RESUB 2-BLD2022-0989+Geotechnical_Report+7.6.2023_5.44.14_PM+3651884August 22, 2022
Updated September 23, 2022
ES-8626.01
North Star Visions, LLC
19020 — 33rd Avenue West, Suite 450
Lynnwood, Washington 98036
Attention: Mr. Lucas Kragt, P.E.
Subject: Geotechnical Evaluation
Proposed Single -Family Residence
Sugar and Scovill Property
10234 — 242nd Place Southwest
Edmonds, Washington
RESUB
VoJul 07 2023
CIOFEDMONDS
EVELOPMENT SERVICES
DEPARTMENT
Earth Solutions NW LLC
Geotechnical Engineering, Construction
Observation/Testing and Environmental Services
Reference: ASPI, LLC, Existing Conditions Map, dated June 20, 2022
PACE Engineers, Building Site Plan, dated September 8, 2022
Malsam Tsang Structural Engineering
Structural Calculations for: Plan 3132-02A, dated July 5, 2022
BLD2022-0989
Tubbs Geosciences
Geotechnical Engineering Report, File No. HAL2-01, dated January 9, 2004
Field Report, dated April 1, 2004
James P. Minard
Geologic Map of the Edmonds East and Part of the Edmonds West Quadrangles
Washington, 1983
United States Department of Agriculture (USDA)
Web Soil Survey (WSS)
Department of Ecology
Stormwater Management Manual for Western Washington
Amended December 2014
Edmonds City Code
Chapter 23.80 (Geologically Hazard Areas)
Dear Mr. Kragt:
As requested, Earth Solutions NW, LLC (ESNW) has prepared this geotechnical evaluation for
the proposed single-family residence; this report has been updated based on site specific
topographic data and proposed site plan. As part of our scope of services, we completed a
subsurface exploration, laboratory and engineering analyses, and prepared this written report
with our findings and recommendations for the proposed project. Based on our evaluation, the
proposed project is feasible from a geotechnical standpoint.
15365 N.E. 90th Street, Suite 100 0 Redmond, WA 98052 0 (425) 449-4704 0 FAX (425) 449-4711
North Star Visions, LLC
August 22, 2022
Updated September 23, 2022
Protect Description
ES-8626.01
Page 2
The subject site is located at 10234 — 242nd Place Southwest in Edmonds, Washington, as
illustrated on the attached Vicinity Map (Plate 1). The site consists of one tax parcel (Snohomish
County parcel number 0055500000-4902) totaling approximately 0.22 acres of land. The
property is currently undeveloped and vegetated primarily by grass and mature trees around the
site perimeter; some invasive vegetation is present along the sloped area in the southwest corner
of the site. Site topography gently to moderately descends towards the north and west; the
southwestern corner of the property moderately to steeply descends to the neighboring property.
The subject site is bordered to the east, south, and west by single-family residences and to the
north by a single-family residence and 242nd Place Southwest.
Based on the referenced site plan, the subject site will be developed with a single-family
residence and associated improvements. Grading activities will include cuts of up to about four
feet to establish the planned building alignments. A rain garden will be constructed near the
southwest corner of the property to control stormwater runoff. Site improvements will also include
underground utility installations.
The proposed residential structure will consist of relatively lightly loaded wood framing supported
on conventional foundations. Based on the referenced structural calculations, wall loads will be
on the order of 1 to 2 kips per linear foot, isolated footing loads will be less than 20 kips, and we
anticipate slab -on -grade loading of 150 pounds per square foot (psf).
If the above design assumptions are incorrect or change, ESNW should be contacted to review
the recommendations in this report. ESNW should review the final design to verify the
geotechnical recommendations provided in this report have been incorporated into the plans.
Subsurface Conditions
As part of this geotechnical evaluation, an ESNW representative observed, logged, and sampled
three hand auger borings on May 11, 2022, advanced at accessible locations within the proposed
development area, using hand tools and a half -inch diameter steel T-probe to probe the subgrade
of the test holes. The approximate locations of the hand auger borings are depicted on the Hand
Auger Boring Location Plan (Plate 2). Please refer to the hand auger boring logs provided as an
attachment to this report for a more detailed description of subsurface conditions. Representative
soil samples collected at the test pit locations were analyzed in general accordance with the
Unified Soil Classification System (USCS) and USDA methods and procedures. ESNW also
reviewed the referenced Tubbs Geosciences geotechnical engineering report that was prepared
for the properties to the west (downslope) of the subject site.
Earth Solutions NW. LLC
North Star Visions, LLC
August 22, 2022
Updated September 23, 2022
Topsoil
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Page 3
Topsoil was observed extending to depths of approximately four to six inches below the existing
ground surface (bgs. The topsoil was characterized by dark brown color and fine organic
material.
Native Soil
Underlying the topsoil, native soil at the test pit locations was observed to consist of silty gravel
with sand, poorly graded sand with silt and gravel, and poorly graded gravel with sand (USCS:
GM, SP-SM, and GP, respectively). Overall soil relative density generally increased with depth,
extending to the maximum exploration depth of about three feet bgs. The native soil was
generally observed in a weakly cemented condition beginning at about one foot bgs at HA-2.
