DNS BLD2021-0811+Geotechnical_Report+7.23.2021_8.59.55_AM+2317878COBALT
G E 0 S C I E N C E S
Geotechnical Investigation
Proposed Four Lot Plat
Parcel No. 00452000400800
Edmonds, Washington
September 24, 2018
GEOTECHNICAL INVESTIGATION
TUKWILA, WASHINGTON
Table of Contents
i.o INTRODUCTION............................................................................................................. 1
2.0 PROJECT DESCRIPTION.............................................................................................. 1
3.0 SITE DESCRIPTION....................................................................................................... 1
4.o FIELD INVESTIGATION............................................................................................... 2
4.1.1 Site Investigation Program...................................................................................
2
5.0 SOIL AND GROUNDWATER CONDITIONS
.............................................................. 2
5.1.1 Area Geology........................................................................................................
2
5.1.2 Groundwater........................................................................................................
3
6.o GEOLOGIC HAZARDS................................................................................................... 3
6.1 Steep Slope Hazard..............................................................................................
3
6.2 Erosion Hazard....................................................................................................
3
6.3 Seismic Hazard....................................................................................................
4
7.o DISCUSSION................................................................................................................... 4
7.1.1 General.................................................................................................................4
8.o RECOMMENDATIONS.................................................................................................. 5
8.1.1 Site Preparation...................................................................................................
5
8.1.2 Temporary Excavations........................................................................................
5
8.1.3 Erosion and Sediment Control..............................................................................
6
8.1.4 Foundation Design...............................................................................................
6
8.1.5 Reinforced Concrete Retaining Walls...................................................................
7
8.1.6 Stormwater Management.....................................................................................
9
8.1.7 Slab-on-Grade......................................................................................................9
8.1.8 Groundwater Influence on Construction
.............................................................10
8.1.9 Utilities...............................................................................................................10
9.o CONSTRUCTION FIELD REVIEWS...........................................................................10
io.o CLOSURE...................................................................................................................11
LIST OF APPENDICES
Appendix A — Statement of General Conditions
Appendix B — Figures
Appendix C — Test Pit Logs
GEOTECHNICAL INVESTIGATION
EDMONDS, WASHINGTON
September 24, 2018
i.o Introduction
COBALT
GEOSCIENCES
In accordance with your authorization, Cobalt Geosciences, LLC (Cobalt) has completed a geotechnical
investigation for the proposed four lot plat located at 7901 - 240th Street SW in Edmonds, Washington
(Figure 1).
The purpose of the geotechnical investigation was to identify subsurface conditions and to provide
geotechnical recommendations for foundation design, stormwater management, earthwork, soil
compaction, and suitability of the on -site soils for use as fill.
The scope of work for the geotechnical evaluation consisted of a site investigation followed by engineering
analyses to prepare this report. Recommendations presented herein pertain to various geotechnical
aspects of the proposed development, including foundation support of the new buildings.
2.0 Project Description
The project includes subdivision of the parcel into four new lots followed by construction of four new
residences and an access roadway. The provided site plans indicate that the roadway will extend north
along the western portion of the property and the residences will be situated generally to fit a relatively
steep slope in the central portion of the property.
Anticipated building loads are expected to be light and site grading will include cuts and fills on the order
of 10 feet or less. Stormwater management may include infiltration devices (if feasible), detention, rain
gardens, and/or detention systems. We should be provided with the plans to verify that our
recommendations are valid.
3.0 Site Description
The site is located at 7901 — 240th Street SW in Edmonds, Washington (Figure 1). The property consists
of one rectangular shaped parcel (No. 00452000400800) with a total area of about o.9 acres.
Based on a review of historic aerial photographs, the property has previously been developed with
residential structures from at least 1958 up to the early to mid-196os.
Currently, the property is undeveloped and vegetated with grasses, ivy, blackberry vines, along with
variable diameter deciduous and evergreen trees.
