: (1) Whenever "Bioswale" is referenced in this appendix, it refers to a "Basic Bioswale" as described in the City of Renton Surface Water Design Manual. (2) For the BMP Option tables herein, the "Bioretention" BMP option refers to Bioretention Cells and the required area listed in the tables reflects the cumulative area of cells required to meet the treatment standard. 111332: SUMMERWIND DIV I II III BMP EVALUATION DETENTION SYSTEM POND AREA OF TRIBUTARY BASIN (ACRES) 20.2 IMPERVIOUSNESS OF TRIBUTARY BASIN 54% WATER QUALITY VOLUME (ACRE-FT) 1.813 ONLINE WQ FLOW RATE (CFS) 3.68 OFFLINE WQ FLOW RATE (CFS) 1.95 BMP OPTION DIMENSIONS DESIGN NOTES WET VAULTs 45’X222’ Insufficient space available PROPRIETARY MEDIA FILTER VAULT, 27” CARTRIDGES WITH ZPG MEDIA(STORMFILTER VAULTS) 147 cartridges, ~ (3) 8’X24’ vaults It may be possible to install a series of vaults along inflow pipe. SANDFILTER VAULT Presettling vault – 33’X100’ Vault size – 130’X260’ Insufficent space MISCELLANEOUS NOTES: - Due to siesmic hazard, only vault type BMP options considered (even though existing facility is pond). - Pond is a “back-up” type pond that provides no water quality benefit. Could modify inlet pipe to have flow routed through pond. Could also add wetpool volume below live storage to add some level of treatment. This would not meet City of Renton standards and would require geotechnical assessment. - Installation of Stormfilters could be done along inflow pipe within pond parcel, although challenging with slopes. This is best option of City wants to meet City of Renton standards and assumed for this analysis. At the same time it is noted that adding wetpool storage and modifying inlet is best option if the goal is to improve water quality at most efficient costs. 111332: SUMMERWIND DIV I II III AS-BUILT DRAWING SUMMARY PLAN VIEW PROFILE POND SECTION DATE OF AS-BUILT DRAWINGS 6/28/1986 TIR PROVIDED Yes ADDRESS N/A ADDITIONAL VIEWS 111342: WINSPER DIV I & II BMP EVALUATION EXISTING DETENTION SYSTEM TYPE POND AREA OF TRIBUTARY BASIN (ACRES) 1.2 TRIBUTARY BASIN IMPERVIOUS PERCENT (%) 55% WATER QUALITY VOLUME (ACRE-FT) 0.110 ONLINE WQ FLOW RATE (CFS) 0.21 OFFLINE WQ FLOW RATE (CFS) 0.11 BMP OPTION DIMENSIONS SITE NOTES & OBSERVATION WET POND 40’X70’ Could convert exist pond to combined pond (but area next to playground and would need to be fenced). WETVAULTs Vault size - 11’X55’ Vault can be accomodated on upstream of pond within the 10-feet easement between cul-de-sac and pond(1). It can also be in cul-de-sac within Renton ROW(2). SANDFILTER VAULT Presettling vault-10’X30’ Vault size- (1) 40’X80’ See note 2 above. PROPRIETARY MEDIA FILTER VAULT, 27” CARTRIDGES WITH ZPG MEDIA(STORMFILTER VAULTS) 8 cartridges, ~ (1) 8’X6’ vault See note 1 above. Plenty of head available. BIOSWALE 190’X10’ Insufficient space available.(3) FILTER STRIP 10’X250’ Not preferred due to steep grade. BIORETENTION 11’X177’ See note 3 above. MEDIA FILTER DRAINS 14’X405’ See note 3 above. Miscelleneous Notes: - The preferred WQ BMP for this location is Stromfilter Vaults due to smaller footprint. - A second option that would not meet City of Renton standards would be to upgrade bottom of existing pond with infiltrative type soils to encourage infiltration. 111342: WINSPER DIV I & II AS-BUILT DRAWING SUMMARY 1.1.1 PLAN VIEW 1.1.2 DETAIL 1.1.3 PROFILE DATE OF AS-BUILT DRAWINGS 02/01/88 TIR PROVIDED Yes ADDRESS 10006 S 32nd Pl, Renton, 98055 111354: SPRINGBROOK TERRACE BMP EVALUATION EXISTING DETENTION SYSTEM TYPE Pond AREA OF TRIBUTARY BASIN (ACRES) 5.2 TRIBUTARY BASIN IMPERVIOUS PERCENTAGE (%) 51% WATER QUALITY VOLUME (ACRE-FT) 0.439 ONLINE WQ FLOW RATE (CFS) 0.97 OFFLINE WQ FLOW RATE (CFS) 0.51 BMP OPTION DIMENSIONS SITE NOTES & OBSERVATION WET POND 60’X130’ Opportunity for wet pond retrofit. May require expansion. WET VAULTs Vault size – 20’X110’ Insufficient space available (narrow road and 10’ easements). Also, deep facility due to steep slopes. SANDFILTER VAULT Presettling vault – 20’X60’ Vault size – (1) 70’X140’ Insufficient space. MEDIA FILTER VAULT, 18” CARTRIDGES WITH ZPG MEDIA(STORMFILTER VAULTS) 58 cartridges, ~ (1) 8’X24’ vaults Sufficient space and head drop within roadway of site. BIOSWALE 16’X300’ Insufficient space (10’ easement width). FILTER STRIP 90’X130’ Insufficient space available. BIORETENTION 11’X700’ Insufficient space available. MEDIA FILTER DRAIN 14’X1850’ Insufficient space available. MISCALLANEOUS NOTES: - Site is within 50’ of 15% slope and geotech report likely required to assess landslide hazard. - Modification of pond to add wet pond storage is likely best option. It would not meet City of Renton standards, but capacity could be increase by incorporating short walls on portion of existing side slopes. 111354: SPRINGBROOK TERRACE AS-BUILT DRAWING SUMMARY PLAN VIEW PROFILE DETAIL DATE OF AS-BUILT DRAWINGS 09/30/83 TIR PROVIDED No ADDRESS NA 111361: HIDDEN CEDARS DIV II BMP EVALUATION EXISTING DETENTION SYSTEM TYPE Pond AREA OF TRIBUTARY BASIN (ACRES)5.2 TRIBUTARY BASIN IMPERVIOUS PERCENT (%)48% WATER QUALITY VOLUME (ACRE-FT)0.428 ONLINE WQ FLOW RATE (CFS)0.92 OFFLINE WQ FLOW RATE (CFS)0.48 BMP OPTION DIMENSIONS SITE NOTES & OBSERVATION WET POND 60’X130’Insufficient space for full volume within pond footprint. WET VAULTs Vault size – 20’X110’Probably sufficient space within roadway. SANDFILTER VAULT Presettling vault – 20’X60’ Vault size – (x) 70’X140’ Probably sufficient space within roadway. PROPRIETARY MEDIA FILTER VAULT, 18” CARTRIDGES WITH ZPG MEDIA(STORMFILTER VAULTS) 55 cartridges, ~ (1) 8’X22’ vault Insufficient available head for filter system. BIOSWALE 11’X200’Insufficient space available. FILTER STRIP 90’X120’Existing System too deep. BIORETENTION 11’X700’Insufficient space available. MEDIA FILTER DRAIN 14’X1750’Insufficient space available. . MISCALLANEOUS NOTES: -This is a spaghnum water quality site. Stormwater eventually outfalls to wetland east side of 123rd Pl SE owned by King County Public Parks. -Site is within 200’ of seismic hazard area and may require geotechnical approval. -Potential open water BMP location on shoulders of 123rd Pl SE. -Combined Wetland not fully meeting standard appears best option. 111361: HIDDEN CEDARS DIV II AS-BUILT DRAWING SUMMARY PLAN VIEW PROFILE DETAIL DATE OF AS-BUILT DRAWINGS 07/10/89 TIR PROVIDED No ADDRESS 18005 124th Ave SE, Renton, 98058 111369: PANTHER MEADOW BMP EVALUATION EXISTING DETENTION SYSTEM TYPE Pond AREA OF TRIBUTARY BASIN (ACRES) 2.9 TRIBUTARY BASIN IMPERVIOUS PERCENTAGE (%) 44% WATER QUALITY VOLUME (ACRE-FT) 0.231 ONLINE WQ FLOW RATE (CFS) 0.51 OFFLINE WQ FLOW RATE (CFS) 0.27 BMP OPTION DIMENSIONS SITE NOTES & OBSERVATION WET POND 50’X100’ Potential detention pond retrofit location, but not fully meet City of Renton standard. WET VAULTs Vault size – 16’X80’ Probably insufficient space. SANDFILTER VAULT Presettling vault – 20’X60’ Vault size – (1) 50’X100’ Probably insufficient space. MEDIA FILTER VAULT, 12” CARTRIDGES WITH ZPG MEDIA(STORMFILTER VAULTS) 46 cartridges, ~ (1) 8’X20’ vault Sufficient space. BIOSWALE 13’X230’ Potential location along outside of detention pond. FILTER STRIP 50’X130’ Potential location along outside of detention pond. BIORETENTION 11’X385’ Probably insufficient space. MEDIA FILTER DRAIN 14’X970’ Insufficient space. MISCALLANEOUS NOTES: - This site contains an existing grass lined-swale that serves the back of several lots in addition to a detention pond. - The detention pond is a “back-up” type pond that provides little water quality benefit. One option is to re-route inflows to pond to let water flow through pond. - Preferred approach is to excavate wetpond in existing pond and add short walls (e.g. 2’ high ecology block) to get approximately 70% of volume to meet current standards and redirect inflows to pond. At same time can investigate infiltration potential. 111369: PANTHER MEADOW AS-BUILT DRAWING SUMMARY PLAN VIEW PROFILE DETAIL DATE OF AS-BUILT DRAWINGS 04/06/89 TIR PROVIDED No ADDRESS N/A 111391: DENNYS RESTAURANT BMP EVALUATION EXISTING DETENTION SYSTEM TYPE Pond AREA OF TRIBUTARY BASIN (ACRES)20.2 TRIBUTARY BASIN IMPERVIOUS PERCENTAGE (%)35% WATER QUALITY VOLUME (ACRE-FT)1.889 ONLINE WQ FLOW RATE (CFS)2.29 OFFLINE WQ FLOW RATE (CFS)1.26 BMP OPTION DIMENSIONS SITE NOTES & OBSERVATION PROPRIETARY MEDIA FILTER VAULT, 18” CARTRIDGES WITH ZPG MEDIA(STORMFILTER VAULTS) 137 cartridges, ~ (3) 8’X24’ vaults See notes below WET VAULTS Vault Size - 50’X250’Probably insufficient space available. SANDFILTER VAULTS Presettling vault-40’X120’ Vault Size- (1) 60’X300’ Probably insufficient space available. MISCALLANEOUS NOTES: -Property owned by WSDOT. -WSDOT ownership could be opportunity for acquiring sufficient space for BMP if WSDOT has surplus space available. 111391: DENNYS RESTAURANT AS-BUILT DRAWING SUMMARY PLAN VIEW DATE OF AS-BUILT DRAWINGS 01/05/82 TIR PROVIDED No ADDRESS 4774 Lake Washington Blvd NE, Renton, 98056 111393: CASTLEWOOD RANCHETTES BMP EVALUATION EXISTING DETENTION SYSTEM TYPE Pond AREA OF TRIBUTARY BASIN (ACRES) 6.0 TRIBUTARY BASIN IMPERVIOUS PERCENT (%) 32% WATER QUALITY VOLUME (ACRE-FT) 0.394 ONLINE WQ FLOW RATE (CFS) 1.01 OFFLINE WQ FLOW RATE (CFS) 0.51 BMP OPTION DIMENSIONS SITE NOTES & OBSERVATION WET POND 55’X 130’ Insufficient space. (1) WET VAULT Vault Size - 30’X150’ See note 1 above SANDFILTER VAULT Presettling vault-15’X45’ Vault Size- (1) 70’X140’ See note 1 above PROPRIETARY MEDIA FILTER VAULT, 18” CARTRIDGES WITH ZPG MEDIA(STORMFILTER VAULTS) 60 CARTRIDGES, ~ (1) 8’X24’ Preferred option due to smaller footprint and less head drop. BIOSWALE 19’X250’ Partial bioswale potential along unimproved NE 8th ROW FILTER STRIP 90’X140’ See note 1 above BIORETENTION 11’X645’ See note 1 above MEDIA FILTER DRAINS 30’X390’ See note 1 above MISCELLENEOUS NOTES: - There is unimproved 30’ width ROW along NE 8th Street from CB#B3 to control structure. A bioswale could be constructed along this corridor. - Pond is a “back- up” type which provide no water quality benefit. Can consider making a flow-through type pond to improve water quality treatment. - Because the bioswale would not meet City of Renton standards, the preferred approach is a Stormwater filter within the unimproved ROW and converting pond to flow-through type. 111393: CASTLEWOOD RANCHETTES AS-BUILT DRAWING SUMMARY PLAN VIEW PROFILE DETAIL DATE OF AS-BUILT DRAWINGS 05/01/81 TIR PROVIDED No ADDRESS 803 139th Ave SE, Renton, 98059 111394: CASTLEWOOD RANCHETTES BMP EVALUATION EXISTING DETENTION SYSTEM TYPE Pond AREA OF TRIBUTARY BASIN (ACRES)13.2 TRIBUTARY BASIN IMPERVIOUS PERCENTAGE (%)24% WATER QUALITY VOLUME (ACRE-FT)0.631 ONLINE WQ FLOW RATE (CFS)1.52 OFFLINE WQ FLOW RATE (CFS)0.78 BMP OPTION DIMENSIONS SITE NOTES & OBSERVATION WET POND 64’X165’Likely insufficient space available. See Misc. Notes. (1) WET VAULTs Vault size – 38’X186’See note 1 above SANDFILTER VAULT Presettling vault – 20’X60’ Vault size – (1) 90’X180’ Insufficient space PROPRIETARY MEDIA FILTER VAULT, 27” CARTRIDGES WITH ZPG MEDIA(STORMFILTER VAULTS) 61 cartridges, ~ (1) 8’X24’ vault Space and head are available upstream of facility along pipe system. System around facility too shallow and flat. BIOSWALE 24’X260’See note 1 above FILTER STRIP 70’X270’See note 1 above BIORETENTION 11’X1010’See note 1 above MEDIA FILTER DRAIN 20’X1160’See note 1 above MISCELLANEOUS NOTES: -The facility is identified as a wetland according to City GIS. Any changes may be prohibited. It is also noted that it is a backup type, such that it may provide little water quality benefit. -It is noted that the surrounding undeveloped area is owned by the City of Renton. Its use and any planned uses is unknown. If the space is available for stormwater facility the potential of retrofit BMPs is expanded. -The Stormfilter Vault is preferred in this location, unless the surrounding City-owned area is available, in which additional options could be explored. The vault could be installed along the inlet pipe to the facility or within the NE 9th St. 111394: CASTLEWOOD RANCHETTES AS-BUILT DRAWING SUMMARY PLAN VIEW PROFILE DETAIL DATE OF AS-BUILT DRAWINGS 05/01/81 TIR PROVIDED No ADDRESS 4782 NE 9th St, Renton, 98059 111408: BERGSMA SHORT PLAT BMP EVALUATION EXISTING DETENTION SYSTEM TYPE Pond AREA OF TRIBUTARY BASIN (ACRES)3.1 TRIBUTARY BASIN IMPERVIOUS PERCENTAGE (%)26% WATER QUALITY VOLUME (ACRE-FT)0.199 ONLINE WQ FLOW RATE (CFS)0.51 OFFLINE WQ FLOW RATE (CFS)0.26 BMP OPTION DIMENSIONS SITE NOTES & OBSERVATION WET POND 50’X90’Insufficient space within existing pond footprint. May need to provide liner. WET VAULTs Vault size – 15’X170’Insufficient space available. SANDFILTER VAULT Presettling vault – 20’X60’ Vault size – (1) 50’X100’ Insufficient space available. PROPRIETARY MEDIA FILTER VAULT, 18” CARTRIDGES WITH ZPG MEDIA(STORMFILTER VAULTS) 31 cartridges, ~ (1) 8’X14’ vault Insufficient available head. BIOSWALE 13’X230’Probably sufficient space available if narrow width and split into the two main swales entering facility. May need to liner and underdrain. FILTER STRIP 50’X130’Infiltration not allowed. BIORETENTION 11’X330’Infiltration not allowed. MEDIA FILTER DRAIN 14’X970’Infiltration not allowed. MISCALLANEOUS NOTES: -Site is within 100’ of open water and infiltration WQ BMPs are not allowed. -Two bioswales appears to be the best option. Consider narrower width. Tributary basin may be smaller than GIS estimated. 111408: BERGSMA SHORT PLAT AS-BUILT DRAWING SUMMARY PLAN VIEW PROFILE DETAIL DATE OF AS-BUILT DRAWINGS 04/01/80 TIR PROVIDED No ADDRESS 18851 103rd Ct SE, Renton, 98055 111421: RIPLEY LN STORM IMPROVEMENT BMP EVALUATION EXISTING DETENTION SYSTEM TYPE Vault (see comment below) AREA OF TRIBUTARY BASIN (ACRES)401.6 TRIBUTARY BASIN IMPERVIOUS PERCENTAGE (%)35% WATER QUALITY VOLUME (ACRE-FT)31.636 ONLINE WQ FLOW RATE (CFS)62.28 OFFLINE WQ FLOW RATE (CFS)32.61 BMP OPTION DIMENSIONS SITE NOTES & OBSERVATION PROPRIETARY MEDIA FILTER VAULT, 27” CARTRIDGES WITH ZPG MEDIA(STORMFILTER VAULTS) Presettling vault- 200’X600’ 2546 CARTRIDGES, ~ (42) 8’X24’ WET VAULTS Vault Size- (1) 190’X920’ SANDFILTER VAULTS Presettling vault-140’X420’ Vault Size- (1) 220’X1100’ MISCALLANEOUS NOTES: -Property owned by King County Parks (formerly BNSF railroad). -Facility likely constructed to allow flow to pass under large 84” sewer and provide sufficient capacity and is not a detention facility. -Large basin and flow would require very large BMP and likely cost prohibitive. 111421: RIPLEY LN STORM IMPROVEMENT AS-BUILT DRAWING SUMMARY PLAN VIEW PROFILE SECTIONS DATE OF AS-BUILT DRAWINGS 3/19/2008 TIR PROVIDED No ADDRESS 4618 Seahawks Way, Renton, 98056 111422: RENTON VILLAGE INTERCEPTOR BMP EVALUATION EXISTING DETENTION SYSTEM TYPE Vault AREA OF TRIBUTARY BASIN (ACRES)736.4 TRIBUTARY BASIN IMPERVIOUS PERCENTAGE (%)31% WATER QUALITY VOLUME (ACRE-FT)54.40 ONLINE WQ FLOW RATE (CFS)125.20 OFFLINE WQ FLOW RATE (CFS)64.40 BMP OPTION DIMENSIONS SITE NOTES & OBSERVATION DESIGN NOTES WET POND 410’X1550’Insufficient space within dense commercial area. WETVAULT Vault size - 250’X1220’Insufficient space available. SANDFILTER VAULT Presettling vault -180’X550’ Vault size - (1) 740’X1480’ Probably sufficient space and head drop. MEDIA FILTER VAULT, 27” CARTRIDGES WITH ZPG MEDIA(STORMFILTER VAULTS) 4995 cartridges,~ (25)8’X24’See Misc. Notes BIOSWALE 272’X1320’Insufficient space available. FILTER STRIP Very Large number Insufficient space available. BIORETENTION Very Large number Insufficient space available. MEDIA FILTER DRAINS Very Large number Insufficient space available. Miscellaneous Notes: -Very large basin and would require a regional water quality treatment facility. There is potentially head available from the inlet of the system east of Talbot to the downstream large pipe and potentially could divert to a regional treatment system but may be prohibited due to fish habitat. City of Redmond contstructed a similar system (media vault) for 900 acres at a cost of $6 million (including a pump station but not including land). -May not be feasible due to cost and permitting as well as land acquisision and technical challenges. 111422: RENTON VILLAGE INTERCEPTOR AS-BUILT DRAWING SUMMARY PLAN VIEW PLAN SNAPSHOT IS FROM RENTON VILLAGE STORM SYSTEM PROJECT, 6/22/2007 PROFILE PROFILE SNAPSHOT IS FROM RENTON VILLAGE STORM SYSTEM PROJECT, 6/22/2007 DETAIL MH #2 DETAIL IS FROM RENTON VILLAGE COMPANY INTERCEPTOR STORM DRAIN, 8/23/1982 DATE OF AS-BUILT DRAWINGS 8/23/1982 TIR PROVIDED No ADDRESS 653 S Renton Village Pl, Renton, 98057 ROLLING HILLS PIPE SYSTEM NORTH BRANCH 117894: SWAN MEADOWS I BMP EVALUATION EXISTING DETENTION SYSTEM TYPE Tank AREA OF TRIBUTARY BASIN (ACRES)1.7 TRIBUTARY BASIN IMPERVIOUS PERCENTAGE (%)52% WATER QUALITY VOLUME (ACRE-FT)0.152 ONLINE WQ FLOW RATE (CFS)0.31 OFFLINE WQ FLOW RATE (CFS)0.17 BMP OPTION DIMENSIONS SITE NOTES & OBSERVATION WET POND 42’X80’Insufficient space within dense residential area. WET VAULTs Vault size – 13’X60’Sufficient space but likely utility conflicts. SANDFILTER VAULT Presettling vault – 10’X30’ Vault size – (1) 40’X80’ Probably sufficient space and head drop. PROPRIETARY MEDIA FILTER VAULT, 18” CARTRIDGES WITH ZPG MEDIA(STORMFILTER VAULTS) 19 cartridges, ~ (1) 8’X11’ vault Sufficient space in roadway and head drop. BIOSWALE 11’X210’Insufficient space available. FILTER STRIP 20’X190’Insufficient space available. BIORETENTION 11’X260’Insufficient space available. MEDIA FILTER DRAIN 14’X600’Insufficient space available. MISCALLANEOUS NOTES: -Site is within 200’ of landslide area and geotechnical approval may be required for non-vault BMPs. Site is also within a groundwater protection area. -Stormfilter vault appears to be best option based on available head and likely being more cost effective than wetvault. 117894: SWAN MEADOWS I AS-BUILT DRAWING SUMMARY PLAN VIEW PROFILE DATE OF AS-BUILT DRAWINGS 02/20/89 TIR PROVIDED No ADDRESS 1325 Camas Ave NE, Renton, 98056 117900: MEADOWN AVE N & N 24TH ST BMP EVALUATION EXISTING DETENTION SYSTEM TYPE Tank AREA OF TRIBUTARY BASIN (ACRES)2.7 TRIBUTARY BASIN IMPERVIOUS PERCENTAGE (%)45% WATER QUALITY VOLUME (ACRE-FT)0.221 ONLINE WQ FLOW RATE (CFS)0.48 OFFLINE WQ FLOW RATE (CFS)0.25 BMP OPTION DIMENSIONS SITE NOTES & OBSERVATION WET POND 50’X100’Insufficient space available. WET VAULTs Vault size – 16’X80’Sufficient space available. SANDFILTER VAULT Presettling vault – 20’X60’ Vault size – (1) 50’X100’ Insufficient space available MEDIA FILTER VAULT, 18” CARTRIDGES WITH ZPG MEDIA(STORMFILTER VAULTS) 29 cartridges, ~ (1) 8’X14’ vault Sufficient space and head available if a CB Filterra used BIOSWALE 13’X230’Insufficient space available. Steep slopes. FILTER STRIP 40’X140’Insufficient space available. BIORETENTION 11’X360’Insufficient space available. MEDIA FILTER DRAIN 14’X920’Insufficient space available. MISCALLANEOUS NOTES: -Site is within 100’ of landslide area and geotechnical approval may be required for non-vault BMPs. -Site is within an APA Zone 1, a groundwater protection area, a wellfield capture zone, and infiltration BMPs are not allowed. -Site is with a steep sloped residential zone with limited space available. -Media filter vault is proposed. Replacing the CBs with Stormfilter Catch Basin unit is proposed to provide elevation head above detention. 117900: MEADOWN AVE N & N 24TH ST AS-BUILT DRAWING SUMMARY PLAN VIEW DETAIL DATE OF AS-BUILT DRAWINGS 07/01/95 TIR PROVIDED No ADDRESS 2435 Garden Ct N, Renton, 98056 117902: TIFFANY PARK DIV 4 BMP EVALUATION EXISTING DETENTION SYSTEM TYPE Tank AREA OF TRIBUTARY BASIN (ACRES)10.2 TRIBUTARY BASIN IMPERVIOUS PERCENTAGE (%)59% WATER QUALITY VOLUME (ACRE-FT)1.059 ONLINE WQ FLOW RATE (CFS)1.94 OFFLINE WQ FLOW RATE (CFS)1.05 BMP OPTION DIMENSIONS SITE NOTES & OBSERVATION WET POND 80’X210’Insufficient space available. WET VAULT Vault size – 35’X170’Insufficient space available. SANDFILTER VAULT Presettling vault – 30’X90’ Vault size – (1) 100’X200’ Insufficient space available. PROPRIETARY MEDIA FILTER VAULT, 18” CARTRIDGES WITH ZPG MEDIA(STORMFILTER VAULTS) 116 cartridges, ~ (2) 8’X24’ vaults Sufficient space and head drop available. BIOSWALE 30’X260’Insufficient space available. Inverts are too low in easement area. FILTER STRIP 410’X60’Insufficient space available. BIORETENTION 11’X1700’Insufficient space available. MEDIA FILTER DRAIN 14’X3700’Insufficient space available. MISCALLANEOUS NOTES: -Site is within 200’ of landslide hazard area and geotechnical approval may be required for non-vault BMPs. -Site is within a groundwater protection area. -The detention tank and the connecting storm pipes are over 10’ deep. Using available head drop in cul- de-sac and stormfilter vaults probably best option (although costly with deep excavation and requiring utility relocations) -May want to analyze downstream BMP opportunities at system outlet. 117902: TIFFANY PARK DIV 4 AS-BUILT DRAWING SUMMARY PLAN VIEW PROFILE DATE OF AS-BUILT DRAWINGS 05/07/79 TIR PROVIDED No ADDRESS 1409 Olympia Ave SE, Renton, 98058 117912: ARMSTRONG AND SANDELIUS BMP EVALUATION EXISTING DETENTION SYSTEM TYPE Tank AREA OF TRIBUTARY BASIN (ACRES)2.2 TRIBUTARY BASIN IMPERVIOUS PERCENTAGE (%)28% WATER QUALITY VOLUME (ACRE-FT)0.132 ONLINE WQ FLOW RATE (CFS)0.37 OFFLINE WQ FLOW RATE (CFS)0.19 BMP OPTION DIMENSIONS SITE NOTES & OBSERVATION WET POND 40’X80’Insufficient space available. WET VAULTs Vault size – 12’X60’Sufficient space and could replace the 36” pipe along 111th with wet vault/detention combo. SANDFILTER VAULT Presettling vault – 10’X30’ Vault size – (1) 40’X80’ Insufficient space and probably insufficient head drop available. MEDIA FILTER VAULT, 18” CARTRIDGES WITH ZPG MEDIA(STORMFILTER VAULTS) 22 cartridges, ~ (1) 8’X11’ vault Sufficient space available upstream of detention tank. Cuts tributary area below 2 AC. BIOSWALE 12’X220’Ditches along 11th Ave SE provide good opportunity. Although probably insufficient space available. FILTER STRIP 30’X160’Infiltration BMPs not allowed. BIORETENTION 11’X230’Infiltration BMPs not allowed. MEDIA FILTER DRAIN 14’X710’Infiltration BMPs not allowed. MISCALLANEOUS NOTES: -This site is within 100’ of open water and infiltration WQ BMPs are not allowed. -Existing ditch along east side of 111th Ave SE. has 20’ ROW between edge of pavement and storm easement. This provides good opportunity for WQ BMPs. -Stormfilter vaults appear to be the best option. Wet vault/bioswale also good options. 117912: ARMSTRONG AND SANDELIUS AS-BUILT DRAWING SUMMARY PLAN VIEW PROFILE DETAIL DATE OF AS-BUILT DRAWINGS 10/09/85 TIR PROVIDED No ADDRESS 16592 111th Ave SE, Renton, 98055 117915: KNUDSON BMP EVALUATION EXISTING DETENTION SYSTEM TYPE Tank AREA OF TRIBUTARY BASIN (ACRES)0.2 TRIBUTARY BASIN IMPERVIOUS PERCENTAGE (%)94% WATER QUALITY VOLUME (ACRE-FT)0.027 ONLINE WQ FLOW RATE (CFS)0.04 OFFLINE WQ FLOW RATE (CFS)0.02 BMP OPTION DIMENSIONS SITE NOTES & OBSERVATION PROPRIETARY MEDIA FILTER VAULT, 12” CARTRIDGES WITH ZPG MEDIA(STORMFILTER VAULTS) Presettling vault- 5’X15’ 4 CARTRIDGES, ~ (1) 8’X6’ Pipe outlet from control structure may have sufficient drop for low-head filter application WET VAULTS Vault Size - 6’X30’Existing easement 10’. To fit in permanent easement, would need approx. 8’x146’ vault. SANDFILTER VAULTS Presettling vault-10’X30’ Vault Size- (1) 10’X50’ Likely insufficient space available. MISCALLANEOUS NOTES: -Facility is located across the street from Facility Number 111361. It could be potentially possible to re- route flow from the Knudson flow control manhole back to Facility Number 111361 should it be retrofitted with wet pond facility and it be at lower elevation grade. This would likely require special approval from the City to modify drainage course. 117915: KNUDSON AS-BUILT DRAWING SUMMARY PLAN VIEW PROFILE DATE OF AS-BUILT DRAWINGS 03/25/92 TIR PROVIDED No ADDRESS 18012 124th Ave SE, Renton, 98058 DETAIL 117916: PARKWOOD SOUTH (DIVISION 1) BMP EVALUATION EXISTING DETENTION SYSTEM TYPE Tank AREA OF TRIBUTARY BASIN (ACRES)5.5 TRIBUTARY BASIN IMPERVIOUS PERCENTAGE (%)55% WATER QUALITY VOLUME (ACRE-FT)0.497 ONLINE WQ FLOW RATE (CFS)1.00 OFFLINE WQ FLOW RATE (CFS)0.53 BMP OPTION DIMENSIONS SITE NOTES & OBSERVATION PROPRIETARY MEDIA FILTER VAULT, 18” CARTRIDGES WITH ZPG MEDIA(STORMFILTER VAULTS) 59 cartridges, ~ (1) 8’X24’Pipes immediately upstream of detention pipes are steep and provide available head for filter system. Would not be able to treat entire development, but large percentage WET VAULTS Vault size - 25’X125’Likely insufficient space available. SANDFILTER VAULTS Presettling vault - 20’X60’ Vault size - (1) 30’X150’ Likely insufficient space available. MISCALLANEOUS NOTES: -See third sheet for upstream profile. 117916: PARKWOOD SOUTH AS-BUILT DRAWING SUMMARY PLAN VIEW DETAIL DATE OF AS-BUILT DRAWINGS 09/15/77 TIR PROVIDED No ADDRESS 2104 Jones Pl SE, Renton, 98055 PROFILE 117917: WINDSOR HEIGHTS BMP EVALUATION EXISTING DETENTION SYSTEM TYPE Tank AREA OF TRIBUTARY BASIN (ACRES)0.3 TRIBUTARY BASIN IMPERVIOUS PERCENTAGE (%)100% WATER QUALITY VOLUME (ACRE-FT)0.036 ONLINE WQ FLOW RATE (CFS)0.05 OFFLINE WQ FLOW RATE (CFS)0.03 BMP OPTION DIMENSIONS SITE NOTES & OBSERVATION WET POND 30’X40’Insufficient space available. WET VAULTs Vault size – (1) 6’X30’Sufficient space available. SANDFILTER VAULT Presettling vault – 5’X15’ Vault size – 15’X30’ Insufficient head drop. PROPRIETARY MEDIA FILTER VAULT, 12” CARTRIDGES WITH ZPG MEDIA(STORMFILTER VAULTS) 4 cartridges, ~ (1) 8’X6’ vaults Insufficient head drop. BIOSWALE 10’X100’Insufficient space available. FILTER STRIP 10’X250’Infiltration BMPs not allowed. BIORETENTION 11’X70’Infiltration BMPs not allowed. MEDIA FILTER DRAIN 14’X100’Infiltration BMPs not allowed. MISCALLANEOUS NOTES: -Site is within 100’ of open water and infiltration BMPs are not allowed. -Site is within 50’ of 15% slope. -It is suggested that the City evaluates whether the existing storm facilities to the east of the detention tank can be retrofited to accomadate more WQ treatment. -Wet vaults appear to be the best option. 117917: WINDSOR HEIGHTS AS-BUILT DRAWING SUMMARY PLAN VIEW PROFILE DETAIL DATE OF AS-BUILT DRAWINGS 08/16/94 TIR PROVIDED No ADDRESS 18475 Main Ave S, Renton, 98055 117918: BENSON WOODS BMP EVALUATION EXISTING DETENTION SYSTEM TYPE Tank AREA OF TRIBUTARY BASIN (ACRES)1.8 TRIBUTARY BASIN IMPERVIOUS PERCENTAGE (%)30% WATER QUALITY VOLUME (ACRE-FT)0.124 ONLINE WQ FLOW RATE (CFS)0.29 OFFLINE WQ FLOW RATE (CFS)0.15 BMP OPTION DIMENSIONS SITE NOTES & OBSERVATION WET POND 40’X70’Insufficient space available. WET VAULT Vault size – 12’X60’Sufficient space available. SANDFILTER VAULT Presettling vault –10’X30’ Vault size – (1) 40’X80’Insufficient head drop. MEDIA FILTER VAULT, 18” CARTRIDGES WITH ZPG MEDIA(STORMFILTER VAULTS) 17 cartridges, ~ (1) 8’X11’ vault Probably insufficient head drop. BIOSWALE 11’X210’Existing system too deep. FILTER STRIP 20’X190’Existing system too deep. BIORETENTION 11’X200’Insufficient space available. MEDIA FILTER DRAIN 14’X560’Insufficient space available. Existing system is too deep. MISCALLANEOUS NOTES: -Existing detention outlets to a wetland constructed as a part of the development. It appears that it was intended to replace a wetland that was filled. It is assumed that this wetland would be not considered a stormwater wetland BMP. If it was, there are opportunities to retrofit the wetland to improve water quality. For example, could redirect inflow to other end of wetland away from wetland outlet. -Wet vault appears to be the best option. 