REVIEWED PLN_RESUB1 BLD2021-0869+Geotech ADDENDUM+8.10.2021_3.33.24_PM+2349456Group Northwest, Inc.
August 4, 2021
Mr. David Jenkins
18914 — 94th Ave W
Edmonds, WA 98020
djseaandski@aol.com
Subject: ADDENDUM LETTER
Geotechnical Engineers, Geologists
& Environmental Specialists
G-5362
PROPOSED ADDITION AND DECK
18914 — 94TH AVE W
EDMONDS, WASHINGTON
Ref: "Geotechnical Report — Critical Areas Report, Proposed Addition and Deck, 18914 — 94th
Ave W, Edmonds, Washington", GEO Group Northwest, March 4, 2021.
Dear Mr. Jenkins:
GEO Group Northwest has been provided with updated surveying for the subject site as shown
on the attached Plate A — New Topographic Survey and asked by your project team to
review/prepare the following addendum to our referenced report regarding the Landslide Hazard
Area and steep slopes. We understand that based upon our referenced report the property owner
is being required to put a notice on the title designating the lot as a Landslide Hazard Area.
INTRODUCTION
In our referenced geotechnical report we noted the following with regard to steep slopes:
"Per the site topographic survey the maximum slope inclination at the site for a minimum
run of 25 feet (min. 10 ft vertical relief) is 46 percent from the horizontal and this slope
area is at the northwest portion of the lot. The west and northwest facing slopes at the
west and northwest yard area range from 23 to 46 percent with the northern half of this
slope area having an average inclination of 44 percent and the southern half having an
average inclination of around 25 percent. The overall maximum height of the west site
slopes is 12 feet. Our slope inclinations noted here include the vertical relief due to
existing landscaping rockeries. "
13705 Bel -Red Road, Bellevue, Washington 98005
Phone 425/649-8757 • Fax 425/649-8758
August 4, 2021 G-5362
Addendum Letter — 18914 94t" Ave W, Edmonds, WA Page 2
We also stated with regard to potential Landslide Hazard Area designation:
"Therefore, based upon our site investigation it is our opinion that the northwest steep
slopes (40% or steeper) at the site may qualify as a Landslide Hazard area, however, the
risk of landsliding at this area is low and is not anticipated to change as a result of the
proposed development. Risks related to landsliding at the steep slope area can be
mitigated by maintaining native drought tolerant vegetation at steep slope areas,
preventing the placement of fills or other structural loads on top of loose overlying soils
at steep slopes and the proper routing of drainage away from steep slope areas. "
LANDSLIDE HAZARD AREAS
GEO Group Northwest has delineated the apparent steep slope area (slope of 40% or steeper) per
the code section 23.80.020 as shown on the attached Plate A — New Topographic Survey. The
code specifies that potential landslide areas may consist of steep slopes having inclinations of
40% or steeper and a minimum height of 10-feet. Additionally, there is a diagram in the code
regarding the determination of top and bottom of slope using the 10-foot minimum horizontal
dimension.
New development at the site is not proposed for the steep slope areas or anywhere within 39-feet
of the delineated on -site steep slope areas. The area of delineated steep slopes having a height of
10-feet or greater is estimated to be around 93 square feet as shown on Plate A. Based upon the
topographic survey the area of 40% or greater slopes at the site is minimal and inconsequential
such that, in our opinion, the subject site does not qualify as a Landslide Hazard Area.
If there are any questions, please do not hesitate to contact us.
GEO Group Northwest, Inc.
August 4, 2021 G-5362
Addendum Letter — 18914 94th Ave W, Edmonds, WA Page 3
Sincerely,
GEO GROUP NORTHWEST, INC.
Adam Gaston
Project Engineer
of W ASy,�
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�Q 20114
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William Chang, P.E.
Principal
Attachment: Plate A — New Topographic Survey
GEO Group Northwest, Inc.
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