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Walmart Store #2516-05
743 Rainier A venue South
Renton, Washington
Technical Information Report
Retail Expansion
Revised October 19, 2012
Revised February 25, 2010
December 30, 2009
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1505 Westlake Ave. N T 206.522.9510
Suite 305 F 206.522.8344
Seattle, WA 98109 www.pacland.com
Prepared By: Sarah Brundidge, P.E.
Jeff Chambers, P.E.
373171
Wal mart#2516-05 Expansion Technical Information Report Renton, Washington
Table of Contents
Section Page
Executive Summary 2
Project Overview 3
1. TIR Worksheet 3
2. Site Location 5
3. Drainage Basins, Site Characteristics, and Sub-basins 6
4. Soils 8
Preliminary Conditions Summary 9
Offsite Analysis 12
1. Upstream Analysis 12
2. Downstream Analysis 12
3. Evidence of Existing or Predicted Problems 14
Retention/Detention Analysis and Design 15
1. Existing Site Hydrology 15
2. Developed Site Hydrology 16
3. Hydrologic Analysis 16
4. Retention/Detention System 16
5. Water Quality 17
6. New PGIS Areas 17
Conveyance System Analysis and Design 19
Special Reports and Studies 20
Basin and Community Planning Areas 21
Other Permits 22
Bond Quantities, Facility Summaries, and Declaration of Covenant 23
Erosion/Sedimentation Control Design 24
1. Erosion Risk Assessment 24
2. Construction Sequence and Procedure 24
3. Trapping Sediment 24
4. Wet Weather TESC 25
Maintenance and Operations Manual 26
Appendices: A — Maintenance and Operations Manual
B — Exhibits/Grading and Drainage Plan
C — Isopluvial Maps
D — Design Calculations
PACLAND Project #10001074 Page 1
Walmart#2516-05 Expansion Technical Information Report Renton, Washington
Executive Summary
Site Location:
The property is located at 743 Rainier Avenue S. in Renton, Washington. The site is
bordered by SW Grady Way to the south, Rainier Avenue and Hardie Avenue SW to the
east, SW Seventh Street to the north and a commercial uses to the west. The site is
currently developed as a 134,352 square foot Walmart discount store. This project
proposes to expand the existing store by approximately 16,000 square feet and increase
the lease area by 1.67 acres to a total of 11.57 acres.
Design Criteria:
The City of Renton uses the King County Surface Water Management Design Manual
(KCSWDM), 1990 Edition, as adopted by the City of Renton. This project will evaluate the
2-year, 10-year, and 100-year storm events for the pre-developed and post-developed
conditions. The existing site is developed and entirely impervious with the exception of
landscape islands and a gravel area. The overall impervious area is decreasing on-site,
therefore detention requirements are not anticipated for this project. However, additional
water quality treatment will be provided for the new pollution generating impervious
surfaces (PGIS).
Table 1
Jurisdictional Requirements
Peak Run-off Control:
2-year: Match predeveloped
10-year: Match predeveloped
100-year: Match predeveloped
Water Quality: 2-year 24-hour duration
Proposed Drainage System:
The project proposes to utilize the existing stormwater system for conveyance and provide
improvements, as necessary, for additional conveyance and water quality treatment. New
PGIS areas will be treated in the proposed bioswale located north of the expansion area.
Additional roof runoff will be tied into the existing 12" pipe which bypasses the existing
bioswale and ties into the City conveyance system. Additional water quality enhancements
have been added downstream of the proposed bioswale.
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 sight 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.
PACLAND Project#10001074 Page 2
Walmart#2516-05 Expansion Technical Information Report Renton,Washington
Project Overview
Page 1 of 2
King County Building and Land Development Division
TECHNICAL INFORMATION REPORT(TIR) WORKSHEET
PART 1 PROJECT OWNER AND PART 2 PROJECT LOCATION
PROJECT ENGINEER AND DESCRIPTION
Project Owner BONNELL FAMILY LLC Project Name WALMART EXPANSION
Address 10047 MAIN STREET#509 Location
phone 425-453-l4 l4 Township 23
Project Engineer JEFF CHAMBERS,P.E. Range 05
9 Section 19
Company
PACLAND
Project Size t 1.57 AC
206-522-9510
Address Phone Upstream Drainage Basin Size AC
PART 3 TYPE OF PERMIT APPLICATION PART 4 OTHER PERMITS
Q Subdivision Q DOF/G HPA El Shoreline Management
C7 Short Subdivision Q COE 404 El Rockery
Q Grading El DOE Dam Safety 0 Structural Vaults
Q Commercial Q FEMA Floodplain 0 Other
Q Other CONSTRUCTION PERMIT
El COE Wetlands 0 HPA
PART 5 SITE COMMUNITY AND DRAINAGE BASIN
CSS Ri&L CORRIDOR/EMPLOYMENT AREA VALLEY
•
Drainage Basin
BLACK RIVER DRAINAGE BASIN
PART 6 SITE CHARACTERISTICS
[] River Q Floodplain
Q Stream _ -_-- Q Wetlands
0 Critical Stream Reach 0 Seeps/Springs
Depressions/Swales El High Groundwater Table
0 Lake El Groundwater Recharge
C7 Steep Slopes _-_- —_ Q Other
C] Lakeside/Erosion Hazard
PART 7 SOILS
Soil Type Slopes Erosion Potential Erosive Velocities
URBAN LAND(Ur) _ AVERAGE 3% LOW LOW
•
Q Additional Sheets Attatched •
` I
1/90
PACLAND Project#10001074 Page 3
Walmart#2516-05 Expansion Technical Information Report Renton, Washington
Page 2 of 2
King County Building and Land Development Division
TECHNICAL INFORMATION REPORT(TIR) WORKSHEET
PART 8 DEVELOPMENT LIMITATIONS
REFERENCE LIMITATION/SITE CONSTRAINT
0 Ch,4-Downstream Analysis NONE KNOWN
Q
Q
El
Q _
Q Additional Sheets Attatched
PART 9 ESC REQUIREMENTS
MINIMUM ESC REQUIREMENTS MINIMUM ESC REQUIREMENTS
DURING CONSTRUCTION FOLLOWING CONSTRUCTION
C] Sedimentation Facilities El Stabilize Exposed Surface
[J Stabilized Construction Entrance (D Remove and Restore Temporary ESC Facilities
El Perimeter Runoff Control 0 Clean and Remove All Silt and Debris
ED Clearing and Grading Restrictions El Ensure Operation of Permanent Facilities
O Cover Practices 0 Flag Limits of NGPES
C] Construction Sequence Q Other
El Other
PART 10 SURFACE WATER SYSTEM
Cl Grass Lined Channel El Tank U Infiltration Method of Analysis
CJ Pipe System p Vault (] Depression SBUH
Open Channel El Energy Dissapator El Flow Dispersal Compensad
Q Dry Pond El Wetland n Waiver of of Eliminated
El Wet Pond El Stream Cl Regional Detention
Brief Description of System Operation Proposed system utilizes existing catch basins and underground pipe which
to a grass lined swale and City system.New CB.pipe and additional swale are included to account for expansion area.
Facility Related Site Limitations Q Additional Sheets Attalched
Reference Facility Limitation
•
PART 11 STRUCTURAL ANALYSIS PART 12 EASEMENTS TRACTS
(May require special structural review)
Q Drainage Easement
0 Cast in Place Vault El Other Q Access Easement
El Retaining Wall Ci Native Growth Protection Easement
Q Rockery i 4'High El Tract
Q Structural on Steep Slope ❑ Other
PART 14 SIGNATURE OF PROFESSIONAL ENGINEER
I or civil engineer under my supervision have visited the site.Actual
site conditions as observed were incorporated Into this worksheet and the
attatchments. To the best of my knowledge the information provided
here Is accurate.
•
1/90
PACLAND Project #10001074 Page 4
Walmart#2516-05 Expansion Technical Information Report Renton, Washington
Site Location
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Location: 743 Rainier Avenue S. Renton, WA 98057
Section/Township/Range: NW Quarter of Section 19, Township 23, Range 05
Parcel/Tax Lot(s): 1923059048, 1923059072
Size: 11.57 acres
City, County, State: Renton, King County, Washington
Governing Agency: City of Renton
Design Criteria: 1990 King County Surface Water Design Manual (KCSWDM) as adopted
by the City of Renton
PACLAND Project#10001074 Page 5
Walmart#2516-05 Expansion Technical Information Report Renton, Washington
Drainage Basins, Subbasins, and Site Characteristics
Drainage Basin
The project site is located in the Black River Drainage Basin which is part of the
Green/Duwamish River Watershed.
