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Firestone Complete Auto Care
17808 108th Ave SE
Renton, Washington, 98055
Technical Information Report
Commercial Redevelopment
1505 Westlake Ave. N T 206.522.9510
Suite 305 F 206.522.8344
Seattle, WA 98109 www.pacland.com
Prepared By: Luke Randles, P.E.
Reviewed By: Bill Fortunato, P.E.
September 2016
Firestone Complete Auto Care Technical Information Report Renton, Washington
PACLAND Project #10439013 Page 1
Section Page
Executive Summary ...................................................................................................................................... 2
Section 1- Project Overview ...................................................................................................................... 4
Figure 1 - TIR Worksheet (KCSWDM 2009) ..................................................................................... 4
Site Location ............................................................................................................................................... 9
Drainage Basins, Subbasins, and Site Characteristics ................................................................ 10
Soils ............................................................................................................................................................. 11
Section 2- Conditions and Requirements Summary ...................................................................... 13
Section 3- Off-Site Analysis ..................................................................................................................... 17
Upstream Analysis .................................................................................................................................. 17
Downstream Analysis ............................................................................................................................ 17
Conclusion ................................................................................................................................................. 18
Section 4- Flow Control and Water Quality Facility Analysis and Design ............................... 19
Hydrologic Analysis ............................................................................................................................... 19
Existing Site Hydrology ........................................................................................................................ 19
Developed Site Hydrology .................................................................................................................. 20
Flow Control Analysis ............................................................................................................................ 20
Water Quality System............................................................................................................................ 21
New PGIS Areas ....................................................................................................................................... 21
Section 5- Conveyance System Analysis and Design ..................................................................... 23
Conveyance............................................................................................................................................... 23
100-Year Flood/Overflow Condition ............................................................................................... 23
Appendices: A – Exhibits
B – Plans
C – Design Calculations
D – Operations and Maintenance Manual
E – Bond Quantities Worksheet
F – Department of Ecology Construction Stormwater General Permit
Coverage Letter
Table of Contents
Firestone Complete Auto Care Technical Information Report Renton, Washington
PACLAND Project #10439013 Page 2
Site Location:
The property is located at 17808 108th Ave SE in Renton, Washington. The site is bordered by
108th Ave SE/WA 515 to the west, Jiffy Lube to the north, a vacant commercial building to the
south, and a 109th Ave SE to the east. The site is currently developed as the Skipper’s Seafood
and Chowder House, which has a building footprint of 2,552 square feet, with associated parking
and landscaping. The entire lot is approximately 0.88 acres in size. This project proposes to
demolish the existing restaurant and parking lot, then redevelop the site to become a Firestone
Complete Auto Care.
The project site lies within the Lower Green River Subwatershed, which is part of the
Green/Duwamish Watershed. It is in the City of Renton Black River drainage basin.
The project site is located in the City of Renton Commercial Mixed Use Overlay District
(Community Planning area). The property is zoned CA (commercial arterial).
Design Criteria:
The City of Renton uses the King County Surface Water Management Design Manual
(KCSWDM), 2009 Edition, as adopted by the City of Renton and the City of Renton Amendments
to the King County Surface Water Design Manual, dated February 2010. The existing site is
developed and primarily impervious with the exception of landscape islands and an
undeveloped piece of land between the parking lot and 109th Ave SE. The overall impervious
area will increase about 3,590 SF due to this project, which will require additional detention.
Additional water quality treatment will be provided to meet the requirements of Core
Requirement #8 as the project will increase the pollution generating impervious surface by more
than 5,000 SF.
Table 1
Jurisdictional Requirements
Peak Runoff Control:
Peak Rate Flow Control Standard
Matching Existing Site Conditions
2-year: Match existing site conditions
10-year: Match existing site conditions
100-year: Match existing site conditions
Water Quality:
Enhanced Basic WQ Treatment
Preceding detention
60% of the developed 2-year peak
flow rate
Downstream of detention The full 2-year release rate from
detention facility
Executive Summary
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PACLAND Project #10439013 Page 3
Proposed Drainage System:
This project proposes to utilize a detention vault for storage and modular wetland for water
quality treatment. The proposed grading will send water from the Northeast corner of the site
toward the West side of the site. There is currently a storm pipe that runs west from 109th Ave SE
toward the building. The proposed pipe will move north toward the Northeast corner of the
site. This pipe will convey water toward the existing water structures on the Northwest corner.
Stormwater will also collect into catch basins along the valley on the east and north side of the
building and then be conveyed to the Northwest corner of the site to the Modular Wetland for
water quality treatment. Then the water will be sent to the detention vault for storage. Then the
water will travel to the existing storm structures in the Northwest corner of the site.
