HomeMy WebLinkAboutRS_ Drainage_TIR_FFCC_190905_v1
ENGINEERING REPORT
TECHNICAL INFORMATION REPORT
FAMILY FIRST COMMUNITY CENTER
RENTON, WA
August 22, 2019
PREPARED FOR:
City of Renton
1055 South Grady Way
Renton, WA 98057
PREPARED THROUGH:
City of Renton
1055 South Grady Way
Renton, WA 98057
PREPARED BY:
COUGHLIN PORTER LUNDEEN
801 Second Avenue, Suite 900
Seattle, WA 98104
P 206.343.0460
CONTACT / Keith Kruger, P.E.
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Technical Information Report
Renton School District
Coughlin Porter Lundeen
Project No. C180040-01
August 22, 2019
TABLE OF CONTENTS
I PROJECT OVERVIEW.................................................................................................................................1
GENERAL DESCRIPTION .............................................................................................................................1
EXISTING CONDITIONS................................................................................................................................1
PROPOSED CONDITIONS............................................................................................................................2
II. CONDITIONS AND REQUIREMENTS SUMMARY.....................................................................................3
CORE REQUIREMENTS:...............................................................................................................................3
SPECIAL REQUIREMENTS:..........................................................................................................................3
PROJECT-SPECIFIC REQUIREMENTS:......................................................................................................4
III. OFF-SITE ANALYSIS...................................................................................................................................5
TASK 1 – STUDY AREA DEFINITION AND MAPS.......................................................................................5
TASK 2 - RESOURCE REVIEW.....................................................................................................................5
TASK 3 - FIELD INSPECTION .......................................................................................................................6
TASK 4 - DRAINAGE SYSTEM DESCRIPTION AND PROBLEM DESCRIPTIONS ...................................7
UPSTREAM ANALYSIS..................................................................................................................................7
CONCLUSION.................................................................................................................................................7
IV. FLOW CONTROL AND WATER QUALITY FACILITY ANALYSIS AND DESIGN.....................................8
EXISTING SITE HYDROLOGY (PART A)......................................................................................................8
DEVELOPED SITE HYDROLOGY (PART B)................................................................................................8
PERFORMANCE STANDARDS AND FLOW CONTROL SYSTEM (PARTS C)..........................................8
WATER QUALITY SYSTEM (PART D)..........................................................................................................9
FLOW CONTROL BEST MANAGEMENT PRACTICES (PART E)...............................................................9
V. CONVEYANCE SYSTEM ANALYSIS AND DESIGN................................................................................11
CONVEYANCE STANDARDS......................................................................................................................11
ON-SITE CONVEYANCE SYSTEMS...........................................................................................................11
VI. SPECIAL REPORTS AND STUDIES.........................................................................................................12
VII. OTHER PERMITS.......................................................................................................................................13
VIII. CSWPPP ANALYSIS AND DESIGN..........................................................................................................14
STANDARD REQUIREMENTS....................................................................................................................14
IX. BOND QUANTITY, FACILITY SUMMARIES, AND DECLARATION OF COVENANT.............................15
X. OPERATION AND MAINTENANCE MANUAL..........................................................................................16
APPENDIX A - FIGURES ...................................................................................................................................17
FIGURE 1 – VICINITY MAP..........................................................................................................................17
FIGURE 2 – EXISTING SITE CONDITIONS................................................................................................17
FIGURE 3 – PROPOSED SITE CONDITIONS............................................................................................17
FIGURE 4 – DRAINAGE BASIN MAP..........................................................................................................17
FIGURE 5 – 100-YR FLOODPLAIN MAP ....................................................................................................17
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FIGURE 6 – OFF-SITE DRAINAGE ANALYSIS MAP.................................................................................17
FIGURE 7 – SOILS MAP ..............................................................................................................................17
FIGURE 8 – UPSTREAM MAP.....................................................................................................................17
APPENDIX B – ENGINEERING CALCULATIONS............................................................................................18
APPENDIX C – CSWPPP...................................................................................................................................19
APPENDIX D – OPERATIONS AND MAINTENANCE MANUAL......................................................................20
APPENDIX E – FACILITIES SUMMARY AND DECLARATIONS OF COVENANT..........................................21
LIST OF TABLES
TABLE 1 - DEVELOPED SITE CONDITIONS AREA BREAKDOWN ................................................2
TABLE 2 - EXISTING SITE CONDITIONS AREA BREAKDOWN.....................................................8
TABLE 3 – DETENTION FACILITY SUMMARY .............................................................................8
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I PROJECT OVERVIEW
GENERAL DESCRIPTION
The following Technical Information Report (TIR) provides the technical information and design analysis
required for developing the Stormwater Drainage and Temporary Erosion and Sedimentation Control
(TESC) Plans for the Family First Community Center. The stormwater design for the project is based on the
requirements set forth by the 2017 City of Renton Surface Water Design Manual (2017 CRSWDM)
The Family First Community Center is located at 16022 116th Avenue SE, Renton WA 98058 (See Figure 1
– Vicinity Map) adjacent to the existing Cascade Elementary School. The property is owned by Renton
School District and is bound by an easement to Pacific Northwest Pipe Line Corporation to the north, 116th
Avenue SE to the west and single-family residences to the east and south. The project is located on a 14.9
acre parcel and the parcel number 152823059034. The project is in the NW ¼ of Section 28, Township 23
North, Range 5 East, Willamette Meridian. The project is currently pursuing a short plat for the development
area, which is 2.72 acres, to separate the Family First Community Center property from the existing
Cascade Elementary School property.