Existing Sub-Basins
The project site has three existing sub-basins. See Exhibit 1 in Appendix B for a depiction
of the existing sub-basins.
Sub-basin A
The majority of the existing roof runoff is collected in roof drain leaders and detained in a
48" CMP pipe behind the store. Once this runoff is released from the control structure, it
bypasses the existing bioswale and enters the City conveyance system in SW Seventh
Street. This sub-basin is approximately 134,215 sf(3.08 ac).
Sub-basin B
On-site surface runoff from north and east of the existing store, as well as a small portion of
the existing roof runoff, are collected and conveyed via a system of curb, gutter, catch
basins and underground conveyance pipes. Runoff is conveyed to the existing biofiltration
swale for water quality treatment and subsequently into the City of Renton storm system.
This sub-basin is approximately 389,441 sf(8.94 ac).
Sub basin C
On-site surface runoff from northeast of the existing store and near the Billy McHale's
restaurant is collected and conveyed via a system of curb, gutter, catch basins and
underground conveyance pipes. This system is conveyed to an existing vault in the City
drainage system upstream of where sub-basin B ties in. This sub-basin is approximately
70,897sf (1.64 ac).
Proposed Sub-Basins
The project site has three existing sub-basins. See Exhibit 2 in Appendix B for a depiction
of the proposed sub-basins.
Sub-basin 1
The existing roof runoff will continue to be collected in roof drain leaders and detained in
a 48" CMP pipe behind the store. Additonal roof runoff from the proposed expansion, as
well as the portion of existing roof which currently discharges to the bioswale, will tie into
the conveyance pipe behind the store. This clean runoff will bypass the existing bioswale.
The proposed sub-basin would be approximately 152,792 sf(3.51 ac).
Sub-basin 2a
On-site surface runoff from north and east of the existing store will continue to be
collected and conveyed via a system of curb, gutter, catch basins and underground
PACLAND Project#10001074 Page 6
Walmart#2516-05 Expansion Technical Information Report Renton, Washington
conveyance pipes. A portion of the existing roof and the PGIS which will be converted to
roof will now become part of sub-basin 1. Runoff is conveyed to the existing biofiltration
swale for water quality treatment and subsequently into the City of Renton storm system.
The proposed sub-basin would be approximately 357,450 sf (8.21 ac).
Sub-basin 2b
Sub-basin 2b is the area that would be collected and treated in the proposed bioswale.
Post-treatment runoff will be conveyed to the existing bioswale and subsequently into the
City of Renton storm system. This sub-basin is approximately 39,839 sf (0.91 ac).
Sub-basin 3
On-site surface runoff from northeast of the existing store and near the Billy McHale's
restaurant is collected and conveyed via a system of curb, gutter, catch basins and
underground conveyance pipes. This system is conveyed to an existing vault in the City
drainage system upstream of where sub-basins 2a and 2b tie in. The tributary area to this
sub-basin would decrease slightly, since a portion of this area will now receive treatment
in the proposed bioswale. Enhanced water quality treatment features will also be provided,
including stormfilters and spill control. The new sub-basin area would be approximately
44,472 sf (1.02 ac).
Table 2, below, shows the area breakdown for the existing and proposed sub-basins.
Table 2
Existing Sub-Basins Proposed Sub-Basins
Surface
A B C 1 2a 2b 3
Roof 131,667 2,685 6,547 150,244 0 0 0
Garden
Center 0 9,186 0 0 4,701 0 0
Landscaping 0 46,604 3,942 0 51,795 8,783 5,112
Pavement
(PGIS) 2,548 297,588 47,066 2,548 276,524 27,496 37,433
Sidewalk 0 15,937 1,095 0 24,430 3,560 1,927
Gravel 0 17,441 12,247 0 0 0 0
Total 134,215 389,441 70,897 152,792 357,450 39,839 44,472
As shown in Table 2, the amount of PGIS area in sub-basins A and C remain the same or
decrease under the proposed conditions. Existing sub-basin B is broken into two sub-basins
(2a and 2b) for the proposed conditions. Sub-basin 2b receives water quality treatment in
the new bioswale; therefore, the total PGIS runoff to the existing bioswale decreases in the
proposed conditions as well.
PACLAND Project#10001074 Page 7
Walmart#2516-05 Expansion Technical Information Report Renton, Washington
Site Characteristics
The property is located at 743 Rainier Avenue S. in Renton, WA. The site is bordered by
SW Grady Way to the south, Rainier Avenue and Hardie Avenue SW to the east, SW
Seventh Street to the north and a Honda dealership to the west. The existing site is
comprised of a 134,352 square foot Walmart store and 9,186 square foot Garden Center
with associated paving, landscaping, and storm drainage system. The site also contains a
6,547 square foot vacant restaurant located north of the Walmart, which will be
demolished by others prior to the start of the Walmart construction.
This project proposes to expand the existing Walmart store to the north, modify existing
the vestibule on the eastern face of the building and add a second vesitibule on the eastern
face of the building. The building will be expanded from 134,352 square feet to 150,244
square feet, the Garden Center would be reduced from 9,186 square feet to 4,701 square
feet, and the new parking lot, landscaping, and bioswale to the north will replace the
existing gravel area. The existing parking area will not be significantly modified from its
original layout, but will include a variable overlay in the front drive aisle and proposed
handicap parking, seal coating the remaining parking areas and minimal landscape island
relocations/modifications. Additional water quality treatment will be provided for the new
pollution generating impervious surfaces.
Table 3, below, displays the overall existing and proposed areas for the entire project site.
Table 3
Surface Existing Area (sf) Proposed Area (sf)
Building/Roof 140,896 150,244
Garden Center 9,186 4,701
Landscaping 50,546 65,690
Pavement (PGIS) 347,205 344,001
Sidewalk 1 7,032 29,917
Gravel 29,688 0
Site Total 594,553 594,553
Soils
Per the Geotechnical Report, prepared by Terracon and dated November 30, 2009, the
site consists of native fine-grained soils which are generally soft to soft to medium stiff and
compressible, and native granular soils which range from loose to very dense.
The site is mapped as Urban Land (Ur) according to the USDA Natural Resource
Conservation Service, Soil Survey for King County Area, Washington. Hydrologic Soil
Group C curve numbers for were used for the design calculations.
PACLAND Project#10001074 Page 8
Walmart#2516-05 Expansion Technical Information Report Renton,Washington
Preliminary Conditions Summary
As required by the 1990 King County Surface Water Design Manual (KCSWDM), this
project is subject to drainage review. Therefore, the storm drainage design for this project
is required to comply with all seven (7) Core Requirements. The requirements have been
met as follows:
Core Requirement #1: Discharge at Natural Location
The discharge from a proposed project must occur at the natural location.
Response: Onsite runoff will be collected, conveyed and, when necessary, treated. All
onsite runoff is subsequently conveyed to the City of Renton stormwater system and
which discharges into Springbrook Creek (Black River). No downstream impacts are
anticipated as a result of the proposed improvements.
Core Requirement #2: Off-site Analysis
All proposed projects must identify the upstream tributary drainage area and perform a
downstream analysis. Levels of analysis required depend on the problems identified or
predicted. At a minimum, a Level 1 analysis must be submitted with the initial permit
application.
Response: The upstream and downstream analyses have been performed and are
summarized on Pages 12-14 of this report.
Core Requirement #3: Runoff Control
Proposed projects must provide runoff controls to limit the developed conditions peak
rates of runoff to the pre-development peak rates for specific storm events based on the
proposed project site existing runoff conditions, and install biofiltration measures.
Response: The proposed project improvements generate a 0.035 cfs increase in the 100-
year peak flow rate. Because the post-developed peak flow is less than 0.5 cfs more than
the existing peak flow, the project is exempt from flow control requirements.
Core Requirement #4: Conveyance System
All conveyance systems for proposed projects must be analyzed, designed and constructed
for existing tributary off-site runoff and developed on-site runoff from the proposed project.
Response: The proposed conveyance system has been designed to convey runoff for the
new impervious surfaces, with spill control in new PGIS areas. Any offsite runoff that
currently flows onsite will continue to be conveyed via the existing stormwater system.
Core Requirement #5: Erosion/Sedimentation Control Plan
All engineering plans for projects that propose to construct new, or modify existing
drainage facilities, must include a plan to install measures to control erosion and
PACLAND Project #10001074 Page 9
Walmart#2516-05 Expansion Technical Information Report Renton, Washington
sedimentation during construction and to permanently stabilize soil exposed during
construction.