The site slopes from west to east at variable magnitudes. There is a steep slope within the central portion
of the property that extends north to south and slopes to the east. The slope is generally 8 to 16 feet in
height and has magnitudes of 30 to ioo percent. The western and eastern portions of the property are
gently sloping to nearly level and the western portion appears to have been graded as an access roadway
at one time.
The site is bordered to the north, west, and east by residential developments and to the south by 240th
Street SW.
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4. o Field Investigation
4.1.1 Site Investigation Program
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The geotechnical field investigation program was completed on August 30, 2018 and included excavating
and sampling five test pits within the property for subsurface analysis. Site access was somewhat limited
due to heavy vegetation.
The soils encountered were logged in the field and are described in accordance with the Unified Soil
Classification System (USCS).
A Cobalt Geosciences field representative conducted the explorations, collected disturbed soil samples,
classified the encountered soils, kept a detailed log of the explorations, and observed and recorded
pertinent site features.
The results of the explorations are presented on the logs enclosed in Appendix C.
5.o Soil and Groundwater Conditions
5.1.1 Area Geology
The site lies within the Puget Lowland. The lowland is part of a regional north -south trending trough that
extends from southwestern British Columbia to near Eugene, Oregon. North of Olympia, Washington,
this lowland is glacially carved, with a depositional and erosional history including at least four separate
glacial advances/retreats. The Puget Lowland is bounded to the west by the Olympic Mountains and to
the east by the Cascade Range. The lowland is filled with glacial and non -glacial sediments consisting of
interbedded gravel, sand, silt, till, and peat lenses.
The Geologic Map of the Edmonds East and West Quadrangle indicates that the site is underlain by
Vashon Glacial Till.
Vashon Glacial Till is typically characterized by an unsorted, non -stratified mixture of clay, silt, sand,
gravel, cobbles and boulders in variable quantities. These materials are typically dense and relatively
impermeable. The poor sorting reflects the mixing of the materials as these sediments were overridden
and incorporated by the glacial ice.
Subsurface Explorations
In general, all of the test pits encountered variable thicknesses of topsoil and vegetation underlain by up
to 8 feet of loose to dense fill. The fill appears to be thickest along the upper bench in the western portion
of the property extending over and into the steep slope in the central portion of the property. The fill was
underlain by weathered and/or unweathered glacial till which consists of medium dense to very dense,
silty -fine to medium grained sand with gravel.
It appears that the site was graded on one or more occasions during previous site development activities.
The depth and extent of the fill could not be fully determined through test pit excavations due to access
limitations.
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5.1.2 Groundwater
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Groundwater was not encountered in any of the test pits. We anticipate that perched groundwater will be
present at the site within 10 feet below existing grades during the winter and early spring months.
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.
6.o Geologic Hazards
6.1 Steep Slope Hazard
The site and adjacent areas contain local steep slope/landslide hazard areas and associated buffer zones.
Within the property, there are slope areas with magnitudes between 3o and too percent and relief of 8 to
16 feet. The steep slope areas appear to have been created through previous grading activities. They
appear mostly unnatural in topography and could be comprised of both fill and native glacial till at depth.
The site and adjacent areas appear stable at this time. The underlying soils are generally medium dense
to very dense and are relatively resistant to global instability. The steep slope locally meets the criteria
described in the Edmonds Municipal Code section 23.80.020 under heading B (item number four). This
criteria describes slopes with magnitudes of 4o percent and relief of 10 feet or more, even if created
through prior grading. The site does not include the other aspects of this code section.
It is our opinion that the relatively steep slope area is stable at this time and slope stability analyses are
not warranted. The proposed construction will result in modification of the slope area, resulting in
greater stability than what currently exists.
The project will not decrease slope stability or pose an unreasonable threat to persons or property on the
site or adjacent areas provided the earthwork and grading activities are periodically monitored by the
geotechnical engineer and performed according to the plans and this report.
6.2 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 15 percent slopes). In general, these soils have a slight
to moderate erosion potential in a disturbed state.
