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Home My WebLink AboutSNP1_TIR_DRAFT_20161209 Draft Technical Information Report Sunset Neighborhood Park Prepared for City of Renton December 13, 2016 1100 112th Ave NE Suite 500 Bellevue, WA 98004 DRAFT DRAFT III Contents Section Page Acronyms and Abbreviations .................................................................................................................... v 1 Project Overview ...................................................................................................................... 1-1 1.1 Existing Site Conditions .......................................................................................................... 1-1 1.1.1 Existing Utilities ......................................................................................................... 1-3 1.1.2 Soils ........................................................................................................................... 1-3 1.2 Proposed Conditions .............................................................................................................. 1-3 2 Conditions and Requirements Summary .................................................................................... 2-1 3 Offsite Analysis ......................................................................................................................... 3-1 3.1 Upstream Analysis ................................................................................................................. 3-1 3.2 Downstream Analysis............................................................................................................. 3-1 4 Flow Control Analysis and Design .............................................................................................. 4-1 4.1 Part A - Existing Site Hydrology .............................................................................................. 4-1 4.2 Part B – Proposed Site Hydrology .......................................................................................... 4-1 4.3 Part C - Performance Standards ............................................................................................ 4-1 4.3.1 Flow Control BMPs .................................................................................................... 4-1 4.3.2 Conveyance ............................................................................................................... 4-2 5 Conveyance System Analysis and Design ................................................................................... 5-1 5.1 Existing Storm Drains ............................................................................................................. 5-1 5.2 Proposed Storm Drains .......................................................................................................... 5-1 5.3 Utilities ................................................................................................................................... 5-2 6 Special Reports and Studies ....................................................................................................... 6-1 7 Other Permits ........................................................................................................................... 7-1 8 ESC Analysis and Design ............................................................................................................ 8-1 8.1 ESC Measures ......................................................................................................................... 8-1 8.1.1 Wet Season Construction ......................................................................................... 8-2 8.1.2 Minimum ESC Requirements After Construction ..................................................... 8-3 9 Bond Quantities, Facility Summaries, and Declaration of Covenant ............................................ 9-1 10 Operations and Maintenance Manual...................................................................................... 10-1 11 References .............................................................................................................................. 11-1 Appendixes A King County Surface Water Design Manual TIR Worksheet B Design Drawings C Calculations Tables Table 4-1 Project Site Land Cover Areas .......................................................................................................... 4-1 DRAFT CONTENTS, CONTINUED Page IV Figures 1-1 Sunset Park Vicinity Map ..................................................................................................................... 1-2 1-2 Soils Map ............................................................................................................................................. 1-4 4-1 Existing (2011) Land Cover .................................................................................................................. 4-4 4-2 Sunset Neighborhood Park Proposed Land Cover .............................................................................. 4-5 DRAFT V Acronyms and Abbreviations Ac Acre BMP best management practice cfs cubic feet per second ESC erosion and sedimentation control GSI green stormwater infrastructure KCSWDM 2009 King County, Washington Surface Water Design Manual NPDES National Pollutant Discharge Elimination System NRCS Natural Resources Conservation Service PGIS pollution-generating impervious surface PGPS pollution-generating pervious surface PSE Puget Sound Energy RdC Ragnar-Indianola association soil ROW right-of-way TDA threshold discharge area TIR technical information report Ur Urban Soil DRAFT DRAFT SECTION 1 1-1 Project Overview Located in Renton, Washington, this project includes the construction of a new Sunset Neighborhood Park and associated facilities. The technical information report (TIR) worksheet in Appendix A lists the general project elements. A project vicinity map is shown in Figure 1-1. The Sunset Neighborhood Park Project is part of a larger Sunset Terrace Redevelopment plan implemented by the City of Renton (City). The City completed and adopted the Sunset Community Plan and Planned Action Environmental Impact Statement (City of Renton, 2010a) in 2010, which included the adoption of the Sunset Area Surface Water Master Plan (City of Renton, 2011). The Sunset Area Surface Water Master Plan identifies stormwater improvements to convey, treat, detain and infiltrate runoff from the existing and future land cover conditions. The Sunset Neighborhood Park Master Plan adopted in 2014 provided a vision and layout of the park to incorporate active and passive recreation and environmental education opportunities. Park design elements include adult fitness equipment, children’s play area, a looped walking pathway system, a small water feature, picnic areas, a picnic gazebo, performance seating/open space lawn area with pergolas and benches, and a restroom building (HBB, 2014). Recent adjacent projects include the