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.
Core Requirement #6: Maintenance and Operation
Maintenance of all drainage facilities constructed or modified by a proposed project is the
responsibility of the property owner except King County may assume maintenance of
drainage facilities constructed for formal Plat Subdivisions and some Short Plat
Subdivisions two years after construction approval.
Response: A Maintenance and Operations Manual is included in Appendix A of this
report.
Core Requirement #7: Bonds and Liability
All drainage facilities for proposed projects (except drainage stub-out connections,
downspout roof drain infiltration systems and downspout dispersion systems for single-
family residential lots) must be constructed in conformance with the bond and liability
requirements of King County Code 9.04.100.
Response: A Bond Quantities worksheet will be included with the final submittal of the
construction documents.
Special Requirement #1: Critical Drainage Areas
Response: The project site does not lie within a designated critical drainage area.
Special Requirement #2: Compliance with an Existing Master Drainage Plan
Response: The project site does not lie within an area covered by an approved Master
Drainage Plan.
Special Requirement #3: Conditions Requiring a Master Drainage Plan
Response: The proposed improvements do not meet the conditions which would require
a Master Drainage Plan.
Special Requirement #4: Adopted Basin or Community Plans
Response: The proposed project lies within the Black River Drainage Basin and the City
Center Community Planning area.
PACLAND Project#10001074 Page 10
Walmart#2516-05 Expansion Technical Information Report Renton, Washington
Special Requirement #5: Special Water Quality Controls
Response: The proposed project will not directly discharge runoff to a regional facility,
receiving water, lake, wetland, or closed depression without on-site peak rate runoff
control or discharge to a Type 1 or 2 stream or Type 1 wetland.
Special Requirement #6: Coalescing Plate Oil/Water Separators
Response: The proposed project will not construct more than 5 acres of new impervious
surface.
Special Requirement #7: Closed Depressions
Response: The project will not discharge runoff to an existing closed depression.
Special Requirement #8: Use of Lakes, Wetlands, or Closed Depressions for Peak Runoff
Rate Control
Response: The project does not propose to use a lake, wetland, or closed depression for
peak rate runoff control.
Special Requirement #9: Delineation of 100 Year Floodplain
Response: The project site lies within Zone X, which is outside the 100 Year and 500 Year
Floodplains.
Special Requirement #10: Flood Protection Facilities for Type 1 and 2 Streams
Response: There are no Type 1 or 2 Streams located on or near the project site.
Special Requirement #11: Geotechnical Analysis and Report
Response: The proposed project does not meet the threshold for this requirement.
However, a Geotechnical Report has been prepared by Terracon Consultants, Inc..
Special Requirement #12: Soils Analysis and Report
Response: The proposed project does not meet the threshold for this requirement.
However, a soils analysis is included in the Geotechnical Report, which was prepared by
Terracon Consultants, Inc..
PACLAND Project #10001074 Page 11
Walmart#2516-05 Expansion Technical Information Report Renton, Washington
Off-Site Analysis
Upstream Analysis
Based on topographic survey and field reconnaissance, there is minimal tributary area to
this site. SW Seventh Street to the north and Hardie Avenue SW/Rainier Avenue S. to the
east intercept stormwater before it reaches the site. Additionally, the existing topography
surrounding the site prevents any significant amount of run-on.
Downstream Analysis
After receiving treatment in the existing bio-swale, runoff enters the municipal stormwater
system in SW Seventh Street. This system continues west for approximately one mile
before discharging to Springbrook Creek (Black River).
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PACLAND Project#10001074 Page 12
Wal mart#2516-05 Expansion Technical Information Report Renton, Washington
# Photo Description
Sub-basin 2 currently
drains to a bioswale
near the SW Seventh
' • `' , . _- Street entrance for
W 1 water quality treatment.
1 _ Runoff from the
proposed
improvements will also
` be routed to this swale
after receiving water
'k quality treatment in the
proposed bioswale.
-- From the existing
bioswale looking east.
Existing roof and off-site
(bank) runoff bypass the
existing bioswale. This
2 runoff is conveyed
directly to the City
stormwater system via a
series of underground
pipes and catch basins.
PACLAND Project#10001074 Page 13
Walmart#2516-05 Expansion Technical Information Report Renton, Washington
# Photo Description
From the SW Seventh
Street entrance looking
north.
Discharge from the
3 existing bioswale joins
the untreated roof and
off-site runoff(sub-basin
1) in the municipal
storm system in SW
Seventh Street.
F:.
From SW Seventh
- Street looking west.
•
The municipal storm
system continues west
`' � ea*~ - — f� - - for approximately one
4 mile before discharging
to Springbrook Creek
(Black River). Sub-basin
3 enters the City system
in SW Seventh Street
upstream of sub-basins
#1 and #2.
Evidence of Existing or Predicted Problems
There is no visible evidence of drainage problems on or near the project site. Per the City
of Renton Utility Systems Division, there is no record of significant flooding or drainage
complaints within 14 mile of 743 Rainier Avenue South. In addition, no drainage problems
are predicted as a result of the proposed improvements.
PACLAND Project#10001074 Page 14
Walmart#2516-05 Expansion Technical Information Report Renton, Washington
Retention/Detention Analysis and Design
The 1990 King County Surface Water Design Manual requires peak runoff control such
that the post-developed peak rate matches that of the predeveloped site for the 2-year, 10-
year, and 100-year storm events. The Santa Barbara Urban Hydrograph (SBUH)
methodology was utilized for the analysis of these stormwater events. Stormshed 3G
software by Engenious Systems, Inc., was used to assist with the modeling.
The rainfall data in Table 4, below, was determined from the 2-, 10-, and 100-year
Isopluvial Maps. A copy of these maps which shows the site location can be found in
Appendix C of this report.
Table 4
Rainfall
Event 24-Hour Rainfall
2-year 2.0 in
10-year 2.9 in
100-year 3.9 in
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 a biofiltration swale located on the northwestern portion of
the site, near the eastern access from SW Seventh Street. After traveling through the swale,
runoff enters the municipal stormwater system located in SW Seventh Street. Currently
there is no detention on the project site. The pre-developed conditions and undetained
peak runoff rates for the entire site (13.65 acres) are shown in Tables 5, 6 and 7 below.
Table 5
Pre-Developed Conditions
Area Condition CN TC
0.68 AC Gravel 89 5 min
11.83 AC Impervious 98 5 min
1.14 AC Landscaping 86 5 min
Table 6
Existing Peak Runoff Rate - SBUH Method
Event Rate
2-year 5.601 cfs
10-year 8.580 cfs
100-year 11.848 cfs
PACLAND Project #10001074 Page 15
Walmart#2516-05 Expansion Technical Information Report Renton, Washington
Table 7
Existing Peak Runoff Rate - Continuous Method
Event Rate
2-year 5.97 cfs
10-year 10.02 cfs
100-year 18.44 cfs
Developed Site Hydrology
Changes to the site include the building expansion, demolition of the existing restaurant,
and paving of the existing gravel area north of the store. The gravel and restaurant rooftop
will be converted to pavement and landscaping and a portion of the existing pavement will
be converted to rooftop. The post-developed conditions and undetained peak runoff rates
for the entire site (13.65 acres) are shown in Tables 8, 9 and 10 below.
Table 8
Post-Developed Conditions
Area Condition CN TC
0 AC Gravel 89 5 min
12.14 AC Impervious 98 5 min
1.51 AC Landscaping 86 5 min
Table 9
Proposed Undetained Peak Runoff Rate -
SBUH Method
Event Rate
2-year 5.645 cfs
10-year 8.619 cfs
100-year 11.883 cfs
Table 10
Proposed Undetained Peak Runoff Rate-
Continuous Method
Event Rate
2-year 5.96 cfs
10-year 10.01 cfs
100-year 18.43 cfs
Hydrologic Analysis
The hydrologic analysis was done using both the Santa Barbara Urban Hydrograph (SBUH)
methodology and continuous modeling. Stormshed 3G software by Engenious Systems,
Inc. was utilized for the SBUH analysis and KCRTS was used for the continuous model
analysis. The existing gravel area was modeled as 50% impervious and 50% pervious in
KCRTS.
PACLAND Project#10001074 Page 16
Walmart#2516-05 Expansion Technical Information Report Renton, Washington
Retention/Detention System
Using the SBUH method for the post-developed conditions, the 100-year peak runoff rate
for the entire site increases by 0.035 cfs. Per Section 1.2.3-5 of the 1990 KCSWDM, if a
proposed project's post-developed peak runoff rate for the 100-year, 24-hour storm is less
than 0.5 cfs more than the pre-developed peak runoff rate, the project is exempt from
runoff control. If the site were analyzed using the continuous modeling method, the 100-
year peak runoff rate for the entire site actually decreases by 0.01 cfs under the post-
developed conditions.