The project consists of the construction of a new one-story community recreational center that is 27,000
square feet and approximately 120 surface parking stalls. The community center will include a new
gymnasium, activity rooms, gathering places, offices, a kitchen, parking lot and associated landscaping and
sidewalks. An existing biofiltration swale and associated storm piping will be removed to accommodate the
new development. The project will be removing the existing water quality treatment facility for the Cascade
Elementary School (biofiltration swale) and replacing the facility with a Modular Wetland System to treat the
pollution generating runoff from the existing site. The project will result in 1.7-acres of new or replaced
impervious area and 1.02-acres of new or replaced pervious area within the parcel. The total project area is
2.72 acres.
EXISTING CONDITIONS
The existing site consists of an 0.6-acre parking lot, a grass field and an existing biofiltration swale on the
southern side of the existing Cascade Elementary School site. The project site is fully developed with
existing stormwater facilities. The topography generally slopes from west to east with the project site outfall
located on the southeast corner of the site. (See Figure 2 – Existing Site Conditions).
The project has two high points located in the center portion of the site and at the western property line, at
elevations of 464 and 465 respectively. The existing low point is located at the southeast corner of the site at
an elevation of 452 feet. The overall drop across the site from the northwest corner down to the southeast
corner is 13 feet.
Stormwater runoff flows from north to south. Stormwater runoff from the existing site consists of surface,
shallow, and piped flow to the existing biofiltration swale located on the south side of the site, which then
discharges to the existing stormwater system at the southeast corner of the site.
There are no critical areas within with the existing site. The adjacent street is 116th Avenue SE located to the
west. 116th Avenue SE is generally flat but slopes down to the south at slopes ranging from 0 percent to 0.5
percent. It is developed with a sidewalk, curb, landscape strip and catch basins on the side adjacent to the
site.
The Soils Conservation Service maps the soils as generally Arents, Alderwood material. A geotechnical
analysis of the site was performed by The Riley Group, Inc (RGI) and published in a report dated June 8,
2018. The RGI investigation found “The site is underlain by up to 11 feet of fill comprised of loose to medium
dense silty sand with varying amounts of gravel over medium dense to very dense silty sand with varying amounts
of gravel, and localized silty sand, sandy gravel, and sand with
some silt and gravel.”
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PROPOSED CONDITIONS
The proposed project consists of the construction of a new one-story community recreational center that is
27,000 square feet and approximately 120 surface parking stalls (see Figure 3 – Proposed Site Conditions).
The community center will include a new gymnasium, activity rooms, gathering places, offices, a kitchen,
parking lot and associated landscaping and sidewalks. The proposed project, including frontage
improvements, will result in 1.7 acres of new or replaced impervious surface, which triggers a “Full Drainage
Review” (2017 City of Renton Surface Water Manual 1.1.2.4) and the analysis of all “Core” and “Special”
requirements. Please see Table 1 – Developed Site Conditions Area breakdown for a summary of the
proposed land coverages.
TABLE 1 - DEVELOPED SITE CONDITIONS AREA BREAKDOWN
LAND COVER AREA (ACRES)DESCRIPTION
Impervious Surface 1.70 Parking and drive aisles, building, and sidewalk
Pervious Surface (Landscape)1.02 Lawn and landscape area
Total Disturbed Area 2.72 Disturbed area
% Impervious Area 62.5%
The Core Requirements include MR #3 flow control for the total disturbed area. The detention facilities are
to be modeled using MGSFlood software with 15-minute time steps. Two detention facilities will provide flow
control: an SC-740 Stormtech Chamber System and a MC-3500 Stormtech Chamber System. Both
Stormtech Chamber systems will discharge to the existing storm system located in the southeast corner of
the site.
The Core Requirements also include MR #8 water quality treatment which will be provided by proprietary
Modular Wetland Systems that will be used to mitigate pollution generating areas. In order to meet Core
Requirement #9: On-Site BMPs, Flow Control Best Management Practices (FCBMPs) include bioretention
and green roof to mitigate target impervious surfaces to the maximum extent feasible. See Section IV for
further detail for the flow control and water quality systems.
