20130325 Additional Language Memo SR 09112013 Tami Merriman
From: Stephanie Ray
Sent: Wednesday, September 11, 2013 12:26 PM
To: Tami Merriman
Cc: Grant Beck
Subject: Stormwater paragraph for SEPA CUP SW Yelm 1A
Attachments: Stephanie Ray.vcf
Additional language related to the stormwater treatment section. Please review and let me know if ok.
The proposed project will have stormwater facilities installed in accordance with the DOE Stormwater Management
Manual for Western Washington (SWMMWW) and the City of Yelm's municipal code. All requirements that are
applicable to this project will be met.
Stormwater runoff from proposed impervious areas will be collected via catch basins and on-site storm pipe and
conveyed to a stormwater detention pond for flow control. The proposed detention pond will be sized using the
Western Washington Hydrology Model (WWHM) to match pre-developed flows using a continuous simulation model. It
is assumed that this project will not create pollution-generating impervious surfaces since the site will restrict vehicular
access to maintenance staff only. The site will be infrequently used by maintenance and therefore is not considered
"subject to vehicular use" according to the definition in SWMMWW Volume I, Section 2.3. The proposed building will
have roofing composed of inert, non-leachable material and therefore wilt not be considered a pollution-generating
impervious surface. Therefore, since the project does not propose any pollution-generating impervious or pervious
surfaces, it is anticipated that minimal water quality facilities will be required.
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