HomeMy WebLinkAboutRS_King_Co_CMF_Preliminary_Drainage_TIR_190426_v1
Draft Stormwater Technical
Information Report
King County Parks – Renton Shop
Central Maintenance Facility
Replacement Project
King County Department of Natural Resources
and Parks - Parks and Recreation Division
January 15, 2019
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Draft Stormwater Technical Information Report
King County Parks - Renton Shop Central Maintenance Facility Replacement Project
January 15, 2019 | i
Certificate of Engineer
The technical material and data contained in this report for the King County Parks, Renton Shop -
Central Maintenance Facility Replacement, Draft Stormwater Technical Information Report
was prepared under the supervision and direction of the undersigned, whose seal, as a professional
engineer licensed to practice as such, is affixed below.
(Signature along with sealed stamp to be provided with Final TIR)
_________________________________
Jim Rhodes, P.E.
Senior Water Resources Engineer
HDR Engineering, Inc.
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Contents
1 Project Overview ................................................................................................................................. 1
1.1 Introduction and Purpose .......................................................................................................... 1
1.2 Project Description and Location .............................................................................................. 1
1.2.1 Project Background ...................................................................................................... 1
1.2.2 Existing Project Site and Adjacent Properties Description......................................... 11
1.2.3 Project Redevelopment Proposal Description ........................................................... 11
1.3 Existing Conditions .................................................................................................................. 12
1.3.1 Site Topography, Drainage, Land Cover, Soils, and Groundwater ............................ 12
1.3.2 Existing Drainage Basin and Threshold Discharge Areas ......................................... 13
1.4 Proposed Conditions ............................................................................................................... 15
1.4.1 Site Grading, Drainage, Land Cover, and Soils ......................................................... 15
1.4.2 Proposed Threshold Discharge Areas ....................................................................... 15
1.5 Land Cover and Change Summary ......................................................................................... 17
2 Conditions and Requirements Summary .......................................................................................... 19
2.1 Drainage Review Classification for Project ............................................................................. 19
2.2 Core Requirements and Project Applicability .......................................................................... 19
2.2.1 CR #1: Discharge at the Natural Location.................................................................. 19
2.2.2 CR #2: Off-site Analysis ............................................................................................. 20
2.2.3 CR #3: Flow Control Facilities .................................................................................... 20
2.2.4 CR #4: Conveyance System ...................................................................................... 21
2.2.5 CR #5: Construction Stormwater Pollution Prevention .............................................. 22
2.2.6 CR #6: Maintenance and Operations ......................................................................... 22
2.2.7 CR #7: Financial Guarantees and Liability ................................................................. 22
2.2.8 CR #8: Water Quality Facilities .................................................................................. 23
2.2.9 CR #9: On-site BMPs ................................................................................................. 23
2.3 Special Requirements and Project Applicability ...................................................................... 24
2.3.1 SR #1: Other Area Specific Requirements ................................................................ 24
2.3.2 SR #2: Flood Hazard Area Delineation ...................................................................... 25
2.3.3 SR #3: Flood Protection Facilities .............................................................................. 25
2.3.4 SR #4: Source Controls.............................................................................................. 25
2.3.5 SR #5: Oil Control ...................................................................................................... 26
2.3.6 SR #6 Aquifer Protection Area ................................................................................... 26
3 Off-site Analysis ................................................................................................................................ 27
3.1 Downstream Analysis .............................................................................................................. 27
3.1.1 Define and Map the Study Area ................................................................................. 27
3.1.2 Review Available Study Area Information .................................................................. 27
3.1.3 Field Inspect the Study Area ...................................................................................... 28
3.1.4 Describe the Drainage System and Drainage Problems ........................................... 28
4 Flow Control, Low-impact Development, Water Quality, and Infiltration Facilities Analysis
and Design ........................................................................................................................................ 29
4.1 Existing Conditions Site Hydrology ......................................................................................... 29
4.2 Proposed Conditions Site Hydrology ...................................................................................... 29
4.3 Stormwater Controls Design Requirements and Performance Standards ............................. 30
4.3.1 Flow Control Facilities ................................................................................................ 30
4.3.2 On-site and Low-impact Development BMPs ............................................................ 33
4.3.3 Water Quality Facilities............................................................................................... 34
4.3.4 Infiltration Facilities ..................................................................................................... 35
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4.4 Flow Control Facilities Preliminary Analysis and Sizing .......................................................... 36
4.4.1 Detention Vaults Flow Control Storage ...................................................................... 36
4.5 Water Quality Treatment Facilities Preliminary Analysis and Sizing ...................................... 37
4.5.1 Detention Vaults Presettling Storage and Surface Area ............................................ 37
4.5.2 Coalescing Plate Oil Water Separators...................................................................... 37
4.5.3 Modular Wetland System Linear Filters ..................................................................... 38
4.6 Infiltration and Reuse Facilities Preliminary Analysis and Sizing ............................................ 38
4.6.1 Combined Infiltration Gallery and Underlying Sand Filter .......................................... 38
4.6.2 Rainwater Harvesting Facilities .................................................................................. 39
5 Conveyance System Analysis and Design ........................................................................................ 40
5.1 Proposed Conveyance Systems ............................................................................................. 40
5.2 Conveyance Systems Analysis and Design ............................................................................ 40
6 Special Reports and Studies ............................................................................................................. 41
7 Other Permits .................................................................................................................................... 41
8 CSWPP Analysis and Design............................................................................................................ 42
8.1 ESC Plan Measures ................................................................................................................ 42
8.2 SW PPS Plan Measures .......................................................................................................... 44
9 Bond Quantities, Facility Summaries, and Declaration of Covenant ................................................ 45
10 Operations and Maintenance Manual ............................................................................................... 45
11 References ........................................................................................................................................ 45
Tables
Table 1. Existing Threshold Discharge Areas Land Cover ........................................................................ 17
Table 2. Proposed Threshold Discharge Areas Land Cover ..................................................................... 18
Table 3. Change in Threshold Discharge Areas Land Cover .................................................................... 18
Table 4. Existing Conditions Hydrology Summary ..................................................................................... 29
Table 5. Proposed Conditions Hydrology Summary .................................................................................. 30
Table 6. Detention Vaults Flow Control Storage Sizing ............................................................................. 37
Table 7. Proposed Primary ESC Measures ............................................................................................... 43
Table 8. Proposed Primary SWPPS Measures ......................................................................................... 44
Figures
Figure 1. TIR Worksheet .............................................................................................................................. 2
Figure 2. Site Location and Critical Areas .................................................................................................... 7
Figure 3A. Existing Threshold Discharge Areas, Site Characteristics, and Downstream Flow
Paths .......................................................................................................................................... 8
Figure 3B. Proposed Threshold Discharge Areas and Site Characteristics ................................................ 9
Figure 4. Site Soils and Subsurface Characteristics .................................................................................. 10
Figure 5. Proposed On-site Stormwater Control Facilities ......................................................................... 31
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Appendices
Appendix A. Project Drainage Review Classification Figures ....................................................................A-1
Appendix B. Hydrologic Analysis for Flow Control Sizing and Water Quality Flow Calculations ..............B-1
Appendix C. Oil-Water Separator and Sand Filter/Infiltration Facilities Sizing Calculations .................... C-1
Appendix D. Storm Drain Conveyance Sizing Calculations ...................................................................... D-1
Appendix E. Preliminary Geotechnical Report (submitted separately)........................................................E-1
Appendix F. Preliminary Site Improvement Drawings (submitted separately) ........................................... F-1
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Acronyms and Abbreviations
ac acre
bgs below ground surface
BMP best management practice
CESF chitosan enhanced sand filtration
cf cubic foot/feet
cfs cubic feet per second
CMF Central Maintenance Facility
CR Core Requirement
CSWPPP construction stormwater pollution prevention plan
ESC erosion and sediment control
GIS geographic information system
GULD General Use Level Designation
LID low-impact development
MOU Memorandum of Understanding
MWS Modular Wetland System
NPDES National Pollutant Discharge Elimination System
NPGPS non-pollution generating pervious surface
O&M operations and maintenance
OWS oil-water separator
PGIS pollution generating impervious surface
PGPS pollution generating pervious surface
PIT pilot infiltration tests
REC Recording
RMC Renton Municipal Code
RSWDM Renton Surface Water Design Manual
sf square feet/foot
SR Special Requirement
SWPPS stormwater pollution prevention and spill control
TDA threshold discharge area
TIR Technical Information Report
TPH total petroleum hydrocarbons
TSS total suspended solids
UIC Underground Injection Control
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1 Project Overview
1.1 Introduction and Purpose
The purpose of this Draft Technical Information Report (TIR) is to document the stormwater control
facilities proposed and their design basis for the King County Department of Natural Resources and
Parks – Parks and Recreation Division (King County Parks), Renton Shop - Central Maintenance
Facility Replacement Project (Project). It is located within the City of Renton, Washington, generally
between NE 3rd and NE 4th Street (to the north), NE 2nd Street and the Renton Transfer and
Recycling Station (to the south), Jefferson Avenue NE (to the east), and a self-storage facility (to the
west).
The City of Renton (City) has lead permitting agency status for the Project, and as such, the facilities
are being designed in compliance with the City’s surface water and stormwater requirements, and
also for consistency with the City’s NPDES MS4 Phase II Permit. The Project is subject to drainage
review under the 2017 City of Renton Surface Water Design Manual (2017 RSWDM). As required
by Section 2.3 of that manual, this drainage report has been prepared in accordance with the City’s
TIR format.
The Draft TIR is consistent with the HDR design team’s (HDR) preliminary design of storm drainage
improvements to serve proposed site redevelopment improvements. The information provided
within this Draft TIR is based on the 60% design concept, and will be updated and expanded upon
for future design submittals as the project design progresses and is modified through the final design
process.
1.2 Project Description and Location
The TIR Worksheet, which provides a detailed summary of the Project has been included as
Figure 1. A site location map showing the Project site location is included in Figure 2. The Project
site drainage subbasins, land cover and downstream flow paths for existing and proposed
(redeveloped) site conditions are shown in Figure 3A and Figure 3B. The Project site soils and
subsurface characterization is shown in Figure 4.
1.2.1 Project Background
King County Parks consists of more than 200 parks, 175 miles of regional trails, and 215 miles of
backcountry trails, totaling more than 28,000 acres of property to operate and maintain. Their
headquarters for operations and maintenance (O&M) is located at the Central Maintenance Facility
(CMF), 3005 NE 4th Street in Renton (see Figure 2). It also houses the dispatch center for all O&M
staff, fleet vehicle and large equipment storage, warehouse and inventory storage, and King County
Parks’ event operations.
King County Parks - Brenda Bradford206-477-2030201 South Jackson Street #700Seattle, Washington 98104Jim Rhodes, PE / Jerry Bibee, PE HDRLAND USE ID #584394Renton Shop - CMF Replacement3005 NE 4th Street, Renton, WAConditional Use PermitJanuary 15, 2019January 15, 201923N5E16206-826-4689 (Jim) / 253-432-5057 (Jerry)CR #1 - Discharge at Natural Location - Proposed adjustment to TDAs for full on-site infiltrationCR #2 - Off-site Analysis - Proposed adjustment from off-site analysis for full on-site infiltration CR #3 - Flow Control Facilities - Proposed adjustment from duration standard for full on-site infiltration
Lower Cedar River
City of Renton Surface Water Design Manual (December 2016)
Highlands
No stormwater operational monitoring for full infiltration;
Construction monitoring under NPDES CGSP
Possible wetland on parcel east of site
On parcels to west and east of site
Wellhead (aquifer) protection area - Zone 2
On parcels to south/east of site
Arents/Everett underlain by
recessional glacial outwash
Low0-2%
Zone 2 - Maplewood
10-yr capture zoneProposed infiltration (at depth) test wells
Limited existing off-site sheet and concentrated
flow paths to off-site infiltration. No off-site storm
drain connections exist or are proposed aside
from overflow connection to south off-site closed
depression infiltration area for redundancy
On-site TDAs P1 and P2 (east-west drainage split for proposed site grades)
replace TDAs E1 and E2 (north-south drainage split for existing site grades);
Other TDAs (P3 - P6 and E3 - E6 are for off-site drainage areas; all infiltrate)
All discharges to infiltration;
2 on-site; 1 off-site (overflow)
Proposed adjustment for
full infiltrationFC (Level 2) not
applicable for full
infiltration without
downstream surface
water discharge
Peak rate flow control for
100 yr design dischargePresettling vault; CP OWS
Vault with Oil Control Baffle
TBD
TBD
TBD
King County Parks
None exist or are required
Industrial (Maintenace and Operations Facility)
Roofs covering selected materials storage areas; perimeter
berms isolating equipment wash pad (to sanitary sewer)
King County Parks to maintain facilities
Coalescing plate oil-water separators (CP OWS) (3)
Pre-setlting and flow control storage vaults (2); Modular Wetland System (MWS)
units (5); infiltration galleries overlaying sand filters (2) - See TIR Figure 5 layout
Two drainage systems serving TDA P1 and P2 site areas - conveyance storm
drains leading to linear flow control vaults, then through CP OWS, MWS filter
units, to infiltration gallery underlain by sand filter; treated flow collection for re-use
See TIR Table 7 for Proposed
ESC Measures
(Final TIR to be signed) Draft TIR dated Janurary 15, 2019
Linear precast vaults
flow control storage
TIR Figure 5
Infiltation galleries
(100-yr)
Collection/pumping
of a portion of treated
runoff to AG storage
tanks for irrigation re-use
Rain garden /
bioretention cell
Linear precast vaults
presettling storage
MWS Linear filters;
sand filters
Coalescing plate OWS
Floating oil booms; tee
risers; oil control baffles
Rain garden / bioretention cell;
Infiltration galleries (100-yr)
Off-site south parcel
overflow path / closed
depression infiltration area
Treatment to 100-yr
detention outflow
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King County Parks is redeveloping the existing CMF with a new and improved facility on Parcel
No. 1434000012. The existing post-World War II-era facility is aging, is not connected to the City’s
sanitary sewer system, and cannot accommodate the planned expansion of staff, equipment, and
vehicles. The replacement facility, developed on the same site, will be called the King County Parks
- Renton Shop. The Renton Shop will address future service needs, be built to current building and
environmental compliance standards, and will accommodate projected future staff growth. The
Renton Shop will allow for additional consolidation of other King County Parks maintenance districts
to the site, greatly improving the function and space for shop operations, enhancing vehicle and
pedestrian safety within the facility with better site circulation and flow, and providing needed office
space, meeting rooms, storage and shop space to support planned growth.
1.2.2 Existing Project Site and Adjacent Properties Description
The Project site was subdivided into an approximately 5.7-acre (248,672 square foot) parcel from a
larger County-owned property in 2016 (REC #20160303900006), and is zoned light industrial.
Adjacent land uses include:
• North: former King County Public Health office building recently purchased for redevelopment by
Renton Technical College
• South: owned by King County Roads Division, vehicle and equipment storage
• East: beyond the Jefferson Avenue NE access road is a vacant private parcel that historically
was mined for sand and gravel and is now being used to accept fill dirt under a City grading
permit
• West: Self-storage business
The Project site is generally flat with a slight slope downward from east to west. Along the western
property line is a short section of steeper slope extending west to the self-storage business. City
critical areas mapping (City of Renton Maps, accessed June 2018) shows this steeper section as a
Regulated Slope, between 15 and 25 percent slope. The site is also within the City’s Wellhead
Protection Area, Zone 2.
The Project site has two existing primary buildings: one houses administrative and supervisory staff,
and the other building is for the field crews. There are additional areas for covered storage
structures, maintenance and construction laydown yard, fleet vehicle parking, and employee parking.
The site is surfaced with gravel and some localized areas of pavement. There are few trees or
landscaping with the exception of a small pocket adjacent to the administration building and along
the west site boundary. The facility is accessed via a single driveway off of the King County-owned
private street along the east property line (Jefferson Avenue NE).
