REVIEWED RESUB2 BLD2023-1461+GEO REPORT +5.3.2024_1.21.04_PM+4236228Group Northwest, Inc.
May 1, 2024
Mr. William Goodman
16624 — 72nd Avenue W
Edmonds, Washington 98026
Geotechnical Engineers, Geologists
& Environmental Specialists
G-6017
Subject: Geotechnical Engineering and Geologic Critical Areas Report
Proposed Residential Garage, 16624 — 72nd Avenue W, Edmonds, Washington
Dear Mr. Goodman:
Per your request, GEO Group Northwest, Inc. is pleased to present this geotechnical engineering
and geologic critical areas report for the proposed new garage at your residence in Edmonds,
Washington. We understand that the City of Edmonds has required a geotechnical report
evaluating geologic critical areas on or in the vicinity of the property be submitted as part of the
building permit application for the project.
SITE AND PROPOSED PROJECT DESCRIPTION
Project Site Location and Description
The site property is located in a residential neighborhood in northern Edmonds, Washington.
The property is approximately rectangular in shape and is 21,408 square feet in size. Other
residential properties are present to the east and south, and rights of way for 166th Place SW are
present to the north and west.
The site property currently is developed with a single-family residence that has a main floor level
and a daylight basement which includes a garage. An asphalt driveway runs from the north
property line to the front of the garage on the west side of the residence. An asphalt paved
parking area also is located in the northeast part of the site. The residence is connected to the
local sewer utility.
13705 Bel -Red Road, Bellevue, Washington 98005
Phone: (425) 649-8757 / E-mail: info@geogroupnw.com
May 1, 2024
Mr. William Goodman
G-6017
Page 2
Overall, the property has gentle to moderate sloping topography that falls toward the south or the
west, except at its west margin and in its southeast corner where the slopes steepen. The primary
features on the property and the topography of the site are illustrated in Plate 2 — Site Plan.
Geologic Background Information
Published geologic mapping of the local vicinity indicates that the site property is underlain with
glacial advance outwash deposits from the Vashon Glaciationl. These deposits typically consist
of fine to medium grained sand, either stratified or unstratified, with lesser silty or gravelly sand
layers. They typically are dense or very dense where they have not been subjected to
weathering. They may contain groundwater in areas where they are underlain with impermeable
soils.
Proposed Project Description
We understand that you propose to construct a detached new garage on the eastern part of the
property as part of a remodeling project. The new garage is planned to be approximately
600 square feet in size, and is planned to be supported on conventional concrete footings and
have a conventional slab -on -grade concrete floor. The location of the proposed garage is
illustrated in Plate 3 — Proposed Project Layout.
We also understand that you plan to remodel the existing residence. The proposed remodeling,
however, will not involve addition to the residence footprint nor additional stories for the
residence.
SITE INVESTIGATION
Site Reconnaissance
On February 8, 2024, we performed a reconnaissance of the site property and of the immediate
vicinity as accessible or observable from the site property or nearby public areas. We found that
the features and topography indicated in the topographic survey are consistent with the
conditions we observed.
1 Geologic Map of the Edmonds East and Part of the Edmonds West Quadrangles, Washington. Washington
Department of Geology and Earth Resources Miscellaneous Field Studies Map MF-1541, 1983.
GEO Group Northwest, Inc.
May 1, 2024
Mr. William Goodman
G-6017
Page 3
Vegetation and landscaping on the site south and east of the residence was observed to consist of
grass lawn, laurel hedges, a few rhododendron bushes, and mulching -surfaced planted landscape
areas. Vegetation and landscaping on the north side of the residence was observed to consist of
mulching -surface planting areas, grass lawn, and border hedging along the east property line.
Vegetation and landscaping on the site west of the residence was observed to consist of mulch -
surfaced and planted areas alongside the asphalt driveway area, two segmental block walls along
the east side of the driveway, and grass lawn south of the driveway. The slope area to the west is
covered with a thick layer of bark chips, mulching, and a discontinuous cover of shrubs and other
plants. We observed no trees having a diameter of greater than 6 inches as measured at breast
height on the property.
We observed no indications of soil instability, erosion or water seepage on the site property. We
also observed that the surface grades on site continued onto the adjacent properties to the south
and east at similar to lesser inclinations, and we also did not observe conditions indicating soil
instability or movement, or water seepage, on the visible portions of these properties.