Geologic Setting
The referenced geologic map resource identifies Vashon till (Qvt) across the site and Advanced
outwash (Qva) mapped immediately to the west of the subject site. As reported on the geologic
map resource, Vashon till typically consists of a nonsorted mixture of clay, silt, sand, pebbles,
cobbles, and boulders. The till was deposited directly by ice advanced over previously deposited
sediment and rocks. The advance outwash in characterized as mostly clean and well -stratified
sand with some pebbles. Additionally, the referenced WSS resource identifies urban land-
Alderwood complex as the primary soil unit underlying the subject site. The Alderwood series
was formed in glacial till plains. Based on our field observations, native soils on the subject site
are generally consistent with the geologic setting outlined in this section.
Groundwater
Groundwater seepage was not observed at the hand auger boring locations during the fieldwork
(May 2022). However, zones of groundwater seepage should be expected in deeper excavations
at this site. Groundwater seepage rates and elevations fluctuate depending on many factors,
including precipitation duration and intensity, the time of year, and soil conditions.
Geologically Hazardous Areas Assessment
As part of this geotechnical evaluation, the referenced chapter of the ECC was reviewed. Based
on our investigation and review, the following topics related to development plans and site
conditions are addressed:
Earth Solutions NW. LLC
North Star Visions, LLC ES-8626.01
August 22, 2022 Page 4
Updated September 23, 2022
Erosion Hazard Areas — ECC 23.80.020.A.
With respect to erosion hazard areas, section 23.80.020 of the ECC defines erosion hazards as
"at least those areas identified by the U.S. Department of Agriculture's Natural Resources
Conservation Service as having a `moderate to severe', `severe', or `very severe' rill and inter -rill
erosion hazard. Erosion hazard areas are also those areas impacted by shoreland and/or stream
bank erosion. Within the city of Edmonds, erosion hazard areas include:
1. Those areas of the city of Edmonds containing soils that may experience severe to very
severe erosion hazard. This group of soils includes, but is not limited to, the following
when they occur on slopes of 15 percent or greater:
a. Alderwood soils (15 to 25 percent slopes);
b. Alderwood/Everett series (25 to 70 percent slopes), and;
c. Everett series (15 to 25 percent slopes).
2. Coastal and stream erosion areas which are subject to the impacts from lateral erosion
related to moving water such as stream channel migration and shoreline retreat;
3. Any area with slopes of 15 percent or greater and impermeable soils interbedded with
granular soils and springs or ground water seepage, and;
4. Areas with significant visible evidence of ground water seepage, and which also include
existing landslide deposits regardless of slope."
The native soil is generally consistent with Alderwood or Everett series soils. Based on the ECC
definition, the areas sloped greater than 15 percent within and adjacent to the property classify
as erosion hazard areas. In our opinion, the proposed construction will not increase the erosion
hazard for the site or adjacent properties, provided typical Best Management Practices (BMPs),
such as silt fences, covering exposed soil, and permanent landscaping, are implemented during
and after construction as warranted.
Earth Solutions NW. LLC
North Star Visions, LLC ES-8626.01
August 22, 2022 Page 5
Updated September 23, 2022
Landslide Hazard Areas — ECC 23.80.020.B.
With respect to landslide hazard areas, section 23.80.020 of the ECC defines landslide hazard
areas as areas potentially subject to landslides based on a combination of geologic, topographic,
and hydrologic factors. They include areas susceptible because of any combination of soil, slope
gradient, slope aspect, structure, hydrology, or other factors. Within the city of Edmonds,
landslide hazard areas specifically include:
1. Areas of ancient or historic failures in Edmonds which include all areas within the earth
subsidence and landslide hazard area as identified in the 1979 report of Robert Lowe
Associates and amended by the 1985 report of GeoEngineers, Inc., and further discussed
in the 2007 report by Landau Associates;
2. Coastal areas mapped as class U (unstable), UOS (unstable old slides) and URS
(unstable recent slides) in the Department of Ecology Washington coastal atlas;
3. Areas designated as quaternary slumps, earthflows, mudflows, or landslides on maps
published by the United States Geological Survey or Washington State Department of
Natural Resources;
4. Any slope of 40 percent or steeper that exceeds a vertical height of 10 feet over a 25-foot
horizontal run. Except for rockeries that have been engineered and approved by the
engineer as having been built according to the engineered design, all other modified
slopes (including slopes where there are breaks in slopes) meeting overall average
steepness and height criteria should be considered potential landslide hazard areas;
5. Any slope with all three of the following characteristics:
a. Slopes steeper than 15 percent;
b. Hillsides intersecting geologic contacts with relatively permeable sediment overlying a
relatively impermeable sediment, and;
c. Springs or ground water seepage.
6. Any area potentially unstable as a result of rapid stream incision or stream bank erosion;
7. Any area located on an alluvial fan, presently subject to, or potentially subject to,
inundation by debris flow or deposition of stream -transported sediments, and;
8. Any slopes that have been modified by past development activity that still meet the slope
criteria.
Earth Solutions NW. LLC
North Star Visions, LLC
August 22, 2022
Updated September 23, 2022
ES-8626.01
Page 6
It is our opinion the site exhibits good slope stability characteristics as indicated by no observed
evidence suggesting previous shallow, debris -flow -type failures or deep-seated rotational failures
and/or movements. Additionally, ESNW did not observe any evidence of active springs or
groundwater seepage during our site visit.