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 31st to April 1st. Erosion control measures should be in place before
the onset of wet weather.
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6.3 Seismic Hazard
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The overall subsurface profile corresponds to a Site Class D as defined by Table 1613.5.2 of the 2015
International Building Code (2015 IBC). A Site Class D applies to an overall profile consisting of dense to
very dense soils within the upper ioo feet.
We referenced the U.S. Geological Survey (USGS) Earthquake Hazards Program Website to obtain values
for Ss, Si, Fa, and F,,. The USGS website includes the most updated published data on seismic conditions.
The site specific seismic design parameters and adjusted maximum spectral response acceleration
parameters are as follows:
PGA (Peak Ground Acceleration, in percent of g)
Ss
126.io% of g
Sl
49.20% of g
Fa
1.00
Fv
1.5o8
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 relatively dense and very fined grained soil deposits that underlie the site have a low liquefaction
potential.
7.o DISCUSSION
7.1.1 General
The site is underlain by undocumented fill and at depth by glacial till. The proposed residential structures
may be supported on shallow foundation systems bearing on medium dense or firmer native soils and
structural fill placed on suitable native soils. Footings should not bear on undocumented fill. Any fill
should be removed fully from below new foundation elements.
Infiltration of stormwater runoff is not feasible at this site. The shallow soil conditions and high
likelihood of shallow seasonal groundwater limit suitability of infiltration devices. We anticipate that
detention systems and possibly dispersion systems, if space allows, will be suitable for stormwater
management at the site.
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8.o Recommendations
8.1.1 Site Preparation
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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 24 inches. Deeper excavations will be necessary below large trees and in areas underlain by
undocumented fill materials.
The fill and native soils consist of silty -sand with gravel. These soils may be used as structural fill
provided they achieve compaction requirements and are within 3 percent of the optimum moisture.
Please note that these soils are highly moisture sensitive. These soils are typically only 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 variably moisture sensitive and may degrade during periods of wet weather and under
equipment traffic. If existing fill is re -used as fill, debris and any organic material should be removed
prior to use.
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.
8.1.2 Temporary Excavations
Based on our understanding of the project, we anticipate that the grading could include local cuts on the
order of approximately io feet or less for basement foundation and utility placement. Excavations should
be sloped no steeper than 1H:iV (Horizontal:Vertical) in medium dense or firmer fill and native soils. If
an excavation is subject to heavy vibration or surcharge loads, we recommend that the excavations be
sloped no steeper than i.5H:iV, 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 to feet of the top of any
temporary cut slope.
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
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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.
8.1.3 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:
• 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.
8.1.4 Foundation Design
The proposed single-family residences 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.
It should be noted that the upper (west) portions of the site are likely underlain by variable thicknesses of
fill and overexcavations of 6 feet or more may be required in foundation areas. All footing excavations
should be periodically monitored by the geotechnical engineer to verify suitable bearing on native soils is
achieved. Backfill and compaction of replaced structural fill should also be monitored and verified on a
periodic to full-time basis.
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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 2,000 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. Interior footings should have a minimum depth of 12 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 i 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.
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.
8.1.5 Reinforced Concrete Retaining Walls
The following table, titled Wall Design Criteria, presents the recommended soil related design
parameters for retaining walls with a level backslope. Contact Cobalt if an alternate retaining wall system
is used.