Based on the results of these analyses, no detention is required or proposed for this
redevelopment.
Water Quality
The proposed redevelopment includes the building expansion, demolition of the existing
restaurant, and paving of the existing gravel area north of the store. The gravel and
restaurant rooftop which are currently non pollution generating impervious surfaces
(NPGIS) will be converted to pavement (PGIS) and landscaping. Additionally, a portion of
the existing pavement (PGIS) will be converted to rooftop (NPGIS).
There is an existing biofiltration swale in the northwestern portion of the site, which was
designed to treat the existing parking lot areas. Because the project will add more than
5,000 sf of new PGIS, additional water quality treatment will be provided.
New PGIS Areas
The new PGIS areas include the gravel area, landscaping, and restaurant rooftop which
will be converted to parking lot, proposed bioswale, and interior landscape islands. It is
not possible to collect the exact area of new PGIS, so runoff from an equivalent area of
currently untreated surface will be conveyed to the proposed biofiltration swale.
The total new area requiring treatment is approximately 0.60 acres and the area that will
receive treatment is equal to 0.91 acres. Exhibit 3 in Appendix A shows a depiction of the
existing undeveloped areas and new PGIS areas. Tables 11 and 12, below, contain the
developed conditions of the proposed bioswale's tributary area as well as the undetained
peak runoff rates.
Table 11
Post-Developed Conditions
Area Condition CN TC
0.71 AC Impervious 98 5 min
0.20 AC Landscaping 86 5 min
Table 12
Post-Developed Peak Runoff Rate (undetained)
Event Rate
2-year 0.3479 cfs
10-year 0.5482 cfs
100-year 0.7686 cfs
PACLAND Project#10001074 Page 1 7
Wal mart#2516-05 Expansion Technical Information Report Renton, Washington
The proposed bioswale was designed per the 1990 King County Surface Water Design
Manual, Section 1.3.5, using the criteria in Table 13 below.
Table 13
Bios wale Design Criteria — Single Event
Criteria Value
2-yr, 24-hr flow 0.3479 cfs
Design Flow Depth 0.25 feet
Manning's Coefficient 0.35
Residence Time 9 minutes
Side Slope 3.0 H:V
The resultant swale design would require a minimum bottom width of 7.52 feet and a
minimum treatment length of 91 feet. If the same swale were designed using a continuous
model and treating 60% of the 2-yr, 24-hr event, the criteria shown in Table 14 would be
used.
Table 14
Bios wale Design Criteria — Continuous
Criteria Value
60% of 2-yr, 24-hr flow 0.213 cfs
Design Flow Depth 0.17 feet
Manning's Coefficient 0.20
Residence Time 9 minutes
Side Slope 3.0 H:V
The resultant swale design would require a minimum bottom width of 5.68 feet and a
minimum treatment length of 111 feet.
The proposed bioswale for this site has an 8 foot bottom width, 115 foot treatment length,
and a 1.0% longitudinal slope. The swale will have an underdrain, and the bottom will be
lined with an impermeable liner. This design exceeds the minimum width and length
required by either method of analysis. Design calculations are located in Appendix D of
this report.
Enhanced Treatment
The new PGIS runoff will receive secondary treatment using StormFilter cartridges
downstream of the proposed bioswale. In order to accommodate 60% of the 2-yr, 24-hr
flow, CONTECH recommends ten (10) cartridges located within a 96" manhole. The cost
estimate for the structure and cartridges is approximately $28,900. The sizing and cost
estimate, as provided by CONTECH, are located in Appendix D of this report.
In addition to the CSF treatment and spill control, runoff from this structure will receive
additional treatment as it is conveyed through the existing bioswale, to the municipal
storm system in SW Seventh Street.
PACLAND Project#10001074 Page 18
Walmart#2516-05 Expansion Technical Information Report Renton,Washington
Conveyance System Analysis and Design
Conveyance
Per the 1990 King County Surface Water Design Manual, Section 4.3.4, the on-site
stormwater conveyance is calculated based on gravity flow analysis of the piping network.
Peak runoff associated with the 25-year storm event has been determined to be adequate.
Structures may overtop under the 100-yr event as allowed by Core Requirement #4.
Uniform Flow Analysis utilizing Manning's equation was employed with a Manning's "n"
value of 0.012.
Manning's equation - Q= 1.49/ xAxR2"xS1"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 total combined area of sub-basins 2a and 2b, the existing conveyance system
is adequate for the 25-yr storm event. All new pipes have been designed to meet or exceed
the 100-yr storm event. Conveyance calculations are located in Appendix D of this report.
Spill Control
Although it is not required under the 1990 KCSWDM, spill control will be implemented as
part of the site improvements. A tee section will be placed in the manhole preceding the
proposed bioswale in order to detain oil and other floatable pollutants before they enter
the downstream drainage system. A second tee will be placed in the manhole preceding
the existing bioswale.
100-Year Flood/Overflow Condition
Review of the most recent FIRM maps indicates that the project site lies within the Zone X,
which is determined to be outside of the 100-year flood plain.
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 SW Seventh Street.
PACLAND Project #10001074 Page 19
Walmart#2516-05 Expansion Technical Information Report Renton, Washington
Special Reports and Studies
The following Special Reports and Studies have been completed for this project:
• Initial Report of Geotechnical Engineering Evaluation — dated November 30, 2009
by Terracon Consultants, Inc..
• Phase I Environmental Site Assessment - dated October 20, 2009 by Terracon
Consultants, Inc..
• Transportation Impact Study— dated October 2009, by Transpo Group.
• Renton Retail Expansion Critical Areas and Habitat Evaluation memo — dated
September 18, 2009 by The Watershed Company.
PACLAND Project#10001074 Page 20
Walmart#2516-05 Expansion Technical Information Report Renton,Washington
Basin and Community Plan Areas
The project site lies within the Black River Drainage Basin and the City Center Community
Planning Area.
PACLAND Project#10001074 Page 21
Walmart#2516-05 Expansion Technical Information Report Renton,Washington
Other Permits
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
• Washington State Department of Ecology NPDES Permit
• Sewer Permit
• Water Permit
• City of Renton Right-of-Way Permit(s)
• King County Health Department
• King County Sewer Treatment
These permits will require approval by the City of Renton Planning Division, King County,
or the Department of Ecology.
PACLAND Project#10001074 Page 22
Walmart#2516-05 Expansion Technical Information Report Renton, Washington
Bond Quantities, Facility Summaries, and Declaration of Covenant
The following items will be submitted upon approval of the Building Permit plans:
• Site Improvement Bond Quantity Worksheet
• Declaration of Covenant for Maintenance and Inspection of Flow Control BMPs
PACLAND Project#10001074 Page 23
Wal mart#2516-05 Expansion Technical Information Report Renton, Washington
Erosion/Sedimentation Control Design
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 expansion area.
5. Grade site.
6. Install water quality elements.
7. Pave site.
8. Remove temporary erosion control features once site is fully stabilized.
3. Trapping Sediment
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.
PACLAND Project#10001074 Page 24
Walmart#2516-05 Expansion Technical Information Report Renton, Washington
The following structural items will be used to control erosion and sedimentation processes:
• Stabilized construction entrances and/or wheel washes
• Filter fabric fences
• Catch Basin Inlet Sediment Protection
• Proper Cover measures
Daily inspection of the erosion control measures will be required during construction.
Any sediment buildup shall be removed and disposed of off-site.
Vehicle tracking of mud off-site shall be avoided. A stabilized construction entrance
and/or wheel wash will be installed at a location to enter the 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 7 days and, in some cases, immediate
seeding will be required.
4. Wet Weather TESC Operating Plan
Work between October 1St and April 30`h must adhere to the Wet Season Special
Provisions noted in the 1990 KCSWDM and NPDES.
PACLAND Project #10001074 Page 25
Wal mart#2516-05 Expansion Technical Information Report Renton, Washington
Maintenance and Operations Manual
See Appendix A for Maintenance and Operations Manual.
