REVIEWED PLN RESUB3 BLD2024-1163+GEO REPORT+10.14.2024_8.41.13_AM+4557053COBALT
GE0SCIENCES
September 30, 2024
Updated October 14, 2024
Teri and Reed Johnson
1234teriPgmail.com
C/O Tanner Bellows
Tanneroalldecks.com
■--------------
Reviewed by
RES U B BLD2024-1163 City of Edmonds ;
Oct 14 2024 Planning Division '
CITY OF EDMONDS
DEVELOPMENT SERVICES
DEPARTMENT
Cobalt Geosciences, LLC
P.O. Box 1792
North Bend, WA 98045
RE: Geologic/Geotechnical Evaluation
Proposed Deck Extension
17122 Talbot Road
Edmonds, Washington
In accordance with your authorization, Cobalt Geosciences, LLC has prepared this report to
discuss the results of our geotechnical evaluation at the referenced site.
The purpose of our evaluation was to provide recommendations for foundation design, grading,
and earthwork.
Site & Project Description
The site is located at 17122 Talbot Road in Edmonds, Washington. The site consists of one
rectangular shaped parcel (No. 27040700102700) with a total area of about 0.31 acres.
The central portion of the property is developed with a single-family residence with daylight
basement, local walls, and driveway. The remainder of the property is undeveloped and vegetated
with grasses, bushes, blackberry vines, ivy, ferns, understory, and variable diameter trees.
The site slopes downward from southeast to northwest at magnitudes of 0 to 35 percent and relief
of about 45 feet.
The GIS topography shows slopes of about 50 percent and relief of 10 to 12 feet near the
residence. These areas have been historically graded and now consist of a 2 tier rockery system
with lower magnitude slopes. These walls are about 3 to 6.5 feet tall and separated by a sloping
bench. The lower rockery is tilted in excess of a typical batter and there is an approximate 18 foot
bench between the walls. The upper wall is about 15 feet from the residence.
The site is bordered to the northwest, northeast, and southwest by residential properties, and to
the southeast by Talbot Road.
The proposed development includes a new deck along the northwest side of the structure. Site
grading may include cuts of 3 feet or less and foundation loads are expected to be light.
Area Geology
The Geologic Map of the Edmonds East Quadrangle indicates that the site is underlain by Vashon
Glacial Till.
Vashon Glacial Till includes mixtures of silt, sand, gravel, and clay in a nonsorted matrix or
diamict. These deposits become denser with depth below a weathered zone.
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Geotechnical Evaluation
Soil & Groundwater Conditions
The geotechnical field investigation program was completed in September 2024 and included
advancing a hand boring near the deck location.
The hand boring encountered loose to medium dense, silty -fine to medium grained sand with
gravel (Glacial Till). There may be areas of fill behind the nearby rockery associated with original
grading and construction.
Groundwater was not observed during the exploration work. Groundwater may become perched
on denser till during a typical wet season.
Water table elevations often fluctuate over time. The groundwater level will depend on a variety
of factors that may include seasonal precipitation, irrigation, land use, climatic conditions and
soil permeability. Water levels at the time of the field investigation may be different from those
encountered during the construction phase of the project. It would be necessary to install one or
more piezometers to determine groundwater depths and fluctuations.
Steep Slope and Landslide Hazard Areas
Most municipal codes typically designate slope areas with magnitudes greater than 40 percent
and relief of at least io feet as potentially geologically hazardous. The site contains steep slope
and erosion hazard areas based on our review of the City of Edmonds GIS Maps.
We note that slope magnitudes are up to 35 percent within and near the property. Areas shown
on the GIS maps indicate 50 percent slopes just northwest of the residence; however, these areas
have lower magnitudes currently due to the construction of a two tier rockery wall system. It
appears that these areas no longer meet the criteria of steep slope hazard areas due to the grading.
We have included discussion of steep slopes as they relate to the former topography.
Code Information
23.80.o6o 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;
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.
