HomeMy WebLinkAbout721174034 Stormwater MgmtAssociated Earth Sciences
February 15,2001
AESI Project No. BE00040A
Blake and Molly Nordstrom
c/o The Reijnen Company
490 Madison Avenue - Suite 101
Bainbridge Island, Washington 98110
Attention: Paul Ziakin
Subject:
Storm water Drainage Considerations
Nordstrom Property North, Parcel C
Jefferson County, Washington
Dear Mr. Ziakin:
In regard to our January 26, 2001 conversation, this letter presents our opinions conce ,rning storm
water drainage for the, property located at 1627 'Thomdyke Road. in Jefferson CoUnty,
Washington. At the request of .The Reijnen Company, Associated Earth. Sciences, Inc.
completed a geotechnical engineering study to satiSfy the requirements of Jefferson County for
construction within a landslide hazard area.
It is our underStanding that Jefferson County has initially required that all storm water runoff
generated at the site be infiltrated on site via infiltration galleries or other similar structures.
Geologic conditions at the site as encountered in our exploration borings consisted primarily of
sand and gravel overlying hard clayey silt. These geologic units were exposed at the bluff face at
elevations consistent with the conditions encountered in our borings.
The presence of a relative!y low-permeability clayey silt unit'below a more Permeable sand and
gravel unit causes ground water to "perch". above the Silt. Evidence of ground water seepage as a
result of perched water was observed at this contact on the bluff face at the time the subsurface
exploration phase of our study was completed., The seepage observed appeared to be directly.
related to recent (1997), active, landslide activity on the bluff.
In our opinion, infiltration of storm water at any location at the site will result in increased
ground water, seePage at the sand/silt contact on the bluff face, and increased risk of future
landslide activity at the site. We recommend conveying all storm water runoff generated at the
· site down the entire height Of the bluff to a suitable discharge point near the base of the bluff via
a "tightline", To accurately determine the specific construction details required for such a
system, we recommend that a civil engineer familiar' with drainage syStems of this type be
consulted. ~
Corporate Office · 91 I Fifth Avenue, Suite 100 · Kirkland, WA 98033 · Phone 425 827-7701 · Fax 425 827-5424
West Sound Office · 179 Madrone Lane North · Bainbridge Island,WA 981 i0 · Phone 206 780-9370 · Fax 206 780-9438
Blake and Molly NordStrom
c/o The Reijnen Company
AESI Project No. BE00040A
February 15,2001
Page 2 ~
We are available to provide additional consultation ~garding the geotechnical aspects of a
,tightline system. If you have any questions or require any additional information, please do not
hesitate to call.
Sincerely,
ASSOCIATED EARTH SCIENCES, INC.
West Sound Office
Robert F. Cousins, P.G.
Project Geologist
EXPIRES 6/22/t9~ ~
John L. Peterson, P.E.
Senior Geotechnical Engineer
cc: Kevin Russell, Jefferson County, Department of Community Development
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