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STORM DRAINAGE REPORT
for
US Bank Expansion
2500 East Valley Road
Renton, WA 98057
Owner and Applicant:
Strada da Valle LLC
5050 1st Ave S, Ste 102
Seattle, WA 98134
(425) 204-1045
Architect:
Cornerstone Architectural Group
Attn: Rick Utt
Kenmore, WA 98028
(206) 682-5000
Engineer:
Ted Dimof, PE
License No. 36042
Bush, Roed and Hitchings
2009 Minor Avenue E
Seattle, WA 98102
(206) 323-4144
Date: May 18, 2017
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Table of Contents
1.0 - Project Overview ................................................................................................................................... 3
2.0 – Conditions and Requirements Summary ............................................................................................ 12
3.0 – Offsite Analysis ................................................................................................................................... 14
4.0 – Flow Control, LID, and Water Quality Facility Analysis and Design .................................................... 15
5.0 – Conveyance System Analysis and Design.......................................................................................... 16
6.0 – Special Reports and Studies............................................................................................................... 16
7.0 – Other Permits...................................................................................................................................... 16
8.0 – CSWPP Analysis and Design ............................................................................................................. 17
9.0 – Bond Quantities, Facility Summaries, and Declaration of Covenant ................................................... 19
10.0 – Operations and Maintenance Manual ............................................................................................... 19
List of Figures
Figure 1.1 TIR Worksheet .................................................................................................................. 4
Figure 1.2 Site Location ................................................................................................................... 10
Figure 1.3 USDA Soil Survey Map ................................................................................................... 11
Figure 1.4 Flow Chart for Determining Minimum Requirements ....................................................... 12
Appendices
Appendix A Stormwater Basin Maps
Figure 1 – Site Overview
Figure 2 – Surface Totals
Appendix B TESC Plan Sheet
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1.0 - Project Overview
The US Bank Expansion project at 2500 East Valley Road is located in Renton, WA in parcel
#3023059133, Lot 3, and is proposed to replace an existing parking lot area with 2,670 sf of expanded
building footprint. The parcel is 3.08 acres while the project limits are restricted to an area of
approximately 6,236 sf, including the concrete surface replaced specifically for the water main
relocation
Existing Conditions:
The existing project area drains to catch basins in the private parking lot to the southwest and southeast
of the project area across relatively flat slopes. These catch basins tie into an existing on-site detention
and water quality system that includes Lots 1 and 2 directly to the north. This on-site storm drainage
system connects and drains into a public storm main in East Valley Road from Lot 2. See Figure 1 –
Project Site Overview.
Post-Developed Conditions:
The proposed building addition will have a negligible effect on the existing drainage patterns. Drainage
from the new roof is proposed to tie directly into the detention system via a perforated pipe connection.
The remaining replaced driveway surfaces will drain to their respective, existing on-site catch basins. No
changes will be made to the existing stormwater conveyance system.
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Figure 1.1 – Technical Information Report (TIR) Worksheet, page 1
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Figure 1.1 – Technical Information Report (TIR) Worksheet, page 2
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Figure 1.1– Technical Information Report (TIR) Worksheet, page 3
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Figure 1.1 – Technical Information Report (TIR) Worksheet, page 4
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Figure 1.1 – Technical Information Report (TIR) Worksheet, page 5
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Figure 1.1 – Technical Information Report (TIR) Worksheet, page 6
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Site Location:
The site is located in Renton, WA. The site address is 2500 East Valley Road. See Figure 1.2 below.
Figure 1.2 – Site Location
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Soils:
Per the USDA Soil map (shown below), the entire site lies within the Tu soil category, Tukwila muck.
However, a Geotechnical Report by Terra Associates, Inc., dated April 17, 2017, identifies the soil as 9.5’
of fill over native alluvial soils. It is assumed that the soils on the project site would be considered Till for
any modeling purposes.
Figure 1.3 – USDA Soil Survey Map
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2.0 – Conditions and Requirements Summary
See the Flow Chart for determining type of drainage review below. See Appendix A for the Surface
Totals Exhibit, which illustrates that new + replaced impervious surfaces are between 2,000 and 5,000
square feet.
Figure 1.4 – Flow Chart for Minimum Requirements
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Per Table 1.1.2.A of the Drainage Manual, all minimum requirements must be analyzed for a Full
Drainage Review.
Core Requirements:
1. Discharge at Natural Location:
The project will not affect the existing discharge location. The existing site area surface runoff is
collected in two existing on-site catch basins and eventually routed to the public system in East
Valley Road. The project will not change the existing discharge location.
2. Offsite Analysis:
The project is exempt from CR#2 since less than 2,000 sf of new impervious surface is added and
no drainage pipes are being altered. See Figure 2 – Project Impervious Surface Totals.
