20170160 Pre Stormwater Drainage Rpt 07192017Preliminary Stormwater Drainage and Utility
Report
Standley Garage Development
Yelm, WA
Prepared for
Joe & Constance Standley
10627 111h Ave Ct SE
Tacoma, WA 98444
(253) 468 -0586
Prepared by
J MJ TEAM
PO Box 66
Sumner, WA 98390
(206) 596 -2020
Justin Jones, PE
July 19, 2017
4 JTEAM
PROJECT ENGINEER'S CERTIFICATION
I hereby certify that this Preliminary Stormwater Drainage Report for Joe & Constance Standley has been prepared
by me or under my supervision and meets minimum standards of City of Yelm and normal standards of engineering
practice. I hereby acknowledge and agree that the jurisdiction does not and will not assume liability for the
sufficiency, suitability, or performance of drainage facilities designed by me.
Justin Jones, PE
TABLE OF CONTENTS
PROJECT OVERVIEW
WATER
SANITARYSEWER
STORMWATER
PROJECT OVERVIEW
The Standley Garage Development site is approximately 21,650 SF in size and consists of a former meat market. The
proposal for this project is to renovate the former meat market into an auto - repair facility. The renovation will
include the removal of a portion of the building at the front of the structure and the conversion of the remaining
into an auto - repair facility. Site and utility work will be included, which will convert the existing gravel site into
landscaping and asphalt driveway improvements.
WATErc
The site is located within the City of Yelm's water service area, and includes an existing water meter which will be
reused. The building's demand on the system will include two employee /customer restrooms, and irrigation for the
proposed landscape areas. As part of the improvements from the meter, a City of Yelm approved reduced pressure
backflow assembly will be provided.
SANITARY SEWER
The site is located within the City of Yelm's sewer service area, but is not connected to the STEP system. A 3" force
main sewer main exists within Stevens ST, near the southwest corner of the site. The existing building does not
currently and is not planned to include floordrains. The sewer demand from the project consists of two
employee /customer restrooms. A 1,000 - gallon STEP tank is proposed to meet the sewer demand. An oil /water
separator is not proposed as the project does not contain floor drains. Typical auto repair contaminants such as oil
and greases will be dealt within the site and by DOE approved best management practices.
STORMWATER
The existing stormwater site is approximately 29% impervious including: 3,100 SF of gravel, 750 SF of concrete, and
2,650 SF of the existing building. The site currently discharges untreated stormwater offsite at the lowest point on
the property, which is toward the north east. There exists an existing drywell at the southeast corner of the building,
which is believed to convey and infiltrate stormwater from the roof.
The proposed improvements include: 11,300 SF of pollution generating asphalt, and 2,500 SF of the existing building
to be maintained, resulting in the site being 64% impervious. Existing gravel and concrete will be removed and
replaced with asphalt resulting in 7,300 SF of new impervious surfaces. A 600 SF bioretention cell has been designed
to collect, treat and infiltrate the asphalt and landscape areas. The roof runoff is planned to be collected and
infiltrated in a drywell. The existing drywell will be evaluated for reuse.
livJTEAM
DOE Stormwater Management Manual - Minimum Requirements
City of Yelm utilizes the 2012 Department of Ecology Stormwater Management Manual. Volume 1 of this manual
describes the minimum requirements for stormwater management for redevelopment sites. Using the flow chart
below, minimum requirements 1 -9 apply to the Standley Garage Development site.
Dues &a prujed resvtt m 2,OW square feet, or more afneor plus replaced hard surface area? DEL
Does the ]and distarbmg activity UmW 7,004 square feet or grwwe
Me
Mininmm RPgw env=s #1 tbrDughM apply to Mum= FEqunrann& K applj s-
the new and replaced had surfaces end the land
disturbed
Nest Qlvestiom
Does the project add 5,000 sgaere feet cw mam of item' hard surfaces?
OR
Cam-ert Y, acres ar more oftegetatiam ro lawn ar landscaped areas?
OR
Ccrosert 2.5 awes or more ofwtn -e vegeitiantopastime?
7es No
Next
QaeMon
�}]L 1{inimnm l7aguiramane [a 2pply fi% to-the Is this a road
new hard surfaces and cans emd related project?
vageurb m areas. Yes
Does the project add 5.000 square beet or more of nm hard smfaees?