PACLAND Project#10001074 Page 26
Walmart#2516-05 Expansion Technical Information Report Renton, Washington
Appendix A — Maintenance and
Operations Manual
PACLAND Project#10001074 Page 27
Walmart#2516-05 Expansion Technical Information Report Renton, Washington
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:
Table 15
Maintenance Checklist for Catch Basins and Inlets
Frequency Drainage .I Problem Conditions To Check For Conditions That Should Exist
System
Feature
M,S General Trash,debris,and Trash or debris in front of the No trash or debris located
sediment in or on catch basin opening is blocking immediately in front of catch
basin capacity by more than 10%. basin opening. Grate is kept
clean and allows water to
enter.
M Sediment or debris(in the basin) No sediment or debris in the
that exceeds 1/3 the depth from catch basin. Catch basin is
the bottom of basin to invert of the dug out and clean.
lowest pipe into or out of the
basin.
M,S Trash or debris in any inlet or pipe Inlet and Outlet pipes free of
blocking more than 1/3 of its trash or debris.
height.
M Structural damage Corner of frame extends more than Frame is even with curb.
to frame and/or top Y,inch past curb face into the
slab street(if applicable).
Top slab has holes larger than 2 Top slab is free of holes and
square inches or cracks wider than cracks.
�Y4 inch(intent is to make sure all
material is running into the basin).
M Frame not sitting flush on top slab, Frame is sitting flush on top
i.e.,separation of more than Y, slab.
inch of the frame from the top
slab.
Cracks in basin Cracks wider than'h inch and Basin replaced or repaired to
walls/bottom longer than 3 feet,any evidence of design standards. Contact a
soil particles entering catch basin professional engineer for
through cracks,or maintenance evaluation.
person judges that structure is
unsound.
A Cracks wider than' inch and No cracks more than Ys inch
longer than 1 foot at the joint of wide at the joint of
any inlet/outlet pipe or any inlet/outlet pipe. Contact a
evidence of soil particles entering professional engineer for
catch basin through cracks. evaluation.
A Settlement/ Basin has settled more than 1 inch Basin replaced or repaired to
misalignment or has rotated more than 2 inches design standards. Contact a
out of alignment. professional engineer for
evaluation.
If you are unsure whether a problem exists, please contact a Professional Engineer.
Comments:
A = Annual (March or April, preferred)
M = Monthly(see schedule)
S = After major storms(use 1-inch in 24 hours as a guideline)
PACLAND Project#10001074 Page 28
Walmart#2516-05 Expansion Technical Information Report Renton, Washington
M,S Fire hazard of other Presence of chemicals such as No color,odor,or sludge.
pollution natural gas,oil,and gasoline. Basin is dug out and clean.
Obnoxious color,odor,or sludge
noted.
M,S Outlet pipe is Vegetation or roots growing in No vegetation or root growth
clogged with inlet/outlet pipe joints that are present.
vegetation more than 6 inches tall and less
than 6 inches apart.
Maintenance Checklist for Conveyance Systems (Pipes)
Frequency Drainage .1 Problem Conditions To Check For Conditions That Should Exist
System
Feature
M,S Pipes Sediment Sediment filling more than 20%of the Pipe cleaned of all sediment and
accumulation pipe. debris.
M Trash and Trash and debris accumulated in No trash or debris in pipes.
debris inlet/outlet pipes(including floatables
and non-floatables).
Damaged Protective coating is damaged;rust is Pipe repaired or replaced.
(rusted,bent, causing more than 50%deterioration to
or crushed) any part of pipe.
�t Any dent that significantly impedes Pipe repaired or replaced.
flow(i.e.,decreases the cross section
area of pipe by more than 20%).
tit Pipe has major cracks or tears allowing Pipe repaired or replaced.
groundwater leakage.
Vanes Catch See Catch Basins Checklist. See Catch Basins Checklist.
basins
If you are unsure whether a problem exists, please contact a Professional Engineer.
Comments:
A = Annual (March or April, preferred)
M = Monthly(see schedule)
S = After major storms(use 1-inch in 24 hours as a guideline)
PACLAND Project#10001074 Page 29
Walmart#2516-05 Expansion Technical Information Report Renton, Washington
Maintenance Checklist for Fencing/Shrubbery Screen/Landscaping
Frequency Drainage J Problem Conditions To Check For Conditions That Should Exist
System
Feature
M General Missing or broken Any defect in the fence or screen Fence is mended or shrubs
parts/dead shrubbery that permits easy entry to a facility replaced to form a solid barrier to
entry.
M,S Erosion Erosion has resulted in an opening Replace soil under fence so that
under a fence that allows entry by no opening exceeds 4 inches in
people or pets. height.
M Unruly vegetation Shrubbery is growing out of control Shrubbery is trimmed and weeded
or is infested with weeds. to provide appealing aesthetics.
Do not use chemicals to control
weeds.
A Wire Damaged parts Posts out of plumb more than 6 Posts plumb to within 1-1/2
Fences inches. inches of plumb.
A Top rails bent more than 6 inches. Top rail free of bends greater than
1 inch.
A Any part of fence(including posts, Fence is aligned and meets design
top rails,and fabric)more than 1 foot standards.
out of design alignment.
A Missing or loose tension wire. Tension wire in place and holding
fabric.
Missing or loose barbed wire that is Barbed wire in place with less
sagging more than 2-1/2 inches than 3-inch sag between posts.
between posts.
Extension arm missing,broken,or Extension arm in place with no
bent out of shape more than 1-1/2 bends larger than Yinch.
inches.
A Deteriorated paint or Part or parts that have a rusting or Structurally adequate posts or
protective coating scaling condition that has affected parts with a uniform protective
structural adequacy. coating.
Openings in fabric Openings in fabric are such that an No openings in fabric.
8-inch diameter ball could fit
through.
tit General Weeds Weeds growing in more than 20%of Remove trash and debris and
Land- (nonpoisonous) the landscaped area(trees and dispose as prescribed by the
scaping shrubs only). County.
M Insect hazard Any presence of poison ivy or other Ditch cleaned of all sediment and
poisonous vegetation or insect nests. debris so that it matches design.
M,S Trash or litter Dumping of yard wastes such as Remove trash and debris and
grass clippings and branches onto dispose as prescribed by the
grounds. Unsightly accumulation of County.
nondegradable materials such as
glass,plastic,metal,foam,and
coated paper.
M,S Erosion of Ground Noticeable rills are seen in Causes of erosion are identified
Surface landscaped areas. and steps taken to slow
down/spread out the water.
Eroded areas are filled,contoured,
and seeded.
A Trees and Damage Limbs or parts of trees or shrubs that Trim trees/shrubs to restore shape.
shrubs are split or broken which affect more Replace trees/shrubs with severe
than 25%of the total foliage of the damage.
tree or shrub.
M Trees or shrubs that have been Replant tree,inspecting for injury
blown down or knocked over. to stem or roots. Replace if
severely damaged.
A Trees or shrubs which are not Place stakes and rubber-coated ties
adequately supported or are leaning around young trees/shrubs for
over,causing exposure of the roots. support.
If you are unsure whether a problem exists, please contact a Professional Engineer.
Comments:
A = Annual (March or April, preferred)
M = Monthly(see schedule)
S = After major storms(use 1-inch in 24 hours as a guideline)
PACLAND Project#10001074 Page 30
Walmart#2516-05 Expansion Technical Information Report Renton, Washington
Maintenance Checklist for StormFilter (Cartridge Type)
Frequency Drainage \ Problem Conditions To Check For Conditions That Should Exist
System
Feature
A Site Trash and Any trash or debris which impairs the Trash and debris removed
Debris function of the facility. from facility.
A Contaminants Any evidence of contaminants or Materials removed and
and pollution pollution such as oils,gasoline, disposed of according to
concrete slurries or paint. applicable regulations.Source
control BMPs implemented if
appropriate.No contaminants
present other than a surface oil
film.
A Life cycle System has not been inspected for three Facility is re-inspected and any
years. needed maintenance is
performed.
A Vault Sediment on Greater than 2 inches of sediment. Vault is free of sediment.
Treatment vault floor
Area
A Sediment on top Greater than'1/2 inch of sediment. Vault is free of sediment.
of cartridges
q Multiple scum Thick or multiple scum lines above top Cause of plugging corrected,
lines above top of cartridges.Probably due to plugged canisters replaced if necessary.
of cartridges canisters or underdrain manifold.
A Vault Damage to wall, Cracks wider than 1/2-inch and any Vault replaced or repaired to
Structure Frame,Bottom, evidence of soil particles entering the design specifications.
and/or Top Slab structure through the cracks,or
qualified inspection personnel
determines the vault is not structurally
sound.
A Baffles Baffles corroding,cracking,warping, Repair or replace baffles to
Damaged and/or showing signs of failure as specification.
determined by maintenance/inspection
person.