117918: BENSON WOODS AS-BUILT DRAWING SUMMARY PLAN VIEW PROFILE DETAIL DATE OF AS-BUILT DRAWINGS 09/10/89 TIR PROVIDED No ADDRESS 18949 111th Pl SE, Renton, 98055 117921: SWAN MEADOWS II BMP EVALUATION EXISTING DETENTION SYSTEM TYPE Tank AREA OF TRIBUTARY BASIN (ACRES)0.8 TRIBUTARY BASIN IMPERVIOUS PERCENT (%)77% WATER QUALITY VOLUME (ACRE-FT)0.094 ONLINE WQ FLOW RATE (CFS)0.16 OFFLINE WQ FLOW RATE (CFS)0.09 BMP OPTION DIMENSIONS SITE NOTES & OBSERVATION WET POND 38’X62’Insufficient space due to adjacent residential area. (1) WETVAULT Vault Size- 10’X60’Sufficient space on the upstream but likely utility conflicts. And about 8’ deep. SANDFILTER VAULT Presettling vault-10’X30’ Vault Size- (1)30’X60’ Sufficient space and head drop on the upstream of existing detention system. (2) PROPRIETARY MEDIA FILTER VAULT, 12” CARTRIDGES WITH ZPG MEDIA(STORMFILTER VAULTS) 14 Cartridges, ~ (1) 8’X11’See note 2 above. BIOSWALE 10’X170’See note 1 above. FILTER STRIP 10’X250’See note 1 above. BIORETENTION 11’X151’See note 1 above. MEDIA FILTER DRAINS 14’X310’See note 1 above. Miscellaneous Notes: -Stormfilter vault appears to be the preferred WQ BMP for this due to smaller footprint and the available head drop. 117921: SWAN MEADOWS II AS-BUILT DRAWING SUMMARY PLAN VIEW PROFILE DETAIL DATE OF AS-BUILT DRAWINGS 2/20/1989 TIR PROVIDED X ADDRESS 1277 Blaine Ave NE, Renton, 98056 117929: BOB BURKE BMP EVALUATION EXISTING DETENTION SYSTEM TYPE Tank AREA OF TRIBUTARY BASIN (ACRES) 2.1 TRIBUTARY BASIN IMPERVIOUS PERCENTAGE (%) 34% WATER QUALITY VOLUME (ACRE-FT) 0.142 ONLINE WQ FLOW RATE (CFS) 0.35 OFFLINE WQ FLOW RATE (CFS) 0.18 BMP OPTION DIMENSIONS SITE NOTES & OBSERVATION WET POND 40’X80’ The existing 48” CMP was constructed within a 50’ easement originally slated for a pond, where the wet pond could be located WET VAULTs Vault size – 13’X60’ Sufficient space adjacent to existing 48” CMP, but deep and less preferred SANDFILTER VAULT Presettling vault – 10’X30’ Vault size – (1) 40’X80’ Probably insufficient head drop available. MEDIA FILTER VAULT, 18” CARTRIDGES WITH ZPG MEDIA(STORMFILTER VAULTS) 21 cartridges, ~ (1) 8’X11’ vault Probably insufficient head drop available. BIOSWALE 12’X210’ Could update existing bioswale to meet City of Renton standards. FILTER STRIP 30’X160’ Existing storm inverts too low. BIORETENTION 11’X230’ Infiltration not allowed. MEDIA FILTER DRAIN 14’X670’ Insufficient space available. MISCALLANEOUS NOTES: - According to City GIS, there is an existing bioswale. It is likely not sized properly and could be easily upgraded. This is the preferred option. 117929: BOB BURKE AS-BUILT DRAWING SUMMARY PLAN VIEW PROFILE DETAIL DATE OF AS-BUILT DRAWINGS 07/02/91 TIR PROVIDED No ADDRESS 19600 92nd Ave S, Renton, 98055 117931: BENSON GLEN BMP EVALUATION EXISTING DETENTION SYSTEM TYPE Tank AREA OF TRIBUTARY BASIN (ACRES)1.7 TRIBUTARY BASIN IMPERVIOUS PERCENTAGE (%)52% WATER QUALITY VOLUME (ACRE-FT)0.157 ONLINE WQ FLOW RATE (CFS)0.31 OFFLINE WQ FLOW RATE (CFS)0.17 BMP OPTION DIMENSIONS SITE NOTES & OBSERVATION WET POND 40’X90’Not feasible due to limited ROW. WET VAULTs Vault size – 13’X70’Sufficient space available, but deep. SANDFILTER VAULT Presettling vault – 10’X30’ Vault size – (x) 40’X80’ Insufficient space and head available. MEDIA FILTER VAULT, 18” CARTRIDGES WITH ZPG MEDIA(STORMFILTER VAULTS) 19 cartridges, ~ (1) 8’X11’ vault Insufficient head drop available. BIOSWALE 11’X210’Not feasible due to limited ROW. FILTER STRIP 20’X190’Insufficient space available. BIORETENTION 11’X260’Insufficient space, but could improve existing bioswale MEDIA FILTER DRAIN 14’X560’Insufficient space available. MISCALLANEOUS NOTES: -The 15% slope area in Appendix A does not apply as this is the existing pond. -Potential to retrofit existing bioswale with bioretention and/or infiltration measures with increased treatment capacity and partially meet treatment standards. This appears to be best. 117931: BENSON GLEN AS-BUILT DRAWING SUMMARY PLAN VIEW PROFILE DETAIL DATE OF AS-BUILT DRAWINGS 08/21/92 TIR PROVIDED No ADDRESS 10900 SE 170th St, Renton, 98055 117936: FERNWOOD EAST BMP EVALUATION EXISTING DETENTION SYSTEM TYPE Tank AREA OF TRIBUTARY BASIN (ACRES)9.4 TRIBUTARY BASIN IMPERVIOUS PERCENTAGE (%)47% WATER QUALITY VOLUME (ACRE-FT)0.762 ONLINE WQ FLOW RATE (CFS)1.66 OFFLINE WQ FLOW RATE (CFS)0.87 BMP OPTION DIMENSIONS SITE NOTES & OBSERVATION WET POND 70’X180’Insufficient space available. WET VAULTs Vault size – 30’X140’Insufficient space available. SANDFILTER VAULT Presettling vault –30’X90’ Vault size – (x) 90’X180’ Insufficient space available. PROPRIETARY MEDIA FILTER VAULT, 18” CARTRIDGES WITH ZPG MEDIA(STORMFILTER VAULTS) 99 cartridges,~ (2) 8’X24’vault Sufficient space and head drop available within roadway at north and south inlet to detention OR one 48’ vault at outlet. BIOSWALE 18’X310’Insufficient space available. Invert elevation too low. FILTER STRIP 320’X60’Infiltration not allowed. BIORETENTION 11’X1220’Infiltration not allowed. MEDIA FILTER DRAIN 14’X3160’Infiltration not allowed. MISCALLANEOUS NOTES: -Site is with 50’ of 15% slope, within 100’ of a landslide hazard area, and hence geotechnical approval is required for non-vault WQ BMPs. Steep slope to east of site limits WQ BMPs in that area. -Site is with groundwater protection area and within 100’ of open water and hence groundwater infiltration is not allowed. -Stormfilter vault(s) appear to be the best option. 117936: FERNWOOD EAST AS-BUILT DRAWING SUMMARY PLAN VIEW PROFILE DETAIL DATE OF AS-BUILT DRAWINGS 05/22/79 TIR PROVIDED Yes ADDRESS 130 Bremerton Ave SE, Renton, 98059 11 7938: CHINQUAPIN RIDGE BMP EVALUATION EXISTING DETENTION SYSTEM TYPE Tank AREA OF TRIBUTARY BASIN (ACRES) 0.6 TRIBUTARY BASIN IMPERVIOUS PERCENTAGE (%) 66% WATER QUALITY VOLUME (ACRE-FT) 0.057 ONLINE WQ FLOW RATE (CFS) 0.11 OFFLINE WQ FLOW RATE (CFS) 0.06 BMP OPTION DIMENSIONS SITE NOTES & OBSERVATION WET POND 30’X50’ See miscellaneous notes (1). WET VAULTs Vault size – 8’X40’ See Note 1 above. SANDFILTER VAULT Presettling vault – 10’X30’ Vault size – (1) 30’X60’ See Note 1 above PROPRIETARY MEDIA FILTER VAULT, 12” CARTRIDGES WITH ZPG MEDIA(STORMFILTER VAULTS) 10 cartridges, ~ (1) 8’X6’ vaults See Note 1 above BIOSWALE 11’X150’ See Note 1 above FILTER STRIP 10’X250’ See Note 1 above. BIORETENTION 11’X100’ See note 1 above. MEDIA FILTER DRAIN 14’X210’ See Note 1 above MISCALLANEOUS NOTES: - The Task 3 memorandum demonstrated that this facility includes an existing bioswale that currently meets City of Renton standards. 117938: CHINQUAPIN RIDGE AS-BUILT DRAWING SUMMARY 1.1.1 PLAN VIEW 1.1.2 PROFILE 1.1.3 DETAIL DATE OF AS-BUILT DRAWINGS 08/14/90 TIR PROVIDED No ADDRESS 11205 SE 190th Pl, Renton, 98055 117940: VALLEY VUE ESTATES BMP EVALUATION EXISTING DETENTION SYSTEM TYPE Tank AREA OF TRIBUTARY BASIN (ACRES)1.0 TRIBUTARY BASIN IMPERVIOUS PERCENTAGE (%)55% WATER QUALITY VOLUME (ACRE-FT)0.116 ONLINE WQ FLOW RATE (CFS)0.15 OFFLINE WQ FLOW RATE (CFS)0.08 BMP OPTION DIMENSIONS SITE NOTES & OBSERVATION PROPRIETARY MEDIA FILTER VAULT, 18” CARTRIDGES WITH ZPG MEDIA(STORMFILTER VAULTS) 9 CARTRIDGES, ~ (1) 8’X6’See Misc. Notes WET VAULTS Vault Size - 12’X60’Easement downstream of facility on private property has a 15’ width SANDFILTER VAULTS Presettling vault-10’X30’ Vault size- (1) 20’X100’ Easement downstream of facility on private property has a 15’ width MISCALLANEOUS NOTES: -Downstream system connects to a separate system from the same development and then is routed to a 200’ long bioswale (assumed to be sized appropriately for the tributary area). -As this facility is already receiving some treatment via the bioswale, it is likely a lower priority for a BMP retrofit. 117940: VALLEY VUE ESTATES AS-BUILT DRAWING SUMMARY PLAN VIEW PROFILE DETAIL DATE OF AS-BUILT DRAWINGS 02/27/97 TIR PROVIDED No ADDRESS 310 S 22nd Pl, Renton, 98055 PROFILE 117941: WEATHERWOOD II BMP EVALUATION EXISTING DETENTION SYSTEM TYPE Tank AREA OF TRIBUTARY BASIN (ACRES) 12.0 TRIBUTARY BASIN IMPERVIOUS PERCENTAGE (%) 50% WATER QUALITY VOLUME (ACRE-FT) 1.021 ONLINE WQ FLOW RATE (CFS) 2.16 OFFLINE WQ FLOW RATE (CFS) 1.13 BMP OPTION DIMENSIONS SITE NOTES & OBSERVATION WET POND 80’X210’ Insufficient space available. WET VAULTs Vault size – 30’X170’ Unlikely sufficient space available east of detention tank. SANDFILTER VAULT Presettling vault – 30’X90’ Vault size – (1) 100’X200’ Insufficient space and head drop available. MEDIA FILTER VAULT, 27” CARTRIDGES WITH ZPG MEDIA(STORMFILTER VAULTS) 86 cartridges, ~ (2) 8’X24’ vaults Sufficient space and head drop available east of detention tank. BIOSWALE 17’X600’ Insufficient space available. FILTER STRIP 500’X50’ Infiltration not allowed. BIORETENTION 11’X1630’ Infiltration not allowed. MEDIA FILTER DRAIN 14’X4110’ Infiltration not allowed. MISCALLANEOUS NOTES: - Site is within aquifer protection area 2, groundwater protection area, and hence lining could be required for any infiltration. - Existing green space along sidewalks does not have enough width for open water BMPs. No nearby facilities look appropriate for retrofit. 15’ easement to the south could be utilized for BMP use however there is not enough space for open water BMPs to fully meet City of Renton standards. - Stormfilter vaults appear to be the best option. Could use diversion structure to two vaults in series upstream of tank inlet where head is available. Would need to look at utility conflicts. 117941: WEATHERWOOD II AS-BUILT DRAWING SUMMARY 1.1.1 PLAN VIEW 1.1.2 PROFILE 1.1.3 POND SECTION DATE OF AS-BUILT DRAWINGS 04/18/79 TIR PROVIDED No ADDRESS 2571 NE 23rd Pl, Renton, 98056 117945: HIDDEN CEDARS DIV II BMP EVALUATION EXISTING DETENTION SYSTEM TYPE Tank AREA OF TRIBUTARY BASIN (ACRES)1.4 TRIBUTARY BASIN IMPERVIOUS PERCENTAGE (%)45% WATER QUALITY VOLUME (ACRE-FT)0.110 ONLINE WQ FLOW RATE (CFS)0.24 OFFLINE WQ FLOW RATE (CFS)0.13 BMP OPTION DIMENSIONS SITE NOTES & OBSERVATION WET POND 40’X70’Insufficient space available. WET VAULTs Vault size –11’X60’Sufficient space available within 20’ easement. SANDFILTER VAULT Presettling vault –10’X30’ Vault size – (x) 40’X80’ Probably sufficient space and head drop available. MEDIA FILTER VAULT, 12” CARTRIDGES WITH ZPG MEDIA(STORMFILTER VAULTS) 22 cartridges, ~ (1) 8’X11’ vault Sufficient space and head drop available at north inlet. BIOSWALE 10’X220’Pipe system too deep to fit within easement. FILTER STRIP 20’X180’Insufficient space available. BIORETENTION 11’X180’Pipe system too deep to fit within easement. MEDIA FILTER DRAIN 14’X460’Insufficient space available. MISCALLANEOUS NOTES: -Note the basin area, flow and sizing was for the north inlet to the detention tank only. There is a second tributary area that connects to the south end at the control structure. The BMP assessment was only for the north portion of the basin. The preferred option in this location is a Stormfilter. -It is also noted that the pipe system tributary from the south appears to drain about the same size area and has available head. A Stormfilter in this system would likely be the preferred choice. The City could approximately double the benefit if this would be added to the project. -It is also noted that the detention system discharges directly to a wetland. WQ retrofits here would benefit the wetland. 117945: HIDDEN CEDARS DIV II AS-BUILT DRAWING SUMMARY PLAN VIEW PROFILE DETAIL DATE OF AS-BUILT DRAWINGS 07/10/89 TIR PROVIDED No ADDRESS N/A 117947: BENSON GLEN BMP EVALUATION EXISTING DETENTION SYSTEM TYPE Tank AREA OF TRIBUTARY BASIN (ACRES)4.6 TRIBUTARY BASIN IMPERVIOUS PERCENTAGE (%)44% WATER QUALITY VOLUME (ACRE-FT)0.371 ONLINE WQ FLOW RATE (CFS)0.82 OFFLINE WQ FLOW RATE (CFS)0.43 BMP OPTION DIMENSIONS SITE NOTES & OBSERVATION WET POND 60’X120’Insufficient space available. WET VAULTs Vault size – 20’X100’Probably sufficient space available. SANDFILTER VAULT Presettling vault – 20’X60’ Vault size – (x) 60’X120’ Probably sufficient space and head drop south of inlet. MEDIA FILTER VAULT, 18” CARTRIDGES WITH ZPG MEDIA(STORMFILTER VAULTS) 49 cartridges, ~ (1) 8’X20’ vault Consider two. Sufficient space and head drop south of inlet and inlet from north. BIOSWALE 15’X290’Insufficient space available. FILTER STRIP 100’X100’Insufficient space available. BIORETENTION 11’X600’Insufficient space available. MEDIA FILTER DRAIN 14’X1570’Insufficient space available. MISCALLANEOUS NOTES: -Existing bioswale located at outlet of detention tank within wetland buffer zone (could not be verified). Any work within wetland buffer zone is not recommended. -Site is within 50’ of 15% slope. -Small undeveloped parcel to the north could be opportunity for BMP with storm easements. -Stormfilter vaults (one on north inlet) and one south of detention tanks (to gain head) appear to be the best option. 117947: BENSON GLEN AS-BUILT DRAWING SUMMARY PLAN VIEW DATE OF AS-BUILT DRAWINGS 08/21/92 TIR PROVIDED No ADDRESS 17032 110th Pl SE, Renton, 98055 PROFILE AND TYPICAL DETENTION TANK DETAILS 117952: CHINQUAPIN RIDGE BMP EVALUATION EXISTING DETENTION SYSTEM TYPE Tank AREA OF TRIBUTARY BASIN (ACRES)2.2 TRIBUTARY BASIN IMPERVIOUS PERCENTAGE (%)63% WATER QUALITY VOLUME (ACRE-FT)0.224 ONLINE WQ FLOW RATE (CFS)0.42 OFFLINE WQ FLOW RATE (CFS)0.23 BMP OPTION DIMENSIONS SITE NOTES & OBSERVATION WET POND 50’X100’Insufficient space available. WET VAULTs Vault size – 16’X80’Insufficient space available. SANDFILTER VAULT Presettling vault –20’X60’ Vault size – (1) 50’X100’Insufficient space available. MEDIA FILTER VAULT, 18” CARTRIDGES WITH ZPG MEDIA(STORMFILTER VAULTS) 25 cartridges, ~ (1) 8’X11’ vault Sufficient space and head drop available at East Inlet. BIOSWALE 12’X260’Insufficient space upstream and downstream (downstream also steep/deep). FILTER STRIP 40’X140’Insufficient space available. BIORETENTION 11’X360’Insufficient space available. MEDIA FILTER DRAIN 14’X800’Insufficient space available. MISCALLANEOUS NOTES: -Detention tanks are approximately 13’ deep (top to IE) and hence there is head drop opportunity at detention tank inlets. Most flow is to east inlet where tributary basin was focused. -Grade break and sloped surface within storm drainage easement provide opportunity for WQ BMPs. However, they would be deep and BMPs would require addition easements, so not preferred. -Stormfilter vaults appear to be the best option. 117952: CHINQUAPIN RIDGE AS-BUILT DRAWING SUMMARY PLAN VIEW PROFILE DATE OF AS-BUILT DRAWINGS 08/14/90 TIR PROVIDED No ADDRESS 11214 SE 188th Pl, Renton, 98055 PROFILE DETAIL 145336: PETETT MEADOWS SHORT PLAT BMP EVALUATION EXISTING DETENTION SYSTEM TYPE Pond AREA OF TRIBUTARY BASIN (ACRES) 1.5 TRIBUTARY BASIN IMPERVIOUS PERCENTAGE (%) 60% WATER QUALITY VOLUME (ACRE-FT) 0.146 ONLINE WQ FLOW RATE (CFS) 0.28 OFFLINE WQ FLOW RATE (CFS) 0.15 BMP OPTION DIMENSIONS SITE NOTES & OBSERVATION WET POND 40’X80’ Retrofit existing pond and add wetpond. Volume would be shy of standard. WET VAULTs Vault size – 13’X60’ Likely insufficient space along roadway. SANDFILTER VAULT Presettling vault – 10’X30’ Vault size – (1) 40’X80’ Insufficient head drop available. MEDIA FILTER VAULT, 12” CARTRIDGES WITH ZPG MEDIA(STORMFILTER VAULTS) 25 cartridges, ~ (1) 8’X11’ vault Insufficient head drop available. BIOSWALE 10’X240’ Insufficient space available (1). FILTER STRIP 20’X190’ See note 1 above. BIORETENTION 11’X230’ See note 1 above. MEDIA FILTER DRAIN 14’X540’ See note 1 above. MISCALLANEOUS NOTES: - Site is within groundwater protection area and identified with Alderwoods type soils. The TIR did not include groundwater information. - A wet pond retrofit that does not fully meet City of Renton standards appears to be the best option. It is likely that 60-70% of volume could be achieved. If this project is advanced, a boring is recommended to determine if infiltration could be included in retrofit (although the standing water is shown in photo, but it could be the result of fines built up). 145336: PETETT MEADOWS SHORT PLAT AS-BUILT DRAWING SUMMARY 1.1.1 PLAN VIEW 1.1.2 PROFILE 1.1.3 POND SECTION DATE OF AS-BUILT DRAWINGS 07/20/05 TIR PROVIDED No ADDRESS 3879 NE 21st St, Renton, 98056 145398: DAVIS AVE S ONE VALLEY PLACE BMP EVALUATION DETENTION SYSTEM Pond AREA OF TRIBUTARY BASIN (ACRES) 12.5 IMPERVIOUSNESS OF TRIBUTARY BASIN 46% WATER QUALITY VOLUME (ACRE-FT) 1.6974 ONLINE WQ FLOW RATE (CFS) 3.64 OFFLINE WQ FLOW RATE (CFS) 1.91 BMP OPTION DIMENSIONS SITE NOTES & OBSERVATION PROPRIETARY MEDIA FILTER VAULT, 27” CARTRIDGES WITH ZPG MEDIA(STORMFILTER VAULTS) 145 CARTRIDGES, ~ (3) 8’X24’ Sufficient head is available to accommodate the vault. WET VAULTS Vault Size- 43’X215’ SANDFILTER VAULTS Presettling vault-32’X100’ Vault Size- 125’X250’ MISCELLANEOUS NOTE: - The goal for this site is enhanced treatment. - Due to site constraints (slope/seismic), BMP options are limited to vault type BMPs. - It is noted that the Task 2/3 initial basin delineation was not correct for this site. This has been updated. - Enhanced treatment assumed to include paired facility of wet vault and StormFilter. In general, it does not appear feasible to provide enhanced treatment for this site without very deep excavations and major walls. A geotechnical report would be required and may not be feasible due to slopes and seismic hazard as well. No preferred option is identified. - One comment about this site is that the original development plans appeared to be for a residential subdivision. Much of the site was developed for the hospital. The City should confirm that no other treatment facilities were constructed in this basin during development. 145398: DAVIS AVE S ONE VALLEY PLACE AS-BUILT DRAWING SUMMARY 1.1.1 PLAN VIEW 1.1.2 PROFILE 1.1.3 DETAIL DATE OF AS-BUILT DRAWINGS 3/31/1982 TIR PROVIDED No ADDRESS 4600 Davis Ave S, Renton 98055 145407: VICTORIA HILLS BMP EVALUATION DETENTION SYSTEM Pond AREA OF TRIBUTARY BASIN (ACRES) 44.6 IMPERVIOUSNESS OF TRIBUTARY BASIN 40% WATER QUALITY VOLUME (ACRE-FT) 3.302 ONLINE WQ FLOW RATE (CFS) 7.92 OFFLINE WQ FLOW RATE (CFS) 4.06 BMP OPTION DIMENSIONS SITE NOTES & OBSERVATION PROPRIETARY MEDIA FILTER VAULT, 27” CARTRIDGES WITH ZPG MEDIA(STORMFILTER VAULTS) 316 CARTRIDGES, ~ (6) 8’X24’ Insufficient space available. WET VAULTS Vault Size- 60’X300’ Insufficient space available. SANDFILTER VAULTS Presettling vault-50’X150’ Vault Size- (1) 190’X380’ Insufficient space available Miscellaneous Notes: - The site location is within a landslide hazard. As a result, no open water type of facility is allowed. A vault type BMP is required. - Based on GIS, Rolling Hills creek flows through the pond and pond acts as a regional facility. It is noted that the tributary area given here is for the Victoria Hills development and does not include some areas to the east. - It is noted that the 24” pipe connecting to control structure as and invert 3’ below the pond bottom. Improvement of water quality could be obtained by installing a new 24” and relocate the pipe so that it enters the pond away from the control manhole. This would not meet any City of Renton standard but would improve water quality. 145407: VICTORIA HILLS AS-BUILT DRAWING SUMMARY 1.1.1 PLAN VIEW 1.1.2 PROFILE 1.1.3 DETAIL DATE OF AS-BUILT DRAWINGS 11/1/1978 TIR PROVIDED Yes ADDRESS 1102 S 23rd St, Renton, 98055 145785: ELIZABETH PLACE BMP EVALUATION EXISTING DETENTION SYSTEM TYPE Tank AREA OF TRIBUTARY BASIN (ACRES)0.9 TRIBUTARY BASIN IMPERVIOUS PERCENTAGE (%)94% WATER QUALITY VOLUME (ACRE-FT)0.115 ONLINE WQ FLOW RATE (CFS)0.19 OFFLINE WQ FLOW RATE (CFS)0.11 BMP OPTION DIMENSIONS SITE NOTES & OBSERVATION PROPRIETARY MEDIA FILTER VAULT, 18” CARTRIDGES WITH ZPG MEDIA(STORMFILTER VAULTS) 11 CARTRIDGES, ~ (1) 8’X6’Sufficient space and head drop. WET VAULTS Vault size - 12’X60’ SANDFILTER VAULTS Presettling vault - 10’X30’ Vault size - (1) 30’X60’ Insufficient space on the east of the existing detention facility. Miscellaneous Notes: -A vault type BMP is required due to site being adjacent to landslide hazard. -Stormfilter Vault is preferred option due to size and available head. It can be placed between the inlet to the tank system and upstream manhole. 145785: ELIZABETH PLACE AS-BUILT DRAWING SUMMARY 1.1.1 PLAN VIEW 1.1.2 PROFILE 1.1.3 DETAIL DATE OF AS-BUILT DRAWINGS 5/2/2000 TIR PROVIDED No ADDRESS 2412 NE 12th St, Renton, 98056 145824: RUDDELLS 2ND ADDITION BMP EVALUATION EXISTING DETENTION SYSTEM TYPE Tank AREA OF TRIBUTARY BASIN (ACRES)3.2 TRIBUTARY BASIN IMPERVIOUS PERCENTAGE (%)27% WATER QUALITY VOLUME (ACRE-FT)0.280 ONLINE WQ FLOW RATE (CFS)0.25 OFFLINE WQ FLOW RATE (CFS)0.14 BMP OPTION DIMENSIONS SITE NOTES & OBSERVATION WET POND 50’X110’Insufficient space available. WET VAULT Vault size – 17’X90’Potentially sufficient space available at outlet of detention tanks. SANDFILTER VAULT Presettling vault –20’X60’ Vault size – (1) 40’X80’ Insufficient head drop and probably insufficient space. MEDIA FILTER VAULT, 12” CARTRIDGES WITH ZPG MEDIA(STORMFILTER VAULTS) 22 cartridges, ~ (1) 8’X11’ vault Probably sufficient space and head drop if provided upstream of CB#6 at north end of site. BIOSWALE 11’X200’Insufficient space available. FILTER STRIP 20’X190’Insufficient space available. BIORETENTION 11’X460’Insufficient space available. MEDIA FILTER DRAIN 14’X480’Insufficient space available. MISCALLANEOUS NOTES: -Site is within 50’ of 15% slope, is within a groundwater protection area, and is likely required to assess landslide hazard. -Slope east of detention tank along NE 10th St. provides sufficient head drop but does not treat same area as site. -Stormfilter upstream of CB#6 would not capture entire basin and not preferred. -Wet vault appears to be the best option but may be challenging due to utility conflicts. This would capture more basin. 145824: RUDDELLS 2ND ADDITION AS-BUILT DRAWING SUMMARY PLAN VIEW PROFILE DATE OF AS-BUILT DRAWINGS 04/14/77 TIR PROVIDED No ADDRESS 3344 NE 10th St, Renton, 98056 DETAIL 145827: PARKWOOD BMP EVALUATION EXISTING DETENTION SYSTEM TYPE Tank AREA OF TRIBUTARY BASIN (ACRES)7.5 TRIBUTARY BASIN IMPERVIOUS PERCENTAGE (%)46% WATER QUALITY VOLUME (ACRE-FT)0.562 ONLINE WQ FLOW RATE (CFS)1.05 OFFLINE WQ FLOW RATE (CFS)0.56 BMP OPTION DIMENSIONS SITE NOTES & OBSERVATION WET POND 61’X156’Insufficient space available. WET VAULTs Vault size – 25’X124’ SANDFILTER VAULT Presettling vault – 20’X60’ Vault size – (1) 70’X140’ Insufficient head drop available PROPRIETARY MEDIA FILTER VAULT, 27” CARTRIDGES WITH ZPG MEDIA(STORMFILTER VAULTS) 42 cartridges, ~ (1) 8’X18’ vault Insufficient head drop available BIOSWALE 20’X250’Probably insufficient space available for full compliance. FILTER STRIP 80’X150’Probably insufficient space available and limited side slope. BIORETENTION 11’X905’Insufficient space available. MEDIA FILTER DRAIN 14’X2000’Insufficient space available and limited side slope MISCALLANEOUS NOTES: -Sufficient space with limited utilities within cul-de-sac for vaults. -Easement north of cul-de-sac could provide an open water treatment area. -Flat pipe slopes. -A substandard option may be to install a diversion manhole with short weir plate between MH 3 and MH2 and route to bioswale within easement to reconnect to MH 2. 145827: PARKWOOD AS-BUILT DRAWING SUMMARY 1.1.1 PLAN VIEW 1.1.2 PROFILE 1.1.3 DETAIL DATE OF AS-BUILT DRAWINGS 09/15/77 TIR PROVIDED No ADDRESS 2101 Aberdeen Ct SE, Renton, 98055 145832: SOUTH KNOLL WATER EXTENSION BMP EVALUATION EXISTING DETENTION SYSTEM TYPE Tank AREA OF TRIBUTARY BASIN (ACRES)8.4 TRIBUTARY BASIN IMPERVIOUS PERCENTAGE (%)29% WATER QUALITY VOLUME (ACRE-FT)0.787 ONLINE WQ FLOW RATE (CFS)0.76 OFFLINE WQ FLOW RATE (CFS)0.43 BMP OPTION DIMENSIONS SITE NOTES & OBSERVATION WET POND 70’X180’Insufficient space available. WET VAULTs Vault size – 30’X150’Probably insufficient space. (1) SANDFILTER VAULT Presettling vault – 30’X90’ Vault size – (1) 60’X120’ See note 1 above. PROPRIETARY MEDIA FILTER VAULT, 27” CARTRIDGES WITH ZPG MEDIA(STORMFILTER VAULTS) 30 cartridges, ~ (1) 8’X14’ vaults Sufficient space within SW 3rd (large area available) and available head towards Oakesdale. BIOSWALE 16’X240’See Note 1 above. FILTER STRIP 90’X100’insufficient space available. BIORETENTION 11’X1270’Insufficient space available. MEDIA FILTER DRAIN 14’X1448’Insufficient space available. MISCALLANEOUS NOTES: -Moderate landslide risk and geotechnical approval may be required for vault BMPs. -Stormfilter is proposed at end of Oakesdale on 3rd (where excess ROW available). Outlet pipe can extend southwest on Oakesdale to catch grade. 145832: SOUTH KNOLL WATER EXTENSION AS-BUILT DRAWING SUMMARY PLAN VIEW PROFILE DETAIL DATE OF AS-BUILT DRAWINGS 04/01/1985 TIR PROVIDED No ADDRESS 250 Oakesdale Ave SW, Renton, 98057 145834: POLLOS ESTATES BMP EVALUATION EXISTING DETENTION SYSTEM TYPE Tank AREA OF TRIBUTARY BASIN (ACRES)2.2 TRIBUTARY BASIN IMPERVIOUS PERCENTAGE (%)48% WATER QUALITY VOLUME (ACRE-FT)0.179 ONLINE WQ FLOW RATE (CFS)0.39 OFFLINE WQ FLOW RATE (CFS)0.20 BMP OPTION DIMENSIONS SITE NOTES & OBSERVATION WET POND 40’X90’Liner required. Probably insufficient space available. WET VAULTs Vault size – 15’X70’Potential location along north side of NE 21st St. Likely too deep SANDFILTER VAULT Presettling vault – 20’X60’ Vault size – (1) 50’X100’ Insufficient space (considering other utilities) PROPRIETARY MEDIA FILTER VAULT, 18” CARTRIDGES WITH ZPG MEDIA(STORMFILTER VAULTS) 23 cartridges, ~ (1) 8’X11’ vault Slope along NE 21st St. and just upstream of upper MH of facility would provide sufficient head. BIOSWALE 12’X220’Insufficient space available. FILTER STRIP 30’X160’Insufficient space available BIORETENTION 11’X280’Insufficient space available. MEDIA FILTER DRAIN 14’X750’insufficient space available. MISCALLANEOUS NOTES: -Moderate landslide hazard. Vault BMPs may require geotechnical approval. -Aquifer protection area/groundwater, groundwater protection area, and wellfield capture zone. Infiltration not allowed and lining may be required. -Recommend redirecting the two inlets to upstream end to a new Stormfilter that discharges to the upstream manhole. 145834: POLLOS ESTATES AS-BUILT DRAWING SUMMARY 1.1.1 PLAN VIEW 1.1.2 PROFILE 1.1.3 DETAIL DATE OF AS-BUILT DRAWINGS 05/05/90 TIR PROVIDED No ADDRESS 2099 Aberdeen Pl NE, Renton, 98056 145836: HIGHBURY PARK BMP EVALUATION EXISTING DETENTION SYSTEM TYPE Tank AREA OF TRIBUTARY BASIN (ACRES) 14.2 TRIBUTARY BASIN IMPERVIOUS PERCENTAGE (%) 41% WATER QUALITY VOLUME (ACRE-FT) 1.0544 ONLINE WQ FLOW RATE (CFS) 2.49 OFFLINE WQ FLOW RATE (CFS) 1.28 BMP OPTION DIMENSIONS SITE NOTES & OBSERVATION PROPRIETARY MEDIA FILTER VAULT, 27” CARTRIDGES WITH ZPG MEDIA(STORMFILTER VAULTS) 99 Cartridges, ~ (2) 8’X24’ Sufficient available head on the upstream of the main detention pipe inflow. WET VAULTS Vault Size- 35’X170’ Insufficient space and available head. SANDFILTER VAULTS Presettling vault-30’X90’ Vault Size- (1) 110’X220’ Insufficient space available head. MISCELLANEOUS NOTES: - Options are limited to vault type BMP as the area is within a seismic zone. - Stormfilter vault is the only potential option due to the available head and small footprint. Would need further assessment to confirm, and/or to develop concept that partially meets City of Renton standards. 145836: HIGHBURY PARK AS-BUILT DRAWING SUMMARY PLAN VIEW PROFILE DETAIL DATE OF AS-BUILT DRAWINGS 9/28/1978 TIR PROVIDED No ADDRESS 448 Edmonds Ave NE, Renton, 98056 145851: YOUNG ADDITION BMP EVALUATION EXISTING DETENTION SYSTEM TYPE Tank AREA OF TRIBUTARY BASIN (ACRES) 1.1 TRIBUTARY BASIN IMPERVIOUS PERCENTAGE (%) 87% WATER QUALITY VOLUME (ACRE-FT) 0.145 ONLINE WQ FLOW RATE (CFS) 0.23 OFFLINE WQ FLOW RATE (CFS) 0.13 BMP OPTION DIMENSIONS SITE NOTES & OBSERVATION WET POND 40’X80’ Insufficient space available. WET VAULTs Vault size – 13’X60’ Would be over 10’ deep. SANDFILTER VAULT Presettling vault – 10’X30’Vault size – (x) 40’X80’ Insufficient space available. MEDIA FILTER VAULT, 12” CARTRIDGES WITH ZPG MEDIA(STORMFILTER VAULTS) 21 cartridges, ~ (1) 8’X11’ vaults Feasible (route flow from CB #4 and #5 to new vault then to detention vault). BIOSWALE 10’X190’ Potential to upgrade exist. Ditch entering CB#4 from east. Within easement. FILTER STRIP 20’X190’ Probably insufficient space. BIORETENTION 230’X11’ Probably insufficient space. MEDIA FILTER DRAIN 14’X440’ Probably insufficient space. MISCELLANEOUS NOTES: - 15% slope within 50’ of site. However, may not be an issue as the downslope side is flat. Could consider some infiltration trench that does not meet City of Renton standards on along south property line. - Groundwater protection area. - Basin needs to be confirmed if this site advances to design. - Preferred option is Stormfilter Vault. 