BLD2020-0679+Geotechnical_Report+7.1.2020_4.23.02_PMRECEIVED
Oct 27 2020
CITY OF EDMONDS
DEVELOPMENT SERVICES
DEPARTMENT
11.11I IX11ffiI:ftel]
COBALT
0 E 0 S C I E N C E S
Geotechnical Investigation
Proposed Residential Development
18711 88th Avenue West
Edmonds, Washington
March 11, 2020
GEOTECHNICAL INVESTIGATION
EDMONDS, WASHINGTON
Table of Contents
i.o INTRODUCTION.............................................................................................................
1
2.0 PROJECT DESCRIPTION..............................................................................................
1
3.0 SITE DESCRIPTION.......................................................................................................
1
4.o FIELD INVESTIGATION...............................................................................................
1
4.1.1 Site Investigation Program...................................................................................
1
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 Erosion Hazard....................................................................................................
3
6.2 Seismic Hazard....................................................................................................
3
7.o DISCUSSION...................................................................................................................
4
7.1.1 General.................................................................................................................4
8.o RECOMMENDATIONS..................................................................................................
4
8.1.1 Site Preparation...................................................................................................
4
8.1.2 Temporary Excavations........................................................................................
4
8.1.3 Erosion and Sediment Control..............................................................................
5
8.1.4 Foundation Design...............................................................................................
6
8.1.5 Stormwater Management.....................................................................................
7
8.1.6 Slab-on-Grade......................................................................................................
7
8.1.E Groundwater Influence on Construction..............................................................
8
8.1.8 Utilities................................................................................................................
8
9.o CONSTRUCTION FIELD REVIEWS............................................................................ 8
io.o CLOSURE.................................................................................................................... 9
LIST OF APPENDICES
Appendix A — Statement of General Conditions
Appendix B — Figures
Appendix C — Exploration Logs
GEOTECHNICAL INVESTIGATION
EDMONDS, WASHINGTON
March 11, 2020
i.o Introduction
COBALT
GEOSCIENCES
In accordance with your authorization, Cobalt Geosciences, LLC (Cobalt) has completed a geotechnical
investigation for the proposed residential development located at 18711 — 88th Avenue West 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 building and stormwater
management.
2.0 Project Description
The project includes construction of a new single-family residence in the central portion of the property.
The existing driveway will be utilized for access to the new residence.
Anticipated building loads are expected to be light to moderate and site grading will include cuts and fills
on the order of 4 feet or less. Stormwater management will include infiltration devices, if feasible. We
should be provided with the final plans when they become available.
3.0 Site Description
The site is located at 18711 — 88th Avenue West in Edmonds, Washington (Figure 1). The property
consists of one irregularly shaped parcel (No. 004346000001504) with a total area of about 0.38 acres.
The central portion of the property is developed with a residence with garage. The remainder of the
property is undeveloped and vegetated with grasses, bushes, and sparse trees.
The site is nearly level to slightly sloping in multiple directions. There are areas of fill in the northeast and
eastern portions of the property. The fill appears to be less than 3 feet thick in most areas.
The site is bordered on all sides by residential properties. A driveway easement extends onto the property
from the west and 88th Avenue West.
4.o Field Investigation
4.1.1 Site Investigation Program
The geotechnical field investigation program was completed on February 21, 202o and included
excavating and sampling two test pits within the property for subsurface analysis.
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COBALT
GEOSCIENCES
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 sampling are presented on the exploration logs enclosed in Appendix C.
5.0 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 Washington — Northwest Quadrant, 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.
Vashon Glacial Till is usually underlain by Vashon Advance Outwash. These materials consist of poorly
graded sand and are typically permeable. Near the contact between these units, outwash can interfinger
with glacial till and be locally underlain by till.