A Filter Media Standing water 9 inches or greater of static water in the No standing water in vault 24
in vault vault for more than 24 hours following hours after a rain event.
a rain event and/or overflow occurs
frequently.Probably due to plugged
filter media,underdrain or outlet pipe.
A Short Circuiting Flows do not properly enter filter Flows go through filter media.
cartridges.
A Underdrains Sediment/ Underdrains or clean-outs partially Underdrains and clean-outs
and Clean- Debris plugged or filled with sediment and/or free of sediment and debris.
Outs debris.
A Inlet/Outlet Sediment Sediment filling 20%or more of the Inlet/outlet pipes clear of
Pipe accumulation pipe. sediment.
A Trash and debris Trash and debris accumulated in No trash or debris in pipes.
inlet/outlet pipes(including floatables
and non-floatables).
Damaged Cracks wider than'h-inch at the joint No cracks more than 14-inch
of the inlet/outlet pipes or any evidence wide at the joint of the
of soil entering at the joints of the inlet/outlet pipe.
inlet/outlet pipes.
A Access Cover/lid not in Cover/lid missing or only partially in Manhole access covered.
Manhole place place.Any open manhole requires
immediate maintenance.
A Locking Mechanism cannot be opened by one Mechanism opens with proper
mechanism not maintenance person with appropriate tools.
working tools.Bolts cannot be seated.Self-
locking cover/lid does not work.
A Cover/lid One maintenance person cannot Cover/lid can be removed and
difficult to remove cover/lid after applying 80 lbs reinstalled by one
remove of lift. maintenance person.
A Ladder rungs Missing rungs,misalignment,rust,or Ladder meets design
PACLAND Project#10001074 Page 31
Walmart#2516-05 Expansion Technical Information Report Renton, Washington
unsafe cracks. standards.Allows
maintenance person safe
access.
A Large access Damaged or Large access doors or plates cannot be Replace or repair access door
doors/plate difficult to opened/removed using normal so it can be opened as
open equipment. designed.
A Gaps,doesn't Large access doors not flat and/or Doors close flat and cover
cover access opening not completely covered. access opening completely.
completely
A Lifting Rings Lifting rings not capable of lifting Lifting rings sufficient to lift or
missing,rusted weight of door or plate. remove door or plate.
Maintenance Checklist for Basic Biofiltration Swale (New and Existing)
Frequency Drainage . Problem Conditions To Check For Conditions That Should Exist
System
Feature
M,S Site Trash and Any trash or debris accumulated at the No trash or debris at the site.
Debris site.
M,S Contaminants Any evidence of contaminants or Materials removed and
and pollution pollution such as oils,gasoline, disposed of according to
concrete slurries or paint. applicable regulations.Source
control BMPs implemented if
appropriate.No contaminants
present other than a surface oil
film.
M,S Swale Sediment Sediment depth exceeds 2 inches in No sediment deposits occur in
Section Accumulation 10%of the swale treatment area. treatment area.Grass growth is
Sediment inhibits grass growth over not inhibited by sediment.
10%of the swale length.Sediment Flow spreads evenly through
inhibits even spreading of flow. swale.
Erosion/ Eroded or scoured swale bottom due to No eroded or scoured areas in
scouring channelization or high flows. bioswale.Cause of erosion or
scour addressed.
tit Poor vegetation Grass is sparse or bare or eroded Swale has no bare spots and
coverage patches occur in more than 10%of the grass is thick and healthy.
swale bottom.
tit Grass too tall Grass excessively tall(greater than 10 Grass is between 3 and 4
inches),grass is thin or nuisance weeds inches tall,thick and healthy.
and other vegetation has taken over. No clippings left in swale.No
nuisance vegetation present.
tit Excessive shade Grass growth is poor because sunlight Healthy grass growth or
does not reach swale. conversion to a wet bioswale.
M,S Constant Continuous flow through the swale, Baseflow removed from swale
baseflow even when it has been dry for weeks or by a low-flow-pea-gravel drain
an eroded,muddy channel has formed or bypassed around the swale.
in the swale bottom.
M,S Standing water Water pools in the swale between Swale freely drains and there
storms or does not drain freely. is no standing water in swale
between storms.
M,S Channelization Flow concentrates and erodes channel No flow channels in swale.
through swale.
M,S Inlet/Outlet See Pipes Checklist. See Pipes Checklist.
Pipes
If you are unsure whether a problem exists, please contact a Professional Engineer.
Comments:
A = Annual (March or April, preferred)
M = Monthly(see schedule)
S = After major storms (use 1-inch in 24 hours as a guideline)
PACLAND Project#10001074 Page 32
Walmart#2516-05 Expansion Technical Information Report Renton, Washington
Appendix B — Exhibits and
Grading and Drainage Plan
PACLAND Project#10001074 Page 33
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Walmart#2516-05 Expansion Technical Information Report Renton, Washington
Appendix C — Isopluvial Maps
PACLAND Project#10001074 Page 34
Walmart#2516-05 Expansion Technical Information Report Renton, Washington
2-Year 24 Hour Isopluvial
______ -,- r R9M.,I.Mw}r'IY
nY _ +.i RAN#IIRT•
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In Inches fi g""" L.1 �`-,
PACLAND Project #10001074 Page 35
Walmart#2516-05 Expansion Technical Information Report Renton, Washington
10-Year 24 Hour Isopluvial
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in Inches `"""" g41• ' `a
PACLAND Project#10001074 Page 36
Walmart#2516-05 Expansion Technical Information Report Renton, Washington
100-Year 24 Hour Isopluvial
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-', ��
in Inches '""° . �•
PACLAND Project#10001074 Page 37
Walmart#2516-05 Expansion Technical Information Report Renton, Washington
Appendix D — Design Calculations
PACLAND Project#10001074 Page 38
Walmart#2516-05 Expansion Technical Information Report Renton, Washington
Hydrology Calculations
PACLAND Project#10001074 Page 39
Page ] of 1
Appended on: Friday, February 05,2010 2:19:29 PM
Existing Event Summary
Event Peak Q (cfs) Peak T(hrs) Hyd Vol (acft) Area (ac) Method
2 yr 24 hr 5.6012 8.00 1.8487 13.65 SBUH
other 5.9341 8.00 1.9598 13.65 SBUH
5 year 6.9299 8.00 2.2942 13.65 SBUH
10 year 8.5796 8.00 2.8544 13.65 SBUH
25 year 10.2184 8.00 3.4169 13.65 SBUH
100 year 11.8483 8.00 3.9808 13.65 SBUH
All results based on storm duration of 24.0 hours. This is ok if all precipitations are appropriate for the
storm duration. If some design event precipitations are for different duration storms, those results are
incorrect
Record Id: Existing
Design Method SBUH Rainfall type TYPEIA.RAC
Hyd Intv 10.00 min Peaking Factor 484.00
Storm Duration 24.00 hrs Abstraction Coeff 0.20
Pervious Area 13.65 ac DCIA 0.00 ac
Pervious CN 96.53 DC CN 0.00
Pervious TC 5.00 min DC TC 0.00 min
I Pervious CN Calc
Description I SubArea Sub cn
Gravel Roads& Parking Lots 0.68 ac 89.00
Open spaces, lawns,parks (>75%grass) 1.16 ac 86.00
Impervious surfaces (pavements,roofs, etc) 11.81 ac 98.00
Pervious Composited CN (AMC 2) 96.5319