Soil Investigation
During our site reconnaissance, we completed a soil boring in the proposed garage location by
using hand -auger equipment and hand tools. Soils encountered in the boring consisted of an
upper layer of apparent fills consisting of loose fine- to medium -grained sand with lesser
proportions of gravel and cobbles to a depth of approximately 2.5 feet. The underlying soils
consisted of fine- to medium -grained sand with minor gravel to the bottom of the boring at
approximately 6.5 feet. These soils were relatively loose to a depth of approximately 4 feet, and
medium dense to dense below. Groundwater was not encountered in the boring.
The soils below 2.5 feet are interpreted to be glacial advance outwash deposits consistent with
those noted in published geologic mapping of the local area. The soil log for the boring is
provided in Attachment A to this report.
GEOLOGIC CRITICAL AREAS
We have reviewed the proposed project in respect to critical areas study and report requirements
contained in ECDC 23.80.050. Our findings, conclusions, and recommendations are presented
in the following sections of this report.
GEO Group Northwest, Inc.
May 1, 2024
Mr. William Goodman
Geologic Critical Areas Identification and Description
Landslide Hazard Areas
G-6017
Page 4
City of Edmonds GIS mapping indicates that landslide hazard areas are present on the southeast
and the southwest parts of the site property.
Southeast Portion of the Site Property
The mapped landslide hazard areas in the southeast corner of the property are shown as being of
small size, having heights of less than 10 feet, and straddling the property lines. The locations of
these areas are illustrated in Plate 4 — Geologic Hazard Areas GIS Mapping.
The topographic survey for the site property indicates that there is a steep slope area in the
southeast part of the property that has a maximum height of approximately 10 to 12 feet and an
inclination of approximately 40 to 45 percent within the property limits. Thus, this steep slope
area meets the minimum criteria to be designated a landslide hazard area per ECDC
23.80.020(B). Its on -site extent is illustrated in Plate 2 — Site Plan and Plate 3 — Proposed Project
Layout.
As noted from our reconnaissance, we observed that this slope continues downward onto
adjacent property to the south and southeast at similar to lesser inclinations. The height of the
off -site portion of the slope area is approximately 30 feet based on City of Edmonds GIS
mapping as illustrated in Plate 4 — Geologic Hazard Areas Mapping; but its inclinations vary
between slightly below to slightly above 40 percent grade. The slope area does not constitute a
bluff condition or have an inclination significantly greater than the typical angle of repose for
vegetated slopes underlain with sandy soils, and the slope area was not observed to exhibit water
seepage. Therefore, it is our opinion that the rate of landslide area expansion due to a 100-year
storm event is estimated to be not more than 1 foot (due to erosion), and is minimal due to
seismic activity.
Southwest Portion of the Site Property
The mapped landslide hazard area in the southwest part of the property is shown as having a
height of up to approximately 6 feet and a length of approximately 100 feet. The location of this
area is illustrated in Plate 4 — Geologic Hazard Areas GIS Mapping.
GEO Group Northwest, Inc.
May 1, 2024
Mr. William Goodman
G-6017
Page 5
The topographic survey, however, indicates that the southwest part of the property has a steep
slope area with a maximum height of approximately 10 to 12 feet, a length of approximately
60 feet, and straddles the west property line. Thus, this steep slope area meets the minimum
criteria to be designated a landslide hazard area per ECDC 23.80.020(B). The extent of this
landslide hazard area is illustrated in Plate 2 — Site Plan and Plate 3 — Proposed Project Layout.
SO Feet or Less from the Site Property
The only landslide hazard areas indicated to be present within 50 feet of project area consist of a
few small discontinuous areas to the south and east of the southeast corner of the site property, as
illustrated in City of Edmonds GIS information. The overall slope inclination encompassing
these areas and immediate surroundings is 40 percent grade or slightly greater.