The currently proposed project includes deck areas along the northwest side of the residence,
within or near an erosion/landslide hazard area. The work can be completed without adversely
affecting these areas and any geologic hazards. This requires proper installation and maintenance
of erosion control measures.
This report provides recommendations to facilitate safe construction, including temporary
excavation recommendations, fill compaction and placement, and foundation design.
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Geotechnical Evaluation
It is our opinion that this work will not affect global or local stability_ provided work is monitored
by the geotechnical engineer and erosion control measures are in place during construction.
The proposed construction will not increase the threat of geologic hazards on adjacent properties,
will not impact other critical areas, and are safe as designed under anticipated conditions.
23.80.07o Development standards — Specific hazards.
A. Erosion and Landslide Hazard Areas. Activities on sites containing erosion or landslide
hazards shall meet the requirements of ECDC, 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;
The provided plans show the deck locations very close to the residence, in already developed and
graded areas. There are no steep slopes close to the deck areas: however, there is a variable
height rockery (up to 6.5 feet). While no setback is required from these areas/features, if deck
foundation areas are located within a 1H:1V envelope from the back toe of the rockery (base of
rockery cut), they should be supported on pin piles. This will limit any surcharging to the wall.
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 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;
The site is currently developed with a residence and graded yard areas. A buffer is not very
relevant to the proposed construction. If a buffer is required, we recommend io feet from the toe
of the northwestern -most rockery wall, where natural slopes begin. The rockery walls are graded
areas with limited magnitude slopes.
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;
Provided earthwork activities are performed in accordance with the approved plans, all runoff is
fully controlled, and periodic geotechnical oversight is performed, the development will not
decrease slope stability on adjacent properties, will not increase surface water discharge or
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Geotechnical Evaluation
sedimentation beyond current levels, and will not impact other critical areas. Temporary and
permanent erosion and sediment control devices should be in at all times during construction.
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
over graded artificial slopes; and
g. Development shall be designed to minimize impervious lot coverage;
The project scope does not pose a risk to critical areas or the need to increase buffers on adjacent
properties. The deck areas are within or very close to the current building footprint and will not
cause any increase or decrease in stability and will be located in already developed or disturbed
areas. Factors of safety in these areas are well above minimum values.
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;
6. Seasonal Restriction. Clearing shall be allowed only from May 1st 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;
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;
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Geotechnical Evaluation
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
We concur with the above code items and have no additional comments at this time.
Erosion Hazard
The Natural Resources Conservation Services (NRCS) maps for Snohomish County indicate that
the site is underlain by Alderwood Urban Land Complex (2 to 8 and 8 to 15 percent slopes).
These soils would have a slight to moderate erosion potential in a disturbed state depending on
the slope magnitude.
It is our opinion that soil erosion potential at this project site can be reduced through landscaping
and surface water runoff control. Typically, erosion of exposed soils will be most noticeable
during periods of rainfall and may be controlled by the use of normal temporary erosion control
measures, such as silt fences, hay bales, mulching, control ditches and diversion trenches. The
typical wet weather season, with regard to site grading, is from October 1st to April 31st. Erosion
control measures should be in place before the onset of wet weather.
Seismic Hazard
The overall subsurface profile corresponds to a Site Class D as defined by Table 1613.5.2 of the
International Building Code (IBC). A Site Class D applies to an overall profile consisting of
medium dense to very dense soils within the upper too feet.
We referenced the U.S. Geological Survey (USGS) Earthquake Hazards Program Website to
obtain values for Ss, S,, Fa, and F,,. The USGS website includes the most updated published data
on seismic conditions. The following tables provide seismic parameters from the USGS web site
with referenced parameters from ASCE 7-16.