Conclusion:
The proposed stormwater management system for this project has been designed in accordance
with regulatory criteria described above and is consistent with sound engineering practice. The
site has been analyzed to determine the requirements for detention and water quality treatment,
and no significant adverse impacts to the stormwater management system are expected as a
result of the proposed development.
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PACLAND Project #10439013 Page 4
Figure 1 - TIR Worksheet (KCSWDM 2009)
Section 1- Project Overview
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PACLAND Project #10439013 Page 5
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Site Location
Figure 2 - Site Location
Location: 17808 108th Ave SE, Renton, WA 98055
Section/Township/Range: NE Quarter of Section 32, Township 23, Range 05
Parcel/Tax Lot(s): 3223059104
Size: 0.88 acres
City, County, State: Renton, King County, Washington
Governing Agency: City of Renton
Design Criteria: 2009 King County Surface Water Design Manual (KCSWDM), and the City of
Renton Amendments to the KCSWDM (February 2010)
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PACLAND Project #10439013 Page 10
Drainage Basins, Subbasins, and Site Characteristics
Drainage Basin
The project site is located in the Lower Green River Subwatershed, which is part of the
Green/Duwamish Watershed. It is in the City of Renton Black River drainage basin.
Existing Subbasins
The design of the existing site used a single basin with an area of 0.88 acres. The southeast
portion of the site of the highest in elevation at 410’. The area gradually sloped west until the
finished floor of the building about 402’. The northeast side of the site starts at an elevation of
408’ and slopes downward toward the west side of the site where it has an elevation of 400’.
This whole subbasin creates a drainage system that allows water to flow from east to west. The
Northwest corner of the site has a catch basin that conveyed water into the municipal
stormwater system. There is another discharge at the Southwest corner of the site due to the
valley that runs east to west along the southern part of the site.
Proposed Subbasins
The proposed storm drainage system will be composed of the same approximate subbasins as
the existing. See Appendix A Exhibit B- Proposed Subbasin, detailing the proposed subbasins.
As shown in Table 2 – Site Areas, the impervious area is decreasing as a result of this
development. Additional landscaping and a reduction in building square footage will allow for
an increase in pervious areas. The areas below are based on the 12.28 acre project site since we
are not proposing changes to the bypass, offsite wetland mitigation area, offsite areas, or the
area of Lots 4 and 6 of the Northern Railroad BSP No. 014-92.
Table 2 – Site Areas
Existing Area (SF) Proposed Area (SF)
Surface
Roof 2552 7700
Landscaping
(Pervious)
15,228 11,095
Pavement
(PGIS)
18,085 13,141
Wood Deck 522 0
Concrete 1,756 6,171
Total 38,107 38,107
Site Characteristics
The property is located at 17808 108th Ave SE in Renton, Washington. The site is bordered by
108th Ave SE/WA 515 to the west, Jiffy Lube to the north, a vacant commercial building to the
south, and a 109th Ave SE to the east. The site is currently developed as the Skipper’s Seafood
and Chowder House, which has a building footprint of 2,552 square feet, with associated parking
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PACLAND Project #10439013 Page 11
and landscaping. The entire lot is approximately 0.88 acres in size. This project proposes to
demolish the existing restaurant and parking lot, then redevelop the site to become a Firestone
Complete Auto Care.
The proposed project will include the construction of an approximately 7,700 SF Firestone
Complete Autocare building. The overall paved area will be approximately 0.30 AC. The change
in impervious surfaces (roof and pavement) is about 0.10 AC, therefore the pollution generated
by impervious surface will be increased. Water quality treatment will be provided for an area
equivalent to the pollution generating impervious surface on site.
Soils
Websoil Survey
Figure 3 - Site Soils (USDA Web Soil Survey Map)
The site is mapped as Alderwood gravelly sandy loam 0 to 8 percent slopes (AgB) and
Alderwood gravelly sandy loam 8 to 15 percent slopes (AgC) according to the USDA Natural
Resource Conservation Service, Web Soil Survey for King County Area, Washington.
Geotechnical Report
The following information was gathered from a report created by Zipper Geo Associates, LLC. on
August 29, 2016. 4 feet deep under the surface, ZGA’s infiltration test recorded that the soil
observed was glacial till with medium dense, light brown with some oxidation, sandy loam with
gravel. Underneath this soil was unweathered glacial till consisting of dense, tan, sandy loam
with gravel. The bottom of the infiltration test was at 8 feet. The report showed dense, tan,
unweathered glacial till at this depth.
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PACLAND Project #10439013 Page 12
No groundwater was observed during the infiltration test. There were also no signs that the
seasonal groundwater may be higher than when observed.