145851: YOUNG ADDITION AS-BUILT DRAWING SUMMARY PLAN VIEW PROFILE DETAIL DATE OF AS-BUILT DRAWINGS 02/21/91 TIR PROVIDED No ADDRESS 1636 Shelton Ave NE, Renton, 98056 D145864: RIDGEVIEW ESTATES BMP EVALUATION EXISTING DETENTION SYSTEM TYPE Tank AREA OF TRIBUTARY BASIN (ACRES) 6.8 TRIBUTARY BASIN IMPERVIOUS PERCENTAGE (%) 52% WATER QUALITY VOLUME (ACRE-FT) 0.589 ONLINE WQ FLOW RATE (CFS) 1.22 OFFLINE WQ FLOW RATE (CFS) 0.64 BMP OPTION DIMENSIONS SITE NOTES & OBSERVATION WET POND 60’X160’ Probably insufficient space. WET VAULTs Vault size – (1) 25’X130’ Probably insufficient space. SANDFILTER VAULT Presettling vault – 20’X60’ Vault size – (1) 80’X160’ Probably insufficient space. PROPRIETARY MEDIA FILTER VAULT, 49” CARTRIDGES WITH ZPG MEDIA(STORMFILTER VAULTS) 49 cartridges, ~ (1) 8’X20’ vault Could replace 50 ftof upstream pipe to increase head and obtain easement within driveway west of exist. easement. BIOSWALE 20’X250’ Potential location at ex. storm ditch along Duvall Ave NE. Probably insufficient space and too deep (1). FILTER STRIP 20’X180’ Potential location at ex. storm ditch along Duvall Ave NE. See Note 1 BIORETENTION 9 cells of 2’X21’ Probably insufficient space. MEDIA FILTER DRAIN 14’X2300’ Probably insufficient space. MISCELLANEOUS NOTES: - Groundwater protection area. - Media Filter in Vault is preferred. - Steep slope to north of detetion tank most likely insufficient for BMP use. Roadway to south provides vault options. 145864: RIDGEVIEW ESTATES AS-BUILT DRAWING SUMMARY PLAN VIEW PROFILE DETAIL DATE OF AS-BUILT DRAWINGS 08/11/88 TIR PROVIDED No ADDRESS 2624 Anacortes Ave NE, Renton, 98059 145869: YOUNG ADDITION BMP EVALUATION EXISTING DETENTION SYSTEM TYPE Tank AREA OF TRIBUTARY BASIN (ACRES) 1.6 TRIBUTARY BASIN IMPERVIOUS PERCENTAGE (%) 47% WATER QUALITY VOLUME (ACRE-FT) 0.129 ONLINE WQ FLOW RATE (CFS) 0.28 OFFLINE WQ FLOW RATE (CFS) 0.15 BMP OPTION DIMENSIONS SITE NOTES & OBSERVATION WET POND 40’X70’ Insufficient space. WET VAULTs Vault size – 12’X60’ Could replace portion of the detentiop pipe with wetvault SANDFILTER VAULT Presettling vault – 10’X30’ Vault size – (1) 40’X80’ Insufficient space. PROPRIETARY MEDIA FILTER VAULT, 12” CARTRIDGES WITH ZPG MEDIA(STORMFILTER VAULTS) 25 cartridges, ~ (1) 8’X11’ vaults Potential oportunity to locate along Union Ave NE. Slope would provide sufficient head drop. BIOSWALE 11’X200’ Probaby insufficient space. FILTER STRIP 20’X190’ Probaby insufficient space. BIORETENTION 11’X200’ Probaby insufficient space. MEDIA FILTER DRAIN 14’X540’ Probaby insufficient space. MISCALLANEOUS NOTES: - Groundwater protection area. - Existing 16’ storm easement along NE 17th St. provides BMP vault oportunities. - Wetvault would likely have fewer utility conflicts and construction impacts than media filter and is preferred. 145869: YOUNG ADDITION AS-BUILT DRAWING SUMMARY PLAN VIEW PROFILE DETAIL DATE OF AS-BUILT DRAWINGS 02/21/91 TIR PROVIDED No ADDRESS 4067 NE 17th St, Renton, 98056 146790: LUND SHORT PLAT BMP EVALUATION EXISTING DETENTION SYSTEM TYPE Pond AREA OF TRIBUTARY BASIN (ACRES) 0.5 TRIBUTARY BASIN IMPERVIOUS PERCENTAGE (%) 28% WATER QUALITY VOLUME (ACRE-FT) 0.0356 ONLINE WQ FLOW RATE (CFS) 0.09 OFFLINE WQ FLOW RATE (CFS) 0.05 BMP OPTION DIMENSIONS SITE NOTES & OBSERVATION WET POND 32’X36’ The wetpond can be accomodated within footprint of existing pond area (Ecology Block wall likely needed) WET VAULTs Vault size – 6.50’X32’ Not preferred because more costly than pond (1) SANDFILTER VAULT Presettling vault – 10’X30’ Vault size – (1) 20’X40’ See Note (1) above PROPRIETARY MEDIA FILTER VAULT, 18” CARTRIDGES WITH ZPG MEDIA(STORMFILTER VAULTS) 52 cartridges, ~ (1) 8’X22’ vaults See Note (1) above BIOSWALE 130’X9’ West of the current pond it a potential location, but likely limited space due to existing wetland. FILTER STRIP 185’X22’ BIORETENTION 75’X11’ MEDIA FILTER DRAIN 170’X15’ MISCELLENEOUS NOTES: - Combined wetpond and detention pond preferred. Further geotech investigations will be required. - The site is outside APA zone. 146790: LUND SHORT PLAT AS-BUILT DRAWING SUMMARY PLAN VIEW PROFILE DETAIL DATE OF AS-BUILT DRAWINGS 6/9/2005 TIR PROVIDED Yes ADDRESS 16345 114th Ave SE, Renton, 98055 166609: SUNSET BLVD/DUVALL AVE NE INT BMP EVALUATION DETENTION SYSTEM Vault AREA OF TRIBUTARY BASIN (ACRES) 0.3 IMPERVIOUSNESS OF TRIBUTARY BASIN 100% WATER QUALITY VOLUME (ACRE-FT) 0.0494 ONLINE WQ FLOW RATE (CFS) 0.07 OFFLINE WQ FLOW RATE (CFS) 0.04 BMP OPTION DIMENSIONS SITE NOTES & OBSERVATION WET POND 33’X44’ Insufficient space due to dense commercial development adjecent to site.(1) WET VAULTs Vault size – 13’X60’ Sufficient space upstream existing wetvault SANDFILTER VAULT Presettling vault – 5’X16’ Vault size – (1) 20’X40’ See note 1 above MEDIA FILTER VAULT, 18” CARTRIDGES WITH ZPG MEDIA(STORMFILTER VAULTS) 6 cartridges, ~ (1) 8’X6’ vault See note 1 above BIOSWALE 24’X256’ See note 1 above FILTER STRIP 6.50’X320’ See note 1 above BIORETENTION 11’X99’ See note 1 above MEDIA FILTER DRAIN 14’X140’ See note 1 above MISCELLANEOUS NOTES: - The existing facility has wet vault as WQ BMP which is 1182 cubic feet. The detention pond was desgned deeper than needed to get the 7’ clearance so it includes an addition wetpool depth of 2’. If this volume is included with the wetvault volume, it could be considered as meeting City of Renton standards. - Therefore, no BMP retrofit is recommended in this location. 166609: SUNSET BLVD/DUVALL AVE NE INT AS-BUILT DRAWING SUMMARY PLAN VIEW PROFILE DETAIL DATE OF AS-BUILT DRAWINGS 6/3/2009 TIR PROVIDED X ADDRESS 4442 NE Sunset Blvd, Renton, 98059 167768: ORCHARD PARK BMP EVALUATION EXISTING DETENTION SYSTEM TYPE Tank AREA OF TRIBUTARY BASIN (ACRES) 4.4 TRIBUTARY BASIN IMPERVIOUS PERCENTAGE (%) 47% WATER QUALITY VOLUME (ACRE-FT) 0.3539 ONLINE WQ FLOW RATE (CFS) 0.77 OFFLINE WQ FLOW RATE (CFS) 0.40 BMP OPTION DIMENSIONS SITE NOTES & OBSERVATION WET POND 53’X123’ Insufficient space available. WET VAULTs Vault size – 20’X100’ Likely insufficent space wihtin road prism considering other utilities and depth(1) SANDFILTER VAULT Presettling vault – 20’X60’ Vault size – (1) 120’X60’ Insufficient space available (2). PROPRIETARY MEDIA FILTER VAULT, 18” CARTRIDGES WITH ZPG MEDIA(STORMFILTER VAULTS) 46 cartridges, ~ (1) 8’X20’ vaults Available head upstream of facility. Could locate in ROW with likely some utility relocations. BIOSWALE 242’X16’ Not a viable option due to restrictive ROW(3) FILTER STRIP 105’X90’ See note 3 above. BIORETENTION 570’X11’ See note 3 above. MEDIA FILTER DRAIN 1470’X14’ See note 3 above. MISCELLENOUS NOTES - The Stormfilter Vault is the preferred WQ BMP on upstream side of the detention pipe due being able to construct it realatively shallow. Some utility relocations likely required. 167768: ORCHARD PARK AS-BUILT DRAWING SUMMARY PLAN VIEW PROFILE DETAIL DATE OF AS-BUILT DRAWINGS 10/10/1991 TIR PROVIDED X ADDRESS 17944 112th Ave SE, Renton, 98055 168953: VILLAGE ON UNION BMP EVALUATION EXISTING DETENTION SYSTEM TYPE Tank (see Misc. notes below) AREA OF TRIBUTARY BASIN (ACRES) 16.5 TRIBUTARY BASIN IMPERVIOUS PERCENTAGE (%) 52% WATER QUALITY VOLUME (ACRE-FT) 1.544 ONLINE WQ FLOW RATE (CFS) 2.70 OFFLINE WQ FLOW RATE (CFS) 1.45 BMP OPTION DIMENSIONS SITE NOTES & OBSERVATION WET POND 90’X260’ Insufficient space available. WET VAULTs Vault size – 40’X210’ Probably insufficinet space availble. SANDFILTER VAULT Presettling vault – 40’X120’ Vault size – (x) 110’X220’ Insufficient head drop and space available. MEDIA FILTER VAULT, 27” CARTRIDGES WITH ZPG MEDIA(STORMFILTER VAULTS) 108 cartridges, ~ (2) 8’X24’ vaults Insufficient head drop available. BIOSWALE 17’X750’ Insufficient space available. FILTER STRIP 45’X710’ Insufficient space available. BIORETENTION 11’X2470’ Insufficient space available. MEDIA FILTER DRAIN 14’X5130’ Insufficient space available. MISCALLANEOUS NOTES: - Site is within 50’ of 15% slope, within 50’ of a landslide hazard area, and hence non-vault WQ BMPs are not allowed. Site is within groundwater protection zone and within steep slopes based upon City GIS (although this could be the existing channel banks. - Facility includes a 200’ grassy swale for treatment prior to infiltration system via three 48” perforated pipes. Any additional water quality BMP will help to protect groundwater only and is not the emphasis of this study. No BMP retrofits are recommended for this site. 168953: VILLAGE ON UNION AS-BUILT DRAWING SUMMARY PLAN VIEW PROFILE DETAIL DATE OF AS-BUILT DRAWINGS 01/30/95 TIR PROVIDED No ADDRESS 501 Shelton Ct NE, Renton, 98056 200040: KELSEY LANE BMP EVALUATION EXISTING DETENTION SYSTEM TYPE Tank AREA OF TRIBUTARY BASIN (ACRES) 2.0 TRIBUTARY BASIN IMPERVIOUS PERCENTAGE (%) 61% WATER QUALITY VOLUME (ACRE-FT) 0.2066 ONLINE WQ FLOW RATE (CFS) 0.33 OFFLINE WQ FLOW RATE (CFS) 0.18 BMP OPTION DIMENSIONS SITE NOTES & OBSERVATION WET POND 46’X94’ Insufficient space and existing system very deep at outlet. WET VAULTs Vault size – 15’X75’ Possible along 108th, but would be very deep. Not preferred. (1) SANDFILTER VAULT Presettling vault – 20’X60’ Vault size – (1) 40’X80’ See note 1 above. MEDIA FILTER VAULT, 18” CARTRIDGES WITH ZPG MEDIA(STORMFILTER VAULTS) 20 cartridges, ~ (1) 8’X11’ vaults Location at upstream end in cul-de-sac feasible and has avaiable space. BIOSWALE 212’X12’ Preferred option. Space and grade available on eastside of 108th Ave SE. FILTER STRIP 185’X21.5’ Bioswale appears better option. BIORETENTION 11’X340’ Not preferred due to a larger footprint as compared to other infiltration BMPs.(2) MEDIA FILTER DRAIN 15’X630’ See noted 2 above. MISCELLENEOUS NOTES: - Confirm existing ROW available (approx. 200’X25’) on east of 108th Ave SE. - Confirm exisitng 12” outlet is at existing road ditch from detention system. 200040: KELSEY LANE AS-BUILT DRAWING SUMMARY PLAN VIEW PROFILE DETAIL DATE OF AS-BUILT DRAWINGS 6/25/1981 TIR PROVIDED X ADDRESS 10804 SE 173rd ST, Renton WA 98055 200041: KELSEY LANE BMP EVALUATION EXISTING DETENTION SYSTEM TYPE Tank AREA OF TRIBUTARY BASIN (ACRES) 0.2 TRIBUTARY BASIN IMPERVIOUS PERCENTAGE (%) 100% WATER QUALITY VOLUME (ACRE-FT) 0.0243 ONLINE WQ FLOW RATE (CFS) 0.04 OFFLINE WQ FLOW RATE (CFS) 0.02 BMP OPTION DIMENSIONS SITE NOTES & OBSERVATION WET POND 30’X28’ Not preferred due to insufficient easement. WET VAULTs Vault size – 6’X26’ Not preferred due to high cost of installation and maintenance. (1) SANDFILTER VAULT Presettling vault – 10’X30’ Vault size – (1) 20’X40’ See note 1 above. PROPRIETARY MEDIA FILTER VAULT, 12” CARTRIDGES WITH ZPG MEDIA(STORMFILTER VAULTS) 3 cartridges, ~ (1) 8’X6’ vaults Vault can be accomodated between control manhole and downstream manhole with available head. BIOSWALE 100’X9’ Insufficent space along 17nds and downstream is too deep.(2) FILTER STRIP 185’X21.50’ Not preferred due to insufficient space. BIORETENTION 50’X11’ See note 2 above. MEDIA FILTER DRAIN 60’X15’ See note 2 above. MISCELLANEOUS NOTES: - Stormfilter appears to be best option. 200041: KELSEY LANE AS-BUILT DRAWING SUMMARY PLAN VIEW PROFILE DETAIL DATE OF AS-BUILT DRAWINGS 6/25/1981 TIR PROVIDED X ADDRESS 10821 SE 172nd St, Renton, 98055 200049: NANTUCKET SHORT PLAT BMP EVALUATION EXISTING SYSTEM Wetvault (no detention) AREA OF TRIBUTARY BASIN (ACRES) 5.4 IMPERVIOUSNESS OF TRIBUTARY BASIN 37% WATER QUALITY VOLUME (ACRE-FT) 0.3772 ONLINE WQ FLOW RATE (CFS) 0.92 OFFLINE WQ FLOW RATE (CFS) 0.47 BMP OPTION DIMENSIONS SITE NOTES & OBSERVATION PROPRIETARY MEDIA FILTER VAULT, 18” CARTRIDGES WITH ZPG MEDIA(STORMFILTER VAULTS) 55 CARTRIDGES, ~ (1) 8’X22’ Sufficient space and head available. (1) WET VAULTS Vault Size- 20’X100’ See Misc. comments below. SANDFILTER VAULTS Presettling vault-20’X60’ Vault Size- (1)20’X60’ Insufficient space available. MISCELLANEOUS NOTES: - It is unusual, but the record drawing indicated this is a wetvault and the short plat did not include detention. - The existing vault is within 100 feet of a slope exceeding 25% and any improvement will need to be a vault type BMP. - The exist vault provides about 2,300 cf of wetvault storage. Current sizing indicated 16,000 cf is required to meet standard. It is likely difficult to locate this much additional storage within the site. Considering utilities and easements.should be upsized to provide the required WQ volume. - Stormfilter is the preferred option. It could be likely be located within in the unused southwest corner portion of Park Ave N and N 28th St. 200049: NANTUCKET SHORT PLAT AS-BUILT DRAWING SUMMARY PLAN VIEW PROFILE DETAIL DATE OF AS-BUILT DRAWINGS 7/1/2015 TIR PROVIDED No ADDRESS 2826 Park Ave N, Renton, 98056 200096: PARKWOOD SOUTH DIV III BMP EVALUATION EXISTING DETENTION SYSTEM TYPE Tank AREA OF TRIBUTARY BASIN (ACRES) 1.3 TRIBUTARY BASIN IMPERVIOUS PERCENTAGE (%) 22% WATER QUALITY VOLUME (ACRE-FT) 0.0518 ONLINE WQ FLOW RATE (CFS) 0.1203 OFFLINE WQ FLOW RATE (CFS) 0.0623 BMP OPTION DIMENSIONS SITE NOTES & OBSERVATION WET POND 35’X45’ Not preferred due to insufficient easement and space. (1) WET VAULTs Vault size – 8’X38’ Not preferred (See Note 1 above) SANDFILTER VAULT Presettling vault – 10’X30’ Vault size – (1) 30’X60’ See note 1 above. MEDIA FILTER VAULT, (STORMFILTER VAULTS) 11 cartridges, ~ (1) 8’X6’ vaults There is available head (at MH 10) and 10’ easement. BIOSWALE 155’X10’ There is a 10-feet easement along the detention pipe. Could have bioswale above it, but likely its too deep for narrow easement (2) FILTER STRIP 215’X15’ Not preferred due to insufficient easement width. BIORETENTION 100’X11’ See note 2 above. MEDIA FILTER DRAIN 85’X15’ See note 2 above. MISCELLENEOUS NOTES: - Note that the basin to this facility was to its upstream and would need to be updated if advanced for design. - Stormfilter at MH 10 appears most feasible. A temporary construction easement would be required. 200096: PARKWOOD SOUTH DIV III AS-BUILT DRAWING SUMMARY PLAN VIEW PROFILE DETAIL DATE OF AS-BUILT DRAWINGS 9/15/1977 TIR PROVIDED No ADDRESS 2089 Edmonds Dr SE, Renton, 98055 Page 1 DRAFT MEMORANDUM DATE: September 9, 2021 TO: Ken Srilofung, PE, CIP Project Manager FROM: Mike Giseburt, PE, WSP Project Manager SUBJECT: Stormwater Facility Retrofit Study – Prioritize and Score Retrofit Opportunities (Task 5 Effort) 1. INTRODUCTION AND BACKGROUND The City of Renton (City) owns and maintains over 400 stormwater facilities constructed as far back as the 1970s to mitigate for the stormwater impacts of urbanization. Between the 1970s and early 1990s, stormwater facilities were primarily focused on providing stormwater storage (i.e., detention). Since the early 1990s, design standards have advanced so that today’s stormwater facilities provide better water quality treatment to mitigate the detrimental impacts of stormwater pollutants on stream water quality and aquatic habitat. Today’s newer stormwater treatment systems target the removal of suspended solids, dissolved heavy metals, nutrients, and petroleum hydrocarbons. Typically, stormwater facilities owned by the City connect to the municipal storm sewer system and drain to the closest water body. The older stormwater detention facilities in the City’s system typically do not include a specific water quality treatment component, and thus are less effective at protecting stream resources from pollutants than the stormwater detention facilities with water quality treatment designed using today’s standards. The City received a grant from the Washington State Department of Ecology (Ecology) to perform a study of many of the existing flow control facilities that have little or no water quality treatment features. The overarching goal is to improve the water quality in multiple streams within the City that are part of the Cedar River/Lake Washington and Duwamish/Green watersheds. The study entails a series of six sequential tasks to be undertaken to prioritize the sites with the greatest potential to improve water quality. The first four tasks, Tasks 1 through 4, are complete and include: Existing Facilities Selection (Task 1) — City staff selected 49 existing flow control facilities for this study primarily based on their understanding that these particular existing facilities provide minimal water quality treatment (see Figure 1). Existing Conditions Summary (Task 2) — This effort is complete and included collecting information and evaluating site conditions of the 49 selected existing facilities. The summarized data includes stormwater best management practice (BMP) type, size, and age; tributary area characteristics; drainage basin information; and other information, all which help characterize the existing facilities and can be used in future tasks to evaluate stormwater treatment performance and site-specific water quality retrofit opportunities. Page 2 Figure 1. Site Map Page 3 Gap Analysis (Task 3) — This effort identified deficiencies (gaps) in the treatment of stormwater at the selected facilities. The analysis compared the existing amount of runoff treatment in the drainage basins to the amount of runoff treatment needed to meet current water quality treatment standards (per the 2017 City of Renton Surface Water Design Manual [SWDM]). It is noted that the City of Renton water quality treatment standards is deemed equivalent to Ecology Standards for development and redevelopment. Identifying Stormwater Retrofit Locations (Task 4) — This effort built upon the treatment gap analysis to identify existing flow control facilities to retrofit with additional runoff treatment benefits. This task developed a preliminary suite of BMP types and sizes for each site while considering site- specific conditions, such as space, topography, conveyance, infiltration potential, and other considerations. The next task, Task 5, is the presented in this memorandum. Prioritizing and Scoring Sites for Stormwater Retrofit Opportunities (Task 5) — This effort develops a method to screen and create a ranked list of retrofit locations identified in Task 4 that focuses on the (a) highest benefit of water quality improvement and (b) most effective opportunities. The next task will be completed as a part of future study efforts. Project Selection, Conceptual Design, and Costs (Task 6) — This effort will include the development of concept designs and cost estimates for the top three prioritized retrofit locations. 2. RECOMMEND BMP RETROFITS Prior to the effort in Task 5, Task 4 performed a base feasibility assessment which identified workable options to provide BMPs that met City of Renton standards without taking up an unreasonable portion of the right-of-way or acquisition of property through new or expanded easements. Task 4 evaluated several types of retrofits and developed preliminary preferred retrofit BMPs as summarized in Table 1. Due to these challenges and site constraints, the StormFilter vault was recommended more frequently than other BMPs, largely due to its small footprint, and ability to meet City of Renton stormwater standards. For some sites that would be extremely difficult to provide treatment meeting Renton standards, a preliminary recommended option is preferred that would not fully meet Renton standards but could still provide a meaningful water quality benefit. For example, converting an existing detention pond to a combined wetpond/detention pond is very economical and results in significant water quality improvement while not fully meeting Renton standards. Table 1 presents a summary of the number and type of recommended preferred retrofits for the 43 sites of the 49 sites that were found to have a workable BMP option. Six of the sites were found to either meet standards or determined not feasible to retrofit. Table 1. Summary of Workable Retrofit BMP Types Retrofit BMP Type Number StormFilter BMP 29 Adding Wetpond Storage or a Pond Retrofit to Existing Detention Pond (2 include Converting “back-up” type facility to a “flow-through” type) 5 Biofiltration (Bioswale and Bioretention) 4 Wetvault 5 Page 4 The StormFilter BMP retrofit type is recommended most frequently. An important distinction is that the Stormfilter BMP type is one of a number of proprietary media filter systems, where media (often in cartridges) absorbs and retains pollutants in stormwater. Other types of media filter systems include EcoStorm Plus, Filterra, BayFilter, and Modular Wetland Systems (that can include plant for additional treatment uptake but are not required) that are approved by the City of Renton Stormwater Manual. When comparing the different types, there tend to be modest advantages and disadvantages between them, and one may be preferred in one situation while a different type may be preferred in another. For the purpose of this report, whenever StormFilter is mentioned, other types of media filter systems approved for use by the City of Renton should also be considered. The ultimately selected media filter type for sites will be selected in future design phase. The six sites where no recommendation is presented are listed below along with a corresponding explanation. Site 117940 - Valley Vue Estates: Currently meets COR treatment standards Site 117938 – Chinquapin Ridge: Currently meets COR treatment standards Site 166609 - Sunset BLVD/Duvall Ave NE: Currently meets COR treatment standards Site 168953 - Village on Union: Includes an infiltration system with no runoff to City drainage system. 111421 - Ripley Lane Storm Improvement Site: Lack of feasible solution due to site constraints 111422 - Renton Village Interceptor Site: Lack of feasible solution due to site constraints 3. BMP RETROFIT SCORING This effort developed a method to screen retrofit locations identified during Task 4. This section evaluates eight (8) criteria for each site. Six of the criteria were scored on a varying scale of 0 to 1, with 1 providing the greatest benefit/rating and partial scores (between 0 and 1) that reflect partial benefit/rating. Two of the criteria, considered most important, were scored on a varying scale of 0 to 2, with 2 providing the greatest benefit. These two criteria included “Level of Retrofit Treatment Achieved” and “Feasibility” and effectively are given a higher weighted value in the scoring system. This results in a total possible maximum score of 10 points. The criteria are: Level of retrofit treatment achieved (meets City water quality standards) Feasibility (site characteristic including constructability, right of way and space available) Receiving water quality Drainage Basin size Drainage Basin prioritization under City’s stormwater management action plan Infiltration potential (type of BMP and hydrologic function) Long term operation and maintenance costs Other benefits (social, economic and environmental) Page 5 A summary of the criteria and scoring system is included on Table 2. The criteria for Level of Retrofit Treatment was given a higher criteria weight because improving stormwater treatment is a primary objective of this study. The criteria for Feasibility was given a higher criteria weight because the City wants to have a high degree of confidence that higher priority projects proposed in this study are implementable, as the City will be investing design resources in future activities. Table 2. Summary of Criteria Scoring Criteria Ratings/Scores Comments Level of Retrofit Treatment Rating Marginally Partially Completely Score 0.5 1 2 Feasibility Rating Difficult Average Good Site characteristics including constructability, right of way and space available Score 0 1 2 Receiving Water Quality Rating Non-Listed Water Body Not Used 303d Listed Score 0 1 Drainage Basin Size Rating <1 acre >1 and <5 acres >5 acres Score 0 .5 1 Drainage Basin Prioritization Rating Low Moderate High Score 0.2 0.5 1 Zero points, or not scored, if located in a basin not considered in the assessment (Duwamish River Basin) Infiltration Potential Rating Low Limited Likely Score 0 0.3 1 Long Term Maintenance Costs Rating High Moderate Low Score 0 0.5 1 Other Benefits Rating Low Moderate High Social, economic, and environmental Score 0 0.5 1 Total Possible Score 10 Much of the information to assess the retrofit sites with these criteria was developed in prior project Task Memorandums 1 through 4. Level of Retrofit Treatment Achieved City stormwater quality standards for development and redevelopment have been developed to comply with Washington State Department of Ecology (Ecology) water quality standards. This criterion evaluates the level of retrofit achieved for the BMPs to potentially improve water quality and meet City of Renton standards at each site. As noted above, the criteria for Level of Retrofit Treatment Achieved was given a higher criteria weight Page 6 because moving towards a goal or meeting City treatment standards is a primary objective for study. Each site was evaluated using the following rating system: A score of 2 was given to sites where a stormwater treatment retrofit BMP would completely meet City water quality standards A score of 1 was given to sites where stormwater treatment would provide a meaningful water quality benefits and only partially meet City water quality standards A score of 0.5 was given to sites where stormwater treatment would provide only marginal water quality benefits and would marginally meet City water quality standards For locations where the sites’ current water quality treatment meet City standards, or no feasible recommended option was developed, no score was assigned. See Comments for additional information. Table 3 presents the scores to meet City water quality standards. Table 3. Meeting City Water Quality Standards Score Site ID Development project name Receiving Water Body Meets water quality standards (marginally/ partially/completely)? Score Comments 111332 Summerwind DIV I II III Greenes Creek Completely 2 111342 Winsper (liberty view I & II) Panther Creek Completely 2 111354 Springbrook terrace Upper Springbrook Creek Partial 1 111361 Hidden cedars DIV II Soos Creek Main Partial 1 111369 Panther meadow Panther Creek Partial 1 111391 Dennys restaurant Lake Washington - East Completely 2 Assume Stormfilters 111393 Castlewood ranchettes Maplewood Creek Completely 2 111394 Castlewood ranchettes Maplewood Creek Completely 2 111408 Bergsma short plat Upper Springbrook Creek Partial 1 111421 Ripley ln storm improvement pr Lake Washington - East Not Scored Not Scored No Feasible Solution Identified 111422 Renton village interceptor Thunder Hills Creek Not Scored Not Scored No Feasible Solution Identified 117894 Swan meadows I Johns Creek Partial 1 Discounted because would not be able to treat entire basin 117900 Meadow Av N & N 24th St South Kennydale Completely 2 117902 Tiffany park DIV 4 Cedar Main Urban Completely 2 117912 Armstrong And Sandelius Soos Creek Main Completely 2 117915 Knudson Soos Creek Main Completely 2 117916 Parkwood South DIV I Thunder Hills Creek Completely 2 Would treat 89-90% of basin Page 7 Site ID Development project name Receiving Water Body Meets water quality standards (marginally/ partially/completely)? Score Comments 117917 Windsor Heights Panther Creek Completely 2 117918 Benson Woods Panther Creek Completely 2 117921 Swan Meadows II Johns Creek Completely 2 117929 Bob Burke Upper Springbrook Creek Completely 2 Revised BMP Retrofit to Wetvault to allow property owner continued use of space within easement. 