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II. CONDITIONS AND REQUIREMENTS SUMMARY
This section addresses the requirements set forth by the Core and Special Requirements listed in Chapter 1
of the City of Renton Surface Water Design Manual.
CORE REQUIREMENTS:
1.Discharge at the Natural Location (1.2.1): Stormwater runoff from the existing site discharges to the
existing City of Renton Stormwater system via surface flow and via a ditch and pipe conveyance system
on the southeast corner of the site. In the developed condition, stormwater runoff will continue to
discharge to the City’s stormwater system via surface and pipe flow.
2.Off-site Analysis (1.2.2): A Level 1 analysis of the upstream and downstream flow paths for the
project was performed on September 9, 2018 and is detailed in Section III. This analysis showed that no
downstream problems will occur by the construction of the project.
3.Flow Control (1.2.3): Level II flow control will be provided by two Stormtech Chamber detention
systems. Further information is presented in Section IV of this report.
4.Conveyance System (1.2.4): Closed pipe systems will be provided for on-site stormwater
conveyance. Further details are provided in Section V.
5.Erosion and Sedimentation Control (1.2.5): Erosion and Sediment Control (ESC) measures will be
provided during construction to address the specific conditions at the site. Further details can be found
in Section VIII.
6.Maintenance and Operations (1.2.6): The proposed storm drainage system will be owned, operated
and maintained by the City of Renton. Further details can be found in Section X.
7.Financial Guarantees and Liability (1.2.7): The Owner and Contractor will obtain all necessary
permits prior to the beginning of construction.
8.Water Quality (1.2.8): The project is considered a “commercial” project and drains to the City of
Renton Stormwater system, therefore, Enhanced Basic water quality is required for this project.
Enhanced Basic water quality treatment will be addressed using proprietary Modular Wetland Systems
to treat runoff from all target surfaces. Further details are provided in Section IV of this report.
9.Flow Control BMPs (1.2.9): Flow Control BMPs will be utilized to maximum extent feasible and will
include bioretention to prevent development-related increases in runoff. Further details are provided in
Section IV of this report.
SPECIAL REQUIREMENTS:
1.Other Adopted Area-Specific Requirements (1.3.1):
Critical Drainage Areas (CDAs): The project site is not located within any Critical Drainage Areas.
Master Drainage Plans (MDPs): There are no known master drainage plans covering this project
site.
Basin Plans (BPs): The project is located within the Lower Cedar River Drainage Basin (see Figure
4 – Drainage Basin Map). The basin plan does not include any special drainage requirements.
Stormwater Compliance Plans (SWCPs): There are no Stormwater Compliance Plans that are
applicable to this project.
Lake Management Plans(LMPs): There are no Lake Management Plans that are applicable to this
project.
Shared Facility Drainage Plans(SFDPs): There are no shared Facility Drainage Plans that are
applicable to this project.
2.Flood Hazard Area Delineation (1.3.2): The project site is not located within the 100-year floodplain
(see Figure 5 – 100-yr Floodplain Map).
3.Flood Protection Facilities (1.3.3): The project will not rely on or modify an existing flood protection
facility.
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4.Source Controls (1.3.4): Not applicable. This project will not include any activities or infrastructure that
will require source control measures.
5.Oil Control (1.3.5): Vehicular traffic on the site will not reach levels that require oil control facilities.
PROJECT-SPECIFIC REQUIREMENTS:
There are no additional requirements for the project. Design and construction will abide by requirements set
forth in these documents and the 2017 City of Renton Surface Water Design Manual.
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III. OFF-SITE ANALYSIS
TASK 1 – STUDY AREA DEFINITION AND MAPS
This off-site analysis examines the stormwater systems upstream and downstream of the Family First
Community Center project, located at 16022 116th Avenue SE, Renton WA, 98058. The Family First
Community Center project consists of the construction of a new recreational center that is approximately
27,000 square feet and will include a new gymnasium, activity rooms, gathering spaces, and a
demonstration kitchen. The community center project will construct 120 surface parking lot stalls and
associated sidewalks and landscape areas. The existing site is roughly 2.7 acres with about 0.6 acres of
impervious area and is not constrained by any critical areas or corresponding buffers. The proposed project
will add or replace roughly 1.7 acres of impervious surface and will not convert any square feet of
impervious area to landscape. The Figure 1 - Vicinity Map and Figure 6 - Off-Site Drainage Analysis Map in
the Appendix depict the location of the project site and the basins being analyzed.
