BLD2023-0640+Geo_Hazard_Statement_of_Risk_-_Geo+5.24.2023_3.51.59_PM+3567831BLD2023-0640
NELSON GEOTECHNICAL
ASSOCIATES. INC.
RECEIVED
Jul 12 2023
CITY OF EDMONDS
DEVELOPMENT SERVICES
DEPARTMENT
MEMORANDUM
105 Palouse Street
Wenatchee, WA 98801
(509) 665-7696
www.nelsongeotech.com
DATE: May 24, 2023
M
-s y
e 0` w"— .
TO: Michael Koh Beng Chye'�
FROM: Khaled M. Shawish, PE
35215
Alex B. Rinaldi, LG, EIT
CC,s,-O-
Ss,�NA�
RE: Geotechnical Hazard Identification/Declaration and Mitigation Statement of Risk
Proposed Koh Residence
15604 — 751h Place West
Edmonds, Washington
NGA File No. 1360822
2023
This memorandum addresses the provisions of ECDC 23.80 regarding the proposed residence
development project located at 15604 — 75`h Place West in Edmonds, Washington. The parcel number
for the subject property is 00513100002410. We have also prepared a geotechnical report dated May 23,
2023, for the project.
The following statements and opinions regarding the proposed development within a landslide hazard
area are based on specific observations made during our site reconnaissance, geotechnical explorations,
and analysis, as well as review of the latest project plan set.
• It is our opinion from a geotechnical standpoint that the plans and specifications prepared by
the structural engineer conform to the recommendations in the geotechnical report.
• It is our opinion that the risk of damage to the proposed development, or to adjacent properties,
from soil instability will be minimized subject to the conditions set forth in the report and that the
proposed development will not increase the potential for soil movement. Minimized shall mean
that the applicant has utilized the best available science and commonly accepted engineering and
architectural practice to minimize, to the extent possible, the risks associated with development
of the property.
Hazard Mitigation Certification
Proposed Koh Residence
Edmonds, Washington
NGA File No. 1360822
May 24, 2023
Page 2
• Probability and statistical analysis of earth movement and landslide occurrence present a number
of complications and difficulties due to the many variables that lead to these types of events and
commonly their unpredictable nature. That said, based on engineering judgment and experience
in the area, we would estimate that the probability of a significant failure on the site is likely to
be less than 10 percent in 25 years.
• We have reviewed sheet C2.0 TESC Plan and Details within the latest civil plan set. Temporary
erosion and sedimentation control measures consist of silt fencing along the west, south, and
north portions of the limits of disturbance, stockpiles protection, a reinforced construction
entrance, and installation of temporary drainage diversion to a sediment trap. In our opinion, the
proposed measures are appropriate for the proposed development and specific conditions
encountered at the site. Specific erosion issues that may arise during development should be
addressed on a case -by -case basis during periodic geotechnical construction monitoring.
• As discussed in the geotechnical report, the site is contained in the lowermost, Zone A of the
North Edmonds Earth Subsidence and Landslide Hazard Area (ECDC 19.10), per the 2007 Landau
Summary report. Hazards presented to the proposed development at this site are specified as
local, small-scale slope instability, as well as potential deep-seated instability. Mitigation
measures recommended for this site and incorporated into the project plans include supporting
all foundation elements on deep foundation extending down to competent undisturbed native
deposits, limiting temporary grading activities, structure setbacks from the crest of the bluff slope
to address shallow instability concerns, and recommendations for proper site management.
Recommendations provided to minimize impacts on the site and reduce the potential for
instability include tightlining all stormwater runoff to the toe of the slope and general
recommendations for slope maintenance.
• Provided the geotechnical recommendations and specifications on the project plans are
implemented during construction, it is our opinion that the risk of large-scale earth movements
to impact the proposed structure have been reduced to the acceptable thresholds set forth in the
code.
We trust this memorandum satisfies your needs at this time. Please contact us if you have any questions
or require additional services.
...
NELSON GEOTECHNICAL ASSOCIATES, INC.