1.2.3 Project Redevelopment Proposal Description
The Renton Shop will modernize the site and provide additional capacity to meet current and future
demand for staff space and equipment/fleet vehicle storage. The Project redevelopment proposal
includes the following major construction and improvement features:
• Demolition of all existing buildings
• Utility work to connect the Project site to the City sanitary sewer system, providing sewer service
capacity across the site and to the south, and to relocate, extend, and upsize the water main
serving the site along Jefferson Avenue NE
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• Storm drainage improvements to serve all Project site and frontage road improvements
consistent with the City’s current stormwater management standards, with goals for full
infiltration of site runoff after on-site detention storage and robust water quality treatment
protective of the City’s underlying sole source aquifer protection zone
• Implementation of sustainable low-impact development (LID) on-site stormwater best
management practices (BMPs), including partial capture, storage, and irrigation reuse of treated
runoff as sustainable stormwater management practices that reduce required infiltration volumes
• Site preparation for paving (asphalt pavement), building construction, and landscaping
• Construction of 3 buildings:
- Administration Building A = 29,200 square feet (2 stories)
- Shops Building B = 16,600 square feet (2 stories)
- Covered Storage Building C = 12,200 square feet
• Administration building housing conference room space, supervisor offices, crew workstations,
and multiple restrooms
• A large equipment and vehicle covered parking area and outdoor wash area
• Miscellaneous sheds for chemical storage, such as fuel containers, fertilizers, pesticides, and
equipment maintenance fluids
• 182 parking spaces for visitors and staff, including five electric vehicle charging spaces and
seven accessible (Americans with Disabilities Act Adult Guideline compliant) spaces
• Perimeter chain link and security fencing to cordon off the shops, storage, and fleet vehicle and
equipment storage area
• Improved site circulation for large delivery trucks with the addition of a second driveway off of the
private access road
• Sustainable building design features, such as net zero energy, with an aspirational goal to
implement portions of Living Building Challenge, to improve energy efficiency and result in lower
life cycle costs than a conventional building design
• Space designated on-site for future Administration Building A expansion area
The Administration Building A will be oriented to take advantage of the southern exposure and
southerly winds to act as natural ventilation and cooling. The Shops Building B is more centrally
located on the site. Along the north and west boundaries, a variety of storage areas will include
ecology block material storage bins, utility trailers and other equipment parking, and Building C.
1.3 Existing Conditions
1.3.1 Site Topography, Drainage, Land Cover, Soils, and Groundwater
The Project site topography is relatively flat, sloping gently to the west from the east site entry at
Jefferson Avenue NE (averaging approximately 1 percent) to a low point approximately 400 feet to
the east, then sloping gently back up to the west site boundary. The entry access road forms a
slight topographic ridge, with site drainage split between the south and north portions of the site.
The south site area drains along a shallow swale at a longitudinal slope of less than 0.5 percent to
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an off-site discharge location along the southeast site boundary. The north portion of the site is
essentially flat (less than 0.5 percent grades in the north-central and northeast site areas) with a few
small depressions where some infiltration occurs. A low point exists about midway between the east
and west site boundaries. Excess runoff generally flows via sheet drainage to the north where it is
dispersed by sheet flows across a vegetated slope on the adjacent parcel to the north.
A steeper vegetated slope exists along the west site boundary, typically ranging from 15 to 25
percent or greater. The slopes on the developed (north) portion of the adjacent south King County
parcel are generally consistent with site grades, sloping gently to the west to a low point along a
drainage swale, then sloping to the south. This King County industrial site to the south, together with
the south portion of the Project site, collectively drain and discharge excess runoff to a closed
depression (infiltration) area on the undeveloped portion of the that south parcel. On the east side of
Jefferson Avenue NE, slopes drop steeply into a deep closed depression area (a prior private sand
and gravel mining pit).
The site land cover consists of a mix of existing buildings and covered storage/maintenance service
areas, with collective roof areas totaling about 19,000 square feet (sf), and beyond those, paved and
other compacted gravel surfaces (collectively hard surfaces) suitable for truck and maintenance
vehicle access throughout the site. A few small pockets of vegetated landscape (trees, shrubs,
grass) totaling approximately 1,500 sf exist at the east end of the largest site building. Some
container and uncovered bin material storage areas exist along the east, north, and south site
boundaries. Slopes to the east and north of the site are primarily vegetated with trees, shrubs, and
grasses.
Soils within the site area below the gravel or asphalt surfacing layer generally consist of a silty gravel
and sand fill material, with variable depths below ground surface (bgs) ranging from 1.5 to 10 feet.
That fill material is underlain by native glacial outwash soils - recessional stratified drift, glaciofluvial
deposits (Qpa) (Aspect 2018). Those underlying outwash soils typically consist of medium-dense,
well-graded to poorly-graded sands (SW or SP) with gravels and some cobbles. Fines content is
low, and therefore those soils are expected to provide significant infiltration potential. For the
deepest prior site boring (extending approximately 27 feet bgs), no underlying till or less permeable
boundary soil layer was detected, and perched or deep groundwater was also not encountered.
From the Aspect review of nearby well logs and HDR interpretations of standing surface water levels
in the gravel pit area adjacent to and east of the Project site, groundwater levels in the site area are
expected to exceed 30 feet bgs.
1.3.2 Existing Drainage Basin and Threshold Discharge Areas
The Project site is located within the Lower Cedar River drainage basin. As noted previously,
existing site drainage does appear to fully infiltrate either on-site or off-site on adjacent parcels.
Based on the City’s GIS utilities database (City of Renton 2018), there are currently no existing
storm drainage connections to the site from City drainage systems in NE 3rd Street to the north, and
NE 1st Street to the south. Those off-site drainage systems, located within City right-of-way, tie
together downstream of the site and collectively discharge to a Lower Cedar River outfall.
The existing site area and off-site areas surrounding the site, including the adjacent off-site east
access road area (Jefferson Avenue NE), are broken down into six threshold discharge areas
(TDAs). Since the affected Project areas drain to various on-site and off-site infiltration areas, the
TDAs were defined around those infiltration discharge locations, which are different from
conventional TDAs definition relating to the manner of downstream surface water discharge
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connections within 0.25 mile of project boundaries. The existing condition TDAs including their
boundaries, drainage areas and patterns, discharge locations, and available water quality treatment
are summarized below and are illustrated in Figure 3A.
TDA E1
TDA E1 includes the north portion of the Project site, north of central site access road, together with
the north portion (west half) of Jefferson Avenue NE road frontage that currently sheet drains onto
the site (see Figure 3A). The TDA E1 tributary drainage area totals 2.96 acres. As described
previously, excess runoff from TDA E1 generally sheet flows to the north site boundary with off-site
dispersed discharge to existing vegetated slopes along the north-central and northwest portions of
the site. The TDA E1 tributary area is classified as both pollution generating impervious surface
(PGIS) for westerly paved areas and pollution generating pervious surface (PGPS) for the east
graveled area, and includes some small areas of non-pollution generating pervious surface
(NPGPS) associated with the limited vegetated surfaces. Drainage from TDA E1 does not currently
receive water quality treatment other than incidental filtration treatment provided by the off-site
vegetated flow path prior to off-site infiltration.
TDA E2
TDA E2 includes the south portion of the Project site, south of the central site access road, together
with the south portion (west half) of Jefferson Avenue NE road frontage that currently sheet drains
onto the site (see Figure 3A). The TDA E2 tributary drainage area totals 2.79 acres. As described
previously, drainage from TDA E2 generally sheet flows to the west, then along a shallow drainage
swale with off-site discharge across an off-site extension of that swale to the adjacent King County
parcel to the south, then along vegetated surfaces to a closed depression/infiltration area on the
undeveloped portion of that south parcel. The TDA E2 tributary area is classified as a split between
PGIS and PGPS. Drainage from TDA E2 does not currently receive water quality treatment, except
for incidental downstream treatment as described for TDA E4
TDA E3
TDA E3 includes that portion of the off-site Jefferson Avenue NE roadway and shoulders fronting,
and extending south of the Project site that do not sheet drain onto the project site, and alternatively
sheet drain onto adjacent parcels to the east and south of the Project site (see Figure 3A). The
TDA E3 tributary drainage area totals 0.52 acres. The TDA E3 tributary area is classified as PGIS.
Drainage from TDA E3 does not currently receive water quality treatment.
TDA 4
TDA E4 includes the off-site area extending south of the Project site that includes the closed
depression area west of the King County/Renton Transfer Station (see Figure 3A). The south
portion of the existing site delivers excess runoff to that area for infiltration in that depression,
beyond that portion that infiltrates through pervious on-site areas. The TDA E4 tributary drainage
area totals 4.89 acres. The north developed portion of the TDA E4 tributary area is classified as a
split between PGIS and PGPS, and the south and west undeveloped portions are classified as
NPGPS. Drainage from TDA E4 does not currently receive water quality treatment, other than
incidental treatment provided along the vegetated portions of the flow path prior to off-site infiltration.
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TDA E5
TDA E5 includes the off-site vegetated slope area extending north of the Project site that appears to
infiltrate runoff from the north portion of the site, beyond that portion that infiltrates through TDA E1
pervious site areas (see Figure 3A). The TDA E5 tributary drainage area totals 0.55 acres. The
TDA E5 tributary area is classified as NPGPS. Drainage from TDA E5 does not currently receive
water quality treatment, other than incidental treatment provided along the vegetated sheet flow path
prior to infiltration.
TDA E6
TDA E6 includes the vegetated slope area along the west side of the Project site that appears to
infiltrate precipitation that falls directly on that slope area (see Figure 3A). The TDA E6 tributary
drainage area totals 0.29 acres. The TDA E6 tributary area is classified as NPGPS. Drainage from
TDA E6 does not currently receive water quality treatment, other than incidental treatment provided
along the vegetated slope prior to infiltration.
1.4 Proposed Conditions
1.4.1 Site Grading, Drainage, Land Cover, and Soils
Proposed site grading and new drainage systems associated with Project redevelopment
improvements are shown conceptually in Figure 3B, and are briefly described as part of the
proposed TDAs below. Beyond new maintenance and operation facility buildings (A, B, and C),
walkways, a vegetated rain garden/bioretention cell, other vegetated planter areas, and other
appurtenant new facility features, the site is proposed for full pavement replacement, consisting of
new asphalt concrete paving that replaces existing pavements and gravel surfaces. Drainage from
the replaced impervious/hard surfaces will be collected conventionally using catch basins inlets
installed at low points and along interior and perimeter curbing. Existing site surfacing and fill
materials will be removed and replaced with imported select fill materials, including pea gravel and
sand near subgrade (collectively for sand filter construction), drain gravel in the infiltration gallery,
and pavement base materials, suitable to proposed uses. Some reuse of suitable excavated
materials as compacted backfill associated with site grading is also expected to occur to minimize
the off-site export and disposal of excavated materials.
1.4.2 Proposed Threshold Discharge Areas
The proposed condition TDAs including their boundaries, drainage areas and patterns, discharge
locations, and proposed detention storage and water quality treatment are generally summarized
below. Please note that the TDA boundaries for proposed site conditions require some adjustment
from existing conditions corresponding to required site grading adjustments associated with site
redevelopment improvements.
TDA P1
TDA P1 includes primarily the west portion of the redeveloped Project site that will be served by a
new on-site drainage system inclusive of subsurface conveyance, flow control, treatment, and
infiltration facility components located in the northwest portion of the Project site (see Figure 3B).
The TDA P1 tributary drainage area totals 3.08 acres. Drainage from this tributary area will be
collected in catch basins, and will be conveyed through various new storm drainage systems that
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connect to a linear detention vault providing both presettling (permanent pool) storage and active
detention storage. Attenuated flows exiting the storage vault will pass through a flow control orifice
and coalescing plate oil-water separator (OWS), then through parallel linear Modular Wetland units.
Discharge from those treatment components will be conveyed through perforated dispersal pipes
within an infiltration gallery that overlays a supplemental treatment (polishing) sand filter. The fully
treated runoff will then be infiltrated over the sand filter subgrade footprint area. The tributary area
will include a rain garden/bioretention cell that collects roof runoff from the new south building roof,
with an overflow connection to the west detention, treatment, and infiltration facilities. In addition, a
sump in the infiltration gallery will function for partial subsurface intercept of treated runoff to allow
pumping to above ground storage tanks for seasonal irrigation reuse.
TDA P2
TDA P2 includes primarily the east portion of the redeveloped Project site that will be served by a
new on-site drainage system inclusive of subsurface conveyance, flow control, treatment, and
infiltration facility components located in the northeast portion of the Project site (see Figure 3B). It
will also include sheet drainage run-on capture from the west half of Jefferson Avenue NE roadway
frontage. The TDA P2 tributary drainage area totals 2.47 acres. Drainage from this tributary area
will be collected in catch basins, and will be conveyed through various new storm drainage systems
that connect to a linear detention vault providing both presettling (permanent pool) storage and
active detention storage. Attenuated flows exiting the storage vault will pass through a flow control
orifice and coalescing plate OWS, then through parallel linear Modular Wetland units. Discharge
from those treatment components will be conveyed through perforated dispersal pipes within an
infiltration gallery that overlays a supplemental treatment (polishing) sand filter. The fully treated
runoff will then be infiltrated over the sand filter subgrade footprint area. In addition, a sump in the
infiltration gallery will function for partial subsurface intercept of treated runoff to allow pumping to
above ground storage tanks for seasonal irrigation reuse.
TDA P3
TDA P3 is consistent with TDA E3, except for changes in off-site Jefferson Avenue NE shoulder and
adjacent slopes land cover associated with proposed linear utility line installations to serve the
Project site (see Figure 3B). The TDA P3 tributary drainage area totals 0.48 acres. TDA P3 land
cover is expected to include some small increases in roadway shoulder PGIS associated with
installation of those utility lines. Flow control and treatment for this area, if it is triggered under
applicable thresholds, will be provided on-site as flow control and treatment tradeoffs for providing
capture and treatment of equivalent or greater areas of unimproved existing sections of the Jefferson
Avenue NE road frontage.
TDA P4
TDA P4 is consistent with TDA E4, except for minor change in grading along the south site boundary
that slightly adjusts the north TDA limit (see Figure 3B). The TDA P4 tributary drainage area totals
4.99 acres. TDA P4 land cover is expected to slightly increase the pervious area with some limited
conversion of PGIS to NPGPS associated with the south site fringe area grading changes. No flow
control and treatment needs for these small area and land cover changes are expected.
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TDA P5
TDA P5 is consistent with TDA E5, except for minor change in grading along the north site boundary
that slightly adjusts the south TDA limit, along with a narrow corridor for other off-site utility
improvements extending to and across NE 3rd Street (see Figure 3B). The TDA P5 tributary
drainage area totals 0.63 acres. TDA P5 land cover is expected to slightly increase the pervious
area with some limited conversion of PGIS to NPGPS associated with the north site fringe area
grading changes. No flow control and treatment needs for these small area and land cover changes
are expected.
TDA P6
TDA P6 is consistent with TDA E6, except for changes minor change in on-site grading along the
west site boundary that slightly adjusts the east TDA limit (see Figure 3B). The TDA P6 tributary
drainage area totals 0.31 acres. TDA P6 land cover is not expected to change since it is entirely
NPGPS. No flow control and treatment needs for these small area changes within TDA P6 are
expected.
1.5 Land Cover and Change Summary
A summary of the existing and proposed land coverage areas within the TDAs, which classifies the
surface areas as PGIS, NPGIS, PGPS, and NPGPS. Examples of those surfaces include pavement
(PGIS), roofs (NPGIS), gravel surfaces (PGPS), and landscape surfaces (NPGPS). TDA areas were
broken down by surface areas in those various land cover categories for existing and proposed
conditions, with results summarized in Tables 1 and 2, and are shown graphically in Figures 3A and
3B. Table 3 provides a comparative land cover change summary for the site land cover
characteristics associated with each TDA for the Project site redevelopment proposal. The results
comparison for TDA 1 and 2 were combined, representative of the total site area minus some fringe
area effects, since the TDA boundaries are different.
Table 1. Existing Threshold Discharge Areas Land Cover
TDA
Existing Surface Areas (sf) Total Area
(acre) Impervious
(%) PGIS NPGIS PGPS NPGPS Imperviou
s Pervious
E1 31,699 12,649 83,024 1,482 1.02 1.94 34.4
E2 27,548 6,739 86,971 0 0.79 2.00 28.3
E3 10,963 11,522 0 0 0.52 0 100
E4 33,573 0 57,586 121,166 0.77 4.12 15.8
E5 0 0 0 23,774 0 0.55 0
E6 0 0 0 12,778 0 0.29 0
Totals for Collective TDAs 11.98 25.8
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Table 2. Proposed Threshold Discharge Areas Land Cover
TDA Proposed Surface Areas (sf) Total Area
(acre) Impervious
(%) PGIS NPGIS PGPS NPGPS Impervious Pervious
P1 72,441 54,939 0 6,796 2.92 0.16 94.9
P2 76,536 11,783 0 19,286 2.03 0.44 82.1
P3 18,141 2,966 0 0 0.48 0 100
P4 33,319 493 57,586 125,860 0.78 4.21 15.6
P5 0 0 0 27,358 0 0.63 0
P6 0 0 0 13.353 0 0.31 0
Totals for Collective TDAs 11.96 52.0
Table 3. Change in Threshold Discharge Areas Land Cover
TDA
Comparison
Proposed to Existing Surface Areas
Change (sf)
Total Area Change
(acre) Impervious
Change
(%) PGIS NPGIS PGPS NPGPS Impervious Pervious
P1+P2/
E1+E2 89,730 47,334 -169,995 24,601 3.15 -3.34 57.8
P3/E3 7,178 -8,557 0 0 -0.03 0 0
P4/E4 -254 493 0 4,194 0.01 0.10 -0.2
P5/E5 0 0 0 3,585 0 0.08 0
P6/E6 0 0 0 575 0 0.01 0
Total for Collective TDAs -0.02 26.2
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2 Conditions and Requirements Summary
2.1 Drainage Review Classification for Project
This project is subject to the City of Renton’s Municipal Code 4-6-030, Drainage (Surface Water)
Standards. City Ordinance 5828, effective January 1, 2017, amended that code section to adopt the
City of Renton 2017 Surface Water Design Manual (RSWDM) based on the City’s amendments to
the 2016 King County Surface Water Design Manual. The 2017 RSWDM is applicable to Renton
projects with permit application after the effective date of the updated manual.
