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STORM DRAINAGE REPORT
for
Starbucks at Airport Plaza
95 Airport Way
Renton, WA 98055
Applicant:
Burkheimer Family LLC
Engineer:
Ted Dimof, PE
License No. 36042
Bush, Roed and Hitchings
2009 Minor Avenue E
Seattle, WA 98102
(206) 323-4144
Date: July 5, 2016
REVISED January 4, 2017
REVISED June 5, 2017
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Table of Contents
1.0 Project Overview .................................................................................................................................... 3
2.0 Conditions and Requirements Summary............................................................................................... 9
3.0 Offsite Analysis ..................................................................................................................................... 11
3.1 Upstream Analysis ............................................................................................................................................... 11
3.2 Downstream Analysis .......................................................................................................................................... 12
4.0 Flow Control and Water Quality Facility Analysis and Design ........................................................... 13
4.1 Existing Site Hydrology (Part A) .......................................................................................................................... 13
4.2 Developed Site Hydrology (Part B) ..................................................................................................................... 13
4.3 Performance Standards (Part C) ......................................................................................................................... 14
4.4 Flow Control System (Part D) .............................................................................................................................. 14
4.5 Water Quality System (Part E) ............................................................................................................................ 14
5.0 Conveyance System Analysis and Design .......................................................................................... 15
6.0 Special Reports and Studies ................................................................................................................ 15
7.0 Other Permits ........................................................................................................................................ 15
8.0 CSWPP Analysis and Design .............................................................................................................. 15
9.0 Bond Quantities, Facility Summaries, and Declaration of Covenant ................................................. 15
10.0 Operations and Maintenance Manual.................................................................................................. 15
11.0 Appendix ............................................................................................................................................... 15
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1.0 - Project Overview
The Renton Starbucks Project at 95 Airport Way, located in King County, parcel numbers 182305-9245
and 000720-0193, proposes to construct a retail building containing a total of 2,097 sf of commercial
use. The site is 0.60 acres including 0.59 acres on property and 0.01 acres of Right-of-Way disturbance.
The total site disturbance will be 0.45 acres (19,602.00 SF). Thirty-six (36) off-street surface parking
spaces, including one (1) handicapped space, will be added to the site.
Existing Conditions:
The site is currently mostly covered by asphalt paved surfaces with perimeter landscaping. The drainage
sheet flows to a ditch that conveys the drainage to the offsite City storm system. The existing surface
areas on site are as follows:
Total Site Area of Disturbance: 19,602.00 SF (0.45 AC)
Non-PGIS: 435.60 SF (0.01 AC)
PGIS: 15,681.60 SF (0.36 AC)
Pervious: 3,484.80 SF (0.08 AC)
See Figure 8 – Existing Stormwater Exhibit
Post-Developed Conditions:
The project will be adding landscape area and reducing the impervious surfacing area of the site. The
amount of pollution generating impervious surfacing will also be reduced. The proposed surface areas
are as follows:
Total Site Area of Disturbance: 19,602.00 SF (0.45 AC)
Non-PGIS: 4,791.60 SF (0.11 AC)
PGIS: 9,583.20 SF (0.22 AC)
Pervious: 5,227.20 SF (0.12 AC)
See Figure 9 – Proposed Stormwater Exhibit
The TIR Worksheet for the project is included as Figure 1.1 on the following pages.
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Site Location:
The site is located in Renton in King County at the corner of Rainier Avenue South and South Tobin
Street. The site address will be 95 Airport Way. See Figure 1.2 below.
Figure 1.2 – Site Location
2.0 – Conditions and Requirements Summary
Per Figure 1.1.2.A, Flow Chart for Determining Type of Drainage Review Required (see Figure 2 in the
Appendix), this project is required to undergo a full drainage review. Per Table 1.1.2.A, Requirements
Applied Under Each Drainage Review Type (see Figure 3 in the Appendix), this project is required to
meet Core Requirements #1 through #8 and Special Requirements #1 through #6 of the 2009 Surface
Water Design Manual as Amended by the City of Renton unless specifically precluded or exempted by
this specific project.