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Wall Design Criteria
"At -rest" Conditions (Lateral Earth Pressure — EFD+)
55 pcf (Equivalent Fluid Density)
"Active" Conditions (Lateral Earth Pressure — EFD+)
35 pcf (Equivalent Fluid Density)
Seismic Increase for "At -rest" Conditions
(Lateral Earth Pressure)
21H* (Uniform Distribution)
Seismic Increase for "Active" Conditions
(Lateral Earth Pressure)
7H* (Uniform Distribution)
Passive Earth Pressure on Low Side of Wall
(Allowable, includes F.S. =1.5)
Level Ground; Neglect upper 2 feet, then 250 pcf EFD+
Soil -Footing Coefficient of Sliding Friction (Allowable;
includes F.S. = 1.5)
0.35
*H is the height of the wall; Increase based on one in 2,500 year seismic event (2 percent probability of being exceeded in 50 years),
EFD — Equivalent Fluid Density
The stated lateral earth pressures do not include the effects of hydrostatic pressure generated by water
accumulation behind the retaining walls. Uniform horizontal lateral active and at -rest pressures on the
retaining walls from vertical surcharges behind the wall may be calculated using active and at -rest lateral
earth pressure coefficients of 0.3 and 0.5, respectively. The soil unit weight of 125 pcf may be used to
calculate vertical earth surcharges.
To reduce the potential for the buildup of water pressure against the walls, continuous footing drains
(with cleanouts) should be provided at the bases of the walls. The footing drains should consist of a
minimum 4-inch diameter perforated pipe, sloped to drain, with perforations placed down and enveloped
by a minimum 6 inches of pea gravel in all directions.
The backfill adjacent to and extending a lateral distance behind the walls at least 2 feet should consist of
free -draining granular material. All free draining backfill should contain less than 3 percent fines
(passing the U.S. Standard No. 200 Sieve) based upon the fraction passing the U.S. Standard No. 4 Sieve
with at least 30 percent of the material being retained on the U.S. Standard No. 4 Sieve. The primary
purpose of the free -draining material is the reduction of hydrostatic pressure. Some potential for the
moisture to contact the back face of the wall may exist, even with treatment, which may require that more
extensive waterproofing be specified for walls, which require interior moisture sensitive finishes.
We recommend that the backfill be compacted to at least go percent of the maximum dry density based
on ASTM Test Method D1557. In place density tests should be performed to verify adequate compaction.
Soil compactors place transient surcharges on the backfill. Consequently, only light hand operated
equipment is recommended within 3 feet of walls so that excessive stress is not imposed on the walls.
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8.1.6 Stormwater Management
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The site is underlain by relatively fine-grained glacial deposits along with variable thicknesses of fill.
These soils have a very low permeability which decreases with depth. It is likely that there will be shallow
perched groundwater throughout the property that further limits infiltration suitability.
We performed an in -situ infiltration test in TP-2 at a depth of 5 feet below grade. Following testing and
application of correction factors, the infiltration rate was o.11 inches per hour, which is lower than what
the Department of Ecology considers to be feasible. We do not recommend utilizing infiltration systems
at the site.
We recommend utilizing shallow dispersion trenches or a combination of detention, dispersion and
overflow connection to City stormwater infrastructure. We can provide additional information upon
request. We should be provided with the final plans for review.
8-IL-7 Slab -on -Grade
We recommend that the upper 24 inches of the existing fill and/or native soils within slab areas be re -
compacted to at least 95 percent of the modified proctor (ASTM D1557 Test Method). Any loose soils
should be removed to a depth at least 2 feet below slab areas prior to slab -on -grade preparation. The fill
should be evaluated prior to imported fill placement to verify stability.
Often, a vapor barrier is considered below concrete slab areas. However, the usage of a vapor barrier could
result in curling of the concrete slab at joints. Floor covers sensitive to moisture typically requires the
usage of a vapor barrier. A materials or structural engineer should be consulted regarding the detailing of
the vapor barrier below concrete slabs. Exterior slabs typically do not utilize vapor barriers.
The American Concrete Institutes ACI 36oR-o6 Design of Slabs on Grade and ACI 302AR-04 Guide for
Concrete Floor and Slab Construction are recommended references for vapor barrier selection and floor
slab detailing.
Slabs on grade may be designed using a coefficient of subgrade reaction of 18o pounds per cubic inch (pci)
assuming the slab -on -grade base course is underlain by structural fill placed and compacted as outlined in
Section 8.1.