TASK 2 - RESOURCE REVIEW
a) Adopted Basin Plans:
According to the King County Drainage Basin iMap, this project is in the Lower Cedar River
Drainage Basin, as depicted in Figure 4 - Drainage Basin Map. The Lower Cedar River Basin and
Nonpoint Pollution Action Plan, adopted in 1997, depicts basin boundaries that are slightly different
than the basin boundaries in the King County Drainage Basin iMap. According to the Lower Cedar
River Basin and Nonpoint Pollution Action Plan, there are not issues regarding potential flooding
erosion and water quality problems upstream nor one mile downstream of the project site, as of
1997.
b) Floodplain/Floodway FEMA Maps:
The project site nor the downstream flow path is not located within a Floodplain/floodway (FEMA).
See Figure 5 – 100-Year Floodplain
c) Other Offsite Analysis Reports:
No offsite analysis reports were available within one mile of the site as of September 2018.
d) Critical Areas:
None of the following Critical Areas are mapped on-site in the downstream flow path:
Coal Mine Hazard Areas
Erosion Hazard Areas
Landslide Hazard Areas
Steep Slope Hazard Areas
Seismic Hazard Areas
Critical Aquifer Recharge Areas
See Figure 6 – Off-Site Drainage Analysis Map.
e) Soils Survey:
The soils that are expected to underlay the project site have been classified by the USDA Natural
Resources Conservation Service (NRCS) as Arents, Alderwood material, 6 to 15 percent slopes (AmC).
See Figure 7 - Soils map.
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f) Wetland Inventory Map:
As of September 2018, no wetlands within the study area are identified on King County’s of City of
Renton’s iMap.
g) Section 303d List of Polluted Waters:
Not applicable to the study area.
h) City of Renton Erosion Maps and Landslide Maps: No Erosion or Landslide Hazards are included within
the study are for this Project. See Figure 6 – Off-Site Drainage Analysis Map.
i) Other reports: Cascade Elementary School Portables Project TIR.
TASK 3 - FIELD INSPECTION
A Level 1 Downstream Analysis site visit was made on 9/6/2018 under dry conditions. Total precipitation for
9/6/2018 was 0 inches. No rainfall occurred on the day prior to the site visit. Results of the field inspection
are shown in the Off-Site Drainage Systems Table attached to Figure 6 - Off-Site Drainage Analysis Map in
the Appendix.
1. Investigate any problems reported or observed during the resource review.
No problems were reported or observed during the resource review.
2. Locate all existing/potential constrictions or lack of capacity in the existing drainage system.
No constrictions or lack of capacity in the existing drainage system was observed.
3. Identify all existing/potential downstream drainage problems as defined in Section 1.2.2.1.
No existing/potential downstream drainage problems were observed.
4. Identify existing/potential overtopping, scouring, bank sloughing, or sedimentation.
No existing/potential overtopping, scouring, bank sloughing, or sedimentation was
observed.
5. Identify significant destruction of aquatic habitat or organisms (e.g., severe siltation, bank erosion,
or incision in a stream).
No significant destruction of aquatic habitat or organisms was observed.
6. Collect qualitative data on features such as land use, impervious surfaces, topography, and soil
types.
The land use of the project site is a school site that consists of approximately 30%
impervious area and sports fields to the east side. The conveyance system drains through
a residential area to the east before reaching 119th Avenue SE, where the road slopes
down to a catch basin before being conveyed farther east. The upstream basin was
delineated by determining what portion of the existing Cascade Elementary School site
drains to the existing bioswale. This existing bioswale will be replaced as a part of the
proposed development and the same basin draining to the bioswale is the upstream basin
for the proposed project. Based on the survey and observations on site, no other upstream
basin was delineated.
7. Collect information on pipe sizes, channel characteristics, drainage structures, and relevant critical
areas (e.g., wetlands, streams, steep slopes).
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See Figure 6 for information on pipe sizes and drainage structures. No critical areas were
observed.
8. Verify tributary basins delineated in Task 1.
Based on the topography onsite, the basin delineation based on the survey and COR maps
was confirmed.
9. Contact neighboring property owners or residents in the area about past or existing drainage
problems and describe these in the report (optional).
This requirement is not applicable for this project.
10. Note the date and weather conditions at the time of the inspection.
The site visit occurred on September 6, 2018. The weather was sunny, and temperature
was 65 degrees.