Yes Me
Do new hard sauces add 5 CF% Dr Is &a totaL of neu phis mpiaced had surfaces
more to &a msting had sauces 5,004 square feet or more, AND dues &B value
amain the prajeet limier" of &E prapased imprusqffEIemts — inchiding
maEDx impro wxmd } — enoeed 50ti of the
assessed valne (or reptacemen %mhze) of dm
Na Yes pyiafg site nnprovements?
NO 8d hl=al
re 7uuemeo� NO
�eS
ND addlhaoal
reqWrama3It5
AR m R &qun mews apply w the new and
replaced hard smiacm amd aomrerted %- egefahom areas.
Figure 24-2 — Flow Chart for determining Requirements fOr Redevelopment
Ya�roma I— ?idirrimrrmr Taclmical Regeeiremraou —Augwr .012
? -I1
IJVJTEAM
Minimum Requirement 1— Preparation of Stormwater Site Plans
The proposed site plan depicts the stormwater design intent which includes a 600 SF bioretention cell designed to
collect, treat and infiltrate the asphalt and landscape areas and a drywell designed to collect and infiltrate roof
runoff. As part of the Civil Permit application detailed stormwater site plans will be developed.
Minimum Requirement 2 — Construction Stormwater Pollution Prevention
As part of the Civil Permit application, the applicant will ensure a Stormwater Pollution Prevention Plan meets
Department of Ecology code.
Minimum Requirement 3 — Source Control of Pollution
This minimum requirement focuses on post- construction, such as the formation of a pollution prevention team, good
housekeeping on the site, preventative maintenance, and spill prevention and cleanup. This will be outlined as part of the
stormwater report at time of the Civil Permit application.
Minimum Requirement 4 — Preservation of Natural Drainage Systems and Outfalls
Stormwater will be captured, treated, and infiltrated within the site by a 600 SF bioretention cell and a 157 CF drywell. No
stormwater will leave the site, ensuring that no adverse effects will be made to the site.
Minimum Requirement 5 — On -Site Stormwater Management
The proposed improvements include: 11,300 SF of pollution generating asphalt, and 2,500 SF of the existing building
to be maintained, resulting in the site being 64% impervious. A 600 SF bioretention cell has been designed to collect,
treat and infiltrate the asphalt and landscape areas. The roof runoff is planned to be collected and infiltrated in a
drywell.
The Standley Garage Development site will utilize LID methods where feasible. The existing roof will use a
downspout full infiltration drywell sized per BMP T5.10A to infiltrate 100% of roof runoff. The asphalt pavement will
use bioretention to collect, treat, and infiltrate runoff. Permeable pavement is not feasible for this site as it is an
auto repair facility with pollution generating hard surfaces. Landscape improvements will be per BMP T5.13.
IJVJTEAM
Minimum Requirement 6 — Stormwater Runoff Treatment
01 schematic
00®
_ — r
Wed l0.46a Bioretention Sizing - Finish Miligated
Ej 'Et E otl cn 1 HIt ICgat ECl
Facility Name
Downstream Connection
Facility Type
F Use simple Binretention
F Underdrain Used
Bioretention Bottom Elevatior
Bioretention Dimensions
Bioretention Length [R] d0 -000
Bioretention Bottom Width (it) 15.000
Freeboard (ft) 0.500
Over -road Flooding (ft) 0.000
Effective Total Depth (R) 3.25
Bottom slope of bioreteniion.(01] 0.000
F Sidewall Invert Location
Front and Back side slope [HN] 3.000
Left Side Slope (HN) 3.000
Right Side Slope (HN) 3.000
Material Layers for
Layer 1 Layer 2 Layer 3
Depth (R) FT5 07 1.500 1 F50
Soil Layer ISMMWW 12 in /hr
Soil Layer SMMWW12in /hr
Soil Layer IGRAVEL
Edit Soil Types
KS at Safety Factor
�f- None f- 2 1-1
Bioretention 1
Outlet 1 Outlet 2 Outlet 3
00�
Bioretention Swale
Quick Swale Size Water Quality Size Facility
Native Infiltration Yes
Measured Infiltration Rate (in /hr)
Reduction Factor (infilt'factor)
Use Wetted Surface Area (sidewalls)
Flow Through Underdrain (ac -It)
Total Outflow (ac -I[]
WQ Percent Filtered 100
Facility Dimension Diagram
Riser Outlet Structure —y
Outlet Structure Data
Riser Height Above hioretention surface (ft)