This Project is required to provide a Full Drainage Review because it meets the following criteria per
Section 1.1.1, Figure 1.1.2.A (see Appendix A), and Section 1.1.2.4 of the 2017 RSWDM:
• Results in greater than 2,000 square feet of new impervious surface, replaced impervious, or
new plus replaced impervious surfaces
• Results in greater than 7,000 square feet of land disturbing activity
• Constructs or modifies a pipe 12 inches or more in size/depth
• Is a redevelopment project proposing improvements of more than $100,000 to an existing high-
use site
• Is under 50 acres in size
Projects that trigger a Full Drainage Review are required to demonstrate that the project complies
with the all nine core requirements (CR) and all five special requirements (SR). Sections 2.1 and 2.2
below provide a summary of how the project will comply with these core and special requirements.
Where a particular requirement is not specifically applicable to the Project, the basis for that
determination is provided.
2.2 Core Requirements and Project Applicability
The following 2017 RSWDM Core Requirements (CR) were evaluated for applicability under the
Project’s Full Drainage Review requirement.
2.2.1 CR #1: Discharge at the Natural Location
All stormwater runoff and surface water from a project must be discharged at a natural location so as
not to be diverted stormwater onto or away from a downstream property. The Project site
stormwater must be discharged in a manner that does not create a significant adverse impact to
downstream properties or to off-site drainage facilities. Drainage facilities are defined as constructed
or engineered features that collect, convey, store, treat, or otherwise manage surface water or
stormwater runoff.
Existing drainage discharge from the Project site and east frontage roadway, beyond that portion
that currently discharges through infiltration over the relatively flat site, is primarily by sheet flow
discharge onto adjacent properties over existing slopes. An off-site drainage channel does exist that
extends to the southeast off of the Project site. No improved on-site drainage system currently
exists. The magnitude of off-site discharges north and south under 100-year event conditions is
expected to exceed 1 cubic foot per second (cfs), although off-site discharges from the smaller fringe
areas is expected to be significantly lower than that threshold.
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The proposed drainage system will collect stormwater runoff from the entire Project site and abutting
improved east access road area, will store/presettle/attenuate that runoff, will provide oil control and
enhanced water quality treatment, and will infiltrate that runoff through proposed on-site infiltration
drain rock galleries and associated underlying sand filter systems (two systems proposed). A pump
and storage tank system is also proposed to allow capture and partial reuse of treated runoff for
seasonal irrigation of the proposed bioretention cell vegetation. The Project site native subsurface
soils underlying upper elevation zone fill material are generally classified as glacial outwash, and are
expected to be well-suited to a full infiltration approach.
No off-site surface water discharges or improved storm drainage conveyance systems extending
downstream from the Project site are proposed, and therefore, increases in off-site runoff will not
occur (decreases will result) under this on-site stormwater management approach. Runoff
discharged through infiltration is expected to contribute to aquifer storage and interflow, and may
result in controlled base flow contributions to off-site surface water systems. Review of the City GIS
mapping does no show evidence of documented wetlands in close proximity to the Project site that
could be indirectly affected by changes in the hydrologic regime, although one potential wetland
exists in the adjacent parcel gravel pit area to the east of the site.
Since there would be an increase in Project site infiltration, coupled with a decrease in off-site
surface discharges, it appears that a Standard Adjustment from CR #1 may be needed.
Alternatively, the City could grant an exception to the need to meet this requirement based on the
expected beneficial reduction in off-site discharges.
2.2.2 CR #2: Off-site Analysis
Projects are required to conduct a Level 1 off-site analysis in accordance with Section 1.1.2 of the
2017 RSWDM. That analysis needs to assess potential off-site drainage and water quality impacts
associated with the site redevelopment proposal. An exception can be granted if the City
determines that there is sufficient information to conclude that a project will not have a significant
adverse impact on the downstream and/or upstream drainage system. Given that the Project
proposes full runoff containment, enhanced treatment, and infiltration to the 100-year event level-of-
protection, and with no off-site surface water discharge, the applicant requests that the City grant an
exception to the need for full off-site analysis. If that analysis is determined to be needed based on
the City’s initial review of the Project stormwater management proposal, a full Level 1 downstream
analysis will be provided and included in a subsequent version of the TIR.
2.2.3 CR #3: Flow Control Facilities
Projects with land cover changes above certain minimum thresholds, typically with added
impervious/hard surfaces exceeding 5,000 square feet, must provide on-site flow control facilities to
mitigate the potential impacts of the added stormwater runoff from targeted surfaces in a manner
and to levels defined in the 2017 RSWDM. However, there are flow control exemptions that can
eliminate or reduce the need for application of CR #3.
Based on the City’s Flow Control Application Map in the 2017 RSWDM, and consistent with Project
pre-application responses, the City has determined that the Project is subject to flow control criteria
defined as the Flow Control Duration Standard – Matching Forested site conditions, but only for
areas draining to streams and subject to flow-related water quality problems such as erosion or
sedimentation. The Project does not propose off-site surface discharge connections under the full
infiltration proposal. Under those conditions, the flow control standard is not applicable, and a
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Standard Adjustment to CR #3 is therefore being requested from the City. An alternative flow control
approach is proposed that would provide up to 100-year event peak rate control in on-site, linear
detention vaults to achieve an attenuated discharge rate equivalent to the design capacity of the
proposed on-site treatment and infiltration facilities. Under this flow control approach, site
conveyance, detention, treatment and infiltration facilities would provide required functions and
protections up through the 100-year event.
The alternative flow control standard, proposed design, and analysis are discussed in more detail in
Section 4.
2.2.4 CR #4: Conveyance System
All engineered conveyance system elements of the Project must be analyzed, designed, and
constructed to provide a minimum level of protection against overtopping, flooding, erosion, and
structural failure, with the following criteria applicable for new conveyance systems associated with
the Project site redevelopment proposal:
• Provide storm drain system and culvert capacities to convey and contain at minimum the 25-year
peak flow under developed conditions for on-site tributary areas, and existing conditions for off-
site tributary areas.
• Check the conveyance capacity up to the proposed conveyance system under 100-year flood
flows (overflow above 25-year event permitted) to confirm it does not aggravate an existing
severe flooding or erosion problem, and also that any overflow is contained on-site and flows to
the natural discharge location.
• Where feasible, conveyance systems shall be constructed using vegetation-lined channels as
opposed to pipe systems, except for required pipe conveyance systems under roadways,
driveways, parking areas, and for roof runoff.
• Provide conveyance systems outfall energy dissipation (rock pad at minimum); where the
discharge is onto a steep slope, a tightline conveyance system must be constructed to the
bottom of slope, with energy dissipation provided at that location.
• Provide spill control for new conveyance systems that receive runoff from non-roof pollution
generating impervious surfaces (PGIS) consistent with Section 4.2.1.1 of the 2017 RSWDM.
• Where on-site pump systems are needed to convey water within the site, those systems need to
meet the design criteria requirements of Section 4.2.3 of the 2017 RSWDM.
The Project site redevelopment proposal will result in the installation of an on-site gravity collection
and conveyance system serving the new and replaced impervious/hard surfaces as well as created
pervious vegetated surfaces. This conveyance system is expected to be limited to various 12-inch
storm drains draining to two constructed primary storage, treatment, and infiltration systems, one in
the west portion of the site, and the other in the east portion of the site. Those systems are
collectively being designed for 100-year conveyance capacity without overflow under maintained
operations. An on-site pump system with conveyance to above-grade storage tanks is also
proposed to facilitate partial reuse of treated stormwater runoff from the site for seasonal irrigation.
The conveyance system design standards, proposal, and analysis are discussed in more detail in
Section 5.
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2.2.5 CR #5: Construction Stormwater Pollution Prevention
Since the Project will conduct construction activities (on-site or off-site) that will clear, grade, or
otherwise disturb the site, it needs to provide stormwater pollution prevention and spill controls to
prevent, reduce, or eliminate, to the maximum extent practical, the discharge of pollutants to on-site
or off-site stormwater systems or watercourses. The 2017 RSWDM requires that erosion and
sediment controls (ESCs) and stormwater pollution prevention and spill controls (SWPPS) be
documented in a comprehensive construction stormwater pollution prevention plan (CSWPPP),
prepared for implementation by the construction contractor. This needs to be completed in
accordance with Sections 1.2.5.1 and 1.2.5.3 of the 2017 RSWDM, and also in compliance with the
expected Project coverage under the NPDES Stormwater General Permit for Construction Activities.
The Project will prepare a CSWPPP to support the final design of the stormwater improvements.
Preliminary narrative documentation of key elements of the CSWPPP, including applicable ESC and
SWPPS measures, is included in the draft TIR, and a conceptual ESC plan is included as part of the
Site Improvement Plans. The full CSWPPP components will be included in the final TIR. The
general methods and BMPs that are anticipated to be needed are discussed in more detail in
Section 8.
2.2.6 CR #6: Maintenance and Operations
It is expected that King County Parks, as the Project owner and a public agency, will have primary
operations and maintenance O&M responsibility for the Project’s on-site stormwater improvements.
Since the associated off-site frontage road improvements are not within a publicly-owned right-of-
way, it is expected that King County Parks will also have that O&M responsibility. The proposed
drainage facilities will need to be maintained and operated in accordance with the maintenance
standards in the 2017 RSWDM, Appendix A, or other proposed unique/supplemental maintenance
standards approved by the City.
Proper O&M of proposed stormwater control facilities is critical to their proper operation and to avoid
on-site and or off-site potential impacts (if overflows were to result due to lack of O&M). This is
particularly true given the reliance on enhanced water quality treatment systems and infiltration
facilities to manage on-site stormwater discharges and provide required protection of the City’s
underlying aquifer.
An O&M plan that summarizes these Project-specific O&M compliance needs will be included in
Section 10 of a subsequent version of the TIR after the proposed design of required stormwater
facility components is reviewed by the City for concurrence.
2.2.7 CR #7: Financial Guarantees and Liability
The financial guarantee requirement of the City under Renton Municipal Code (RMC) Section
4-6-030 for all newly constructed or modified drainage systems proposed by a project are not
expected to directly apply since the project owner is public agency. King County Parks and the City
will need to discuss how this requirement will be handled for this Project, either as a Standard
Adjustment from CR #7, or as implemented though a Memorandum of Understanding (MOU) or
similar agreement) between the County and City.
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2.2.8 CR #8: Water Quality Facilities
As a redevelopment project, the Project needs to provide water quality facilities to treat the runoff
from the new and replaced PGIS and new PGPS targeted for treatment that are not fully dispersed,
as defined in Section 1.2.8 of the 2017 RSWDM. In accordance with the City’s land use-specific
water quality facility requirements described in Section 1.2.8.1 of the 2017 RSWDM, since the
Project is an industrially-zoned site where more than 50 percent of the on-site runoff that drains to
proposed water quality facilities is from an industrial use, then the Enhanced Basic Water Quality
Menu (enhanced treatment) applies.
The only potentially applicable exception to CR #8 is a reduction in treatment level to the Basic
Water Quality Menu (basic treatment) if that runoff is infiltrated in accordance with the requirements
of Section 5.2 of the Renton SWDM. This exception does not apply where runoff is infiltrated within
0.25 mile of a fresh water designated for or having an aquatic life use, and where subgrade soils do
not meet the groundwater protection standards defined in Section 5.2.1 of the 2017 Renton SWDM.
The exception cannot be fully evaluated until additional subsurface geotechnical investigation and
infiltration testing is completed. However, since the Project is located in the Zone 2 of City’s Aquifer
Protection Zone, it is expected that enhanced treatment will be needed regardless of whether the
Project meets that exception criteria. That level of treatment also provides added protection for the
long-term functionality of the proposed on-site infiltration facilities that are located downstream of the
enhanced treatment.
The water quality requirement for this project will be satisfied by installing various water quality
BMPs (i.e., presettling wet pool storage, coalescing plate oil-water separators, Linear Modular
Wetland filters, and sand filters), that individually (for some components) and collectively (for all
components) satisfy the 2017 RSWDM requirements for enhanced treatment and oil control (see
SR #5). Modular Wetland System Linear proprietary treatment facilities included in the treatment
train also have general use level designation (GULD) approval for enhanced water quality treatment
from the Washington State Department of Ecology (Ecology). The water quality facilities are being
sized to treat attenuated runoff for up to the 100-year event prior to infiltration, which extends beyond
the minimum requirements of the 2017 RSWDM. As noted above, that proposed increased level of
treatment will be more protective of the Project’s infiltration facilities and the City’s Aquifer Protection
Zone.
The Water Qualities Facilities treatment standards and the specific requirements for the Project
design are discussed in more detail in Section 4.
2.2.9 CR #9: On-site BMPs
As a redevelopment project, the Project needs to provide on-site BMPs to mitigate the impacts of
stormwater runoff generated new impervious surfaces, new pervious surfaces, existing impervious
surfaces, and replaced impervious surfaces targeted for mitigation in accordance with Section 1.2.9
of the 2017 RSWDM. On-site BMPs are techniques, facilities, and controls for dispersing, infiltrating,
and otherwise reducing or preventing development-related increases in site runoff at or near the
runoff sources. Beyond reduction in project runoff footprint, on-site BMPs include preservation and
use of native vegetated surfaces to fully disperse runoff, use of other pervious surfaces to disperse
runoff, roof downspout infiltration, permeable pavements, bioretention, and limited infiltration
systems. On-site BMPs are required to be applied in accordance with the requirements and design
specifications of each BMP, where determined to be technically feasible, as included in Appendix C,
Section C.2 of the 2017 RSWDM.
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Since the Project proposed to fully infiltrate on-site runoff from the redeveloped site and contributing
off-site road frontage areas, it should meet the flow control facility exception criteria provided in
Section 1.2.9 of the 2017 RSWDM. That exemption criterion is for impervious surfaces served by an
infiltration facility in accordance with flow control facility requirements, the facility implementation
requirements, and the design criteria for infiltration facilities contained in Sections 1.2.3.1, 1.2.3.2,
and Section 5.2 respectively, of the 2017 RSWDM.
The Project plans to install a rain garden/bioretention cell on the south side of the site to capture,
evapo-transpire, and infiltrate roof runoff from the most southerly proposed building on the site, and
also to connect that facility in overflow to the proposed west treatment and infiltration facilities. In
addition, the Project plans to install a pump system and storage tank(s) to partially collect treated
runoff from a portion of the site, lift it into above-ground storage tanks, and reuse it for supplemental
seasonal irrigation of the rain garden/bioretention cell, thus achieving sustainable reuse of the
captured runoff.
The On-site BMPs and other stormwater runoff reduction BMP approaches proposed for integration
into the Project are discussed in more detail Section 4.
2.3 Special Requirements and Project Applicability
The following 2017 RSWDM SRs were evaluated for Project applicability under the Project’s need
for Full Drainage Review.
2.3.1 SR #1: Other Area Specific Requirements
Beyond the 2017 RSWDM, the Project needs to maintain consistency with the other adopted
regulations and plans within the City of Renton (and King County as the site owner) that apply
requirements for controlling drainage on an area-specific basis. Those requirements could have a
more direct bearing on the drainage design for the Project. Those regulations and plans generally
include:
• Master Drainage Plans
• Basin Plans
• Salmon Conservation Plans
• Lake Management Plans
• Hazard Mitigation Plans
• Shared Drainage Facility Plans
Based on initial research regarding these types of available plans within the Project vicinity, the
following documents were identified:
• King County Department of Natural Resources, Lower Cedar River Basin and Non-Point
Pollution Action Plan (King County DNR 1997) – This previous King County-approved basin plan
is not expected to contain more current supplemental requirements regarding required basin
stormwater management controls than contained in the 2017 RSWDM requirements.
• City of Renton, Lower Cedar River Chinook Salmon Habitat Restoration Assessment Plan
(Herrera Environmental Consultant 2015) – This salmon conservation plan appears to be
focused on riverine habitat project improvement opportunities and recommendations, and does
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not address basin-related stormwater controls. Therefore, it is not expected to supersede any
drainage requirements of the 2017 RSWDM.
After review of the Draft TIR, the City may identify other adopted plans or related regulations that
have other area-specific requirements that could be applicable to the Project site drainage
evaluation and design. If so, those requirements will be integrated into a subsequent version of the
TIR.