117931 Benson Glen Panther Creek Partial 1 Upgrade existing swale 117936 Fernwood East Maplewood Creek Completely 2 117938 Chinquapin Ridge Panther Creek Not Scored Not Scored Currently meets City standards 117940 Valley Vue Estates Panther Creek Not Scored Not Scored Currently has 200' bioswale. No improvements recommended 117941 Weatherwood II Lower May Creek Completely 2 117945 Hidden Cedars DIV II Soos Creek Main Completely 2 117947 Benson Glen Panther Creek Completely 2 117952 Chinquapin Ridge Panther Creek Completely 2 145336 Petett Meadows Short Plat Honey Creek Partial 1 145398 Davis Av S One Valley Place Upper Springbrook Creek Partial 1 Needs City investigation - Enhanced Treatment Required 145407 Victoria Hills Rolling Hills Creek Partial 1 Would require variance from code to utilize pond next to steep slope 145785 Elizabeth Place Johns Creek Completely 2 145824 Ruddells 2nd Addition Johns Creek Completely 2 145827 Parkwood Thunder Hills Creek Partial 1 145832 South Knoll Water Extension South Renton Completely 2 145834 Pollos Estates Lower May Creek Completely 2 145836 Highbury Park Johns Creek Completely 2 145851 Young Addition Honey Creek Completely 2 Assume Stormfilter for road runoff only, other non-pgis runoff bypass 145864 Ridgeview Estates May Creek Completely 2 145869 Young Addition Honey Creek Completely 2 146790 Lund Short Plat Thunder Hills Creek Completely 2 Treat only for PGIS in basin (allow roof runoff to bypass) 166609 Sunset Blvd/Duvall Ave NE Int Honey Creek Not Scored Not Scored Currently meets City standards 167768 Orchard Park Panther Creek Completely 2 Can collect about 85% of development 168953 Village On Union Cedar Main Urban Not Scored. Not Scored Current Infiltration System - Not Scored 200040 Kelsey Lane Panther Creek Completely 2 If satisfactory infiltration rates Page 8 Site ID Development project name Receiving Water Body Meets water quality standards (marginally/ partially/completely)? Score Comments 200041 Kelsey Lane Panther Creek Completely 2 200049 Nantucket Short Plat South Kennydale Completely 2 Current treatment undersized 200096 Parkwood South DIV III Thunder Hills Creek Completely 2 Requires two smaller Stormfilters Feasibility (site characteristics including constructability, right of way and space available) This criterion evaluates site characteristics and the feasibility of construction of the BMPs. The criteria for Feasibility was given a higher criteria weight because the City wants to have a high degree of confidence that higher priority projects proposed in this study are implementable, as the City will be investing design resources in future activities. Issues with feasibility often increase the cost of implementation and/or delay implementation because of difficulty to obtain easements/right-of-way. Each site was evaluated using the following rating system: A score of 2 was given to sites where BMPs that would be very easy and simple to construct, that there is more than the minimal amount of right of way and publicly owned space available and that the is very little potential for conflicting lands uses in the area. A score of 1 was given to sites where there would be marginally enough space to construct and that there is an average potential for conflicting land uses in the area. A score of 0 was given to sites where BMPs would be difficult to construct. Where space is limited and where there is a high potential for conflicting land uses in the area. For locations where the sites’ current water quality treatment meet City standards, or no feasible recommended option was developed, no score was assigned. See Comments for additional information. Table 4 presents the scores for the feasibility to construction the BMPs evaluated. Table 4. Feasibility Score Site ID Development Project Name Receiving Water Body Feasibility – Site Characteristics Score Comments 111332 Summerwind DIV I II III Greenes Creek Average 1 Due to lack of space 111342 Winsper (liberty view I & II) Panther Creek Average 1 Likely need HOA approval 111354 Springbrook terrace Upper Springbrook Creek Good 2 111361 Hidden cedars DIV II Soos Creek Main Good 2 Geotechnical Approval Needed due to slope 111369 Panther meadow Panther Creek Good 2 111391 Dennys restaurant Lake Washington - East Difficult 0 Site Owned by WSDOT so likely not feasible 111393 Castlewood ranchettes Maplewood Creek Good 2 Would need to confirm no utility conflicts Page 9 Site ID Development Project Name Receiving Water Body Feasibility – Site Characteristics Score Comments 111394 Castlewood ranchettes Maplewood Creek Good 2 111408 Bergsma short plat Upper Springbrook Creek Average 1 Would likely need property owner approval 111421 Ripley ln storm improvement pr Lake Washington - East Not Scored Not Scored No Feasible Solution Identified 111422 Renton village interceptor Thunder Hills Creek Not Scored Not Scored No Feasible Solution Identified 117894 Swan meadows I Johns Creek Good 2 117900 Meadow Av N & N 24th St South Kennydale Average 1 Would need to fit in ROW 117902 Tiffany park DIV 4 Cedar Main Urban Average 1 Would need to fit in Cul-de-sac and avoid utilities/also deep 117912 Armstrong And Sandelius Soos Creek Main Average 1 Would be significant impact to property owner 117915 Knudson Soos Creek Main Good 2 Would likely need property owner approval 117916 Parkwood South DIV I Thunder Hills Creek Good 2 Some concern with utilities conflicts, but there are several locations vault could go. 117917 Windsor Heights Panther Creek Average 1 Would need to split into two vaults and replace some existing detention pipe. 117918 Benson Woods Panther Creek Good 2 Would likely need to replace some of existing detention pipe. 117921 Swan Meadows II Johns Creek Good 2 Would likely need to split into two vaults 117929 Bob Burke Upper Springbrook Creek Good 2 117931 Benson Glen Panther Creek Good 2 117936 Fernwood East Maplewood Creek Difficult 0 Due to slopes and space 117938 Chinquapin Ridge Panther Creek Not scored Not scored Currently Meets City Standards 117940 Valley Vue Estates Panther Creek Not Scored Not scored Currently has 200' bioswale. No improvements recommended 117941 Weatherwood II Lower May Creek Average 1 In ROW - potential for utility conflicts 117945 Hidden Cedars DIV II Soos Creek Main Good 2 117947 Benson Glen Panther Creek Average 1 In ROW and grade challenged 117952 Chinquapin Ridge Panther Creek Average 1 Challenging to pick up all flows 145336 Petett Meadows Short Plat Honey Creek Good 2 145398 Davis Av S One Valley Place Upper Springbrook Creek Difficult 0 Deep Excavations/Walls would be needed 145407 Victoria Hills Rolling Hills Creek Average 1 Would require variance from code to utilize pond next to steep slope 145785 Elizabeth Place Johns Creek Good 2 Page 10 Site ID Development Project Name Receiving Water Body Feasibility – Site Characteristics Score Comments 145824 Ruddells 2nd Addition Johns Creek Good 2 145827 Parkwood Thunder Hills Creek Average 1 145832 South Knoll Water Extension South Renton Good 2 145834 Pollos Estates Lower May Creek Good 2 145836 Highbury Park Johns Creek Average 1 145851 Young Addition Honey Creek Good 2 145864 Ridgeview Estates May Creek Good 2 145869 Young Addition Honey Creek Good 2 146790 Lund Short Plat Thunder Hills Creek Good 2 166609 Sunset Blvd/Duvall Ave NE Int Honey Creek Not scored Not scored Currently meets City standards 167768 Orchard Park Panther Creek Good 2 168953 Village On Union Cedar Main Urban Not scored Not scored Current Infiltration System - Not Scored 200040 Kelsey Lane Panther Creek Good 2 Assumes no significant utility relocation needed 200041 Kelsey Lane Panther Creek Good 2 200049 Nantucket Short Plat South Kennydale Good 2 200096 Parkwood South DIV III Thunder Hills Creek Good 2 Receiving water quality This criterion evaluates the receiving water quality for each site. Receiving waters classified by Ecology under Clean Water Act standards as “303(d)” have been identified as impaired and threatened waters. Waters that are identified as “303(d)” would benefit more from the water quality improvement projects. Each site was evaluated using the following rating system: - A score of 1 was given to sites where the receiving water body is listed as “303(d)” under all but one circumstance. - A score of 0 was given to sites not listed as “303(d)”. For locations where the sites’ current water quality treatment meet City standards, or no feasible recommended option was developed, no score was assigned. See Comments for additional information. Table 5 presents the scores for the receiving water body quality. Table 5. Receiving Water Body Quality Score Site ID Development Project Name Receiving Water Body Water Body listed as “303(d)” (yes/no) Score Pollutant(s) of Concern 111332 Summerwind DIV I II III Greenes Creek Yes 1 Temperature 111342 Winsper (liberty view I & II) Panther Creek No 0 Page 11 Site ID Development Project Name Receiving Water Body Water Body listed as “303(d)” (yes/no) Score Pollutant(s) of Concern 111354 Springbrook terrace Upper Springbrook Creek Yes 1 Bioassessment 111361 Hidden cedars DIV II Soos Creek Main No 0 111369 Panther meadow Panther Creek No 0 111391 Dennys restaurant Lake Washington – East Yes 1 Sediment Bioassay 111393 Castlewood ranchettes Maplewood Creek No 0 111394 Castlewood ranchettes Maplewood Creek No 0 111408 Bergsma short plat Upper Springbrook Creek No 0 111421 Ripley ln storm improvement pr Lake Washington – East Not Scored Not scored Sediment Bioassay. No feasible solution identified. 111422 Renton village interceptor Thunder Hills Creek Not Scored Not scored No feasible solution identified. 117894 Swan meadows I Johns Creek Yes 1 Temperature, Bacteria, Dissolved Oxygen 117900 Meadow Av N & N 24th St South Kennydale Yes 1 Bacteria 117902 Tiffany park DIV 4 Cedar Main Urban No 0 117912 Armstrong And Sandelius Soos Creek Main No 0 117915 Knudson Soos Creek Main No 0 117916 Parkwood South DIV I Thunder Hills Creek No 0 117917 Windsor Heights Panther Creek No 0 117918 Benson Woods Panther Creek Yes 1 Bioassessment 117921 Swan Meadows II Johns Creek Yes 1 Temperature, Bacteria, Dissolved Oxygen 117929 Bob Burke Upper Springbrook Creek Yes 1 Bioassessment 117931 Benson Glen Panther Creek Yes 1 Bioassessment 117936 Fernwood East Maplewood Creek No 0 117938 Chinquapin Ridge Panther Creek Not Scored Not scored Bioassessment. Currently Meets City Standards 117940 Valley Vue Estates Panther Creek Not Scored Not scored Currently has 200' bioswale. No improvements recommended 117941 Weatherwood II Lower May Creek Yes 1 Bioassessment, Temperature, Bacteria 117945 Hidden Cedars DIV II Soos Creek Main No 0 117947 Benson Glen Panther Creek No 0 117952 Chinquapin Ridge Panther Creek No 0 145336 Petett Meadows Short Plat Honey Creek No 0 145398 Davis Av S One Valley Place Upper Springbrook Creek No 0 145407 Victoria Hills Rolling Hills Creek Yes 1 Bioassessment Page 12 Site ID Development Project Name Receiving Water Body Water Body listed as “303(d)” (yes/no) Score Pollutant(s) of Concern 145785 Elizabeth Place Johns Creek Yes 1 Temperature, Bacteria, Dissolved Oxygen 145824 Ruddells 2nd Addition Johns Creek No 0 145827 Parkwood Thunder Hills Creek No 0 145832 South Knoll Water Extension South Renton Yes 1 Temperature; Dissolve Oxygen, Bacteria, Bioassessment 145834 Pollos Estates Lower May Creek Yes 1 Bioassessment, Temperature, Bacteria 145836 Highbury Park Johns Creek Yes 1 Temperature, Bacteria, Dissolved Oxygen 145851 Young Addition Honey Creek No 0 145864 Ridgeview Estates May Creek Yes 1 Temperature 145869 Young Addition Honey Creek No 0 146790 Lund Short Plat Thunder Hills Creek No 0 166609 Sunset Blvd/Duvall Ave NE Int Honey Creek Not Scored Not Scored Currently meets City standards 167768 Orchard Park Panther Creek Yes 1 Bioassessment 168953 Village On Union Cedar Main Urban Not Scored Not Scored pH, Temperature, Dissolved Oxygen. Current Infiltration System - Not Scored 200040 Kelsey Lane Panther Creek Yes 1 Bioassessment 200041 Kelsey Lane Panther Creek Yes 1 Bioassessment 200049 Nantucket Short Plat South Kennydale Yes 1 Temperature, Bacteria 200096 Parkwood South DIV III Thunder Hills Creek No 0 Drainage Basin Size This criterion evaluates the size of the drainage basin, which is the portion of land drained by a river and its tributaries. A larger drainage basin would benefit more from the water quality improvement projects. Each site was evaluated using the following rating system: - A score of 1 was given to sites where the drainage basin was equal to or larger than 5 acres - A score of 0.5 was given to sites where the drainage basin was larger than 1 acre and less than 5 acres - A score of 0 was given to sites where the drainage basin was equal to or less than 1 acre. - For locations where the sites’ current water quality treatment meet City standards, or no feasible recommended option was developed, no score was assigned. See Comments for additional information. Table 6 presents the scores for the drainage basin size. Page 13 Table 6. Drainage Basin Size Score Site ID Development Project Name Receiving Water Body Drainage Basin Size (Acres) Score 111332 Summerwind DIV I II III Greenes Creek 20.2 1 111342 Winsper (liberty view I & II) Panther Creek 1.2 0.5 111354 Springbrook terrace Upper Springbrook Creek 5.2 1 111361 Hidden cedars DIV II Soos Creek Main 5.2 1 111369 Panther meadow Panther Creek 2.9 0.5 111391 Dennys restaurant Lake Washington – East 20.2 1 111393 Castlewood ranchettes Maplewood Creek 6.0 1 111394 Castlewood ranchettes Maplewood Creek 13.2 1 111408 Bergsma short plat Upper Springbrook Creek 3.1 0.5 111421 Ripley ln storm improvement pr Lake Washington – East 401.6 Not Scored 111422 Renton village interceptor Thunder Hills Creek 736.4 Not Scored 117894 Swan meadows I Johns Creek 1.7 0.5 117900 Meadow Av N & N 24th St South Kennydale 2.7 0.5 117902 Tiffany park DIV 4 Cedar Main Urban 10.2 1 117912 Armstrong And Sandelius Soos Creek Main 2.2 0.5 117915 Knudson Soos Creek Main 0.2 0 117916 Parkwood South DIV I Thunder Hills Creek 5.5 1 117917 Windsor Heights Panther Creek 0.3 0 117918 Benson Woods Panther Creek 1.8 0.5 117921 Swan Meadows II Johns Creek 0.8 0 117929 Bob Burke Upper Springbrook Creek 2.1 0.5 117931 Benson Glen Panther Creek 1.7 0.5 117936 Fernwood East Maplewood Creek 9.4 1 117938 Chinquapin Ridge Panther Creek 0.6 Not Scored 117940 Valley Vue Estates Panther Creek 1.0 Not Scored 117941 Weatherwood II Lower May Creek 12.0 1 117945 Hidden Cedars DIV II Soos Creek Main 1.4 0.5 117947 Benson Glen Panther Creek 4.6 0.5 117952 Chinquapin Ridge Panther Creek 2.2 0.5 145336 Petett Meadows Short Plat Honey Creek 1.5 0.5 145398 Davis Av S One Valley Place Upper Springbrook Creek 11.3 1 145407 Victoria Hills Rolling Hills Creek 44.6 1 145785 Elizabeth Place Johns Creek 0.9 0 145824 Ruddells 2nd Addition Johns Creek 3.2 0.5 145827 Parkwood Thunder Hills Creek 7.5 1 145832 South Knoll Water Extension South Renton 8.4 1 145834 Pollos Estates Lower May Creek 2.2 0.5 Page 14 Site ID Development Project Name Receiving Water Body Drainage Basin Size (Acres) Score 145836 Highbury Park Johns Creek 14.2 1 145851 Young Addition Honey Creek 1.1 0.5 145864 Ridgeview Estates May Creek 6.8 1 145869 Young Addition Honey Creek 1.1 0.5 146790 Lund Short Plat Thunder Hills Creek 0.5 0 166609 Sunset Blvd/Duvall Ave NE Int Honey Creek 0.3 Not Scored 167768 Orchard Park Panther Creek 4.4 0.5 168953 Village On Union Cedar Main Urban 16.5 Not Scored 200040 Kelsey Lane Panther Creek 2.0 0.5 200041 Kelsey Lane Panther Creek 0.2 0 200049 Nantucket Short Plat South Kennydale 5.4 1 200096 Parkwood South DIV III Thunder Hills Creek 1.3 0.5 Drainage Basin prioritization under the City’s Stormwater Management Action Plan The City holds a National Pollutant Discharge Elimination System Western Washington Phase II municipal stormwater permit (NPDES Permit) from the Washington Department of Ecology (Ecology). The permit was renewed and became effective on August 1, 2019, and it requires each permittee to develop a Stormwater Management Action Plan (SMAP) for a high priority watershed. A SMAP outlines strategies and projects to improve watershed conditions. In support of the SMAP, the City is in the process of an assessment and prioritization of six of Renton’s seven drainage basins and completed a Preliminary Receiving Waters Assessment and Stormwater Management Memorandum in October 2020. This criterion evaluates the influence of stormwater management of the existing conditions on receiving waters as described in the October 2020 memorandum. The memorandum determined if the receiving water body had a high, medium or low influence on water quality in the receiving body of water and a high, medium or low influence on the receiving water hydrology. Each retrofit site was evaluated using the following rating system: A score of 1 was given to sites where the stormwater management influence (SMI) on hydrology was high, and the SMI on water quality was medium (note, medium was the highest score given for water quality). This would apply to BMPs located in the Black River, West Lake Washington, and East Lake Washington drainage basins. A score of 0.5 was given to sites where the SMI on hydrology was high and the SMI on water quality was low. This would apply to BMPs located in the May Creek and Soos Creek drainage basins. A score of 0.2 was given to sites where SMI on hydrology was low (note, no sites were rated medium) and the SMI on water quality was also low. This would apply to sites located in the Lower Cedar River drainage basin. Page 15 A score of 0 was given to sites that were located in the Duwamish River basin. The Duwamish River basin does not meet the size criteria for further assessment of receiving waters evaluation. For locations where the sites’ current water quality treatment meet City standards, or no feasible recommended option was developed, no score was assigned. See Comments for additional information. This scoring criteria may be further refined once the next steps of the NPDES SMAP requirements are complete. The next steps would be a more detailed study of the influence of the basins on the receiving waters following all of the steps in the SMAP guidance, and a ranking system will be completed to prioritize the basins. Table 7 presents the scores for the Drainage Basin Prioritization. Table 7. Drainage Basin Prioritization Score Site ID Development Project Name Receiving Water Body Drainage Basin Name Score 111332 Summerwind DIV I II III Greenes Creek May Creek 0.5 111342 Winsper (liberty view I & II) Panther Creek Black River 1 111354 Springbrook terrace Upper Springbrook Creek Black River 1 111361 Hidden cedars DIV II Soos Creek Main Soos Creek 0.5 111369 Panther meadow Panther Creek Black River 1 111391 Dennys restaurant Lake Washington – East Lake Washington – East 1 111393 Castlewood ranchettes Maplewood Creek Soos Creek 0.5 111394 Castlewood ranchettes Maplewood Creek Soos Creek 0.5 111408 Bergsma short plat Upper Springbrook Creek Black River 1 111421 Ripley ln storm improvement pr Lake Washington – East Lake Washington – East Not Scored 111422 Renton village interceptor Thunder Hills Creek Black River Not Scored 117894 Swan meadows I Johns Creek Lake Washington – East 1 117900 Meadow Av N & N 24th St South Kennydale Lake Washington – East 1 117902 Tiffany park DIV 4 Cedar Main Urban Lower Cedar River 0.2 117912 Armstrong And Sandelius Soos Creek Main Soos Creek 0.5 117915 Knudson Soos Creek Main Soos Creek 0.5 117916 Parkwood South DIV I Thunder Hills Creek Black River 1 117917 Windsor Heights Panther Creek Black River 1 117918 Benson Woods Panther Creek Black River 1 117921 Swan Meadows II Johns Creek Lake Washington – East 1 117929 Bob Burke Upper Springbrook Creek Black River 1 117931 Benson Glen Panther Creek Black River 1 117936 Fernwood East Maplewood Creek Lower Cedar River 0.2 117938 Chinquapin Ridge Panther Creek Black River Not Scored 117940 Valley Vue Estates Panther Creek Black River Not Scored 117941 Weatherwood II Lower May Creek May Creek 0.5 117945 Hidden Cedars DIV II Soos Creek Main Soos Creek 0.5 117947 Benson Glen Panther Creek Black River 1 Page 16 Site ID Development Project Name Receiving Water Body Drainage Basin Name Score 117952 Chinquapin Ridge Panther Creek Black River 1 145336 Petett Meadows Short Plat Honey Creek May Creek 0.5 145398 Davis Av S One Valley Place Upper Springbrook Creek Black River 1 145407 Victoria Hills Rolling Hills Creek Black River 1 145785 Elizabeth Place Johns Creek Lake Washington – East 1 145824 Ruddells 2nd Addition Johns Creek Lake Washington – East 1 145827 Parkwood Thunder Hills Creek Black River 1 145832 South Knoll Water Extension South Renton Black River 1 145834 Pollos Estates Lower May Creek May Creek 0.5 145836 Highbury Park Johns Creek Lake Washington – East 1 145851 Young Addition Honey Creek May Creek 0.5 145864 Ridgeview Estates May Creek May Creek 0.5 145869 Young Addition Honey Creek May Creek 0.5 146790 Lund Short Plat Thunder Hills Creek Black River 1 166609 Sunset Blvd/Duvall Ave NE Int Honey Creek May Creek Not Scored 167768 Orchard Park Panther Creek Black River 1 168953 Village On Union Cedar Main Urban Lower Cedar River Not Scored 200040 Kelsey Lane Panther Creek Black River 1 200041 Kelsey Lane Panther Creek Black River 1 200049 Nantucket Short Plat South Kennydale Lake Washington – East 1 200096 Parkwood South DIV III Thunder Hills Creek Black River 1 Infiltration potential (type of BMP and hydrology function) This criterion evaluates the infiltration potential and hydrology function of each BMP. This criterion rates sites that have soils/site characteristics favorable to infiltration and where the preliminary BMP type includes a hydrologic infiltration characteristic. The types of BMP retrofits that incorporate a hydrologic infiltrative function include bioswales/CABS, media filter drains, and bioretention cells. The BMP retrofits that do not include a hydrologic infiltrative function include wetpond/wetvault, Stormfilter, and sandfilter vault. It is noted that the City’s stormwater manual includes requirements limiting stormwater infiltration BMPs. Infiltration must be outside critical areas and applicable buffers. See Task 4 memorandum for more information on the infiltration requirements. Each site was evaluated using the following rating system: A score of 1 was given to sites where there was a likely potential for infiltration and the preliminary recommended BMP included the potential for a hydrologic/infiltrative type function. A score of 0.3 was given to sites where there is either (1) limited potential for infiltration and the preliminary recommended BMP included the potential for a hydrologic/infiltrative function; or (2) where there is likely potential for infiltration and the preliminary recommended water quality treatment BMP did not include a hydrologic/infiltrative function, but that it would be possible to add Page 17 other enhancements to the site to encourage infiltration. An example of the latter case is where the preliminary recommended BMP retrofit is a stormfilter vault, but the site offers other infiltration potential for a smaller catchment or localized area. A score of 0 was given to sites with a low potential for infiltration and the preliminary recommended BMP did not included the potential for a hydrologic/infiltrative type function hydrologic function. For locations where the sites’ current water quality treatment meet City standards, or no feasible recommended option was developed, no score was assigned. Table 8 presents the scores for the infiltration potential. Table 8. Infiltration Potential Score Site ID Development Project Name Receiving Water Body BMP Retrofit with Infiltration Potential Score 111332 Summerwind DIV I II III Greenes Creek Low 0 111342 Winsper (liberty view I & II) Panther Creek Low 0 111354 Springbrook terrace Upper Springbrook Creek Low 0 111361 Hidden cedars DIV II Soos Creek Main Low 0 111369 Panther meadow Panther Creek Low 0 111391 Dennys restaurant Lake Washington – East Low 0 111393 Castlewood ranchettes Maplewood Creek Likely 1 111394 Castlewood ranchettes Maplewood Creek Low 0 111408 Bergsma short plat Upper Springbrook Creek Low 0 111421 Ripley ln storm improvement pr Lake Washington – East Not Scored Not Scored 111422 Renton village interceptor Thunder Hills Creek Not Scored Not Scored 117894 Swan meadows I Johns Creek Low 0 117900 Meadow Av N & N 24th St South Kennydale Low 0 117902 Tiffany park DIV 4 Cedar Main Urban Low 0 117912 Armstrong And Sandelius Soos Creek Main low 0 117915 Knudson Soos Creek Main Low 0 117916 Parkwood South DIV I Thunder Hills Creek Low 0 117917 Windsor Heights Panther Creek Low 0 117918 Benson Woods Panther Creek Low 0 117921 Swan Meadows II Johns Creek Low 0 117929 Bob Burke Upper Springbrook Creek Limited 0.3 117931 Benson Glen Panther Creek likely 1 117936 Fernwood East Maplewood Creek Low 0 117938 Chinquapin Ridge Panther Creek Not Scored Not Scored 117940 Valley Vue Estates Panther Creek Not Scored Not Scored 117941 Weatherwood II Lower May Creek Low 0 117945 Hidden Cedars DIV II Soos Creek Main Low 0 117947 Benson Glen Panther Creek Low 0 Page 18 Site ID Development Project Name Receiving Water Body BMP Retrofit with Infiltration Potential Score 117952 Chinquapin Ridge Panther Creek Low 0 145336 Petett Meadows Short Plat Honey Creek Low 0 145398 Davis Av S One Valley Place Upper Springbrook Creek Low 0 145407 Victoria Hills Rolling Hills Creek Low 0 145785 Elizabeth Place Johns Creek Low 0 145824 Ruddells 2nd Addition Johns Creek Low 0 145827 Parkwood Thunder Hills Creek limited 0.3 145832 South Knoll Water Extension South Renton Low 0 145834 Pollos Estates Lower May Creek Low 0 145836 Highbury Park Johns Creek Low 0 145851 Young Addition Honey Creek Low 0 145864 Ridgeview Estates May Creek Low 0 145869 Young Addition Honey Creek Low 0 146790 Lund Short Plat Thunder Hills Creek Low 0 166609 Sunset Blvd/Duvall Ave NE Int Honey Creek Not Scored Not Scored 167768 Orchard Park Panther Creek Low 0 168953 Village On Union Cedar Main Urban Not Scored Not Scored 200040 Kelsey Lane Panther Creek limited 0.3 200041 Kelsey Lane Panther Creek Low 0 200049 Nantucket Short Plat South Kennydale Low 0 200096 Parkwood South DIV III Thunder Hills Creek Low 0 Long term operation and maintenance costs This criterion considers the relative long-term operation and maintenance costs needed for the BMPs. The annual maintenance cost for typical stormwater facilities presented in the Cost Analysis Report (Herrera, 2013) was used to assess the relative cost estimates for the maintenance of the different BMP types. This report provides both construction and maintenance cost for a wide variety of project sites and conditions. Each site was evaluated using the following rating system: - A score of 1 was given to BMPs where there is a low potential for operation and maintenance costs. The BMPs in this category were bioswales, wetpond/combined detention pond wetponds, bioretention, and wetvault. - A score of 0 was given to sites with higher operational and maintenance cost. The BMPs in this category include media filter and stormfilter systems. - For locations where the sites’ current water quality treatment meet City standards, or no feasible recommended option was developed, no score was given. Table 9 presents the scores for the long-term operation and maintenance costs. Page 19 Table 9. Long-term Operation and Maintenance Costs Score Site ID Development Project Name Receiving Water Body BMP Retrofit Type Score 111332 Summerwind DIV I II III Greenes Creek Stormfilter 0 111342 Winsper (liberty view I & II) Panther Creek Stormfilter 0 111354 Springbrook terrace Upper Springbrook Creek Wetpond 1 111361 Hidden cedars DIV II Soos Creek Main Wetpond 1 111369 Panther meadow Panther Creek Wetpond 1 111391 Dennys restaurant Lake Washington - East Stormfilter 0 111393 Castlewood ranchettes Maplewood Creek Stormfilter 0 111394 Castlewood ranchettes Maplewood Creek Stormfilter 0 111408 Bergsma short plat Upper Springbrook Creek Bioswale 1 111421 Ripley ln storm improvement pr Lake Washington - East None selected 0 111422 Renton village interceptor Thunder Hills Creek Not Scored Not Scored 117894 Swan meadows I Johns Creek Stormfilter 0 117900 Meadow Av N & N 24th St South Kennydale Stormfilter 0 117902 Tiffany park DIV 4 Cedar Main Urban Stormfilter 0 117912 Armstrong And Sandelius Soos Creek Main Wetvault 1 117915 Knudson Soos Creek Main Stormfilter 0 117916 Parkwood South DIV I Thunder Hills Creek Stormfilter 0 117917 Windsor Heights Panther Creek Wetvault 1 117918 Benson Woods Panther Creek Wetvault 1 117921 Swan Meadows II Johns Creek Stormfilter 0 117929 Bob Burke Upper Springbrook Creek Wetvault Not Scored 117931 Benson Glen Panther Creek Bioretention 1 117936 Fernwood East Maplewood Creek Stormfilter 0 117938 Chinquapin Ridge Panther Creek Not Scored Not Scored 117940 Valley Vue Estates Panther Creek Not Scored Not Scored 117941 Weatherwood II Lower May Creek Stormfilter 0 117945 Hidden Cedars DIV II Soos Creek Main Stormfilter 0 117947 Benson Glen Panther Creek Stormfilter 0 117952 Chinquapin Ridge Panther Creek Stormfilter 0 145336 Petett Meadows Short Plat Honey Creek Wetpond 1 145398 Davis Av S One Valley Place Upper Springbrook Creek Stormfilter 0 145407 Victoria Hills Rolling Hills Creek pond