Harrington Avenue Green Connections, Sunset Terrace Regional Stormwater Facility, King County Library, and Sunset Lane NE projects. The Harrington Avenue Green Connections Project, constructed in 2014, installed roadside rain gardens along Harrington Avenue just north of the Sunset Neighborhood Park site. The Sunset Terrace Regional Stormwater Facility, completed in 2015 within the Sunset Neighborhood Park, utilizes bioretention cells and infiltration to improve the water quality of the Sunset Area Community pollution generating surfaces, which discharge to Johns Creek and Lake Washington. A new King County Branch Library was constructed in 2015 at the corner of NE 10th Street and Sunset Lane NE. The City also recently constructed the Sunset Lane NE project (also part of the larger Sunset Terrace Redevelopment Plan) which realigned the existing roadways to allow for development of the park. The Sunset Neighborhood Park will be designed and constructed in two phases. The design of Phase 1 is currently underway and construction is anticipated to be complete in 2017. Future phases of the design and construction will come later as funding becomes available. This Technical Information Report (TIR) reflects the fully built-out Sunset Neighborhood Park (including all future phases) project for City permitting purposes. 1.1 Existing Site Conditions Site conditions in 2011 are considered to be the project’s pre-developed (existing) conditions (back to Sunset Area Community Planned Action FEIS [City of Renton, 2010a] land cover conditions) for the City’s full drainage review purposes. The project site is located in the Sunset Community area of Renton and consists of mixed single-family and multi-family residential and commercial neighborhoods with adjacent schools and public lands. The terrain on the project site is relative flat, with a less than 5 percent average slope toward the south. In 2011, the project site consisted of a multi-family residential neighborhood owned by the Renton Housing Authority, and included 13 residential buildings and their associated driveways, concrete walkways, utilities, and public roadway. The land to the north (upstream) of the site is a mix of single-family residential, residential roadway, and commercial lots hosting several businesses. Due to the recent completion of the Sunset Lane NE project and Sunset Terrace Regional Facility project, at the time of park construction under this project, none of the housing will remain, most of the underground utilities will have been removed, and a stabilized ground surface will be present. New utilities DRAFT LENTOWN SBat1g0<St Tukwila Starflre Sports • V ACME Bowling, 11 Billiards & Events PROJECT-NO: 677149 S 1171hS1 S 11.tthSI .s.'120,hst Bryn Mawr-Skyway S116rhSt S 132nd St I "' t : \ PROJE£T SITE .... N 3rd St Renton , Berliner Pub s F\.vetor VICINITY MAP NOTTO SCALE FIGURE 1-1SUNSET PARK VICINITY MAP E121hSt ,e, Renton Technical College NORTH DRAFT SECTION 1 PROJECT OVERVIEW SUNSETPARK_TIR_DRAFT_20161209/[INSERT JETT ID] 1-3 including water, sewer, power, telecommunication, and gas will be installed around the park by the Sunset Lane NE project. The surface water runoff from this site generally sheet flows to the southwest onto adjacent roadways, and is collected in existing storm drains in Harrington Avenue NE and Sunset Lane NE. These then connect into a 24-inch storm drain in NE Sunset Boulevard. The project area drains to Johns Creek and ultimately Lake Washington. 1.1.1 Existing Utilities Existing utilities along Harrington Ave NE, NE 10th Street and Sunset Lane NE and within the site include: • Sanitary sewer owned by the City of Renton • Water owned by the City of Renton • Underground power owned by Puget Sound Energy (PSE) • Gas main owned by PSE 1.1.2 Soils Soils at the site are mapped as Ragnar-Indianola association, sloping (RdC) and Arents, Alderwood material, 6 to 15 percent slopes (AmC) according to the Natural Resources Conservation Service (NRCS) Web Soil Survey (2014). Ragnar-Indianola association soil is classified as a Hydrologic Group A soil, which is characterized as relatively permeable outwash soils with a high capacity for infiltration. The Arents, Alderwood soil is classified as a Hydrologic Group B soil, which is characterized by low to moderately low capability to transmit water. Soils to the north and west of the site are mapped as Urban land (Ur). Urban land is classified as a Hydrological Group C soil, which is characterized as relatively impermeable glacial till overlain by weathered sand and gravel. See Figure 1-2 for the NRCS soil type map of the project area. Detailed soil information and boring locations for the northeast corner of the site (location of the regional stormwater facility) can be found in Sunset Stormwater Retrofit Low-Impact Development Project Geotechnical Data and Recommendations Report (CH2M HILL, 2012). 1.2 Proposed Conditions Proposed conditions are defined as the fully built-out conditions of the Sunset Neighborhood Park, including both Phase 1 and all future phases. Refer to Section 4.2 below for a full description of proposed site conditions. DRAFT DRAFT Soil Map—King County Area, Washington Natural Resources Conservation Service Web Soil Survey National Cooperative Soil Survey Page 1 of 352608705260920526097052610205261070526112052611705260870526092052609705261020526107052611205261170561300561350561400561450561500561550561600561650561700561750561800 561300 561350 561400 561450 561500 561550 561600 561650 561700 561750 561800 47° 30' 4'' N 122° 11' 10'' W47° 30' 4'' N122° 10' 44'' W47° 29' 53'' N 122° 11' 10'' W47° 29' 53'' N 122° 10' 44'' WN Map projection: Web Mercator Corner coordinates: WGS84 Edge tics: UTM Zone 10N WGS84 0 100 200 400 600Feet 0 35 70 140 210Meters Map Scale: 1:2,480 if printed on A landscape (11" x 8.5") sheet.DRAFT MAP LEGEND MAP INFORMATION Area of Interest (AOI) Area of Interest (AOI) Soils Soil Map Unit Polygons Soil Map Unit Lines Soil Map Unit Points Special Point Features Blowout Borrow Pit Clay Spot Closed Depression Gravel Pit Gravelly Spot Landfill Lava Flow Marsh or swamp Mine or Quarry Miscellaneous Water Perennial Water Rock Outcrop Saline Spot Sandy Spot Severely Eroded Spot Sinkhole Slide or Slip Sodic Spot Spoil Area Stony Spot Very Stony Spot Wet Spot Other Special Line Features Water Features Streams and Canals Transportation Rails Interstate Highways US Routes Major Roads Local Roads Background Aerial Photography The soil surveys that comprise your AOI were mapped at 1:24,000. Warning: Soil Map may not be valid at this scale. Enlargement of maps beyond the scale of mapping can cause misunderstanding of the detail of mapping and accuracy of soil line placement. The maps do not show the small areas of contrasting soils that could have been shown at a more detailed scale. Please rely on the bar scale on each map sheet for map measurements. Source of Map: Natural Resources Conservation Service Web Soil Survey URL: http://websoilsurvey.nrcs.usda.gov