REVIEWED RESUB 5_ENG2022-0536_Geo Letter_10.25.2024_1.29.10_PM_4582301RESU B panGEC)
Oct 252024 INCORPORATED
CITY OF EDMONDS Jeotechnical & Earthquake
DEVELOPMENT SERVICES Engineering Consultants
DEPARTMENT
October 25, 2024
File No. 02-063
Ms. Elana Shippen
18101 Sunset Way,
Edmonds, WA 98026
Subject: Impact Review of Drainage Improvements
Plan Review Comments #4 10/3/2024
Permit Number ENG2022-0536
18101 Sunset Way
Edmonds, Washington
Dear Elana:
As requested, this letter presents our assessment of the proposed drainage improvements at your
house at 18101 Sunset Way in Edmonds, prepared by CG Engineering. This letter is in response
to the City of Edmonds Plan Review #4, dated October 3, 2024.
Item 17: Review #4 10/3/2024 — Comment kept for refence. Provide an update letter as
directed. Ref. Review #3 4/30/2024 and Review #2 12/28/2023. Both stating that updated letters
from the Geotechnical Engineer approving the updated proposed TESC, stormwater management
system and/or ground disturbance.
We have reviewed the updated plans dated October 25, 2024, and, in our opinion, the proposed
TESC measures will adequately protect against the release of soil material from the construction
site. We have also reviewed the proposed stormwater management system and, in our opinion, if
constructed in accordance with design plans, the system will protect critical areas against
uncontrolled release of stormwater or ground disturbance.
Item 1 under the section titled "Specific Comments" requires a letter from the Geotechnical
Engineer addressing the impacts of this specific proposed system to the subject site, as previous
reports addressed systems with different configurations. We have reviewed the current
proposed configuration regarding potential impacts of the drainage improvements on the
Landslide Hazard and Erosion Hazard area identified on your property by the City of Edmonds
in their Critical Area Determination (CRA2022-0115) letter dated August 17, 2022. We have
3414 NE 55 h Street
Seattle, WA 98105
(206)262-0370
Proposal for Geotechnical Engineering Services
18101 Sunset Way, Seattle, WA
October 25, 2024
reviewed CG Engineering's Detention and Drainage plan which shows a 36 inch CMP detention
vault, 31 feet in length, located 8 feet off of and parallel to the lower level patio, and drainage
collection lines for roof and driveway drainage. The outfall from the detention vault will consist
of 58 feet of 6-inch PVC drain line routed to a catch basin located along the eastern property in a
5-foot utility easement, per plan map. Based on the site plans, the closest facility approach to the
steep slope hazard area is at the west end of the retention vault, which is a minimum of 20 feet
from the top of the steep slope area. Accordingly, the proposed improvements do not fall within
the hazard area or the 10-foot buffer area per 23.80.020.13 of the Edmonds Municipal Code.
Based on our boring PG-3, drilled in the area of the planned improvements, the underlying soils
are dense and stable, and the impact of the construction excavations will be minimal. In our
opinion, as long as the improvements are located as shown on CG's plans, the risk of impact to
the Landslide and Erosion Hazard area is low.
Sincerely,
Stephen H. Evans, L.E.G.
Senior Engineering Geologist
W. Paul Grant, P.E.
Principal Geotechnical Engineer
02-063 18101 Sunset Way Drainage Improvements Review 2024-rev 1.doc 2 PanGEI