APPROVED Niesel - Rodriguez Supplemental Geotechnical Peer Review Letter_10.3.2023LALANDAU
A S S O C I A T E S
October 3, 2023
Transmitted via email to: Denise.Nelson@edmondswo.gov
City of Edmonds
121 5th Ave. N
Edmonds, WA 98020
Attn: Ms. Denise Nelson, CPT, Senior Permit Coordinator
Re: Supplemental Geotechnical Peer Review
Niesel and Rodriguez —18500 and 18418 Olympic View Dr
Building Permit No. BLD2023-1060 and BLD2023-1063
Edmonds, Washington
Landau Project No. 0074220.010.011
Dear Ms. Nelson:
Applicants propose to construct soldier pile walls at 18500 (Niesel Residence, BLD2023-1060) and
18418 (Rodriguez Residence, BLD2023-1063) Olympic View Drive in Edmonds, Washington (site) to
repair and stabilize a slope that was impacted by a landslide event that occurred in December 2022.
Landau Associates, Inc. (Landau) previously reviewed the applicant's permit submittal packages and
summarized its findings in a letter dated September 22, 2023. The applicant's design consultants have
prepared revised permit submittals to address Landau's review comments.
At the City of Edmonds' (City) request, Landau has reviewed the revised permit submittals. The review
was completed in accordance with the scope outlined in Task Order Nos. 23-09 and 23-10, issued
under the amended Professional Services Agreement dated January 23, 2023 between the City and
Landau.
Landau reviewed geotechnical portions of the following documents for compliance with Chapters
23.80 of the Edmonds Community Development Code (ECDC):
• Aspect Consulting, LLC. 2023. BLD2023-1060. Response to City of Edmonds Review Comments
letter. October 2.
• Aspect Consulting, LLC. 2023. BLD2023-1063. Response to City of Edmonds Review Comments
letter. October 2.
• Aspect Consulting, LLC. 2023. Niesel Residence Slope Stabilization Plan Set. Revised September
29.
• Aspect Consulting, LLC. 2023. Rodriguez Residence Slope Stabilization Plan Set. Revised
September 29.
SEATTLE
155 NE 100th Street, Ste 302, Seattle, WA 98125 T 206.631.8680 landauinc.com
Supplemental Peer Review - Niesel and Rodriguez Residences
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Comments from Landau's September 2023 review are reproduced below in italics. The comments are
followed by a brief assessment of the applicant's response:
Review Comment: Per Section 23.80.050(C)6, 23.80.070(A)1, and 23.80.070(A)2 of the ECDC, the
geotechnical report shall provide minimum buffer and setback recommendations for avoiding
the landslide or erosion hazard. To be in accordance with the ECDC, Aspect Consulting (Aspect)
should provide recommendations for buffers and setbacks from the hazard areas.
Response:
The geotechnical addenda conclude that a setback recommendation is not applicable due to the
nature of the projects. Landau interprets this statement to mean that no buffer or setback is
recommended for the projects. In Landau's opinion, this comment has been resolved.
• Review Comment: Per Section 23.80.050(F)1 of the ECDC, the critical areas report shall include a
copy of the site plan which includes the following:
— The height of slope, slope gradient, and cross-section of the project area,
— The location of springs, seeps, or other surface expressions of ground water on or within
200 feet of the project area or that have the potential to be affected by the proposal,
and
— The location and description of surface water runoff features.
To be in accordance with the ECDC, Aspect should provide site plans in its geotechnical reports
that include this information.
Response:
Details regarding existing slope configuration have been added to sheet C-1 of the project plans.
The location and description of surface water runoff features (stormwater infrastructure) are
shown on Sheet C-4 of Rev 2 of Project plans. In Landau's opinion, this comment has been
resolved.
Review Comment: Per Section 23.80.060(A) of the ECDC, alterations of geologically hazardous
areas or associated buffers may only occur for activities that:
— Will not increase the threat of the geological hazard to adjacent properties beyond
predevelopment conditions,
— Will not adversely impact other critical areas,
— Are designed so that the hazard to the project is eliminated or mitigated to a level equal
to or less than predevelopment conditions, and
— Are certified as safe as designed and under anticipated conditions by a qualified
engineer or geologist, licensed in the state of Washington.
To be in accordance with the ECDC, the geotechnical reports should address these development
standards.
Response:
While the geotechnical addenda by Aspect do not specifically address the requirements of
Section 23.80.060(A) of the ECDC, it is Landau's understanding that the intent of the designs is
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Supplemental Peer Review - Niesel and Rodriguez Residences
October 3, 2023
to meet these development standards. Therefore, it is Landau's opinion that this comment has
been resolved.
• Review Comment: Per Section 23.80.050(F)2.d of the ECDC, the hazard analysis shall include an
estimate of slope stability as well as an estimate of the effect construction and placement of
structures will have on the slope over the estimated life of the structure. To be in accordance
with the ECDC, this information should be added to the geotechnical evaluations by Aspect
Consulting, LLC.
Response:
The geotechnical addenda by Aspect have been updated to include the results of slope stability
analyses, as well as estimates of the effect that construction and placement of the proposed
soldier pile walls will have on the slope over the estimated life of the walls. In Landau's opinion,
this comment has been resolved.
