HomeMy WebLinkAboutSWP272235 ' STORM DRAINAGE REPORT
for
' SOUND MITSUBISHI SUBARU
USED CARS
SOUTH GRADY WAY
RENTON, WA
Prepared For:
SOUND MITSUBISHI SUBARU i
Renton, WA 98055 1
OC WA
zfL
' 6157
ONST
AL�
' EXPIRES 9/21/
Prepared By:
WARNER ENGINEERING P,ANvING
' 5122 Olympic Drive NW, Suite B204 cm of RENTON
Gig Harbor, WA 98335
(206) 858-8577
October 11, 1995
Job Number: 023002
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' TABLE OF CONTENTS
' I. Project Overview
' II. Existing Conditions Summary
III. Developed Conditions Summary
1 IV. Discussion of Core Requirements
' V. Discussion of Special Requirements
' VI. Conveyance System Analysis and Design
VIL Water Quality Analysis and Design
' VHL Appendices
Appendix A- Vicinity Map
' Appendix B - SCS Soil Map
Appendix C - Predeveloped Basin Map
Appendix D -Postdeveloped Basin Map
Appendix E - Isopluvial Maps: 2-, 10-, 100- Year
Appendix F - Runoff Coefficients
Appendix G- Waterworks program Calculations
' Pre-developed Data
Post-developed Data
Appendix H- Technical Information Report Worksheet
IX. References
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' L PROJECT OVERVIEW
tThis project is a new Mitsubishi Subaru used car dealership. The site is bounded on the
north by SW Grady Way, and is east of the intersection of SW Grady Way and Rainier
Ave. The project encompasses development of the entire 1 acre site. The work shall
include the construction of a 960 SF modular building, and paving a parking and vehicle
display area. See Appendix A for a vicinity map.
11. EXISTING CONDITIONS SUMMARY
' SOILS
Soils on the site are identified by the SCS Soil Survey for King County' as Urban Land
' (U)- see Appendix B for SCS Soils information. The SCS description is as follows:
' Urban land(U) is soil that has been modified by disturbance of the natural layers
with additions of fill material several feet thick to accommodate large industrial
and housing installations. In the Green River Valley the fill ranges from about 3
' to more than 12 feet in thickness, and from gravelly sandy loam to gravelly loam
in texture. The erosion hazard is slight to moderate. No capability or woodland
classification.
' We will assume that a hydrologic soil group C soil is present on the site.
' EXISTING DEVELOPMENT AND DRAINAGE
The site currently is comprised of paved and gravel areas which are used for vehicle
' parking. The site is level with a very little vertical relief. Surface drainage on site is sheet
flow to existing catch basins located near the northeast and southwest corners of the
property. That flow enters the existing City storm system. See the Vicinity Map in
Appendix A and the Predeveloped Basin Map in Appendix C.
OFF-SITE AND DOWNSTREAM DRAINAGE
There is no off-site drainage onto this site. See the Predeveloped Basin Map, Appendix C.
' Water leaving this site is picked up by two existing catch basins located along the east side
of the property. That storm system flows east in an 8" pipe and then south in a 12" pipe
' which changes to a 24" pipe. It outlets to a ditch along the north side of I-405. At that
point it continues west in the ditch. It re-enters a storm system which flows south under
I-405. The system discharges to a ditch which flows south along the east side of Hwy.
' 167. It re-enters a storm system which flows west under Hwy. 167. That system flows
south and then east along SW 19th Street. It continues flowing west to the pumping
station at Oaksdale Ave SW. The pumped water is discharged to a system which outlets
' to Springbrook Creek. Springbrook Creek flows northwest to the Green River.
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III. DEVELOPED CONDITIONS SUMMARY
l� ON-SITE DEVELOPMENT AND DRAINAGE
The new dealership building will be a modular type structure of approximately 960 square
' feet and be located along the south property line Vehicle parking and display areas will
comprise the remainder of the site. Storm drainage for the site will be as follows:
The site will be graded to sheet flow to three catch basins. The system will discharge to
the water quality oil/water separator and is then released to the existing catch basin and 8"
line at the northwest corner of the site. The increase in run-off from the Pre-developed
condition to the Developed condition is less that 0.5 cfs, therefore no detention is
proposed for this site.