retrofit 1 145785 Elizabeth Place Johns Creek Stormfilter 0 145824 Ruddells 2nd Addition Johns Creek Wetvault 1 145827 Parkwood Thunder Hills Creek bioswale 1 145832 South Knoll Water Extension South Renton Stormfilter 0 145834 Pollos Estates Lower May Creek Stormfilter 0 145836 Highbury Park Johns Creek Stormfilter 0 Page 20 Site ID Development Project Name Receiving Water Body BMP Retrofit Type Score 145851 Young Addition Honey Creek Stormfilter 0 145864 Ridgeview Estates May Creek Stormfilter 0 145869 Young Addition Honey Creek Stormfilter 0 146790 Lund Short Plat Thunder Hills Creek Stormfilter 0 166609 Sunset Blvd/Duvall Ave NE Int Honey Creek Not Scored Not Scored 167768 Orchard Park Panther Creek Stormfilter 0 168953 Village On Union Cedar Main Urban Not Scored Not Scored 200040 Kelsey Lane Panther Creek Bioswale 1 200041 Kelsey Lane Panther Creek Stormfilter 0 200049 Nantucket Short Plat South Kennydale Stormfilter 0 200096 Parkwood South DIV III Thunder Hills Creek Stormfilter 0 Other benefits (social, economic and environmental) This criterion completes a qualitative assessment of the potential for additional social, economic and environmental benefits of the BMPs. Each site was evaluated using the following rating system: A score of 1 was given to BMPs where there would be a high potential of the benefits to the aesthetics, increase of wildlife habitat and potential improvements to adjacent public and private lands, including potential reduction of flooding to adjacent homes and businesses, and creating public education opportunities. A score of 0.5 was given to sites where there would be a moderate potential of the benefits one or more of the following: aesthetics, increase of wildlife habitat and potential improvements to adjacent public and private lands, including potential reduction of flooding to adjacent homes and businesses; creating public education opportunities. A score of 0 was given to sites with little potential of the benefits to the aesthetics, increase of wildlife habitat and potential improvements to adjacent public and private lands, including potential reduction of flooding to adjacent homes and businesses, and creating public education opportunities. An example is an underground vault system in an isolated location away from the community. For locations where the sites’ current water quality treatment meet City standards, or no feasible recommended option was developed, no score was assigned. See Comments for additional information. Table 10 presents the scores for the social, economic and environmental benefits. Page 21 Table 10. Other Benefits Score Site ID Development Project Name Receiving Water Body Type of Benefit Score Comments 111332 Summerwind DIV I II III Greenes Creek Little Other Benefits 0 111342 Winsper (liberty view I & II) Panther Creek Moderate 0.5 Potential for Educational opportunity near trail 111354 Springbrook terrace Upper Springbrook Creek Moderate 0.5 Env. Enhancement if create wetland 111361 Hidden cedars DIV II Soos Creek Main Moderate 0.5 Env. Enhancement if create wetland 111369 Panther meadow Panther Creek Moderate 0.5 Env. Enhancement if create wetland 111391 Dennys restaurant Lake Washington - East Moderate 0.5 Site owned by WSDOT. May be opportunity for joint project, but feasibility is likely low. Current site is abandoned Denny's 111393 Castlewood ranchettes Maplewood Creek Moderate 0.5 111394 Castlewood ranchettes Maplewood Creek Moderate 0.5 Would help protect existing wetland 111408 Bergsma short plat Upper Springbrook Creek Little Other Benefits 0 111421 Ripley ln storm improvement pr Lake Washington - East Little Other Benefits Not Scored 111422 Renton village interceptor Thunder Hills Creek Not Scored Not Scored 117894 Swan meadows I Johns Creek Moderate 0.5 117900 Meadow Av N & N 24th St South Kennydale Moderate 0.5 117902 Tiffany park DIV 4 Cedar Main Urban Moderate 0.5 117912 Armstrong And Sandelius Soos Creek Main Little Other Benefits 0 117915 Knudson Soos Creek Main Little Other Benefits 0 117916 Parkwood South DIV I Thunder Hills Creek Moderate 0.5 117917 Windsor Heights Panther Creek Moderate 0.5 117918 Benson Woods Panther Creek Little Other Benefits 0 Dead end street 117921 Swan Meadows II Johns Creek Moderate 0.5 117929 Bob Burke Upper Springbrook Creek Little Other Benefits 0 Dead end street 117931 Benson Glen Panther Creek Moderate 0.5 117936 Fernwood East Maplewood Creek Little Other Benefits 0 117938 Chinquapin Ridge Panther Creek Not Scored Not Scored 117940 Valley Vue Estates Panther Creek Not Scored Not Scored 117941 Weatherwood II Lower May Creek Moderate 0.5 117945 Hidden Cedars DIV II Soos Creek Main Moderate 0.5 117947 Benson Glen Panther Creek Moderate 0.5 117952 Chinquapin Ridge Panther Creek Moderate 0.5 145336 Petett Meadows Short Plat Honey Creek Moderate 0.5 145398 Davis Av S One Valley Place Upper Springbrook Creek Little Other Benefits 0 145407 Victoria Hills Rolling Hills Creek Moderate 0.5 Page 22 Site ID Development Project Name Receiving Water Body Type of Benefit Score Comments 145785 Elizabeth Place Johns Creek Moderate 0.5 145824 Ruddells 2nd Addition Johns Creek Moderate 0 145827 Parkwood Thunder Hills Creek Little Other Benefits 0 145832 South Knoll Water Extension South Renton Moderate 0.5 145834 Pollos Estates Lower May Creek Moderate 0.5 145836 Highbury Park Johns Creek Moderate 0.5 145851 Young Addition Honey Creek Moderate 0.5 145864 Ridgeview Estates May Creek Moderate 0.5 145869 Young Addition Honey Creek Moderate 0.5 146790 Lund Short Plat Thunder Hills Creek Moderate 0.5 166609 Sunset Blvd/Duvall Ave NE Int Honey Creek Not Scored Not Scored 167768 Orchard Park Panther Creek Moderate 0.5 168953 Village On Union Cedar Main Urban Not Scored Not Scored 200040 Kelsey Lane Panther Creek Moderate 0.5 200041 Kelsey Lane Panther Creek Moderate 0.5 200049 Nantucket Short Plat South Kennydale Moderate 0.5 200096 Parkwood South DIV III Thunder Hills Creek Moderate 0.5 4. BMP RETROFIT PRIORITIZING The conclusion of this task is providing results of the prioritization process. Score for all eight criteria are totaled for each retrofit site. This creates a ranked list of the retrofits from highest overall score to lowest overall score. No rank was given for locations where the sites’ current water quality treatment meet City standards, or no feasible recommended option was developed. This list, presented in Table 11, allows the City to make more informed decisions on the order of BMP retrofits, focusing on the highest benefit of water quality improvement and most effective opportunities. Table 11. Retrofit Site Prioritizing Results Priority Rank Site ID Development Project Name Receiving Water Body BMP Retrofit type Total Score 1 200040 Kelsey Lane Panther Creek Bioswale 8.3 2 117931 Benson Glen Panther Creek Bioretention 8 3 111354 Springbrook Terrace Upper Springbrook Creek Wetpond 7.5 4 117918 Benson Woods Panther Creek Wetvault 7.5 5 145832 South Knoll Water Extension South Renton Stormfilter 7.5 6 200049 Nantucket Short Plat South Kennydale Stormfilter 7.5 7 111393 Castlewood Ranchettes Maplewood Creek Stormfilter 7 8 145864 Ridgeview Estates May Creek Stormfilter 7 9 167768 Orchard Park Panther Creek Stormfilter 7 Page 23 Priority Rank Site ID Development Project Name Receiving Water Body BMP Retrofit type Total Score 10 117929 Bob Burke Upper Springbrook Creek Wetvault 6.8 11 117916 Parkwood South DIV I Thunder Hills Creek Stormfilter 6.5 12 117921 Swan Meadows II Johns Creek Stormfilter 6.5 13 145407 Victoria Hills Rolling Hills Creek Wetpond 6.5 14 145785 Elizabeth Place Johns Creek Stormfilter 6.5 15 145824 Ruddells 2nd Addition Johns Creek Wetvault 6.5 16 145834 Pollos Estates Lower May Creek Stormfilter 6.5 17 145836 Highbury Park Johns Creek Stormfilter 6.5 18 200041 Kelsey Lane Panther Creek Stormfilter 6.5 19 111361 Hidden Cedars DIV II Soos Creek Main Wetpond 6 20 111369 Panther Meadow Panther Creek Wetpond 6 21 111394 Castlewood Ranchettes Maplewood Creek Stormfilter 6 22 117894 Swan Meadows I Johns Creek Stormfilter 6 23 117900 Meadow Av N & N 24th St South Kennydale Stormfilter 6 24 117941 Weatherwood II Lower May Creek Stormfilter 6 25 200096 Parkwood South DIV III Thunder Hills Creek Stormfilter 6 26 111332 Summerwind DIV I II III Greenes Creek Stormfilter 5.5 27 111391 Dennys Restaurant Lake Washington - East Stormfilter 5.5 28 117917 Windsor Heights Panther Creek Wetvault 5.5 29 117945 Hidden Cedars DIV II Soos Creek Main Stormfilter 5.5 30 145336 Petett Meadows Short Plat Honey Creek Wetpond 5.5 31 145851 Young Addition Honey Creek Stormfilter 5.5 32 145869 Young Addition Honey Creek Stormfilter 5.5 33 146790 Lund Short Plat Thunder Hills Creek Stormfilter 5.5 34 145827 Parkwood Thunder Hills Creek bioswale 5.3 35 111342 Winsper (Liberty View I & II) Panther Creek Stormfilter 5 36 117912 Armstrong And Sandelius Soos Creek Main Wetvault 5 37 117947 Benson Glen Panther Creek Stormfilter 5 38 117952 Chinquapin Ridge Panther Creek Stormfilter 5 39 117902 Tiffany Park DIV 4 Cedar Main Urban Stormfilter 4.7 40 111408 Bergsma Short Plat Upper Springbrook Creek Bioswale 4.5 41 117915 Knudson Soos Creek Main Stormfilter 4.5 42 117936 Fernwood East Maplewood Creek Stormfilter 3.2 43 145398 Davis Av S One Valley Place Upper Springbrook Creek Stormfilter 3 Not Ranked 111421 Ripley Ln Storm Improvement Pr Lake Washington - East Not Feasible Not Scored Not Ranked 111422 Renton Village Interceptor Thunder Hills Creek Not Feasible Not Scored Not Ranked 117938 Chinquapin Ridge Panther Creek Currently meets City standards Not Scored Not Ranked 117940 Valley Vue Estates Panther Creek Currently has 200' bioswale. No improvements recommended Not Scored Page 24 Priority Rank Site ID Development Project Name Receiving Water Body BMP Retrofit type Total Score Not Ranked 166609 Sunset Blvd/Duvall Ave NE Int Honey Creek Currently meets City standards Not Scored Not Ranked 168953 Village On Union Cedar Main Urban Current Infiltration System Not Scored Bold indicates Sites Selected as Top three In the next future Task (Task 6) for this project, detailed concept design plan sketches of the improvements and cost estimates will be developed for three of the highest scored BMP Retrofits. Due to the qualitative means of selecting “scoring weights” to criteria and “numeric scores”, WSP developed sketch mark-ups of the top 10 BMP Retrofits sites to show the concept location and approximate size of the BMP retrofit. These mark-ups, shown in red, were added to the Task 4 Memorandum BMP Evaluation sketches (i.e., the Task 4 Memorandum Appendix D drawings) and included in Attachment A of this Task 5 Memorandum. Following a review of the scoring results and review of the marked-up sketches in Attachment A, the City selected the following three sites for concept development: 200040 Kelsey Lane 117931 Benson Glen 145832 South Knoll Water Extension The first two were the highest storing sites. Site number 1458932 (South Knoll Water Extension) had the third highest score which was tied with four other sites. Of the four tied sites, the South Knoll Water Extension would treat the largest basin area and appear very feasible and so was selected over the other three sites. Page 25 ATTACHMENT A CONCEPT LOCATIONS OF TOP 10 BMP RETROFIT SITES 111354: SPRINGBROOK TERRACE BMP EVALUATION EXISTING DETENTION SYSTEM TYPE Pond AREA OF TRIBUTARY BASIN (ACRES) 5.2 TRIBUTARY BASIN IMPERVIOUS PERCENTAGE (%) 51% WATER QUALITY VOLUME (ACRE-FT) 0.439 ONLINE WQ FLOW RATE (CFS) 0.97 OFFLINE WQ FLOW RATE (CFS) 0.51 BMP OPTION DIMENSIONS SITE NOTES & OBSERVATION WET POND 60’X130’ Opportunity for wet pond retrofit. May require expansion. WET VAULTs Vault size – 20’X110’ Insufficient space available (narrow road and 10’ easements). Also, deep facility due to steep slopes. SANDFILTER VAULT Presettling vault – 20’X60’ Vault size – (1) 70’X140’ Insufficient space. MEDIA FILTER VAULT, 18” CARTRIDGES WITH ZPG MEDIA(STORMFILTER VAULTS) 58 cartridges, ~ (1) 8’X24’ vaults Sufficient space and head drop within roadway of site. BIOSWALE 16’X300’ Insufficient space (10’ easement width). FILTER STRIP 90’X130’ Insufficient space available. BIORETENTION 11’X700’ Insufficient space available. MEDIA FILTER DRAIN 14’X1850’ Insufficient space available. MISCALLANEOUS NOTES: - Site is within 50’ of 15% slope and geotech report likely required to assess landslide hazard. - Modification of pond to add wet pond storage is likely best option. It would not meet City of Renton standards, but capacity could be increase by incorporating short walls on portion of existing side slopes. Add Wetpond Storage to Existing Detention Pond 111354: SPRINGBROOK TERRACE AS-BUILT DRAWING SUMMARY PLAN VIEW PROFILE DETAIL DATE OF AS-BUILT DRAWINGS 09/30/83 TIR PROVIDED No ADDRESS NA 111393: CASTLEWOOD RANCHETTES BMP EVALUATION EXISTING DETENTION SYSTEM TYPE Pond AREA OF TRIBUTARY BASIN (ACRES) 6.0 TRIBUTARY BASIN IMPERVIOUS PERCENT (%) 32% WATER QUALITY VOLUME (ACRE-FT) 0.394 ONLINE WQ FLOW RATE (CFS) 1.01 OFFLINE WQ FLOW RATE (CFS) 0.51 BMP OPTION DIMENSIONS SITE NOTES & OBSERVATION WET POND 55’X 130’ Insufficient space. (1) WET VAULT Vault Size - 30’X150’ See note 1 above SANDFILTER VAULT Presettling vault-15’X45’ Vault Size- (1) 70’X140’ See note 1 above PROPRIETARY MEDIA FILTER VAULT, 18” CARTRIDGES WITH ZPG MEDIA(STORMFILTER VAULTS) 60 CARTRIDGES, ~ (1) 8’X24’ Preferred option due to smaller footprint and less head drop. BIOSWALE 19’X250’ Partial bioswale potential along unimproved NE 8th ROW FILTER STRIP 90’X140’ See note 1 above BIORETENTION 11’X645’ See note 1 above MEDIA FILTER DRAINS 30’X390’ See note 1 above MISCELLENEOUS NOTES: - There is unimproved 30’ width ROW along NE 8th Street from CB#B3 to control structure. A bioswale could be constructed along this corridor. - Pond is a “back- up” type which provide no water quality benefit. Can consider making a flow-through type pond to improve water quality treatment. - Because the bioswale would not meet City of Renton standards, the preferred approach is a Stormwater filter within the unimproved ROW and converting pond to flow-through type. Stormfilter Vault (need to confirm pipe elevation) Make "flow-thru" type pond 111393: CASTLEWOOD RANCHETTES AS-BUILT DRAWING SUMMARY PLAN VIEW PROFILE DETAIL DATE OF AS-BUILT DRAWINGS 05/01/81 TIR PROVIDED No ADDRESS 803 139th Ave SE, Renton, 98059 117918: BENSON WOODS BMP EVALUATION EXISTING DETENTION SYSTEM TYPE Tank AREA OF TRIBUTARY BASIN (ACRES)1.8 TRIBUTARY BASIN IMPERVIOUS PERCENTAGE (%)30% WATER QUALITY VOLUME (ACRE-FT)0.124 ONLINE WQ FLOW RATE (CFS)0.29 OFFLINE WQ FLOW RATE (CFS)0.15 BMP OPTION DIMENSIONS SITE NOTES & OBSERVATION WET POND 40’X70’Insufficient space available. WET VAULT Vault size – 12’X60’Sufficient space available. SANDFILTER VAULT Presettling vault –10’X30’ Vault size – (1) 40’X80’Insufficient head drop. MEDIA FILTER VAULT, 18” CARTRIDGES WITH ZPG MEDIA(STORMFILTER VAULTS) 17 cartridges, ~ (1) 8’X11’ vault Probably insufficient head drop. BIOSWALE 11’X210’Existing system too deep. FILTER STRIP 20’X190’Existing system too deep. BIORETENTION 11’X200’Insufficient space available. MEDIA FILTER DRAIN 14’X560’Insufficient space available. Existing system is too deep. MISCALLANEOUS NOTES: -Existing detention outlets to a wetland constructed as a part of the development. It appears that it was intended to replace a wetland that was filled. It is assumed that this wetland would be not considered a stormwater wetland BMP. If it was, there are opportunities to retrofit the wetland to improve water quality. For example, could redirect inflow to other end of wetland away from wetland outlet. -Wet vault appears to be the best option. Wetvault 117918: BENSON WOODS AS-BUILT DRAWING SUMMARY PLAN VIEW PROFILE DETAIL DATE OF AS-BUILT DRAWINGS 09/10/89 TIR PROVIDED No ADDRESS 18949 111th Pl SE, Renton, 98055 117929: BOB BURKE BMP EVALUATION EXISTING DETENTION SYSTEM TYPE Tank AREA OF TRIBUTARY BASIN (ACRES) 2.1 TRIBUTARY BASIN IMPERVIOUS PERCENTAGE (%) 34% WATER QUALITY VOLUME (ACRE-FT) 0.142 ONLINE WQ FLOW RATE (CFS) 0.35 OFFLINE WQ FLOW RATE (CFS) 0.18 BMP OPTION DIMENSIONS SITE NOTES & OBSERVATION WET POND 40’X80’ The existing 48” CMP was constructed within a 50’ easement originally slated for a pond, where the wet pond could be located WET VAULTs Vault size – 13’X60’ Sufficient space adjacent to existing 48” CMP, but deep and less preferred SANDFILTER VAULT Presettling vault – 10’X30’ Vault size – (1) 40’X80’ Probably insufficient head drop available. MEDIA FILTER VAULT, 18” CARTRIDGES WITH ZPG MEDIA(STORMFILTER VAULTS) 21 cartridges, ~ (1) 8’X11’ vault Probably insufficient head drop available. BIOSWALE 12’X210’ Could update existing bioswale to meet City of Renton standards. FILTER STRIP 30’X160’ Existing storm inverts too low. BIORETENTION 11’X230’ Infiltration not allowed. MEDIA FILTER DRAIN 14’X670’ Insufficient space available. MISCALLANEOUS NOTES: - According to City GIS, there is an existing bioswale. It is likely not sized properly and could be easily upgraded. This is the preferred option. Wetvault (approx. 9-10 feet deep)* *Recommend wetvault to allow property owners to maintain use of property 117929: BOB BURKE AS-BUILT DRAWING SUMMARY PLAN VIEW PROFILE DETAIL DATE OF AS-BUILT DRAWINGS 07/02/91 TIR PROVIDED No ADDRESS 19600 92nd Ave S, Renton, 98055 117931: BENSON GLEN BMP EVALUATION EXISTING DETENTION SYSTEM TYPE Tank AREA OF TRIBUTARY BASIN (ACRES)1.7 TRIBUTARY BASIN IMPERVIOUS PERCENTAGE (%)52% WATER QUALITY VOLUME (ACRE-FT)0.157 ONLINE WQ FLOW RATE (CFS)0.31 OFFLINE WQ FLOW RATE (CFS)0.17 BMP OPTION DIMENSIONS SITE NOTES & OBSERVATION WET POND 40’X90’Not feasible due to limited ROW. WET VAULTs Vault size – 13’X70’Sufficient space available, but deep. SANDFILTER VAULT Presettling vault – 10’X30’ Vault size – (x) 40’X80’ Insufficient space and head available. MEDIA FILTER VAULT, 18” CARTRIDGES WITH ZPG MEDIA(STORMFILTER VAULTS) 19 cartridges, ~ (1) 8’X11’ vault Insufficient head drop available. BIOSWALE 11’X210’Not feasible due to limited ROW. FILTER STRIP 20’X190’Insufficient space available. BIORETENTION 11’X260’Insufficient space, but could improve existing bioswale MEDIA FILTER DRAIN 14’X560’Insufficient space available. MISCALLANEOUS NOTES: -The 15% slope area in Appendix A does not apply as this is the existing pond. -Potential to retrofit existing bioswale with bioretention and/or infiltration measures with increased treatment capacity and partially meet treatment standards. This appears to be best. Expand existing bioswale with larger biofiltration swale 117931: BENSON GLEN AS-BUILT DRAWING SUMMARY PLAN VIEW PROFILE DETAIL DATE OF AS-BUILT DRAWINGS 08/21/92 TIR PROVIDED No ADDRESS 10900 SE 170th St, Renton, 98055 145832: SOUTH KNOLL WATER EXTENSION BMP EVALUATION EXISTING DETENTION SYSTEM TYPE Tank AREA OF TRIBUTARY BASIN (ACRES)8.4 TRIBUTARY BASIN IMPERVIOUS PERCENTAGE (%)29% WATER QUALITY VOLUME (ACRE-FT)0.787 ONLINE WQ FLOW RATE (CFS)0.76 OFFLINE WQ FLOW RATE (CFS)0.43 BMP OPTION DIMENSIONS SITE NOTES & OBSERVATION WET POND 70’X180’Insufficient space available. WET VAULTs Vault size – 30’X150’Probably insufficient space. (1) SANDFILTER VAULT Presettling vault – 30’X90’ Vault size – (1) 60’X120’ See note 1 above. PROPRIETARY MEDIA FILTER VAULT, 27” CARTRIDGES WITH ZPG MEDIA(STORMFILTER VAULTS) 30 cartridges, ~ (1) 8’X14’ vaults Sufficient space within SW 3rd (large area available) and available head towards Oakesdale. BIOSWALE 16’X240’See Note 1 above. FILTER STRIP 90’X100’insufficient space available. BIORETENTION 11’X1270’Insufficient space available. MEDIA FILTER DRAIN 14’X1448’Insufficient space available. MISCALLANEOUS NOTES: -Moderate landslide risk and geotechnical approval may be required for vault BMPs. -Stormfilter is proposed at end of Oakesdale on 3rd (where excess ROW available). Outlet pipe can extend southwest on Oakesdale to catch grade. Media Vault (e.g. Stormfilter) 145832: SOUTH KNOLL WATER EXTENSION AS-BUILT DRAWING SUMMARY PLAN VIEW PROFILE DETAIL DATE OF AS-BUILT DRAWINGS 04/01/1985 TIR PROVIDED No ADDRESS 250 Oakesdale Ave SW, Renton, 98057 D145864: RIDGEVIEW ESTATES BMP EVALUATION EXISTING DETENTION SYSTEM TYPE Tank AREA OF TRIBUTARY BASIN (ACRES) 6.8 TRIBUTARY BASIN IMPERVIOUS PERCENTAGE (%) 52% WATER QUALITY VOLUME (ACRE-FT) 0.589 ONLINE WQ FLOW RATE (CFS) 1.22 OFFLINE WQ FLOW RATE (CFS) 0.64 BMP OPTION DIMENSIONS SITE NOTES & OBSERVATION WET POND 60’X160’ Probably insufficient space. WET VAULTs Vault size – (1) 25’X130’ Probably insufficient space. SANDFILTER VAULT Presettling vault – 20’X60’ Vault size – (1) 80’X160’ Probably insufficient space. PROPRIETARY MEDIA FILTER VAULT, 49” CARTRIDGES WITH ZPG MEDIA(STORMFILTER VAULTS) 49 cartridges, ~ (1) 8’X20’ vault Could replace 50 ftof upstream pipe to increase head and obtain easement within driveway west of exist. easement. BIOSWALE 20’X250’ Potential location at ex. storm ditch along Duvall Ave NE. Probably insufficient space and too deep (1). FILTER STRIP 20’X180’ Potential location at ex. storm ditch along Duvall Ave NE. See Note 1 BIORETENTION 9 cells of 2’X21’ Probably insufficient space. MEDIA FILTER DRAIN 14’X2300’ Probably insufficient space. MISCELLANEOUS NOTES: - Groundwater protection area. - Media Filter in Vault is preferred. - Steep slope to north of detetion tank most likely insufficient for BMP use. Roadway to south provides vault options. Media Vault(e.g., StormfilterVault)Media Vault(e.g., StormfilterVault)Two Smaller Media Vaults 145864: RIDGEVIEW ESTATES AS-BUILT DRAWING SUMMARY PLAN VIEW PROFILE DETAIL DATE OF AS-BUILT DRAWINGS 08/11/88 TIR PROVIDED No ADDRESS 2624 Anacortes Ave NE, Renton, 98059 167768: ORCHARD PARK BMP EVALUATION EXISTING DETENTION SYSTEM TYPE Tank AREA OF TRIBUTARY BASIN (ACRES) 4.4 TRIBUTARY BASIN IMPERVIOUS PERCENTAGE (%) 47% WATER QUALITY VOLUME (ACRE-FT) 0.3539 ONLINE WQ FLOW RATE (CFS) 0.77 OFFLINE WQ FLOW RATE (CFS) 0.40 BMP OPTION DIMENSIONS SITE NOTES & OBSERVATION WET POND 53’X123’ Insufficient space available. WET VAULTs Vault size – 20’X100’ Likely insufficent space wihtin road prism considering other utilities and depth(1) SANDFILTER VAULT Presettling vault – 20’X60’ Vault size – (1) 120’X60’ Insufficient space available (2). PROPRIETARY MEDIA FILTER VAULT, 18” CARTRIDGES WITH ZPG MEDIA(STORMFILTER VAULTS) 46 cartridges, ~ (1) 8’X20’ vaults Available head upstream of facility. Could locate in ROW with likely some utility relocations. BIOSWALE 242’X16’ Not a viable option due to restrictive ROW(3) FILTER STRIP 105’X90’ See note 3 above. BIORETENTION 570’X11’ See note 3 above. MEDIA FILTER DRAIN 1470’X14’ See note 3 above. MISCELLENOUS NOTES - The Stormfilter Vault is the preferred WQ BMP on upstream side of the detention pipe due being able to construct it realatively shallow. Some utility relocations likely required. Media Vault(e.g. StormfilterVault) 167768: ORCHARD PARK AS-BUILT DRAWING SUMMARY PLAN VIEW PROFILE DETAIL DATE OF AS-BUILT DRAWINGS 10/10/1991 TIR PROVIDED X ADDRESS 17944 112th Ave SE, Renton, 98055 200040: KELSEY LANE BMP EVALUATION EXISTING DETENTION SYSTEM TYPE Tank AREA OF TRIBUTARY BASIN (ACRES) 2.0 TRIBUTARY BASIN IMPERVIOUS PERCENTAGE (%) 61% WATER QUALITY VOLUME (ACRE-FT) 0.2066 ONLINE WQ FLOW RATE (CFS) 0.33 OFFLINE WQ FLOW RATE (CFS) 0.18 BMP OPTION DIMENSIONS SITE NOTES & OBSERVATION WET POND 46’X94’ Insufficient space and existing system very deep at outlet. WET VAULTs Vault size – 15’X75’ Possible along 108th, but would be very deep. Not preferred. (1) SANDFILTER VAULT Presettling vault – 20’X60’ Vault size – (1) 40’X80’ See note 1 above. MEDIA FILTER VAULT, 18” CARTRIDGES WITH ZPG MEDIA(STORMFILTER VAULTS) 20 cartridges, ~ (1) 8’X11’ vaults Location at upstream end in cul-de-sac feasible and has avaiable space. BIOSWALE 212’X12’ Preferred option. Space and grade available on eastside of 108th Ave SE. FILTER STRIP 185’X21.5’ Bioswale appears better option. BIORETENTION 11’X340’ Not preferred due to a larger footprint as compared to other infiltration BMPs.(2) MEDIA FILTER DRAIN 15’X630’ See noted 2 above. MISCELLENEOUS NOTES: - Confirm existing ROW available (approx. 200’X25’) on east of 108th Ave SE. - Confirm exisitng 12” outlet is at existing road ditch from detention system. New bioswale(or bioifiltrationswale) 200040: KELSEY LANE AS-BUILT DRAWING SUMMARY PLAN VIEW PROFILE DETAIL DATE OF AS-BUILT DRAWINGS 6/25/1981 TIR PROVIDED X ADDRESS 10804 SE 173rd ST, Renton WA 98055 200049: NANTUCKET SHORT PLAT BMP EVALUATION EXISTING SYSTEM Wetvault (no detention) AREA OF TRIBUTARY BASIN (ACRES) 5.4 IMPERVIOUSNESS OF TRIBUTARY BASIN 37% WATER QUALITY VOLUME (ACRE-FT) 0.3772 ONLINE WQ FLOW RATE (CFS) 0.92 OFFLINE WQ FLOW RATE (CFS) 0.47 BMP OPTION DIMENSIONS SITE NOTES & OBSERVATION PROPRIETARY MEDIA FILTER VAULT, 18” CARTRIDGES WITH ZPG MEDIA(STORMFILTER VAULTS) 55 CARTRIDGES, ~ (1) 8’X22’ Sufficient space and head available. (1) WET VAULTS Vault Size- 20’X100’ See Misc. comments below. SANDFILTER VAULTS Presettling vault-20’X60’ Vault Size- (1)20’X60’ Insufficient space available. MISCELLANEOUS NOTES: - It is unusual, but the record drawing indicated this is a wetvault and the short plat did not include detention. - The existing vault is within 100 feet of a slope exceeding 25% and any improvement will need to be a vault type BMP. - The exist vault provides about 2,300 cf of wetvault storage. Current sizing indicated 16,000 cf is required to meet standard. It is likely difficult to locate this much additional storage within the site. Considering utilities and easements.should be upsized to provide the required WQ volume. - Stormfilter is the preferred option. It could be likely be located within in the unused southwest corner portion of Park Ave N and N 28th St. Stormfilter Vault 200049: NANTUCKET SHORT PLAT AS-BUILT DRAWING SUMMARY PLAN VIEW PROFILE DETAIL DATE OF AS-BUILT DRAWINGS 7/1/2015 TIR PROVIDED No ADDRESS 2826 Park Ave N, Renton, 98056 Page 1 DRAFT MEMORANDUM DATE: December 22nd, 2021 TO: Ken Srilofung, PE, CIP Project Manager FROM: Mike Giseburt, PE, WSP Project Manager SUBJECT: Stormwater Facility Retrofit Study – Retrofit Project Selection and Concept Design (Task 6 Effort) 1. INTRODUCTION AND BACKGROUND The City of Renton (City) owns and maintains over 400 stormwater facilities constructed as far back as the 1970s to mitigate for the stormwater impacts of urbanization. Between the 1970s and early 1990s, stormwater facilities were primarily focused on providing stormwater storage (i.e., detention). Since the early 1990s, design standards have advanced so that today’s stormwater facilities provide better water quality treatment to mitigate the detrimental impacts of stormwater pollutants on stream water quality and aquatic habitat. Today’s newer stormwater treatment systems target the removal of suspended solids, dissolved heavy metals, nutrients, and petroleum hydrocarbons. Typically, stormwater facilities owned by the City connect to the municipal storm sewer system and drain to the closest water body. The older stormwater detention facilities in the City’s system typically do not include a specific water quality treatment component, and thus are less effective at protecting stream resources from pollutants than the stormwater detention facilities with water quality treatment designed using today’s standards. The City received a grant from the Washington State Department of Ecology (Ecology) to perform a study of many of the existing flow control facilities that have little or no water quality treatment features. The overarching goal is to improve the water quality in multiple streams within the City that are part of the Cedar River/Lake Washington and Duwamish/Green watersheds. The study entails a series of six sequential tasks to be undertaken to prioritize the sites with the greatest potential to improve water quality. The first five tasks, Tasks 1 through 5, are complete and include: Existing Facilities Selection (Task 1) — City staff selected 49 existing flow control facilities for this study primarily based on their understanding that these particular existing facilities provide minimal water quality treatment (see Figure 1). Existing Conditions Summary (Task 2) — This effort included collecting information and evaluating site conditions of the 49 selected existing facilities. The summarized data includes stormwater best management practice (BMP) type, size, and age; tributary area characteristics; drainage basin information; and other information, all which helped characterize the existing facilities and were used in future tasks to evaluate stormwater treatment performance and site-specific water quality retrofit opportunities. Page 2 Figure 1. Site Map Page 3 Gap Analysis (Task 3) — This effort identified deficiencies (gaps) in the treatment of stormwater at the selected facilities. The analysis compared the existing amount of runoff treatment in the drainage basins to the amount of runoff treatment needed to meet current water quality treatment standards (per the 2017 City of Renton Surface Water Design Manual [SWDM]). It is noted that the City of Renton water quality treatment standards are deemed equivalent to Ecology Standards for development and redevelopment. Identifying Stormwater Retrofit Locations (Task 4) — This effort built upon the treatment gap analysis to identify existing flow control facilities to retrofit with additional runoff treatment benefits. This task developed a preliminary suite of BMP types and sizes for each site while considering site-specific conditions, such as space, topography, conveyance, infiltration potential, and other considerations. Prioritizing and Scoring Sites for Stormwater Retrofit Opportunities (Task 5) — This effort developed a method to screen and create a ranked list of retrofit locations identified in Task 4 that focuses on the (a) highest benefit of water quality improvement and (b) most effective opportunities. It resulted in the selection of three flow control facilities to advance with more detailed concept designs. These included Kelsey Lane, Benson Glen, and South Knoll. The final task, Task 6, is the presented in this memorandum. Project Selection, Conceptual Design, and Costs (Task 6) – This effort includes the development of concept designs and cost estimates for the top three prioritized retrofit location. 