SO to 200 Feet from the Site Property
Other landslide hazard areas are illustrated in City of Edmonds GIS information at distances
ranging between 50 and 200 feet from project location. These areas mostly are located south,
southeast, or north of the project location, as illustrated in Plate 4 - Geologic Hazard Areas GIS
Mapping. We reviewed the distance and topographic relationships of these areas with respect to
the project location. We observed that these areas are either 1) separated from the project
location by topographic features which provide separation of potential impacts to the project
location, 2) have slope orientations which are directed such potential impacts to the project
location are avoided, or 3) are at distances from the project area which are much greater than
their heights. Therefore, we conclude that these areas do not have the potential to be affected by
the proposed project or vice versa.
Erosion Hazard Areas
City of Edmonds GIS mapping indicates that erosion hazard areas are present on portions of the
project property and of adjacent properties. These areas are shown in Plate 4 —Geologic Critical
Areas GIS Mapping.
According to information from the USDA Natural Resources Conservation Service (MRCS),
surface soils on the property are mapped as Alderwood series gravelly sandy loam. These soils
typically have a parent material of glacial drift or outwash over dense glacio-marine deposits.
GEO Group Northwest, Inc.
May 1, 2024
Mr. William Goodman
G-6017
Page 6
The soils found at the site are similar to those described as Alderwood series soils. Per ECDC
23.80.020(A), soils of the Alderwood series on slopes steeper than 15 percent grade are
designated as erosion hazard areas.
The topographic survey of the site indicates that a majority of the site property (the areas west,
northwest, and southeast of the residence) including the proposed project area has slopes of
greater than 15 percent grade, and therefore meet the criteria to be designated erosion hazard
areas.
Geologic Hazards Assessment
In our opinion, the potential for landsliding as a result of the proposed project is minimal because
of the following factors:
• the distance between the proposed garage and the landslide hazard areas,
• the slope heights and inclinations of the landslide hazard areas being marginally greater
than the minimum criteria for their designation;
• the light loads that would be imposed by the proposed garage,
• the minimal amount of net cut and fill needed to construct the proposed garage; and
• the unsaturated sandy soil conditions found in the project area during our investigation.
The potential for erosion of exposed soils in and downslope of the project location during
construction exists if temporary controls are not implemented. Also, if these soils that are left
exposed after construction, there exists a potential for them to undergo erosion unless they are re -
stabilized. Such erosion, if it were to occur, would have its impact limited by the downslope and
cross -slope grass lawn area and by the pervious, sandy character of the soils. Therefore, we
recommend that mitigation measures to address the potential for soil erosion during and
following the project be included in the project plans.
Landslide Hazard Area Buffer and Building Setback
We reviewed the buffer and building setback criteria for landslide hazard areas in ECDC
23.80.070. We recommend a building setback width of 15 feet as measured from the top of the
(steep slope) landslide hazard area be set for the site property. This distance is equal to or
slightly greater than the height of the steep slope. We conclude that the proposed building
GEO Group Northwest, Inc.
May 1, 2024
Mr. William Goodman
G-6017
Page 7
setback width will minimize the risk of property damage, death, or injury from landslides caused
by the proposed project.
Based on the site conditions found during our investigation and the limited nature of the
proposed project (construction of an at -grade residential garage), it is our opinion that a landslide
hazard area buffer for the proposed project can be identical in width and location to the
recommended building setback for the project.
Mitigation of Long -Term Impacts to Geologic Critical Areas
To mitigate the potential for temporary or long-term impacts to the landslide hazard and erosion
hazard areas on the site property and immediate vicinity, we recommend that a temporary
erosion and sediment control plan (TESL), and a soil re -stabilization plan should be included in
the proposed project plans. Measures to include in the TESC are provided below in the
Recommendations portion of this report. Our recommendations for the re -stabilization plan
include the following:
• measures to prevent the concentrated discharge of surface water onto slopes having
inclinations steeper than 15 percent grade;
• limiting the inclination of permanent slopes in the project area to not more than 2.5H:1 V;
and
• re -stabilizing soils exposed by construction with new vegetation or other protective
landscape materials or surfacing (i.e., pavers, crushed stone, etc.) at the end of the
project.
Conclusions
We have developed the following conclusions regarding critical areas considerations and the
proposed project. These conclusions are conditioned that the recommendations presented in this
report are properly followed.
It is our conclusion that the proposed project satisfies the standards described in ECDC
23.80.070.A.4 in the following respects.
GEO Group Northwest, Inc.