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Per Reference 11-A, Flow Control Applications Map (see Figure 4 in the Appendix), the site is required to
meet the Peak Rate Flow Control Standard (Existing Site Conditions). This means that the site in the
redeveloped condition must at least match the existing site conditions 2, 10 and 100 year peak rate
runoff flow rates (see Figure 5 in the Appendix).
Core Requirements:
1. Discharge at Natural Location:
The majority of the site is covered with an existing asphalt paved parking lot with landscaping at
the west and south edges. The site drains to a private storm water ditch along the northern
frontage of S. Tobin Street. The ditch outlets into the public storm drain in Lake Avenue S.
2. Offsite Analysis:
A Level 1 Offsite Analysis was conducted. This analysis is detailed in Section 3.0 of this report.
3. Flow Control:
The site falls within the City’s peak rate flow control standard (existing site conditions). Per
figure 1.1.2.A of the 2009 City of Renton Surface Water Design Manual Amendment, a Full
Drainage Review is required. Since the site is under the peak flow control and is subject to
existing site conditions, the site is reducing the amount of impervious surfacing from existing
conditions, and the peak rates are all reducing, no flow control is required. A description of the
existing and proposed conditions are detailed in Section 4.0 of this report along with KCRTS
results showing the reductions in the peak flow rates.
4. Conveyance System:
The site will sheet flow to a collection points and be conveyed via new storm pipes into the
existing exiting site system.
5. Erosion and Sediment Control:
A TESC plan has been developed for this project. Catch basin protection, filter fabric fencing,
tree protection, and sediment control shall be implemented on site. A copy of the erosion
control plan and erosion control details are included in the Appendix as Figure 6 and Figure 7
respectively.
6. Maintenance and Operations:
The proposed water quality canister catch basin requires routine yearly maintenance. A stand-
alone maintenance manual will be provided on request.
7. Financial Liability:
The project will provide all bonding and/or assignment of savings as required for the
development’s construction and warranty periods.
8. Water Quality:
The site’s storm water will be discharged through ZPG filled StormFilter cartridges. The sizing for
these cartridges is in Section 4.5.
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Special Requirements:
1. Other Adopted Area-Specific Requirements:
No other area specific requirements are in place.
2. Flood Hazard Area Delineation:
The project is not within a flood hazard area.
3. Flood Protection Facilities:
This project is not within a flood hazard area.
4. Source Control:
The intention of source control BMPs is to prevent storm water from coming in contact with
pollutants. To this end, regular cleaning and maintenance of the storm water system is a key
element. Inspect and clean treatment BMPs, conveyance systems, and catch basins as needed,
and determine whether improvements in O & M are needed. Promptly repair any deterioration
threatening the structural integrity of the facilities. These include replacement of clean-out
gates, catch basin lids, and rock in emergency spillways. Ensure that storm sewer capacities are
not exceeded and that heavy sediment discharges to the sewer system are prevented. Regularly
remove debris and sludge from BMPs used for peak-rate control, treatment, etc. and discharge
to a sanitary sewer if approved by the sewer authority or truck to a local or state government
approved disposal site. Clean catch basins when the depth of deposits reaches 60 percent of
the sump depth as measured from the bottom of basin to the invert of the lowest pipe into or
out of the basin. However, in no case should there be less than six inches clearance from the
debris surface to the invert of the lowest pipe. Clean woody debris in a catch basin as frequently
as needed to ensure proper operation of the catch basin.
5. Oil Control:
Per Section 1.3.5 Special Requirement #5: Oil Control of the City of Renton 2009 Surface Water
Design Manual Amendment, oil control is required if the project site is a high-use-site defined as
having an expected average daily traffic count equal or greater than 100 vehicles per 1,000
square feet of gross building area. Drive-thru coffee uses typically have higher counts than this
minimum threshold therefore oil control is proposed. See Section 4.5 of this report for further
information.
3.0 – Offsite Analysis
3.1 - Upstream Analysis
All upstream areas are contained within manmade drainage systems.
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3.2 – Downstream Analysis
A level 1 downstream analysis was conducted. See Figure 8 below.