Based on site observations and review of available topographic data, the slope located in the
southwest corner of the subject site moderately to steeply descends about 16 to 18. Based on
site specific topographic data, a portion of the on -site slope area is up to approximately 50 percent
across and elevation change of less than 10 feet; based on interpolation of the off -site slope area,
it is likely that a portion of the slope is 40 percent or steeper across an elevation change of at
least 10 feet. In this respect, it is likely that at least a portion of the slope area would be
considered a landslide hazard area per above criterion 4.
Mapping of Geologically Hazardous Areas — ECC 23.80.030
Review of available geologically hazardous areas indicates the slope area in the southwest
corner of the site is an erosion hazard area and a portion of the slope is a landslide hazard area;
we understand these designations are based on lidar topographic data only.
Special Study and Report Requirements — ECC 23.80.050
A. This geotechnical report and geological hazards assessment was completed by a
professional engineer licensed in the state of Washington with experience analyzing
geologic hazards throughout the Puget Sound region.
B. The following areas have been reviewed and addressed:
1. The project area includes the subject site as delineated in the referenced site plan.
2. Other similarly localized areas of 15 to 40 percent slopes are mapped within 200 feet
of the subject site.
C. This geological hazards assessment included a field investigation and an assessment of
geologic hazards. This geotechnical report has been prepared, stamped, and signed by
a qualified professional.
1. It is our opinion the level of analysis completed for this geological hazards assessment
is appropriate for the scale and scope of the project and scale of the geological hazard
areas present.
2. A discussion of all geologically hazardous areas on the site and any geologically
hazardous areas off site potentially impacted by the proposed project is provided in
this report.
Earth Solutions NW. LLC
North Star Visions, LLC
August 22, 2022
Updated September 23, 2022
ES-8626.01
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3. Based on the results of our study and on -site observations, the proposed project will
not decrease slope stability or pose an unreasonable threat to persons or property
either on or off site. These conclusions are based on the current conditions of the
slope in question and proposed site design; grades will be lowered in the project area
and the building will be appropriately setback from the top of the steep slope area.
4. This geological hazard assessment is provided as adequate information to comply with
requirements of ECC geological hazards.
5. This geotechnical report generally follows the guidelines set forth in the Washington
State Department of Licensing Guidelines for Preparing Engineering Geology Reports
in Washington (2006).
6. It is our opinion a landslide hazard minimum building setback of 10 feet (as measured
from face of slope, see Plate 3), and erosion hazard mitigation recommendations are
provided in this report.
D. We are not aware of a previous study completed for the subject site. We reviewed the
referenced geotechnical report that was prepared for the adjacent properties to the west.
E. The mitigation recommendations include a minimum 10-foot building setback, erosion
control measures, directing stormwater away from the slope area, and installing an
impermeable liner for the proposed rain garden.
F. This geological hazards assessment and geotechnical report should be reviewed as part
of the overall submittal package.
1. Please refer to the referenced site plan prepared by PACE Engineers.
a. The height of the slopes and slope gradients are discussed in this report have been
determined using both site specific topographic data and publicly available
topography data.
b. Springs, seeps, or other surface expressions of groundwater were not observed on
or immediately adjacent to the site.
c. Surface water runoff features were not observed within the subject site.
2. Requested hazard analysis items:
a. Vegetative cover across the landslide hazard area generally consists of mature
trees with invasive ivy and blackberry groundcover.
b. Subsurface conditions are described in the Subsurface Conditions section of this
report.
Earth Solutions NW. LLC
North Star Visions, LLC
August 22, 2022
Updated September 23, 2022
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c. Surface and groundwater conditions are discussed in previous sections of this
report. Based on site surface and subsurface conditions, there may have been
some minor grade cuts in some areas of the site. Based on surface conditions and
review of the referenced Tubbs Geosciences field report, the portion of the slope
that extends on the neighboring property was previously cut to existing slope
gradients and a tiered block wall was constructed at the toe.
d. The slopes within and adjacent to the subject site generally exhibit good overall
stability. We anticipate very low impact on the stability of the slope from the
proposed project.
e. The slopes within and adjacent to the subject site are not characterized as bluffs
and we do not anticipate a retreat of the slopes to occur.
f. Based on the slope conditions and historic modifications to the toe of the slope on
the adjacent property, it is our opinion that the run -out hazard of the slope would
likely be associated with surficial debris flow and toppling of the block walls within
the adjacent property. This would likely be a result of saturation of surficial looser
soil along the slope.
g. The proposed project will include lowering grades to the northeast of the slope area.
The stability of the slope area is considered good.
h. We recommend the building be setback at least 10 feet from the face of the steep
slope area (see Plate 3).
The proposed surface and subsurface drainage system is designed to collect
stormwater and groundwater within the proposed project area and direct it to a
controlled stormwater system. We recommend installing an impermeable liner for
the proposed rain garden. It is our opinion that the vulnerability of the site to erosion
will not be increased by the proposed surface and subsurface drainage system.
k. In our opinion, if the proposed addition and deck are supported on a deep
foundation system as recommended in this report, the location of the improvements
are suitable relative to the potential landslide hazard area.