2.3.2 SR #2: Flood Hazard Area Delineation
Flood hazard areas are composed of the 100-year floodplain, zero-rise flood fringe, zero-rise
floodway, and FEMA floodway. If a proposed project contains or is adjacent to a flood hazard area
as determined by the City, SR #2 requires the project to determine those flood hazard components
that are applicable and delineate them on the project’s site improvement plans and recorded maps.
City regulations and restrictions regarding development within a 100-year floodplain are found in the
City’s Critical Areas Code under RMC 4-3-050.
Review of FEMA regulatory floodplain maps suggest that the Project site does not fall within the
regulatory 100-year floodplain or floodway and associated flood hazard areas. Therefore, SR #2
does not apply to the Project.
2.3.3 SR #3: Flood Protection Facilities
Flood protection facilities, such as levees and revetments require a high level of confidence in their
structural integrity and performance. Proper analysis, design, and construction are necessary to
protect against the potentially catastrophic consequences if such facilities should fail. Where
applicable, the City can require compliance and conformance with specific code requirements,
standards, and outside agency design guidelines for those facilities needing evaluation by a licensed
professional engineer.
Since the Project is an upland site not directly adjacent to riverine or stream resources, and does not
rely on existing or proposed flood protection facilities for flood protection, SR #3 does not apply to
the Project.
2.3.4 SR #4: Source Controls
Source controls are typically required by the City for commercial sites to prevent rainfall from coming
into contact with pollutants, thereby reducing the likelihood that pollutants will enter public waterways
that could contribute to violation of water quality standards or City stormwater discharge permit
limits. Source controls consist of both structural source control measures (i.e., contained concrete
pads, roof covers) and non-structural source control measures (i.e., temporary covering of material
storage piles, isolating sources of pollutants). Source control BMP needs are dependent on site
activities and operations.
The Project site is industrially-zoned, with expected activities and operations similar to commercial
site uses that require use-specific source controls. Therefore, it is expected that specific Project site
source control BMP measures will be applicable as they are identified during the drainage review
process.
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2.3.5 SR #5: Oil Control
The Project proposes redevelopment of an existing industrial use for central O&M facilities where the
cost of improvements will exceed $100,000. It will also result in the installation of new plus replaced
impervious surfaces that exceed 5,000 square feet. It is expected that the City will therefore
designate the site as high-use, and will likely require that oil control be provided for, at minimum,
those impervious, pollution-generating portions of the redeveloped Project site that could be subject
to on-site truck traffic, construction/maintenance equipment operations and haul in/out, and
diesel/stationary equipment use. These uses are subject to potential fuel/oil leakage and/or
lubricating oil and grease residuals. A truck/equipment washing pad is also planned for the site,
however, process discharge from the area would separately be to the sanitary sewer system.
High-use oil control options are selected to capture and detain oil and associated pollutants. The
goal of this treatment is no visible sheen in runoff leaving the facility, or less than 10 mg/L total
petroleum hydrocarbons (TPH) in the runoff, depending on the oil control facility options used. Oil
control options for the Project site, consistent with City requirements for similar installations in public
road right-of-ways, include coalescing plate oil-water separators and baffled, gravity-type OWSs,
typically called American Petroleum Institute (API) OWS. The City does not consider the use of
catch basin inserts alone as sufficient for providing oil control.
Given the need to preserve and protect the proposed infiltration facilities, the desire for partial reuse
of treated runoff, and the site being located in a Zone 2 Aquifer Protection Area, the Project
proposes that oil control conservatively be provided for the entire Project site to demonstrate full
compliance with SR #5. The project proposes use of two coalescing plate OWS, one for each
improved drainage system serving the site. Those oil-control facilities would be located downstream
of flow control and presettling vault facilities (receiving attenuated site discharges), but upstream of
other enhanced treatment, reuse capture, and infiltration gallery facilities.
The oil control facility treatment standards and the specific requirements for the Project design are
discussed in more detail in Section 4.
2.3.6 SR #6 Aquifer Protection Area
Aquifer protection areas (APA) are identified in accordance with the City RMC 4-3-050.
Reference 15-B in the 2017 RSWDM shows that the Project site is located within Zone 2 of the
City’s APA. Therefore, SR #6 requires the Project to determine the specific APA components that
are applicable and delineate them on the Project’s site improvements plans. Those requirements
are expected to include the need to enhanced treatment of all site discharges planned to be
infiltrated within the APA.
The Project drainage system proposes presettling, oil control, and enhanced water quality treatment
facility improvements, sized to treat attenuated discharges from up to the 100-year storm event from
on-site and adjacent off-site road frontage sources. It also proposes partial capture of treated runoff
for pumping to storage tanks, and irrigation reuse. These robust treatment and reuse BMP
measures, exceeding 2017 RSWDM requirements, are targeted to be sufficient to meet the City’s
Zone 2 APA requirements.
The APA treatment requirements for the Project design are discussed in more detail in Section 4.
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3 Off-site Analysis
3.1 Downstream Analysis
An off-site drainage analysis is typically required to assess existing drainage conditions and problem
areas downstream from a project site. It provides information to determine whether supplemental
runoff flow control or water quality mitigation is needed beyond that otherwise required under the
City’s stormwater minimum requirements. A Level 1 downstream analysis is typically the minimum
level of off-site analysis completed, as prescribed in Sections 1.2.2 and Section 2.3.1.1 of the 2017
RSWDM, unless exempted by the City.
The Level 1 downstream analysis is a qualitative survey of each downstream system and is intended
to identify flooding, erosion, and water quality problems and potential wetland impacts. The steps for
completing the off-site analysis are described in the following sections.
3.1.1 Define and Map the Study Area
Figure 3A provides a map of the Project area showing the site and adjacent off-site TDA drainage
areas, land cover, and downstream flow paths for stormwater discharges under existing conditions.
The limits of downstream analysis typically extends a minimum of 0.25-mile downstream from the
site boundary along the drainage flow paths, but can extend up to 1.0-mile if downstream drainage
problems are identified.
The Project site does not currently include any storm drain improvements or off-site drainage
connections beyond surficial flow paths that extend off-site for conveyance of runoff not infiltrated
on-site. As such, the existing off-site discharge paths are very limited due to the effects of runoff
dispersal and infiltration that occurs adjacent to and north and south of the site. The flow path
extending south of the site is limited to an earth swale approximately 550 feet in length. It extends
from the southwest site boundary to a closed depression that infiltrates site runoff on the adjacent
King County parcel to the south. To the north of the site, residual site runoff that is not infiltrated on-
site is understood to be dispersed linearly along the northwest boundary of the site over a 50- to
75-foot length vegetated flow path, where it appears to infiltrate.
3.1.2 Review Available Study Area Information
A resources review is required for the Project study area to identify any existing hazards related to
flooding, erosion, and water quality problems. This review was based on research conducted on
various websites, and through use of the City’s online GIS interactive mapping tool (City of Renton
2018).
Basin Plans of Basin Reconnaissance Summary Reports
Based on initial research regarding these types of available plans within the Project vicinity, the
following documents were identified:
• King County Department of Natural Resources, Lower Cedar River Basin and Non-Point
Pollution Action Plan (King County DNR 1997)
• City of Renton, Lower Cedar River Chinook Salmon Habitat Restoration Assessment Study
(Herrera Environmental Consultants 2015)
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These documents are not expected to provide unique stormwater management guidelines for the
Project site beyond those contained in the 2017 RSWDM.
Topographic and Aerial Mapping for Site and Adjacent Areas
Off-site topographic mapping beyond the limits of the site topographic mapping was reviewed using
the City’s online GIS viewer. This information provided confirmation of presence of the closed
depression/infiltration area on the adjacent King County parcel south of the site. It also provided
information regarding the characteristics of the graded slope areas to the north and west of the site.
Google Earth aerial mapping (Google Earth 2018) was also reviewed to provide additional definition
on on-site and off-site drainage flow paths and existing land cover.
Critical Areas Mapping for Site and Adjacent Areas
Information obtained regarding critical areas on or in proximity to the Project site suggest:
• The Project site or adjacent area is not within a floodplain or floodway (Zone X) per City of
Renton Flood Insurance Rate Map (FIRM), Map Number 53033C0981G (City of Renton 2017a).
• The Project site is not within a potential landslide hazard, steep slope, erosion hazard area per
the City of Renton online GIS viewer (Renton 2018). There are some regulated slope areas
including steep slopes, some exceeding 25 percent, adjacent to and primarily east and west of
the site (see Figure 2 for their locations).
• No wetlands appear to exist on the site. One potential off-site wetland was identified on a
private parcel (gravel pit) to the east of the site, but no other information was found to identify its
regulatory status.
• The site is within a wellhead (aquifer) protection area, Zone 2 (Maplewood 10-year capture
zone).
• No documented drainage complaints were found for the Project site or in close proximity.
3.1.3 Field Inspect the Study Area
A drainage field reconnaissance investigation of the site has not yet been conducted. Once
completed, results of that field investigation will be added to this section in the next version of the
TIR.
3.1.4 Describe the Drainage System and Drainage Problems
The downstream drainage system is very limited since no downstream surface water connections
have currently been identified. The City GIS also does not identify nearby downstream flooding,
erosion, or water quality problems in close proximity to the site. In addition, full on-site infiltration of
the redeveloped site and tributary off-site run-on is proposed with site improvements. Therefore,
further description and analysis of the downstream drainage systems is not included in the draft TIR.
If required, this section will be expanded based on the City direction about the specific requirements
that would apply under these unique site and off-site conditions.
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4 Flow Control, Low-impact Development,
Water Quality, and Infiltration Facilities
Analysis and Design
4.1 Existing Conditions Site Hydrology
The Project site falls within the Lower Cedar River Drainage Basin. The site area totals 5.71 acres,
and an additional 0.25 acres of the Jefferson Avenue NE frontage (west half) contributes to the site
drainage. This Project site and off-site road frontage area is further broken down under existing
conditions as 2.96 acres contributing to TDA E1 north site drainage and off-site dispersed discharge
to infiltration, 2.79 acres contributing to the TDA E2 south site drainage and off-site discharge to
infiltration, and 0.29 acres of TDA E6 with dispersed slope discharge to the west. The remainder of
the affected drainage within TDA E3, E4, and E5 discharge to adjacent off-site parcels. The existing
TDA boundaries, off-site discharge locations, and downstream flow paths are shown in Figure 3A.
Existing land cover within these TDA areas is shown in Table 1 (Section 1.5)
The Project area hydrology under existing land cover conditions was analyzed for TDA 1 and 2 using
the continuous simulation MGSFlood model to provide an estimate of existing condition peak flows
and volumes that could be potentially be discharged off-site to adjacent parcels. Other TDA
discharges do not affect proposed stormwater control facilities, and were therefore not analyzed. For
this analysis, existing site pervious soils were conservatively assumed to be till (likely under-
simulates on-site infiltration effects that appears to occur through silty sand/gravel fill soils). The
existing conditions analysis was run at a 15-minute time step to capture the effects of higher
intensity, short duration precipitation along with the expected short lag time in runoff generation from
on-site and off-site areas. The resulting recurrence interval peak flow and annual average runoff
volume estimates from this analysis are shown in Table 4.
Table 4. Existing Conditions Hydrology Summary
TDA
Existing
Impervious
Surface Area
(ac)
Existing
Pervious
Surface
Area
(ac)
Simulated Recurrence
Interval Event Peak Flow
(cfs)
Simulated
Water
Quality
Online
Design Flow
(cfs)
Simulated
Average Annual
Runoff Volume
(ac-ft/yr) 2-Year 10-Year 100-Year
E1 1.94 1.02 0.6 1.0 2.0 NA 5.4
E2 0.79 2.00 0.4 0.7 1.2 NA 3.4
4.2 Proposed Conditions Site Hydrology
The Project will fully regrade and redevelop the site with associated changes to the site land cover.
More of the site area will exhibit fully impervious runoff characteristics (i.e., larger building roof areas,
conversion of compacted gravel surfaces to asphalt concrete pavement). Therefore, there will be
some expected increases in redeveloped site peak flows and runoff volumes that will need to be
accommodated by the proposed on-site stormwater control facilities.
The total TDA P1 and P2 area equates closely to the collective on-site and off-site areas for TDA E1
and E2. TDA P1 will drain to the west improved site drainage flow control, treatment, and infiltration
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facilities, whereas TDA P2 will drain to the similar east site drainage improvements. Proposed land
cover within these TDA areas is shown in Table 2 (Section 1.5). For proposed conditions, on-site
flow control, treatment, and infiltration facilities are targeted to control runoff up to the 100-year event
without overflow conveyance or off-site discharge.
The Project area hydrology under proposed TDA land cover conditions was also analyzed using the
continuous simulation MGSFlood model to provide an estimate of proposed condition peak flows
and volumes that will need to be controlled and mitigated by the on-site drainage improvements. For
that analysis, beyond the rapid runoff response expected from the highly impervious pavement
areas, runoff response from proposed vegetated surfaces were assumed to be from outwash soils to
properly simulate the effects of on-site infiltration targeted in design of those site features. The
proposed conditions analysis was also run at a 15-minute time step to capture the effects of higher
intensity, short duration precipitation along with the expected short lag time in runoff generation from
on-site and off-site areas. The resulting recurrence interval peak flows, water quality (online) flows,
and annual average runoff volume estimates from this analysis are shown in Table 5. These
estimates are for inflows to the proposed flow control facilities. Detention outflows at lower,
attenuated design flow rates will subsequently be delivered through the water quality treatment and
infiltration facilities (through 100-year event level). Results demonstrating the detention flow control
size requirement and targeted design outflows for sizing of treatment and infiltration facilities are
summarized separately in Section 4.4 below.
Table 5. Proposed Conditions Hydrology Summary
TDA
New and
Replaced
Impervious
Surface Area
(ac)
New
Pervious
Surface
Area
(ac)
Simulated Recurrence Interval
Event Peak Flow (cfs)
Simulated
Water Quality
Online
Design Flow
(cfs)
Simulated
Average
Annual Runoff
Volume (ac-
ft/yr) 2-Year 10-Year 100-Year
P1 2.92 0.16 1.1 1.6 3.0 0.42 8.5
P2 2.03 0.44 0.8 1.2 2.3 0.29 6.3
4.3 Stormwater Controls Design Requirements and
Performance Standards
The Project will provide collection, conveyance, flow control, water quality treatment, and infiltration
improvements to manage stormwater runoff from the site. Figure 5 illustrates those proposed on-
site stormwater control facilities as described and analyzed in more detail in the following sections.
To comply with the 2017 RSWDM requirements and proposed Standard Adjustments, stormwater
controls are being designed in accordance with the following performance standards.
4.3.1 Flow Control Facilities
The Project triggers the requirement for CR #3 - Flow Control Facilities as previously described in
Section 2.2.3, since a direct discharge exemption does not apply. The Flow Control Duration
Standard – Matching Forested site conditions applies in the Project site area, but only for areas that
drain to streams and are subject to flow-related water quality problems such as erosion or
sedimentation. Since the Project does not propose off-site surface discharge connections under the
full infiltration proposal, this flow control standard is not applicable to the site, and a Standard
Adjustment to CR #3 is therefore being requested from the City.
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An alternative flow control approach is proposed that would provide up to 100-year event peak rate
flow control in on-site, linear detention vaults to achieve a maximum attenuated discharge rate
equivalent to the design capacity of the proposed on-site treatment and infiltration facilities within
and underlying the U-shaped storage facilities. Under this modified flow control approach, site
conveyance, detention, treatment and infiltration facilities would provide required functions and
protections up through the 100-year event.
The proposed flow control facilities need to mitigate the runoff from the targeted developed surfaces
within the TDA, inclusive of new and replaced impervious surfaces and pervious surfaces that are
not fully dispersed in accordance with the 2017 RSWDM. Full dispersion for the redeveloped Project
site is not feasible; therefore, targeted surfaces for the Project site include all new and replaced
impervious and pervious surfaces within each TDA. The hydrologic analysis for proposed conditions
in Section 4.2 considers those redeveloped site targeted surfaces.
4.3.2 On-site and Low-impact Development BMPs
The Project improvements trigger the requirement for CR #9 - On-site BMPs, or LID BMPs, as
previously discussed in Section 2.2.9. However, within TDA P3, a Basic Exemption to this
requirement is expected to apply for utility improvements in the off-site road frontage, assuming their
new and replaced impervious surfaces and disturbance areas fall within the exemption limits (2,000
sf for impervious surfaces, and 7,000 sf for disturbed surfaces). The Project improvements in TDAs
P1 and P2 may also meet the flow control facility exemption criteria under this requirement since
flow control and full-infiltration are proposed for those collective target surfaces. Even if not fully
exempt from the On-site BMPs requirement, the Project proposes to incorporate sustainable LID
BMPs that should fully meet the flow control, water quality control, and runoff volume reduction
objectives of the On-site BMPs core requirement as follows:
• BMP C2.2 – Full Infiltration: Full infiltration is proposed for all target surfaces in TDA P1 and P2
up to the 100-year event, to be achieved through two proposed on-site infiltration galleries (one
in each TDA), with prior presettling and on-site flow control vaults, coalescing plate OWS and
linear Modular Wetland enhanced filtration treatment, and polishing treatment through a sand
filter below the drain rock infiltration galleries. Design criteria for each of these BMPs needs to
comply with the Full Infiltration On-site BMP minimum design requirements contained in
Appendix C, Section C.2 of the 2017 RSWDM.