3. Flow Control:
The project is exempt from CR#3 since it adds less than 5,000 sf of new and replaced impervious
surface and less than ¾ acres of new pervious surface. See Figure 2 – Project Impervious
Surface Totals.
4. Conveyance System:
The project does not alter or add any storm drainage facility. In addition, changes to the flow
characteristics are negligible, since the net gain in impervious surface is only about 650 sf.
5. Erosion and Sediment Control:
A TESC plan has been developed to contain sediment and prevent erosion.
6. Maintenance and Operations:
N/A
7. Financial Liability:
N/A
8. Water Quality:
The project is exempt from CR#8 since the amount of new and replaced PGIS is less than 5,000
sf. See Figure 3 – Project PGIS Totals
9. On-Site BMPs:
The site has more than 2,000 sf of new and replaced impervious surface and On-Site BMPs are
required to be evaluated to the maximum extent feasible. The perforated pipe connection BMP
has been used for new roof surface. See Appendix B.
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Special Requirements:
1. Other Adopted Area-Specific Requirements:
None.
2. Flood Hazard Area Delineation:
According to FEMA floodplain map number 53033C0979 F, revised May 16, 1995, the project
site lies near, but completely outside a 100-yr Special Flood Hazard Area, Zone AH floodplain
area with an elevation listed at 16’. The existing building and the proposed addition are well
above the floodplain at elevation of ±22’ (which is 6’ above the flooding level).
3. Flood Protection Facilities:
No levees or flood facilities exist on site.
4. Source Control:
Source control BMPs will be implemented for the new structure.
5. Oil Control:
The site is not a high-use site and no additional oil control is required.
6. Aquifer Protection Areas:
The site is not within a groundwater protection area.
3.0 – Offsite Analysis
None required.
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4.0 – Flow Control, LID, and Water Quality Facility Analysis and Design
Existing Site Hydrology (Part A)
The existing site is a small portion of a 3.08 acre parcel. This parcel, in combination with the two parcels
to the north, has an existing on-site stormwater detention and water quality system is tributary to the
public storm drain system in East Valley Road. As shown on Figure 1 of Appendix A, the existing site
drains to two existing catch basins that then tie into the on-site drainage system. Approximately half of
project site area flows to the catch basin to the southeast and the other half flows towards the catch
basin to the southwest.
Developed Site Hydrology (Part B)
The proposed redevelopment of the site makes no changes to the existing site stormwater system and
will make only slight changes to the site’s drainage. The 2,670 sf of additional roof area will be directed
away from the existing catch basins and directed to the on-site detention system via a perforated pipe
connection. This will have no effect on the volume of surface water flowing into the detention system
and will slightly decrease the volume flowing to the existing catch basins.
Performance Standards (Part C)
The project is exempt from both flow control and water quality standards since the total new and
replaced impervious surface is less than 5,000 sf. The project does trigger Minimum Requirement #9 for
on-site BMP requirements, as the new and replaced impervious surface total is greater than 2,000 sf.
Since the project site is less than 22,000 sf, the Small Lot BMP requirements for individual lots apply to
this project. The Small Lot BMP list was evaluated for implementation to the maximum extent feasible.
1. Full dispersion is infeasible because the site is fully developed and there is no feasible location
for full dispersion.
2. Limited infiltration is infeasible due to the soil type and lack of location for an infiltration facility.
The soil type in the area is till, as described in Section 1 of this report.
3. Full infiltration, limited infiltration, rain gardens, bioretention, and permeable pavement are all
infeasible due to the soils and space restrictions.
4. Basic dispersion is infeasible due to site constraints.
5. Reduced Impervious Surface Credit is infeasible due to site restrictions. There is no native
growth on site that would qualify for Native Growth Retention Credit. No existing trees are
eligible for the Tree Retention Credit.
6. New pervious surfaces will be maintained per the soil amendment BMPs as detailed in Appendix
C, Section C.2.13 of the SWDM.
7. The new roof surface will be mitigated with the proposed perforated pipe connection.
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Flow Control System (Part D)
Not required due to new and replaced impervious surfaces less than 5,000 sf.
Water Quality System (Part E)
Not required due to new and replaced pollution generating impervious surfaces less than 5,000 sf.
5.0 – Conveyance System Analysis and Design
There is no change to the existing on-site stormwater system.
6.0 – Special Reports and Studies
1. Geotechnical Report by Terra Associates, Inc., project #T-7638, dated April 17, 2017
2. Critical Areas Determination Report by Wetland Resources, Inc., project #17029, dated May 2017
7.0 – Other Permits
None
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8.0 – CSWPP Analysis and Design
ESC Measures:
The following ESC measures listed in the 2017 Renton SWDM have been evaluated for use on the
proposed site. Each measure is listed and designated as being used or not being used, and, if not being
used, a discussion on why is provided.