TASK 4 - DRAINAGE SYSTEM DESCRIPTION AND PROBLEM DESCRIPTIONS
See Figure 6 for a map of the downstream drainage system. The site currently discharges from a catch
basin at the southeast corner of the site located directly downstream of an existing bioswale and then
through a series of catch basins in residential streets. This catch basin and bioswale will be replaced as a
part of the proposed development. Downstream of the replaced catch basin, stormwater is conveyed
approximately 200 feet through an existing 15” pipe to an existing type 1 catch basin located at the
southeast corner of the Cascade Elementary School property. Stormwater is then conveyed roughly 320
feet to a type two catch basin located in 119th Ave SE, which is adjacent to the property. Stormwater is then
conveyed approximately 300 feet through a 24” concrete pipe at approximately 2% to another type two
catch basin located in 120th Ave SE. From here stormwater is directed through a 24” concrete pipe at 2%
slope to a type two catch basin located in 121st Ave SE, approximately 300 feet downstream. See Off-Site
Drainage System (attached to Figure 6) for more information regarding the downstream drainage system.
UPSTREAM ANALYSIS
Approximately 4 acres of upstream area currently flows to the existing bioswale located onsite. The
upstream basin was delineated by determining what portion of the existing Cascade Elementary School site
drains to the existing bioswale. This existing bioswale will be replaced as a part of the proposed
development and the same basin draining to the bioswale is the upstream basin for the proposed project.
Based on the survey and observations on site, no other upstream basin was delineated. See Figure 8 for
the upstream basin delineation.
CONCLUSION
Based on the observations made during the Level 1 downstream analysis that was performed on 9/6/2018,
no existing or potential downstream drainage issues such as flooding, overtopping, or erosion were evident.
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IV. FLOW CONTROL AND WATER QUALITY FACILITY ANALYSIS AND
DESIGN
EXISTING SITE HYDROLOGY (PART A)
The existing site consists of a park with a grass field, parking lot and landscaping area (See Figure 2 –
Existing Site Conditions). The site slopes in a southeasterly direction with drainage described in Section III
Downstream Analysis. These conditions are summarized in Table 2 below.
TABLE 2 - EXISTING SITE CONDITIONS AREA BREAKDOWN
LAND COVER AREA (ACRES)DESCRIPTION
Impervious Area 0.53 Existing parking lot
Pervious & Landscape 2.19 Grass Field and Native vegetation
Total Project Area 2.72
% Impervious Area 19.5%
DEVELOPED SITE HYDROLOGY (PART B)
The developed site will increase the amount of impervious area to 1.70 acres and the remaining site area
with be pervious landscaping or bioretention and green roof areas. (See Figure 3 – Proposed Site
Conditions). The area impacted by the development is 2.72 acres.
The project will be using two Stormtech Chamber detention systems to meet the project’s flow control
requirements. By dividing into two different size chamber systems, the project can utilize the existing
topography to minimize earthwork. However, the project will only have one discharge location.
PERFORMANCE STANDARDS AND FLOW CONTROL SYSTEM (PARTS C)
Level II flow control (conservation flow control assuming historic site conditions) is required for this project.
Level II flow control requires the proposed discharge durations to match the predeveloped durations for the
range of predeveloped discharge rates from 50 percent of the 2-year peak flow up to the full 50-year peak
flow. MGSFlood software will be used to size the detention facilities in compliance with the CRSWDM
standards. The calculations for the detention facilities will be included in Appendix B of the final report.
Runoff from the site will be detained in two detention facilities, an SC-310 Stormtech Chamber system and a
MC-3500 Stormtech Chamber system. The proposed detention volumes are summarized in Table 3 below.
TABLE 3 – DETENTION FACILITY SUMMARY
DETENTION FACILITY PROVIDED
[CF]
SC-310 StormTech Chambers 18,415
MC-3500 StormTech Chambers 30,087
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WATER QUALITY SYSTEM (PART D)
Under Core Requirement #8 the project is required to provide Enhanced Basic water quality treatment for
the pollution generating surfaces. To meet the water quality standards, the project will treat pollution
generating surfaces by using two proprietary Modular Wetland Systems (MWS). Water quality design
calculations will be provided in Appendix B of the final report.
The Family First Community Center project will be removing the biofiltration swale that is currently being
used as a water quality treatment facility for the Cascade Elementary School site. One of the proposed
Modular Wetland System will be used to treat the pollution generating runoff from the existing Cascade
Elementary School site in replacement of the biofiltration swale.
The other Modular Wetland System will be used to treat the pollution generating runoff from the proposed
pollution generating surfaces that will be constructed as a part of the Family First Community Center project
before discharging to the existing City of Renton stormwater system.
The MWSs are sized according to flow rates. They are located downstream of the detention facilities and so
are sized to treat the full 2-year release rate post detention. Runoff enters each MWS vault via pipe. In the
vault, trash, sediment and debris are separated before runoff enters the pre-filter cartridges. The pre-filter
cartridges utilize a media filter material which removes over 80 percent of total suspended solids and over
90 percent of hydrocarbons. After pre-filtering, the runoff enters a chamber with a patented wetland media.
The wetland media removes any phosphorous in the water. The MWSs have an internal bypass weir for
large storm events (up to the 100-year event).