Coordinate System: Web Mercator (EPSG:3857) Maps from the Web Soil Survey are based on the Web Mercator projection, which preserves direction and shape but distorts distance and area. A projection that preserves area, such as the Albers equal-area conic projection, should be used if more accurate calculations of distance or area are required. This product is generated from the USDA-NRCS certified data as of the version date(s) listed below. Soil Survey Area: King County Area, Washington Survey Area Data: Version 10, Sep 30, 2014 Soil map units are labeled (as space allows) for map scales 1:50,000 or larger. Date(s) aerial images were photographed: Aug 31, 2013—Oct 6, 2013 The orthophoto or other base map on which the soil lines were compiled and digitized probably differs from the background imagery displayed on these maps. As a result, some minor shifting of map unit boundaries may be evident. Soil Map—King County Area, Washington Natural Resources Conservation Service Web Soil Survey National Cooperative Soil Survey Page 2 of 3DRAFT Map Unit Legend King County Area, Washington (WA633) Map Unit Symbol Map Unit Name Acres in AOI Percent of AOI AmC Arents, Alderwood material, 6 to 15 percent slopes 5.2 16.8% RdC Ragnar-Indianola association, sloping 18.8 60.1% Ur Urban land 7.2 23.1% Totals for Area of Interest 31.2 100.0% Soil Map—King County Area, Washington Natural Resources Conservation Service Web Soil Survey National Cooperative Soil Survey Page 3 of 3DRAFT SECTION 2 2-1 Conditions and Requirements Summary The City has adopted the 2009 King County, Washington, Surface Water Design Manual (KCSWDM) along with the City of Renton Amendments to the King County Surface Water Design Manual (City of Renton, 2010b) for the design of stormwater facilities. See Performance Standards in Section 4.3 of this report for information about the City’s flow control BMPs and conveyance performance standards applicable to the project. Per the 2009 City of Renton Surface Water Design Manual, the Sunset Neighborhood Park Project is subject to a full drainage review because it results in more than 2,000 square feet of new plus replaced impervious area. Typically in a full drainage review, Core Requirements 1 through 8 as well as Special Requirements 1 through 6 apply to the project. This project will be exempt from some of the core requirements and special requirements. A summary of which requirements will be required or exempt and why is provided below. Core Requirements #1 (Discharge at Natural Location): There are no exemptions to this requirement; therefore, it will apply to this project. All stormwater runoff from the project under proposed conditions will be discharged at the natural location and not diverted to or away from any other downstream areas. Core Requirement #2 (Offsite Analysis): A Level 1 analysis per the Amendments to the King County Surface Water Design Manual (City of Renton, 2010b) is considered to be sufficient because the entire downstream route within the required quarter-mile analysis area is contained in a piped conveyance system. Core Requirement #3 (Flow Control): The project is within a Basic Flow Control Area per the Sunset Area Surface Water Master Plan (CH2M HILL, 2011). Because it will reduce the amount of impervious surface area within the site, the proposed project will create less runoff than that under existing conditions. Therefore, it is assumed to meet the requirement to match existing peak runoff rates, and no flow control facilities are required. The project is subject to Large Lot Low Impervious flow control BMP requirements per the KCSWDM (2009) Section 5.2. Flow control BMPs to be implemented include rain gardens, permeable pavement (park sidewalks), and an infiltration (gravel filled) trench for restroom building rooftop runoff, as well as some limited basic dispersion provided by the park’s shrub and lawn planted areas. Core Requirement #4 (Conveyance System): A new conveyance system was designed as part of the Sunset Lane NE project, which realigned roadways adjacent to the Sunset Neighborhood Park project site. The storm drains for the Sunset Neighborhood Park will tie into this new conveyance system via a 24-inch storm drain pipe that flows to the west along the north side of NE Sunset Boulevard, after leaving the park site. The new conveyance system for the Sunset Neighborhood Park will be designed for a minimum of the 25- year design storm with a minimum of 6 inches of freeboard within each catch basin or manhole per the Amendments to the King County Surface Water Design Manual (City of Renton, 2010b). Core Requirement #5 (Erosion & Sediment Control (ESC)): There are no exemptions for this requirement; therefore, it will apply to this project. ESC plans will be included with the construction plans, and a Construction Stormwater Pollution Prevention Plan will be submitted by the contractor. Core Requirement #6 (Maintenance & Operations): There are no exemptions for the requirement; therefore, it will apply to this project. Maintenance and operations for the site stormwater conveyance used on this project will be entirely owned and operated by the City’s Community Services Department. Core Requirement #7 (Financial Guarantees & Liability): There are no exemptions for this requirement; therefore, it will apply to the contractor awarded to construct this project. Core Requirement #8 (Water Quality): There are no water quality facilities proposed for this project. This project includes just under 31,000 square feet (0.71 acre) of impervious pathway surface, including an infrequently used maintenance access driveway. Because this maintenance access driveway is not regularly DRAFT SECTION 2 CONDITIONS AND REQUIREMENTS SUMMARY 2-2 used by motor vehicles, it is not considered to be a pollution-generating impervious surface (PGIS). Other impervious surface area on the project site (total of 0.80 acre) includes restroom building rooftop, curb, and picnic areas, none of which are considered PGIS. The lawn areas in the fully built park (all phases) may be considered pollution-generating pervious surface (PGPS) because they may be subject to the use of pesticides and fertilizers and loss of soil. The requirement for a basic water quality treatment facility for PGPS at the site may be waived if there is a good faith agreement with the City for a landscape management plan to control solids, pesticides, and fertilizers leaving the site. Sheet flow from the park’s lawn areas will drain to bioretention areas (swales and rain gardens) at the southwestern edge in a future phase, which will provide some water quality treatment. Special Requirement #1 (Other Adopted Requirements): This project is within the Sunset Area Surface Water Master Plan (CH2M HILL, 2011) area and subject to those requirements. Special Requirement #2 (Flood Hazard Area Delineation): The project is not located in a flood hazard area based on Figure 4-3-050Q2 of the City of Renton Municipal Code; therefore, this