• BMP C2.6 – Bioretention: Runoff drainage from Building A is proposed to be discharged to a
vegetated bioretention cell to be constructed south of that building. This facility is proposed for
infiltrating bioretention with treatment achieved prior to infiltration through the bioretention soil
mix media (although the NPGIS roof area should not require that). Design criteria for this BMP
needs to comply with the Bioretention On-site BMP minimum design requirements contained in
Appendix C, Section C.2 of the 2017 RSWDM.
• BMP C2.8 – Rainwater Harvesting: Rainwater harvesting is proposed through the partial capture
of detained and treated TDA P1 and P2 runoff prior discharge through on-site infiltration. That
runoff will be pumped to above- ground storage tanks for storage and seasonal irrigation reuse
for on-site revegetated surfaces (including the proposed bioretention cell). Design criteria for this
BMP needs to comply with the Rainwater Harvesting On-site BMP minimum design
requirements contained in Appendix C, Section C.2 of the 2017 RSWDM.
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• BMP C2.11 – Perforated Pipe Connection: Perforated pipe connections are proposed as part of
design of the proposed infiltration gallery to disperse treated runoff over the proposed
subsurface sand filter prior to runoff infiltration into subgrade soils. Design criteria for this BMP
needs to comply with the Perforated Pipe Connection On-site BMP minimum design
requirements contained in Appendix C, Section C.2 of the 2017 RSWDM.
• BMP C2.13 – Soil Amendment: For those areas of the site to remain as previous, revegetated
soils, new, replaced and disturbed area topsoil will be amended with organic materials (typically
compost). Design criteria for this BMP needs to comply with the Soil Amendment On-site BMP
minimum design requirements contained in Appendix C, Section C.2 of the 2017 RSWDM.
Other On-site BMPs may also be incorporated through final design to maximize the LID benefits and
sustainable runoff reuse practices to be achieved through site redevelopment.
4.3.3 Water Quality Facilities
The Project triggers the requirement for CR #8 – Water Quality as previously described in Section
2.2.8, since a Project-specific exception does not appear to apply. Since the Project is an
industrially-zoned site where more than 50 percent of the on-site runoff that drains to proposed water
quality facilities is from an industrial use, then the Enhanced Basic Water Quality Menu (enhanced
treatment) applies. Also, in accordance with SR #5 – Oil Control, the Project site, or a portion
thereof, is expected to be classified by the City as high-use, requiring the application of oil-control
BMPs.
Enhanced treatment BMPs are required to meet the following performance standards:
• 80 percent removal of total suspended solids (TSS) for flows/volumes up to and including the
water quality design flow and volume, that represents 91 perecnt of the annual runoff volume in
a typical rainfall year
• Greater than 30 percent reduction of dissolved copper, and greater than 60 percnt removal of
dissolved zinc for the water quality design flow and volume (based on specific ranges of
untreated concentrations)
Application of the 2017 RSWDM BMPs from the Enhanced Basic Treatment Menu, selected paired
Basic Treatment BMPs in series, or use of proprietary Ecology-approved treatment BMPs for
Enhanced Treatment meets those performance standards. This is based on the presumptive
approach provided that BMP-specific design criteria as contained in Sections 6.2 through 6.8 of the
2017 RSWDM are adhered to.
Water quality oil control BMP requirements for the Project under assumption of a high-use site
designation will need to meet the following performance standards:
• Removal of oil particles 60 micron and larger for the water quality design event (off-line design
flow)
• Oil and grease effluent quality of 10 to 15 milligrams per liter for the water quality design event
Acceptable oil control BMPs in the 2017 RSWDM for high use sites include baffle-type OWS and
coalescing plate-type OWS. The Project will need to comply with design requirements and criteria
for those BMPs as contained in Section 6.6.2 of the 2017 RSWDM.
The Project needs to provide water quality treatment facilities to mitigate runoff water quality from
the new and replaced PGIS and new PGPS that are not fully dispersed. The comprehensive water
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quality treatment proposed for the Project will include installing various water quality BMPs in series,
ranging from presettling (wet pool) storage, coalescing plate OWS, linear Modular Wetland filters,
and sand filters that collectively exceed the 2017 RSWDM requirements for oil control and enhanced
treatment. Proprietary treatment facilities included in the treatment train also have GULD approval
for enhanced water quality treatment from Ecology. The water quality facilities are being sized to
treat attenuated runoff for up to the 100-year event prior to infiltration, which extends considerably
beyond the water quality event treatment flow/volume requirements in the RSWDM. The robust
water quality treatment level targeted with improvements, assuming properly maintained, are
expected to be protective of the Project’s infiltration facilities and the City’s aquifer protection needs.
4.3.4 Infiltration Facilities
In order to satisfy CR #1 – Discharge at Natural Locations, avoid the need for a new off-site
connection to the City’s storm drainage system(s) downstream from the Project site, and to minimize
on-site flow control needs under CR# 3 – Flow Control, full infiltration of redeveloped on-site area
runoff coupled with off-site road frontage (west half) runoff is proposed (similar to existing conditions
where infiltration occurs both on-site and off-site). Water quality treatment facilities meeting the
performance standards described in Section 4.3.2 above would precede runoff proposed for on-site
infiltration into native subgrade (glacial outwash) soils. Peak rate flow control through the 100-year
event prior to treatment is proposed to attenuate targeted surfaces runoff and reduce the sizing
needs of both water quality treatment and infiltration facilities.
The proposed infiltration facilities will need to satisfy the design requirements and performance
standards contained in Section 5.2 of the 2017 RSWDM that include:
• Establishing that adequate depth of permeable soils and separation to high groundwater exists
below the bottom of the proposed infiltration facilities, as determined through subsurface
exploration boring logs and soil samples characterization and testing. That minimum depth
value is typically a minimum of 3 feet when confirmed by a groundwater mounding analysis, and
5 feet otherwise.
• Confirming subgrade soils design infiltration rates through pilot infiltration tests (PIT) or other
equivalent infiltration field testing as approved by the City, and applying suitable correction
factors to measured infiltration rates in accordance with the 2017 RSWDM.
• Completing a groundwater mounding analysis meeting the requirements of Section 5.2.1 of the
2017 RSWDM for infiltration facilities serving more than 1 acre and with less than 15 feet of
separation between the bottom of the proposed facilities and either a restrictive soil layer or
groundwater.
• Conducting field performance testing on the proposed infiltration facilities during construction
with correction factors applied to confirm the design infiltration rate, and if not confirmed, adjust
the required size of the infiltration facility.
• Providing 100-year conveyance overflow from the proposed infiltration facility to a suitable off-
site drainage connection as a contingency if there is a restriction in infiltration rate due to partial
plugging of the facility, unless the City concurs that a further reduction in the design infiltration
rate (by one-half) is sufficient to achieve proper infiltration performance up to the 100-year event,
as can be applied in closed depression systems.
• Providing a spill control device upstream from the proposed infiltration facility, typically a tee
section with an elevated riser to the overflow elevation.
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• Providing presettling upstream of the infiltration facility, either as a basic treatment BMP or a
presettling pond or vault sized to a minimum of 25 percent of the basic treatment water quality
volume requirement.
• Protecting infiltration facilities subgrade from erosion and sediment deposition during
construction through alternative routing of construction runoff and applying appropriate source
control and construction operations BMPs.
• Protecting off-site groundwater from potential water level and quality impacts through controlling
possible groundwater mounding effects and providing required water quality treatment prior to
infiltration (oil control and basic treatment facilities at minimum for an industrial site)
• Providing required setbacks of infiltration facilities from any identified steep slope or landslide
hazard areas.
• Registering any proposed infiltration wells that are classified as Underground Injection Control
(UIC) facilities with Ecology, and complying with UIC regulation requirements for their design,
installation, and operation.
4.4 Flow Control Facilities Preliminary Analysis and Sizing
4.4.1 Detention Vaults Flow Control Storage
Peak rate flow control (through the 100-year event) will be provided for TDA P1 and P2 targeted
surfaces through the installation of linear, pre-cast, subsurface detention vaults aligned around the
perimeter of the two targeted on-site infiltration galleries (in U-shaped configurations), one in the
west portion of the site (serving TDA P1), and a second in the east portion of the site (serving TDA
P2). The vaults will be installed on a level grade, and will include a presettling (dead) storage
component, a flow control storage (active) storage component, and a freeboard (inactive) storage
component. The presettling storage component sizing basis is described in Section 4.5.1. The flow
control and freeboard storage components sizing basis are described below.
Both flow control facilities for TDA P1 and P2 were sized using the MGSFlood continuous simulation
hydrologic model (as approved for use in the 2017 RSWDM), and based on the extended
precipitation time-series data set for the Puget Sound East, 40 inch MAP Climate Region. The
model was run at a 15-minute time step given the relatively small TDA sizes and highly impervious
character of the improved site surfaces. For preliminary design, detention outflows were modeled
using a single orifice control sized to control the 100-year event peak outflow to the design flow for
the proposed downstream water quality treatment and infiltration facilities. A 10-foot interior width
vault with a maximum 4.5-foot active storage depth was used for the storage routing analysis
consistent with preliminary design layout of the linear vault system. The analysis was conducted
using preliminary design lengths of the linear vault system estimated to be approximately 358 feet
for the TDA 1 west and 326 feet for the TDA 2 east drainage system. The estimated orifice sizes to
fully utilize the available active storage volume while maximizing peak flow reduction for the
preliminary analysis are 3.125-inch-diameter for the TDA 1 west and 2.25-inch-diameter for the
TDA 2 east drainage system.
Table 6 summarizes the detention vault simulated inflows, outflows, simulated flow control volume,
and estimated freeboard storage volumes for the 100-year event for the tributary impervious and
pervious surfaces within each TDA. The supporting MGSFlood modeling reports providing the
preliminary design analysis to determine the controlled outflow for the available flow control storage
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volumes are included in Appendix B. Freeboard storage was estimated based on the resulting vault
surface area at 1-foot targeted depth.
Table 6. Detention Vaults Flow Control Storage Sizing
TDA New and
Replaced
Impervious
Surface Area
(ac)
New
Pervious
Surface
Area
(ac)
Detention Vault
Simulated
100-Year Event
Inflow
(cfs)
Detention Vault
Simulated
100-Year Event
Outflow
(cfs)
Detention Vault
Simulated Flow
Control (Active)
Storage
(cf)
Detention Vault
Freeboard
(Inactive)
Storage
(cf)
P1 2.92 0.16 3.0 0.52 16,110 3,580
P2 2.03 0.44 2.3 0.27 14,670 3,260
4.5 Water Quality Treatment Facilities Preliminary Analysis
and Sizing
4.5.1 Detention Vaults Presettling Storage and Surface Area
Presettling storage required in the proposed detention vaults within TDAs P1 and P2 was estimated
using the 2017 RSWDM criteria for pretreatment upstream of infiltration facilities (although other
downstream treatment is provided). That criteria requires a minimum presettling storage volume
equal to 25 percent of the water quality event volume (basic wet pond volume). Based on the
MGSFlood modeling analysis (Appendix B), the basic wet pond water quality volume totals
approximately 13,030 cubic feet (cf) for TDA 1 west and 9,440 cf for TDA 2 east drainage system
simulated runoff. The targeted presettling storage volume was therefore estimated to be 3,260 cf for
the TDA 1 west and 2,360 cf for TDA 2 east drainage system, which equates to average presettling
storage depth needs of approximately 0.91 and 0.72 feet, respectively, over the proposed vault
footprint areas. A check was also made to confirm that the presettling storage area meets that
required for design of the coalescing plate OWS forebay (20 sf per 10,000 sf of tributary drainage
area). The proposed presettling surface areas (3,580 sf and 3,260 sf, respectively) significantly
exceed the minimum presettling surface areas required under that criteria (approximately 270 sf and
220 sf respectively).
4.5.2 Coalescing Plate Oil Water Separators
Analysis was conducted for preliminary sizing of the proposed coalescing plate OWS consistent with
Section 6.6.2.1 of the RSWDM. The separators are targeted to treat all runoff up through the
100-year event (exceeding the typical water quality event off-line design flow basis). The preliminary
estimate of the 100-year attenuated design flow for each coalescing plate separator serving TDAs
P1 and P2 as reported in Table 6 are 0.52 cfs for the TDA 1 west and 0.27 cfs for the TDA 2 east
drainage system.
Based on Figure 6.6.2.B and equation 6-33 of the 2017 RSWDM, the preliminary sizing of the
required effective (horizontal) surface area of the coalescing plate media are approximately 850 sf
and 480 sf, respectively, for the east and west separator coalescing plate packs (see Appendix C).
The actual width of plates would be larger since the plates are installed inclined, typically between
45 and 60 degrees. The preliminary estimate of the required minimum plate pack length is
approximately 18 feet and 10 feet respectively, based on an assumed plate pack width of 2.0 feet
and height of 3.0 feet (consistent with targeted operating hydraulic head). This assumes an average
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plate spacing of 1.5-inch for a total of 24 plates over the 3-foot plate pack height. The spacing of
required baffles for sediment retention upstream of, and oil retention downstream of the plate pack
creating the required OWS forebay and afterbay, is based on design criteria contained in Section
6.6.2.2 of the 2017 RSWDM.
The OWS vault enclosing these separator components would extend to finish grade, with hatches
provided for maintenance access. Shut-off valves are also included on the discharge piping along
with elevated tee-style outlets to avoid the discharge accumulated oils during separator maintenance
and normal operations. These and other coalescing plate OWS design criteria will be refined based
on input from potential suppliers during final design of improvements.
4.5.3 Modular Wetland System Linear Filters
Enhanced water quality treatment is proposed to be provided through the use of multiple Modular
Wetland System (MWS) Linear filter units. This proprietary treatment BMP is a horizontal flow media
biofiltration unit contained in a precast concrete vault. It consist of three chambers, and uses a
proprietary wetland media in the primary biofiltration chamber. W etland or other plantings are
typically installed in the biofiltration chamber, although that is not required. It includes an upstream
pretreatment chamber with optional pretreatment media cells, as well as a downstream discharge
chamber. It can be installed with or without an external high flow bypass, to bypass higher flows
beyond the water quality event. The MWS Linear 2.0 has received Ecology GULD approval (2014)
for enhanced water quality treatment.
Based on the targeted 100-year attenuated design flow of approximately 0.52 cfs and 0.27 cfs,
respectively, for the west and east drainage systems, and considering the manufacturer standard
units flow-based sizing, parallel MWS-L-4-21 units (4-foot x 21-foot footprint size each) were
selected for preliminary design application. The filter media surface area and design flow capacity of
each unit is reported by the manufacturer to be 117 sf and 0.27 cfs, respectively, for each unit.
Therefore, two MWS Linear units are required for the west drainage system treatment, and one unit
is required for the east drainage system treatment. In addition, an extra unit is proposed for each
drainage system, normally closed by shutoff valve, to provide 50 percent or greater redundancy in
treatment level in the event occlusion of the primary treatment filter unit(s). In that event, the
redundant unit could be operated until the filter media in the other unit(s) is replaced. Since full
treatment of runoff is proposed through the 100-year event, and bypass of untreated flows to the
infiltration gallery facilities is not desired, no external high flow bypass is proposed. The estimated
differential hydraulic design head across these units considered for preliminary design is 2.5 feet.
The MWS treatment unit vaults would also extend to finish grade. Because of their required depth
associated with the hydraulic profile of system components, use of wetland vegetation in the
biofiltration chambers may not be possible, and if so, hatches will be installed at finish grade for
maintenance and filter media replacement access.
4.6 Infiltration and Reuse Facilities Preliminary Analysis
and Sizing
4.6.1 Combined Infiltration Gallery and Underlying Sand Filter
Drain rock infiltration galleries with perforated flow dispersal piping within them, and connected to the
MWS treated discharges, are proposed to overlay a basic treatment sand filter installed at subgrade.
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A graded filter layer (pea gravel) would be installed between the drain rock and sand filter media,
and also under the sand filter to transition to subgrade soils without use of a geotextile fabric (to
minimize potential for sand media and subgrade occlusion/plugging). The sand filter will function to
polish previously treated runoff, and to protect the subgrade glacial outwash soils infiltration
characteristics. The basic sand filter footprint area need was determined using Darcy’s Law
assuming a design hydraulic conductivity (permeability) rate of 1.0 in/hr, consistent with Section
6.5.2.1 of the 2017 RSWDM. This rate should also be consistent with the corrected subgrade
hydraulic conductivity based on estimated infiltration rates through the outwash sand/gravel
materials (minimal fines) at more than 3 in/hr, and adjusted for long-term performance based on a
cumulative correction factor of 0.33. Field infiltration testing has not yet been completed to validate
the subgrade infiltration rate. Therefore, infiltration facility sizing is expected to require further
adjustment after the design hydraulic conductivity has been substantiated.