FLOW CONTROL BEST MANAGEMENT PRACTICES (PART E)
Flow Control Best Management Practices (FCBMP) are required to be implemented to the Maximum Extent
Feasible (MEF) in accordance with Core Requirement #9. FCBMP rely heavily on infiltration and/or
dispersion over flat or gentle slopes. The geotechnical analysis concludes that site soils are not infiltrative,
which renders most FCBMPs infeasible.
The project site is larger than 22,000 square feet and therefore must comply with Section 1.2.9.2.2 Large
Lot BMP Requirements. Flow control BMP requirements that must be applied to the maximum extent
feasible are as follows:
1.Full Dispersion: Due to site constraints, the required length and wide of the flow path for full
dispersion cannot be met.
2.Full Infiltration of Roof Runoff: A geotechnical analysis of site soils found that the conditions
onsite are not compatible with stormwater infiltration and recommended that the project not utilize
infiltration.
3. All target impervious surface not mitigated by #1 or #2 must be mitigated to the maximum extent
feasible using one or more of the following BMPs:
a.Full Infiltration: Full infiltration is not feasible because the soils do not permit infiltration
according to an analysis performed by the geotechnical engineer.
b.Limited Infiltration: According to the analysis performed by the geotechnical engineer, the
conditions onsite do not allow for infiltration using shallow or deep infiltration strategies.
c.Bioretention: Non-infiltrative Bioretention will be utilized to the meet the Core Requirement
#9.
d.Permeable Pavement: Permeable pavement is not feasible due to the poor infiltrative
soils.
4.Basic Dispersion: Due to site constraints, the required length and wide of the flow path for basic
dispersion cannot be met.
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5.BMP Implementation: The amount of target impervious surfaces required to drain to a FCBMP is
detailed in Section 1.2.9.2.2.5 of the CRSWDM. “For projects that will result in impervious surface
coverage of 45%-65% on the buildable portion of the site/lot, flow control BMPs must be applied to
50% of the target impervious surfaces reduced by 1.5% for each 1% of impervious surface
coverage above 45% (e.g. impervious of 55% results in a requirement of FCBMPs applied to 35%
of target impervious surfaces.)” This project will result in impervious surface coverage of 63% on
the buildable portion of the parcel. Therefore, FCBMPs must be applied to 23% (0.39 acres) of the
target impervious surfaces. The project is providing non-infiltrating bioretention to mitigate the
required amount of target impervious area.
6.Soil Quality Preservation: The soil quality of new pervious surfaces will be protected by the
application of compost-amended soils and native topsoil will be retained to the maximum extent
practicable in accordance with City of Renton requirements.
7.Perforated Pipe Connection: Due to the existing soil, topography, programming needs, and site
constraints there are no feasible locations onsite for a perforated pipe connection.
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V. CONVEYANCE SYSTEM ANALYSIS AND DESIGN
CONVEYANCE STANDARDS
The conveyance systems have been designed to meet the requirements set forth in Chapter 4 of the 2017
CRSWDM. The requirements and the way the design will meet them are presented, below.
1.Facilities must convey the 100-year flow without overtopping the crown of the roadway, flooding
buildings, and if sheet flow occurs it must pass through a drainage easement. Facilities will be
designed to convey the 100-year storm without affecting surrounding infrastructure. No sheet flow to
neighboring properties is expected to occur.
2.New pipe systems and culverts must convey the 25-year flow. New pipe systems are designed to
convey the 25-year flow without overtopping structures.
3.Bridges must convey the 100-year flow and provide a minimum of two feet, varying up to six
feet, of clearance based on 25% of the mean channel width. This project will not construct bridges.
4.Drainage ditches must convey the 25-year flow with 0.5 feet of freeboard and the 100-year flow
without overtopping. This project will not construct drainage ditches.
5.Floodplain Crossings must not increase the base flood elevation by more than 0.01 feet and
shall not reduce the flood storage volume. Piers shall not be constructed in the FEMA floodway.
There are no floodplain crossings or piers associated with this project.
6.Stream Crossings shall require a bridge for Class 1 Streams that does not disturb or banks. For
Type 2 and Type 3 steams, open bottom culverts or other method may be used that will not
harm the stream or inhibit fish passage. There are no stream crossings associated with this project.
7.Discharge at natural location is required and produce no significant impacts to the downstream
property. This project will provide Level II flow control and will discharge at the natural location. The
flow control facilities will reduce the rate of flow discharging from the existing site.
ON-SITE CONVEYANCE SYSTEMS
Existing Conditions
The existing conveyance system consists of catch basins, storm pipes and a biofiltration swale. The existing
biofiltration swale and some of the existing catch basins and storm pipes that are located within the
development area will be removed and new catch basins and storm pipes will be installed.
