18025.doe.sec.1 Proj Descrip Page 1-2____________________________________________________
18025 Drainage Report 1-2
PART 1 – PROJECT SITE ANALYSIS AND DATA
Permit Requested: Site Plan Review
Other Permits Required: Building Permit
Grading/Earthwork
SEPA Review
Agency Permit No.: Pending
Site Address: 939 Northern Pacific Rd
Yelm, Washington 98597
Section, Township, Range: Section 19
Township 17
Range 02E, W.M
Total Site Area: 13.93 Acres
Zoning: I - Industrial
Project Overall Description
The project includes the development of an auto wrecking yard named, Yelm Auto Recycling,
on lot 64300900200. Development will include 4 structures to be used for office space, storage
and general shop/maintenance space. Construction will also include onsite customer parking,
graveled and paved vehicle storage yards, water, sewer, and power service, stormwater
facilities. Frontage improvements are proposed, but will be deferred until required by the City.
Proposed Flow Control Improvements
The flow control facilities consist of bioretention cells, infiltration trenches and infiltration cells.
Test pits dug at the facility locations revealed infiltration rates more than 100 in/hr. For design
purposes, stormwater facilities were modeled with 20 in/hr. The soils report can be found in
Appendix #2 of this document.
Proposed Water Quality Improvements
The water quality facilities consist of bioretention cells. The bioretention cells are designed to
treat 91% of the runoff profile. The bioretention cells utilize a 12 in/hr design infiltration rate with
a Ksat safety factor of 4.
Proposed Conveyance System
The proposed conveyance systems will consist of Type I catch basins and conveyance pipe in
various sizes to distribute stormwater to the proposed stormwater facilities. Surface flow will
also be handled using clay lined V ditches.
Proposed Discharge Location
The project site will infiltrate all runoff at the proposed infiltration trenches/cells.