2. RECOMMENDED RETROFIT SITES Prior to the effort in Task 6, Task 5 developed a method to prioritize retrofit locations. Eight criteria were evaluated to screen and create a ranked list for the BMP retrofit locations identified in Task 4. See Task 5 memorandum for more information on the prioritizing and scoring sites for stormwater retrofit locations. The criteria were: - Level of retrofit treatment achieved (meets City water quality standards) - Feasibility (site characteristic including constructability, right of way and space available) - Receiving water quality - Drainage Basin size - Drainage Basin prioritization under City’s stormwater management action plan - Infiltration potential (type of BMP and hydrologic function) - Long term operation and maintenance costs - Other benefits (social, economic, and environmental) The City reviewed the scoring results presented in the Task 5 memorandum and selected three sites for concept development, identified in Table 1. Figure 2 shows the general locations of these three sites. Table 1. Selected Site for Concept Development Site ID Development Project Name Receiving Water Body Preliminary BMP Retrofit type 200040 Kelsey Lane Panther Creek Bioswale 117931 Benson Glen Panther Creek Bioretention 145832 South Knoll South Renton Media Vault Page 4 Figure 2. Recommended Retrofit Site Map (Not to Scale) 3. RETROFIT CONCEPT DEVELOPMENT Previous tasks identified the potential BMP retrofit types and sizes based on simplified hydrology and a review of available desktop information such as as-built drawings, Google Earth, and City of Renton (COR) GIS mapping. This task, Task 6, completed the following more thorough investigations for the retrofit concept development: - New hydrologic models were developed to more accurately estimate water quality design flow. - Site visits were conducted to observe site conditions, assess potential conflicts with underground or overhead utilities, and assess the space available for a BMP facility. - A new preliminary base map was developed using information available from COR GIS (such as water and sewer where available). Two of the three sites (Benson Glen and Kelsey Lane) are located within the Soos Creek Water and Sewer District. For these sites, the District was contacted to obtain information on water and sewer locations to show approximate locations on the base maps. - Based on the investigations above, the BMP retrofit types identified in Task 4 were re-assessed to either confirm or modify the best approach at each site. - A concept plan was developed at each site. Once the concept was complete, it was re-assessed to evaluate whether it would achieve a full retrofit to current City of Renton water quality standards. Page 5 - Cost estimates were developed for public bid item unit prices and estimated quantities. Cost estimates included the construction and design contingencies as noted in section 7 of this memorandum. 4. KELSEY LANE The basin area for the Kelsey Lane site is located in southern Renton near the intersection of 108th Ave SE and SE 173rd Street. The basin area draining to the Kelsey Lane Detention Facility consists of approximately 1.97 acres and is dominated by single family residential land use with some newer condominiums along the boundaries of the drainage basin. A figure showing the basin area and drainage system that contributes to the Kelsey Lane Detention Facility is included in Appendix A. Site photos of existing conditions are included in Appendix B. Existing Conditions Current flows enter the Kelsey Lane Detention System along the southern edge of the Kelsey Court Condominiums. From there, flows are conveyed to the existing ditch along the eastern side of 108 th Ave SE. Strom water flows south and is picked up again at SE 173rd Street. Flows cross under the road and are discharged to the undeveloped area between Benson Road S, Benson Drive S and 108 th Ave SE. Flow from the Kelsey Court Condominiums connects to the system just downstream of the detention tank. Because the possible existing flow/water quality facilities that are part of the Kelsey Court Condominiums is unknown, these flows were excluded from the model and the design routes these flows to the existing ditch on the east side of 108th Ave SE (maintaining its flow pattern). Project Components Task 5 identified that the existing road ditch along the east side 108th Ave SE could be retrofitted and turned into a compost amended bioswale (CABS) to meet the criteria for the basic water quality menu as outlined in Chapter 6 of the Renton SWDM. It was determined that existing water and sewer lines just east of the existing ditch would conflict with the CABS, so an alternative of routing flow along the west side of 108th Ave SE was proposed. In order to properly size a CABS for Kelsey Lane, a new hydrologic model was developed in Ecology’s stormwater hydrologic model (WWHM) to determine the 2-year release rate from the Kelsey Lane Detention Facility. The land use types determined from the GIS data collected in Task 2 were used in the WWHM model. The detention tank configuration was determined from As-Builts (Townsend, 1981) provided by the City of Renton. The 2-year release rate calculated from the WWHM model used in sizing calculations for the CABS is 0.336 cfs. The WWHM model results are included in Appendix C. The CABS was sized using the WSDOT Basic Bioswale Spreadsheet which follows the design method outlined in section 6.3.1.1 for the Renton SWDM. The spreadsheet is included in Appendix C. The CABS was not sized as a wet bioswale because the existing detention facility does not provide Flow Control Duration Standard or Flood Problem Flow Control Standard. Based on the 2-year release rate, the length of the CABS was designed to be approximately 175 feet in length. A concept of the design is presented in Appendix D. Feasibility Considerations for Kelsey Lane: - The swale bed elevation could follow the existing system elevations assuming infiltration testing meets infiltration criteria. Otherwise, if an underdrain is required, an assessment of grades would be needed to confirm a free draining underdrain can be attained. - There is a private storm sewer connection to the City of Renton owned system just downstream from the detention tank. For this concept design, possible flows from this connection have been excluded. It is Page 6 unknown if an existing water quality feature is located upstream of the private connection as part of the development. This could be investigated in future design phases. If there is no treatment for this development, it may be possible to include it in the treated area for Kelsey Lane. - Along the proposed swale, the slope to the west varies from a cut to fill slope. Although the exact location of the west right-of-way (ROW) boundary is preliminary until survey is complete, it is anticipated that a short concrete or rock wall 1 to 3 feet in height may be needed to keep the portions of the swale improvement within the ROW. Sheet 2 of the concept plan in Appendix D illustrates a concept showing how the swale could be constructed in both a cut and fill slope. Shoring or temporary cut/fill construction easements from private properties may be needed for locations with walls. 5. BENSON GLEN The basin area for the Benson Glen site is located in southern Renton near the intersection of SE 170 th Street and SE 169th Place. The basin area draining to the Benson Glen Detention Facility consists of approximately 1.70 acres and is dominated by single family residential land use. A figure showing the basin area and drainage system that contributes to the Benson Glen Detention Facility is included in Appendix A. Site photos of existing conditions are included in Appendix B. Existing Conditions Current flows enter the Benson Glen Detention System in the intersection of SE 170th Street and 109th Place SE. The Benson Glen Detention System consists of four detention pipes that are controlled with a flow control manhole and then all routed through the existing bioswale. No by-pass system exists for the existing bioswale. Flows exit the swale along SE 170th Place and continue flowing west through the City of Renton stormwater system. Project Components Task 5 identified that the existing bioswale at the corner of SE 170th Street and SE 169th Place could be retrofitted with bioretention for increased treatment capacity to partially meet treatment standards. Section 6.1.1 of the Renton SWDM specifies that sizing of Bioretention is to be done using an approved continuous runoff model to pass at least 91% of the influent runoff file through the imported soil mix. A WWHM model was built to model the existing detention tanks and the retrofitted bioretention swale. To start, the existing bioswale dimensions were taken from the as-builts (PAC-TECH, 1992) for the site and entered into the WWHM model. Using the new Type 2 high performance bioretention soil mix (HPBSM) (Ecology, 2021), it was determined that 56% of the water quality flow rate would be treated. It might be possible to increase the length and width of the bioretention swale by reducing the side slopes and re-grading the swale. Using the WWHM model, it was determined that 70% of the water quality flow rate could be treated if the length of the swale was increased by 20 feet and the width of the swale was increased by 2 feet. Field topographic survey, including property boundaries, will be needed to fully assess the extent to which the bioswale footprint can be expanded in future design phases. The WWHM model results are included in Appendix C. The proposed layout of the modified biofiltration swale is include in Appendix D. Feasibility Considerations for Benson Glen - A concrete or rock wall could be installed along the northern and western property boundaries to increase the bed area by eliminating the need for side slopes. A complete site survey is needed to fully assess this option. See the alternative bioretention swale section detail on the drawing in Appendix D. Page 7 - The bioretention bed elevation could follow the existing system elevations assuming infiltration testing meets infiltration criteria. Otherwise, if an underdrain is required, an assessment of grades would be needed to confirm a free draining underdrain can be attained. It is noted that the pipe system downstream of the swale outlet is at a slope of 1.67 percent. It would be possible to lower the grade of this downstream pipe system and achieved enough elevation drop for an underdrain if it cannot be obtained within the site. - There is not enough space available in the existing bioswale for a retrofit that would treat 91% of the influent runoff through the HPBSM. A proprietary media (ex. Filterra) could be used with an underdrain to increase treatment efficacy. This would be considered during future design phases. It is likely that if the downstream pipe system were lowered and a proprietary media with underdrains were used, the full 91% of runoff volume could be treated, however, a complete site survey is needed to fully assess this option. 6. SOUTH KNOLL The basin area for the South Knoll site is located in western Renton near the intersection of Oakesdale Ave SW and SW 3rd Place. The basin area draining to the South Knoll Detention Facility consists of approximately 8.37 acres and is dominated by single family residential land use. A portion of the tributary area is outside of the City of Renton in King County. A figure showing the basin area and drainage system that contributes to the South Knoll Detention Facility is included in Appendix A. Site photos of existing conditions are included in Appendix B. Existing Conditions Current flows enter the South Knoll Detention System approximately 100 feet north of the intersection of Oaksedale Ave SW and SE 3rd Place. Flows from the South Knoll Detention System join with another branch of the stormwater system in the intersection of Oakesdale Ave SW and SW 3rd Place. After this connection, flows are conveyed southwest along Oakesdale Ave SW eventually across SW Sunset Boulevard to an outfall to the Black River. Project Components Task 5 identified that a proprietary media filter vault would be best for South Knoll due to space requirements. In order to properly size a proprietary media vault for South Knoll, a new hydrologic model was developed using WWHM to determine the water quality flow rate for the South Knoll Detention Facility. The land use types determined from the GIS data collected in Task 2 were used in the WWHM model. The Renton SWDM specifies that the 2-year release rate is to be used to size proprietary media vaults downstream of detention. For South Knoll, it was determined that the detention tank, built in the early 80s, was built to previous design standards and the 2-year release rate from the WWHM model would cause the proprietary media vault to be significantly oversized. Thus, for this concept design, the water quality flow rate calculated from the WWHM model was used in sizing calculations for a proprietary media vault, which is 0.28 cfs. The WWHM model results are included in Appendix C. A Modular Wetland System – Linear (LMW) is proposed for South Knoll. The LMW will use a side-by-side orientation with an internal bypass weir wall to bypass peak flows. This configuration minimizes system length, providing a highly compact footprint. A standard detail provided by the manufacturer is included in Appendix D. To treat only the flows from the existing detention system, the outflows from the detention facility control structure will be redirected to the proposed LMW. The LMW will be placed in the intersection of SW 3 rd Place and Oakesdale Ave SW. The proposed layout is included in Appendix D. Page 8 Feasibility Considerations - Re-routing a water line will likely be needed due to the alignment conflict between the new storm and existing water. - As noted above, the water quality design flows were used for sizing rather than the 2-year outflows from the detention facility. During future design phases, additional hydrologic analysis will be needed to confirm that the volume to be treated meets the 91% standard. This could result in slight change in LMW sizing. To account for this, an allowance of 30% is added to the cost of the LMW unit provide by the manufacturer. 7. COST ESTIMATES A planning level cost estimate was developed by estimating construction quantities and applying the consultant team’s knowledge of current unit contract pricing of common construction items. Cost estimates include construction and design contingencies as noted below: - 10% allowance for other non-identified bid items - 40% construction contingency - 5% allowance for project administration costs - 40% engineering design (such as design, permitting, geotechnical, and public involvement) - 15% construction engineering No cost for land acquisition was assumed for Benson Glen, Kelsey Lane, and South Knoll. The Benson Glen existing facility is located in a public “Tract G” and it is assumed that the City has complete access, which should be confirmed prior to beginning future design phases. The Kelsey Lane retrofit included costs for limited shoring to avoid easements and land acquisitions. See project cost estimates in Table 2 below for each of the three sites. Table 2. Project Cost Estimates Site ID Development Project Name Cost Estimate 200040 Kelsey Lane $325,000 117931 Benson Glen $192,000 145832 South Knoll $767,000 A cost estimate breakdown sheet is provided for each site in Appendix E. 8. REFERENCES Ecology, 2021. Guidance on using new high performance bioretention soil mixes. Washington State Department of Ecology. May 2021. Renton, 2016. City of Renton Surface Water Design Manual. City of Renton Public Work Department Surface Water Utility. December 12, 2016. PAC-TECH, 1992. Threshold 1 Storm Drain Improvements 108th Avenue SE. PAC-TECH Engineering, Inc. June 15, 1992. Townsend, 1981. Kelsey Lane Street & Storm Drainage. Townsend-Chastain & Assoc., Inc. March 1981. Pool, 1985. South Knoll Paving & Storm Drainage Plan & Profile. Pool Engineering, Inc. April 1985. Page 9 APPENDIX A – BASIN AREA FIGURES Existing UndergroundDetention Pipe 200040 SE 173rd St SE 172nd St Private Rd 108th Ave SEBenson Rd S110th Ln SEAccess Rd108th Ave SE£ 0 100 20050Feet Kelsey Lane (Asset ID 200040) CITY OF RENTON STORM WATERFACILITY RETROFIT STUDY Legend Approx. Tributary Area To Facility Existing WQ Treatment BMPs Associated with Detention Facility's Tributary Basin Structure Type !H Bioswale Media Filter Drain #0 Modified Media Filter Drain Stormfilter - Contech 'Stormwater Wetland 'Wet Pond "6 Wet Vault Storm Water Detention Facility Stormwater Pipe !H Existing UndergroundDetention Pipe 117931 SE 168th St SE 170th St 108th Ave SEPrivate Rd SE 169th Pl 110th Pl SEPrivate Rd £ 0 100 20050Feet Benson Glen (Asset ID 117931) CITY OF RENTON STORM WATERFACILITY RETROFIT STUDY Legend Approx. Tributary Area To Facility Existing WQ Treatment BMPs Associated with Detention Facility's Tributary Basin Structure Type !H Bioswale Media Filter Drain #0 Modified Media Filter Drain Stormfilter - Contech 'Stormwater Wetland 'Wet Pond "6 Wet Vault Storm Water Detention Facility Stormwater Pipe Existing DetentionPipe (Directed to Control Manhole inSW 3rd Place)14 5 83 145832 S 134th St 80th Ave SPowell Ave SWOakesdale Ave SWSW Langston Rd S 1 3 4 th P lS Langston R d S 135th St Naches Ave SW£ 0 100 20050Feet South Knoll (Asset ID 145832) CITY OF RENTON STORM WATERFACILITY RETROFIT STUDY Legend Approx. Tributary Area To Facility Existing WQ Treatment BMPs Associated with Detention Facility's Tributary Basin Structure Type !H Bioswale Media Filter Drain #0 Modified Media Filter Drain Stormfilter - Contech 'Stormwater Wetland 'Wet Pond "6 Wet Vault Storm Water Detention Facility Stormwater Pipe Page 10 APPENDIX B – SITE PHOTOS PHOTOGRAPHIC LOG City of Renton STORMWATER FACILITY RETROFIT STUDY 31402768.00.06.00 Page 1 Photo No. Date 1 October 29, 2021 Kelsey Lane Existing drainage ditch along east side of 108th Ave SW; View north Photo No. Date 2 October 29, 2021 Kelsey Lane Inlet pipes to existing drainage ditch; View northeast PHOTOGRAPHIC LOG City of Renton STORMWATER FACILITY RETROFIT STUDY 31402768.00.06.00 Page 2 Photo No. Date 3 October 29, 2021 Kelsey Lane Existing drainage ditch and proposed location of new bioswale on west side of 108th Ave SE; View northwest Photo No. Date 4 October 29, 2021 Benson Glen Street level view of existing drainage swale; View west PHOTOGRAPHIC LOG City of Renton STORMWATER FACILITY RETROFIT STUDY 31402768.00.06.00 Page 3 Photo No. Date 5 October 29, 2021 Benson Glen Existing drainage swale; View west Photo No. Date 6 October 29, 2021 Benson Glen Existing retaining wall; View east PHOTOGRAPHIC LOG City of Renton STORMWATER FACILITY RETROFIT STUDY 31402768.00.06.00 Page 4 Photo No. Date 7 October 29, 2021 South Knoll Intersection of Oaksedale Ave SW and SW 3rd Place; View northeast Photo No. Date 8 October 29, 2021 South Knoll Intersection of Oaksedale Ave SW and SW 3rd Place; View north Page 11 APPENDIX C – DESIGN OUPUT Kelsey Lane WWHM2012 PROJECT REPORT ___________________________________________________________________ Project Name: Kelsey Lane Predeveloped Tank Site Name: Kelsey Lane Site Address: City : Renton Report Date: 12/3/2021 Gage : Seatac Data Start : 1948/10/01 Data End : 2009/09/30 Precip Scale: 1.00 Version Date: 2019/09/13 Version : 4.2.17 ___________________________________________________________________ Low Flow Threshold for POC 1 : 50 Percent of the 2 Year ___________________________________________________________________ High Flow Threshold for POC 1: 50 year ___________________________________________________________________ PREDEVELOPED LAND USE Name : Basin 1 Bypass: No GroundWater: No Pervious Land Use acre A B, Forest, Mod 1.966 Pervious Total 1.966 Impervious Land Use acre Impervious Total 0 Basin Total 1.966 ___________________________________________________________________ Element Flows To: Surface Interflow Groundwater ___________________________________________________________________ MITIGATED LAND USE Name : Basin 1 Bypass: No GroundWater: No KELSEY LANE BIOSWALE SIZING Pervious Land Use acre A B, Lawn, Mod .386 C, Lawn, Mod .371 Pervious Total 0.757 Impervious Land Use acre ROADS MOD 1.184 ROADS STEEP 0.025 Impervious Total 1.209 Basin Total 1.966 ___________________________________________________________________ Element Flows To: Surface Interflow Groundwater Tank 1 Tank 1 ___________________________________________________________________ Name : Tank 1 Tank Name: Tank 1 Dimensions Depth: 4 ft. Tank Type : Circular Diameter : 4 ft. Length : 223 ft. Discharge Structure Riser Height: 4 ft. Riser Diameter: 12 in. Orifice 1 Diameter: 3.5 in. Elevation: 0 ft. Element Flows To: Outlet 1 Outlet 2 ___________________________________________________________________ Tank Hydraulic Table Stage(feet) Area(ac.) Volume(ac-ft.) Discharge(cfs) Infilt(cfs) 0.0000 0.000 0.000 0.000 0.000 0.0444 0.004 0.000 0.070 0.000 0.0889 0.006 0.000 0.099 0.000 0.1333 0.007 0.000 0.121 0.000 0.1778 0.008 0.001 0.140 0.000 0.2222 0.009 0.001 0.156 0.000 0.2667 0.010 0.001 0.171 0.000 0.3111 0.011 0.002 0.185 0.000 0.3556 0.011 0.002 0.198 0.000 0.4000 0.012 0.003 0.210 0.000 0.4444 0.012 0.003 0.221 0.000 0.4889 0.013 0.004 0.232 0.000 CONTROL STRUCTURE SIZES BASED ON AS- BUILTS 0.5333 0.013 0.005 0.242 0.000 0.5778 0.014 0.005 0.252 0.000 0.6222 0.014 0.006 0.262 0.000 0.6667 0.015 0.007 0.271 0.000 0.7111 0.015 0.007 0.280 0.000 0.7556 0.016 0.008 0.289 0.000 0.8000 0.016 0.009 0.297 0.000 0.8444 0.016 0.009 0.305 0.000 0.8889 0.017 0.010 0.313 0.000 0.9333 0.017 0.011 0.321 0.000 0.9778 0.017 0.012 0.328 0.000 1.0222 0.017 0.013 0.336 0.000 1.0667 0.018 0.013 0.343 0.000 1.1111 0.018 0.014 0.350 0.000 1.1556 0.018 0.015 0.357 0.000 1.2000 0.018 0.016 0.364 0.000 1.2444 0.019 0.017 0.370 0.000 1.2889 0.019 0.017 0.377 0.000 1.3333 0.019 0.018 0.383 0.000 1.3778 0.019 0.019 0.390 0.000 1.4222 0.019 0.020 0.396 0.000 1.4667 0.019 0.021 0.402 0.000 1.5111 0.019 0.022 0.408 0.000 1.5556 0.020 0.023 0.414 0.000 1.6000 0.020 0.024 0.420 0.000 1.6444 0.020 0.024 0.426 0.000 1.6889 0.020 0.025 0.432 0.000 1.7333 0.020 0.026 0.437 0.000 1.7778 0.020 0.027 0.443 0.000 1.8222 0.020 0.028 0.448 0.000 1.8667 0.020 0.029 0.454 0.000 1.9111 0.020 0.030 0.459 0.000 1.9556 0.020 0.031 0.464 0.000 2.0000 0.020 0.032 0.470 0.000 2.0444 0.020 0.033 0.475 0.000 2.0889 0.020 0.034 0.480 0.000 2.1333 0.020 0.034 0.485 0.000 2.1778 0.020 0.035 0.490 0.000 2.2222 0.020 0.036 0.495 0.000 2.2667 0.020 0.037 0.500 0.000 2.3111 0.020 0.038 0.505 0.000 2.3556 0.020 0.039 0.510 0.000 2.4000 0.020 0.040 0.515 0.000 2.4444 0.020 0.041 0.519 0.000 2.4889 0.019 0.042 0.524 0.000 2.5333 0.019 0.043 0.529 0.000 2.5778 0.019 0.043 0.533 0.000 2.6222 0.019 0.044 0.538 0.000 2.6667 0.019 0.045 0.542 0.000 2.7111 0.019 0.046 0.547 0.000 2.7556 0.019 0.047 0.551 0.000 2.8000 0.018 0.048 0.556 0.000 2.8444 0.018 0.048 0.560 0.000 2.8889 0.018 0.049 0.565 0.000 2.9333 0.018 0.050 0.569 0.000 2.9778 0.017 0.051 0.573 0.000 3.0222 0.017 0.052 0.577 0.000 3.0667 0.017 0.052 0.582 0.000 3.1111 0.017 0.053 0.586 0.000 3.1556 0.016 0.054 0.590 0.000 3.2000 0.016 0.055 0.594 0.000 3.2444 0.016 0.055 0.598 0.000 3.2889 0.015 0.056 0.602 0.000 3.3333 0.015 0.057 0.606 0.000 3.3778 0.014 0.058 0.611 0.000 3.4222 0.014 0.058 0.615 0.000 3.4667 0.013 0.059 0.618 0.000 3.5111 0.013 0.059 0.622 0.000 3.5556 0.012 0.060 0.626 0.000 3.6000 0.012 0.061 0.630 0.000 3.6444 0.011 0.061 0.634 0.000 3.6889 0.011 0.062 0.638 0.000 3.7333 0.010 0.062 0.642 0.000 3.7778 0.009 0.062 0.646 0.000 3.8222 0.008 0.063 0.649 0.000 3.8667 0.007 0.063 0.653 0.000 3.9111 0.006 0.064 0.657 0.000 3.9556 0.004 0.064 0.661 0.000 4.0000 0.000 0.064 0.664 0.000 4.0444 0.000 0.000 0.767 0.000 ___________________________________________________________________ ___________________________________________________________________ ANALYSIS RESULTS Stream Protection Duration ___________________________________________________________________ Predeveloped Landuse Totals for POC #1 Total Pervious Area:1.966 Total Impervious Area:0 ___________________________________________________________________ Mitigated Landuse Totals for POC #1 Total Pervious Area:0.757 Total Impervious Area:1.209 ___________________________________________________________________ Flow Frequency Return Periods for Predeveloped. POC #1 Return Period Flow(cfs) 2 year 0.001705 5 year 0.002814 10 year 0.0038 25 year 0.005395 50 year 0.006882 100 year 0.008666 Flow Frequency Return Periods for Mitigated. POC #1 Return Period Flow(cfs) 2 year 0.335874 5 year 0.392164 10 year 0.429602 2 YEAR FLOW RATE FROM DETENTION TANK USED AS WATER QUALITY FLOW RATE IN SWALE DESIGN SPREADSHEET 25 year 0.477269 50 year 0.513131 100 year 0.549362 ___________________________________________________________________ Stream Protection Duration Annual Peaks for Predeveloped and Mitigated. POC #1 Year Predeveloped Mitigated 1949 0.001 0.393 1950 0.004 0.409 1951 0.004 0.329 1952 0.002 0.289 1953 0.002 0.288 1954 0.002 0.292 1955 0.002 0.333 1956 0.002 0.317 1957 0.002 0.346 1958 0.002 0.290 1959 0.002 0.287 1960 0.002 0.304 1961 0.002 0.312 1962 0.001 0.281 1963 0.002 0.321 1964 0.002 0.320 1965 0.002 0.341 1966 0.002 0.291 1967 0.002 0.373 1968 0.002 0.382 1969 0.002 0.319 1970 0.001 0.310 1971 0.002 0.342 1972 0.011 0.387 1973 0.002 0.253 1974 0.002 0.326 1975 0.002 0.350 1976 0.002 0.289 1977 0.001 0.294 1978 0.002 0.359 1979 0.001 0.383 1980 0.002 0.393 1981 0.002 0.344 1982 0.002 0.461 1983 0.002 0.384 1984 0.002 0.284 1985 0.002 0.336 1986 0.001 0.323 1987 0.001 0.369 1988 0.002 0.302 1989 0.002 0.337 1990 0.002 0.523 1991 0.004 0.467 1992 0.002 0.286 1993 0.001 0.282 1994 0.001 0.276 1995 0.002 0.298 1996 0.015 0.355 1997 0.002 0.336 1998 0.001 0.334 1999 0.004 0.498 2000 0.001 0.341 2001 0.002 0.321 2002 0.001 0.387 2003 0.002 0.329 2004 0.002 0.528 2005 0.002 0.311 2006 0.002 0.284 