16-217 10000 Edmonds Way ECA.PDF
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3213Eastlake Avenue East Suite B
Seattle, WA 98102-7127
Tel (206) 262-0370
Fax (206) 262-0374
Geotechnical & Earthquake
Engineering Consultants
February 23, 2017
File No. 16-217
Mr. Anthony Jansen
Westgate Village, LLC
4025 Delridge Way SW #530
Seattle WA 98104
Re: Geotechnical Report Addendum
Edmonds Critical Areas Review – CRA 2016-0133
Westgate Village
Edmonds, WA
Dear Mr. Jansen,
This letter provides an addendum to PanGEO’s geotechnical report for the above property
(PanGEO, 2016) to address landslide and erosion critical areas that have been mapped on the
property by the City of Edmonds as identified in the City’s letter of November 29, 2016. The
following briefly discusses our findings and conclusions.
LANDSLIDE HAZARD
HAZARD CLASSIFICATION
The hillside slope on the southwest side of the proposed development has been mapped as a
potential landslide hazard because the steepness of the slope (40% on the western parcel (parcel
B) and 60% on the eastern slope (parcel A) as shown in Figure 2 (PanGEO, 2016) and the height
of the slope of about 60’ (EMC 23.80.020.B.4). The steeper slope on parcel A appears to be
related to hillside grading in conjunction with the development of the shopping center and the
permanent retaining wall at the toe of the slope. The slope on parcel B appears to be native and
not altered from the prior development on the parcel.
Geotechnical Critical Areas Review
Westgate Village
February 23, 2017
16-217 10000 Edmonds Way ECA.pdf PanGEO, Inc. Page 2
SURFACE CONDITIONS
Both parcels are vegetated with conifers with minimal underbrush. All trees were straight and
did not exhibit any evidence of hillside creep. Furthermore, we did not observe any evidence of
past landslides on the hillside slope as related to hummocks or locally steep slopes that might be
suggestive of a slump. Finally, we did not observe any evidence of springs or surface erosion on
the hillside slopes. Accordingly, there does not appear to be any evidence of historical landslide
activity on the hillside.
SUBSURFACE CONDITIONS
Subsurface conditions on the hillside slope were explored with one boring, B-3, which was
drilled at the location shown on Figure 2 (PanGEO, 2016). Boring B-3 encountered dense to
very dense glacial till to a depth of 10 feet, at which point the boring was terminated.
STABILITY EVALUATION
Glacial till has a friction angle of at least 38 degrees and a cohesion of at least 500 psf. Based on
past experience, these strength properties would yield static and dynamic stability factors well in
excessive of 2. As discussed in the geotechnical report (PanGEO, 2016), hillside cuts needed for
the installation of the below grade parking will require temporary shoring walls for the hillside
cut and basement walls of the new construction will provide permanent support to the toe of the
slope.
CONCLUSION
The existing hillside above the proposed development is underlain by competent glacial till
which does not represent a potential landslide hazard, as confirmed by the absence of any
landslide features at the site and the absence of any springs on the hillside. Hen ce, in our
opinion, buffers are not required for the proposed development.
EROSION HAZARD
SURFACE CONDITIONS
As previously discussed, the hillside is underlain by glacial till. Glacial till has a low potential
for erosion. Springs or erosional features were not observed on the hillside.
Geotechnical Critical Areas Review
Westgate Village
February 23, 2017
16-217 10000 Edmonds Way ECA.pdf PanGEO, Inc. Page 3
CONCLUSION
Because the hillside is underlain by erosion resistant material, and because there is no evidence
of springs or erosional rills on the hillside, we believe that hillside erosion is not a hazard for the
proposed site development.
CONCLUSIONS
In accordance with ECDC 23.80.050, we believe that the project site and the adjacent hillside
slopes are stable and not susceptible to landslide and erosion hazards. Furthermore, the proposed
development will not decrease slope stability or pose an unreasonable threat to persons or
property either on or off site, as described above
We appreciate the opportunity to be of service. If you have questions or need additional
information, please contact our office.
Sincerely,
W. Paul Grant, P.E.
Principal Geotechnical Engineer
Geotechnical Critical Areas Review
Westgate Village
February 23, 2017
16-217 10000 Edmonds Way ECA.pdf PanGEO, Inc. Page 4
REFERENCES
PanGEO, 2016, Geotechnical Report, Westgate Village, 10000 Edmonds Way, Edmonds,
Washington: Report to Westgate Village, September 17.