Developed Conditions
The developed on-site conveyance system will consist of catch basins and storm pipes. The existing storm
pipe that conveys runoff from the existing Cascade Elementary school site that will be removed to construct
the new Family First Community Center building will be rerouted to the existing conveyance system. The
conveyance system conveys runoff from the redevelopment and upstream areas to the existing conveyance
system. There will be one connection point to the existing storm system. The connection point to the existing
system is in the southeast corner of the site, where the Family First project and the rerouted stormwater
from the Cascade ES site will discharge. Peak flow rates for the proposed conveyance systems will be
calculated using the Rational Method. The hydraulic grade line will be calculated using the Direct Step
Backwater Method. Calculations showing the sizing of the on-site system will be included in the final report.
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VI. SPECIAL REPORTS AND STUDIES
1. Geotechnical Engineering Report. Renton, Washington. Prepared by The Riley Group, Incorporated on
June 8, 2018.
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VII. OTHER PERMITS
This project will require building and demolition permits from the City of Renton and an NPDES permit from
the Department of Ecology. The NPDES will include a SWPPP and a spill prevention and cleanup report
(included in the SWPPP).
FAMILY FIRST COMMUNITY CENTER
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VIII. CSWPPP ANALYSIS AND DESIGN
This section lists the requirements that were met when designing the TESC plan for this site. The project will
be publicly bid and a contractor will be determined at a future date.
STANDARD REQUIREMENTS
Erosion/Sedimentation Plan shall include the following:
1. Clearing Limits – Construction limits are delineated on the project erosion control plans and shall be
physically surveyed and marked on site.
2. Cover Measures – Contractor will use plastic sheeting, hydroseeding, and mulching to protect soils
from erosion.
3. Perimeter Protection – Temporary construction fencing will be used to delineate and protect the
project clearing limits and provide a secure site. Silt fencing and interceptor swales will be used to
prevent sediment-laden water from discharging from the site.
4. Traffic Area Stabilization – Stabilized construction entrances, wheel wash, and quarry spalls will be
used for traffic area stabilization.
5. Sediment Retention – Site temporary erosion and sediment control plans will include baker tanks,
temporary sediment pond, and catch basin protection to provide sediment control.
6. Surface Water Collection – Interceptor swales will be used in the appropriate areas of the site to
collect stormwater runoff. The swales are then routed to the sediment pond and baker tanks.
7. Dewatering Control – Dewatering is not necessary for this site; therefore, no dewatering control
measures are implemented.
8. Dust Control – Soils will be appropriately sprinkled with water to limit airborne dust during dry weather.
9. Flow Control –Discharge from the baker tanks and sediment pond will be restricted and will therefore
serve as a flow control measure during construction.
10. Control Pollutants – The discharged runoff from the construction site will be monitored for turbidity and
pollutants before leaving the site.
11. Protect Existing and Proposed Flow Control BMPs – Proposed FCBMPs consist of bioretention, and
green roof. The bioretention areas will be protected during construction.
12. Maintain BMPs – BMPs for the project will be monitored for effectiveness on a regular basis. The
Construction Stormwater Pollution Prevention (CSWPP) Supervisor will typically monitor the BMPs and
ensure they are repaired and replaced as necessary.
13. Manage the Project – The BMPs will be inspected maintained and repaired as needed to ensure their
intended performance. Site inspections and monitoring will be in accordance with the Construction
Stormwater General Permit, specific BMP conditions and the City of Renton requirements. The SWPP
will be maintained and updated and any updates will be coordinated with the site inspector.
FAMILY FIRST COMMUNITY CENTER
15
IX. BOND QUANTITY, FACILITY SUMMARIES, AND DECLARATION OF
COVENANT
A Facility Summary, Bond Quantity Worksheet and Declaration of Covenants for Leachable Materials,
Stormwater Facilities and BMPs, and Clearing Limits will be included in Appendix E of the final report.
FAMILY FIRST COMMUNITY CENTER
16
X. OPERATION AND MAINTENANCE MANUAL
The Operations and Maintenance manual will be provided in Appendix D of the final drainage report.
FAMILY FIRST COMMUNITY CENTER
APPENDIX A - FIGURES
FIGURE 1 – VICINITY MAP
FIGURE 2 – EXISTING SITE CONDITIONS
FIGURE 3 – PROPOSED SITE CONDITIONS
FIGURE 4 – DRAINAGE BASIN MAP
FIGURE 5 – 100-YR FLOODPLAIN MAP
FIGURE 6 – OFF-SITE DRAINAGE ANALYSIS MAP
FIGURE 7 – SOILS MAP
FIGURE 8 – UPSTREAM MAP
4,514752
City of Renton Print map Template
This map is a user generated static output from an Internet mapping site and
is for reference only. Data layers that appear on this map may or may not be
accurate, current, or otherwise reliable.