Water quality for those areas subject to vehicular traffic will be by use of a baffle type
' oil/water separator. Due to the small area on the site, a biofiltration swale is not possible.
A baffle-type oil/water separator is proposed using a manhole rather than a large vault
since the volume of the water quality storm is only 0.04 ac-ft or 1600 cf with a rate of
' Liol0.10 cfs. Seethe Postdeveloped Basin Map, Appendix D.
OFF-SITE IMPROVEMENTS AND DRAINAGE
' No off site improvements are proposed.
' IV. DISCUSSION OF CORE REQUIREMENTS
' Core Requirement #1 - Discharge at the Natural Location
As discussed in EXISTING CONDITIONS SUMMARY above, the site drainage
' currently drains to the existing catch basins located along the east property line. The
proposed storm system will connect to this same storm system.
' Core Requirement #2 - Off-Site Analysis
No offsite drainage enters the site. See Appendix C- Predeveloped Basin Map. A Level
One Downstream Analysis is described in the Existing Conditions Summary. There are no
known drainage problems in this system.
' Core Requirement #3 - Runoff Control
tThis site is exempt from On-site Peak Rate Runoff Control because the increase in the
peak runoff is less than 0.5 cfs more than the peak runoff rate for the existing site
' conditions.
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' Core Requirement#4 - Conveyance System
The project storm system will convey the site 100 year design storm.
' Core Requirement #5 - Erosion/Sedimentation Control Plan
An Erosion and sedimentation plan has been developed for this site as outlined in the King
' County Surface Water Design Manual. CB inlet protection and CB inlet sediment trap
will be installed.
' Core Requirement #6 -Maintenance and Operation
Maintenance and operation of all of the stormwater system on this site will be the
' responsibility of the Renton Mitsubishi Subaru Dealership.
' Core Requirement #7 - Bonds and Liability
Bonds and liability insurance will be provided by the Renton Mitsubishi Subaru
' Dealership.
' V. DISCUSSION OF SPECIAL REQUIREMENTS
Special Requirement #1 - Critical Drainage Areas
' The City has not indicated that this site is in a critical drainage basin.
Special Requirement #2 - Compliance With Existing Master Drainage Plan
There is no existing known Master Drainage Plan that includes this site.
' Special Requirement #3 - Conditions Requiring a Master Drainage Plan
' This project site does not trigger any of the thresholds that require a Master Drainage
Plan.
' Special Requirement #4 - Adopted Basin or Community Plans
The site is not in any known adopted basin or community plans.
Special Requirement #5 - Special Water Quality Controls
' There is less than 1 acre of new impervious area subject to vehicular traffic. This project
provides a water quality oiUwater separator system that is designed per Department of
' Ecology Stormwater Management Manual for the Puget Sound.
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' Special Requirement #6 - Coalescing Plate Oil/Water Separators
' This site is will have less than 5000 square feet that is subject to petroleum storage, high
vehicle usage, or heavy equipment use and is therefore exempt from a coalescing plate
toil/water separator.
Special Requirement #7 - Closed Depression
There are no closed depressions on the project site.
' Special Requirement #8 - Use of Lakes Wetlands or Closed Depressions for Peak Runoff
Control
The project will not use a lake, wetland or closed depression for peak runoff control.
' Special Requirement 49 - Delineation of 100 Year F000dplain
The project falls within 100 year floodplain zone AH. According to the Federal
' Emergency Management Agency Community Map Numbers 53033C0328D and
53033C0329D dated September 29, 1989 portions of the surveyed property are inundated
by the 100-year flood. Flood depth of I to 3 feet (usually areas of ponding).
' Special Requirement#10 -Flood Protection Facilities for Type 1 and 2 Streams
This project does not abut a Type I or 2 stream and we do not propose to construct a
t new, or modify an existing, flood protection facility. This site is therefore exempt from
this requirement.
