HomeMy WebLinkAboutRS_Drainage_Report_Part_1_Page_Set_211222_v1DRAINAGE REPORT
The Home Depot
901 S Grady Way,
Renton, WA 98057
Prepared by:
LARS ANDERSEN & ASSOCIATES, INC.
4694 W. JACQUELYN AVENUE, FRESNO, CA 93722-6405
PHONE (559) 276-2790 FAX (559) 276-0850
WEBSITE: WWW.LARSANDERSEN.COM
Project No: 19165
December 21, 2021
RECEIVED
12/22/2021 JDing
PLANNING DIVISION
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Table of Contents
Section Page
1 Project Overview 2
2 Conditions and Requirements Summary 2
3 Offsite Analysis 4
4 Flow Control and Water Quality Facility Analysis and Design 4
5 Conveyance System Analysis and Design 7
6 Special Reports and Studies 7
7 Other Permit 7
8 CSWPPP Analysis and Design 7
9 Bond Quantities, Facility Summaries, and Declaration of Covenant 8
10 Operations and Maintenance Manual 8
Appendix Title
A Site Map
B City of Renton Flow Control Applications Map
C ALTA Survey
D Conceptual Plans
E CSWPP Plan
F Existing Civil Plans
G Operations and Maintenance Measures
H Technical Information Report (TIR) Worksheet
I Geotech Memo
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Section 1 – Project Overview
The project site is located at 901 S Grady Way, just Northeast of the 405 and 167 highway exchange. The
site is fully developed and the former location of a Sam’s Club retail store. The site is approximately 15.4
AC with an existing building located on it that is currently 135,373 SF. The project calls for the
redevelopment of the existing building and adjacent improvements, including pavements, curbs, and
landscaping. Proposed grading activities will be limited and will aim to match existing drainage patterns.
Section 2 – Conditions and Requirements Summary
The site is fully developed with sections of concrete pavement, asphalt pavement, and landscaping. The
existing landscaping includes lawn within the parking lot and adjacent areas and brushy sloped areas.
See Table 2.1 for a breakdown of the existing areas. The site is currently designed to slope away from
the existing building, primarily towards the adjacent streets of Grady Way and Talbot Rd S. The site is
serviced by an existing, extensive stormwater system. Surface runoff is collected in various drain inlets
throughout the site and then delivered via underground storm line system. Said water is treated with
existing oil separators and biofiltration basins. Stormwater is then discharged via a storm drain at the
northwest side of the site into the Grady Way South public storm system and through a storm drain at
the south corner of the site that outfalls into a 48” culvert under SR-515 (Talbot Rd). See Appendix F –
Existing Plans for more details.
The proposed project aims to utilize the existing stormwater system as-is, not changing the current
discharging locations. The proposed improvements will result in a reduction of impervious pavements
and an increase in pervious area, specifically lawn area, by 1,527 SF. See Table 2.2 for more details.
Because the project calls for over 2,000 SF of new plus replaced impervious surface but less than 50
acres of new impervious surface, it is subject to a Full Drainage Review per the City of Renton Surface
Water Design Manual (SWDM). See Table 2.3 for complete pollution generated surface areas. As per the
SWDM, a Full Drainage Review results in the project adhering to the 9 core and 6 special requirements
barring exception):
Core Requirements
Core Requirement #1: Discharge at the Natural Location
The site currently discharges via a storm drain at the northwest side of the site into the Grady
Way South public storm system and through a storm drain at the south corner of the site that
outfalls into a 48” culvert under SR-515 (Talbot Rd). The proposed project intends to utilize the
existing discharge points.
Core Requirement #2: Offsite Analysis
Exempt on account of maintaining existing rate, volume, duration, and locations of discharges to
and from the site.
Core Requirement #3: Flow Control
The project does not intend to increase the peak flow rate. In fact, the project will reduce the
peak flow rates slightly. The existing stormwater system also already incorporates flow control
structures, and the project intends to continue utilizing them.
Core Requirement #4: Conveyance System
The existing conveyance system will continue to be utilized for the proposed project.
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Core Requirement #5: Erosion and Sediment Control
There is limited risk of erosion and sediment introduction into the existing stormwater system
as there is limited grading activities. Regardless, the project will implement erosion and
sediment measures per the SWDM during construction.
Core Requirement #6: Maintenance and Operations
All drainage facilities are to be located on-site and will be privately maintained by the site
owner. A standard Operations and Maintenance Manual to be submitted.
Core Requirement #7: Financial Guarantees and Liability
Not applicable as there will be no new structures installed.
Core Requirement #8: Water Quality
The site is currently serviced by 3 separate biofiltration swales and oil separators.