Seismic Design Parameters (ASCE 7-16)
Site
Spectral
Spectral
Site
Design Spectral
Design PGA
Class
Acceleration
Acceleration
Coefficients
Response
at 0.2 sec. (g)
at 1.o sec. (g)
Parameters
Fa
F„
SDS
SDl
D
1.315
0.466
1.0
Null
0.876
Null
0.564
Additional seismic considerations include liquefaction potential and amplification of ground
motions by soft/loose soil deposits. The liquefaction potential is highest for loose sand with a
high groundwater table. The site has a low likelihood of liquefaction. For items listed as "Null"
see Section 11.4.8 of the ASCE.
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Updated October 14, 2024
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Geotechnical Evaluation
Conclusions and Recommendations
General
The site is underlain by relatively dense glacial till, which becomes denser with depth. The
proposed deck may be supported on isolated or strip footings bearing on medium dense native
soils or on properly compacted structural fill placed on the suitable native soils. If any foundation
elements will be located within a 1H:1V envelope from the toe of the rockery cuts, they should be
supported on small diameter driven pipe piles extending to refusal. This will limit any effect of
surcharges onto the rockery or backfill. The proposed deck will not increase or decrease the risk
of soil movements or erosion in this area or on adjacent properties.
Site Preparation
Trees, shrubs and other vegetation should be removed prior to stripping of surficial organic -rich
soil and fill. Based on observations from the site investigation program, it is anticipated that the
stripping depth will be 6 to 18 inches. Deeper excavations will be necessary below former
foundation areas in any areas underlain by undocumented fill.
The native soils consist of silty -sand with gravel. Some of the native soils may be used as
structural fill provided they achieve compaction requirements and are within 3 percent of the
optimum moisture. Some of these soils may only be suitable for use as fill during the summer
months, as they will be above the optimum moisture levels in their current state. These soils are
highly moisture sensitive and may degrade during periods of wet weather and under equipment
traffic. We anticipate that unless work occurs during the summer, imported fill will be required.
Imported structural fill should consist of a sand and gravel mixture with a maximum grain size of
3 inches and less than 5 percent fines (material passing the U.S. Standard No. 200 Sieve).
Structural fill should be placed in maximum lift thicknesses of 12 inches and should be compacted
to a minimum of 95 percent of the modified proctor maximum dry density, as determined by the
ASTM D 1557 test method.
Temporary Excavations
Based on our understanding of the project, we anticipate that the grading could include local cuts
on the order of approximately 3 feet or less for foundation placement. Temporary excavations
should be sloped no steeper than 1.5H:1V (Horizontal:Vertical) in loose native soils and fill and
1H:1V in medium dense native soils. If an excavation is subject to heavy vibration or surcharge
loads, we recommend that the excavations be sloped no steeper than 2H:1V, where room permits.
Temporary cuts should be in accordance with the Washington Administrative Code (WAC) Part
N, Excavation, Trenching, and Shoring. Temporary slopes should be visually inspected daily by a
qualified person during construction activities and the inspections should be documented in daily
reports. The contractor is responsible for maintaining the stability of the temporary cut slopes
and reducing slope erosion during construction.
Temporary cut slopes should be covered with visqueen to help reduce erosion during wet weather,
and the slopes should be closely monitored until the permanent retaining systems or slope
configurations are complete. Materials should not be stored or equipment operated within 10 feet
of the top of any temporary cut slope.
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Geotechnical Evaluation
Soil conditions may not be completely known from the geotechnical investigation. In the case of
temporary cuts, the existing soil conditions may not be completely revealed until the excavation
work exposes the soil. Typically, as excavation work progresses the maximum inclination of
temporary slopes will need to be re-evaluated by the geotechnical engineer so that supplemental
recommendations can be made. Soil and groundwater conditions can be highly variable.
Scheduling for soil work will need to be adjustable, to deal with unanticipated conditions, so that
the project can proceed and required deadlines can be met.
