REVIEWED PLN_RESPONSE -GEO LETTERSullivan Deck
1128 Sea Vista Place
Edmonds, Washington
Tom Sullivan
c/o Tom Leren, The Leren Company Inc.
1128 Sea Vista PI
Edmonds, WA 98020-4653
Attention: Mr. Tom Leren
Subject: Plan Review Comment Response
Sullivan Deck - (CRA2021-0007)
Mr. Leren:
April 2, 2021
Project #21021
The purpose of this letter is to provide our response to the referenced plan review comments
(City of Edmonds, July 29, 2021). For the sake of brevity, this letter will assume that readers
have general knowledge of the subject property and the proposed deck replacement/addition.
Review Comment Response
The geotechnical-related plan review comments from the referenced correspondence are
shown below for ease of reference, and our response will follow each comment or group of
comments, as appropriate.
3, Critical Areas Determination; A critical areas determination was completed for the
property which indicated that the property is within a Geologically Hazardous Area
for erosion and landslide hazards
• A Geotech report has been provided, however the Geotech report must
specifically address ECDC 23.80.060 and ECDC 23.80.070 for the landslide hazard
Response:
As stated in our referenced report (South Fork Geosciences, April 2, 2021), the adjacent
mapped potential landslide hazard area on the adjacent property to the south. Based on our
assessment, the only landslide hazard area criteria that is met by the field conditions is that the
slope is in excess of 40 percent and over 10 feet in vertical height. The Vashon lodgement till
sediments underlying these properties are glacially consolidated and are not prone to deep-
seated rotational type failures. As stated in the referenced report, due to the slope orientation
and the location of the proposed deck foundations, it is our opinion that the adjacent property
is not adversely affected by the proposed deck construction and the proposed deck is not
adversely affected by the mapped potential landslide hazard area.
To specifically address the aforementioned code sections, we will show the code sections for
reference and address each item or group of items as appropriate.
ECDC 23.80.060 Development standards - General requirements,
A. Alterations of geologically hazardous areas or associated buffers may only occur
for activities that:
1. Will not increase the threat of the geological hazard to adjacent properties
beyond predevelopment conditions;
2. Will not adversely impact other critical areas;
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Sullivan Deck
1128 Sea Vista Place
Edmonds, Washington
April 2, 2021
Project #21021
3. Are designed so that the hazard to the project is eliminated or mitigated to a
level equal to or less than predevelopment conditions; and
4. Are certified as safe as designed and under anticipated conditions by a qualified
engineer or geologist, licensed in the state of Washington.
B. Critical Facilities Prohibited. Critical facilities shall not be sited within geologically
hazardous areas unless there is no other practical alternative, [Ord, 4026 ,§ 1 (Att,
A), 2016; Ord, 3527 § 2, 2004].
ECDC 23.80.060 Response:
The proposed development does not alter any geologically hazardous areas or buffers. The
mapped erosion hazard area is a "stable erosion hazard" and it is our opinion erosion hazards
are a non -issue with respect to the proposed construction. The landslide hazard area is on the
adjacent property, and due to the previous development, current land use, and the lack of
evidence of past or recent instability, the landslide hazard area presently exists in a "zero
buffer" state, which is appropriate for the site condition. It is our opinion that the proposed
construction does not exacerbate risk to adjacent properties (Condition Al), will not adversely
impact other critical areas (Condition A2), due to the deck location mitigation is not required
(Condition A3), and the planned finished condition will be safe as designed under anticipated
conditions by a licensed engineering geologist (Andrew L. Glandon, LEG, State of Washington,
License #2689) (Condition A4). There are no critical facilities associated with the proposed
project (Condition B).
23.80.070 Development standards - Specific hazards
A. Erosion and Landslide Hazard Areas. Activities on sites containing erosion or
landslide hazards shall meet the requirements of ECDC 23.80.060, Development
standards - General requirements, and the specific following requirements:
1. Minimum Building Setback. The minimum setback shall be the distance
required to ensure the proposed structure will not be at risk from landslides for
the life of the structure, considered to be 120 years, and will not cause an
increased risk of landslides taking place on or off the site. A setback shall be
established from all edges of landslide hazard areas. The size of the setback
shall be determined by the director consistent with recommendations provided
in the geotechnical report to eliminate or minimize the risk of property
damage, death, or injury resulting from landslides caused in whole or part by
the development, based upon review of and concurrence with a critical areas
report prepared by a qualified professional;
ECDC 23.80.070 Response:
As stated in our referenced report (South Fork Geosciences, April 2, 2021), due to the slope
orientation and the location of the proposed deck foundations, it is our opinion that planned
deck foundations as designed are adequately set back from the mapped potential landslide
hazard area on the adjacent property to the south.
2. Buffer Requirements. A buffer may be established with specific requirements
and limitations, including but not limited to, drainage, grading, irrigation, and
vegetation. Buffer requirements shall be determined by the director consistent
with recommendations provided in the geotechnical report to eliminate or
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Sullivan Deck
1128 Sea Vista Place
Edmonds, Washington
April 2, 2021
Project #21021
minimize the risk of property damage, death, or injury resulting from landslides
caused in whole or part by activities within the buffer area, based upon review
of and concurrence with a critical areas report prepared by a qualified
professional;
Response:
Due to the very minor grading associated with the proposed construction, the previous
development of the properties, and the orientation and low overall vertical height, it is our
opinion that a landslide hazard area buffer is not warranted by the site conditions.