Core Requirement #9: On-site BMPs
The project will implement drain inlet protection, concrete wash outs, material storage area,
and other measures per the SWDM.
Special Requirements
Special Requirement #1: Other Adopted Area-Specific Requirements
The project does not fall under any other known Adopted Area-Specific requirements.
Special Requirement #2: Flood Hazard Area Delineation
The project is not located within a flood hazard area.
Special Requirement #3: Flood Protection Facilities
The project is not located near a Class 1 or 2 stream and does not propose to modify or
construct a flood protection facility.
Special Requirement #4: Source Control
Water quality source control measures will be utilized during the construction of the project in
according to the SWDM.
Special Requirement #5: Oil Control
This site does not fall under the requirements for oil control as the number vehicles/ day are
expected is below the limit of 13, 500 vehicles/ day for this site nor does the project involve the
maintenance storage and use of the site by a fleet of 25 or more diesel vehicles, heavy trucks,
buses, etc. Therefore, special treatment of stormwater runoff will not be necessary or required
for the proposed store.
Special Requirement #6: Aquifer Protection Area
This site does not fall within the City’s Aquifer Protection Area Zones 1 nor 2.
Table 2.1
Existing Surfaces
Surface Type Area (SF)
Landscape 191261
Lawn) 111902
Light Forrest) 79359
Pavement 478539
Total 669800
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Table 2.2
Proposed Surfaces
Surface Type Area (SF)
Landscape 192788
Lawn) 113429
Light Forrest) 79359
Pavement 477012
Total 669800
Table 2.3
Proposed PG Surfaces
Surface Type Area (SF)
Replaced PGPS 643
New PGPS 5553
Replaced PGIS 33909
New PGIS 4026
Section 3 – Offsite Analysis
As stated in Section 1, proposed surface improvements call for matching drainage patterns. As stated in
Section 2, the project will result in a decrease of 1,527 SF of pavement area and maintain the existing
discharge points. For these reasons, the project will not change the rate, volume, duration, nor locations
of discharges to and from the site; therefore, the project is exempt from Offsite Analysis.
Section 4 – Flow Control and Water Quality Facility Analysis and Design
Flow Control
Per the City of Renton Flow Control Applications Map (Appendix B), the project must adhere to Peak
Rate Flow Control Standard. This means it must match existing site conditions 2, 10 and 100-year peak-
rate runoff for areas draining to constructed (man-made) or highly modified drainage systems so as not
to create a downstream flooding problem. See Tables 4.1-4.7 to see this done. More specifically, Table
4.7 shows that there is in fact a slight decrease in peak flows after improvements. For this reason, the
project is exempt from installing flow control devices. It is also important to note that there already exist
flow control structures within the stormwater system (see Appendix F). Existing structures shall be
inspected, cleaned, and maintained for continued use.
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Table 4.1
Ex. Runoff Coefficient
Area Cx A (ac) C
Ex. LS (L) 0.25 2.57
0.70Ex. LS (LF) 0.15 1.82
Ex. Pavement 0.9 10.99
Table 4.2
Existing Tc
Count Area kR so (ft/ft) V (fps) L (ft) tt (min) Tt (min) Tc (min)
14 XLS-L-1 7 0.015 0.86 10 0.19 2.7
43.7
1 XLS-L-2 7 0.025 1.11 40 0.60 0.6
1 XLS-L-3 7 0.005 0.49 345 11.62 11.6
12 XLS-L-4 7 0.01 0.70 10 0.24 2.9
1 XLS-L-5 7 0.05 1.57 130 1.38 1.4
1 XLS-L-6 7 0.105 2.27 75 0.55 0.6
1 XLS-L-7 7 0.02 0.99 30 0.51 0.5
1 XLS-L-8 7 0.015 0.86 70 1.36 1.4
1 XLS-LF 2.5 0.2 1.12 75 1.12 1.1
1 XP-1 10 0.01 1.00 665 11.08 11.1
1 XP-2 10 0.0175 1.32 265 3.34 3.3
1 XP-3 10 0.02 1.41 100 1.18 1.2
1 XP-4 11 0.015 1.35 40 0.49 0.5
2 XP-5 11 0.01 1.10 160 2.42 4.8
Table 4.3
Existing Intensity
Storm Tc (min) aR bR iR PR (in) I (in/hr)
2-yr 43.7 1.58 0.58 0.18 2 0.35
10-yr 43.7 2.44 0.64 0.22 2.9 0.63
100-yr 43.7 2.61 0.63 0.24 3.9 0.94
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Table 4.4
Pr. Runoff Coefficient
Area Cx A (ac) C
Pr. LS (L) 0.25 2.60
0.70Pr. LS (LF) 0.15 1.82
Ex. Pavement 0.9 10.95