I. Surface and subsurface drainage should be designed to minimize impacts to the
steep slope area. Based on relatively permeable soil over relatively impermeable
soil present, we do not recommend infiltration systems within 50 feet of the potential
landslide hazard area.
3. This geotechnical engineering study was prepared by a licensed engineer.
a. Geotechnical design parameters are provided within this report.
b. Drainage and subdrainage recommendations are provided within this report.
Earth Solutions NW. LLC
North Star Visions, LLC ES-8626.01
August 22, 2022 Page 9
Updated September 23, 2022
c. Earthwork recommendations are provided within this report.
d. In our opinion, no slope stabilization measures are necessary and no seismically
unstable soils were identified.
G. It is our opinion the site erosion hazard areas should be considered stable.
H. Based on the results of our study, the site does not contain any seismic hazard areas.
Development Standards (General Requirements) — ECC 23.80.060
Based on the results of our geological hazards assessment, the proposed project will not increase
the threat of the geological hazard to adjacent properties beyond predevelopment conditions, the
proposed project will not adversely impact other critical areas, the proposed project is designed
so that the hazard to the project is eliminated or mitigated to a level equal to or less than
predevelopment conditions, and the project is certified as safe as designed under anticipated
conditions.
Development Standards (Specific Hazards) — ECC 23.80.070
1. We recommend the building be setback at least 10 feet from the face of the steep slope
area (see Plate 3).
2. It is our opinion that a buffer is not necessary for the currently proposed project.
3. We understand the proposed project may include minimal alteration of the slope area
to remove invasive vegetation groundcover and establish a native vegetation
groundcover system. Provided the recommendations in this report and subsequent
geotechnical recommendations are incorporated into the design and construction of
the project, the proposed alteration will not increase surface water discharge or
sedimentation to adjacent properties beyond predevelopment conditions, will not
decrease slope stability on adjacent properties, and such alterations will not adversely
impact other critical areas.
4. a. The proposed project will include lowering grades to the northeast of the slope area.
In this respect, the proposed project will not decrease the factor of safety for the
subject property or adjacent properties.
b. It is our opinion that the structures and improvements have been located and
engineered in a manner which sufficiently mitigates impacts to geologically
hazardous areas.
c. The proposed project is designed to minimize alterations to the natural contours of
the site and will not alter grades of the steep slope area.
Earth Solutions NW. LLC
North Star Visions, LLC
August 22, 2022
Updated September 23, 2022
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d. The structures and improvements have been located and engineered in a manner
that retains the most critical portions of slope areas (southwest corner of the site)
as well as natural landforms and vegetation.
e. The proposed development will not result in greater risk or a need for increased
buffers on neighboring properties.
f. Based on the minimal construction, artificial alteration of the existing slopes will not
be necessary.
5. We understand removal of invasive groundcover within the steep slope area is being
considered, and would be replaced with native vegetation groundcover.
6. It is our opinion that this site should not be restricted to seasonal clearing and grading
work. This opinion is based on the relatively small scope of the project and relatively
low risk of erosion based on the proposed grading. However, if work is completed
during wet weather, additional duration and cost should be anticipated to implement
erosion control BMPs and mitigate negative impacts of runoff.
7. We are not aware of proposed point discharges.
Temporary Excavations
For temporary cuts taller than four feet, we recommend sloping or benching the cuts with a 1 H:1 V
gradient. Steeper inclinations can be evaluated by ESNW during construction based on exposed
soil conditions.
Structural Fill
Structural fill is defined as compacted soil placed in foundation, slab -on -grade, roadway,
permanent slope, retaining wall, and utility trench backfill areas. Structural fill placed and
compacted during site grading activities should meet the following specifications and guidelines:
• Structural fill material
• Moisture content
• Relative compaction
• Loose lift thickness (maximum)
Granular soil*
At or slightly above optimum
95 percent (Modified Proctor)
12 inches
Existing soil may not be suitable for use as structural fill unless at (or slightly above) the optimum moisture content
at the time of placement and compaction.
** Soil shall not be placed dry of optimum and should be evaluated by ESNW during construction.
Earth Solutions NW. LLC
North Star Visions, LLC
August 22, 2022
Updated September 23, 2022
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With respect to underground utility installations and backfill, local jurisdictions may dictate the soil
type(s) and compaction requirements. Unsuitable material or debris must be removed from
structural areas if encountered.
If structural fill is placed on sloped grades, the slope should be keyed and benched prior to placing
fill. ESNW should review grading plans and provide additional recommendations as necessary.
Foundations
The proposed structure can be supported on conventional spread and continuous footings
bearing on undisturbed, competent native soil, compacted native soil, or new structural fill.
Competent native soils, suitable for support of the foundation, should be encountered beginning
at depths of approximately one to three feet bgs. Where loose or unsuitable soil conditions are
encountered at foundation subgrade elevations during site preparation activities, compaction of
the soils to the specifications of structural fill, or overexcavation and replacement with granular
structural fill will be necessary. Compaction of the soil to the levels necessary for use as structural
fill may be difficult during wet weather conditions. Organic material exposed at foundation
subgrade elevations must be removed and grades restored with structural fill.