requirement will not apply to this project. Special Requirement #3 (Flood Protection Facilities): This project does not rely on or modify any flood protection facilities and will be exempt from Special Requirement #3. Special Requirement #4 (Source Control): This project is a public park development within City-owned property and does not require a commercial building or commercial site development permit; therefore it is exempt from Special Requirement #4. Special Requirement #5 (Oil Control): This project includes only periodic vehicle access for park maintenance, via the driveway in the northeast portion of the park. Oil control is only required for sites with high-use characteristics as defined by Chapter 1 of the Amendments to the King County Surface Water Design Manual (City of Renton, 2010b). This project does not include any high-use site characteristics and is therefore exempt from oil control requirements. Special Requirement #6 (Aquifer Protection Area): This project is located within Zone 2 of an Aquifer Protection Area based on Figure 4-3-050Q1 of the City of Renton Municipal Code. Open stormwater facilities and conveyance systems such as treatment ponds, stormwater wetlands, infiltration facilities and ditches may be required to use a liner in accordance with Section 1.2.4.3 of the City of Renton Amendments to the 2009 King County Surface Water Design Manual. However, rain gardens do not require liners, per the Amendments to the King County Surface Water Design Manual (City of Renton, 2010b), Section 6.2.4 (Facility Liners). DRAFT SECTION 3 3-1 Offsite Analysis A desktop offsite analysis was performed to provide upstream and downstream analysis for the project. The study area extends to 1/4-mile downstream of the downstream discharge point on NE Sunset Boulevard. The existing drainage system consists of a buried pipe network. Refer to Section 1 for a description of existing drainage systems. 3.1 Upstream Analysis There are no offsite basins that discharge into the Sunset Park project limits. All stormwater runoff from roadways and offsite basins discharge into the existing storm drain system within the Sunset Lane NE right- of-way. 3.2 Downstream Analysis There is a single discharge location where stormwater will leave the project site, located at Sunset Lane NE just southwest of the project site (see Drawing C-9 in Appendix B). The project is located in one Threshold Discharge Area (TDA). The following downstream analysis information is excerpted from the Sunset Lane NE Project TIR (Perteet, 2015), which includes the storm drain system immediately downstream of the Sunset Neighborhood Park Project and provides the necessary downstream analysis information for this project as well: No downstream analysis was performed in the field for this project because the entire downstream route is within a piped conveyance system with no known problem areas other than possible capacity issues addressed in the Sunset Area Storm Water Master Plan. After leaving Sunset Lane NE, runoff continues in the 24 inch diameter piped conveyance system which flows to the west along the north side of NE Sunset Boulevard. This system remains piped until it crosses under Interstate 405 and outfalls into a series of wetlands beginning near the intersection of Lake Washington Boulevard with Park Avenue N. These wetlands are connected in a series by culverts; when one wetland reaches capacity it begins to overflow to the wetland downstream of it. This series of wetlands eventually outfalls into a creek, which flows in the northwesterly direction within Gene Coulon Memorial Beach Park, and then out into Lake Washington. DRAFT SECTION 4 4-1 Flow Control Analysis and Design 4.1 Part A - Existing Site Hydrology Under existing conditions, surface water runoff from this site generally drains overland via sheet flow toward the southwest and is collected in existing storm drains in Sunset Lane NE and Harrington Avenue NE. The entire Sunset Neighborhood Park Project area is within one TDA. The Sunset Terrace Regional Stormwater Facility features rain gardens already within the park that currently receive runoff from a tributary area consisting of public right of way on Sunset Boulevard (State Route [SR] 900), NE 10th Street and the proposed King County Library, and also private property on the Greater Highland Shopping Center. Runoff from the western portion of NE 10th Street is also conveyed directly to the facility. These tributary areas and drainage features were reviewed separately as part of the Sunset Terrace Regional Stormwater Facility Project, constructed in 2015. 4.2 Part B – Proposed Site Hydrology Under proposed conditions, surface water runoff will sheet flow generally to the southwest and into proposed French Drains that will convey stormwater to a series of new catch basins and storm drain pipe along the recently realigned Sunset Lane NE. In a future phase, these French Drains will be replaced with rain gardens and swales along the park’s southwestern edge. This system will connect to existing catch basin #13 (shown in Drawing C-9 in Appendix B) in Sunset Lane NE just southwest of the site boundary, which will convey stormwater through the existing piped stormwater conveyance system within the City’s right-of- way. There is no other tributary area to project site. All adjacent roadways drain directly to the existing piped conveyance system within the roadway right-of-way. Impervious surface area on the proposed site will include impervious pathways (pedestrian and maintenance vehicle access), two restroom buildings, a gazebo, picnic areas with tables, and 6-inch concrete curb along the pervious pathways. Pervious surface area will include landscaped planting areas, rain gardens, lawn, pervious pathways, and pervious rubberized safety surfacing at the playground and adult fitness areas. The pervious playground and adult fitness areas will include an underdrain to collect runoff and direct it into the piped stormwater conveyance system on Sunset Lane NE. Existing (2011) and proposed land cover areas are listed below in Table 4-1 and shown in Figures 4-1 (existing) and 4-2 (proposed). Table 4-1. Project Site Land Cover Areas Land Cover Type Existing (2011) acres Proposed (full park build-out) acres Total Impervious Surface 1.66 0.80 Total Pervious Surface 1.55 2.41 Total 3.2 3.2 4.3 Part C - Performance Standards The following describe the performance standards to be used for flow control BMPs and conveyance. 