Figure 8 – Downstream Flow Path
The site drainage discharges to the City drainage system in Lake Avenue S on the north side of South
Tobin Street into a Type 2 manhole. From this manhole the drainage flows south through a 12 inch
diameter concrete pipe to another Type 2 manhole on the south side of South Tobin Street. From this
Downstream
Flow Path
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manhole the drainage continues to flow south in Lake Avenue South through a 24 inch diameter CPEP
pipe, across South 2nd Street to a Type 2 manhole at the north edge of the Village Square Shopping
Center. The drainage flows through the Village Square Shopping Center via 30 inch – 36 inch CPEP pipes
until it gets to the intersection of Rainier Avenue South and South 3rd Street. At this point the drainage
discharges into a non-circular RCP drainage culvert that continues to the southwest. The full distance of
this run from the site to the intersection of Rainier Avenue South and South 3rd Street is 0.32 miles.
4.0 – Flow Control and Water Quality Facility Analysis and Design
4.1 – Existing Site Hydrology (Part A)
The site falls within the City’s peak rate flow control standard (existing site conditions). Per figure 1.1.2.A
of the 2009 City of Renton Surface Water Design Manual Amendment, a Full Drainage Review is
required. The site is currently mostly covered by asphalt paved surfaces with perimeter landscaping.
The drainage sheet flows to a ditch that conveys the drainage to the offsite City storm system. The
existing surface areas on site are as follows:
Total Site Area of Disturbance: 19,602.00 SF (0.45 AC)
Non-PGIS: 435.60 SF (0.01 AC)
PGIS: 15,681.60 SF (0.36 AC)
Pervious: 3,484.80 SF (0.08 AC)
See Figure 8 – Existing Stormwater Exhibit in the Appendix.
4.2 – Developed Site Hydrology (Part B)
The project will be adding landscape area and reducing the impervious surfacing area of the site. The
amount of pollution generating impervious surfacing will also be reduced. The proposed surface areas
are as follows:
Total Site Area of Disturbance: 19,602.00 SF (0.45 AC)
Non-PGIS: 4,791.60 SF (0.11 AC)
PGIS: 9,583.20 SF (0.22 AC)
Pervious: 5,227.20 SF (0.12 AC)
See Figure 9 – Proposed Stormwater Exhibit in the Appendix.
Peak flows for both the existing conditions and the proposed conditions were calculated using the King
County Runoff Time Series. The results are as follows:
Existing: Proposed:
100 yr - 0.477 cfs 100 yr - 0.456 cfs
10 yr - 0.242 cfs 10 yr - 0.222 cfs
2 yr - 0.176 cfs 2 yr - 0.161 cfs
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Per the City of Renton 2009 Surface Water Design Manual Amendment, the facility requirement in Peak
Rate Runoff Control Standard Areas may be waived for any threshold discharge area of a redevelopment
project in which the target surfaces will generate no more than a 0.1 cfs increase in the existing site
conditions 100 year peak flow and the increased runoff from the target surfaces will not significantly
impact a critical area, severe flooding problem, or severe erosion problem. Since the proposed 100 year
peak rate is 0.456 cfs while the existing 100 year peak rate is 0.477 cfs, a decrease of 0.021 cfs, the
criteria for this exception is met since the 100 year peak rate is reduced and there is a reduced runoff
from the target surfaces. Therefore no flow control measures are required or proposed.
4.3 – Performance Standards (Part C)
Flow Control Requirements:
Flow control will not be required on this site since the peak rates will be reduced.
Conveyance System Capacity Requirements:
The site will have all new piped conveyance system. Per Section 1.2.4.1 of the Surface Water Manual,
piped systems must be designed at a minimum to carry the 25-year peak flow, and to ensure that 100-
year runoff events do not cause severe flooding or severe erosion problems. Conveyance calculations
have been conducted and the results are provided in the Appendix.
Water Quality Treatment Requirements:
The site lies within the basic water quality treatment area. StormFIlter cartridges will be used for water
quality treatment.
4.4 - Flow Control System (Part D)
Since the site is reducing the amount of impervious surfacing and reducing the amount of runoff from
the site, no flow control is required.
4.5 - Water Quality System (Part E)
StormFilter cartridges are proposed to meet the water quality treatment requirements.
