Larsen – ESLHA Addition Second Supplemental Peer Review 11.9.2020LANDAU
AssociATEs
November 9, 2020
City of Edmonds
121 5th Ave. N
Edmonds, WA 98020
Attn: Ms. Kristin Johns, Senior Permit Coordinator, City of Edmonds, Building Division
Transmitted via email to: kristin.johns@edmondswa.gov
Re: Second Supplemental Geotechnical Peer Review
Larsen — ESLHA Addition
Building Permit No. BLD2020-0564
Edmonds, Washington
LAI Project No. 0074207.030.031
Dear Ms. Johns:
An applicant proposes to construct a residential addition at 7329 158th Street Southwest in
Edmonds, Washington (site) and has submitted a permit application to the City of Edmonds (City).
Landau Associates, Inc. (LAI) understands that the site is located within an Earth Subsidence and
Landslide Hazard Area. LAI previously reviewed the applicant's permit submittal package and
summarized its review comments in technical memoranda, dated August 6 and September 30,
2020. The applicant's design consultants have addressed LAI's most recent comments and
prepared a revised permit submittal.
At the City's request, LAI has completed a supplemental geotechnical peer review of the revised
permit submittal. LAI's peer review was completed in accordance with the terms presented in
Task Order No. 20-09, issued under the On -Call Geotechnical and Environmental Engineering
Services Agreement between LAI and the City, effective January 23, 2020.
LAI reviewed geotechnical portions of the following documents for compliance with Chapters
19.10 and 23.80 of the Edmonds Community Development Code (ECDC):
• CG Engineering. 2020. Civil Plan Set. October 27.
• H2D Architecture + Design. 2020. Architectural Permit Set. October 28.
• Nelson Geotechnical Associates, Inc. 2020. Geotechnical Plan Review Letter. October 22.
The review comments from LAI's September 30, 2020 memorandum are reproduced below in
italics. LAI has included a description of the applicant's response to each review comment:
130 2nd Avenue South • Edmonds, Washington 98020 • (425) 778-0907 • www.landauinc.com
Geotechnical Review: Larsen — ESLHA Addition
Landau Associates
Review Comment: In its preliminary evaluation, Nelson Geotechnical Associates, Inc. (NGA)
recommends constructing a debris catchment wall in, or adjacent to, the proposed
addition; however, the evaluation does not include lateral earth pressures that can be used
to design the wall. The evaluation should be updated to include lateral earth pressures,
consistent with a debris flow impact against the face of the wall.
Response: NGA recommends using a lateral earth pressure value of 100 pounds per cubic
foot to design the debris catchment wall. In its revised geotechnical plan review letter,
dated October 22, 2020, NGA provides supporting data, indicating that the design of the
proposed catchment wall accounts for impact loading and the volume of debris that could
accumulate behind the wall following a landslide. This comment has been addressed.
• Review Comment: The debris catchment wall recommended by NGA is not identified in the
plan sets reviewed by LAI. The applicant's permit submittal should be updated to include
the proposed location and configuration of the debris catchment wall.
Response: The plan set has been updated to include the proposed location and
configuration of the debris catchment wall. This comment has been addressed.
• Review Comment: NGA's preliminary evaluation does not recommend a minimum building
setback from the hazard area, as required in Section 23.80.070.1 of the ECDC. The
evaluation should be updated accordingly.
Response: LAI recognizes that a debris catchment wall is proposed in lieu of a minimum
building setback. This approach does not accord with the exact requirements of the ECDC.
If the debris catchment wall is designed and constructed adequately, it should satisfy the
intent of the City's development standards, which is to protect life safety in the event of a
landslide. This comment has been addressed.
• Review Comment: NGA's preliminary evaluation does not recommend a buffer distance
from the hazard area, as required in Section 23.80.070.2 of the ECDC. The evaluation
should be updated accordingly.
Response: LAI understands that the proposed debris catchment wall has been designed to
provide a buffer between the hazard area and the structure. If the debris catchment wall
is designed and constructed adequately, it should satisfy the intent of the City's
development standards, which is to protect life safety in the event of a landslide. This
comment has been addressed.
This letter has been prepared to facilitate the City of Edmonds' evaluation of permit submittal
documents related to the proposed residential addition at 7329 158th Street Southwest in
Edmonds, Washington. Landau Associates reviewed geotechnical portions of the permit submittal
documents for compliance with Chapters 19.10 and 23.80 of the Edmonds Community
Development Code and for conformance with conventionally accepted geotechnical engineering
practices. Review of non-geotechnical documents was completed for the sole purpose of verifying
compliance with the recommendations in Nelson Geotechnical Associates' geotechnical report.
Landau Associates' peer review does not diminish the responsibility of the applicant's
geotechnical and design consultants.
November 9, 2020
Geotechnical Review: Larsen — ESLHA Addition
Landau Associates
If you have questions or comments, please contact the undersigned at (425) 329-0251 or at
sgertz@landauinc.com.
LANDAU ASSOCIATES, INC.
Sean Gertz, PE
Senior Project Engineer
SY"- L4d
Steven R. Wright, PE
Principal
SMG/SZW/mcs
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November 9, 2020