Pervious TC Calc
Type Description Length Slope I Coeff Misc TT
' Shallow Paved and gravel areas (n=0.012) 300.00 ft 1.0% 0.012 1.8691 min '
Pervious TC 1.8691 min
Licensed to: PACLAND - Seattle
file://S:\Washington\Renton\grimes\Rainier Ave & 7th Expansion\4Reports\Storm\Stormsh... 2/5/2010
Page 1 of 1
Appended on: Friday, February 05,2010 2:19:46 PM
Proposed Event Summary
Event Peak Q (cfs) Peak T(hrs) Hyd Vol (acft) Area (ac) Method
2 yr 24 hr 5.6456 8.00 1.8644 13.65 SBUH
other 5.9781 8.00 1.9756 13.65 SBUH
5 year 6.9723 8.00 2.3105 13.65 SBUH
10 year 8.6193 8.00 2.8713 13.65 SBUH
25 year 10.2555 8.00 3.4343 13.65 SBUH
100 year 11.8829 8.00 3.9987 13.65 SBUH
All results based on storm duration of 24.0 hours. This is ok if all precipitations are appropriate for the
storm duration. If some design event precipitations are for different duration storms, those results are
incorrect
Record Id: Proposed
Design Method SBUH 'Rainfall type TYPE IA.RAC
Hyd Intv 10.00 min Peaking Factor 484.00
Storm Duration 24.00 hrs Abstraction Coeff 0.20
Pervious Area 13.65 ac DCIA 0.00 ac
Pervious CN 96.67 DC CN 0.00
Pervious TC 5.00 min DC TC 0.00 min
y
Pervious CN Calc
Description SubArea Sub cn
Impervious surfaces (pavements,roofs, etc) 12.14 ac 98.00
Open spaces,lawns,parks(>75%grass) 1.51 ac 86.00
Pervious Composited CN (AMC 2) 96.6725
Pervious TC Calc
Type Description Length Slope Coeff Misc TT
Sheet Smooth Surfaces. 30.00 ft 2.0% 0.011 0.00 in 0.5232 min
Int Channel CMP pipe(n=0.024) 200.00 ft 0.5% 0.024 2.2202 min
Pervious TC 2.7434 min
Licensed to: PACLAND - Seattle
file://S:\Washington\Renton\grimes\Rainier Ave& 7th Expansion\4Reports\Stonn\Stormsh... 2/5/2010
Walmart#2516-05 Expansion Technical Information Report Renton, Washington
Bioswale Design Calculations
PACLAND Project#10001074 Page 40
Page 1 of 1
Appended on: Monday,February 08,2010 9:58:42 AM
Proposed Event Summary
Event Peak Q (cfs) Peak T (hrs) Hyd Vol (acft) Area (ac) Method
2 yr 24 hr 0.3479 8.00 0.1149 0.91 SBUH
other 0.3702 8.00 0.1222 0.91 SBUH
5 year 0.4371 8.00 0.1442 0.91 SBUH
10 year 0.5482 8.00 0.1811 0.91 SBUH
25 year 0.6587 8.00 0.2183 _ 0.91 SBUH
100 year 0.7686 8.00 0.2557 0.91 SBUH
All results based on storm duration of 24.0 hours. This is ok if all precipitations are appropriate for the
storm duration. If some design event precipitations are for different duration storms,those results are
incorrect
Record Id: Proposed
Design Method SBUH Rainfall type TYPE1A.RAC
Hyd Intv 10.00 min Peaking Factor 484.00
Storm Duration 24.00 hrs Abstraction Coeff 0.20
Pervious Area 0.91 ac DCIA 0.00 ac
Pervious CN 95.36 DC CN 0.00
Pervious TC 5.00 min DC TC 0.00 min
Pervious CN Calc
Description SubArea Sub en
Impervious surfaces(pavements,roofs, etc) 0.71 ac 98.00
Open spaces, Iawns,parks (>75%grass) 0.20 ac 86.00
Pervious Composited CN(AMC 2) 95.3626
Pervious TC Calc
Type Description Length Slope Coeff Misc TT
Sheet Smooth Surfaces. 30.00 ft 2.0% 0.011 0.00 in 0.5232 min
1
Int Channel CMP pipe(n=0.024) 200.00 ft 0.5% 10.024 I 2.2202 min
Pervious TC 2.7434 min
Licensed to: Engenious Systems, Inc.
file://S:\Washington\Renton\grimes\Rainier Ave& 7th Expansion\4Reports\Storm\Stormsh... 2/8/2010
BIOSWALE DESIGN
(500 Vi)
Project name: Renton, WA Date: 1/29/10
Project number: 10001074 Designer: AKP
Swale Title: On-Site
Preliminary Steps (P)
Step#
P-1 Qwq(2-yr, 24-hr): 0.348 cfs Water quality design flow
P-2 Slope of swale 0.01 ft/ft Swale slope < 2%, underdrains required
P-3 Select vegetation to be used Grass Legume Mix
Design Steps (D)
Step#
D-1 Design flow depth (y): 0.25 ft
D-2 Manning's roughness coeff(n,.,,): 0.35
D-3 Side slope(Z): 3.0 H:V
D-4a Swale bottom width(b): 7.52 ft
b—Q*n/1.486*y"1.667*s"0.5-Z*y
D-4b Top Width (T) °9:02 ft
T—b+2*y*z
D-5 Area 2.07 sf
A—(b*y)+(Z*y"2)
D-6 Flow Velocity 0:17 fps 90.9 =Length (Feet)w/9 min res time
v—Q/A
D-7 Is design adequate? Yom. Okay-V < 1.5 fps proceed to step SC-1
D-8 Degree of retardance D Table 1I1-6.2 (D or E)
D-9 First Approx for VR 1.70 Table III-6.6, n = nwq from step D-2
D-10 Hydraulic Radius i"i ft
R = V*RNmax
D-11 Actual VR
VR— 1.486*R"1.667*s"0.5/n
D-12 % difference :
D-13 Actual V "`-Ya;`-; fps
V—VR/R
D-14 Channel X-sec area sf
A=Q/A
D-15a New Swale bottom width (b): ft
b=Aly-Z*y
D-15b Channel width T I - ft
T—b+2"y*z
D-16 if biofiltration swale is still too wide, see DOE page 111-6-17 for more info and options
Stability Check Steps (SC)
Step#
SC-1 Qwq(100-yr, 24-hr): 0.78 cfs
SC-2a Condition of vegetation Good (Good or Fair)
SC-2b Height of grass @ first storm 0.25 ft
SC-3 Degree of retardance D Table III-6.2 (D or E)
SC-4 Max allowed Velocity 3.00 fps Table III-6.3
SC-5 Trial Mannings n 0.043 (Good initial choice 0.04)
SC-6 First Approx for VR 2.70 Table III-6.6
BIOSWALE DESIGN
SC-7 Hydraulic Radius 0.90 it
R — V*R/Vmax
SC-8 Actual VR 2.93
VR- 1.486*R"1.667*s"0.5/n
SC-9 °k, difference 7.95
SC-10 Actual V 3.26 Ips
V—VR/R
SC-11 X-sec area 0.24 sf
A—Q/V
SC-12 Compare A with orig Yes Swale is stable
New y— 1.2 ft
New b— 8.00 ft
b—Q*n11.486"y"1.667*s"0.5-Z*y
New T— 15.20 ft
T—b+2*y*z
SC-13 Depth of flow 1.2 ft
y-(t-b)/2z
SC-14 Total swale depth 2.20 ft
yt—y+1
SC-15 Hydraulic Radius 1.16 tt
R—(b*yt+Z'yt"2)/(b+2yt*(Z"2+ 11"0.5
SC-162 Channel X-sec area 32.12 sf
SC-16k Channel Capacity 15.06 cfs Okay,Capacity > 100-yr,24-hr Storm
Q= 1.486*A'R"0.677*s"0.5/n
1. 1
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SPOKE WITH:
E3Y COMPANY:
PEOIEi�: TELEPHONE#:
SWhL>r CALLS cooliwuoas ?tET1-100
r(uz15 - .-Y2 FLDal = 0.35.5 c.F5
607. (0.355 ) = 0.113 C.FS
boTToM W Iall-1 • b .7._12.2.1,11 0.po _ S.6$
1.({q(0.'67)14'7(Qol)as
FLou.t vE.Loa1' : \l,A - L213 : ,0.206 Gf,S
5.68 Co.167)+3(0.167)Z
5JALE. LENGTH: L= .540(0.20‘) = 111.2 ?'4
Walmart#2516-05 Expansion Technical Information Report Renton, Washington
StormFilter Cartridge Sizing and Cost Estimate
PACLAND Project#10001074 Page 41
Page l of I
Appended on: Monday, February 08,2010 9:58:42 AM
Proposed Event Summary
Event Peak Q (cfs) Peak T (hrs) Hyd Vol (acft) Area (ac) Method
2 yr 24 hr 0.3479 8.00 0.1149 0.91 SBUH
other 0.3702 8.00 0.1222 0.91 SBUH
5 year 0.4371 8.00 0.1442 0.91 SBUH
l0 year 0.5482 8.00 0.1811 0.91 SBUH
25 year 0.6587 8.00 0.2183 0.91 SBUH
100 year 0.7686 8.00 0.2557 0.91 SBUH
All results based on storm duration of 24.0 hours. This is ok if all precipitations are appropriate for the
storm duration. If some design event precipitations are for different duration storms,those results are
incorrect
Record Id: Proposed
Design Method SBUH Rainfall type TYPE1A.RAC
Hyd Intv 10.00 min Peaking Factor 484.00
Storm Duration 24.00 hrs Abstraction Coeff 0.20
Pervious Area 0.91 ac DCIA 0.00 ac
Pervious CN 95.36 DC CN 0.00
Pervious TC 5.00 min DC TC 0.00 min
Pervious CN Calc
1 Description SubArea Sub cn
Impervious surfaces (pavements,roofs, etc) 0.71 ac 98.00
Open spaces,lawns,parks (>75%grass) 0.20 ac 86.00
Pervious Composited CN(AMC 2) 95.3626
Pervious TC Calc
Type Description Length Slope Coeff Misc TT
Sheet Smooth Surfaces. 30.00 ft 2.0% 0.011 0.00 in 0.5232 min
Int Channel CMP pipe(n=0.024) 200.00 ft 0.5% 0.024 2.2202 min 1
Pervious TC 2.7434 min
Licensed to: Engenious Systems, Inc.