ZGA performed a single small-scale Pilot Infiltration Test per standard of the Storm Water
Manual. The results of the test were that the infiltration test was approximately 0.21
inches/hour. According to Table 3.7 in the City of Renton’s Amendments to the King County
Storm Water Design Manual, a correction factor of 4 must be used to derive the design
infiltration rate from the observed short term infiltration rate. After applying this correction
factor, the site has a design infiltration rate of 0.05 in/hr.
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PACLAND Project #10439013 Page 13
As required by the 2009 King County Surface Water Design Manual (KCSWDM) and City of
Renton Amendment, this project is subject to a full drainage review. Therefore, the storm
drainage design for this project is required to comply with all eight (8) Core Requirements, and
six (6) Special Requirements. The requirements have been met as follows:
Core Requirement #1: Discharge at Natural Location
All surface and storm water runoff from a project must be discharged at the natural location so
as not to be diverted onto or away from downstream properties. The manner in which runoff is
discharged from the project site must not create a significant adverse impact to downhill
properties or drainage systems.
Response: Onsite runoff will be collected, conveyed and, when necessary, treated. All onsite runoff
is subsequently conveyed to the City of Renton stormwater system. The city system discharges
northwest of the site into Panther Creek. No downstream impacts are anticipated as a result of the
proposed improvements as the impervious area will remain approximately the same.
Core Requirement #2: Off-site Analysis
All proposed projects must submit an offsite analysis report that assesses potential offsite
drainage and water quality impacts associated with development of the project site and propose
appropriate mitigation of those impacts. The initial permit submittal shall include, at minimum, a
Level 2 downstream analysis.
Response: See Section 3 of this report for a complete off-site analysis. A Level 2 downstream
analysis will be submitted upon civil plan submittal.
Core Requirement #3: Flow Control
All proposed projects, including redevelopment projects, must provide onsite flow control
facilities or flow control BMPs or both to mitigate the impacts of storm and surface runoff
generated by new impervious surface, new pervious surface, and replaced impervious surface
targeted for flow mitigation.
Response: (Waiting on KCRTS)
Per the exceptions listed in section 1.2.3.1-A of the City of Renton Amendment to the KCSWDM the
project is exempt from flow control requirements as it doesn’t increase the 100-year peak flow and
is not expected to significantly impact a critical area, or cause severe flooding or erosion problems.
The proposed 12.28 acre site generates 4.84 cfs, a 0.17 cfs decrease in the 100-year peak flow
rate from the existing site conditions. Therefore, additional flow control facilities, beyond the
existing stormwater ponds and flow control structure, are not proposed as part of this project. A
Section 2- Conditions and Requirements
Summary
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PACLAND Project #10439013 Page 14
detailed summary and analysis of the existing and proposed conditions is provided in Section 4 of
this report.
Core Requirement #4: Conveyance System
All engineered conveyance system elements for proposed projects must be analyzed, designed,
and constructed to provide a minimum level of protection against overtopping, flooding,
erosion, and structural failure.
Response: Portions of the existing conveyance system will be reused as part of this project with
additional conveyance added to accommodate the new building configuration and site layout. The
proposed conveyance system has been designed to convey the 100-year peak flow.
Core Requirement #5: Erosion and Sediment Control
All proposed projects that will clear, grade, or otherwise disturb the site must provide erosion
and sediment controls to prevent, to the maximum extent practicable, the transport of sediment
from the project site to downstream drainage facilities, water resources, and adjacent properties.
Both temporary and permanent ESC measures shall be implemented.
Response: Erosion and sediment control requirements will be an integral part of the project
construction documents. These measures will include methods to reduce erosion of onsite site soils
and to prevent sediments from inadvertently leaving the project site. Additionally, the ESC
measures will prevent sediment-laden discharge from entering the wetland or existing stormwater
water quality or flow control facilities.
Core Requirement #6: Maintenance and Operations
Maintenance and operation of all drainage facilities is the responsibility of the property owner,
except those facilities for which the City of Renton assumes maintenance and operation, and
must be maintained and operated in accordance with King County or other maintenance
standards as approved by the City of Renton.
Response: An Operations and Maintenance Manual is included in this report- see Section 10.
Core Requirement #7: Financial Guarantees and Liability
In accordance with RMC 4-6-030J, RDSD shall require all persons constructing any surface water
facilities (including flow control/water quality facilities, conveyance systems, erosion control, and
road drainage), to post with the City of Renton a bond, assignment of funds or certified check.
The applicant must also maintain liability insurance.
Response: See Section 9- Bond Quantities, Facility Summaries, and Declaration of Covenant. The
Site Improvement Bond Quantity Worksheet and Declarations of Covenants will be submitted
upon approval of the Building Permit plans.