Provided the structure will be supported as described above, the following parameters can be
used for design of the new foundations:
• Allowable soil bearing capacity 2,500 psf
• Passive earth pressure 300 pcf (equivalent fluid)
• Coefficient of friction 0.40
The passive earth pressure and coefficient of friction values include a safety factor of 1.5. A one-
third increase in the allowable soil bearing capacity can be assumed for short-term wind and
seismic loading conditions.
With structural loading as expected, total settlement in the range of one inch is anticipated, with
differential settlement of about one-half inch. The majority of the settlements should occur during
construction, as dead loads are applied.
Slab -on -Grade Floors
Slab -on -grade floors for the proposed residential structure should be supported on a well -
compacted, firm, and unyielding subgrade. Where feasible, native soils exposed at the slab -on -
grade subgrade level can likely be compacted in -situ to the specifications described in this
section. Unstable or yielding areas of subgrade should be recompacted, or overexcavated and
replaced with suitable structural fill, prior to construction of the slab.
Earth Solutions NW. LLC
North Star Visions, LLC
August 22, 2022
Updated September 23, 2022
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A capillary break consisting of a minimum of four inches of free -draining crushed rock or gravel
should be placed below the slab. The free -draining material should have a fines content of 5
percent or less (where the fines content is defined as the percent passing the Number 200 sieve,
based on the minus three -quarter -inch fraction). In areas where slab moisture is undesirable,
installation of a vapor barrier below the slab should be considered. If a vapor barrier is utilized,
it should be a material specifically designed for use as a vapor barrier and should be installed in
accordance with manufacturer specifications.
Retaining Walls
Retaining walls must be designed to resist earth pressures and applicable surcharge loads. The
following parameters may be used for design:
• Active earth pressure (unrestrained condition)
• At -rest earth pressure (restrained condition)
• Traffic surcharge (passenger vehicles)
• Passive earth pressure
• Coefficient of friction
• Seismic surcharge
Where applicable.
** Where H equals the retained height (in feet).
35 pcf (equivalent fluid)
55 pcf
70 psf (rectangular distribution) *
300 pcf (equivalent fluid)
M1
8H psf**
A factor -of -safety of 1.5 has been applied to the passive earth pressure and coefficient of friction
values provided in this section. The above design parameters are based on a level backfill
condition and level grade at the wall toe. Revised design values will be necessary if sloping
grades are to be used above or below retaining walls. Additional surcharge loading from adjacent
foundations, sloped backfill, or other relevant loads should be included in the retaining wall
design.
Retaining walls should be backfilled with free -draining material that extends along the height of
the wall and a distance of at least 18 inches behind the wall. In lieu of 18 inches of a free draining
material, a drainage mat can be considered. ESNW should evaluate the suitability of drainage
mat application during construction. The upper 12 inches of the wall backfill may consist of a
less permeable soil, if desired. A perforated drainpipe should be placed along the base of the
wall and connected to an approved discharge location. A typical retaining wall drainage detail is
provided on Plate 4. If drainage is not provided, hydrostatic pressures should be included in the
wall design.
Earth Solutions NW. LLC
North Star Visions, LLC
August 22, 2022
Updated September 23, 2022
Seismic Design
ES-8626.01
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The 2018 International Building Code (2018 IBC) recognizes the most recent edition of the
Minimum Design Loads for Buildings and Other Structures manual (ASCE 7-16) for seismic
design, specifically with respect to earthquake loads. Based on the soil conditions encountered
at the test pit locations, the parameters and values provided below are recommended for seismic
design per the 2018 IBC.
Parameter
Value
Site Class
D*
Mapped short period spectral response acceleration, Ss (g)
1.28
Mapped 1-second period spectral response acceleration, S1 (g)
0.449
Short period site coefficient, Fa
1.0
Long period site coefficient, F„
1.851 **
Adjusted short period spectral response acceleration, SMs (g)
1.28
Adjusted 1-second period spectral response acceleration, SM1 (g)
0.831**
Design short period spectral response acceleration, SIDS (g)
0.853
Design 1-second period spectral response acceleration, SD1 (g)
0.554**
* Assumes dense native soil conditions, encountered to a maximum depth of 3.0 feet bgs during the May 2022 field
exploration, remain dense to at least 100 feet bgs.
** Values assume Fv may be determined using linear interpolation per Table 11.4-2 in ASCE 7-16.
Liquefaction
Liquefaction is a phenomenon where saturated and loose cohesionless soil suddenly loses
internal strength and behaves as a fluid. This behavior is in response to increased pore water
pressures resulting from an earthquake or another intense ground shaking. In our opinion, site
susceptibility to liquefaction may be considered low. The depth of the regional groundwater table,
and the composition and relative density of the native soil were the primary bases for this opinion.
Drainage
Zones of perched groundwater seepage should be anticipated in site excavations depending on
the time of year grading operations take place. Temporary measures to control surface water
runoff and groundwater during construction would likely involve passive elements such as
interceptor trenches and sumps. ESNW should be consulted during preliminary grading to
identify areas of seepage and to provide recommendations to reduce the potential for instability
related to seepage effects.
Earth Solutions NW. LLC
North Star Visions, LLC ES-8626.01
August 22, 2022 Page 14
Updated September 23, 2022
Finish grades should be designed to direct surface water away from structures and slopes.
