2025.0071-2025.0463.PR0003 05 - Panda Express Yelm Ave - Prelim TIR (287)
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1104 E Yelm Ave, Yelm, WA 98597
1.0 PROJECT OVERVIEW
The project is located at 1104 East Yelm Ave, Yelm, WA 98597. More generally, the
site is located in Section 30, township 17, Range 2E.
The project consists of a single 1.08
acre parcel, Parcel ID#
22730110208. The site is currently
vacant/undeveloped and the
current ground cover consists of
grass, weeds, and bare soils. The
site consists of a single drainage
basin which is tributary to Nisqually
Watershed. The current site is
relatively flat and current slopes
onsite are considered minimal. The
project proposes the construction
of a new Panda Express Restaurant
with associated drive though, drive
lanes, parking lot, utilities, and
landscaping. Refer to the
Developed Conditions Exhibit included in Section 3.0.
Per Geotechnical Report by Terracon, measured infiltration rates onsite are 15 in/hr
in the northwest corner and 21 in/hr in the southeast with design infiltration rates of
7.5 in/hr and 15.5 in/hr respectively. The full Geotechnical Engineering report is
provided in Section 5.0 of this report.
The proposed improvements for this project is greater than 5,000 square feet of new
plus replaced impervious area, thus the project, per Figure I-3.1 of the 2019
Department of Ecology Stormwater Management Manual for Western Washington
(SWMMWW) is required to meet Minimum Requirements 1 – 9 SWMMWW. The
project was designed to satisfy the requirements of the SWMMWW as adopted by
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1104 E Yelm Ave, Yelm, WA 98597
City of Yelm.
2.0 MINIMUM REQUIREMENTS
The project proposes more than 5,000 square feet of new impervious area and will
therefore comply with Minimum Requirements 1 – 9 of the SWMMWW as adopted by
the City of Yelm. Minimum requirements are listed and met as detailed below.
Core Requirement #1: Stormwater Site Planning:
Stormwater Site Plans (under separate cover) and this Technical Information Report
(TIR) herein have been prepared for the subject property to satisfy Minimum
Requirement #1.
Core Requirement #2: Construction Stormwater Pollution Prevention Plan
(CSWPPP):
A Construction SWPPP will be provided during a later stage of design and will propose
erosion control measures per the 2019 SWMMWW standards under separate cover,
under separate cover.
Core Requirement #3: Source Control of Pollution:
All stormwater runoff from the site will be routed to a Contech Filterra before being
routed to an ADS StormTech MC-3500 where the stormwater will infiltrate in the
surrounding soils.
Core Requirement #4: Preservation of Natural Drainage Systems and Outfalls:
The developed drainage will be designed to match the existing site discharge
location. Runoff generated on the lot will be routed to an onsite detention/infiltration
facility and will infiltrate onsite. In the existing condition, stormwater from the
undeveloped site infiltrates into the native soils.
Core Requirement #5: Onsite Stormwater Management:
BMP T5.13 Post-Construction Soil Quality and Depth will be applied to all disturbed
pervious areas. Runoff generated, from impervious surfaces, on the lot will be
managed using water quality treatment infrastructure (Contech Filtera system) pre-
detention and conveyed to a below ground detention/infiltration system, ADS
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1104 E Yelm Ave, Yelm, WA 98597
StormTech MC-3500 buried arch structure system located in the northeast portion of
the site.
Core Requirement #6: Runoff Treatment:
The project proposes more than 5,000 square feet of pollution-generating impervious
surface, runoff treatment is required. Stormwater runoff from pollution-generating
impervious surface will be collected and flow through a Contech Filterra before being
conveyed to the proposed ADS StormTech system. See Section 3.0 of this report for
more information regarding how the project meets the runoff treatment
requirements.
Core Requirement #7: Flow Control:
The project will comply with this requirement by matching developed discharge
durations to pre-developed durations SWMMWW Flow control requirement will be
met through infiltration onsite.
Core Requirement #8: Wetlands Protection:
There are no known existing wetlands located on or near the project site.
Core Requirement #9: Operation and Maintenance:
The Operation and Maintenance Manual for the subject project is included as a
supplementary document to this drainage report. See Section 7.0 of this report.
Define and Map the Study Area
The project is comprised of one parcel (Parcel ID# 22730110208). See Section 3.0 of
this report for the Existing Conditions Exhibit and the Developed Conditions Exhibit.
A Downstream Drainage Exhibit is provided at the end of this section that shows the
site area boundaries and the observed stormwater runoff path from the site.
Resource Review
The best available resource information was reviewed for existing and potential
problems. The following is a summary of the findings from the information used in
preparing this report.
· Per the Geotechnical Report prepared by Terracon dated April 21, 2025
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1104 E Yelm Ave, Yelm, WA 98597
(attached in Section 6 of this report), (attached in Section 6 of this report),
onsite soils consist of loose to medium dense, well-graded gravel with silt
and sand, medium dense to very dense gravel with silt and or sand with silt
and gravel. The soils are suitable for infiltration.