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PACLAND Project #10439013 Page 15
Core Requirement #8: Water Quality
All proposed projects, including redevelopment projects, must provide water quality (WQ)
facilities to treat the runoff from those new and replaced pollution-generating impervious
surfaces and new pollution-generating pervious surfaces targeted for treatment.
Response: The proposed project improvements will decrease the pollution generating impervious
surface (PGIS) by 0.11 AC. The site currently has accommodation for 0.42 AC of PGIS. Enhanced
Basic Treatment is required if more than 50% of the runoff that drains to the proposed treatment
facility is from commercial land use. Additional Enhanced Basic Water Quality treatment will be
provided for the increase in impervious surfaces on site. Additionally, an oil/water separator, which
will discharge to the sanitary sewer system, will be provided for discharges from the building. A
detailed summary and analysis of the water quality basin and design is provided in Section 4 of
this report.
Special Requirement #1: Other Adopted Area-Specific Requirements
The City of Renton may apply requirements for controlling drainage on an area-specific basis.
Potential other adopted area-specific requirements may include: Master Drainage Plans, Basin
Plans, Stormwater Compliance Plans, etc.
Response: The project site is within Washington State Water Resource Inventory Area 9:
Green/Duwamish and Central Puget Sound Watershed Salmon Habitat Recovery. However, the
proposed project will have no effect on any salmon habitats. The project site does not lie within
any City of Renton Master Drainage or Basin Plans.
Special Requirement #2: Flood Hazard Area Delineation
If a proposed project contains or is adjacent to a flood hazard area as determined by the Renton
Department of Storm Drainage, the project must determine those components that are
applicable and delineate them on the project’s site improvement plans and recorded maps.
Response: The project site does not lie within or adjacent to a City of Renton Flood Hazard Area
(determined by FEMA FIRM Panel 53033C0979F dated May 16, 1995) and therefore does not need
to apply the provisions of this requirement.
Special Requirement #3: Flood Protection Facilities
Proper analysis, design, and construction are necessary to protect against the potentially
catastrophic consequences if flood protection facilities such as levees and revetments should
fail.
Response: The proposed project will not rely on an existing flood protection facility, or modify or
construct a new flood protection facility.
Special Requirement #4: Source Control
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PACLAND Project #10439013 Page 16
If a proposed project requires a commercial building or commercial site development permit
then the water quality source controls applicable to the proposed project shall be applied in
accordance with the King County Stormwater Pollution Prevention Manual and Renton Municipal
Code IV.
Response: Water quality source controls will be applied in accordance with the KCSWDM and
Renton Municipal Code IV. A pollution prevention plan has been included in section 8 of this
report.
Special Requirement #5: Oil Control
Projects proposing to develop or redevelop a high-use site must provide oil control in addition
to other water quality controls required.
Response: High use sites area defined as a commercial or industrial site that (1) has an expected
average daily traffic count equal to or greater than 100 vehicles/1,000 SF of gross building area:
(2) is subject to petroleum storage in excess of 1,500 gallons per year; (3) is subject to use, storage,
or maintenance of a fleet of 25 or more diesel vehicles. The proposed development does not exceed
any of these thresholds, and is therefore not required to provide oil control.
Special Requirement #6: Aquifer Protection Area
If a proposed project is located within the Aquifer Protection Area as identified in the RMC 4-3-
050, this special requirement requires the project to determine those components that are
applicable and delineate them on the project’s site improvement plans.
Response: The project is not located within an Aquifer Protection Area, and therefore this
requirement does not apply.
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PACLAND Project #10439013 Page 17
Upstream Analysis
The municipal storm system coming from 109th Ave SE ties into the existing private storm
system on the East side of the site. There is minimal tributary area attributes water to the site.
Stormwater runoff flows from the nearby residential streets and is guided by curbs into catch
basins before it reaches this site.
Downstream Analysis
After the runoff passes through the existing stormwater detention/treatment facilities, runoff
enters the municipal stormwater system at 108th Ave SE. After crossing over 108th Ave SE, the
system travels northwest about 2500 feet until discharge into Panther Creek. As discussed
earlier in the report, the storm runoff leaves the site at the northwest corner and enters into the
Renton Municipal storm system. The system runs underneath the Fred Meyer strip mall and
across SE Carr Rd until feeding into Panther Creek. A map of the downstream analysis can be
seen in Figure 4.
Figure 4 - Downstream Area (Renton COR Maps)
Section 3- Off-Site Analysis
DISCHARGE
POINT
PROJECT
SITE
POINT OF
ENTRY TO CITY
OF RENTON
STORM SYSTEM
PANTHER
CREEK
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PACLAND Project #10439013 Page 18
Conclusion
The existing downstream stormwater facilities have been analyzed and after discussions with the
City Engineer, as long as the project site does not increase the overall impervious area from its
existing conditions, it is expected that there will be no adverse impacts to the downstream
facilities because the developed peak flow rate leaving the developed site will be less than the
existing peak flow rate. See Section 4 for further explanation.