Grades adjacent to structures and slopes should be sloped away at a gradient of at least 2
percent for a horizontal distance of up to 10 feet or the maximum allowed by adjacent structures.
In our opinion, foundation drains should be installed along building perimeter footings. A typical
footing drain detail is provided on Plate 5.
Rain Garden
We understand a rain garden is proposed immediately northeast of the southwest slope area.
We recommend installing an impermeable liner for the proposed rain garden. If an alternative
rain garden location is considered or pursued, ESNW can reevaluate this recommendation.
Infiltration and LID Evaluation
As indicated in the Subsurface Conditions section, native soils encountered during our fieldwork
were characterized primarily as dense coarse -grained soil. Based on the results of USDA textural
analyses, the native soils at depth were classified primarily as gravelly loamy coarse sand and
gravelly sandy loam with fines contents of about 10 to 12 percent at depth.
While the dense coarse -grained site soil may exhibit a low infiltration capacity, infiltration should
be considered infeasible due to the sloped topography along the west side of the property.
Attempted infiltration would present reasonable concern of erosion and downgradient flooding.
Limitations
This geotechnical evaluation report has been prepared for the exclusive use of North Star Visions,
LLC and their representatives. The recommendations and conclusions provided in this report
are professional opinions consistent with the level of care and skill that is typical of other members
in the profession currently practicing under similar conditions in this area. A warranty is not
expressed or implied. Variations in the soil and groundwater conditions observed at the test sites
may exist and may not become evident until construction. ESNW should reevaluate the
conclusions in this report if variations are encountered.
Additional Services
ESNW should be retained to provide additional geotechnical services in association with this
project, including testing and consulting services during construction. ESNW should have an
opportunity to review final project plans with respect to geotechnical recommendations provided
in this letter.
Earth Solutions NW. LLC
North Star Visions, LLC
August 22, 2022
Updated September 23, 2022
ES-8626.01
Page 15
We trust this letter meets your current needs. Should you have questions, or if any additional
information is required, please call.
Sincerely,
EARTH SOLUTIONS NW, LLC
Adam Z. Shier, L.G.
Project Geologist
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Henry T. Wright, P.E.
Associate Principal Engineer
Attachments: Plate 1
— Vicinity Map
Plate 2
— Hand Auger Boring Location Plan
Plate 3
— Foundations Adjacent to Slopes
Plate 4
— Retaining Wall Drainage Detail
Plate 5
— Footing Drain Detail
Hand Auger Boring Logs
Grain Size
Distribution
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Open StreetMap.org
1 NER.-
40
Vicinity Map
Sugar and Scovill Property
Edmonds, Washington
NOTE: This plate may contain areas of color. ESNW cannot be
Drwn. MRS
Date 07/26/2022
Proj. No. 8626.01
responsible for any subsequent misinterpretation of the information
Checked HTW
Date July 2022
Plate 1
resulting from black & white reproductions of this plate.
, I
/ � w
/ � I
400 / I
/ \ ' HA-3
I
/ HA7 — HA-2
400 El
I I I
I
� I I
� I I
I
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� I I
1
244TH STREET S.W.
LEGEND
HA-1 Approximate Location of
— — ESNW Hand Auger Boring,
Proj. No. ES-8626.01, May 2022
Subject Site
Existing Building
NOTE: The graphics shown on this plate are not intended for design
purposes or precise scale measurements, but only to illustrate the
approximate test locations relative to the approximate locations of
existing and / or proposed site features. The information illustrated
is largely based on data provided by the client at the time of our
study. ESNW cannot be responsible for subsequent design changes
or interpretation of the data by others.
NOT - TO - SCALE
Hand Auger Boring Location Plan
Sugar and Scovill Property
Edmonds, Washington
NOTE: This plate may contain areas of color. ESNW cannot be Drwn. MRS Date 07/25/2022 Pro No. 8626.01
responsible for any subsequent misinterpretation of the information J
resulting from black & white reproductions of this plate. Checked HTW Date July 2022 Plate 2
Foundations Adjacent to Slopes
Sugar and Scovill Property
Edmonds, Washington
Drwn. MRS Date 09/22/2022 Proj. No. 8626.01
Checked HTW Date Sept. 2022 Plate 3
18" Min.
0 0 o 0 o O
°o o �p � �° �0 .0
po o °o�0 0o0 ° ��o 0 �oo
0
0
0 00° 0000�oo 00000
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0 0 0 0 oo .0 o, o 8 0
00 o o oo O
0
0 0 0 o o o o
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0 o o 0 0 0 0 o 0
0 0 o0 00° 0 o o
00 0 op oo 0 o o o
0
0 0o Oo 0 0 Oo0o O oo o
00
00
0 0 oo o p
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0 0 0 0 oo
0 0 0 000 o0 o 000
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0
0 o So o0 0 0 0 0
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NOTES:
• Free -draining Backfill should consist
of soil having less than 5 percent fines.
Percent passing No. 4 sieve should be
25 to 75 percent.
• Sheet Drain may be feasible in lieu
of Free -draining Backfill, per ESNW
recommendations.
• Drain Pipe should consist of perforated,
rigid PVC Pipe surrounded with 1-inch
Drain Rock.