4.3.1 Flow Control BMPs Existing and proposed land use types on the project site are compared in Table 4-1 above. Impervious surface area on the site is being reduced as a result of the project, and replaced with pervious pathways and vegetated areas (both lawn and shrub/landscaped). The net decrease in impervious surface area is 1.1 acres. DRAFT SECTION 4 FLOW CONTROL ANALYSIS AND DESIGN 4-2 No flow control facilities are currently required or proposed. Large Lot Low Impervious BMPs (per Section 5.2.1.2 of the KCSWDM) to be implemented include the following: •Rain Gardens: The areas upstream of the proposed rain gardens along the southwestern park boundary are mostly pervious lawn and some permeable pavement walkways; the impervious picnic gazebo will drain first to the planted areas upslope from the rain gardens. Runoff from the impervious pathways will sheet flow into lawn areas. Rain gardens and bioretention swales are proposed with 18 inches of bioretention soil, 6 inches of available ponding depth and 6-inch underdrain pipes connecting to the receiving piped conveyance system (24-inch storm drain). See Drawing C-10_P in Appendix B. •Permeable Pavement: The park will include just under 6,000 square feet (0.14 acre) of pedestrian walkways to be composed of permeable pavement (porous concrete). Permeable pavement walkways will be composed of 4 inches of pervious cement concrete at a 1.5 percent cross slope, with 8 inches of aggregate base. Construction geotextile will be installed on the sides. Curbs will be 6-inch cement concrete curbs installed flush with the porous concrete section. As noted earlier, the rubberized safety surfacing at the playground and adult fitness areas will also be pervious and fitted with underdrains that will connect to the piped conveyance system at the south end of the park. Until these areas are installed in a future phase, these areas will be drained via sheet flow to a French Drain located adjacent to the impervious concrete pathway. See Drawings C-8 and C-9 in Appendix B. •Gravel Filled Trench: Gravel filled trenches will receive runoff from the restroom building rooftops (approximately 600 square feet of impervious surface) via a Type 2 catch basin fitted with a down- turned elbow. These trenches will provide some infiltration for rooftop runoff. Per KCSWDM Section C.2.2.3, the trenches will be at least 20 feet in total length (20 feet per 1,000 square feet of impervious surface is required) and 2 feet in width. The trenches will be filled with at least 18 inches of washed drain rock, and will be more than 15 feet from the buildings. See Drawing C-10 in Appendix B. •Dispersion: Full dispersion of impervious rooftop and pathway surfaces is not possible on the park site because there are no available native (forested) vegetated areas. Some limited dispersion of runoff will occur through the shrub and groundcover areas in the park’s northeastern area, as well as in the lawn areas located throughout the park, adjacent to the pathways. Sheet flow from the lawn area in the western portion of the park will drain to a French Drain with a 6-inch underdrain pipe until bioretention swales and rain gardens are installed after Phase 1. This French Drain will discharge to the existing piped conveyance system described below in Section 4.3.2. 4.3.2 Conveyance The project’s stormwater conveyance facilities will consist primarily of catch basins and storm drains. The capacity of the new and existing storm drains was analyzed using the Rational Method according to Section 3.2.1 of the KCSWDM (2009). See Appendix C for pipe capacity calculations. 4.3.2.1 Proposed Storm Drains All new conveyance systems will be designed for the 25-year storm. Uniform flow conditions will be used to initially size pipes for capacity. Final pipe sizes will be verified using simple backwater analysis. Excel spreadsheets will be used in both analyses, with the following assumptions: •Pipe material – Smooth wall pipe (concrete or ductile iron pipe) with Manning’s n = 0.014 (uniform) •Minimum pipe diameter – 12 inches •Minimum cover – 2 feet; if lower cover is needed, use class 5 reinforced concrete pipe (RCP) or ductile iron pipe DRAFT SECTION 4 FLOW CONTROL ANALYSIS AND DESIGN 4-3 • Minimum velocity: 3 feet per second (fps) • Match crowns at junctions with changes in pipe diameter where possible The project will be designed to use drainage structures from the City of Renton’s Standard Plans. In general, Type 1 and 1L CBs will be used. The maximum pipe diameter for Type 1 CBs is 15 inches, and a maximum of 5 vertical feet will be allowed between the finished grade and the pipe invert. 4.3.2.2 Inlets on a Continuous Grade The new inlets used on this project are catch basins with vaned grates. Inlet capacity was not analyzed because the tributary area is relatively small and outside of vehicle travel lanes. 4.3.2.3 Sag Inlets There are no sag inlets used on this project. DRAFT DRAFT DRAFT DRAFT FIGURE 4-2 (TIR)DRAFT DRAFT SECTION 5 5-1 Conveyance System Analysis and Design This section describes assumptions and site conditions to justify the conveyance design. Permanent conveyance facilities will include catch basin inlets, manholes, 12-inch-diameter storm drains, and 6-inch diameter underdrains. 5.1 Existing Storm Drains The Sunset Lane NE project analyzed the capacity of the receiving conveyance system, and sized the conveyance system for the 25-year design storm event using the King County Backwater Spreadsheet. A 24- inch HDPE storm drain (see Drawing C-9 in Appendix B) collects stormwater runoff from the park as well as the conveyance systems constructed under the Sunset Lane NE project. The following is excerpted from the Sunset Lane NE project TIR (Perteet, 2015): The first conveyance system is a series of catch basins and closed pipes which collect gutter flow from Sunset Lane NE between NE 10th Street and Harrington Avenue NE (Station 10+00 to Station 13+75) and also from NE 10th Street between Harrington Avenue NE and NE Sunset Boulevard (Station 22+50 to 27+00). This system flows to the southeast along the north side of NE 10th Street and then turns to the southwest at Sunset Lane NE and flows along the east side of Sunset Lane NE. It will intercept the emergency overflow from the regional stormwater facility, which was assumed to be in complete failure for conveyance pipe capacity analysis. At the intersection of Sunset Lane NE with Harrington Avenue NE the conveyance system will continue in a southerly direction along the west side of Harrington Avenue NE. The system will connect to the existing system in NE Sunset Boulevard. This system will also intercept offsite flow at the intersection of NE 10th Street with Sunset Lane NE, from the new library property, and the excess flows from the proposed flow splitter being installed as part of the park’s regional stormwater facility. The second conveyance system collects runoff from the rest of the Sunset Lane NE project, Station 13+75 to Station 22+50. The conveyance system follows the proposed roadway down to a low point at station 16+51. At the low point the system leaves Sunset Lane NE through a proposed utility easement on the RHA property. The pipe flows perpendicular to Sunset Lane NE and connects into the existing conveyance system on NE Sunset Boulevard. This system intercepts offsite flow north of NE 10th Street from Harrington Avenue NE, and Glennwood Avenue NE, the future developments to the southwest of Sunset Lane NE, and the park property. To be conservative, the