THIS MAP IS NOT TO BE USED FOR NAVIGATIONWGS_1984_Web_Mercator_Auxiliary_Sphere
Notes
None
09/04/2018
Legend
512 0 256 512 Feet
Information Technology - GIS
RentonMapSupport@Rentonwa.gov
Erosion hazard - high
Floodway
Special Flood Hazard Areas (100 year flood)
Landslide
Very High
High
Moderate
Unclassified
Slope City of Renton
>15% & <=25%
>25% & <=40% (Sensitive)
>40% & <=90% (Protected)
>90% (Protected)
Environment Designations
Natural
Shoreline High Intensity
Shoreline Isolated High Intensity
Shoreline Residential
Urban Conservancy
Jurisdictions
Streams (Classified)
<all other values>
Type S Shoreline
Type F Fish
Type Np Non-Fish
Type Ns Non-Fish Seasonal
Unclassified
Not Visited
Wetlands
5' Primary
5' Intermediate
Network Structures
Inlet
Manhole
Utility Vault
Unknown Structure
Control Structure
Pump Station
Discharge Point
Water Quality
Detention Facilities
Pond
Tank
Vault
Wetland
Stormwater Main
Culvert
Open Drains
Facility Outline
Private Network Structures
Inlet
Manhole
Utility Vault
Unknown Structure
Private Control Structure
Private Discharge Point
Private Water Quality
Soil Map—King County Area, Washington
(Family First Community Center)
Natural Resources
Conservation Service
Web Soil Survey
National Cooperative Soil Survey
9/4/2018
Page 1 of 3525625052563005256350525640052564505256500525655052566005256650525625052563005256350525640052564505256500525655052566005256650561340561390561440561490561540561590561640
561340 561390 561440 561490 561540 561590 561640
47° 27' 37'' N 122° 11' 10'' W47° 27' 37'' N122° 10' 55'' W47° 27' 24'' N
122° 11' 10'' W47° 27' 24'' N
122° 10' 55'' WN
Map projection: Web Mercator Corner coordinates: WGS84 Edge tics: UTM Zone 10N WGS84
0 50 100 200 300
Feet
0 30 60 120 180
Meters
Map Scale: 1:2,030 if printed on A portrait (8.5" x 11") sheet.
Soil Map may not be valid at this scale.
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:
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 13, Sep 7, 2017
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
(Family First Community Center)
Natural Resources
Conservation Service
Web Soil Survey
National Cooperative Soil Survey
9/4/2018
Page 2 of 3
Map Unit Legend
Map Unit Symbol Map Unit Name Acres in AOI Percent of AOI
AgC Alderwood gravelly sandy
loam, 8 to 15 percent slopes
0.2 1.1%
AmC Arents, Alderwood material, 6
to 15 percent slopes
16.8 98.9%
Totals for Area of Interest 17.0 100.0%
Soil Map—King County Area, Washington Family First Community Center
Natural Resources
Conservation Service
Web Soil Survey
National Cooperative Soil Survey
9/4/2018
Page 3 of 3
2,400400
City of Renton Print map Template
This map is a user generated static output from an Internet mapping site and
is for reference only. Data layers that appear on this map may or may not be
accurate, current, or otherwise reliable.
THIS MAP IS NOT TO BE USED FOR NAVIGATIONWGS_1984_Web_Mercator_Auxiliary_Sphere
Notes
None
09/07/2018
Legend
272 0 136 272 Feet
Information Technology - GIS
RentonMapSupport@Rentonwa.gov
Environment Designations
Natural
Shoreline High Intensity
Shoreline Isolated High Intensity
Shoreline Residential
Urban Conservancy
Jurisdictions
Streams (Classified)
<all other values>
Type S Shoreline
Type F Fish
Type Np Non-Fish
Type Ns Non-Fish Seasonal
Unclassified
Not Visited
Wetlands
5' Primary
5' Intermediate
FAMILY FIRST COMMUNITY CENTER
APPENDIX B – ENGINEERING CALCULATIONS
All engineering calculations will be provided in the final drainage report.
FAMILY FIRST COMMUNITY CENTER
APPENDIX C – CSWPPP
The CSWPPP will be provided in the final drainage report.
FAMILY FIRST COMMUNITY CENTER
APPENDIX D – OPERATIONS AND MAINTENANCE MANUAL
The Operations and Maintenance manual will be provided in the final drainage report.
FAMILY FIRST COMMUNITY CENTER
APPENDIX E – FACILITIES SUMMARY AND DECLARATIONS OF
COVENANT
The Facilities Summary and Declarations of Covenant will be provided in the final drainage report.