Geotech Letter for Infiltration SystemL�� COBALT
GEOSCIENCES
July 6, 2022
Tom Leren
tom _ lerendesign.com
RE: Field Report
Proposed Residence
541— 12t' Avenue North
Edmonds, Washington
Cobalt Geosrienoes, LLC
P.Q. Sox 82243
Kenmore, Washington 98o28
In accordance with your authorization, Cobalt Geosciences, LLC (Cobalt) was on site on July 5,
2022 to observe the excavation for the infiltration gallery east of the residence. The area was
excavated generally per plan based on our observations. We note that washed rock was in place at
the base of the excavation; however, the underlying soils were exposed in some locations. The
soils appear consistent with those described on the test pit logs and geotechnical report by Liu
and Associates.
The soils at the base of the system are relatively dense, which will likely result in a slower vertical
infiltration rate than what was assumed by Liu. We recommend backfilling the entire infiltration
gallery with 2 inch clean rock (no fines). The upper 12 inches may consist of 518 inch minus to
prepare the subgrade for the new concrete driveway.
Sincerely,
Cobalt Geosciences, LLC
Phil Haberman, PE, LG, LEG
Principal
www,cobaltgeo.com (206) 331-1097