A perimeter drainage system is recommended unless interior slab areas are elevated a minimum of 12
inches above adjacent exterior grades. If installed, a perimeter drainage system should consist of a 4 inch
diameter perforated drain pipe surrounded by a minimum 6 inches of drain rock wrapped in a non -woven
geosynthetic filter fabric to reduce migration of soil particles into the drainage system. The perimeter
drainage system should discharge by gravity flow to a suitable stormwater system.
Exterior grades surrounding buildings should be sloped at a minimum of one percent to facilitate surface
water flow away from the building and preferably with a relatively impermeable surface cover
immediately adjacent to the building.
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8.1.8 Groundwater Influence on Construction
Groundwater was not encountered in the test pits. We anticipate that perched groundwater develops
during the wetter months between layers weathered glacial till and/or fill and underlying dense to very
dense soils. Seasonal groundwater will likely be encountered within 10 feet of the ground surface.
During the winter -spring months, we anticipate that sump excavations and small diameter pumps
systems will adequately de -water short-term excavations, if required. Any system should be designed by
the contractor. We can provide additional recommendations upon request.
8.1.9 Utilities
Utility trenches should be excavated according to accepted engineering practices following OSHA
(Occupational Safety and Health Administration) standards, by a contractor experienced in such work.
The contractor is responsible for the safety of open trenches. Traffic and vibration adjacent to trench
walls should be reduced; cyclic wetting and drying of excavation side slopes should be avoided.
Depending upon the location and depth of some utility trenches, groundwater flow into open excavations
could be experienced, especially during or shortly following periods of precipitation.
In general, silty and sandy soils were encountered at shallow depths in the explorations at this site. These
soils have variable cohesion and density and will have a tendency to cave or slough in excavations.
Shoring or sloping back trench sidewalls is required within these soils in excavations greater than 4 feet
deep.
All utility trench backfill should consist of imported structural fill or suitable on site soils. Utility trench
backfill placed in or adjacent to buildings and exterior slabs should be compacted to at least 95 percent of
the maximum dry density based on ASTM Test Method D1557. The upper 5 feet of utility trench backfill
placed in pavement areas should be compacted to at least 95 percent of the maximum dry density based
on ASTM Test Method D1557. Below 5 feet, utility trench backfill in pavement areas should be compacted
to at least 90 percent of the maximum dry density based on ASTM Test Method D1557. Pipe bedding
should be in accordance with the pipe manufacturer's recommendations.
The contractor is responsible for removing all water -sensitive soils from the trenches regardless of the
backfill location and compaction requirements. Depending on the depth and location of the proposed
utilities, we anticipate the need to re -compact existing fill soils below the utility structures and pipes. The
contractor should use appropriate equipment and methods to avoid damage to the utilities and/or
structures during fill placement and compaction procedures.
9.o 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:
■ Monitor and test structural fill placement and soil compaction
■ Observe bearing capacity at foundation locations
■ Observe slab -on -grade preparation
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■ Observe excavation stability
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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.
io.o Closure
This report was prepared for the exclusive use of Luke Shamp and his 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 Luke Shamp 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.
Respectfully submitted,
Cobalt Geosciences, LLC
Original signed by:
HONry9
WASH'/y
W
;01 54896 0 <�
I IST
FSS'ONA1.ti��
Exp. 6/26/2020
Phil Haberman, PE, LG, LEG
Principal
PH/sc
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uwD \ 111 WIMAI
Statement of General Conditions
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 parry without the express written consent of Cobalt Geosciences and the
Client. Any use which a third parry 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 party 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.
LIVIWIJAZ 1WIII
Figures: Vicinity Map, Site Plan
10.2
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24oth Street SW MAP Kenmore, 1OA 98028
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APPENDIX C
Test Pit Logs
Test Pit TP-i
USCS Graphic
Topsoil/Vegetation
SM Fill
4'............. X................................ ......
SM \ Weathered Glacial Till?
6' ............... ..................... .........
I
SM Glacial Till
y.
Test Pit TP-2
USCS
Graphic
Topsoil/Vegetation
1' ............................................. ...