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PACLAND Project #10439013 Page 19
The City of Renton Amendment to the KCSWDM applies flow control standards based on
geographic areas as determined by the Flow Control Application Map. The project site lies
within a Conservation Flow Control Area. This requires a level 2 downstream analysis. This area
requires peak runoff control within the Flow Control Duration Standard Matching Existing Site
Conditions area such that it matches the flow duration of predeveloped rates for the existing
site conditions over the range of flows extending from 50% of 2-year up to the full 50-year flow.
This matches the flow duration of predeveloped rates for the existing site conditions over the
range of flows extending from 50% of 2-year up to the full 50-year flow.
Hydrologic Analysis
The existing and proposed site conditions were evaluated using both the King County Runoff
Time Series (KCRTS) The detailed KCRTS output has been included in Appendix C – Design
Calculations.
The historic 1-hour duration in the Sea-Tac rainfall region (location scale factor ST-1.0) was used
to model runoff in KCRTS.
Existing Site Hydrology
The existing site includes a storm drainage system designed to collect storm water at
strategically placed catch basins throughout the site. The storm water is then conveyed through
underground pipes to the northwest corner of the site where it ties into the Renton Municipal
System. The municipal stormwater system routes to a discharge point of Panther Creek across
SE Carr Rd. The existing detention basin was designed to release flows at or below the pre-
developed rates for the 2, 10, and 100 year storms. The pre-developed conditions and existing
peak runoff rates for the project site area are shown in Tables 4 and 5 below. Existing peak
runoff rates were determined using the King County Runoff Time Series modeling software and
the calculations can be found in Appendix C.
Table 4
Pre-Developed (Existing)
Conditions
Area Condition
7.94 AC Pavement (PGIS)
2.74 AC Landscape/Wetland
1.42 AC Roof
Table 5
Existing Peak Runoff Rate
Event Rate (cfs)
Section 4- Flow Control and Water Quality Facility Analysis
and Design
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PACLAND Project #10439013 Page 20
2-year 2.54
10-year 3.03
100-year 5.01
Developed Site Hydrology
The proposed project will have similar hydrology to the existing site. It is anticipated that the
existing systems (conveyance, detention, and treatment) will be utilized as the overall site
hydrology and division of subbasins will remain approximately the same. The amount of
pervious area is increasing due to a reduction in building size and additional landscaping,
however the site PGIS will be increased as a result of the decrease in building size. The post-
developed conditions and un-detained peak runoff rates for the entire attributed basin area
(12.28 acres) are shown in Tables 6 and 7 below. Developed peak runoff rates were determined
using the King County Runoff Time Series modeling software and the calculations can be found
in Appendix C.
Table 6
Post-Developed Conditions
Area Condition
8.22 AC Pavement (PGIS)
3.60 AC Landscape/Wetland
0.46 AC Roof
Table 7
Developed Peak Runoff Rate
Event Rate (cfs)
2-year 2.43
10-year 2.91
100-year 4.84
Flow Control Analysis
The post developed 100-year peak runoff rate for the overall site decreases by 0.17 cfs from the
existing condition. Because the project is located in the Peak Rate Flow Control Standard area
and does not increase its developed 100-year peak runoff rate, any additional flow control
facility requirement is waived for this project.
The existing flow control facilities consist of the following structures inside of a 54-inch diameter
catch basin manhole; a 1-inch diameter orifice with an outlet elevation of 10.87, a 3.5-inch
diameter orifice with an outlet elevation of 15.00, a 6-inch diameter elbow with an outlet
elevation of 15.50, and a 15-inch diameter restrictor with an overflow elevation of 16.50. The
control structure discharges to a 15-inch storm drain pipe before connecting into the Renton
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PACLAND Project #10439013 Page 21
Municipal storm system. See Appendix B for the Act III Theater Drainage Report, which includes
illustrations and calculations for the existing flow control system.
Water Quality System
The proposed redevelopment includes demolition of the existing theater; construction of the
sales, service, car wash, and presentation buildings, reconfigurations of landscape islands and
repaving of the existing parking area. The roofs of the proposed buildings will be considered
non pollution-generating impervious surfaces (NPGIS). While the overall impervious area of the
site will be reduced as part of this project, the amount of pollution-generating impervious
surfaces (PGIS) will be increasing since the existing building footprint will be replaced with new
PGIS.
There are two existing grass-lined biofiltration swales which discharge to three water quality
ponds in series. The swales and water quality ponds were sized for the existing impervious area,
as detailed by the drainage report by Horton Davis and Associates. The project will add 0.28 AC
of new PGIS. This is more than 5,000 SF of new PGIS; therefore additional water quality
treatment will be provided.