file://S:\Washington\Renton\grimes\Rainier Ave& 7th Expansion\4Reports\Storm\Stormsh... 2/8/201 0
BIOSWALE DESIGN
("OLIN)
Project name: Renton, WA Date: 1/29/10
Project number: 10001074 Designer: AKP
Swale Title: On-Site
Preliminary Steps (P)
Step#
P-1 Qwq(2-yr,24-hr): 0.348 cfs Water quality design flow
P-2 Slope of swale 0.01 ft/ft Swale slope < 2%, underdrains required
P-3 Select vegetation to be used Grass Legume Mix
Design Steps (D)
Step#
D-1 Design flow depth (y): 0.25 ft
D-2 Manning's roughness coeff(rn.,,): 0.35
D-3 Side slope(Z): 3.0 H:V
D-4a Swale bottom width (b): 7.52 ft
b—Q*n11.486*y"1.667*s'0.5-Z*y
D-4b Top Width (T) .9.02 ft
T—b+2*y*z
D-5 Area 2.07 sf
A—(b*y)+(Z*y"2)
D-6 Flow Velocity 0.17 fps 90.9 =Length (Feet)w/9 min res time
v=QIA
D-7 Is design adequate? Yes. Okay-V < 1.5 fps proceed to step SC-1
D-8 Degree of retardance D Table III-6.2 (D or E)
D-9 First Approx for VR 1.70 Table III-6.6, n = nwq from step D-2
D-10 Hydraulic Radius MEM ft
R = V*RNmax
D-11 Actual VR
VR—1.486*R"1.667*s"0.5/n
D-12 % difference
D-13 Actual V MEM fps
V—VR/R
D-14 Channel X-sec area - sf
A=Q/A
D-15a New Swale bottom width (b): `- - ft
b=Aly-Z*y
D-15b Channel width T - ft
T—b+2*y*z
D-16 If biofiltration swale is still too wide, see DOE page(11-6-17 for more info and options
Stability Check Steps (SC)
Step#
SC-1 Qwq(100-yr, 24-hr): 0.78 cfs
SC-2a Condition of vegetation Good (Good or Fair)
SC-2b Height of grass(q?first storm 0.25 ft
SC-3 Degree of retardance D Table III-6.2 (D or E)
SC-4 Max allowed Velocity 3.00 fps Table III-6.3
SC-5 Trial Mannings n 0.043 (Good initial choice 0.04)
SC-6 First Approx for VR 2.70 Table III-6.6
BIOSWALE DESIGN
SC-7 Hydraulic Radius 0.90 ft
R = V*R/Vmax
SC-8 Actual VR 2.93
VR-1.486*R"1.667*s"0.5/n
SC-9 % difference 7:95
SC-10 Actual V r, x.26 fps
V=VR/R
SC-11 X-sec area 0.24 sf
A—Q/V
SC-12 Compare A with orig Ycs Swale is stable
New y— 1.2 ft
New b— 8.00 ft
b—Q*n/1.486*y"1.667*s"0.5-Z 0 y
New T— 15.20 ft
T=b+2*y*z
SC-13 Depth of flow 1.2 ft
y—(t-b)/2z
SC-14 Total swale depth 1 2.20 ft
yt=y+1
SC-15 Hydraulic Radius 1.16 ft
R=(b*yt+Z'yt"2)/(b+2yt*(Z"2+ 1)^0.5
SC-16i Channel X-sec area 1, 32.12 sf
SC-16k Channel Capacity 15.06 cfs Okay,Capacity > 100-yr,24-hr Storm
Q= 1.486*A'R"0.677*s"0.5/n
DATE: SPOKE WITH:
BY. COMPANY:
PROJECT: TELEPHONE#:
WWW.PACLAND.COM
SwAL.E CALLS CASIFJ(, col-yriw 400$ ME1l-100
KCJZTS - 2-YR. FLoki = a355 CFS
O7, (o-355) .- O.213 CFS
bo TTOM W 1 t7T H • 137-2_12.11111).20) S.68 V-
I.14iCO.167)14'7("I)°
F OUJ v rc uoc..fy = = O 1[3 _ 0.206 c
5.68 65.167)+3(0.167 L
SWALE. LENGT: L_= 540 Cn.246) = 111.2 •c4
Walmart#2516-05 Expansion Technical Information Report Renton, Washington
Conveyance Calculations
PACLAND Project#10001074 Page 42
Wal mart#2516-05 Expansion Technical Information Report Renton, Washington
Combined Sub-basins 2a and 2b
Proposed sub-basins 2a and 2b combine in an existing 18" storm pipe which precedes the
existing bioswale. It is assumed that the original conveyance was designed for the 25-yr
storm event.
These combined sub-basins have a total area of 397,289 sf (9.12 acres), with a 10-yr flow
of 5.66 cfs and a 25-yr flow equal to 6.76 cfs.
Manning's equation - Q= 1.49n 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)
Flow rate assuming existing 18" pipe is 95% full:
Q= 1.49/ x(1.734)x(0.4297)213x(0.0031)1/2 = 6.83 cfs
0.012
Based on the above calculation, the conveyance capacity of the existing 18" pipe is
sufficient for the combined sub-basins under the 25-yr storm event.
Proposed Sub-basin 2b
Sub-basin 2b consists of new impervious surface as well as a new conveyance/water
quality system. The conveyance in this sub-basin has been designed to meet or exceed the
100-yr storm event. The total sub-basin area is equal to 39,839 sf (0.91 acres), with a 100-
year flow equal to 0.7686 cfs.
Flow rate assuming existing 12" pipe is 50% full:
Q= 1.490.012
= 1.490.012x(0.3927)x(0.250)2"3x(0.005)1"2 = 1.368 cfs
Based on the above calculation, the conveyance capacity of the proposed 12" pipe is
sufficient for the 100-yr storm event.
PACLAND Project#10001074 Page 43
Page 1 of 1
Appended on: Thursday, February 25,2010 10:42:53 AM
Proposed Event Summary
Event Peak Q (cfs) Peak T (hrs) Hyd Vol (acft) Area (ac) Method
2 yr 24 hr 3.6649 8.00 1.2089 9.12 SBL'H
other 3.888 8.00 1.2827 9.12 SBUH
5 year 4.5555 8.00 1.5052 9.12 SBUH
10 year 5.6619 8.00 1.8783 9.12 SBUH
25 year 6.7612 8.00 2.2532 9.12 SBUH
100 year 7.8542 8.00 2.6294 9.12 SBUH
All results based on storm duration of 24.0 hours. This is ok if all precipitations are appropriate for the
storm duration. If some design event precipitations are for different duration storms, those results are
incorrect
Record Id: Proposed
Design Method SBUH Rainfall type TYPE1A.RAC
Hyd Intv 10.00 min Peaking Factor 484.00
Storm Duration 24.00 hrs Abstraction Coeff 0.20
Pervious Area 9.12 ac DCIA 0.00 ac
Pervious CN 96.17 DC CN 0.00
Pervious TC 5.00 min DC TC 0.00 min
Pervious CN Calc
Description SubArea Sub en
Impervious surfaces (pavements, roofs, etc) 7.73 ac 98.00
Open spaces, lawns,parks (>75%grass) 1.39 ac 86.00
Pervious Composited CN (AMC 2) 96.1711
Pervious TC Calc
Type Description Length Slope Coeff Misc TT
Sheet Smooth Surfaces. 30.00 ft 2.0% 0.011 0.00 in 0.5232 min
Int Channel CMP pipe (n=0.024) 200.00 ft 0.5% 0.024 2.2202 min
Pervious TC 2.7434 min
Licensed to: Engenious Systems, Inc.
file://S:\Washington\Renton\grimes\Rainier Ave& 7th Expansion\4Reports\Storm\Storms... 2/25/2010