Sunset Lane NE conveyance analysis assumed that the future developments to the southwest of Sunset Lane NE were 100% impervious. This storm drain system has calculated the 25-year peak flow rate from the park to be 5.19 cubic feet per second (cfs) based on a preliminary assumption that the park would be half impervious surface area. 5.2 Proposed Storm Drains Proposed storm drains were analyzed for the 25-year design storm according to the Rational Method as described in the KCSWDM (2009). A new storm drain system will collect and convey stormwater from the site into existing catch basin #13 in Sunset Lane NE, which discharges into the existing 24-inch storm drain described above. The new storm drain system will include eight new catch basins and 12-inch storm drain pipes along the southern site boundary under Phase 1, as well as two temporary 6-inch French Drains. Stormwater runoff from the eastern portion of the park will drain to a temporary 6-inch French Drain located along the main central pathway, then into a series of catch basins and 12-inch storm pipes. Runoff from the western portion of the site will sheet flow across the mainly lawn-covered slope into a temporary French Drain, then into another 12-inch storm drain. Both of these systems will discharge to the existing 24- inch storm drain that runs southwest toward NE Sunset Boulevard via an existing catch basin in Sunset Lane NE. In a future phase, the temporary French Drains will be replaced with a system of swales and rain gardens DRAFT SECTION 5 CONVEYANCE SYSTEM ANALYSIS AND DESIGN 5-2 along the southwestern boundary of the park (capturing runoff from the western park area) and a pervious rubberized playground surface with an underdrain. The Sunset Lane NE project analyzed the capacity of the receiving conveyance system in Sunset Lane NE, assuming a park with half impervious, half pervious land cover and calculated a basin flow rate of 5.19 cfs. The actual land cover of the fully built Sunset Neighborhood Park will be 25% impervious. To be conservative, the Rational Method used to calculate the flow rate from the fully developed park assumed that the entire park drained into one catch basin and one discharge point. Based on this conservative assumption, the 25-year design peak flow rate is 3.61 cfs. The new Sunset Park 12-inch storm drains will have adequate capacity for this flow rate. See calculations provided in Appendix C. Also, because the calculated basin flow rate from the park (see Appendix C) is less than that estimated by the Sunset Lane NE project for the 25-year design storm for the purpose of analyzing the receiving conveyance system, the downstream storm drain system is known to have adequate capacity. The proposed storm drain configuration is shown and detailed on plan sheets in Appendix B. 5.3 Utilities An existing gas main traverses the park site from north to south, just west of the proposed restroom buildings. This gas main will be protected in-place. A new water line and sanitary sewer line will be installed during Phase 1 to serve the park restroom buildings as well as the water feature that will be installed in a future phase. These utilities will connect to existing water mains and sanitary sewers in NE 10th Street, which is the park site’s northern boundary. Electrical service will also connect to the park’s restroom buildings from the northeastern corner (NE 10th Street). Pedestrian lights will have been installed along the pathways next to the park boundary under the Sunset Lane NE project or will be installed during Phase 1 construction. The preference is to place new storm drains under the curb/gutter line along Sunset Lane NE. This is proposed where no utility conflicts are noted. Potholing will be performed to identify the location and depth of the utilities. The design may work around the existing utilities or the utilities will be relocated. DRAFT SECTION 6 6-1 Special Reports and Studies The Sunset Area Surface Water Master Plan (CH2M HILL, 2011) discusses constructing green stormwater infrastructure (GSI) in key areas within the Sunset Study Area. Harrington Avenue NE as well as the planned park located in the center of the proposed Sunset Lane NE loop were identified as locations to construct GSI. The Harrington Avenue NE GSI project was constructed in 2014. The Sunset Terrace Regional Stormwater Facility within the Phase 1 park area was constructed in 2015, and utilized the Sunset Stormwater Retrofit Low-Impact Development Project Geotechnical Data and Recommendations Report (CH2M HILL, 2012). These related projects do not affect the drainage requirements for the Sunset Neighborhood Park Project, but are good to be aware of as design and construction move forward. The Master Plan proposes to construct a new storm drain under Glennwood Avenue NE where there are currently no stormwater conveyance facilities. The Master Plan shows the proposed Glennwood Avenue NE storm drain system connecting into the storm drain system along Harrington Avenue NE which is being removed as part of the Sunset Lane NE project. Runoff from the area that this proposed storm drain system along Glennwood Avenue NE will most likely collect was accounted for in the backwater analysis used to size the proposed new conveyance system along Sunset Lane NE (Perteet, 2015). The Sunset Neighborhood Park project is partially located within a Zone 2 Aquifer Protection Area. The City of Renton Amendments to the King County Surface Water Design Manual states that if a project is within a Zone 2 aquifer protection area, flow control and water quality treatment facilities may require lining. This requirement is not applicable for the proposed project, because no flow control or water quality facilities are proposed. There are steep slopes to the west of the Sunset Lane NE project, however construction activities and stormwater infrastructure will remain at least 80 feet from the top of the slope. There will be a Temporary Erosion and Sediment Control (ESC) plan as part of the project plan set, and the contractor will be required to prepare a project Stormwater Pollution Prevention Plan (SWPPP). Proposed drainage facilities for this project do not rely on soil properties; therefore, no geotechnical investigation is needed at this time. No other special reports or studies apply to this project. DRAFT DRAFT SECTION 7 7-1 Other Permits The following permits are anticipated for the project: •General Construction Stormwater Permit and Notice of Intent – Washington Department of Ecology •Clearing and Grading Permit – City of Renton DRAFT DRAFT SECTION 8 8-1 ESC Analysis and Design An Erosion and Sedimentation Control (ESC) plan will be developed for the final contract plans in accordance with the City of Renton Amendments to the King County Surface Water Design Manual and KCSWDM Appendix D. ESC plans are shown in Drawings C-1, C-2 and C-3 in Appendix B. To avoid erosion and the transport of sediment offsite, the contractor will implement temporary control