2007 0.023 0.486 2008 0.002 0.505 2009 0.002 0.379 ___________________________________________________________________ Stream Protection Duration Ranked Annual Peaks for Predeveloped and Mitigated. POC #1 Rank Predeveloped Mitigated 1 0.0228 0.5277 2 0.0153 0.5226 3 0.0113 0.5051 4 0.0041 0.4979 5 0.0041 0.4859 6 0.0036 0.4666 7 0.0036 0.4608 8 0.0018 0.4094 9 0.0016 0.3932 10 0.0016 0.3927 11 0.0016 0.3874 12 0.0016 0.3874 13 0.0016 0.3841 14 0.0016 0.3826 15 0.0016 0.3822 16 0.0016 0.3786 17 0.0016 0.3732 18 0.0016 0.3688 19 0.0016 0.3592 20 0.0016 0.3553 21 0.0016 0.3496 22 0.0016 0.3461 23 0.0016 0.3443 24 0.0016 0.3424 25 0.0016 0.3412 26 0.0016 0.3406 27 0.0016 0.3375 28 0.0016 0.3362 29 0.0016 0.3360 30 0.0016 0.3339 31 0.0015 0.3328 32 0.0015 0.3294 33 0.0015 0.3286 34 0.0015 0.3264 35 0.0015 0.3231 36 0.0015 0.3211 37 0.0015 0.3207 38 0.0015 0.3197 39 0.0015 0.3186 40 0.0015 0.3166 41 0.0015 0.3123 42 0.0015 0.3109 43 0.0015 0.3098 44 0.0015 0.3038 45 0.0015 0.3018 46 0.0015 0.2980 47 0.0015 0.2936 48 0.0015 0.2915 49 0.0015 0.2907 50 0.0015 0.2901 51 0.0015 0.2891 52 0.0015 0.2886 53 0.0015 0.2882 54 0.0015 0.2866 55 0.0015 0.2864 56 0.0015 0.2844 57 0.0015 0.2838 58 0.0014 0.2816 59 0.0013 0.2806 60 0.0012 0.2756 61 0.0012 0.2530 ___________________________________________________________________ Stream Protection Duration POC #1 The Facility FAILED Facility FAILED duration standard for 1+ flows. Flow(cfs) Predev Mit Percentage Pass/Fail 0.0009 2920 579423 19843 Fail 0.0009 2488 565948 22747 Fail 0.0010 2122 553542 26085 Fail 0.0010 1798 541778 30132 Fail 0.0011 1504 530656 35282 Fail 0.0012 1294 519962 40182 Fail 0.0012 1087 510123 46929 Fail 0.0013 850 500498 58882 Fail 0.0013 628 491301 78232 Fail 0.0014 477 482531 101159 Fail 0.0015 330 474404 143758 Fail 0.0015 191 466276 244123 Fail 0.0016 41 458576 1118478Fail 0.0016 35 451304 1289440Fail 0.0017 33 444031 1345548Fail 0.0018 31 437187 1410280Fail 0.0018 30 430770 1435900Fail 0.0019 29 424568 1464027Fail 0.0019 29 418365 1442637Fail 0.0020 29 412590 1422724Fail 0.0021 28 407029 1453675Fail 0.0021 28 401682 1434578Fail 0.0022 27 396334 1467903Fail 0.0023 27 391201 1448892Fail 0.0023 27 386496 1431466Fail 0.0024 27 381790 1414037Fail 0.0024 26 377298 1451146Fail 0.0025 25 373021 1492084Fail 0.0026 25 368529 1474116Fail 0.0026 24 364465 1518604Fail 0.0027 23 360401 1566960Fail 0.0027 23 356551 1550221Fail 0.0028 23 352915 1534413Fail 0.0029 22 349065 1586659Fail 0.0029 22 345643 1571104Fail 0.0030 21 342007 1628604Fail 0.0030 21 338799 1613328Fail 0.0031 21 335590 1598047Fail 0.0032 21 332382 1582771Fail 0.0032 21 329174 1567495Fail 0.0033 20 326179 1630895Fail 0.0033 19 323185 1700973Fail 0.0034 19 320404 1686336Fail 0.0035 18 317624 1764577Fail 0.0035 18 314843 1749127Fail 0.0036 16 312276 1951725Fail 0.0037 16 309710 1935687Fail 0.0037 16 307143 1919643Fail 0.0038 16 304577 1903606Fail 0.0038 15 302224 2014826Fail 0.0039 15 299871 1999140Fail 0.0040 15 297518 1983453Fail 0.0040 15 295165 1967766Fail 0.0041 15 293027 1953513Fail 0.0041 14 290888 2077771Fail 0.0042 13 288749 2221146Fail 0.0043 13 286824 2206338Fail 0.0043 13 284685 2189884Fail 0.0044 13 282760 2175076Fail 0.0044 13 280835 2160269Fail 0.0045 12 278910 2324250Fail 0.0046 12 277199 2309991Fail 0.0046 11 275274 2502490Fail 0.0047 11 273563 2486936Fail 0.0048 11 271852 2471381Fail 0.0048 11 270141 2455827Fail 0.0049 11 268429 2440263Fail 0.0049 10 266932 2669320Fail 0.0050 10 265221 2652210Fail 0.0051 10 263724 2637240Fail 0.0051 9 262227 2913633Fail 0.0052 9 260729 2896988Fail 0.0052 9 259232 2880355Fail 0.0053 9 257735 2863722Fail 0.0054 9 256238 2847088Fail 0.0054 8 254954 3186925Fail 0.0055 8 253457 3168212Fail 0.0055 8 252174 3152175Fail 0.0056 8 250891 3136137Fail 0.0057 8 249607 3120087Fail 0.0057 8 248324 3104050Fail 0.0058 8 247041 3088012Fail 0.0058 8 245757 3071962Fail 0.0059 8 244474 3055925Fail 0.0060 8 243191 3039887Fail 0.0060 8 242121 3026512Fail 0.0061 8 240838 3010475Fail 0.0062 8 239768 2997100Fail 0.0062 8 238699 2983737Fail 0.0063 8 237630 2970375Fail 0.0063 8 236560 2957000Fail 0.0064 8 235491 2943637Fail 0.0065 8 234421 2930262Fail 0.0065 8 233352 2916900Fail 0.0066 8 232282 2903525Fail 0.0066 8 231213 2890162Fail 0.0067 8 230143 2876787Fail 0.0068 8 229074 2863425Fail 0.0068 8 228218 2852725Fail 0.0069 8 227149 2839362Fail _____________________________________________________ The development has an increase in flow durations from 1/2 Predeveloped 2 year flow to the 2 year flow or more than a 10% increase from the 2 year to the 50 year flow. The development has an increase in flow durations for more than 50% of the flows for the range of the duration analysis. ___________________________________________________________________ Water Quality BMP Flow and Volume for POC #1 On-line facility volume: 0 acre-feet On-line facility target flow: 0 cfs. Adjusted for 15 min: 0 cfs. Off-line facility target flow: 0 cfs. Adjusted for 15 min: 0 cfs. ___________________________________________________________________ LID Report LID Technique Used for Total Volume Volume Infiltration Cumulative Percent Water Quality Percent Comment Treatment? Needs Through Volume Volume Volume Water Quality Treatment Facility (ac-ft.) Infiltration Infiltrated Treated (ac-ft) (ac-ft) Credit Total Volume Infiltrated 0.00 0.00 0.00 0.00 0.00 0% No Treat. Credit Compliance with LID Standard 8 Duration Analysis Result = Passed ___________________________________________________________________ Perlnd and Implnd Changes No changes have been made. ___________________________________________________________________ This program and accompanying documentation are provided 'as-is' without warranty of any kind. The entire risk regarding the performance and results of this program is assumed by End User. Clear Creek Solutions Inc. and the governmental licensee or sublicensees disclaim all warranties, either expressed or implied, including but not limited to implied warranties of program and accompanying documentation. In no event shall Clear Creek Solutions Inc. be liable for any damages whatsoever (including without limitation to damages for loss of business profits, loss of business information, business interruption, and the like) arising out of the use of, or inability to use this program even if Clear Creek Solutions Inc. or their authorized representatives have been advised of the possibility of such damages. Software Copyright © by : Clear Creek Solutions, Inc. 2005-2021; All Rights Reserved. RT.04 - Basic Biofiltration Swale and Compost Amended Biofiltration Swale Project:City of Renton Water Quality Retrofit Designed By: Sarah Gillespie Description:Kelsey Lane Basic Bioswale Checked By: BASIC BIOSWALE AND COMPOST AMENDED BIOSWALE SPREADSHEET VERSION 2.1 Design Steps D-1 Determine runoff treatment design flow rate Qwq Qwq 0.186 Runoff treatment design flow rate from MGS Flood OR SBUH; MGSFlood reports an online and offline flow rate, please enter the applicable design flow rate D-2 Determine the biofiltration design flow rate (Qbiofil) Is the bioswale in eastern WA?No 1.32 Is bioswale online or offline?online Qbiofil 0.337 runoff treatment design flow rate D-3 Determine the longitudinal slope of the proposed biofiltration swale (ft/ft) s 0.015 ft/ft D-4 Select a soil and vegetation cover suitable for the biofiltration swale soil/veg <--Use pull down box Manning's n=0.22 D-5 Select the design depth of flow y (see HRM Table 5-4) y 0.33 (ft) design depth of flow; for basic biofiltration swale and CABS = 4" max (0.33 ft max) for WQ event D-6 Select a trapezoidal swale cross-sectional shape. D-7 <--manning's changed HRM Chapter 5 Equation E-11 Use Excel Solver D-7a Qbiofil 0.337 cfs - runoff treatment design flow rate A 1.038 ft2 - wetted area R 0.245 ft - hydraulic radius s 0.015 ft/ft longitudinal slope of swale n 0.22 Manning's coefficient b 2.16 ft - bioswale bottom width zforeslope 3.00 horizontal number of bioswale slope i.e. 1V:3H, z=3 in this instance zbackslope 3.00 horizontal number of bioswale slope i.e. 1V:3H, z=3 in this instance y 0.330 ft - design depth flow = maximum depth of flow Qbiofil 0.337 Note: Depth of flow for basic biofiltration swale and CABS = 4" max (0.33 ft max) for WQ event D-7b If the swale calculations above give a swale width less than 2 feet wide, re-run calculations with 2 foot wide swale, solve for depth y Or if redesigning swale with different dimensions, use below calculator and use Excel Goal Seek to determine new depth of flow. Qbiofil 0.337 cfs - runoff treatment design flow rate A 0.000 ft2 - wetted area R #DIV/0!ft - hydraulic radius s 0.015 ft/ft longitudinal slope of swale n 0.22 Manning's coefficient b ft - enter new bottom width if applicable (2 foot is minimum) zforeslope 3.00 horizontal number of bioswale slope i.e. 1V:3H, z=3 in this instance zbackslope 3.00 horizontal number of bioswale slope i.e. 1V:3H, z=3 in this instance y ft - design depth flow Qbiofil #DIV/0! Note: Depth of flow for basic biofiltration swale and CABS = 4" max (0.33 ft max) for WQ event Minimum bioswale bottom width is 2 feet 6-month 24 hr precip depth (in) From HRM Table 5-3 Use Manning's Eq and first approximations relating hydraulic radius and dimensions to get width for trapezoidal cross section cfs - use goal seek under "What-If Analysis" in the "DATA" menu to set this cell equal to Qbiofil above changing the "b" value Grass-legume mix on lightly compacted topsoil cfs - use goal seek under "What-If Analysis" in the "DATA" menu to set this cell equal to Qbiofil above changing the "y" value n sARQbiofil 2 1 3 2 49.15.0 67. 49.1 s nQARbiofil Basic-and-wet-biofiltration-swale-design_Kelsey Lane 12/6/2021 2:36 PM Version 2.1 2 YEAR FLOW RATE FROM DETENTION TANK D-8 Enter Final Bioswale Dimensions from the calculations in Step D-7a or D-7b Enter Final Swale Area 1.038 ft2 - Wetted Area Enter Final Swale R 0.245 ft - hydraulic radius Enter Final Swale slope s 0.015 ft/ft longitudinal slope of swale Enter Final Swale n 0.22 Manning's coefficient Enter Final Swale bottom width b 2.16 ft - swale bottom width Enter Final Swale zforeslope 3.00 horizontal number of bioswale slope i.e. 1V:3H, z=3 in this instance Enter Final Swale zbackslope 3.00 horizontal number of bioswale slope i.e. 1V:3H, z=3 in this instance Enter Final Swale flow depth y 0.330 ft - design depth flow D-9 Computer the flow velocity at Qbiofil HRM Chapter 5 Equation E-12 Vbiofil 0.32 ft/sec - flow velocity; 1 ft/sec maximum Flow veloicty is OK since it is less than 1 ft/sec D-10 Compute Swale Length L (ft) t 540 seconds - 9 minutes (540 seconds) for CABS, Basic, and Wet bioswale L 175.06 ft - required length of bioswale; If swale is less than 100 feet, make swale have narrower bottom width (2 foot minimum) and repeat Steps D-7 - D-10 and recalculate to get length over 100 feet or keep swale bottom width make swale length 100 feet minimum D-11 Does the bioswale need to be redesigned to fit within the provided right of way? No Continue to Step FC-1 Freeboard Check (Online Swales Only) FC-1 Q50yr 0.51 1.00 Safety Factor (For MGSFlood, 1.0 if using extended time series, 1.6 if using station data) Qconvey 0.51 cfs - Q50yr x saftey factor FC-2 n 0.03 (lowest possible Manning's from HRM) FC-3 depth y 0.14 ft - design depth flow A 0.35 ft2 - wetted area R 0.116 ft - hydraulic radius S 0.015 ft/ft longitudinal slope of swale b 2.16 ft - swale bottom width zforeslope 3.00 horizontal number of bioswale slope i.e. 1V:3H, z=3 in this instance zbackslope 3.00 horizontal number of bioswale slope i.e. 1V:3H, z=3 in this instance Qconvey 0.51 FC-4 D(total)1.14 175.06 ft 2.2 ft 0.015 ft/ft 3.0 3.0 0.33 ft 1.14 ft Swale Longitudinal Slope zforeslope zbackslope WQ Depth Swale Depth (includes 1 ft Freeboard) cfs - MGSFlood, use the 50 year 15 minute time step, see HRM. If using station data, use the 100 year, 1 hour rate and multiply by the safety factor below. cfs - use goal seek under "What-If Analysis" in the "DATA" menu to set this cell equal to Qconvey above changing the "y" value ft, total required swale depth. Does not take into account design standards for minimum ditch depth from the Design Manual (roadway sections) Final Swale Dimensions Swale Length Bottom Width A QV biofil biofil tVLbiofil Basic-and-wet-biofiltration-swale-design_Kelsey Lane 12/6/2021 2:36 PM Version 2.1 Benson Glen WWHM2012 PROJECT REPORT ___________________________________________________________________ Project Name: Benson Glen Site Name: Benson Glen Site Address: City : Report Date: 12/1/2021 Gage : Seatac Data Start : 1948/10/01 Data End : 2009/09/30 Precip Scale: 1.00 Version Date: 2019/09/13 Version : 4.2.17 ___________________________________________________________________ Low Flow Threshold for POC 1 : 50 Percent of the 2 Year ___________________________________________________________________ High Flow Threshold for POC 1: 50 year ___________________________________________________________________ PREDEVELOPED LAND USE Name : Basin 1 Bypass: No GroundWater: No Pervious Land Use acre A B, Lawn, Mod .742 A B, Lawn, Steep .001 Pervious Total 0.743 Impervious Land Use acre ROADS MOD 0.961 Impervious Total 0.961 Basin Total 1.704 ___________________________________________________________________ Element Flows To: Surface Interflow Groundwater ___________________________________________________________________ MITIGATED LAND USE Name : Basin 1 Bypass: No BENSON GLEN - EXISTING SWALE WITH HPBSM GroundWater: No Pervious Land Use acre A B, Lawn, Mod .742 A B, Lawn, Steep .001 Pervious Total 0.743 Impervious Land Use acre ROADS MOD 0.961 Impervious Total 0.961 Basin Total 1.704 ___________________________________________________________________ Element Flows To: Surface Interflow Groundwater Tank 1 Tank 1 ___________________________________________________________________ Name : Tank 1 Tank Name: Tank 1 Dimensions Depth: 4 ft. Tank Type : Circular Diameter : 4 ft. Length : 270 ft. Discharge Structure Riser Height: 3.5 ft. Riser Diameter: 12 in. Orifice 1 Diameter: 1.73 in. Elevation: 0 ft. Orifice 2 Diameter: 1.91 in. Elevation: 2.15 ft. Element Flows To: Outlet 1 Outlet 2 Surface retention 1 ___________________________________________________________________ Tank Hydraulic Table Stage(feet) Area(ac.) Volume(ac-ft.) Discharge(cfs) Infilt(cfs) 0.0000 0.000 0.000 0.000 0.000 0.0444 0.005 0.000 0.017 0.000 0.0889 0.007 0.000 0.024 0.000 0.1333 0.008 0.000 0.029 0.000 0.1778 0.010 0.001 0.034 0.000 0.2222 0.011 0.001 0.038 0.000 0.2667 0.012 0.002 0.041 0.000 0.3111 0.013 0.002 0.045 0.000 0.3556 0.014 0.003 0.048 0.000 0.4000 0.014 0.004 0.051 0.000 CONTROL STRUCTURE SIZES BASED ON AS-BUILTS 0.4444 0.015 0.004 0.054 0.000 0.4889 0.016 0.005 0.056 0.000 0.5333 0.016 0.006 0.059 0.000 0.5778 0.017 0.006 0.061 0.000 0.6222 0.018 0.007 0.064 0.000 0.6667 0.018 0.008 0.066 0.000 0.7111 0.019 0.009 0.068 0.000 0.7556 0.019 0.010 0.070 0.000 0.8000 0.019 0.011 0.072 0.000 0.8444 0.020 0.012 0.074 0.000 0.8889 0.020 0.012 0.076 0.000 0.9333 0.021 0.013 0.078 0.000 0.9778 0.021 0.014 0.080 0.000 1.0222 0.021 0.015 0.082 0.000 1.0667 0.021 0.016 0.083 0.000 1.1111 0.022 0.017 0.085 0.000 1.1556 0.022 0.018 0.087 0.000 1.2000 0.022 0.019 0.089 0.000 1.2444 0.023 0.020 0.090 0.000 1.2889 0.023 0.021 0.092 0.000 1.3333 0.023 0.022 0.093 0.000 1.3778 0.023 0.023 0.095 0.000 1.4222 0.023 0.024 0.096 0.000 1.4667 0.023 0.025 0.098 0.000 1.5111 0.024 0.026 0.099 0.000 1.5556 0.024 0.028 0.101 0.000 1.6000 0.024 0.029 0.102 0.000 1.6444 0.024 0.030 0.104 0.000 1.6889 0.024 0.031 0.105 0.000 1.7333 0.024 0.032 0.106 0.000 1.7778 0.024 0.033 0.108 0.000 1.8222 0.024 0.034 0.109 0.000 1.8667 0.024 0.035 0.111 0.000 1.9111 0.024 0.036 0.112 0.000 1.9556 0.024 0.037 0.113 0.000 2.0000 0.024 0.038 0.114 0.000 2.0444 0.024 0.040 0.116 0.000 2.0889 0.024 0.041 0.117 0.000 2.1333 0.024 0.042 0.118 0.000 2.1778 0.024 0.043 0.136 0.000 2.2222 0.024 0.044 0.147 0.000 2.2667 0.024 0.045 0.156 0.000 2.3111 0.024 0.046 0.163 0.000 2.3556 0.024 0.047 0.169 0.000 2.4000 0.024 0.048 0.175 0.000 2.4444 0.024 0.049 0.180 0.000 2.4889 0.024 0.050 0.185 0.000 2.5333 0.023 0.052 0.190 0.000 2.5778 0.023 0.053 0.195 0.000 2.6222 0.023 0.054 0.199 0.000 2.6667 0.023 0.055 0.203 0.000 2.7111 0.023 0.056 0.207 0.000 2.7556 0.023 0.057 0.211 0.000 2.8000 0.022 0.058 0.215 0.000 2.8444 0.022 0.059 0.219 0.000 2.8889 0.022 0.060 0.223 0.000 2.9333 0.021 0.061 0.226 0.000 2.9778 0.021 0.062 0.230 0.000 3.0222 0.021 0.063 0.233 0.000 3.0667 0.021 0.064 0.237 0.000 3.1111 0.020 0.065 0.240 0.000 3.1556 0.020 0.065 0.243 0.000 3.2000 0.019 0.066 0.246 0.000 3.2444 0.019 0.067 0.249 0.000 3.2889 0.019 0.068 0.252 0.000 3.3333 0.018 0.069 0.256 0.000 3.3778 0.018 0.070 0.259 0.000 3.4222 0.017 0.071 0.261 0.000 3.4667 0.016 0.071 0.264 0.000 3.5111 0.016 0.072 0.280 0.000 3.5556 0.015 0.073 0.409 0.000 3.6000 0.014 0.073 0.606 0.000 3.6444 0.014 0.074 0.848 0.000 3.6889 0.013 0.075 1.117 0.000 3.7333 0.012 0.075 1.396 0.000 3.7778 0.011 0.076 1.667 0.000 3.8222 0.010 0.076 1.914 0.000 3.8667 0.008 0.077 2.123 0.000 3.9111 0.007 0.077 2.288 0.000 3.9556 0.005 0.077 2.408 0.000 4.0000 0.000 0.077 2.500 0.000 4.0444 0.000 0.000 2.623 0.000 ___________________________________________________________________ Name : Bioretention 1 Bottom Length: 60.00 ft. Bottom Width: 8.00 ft. Material thickness of first layer: 1.5 Material type for first layer: SMMWW 12 in/hr Material thickness of second layer: 1 Material type for second layer: Sand Material thickness of third layer: 1.5 Material type for third layer: GRAVEL Infiltration On Infiltration rate: 0.3 Infiltration safety factor: 1 Total Volume Infiltrated (ac-ft.): 89.707 Total Volume Through Riser (ac-ft.): 70.874 Total Volume Through Facility (ac-ft.): 160.581 Percent Infiltrated: 55.86 Total Precip Applied to Facility: 9.538 Total Evap From Facility: 2.832 Underdrain not used Discharge Structure Riser Height: 0.5 ft. Riser Diameter: 12 in. Element Flows To: Outlet 1 Outlet 2 ___________________________________________________________________ Type 2 HPBSM Bioretention 1 Hydraulic Table Stage(feet) Area(ac.) Volume(ac-ft.) Discharge(cfs) Infilt(cfs) 0.0000 0.0617 0.0000 0.0000 0.0000 0.0714 0.0606 0.0002 0.0000 0.0000 0.1429 0.0594 0.0004 0.0000 0.0000 0.2143 0.0583 0.0006 0.0000 0.0000 0.2857 0.0572 0.0008 0.0000 0.0000 0.3571 0.0561 0.0013 0.0000 0.0007 0.4286 0.0550 0.0018 0.0000 0.0013 0.5000 0.0539 0.0023 0.0000 0.0015 0.5714 0.0528 0.0028 0.0000 0.0027 0.6429 0.0518 0.0033 0.0000 0.0029 0.7143 0.0507 0.0039 0.0000 0.0033 0.7857 0.0497 0.0045 0.0000 0.0033 0.8571 0.0486 0.0052 0.0000 0.0033 0.9286 0.0476 0.0058 0.0000 0.0033 1.0000 0.0466 0.0065 0.0000 0.0033 1.0714 0.0455 0.0072 0.0000 0.0033 1.1429 0.0445 0.0079 0.0000 0.0033 1.2143 0.0435 0.0087 0.0000 0.0033 1.2857 0.0425 0.0095 0.0000 0.0033 1.3571 0.0415 0.0103 0.0000 0.0033 1.4286 0.0406 0.0111 0.0000 0.0033 1.5000 0.0396 0.0120 0.0000 0.0033 1.5714 0.0386 0.0128 0.0000 0.0033 1.6429 0.0377 0.0136 0.0000 0.0033 1.7143 0.0367 0.0144 0.0000 0.0033 1.7857 0.0358 0.0153 0.0000 0.0033 1.8571 0.0349 0.0161 0.0000 0.0033 1.9286 0.0340 0.0171 0.0000 0.0033 2.0000 0.0331 0.0180 0.0000 0.0033 2.0714 0.0322 0.0189 0.0000 0.0033 2.1429 0.0313 0.0199 0.0000 0.0033 2.2143 0.0304 0.0209 0.0000 0.0033 2.2857 0.0295 0.0220 0.0000 0.0033 2.3571 0.0286 0.0230 0.0000 0.0033 2.4286 0.0278 0.0241 0.0000 0.0033 2.5000 0.0269 0.0253 0.0000 0.0033 2.5714 0.0261 0.0265 0.0000 0.0033 2.6429 0.0253 0.0277 0.0000 0.0033 2.7143 0.0244 0.0289 0.0000 0.0033 2.7857 0.0236 0.0302 0.0000 0.0033 2.8571 0.0228 0.0315 0.0000 0.0033 2.9286 0.0220 0.0329 0.0000 0.0033 3.0000 0.0212 0.0342 0.0000 0.0033 3.0714 0.0204 0.0356 0.0000 0.0033 3.1429 0.0197 0.0370 0.0000 0.0033 3.2143 0.0189 0.0385 0.0000 0.0033 3.2857 0.0181 0.0400 0.0000 0.0033 3.3571 0.0174 0.0415 0.0000 0.0033 3.4286 0.0166 0.0431 0.0000 0.0033 3.5000 0.0159 0.0446 0.0000 0.0033 3.5714 0.0152 0.0463 0.0000 0.0033 3.6429 0.0145 0.0479 0.0000 0.0033 3.7143 0.0138 0.0496 0.0000 0.0033 3.7857 0.0131 0.0513 0.0000 0.0033 3.8571 0.0124 0.0530 0.0000 0.0033 3.9286 0.0117 0.0548 0.0000 0.0033 4.0000 0.0110 0.0566 0.0000 0.0033 Surface retention 1 Hydraulic Table Stage(feet) Area(ac.) Volume(ac-ft.) Discharge(cfs) To Amended(cfs) Wetted Surface 4.0000 0.0617 0.0566 0.0000 0.1333 0.0000 4.0714 0.0629 0.0611 0.0000 0.1333 0.0000 4.1429 0.0640 0.0656 0.0000 0.1460 0.0000 4.2143 0.0652 0.0702 0.0000 0.1524 0.0000 4.2857 0.0663 0.0749 0.0000 0.1587 0.0000 4.3571 0.0675 0.0797 0.0000 0.1651 0.0000 4.4286 0.0687 0.0846 0.0000 0.1714 0.0000 4.5000 0.0699 0.0895 0.0000 0.1778 0.0000 4.5714 0.0711 0.0945 0.2020 0.1841 0.0000 4.6429 0.0723 0.0997 0.5635 0.1905 0.0000 4.7143 0.0735 0.1049 0.9966 0.1968 0.0000 4.7857 0.0748 0.1102 1.4294 0.2032 0.0000 4.8571 0.0760 0.1156 1.7939 0.2095 0.0000 4.9286 0.0773 0.1210 2.0472 0.2159 0.0000 5.0000 0.0785 0.1266 2.2033 0.2222 0.0000 5.0714 0.0798 0.1323 2.3809 0.2286 0.0000 5.1429 0.0810 0.1380 2.5253 0.2349 0.0000 5.2143 0.0823 0.1438 2.6619 0.2413 0.0000 5.2857 0.0836 0.1498 2.7918 0.2476 0.0000 5.3571 0.0849 0.1558 2.9160 0.2540 0.0000 5.4286 0.0862 0.1619 3.0351 0.2603 0.0000 5.5000 0.0875 0.1681 3.1496 0.2667 0.0000 5.5714 0.0889 0.1744 3.2602 0.2730 0.0000 5.6429 0.0902 0.1808 3.3671 0.2794 0.0000 5.7143 0.0915 0.1873 3.4707 0.2857 0.0000 5.7857 0.0929 0.1939 3.5713 0.2921 0.0000 5.8571 0.0942 0.2005 3.6692 0.2984 0.0000 5.9286 0.0956 0.2073 3.7645 0.3048 0.0000 6.0000 0.0970 0.2142 3.8575 0.3111 0.0000 6.0714 0.0984 0.2212 3.9483 0.3175 0.0000 6.1429 0.0997 0.2283 4.0370 0.3238 0.0000 6.2143 0.1011 0.2354 4.1238 0.3302 0.0000 6.2857 0.1025 0.2427 4.2089 0.3365 0.0000 6.3571 0.1040 0.2501 4.2922 0.3429 0.0000 6.4286 0.1054 0.2576 4.3740 0.3492 0.0000 6.5000 0.1068 0.2651 4.4542 0.3556 0.0000 6.5000 0.1068 0.2651 4.5331 0.3556 0.0000 ___________________________________________________________________ Name : Surface retention 1 Element Flows To: Outlet 1 Outlet 2 Bioretention 1 ___________________________________________________________________ ___________________________________________________________________ ANALYSIS RESULTS Stream Protection Duration ___________________________________________________________________ Predeveloped Landuse Totals for POC #1 Total Pervious Area:0.743 Total Impervious Area:0.961 ___________________________________________________________________ Mitigated Landuse Totals for POC #1 Total Pervious Area:0.743 Total Impervious Area:0.961 ___________________________________________________________________ Flow Frequency Return Periods for Predeveloped. POC #1 Return Period Flow(cfs) 2 year 0.432618 5 year 0.5562 10 year 0.643072 25 year 0.758829 50 year 0.849559 100 year 0.944259 Flow Frequency Return Periods for Mitigated. POC #1 Return Period Flow(cfs) 2 year 0.140799 5 year 0.207803 10 year 0.262409 25 year 0.344541 50 year 0.416273 100 year 0.497948 ___________________________________________________________________ Stream Protection Duration Annual Peaks for Predeveloped and Mitigated. POC #1 Year Predeveloped Mitigated 1949 0.545 0.173 1950 0.563 0.159 1951 0.351 0.186 1952 0.279 0.104 1953 0.334 0.110 1954 0.362 0.109 1955 0.409 0.193 1956 0.387 0.125 1957 0.400 0.192 1958 0.347 0.125 1959 0.385 0.113 1960 0.368 0.178 1961 0.356 0.112 1962 0.307 0.090 1963 0.374 0.097 1964 0.369 0.116 1965 0.431 0.108 1966 0.305 0.110 1967 0.551 0.191 1968 0.656 0.110 1969 0.385 0.123 1970 0.389 0.101 1971 0.473 0.116 1972 0.510 0.224 1973 0.309 0.114 1974 0.441 0.102 1975 0.470 0.198 1976 0.357 0.110 1977 0.354 0.103 1978 0.523 0.177 1979 0.631 0.104 1980 0.654 0.147 1981 0.408 0.127 1982 0.585 0.223 1983 0.485 0.137 1984 0.316 0.091 1985 0.402 0.113 1986 0.351 0.216 1987 0.551 0.212 1988 0.368 0.100 1989 0.577 0.094 1990 0.848 0.490 1991 0.652 0.278 1992 0.315 0.126 1993 0.398 0.098 1994 0.348 0.082 1995 0.371 0.122 1996 0.528 0.223 1997 0.398 0.197 1998 0.399 0.121 1999 0.853 0.187 2000 0.395 0.156 2001 0.492 0.101 2002 0.503 0.226 2003 0.513 0.109 2004 0.829 0.488 2005 0.325 0.186 2006 0.322 0.121 2007 0.831 0.426 2008 0.616 0.477 2009 0.606 0.202 ___________________________________________________________________ Stream Protection Duration Ranked Annual Peaks for Predeveloped and Mitigated. POC #1 Rank Predeveloped Mitigated 1 0.8528 0.4896 2 0.8481 0.4883 3 0.8308 0.4768 4 0.8289 0.4257 5 0.6557 0.2782 6 0.6542 0.2259 7 0.6518 0.2244 8 0.6306 0.2235 9 0.6163 0.2233 10 0.6059 0.2156 11 0.5848 0.2117 12 0.5768 0.2018 13 0.5633 0.1979 14 0.5512 0.1966 15 0.5506 0.1927 16 0.5449 0.1915 17 0.5283 0.1906 18 0.5234 0.1873 19 0.5126 0.1864 20 0.5105 0.1858 21 0.5027 0.1783 22 0.4925 0.1773 23 0.4852 0.1731 24 0.4728 0.1588 25 0.4695 0.1559 26 0.4407 0.1472 27 0.4311 0.1371 28 0.4086 0.1271 29 0.4081 0.1258 30 0.4018 0.1254 31 0.4002 0.1247 32 0.3987 0.1228 33 0.3984 0.1223 34 0.3979 0.1214 35 0.3948 0.1212 36 0.3888 0.1157 37 0.3865 0.1156 38 0.3852 0.1139 39 0.3846 0.1126 40 0.3738 0.1126 41 0.3705 0.1117 42 0.3695 0.1103 43 0.3684 0.1098 44 0.3678 0.1097 45 0.3623 0.1096 46 0.3566 0.1094 47 0.3558 0.1090 48 0.3542 0.1083 49 0.3511 0.1040 50 0.3506 0.1037 51 0.3477 0.1033 52 0.3474 0.1016 53 0.3336 0.1014 54 0.3246 0.1011 55 0.3220 0.0998 56 0.3162 0.0982 57 0.3152 0.0968 58 0.3092 0.0944 59 0.3066 0.0915 60 0.3045 0.0901 61 0.2792 0.0822 ___________________________________________________________________ Stream Protection Duration POC #1 The Facility PASSED The Facility PASSED. Flow(cfs) Predev Mit Percentage Pass/Fail 0.2163 1367 164 11 Pass 0.2227 1261 148 11 Pass 0.2291 1133 135 11 Pass 0.2355 1049 128 12 Pass 0.2419 953 124 13 Pass 0.2483 867 112 12 Pass 0.2547 783 102 13 Pass 0.2611 697 96 13 Pass 0.2675 637 87 13 Pass 0.2739 580 72 12 Pass 0.2803 529 61 11 Pass 0.2867 492 55 11 Pass 0.2931 452 49 10 Pass 0.2995 425 44 10 Pass 0.3059 387 42 10 Pass 0.3123 364 42 11 Pass 0.3187 331 41 12 Pass 0.3250 306 34 11 Pass 0.3314 284 33 11 Pass 0.3378 268 31 11 Pass 0.3442 250 31 12 Pass 0.3506 232 30 12 Pass 0.3570 212 27 12 Pass 0.3634 196 23 11 Pass 0.3698 186 22 11 Pass 0.3762 174 22 12 Pass 0.3826 168 21 12 Pass 0.3890 155 18 11 Pass 0.3954 141 17 12 Pass 0.4018 130 17 13 Pass 0.4082 124 17 13 Pass 0.4146 114 15 13 Pass 0.4210 109 14 12 Pass 0.4274 102 11 10 Pass 0.4338 91 10 10 Pass 0.4402 90 10 11 Pass 0.4466 86 9 10 Pass 0.4530 84 8 9 Pass 0.4594 76 7 9 Pass 0.4658 71 7 9 Pass 0.4722 67 6 8 Pass 0.4786 63 4 6 Pass 0.4850 63 4 6 Pass 0.4914 57 0 0 Pass 0.4978 53 0 0 Pass 0.5041 51 0 0 Pass 0.5105 49 0 0 Pass 0.5169 42 0 0 Pass 0.5233 39 0 0 Pass 0.5297 35 0 0 Pass 0.5361 34 0 0 Pass 0.5425 34 0 0 Pass 0.5489 32 0 0 Pass 0.5553 29 0 0 Pass 0.5617 27 0 0 Pass 0.5681 23 0 0 Pass 0.5745 23 0 0 Pass 0.5809 21 0 0 Pass 0.5873 20 0 0 Pass 0.5937 20 0 0 Pass 0.6001 19 0 0 Pass 0.6065 18 0 0 Pass 0.6129 18 0 0 Pass 0.6193 17 0 0 Pass 0.6257 16 0 0 Pass 0.6321 15 0 0 Pass 0.6385 15 0 0 Pass 0.6449 15 0 0 Pass 0.6513 14 0 0 Pass 0.6577 11 0 0 Pass 0.6641 9 0 0 Pass 0.6705 7 0 0 Pass 0.6769 7 0 0 Pass 0.6833 7 0 0 Pass 0.6896 7 0 0 Pass 0.6960 7 0 0 Pass 0.7024 7 0 0 Pass 0.7088 7 0 0 Pass 0.7152 7 0 0 Pass 0.7216 7 0 0 Pass 0.7280 7 0 0 Pass 0.7344 7 0 0 Pass 0.7408 7 0 0 Pass 0.7472 7 0 0 Pass 0.7536 7 0 0 Pass 0.7600 6 0 0 Pass 0.7664 6 0 0 Pass 0.7728 5 0 0 Pass 0.7792 5 0 0 Pass 0.7856 4 0 0 Pass 0.7920 4 0 0 Pass 0.7984 4 0 0 Pass 0.8048 4 0 0 Pass 0.8112 4 0 0 Pass 0.8176 4 0 0 Pass 0.8240 4 0 0 Pass 0.8304 3 0 0 Pass 0.8368 2 0 0 Pass 0.8432 2 0 0 Pass 0.8496 1 0 0 Pass _____________________________________________________ ___________________________________________________________________ Water Quality BMP Flow and Volume for POC #1 On-line facility volume: 0.142 acre-feet On-line facility target flow: 0.1103 cfs. Adjusted for 15 min: 0.1103 cfs. Off-line facility target flow: 0.0707 cfs. Adjusted for 15 min: 0.0707 cfs. ___________________________________________________________________ LID Report LID Technique Used for Total Volume Volume Infiltration Cumulative Percent Water Quality Percent Comment Treatment? Needs Through Volume Volume Volume Water Quality Treatment Facility (ac-ft.) Infiltration Infiltrated Treated (ac-ft) (ac-ft) Credit retention 1 POC Y 146.13 160.58 89.71 N 55.86 89.71 55.86 Tank 1 N 140.03 N 0.00 Total Volume Infiltrated 286.16 160.58 89.71 28.53 89.71 90 / 161 = 56%Treat. Credit = 56% Compliance with LID Standard 8 Duration Analysis Result = Passed ___________________________________________________________________ Perlnd and Implnd Changes No changes have been made. ___________________________________________________________________ This program and accompanying documentation are provided 'as-is' without warranty of any kind. The entire risk regarding the performance and results of this program is assumed by End User. Clear Creek Solutions Inc. and the governmental licensee or sublicensees disclaim all warranties, either expressed or implied, including but not limited to implied warranties of program and accompanying documentation. In no event shall Clear Creek Solutions Inc. be liable for any damages whatsoever (including without limitation to damages for loss of business profits, loss of business information, business interruption, and the like) arising out of the use of, or inability to use this program even if Clear Creek Solutions Inc. or their authorized representatives have been advised of the possibility of such damages. Software Copyright © by : Clear Creek Solutions, Inc. 2005-2021; All Rights Reserved. 