Two Modular Wetland Stormwater Biofiltration Systems are proposed to meet the Enhanced
Basic Water requirement in King County Surface Water Design Manual. The Enhanced basic
treatment will be provided for the increased PGIS.
New PGIS Areas
The new PGIS is a result of the revisions to the site layout and the reduced building size. It isn’t
possible to collect the exact area of new PGIS however the majority of the new PGIS, located
within the existing building footprint, will be treated. There are two Water Quality Basins within
the proposed vehicle storage area and will be greater in size than the increase in the new PGIS.
The total area in the proposed Water Quality Basins is 1.14 AC. Exhibit 3 - Water Quality Basin in
Appendix A depicts the area to be treated. Tables 8 and 9, below, contain the developed
conditions of each treatment basins as well as the water quality design flow rate (60% of the
developed 2-year peak flow rate). This water quality design flow rate was provided to Modular
Wetlands in order for them to size the proposed treatment facilities. Sizing criteria and design of
the Modular Wetlands structures is provided in Appendix C.
Table 8
Water Quality Basins
Basin Area Condition
A 0.68 AC Pavement (PGIS)
0 AC Landscape/Wetland
0 AC Roof
B 0.46 AC Pavement (PGIS)
0 AC Landscape/Wetland
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PACLAND Project #10439013 Page 22
0 AC Roof
Table 9
Water Quality Flow Rates and Facility Sizing
Basin Event Rate (cfs) MWS-L-4-8-V
(Structure 21)
Treatment Flow
Rate (cfs)
MWS-L-4-6-V
(Structure 26)
Treatment Flow
Rate (cfs)
A 2-year 0.17
60% of 2-year 0.10 0.102
B 2-year 0.12
60% of 2-year 0.07 0.07
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Conveyance
Per the 2009 King County Surface Water Design Manual, Section 4.2.1.2, the on-site stormwater
conveyance can be calculated based on gravity flow analysis of the piping network. Peak run-off
associated with and up to a 25-year storm event has been determined to be adequate. Uniform
flow analysis utilizing Manning’s equation, shown below, was employed with a Manning’s
Roughness Coefficient (n) of 0.012.
Manning’s equation - Q=n49.1 xAxR2/3xS1/2
With: Q = Flow (CFS)
n = Manning’s Roughness Coefficient (0.012)
A = Flow Area (SF)
R = Hydraulic Radius = Area /Wetted Perimeter (LF)
S = Slope of the pipe (ft/ft)
Based on the revised basin areas and existing pipe sizes, the existing conveyance system is
adequate for the 25-year storm event. All new conveyance pipes will also be designed to convey
the 25-year storm event. Additionally, the overflow from a 100-year storm event will not create
or aggravate a severe flooding problem or severe erosion problem. See Appendix C for
conveyance design calculations.
100-Year Flood/Overflow Condition
Review of the current FEMA FIRM maps (Panels 0978F, 0979 F) indicates that the project site lies
within the Zone X, which is determined to be outside of the 100-year flood plain. If the existing
storm system were to experience a major storm event, the stormwater detention area would
overflow in to the rear access drive, and along the road westerly towards Lind Ave SW.
The stormwater system for this project has been designed to address the storm events in
accordance with design criteria described previously. In the event of a larger storm, it is unlikely
that the system would fail. Based on a review of the site and immediate surroundings, the
overflow of the stormwater conveyance system would allow surface water to sheet flow to the
public storm system in Lind Avenue.
Section 5- Conveyance System Analysis and Design
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The following Special Reports and Studies were used or have been completed for this project:
Drainage Calculations for Act III Theaters, City of Renton, Washington- dated August 8,
1996 by Horton Dennis & Associates Inc.
Report for Detailed Wetland Mitigation Plan, presented to Act III Theaters, City of Renton,
Washington- dated September 16, 1996 by W & H Pacific.
Wetland Study – dated approximately December 1991 by David Evans and Associates,
Inc.
Geotechnical Investigation- by Zipper Geo Associates
FEMA FIRM Panels 0978F and 0979F dated May 16, 1995
Wetland Study - by H & S Consultants
Section 6- Special Reports and Studies
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PACLAND Project #10439013 Page 25
The following governmental approvals or permits will likely be required for this project: City of Renton SEPA Determination City of Renton Site Plan Review City of Renton Building Permit City of Renton Construction Permit City of Renton Demolition Permit Washington State Department of Ecology, NOI Coverage under the NPDES Permit. A copy of the Permit Coverage Letter is provided in Appendix F. These permits will require approval by the City of Renton Planning Division or the Department of Ecology.