Special Requirement#11 - Geotechnical Analysis and Report
A geotechnical analysis and report is not required for this project.
Special Requirement #12 - Soils Analysis and Report
' A geotechnical analysis and report is not required for this project.
' Special Requirement #13 - Aquifer Recharge and Protection Areas
' This site is not in an aquifer recharge or protection area.
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' VL CONVEYANCE SYSTEM ANALYSIS AND DESIGN
See Appendix G. Summarized below are the design data
Constants
Pz = 2 in. Soil Type C
' P,p = 2.9 in. CN= 86.0 grass
P100 = 3.9 in. CN= 89.0 gravel
CN=98.0 impervious
' Existing conditions
' Q100= 0.77 cfs Ace,,= 0.54 ac T, = 10 min.
A„n = 0.52 ac
' Developed conditions
' Q100- 0.83 cfs Ace,,,= 0.12 ac T, = 10 min.
Aimp = 0.94 ac
Maximum flow rate= 1)100,,, = 0.83 cfs
' All pipes on site are 8" ADS N-12 at 0.50% which have a capacity of 0.94 cfs. Therefore
the conveyance system is sized to adequately handle the 100-year storm event.
VII. WATER QUALITY ANALYSIS AND DESIGN
' A. The oil/water separator orifice is sized for the 100-year storm event so that only
extreme events will cause an overflow situation
' Q = CA(2gh)"=0.83 cfs h = 2.35 ft. g =32.2 C = 0.62
' A = 0.83 cfs/{0.62[2(32.2)(2.35 ft)]"I = 0.1088 sf.
' A= (3.14/4)DZ D = (4A/3.14)0'S = 0.37 ft=4.46 in.
Use D = 4.5"
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' V. APPENDICES
Appendix A - Vicinity Map
Appendix B - SCS Soil Map
' Appendix C - Predeveloped Basin Map
Appendix D - Postdeveloped Basin Map
Appendix E - Isopluvial Maps: 2-, 10-, 100- Year
Appendix F - Runoff Coefficients
Appendix G- Waterworks program Calculations
Pre-developed Data
Post-developed Data
Appendix H - Technical Information Report Worksheet
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a w2 APPENDIX A
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I . APPENDIX B
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' KING COUNTY, WASHINGTON, SURFACE WATER DESIGN MANUAL
' (2) CN values can be area weighted when they apply to pervious areas of similar CN's (within 20
CN points). However, high CN areas should not be combined with low CN areas (unless the
low CN areas are less than 15% of the subbasin). In this case, separate hydrographs should be
' generated and summed to form one hydrograph.
FIGURE 3.5.2A HYDROLOGIC SOIL GROUP OF THE SOILS IN KING COUNTY
1
' HYDROLOGIC T
SOIL GROUP GROUP*
SOIL GROUP
' C Orcas Peat Alderv+ood C Oridia Arents, Alderv+ood f.Saterial B Ovall Arents, Everett Material C OvaflPilch ck Bellingh D Puget
Bellingham B
p Puyallup
Bckle D Ragnar B
Buckle Variable Renton D
Coastal Beaches' Variable
D Riverwash iable Ewic C Salal Silt Loam C
Edgeverett k ALB 'Sammamish D
Everett D
Indianola A Seattle D
' Kitsap C Shacar C
Klaus C Si Silt D
Mixed Alluvial Land Variable Snohomish C
Sultan
Neilton A D
' T kwil
Newberg Urban Var'able
Nooksack
Normal Sandy Loam D Woodinville D
r.)
' HYDROLOGIC SOIL GROUP CLASSIFICATIONS
n when A. chop runoff y of depot miwell-to-excessively). Soils dhigh
9 drained infiltration
sands or l gravels.
These soilsha have thoroughly high rate of water wetted, and ring
transmission.
on
ates when thoroughly
B con
sisting ch chiefly of moderately runoff )fineotlls o moderately
coarse teerate lxtur'es. rThese soils have a moderate ratedof
water transmission.