If any variations or undesirable conditions are encountered during construction, we should be
notified so that supplemental recommendations can be made. If room constraints or
groundwater conditions do not permit temporary slopes to be cut to the maximum angles allowed
by the WAC, temporary shoring systems may be required. The contractor should be responsible
for developing temporary shoring systems, if needed. We recommend that Cobalt Geosciences
and the project structural engineer review temporary shoring designs prior to installation, to
verify the suitability of the proposed systems.
Foundation Design
Shallow Isolated Footings
The proposed deck may be supported on shallow spread footing foundation systems bearing on
undisturbed medium dense or firmer native soils or on properly compacted structural fill placed
on the suitable native soils. If structural fill is used to support foundations, then the zone of
structural fill should extend beyond the faces of the footing a lateral distance at least equal to the
thickness of the structural fill. Any undocumented fill should be removed and replaced with
structural fill below foundation elements.
These recommendations apply to footings outside of a 1H:1V from the back base of the cut for the
nearby rockery walls. Any footings within that zone must be supported on pin piles.
For shallow foundation support, we recommend widths of at least 18 and 24 inches, respectively,
for continuous wall and isolated column footings supporting the proposed structure. Provided
that the footings are supported as recommended above, a net allowable bearing pressure of 1,500
pounds per square foot (psf) may be used for design.
A 1/3 increase in the above value may be used for short duration loads, such as those imposed by
wind and seismic events. Structural fill placed on bearing, native subgrade should be compacted
to at least 95 percent of the maximum dry density based on ASTM Test Method D1557. Footing
excavations should be inspected to verify that the foundations will bear on suitable material.
Exterior footings should have a minimum depth of 18 inches below pad subgrade (soil grade) or
adjacent exterior grade, whichever is lower.
If constructed as recommended, the total foundation settlement is not expected to exceed 1 inch.
Differential settlement, along a 25-foot exterior wall footing, or between adjoining column
footings, should be less than 1/2 inch. This translates to an angular distortion of 0.002. Most
settlement is expected to occur during construction, as the loads are applied. However, additional
post -construction settlement may occur if the foundation soils are flooded or saturated. All
footing excavations should be observed by a qualified geotechnical consultant.
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Geotechnical Evaluation
Resistance to lateral footing displacement can be determined using an allowable friction factor of
0.35 acting between the base of foundations and the supporting subgrades. Lateral resistance for
footings can also be developed using an allowable equivalent fluid passive pressure of 250 pounds
per cubic foot (pcf) acting against the appropriate vertical footing faces (neglect the upper 12
inches below grade in exterior areas).
The allowable friction factor and allowable equivalent fluid passive pressure values include a
factor of safety of 1.5. The frictional and passive resistance of the soil may be combined without
reduction in determining the total lateral resistance. A 1/3 increase in the above values may be
used for short duration transient loads.
Care should be taken to prevent wetting or drying of the bearing materials during construction.
Any extremely wet or dry materials, or any loose or disturbed materials at the bottom of the
footing excavations, should be removed prior to placing concrete. The potential for wetting or
drying of the bearing materials can be reduced by pouring concrete as soon as possible after
completing the footing excavation and evaluating the bearing surface by the geotechnical engineer
or his representative.
Pin Pile Option
For footings within 1H:1V of the nearby rockery, isolated footings for the new deck should be
supported on small diameter driven pipe piles. We anticipate pile depths of 5 to io feet.
Piles may consist of 2 inch diameter Schedule 8o galvanized pipes with mechanical couplers.
Refusal criteria is at least 3 cycles of 6o seconds per inch of penetration using an 8o to 140 pound
pneumatic hammer. Piles may be designed with an axial capacity of 3 tons each. Battered piles
may be used to increase lateral support at a maximum 1H:5V batter.
Lateral resistance for footings can also be developed using an allowable equivalent fluid passive
pressure of 250 pounds per cubic foot (pcf) acting against the appropriate vertical footing faces
(neglect the upper 12 inches below grade in exterior areas).
Exterior footings should have a minimum depth of 18 inches below pad subgrade (soil grade) or
adjacent exterior grade, whichever is lower.