Using the proposed preliminary design footprint areas for the west and east infiltration gallery
footprints (15,600 and 14,400 sf, respectively), a spreadsheet analysis was conducted to determine
the required hydraulic design depth above the sand filter surface within the drain rock infiltration
gallery (see Appendix C). The results of that preliminary analysis are a required hydraulic design
depth above the filter surface of approximately 1 foot for the west facility, and no depth (at the sand
filter surface) for the east facility. Some added design flow reduction will occur with flow routing
through the available storage in the drain rock voids above the sand filter, but that beneficial effect
was not accounted for in preliminary design. Design requirements for the sand filter will be in
accordance with Section 6.5.2.2 of the 2-17 Renton SWDM, considering noted adjustments for sand
filters combined with infiltration facilities.
4.6.2 Rainwater Harvesting Facilities
Partial capture of treated site runoff from TDAs P1 and P2 is proposed via pumping to proposed
above-ground storage tanks for sustainable reuse as part of the site irrigation system (subject to
seasonal availability of flows for capture). For both the west and east drainage systems, the treated
runoff would be captured in a catch basin sump near the discharge from the MWS treatment units,
with pump installed in external wet well to route desired flows to proposed above-ground storage
tanks (5,000 gallons each assumed for preliminary design). Three storage tanks are proposed for
the west drainage system, and two tanks are proposed for the east system.
The required sizing of the wet well and submersible pump will be establish in final design, but the
reuse pumping capacity is expected to range between 100 and 300 gallons per minute (0.22 to 0.67
cfs), with a pumping head requirement likely in excess of 40 feet, and with a pump horsepower
rating consistent with storage tanks and piping system design. The overflow from the catch basin
sump would be to the flow dispersal piping in the infiltration gallery. Therefore, some reduction in
the infiltration facilities design flow rate would result when pumping to storage occurs. It is expected
that the irrigation reuse would primarily be for the rain garden/bioretention cell vegetation, and would
be provided through a drip irrigation system tied to the storage tanks (using the available hydraulic
head), or through pumping from the storage tanks. The analysis and sizing details for these
proposed system components will be confirmed in final design after concurrence is achieved
regarding the rainwater harvesting, storage, and reuse design concept.
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40 | January 15, 2019
5 Conveyance System Analysis and Design
5.1 Proposed Conveyance Systems
The redeveloped site will install multiple storm drain conveyance systems within TDA P1 and P2, to
collect and convey the regraded site runoff to the proposed east and west linear flow control and
presettling vaults. Off-site sheet flow run-on intercepted from the Jefferson Avenue NE road
frontage (west half) will contribute to the east storm drain collection and conveyance system. Those
conveyance systems will consist of various segments of new storm drain pipe (all 12-inch PVC or
CPEP with smooth interior wall as assumed for preliminary design), together with interconnected
catch basins (both Type 1 and Type 2). Grated inlets at catch basins will be located along flow lines
and at low points in the restored finish grade surface, with spacing typically less than 100 feet (a few
segments will exceed that). The depth of storm drain installation (to pipe invert elevations) will vary
between approximately 4 feet and 7 feet below finish grade.
The conveyance system is proposed to be installed at a flow line gradient averaging approximately
0.75 percent, although the required hydraulic gradient under tailwater surcharge to convey up to the
100-year the design flows (variable in each system reach) is expected to be less than 0.5 percent.
Conveyance system outfalls to the flow control vault will typically be located in the active flow control
storage zone to avoid plugging with sediments that can accumulate in the vault bottom, and to
provide some beneficial outfall energy dissipation. Under maximum flow control storage conditions,
some backwater submergence of the new storm drains will occur, but that effect is limited and still
results in upstream water level containment extending upstream from the vaults. The locations and
alignments of the primary storm drain conveyance systems proposed for preliminary design are
shown in Figure 4, and those are shown in more detail, including preliminary profiles, in the draft Site
Improvement Drawings.
5.2 Conveyance Systems Analysis and Design
Conveyance system analysis supporting preliminary design of drainage improvements is currently
limited to confirming the adequacy of the minimum storm drain pipe size applied (12-inch-diameter)
under the targeted drainage system average hydraulic gradient (0.5 percent under full flow) will
provide adequate hydraulic capacity for expected 100-year event design flows. Hydrologic analysis
reported in Section 4.2 (Table 5) for proposed conditions was conducted initially only for the full TDA
drainage areas, and will be broken down further into the individual conveyance system segments in
the final TIR.
For preliminary assessment, the approximately 5.6-acre combined TDAs P1 and P2 area was
broken down equally into the four primary drainage conveyance systems proposed (two within each
TDA). Under that assumption, the average drainage area tributary to each system would be
1.4-acre, and based on 100-year conveyance discharges computed using a conservative Rational
Method analysis approach, the maximum design flow for each storm drain conveyance system is
expected to be less than 2.5 cfs (see Appendix D).
For a hydraulically-smooth,12-inch-diameter storm drain flowing full at 0.5 percent hydraulic
gradient, the computed conveyance capacity of that storm drain would be limited to approximately
3.0 cfs (see Appendix D). At the assumed maximum design flow in each conveyance system, the
required hydraulic gradient would be approximately 0.4 percent. With a maximum length of drainage
conveyance system in the preliminary design layout being less than 300 feet, the total friction head
Draft Stormwater Technical Information Report
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loss over that pipe length would be limited to approximately 1.2 feet. Considering minor hydraulic
losses (inlet, catch basin, bends, outlet), conservatively at 50 percent of friction loss, it is expected
that the total head loss in each system would be less than approximately 1.8 foot. Adding that value
to the maximum flow control water levels targeted in the detention vaults results in maximum
conveyance system water levels that would be fully contained throughout the proposed drainage
systems. Therefore, based on these preliminary assumptions, no 100-year overflow is expected to
occur within the proposed drainage systems. A full hydraulic analysis of the various conveyance
systems will be completed in final design to confirm these preliminary findings.
6 Special Reports and Studies
A preliminary geotechnical report has been completed (Aspect 2018) and is included in Appendix E.
Further geotechnical exploration tailored to the design of the proposed on-site storm drainage
systems and associated infiltration facilities is proposed and will be completed to support the final
design of improvements. That evaluation will include site infiltration testing in the targeted depth
range of infiltration facilities. If a groundwater mounding analysis is determined to be needed by the
City, that analysis would be completed and reported on as part of the findings of those further
subsurface investigations and infiltration testing.
No other special study needs and reports associated with the design of site drainage improvements
have been identified at this time.
7 Other Permits
A list of permits, approvals, and notifications expected to be required for Project implementation
includes:
City of Renton
• Administrative Conditional Use Permit (CUP) Modification
• Site Plan Review
• Demolition Permit
• Grade and Fill Permit
• Building Permit – Commercial/Multi-family
• Civil Construction Permit
• Sign Permit
• Utility Construction Permit
Renton Regional Fire Authority
• Fire Alarm Installation Approval
• Sprinkler Suppression System Installation Approval
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Seattle King County Public Health Department
• Wastewater Tank Abandonment Report
King County Parks and Recreation
• SEPA Environmental Checklist
Washington Department of Ecology
• NPDES Construction General Stormwater Permit Coverage
Puget Sound Clean Air Agency
• Notice of Construction
8 CSWPP Analysis and Design
This initial draft version of this TIR includes a narrative description of the conceptual Temporary
Erosion and Sedimentation Control (TESC) plan and proposed BMPs as a component of the full
CSWPPP that will be provided as part of the final TIR. The SWPPS plan key components are also
described below, and will be expanded on in the final TIR. The CSWPPP will follow standards
contained in Appendix D of the 2017 RSWDM, both for ESC and SWPPPS. Once completed, a
copy of the CSWPPP document must be maintained on-site and available for City staff access and
review during construction. The contractor will be required to implement required BMPs, provide
TESC construction oversight, conduct required monitoring and reporting, provide construction
stormwater permit compliance, and modify/update the CSWPPP consistent with their
means/methods of construction.
8.1 ESC Plan Measures
The Project will provide full redevelopment of the site including the following land disturbing
activities:
• Install ESC measures including source control BMPs, a sedimentation pond, and construction
runoff treatment and discharge facilities.
• Demolish existing buildings and other above ground material storage facilities.
• Remove underground storage tanks, an existing drain field, and any associated contaminated
soils encountered.
• Conduct major excavation to install stormwater facilities and regrade the site.
• Excavate and import select backfill materials for on-site and off-site utility installations and as the
base for new pavements and building foundations.
• Stockpile and manage excavated materials on-site for partial reuse.
• Export excess materials for off-site disposal.
• Revegetate and fully stabilize disturbed areas beyond the new building and pavement limits.
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As such, a comprehensive ESC plan and proper contractor implementation of that plan will be
needed to meet the City-required ESC performance standards and comply with NPDES
Construction Stormwater General Permit conditions. Table 7 summarizes the primary ESC BMP
measures expected to be needed within the various categories for anticipated Project construction
activities, based on guidance and criteria provided in Appendix D of the 2017 Renton SWDM. Those
ESC measures are illustrated on the Erosion Control Plan drawings together with City Standard Plan
drawing references as included with the Site Improvement Plans (see Appendix F).
Table 7. Proposed Primary ESC Measures
ESC Category Applicable ESC Measure from
2017 RSWDM (Appendix D)
On-site and Off-site Application
of Proposed ESC Measures
Clearing limits Plastic high visibility fencing Site perimeter, work areas, and
vegetation preservation limits
Cover measures
Surface roughening
Mulching
Jute matting
Plastic covering
Straw wattles
Hydroseeding
Sodding
Graded slopes erosion control
Disturbed areas, planting areas
Restored slope restoration
Temporary stockpile cover
Restored slopes restoration
Disturbed soils stabilization
Disturbed soils stabilization
Perimeter protection
Temporary fencing/gate
Silt fence
Vegetated strip
Compost sock
Perimeter construction security
Linear sediment retention
Perimeter flow dispersal
Stockpile perimeter
Traffic area stabilization
Stabilized construction entrance
Construction road stabilization
Wheel wash
At site entrance/exit
On-site construction roads
Near construction vehicles site exit
Sediment retention
Sediment trap
Sediment pond
Storm drain inlet protection
On-site swales discharge points
Runoff collection/treatment area
Off-site storm drain inlets
Surface water collection and
conveyance
Interceptor pipe/swale
Pipe slope drains
Ditches/check dams
Outlet protection
Drainage intercept areas
Conveyance on slopes
Site conveyance alignments
Temporary storm drain outlets
Dewatering control Temporary wells, sumps, pumps, and
discharge piping Site excavations dewatering
Dust control Watering Site-wide and off-site disturbed area
Flow control Temporary ponds/tanks If needed - discharge to infiltration
Protect existing and
proposed stormwater
facilities and BMPs
BMPs damage protection
Protect infiltration function
Site-wide and off-site disturbed area
Construction runoff infiltration areas
Maintain protective BMPs Maintain BMPs
Remove BMPs, stabilize surfaces
Site-wide and off-site disturbed area
BMP placement locations
Manage the project CESCL inspection, monitoring
CSWPPP updating
Site-wide and off-site disturbed area
Ongoing updates, maintain on-site
These components are shown on the conceptual ESC plan as part of the Site Improvement Plans
(Appendix F). The contractor is required to assign an ESC supervisor to the Project. The ESC
supervisor must be a certified professional in ESC or a Certified Erosion and Sediment Control Lead.
The ESC supervisor will be responsible for the inspection, maintenance, and performance review of
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all ESC measures, as well as maintaining compliance with NPDES Construction Stormwater Permit
conditions.
8.2 SWPPS Plan Measures
The SWPPS plan proposes site construction activities and control measures intended to prevent
pollutants from coming into contact with site drainage, surface water, or groundwater. Table 8
summarizes the primary SWPPS control measures expected to be needed for anticipated Project
construction activities, based on guidance and criteria provided in Appendix D of the 2017 Renton
SWDM.
Table 8. Proposed Primary SWPPS Measures
SWPPS Category Applicable SWPPS Measure
from 2017 RSWDM (Appendix D)
On-site and Off-site Application
of Proposed SWPPS Measures
Follow effective pollutant
handling and disposal
procedures
Concrete handling and washout
facilities
Saw-cutting runoff controls
Use good housekeeping practices
Apply construction concrete washoff
and washout controls
Provide cover and
containment for materials,
fuel and other pollutants
Materials delivery, storage and
containment
Provide containment of fuels and oils,
and other pollutants;
Isolate construction fueling areas;
provide timely spill response;
Provide covered bins for contaminated
soils to be removed
Maximize pollutant control
and minimize pollutant
sources
Construction stormwater filtration Use chitosan enhanced sand filtration
(if needed)
Protect from spills and drips
of petroleum products and
other pollutants
Maintain protective BMPs
Designate contained site areas for
construction vehicles parking;
Use drip pans and oil booms
containment when not in use
Avoid over-application or
untimely application of
chemicals and fertilizers
Manage the project Do not use chemical additives for soil
stabilization
Prevent or treat
contamination of stormwater
runoff by pH modifying
sources
PH control for high PH water Use CO2 sparging or compost sock
filtration (if needed)
Given the large amount of earthwork on this Project, it is expected that filtration treatment of site
runoff during construction will be required. For the draft TIR, this treatment is conceptually shown to
be a chitosan enhanced sand filtration (CESF) system, located downstream from the sedimentation
pond as currently proposed in the southeast corner of the site. This treatment system, which has
Ecology GULD approval for construction runoff treatment, includes various components including
pumping, flocculation/settling, sediment/sludge storage tanks, pressure sand filtration pods, as-
needed recycle through treatment, and discharge facilities. It is assumed that discharge from this
process will be to the south-side swale that exits the site and flows to a closed depression/infiltration
area on the south King County parcel. The construction runoff treatment process will be analyzed
and illustrated in more detail during final design and will be documented in the final TIR.
Draft Stormwater Technical Information Report
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January 15, 2019 | 45
9 Bond Quantities, Facility Summaries, and
Declaration of Covenant
Bond Quantities, Facility Summaries, and Declaration of Covenant, to the extent applicable to King
County projects, and required by the City, will be provided in the final TIR.
10 Operations and Maintenance Manual
An Operations and Maintenance Manual for the non-standard stormwater facilities and BMPs
proposed by to be constructed or installed by the project, and operated by King County, will be
provided as an Appendix in the final TIR once the design of those items has progressed through
100% design. Standard facilities and BMPs will be operated and maintained in accordance with
Appendix A of the 2017 RSWDM.
11 References
Aspect Consultants 2018. Preliminary Geotechnical Evaluation, King County Parks and Recreation
Division – Renton Shop, 3005 4th Street NW, Renton, Washington. Prepared for HDR
Architecture, In. March 20, 2018.
City of Renton 2018. City of Renton Online GIS viewer,
http://rp.rentonwa.gov/HTML5Public/Index.HTML?viewer=CORMaps. Accessed December
2018.
City of Renton 2017. City of Renton Surface Water Design Manual. City of Renton Public Works
Department, Surface Water Utility. December 12, 2016 (Effective January 1, 2017).
City of Renton 2017a. FEMA Flood Insurance Rate Map (FIRM), King County, Washington and
Incorporated Areas, City of Renton Map No. 5033C0981G (Preliminary). Revised September
15, 2017.
Google Earth Pro 2018. Aerial Imaging and Mapping Viewer of City of Renton. Accessed
December 2018.
Herrera Environmental Consultants 2015. Lower Cedar River Chinook Salmon Habitat Restoration
Assessment Study, Habitat Restoration Site Potential and Feasibility Analysis Report.
Prepared for the City of Renton. November 5, 2015.
King County 1997. Lower Cedar River Basin and Nonpoint Pollution Action Plan. Prepared in
Coordination with City of Renton and Washington State Department of Ecology. Adopted by
Metropolitan King County Council July 1997.