LEGEND:
Q 00o O
p o000 Free -draining Structural Backfill
-inch Drain Rock
%. of of of ti
Structural
Fill
Perforated Rigid Drain Pipe
(Surround in Drain Rock)
SCHEMATIC ONLY - NOT TO SCALE
NOT A CONSTRUCTION DRAWING
Retaining Wall Drainage Detail
Sugar and Scovill Property
Edmonds, Washington
Drwn. MRS Date 09/22/2022 Proj. No. 8626.01
Checked HTW Date Sept. 2022 1 Plate 4
Perforated Rigid Drain Pipe
(Surround in Drain Rock)
NOTES:
• Do NOT tie roof downspouts
to Footing Drain.
• Surface Seal to consist of
12" of less permeable, suitable
soil. Slope away from building.
LEGEND:
Surface Seal: native soil or
other low -permeability material
B.* - _- - - _... " - "
1-inch Drain Rock
SCHEMATIC ONLY - NOT TO SCALE
NOT A CONSTRUCTION DRAWING
Earth
Solutions
NW uc
Footing Drain Detail
Sugar and Scovill Property
Edmonds, Washington
Drwn. MRS Date 09/22/2022 Proj. No. 8626.01
Checked HTW Date Sept. 2022 Plate 5
Earth Solutions NWLLC
SOIL CLASSIFICATION CHART
MAJOR DIVISIONS
SYMBOLS
TYPICAL
DESCRIPTIONS
GRAPH
I LETTER
GRAVEL
AND
CLEAN
GRAVELS
• �••
.�
GW
WELL -GRADED GRAVELS, GRAVEL -
SAND MIXTURES, LITTLE OR NO
FINES
° �a o �a
o p�o p
Q oQ
GAP
POORLY -GRADED GRAVELS,
GRAVEL - SAND MIXTURES, LITTLE
OR NO FINES
GRAVELLY
SOILS
(LITTLE OR NO FINES)
COARSE
GRAINED
SOILS
MORE THAN 50%
OF COARSE
GRAVELS WITH
FINES
°
�0
00
D
O
GM
SILTY GRAVELS, GRAVEL - SAND -
SILT MIXTURES
FRACTION
RETAINED ON NO.
4 SIEVE
(APPRECIABLE
AMOUNT OF FINES)
�±�
V
CLAYEY GRAVELS, GRAVEL - SAND -
CLAY MIXTURES
SAND
AND
CLEAN SANDS
SW
WELL -GRADED SANDS, GRAVELLY
SANDS, LITTLE OR NO FINES
MORE THAN 50%
OF MATERIAL IS
SP
POORLY -GRADED SANDS,
GRAVELLY SAND, LITTLE OR NO
FINES
LARGER THAN
N0. 200 SIEVE
SIZE
SANDY
SOILS
(LITTLE OR NO FINES)
SANDS WITH
FINES
c
SM
SILTY SANDS, SAND - SILT
MIXTURES
MORE THAN 50%
OF COARSE
FRACTION
PASSING ON NO.
4 SIEVE
(APPRECIABLE
AMOUNT OF FINES)
CC
S
CLAYEY SANDS, SAND - CLAY
MIXTURES
INORGANIC SILTS AND VERY FINE
ML
SANDS, ROCK FLOUR, SILTY OR
CLAYEY FINE SANDS OR CLAYEY
SILTS WITH SLIGHT PLASTICITY
CL
INORGANIC CLAYS OF LOW TO
MEDIUM PLASTICITY, GRAVELLY
CLAYS, SANDY CLAYS, SILTY CLAYS,
LEAN CLAYS
FINE
GRAINED
SOILS
SILTS
AND LIQUID LIMIT
LESS THAN 50
CLAYS
— — —
OL
ORGANIC SILTS AND ORGANIC
SILTY CLAYS OF LOW PLASTICITY
MORE THAN 50%
OF MATERIAL IS
SMALLER THAN
NO. 200 SIEVE
MH
INORGANIC SILTS, MICACEOUS OR
DIATOMACEOUS FINE SAND OR
SILTY SOILS
SIZE
SILTS LIQUID LIMIT
AND GREATER THAN 50
CLAYS
CH
INORGANIC CLAYS OF HIGH
PLASTICITY
OH
ORGANIC CLAYS OF MEDIUM TO
HIGH PLASTICITY, ORGANIC SILTS
HIGHLY ORGANIC SOILS
PT
PEAT, HUMUS, SWAMP SOILS WITH
HIGH ORGANIC CONTENTS
DUAL SYMBOLS are used to indicate borderline soil classifications.
The discussion in the text of this report is necessary for a proper understanding of the nature
of the material presented in the attached logs.
r Earth Solutions NW, LLC
15365 N.E. 90th Street, Suite 100
Redmond, Washington 98052
Telephone: 425-449-4704
Fax: 425-449-4711
BORING NUMBER HA-1
PAGE 1 OF 1
PROJECT NUMBER ES-8626.01 PROJECT NAME Sugar and Scovill Property
DATE STARTED 5/11/22 COMPLETED 5/11/22 GROUND ELEVATION
DRILLING CONTRACTOR ESNW Rep LATITUDE LONGITUDE
LOGGED BY HTW CHECKED BY HTW GROUND WATER LEVEL:
NOTES S7 AT TIME OF DRILLING
SURFACE CONDITIONS Grass AFTER DRILLING
w
CL
_
wJ
~W
CO
TESTS
_
CL
O
d7
u/i
Q
W
p
Q Z
0
0.0
TPSL-..