If constructed as recommended, the total foundation settlement is not expected to exceed 1 inch.
Differential settlement, along a 25-foot exterior wall footing, or between adjoining column
footings, should be less than 1/2 inch. This translates to an angular distortion of 0.002. Most
settlement is expected to occur during construction, as the loads are applied. However, additional
post -construction settlement may occur if the foundation soils are flooded or saturated. All
footing excavations should be observed by a qualified geotechnical consultant.
Erosion and Sediment Control
Erosion and sediment control (ESC) is used to reduce the transportation of eroded sediment to
wetlands, streams, lakes, drainage systems, and adjacent properties. Erosion and sediment
control measures should be implemented, and these measures should be in general accordance
with local regulations. At a minimum, the following basic recommendations should be
incorporated into the design of the erosion and sediment control features for the site:
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Geotechnical Evaluation
• Schedule the soil, foundation, utility, and other work requiring excavation or the disturbance
of the site soils, to take place during the dry season (generally May through September).
However, provided precautions are taken using Best Management Practices (BMP's), grading
activities can be completed during the wet season (generally October through April).
• All site work should be completed and stabilized as quickly as possible.
• Additional perimeter erosion and sediment control features may be required to reduce the
possibility of sediment entering the surface water. This may include additional silt fences, silt
fences with a higher Apparent Opening Size (AOS), construction of a berm, or other filtration
systems.
• Any runoff generated by dewatering discharge should be treated through construction of a
sediment trap if there is sufficient space. If space is limited other filtration methods will need
to be incorporated.
CONSTRUCTION FIELD REVIEWS
Cobalt Geosciences should be retained to provide part time field review during construction in
order to verify that the soil conditions encountered are consistent with our design assumptions
and that the intent of our recommendations is being met. This will require field and engineering
review to:
■ Verify pile depths and refusal criteria
■ Verify soil bearing
Geotechnical design services should also be anticipated during the subsequent final design phase
to support the structural design and address specific issues arising during this phase. Field and
engineering review services will also be required during the construction phase in order to
provide a Final Letter for the project.
CLOSURE
This report was prepared for the exclusive use of Teri and Reed Johnson and their appointed
consultants. Any use of this report or the material contained herein by third parties, or for other
than the intended purpose, should first be approved in writing by Cobalt Geosciences, LLC.
The recommendations contained in this report are based on assumed continuity of soils with
those of our test holes and assumed structural loads. Cobalt Geosciences should be provided with
final architectural and civil drawings when they become available in order that we may review our
design recommendations and advise of any revisions, if necessary.
Use of this report is subject to the Statement of General Conditions provided in Appendix A. It is
the responsibility of Teri and Reed Johnson who is identified as "the Client" within the Statement
of General Conditions, and its agents to review the conditions and to notify Cobalt Geosciences
should any of these not be satisfied.
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September 30, 2024
Updated October 14, 2024
Page to of it
Geotechnical Evaluation
Sincerely,
Cobalt Geosciences, LLC
WA
7
541396 �� Q�231 eo`0�,`y/
IONAL� t FriILLJP HABERMAN
10/14/2024
Phil Haberman, PE, LG, LEG
Principal
www.cobaltgeo.com (2o6) 331-1097
September 30, 2024
Updated October 14, 2024
Page n of n
Geotechnical Evaluation
Statement of General Conditions
USE OF THIS REPORT: This report has been prepared for the sole benefit of the Client or its
agent and may not be used by any third party without the express written consent of Cobalt
Geosciences and the Client. Any use which a third party makes of this report is the responsibility
of such third parry.
BASIS OF THE REPORT: The information, opinions, and/or recommendations made in this
report are in accordance with Cobalt Geosciences present understanding of the site specific
project as described by the Client. The applicability of these is restricted to the site conditions
encountered at the time of the investigation or study. If the proposed site specific project differs
or is modified from what is described in this report or if the site conditions are altered, this report
is no longer valid unless Cobalt Geosciences is requested by the Client to review and revise the
report to reflect the differing or modified project specifics and/or the altered site conditions.
