HomeMy WebLinkAboutRS_Geotechnical_Addendum_180103_v1.pdfJanuary 3, 2018
ES -0895.04
RJ Development
401 Central Street Southeast
Olympia, Washington 98501
Attention: Mr. Frank Durocher
Subject: Geotechnical Addendum
Stormwater Management
Proposed Senior Housing Complex
4500 Talbot Road South
Renton, Washington
Reference: Earth Solutions NW, LLC
Geotechnical Engineer Study
Project No. ES -0895.03, dated August 3, 2017
SCJ Alliance
Storm Drainage Plan, Sheet 4 of 6
Project No. 2386.03, December 2017
Dear Mr. Durocher:
Earth
I Solutions
NW«<
Earth Solutions NW LLC
• Geotechnical Engineering
• Construction Monitoring
• Environmental Sciences
As requested, Earth Solutions NW, LLC (ESNW) has prepared this geotechnical addendum
letter addressing on-site stormwater management systems for the subject project. Subsequent
to completing the referenced geotechnical report, site drainage has been designed.
Based on review of the referenced Drainage Sheet, a stormcapture vault (vault) will be
constructed underneath a parking area within the western portion of the site will be utilized for
means of stormwater management. The vault will include an open bottom intended to allow
infiltration where practical, but has been designed for full detention, recognizing the very limited
infiltration capacity of the site soils. In general, dense to very dense silty sand and sandy silt
was encountered at depth within the approximate proposed vault location. Based on our
experience with similar soil types in the area, these deposits typical exhibit very low infiltration
rates. In our opinion, the proposed vault system should perform as intended for the subject
site, with the understanding that the soils ability to infiltration will be marginal.
1805 - 136th Place N.E., Suite 201 0 Bellevue, WA 98005 • (425) 449-4704 • FAX (425) 449-4711
RJ Development
January 3, 2018
ES -0895.04
Page 2
Relatively clean sands and gravels were encountered at a limited number of test pits. However,
these deposits were isolated in extent and not suitable to accommodate full infiltration. The
predominant presence of fine-grained glacial till across the site, in our opinion, necessitates the
incorporation of a facility that can act as a detention system in addition to limited infiltration. In
our opinion, the proposed vault is acceptable from a geotechnical standpoint.
We trust this letter meets your current needs
information is required, please call.
Sincerely,
EARTH SOLUTIONS NW, LLC
i)
�ffe alsen
Geologist
If you have any questions, or if additional
R' CAMP
sit
ry 1
761
SINAL �1nj1�g
Kyle R. Campbell, P.E.
Principal Engineer
Earth Solutions NW, LLC