Explorations
Test Pit TP-1 encountered 6 inches of topsoil and vegetation underlain by approximately 1.5 feet of loose
to medium dense, silty -fine to medium grained sand with gravel (Fill). This layer was underlain by
approximately 3 feet of loose to medium dense, silty -fine to medium grained sand with gravel (Weathered
Glacial Till). These materials were underlain by dense to very dense, silty -fine to medium grained sand
with gravel (Glacial Till), which continued to the termination depth of TP-i.
Test Pit TP-2 encountered 6 inches of topsoil and vegetation underlain by approximately 2 feet of loose to
medium dense, silty -fine to medium grained sand with gravel (Fill). This layer was underlain by medium
dense, fine to medium grained sand trace gravel (Advance Outwash), which continued to the termination
depth of TP-2.
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5.1.2 Groundwater
COBALT
GEOSCIENCES
Groundwater was not encountered in any of the explorations. There is a chance that perched
groundwater may be encountered during late winter and early spring months. We anticipate that
groundwater would be perched between fill or weathered till and underlying unweathered glacial till.
Groundwater will not likely be present within the outwash sands.
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
6a 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 percent slopes). These soils would have a slight to
severe 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 31st to April 1st. Erosion control measures should be in place before
the onset of wet weather.
6.2 Seismic Hazard
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 too feet.
We referenced the U.S. Geological Survey (USGS) Earthquake Hazards Program Website to obtain values
for Ss, Sl, 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 130.00% of g
S, 45.90% of g
Fa 1.00
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 soil deposits that underlie the site have a low liquefaction potential.
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7.o DISCUSSION
7.1.1 General
COBALT
GEOSCIENCES
The site is underlain by weathered and unweathered glacial till and advance outwash. The proposed
residential structure may be supported on a shallow foundation system bearing on medium dense or
firmer native soils and/or structural fill placed on suitable native soils. Local overexcavation of fill and/or
loose soils may be necessary below proposed foundation elements.
Infiltration of stormwater runoff is feasible in some portions of the property. Based on our observations,
the site is at or near the contacts between till and outwash. Infiltration is generally feasible in outwash
sands, which were encountered in the eastern portion of the property, near TP-2.
8. o Recommendations
8.m 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 12 inches. Deeper excavations will be necessary below large trees and in any areas underlain
by undocumented fill materials.
The native soils consist of silty -sand with gravel and poorly graded 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. 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 variably moisture
sensitive and may degrade during periods of wet weather and under equipment traffic.
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 4 feet or less for foundation and utility placement. Any deeper excavations should
be sloped no steeper than 1.5H:1V in loose soils, 1H:1V in medium dense native soils and 3/4H:1V in
dense to very 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.
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GEOSCIENCES
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 io 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
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.
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8.1.4 Foundation Design
COBALT
GEOSCIENCES
The proposed residential building may be supported on a shallow spread footing foundation system
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.
For shallow foundation support, we recommend widths of at least 16 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 2,500 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. 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 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.
Resistance to lateral footing displacement can be determined using an allowable friction factor of 0.40
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 225 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.
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.
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8.1.5 Stormwater Management
COBALT
GEOSCIENCES
The site is underlain by glacial till and advance outwash. At the contact between these units, till and
outwash can be interfingered or layered. In general, infiltration is only feasible in the outwash soils,
which we encountered in the area of TP-2. There may be other areas within the property underlain by
outwash; however, additional exploration work will be required to confirm the locations.
We performed a small-scale pilot infiltration test in TP-2 at a depth of 6 feet below grade. Following
testing and application of correction factors for site variability (0.33), testing (0.4), and influent control
(o.9), the infiltration rate was determined to be 1.8 inches per hour. We recommend utilizing one or more
drywells in the vicinity of TP-2 to manage stormwater runoff. We can provide additional
recommendations once a civil plan has been prepared.
We should be provided with final plans for review to determine if the intent of our recommendations has
been incorporated or if additional modifications are needed.
8.1.6 Slab -on -Grade
We recommend that the upper 12 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).
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. A minimum 4 inch thick capillary break should be placed over the prepared subgrade.
This may consist of pea gravel or 5/8 inch clean angular rock.