KCRTS Land Use Parameters: 0.22 acres PGIS; 15-minute time series
Water Quality Flowrate:
2 year flow: 0.105 cfs per KCRTS output.
Per King County Surface Water Design Manual, use 35% of 2 year flow
(0.35)(0.105) = 0.0368 cfs
Use 27" high cartridges – 11.3 gpm/cartridge
using ZPG for media
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N (cartridges) = (0.0368 cfs)*(449 gpm/cfs)
11.3 gpm/cartridge
= 1.46; use 2 cartridges
Per the 2009 King County Surface Water Design Manual Section 6.1.5 High-Use Menu, Oil Control Option
1, catch basin inserts are acceptable for oil control on a high-use site.
5.0 – Conveyance System Analysis and Design
The conveyance system has been designed to convey the 100 year storm event. Conveyance calculations
and a Flow Calculations Exhibit (Figure 10) is provided in the Appendix.
6.0 – Special Reports and Studies
N/A
7.0 – Other Permits
A building permit is required by the City of Renton
8.0 – CSWPP Analysis and Design
ESC Measures:
Use of filter fabric fencing, catch basin inserts, and selective pavement removal will be used to control
sediment and prevent any erosion possibilities.
9.0 – Bond Quantities, Facility Summaries, and Declaration of Covenant
The project will provide all City of Renton bonding and/or assignment of savings as required for the
development’s construction and warranty periods. A bond quantity worksheet and Declaration of
Covenant have been submitted to the City.
10.0 – Operations and Maintenance Manual
The operations and maintenance schedule has been included within the Declaration of Covenant. Which
has been submitted to the City under separate cover.
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Appendix
Starbucks at Airport Plaza
Storm Water Hydrology * Rational Method
Initail Tc=6.3 TFD 6/05/17 BRH #2016067
Initial acres=0
Design Storm=100 a=2.61 Watercourse types:
Intensity=3.9 b=0.63 1 Forest w/ heavy gound litter
2 Minimum tillage cultivation
3 Short grass pasture & lawns
4 Nearly bare ground
5 Grassed waterway
6 Paved area
CB#1 - CO# 1 CO#1 - CO#2 CO#2 - CO#3 CO#3 - SWCB#1 SWCB#1 - EX CB
Tc (min.)=6.30 Tc (min.)=6.30 Tc (min.)=6.30 Tc (min.)=6.30 Tc (min.)=6.30
Area (acres)=0.005 Area (acres)=0.00 Area (acres)=0.05 Area (acres)=0.297 Area (acres)=0.00
C=0.85 C=0.85 C=0.85 C=0.85 C=0.85
∑AC=0.004 ∑AC=0.004 ∑AC=0.047 ∑AC=0.25 ∑AC=0.25
I=3.19 I=3.19 I=3.19 I=3.19 I=3.19
Q Design (cfs)=0.01 Q Design (cfs)=0.01 Q Design (cfs)=0.15 Q Design (cfs)=0.81 Q Design (cfs)=0.81
Pipe:Pipe:Pipe:Pipe:Pipe:
Invert in=32.71 Invert in=32.19 Invert in=30.91 Invert in=29.19 Invert in=27.23
Invert out=32.19 Invert out=30.91 Invert out=29.19 Invert out=28.47 Invert out=26.84
Length (ft.)=26 Length (ft.)=64 Length (ft.)=86 Length (ft.)=11 Length (ft.)=39
n=0.012 n=0.012 n=0.012 n=0.012 n=0.012
Dia. (inches)=8 Dia. (inches)=8 Dia. (inches)=8 Dia. (inches)=8 Dia. (inches)=8
% Slope=2 % Slope=2 % Slope=2 % Slope=6.545 % Slope=1
Q Full (cfs)=1.85 Q Full (cfs)=1.85 Q Full (cfs)=1.85 Q Full (cfs)=3.35 Q Full (cfs)=1.31
V Full (fps)=5.30 V Full (fps)=5.30 V Full (fps)=5.30 V Full (fps)=9.59 V Full (fps)=3.75
Q Design/Q Full=0.7%Q Design/Q Full=0.7%Q Design/Q Full=8.1%Q Design/Q Full=24.1%Q Design/Q Full=61.6%
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