Review Comment: Per Section 23.80.050(F)2.e of the ECDC, the hazard analysis shall include an
estimate of the bluff retreat rate or an estimate of the percent risk of landslide area expansion
that recognizes and reflects potential catastrophic events such as seismic activity or a 100-year
storm event. To be in accordance with the ECDC, this information should be added to the
geotechnical evaluations by Aspect Consulting, LLC.
Response:
The geotechnical addenda by Aspect indicate that bluff retreat and landslide area expansion
"will be essentially stopped for the lifetime of the wall, which is expected to be several
decades." In Landau's opinion, this comment has been resolved.
Review Comment: Per Section 23.80.050(F)2.f of the ECDC, the hazard analysis shall include
consideration of the run -out hazard of landslide debris and/or the impacts of landslide run -out
on downslope properties. To be in accordance with the ECDC, this information should be added
to the geotechnical evaluations by Aspect Consulting, LLC.
Response:
The geotechnical addenda by Aspect indicate that because the damaged stormwater
infrastructure located upstream of the site has been repaired, and the soldier pile wall will
increase the overall stability of the slope, the run -out hazard on downslope properties will be
greatly reduced. In Landau's opinion, this comment has been resolved.
Review Comment: Per Section 23.80.070(A)4.a of the ECDC, the proposed development shall not
decrease the factor of safety for landslide occurrences below the limits of 1.5 for static conditions
and 1.2 for dynamic conditions. The Geotechnical Basis of Design Reports state that the soldier
pile walls are not designed for incremental seismic loading per the 2022 Washington State
Department of Transportation (WSDOT) Geotechnical Design Manual (GDM) Section 6-1.2.1.
Additionally, the geotechnical Basis of Design Reports do not include the results of global
stability analyses under seismic conditions.
Response:
The geotechnical addenda by Aspect have been updated to include the results of global stability
analyses under static and pseudo -static conditions, indicating that the proposed improvements
meet the required factors of safety of 1.2 for seismic conditions and 1.5 for static conditions. In
Landau's opinion, this comment has been resolved.
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Review Comment: To be in accordance with the ECDC, seismic analyses of the soldier pile walls
and the overall slope should be completed. This information should be added to the geotechnical
evaluations by Aspect Consulting, LLC. If stability at the proposed development site is below the
established factor of safety limits of 1.5 and 1.2 for static and seismic, Aspect may provide
practicable approaches to reduce risk to human safety and improve the factor of safety for
landsliding, however in no case shall the existing factor of safety be reduced for the subject
property or adjacent properties. These additional analyses may result in the need to modify the
designs of the soldier pile walls.
Response:
The geotechnical addenda by Aspect have been updated to include the results of global stability
analyses under static and pseudo -static conditions, indicating that the proposed improvements
meet the required factors of safety of 1.2 for seismic conditions and 1.5 for static conditions. In
Landau's opinion, this comment has been resolved.
During review of the resubmittal documents, Landau identified the following additional comment:
• Section 23.80.060(A)3 of the ECDC requires that the designer certify that the proposed
improvements will:
— The alteration will not increase surface water discharge or sedimentation to adjacent
properties beyond predevelopment conditions,
— The alteration will not decrease slope stability on adjacent properties, and
— Such alterations will not adversely impact other critical areas.
To be in accordance with the ECDC, the geotechnical addenda by Aspect should be revised to
include the required certifications, if appropriate.
Additionally, based on a teleconference discussion with Aspect, Landau understands that preparation
of storm drainage designs will be completed by Aspect under a separate permit package. Appropriate
stormwater control is imperative to long term stability of the slope; therefore, Landau recommends
storm drainage features that are compatible with the proposed soldier pile walls be constructed as
soon as possible following completion of the walls.
This letter has been prepared to facilitate the City of Edmonds' evaluation of permit submittal
documents for the proposed slope stabilization at 18500 and 18418 Olympic View Drive in Edmonds,
Washington. Landau reviewed geotechnical portions of the documents for compliance with Chapter
23.80 of the Edmonds Community Development Code and for conformance with standard
geotechnical engineering practices. Review of non-geotechnical documents was completed for the
sole purpose of verifying compliance with the recommendations in Aspect Consulting, LLC's
geotechnical engineering report. Landau's peer review does not diminish the responsibility of the
applicant's geotechnical consultant to serve as the project's geotechnical engineer of record.
Furthermore, the applicant's consultants are responsible for preparing a design suitable for site
conditions.
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Supplemental Peer Review - Niesel and Rodriguez Residences
October 3, 2023
CLOSING
If you have questions or comments, please contact Sean Gertz at 425.329.0251 or at
sgertz@landauinc.com.
LANDAU ASSOCIATES, INC.
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Carson Wall, EIT
Senior Staff EIT
Sean Gertz, PE
Associate Engineer
CEW/SMG/SZW/tmh
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REFERENCES
City of Edmonds. Edmonds Community Development Code, Chapter 23.80 Geologically Hazardous
Areas. Current through Ordinance 4269, passed April 25, 2023.
Landau Associates, Inc. and Aspect Consulting, LLC. 2023. Conference Call. Steven Wright, Sean Gertz,
Erik Anderson, Matthew von der Ahe, and Julia Martz. October 2.
5 landauinc.com