56% Water Quality Treated WWHM2012 PROJECT REPORT ___________________________________________________________________ Project Name: Benson Glen Site Name: Benson Glen Site Address: City : Report Date: 12/1/2021 Gage : Seatac Data Start : 1948/10/01 Data End : 2009/09/30 Precip Scale: 1.00 Version Date: 2019/09/13 Version : 4.2.17 ___________________________________________________________________ Low Flow Threshold for POC 1 : 50 Percent of the 2 Year ___________________________________________________________________ High Flow Threshold for POC 1: 50 year ___________________________________________________________________ PREDEVELOPED LAND USE Name : Basin 1 Bypass: No GroundWater: No Pervious Land Use acre A B, Lawn, Mod .742 A B, Lawn, Steep .001 Pervious Total 0.743 Impervious Land Use acre ROADS MOD 0.961 Impervious Total 0.961 Basin Total 1.704 ___________________________________________________________________ Element Flows To: Surface Interflow Groundwater ___________________________________________________________________ MITIGATED LAND USE Name : Basin 1 Bypass: No BENSON GLEN - MODIFIED SWALE WITH HPBSM GroundWater: No Pervious Land Use acre A B, Lawn, Mod .742 A B, Lawn, Steep .001 Pervious Total 0.743 Impervious Land Use acre ROADS MOD 0.961 Impervious Total 0.961 Basin Total 1.704 ___________________________________________________________________ Element Flows To: Surface Interflow Groundwater Tank 1 Tank 1 ___________________________________________________________________ Name : Tank 1 Tank Name: Tank 1 Dimensions Depth: 4 ft. Tank Type : Circular Diameter : 4 ft. Length : 270 ft. Discharge Structure Riser Height: 3.5 ft. Riser Diameter: 12 in. Orifice 1 Diameter: 1.73 in. Elevation: 0 ft. Orifice 2 Diameter: 1.91 in. Elevation: 2.15 ft. Element Flows To: Outlet 1 Outlet 2 Surface retention 1 ___________________________________________________________________ Tank Hydraulic Table Stage(feet) Area(ac.) Volume(ac-ft.) Discharge(cfs) Infilt(cfs) 0.0000 0.000 0.000 0.000 0.000 0.0444 0.005 0.000 0.017 0.000 0.0889 0.007 0.000 0.024 0.000 0.1333 0.008 0.000 0.029 0.000 0.1778 0.010 0.001 0.034 0.000 0.2222 0.011 0.001 0.038 0.000 0.2667 0.012 0.002 0.041 0.000 0.3111 0.013 0.002 0.045 0.000 0.3556 0.014 0.003 0.048 0.000 0.4000 0.014 0.004 0.051 0.000 0.4444 0.015 0.004 0.054 0.000 0.4889 0.016 0.005 0.056 0.000 0.5333 0.016 0.006 0.059 0.000 0.5778 0.017 0.006 0.061 0.000 0.6222 0.018 0.007 0.064 0.000 0.6667 0.018 0.008 0.066 0.000 0.7111 0.019 0.009 0.068 0.000 0.7556 0.019 0.010 0.070 0.000 0.8000 0.019 0.011 0.072 0.000 0.8444 0.020 0.012 0.074 0.000 0.8889 0.020 0.012 0.076 0.000 0.9333 0.021 0.013 0.078 0.000 0.9778 0.021 0.014 0.080 0.000 1.0222 0.021 0.015 0.082 0.000 1.0667 0.021 0.016 0.083 0.000 1.1111 0.022 0.017 0.085 0.000 1.1556 0.022 0.018 0.087 0.000 1.2000 0.022 0.019 0.089 0.000 1.2444 0.023 0.020 0.090 0.000 1.2889 0.023 0.021 0.092 0.000 1.3333 0.023 0.022 0.093 0.000 1.3778 0.023 0.023 0.095 0.000 1.4222 0.023 0.024 0.096 0.000 1.4667 0.023 0.025 0.098 0.000 1.5111 0.024 0.026 0.099 0.000 1.5556 0.024 0.028 0.101 0.000 1.6000 0.024 0.029 0.102 0.000 1.6444 0.024 0.030 0.104 0.000 1.6889 0.024 0.031 0.105 0.000 1.7333 0.024 0.032 0.106 0.000 1.7778 0.024 0.033 0.108 0.000 1.8222 0.024 0.034 0.109 0.000 1.8667 0.024 0.035 0.111 0.000 1.9111 0.024 0.036 0.112 0.000 1.9556 0.024 0.037 0.113 0.000 2.0000 0.024 0.038 0.114 0.000 2.0444 0.024 0.040 0.116 0.000 2.0889 0.024 0.041 0.117 0.000 2.1333 0.024 0.042 0.118 0.000 2.1778 0.024 0.043 0.136 0.000 2.2222 0.024 0.044 0.147 0.000 2.2667 0.024 0.045 0.156 0.000 2.3111 0.024 0.046 0.163 0.000 2.3556 0.024 0.047 0.169 0.000 2.4000 0.024 0.048 0.175 0.000 2.4444 0.024 0.049 0.180 0.000 2.4889 0.024 0.050 0.185 0.000 2.5333 0.023 0.052 0.190 0.000 2.5778 0.023 0.053 0.195 0.000 2.6222 0.023 0.054 0.199 0.000 2.6667 0.023 0.055 0.203 0.000 2.7111 0.023 0.056 0.207 0.000 2.7556 0.023 0.057 0.211 0.000 2.8000 0.022 0.058 0.215 0.000 2.8444 0.022 0.059 0.219 0.000 2.8889 0.022 0.060 0.223 0.000 2.9333 0.021 0.061 0.226 0.000 2.9778 0.021 0.062 0.230 0.000 3.0222 0.021 0.063 0.233 0.000 3.0667 0.021 0.064 0.237 0.000 3.1111 0.020 0.065 0.240 0.000 3.1556 0.020 0.065 0.243 0.000 3.2000 0.019 0.066 0.246 0.000 3.2444 0.019 0.067 0.249 0.000 3.2889 0.019 0.068 0.252 0.000 3.3333 0.018 0.069 0.256 0.000 3.3778 0.018 0.070 0.259 0.000 3.4222 0.017 0.071 0.261 0.000 3.4667 0.016 0.071 0.264 0.000 3.5111 0.016 0.072 0.280 0.000 3.5556 0.015 0.073 0.409 0.000 3.6000 0.014 0.073 0.606 0.000 3.6444 0.014 0.074 0.848 0.000 3.6889 0.013 0.075 1.117 0.000 3.7333 0.012 0.075 1.396 0.000 3.7778 0.011 0.076 1.667 0.000 3.8222 0.010 0.076 1.914 0.000 3.8667 0.008 0.077 2.123 0.000 3.9111 0.007 0.077 2.288 0.000 3.9556 0.005 0.077 2.408 0.000 4.0000 0.000 0.077 2.500 0.000 4.0444 0.000 0.000 2.623 0.000 ___________________________________________________________________ Name : Bioretention 1 Bottom Length: 80.00 ft. Bottom Width: 10.00 ft. Material thickness of first layer: 1.5 Material type for first layer: SMMWW 12 in/hr Material thickness of second layer: 1 Material type for second layer: Sand Material thickness of third layer: 1.5 Material type for third layer: GRAVEL Infiltration On Infiltration rate: 0.3 Infiltration safety factor: 1 Total Volume Infiltrated (ac-ft.): 111.18 Total Volume Through Riser (ac-ft.): 46.797 Total Volume Through Facility (ac-ft.): 157.977 Percent Infiltrated: 70.38 Total Precip Applied to Facility: 6.927 Total Evap From Facility: 2.826 Underdrain not used Discharge Structure Riser Height: 0.5 ft. Riser Diameter: 12 in. Element Flows To: Outlet 1 Outlet 2 ___________________________________________________________________ Increased Length by 20 feet and increased width by 2 feet Bioretention 1 Hydraulic Table Stage(feet) Area(ac.) Volume(ac-ft.) Discharge(cfs) Infilt(cfs) 0.0000 0.0525 0.0000 0.0000 0.0000 0.0714 0.0518 0.0003 0.0000 0.0000 0.1429 0.0511 0.0006 0.0000 0.0000 0.2143 0.0504 0.0009 0.0000 0.0000 0.2857 0.0496 0.0013 0.0000 0.0000 0.3571 0.0489 0.0016 0.0000 0.0012 0.4286 0.0482 0.0023 0.0000 0.0021 0.5000 0.0475 0.0030 0.0000 0.0025 0.5714 0.0468 0.0037 0.0000 0.0045 0.6429 0.0461 0.0045 0.0000 0.0048 0.7143 0.0455 0.0052 0.0000 0.0056 0.7857 0.0448 0.0060 0.0000 0.0056 0.8571 0.0441 0.0068 0.0000 0.0056 0.9286 0.0434 0.0076 0.0000 0.0056 1.0000 0.0427 0.0084 0.0000 0.0056 1.0714 0.0421 0.0093 0.0000 0.0056 1.1429 0.0414 0.0101 0.0000 0.0056 1.2143 0.0408 0.0110 0.0000 0.0056 1.2857 0.0401 0.0119 0.0000 0.0056 1.3571 0.0395 0.0129 0.0000 0.0056 1.4286 0.0388 0.0138 0.0000 0.0056 1.5000 0.0382 0.0148 0.0000 0.0056 1.5714 0.0375 0.0156 0.0000 0.0056 1.6429 0.0369 0.0165 0.0000 0.0056 1.7143 0.0363 0.0174 0.0000 0.0056 1.7857 0.0356 0.0183 0.0000 0.0056 1.8571 0.0350 0.0192 0.0000 0.0056 1.9286 0.0344 0.0201 0.0000 0.0056 2.0000 0.0338 0.0211 0.0000 0.0056 2.0714 0.0332 0.0221 0.0000 0.0056 2.1429 0.0326 0.0231 0.0000 0.0056 2.2143 0.0320 0.0241 0.0000 0.0056 2.2857 0.0314 0.0251 0.0000 0.0056 2.3571 0.0308 0.0261 0.0000 0.0056 2.4286 0.0302 0.0272 0.0000 0.0056 2.5000 0.0296 0.0283 0.0000 0.0056 2.5714 0.0290 0.0295 0.0000 0.0056 2.6429 0.0285 0.0306 0.0000 0.0056 2.7143 0.0279 0.0318 0.0000 0.0056 2.7857 0.0273 0.0330 0.0000 0.0056 2.8571 0.0268 0.0342 0.0000 0.0056 2.9286 0.0262 0.0355 0.0000 0.0056 3.0000 0.0257 0.0367 0.0000 0.0056 3.0714 0.0251 0.0380 0.0000 0.0056 3.1429 0.0246 0.0393 0.0000 0.0056 3.2143 0.0240 0.0406 0.0000 0.0056 3.2857 0.0235 0.0419 0.0000 0.0056 3.3571 0.0230 0.0433 0.0000 0.0056 3.4286 0.0224 0.0447 0.0000 0.0056 3.5000 0.0219 0.0461 0.0000 0.0056 3.5714 0.0214 0.0475 0.0000 0.0056 3.6429 0.0209 0.0489 0.0000 0.0056 3.7143 0.0204 0.0504 0.0000 0.0056 3.7857 0.0199 0.0519 0.0000 0.0056 3.8571 0.0194 0.0534 0.0000 0.0056 3.9286 0.0189 0.0549 0.0000 0.0056 4.0000 0.0184 0.0565 0.0000 0.0056 Surface retention 1 Hydraulic Table Stage(feet) Area(ac.) Volume(ac-ft.) Discharge(cfs) To Amended(cfs) Wetted Surface 4.0000 0.0525 0.0565 0.0000 0.2222 0.0000 4.0714 0.0533 0.0602 0.0000 0.2222 0.0000 4.1429 0.0540 0.0641 0.0000 0.2434 0.0000 4.2143 0.0547 0.0679 0.0000 0.2540 0.0000 4.2857 0.0555 0.0719 0.0000 0.2646 0.0000 4.3571 0.0562 0.0759 0.0000 0.2751 0.0000 4.4286 0.0570 0.0799 0.0000 0.2857 0.0000 4.5000 0.0577 0.0840 0.0000 0.2963 0.0000 4.5714 0.0585 0.0882 0.2020 0.3069 0.0000 4.6429 0.0592 0.0924 0.5635 0.3175 0.0000 4.7143 0.0600 0.0966 0.9966 0.3280 0.0000 4.7857 0.0608 0.1009 1.4294 0.3386 0.0000 4.8571 0.0616 0.1053 1.7939 0.3492 0.0000 4.9286 0.0623 0.1097 2.0472 0.3598 0.0000 5.0000 0.0631 0.1142 2.2033 0.3704 0.0000 5.0714 0.0639 0.1188 2.3809 0.3810 0.0000 5.1429 0.0647 0.1233 2.5253 0.3915 0.0000 5.2143 0.0655 0.1280 2.6619 0.4021 0.0000 5.2857 0.0663 0.1327 2.7918 0.4127 0.0000 5.3571 0.0671 0.1375 2.9160 0.4233 0.0000 5.4286 0.0679 0.1423 3.0351 0.4339 0.0000 5.5000 0.0687 0.1472 3.1496 0.4444 0.0000 5.5714 0.0696 0.1521 3.2602 0.4550 0.0000 5.6429 0.0704 0.1571 3.3671 0.4656 0.0000 5.7143 0.0712 0.1622 3.4707 0.4762 0.0000 5.7857 0.0720 0.1673 3.5713 0.4868 0.0000 5.8571 0.0729 0.1725 3.6692 0.4974 0.0000 5.9286 0.0737 0.1777 3.7645 0.5079 0.0000 6.0000 0.0746 0.1830 3.8575 0.5185 0.0000 6.0714 0.0754 0.1884 3.9483 0.5291 0.0000 6.1429 0.0763 0.1938 4.0370 0.5397 0.0000 6.2143 0.0771 0.1992 4.1238 0.5503 0.0000 6.2857 0.0780 0.2048 4.2089 0.5608 0.0000 6.3571 0.0788 0.2104 4.2922 0.5714 0.0000 6.4286 0.0797 0.2160 4.3740 0.5820 0.0000 6.5000 0.0806 0.2218 4.4542 0.5926 0.0000 6.5000 0.0806 0.2218 4.5331 0.5926 0.0000 ___________________________________________________________________ Name : Surface retention 1 Element Flows To: Outlet 1 Outlet 2 Bioretention 1 ___________________________________________________________________ ___________________________________________________________________ ANALYSIS RESULTS Stream Protection Duration ___________________________________________________________________ Predeveloped Landuse Totals for POC #1 Total Pervious Area:0.743 Total Impervious Area:0.961 ___________________________________________________________________ Mitigated Landuse Totals for POC #1 Total Pervious Area:0.743 Total Impervious Area:0.961 ___________________________________________________________________ Flow Frequency Return Periods for Predeveloped. POC #1 Return Period Flow(cfs) 2 year 0.432618 5 year 0.5562 10 year 0.643072 25 year 0.758829 50 year 0.849559 100 year 0.944259 Flow Frequency Return Periods for Mitigated. POC #1 Return Period Flow(cfs) 2 year 0.134776 5 year 0.201398 10 year 0.256221 25 year 0.339351 50 year 0.412484 100 year 0.496243 ___________________________________________________________________ Stream Protection Duration Annual Peaks for Predeveloped and Mitigated. POC #1 Year Predeveloped Mitigated 1949 0.545 0.170 1950 0.563 0.156 1951 0.351 0.181 1952 0.279 0.100 1953 0.334 0.105 1954 0.362 0.103 1955 0.409 0.188 1956 0.387 0.121 1957 0.400 0.188 1958 0.347 0.121 1959 0.385 0.108 1960 0.368 0.175 1961 0.356 0.107 1962 0.307 0.082 1963 0.374 0.093 1964 0.369 0.107 1965 0.431 0.105 1966 0.305 0.105 1967 0.551 0.187 1968 0.656 0.105 1969 0.385 0.118 1970 0.389 0.101 1971 0.473 0.111 1972 0.510 0.220 1973 0.309 0.110 1974 0.441 0.098 1975 0.470 0.195 1976 0.357 0.105 1977 0.354 0.099 1978 0.523 0.121 1979 0.631 0.094 1980 0.654 0.144 1981 0.408 0.110 1982 0.585 0.221 1983 0.485 0.115 1984 0.316 0.088 1985 0.402 0.109 1986 0.351 0.210 1987 0.551 0.206 1988 0.368 0.096 1989 0.577 0.091 1990 0.848 0.487 1991 0.652 0.272 1992 0.315 0.121 1993 0.398 0.095 1994 0.348 0.079 1995 0.371 0.117 1996 0.528 0.219 1997 0.398 0.192 1998 0.399 0.116 1999 0.853 0.184 2000 0.395 0.153 2001 0.492 0.099 2002 0.503 0.220 2003 0.513 0.105 2004 0.829 0.481 2005 0.325 0.183 2006 0.322 0.117 2007 0.831 0.425 2008 0.616 0.478 2009 0.606 0.198 ___________________________________________________________________ Stream Protection Duration Ranked Annual Peaks for Predeveloped and Mitigated. POC #1 Rank Predeveloped Mitigated 1 0.8528 0.4872 2 0.8481 0.4810 3 0.8308 0.4782 4 0.8289 0.4251 5 0.6557 0.2724 6 0.6542 0.2206 7 0.6518 0.2205 8 0.6306 0.2198 9 0.6163 0.2186 10 0.6059 0.2104 11 0.5848 0.2058 12 0.5768 0.1976 13 0.5633 0.1950 14 0.5512 0.1917 15 0.5506 0.1880 16 0.5449 0.1880 17 0.5283 0.1865 18 0.5234 0.1837 19 0.5126 0.1831 20 0.5105 0.1813 21 0.5027 0.1752 22 0.4925 0.1701 23 0.4852 0.1562 24 0.4728 0.1527 25 0.4695 0.1438 26 0.4407 0.1213 27 0.4311 0.1212 28 0.4086 0.1210 29 0.4081 0.1205 30 0.4018 0.1181 31 0.4002 0.1173 32 0.3987 0.1168 33 0.3984 0.1160 34 0.3979 0.1152 35 0.3948 0.1112 36 0.3888 0.1097 37 0.3865 0.1096 38 0.3852 0.1087 39 0.3846 0.1081 40 0.3738 0.1070 41 0.3705 0.1069 42 0.3695 0.1053 43 0.3684 0.1053 44 0.3678 0.1053 45 0.3623 0.1052 46 0.3566 0.1052 47 0.3558 0.1046 48 0.3542 0.1029 49 0.3511 0.1013 50 0.3506 0.0999 51 0.3477 0.0994 52 0.3474 0.0988 53 0.3336 0.0978 54 0.3246 0.0961 55 0.3220 0.0946 56 0.3162 0.0942 57 0.3152 0.0931 58 0.3092 0.0908 59 0.3066 0.0881 60 0.3045 0.0817 61 0.2792 0.0790 ___________________________________________________________________ Stream Protection Duration POC #1 The Facility PASSED The Facility PASSED. Flow(cfs) Predev Mit Percentage Pass/Fail 0.2163 1367 151 11 Pass 0.2227 1261 139 11 Pass 0.2291 1133 131 11 Pass 0.2355 1049 124 11 Pass 0.2419 953 114 11 Pass 0.2483 867 103 11 Pass 0.2547 783 97 12 Pass 0.2611 697 86 12 Pass 0.2675 637 74 11 Pass 0.2739 580 61 10 Pass 0.2803 529 54 10 Pass 0.2867 492 49 9 Pass 0.2931 452 42 9 Pass 0.2995 425 42 9 Pass 0.3059 387 41 10 Pass 0.3123 364 39 10 Pass 0.3187 331 34 10 Pass 0.3250 306 32 10 Pass 0.3314 284 31 10 Pass 0.3378 268 31 11 Pass 0.3442 250 29 11 Pass 0.3506 232 27 11 Pass 0.3570 212 23 10 Pass 0.3634 196 22 11 Pass 0.3698 186 22 11 Pass 0.3762 174 21 12 Pass 0.3826 168 19 11 Pass 0.3890 155 17 10 Pass 0.3954 141 17 12 Pass 0.4018 130 17 13 Pass 0.4082 124 16 12 Pass 0.4146 114 14 12 Pass 0.4210 109 14 12 Pass 0.4274 102 11 10 Pass 0.4338 91 9 9 Pass 0.4402 90 9 10 Pass 0.4466 86 9 10 Pass 0.4530 84 7 8 Pass 0.4594 76 7 9 Pass 0.4658 71 7 9 Pass 0.4722 67 5 7 Pass 0.4786 63 5 7 Pass 0.4850 63 1 1 Pass 0.4914 57 0 0 Pass 0.4978 53 0 0 Pass 0.5041 51 0 0 Pass 0.5105 49 0 0 Pass 0.5169 42 0 0 Pass 0.5233 39 0 0 Pass 0.5297 35 0 0 Pass 0.5361 34 0 0 Pass 0.5425 34 0 0 Pass 0.5489 32 0 0 Pass 0.5553 29 0 0 Pass 0.5617 27 0 0 Pass 0.5681 23 0 0 Pass 0.5745 23 0 0 Pass 0.5809 21 0 0 Pass 0.5873 20 0 0 Pass 0.5937 20 0 0 Pass 0.6001 19 0 0 Pass 0.6065 18 0 0 Pass 0.6129 18 0 0 Pass 0.6193 17 0 0 Pass 0.6257 16 0 0 Pass 0.6321 15 0 0 Pass 0.6385 15 0 0 Pass 0.6449 15 0 0 Pass 0.6513 14 0 0 Pass 0.6577 11 0 0 Pass 0.6641 9 0 0 Pass 0.6705 7 0 0 Pass 0.6769 7 0 0 Pass 0.6833 7 0 0 Pass 0.6896 7 0 0 Pass 0.6960 7 0 0 Pass 0.7024 7 0 0 Pass 0.7088 7 0 0 Pass 0.7152 7 0 0 Pass 0.7216 7 0 0 Pass 0.7280 7 0 0 Pass 0.7344 7 0 0 Pass 0.7408 7 0 0 Pass 0.7472 7 0 0 Pass 0.7536 7 0 0 Pass 0.7600 6 0 0 Pass 0.7664 6 0 0 Pass 0.7728 5 0 0 Pass 0.7792 5 0 0 Pass 0.7856 4 0 0 Pass 0.7920 4 0 0 Pass 0.7984 4 0 0 Pass 0.8048 4 0 0 Pass 0.8112 4 0 0 Pass 0.8176 4 0 0 Pass 0.8240 4 0 0 Pass 0.8304 3 0 0 Pass 0.8368 2 0 0 Pass 0.8432 2 0 0 Pass 0.8496 1 0 0 Pass _____________________________________________________ ___________________________________________________________________ Water Quality BMP Flow and Volume for POC #1 On-line facility volume: 0.142 acre-feet On-line facility target flow: 0.1103 cfs. Adjusted for 15 min: 0.1103 cfs. Off-line facility target flow: 0.0707 cfs. Adjusted for 15 min: 0.0707 cfs. ___________________________________________________________________ LID Report LID Technique Used for Total Volume Volume Infiltration Cumulative Percent Water Quality Percent Comment Treatment? Needs Through Volume Volume Volume Water Quality Treatment Facility (ac-ft.) Infiltration Infiltrated Treated (ac-ft) (ac-ft) C redit retention 1 POC Y 143.76 157.98 111.18 N 70.38 111.18 70.38 Tank 1 N 140.03 N 0.00 Total Volume Infiltrated 283.79 157.98 111.18 35.65 111.18 111 / 158 = 70Treat. Credit = 70% Compliance with LID Standard 8 Duration Analysis Result = Passed ___________________________________________________________________ Perlnd and Implnd Changes No changes have been made. ___________________________________________________________________ This program and accompanying documentation are provided 'as-is' without warranty of any kind. The entire risk regarding the performance and results of this program is assumed by End User. Clear Creek Solutions Inc. and the governmental licensee or sublicensees disclaim all warranties, either expressed or implied, including but not limited to implied warranties of program and accompanying documentation. In no event shall Clear Creek Solutions Inc. be liable for any damages whatsoever (including without limitation to damages for loss of business profits, loss of business information, business interruption, and the like) arising out of the use of, or inability to use this program even if Clear Creek Solutions Inc. or their authorized representatives have been advised of the possibility of such damages. Software Copyright © by : Clear Creek Solutions, Inc. 2005-2021; All Rights Reserved. 70% Water Quality Treated South Knoll WWHM2012 PROJECT REPORT ___________________________________________________________________ Project Name: South Knoll Site Name: South Knoll Site Address: City : Renton Report Date: 12/17/2021 Gage : Seatac Data Start : 1948/10/01 Data End : 2009/09/30 Precip Scale: 1.00 Version Date: 2019/09/13 Version : 4.2.17 ___________________________________________________________________ Low Flow Threshold for POC 1 : 50 Percent of the 2 Year ___________________________________________________________________ High Flow Threshold for POC 1: 50 year ___________________________________________________________________ PREDEVELOPED LAND USE Name : Basin 1 Bypass: No GroundWater: No Pervious Land Use acre C, Forest, Mod 8.37 Pervious Total 8.37 Impervious Land Use acre Impervious Total 0 Basin Total 8.37 ___________________________________________________________________ Element Flows To: Surface Interflow Groundwater ___________________________________________________________________ MITIGATED LAND USE Name : Basin 1 Bypass: No GroundWater: No Pervious Land Use acre C, Lawn, Mod 3.29 C, Lawn, Steep 2.54 Pervious Total 5.83 Impervious Land Use acre ROADS MOD 1.79 ROADS STEEP 0.75 Impervious Total 2.54 Basin Total 8.37 ___________________________________________________________________ Element Flows To: Surface Interflow Groundwater ___________________________________________________________________ ___________________________________________________________________ ANALYSIS RESULTS Stream Protection Duration ___________________________________________________________________ Predeveloped Landuse Totals for POC #1 Total Pervious Area:8.37 Total Impervious Area:0 ___________________________________________________________________ Mitigated Landuse Totals for POC #1 Total Pervious Area:5.83 Total Impervious Area:2.54 ___________________________________________________________________ Flow Frequency Return Periods for Predeveloped. POC #1 Return Period Flow(cfs) 2 year 0.249218 5 year 0.408366 10 year 0.510695 25 year 0.63242 50 year 0.716735 100 year 0.795489 Flow Frequency Return Periods for Mitigated. POC #1 Return Period Flow(cfs) 2 year 1.697982 5 year 2.367937 10 year 2.859051 25 year 3.535391 50 year 4.080916 100 year 4.66316 ___________________________________________________________________ Stream Protection Duration Annual Peaks for Predeveloped and Mitigated. POC #1 Year Predeveloped Mitigated 1949 0.287 2.661 1950 0.340 2.440 1951 0.545 1.504 1952 0.171 0.976 1953 0.138 1.010 1954 0.212 1.360 1955 0.339 1.484 1956 0.273 1.532 1957 0.220 1.803 1958 0.245 1.215 1959 0.210 1.105 1960 0.376 1.697 1961 0.207 1.411 1962 0.129 0.991 1963 0.176 1.562 1964 0.250 1.418 1965 0.166 1.879 1966 0.160 1.149 1967 0.383 2.532 1968 0.215 2.511 1969 0.210 1.735 1970 0.168 1.582 1971 0.190 1.905 1972 0.413 2.281 1973 0.183 0.881 1974 0.203 1.892 1975 0.283 1.876 1976 0.202 1.493 1977 0.030 1.408 1978 0.171 1.798 1979 0.103 1.881 1980 0.487 3.357 1981 0.153 1.571 1982 0.316 2.671 1983 0.270 1.855 1984 0.163 1.161 1985 0.097 1.505 1986 0.427 1.539 1987 0.377 1.731 1988 0.149 1.017 1989 0.099 1.581 1990 0.902 4.274 1991 0.479 3.276 1992 0.195 1.325 1993 0.191 1.175 1994 0.064 0.940 1995 0.273 1.348 1996 0.632 2.429 1997 0.488 1.688 1998 0.119 1.637 1999 0.535 3.912 2000 0.190 1.676 2001 0.034 1.530 2002 0.220 2.283 2003 0.329 2.390 2004 0.351 3.639 2005 0.261 1.434 2006 0.293 1.418 2007 0.682 3.977 2008 0.831 3.067 2009 0.388 1.983 ___________________________________________________________________ Stream Protection Duration Ranked Annual Peaks for Predeveloped and Mitigated. POC #1 Rank Predeveloped Mitigated 1 0.9025 4.2742 2 0.8315 3.9771 3 0.6821 3.9122 4 0.6320 3.6385 5 0.5445 3.3567 6 0.5348 3.2762 7 0.4877 3.0675 8 0.4866 2.6710 9 0.4787 2.6606 10 0.4271 2.5324 11 0.4134 2.5108 12 0.3876 2.4402 13 0.3827 2.4290 14 0.3770 2.3901 15 0.3757 2.2832 16 0.3514 2.2808 17 0.3405 1.9832 18 0.3387 1.9047 19 0.3289 1.8915 20 0.3156 1.8813 21 0.2933 1.8792 22 0.2868 1.8762 23 0.2827 1.8546 24 0.2734 1.8030 25 0.2729 1.7984 26 0.2700 1.7353 27 0.2607 1.7311 28 0.2504 1.6974 29 0.2446 1.6880 30 0.2202 1.6759 31 0.2202 1.6367 32 0.2154 1.5817 33 0.2120 1.5811 34 0.2098 1.5706 35 0.2096 1.5623 36 0.2066 1.5389 37 0.2031 1.5322 38 0.2020 1.5305 39 0.1954 1.5055 40 0.1908 1.5037 41 0.1900 1.4932 42 0.1900 1.4838 43 0.1832 1.4339 44 0.1765 1.4183 45 0.1709 1.4176 46 0.1707 1.4106 47 0.1683 1.4083 48 0.1664 1.3597 49 0.1626 1.3476 50 0.1599 1.3252 51 0.1528 1.2151 52 0.1488 1.1749 53 0.1381 1.1607 54 0.1286 1.1487 55 0.1194 1.1050 56 0.1033 1.0168 57 0.0985 1.0102 58 0.0965 0.9911 59 0.0641 0.9759 60 0.0341 0.9396 61 0.0296 0.8815 ___________________________________________________________________ Stream Protection Duration POC #1 The Facility FAILED Facility FAILED duration standard for 1+ flows. Flow(cfs) Predev Mit Percentage Pass/Fail 0.1246 17263 89747 519 Fail 0.1306 15620 84357 540 Fail 0.1366 14176 79331 559 Fail 0.1426 12893 74711 579 Fail 0.1485 11672 70348 602 Fail 0.1545 10596 66412 626 Fail 0.1605 9640 62776 651 Fail 0.1665 8823 59161 670 Fail 0.1725 8094 55953 691 Fail 0.1784 7392 52980 716 Fail 0.1844 6774 50178 740 Fail 0.1904 6222 47569 764 Fail 0.1964 5760 45045 782 Fail 0.2024 5330 42778 802 Fail 0.2083 4941 40660 822 Fail 0.2143 4588 38650 842 Fail 0.2203 4259 36682 861 Fail 0.2263 3961 34864 880 Fail 0.2323 3649 33195 909 Fail 0.2382 3397 31591 929 Fail 0.2442 3142 30137 959 Fail 0.2502 2924 28682 980 Fail 0.2562 2712 27399 1010 Fail 0.2622 2492 26180 1050 Fail 0.2682 2321 24961 1075 Fail 0.2741 2137 23827 1114 Fail 0.2801 1973 22715 1151 Fail 0.2861 1826 21667 1186 Fail 0.2921 1703 20679 1214 Fail 0.2981 1577 19738 1251 Fail 0.3040 1443 18846 1306 Fail 0.3100 1325 17967 1356 Fail 0.3160 1232 17152 1392 Fail 0.3220 1161 16570 1427 Fail 0.3280 1094 15849 1448 Fail 0.3339 1026 15195 1480 Fail 0.3399 962 14572 1514 Fail 0.3459 895 13978 1561 Fail 0.3519 837 13424 1603 Fail 0.3579 773 12876 1665 Fail 0.3639 727 12393 1704 Fail 0.3698 680 11860 1744 Fail 0.3758 633 11394 1800 Fail 0.3818 595 10955 1841 Fail 0.3878 557 10558 1895 Fail 0.3938 508 10155 1999 Fail 0.3997 475 9770 2056 Fail 0.4057 431 9428 2187 Fail 0.4117 389 9058 2328 Fail 0.4177 358 8746 2443 Fail 0.4237 329 8427 2561 Fail 0.4296 301 8106 2693 Fail 0.4356 272 7839 2881 Fail 0.4416 244 7555 3096 Fail 0.4476 219 7287 3327 Fail 0.4536 199 7024 3529 Fail 0.4595 177 6752 3814 Fail 0.4655 154 6506 4224 Fail 0.4715 132 6282 4759 Fail 0.4775 119 6083 5111 Fail 0.4835 106 5899 5565 Fail 0.4895 95 5683 5982 Fail 0.4954 84 5473 6515 Fail 0.5014 75 5302 7069 Fail 0.5074 69 5133 7439 Fail 0.5134 61 4962 8134 Fail 0.5194 54 4783 8857 Fail 0.5253 46 4611 10023 Fail 0.5313 39 4434 11369 Fail 0.5373 30 4284 14280 Fail 0.5433 25 4149 16596 Fail 0.5493 22 4004 18200 Fail 0.5552 20 3854 19270 Fail 0.5612 17 3730 21941 Fail 0.5672 14 3608 25771 Fail 0.5732 12 3503 29191 Fail 0.5792 8 3364 42050 Fail 0.5852 7 3258 46542 Fail 0.5911 7 3153 45042 Fail 0.5971 7 3054 43628 Fail 0.6031 6 2956 49266 Fail 0.6091 6 2873 47883 Fail 0.6151 6 2800 46666 Fail 0.6210 6 2723 45383 Fail 0.6270 6 2631 43850 Fail 0.6330 5 2554 51080 Fail 0.6390 5 2494 49880 Fail 0.6450 5 2430 48600 Fail 0.6509 5 2368 47360 Fail 0.6569 5 2319 46380 Fail 0.6629 5 2248 44960 Fail 0.6689 5 2177 43540 Fail 0.6749 4 2123 53075 Fail 0.6808 4 2072 51800 Fail 0.6868 3 2021 67366 Fail 0.6928 3 1952 65066 Fail 0.6988 3 1890 63000 Fail 0.7048 3 1828 60933 Fail 0.7108 3 1782 59400 Fail 0.7167 3 1733 57766 Fail _____________________________________________________ The development has an increase in flow durations from 1/2 Predeveloped 2 year flow to the 2 year flow or more than a 10% increase from the 2 year to the 50 year flow. The development has an increase in flow durations for more than 50% of the flows for the range of the duration analysis. ___________________________________________________________________ Water Quality BMP Flow and Volume for POC #1 On-line facility volume: 0.573 acre-feet On-line facility target flow: 0.5042 cfs. Adjusted for 15 min: 0.5042 cfs. Off-line facility target flow: 0.2768 cfs. Adjusted for 15 min: 0.2768 cfs. ___________________________________________________________________ LID Report LID Technique Used for Total Volume Volume Infiltration Cumulative Percent Water Quality Percent Comment Treatment? Needs Through Volume Volume Volume Water Quality Treatment Facility (ac-ft.) Infiltration Infiltrated Treated (ac-ft) (ac-ft) Credit Total Volume Infiltrated 0.00 0.00 0.00 0.00 0.00 0% No Treat. Credit Compliance with LID Standard 8 Duration Analysis Result = Failed ___________________________________________________________________ Perlnd and Implnd Changes No changes have been made. ___________________________________________________________________ This program and accompanying documentation are provided 'as-is' without warranty of any kind. The entire risk regarding the performance and results of this program is assumed by End User. Clear Creek Solutions Inc. and the governmental licensee or sublicensees disclaim all warranties, either expressed or implied, including but not limited to implied warranties of program and accompanying documentation. In no event shall Clear Creek Solutions Inc. be liable for any damages whatsoever (including without limitation to damages for loss of business profits, loss of business information, business interruption, and the like) arising out of the use of, or inability to use this program even if Clear Creek Solutions Inc. or their authorized representatives have been advised of the possibility of such damages. Software Copyright © by : Clear Creek Solutions, Inc. 2005-2021; All Rights Reserved. Off-Line Water Quality Flow Rate used for sizing Modular Wetland Linear Page 12 APPENDIX D – CONCEPT DESIGN EXHIBITS