' C. (Moderately high runoff potential). Soils having slow infiltration rates when thoroughly wetted, and
consisting chiefly of soils with a layer that impedes downward movement of water, or soils with moderately
fine to line textures. These soils have a slow rate of water transmission.
' D. (High runoff potential). Soils having very slow infiltration rates when thoroughly wetted and consisting.
chiefly of clay soils with a high swelling potential, soils with a permanent high water table, soils with a
hardpan or clay layer at or near the surface, and shallow soils over nearly impervious material. These soils
have a very slow rate of water transmission.
' • From SCS, TR-55, Second Edition,June 1986. Exhibit A-1. Revisions made from SOS, Soil Interpretation
Record, Form #5, September 1988.
' 3.5.2-2 11192
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' KING COUNTY, WASHINGTON, SURFACE WATER DESIGN APPENDIXF
TABUS 2B SSCS WESTERN WASHINGTON RUNOFF CURVE NMIBERS
SCS WESTERN WASHINGTON RUNOFF CURVE NUMBERS (Published by SCS in 1982)
' Runoff curve numbers for selected agricultural, suburban and urban land use for Type 1A
rainfall distribution, 24-hour storm duration.
CURVE NUMBERS BY
' HYDROLOGIC SOIL GROUP
LAND USE DESCRIPTION A B C D
Cullivated land(1): winter condition 88 91 94 95
' Mountain open areas: low growing brush and grasslands 74 82 89 92
Meadow or pasture: I 65 78 85 89
' W 55 72 81 86
ood or forest land: undisturbed or older second growth 42 64 76 81
Wood or forest land: young second growth or brush
Orchard: with cover crop
81 88 92 94
Open spaces, lawns, parks, golf courses, cemeteries,
landscaping.
good condition: grass cover on 75%
' or more of the area 68 50 O 90
fair condition: grass cover on 50% 77 85 90 92
to 75°% of the area
' Gravel roads and parking lots 76 85 89 91
Dirt roads and parking lots 72 82 89
Impervious surfaces, pavement, roofs, etc. 98 to 98 98 _
Open water bodies: Takes, wetlands, ponds, etc. 100 100 0 100
—j
Single Family Residential (2)
' Dwelling Unit/Gross Acre °% Impervious (3) Separate curve number
1.0 DU/GA shall be selected
1.5 DU/GA 20
2.0 DU/GA 25 for pervious and
' 2.5 DU/GA 30 impervious portion
3.0 DU/GA 34 of the site or basin
3.5 DU/GA 38
4.0 DU/GA 42
' 4.5 DU/GA 46
5.0 DU/GA 48
5.5 DU/GA 50
6.0 DU/GA 52
' 6.5 DU/GA 54
7.0 DU/GA 56
Planned unit developments, % impervious
' condominiums, apartments, must be computed
commercial business and
industrial areas.
' (1) For a more detailed description of agricultural land use curve numbers refer to National Engineering
Handbook, Section 4, Hydrology, Chapter 9, August 1972.
(2) Assumes roof and driveway runoff is directed into street/storm system.
(3) The remaining pervious areas (lawn) are considered to be in good condition for these curve numbers.