Riser Diameter (in) Fo—,J
Riser Type Flat —y
Orifice Diameter Height
Number (in) (ft)
1 Fo----fl Fo----fl
2 Fo_--fl Fo__ -fl
3 F0---fl F0__ -fl
Show Bioretention Open Table
Bioretention Volume at Riser Head (ac -R) .074
1
I otal Volume Intlltrated [ac -rt]
4/.334
F3 _ �
Total Volume Through Riser (ac -ft]
0
�
Total Volume Through Facility(acft)
47.334
NO _�
FP7, 7e nt1nfi11,ated
100
Precipitation on Facility (acre -It)
3.23
Evaporation from Facility (acre -ft)
1.524
�J
Commercial Toolbox
_ — r
Wed l0.46a Bioretention Sizing - Finish Miligated
Ej 'Et E otl cn 1 HIt ICgat ECl
Facility Name
Downstream Connection
Facility Type
F Use simple Binretention
F Underdrain Used
Bioretention Bottom Elevatior
Bioretention Dimensions
Bioretention Length [R] d0 -000
Bioretention Bottom Width (it) 15.000
Freeboard (ft) 0.500
Over -road Flooding (ft) 0.000
Effective Total Depth (R) 3.25
Bottom slope of bioreteniion.(01] 0.000
F Sidewall Invert Location
Front and Back side slope [HN] 3.000
Left Side Slope (HN) 3.000
Right Side Slope (HN) 3.000
Material Layers for
Layer 1 Layer 2 Layer 3
Depth (R) FT5 07 1.500 1 F50
Soil Layer ISMMWW 12 in /hr
Soil Layer SMMWW12in /hr
Soil Layer IGRAVEL
Edit Soil Types
KS at Safety Factor
�f- None f- 2 1-1
Bioretention 1
Outlet 1 Outlet 2 Outlet 3
00�
Bioretention Swale
Quick Swale Size Water Quality Size Facility
Native Infiltration Yes
Measured Infiltration Rate (in /hr)
Reduction Factor (infilt'factor)
Use Wetted Surface Area (sidewalls)
Flow Through Underdrain (ac -It)
Total Outflow (ac -I[]
WQ Percent Filtered 100
Facility Dimension Diagram
Riser Outlet Structure —y
Outlet Structure Data
Riser Height Above hioretention surface (ft)
Riser Diameter (in) Fo—,J
Riser Type Flat —y
Orifice Diameter Height
Number (in) (ft)
1 Fo----fl Fo----fl
2 Fo_--fl Fo__ -fl
3 F0---fl F0__ -fl
Show Bioretention Open Table
Bioretention Volume at Riser Head (ac -R) .074
1
I otal Volume Intlltrated [ac -rt]
4/.334
F3 _ �
Total Volume Through Riser (ac -ft]
0
�
Total Volume Through Facility(acft)
47.334
NO _�
FP7, 7e nt1nfi11,ated
100
Precipitation on Facility (acre -It)
3.23
Evaporation from Facility (acre -ft)
1.524
Stormwater run -off treatment will be achieved through the bioretention cell located on site. The asphalt pavement is a
pollution generating surface and will drain to the bioretention cell on site. The bioretention cell is sized to treat the
asphalt pavement, as well as the surrounding landscape areas.
The bioretention cell has been sized using the Western Washington Hydrology Model (WWHM) based on the following
criteria:
• 1.5' thick bioretention soil mix layer
• 1.5' ponding depth
• 100% native infiltration
• Minimum 91% water quality
IJVJTEAM
Minimum Requirement 7 — Flow Control
Based on the DOE's minimum requirement flow chart for redevelopment, flow control is required for new and replaced
hardscape, and converted vegetation areas. This results in allowable release rates equal to half the 2 -year and the full 50-
year flows from the site based on the forested condition.
The existing roof will use a 157 CF downspout full infiltration drywell sized per BMP T5.10A to infiltrate 100% of roof
runoff. The asphalt pavement and landscape areas will drain to a bioretention cell sized to infiltrate 100% of runoff
from these areas. Sizing is based on the 3" per hour infiltration rate of the DOE bioretention soil mix governing the
design due high infiltration capabilities in the native soil.
Drywell and bioretention sizing results in 100% infiltration of site runoff and no stormwater discharging from the
site.
Minimum Requirement 8 — Wetlands Protection
There are no wetlands located within the development site.
Minimum Requirement 9 — Operations and Maintenance
The project will include the development of an O &M manual in accordance with the DOE Stormwater Manual. This
manual will be developed at the time of permitting and include a log of maintenance activities to be kept on -site for city
inspection
IJVJTEAM