SM Fill
2' ............ ............................. ......
SM \ Weathered Glacial Till
3' ............... .................../ ...........
SM Glacial Till i
0-1' Vegetation/Topsoil
1-4' Silty Sand with Gravel (SM)
Loose to medium dense, silty -fine to medium grained sand with
gravel and roots, dark yellowish brown to grayish brown, dry. (Fill)
4-6' Silty Sand with Gravel (SM)
Loose to medium dense, silty -fine to medium grained sand with
gravel, mottled yellowish brown to grayish brown, moist.
(Weathered Glacial Till?)
6-8' Silty Sand with Gravel (SM)
Dense to very dense, silty -fine to medium grained sand with gravel,
grayish brown, moist. (Glacial Till)
End of Test Pit 8'
No Groundwater
No Caving
0-1' Vegetation/Topsoil
1-2' Silty Sand with Gravel (SM)
Loose to medium dense, silty -fine to medium grained sand with
gravel and roots, dark yellowish brown to grayishb brown, dry. (Fill)
2-3' Silty Sand with Gravel (SM)
Loose to medium dense, silty -fine to medium grained sand with
gravel, mottled yellowish brown to grayish brown, dry to moist.
(Weathered Glacial Till)
3-10' Silty Sand with Gravel (SM)
Dense to very dense, silty -fine to medium grained sand with gravel,
grayish brown, moist. (Glacial Till)
End of Test Pit io'
No Groundwater
No Caving
Test Pit TP-3 Graphic
USCS ^� 0-2' Vegetation/Topsoil
Topsoil/Vegetation
2'........................................... ....
SM Weathered Glacial
Till
4................. .......................... .........{
SM Glacial Till '
2-4' Silty Sand with Gravel (SM)
Loose to medium dense, silty -fine to medium grained sand with
gravel, mottled yellowish brown to grayish brown, moist.
(Glacial Till)
4-7' Silty Sand with Gravel (SM)
Dense to very dense, silty -fine to medium grained sand with gravel,
grayish brown, moist. (Glacial Till)
End of Test Pit 7'
No Groundwater
No Caving
Proposed Four Lot Plat
24oth Street SW
Edmonds, Washington
TEST PIT
LOGS
Cobalt Geosciences, LLC
P.O. Box 82243
Kenmore, WA 98028
(2o6) 331-1097
www.cobaltgeo.com
cobaltgeo@gmail.com
Test Pit TP-4
USCS Graphic
Topsoil/Vegetation
SM Fill
6' ............... ..................... .........
SM Glacial Till y
Test Pit TP-5
USCS Graphic
Topsoil/Vegetation
SM Fill
81 ............... ..................... .........
SM Glacial Till i
0-1' Vegetation/Topsoil
1-6' Silty Sand with Gravel (SM)
Loose to medium dense, silty -fine to medium grained sand with
gravel, asphalt, debris, and roots, dark yellowish brown to
grayish brown, dry. (Fill)
6-8' Silty Sand with Gravel (SM)
Dense to very dense, silty -fine to medium grained sand with gravel,
grayish brown, moist. (Glacial Till)
End of Test Pit 8'
No Groundwater
No Caving
0-1' Vegetation/Topsoil
1-8' Silty Sand with Gravel (SM)
Loose to medium dense, silty -fine to medium grained sand with
gravel, debris, and roots, dark yellowish brown to grayishb brown,
dry. (Fill)
8-1o' Silty Sand with Gravel (SM)
Dense to very dense, silty -fine to medium grained sand with gravel,
grayish brown, moist. (Glacial Till)
End of Test Pit io'
No Groundwater
No Caving
Proposed Four Lot Plat
24oth Street SW
Edmonds, Washington
TEST PIT
LOGS
Cobalt Geosciences, LLC
P.O. Box 82243
Kenmore, WA 98028
(2o6) 331-1097
www.cobaltgeo.com
cobaltgeo@gmail.com