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Appendix A. Project Drainage Review
Classification Figures
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Appendix B. Hydrologic Analysis for Flow Control
Sizing and Water Quality Flow Calculations
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—————————————————————————————————
MGS FLOOD
PROJECT REPORT
Program Version: MGSFlood 4.46
Program License Number: 200510004
Project Simulation Performed on: 01/10/2019 12:47 PM
Report Generation Date: 01/10/2019 12:47 PM
—————————————————————————————————
Input File Name: 190104_KC CMF_EX1.fld
Project Name: King County CMF
Analysis Title: TDA E1 – North
Comments:
———————————————— PRECIPITATION INPUT ————————————————
Computational Time Step (Minutes): 15
Extended Precipitation Time Series Selected
Climatic Region Number: 15
Full Period of Record Available used for Routing
Precipitation Station : 96004005 Puget East 40 in_5min 10/01/1939-10/01/2097
Evaporation Station : 961040 Puget East 40 in MAP
Evaporation Scale Factor : 0.750
HSPF Parameter Region Number: 1
HSPF Parameter Region Name : USGS Default
********** Default HSPF Parameters Used (Not Modified by User) ***************
********************** WATERSHED DEFINITION ***********************
Predevelopment/Post Development Tributary Area Summary
Predeveloped Post Developed
Total Subbasin Area (acres) 2.960 2.960
Area of Links that Include Precip/Evap (acres) 0.000 0.000
Total (acres) 2.960 2.960
----------------------SCENARIO: PREDEVELOPED
Number of Subbasins: 1
---------- Subbasin : Subbasin 1 ----------
-------Area (Acres) --------
Till Grass 1.940
Impervious 1.020
----------------------------------------------
Subbasin Total 2.960
----------------------SCENARIO: POSTDEVELOPED
Number of Subbasins: 1
---------- Subbasin : Subbasin 1 ----------
-------Area (Acres) --------
Till Grass 1.940
Impervious 1.020
----------------------------------------------
Subbasin Total 2.960
************************* LINK DATA *******************************
----------------------SCENARIO: PREDEVELOPED
Number of Links: 0
************************* LINK DATA *******************************
----------------------SCENARIO: POSTDEVELOPED
Number of Links: 1
------------------------------------------
Link Name: New Copy Lnk1
Link Type: Copy
Downstream Link: None
**********************FLOOD FREQUENCY AND DURATION STATISTICS*******************
----------------------SCENARIO: PREDEVELOPED
Number of Subbasins: 1
Number of Links: 0
----------------------SCENARIO: POSTDEVELOPED
Number of Subbasins: 1
Number of Links: 1
***********Groundwater Recharge Summary *************
Recharge is computed as input to Perlnd Groundwater Plus Infiltration in Structures
Total Predeveloped Recharge During Simulation
Model Element Recharge Amount (ac-ft)
-----------------------------------------------------------------------------------------------
Subbasin: Subbasin 1 237.089
_____________________________________
Total: 237.089
Total Post Developed Recharge During Simulation
Model Element Recharge Amount (ac-ft)
-----------------------------------------------------------------------------------------------
Subbasin: Subbasin 1 237.089
Link: New Copy Lnk1 0.000
_____________________________________
Total: 237.089
Total Predevelopment Recharge Equals Post Developed
Average Recharge Per Year, (Number of Years= 158)
Predeveloped: 1.501 ac-ft/year, Post Developed: 1.501 ac-ft/year
***********Water Quality Facility Data *************
----------------------SCENARIO: PREDEVELOPED
Number of Links: 0
----------------------SCENARIO: POSTDEVELOPED
Number of Links: 1
********** Link: New Copy Lnk1 **********
Infiltration/Filtration Statistics--------------------
Inflow Volume (ac-ft): 847.45
Inflow Volume Including PPT-Evap (ac-ft): 847.45
Total Runoff Infiltrated (ac-ft): 0.00, 0.00%
Total Runoff Filtered (ac-ft): 0.00, 0.00%
Primary Outflow To Downstream System (ac-ft): 847.45
Secondary Outflow To Downstream System (ac-ft): 0.00
Percent Treated (Infiltrated+Filtered)/Total Volume: 0.00%
Runoff Peak Discharges
***********Compliance Point Results *************
Scenario Predeveloped Compliance Subbasin: Subbasin 1
Scenario Postdeveloped Compliance Link: New Copy Lnk1
*** Point of Compliance Flow Frequency Data ***
Recurrence Interval Computed Using Gringorten Plotting Position
Predevelopment Runoff Postdevelopment Runoff
Tr (Years) Discharge (cfs) Tr (Years) Discharge (cfs)
----------------------------------------------------------------------------------------------------------------------
2-Year 0.553 2-Year 0.553
5-Year 0.745 5-Year 0.745
10-Year 0.984 10-Year 0.984
25-Year 1.315 25-Year 1.315
50-Year 1.732 50-Year 1.732
100-Year 2.033 100-Year 2.033
200-Year 2.124 200-Year 2.124
—————————————————————————————————
MGS FLOOD
PROJECT REPORT
Program Version: MGSFlood 4.46
Program License Number: 200510004
Project Simulation Performed on: 01/10/2019 12:58 PM
Report Generation Date: 01/10/2019 12:59 PM
—————————————————————————————————
Input File Name: 190104_KC CMF_EX2.fld
Project Name: King County CMF
Analysis Title: TDA E2 - South
Comments:
———————————————— PRECIPITATION INPUT ————————————————
Computational Time Step (Minutes): 15
Extended Precipitation Time Series Selected
Climatic Region Number: 1
Full Period of Record Available used for Routing
Precipitation Station : 95003205 Puget West 32 in_5min 10/01/1939-10/01/2097
Evaporation Station : 951032 Puget West 32 in MAP
Evaporation Scale Factor : 0.750
HSPF Parameter Region Number: 1
HSPF Parameter Region Name : USGS Default
********** Default HSPF Parameters Used (Not Modified by User) ***************
********************** WATERSHED DEFINITION ***********************
Predevelopment/Post Development Tributary Area Summary
Predeveloped Post Developed
Total Subbasin Area (acres) 2.790 2.790
Area of Links that Include Precip/Evap (acres) 0.000 0.000
Total (acres) 2.790 2.790
----------------------SCENARIO: PREDEVELOPED
Number of Subbasins: 1
---------- Subbasin : Subbasin 1 ----------
-------Area (Acres) --------
Till Grass 2.000
Impervious 0.790
----------------------------------------------
Subbasin Total 2.790
----------------------SCENARIO: POSTDEVELOPED
Number of Subbasins: 1
---------- Subbasin : Subbasin 1 ----------
-------Area (Acres) --------
Till Grass 2.000
Impervious 0.790
----------------------------------------------
Subbasin Total 2.790
************************* LINK DATA *******************************
----------------------SCENARIO: PREDEVELOPED
Number of Links: 0
************************* LINK DATA *******************************
----------------------SCENARIO: POSTDEVELOPED
Number of Links: 1
------------------------------------------
Link Name: New Copy Lnk1
Link Type: Copy
Downstream Link: None
**********************FLOOD FREQUENCY AND DURATION STATISTICS*******************
----------------------SCENARIO: PREDEVELOPED
Number of Subbasins: 1
Number of Links: 0
----------------------SCENARIO: POSTDEVELOPED
Number of Subbasins: 1
Number of Links: 1
***********Groundwater Recharge Summary *************
Recharge is computed as input to Perlnd Groundwater Plus Infiltration in Structures
Total Predeveloped Recharge During Simulation
Model Element Recharge Amount (ac-ft)
-----------------------------------------------------------------------------------------------
Subbasin: Subbasin 1 200.086
_____________________________________
Total: 200.086
Total Post Developed Recharge During Simulation
Model Element Recharge Amount (ac-ft)
-----------------------------------------------------------------------------------------------
Subbasin: Subbasin 1 200.086
Link: New Copy Lnk1 0.000
_____________________________________
Total: 200.086
Total Predevelopment Recharge Equals Post Developed
Average Recharge Per Year, (Number of Years= 158)
Predeveloped: 1.266 ac-ft/year, Post Developed: 1.266 ac-ft/year
***********Water Quality Facility Data *************
----------------------SCENARIO: PREDEVELOPED
Number of Links: 0
----------------------SCENARIO: POSTDEVELOPED
Number of Links: 1
********** Link: New Copy Lnk1 **********
Infiltration/Filtration Statistics--------------------
Inflow Volume (ac-ft): 542.94
Inflow Volume Including PPT-Evap (ac-ft): 542.94
Total Runoff Infiltrated (ac-ft): 0.00, 0.00%
Total Runoff Filtered (ac-ft): 0.00, 0.00%
Primary Outflow To Downstream System (ac-ft): 542.94
Secondary Outflow To Downstream System (ac-ft): 0.00
Percent Treated (Infiltrated+Filtered)/Total Volume: 0.00%
Runoff Peak Discharges
***********Compliance Point Results *************
Scenario Predeveloped Compliance Subbasin: Subbasin 1
Scenario Postdeveloped Compliance Link: New Copy Lnk1
*** Point of Compliance Flow Frequency Data ***
Recurrence Interval Computed Using Gringorten Plotting Position
Predevelopment Runoff Postdevelopment Runoff
Tr (Years) Discharge (cfs) Tr (Years) Discharge (cfs)
----------------------------------------------------------------------------------------------------------------------
2-Year 0.391 2-Year 0.391
5-Year 0.558 5-Year 0.558
10-Year 0.697 10-Year 0.697
25-Year 1.063 25-Year 1.063
50-Year 1.103 50-Year 1.103
100-Year 1.160 100-Year 1.160
200-Year 1.218 200-Year 1.218
—————————————————————————————————
MGS FLOOD
PROJECT REPORT
Program Version: MGSFlood 4.46
Program License Number: 200510004
Project Simulation Performed on: 01/09/2019 1:59 PM
Report Generation Date: 01/09/2019 1:59 PM
—————————————————————————————————
Input File Name: 190103_KC CMF_PR1.fld
Project Name: King County CMF
Analysis Title: TDA P1 – West Drainage System
Comments:
———————————————— PRECIPITATION INPUT ————————————————
Computational Time Step (Minutes): 15
Extended Precipitation Time Series Selected
Climatic Region Number: 15
Full Period of Record Available used for Routing
Precipitation Station : 96004005 Puget East 40 in_5min 10/01/1939-10/01/2097
Evaporation Station : 961040 Puget East 40 in MAP
Evaporation Scale Factor : 0.750
HSPF Parameter Region Number: 1
HSPF Parameter Region Name : USGS Default
********** Default HSPF Parameters Used (Not Modified by User) ***************
********************** WATERSHED DEFINITION ***********************
Predevelopment/Post Development Tributary Area Summary
Predeveloped Post Developed
Total Subbasin Area (acres) 3.070 3.070
Area of Links that Include Precip/Evap (acres) 0.000 0.000
Total (acres) 3.070 3.070
----------------------SCENARIO: PREDEVELOPED
Number of Subbasins: 1
---------- Subbasin : Subbasin 1 ----------
-------Area (Acres) --------
Till Grass 1.600
Impervious 1.470
----------------------------------------------
Subbasin Total 3.070
----------------------SCENARIO: POSTDEVELOPED
Number of Subbasins: 1
---------- Subbasin : Subbasin 1 ----------
-------Area (Acres) --------
Till Grass 0.160
Impervious 2.910
----------------------------------------------
Subbasin Total 3.070
************************* LINK DATA *******************************
----------------------SCENARIO: PREDEVELOPED
Number of Links: 0
************************* LINK DATA *******************************
----------------------SCENARIO: POSTDEVELOPED
Number of Links: 1
------------------------------------------
Link Name: New Structure Lnk1
Link Type: Structure
Downstream Link: None
Prismatic Pond Option Used
Pond Floor Elevation (ft) : 100.00
Riser Crest Elevation (ft) : 104.50
Max Pond Elevation (ft) : 106.00
Storage Depth (ft) : 4.50
Pond Bottom Length (ft) : 358.0
Pond Bottom Width (ft) : 10.0
Pond Side Slopes (ft/ft) : L1= 0.00 L2= 0.00 W1= 0.00 W2= 0.00
Bottom Area (sq-ft) : 3580.
Area at Riser Crest El (sq-ft) : 3,580.
(acres) : 0.082
Volume at Riser Crest (cu-ft) : 16,110.
(ac-ft) : 0.370
Area at Max Elevation (sq-ft) : 3580.
(acres) : 0.082
Vol at Max Elevation (cu-ft) : 21,480.
(ac-ft) : 0.493
Massmann Infiltration Option Used
Hydraulic Conductivity (in/hr) : 0.00
Depth to Water Table (ft) : 100.00
Bio-Fouling Potential : Low
Maintenance : Average or Better
Riser Geometry
Riser Structure Type : Circular
Riser Diameter (in) : 24.00
Common Length (ft) : 0.000
Riser Crest Elevation : 104.50 ft
Hydraulic Structure Geometry
Number of Devices: 1
---Device Number 1 ---
Device Type : Circular Orifice
Control Elevation (ft) : 100.00
Diameter (in) : 3.13
Orientation : Horizontal
Elbow : Yes
**********************FLOOD FREQUENCY AND DURATION STATISTICS*******************
----------------------SCENARIO: PREDEVELOPED
Number of Subbasins: 1
Number of Links: 0
----------------------SCENARIO: POSTDEVELOPED
Number of Subbasins: 1
Number of Links: 1
********** Link: New Structure Lnk1 ********** Link WSEL Stats
WSEL Frequency Data(ft)
(Recurrence Interval Computed Using Gringorten Plotting Position)
Tr (yrs) WSEL Peak (ft)
======================================
1.05-Year 100.947
1.11-Year 101.070
1.25-Year 101.206
2.00-Year 101.616
3.33-Year 102.084
5-Year 102.340
10-Year 102.859
25-Year 103.449
50-Year 104.056
100-Year 104.346
***********Groundwater Recharge Summary *************
Recharge is computed as input to Perlnd Groundwater Plus Infiltration in Structures
Total Predeveloped Recharge During Simulation
Model Element Recharge Amount (ac-ft)
-----------------------------------------------------------------------------------------------
Subbasin: Subbasin 1 195.537
_____________________________________
Total: 195.537
Total Post Developed Recharge During Simulation
Model Element Recharge Amount (ac-ft)
-----------------------------------------------------------------------------------------------
Subbasin: Subbasin 1 19.554
Link: New Structure Lnk1 0.000
_____________________________________
Total: 19.554
Total Predevelopment Recharge is Greater than Post Developed
Average Recharge Per Year, (Number of Years= 158)
Predeveloped: 1.238 ac-ft/year, Post Developed: 0.124 ac-ft/year
***********Water Quality Facility Data *************
----------------------SCENARIO: PREDEVELOPED
Number of Links: 0
----------------------SCENARIO: POSTDEVELOPED
Number of Links: 1
********** Link: New Structure Lnk1 **********
Basic Wet Pond Volume (91% Exceedance): 13025. cu-ft
Computed Large Wet Pond Volume, 1.5*Basic Volume: 19537. cu-ft
Infiltration/Filtration Statistics--------------------
Inflow Volume (ac-ft): 1336.87
Inflow Volume Including PPT-Evap (ac-ft): 1336.87
Total Runoff Infiltrated (ac-ft): 0.00, 0.00%
Total Runoff Filtered (ac-ft): 0.00, 0.00%
Primary Outflow To Downstream System (ac-ft): 1343.22
Secondary Outflow To Downstream System (ac-ft): 0.00
Percent Treated (Infiltrated+Filtered)/Total Volume: 0.00%
***********Compliance Point Results *************
Scenario Predeveloped Compliance Subbasin: Subbasin 1
Scenario Postdeveloped Compliance Link: New Structure Lnk1
Flow Control Vault Peak Outflows
*** Point of Compliance Flow Frequency Data ***
Recurrence Interval Computed Using Gringorten Plotting Position
Predevelopment Runoff Postdevelopment Runoff
Tr (Years) Discharge (cfs) Tr (Years) Discharge (cfs)
----------------------------------------------------------------------------------------------------------------------
2-Year 0.688 2-Year 0.315
5-Year 0.906 5-Year 0.379
10-Year 1.114 10-Year 0.419
25-Year 1.500 25-Year 0.460
50-Year 1.935 50-Year 0.499
100-Year 2.344 100-Year 0.516
200-Year 2.398 200-Year 0.517
Flow Control Vault Water Quality Inflows
On-Line Facility Design Discharge Rate (cfs): 0.424
Off-Line Facility Design Discharge Rate (cfs): 0.236
Flow Control Vault Peak Inflows
Predevelopment Runoff Postdevelopment Runoff
Tr (Years) Discharge (cfs) Tr (Years) Discharge (cfs)
----------------------------------------------------------------------------------------------------------------------
2-Year 0.688 2-Year 1.101
5-Year 0.906 5-Year 1.422
10-Year 1.114 10-Year 1.629
25-Year 1.500 25-Year 2.064
50-Year 1.935 50-Year 2.578
100-Year 2.344 100-Year 3.029
200-Year 2.398 200-Year 3.127
—————————————————————————————————
MGS FLOOD
PROJECT REPORT
Program Version: MGSFlood 4.46
Program License Number: 200510004
Project Simulation Performed on: 01/09/2019 2:12 PM
Report Generation Date: 01/09/2019 2:13 PM
—————————————————————————————————
Input File Name: 190104_KC CMF_PR2.fld
Project Name: King County CMF
Analysis Title: TDA P2 – East Drainage System
Comments:
———————————————— PRECIPITATION INPUT ————————————————
Computational Time Step (Minutes): 15
Extended Precipitation Time Series Selected
Climatic Region Number: 15
Full Period of Record Available used for Routing
Precipitation Station : 96004005 Puget East 40 in_5min 10/01/1939-10/01/2097
Evaporation Station : 961040 Puget East 40 in MAP
Evaporation Scale Factor : 0.750
HSPF Parameter Region Number: 1
HSPF Parameter Region Name : USGS Default
********** Default HSPF Parameters Used (Not Modified by User) ***************
********************** WATERSHED DEFINITION ***********************
Predevelopment/Post Development Tributary Area Summary
Predeveloped Post Developed
Total Subbasin Area (acres) 2.470 2.470
Area of Links that Include Precip/Evap (acres) 0.000 0.000
Total (acres) 2.470 2.470
----------------------SCENARIO: PREDEVELOPED
Number of Subbasins: 1
---------- Subbasin : Subbasin 1 ----------
-------Area (Acres) --------
Till Grass 2.230
Impervious 0.240
----------------------------------------------
Subbasin Total 2.470
----------------------SCENARIO: POSTDEVELOPED
Number of Subbasins: 1
---------- Subbasin : Subbasin 1 ----------
-------Area (Acres) --------
Till Grass 0.440
Impervious 2.030
----------------------------------------------
Subbasin Total 2.470
************************* LINK DATA *******************************
----------------------SCENARIO: PREDEVELOPED
Number of Links: 0
************************* LINK DATA *******************************
----------------------SCENARIO: POSTDEVELOPED
Number of Links: 1
------------------------------------------
Link Name: New Structure Lnk1
Link Type: Structure
Downstream Link: None
Prismatic Pond Option Used
Pond Floor Elevation (ft) : 100.00
Riser Crest Elevation (ft) : 104.50
Max Pond Elevation (ft) : 106.00
Storage Depth (ft) : 4.50
Pond Bottom Length (ft) : 326.0
Pond Bottom Width (ft) : 10.0
Pond Side Slopes (ft/ft) : L1= 0.00 L2= 0.00 W1= 0.00 W2= 0.00
Bottom Area (sq-ft) : 3260.
