REVIEWED BLD BLD2024-0235+Geotechnical_Report+3.12.2024_9.49.52_AM+4121402COBALT
GE0SCIENCES
February 27, 2024
Douglas and Amy Subcleff
DsubcleffPgmail.com
C/O Richard Okimoto
raoarchooutlook.com
RE: Plan Review
Proposed Residence
88xx 189Th Place SW
Edmonds, Washington
RECEIVED
Mar 13 2024
CITY OF EDMONDS
DEVELOPMENT SERVICES Cobalt Geosciences, LLC
DEPARTMENT P.O. Box 1792
North Bend, WA 98045
.........................I.....................4
REVIEWED
BY
CITY OF EDMONDS
BUILDING DEPARTMENT::
............................................... e
In accordance with your authorization, Cobalt Geosciences, LLC has prepared this letter to
discuss our plan review of the proposed project. In preparation of this letter, we have reviewed
the civil plans by Effective Engineering, PLLC dated December 1, 2023 and November 22, 2023.
The plans appear to include relevant information from our previous geotechnical report. Roof
runoff will be routed into City infrastructure, which we recommend.
The plans indicate the use of permeable pavements for flow control. Provided there is a
subsurface interceptor drain constructed along the downslope side (west) of the paver locations,
the risk to adjacent properties will be maintained at the current level.
Alternatively, the underlying weathered glacial till could be graded at low magnitudes toward the
central portion of the driveway/parking area so that water does not freely migrate to the west. No
interceptor drain would be necessary if the underlying soils are graded slightly away from any
adjacent slopes or other properties.
We note that any cutoff drain must penetrate at least 12 inches into dense to very dense glacial till
as confirmed by the geotechnical engineer during construction. The interceptor trench system
should be at least 12 inches in width with a 4 inch diameter perforated PVC pipe at the base of the
trench. We recommend use of 1-1/2 inch washed rock around and over the pipe as well as 2 to 3
inches below the pipe to allow for siltation. The rock should extend at least several inches above
the base of the subgrade for permeable pavements.
Mirafi MoN fabric should be placed over the rock prior to backfill placement up to the ground
surface. Trench backfill over the rock should be compacted to 95 percent of the modified proctor
in 12 inch thick lifts.
We should verify aspects of construction, including soil bearing of foundation areas, foundation
drainage placement, any fill and compaction, slab on grade, excavation stability, and pavement
subgrades and interceptor trenching (if utilized).
www.cobaltgeo.com (2o6) 331-1097
February 27, 2024
Page 2 of 2
Plan Review
Sincerely,
Cobalt Geosciences, LLC
r H0Ny
Pam w:
jC S`F<•„
54896
'IrCIS1 ER`��
�SS� iONA
2/27/2024
Phil Haberman, PE, LG, LEG
Principal
www.cobaltgeo.com (206) 331-1097