4ir
3.5.2-3 11/92
' APPENDIX G
9/7/95 4 : 6:9 pm Warner Engineering page 1
' SOUND MITSUBISHI SUBARU USED CARS
STORM DRAINAGE ANALYSIS
PREPARED BY: C. LEVEY
' BASIN SUMMARY
BASIN ID: POST NAME: 100-YEAR POSTDEVELOPED STORM
SBUH METHODOLOGY
TOTAL AREA. . . . . . . : 1. 06 Acres BASEFLOWS: 0.00 cfs
' RAINFALL TYPE. . . . : TYPElA PERV IMP
PRECIPITATION. . . . : 3. 90 inches AREA. . : 0. 12 Acres 0.94 Acres
TIME INTERVAL. . . . : 10.00 min CN. . . . : 86. 00 98 . 00
TC. . . . : 10. 00 min 5.00 min
ABSTRACTION COEFF: 0. 20
PEAK RATE: 0.83 cfs VOL: 0. 31 Ac-ft TIME: 480 min
BASIN ID: PRE NAME: 100-YEAR PREDEVELOPED STORM
SBUH METHODOLOGY
TOTAL AREA. . . . . . . : 1. 06 Acres BASEFLOWS: 0. 00 cfs
' RAINFALL TYPE. . . . : TYPElA PERV IMP
PRECIPITATION. . . . : 3 . 90 inches AREA. . : 0. 12 Acres 0.94 Acres
TIME INTERVAL. . . . : 10. 00 min CN. . . . : 86. 00 93 .98
TC. . . . : 10. 00 min 5. 00 min
' ABSTRACTION COEFF: 0. 20
PEAK RATE: 0. 77 cfs VOL: 0. 28 Ac-ft TIME: 480 min
' 10/2/95 1:7 : 17 pm Warner Engineering page 1
' SOUND MITSUBISHI USED CARS
STORM DRAINAGE ANALYSIS
PREPARED BY: C. M. MODJESKI
' BASIN SUMMARY=====_______________________
t BASIN ID: post NAME: 6-MONTH DEVELOPED STORM
SBUH METHODOLOGY
TOTAL AREA. . . . . . . : 1. 06 Acres BASEFLOWS: 0. 00 cfs
' RAINFALL TYPE. . . . : TYPEIA PERV IMP
PRECIPITATION. . . . : 0. 66 inches AREA. . : 0.94 Acres 0. 12 Acres
TIME INTERVAL. . . . : 10. 00 min CN. . . . : 98. 00 86.00
TC. . . . : 5. 00 min 10. 00 min
ABSTRACTION COEFF: 0 . 20
PEAK RATE: 0. 10 cfs VOL: 0 . 04 Ac-ft TIME: 480 min
1
yar - APPENDIX H
d { 4 r
Page 1 of 2
King County Building and Land Development Division
TECHNICAL INFORMATION REPORT (TIR) WORKSHEET
PART I PROJECT OWNER AND PART 2 PROJECT LOCATION
PROJECT ENGINEER AND DESCRIPTION
' ProjectOwner (�IGh ��lilcr qf-w Project Name Sound trit4'50bishi Subaru
Address760 ?,- intor' Ave < 1I�e�,A Location
' Phone Township 23 N
Project Engineer ra.4 (0dr-ne1 Range 5E
' Company Warner Enaineeriq Section FJ� 19 Project Size I.b AC —
Address Phone 5127. 6('ANiztc Dr IJUJ Sk L320 Upstream Drainage Basin Size tJcne- AC
G; llarber uuA 99331 'Zo&,-rS9-9r2,77
PART 4 OTHER PERMITS
' Q Subdivision • Q DOF/G HPA Q Shoreline Management
' Q Short Subdivision Q COE 404 Q Rockery
E] Grading Q DOE Dam Safety Q Structural Vaults
Q Commercial Q FEMA Floodplain Q Other
' Q Other Q COE Wetlands Q HPA
PART 6 SITE COMMUNITY AND - .
'( Community
2enko n
' Drainage Basin
Green SL'%ie,r-
CHARACTERISTICSPART 6 SITE
' Q River Q Floodpiain
Q Stream Q Wetlands
' Q Critical Stream Reach Q Seeps/Springs
Q Depressions/Swales Q High Groundwater Table
Q Lake Q Groundwater Recharge
' Q Steep Slopes 0 Other Fla+ Ss rt in ttrh a n 2f e&
Q Lakeside/Erosion Hazard
Soil Type Slopes Erosion Potential Erosive Velocities
' �rauPll. kla} h+ 46, MederaAe 2 -FPS
n
C urban l.and�
' Q Additional Sheets Attatched
1/90
Page 2..
