HomeMy WebLinkAboutRS_GeotechnicalReport_amendment_230303_V1Cobalt Geosciences, LLC
P.O. Box 82243
Kenmore, Washington 98028
www.cobaltgeo.com (206) 331-1097
March 3, 2023
Satwant Singh
pmvrsingh@gmail.com
RE: Permit Renewal
Proposed Townhomes
1600 Grant Avenue South
Renton, Washington
In accordance with your authorization, Cobalt Geosciences, LLC has prepared this letter to
discuss permit renewal.
We note that much of the planned construction is nearly completed. It is our opinion that the
construction can continue per plan. Based on our observations at the site and observations
during periodic site visits during grading, we recommend routing runoff from impervious
surfaces to the detention system.
Infiltration systems are not feasible at this site due to several factors. These include the presence
of glacial till soils which are nearly impermeable and act as an aquitard; location and elevations of
new buildings (possible intrusion behind walls and into buildings); presence of shallow perched
groundwater in many areas (zero to minimal clearance above groundwater); presence of newer
structural fills over the native soils (not suitable to infiltrate into fills), and slope magnitudes
generally in excess of 15 percent in most locations.
We anticipate that final landscaping and any additional planned grading/construction will occur
per the approved plans during the upcoming dry grading season.
Sincerely,
Cobalt Geosciences, LLC
Phil Haberman, PE, LG, LEG 3/3/2023
Principal
PH/sc