Table 4.5
Proposed Tc
Count Area kR so (ft/ft) V (fps) L (ft) tt (min) Tt (min) Tc (min)
16 PLS-L-1 7 0.015 0.86 10.5 0.20 3.3
44.3
1 PLS-L-2 7 0.025 1.11 40 0.60 0.6
1 PLS-L-3 7 0.005 0.49 345 11.62 11.6
12 PLS-L-4 7 0.01 0.70 10.5 0.25 3.0
1 PLS-L-5 7 0.05 1.57 130 1.38 1.4
1 PLS-L-6 7 0.105 2.27 75 0.55 0.6
1 PLS-L-7 7 0.02 0.99 30 0.51 0.5
1 PLS-L-8 7 0.015 0.86 70 1.36 1.4
1 PLS-LF 2.5 0.2 1.12 75 1.12 1.1
1 PP-1 10 0.01 1.00 665 11.08 11.1
1 PP-2 10 0.0175 1.32 265 3.34 3.3
1 PP-3 10 0.02 1.41 100 1.18 1.2
1 PP-4 11 0.015 1.35 40 0.49 0.5
2 PP-5 11 0.01 1.10 160 2.42 4.8
Table 4.6
Proposed Intensity
Storm Tc (min) aR bR iR PR (in) I (in/hr)
2-yr 44.3 1.58 0.58 0.18 2 0.35
10-yr 44.3 2.44 0.64 0.22 2.9 0.62
100-yr 44.3 2.61 0.63 0.24 3.9 0.93
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Table 4.7
Peak Runoff Rates
Storm Area C I (in/hr) A (ac) Q (cfs)
2-yr Existing 0.70 0.35 15.376 3.82
10-yr 0.70 0.63 15.376 6.82
100-yr 0.70 0.94 15.376 10.19
2-yr Proposed 0.70 0.35 15.376 3.78
10-yr 0.70 0.62 15.376 6.74
100-yr 0.70 0.93 15.376 10.06
Water Quality
Because the project falls under commercial land use, it must adhere to Enhanced Basin WQ measures.
As seen in the Existing Plans (Appendix F), the existing site currently utilizes (2) separate oil separator
structures and (3) biofiltration basins to meet these WQ standards. The project intends to inspect, clean,
and maintain said facilities for continued use.
Section 5 – Conveyance System Analysis and Design
The existing conveyance system was designed to serve the existing site during a 100-yr event. It includes
the underground storm pipe system as well as the concrete aqueduct. The project intends to continue
using and maintaining the existing system.
Section 6 – Special Reports and Studies
There are no special reports nor studies required for this project.
Section 7 – Other Permit
There are no other permits required for the project.
Section 8 – CSWPPP Analysis and Design
The below measures will be implemented for the project per the SWDM. See Appendix
ESC Measures
o Flow Control
o Dust Control
o Control Pollutants
o Protect Existing Stormwater Facilities and On-site BMPs
o Maintain Protective BMPs
o Manage the Project
SWPPS Measures
o Follow effective pollutant handling and disposal procedures.
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o Provide cover and containment for materials, fuel and other pollutants.
o Manage the project site to maximize pollutant control and minimize pollutant sources.
o Protect from spills and drips of petroleum products and other pollutants.
o Avoid overapplication or untimely application of chemicals and fertilizers.
Section 9 – Bond Quantities, Facility Summaries, and Declaration of Covenant
There are no new facilities proposed for this project. Any further information shall be provided upon
later submittal.
Section 10 – Operations and Maintenance Manual
All drainage facilities to be maintained privately as specified per the SWDM. A copy of the Operation and
Maintenance Manual submitted as part of the permit application for flow control and water quality
treatment facilities shall be retained on site and shall be transferred with the property to the new
owner. A log of maintenance activity indicating when cleaning occurred and where waste was disposed
of shall also be kept by the owner and be available for inspection by the City. See Appendix G for
operations and maintenance standards.
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Appendix A – Site Map
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Valley RdEast Valley Rd,§-
405 405 405
µ0 12 Miles
Flow Control Application
Map Reference 15-A Date: 01/09/2014
Flow Control Standards Peak Rate Flow Control
Standard (Existing Site Conditions)Flow Control
Duration Standard (Existing
Site Conditions)Flow Control Duration Standard (
Forested Conditions)Flood
Problem Flow Unincorporated
King County Flow Control StandardsRenton
City Limits Potential Annexation Area Appendix B -
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Appendix F
FLOW CONTROL
OIL POLLUTION
OILPOLLUTIONOILSEPERATOR
FLOW SEPARATOR
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