King County Building and Land Development Division
TECHNICAL INFORMATION REPORT (TIR) WORKSHEET _
y'
-PARTS DEVELOPMENT LIMITATIONS
REFERENCE LIMITATION/SITE CONSTRAINT
' 0 Ch.4-Downstream Analysis tJone - Si+e ti i, li�iPS �r r ' F� 5 C 5 t'XC1n�1ic 1
O
t O
O
O
Q Additional Sheets Attatched
PART 9 ESC REQUIREMENTS
' MINIMUM ESC REQUIREMENTS MINIMUM ESC REQUIREMENTS
' DURING CONSTRUCTION FOLLOWING CONSTRUCTION
[El' Sedimentation Facilities EEr Stabilize Exposed Surface
71 Stabilized Construction Entrance � Remove and Restore Temporary ESC Facilities
' f---I Perimeter Runoff Control []' Clean and Remove All Silt and Debris
I] Clearing and Grading Restrictions E2" Ensure Operation of Permanent Facilities
0 Cover Practices E::] Flag Umits of NGPES
' GZ Construction Sequence (] Other
ED Other
PART 10 SURFACE WATER SYSTEM
F-1 Grass Lined Channel EJ Tank a Infiltration Method of Analysis
C:�r Pipe System (] Vault Depression 5G5
(] Open Channel Energy Dissapator 0 Flow Dispersal Compensation/Mitigation
Dry Pond Welland O Waiver of Eliminated Site Storage
Wet Pond 0 Stream 0 Regional Detention None
' Brief Description of System Operation Cnich bas.ns Ulkenk ;lows onA corr4 Mows +0 Wc�_er
g_po,0-� n'Uwnker Seoaroker h'ch dischar4ti JI-e Gt. Storm su-�cn� tL`k�b�k de nitien
' Facility Related Site Limitations I] Additional Sheets Attatched
Reference Facility Limitation
3g
' • UCTURAL ANALYSIS PART12 EASEMENTSfTrAGIS
•. require•special C ti
Drainage Easem@ j t r-3 c
*� p a
AT
O Cast in Place Vault 0 Other Q Access Easeme
0 Retaining Wall Native Growth Ptec on Ea
0 Rockery>4'High Q Tract a'+< �
t+. 16157
Structural on Sleep Slope (] OtherPART 14 SIGNATURE OF PROFESSIONAL ENGINEER
g?Q k�ist �
`J
I or a civil engineer under my supervision have visited the site. Actual EXPI s 9/21/
' site conditions as observed were incorporated into this worksheet and the
attatchments. To the best of my knowledge the information provided
here is accurate. s �v
1/90
' VI. REFERENCES
' 1. Soil Surveyof King County Area, Washington. United States Department of
Agriculture, Soil Conservation Service. November 1973.
' 2. Stormwater Management Manual for the Puget Sound Basin. Washington State
Department of Ecology. February, 1992.
3. Waterworks. Software for Hydrology. Version 2.7. Engenious Systems, Inc.
Seattle, Washington.
