HomeMy WebLinkAboutStormwater Plan Review for BLD98-01066 - PLN General - 4/29/1999 MASON COUNTY
PUBLIC WORKS DIRECTOR/COUNTY ROAD ENGINEER
Shelton,Washington 98584
DATE: April29, 1999
INTER-DEPARTMENTAL COMMUNICATIONS
TO: Allan H. Borden, DCD-Planner
FROM: Alan A. Tahja, P/W- Co. Hydr. Engr. DCD WO# 9847
SUBJ: Stormwater Plan Review NAME: North Mason Eagles
BLD98-1066
Allan,
A"PARKING LOT STORM DRAINAGE ANAL YSIS"prepared by Whiteley Engineering has
been received and reviewed by Public Works for the proposed construction of a parking area
intended to serve the developing North Mason Eagles Clubhouse. The plan also provides for the
parking lot layout and geometry which complies with Mason County's Parking Ordinance
standards, and is considered acceptable.
The stormwater features promoted in the analysis fall short of meeting either Mason County's
Parking Ordinance requirements, or Ecology's minimum standards for water quality treatment or
discharge standards. Washington State's Department of Transportation has been contacted as the
recipient of stormwater runoff generated from this site, and are requesting that any flows
delivered to their right of way from commercial properties conform to Puget Sound Water
Quality Authority's (PSWQA) downstream erosion control discharge rates. Mason County's
Parking Ordinance requires retention of parking and loading area runoff onsite, or disposal of
surface water as directed by the Public Works Director. In cases where infiltration of parking &
loading area runoff is not feasible or is impractical, Public Works accepts discharges from
developing sites which comply with PSWQA BMP standards. With this site draining to the State
highway ditch,the applicable standard is PSWQA's downstream erosion control discharge rates.
Retaining parking area runoff onsite by infiltrating it into the ground could relieve the proponent
from WSDOT requirements, and also diminish the project's obligation to downstream receiving
properties,but retention facilities typically need to address runoff treatment of the water quality
design storm as defined by the PSWQA, before infiltration is allowed.
In late 1997, Mason County adopted the Puget Sound Water Quality Authority's Technical
Manual with the exception of Chapter I-2,the minimum stormwater control requirements.
Chapter I-2 of the Manual was replaced with a very similar County version which was
determined technically equivalent by Ecology. Either version of Chapter I-2 typically leads to the
same results.
File: H:\WP\STRMWTR\REVIEWS\NM-EAGLS. ID2
Besides providing for permanent runoff control,the Stormwater Site Plan(SSP as defined by
Ecology) should contain provisions for temporary erosion and sediment control , and
restabilization of disturbed soils during and after construction of the proposed parking facilities.
I have discussed the proposed stromwater plan with the project engineer, who I'm sorry to say,
was not informed of Mason County's adoption of Ecology's technical manual. The proposed
stormwater control plan should be returned to the applicant for revision and compliance with
PSWQA's minimum development/redevelopment standards as contained in their technical
manual.
Please feel free to contact me at County extension 461 if you or the applicant have any questions
regarding this review.
Sin erely,
c7z r
Al4n A. Tahj a
File: H:\WP\STRMWTR\REVIEWS\NM-EAGLS.ID2
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