STANDARD OF CARE: Preparation of this report, and all associated work, was carried out in
accordance with the normally accepted standard of care in the state of execution for the specific
professional service provided to the Client. No other warranty is made.
INTERPRETATION OF SITE CONDITIONS: Soil, rock, or other material descriptions, and
statements regarding their condition, made in this report are based on site conditions
encountered by Cobalt Geosciences at the time of the work and at the specific testing and/or
sampling locations. Classifications and statements of condition have been made in accordance
with normally accepted practices which are judgmental in nature; no specific description should
be considered exact, but rather reflective of the anticipated material behavior. Extrapolation of in
situ conditions can only be made to some limited extent beyond the sampling or test points. The
extent depends on variability of the soil, rock and groundwater conditions as influenced by
geological processes, construction activity, and site use.
VARYING OR UNEXPECTED CONDITIONS: Should any site or subsurface conditions be
encountered that are different from those described in this report or encountered at the test
locations, Cobalt Geosciences must be notified immediately to assess if the varying or unexpected
conditions are substantial and if reassessments of the report conclusions or recommendations are
required. Cobalt Geosciences will not be responsible to any parry for damages incurred as a result
of failing to notify Cobalt Geosciences that differing site or sub -surface conditions are present
upon becoming aware of such conditions.
PLANNING, DESIGN, OR CONSTRUCTION: Development or design plans and
specifications should be reviewed by Cobalt Geosciences, sufficiently ahead of initiating the next
project stage (property acquisition, tender, construction, etc), to confirm that this report
completely addresses the elaborated project specifics and that the contents of this report have
been properly interpreted. Specialty quality assurance services (field observations and testing)
during construction are a necessary part of the evaluation of sub -subsurface conditions and site
preparation works. Site work relating to the recommendations included in this report should only
be carried out in the presence of a qualified geotechnical engineer; Cobalt Geosciences cannot be
responsible for site work carried out without being present.
www.cobaltgeo.com (2o6) 331-1097
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Approximate Hand Boring Location
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Cobalt Geosciences, LLC
Proposed Deck
SITE
P.O. Box
Kenmore,, WA WA 98028
-COBALT
7122 Talbot Road
MAP
(2o6) 331-1097
www.cobaltgeo.com
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E 0 S C I E N C E S
Edmonds, Washington
FIGURE i
cobaltgeo(&gmail.com
Unified Soil Classification System (USCS)
MAJOR DIVISIONS
SYMBOL
TYPICAL DESCRIPTION
Clean Gravels
Gw
Well -graded gravels, gravels, gravel -sand mixtures, little or no fines
Gravels
(more than 50%
(less than 5%
fines)
GP
Poorly graded gravels, gravel -sand mixtures, little or no fines
COARSE
GRAINED
SOILS
of coarse fraction
retained on No. 4
sieve)
Gravels with
Fines
(more than 12%
fines)
GM
Silty gravels, gravel -sand -silt mixtures
GC
Clayey gravels, gravel -sand -clay mixtures
(more than 50%
retained on
Clean Sands
:•: sw
Well -graded sands, gravelly sands, little or no fines
No. 200 sieve)
Sands
(50% or more
of coarse fraction
(less than 5%
fines)
sP
Poorly graded sand, gravelly sands, little or no fines
passes the No. 4
sieve)
Sands with
Fines
sM
Silty sands, sand -silt mixtures
(more than 12%
fines)
sc
Clayey sands, sand -clay mixtures
ML
Inorganic silts of low to medium plasticity, sandy silts, gravelly silts,
FINE GRAINED
(50% or more
Silts and Clays
(liquid limit less
than 50)
Inorganic
cL
or clayey silts with slight plasticity
Inorganic clays of low to medium plasticity, gravelly clays, sandy clays
silty clays, lean clays
Organic rganic
oL
Organic silts and organic silty clays of low plasticity
passes the
MH
Inorganic silts, micaceous or diatomaceous fine sands or silty soils,
No. 200 sieve)
Silts and Clays
(liquid limit 50 or
more)
Inorganic
elastic silt
CH
Inorganic clays of medium to high plasticity, sandy fat clay,
or gravelly fat clay
Organic
OHOrganic
clays of medium to high plasticity, organic silts
HIGHLY ORGANIC
SOILS
Primarily organic matter, dark in color,
and organic odor
PT
Peat, humus, swamp soils with high organic content (ASTM D4427)
Classification of Soil Constituents
MAJOR constituents compose more than 50 percent,
by weight, of the soil. Major constituents are capitalized
(i.e., SAND).