3, Alterations. Alterations of an erosion or landslide hazard area, minimum
building setback and/or buffer may only occur for activities for which a hazards
analysis is submitted and certifies that;
a. The alteration will not increase surface water discharge or sedimentation to
adjacent properties beyond predevelopment conditions;
b. The alteration will not decrease slope stability on adjacent properties; and
c. Such alterations will not adversely impact other critical areas;
Response:
No geologically hazardous areas or associated buffers/setbacks will be altered by the proposed
construction. It is our opinion that the proposed deck construction will not increase surface
water discharge or sedimentation, decrease slope stability, or adversely impact other critical
areas on the subject or adjacent properties.
4, Design Standards within Erosion and Landslide Hazard Areas. Development
within an erosion or landslide hazard area and/or buffer shall be designed to
meet the following basic requirements unless it can be demonstrated that an
alternative design that deviates from one or more of these standards provides
greater long-term slope stability while meeting all other provisions of this title.
The requirement for long-term slope stability shall exclude designs that require
regular and periodic maintenance to maintain their level of function. The basic
development design standards are:
a. 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. If stability at the proposed development site is
below these limits, the proposed development shall provide practicable
approaches to reduce risk to human safety and improve the factor of safety
for landsliding. In no case shall the existing factor of safety be reduced for
the subject property or adjacent properties;
b. Structures and improvements shall be clustered to avoid geologically
hazardous areas and other critical areas;
c. Structures and improvements shall minimize alterations to the natural
contour of the slope, and foundations shall be tiered where possible to
conform to existing topography;
d. Structures and improvements shall be located to preserve the most critical
portion of the site and its natural landforms and vegetation;
e. The proposed development shall not result in greater risk or a need for
increased buffers on neighboring properties;
f, The use of retaining walls that allow the maintenance of existing natural
slope area is preferred o ver graded artificial slopes; and
g. Development shall be designed to minimize impervious lot coverage;
SOUTH FORK GEOSCIENCES, PLLC Page 3
PO Box 1 275
NORTH BEND, WA 98045
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Sullivan Deck
1128 Sea Vista Place
Edmonds, Washington
April 2, 2021
Project #21021
Response:
Since the mapped potential landslide hazard is on the adjacent property with no required
buffer, and there are not erosion hazards (stable erosion hazard area) on the subject property,
no geologically hazardous areas or associated buffers will be altered by the proposed
construction. As such, these design standards are not applicable.
5. Vegetation Retention, Unless otherwise provided or as part of an approved
alteration, removal of vegetation from an erosion or landslide hazard area or
related buffer shall be prohibited;
Response:
The proposed construction does not require vegetation removal from landslide hazard areas or
associated buffers.
6. Seasonal Restriction, Clearing shall be allowed only from May 15t to October 1st
of each year; provided, that the director may extend or shorten the dry season
on a case -by -case basis depending on actual weather conditions, except that
timber harvest, not including brush clearing or stump removal, may be allowed
pursuant to an approved forest practice permit issued by the city of Edmonds
or the Washington State Department of Natural Resources;
Response:
It is our opinion that there are not any site conditions that warrant a seasonal restriction for the
proposed construction. However, shortening the seasonal restriction is at the Director's
discretion.
7, Point Discharges. Point discharges from surface water facilities and roof drains
onto or upstream from an erosion or landslide hazard area shall be prohibited
except as follows:
a. Conveyed via continuous storm pipe downslope to a point where there are
no erosion hazard areas downstream from the discharge;
b. Discharged at flow durations matching predeveloped conditions, with
adequate energy dissipation, into existing channels that previously
conveyed storm water runoff in the predeveloped state; or
c. Dispersed discharge upslope of the steep slope onto a low -gradient,
undisturbed buffer demonstrated to be adequate to infiltrate all surface
and storm water runoff, and where it can be demonstrated that such
discharge will not increase the saturation of the slope; and
Response:
The modest size increase of the existing pervious deck will not create significant point
discharges or increase flows/flow durations.
S. Prohibited Development. On -site sewage disposal systems, including drain
fields, shall be prohibited within erosion and landslide hazard areas and related
buffers
Response:
Not applicable to the proposed project.
B. Earth Subsidence and Landslide Hazard Area. In addition to the requirements of
this chapter, development proposals for lands located within the earth subsidence
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Sullivan Deck
1128 Sea Vista Place
Edmonds, Washington
April 2, 2021
Project #21021
and landslide hazard area as indicated on the critical areas inventory shall be
subject to the provisions of Chapter 19.10 ECDC,
Response:
Not applicable to the proposed project.
C, Seismic Hazard Areas. Activities proposed to be located in seismic hazard areas
shall meet the standards of ECDC 23, 80, 060, Development standards — General
requirements, [Ord 4026 § 1 (Att. A), 2016; Ord 3527 § 2, 2004].
Response:
Due to the dense, Vashon lodgement till sediments present, there are no seismic hazard areas
on or adjacent to the subject property.
Closure
We have enjoyed working with you on this project and are confident that the information
provided in this letter will aid in the permitting of your project. If there are any questions about
this letter, as I free to contact us.
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Andrew L. Glandon
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Engineering Geologist / Owner
South Fork Geosciences, PLLC
References:
"City of Edmonds, Plan Review Comments - RE: Plan Check BLD2021-0986, 1128 Sea Vista PI., Single
Family Deck" City of Edmonds, Michele Szafran, July 29, 2021
"Subject: Geologic Hazards Assessment and Soil Design Recommendations Sullivan Deck — (CRA2021-
0007)", South Fork Geosciences, Project #21021, April 2, 2021
"Subsurface Conditions, Geologic Hazards, and Preliminary Design Recommendations, Hachler
Residence Addition, 1140 Sea Vista Place, Edmonds, Washington", South Fork Geosciences, Project
#17056, June 19, 2017
"Subject: Critical Areas Determination (CRA2021-0007) Site Address: 1128 SEA VISTA PL", City of
Edmonds, Michele Szafran, February 2, 2021
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PO Box 1 275
NORTH BEND, WA 98045
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