1. Clearing Limits
The limits of clearing and surface replacement are designated on the plans and will be clearly
marked prior to the start of construction.
2. Cover Measures
No soils will be left exposed outside the project area. Straw mulch will be used to cover
landscaped areas if necessary.
3. Perimeter Protection
Chain link fencing will be used outside of the site to isolate construction activities from the
public.
4. Traffic Area Stabilization
The area of ground disturbance is not of sufficient size to require any stabilization measures.
5. Sediment Retention
Any construction stormwater drainage will be collected and routed through the onsite
mitigation system, as described in the following two paragraphs.
During the foundation construction phase a sediment trap will be constructed per Section
D.2.1.5.1 of the Renton SWDM. The sediment trap shall initially be located per the TESC Plan
(See Appendix B), and will be relocated as the CSWPP lead determines to work with Contractor
staging the excavation and grading.
Sizing for the sediment trap was determined by the methods outlined in Section D.2.1.5.1 of
Appendix D of the Renton SWDM. The design flow was determined using WWHM 2012 with
0.084 acres of flat parking with a 15-min time step. The resulting 2-year peak runoff is 0.032 CFS
for the site. Using the equation “SA = 2,080 SF x cfs of inflow”, the resulting minimum surface
area is 67 SF.
6. Surface Water Collection
Any construction stormwater drainage will be collected and conveyed to the sediment trap with
ditches and a pump as shown on the TESC Plan.
7. Dewatering Control
It is not anticipated that any dewatering will be required.
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8. Dust Control
Preventative measures to minimize wind transport of soil shall be implemented when a traffic
hazard may be created or when sediment transported by wind is likely to be deposited in water
resources.
9. Flow Control
Flow control will be performed by pumping out the sediment trap and using baker tanks as
necessary.
10. Control Pollutants (also see SWPPS Measures below)
Catch basin inlet protection is specified in the TESC plan to capture any sediment laden runoff
during the construction phase. Equipment used on site will be required to be in good, working
order. In addition, concrete handling, sawcutting and surfacing pollution prevention, and
material delivery and storage containment BMPs will be implemented.
11. Protect Existing and Proposed Stormwater Facilities and On-site BMPs
The contractor will be required to maintain all existing and proposed BMPS on the site until all
soils are stabilized on the site at the end of construction.
12. Maintain Protective BMPs
The contractor will be required to maintain protection measures to ensure continued
performance of their intended function, to prevent adverse impacts to existing BMPs/facilities
and areas of proposed BMPs/facilities, and protect other disturbed areas of the project, if any.
13. Manage the Project
The contractor will be required to manage coordination and timing of site development
activities relative to ESC concerns. Timely inspection, maintenance and update of protective
measures will be provided by the contractor to effectively manage the project and ensure the
success of protective ESC and SWPPS design and implementation.
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9.0 – Bond Quantities, Facility Summaries, and Declaration of Covenant
It is our understanding that there are no requirements for bonding, facility summaries, or a declaration
of covenant for this small redevelopment project.
10.0 – Operations and Maintenance Manual
N/A.
Appendix A
Stormwater Basin Maps
134,074 SQ. FT.
3.0779 ACRES56,508 SQ. FT.
1.2973 ACRES
98102-3513
BUSH, ROED & HITCHINGS, INC.
2009 MINOR AVE. EAST
SEATTLE, Washington
LAND SURVEYORS & CIVIL ENGINEERS
FAX# (206) 323-7135
(206) 323-4144
1-800-935-0508
FIGURE 1 - SITE OVERVIEW
US BANK EXPANSION
US BANK
RENTON KING WASHINGTON
98102-3513
BUSH, ROED & HITCHINGS, INC.
2009 MINOR AVE. EAST
SEATTLE, Washington
LAND SURVEYORS & CIVIL ENGINEERS
FAX# (206) 323-7135
(206) 323-4144
1-800-935-0508
FIGURE 2 - PROJECT IMPERVIOUS SURFACE TOTALS
US BANK EXPANSION
US BANK
RENTON KING WASHINGTON
98102-3513
BUSH, ROED & HITCHINGS, INC.
2009 MINOR AVE. EAST
SEATTLE, Washington
LAND SURVEYORS & CIVIL ENGINEERS
FAX# (206) 323-7135
(206) 323-4144
1-800-935-0508
FIGURE 3 - PROJECT PGIS TOTALS
US BANK EXPANSION
US BANK
RENTON KING WASHINGTON
Appendix B
TESC and Drainage Plan Sheet
5/18/1798102-3513BUSH, ROED & HITCHINGS, INC.2009 MINOR AVE. EASTSEATTLE, WashingtonLAND SURVEYORS & CIVIL ENGINEERSFAX# (206) 323-7135TESC AND DRAINAGE PLAN