measures during the construction phase of the project. During construction, stormwater runoff will be conveyed in the existing conveyance systems, which are primarily storm drains. ESC measures will be needed to prevent runoff from causing erosion and discharging sediment into the existing drainage system during and after construction. Appropriate ESC measures will be needed for construction activities on existing storm drain systems. The contractor will be responsible for the phasing of erosion and sediment control measures so that they are coordinated with the staging of construction activities. Additionally, the contractor will be responsible for inspection and maintenance of temporary controls during construction, including removal of accumulated sediment, and for the removal of the controls and remaining accumulated sediment at the end of construction. The project will follow the requirements listed in the National Pollutant Discharge Elimination System (NPDES) General Construction Stormwater Permit. The contractor will prepare a stormwater pollution prevention plan (SWPPP) following the 12 elements listed in the KCSWDM, and the SWPPP will be updated as site conditions change. Permanent measures will be implemented where needed to stabilize disturbed soils at project completion. 8.1 ESC Measures The following ESC measures will be provided, as further detailed on ESC plan sheets in Appendix B: • Clearing Limits – Clearing limits will be delineated on the construction plans. Silt fence or wattles will be installed down slope of any fill slopes to prevent offsite sediment migration. • Cover Measures – The contractor will provide temporary and permanent cover measures where needed to protect disturbed areas. Mulching will be used in accordance with the KCSWDM’s Erosion and Sediment Control Standards Appendix D to provide immediate, temporary protection from erosion and to enhance plant growth. Nets and blankets may be used according to Erosion and Sediment Control Standards Appendix D to provide additional protection and to hold seed and mulch in place on slopes. Disturbed areas will be seeded as a permanent cover measure to reduce erosion. • Perimeter Protection – To reduce the transport of sediment off site, the contractor will provide catch basin filters and street sweeping as indicated on the final construction drawings and as needed. • Traffic Area Stabilization – Stabilized construction entrances will be installed at all construction vehicle access locations. • Sediment Retention – Catch basin filters (inlet protection) will provide sediment retention at the locations shown on the final construction drawings. • Surface Water Collection – Surface water control will be provided by using the existing and new drainage conveyance systems. Surface water will not be discharged into the existing bioretention cells, which are to be protected with silt fences as shown on Drawing C-2 in Appendix B. • Dewatering Control – Groundwater is not expected to be encountered during construction because the site sits at the top of a steep slope and the soils in the area have high infiltration capacity. If DRAFT SECTION 8 ESC ANALYSIS AND DESIGN 8-2 groundwater is encountered during construction, it may be pumped to an onsite sediment trap or to a catchment created by sandbags with an overflow into a catch basin containing a catch basin insert. • Dust Control – If necessary, the contractor will use water according to KCSWDM Section 3.8 to prevent wind transport of soil. Exposed soils will be sprayed until wet and resprayed as needed. When using water for dust control, the contractor will spray exposed soils until they are wet, but runoff should not be generated by spraying. Oil shall not be used for dust control. At the contractor’s option, a tackifier may be used with approval from the Engineer and the City. • Flow Control – A sediment trap is proposed during construction at the southwest portion of the site, and will provide sediment retention and possible flow control as needed. See Drawing C-2 in Appendix B. Construction activities will remove and permanently reduce the amount of impervious surface area on the site. Excessive runoff during construction is not anticipated, because the site will be mostly pervious. • ESC Implementation - All ESC measures will be inspected and maintained on a regular basis following the maintenance requirements listed for each BMP, as described in KCSWDM Erosion and Sediment Control Standards Appendix D. The contractor will designate a certified ESC Supervisor and will give his or her name, address, and phone number to the City before construction begins. The ESC Supervisor will inspect the site at least once a month during the dry season, weekly during the wet season, and within 24 hours of each runoff-producing storm. If the City of Renton requires a written record of maintenance activities, a standard ESC maintenance report will be used as a written record of all maintenance. The proposed ESC measures for the project will be further detailed in the final contract plans. Construction for this project will not be located within a stream buffer, a wetland or associated buffer, or within 50 feet of a lake. 8.1.1 Wet Season Construction If soils are exposed between October 1 and March 31, the contractor will mulch and seed as much disturbed area as possible by the first week of October to provide grass cover for the wet season. The contractor will also conform to the following wet season special provisions: 1. Apply cover measures to disturbed areas that are to remain unworked for more than 2 days. 2. Protect stockpiles that are to remain unworked for more than 12 hours. No area is to be left uncovered/denuded longer than 12 hours. 3. Provide onsite supplies of cover materials sufficient to cover all disturbed areas. 4. Seed all proposed lawn areas that are to be unworked during the wet season by the end of the first week of October. 5. Apply mulch to all other areas that are unworked for protection. 6. Maintain a minimum of 50 linear feet of silt fence (and the necessary stakes) on site for every acre of disturbed area. 7. Provide construction road and parking lot stabilization areas for all sites, unless underlain by coarse grain soil. 8. Provide sediment retention as required. 9. Provide additional surface water controls as required. 10. Implement construction phasing and more conservative BMPs for construction activity near surface waters (to be evaluated by contractor). DRAFT SECTION 8 ESC ANALYSIS AND DESIGN 8-3 11. Runoff generated from dewatering activities is to be treated using suitable methods for the site. Review and maintain ESC measures on a weekly basis and within 24 hours after any runoff-producing event. 8.1.2 Minimum ESC Requirements After Construction Before obtaining final construction approval, the following conditions must be met: 1. All disturbed areas of the site should be vegetated or otherwise permanently stabilized. At a minimum, disturbed areas will be seeded and mulched to provide a high likelihood that sufficient cover will develop shortly after final approval. If seeded during the dry season, the seeded area will be irrigated as necessary to maintain the sprouted vegetation until the start of the wet season. 