1
1
1
1
1
1
1
1
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1
9
3/14/96 11: 16 : 55 am Warner Engineering page 1
SOUND USED CARS
WATER QUALITY STORM
PREPARED BY: C. LEVEY
------------
BASIN SUMMARY
BASIN ID: WQ NAME: WATER QUALITY
SBUH METHODOLOGY
TOTAL AREA. . . . . . . : 1. 19 Acres BASEFLOWS: 0. 00 cfs
RAINFALL TYPE. . . . : TYPElA PERV IMP
PRECIPITATION. . . . : 0. 67 inches AREA. . : 0. 12 Acres 1. 07 Acres
TIME INTERVAL. . . . : 10. 00 min CN. . . . : 86. 00 98 . 00
TC. . . . : 10. 00 min 5. 00 min
ABSTRACTION COEFF: 0. 20
PEAK RATE: 0 . 12 cfs VOL: 0. 04 Ac-ft TIME: 480 min
Sound Used Cars -Water Quality
Worksheet for Circular Channel
Project Description
Project File untitled
Worksheet Water Quality Storm
Flow Element Circular Channel
Method Manning's Formula
Solve For Channel Depth
Input Data
Mannings Coefficient 0.012
Channel Slope 0.500000%
Diameter 4.00 in
Discharge 0.12 fta/s FL,Ou;RATE O7= t.vFiTER Q"),qL ITY 5-Topo—
Results
Depth 0.23 ft --e-- -DLcPTH OF- WRTE2 OVAL-ITY STORYn tN 4" PIPE
Flow Area 0.06 ft2 &XITING C802A 6'_4VEPSION 5TCuCTU?Et� Rob
Wetted Perimeter 0.65 ft G`A_TTEKI/JGU O(L/V_-3A- .f= SEPARRTOR
Top Width 0.31 ft
Critical Depth 0.19 ft
Percent Full 69.11 %
Critical Slope 0.008213 ft/ft
Velocity 1.87 ft/s
Velocity Head 0.05 ft
Specific Energy 0.28 ft
Froude Number 0.72
Maximum Discharge 0.16 ft3/s
Full Flow Capacity 0.15 ft3/s 4— CAPACITY01= 41' pIPF
Full Flow Slope 0.003388 ft/ft
Flow is subcritical.
L)kTEIZ QuAc 11y5TOIZj I = 3�z = Or(o'J IN
Mar 14, 1996 Wamer Engineering FlowMasler v4.1
12:58:47 Haestad Methods, Inc. 37 Brookside Road Waterbury,CT 06708 (203)755-1666 Page 1 of 1
FOR DISTRIBUTION TO:
® Water Utility ® Building Division
Wastewater Utility Public Works Constr Inspector
Surface Water Utility ® Fire Prevention
FA Maintenance Services
® Transportation Systems
Project: SOOnc1 Y11tf�,i�1niS bQrlt 2225
Location: ` ` L —T—
Attached please rind copies or:
® PERMIT ® BILLS OF SALE
® RECEIPT COST DATA INVENTORY
® LETTER OF SPECIAL BILLING ® EASEMENT(S)
STUB SERVICE AGREEMENT [� COPY OF AS-BUILT
® PRECON NOTES
® PRECON ATTENDEES
DRAINAGE REPORT
® MEMO-WATER BREAKDOWN
® MAP WITH NEW MAINS AND VALVES
® OTHER
Date:
C;TB:PRECON:DISTPRM
WARNER ENGINEERING Civil Engineering a Planning
5122 Olympic Dr. NW Office(206)858-8577
Suite 8204 Fax (206)858-8579
Gig Harbor,WA 98335
March 14, 1996
C11'y OF RENTON
Clinton E. Morgan RECEIVED
City of Renton 19 1996
Development Services @iUYLDYN
200 Mill Avenue South G DIVISION
Renton, Washington 98005
Fax# (206) 2.77-4428
Re: Sound Mitsubishi Subaru - Used Cars
Dear Mr. Morgan,
As we discussed on the phone earlier today, the owner for the above project feels that the current
coalescing plate oil/water separator design is cost prohibitive. As you may recall, our design
plans, dated 01/25/96, and storm drainage report, dated 01/05/96, show the coalescing plate
oil/water separator to be on-line. Since the oil/water separator was on-line and all site flows
would pass through it, we designed it to handle the 100-year, 24-hour storm event. Installing this
unit was priced at approximately $24,000.
I have discussed this matter with the owner's representative for this project and explained to him
that the primary reason this structure was designed to be on-line, rather than off-line, was to
reduce the number of catch basins needed for the project. I also explained to him that the City of
Renton only requires lower frequency storm events to go through water quality (1/3 of the value
of the 2-year, 24-hour rainfall). It is the owner's desire to modify the design and install the
oil/water separator off-line, routing only the required runoff through the oil/water separator and
bypassing the rest of the flows.
I am attaching a drawing showing the revised location of the oil/water separator. The new
oil/water separator shall have a capacity at 0.50 gpm/sf equal to 60 gpm. Supporting calculations
are shown below. The water quality storm runoff was calculated using Waterworks, a hydraulic
modeling program.