May 1, 2024
Mr. William Goodman
G-6017
Page 8
• the slope heights and inclinations of the landslide hazard areas are marginally greater
than the minimum criteria for their designation (standard a);
• the distance between the proposed garage and the landslide hazard areas
(standards b and d),
• the light loads that would be imposed by the proposed garage (standard a),
• the minimal amount of net cut and fill needed to construct the proposed garage
(standards c and d); and
• the footprint of the proposed garage is limited to that appropriate for a 2- car garage, and
no increase of the driveway is proposed (standard e).
• the potential for geologic hazard to adjacent properties will not be increased, relative to
pre -project conditions.
• the hazard to the proposed project from soil instability or erosion is mitigated to minimal
levels.
Other critical areas, including stream or wetland areas, critical aquifer recharge areas, and
frequently flooded areas, are not documented to be present on or near to the site property.
Therefore, the proposed project will not adversely affect other critical areas.
GEOTECHNICAL ENGINEERING RECOMMENDATIONS
In our opinion, the proposed garage can be supported on conventional concrete footings that bear
on undisturbed medium dense to dense soils or on structural fill that is placed on a subgrade of
these soils. The findings from our investigation indicate that medium dense or dense soils
suitable for supporting conventional concrete footings are present at depths of up to
approximately 4 feet below existing grade. Our recommendations regarding these and other
geotechnical aspects for the proposed project are presented below in the following sections of
this report.
GEO Group Northwest, Inc.
May 1, 2024
Mr. William Goodman
Site Seismic Design Classification
G-6017
Page 9
In our opinion, the project site can be assigned Seismic Site Class D (Medium Dense Soil
Profile), per the International Building Code 2018 Edition (IBC 2018). Our determination is
based upon the findings from our subsurface investigation activities and our knowledge and
understanding of the typical deeper subsurface soil conditions in the site vicinity.
The seismic design parameters applicable for the site based on this site class per IBC 2018 are as
follows:
S, = 1.320g Sm, = 1.320g Sd, = 0.880g S1 = 0.469g
The peak ground acceleration for the site adjusted for site class effects is 0.624g
Earthwork
Site Clearing and Erosion Control
The area where construction work will be performed should be cleared of vegetation, topsoil,
organics, debris, fills, and any other deleterious materials that are found. These materials should
be hauled off site or used for landscaping, as appropriate; they should not be used as structural
fill for the project.
Temporary erosion and sedimentation controls (TESCs) should be installed as part of site
clearing activities. TESCs for the project can include using silt fences, check dams, straw mulch,
hay bales, and a stabilized construction entrance. The silt fences or other barrier controls should
be placed along the cross -slope and down -slope boundaries of the disturbed areas to prevent
sediment -laden runoff from being discharged off site. Exposed soils, including stockpiled soils,
should be covered with plastic sheeting when they are not being worked.
Excavations and Slopes
Temporary excavation slopes should not be greater than the limits specified in local, state and
federal government safety regulations. We recommend that temporary excavations 4 feet or
more in depth be sloped no steeper than 1H:1V (Horizontal: Vertical). If water seepage or other
adverse conditions are observed during excavation, temporary cuts may need to have shallower
GEO Group Northwest, Inc.
May 1, 2024
Mr. William Goodman
inclinations. Permanent unreinforced slopes at the site should be inclined no steeper than
2.5H:IV.
G-6017
Page 10
Surface runoff should not be allowed to flow over the top of slopes into excavations. During wet
weather, exposed slopes should be covered with plastic sheeting to prevent erosion or softening.
We recommend that we visit the site during excavation of cut slopes to verify anticipated
geologic conditions and to evaluate slope stability, particularly if groundwater seepage, caving
soils, or debris are encountered.
Subgrade Preparation
After the completion of site clearing and excavation, soils in areas to receive structural fill,
concrete slabs, sidewalks, or pavements, should be prepared to a firm, unyielding condition. The
prepared subgrade should be observed and approved by the geotechnical engineer. Any detected
soft spots or disturbed areas should be compacted or excavated and replaced with compacted
structural fill or crushed rock as directed by the geotechnical engineer.