2. Temporary ESC measures such as silt fences, pipe slope drains, construction entrances, and storm drain inlet protection will be removed. 3. All permanent surface water facilities including catch basins, manholes, pipes, ditches, and channels will be cleaned of silt and debris. DRAFT DRAFT SECTION 9 9-1 Bond Quantities, Facility Summaries, and Declaration of Covenant This is a Public Works project to be entirely owned and maintained by the City of Renton. As such, a bond quantities worksheet and Declaration of Covenant are not required for this project. Also, because no flow control or water quality facilities are included in the project, Flow Control and Water Quality Summary Sheets are not required. DRAFT DRAFT SECTION 10 10-1 Operations and Maintenance Manual An operations and maintenance manual is not provided here, because this is a Public Works project and the City will assume maintenance and operation of all systems. DRAFT DRAFT 11-1 References CH2M HILL. 2011. Sunset Area Surface Water Master Plan. Prepared for the City of Renton, Washington. April. CH2M HILL. 2012. Sunset Stormwater Retrofit Low-Impact Development Project Geotechnical Data and Recommendations Report. Prepared for the City of Renton, Washington. August. City of Renton. 2010a. Draft Sunset Area Community Planned Action NEPA/SEPA Environmental Impact Statement. Prepared for City of Renton and Renton Housing Authority. http://rentonwa.gov/uploadedFiles/Business/CED/planning/2010/Vol1_SunsetArea-PA_DraftEIS.pdf. City of Renton Community and Economic Development, Renton, Washington. December. City of Renton. 2010b. Amendments to King County Surface Water Design Manual. http://rentonwa.gov/uploadedFiles/Government/PW/UTILITIES/Surface_Water/City%20Amendments%20to %20the%20King%20County%20Surface%20Water%20Design%20Manual.pdf. City of Renton, Public Works Department, Surface Water Utility, Washington. February. HBB. 2014. Sunset Neighborhood Park Master Plan Report. Prepared for City of Renton, Washington. December 2014. King County Department of Natural Resources. 2009. King County, Washington Surface Water Design Manual. Perteet. 2015. Sunset Lane NE Draft Stormwater Technical Information Report. Prepared for City of Renton, Washington. October. United States Department of Agriculture (USDA). 2014. Soil Survey, Natural Resources Conservation Service, Web Soil Survey. http://websoilsurvey.nrcs.usda.gov/. September. DRAFT DRAFT Appendix A TIR WorksheetDRAFT DRAFT DRAFT DRAFT DRAFT DRAFT DRAFT DRAFT Appendix B Design Drawings DRAFT DRAFT DRAFT DRAFT DRAFT DRAFT SUNSET NEIGHBORHOOD PARK LEGEND: INLET PROTECTION, SEE WSDOT STANDARD PLAN NO. I-40.20-00 6' ' TEMPORARY CHAINLINK AND HIGH VISIBILITY FENCE SILT FENCE, SEE WSDOT STANDARD PLAN NO. I-30.15-02 CONSTRUCTION ENTRANCE, SEE WSDOT STANDARD PLAN NO. I-80.10-02 X PROTECT IN PLACE EXISTING GAS MAIN INSTALL INLET PROTECTION, TYP. INSTALL CHAINLINK AND HIGH VISIBILITY FENCE AROUND PERIMETER INSTALL CONSTRUCTION ENTRANCE PLACE STEEL PLATES IN ROADWAY AT CONSTRUCTION ENTRANCE TO PROTECT EXISTING UTILITIES (VALVES) IN ROADWAY NOTES: 1. THE IMPLEMENTATION OF ALL TESC AND THE CONSTRUCTION, MAINTENANCE, REPLACEMENT, AND UPGRADING OF THESE TESC PLAN FACILITIES IS THE RESPONSIBILITY OF THE CONTRACTOR UNTIL ALL CONSTRUCTION IS APPROVED. 2. THE BOUNDARIES OF THE CONSTRUCTION LIMITS SHOWN ON THIS PLAN SHALL BE CLEARLY FLAGGED WITH HIGH VISIBILITY FENCING IN THE FIELD PRIOR TO CONSTRUCTION. DURING THE CONSTRUCTION PERIOD, NO DISTURBANCE AND/OR MATERIAL/EQUIPMENT STAGING SHALL BE PERMITTED BEYOND THE FLAGGED CONSTRUCTION LIMITS. THE FLAGGING SHALL BE MAINTAINED BY THE CONTRACTOR FOR THE DURATION OF CONSTRUCTION. 3. TESC FACILITIES AND MEASURES SHALL BE CONSTRUCTED AND/OR INSTALLED PRIOR TO ANY GRADING, EARTH-DISTURBING ACTIVITY, OR EXTENSIVE LAND CLEARING IN ACCORDANCE WITH THE APPROVED TEMPORARY EROSION SEDIMENTATION CONTROL PLAN. THESE FACILITIES MUST BE SATISFACTORILY MAINTAINED. 4. SEE DRAWING C-1 FOR TEMPORARY EROSION/SEDIMENT CONTROL (TESC) GENERAL NOTES. PEDESTRIAN LIGHTS INSTALLED DURING SUNSET LANE NE CONSTRUCTION, TYP. (NIC) INTERCEPTOR DITCH DRAFT DRAFT DRAFT DRAFT DRAFT DRAFT DRAFT DRAFT DRAFT DRAFT DRAFT DRAFT DRAFT DRAFT DRAFT DRAFT DRAFT DRAFT SUNSET NEIGHBORHOOD PARK NOTES: 1. SEE ELECTRICAL PLAN FOR ELECTRICAL AND TELECOMMUNICATIONS UTILITIES. 3. SEE BUILDING MECHANICAL DRAWINGS FOR WATER SERVICE, VENTING AND OTHER PLUMBING INFORMATION. REPLACE EXISTING 8" SS CLEANOUT PER CITY OF RENTON STD. PLAN NO. 403.1 FUTURE PHASE STORAGE TANK TEMPORARY CAP FOR FUTURE CONNECTION IE = 330 PROTECT IN PLACE EXISTING GAS MAIN LEGEND: WATER LINE SANITARY SEWER LINE. W SS 4" SS PROVIDE TEMPORARY CAP AT FINISHED FLOOR FOR FUTURE CONNECTION TO WATER FEATURE 4" SS (TYP. OF 3) (/%2: IE = 328.26 (/%2: IE = 330.80 6" SS CLEANOUT PER CITY OF RENTON STD. PLAN NO. 403.1 85 LF OF 6" SS AT 2% SLOPE 70 LF OF 6" SS AT 3.6% SLOPE 2" WATER SERVICE EXISTING 8" DI WATER MAIN EXISTING 12" DI WATER MAIN INSTALL 1.5" OUTLET SERVICE SADDLE FOR CONNECTION TO INDOOR PLUMBING 6" PVC CASING FOR FUTURE WATER FEATURE. PROVIDE TEMPORARY CAPS AT BOTH ENDS 8"x6" REDUCER PEDESTRIAN LIGHTS INSTALLED DURING SUNSET LANE NE CONSTRUCTIONS, TYP. (NIC) ABBREVIATIONS IE SS STD LT DI MJ FL CL EL INVERT ELEVATION SANITARY SEWER STANDARD LINEAL FEET DUCTILE IRON MECHANICAL JOINT FLANGE CENTERLINE ELEVATION STA LT STATION LEFT EX 2" WATER METER DCVA OUTSIDE OF ROW PER CITY OF RENTON STD. PLAN 340.8 EX. IRRIGATION METER EX. RAIN GARDEN EX. RAIN GARDEN DRAFT DRAFT Appendix C CalculationsDRAFT DRAFT BASIN FLOW Calculations Project:Sunset Neighborhood Park Proj. No:677149 Date:12/9/2016 Rational Method Catch Basin Rainfall Intensity IR Impervious C Impervious Area (ac)Pervious C Pervious Area (ac)Cc 01 2.733941 0.9 0.8 0.25 2.4 0.4125 PR iR aR bR s0 Tc L 3.4 0.8041 2.66 0.65 0.0273 6.3 330 Basin Flow Rate (cfs) 3.61 DRAFT Page 2 of 2 STORM PIPE Calculations Project:Sunset Neighborhood Park Proj. No:677149 Date:12/9/2016 Location U/S D/S I.E. Adjusted L Diam.Available Q Finished Grade U/S D/S Cal'd Slope of of Q Q V From To Slope of Pipe Pipe Full Check Full Cover ID#ID#(cfs)(ft)(ft)(ft)(ft)%Pipe (ft)(n=)(in)(cfs)cfs (fps)check 1 2 3 14 15 16 17 18 19 22 23 24 25 26 27 28 7 6 3.61 336.60 336.90 332.60 331.90 2.33%2.33%30 0.014 12 5.07 ok 6.45 4.00 6 5 3.61 336.90 336.10 331.90 331.10 1.45%1.45%55 0.014 12 4.00 ok 5.09 5.00 5 4 3.61 336.10 333.70 331.10 328.70 3.43%3.43%70 0.014 12 6.14 ok 7.82 5.00 4 3 3.61 333.70 331.15 328.70 326.15 4.25%4.25%60 0.014 12 6.84 ok 8.71 5.00 3 2 3.61 331.15 329.90 326.15 324.90 2.08%2.08%60 0.014 12 4.79 ok 6.10 5.00 2 1 3.61 329.90 328.85 324.90 324.35 1.57%1.57%35 0.014 12 4.16 ok 5.29 5.00 1 13 3.61 328.85 328.24 324.35 323.94 1.64%1.64%25 0.014 12 4.25 ok 5.41 4.50 DRAFT