· The site does not contain wetlands (City of Yelm Web Map)
· The site is in an Extreme Critical Aquifer Recharge Area (City of Yelm GIS)
· The site is not located in a Floodplain or a FEMA floodway (FEMA, 5/8/2024)
· The site is not located in a Landslide Hazard Area (City of Yelm GIS)
· The site is located in the Nisqually Watershed (Department of Ecology Water
Resource Inventory Area)
Onsite Basin
The site contains grass, weeds, and bare soil. It is bound to the north by a commercial plaza
property, to the east by Plaza Dr. Road, to the south by Yelm Ave E (WA SR-507), and to the
west by a road. The site is located in the Nisqually Watershed and onsite runoff is ultimately
tributary to the Nisqually River.
The site consists of a single basin, in which runoff generally infiltrates onsite. Runoff from
the adjacent roadways enters a swale either northeast or southwest of WA-507 where
stormwater again infiltrates into the soils.
Per the Geotechnical Report prepared by Terracon dated April 21, 2025 (attached in Section
5.0 of this report), onsite soils consist of outwash deposits/possible fill of glacially
consolidated deposits at varying depths. Soils onsite are suitable for infiltration.
Upstream Area
In the existing condition, surface runoff from adjacent property to the north is captured by a
series of catch basins onsite and no stormwater appears to trespass the proposed site.
Drainage System Description:
Refer to the Downstream Drainage Exhibit for the path referred to in this section. Per the pre
submission meeting, January 22, 2025, there are no drainage complaints or any known issues
with the site. An erosion and sedimentation control plan will be designed to reduce the
discharge of sediment-laden runoff from the site. The plan will be comprised of temporary
measures (rock entrance, filter fence, straw mulch, etc.) as well as permanent measures
(hydroseeding and landscaping). ESC facilities will be periodically inspected and maintained
as necessary during construction to minimize impacts to the downstream systems.
Existing Downstream Drainage Path
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1104 E Yelm Ave, Yelm, WA 98597
The majority of onsite runoff is infiltrated on site. There is no existing known stormwater
infrastructure onsite and there are no known issues or complaints with runoff from the site.
3.0 STORMWATER MITIGATION
The site contains a single threshold discharge area (TDA) as all flows converge within a
quarter mile of the project site. The Basin flows in the developed condition will be conveyed
to an ADS StormTech Chamber system and will be infiltrated onsite. Please see the
Developed Conditions Exhibit in Section 3.0 of this report.
3.1 ONSITE STORMWATER MANAGEMENT
The drainage analysis was modeled using the Western Washington Hydrology Model
software program (WWHM2012), which is recognized as an approved model in the
SWMMWW. The project was modeled using a 15-minute timestep in accordance with
the SWMMWW.
The project was modeled with the following parameters:
Rainfall Gage: Lake Lawrence
Scale Factor: 0.857
Existing Conditions
The existing onsite basin consists of a 1.08-acre parcel, and a frontage basin of 0.06
acres. Approximately 0.90 acres will be disturbed onsite in the developed conditions,
leaving a total targeted basin area of 0.96 acres. The site contains grass and exposed
soils. Refer to the Existing Conditions Exhibit included in this section.
The areas used to compute the drainage calculations associated with the existing
basin conditions, as well as the corresponding WWHM output, are summarized on
the following pages of this report.
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1104 E Yelm Ave, Yelm, WA 98597
EXISTING CONDITIONS
Forest
Parcel 39,212 sf
Frontage 2,405 sf
Total Lawn (Soil Group C - Till) 41,617 sf
TOTAL EXISTING CONDITIONS 41,617 sf
Flow Frequency Return Periods for Predeveloped. POC #1
Return Period Flow(cfs)
2 year 0.0420
5 year 0.0753
10 year 0.1042
25 year 0.1496
50 year 0.1904
100 year 0.2380
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1104 E Yelm Ave, Yelm, WA 98597
The project proposes greater than 5,000 square feet of PGIS. Therefore, per
Water Quality design and features will be provided in the Final Design and TIR.
Figure I-3.1 of Volume I of the SWMMWW, basic water quality treatment is required.
The project proposes a Contech Filterra water quality system
The Contech Filterra water quality will be installed pre-detention/infiltration and are
therefore required to treat the full 2-year peak flow prior to conveyance into the on-
site infiltration system. See below for water quality treatment flow rates from the
2012 WWHM model.
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1104 E Yelm Ave, Yelm, WA 98597
4.0 STORMWATER POLLUTION PREVENTION PLAN
Design of the SWPPP will be completed in accordance with the DOE Manual and provided at
during the construction permit phase of the project.
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1104 E Yelm Ave, Yelm, WA 98597
6.0 OTHER PERMITS
No other permits are required for the construction of the subject single-family
residence.
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1104 E Yelm Ave, Yelm, WA 98597
7.0 OPERATIONS AND MAINTENANCE
Operations and maintenance information will be provided during a future phase of
the project. The operation and maintenance manual will be prepared in accordance
with the DOE Manual.
APPENDIX A
FULL WHHM OUTPUT – ADS StormTech MC-3500