Structural Fill
Structural fill is typically defined as earthen material that is placed below buildings (including
foundations and on -grade slab floors), sidewalks, driveways, or other structures, and provides
support to those structures. Soils that meet the material specifications for structural fill as
presented below in this report, or are otherwise approved by the geotechnical engineer, can be
used for structural fill. Material which is stored on site for later use as structural fill should be
covered with plastic sheeting to protect it from moisture if its usability is sensitive to its moisture
content. Structural fill material should be placed and compacted in accordance with the
recommendations provided below or as otherwise approved by the geotechnical engineer during
construction.
Fill Material Specifications
Earthen material to be used as structural fill should be a predominantly granular material without
clumps; free of organic material, debris, or other deleterious substances; and have a maximum
particle size of three (3) inches in diameter. During wet weather, we recommend that the
material be fully granular in character and have a fines content (passing a #200 sieve) of less
than 5 percent.
GEO Group Northwest, Inc.
May 1, 2024
Mr. William Goodman
G-6017
Page 11
The material should be placed at or near its optimum moisture content. If the material is too wet
to be compacted to the required degree, it will be necessary to dry the material by aeration
(which may be difficult) or replace the material with an alternative suitable material in order to
achieve the recommended compaction.
We anticipate that the sandy site soils found during our investigation will be acceptable for use
as structural fill, provided that they are free of deleterious materials including oversized cobbles,
and have an appropriate moisture content for achieving proper compaction.
Compaction Specifications
Structural fill material placed under foundation footings and concrete floor slabs should be
compacted to at least 92 percent of its maximum dry density as determined by ASTM D 1557.
Structural fill material under exterior slabs or pavements should be compacted to at least
90 percent of its maximum dry density, except for the top 12 inches of the material, which
should be compacted to at least 95 percent of its maximum dry density.
Structural fill material should be spread and compacted in lifts that are 10 inches or less in
thickness in an un-compacted state. The compacted fill material should be field tested by using
ASTM Designations D2922 and D3017, Nuclear Probe Method, to verify that the required
degree of compaction has been achieved.
Foundations
Conventional Concrete Footings
New conventional strip and column footings should bear directly on medium dense to dense
native soils or on compacted structural fill that has been placed on a compacted subgrade of
native medium dense soils. Our recommended design criteria for conventional footing
foundations supported in this manner are provided below.
- Allowable bearing pressure, including all dead and live loads:
Medium dense to dense undisturbed soil = 1,500 psf
Structural fill placed on medium dense to dense soil = 1,500 psf
- Minimum depth to base of perimeter footing below adjacent exterior grade = 18 inches
GEO Group Northwest, Inc.
May 1, 2024
Mr. William Goodman
G-6017
Page 12
- Minimum depth to base of interior footing below top of floor slab = 12 inches
- Minimum width of wall footings = 16 inches
- Minimum lateral dimension of column footings = 24 inches
- Estimated post -construction total settlement (in existing house
footprint or to southwest) ='/2 inch
- Estimated post -construction differential settlement (in existing house
footprint or to southwest)
= %2 inch
Structural fill used to support footings should extend laterally beyond the footing edges by a
distance equal to the fill thickness. We also recommend that the subgrade on which the fill is
placed be compacted in place to a firm condition.
A one-third increase in the above allowable bearing pressures can be used when considering
short-term transitory wind or seismic loads. Lateral loads against the building foundations can
be resisted by friction between the foundation and the supporting compacted fill subgrade or by
passive earth pressure acting on the buried portion of the foundations. For the latter case, the
foundations must be poured "neat" against the existing undisturbed soil or be backfilled with
compacted structural fill. Our recommended parameters, which include a factor of safety of 2.0,
are as follows:
- Passive Pressure (Lateral Resistance)
300 pcf, equivalent fluid weight, for structural fill or competent undisturbed
native soil
- Coefficient of Friction (Friction Factor)
0.35 for competent undisturbed native soil or structural fill
Concrete Slabs -on -Grade
We recommend that the garage slab -on -grade floor be supported on compacted medium dense
native soil or on structural fill that is placed on a subgrade of compacted medium dense native
soil. To avoid moisture build-up on the subgrade, floor slabs should be placed on a capillary
break, which is in turn placed on the prepared subgrade. The capillary break should consist of a
GEO Group Northwest, Inc.