Area at Riser Crest El (sq-ft) : 3,260.
(acres) : 0.075
Volume at Riser Crest (cu-ft) : 14,670.
(ac-ft) : 0.337
Area at Max Elevation (sq-ft) : 3260.
(acres) : 0.075
Vol at Max Elevation (cu-ft) : 19,560.
(ac-ft) : 0.449
Massmann Infiltration Option Used
Hydraulic Conductivity (in/hr) : 0.00
Depth to Water Table (ft) : 100.00
Bio-Fouling Potential : Low
Maintenance : Average or Better
Riser Geometry
Riser Structure Type : Circular
Riser Diameter (in) : 24.00
Common Length (ft) : 0.000
Riser Crest Elevation : 104.50 ft
Hydraulic Structure Geometry
Number of Devices: 1
---Device Number 1 ---
Device Type : Circular Orifice
Control Elevation (ft) : 100.00
Diameter (in) : 2.25
Orientation : Horizontal
Elbow : Yes
**********************FLOOD FREQUENCY AND DURATION STATISTICS*******************
----------------------SCENARIO: PREDEVELOPED
Number of Subbasins: 1
Number of Links: 0
----------------------SCENARIO: POSTDEVELOPED
Number of Subbasins: 1
Number of Links: 1
Flow Control Vault Stage
********** Link: New Structure Lnk1 ********** Link WSEL Stats
WSEL Frequency Data(ft)
(Recurrence Interval Computed Using Gringorten Plotting Position)
Tr (yrs) WSEL Peak (ft)
======================================
1.05-Year 101.021
1.11-Year 101.141
1.25-Year 101.309
2.00-Year 101.728
3.33-Year 102.118
5-Year 102.451
10-Year 103.022
25-Year 103.922
50-Year 104.315
100-Year 104.478
***********Groundwater Recharge Summary *************
Recharge is computed as input to Perlnd Groundwater Plus Infiltration in Structures
Total Predeveloped Recharge During Simulation
Model Element Recharge Amount (ac-ft)
-----------------------------------------------------------------------------------------------
Subbasin: Subbasin 1 272.530
_____________________________________
Total: 272.530
Total Post Developed Recharge During Simulation
Model Element Recharge Amount (ac-ft)
-----------------------------------------------------------------------------------------------
Subbasin: Subbasin 1 53.773
Link: New Structure Lnk1 0.000
_____________________________________
Total: 53.773
Total Predevelopment Recharge is Greater than Post Developed
Average Recharge Per Year, (Number of Years= 158)
Predeveloped: 1.725 ac-ft/year, Post Developed: 0.340 ac-ft/year
***********Water Quality Facility Data *************
----------------------SCENARIO: PREDEVELOPED
Number of Links: 0
----------------------SCENARIO: POSTDEVELOPED
Number of Links: 1
********** Link: New Structure Lnk1 **********
Basic Wet Pond Volume (91% Exceedance): 9441. cu-ft
Computed Large Wet Pond Volume, 1.5*Basic Volume: 14162. cu-ft
Infiltration/Filtration Statistics--------------------
Inflow Volume (ac-ft): 998.63
Inflow Volume Including PPT-Evap (ac-ft): 998.63
Total Runoff Infiltrated (ac-ft): 0.00, 0.00%
Total Runoff Filtered (ac-ft): 0.00, 0.00%
Primary Outflow To Downstream System (ac-ft): 999.87
Secondary Outflow To Downstream System (ac-ft): 0.00
Percent Treated (Infiltrated+Filtered)/Total Volume: 0.00%
Flow Control Vault Peak Outflows
***********Compliance Point Results *************
Scenario Predeveloped Compliance Subbasin: Subbasin 1
Scenario Postdeveloped Compliance Link: New Structure Lnk1
*** Point of Compliance Flow Frequency Data ***
Recurrence Interval Computed Using Gringorten Plotting Position
Predevelopment Runoff Postdevelopment Runoff
Tr (Years) Discharge (cfs) Tr (Years) Discharge (cfs)
----------------------------------------------------------------------------------------------------------------------
2-Year 0.297 2-Year 0.169
5-Year 0.453 5-Year 0.201
10-Year 0.655 10-Year 0.223
25-Year 0.957 25-Year 0.254
50-Year 1.215 50-Year 0.267
100-Year 1.352 100-Year 0.272
200-Year 1.483 200-Year 0.703
Flow Control Vault Water Quality Inflows
On-Line Facility Design Discharge Rate (cfs): 0.293
Off-Line Facility Design Discharge Rate (cfs): 0.163
Flow Control Vault Peak Inflows (cfs)
Predevelopment Runoff Postdevelopment Runoff
Tr (Years) Discharge (cfs) Tr (Years) Discharge (cfs)
----------------------------------------------------------------------------------------------------------------------
2-Year 0.297 2-Year 0.792
5-Year 0.453 5-Year 1.015
10-Year 0.655 10-Year 1.199
25-Year 0.957 25-Year 1.582
50-Year 1.215 50-Year 1.879
100-Year 1.352 100-Year 2.303
200-Year 1.483 200-Year 2.353
Draft Stormwater Technical Information Report
King County Parks – Renton Shop Central Maintenance Facility Replacement Project
January 15, 2019 | C-1
Appendix C. Oil-Water Separator and Sand
Filter/Infiltration Facilities Sizing Calculations
Draft Stormwater Technical Information Report
King County Parks – Renton Shop Central Maintenance Facility Replacement Project
C-2 | January 15, 2019
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Height
(ft) Width (ft)
Length
(ft)
No. of
Plates
P1 (West)0.52 845 3.0 2.0 18.0 24
P2 (East)0.27 439 3.0 2.0 10.0 24
Ah = Required horizontal surface area of coalescing plate media, sf
Preliminary Coalescing Plate Oil-Water Separator Sizing - CMF Proposed West and East Drainage Systems
TDA
CP OWS Treatment
Design Flow, 100-yr
Detention Outflow, Q
(cfs)
Computed Effective
(Horizontal) Surface
Area of Required CP
Media, Ah (sf)
Coalescing Plate Pack Estimated Size
Q = Water quality treatment design flow, cfs
This page intentionally left blank.
Elevation Total Area Areab Areaperim Rock Voids Storage Rock Voids Storage ib iperim Infiltration Discharge Overflow Stage Areab
(feet)(sf)(sf)(sf)(cu ft)(ac-ft)(feet/foot)(in/hr)(cfs)(cfs)(feet)(ac)Notes
314.90 15,600 15,600 0 0 0.00 1.00 1.00 0.36 0.0 0.00 0.358 Top of sand filter elevation targeted as 314.9
315.00 15,600 15,600 0 156 0.00 1.07 1.03 0.39 0.0 0.10 0.358 Pea gravel filter between drain rock and sand
315.50 15,600 15,600 0 936 0.02 1.40 1.20 0.51 0.0 0.60 0.358 Pea gravel filter between drain rock and sand
316.00 15,600 15,600 0 3,276 0.08 1.73 1.37 0.63 0.0 1.10 0.358 1" minus drain rock above
316.50 15,600 15,600 0 5,616 0.13 2.07 1.53 0.75 0.0 1.60 0.358
317.00 15,600 15,600 0 7,956 0.18 2.40 1.70 0.87 0.0 2.10 0.358
317.50 15,600 15,600 0 10,296 0.24 2.73 1.87 0.99 0.0 2.60 0.358
318.00 15,600 15,600 0 12,636 0.29 3.07 2.03 1.11 0.0 3.10 0.358
Infiltration Flow Using Darcy Equation
Q=kiA
k=1.00 in/hr Overflow Q=CLH^1.5
k=2.315E-05 ft/s C=0.0
ib=(water depth+media depth)/media depth L = 0.0 feet
iperim=(water depth/2+media depth)/media depth Crest Elevation 0.00 feet
Filter Media Depth=1.5 feet
Filter Surface Area=15600 sf
ac = acre
ac ft = acre feet
Areab = area bottom
Areaperim = area perimeter
cfs = cubic feet per second
cu ft = cubic feet
ft/s = feet per second
Ib = hydraulic gradient bottom
Iperim = hydraulic gradient perimeter
in/hr = inches per hour
sf = square feet
Sand Filter Treatment and Infiltration Analysis - CMF TDA P2 - West Drainage System
1 of 1
Elevation Total Area Areab Areaperim Rock Voids Storage Rock Voids Storage ib iperim Infiltration Discharge Overflow Stage Areab
(feet)(sf)(sf)(sf)(cu ft)(ac-ft)(feet/foot)(in/hr)(cfs)(cfs)(feet)(ac)Notes
317.50 14,400 14,400 0 0 0.00 1.00 1.00 0.33 0.0 0.00 0.331 Top of sand filter elevation targeted as 317.5
317.60 14,400 14,400 0 144 0.00 1.07 1.03 0.36 0.0 0.10 0.331 Pea gravel filter between drain rock and sand
318.00 14,400 14,400 0 720 0.02 1.33 1.17 0.44 0.0 0.50 0.331 Pea gravel filter between drain rock and sand
318.50 14,400 14,400 0 2,880 0.07 1.67 1.33 0.56 0.0 1.00 0.331 1" minus drain rock above
319.00 14,400 14,400 0 5,040 0.12 2.00 1.50 0.67 0.0 1.50 0.331
319.50 14,400 14,400 0 7,200 0.17 2.33 1.67 0.78 0.0 2.00 0.331
320.00 14,400 14,400 0 9,360 0.21 2.67 1.83 0.89 0.0 2.50 0.331
320.50 14,400 14,400 0 11,520 0.26 3.00 2.00 1.00 0.0 3.00 0.331
Infiltration Flow Using Darcy Equation
Q=kiA
k=1.00 in/hr Overflow Q=CLH^1.5
k=2.315E-05 ft/s C=0.0
ib=(water depth+media depth)/media depth L = 0.0 feet
iperim=(water depth/2+media depth)/media depth Crest Elevation 0.00 feet
Filter Media Depth=1.5 feet
Filter Surface Area=14400 sf
ac = acre
ac ft = acre feet
Areab = area bottom
Areaperim = area perimeter
cfs = cubic feet per second
cu ft = cubic feet
ft/s = feet per second
Ib = hydraulic gradient bottom
Iperim = hydraulic gradient perimeter
in/hr = inches per hour
sf = square feet
Sand Filter Treatment and Infiltration Analysis - CMF TDA P2 - East Drainage System
1 of 1
Draft Stormwater Technical Information Report
King County Parks – Renton Shop Central Maintenance Facility Replacement Project
January 15, 2019 | D-1
Appendix D. Storm Drain Conveyance Sizing
Calculations
Draft Stormwater Technical Information Report
King County Parks – Renton Shop Central Maintenance Facility Replacement Project
D-2 | January 15, 2019
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STORM SEWER DESIGN (English Units)
This spreadsheet accomplishes a storm sewer design using the rational method. Enter the data in the non-shaded areas only.
Please use one spreadsheet per stormsewer run.
JB - HDR
Enter Here
m =8.75 n =0.545 100 0.5 0.5
Location Discharge Drain Design Drain Profile
Drain Located On From Sta. To Sta. Source of
Drainage
Drainage
Area A
(acre)
Runoff
Coeff. C
CA (acre) Sum
CA
(acre)
Tc Across
Area
(minutes)
Total Tc = Col.
8a + Tc across
pipe length
(minutes)
Rainfall
Intensity
(in/hr)
Runoff (cfs) Contrib.
Inflow
(cfs)
Total Flow
(cfs)
Pipe Dia.
(in)
Manning
roughness
coefficient
"n"
Pipe
Slope
(ft/ft)
Velocity Of
Flow
(ft/s)
Pipe
Capacity
(cfs)
Pipe Velocity Check (Desirable
Minimum 3 ft/sec; Desirable
Maximum 10 ft/sec for Column 16)
Pipe Capacity Check (Column 13
vs. Column 17)
Pipe
Length***
(ft)
Elevation
Change (ft)
Upstr.
Invert Elev.
(ft)
Downstr.
Invert Elev.
(ft)
Upstr.
Ground
Elev. (ft)
Downstr.
Ground
Elev.
(ft)
Upstr. Pipe Cover (ft) Downstr. Pipe Cover (ft)
1 2 3 4 5 6 7 8 8a 9 10 11 12 13 14 14a 15 16 17 17a 17b 18 19 20 21 22 23 24 25
TDA P1/P2 1.40 0.90 1.26 1.26 15.0 15.0 2.00 2.52 0.00 2.52 12 0.011 0.0050 3.79 2.97 VELOCITY OK ADEQUATE PIPE CAPACITY 300 1.50 326.00 324.50 330.00 330.00 2.46 3.96
(25% of PI+P2)
See WSDOT Hydraulic Manual 6-5 for explanation of columns. http://www.wsdot.wa.gov/eesc/design/hydraulics/
Notes: Column 12 represents inflow from a storm sewer line, branch, an offsite source that flows into the trunk line being analyzed.
The conservative assumption is that the flow enters the storm sewer run at the upstream end of the run being analyzed.
For pipe cover calculation, Pipe cover = (Ground or Rim Elevation - Pipe invert elevation) - (pavement thickness) - (top of pipe thickness) - (pipe diameter).
The pipe thickness is based on the pipe diameter per WSDOT Manual Concrete for Shallow Pipe Cover Installations Fill Height Table 8-11.2
Please specify the largest pipe thickness of the storm sewer run being analyzed.
The spreadsheet will only calculate one storm sewer line at a time. Please copy the "Blank Template" and use this for calculating new storm sewer lines.
If analyzing complicated stormsewer system with multiple lateral lines to the trunk line, it is recommended that Stormshed be used to
model the conveyance system. Please contact your region Hydraulic Contact.
WARNING: START YOUR STORMSEWER RUN ON ROW 12. DO NOT SKIP ANY ROWS IN BETWEEN. USE ONE SHEET PER STORMSEWER RUN
Please report any problems to the WSDOT HQ Hydraulics Office.
Project Name: King Co Renton Shop CMF Replacement - Preliminary Conveyance System Sizing Check - TDA P1 (West) and P2 (East) Drainage Systems Designed By:
Project Office:
Design Storm Event = Pavement thickness (ft) =Pipe Thickness (inches) =
1/13/2019 8:58 PM 1 of 1 CMF Conveyance Sizing (version 1).xls PE Conveyance Analysis
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Draft Stormwater Technical Information Report
King County Parks – Renton Shop Central Maintenance Facility Replacement Project
January 15, 2019 | E-1
Appendix E. Preliminary Geotechnical Report
(submitted separately)
Draft Stormwater Technical Information Report
King County Parks – Renton Shop Central Maintenance Facility Replacement Project
E-2 | January 15, 2019
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Draft Stormwater Technical Information Report
King County Parks – Renton Shop Central Maintenance Facility Replacement Project
January 15, 2019 | F-1
Appendix F. Preliminary Site Improvement
Drawings (submitted separately)
Draft Stormwater Technical Information Report
King County Parks – Renton Shop Central Maintenance Facility Replacement Project
F-2 | January 15, 2019
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