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Kirkland Office | 911 Fifth Avenue | Kirkland, WA 98033 P | 425.827.7701
Mount Vernon Office | 508 S. Second Street, Suite 101 | Mount Vernon, WA 98273 P | 425.827.7701
Tacoma Office | 1552 Commerce Street, Suite 102 | Tacoma, WA 98402 P | 253.722.2992
www.aesgeo.com
July 25, 2019
Project No. 190275E001
Mr. Marland Franco
2855 Blaine Avenue NE
Renton, Washington 98056
Subject: Limited Geotechnical Report
Steep Slope Restoration
2855 Blaine Avenue NE
Renton, Washington
Dear Mr. Franco:
The purpose of this letter is to respond to a request for a geotechnical report by the City of Renton
(City) Planning Division. At your request, Associated Earth Sciences, Inc. (AESI) recently performed
a geotechnical reconnaissance of the slope, and reviewed available geotechnical and geologic
information in the vicinity of the site. No subsurface explorations or testing of soil was performed.
SITE DESCRIPTION
We understand that backyard of your residence located at 2855 Blaine Avenue NE in Renton,
Washington is adjacent to a moderately forested steep slope. You informed us that you placed
pieces of broken concrete on a small area near the top of the slope which was relatively free of
vegetation to provide some armoring for erosion. We understand that in the process of doing this
work, your neighbor contacted the City of Renton to report that you were completing work in a
critical area without the appropriate City permit. The City notified you that you were in violation
and required a geotechnical engineer to observe the work area and provide conclusions regarding
the impact to slope stability and provide recommendations as necessary to mitigate the area
disturbed on the slope.
SLOPE CONDITIONS
An experienced geotechnical engineer from our firm visited the site, met with you and observed
the current slope conditions on July 2, 2019. The area of concern is located near the top of a
Franco Residence
Renton, Washington Limited Geotechnical Report
July 25, 2019 ASSOCIATED EARTH SCIENCES, INC.
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northern-facing steep slope that is approximately 30 feet tall based on review of topographic
information from the King County iMap website. The slope descends at an inclination estimated to
be from 80 to 100 percent. The area is roughly triangular and measures about 10 feet wide at the
top and narrows to a point about 15 feet down the slope. The area is mostly comprised of exposed
soil with scattered concrete rubble pieces across the slope with some topsoil and landscaping
debris. A small pile of stacked dried wood tree branches/limbs was present at the top of the slope.
Established vegetation on either side of the area consists of ivy, small ferns which provide ground
cover, and predominantly large-diameter trees that provide a thick overhead canopy. The slope is
relatively continuous with similar slope inclination and vegetation on adjacent properties to the
east and west of the site.
We reviewed Light Detection and Ranging (LIDAR) data, which is a remote sensing technology
that measures distance to a target by illuminating that target with a pulsed laser light, and
measuring the reflected pulses with a sensor. Review of the LIDAR topography does not indicate
historic large-scale landsliding at or adjacent to the site.
City of Renton Sensitive Areas Map (November 12, 2014) indicates that the site and neighboring
properties are considered to have a “Moderate” landslide hazard severity.
SUBSURFACE CONDITIONS
We interpreted subsurface conditions at the site based on review of available geologic mapping
and observations made during our site reconnaissance. Hand probing with a ½-inch diameter steel
t-rod, into the slope of about 24 inches penetration indicates the surficial soils are loose. Geologic
mapping indicates the site to be underlain by pre-Fraser fine-grained deposits (Derek B. Booth,
Kathy A. Troost, and Aaron P. Wischer, Geologic Map of King County, Washington, March 2007).
The pre-Fraser fine-grained deposit typically consists of glacially overridden silt and clay.
CONCLUSIONS AND RECOMMENDATIONS
In our opinion, the action of placing the concrete rubble pieces on the steep slope below your
property has not increased the existing landslide hazard risk. The biggest issue in our opinion
would be protecting this area from future erosion. We recommend revegetation of the portion of
the slope that has been disturbed to minimize the potential for erosion. Given the relatively small
area and steepness of the slope, practical repair options are somewhat limited. In our opinion, the
most cost-effective approach given the shady conditions due to the vegetation canopy, would be
to plant similar native vegetation in this area that exists on the slope such as ferns combined with
an erosion geofabric such as jute matting. While use of a geocell product could be considered for
Franco Residence
Renton, Washington Limited Geotechnical Report
steep slope applications with difficult revegetation issues, we consider use of geocell in this
particular case excessive.
CLOSURE
We trust this letter meets your current needs. Should you have any questions, please contact us at
your convenience.
Sincerely,
ASSOCIATED EARTH SCIENCES, INC.
Kirkland, Washington
Matthew A. Miller, P.E.Stephen A. Siebert, P.E.
Principal Engineer Associate Geotechnical Engineer
July 25, 2019 ASSOCIATED EARTH SCIENCES, INC.
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