May 1, 2024
Mr. William Goodman
G-6017
Page 13
layer, at least 6 inches thick, of free -draining crushed rock or gravel containing no fines and no
more than five percent material finer than a No. 4 sieve. A vapor barrier should be placed over
the capillary break to reduce upward transmission of water vapor through the slab, if such
transmission is undesirable.
Surface Drainage
During construction, water should not be allowed to stand in areas where footings, slabs, or
pavements are to be constructed. In our opinion, storm water drainage from the new garage roof
can be managed by using one or more downspouts that discharge to splash blocks with gravel -
lined dispersion pads because of the sandy and unsaturated soil conditions in the project area.
We recommend that the splash block and dispersion pad layout be consistent with applicable
standard drainage design details. Final grading of the project area also should not be set to
promote the concentrated flow of surface water onto the steep slope area at southeast corner of
the site and should not be directed onto adjacent properties.
Subsurface Drainage
In our opinion, footing drains alongside perimeter foundations for the proposed garage are not
needed, from a geotechnical perspective, and can be waived for the project.
LIMITATIONS
This report has been prepared for the specific application to this site for the exclusive use of
Mr. William Goodman and his authorized assignees or agents. Any other use of this report is
solely at the user's own risk. We recommend that this addendum be included in its entirety in
the project contract documents for reference during construction.
The recommendations presented in this report are our professional opinion derived in a manner
consistent with the level of care and skill ordinarily exercised by other members of the
profession currently practicing under similar conditions in this area and within the project
schedule and budget constraints. No warranty is expressed or implied. If conditions are found to
differ from those described in this report, we should be notified so that the relevant
recommendations in this report can be re-evaluated and modified if appropriate.
GEO Group Northwest, Inc.
May 1, 2024
Mr. William Goodman
CLOSING
G-6017
Page 14
We appreciate this opportunity to provide you with geotechnical engineering services. Please
feel free to contact us if you have any questions regarding this letter.
Sincerely,
GEO GROUP NORTHWEST, INC.
5/1/2024
Keith Johnson
Project Geologist
Illustrations:
5/ 1 /2024
Plate 1 — Site Location Map
Plate 2 — Site Plan
William Chang, P.E.
Principal Engineer
Plate 3 — Local Geologic Hazard Areas GIS Mapping
Plate 4 — Vicinity Geologic Hazard Areas GIS Mapping
Attachment:
Attachment A — Soil Boring Log
GEO Group Northwest, Inc.
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Group Northwest, Inc.
PROPOSED RESIDENTIAL GARAGE
— Geotechnical Engineers, Geologists, &
Environmental Scientists 16624 - 72ND AVENUE W
EDMONDS, WASHINGTON
SCALE: 1" = 2,000' DATE: 2/23/2024 1 MADE: KJ CHKD: WC JOB NO: G-6017 PLATE 1
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Source: Topographic Survey for Bill & Michelle Goodman, by Pacific Coast Surveys, Inc., dated 1/20/24. SCALE: 1 INCH = 40 FEET
SITE PLAN
Group Northwest, Inc. PROPOSED RESIDENTIAL GARAGE
— Geotechnical Engineers, Geologists, & 16624 - 72ND AVENUE W
Environmental Scientists EDMONDS, WASHINGTON
SCALE: 1" = 40' DRAWN: KJ CHECKED: WC DATE: 2/23/2024 PROJECT NO.: G-6017 PLATE 2
Source: Topographic Survey for Bill & Michelle Goodman, by Pacific Coast Surveys, Inc., dated 1/20/24.
1 Cl%Ck1l%
_ _ EXPLORATORY SOIL BORING
(APPROX. LOCATION)
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0 40 80
SCALE: 1 INCH = 40 FEET
PROPOSED PROJECT LAYOUT
Group Northwest, Inc. PROPOSED RESIDENTIAL GARAGE
- Geotechnical Engineers, Geologists, & 16624 - 72ND AVENUE W
Environmental Scientists EDMONDS, WASHINGTON
SCALE: 11, = 40' DRAWN: KJ CHECKED: WC DATE: 2/23/2024 PROJECT NO.: G-6017 PLATE 3
r, City of Edmonds Map Title
SITE
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PROPERTY 16618� N
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❑ Severe Erosion Hazard 15%-40%
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0 111.92 223.8 Feet 2,000 166.7 This map is a user generated output t d static out tfrom an Internet mapping
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reference only. Data layers that appear on
this map may or may not be accurate,
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current, or otherwise reliable.