Section 7- Other Permits
Firestone Complete Auto Care Technical Information Report Renton, Washington
PACLAND Project #10439013 Page 26
All erosion and sediment control measures shall be governed by the requirements of the City of
Renton and the Washington State Department of Ecology. A temporary erosion and
sedimentation control plan will be prepared to assist the contractor in complying with these
requirements. The Erosion and Sediment Control (ESC) plan will be included with the
construction plans.
1. Erosion Risk Assessment
The degree of erosion risk on the proposed project site is minimal. The following factors
contribute to a low degree of erosion risk:
Slope across the site is minimal. Runoff will not travel at high velocities across the site
and, therefore, will not cause noticeable erosion impacts.
The site consists primarily of impervious surfaces.
2. Construction Sequence and Procedure
The proposed development will include an erosion/sedimentation control plan designed to
prevent sediment-laden run-off from leaving the site during construction. The erosion potential
of the site is influenced by four major factors: soil characteristics, vegetative cover, topography,
and climate. Erosion/sedimentation control is achieved by a combination of structural
measures, cover measures, and construction practices that are tailored to fit the specific site.
Prior to the start of any grading activity upon the site, all erosion control measures, including
stabilized construction entrances, shall be installed in accordance with the construction
documents.
The best construction practice will be employed to properly clear and grade the site and to
schedule construction activities. The planned construction sequence for the construction of the
site is as follows:
1. Attend a pre-construction meeting with the City of Renton.
2. Install temporary erosion control features.
3. Demolish existing structure(s).
4. Clear and grub expansion area.
5. Grade site.
6. Construct buildings.
7. Pave site and install landscaping.
8. Remove temporary erosion control features once site is fully stabilized.
3. Trapping Sediment
Section 8- CSWPPP Analysis and Design
Firestone Complete Auto Care Technical Information Report Renton, Washington
PACLAND Project #10439013 Page 27
Structural control measures will be used to reduce erosion and retain sediment on the
construction site. The control measures will be selected to fit specific site and seasonal
conditions.
The following structural items will be used to control erosion and sedimentation processes:
Stabilized construction entrances
Filter fabric fences
Catch Basin Inlet Sediment Protection
Proper Cover measures
Weekly inspection of the erosion control measures will be required during construction. Any
sediment buildup shall be removed and disposed of off-site.
A stabilized construction entrance will be installed at the site entrance to avoid vehicle tracking
off mud off-site. The entrances are a minimum requirement and may be supplemented if
tracking of mud onto public streets becomes excessive. In the event that mud is tracked off site,
it shall be swept up and disposed of off site on a daily basis. Depending on the amount of
tracked mud, a vehicle road sweeper may be required.
Because vegetative cover is the most important form of erosion control, construction practices
must adhere to stringent cover requirements. More specifically, the contractor will not be allowed
to leave soils open for more than 14 days and, in some cases, immediate seeding will be required.
4. Wet Season TESC Operating Plan
Work between October 1st and April 30th must adhere to the Wet Season Special Provisions
noted in the 2009 KCSWDM.
Firestone Complete Auto Care Technical Information Report Renton, Washington
PACLAND Project #10439013 Page 28
The following items will be submitted upon application for the civil permits:
Declaration of Covenant for Privately Maintained Flow Control BMPs
Declaration of Covenant for Privately Maintained Flow Control and WQ Facilities
See Appendix E for a copy of the Bond Quantities Worksheet
Section 9- Bond Quantities, Facility Summaries, and Declaration of
Covenant
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PACLAND Project #10439013 Page 29
A manual detailing the operations and maintenance for all privately-maintained flow control and
water quality facilities has been prepared and can be found in Appendix D. This manual will also
include Appendix A of the KCSWDM (Maintenance Requirements for Flow Control, Conveyance,
and WQ Facilities).