Minor constituents compose 12 to 50 percent of the soil
and precede the major constituents (i.e., silty SAND).
Minor constituents preceded by "slightly" compose
5 to 12 percent of the soil (i.e., slightly silty SAND).
Trace constituents compose o to 5 percent of the soil
(i.e., slightly silty SAND, trace gravel).
Relative Density
(Coarse Grained Soils)
Consistency
(Fine Grained Soils)
N, SPT,
Relative
N, SPT,
Relative
Blows/FT
Density
Blows/FT
Consistency
0-4
Very loose
Under 2
Very soft
4 -10
Loose
2-4
Soft
10 - 30
Medium dense
4-8
Medium stiff
30 - 50
Dense
8 -15
Stiff
Over 50
Very dense
15 - 30
Very stiff
Over 3o
Hard
Grain Size Definitions
Description
Sieve Number and/or Size
Fines
<#200 (o.o8 mm)
Sand
-Fine
#200 to #40 (o.o8 to 0.4 mm)
-Medium
#40 to #10 (0.4 to 2 mm)
-Coarse
#10 to #4 (2 to 5 mm)
Gravel
-Fine
#4 to 3/4 inch (5 to 19 mm)
-Coarse
3/4 to 3 inches (19 to 76 mm)
Cobbles
3 to 12 inches (75 to 305 mm)
Boulders
>12 inches (305 mm)
1 Moisture Content Definitions 1
Dry Absence of moisture, dusty, dry to the touch
Moist Damp but no visible water
Wet Visible free water, from below water table
Cobalt Geosciences, LLC
P.O. Box 82243
Kenmore, WA 98028
Soil Classification Chart
Figure Ci
(2o6) 331-1097
_
www.cobaltgeo.com
cobaltgeo(&gmail.com
Log of Hand Boring
HB-1
Date: September 2024
Depth: 6'
Initial Groundwater: None
Contractor:
Elevation: N/A
Sample Type: Grab
Method: Hand Auger
Logged By: PH Checked By: SC
Final Groundwater: N/A
o
o
Moisture Content (%)
Plastic Liquid
�
t
_ >
O
U
�, 0
-
-
o
U
t
Q
>_
L
O
Material Description
Limit Limit
SPT N-Value
o
E 9
m
0
"n
?
o
G
0 10 20 30 40 50
---
-
----
--
---
SM
Vegetation/Topsoil
--------------------------------------------
Loose to medium dense, silty -fine to medium grained sand
with gravel and cobbles, dark yellowish brown to yellowish brown,
moist. (Weathered Glacial Till)
—2
--3
-
----
---
--
SM
---------------------------------------------
Medium dense to dense, silty -fine to medium grained sand,
mottled yellowish brown to grayish brown, moist. (Glacial Till)
—4
—5
-fit:
End of Hand Boring 6'
—7
—8
—9
— 10
Proposed Deck
17122 Talbot Road
Edmonds, Washington
Exploration
Logs
Cobalt Geosciences, LLC
P.O. Box 82243
Kenmore, WA 98028
(2o6) 331-1097
www.cobaltgeo.com
cobaltgeopgmail.com