THIS MAP IS NOT TO BE USED
FOR DESIGN OR CONSTRUCTION
200 FEET
Source: City of Edmonds GIS.
GEOLOGIC CRITICAL AREAS GIS MAPPING
Group Northwest, Inc. PROPOSED RESIDENTIAL GARAGE
- Geotechnical Engineers, Geologists, & 16624 - 72ND AVENUE W
Environmental Scientists EDMONDS, WASHINGTON
SCALE: As Shown I DRAWN: KJ CHECKED: WC I DATE: 2/23/2024 1 PROJECT NO.: G-6017 I PLATE 4
ATTACHMENT A
G-6017
SOIL BORING LOG
GEO Group Northwest, Inc.
SOIL CLASSIFICATION & PENETRATION TEST DATA EXPLANATION
UNIFIED SOIL CLASSIFICATION SYSTEM (USCS)
MAJOR DIVISION GROUP TYPICAL DESCRIPTION LABORATORY CLASSIFICATION CRITERIA
SYMBOL
CLEAN
GRAVELS
GRAVELS
(little or no
COARSE-
(More Than Half
fines)
GRAINED SOILS
Coarse Fraction is
Larger Than No. 4
Sieve)
DIRTY
GRAVELS
(with some
fines)
SANDS
CLEAN
SANDS
(More Than Half
More Than Half by
Coarse Fraction is
(little or no
Weight Larger
Smaller Than No. 4
fines)
Than No. 200
Sieve)
Sieve
DIRTY
SANDS
(with some
fines)
SILTS
Liquid Limit
(Below A -Line on
< 50%
Plasticity Chart,
Liquid Limit
FINE-GRAINED
Negligible
SOILS
Organics)
> 50%
CLAYS
Liquid Limit
(Above A -Line on
< 50%
Plasticity Chart,
Liquid Limit
Negligible
Organics)
> 50%
Less Than Half by
Weight Larger
Liquid Limit
Than No. 200
ORGANIC SILTS
< 50%
Sieve
& CLAYS
(Below A -Line on
Plasticity Chart)
Liquid Limit
> 50%
HIGHLY ORGANIC SOILS
GW WELL GRADED GRAVELS, GRAVEL -SAND
MIXTURE, LITTLE OR NO FINES CONTENT
OF FINES BELOW
GP POORLY GRADED GRAVELS, AND GRAVEL -SAND 5%
MIXTURES LITTLE OR NO FINES
GM
GC
Sw
69 i
SM
SC
MIL
MH
CL
CH
OL
OH
Pt
SOIL PARTICLE SIZE
U.S. STANDARD SIEVE
FRACTION
Passing Retained
Size
Size
Sieve
Sieve
(MM)
(mm' i
SILT / CLAY
#200
0.075
SAND
FINE
#40
0.425
#200
0.075
MEDIUM
#10
2.00
#40
0.425
COARSE
#4
4.75
#10
2.00
GRAVEL
FINE
0.75"
19
#4
4.75
COARSE
3"
76
0.75"
19
COBBLES
76 mm to 203 mm
BOULDERS
> 203 mm
ROCK
> 76 mm
FRAGMENTS
ROCK
>0.76 cubic meter in volume
SILTY GRAVELS, GRAVEL -SAND -SILT MIXTURES
CLAYEY GRAVELS, GRAVEL -SAND -CLAY
MIXTURES
WELL GRADED SANDS, GRAVELLY SANDS,
LITTLE OR NO FINES
POORLY GRADED SANDS, GRAVELLY SANDS,
LITTLE OR NO FINES
SILTY SANDS, SAND -SILT MIXTURES
CONTENT
OF FINES EXCEEDS
12%
CONTENT
OF FINES BELOW
5%
CONTENT OF FINES
EXCEEDSI2%
Cc = (D30)2 / (D10 " D60) between 1 and 3
CLEAN GRAVELS NOT MEETING ABOVE
REQUIREMENTS
GM: ATTERBERG LIMITS BELOW "A" LINE.