-
0.5
o
o °
-
MC=9.1%
°
GM
° °
2.5
MC = 8.9%
Fines = 12.1 %
°
° °
MATERIAL DESCRIPTION
Dark brown gravelly TOPSOIL
Brown silty GRAVEL with sand, loose to medium dense, moist to wet
-trace fine to medium roots to BOH
-becomes medium dense, light brown
-becomes tan, dense, moist
[USDA Classification: very gravelly sandy LOAM]
Hand auger boring terminated at 3.0 feet below existing grade due to refusal on gravel. No
groundwater encountered during excavation. No caving observed.
LIMITATIONS: Ground elevation (if listed) is approximate; the test location was not surveyed.
Coordinates are approximate and based on the WGS84 datum. Do not rely on this test log as a
standalone document. Refer to the text of the geotechnical report for a complete understanding
of subsurface conditions.
r Earth Solutions NW, LLC
15365 N.E. 90th Street, Suite 100
Redmond, Washington 98052
Telephone: 425-449-4704
Fax: 425-449-4711
BORING NUMBER HA-2
PAGE 1 OF 1
PROJECT NUMBER ES-8626.01 PROJECT NAME Sugar and Scovill Property
DATE STARTED 5/11/22 COMPLETED 5/11/22 GROUND ELEVATION
DRILLING CONTRACTOR ESNW Rep LATITUDE LONGITUDE
LOGGED BY HTW CHECKED BY HTW GROUND WATER LEVEL:
NOTES S7 AT TIME OF DRILLING
SURFACE CONDITIONS Grass AFTER DRILLING
w
_
CL
~W
_
wJ
CO
TESTS
Q O
MATERIAL DESCRIPTION
p
d7
fy
Q Z
0
0.0
TPSL
Dark brown gravelly TOPSOIL
0.5
SP-
:'TT
Gray poorly graded SAND with silt and gravel, dense to very dense, moist
MC = 9.2% SM
1.0
-weakly cemented
Fines = 10.5%
[USDA Classification: very gravelly loamy coarse SAND]
Hand auger boring terminated at 1.0 foot below existing grade due to refusal on cemented soil.
No groundwater encountered during excavation. No caving observed.
LIMITATIONS: Ground elevation (if listed) is approximate; the test location was not surveyed.
Coordinates are approximate and based on the WGS84 datum. Do not rely on this test log as a
standalone document. Refer to the text of the geotechnical report for a complete understanding
of subsurface conditions.
r Earth Solutions NW, LLC
15365 N.E. 90th Street, Suite 100
Redmond, Washington 98052
Telephone: 425-449-4704
Fax: 425-449-4711
BORING NUMBER HA-3
PAGE 1 OF 1
PROJECT NUMBER ES-8626.01 PROJECT NAME Sugar and Scovill Property
DATE STARTED 5/11/22 COMPLETED 5/11/22 GROUND ELEVATION
DRILLING CONTRACTOR ESNW Rep LATITUDE LONGITUDE
LOGGED BY HTW CHECKED BY HTW GROUND WATER LEVEL:
NOTES S7 AT TIME OF DRILLING
SURFACE CONDITIONS Grass AFTER DRILLING
w
CL
_
wJ
~W
CO
TESTS
_
Q O
MATERIAL DESCRIPTION
QCL
z
0
Dark brown gravelly TOPSOIL
TPSL 0.5
° Brown poorly graded GRAVEL with sand, loose to medium dense, moist to wet
o °
GP
oO� -becomes light brown, medium dense
MC = 5.0% °
Fines = 4.7% o O -BOH probed dense
2.0 [USDA Classification: extremely gravelly coarse SAND]
Hand auger boring terminated at 2.0 feet below existing grade due to refusal on gravel. No
groundwater encountered during excavation. No caving observed.
LIMITATIONS: Ground elevation (if listed) is approximate; the test location was not surveyed.
Coordinates are approximate and based on the WGS84 datum. Do not rely on this test log as a
standalone document. Refer to the text of the geotechnical report for a complete understanding
of subsurface conditions.
Earth Solutions NW, LLC GRAIN SIZE DISTRIBUTION
15365 N.E. 90th Street, Suite 100
WWI Redmond, Washington 98052
Telephone: 425-449-4704
Fax: 425-449-4711
PROJECT NUMBER ES-8626.01 PROJECT NAME Sugar and Scovill Property
U.S. SIEVE OPENING IN INCHES U.S. SIEVE NUMBERS I HYDROMETER
6 4 3 2 1 3/4 1 /23/8 3 4 6 810 1416 20 30 40 50 60 100140 200
100
95
90
85
80
75
70
65
H
60
w
� 55
m
w 50
z
LL
45
z
w
40
w
a
35
30
25
20
15
10
5
0
Ll
100 10 1 0.1 0.01 0.001
GRAIN SIZE IN MILLIMETERS
COBBLES
GRAVEL
SAND
SILT OR CLAY
coarse fine
coarse medium fine
0
S
w
N
z
9
0