Constants:
Pz=2in
Water Quality Precipitation= 0.33(2 in)=0.67 in.
Soil Type C
CN= 86.0 grass, CN= 98.0 impervious
Developed Conditions
Av ,,,= 0.12 ac, T,= 10 min
A;,,,P= 0.94 ac, T,= 5 min
Qom,q w t,= 0.12 cfs= 53.8 gpm
New Catch Basin 2A will act as a diversion structure. The water quality storm (1/3P2) will be
conveyed to the oil/water separator through the 4" pipe exiting Catch Basin 2A. Flows larger
than the water quality storm will bypass the oil/water separator through the 8" pipe exiting the
catch basin. I used Flowmaster, a hydraulic modeling program, to calculate the level of the water
quality storm in Catch Basin 2A. The computer printout is attached. The invert elevation for the
8" bypass pipe has been set at the water surface of the water quality storm (19.66ft + 0.23ft =
19.89ft).
Flowmaster was also used to calculate the capacity of the 4" pipes connecting the oil/water
separator to the rest of the storm system. The flowrate of the water quality storm is 0.12 cfs.
The capacity of the 4" pipes are 0.16 cfs with a slope of 0.50%, therefore, the pipes are
adequately sized.
If you have any questions, please call me at 206-858-8577.
Sincerely, IN E.
A,OV WASH L�
Cynthia E. Levey, P.E. z
Project Engineer 32800 w
/ST�
IONA1,
EXPIRES 05/24/ q
WARNER ENGINEERING 5122Olympic Dr.NW Suite B204 Gig Harbor,WA 98335.Office(206)858-8577 • Fax(206)858-8579
COALESCING PLATE OIL/WATER AP P E.
SEPARATOR (IE=19.66)
CAPACITY AT 0.50 GPM/SF by:
= 60 GPM; USE PIPE INC. Y•--� 91 " � z
MODEL 466—SA OR
APPROVED EQUAL
SrONAi, F� lAl
CB#2A AND CB#2B SHALL CB#2A, TYPE 1 EXPIRES OS 2.�]
HAVE SOLID LOCKING LIDS RIM---22.50
PER CITY OF RENTON IE.=19.66 (4"W, 8"SE)
STANDARD PLAN B020. IE.=19.89 (8"NW)
CB#1 , TYPE1 0122B. LY-PE 1
RIM=23.90 RIM=22.60
IE.=19.56 (4"S, 8"NE,SW) IE.=19.66 (4"E,N)
START NEW CURB
'® ,,,,�-TM OP1 CORNER C.kP
EL 22 99' 3
t r - --CURB RAMP 3 5
USE ALTERNATE
10 LF-8"O ADS N-12 00.60%
�. CB 1 20 LF-4"sb ADS N-12 01 .44%
c �► - STREET LIGHT
C►B 2B p7 - 23 LF-8"O ADS N-12 00.50%
~SIGNAL OIL/WATER SEPARATOR
8' ... .... .�� .. .:.22.60
: �: - MATCH EDGE
. 0::..:..::.: '. . ..: :.: ' . . . ..:.. .. OF EX, PAVEMENT
,,.0° .23,00.: .
.. .. .... . .. .... .. '.. . .
. . . . .
I ::...•..•..... ... ... ...•. . ... :':':'. ::' CB 2, TYP
E 1
. : : : ::. ...
:::: :: '': . ... RIM=22.4
''' . ...
IE.=19.69 {8"
.:.. . .... ... ..... . NW,W,SW)
SCALE: 1 0- "
WARNER ENGINEERING SOUND MITSUBISHI SUBARU DRAWN BY: CEL
USED CARS JOB NO.: 023002
5122 Olympic Dr. NW Office (206) 858-8577 OIL,/WATER SEPARATOR DATE: 03/14/96
Suite B204 Fox (206) 858-8579 REVISIONS Gig Harbor, WA 98335 PAGE: 1 OF 1