or P.I. LESS THAN 4
GC: ATTERBERG LIMITS ABOVE "A" LINE.
or P.I. MORE THAN 7
Cu = (D60 / D10) greater than 6
Cc = (D30)2 / (D10 " D60) between land 3
CLEAN SANDS NOT MEETING ABOVE
REQUIREMENTS
ATTERBERG LIMITS BELOW "A" LINE
with P.I. LESS THAN 4
CLAYEY SANDS, SAND -CLAY MIXTURES ATTERBERG LIMITS ABOVE "A" LINE
with P.I. MORE THAN 7
INORGANIC SILTS, ROCK FLOUR, SANDY SILTS
OF SLIGHT PLASTICITY
60
INORGANIC SILTS, MICACEOUS OR
50
DIATOMACEOUS, FINE SANDY OR SILTY SOIL
INORGANIC CLAYS OF LOW PLASTICITY,
40 -
GRAVELLY, SANDY, OR SILTY CLAYS, LEAN
x
w
CLAYS
Z
30 -
INORGANIC CLAYS OF HIGH PLASTICITY, FAT
>_
CLAYS
U
20 -
ORGANIC SILTS AND ORGANIC SILTY CLAYS OF
J
LOW PLASTICITY
a
10
7—
ORGANIC CLAYS OF HIGH PLASTICITY
4—
.'
0 10 20 30 40 50 60 70 80 90 100
PEAT AND OTHER HIGHLY ORGANIC SOILS LIQUID LIMIT (%)
GENERAL GUIDANCE FOR ENGINEERING PROPERTIES OF SOILS, BASED ON STANDARD
PENETRATION TEST (SPT) DATA
SANDY SOILS
SILTY & CLAYEY SOILS
Unconfined
Blow Counts
Relative
Friction Angle,
Blow Counts
N
Density, %
degrees
Description
P
N
Strength qu,
Descri lion
P
tsf
0-4
0-15
Very Loose
<2
<0.25
Very soft
4-10
15 - 35
26 - 30
Loose
2-4
0.25 - 0.50
Soft
10-30
35 - 65
28 - 35
Medium Dense
4-8
0.50 - 1.00
Medium Stiff
30-50
65 - 85
35 - 42
Dense
8 - 15
1.00 - 2.00
Stiff
> 50
85 - 100
38 - 46
Very Dense
15 - 30
2.00 - 4.00
Very Stiff
> 30
> 4.00
Hard
Group Northwest, Inc.
Geotechnical Engineers, Geologists, &
Environmental Scientists
13705 Bel -Red Road Bellevue, Washington 98005
Phone: (425) 649-8757 E-mail: info@geogroupnw.com
PLATE
Al
BORING HA-1
LOGGED BY: KJ DATE EXCAVATED: 2/8/24
GROUND ELEV:
DEPTH
ft.
USCS
SOIL DESCRIPTION
SAMPLE
No.
Water
%
OTHER TESTS/
COMMENTS
SP
1
SAND with GRAVEL and COBBLES, brown, damp, loose, sand is fine to
medium grained, trace fines, 35% coarse gravel to small cobbles, rare
11.7
small brick flakes (APPARENT FILL).
2
------
----------------------------------------------------
16.5
Probe 30" at 2.5'.
3
SP-SM
SAND to SILTY SAND, brown and dark grayish brown, loose, moist,
sand is fine to medium grained, 10-15% fines, some mottling and fine
black organics and large fresh roots at 4 feet (APPARENT TOPSOIL).
4
Probe 12"
SAND to SILTY SAND, brown, loose, moist, sand is fine to medium
5
------
grained, 5-10% gravel, some mottling.
----------------------------------------------------
6
SP
SAND, brownish gray, medium dense to dense, moist, sand is fine to
20.1
Probe 1" to 2".
medium grained, trace fines, 5-10% gravel, no mottling or oxide staining
(NATIVE SOIL).
17.5
Probe 1" to 2".
7
Bottom of boring at 6.5 feet below ground surface.
No groundwater encountered.
8
9
10
BORING LOG
Group Northwest Inc. PROPOSED RESIDENTIAL GARAGE
� 16624 - 72ND AVENUE W
Geotechnical Engineers, Geologists, & EDMONDS, WASHINGTON
Environmental Scientists