Section 10- Operations and Maintenance Manual
Firestone Complete Auto Care Technical Information Report Renton, Washington
PACLAND Project #10507003
Appendix A – Exhibits
Firestone Complete Auto Care Technical Information Report Renton, Washington
PACLAND Project #10507003
EXHIBIT A – EXISTING SUBBASIN
Firestone Complete Auto Care Technical Information Report Renton, Washington
PACLAND Project #10507003
Firestone Complete Auto Care Technical Information Report Renton, Washington
PACLAND Project #10507003
EXHIBIT B – PROPOSED SUBBASIN
Firestone Complete Auto Care Technical Information Report Renton, Washington
PACLAND Project #10507003
Firestone Complete Auto Care Technical Information Report Renton, Washington
PACLAND Project #10507003
Appendix C – Design Calculations
Firestone Complete Auto Care Technical Information Report Renton, Washington
PACLAND Project #10507003
PRE-DEVELOPED CONDITIONS
PRE-DEVELOPED PEAK FLOW RATES
Firestone Complete Auto Care Technical Information Report Renton, Washington
PACLAND Project #10507003
DEVELOPED CONDITIONS
DEVELOPED PEAK FLOW RATES
Firestone Complete Auto Care Technical Information Report Renton, Washington
PACLAND Project #10507003
WATER QUALITY BASIN A CONDITIONS
WATER QUALITY BASIN A PEAK FLOW RATES
Firestone Complete Auto Care Technical Information Report Renton, Washington
PACLAND Project #10507003
MODULAR WETLANDS SIZING CRITERIA FOR STRUCTURE 21
Firestone Complete Auto Care Technical Information Report Renton, Washington
PACLAND Project #10507003
WATER QUALITY BASIN B CONDITIONS
WATER QUALITY BASIN B PEAK FLOW RATES
Firestone Complete Auto Care Technical Information Report Renton, Washington
PACLAND Project #10507003
MODULAR WETLANDS SIZING CRITERIA FOR STRUCTURE 26
Firestone Complete Auto Care Technical Information Report Renton, Washington
PACLAND Project #10507003
Conveyance Design Calculations
Manning’s equation: Q=n49.1 xAxR2/3xS1/2
With: Q = Flow (CFS)
n = Manning’s Roughness Coefficient (0.012)
A = Flow Area (SF)
R = Hydraulic Radius = Area /Wetted Perimeter (LF)
S = Slope of the pipe (ft/ft)
12” Pipe @ 0.5% slope:
Q=n49.1 xAxR2/3xS1/2 = 1.00 CFS
n = 0.012
A = 0.771 (SF)
R = 0.286 @ 95% full
S = 0.005
Firestone Complete Auto Care Technical Information Report Renton, Washington
PACLAND Project #10507003
Appendix D – Operations and Maintenance Manual
Firestone Complete Auto Care Technical Information Report Renton, Washington
PACLAND Project #10507003
Maintain Stormwater Facilities
The owner or operator of the project shall be responsible for maintaining the stormwater
facilities in accordance with local requirements. Proper maintenance is important for adequate
functioning of the stormwater facilities. The following maintenance program is recommended
for this project:
King County Surface Water Design Manual
Firestone Complete Auto Care Technical Information Report Renton, Washington
PACLAND Project #10507003
Firestone Complete Auto Care Technical Information Report Renton, Washington
PACLAND Project #10507003
Firestone Complete Auto Care Technical Information Report Renton, Washington
PACLAND Project #10507003
Firestone Complete Auto Care Technical Information Report Renton, Washington
PACLAND Project #10507003
Firestone Complete Auto Care Technical Information Report Renton, Washington
PACLAND Project #10507003
Firestone Complete Auto Care Technical Information Report Renton, Washington
PACLAND Project #10507003
Firestone Complete Auto Care Technical Information Report Renton, Washington
PACLAND Project #10507003
Firestone Complete Auto Care Technical Information Report Renton, Washington
PACLAND Project #10507003
Firestone Complete Auto Care Technical Information Report Renton, Washington
PACLAND Project #10507003
Firestone Complete Auto Care Technical Information Report Renton, Washington
PACLAND Project #10507003
Firestone Complete Auto Care Technical Information Report Renton, Washington
PACLAND Project #10507003
Firestone Complete Auto Care Technical Information Report Renton, Washington
PACLAND Project #10507003
Firestone Complete Auto Care Technical Information Report Renton, Washington
PACLAND Project #10507003
Firestone Complete Auto Care Technical Information Report Renton, Washington
PACLAND Project #10507003
Firestone Complete Auto Care Technical Information Report Renton, Washington
PACLAND Project #10507003
Firestone Complete Auto Care Technical Information Report Renton, Washington
PACLAND Project #10507003
Firestone Complete Auto Care Technical Information Report Renton, Washington
PACLAND Project #10507003
Firestone Complete Auto Care Technical Information Report Renton, Washington
PACLAND Project #10507003
Firestone Complete Auto Care Technical Information Report Renton, Washington
PACLAND Project #10507003
Firestone Complete Auto Care Technical Information Report Renton, Washington
PACLAND Project #10507003
Firestone Complete Auto Care Technical Information Report Renton, Washington
PACLAND Project #10507003
Firestone Complete Auto Care Technical Information Report Renton, Washington
PACLAND Project #10507003
Firestone Complete Auto Care Technical Information Report Renton, Washington
PACLAND Project #10507003
Firestone Complete Auto Care Technical Information Report Renton, Washington
PACLAND Project #10507003
Firestone Complete Auto Care Technical Information Report Renton, Washington
PACLAND Project #10507003
Firestone Complete Auto Care Technical Information Report Renton, Washington
PACLAND Project #10507003
Appendix E – Bond Quantities Worksheet