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 4 inch thick capillary break material should be placed over the prepared subgrade. This
could include pea gravel or 5/8 inch clean angular rock.
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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GEOTECHNICAL INVESTIGATION GEOSCIENCES
EDMONDS, WASHINGTON
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8.1.7 Groundwater Influence on Construction
Groundwater was not encountered in any of the explorations. There is a chance that light groundwater
could be encountered above the unweathered glacial till, where encountered. The depth to groundwater
would likely be 3 to 8 feet below grade in those areas. In areas where outwash is present, groundwater is
not expected to be encountered.
If groundwater is encountered, 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.
8.1.8 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 soils were encountered at shallow depths in the explorations at this site. These soils have
low 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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■ Verify infiltration system soil conditions
■ Observe excavation stability
COBALT
GEOSCIENCES
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 Mark Echelbarger 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 Mark Echelbarger 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:
WV A
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Exp. 6/26/2020
Phil Haberman, PE, LG, LEG
Principal
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APPENDIX A
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 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 party.
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.
APPENDIX B
Figures: Vicinity Map, Site Plan
10.2
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o s { TN MN l�
NATIONAL MILES
7000 0 ,rot, 2mo a000 two 40 1571s`
L, GEOGRAPHIC t 0 KIIOME ERS FEET
I A
I'M 0 MMM tlRln 02117l1a
r Cobalt Geosciences, LLC
P.O. Box 82243 Proposed Single -Family Residence VICINITY MAP
-� Kenmore, WA 98028 18 11 - $$th Avenue West
(2o6) 331-1097 %
_ www.cobaltgeo.com Edmonds, Washington FIGURE i
cobaltgeo(d_) gmail.com
R70R 87c��
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1
Subject io
Property
1
86�7
TP-i Approximate
Test Pit N
Location A
Not to Scale
Cobalt Geosciences, LLC
Prop
osed d Residence SITE PLAN P.O. Box 82243
p Kenmore, WA 98028
_ COBALT 18711- 88th Avenue West (206) 331-1097
�`— ' S C I E N C E S Edmonds, Washington FIGURE 2 www.cobaltgeo.com
cobaltgeoogmail.com
APPENDIX C
Exploration Logs
Date: February 21, 2020 Depth: 6.5' Groundwater: None
Contractor: Client Provided Elevation: Logged By: PH Checked By: SC
U) o Moisture Content (%)
- Plastic Liquid
U E Limit Limit
} 6
0 N Material Description
o 'E? o DCP Equivalent N-Value
O 0 10 20 30 40 50
------
----
--
Topsoil/Grass
---------------------------------------------
1
•..
SM
Loose to medium dense, silty -fine to medium grained sand with gravel
dark yellowish brown, moist.
:.
(Fill)
-----------------------------------------
SM
Loose to medium dense, silty -fine to medium grained sand with gravel
3
reddish brown to yellowish brown, moist.
(Weathered Glacial Till)
4
---
----
— — —
SM
---------------------------------------------
Dense to very dense, silty -fine to medium grained sand with gravel,
b
grayish brown, moist. (Glacial Till)
7
End of Test Pit 6.5'
8
9
10
Test Pit TP-2
Date: February 21, 2020 Depth: 10' Groundwater: None
Contractor: Client Provided Elevation: Logged By: PH Checked By: SC
0) o Moisture Content (�)
N JO -0 Plastic 1 Liquid
U E Limit Limit
t � L
U N Material Description
o c ? o DCP Equivalent N-Value
C 0 10 20 30 40 50
— — — — — — —
----
��
--
TopsoilGrass------------------------------------
1
SP/
Loose to medium dense, silty -fine to medium grained sand with gravel
SM
yellowish brown to grayish brown. (Fill)
2------------------------------------------------
3
s,-: ti; ;
SP
Medium dense, fine to medium grained sand with gravel trace silt,
grayish brown, moist. (Advance Outwash)
4
5
b
7:
8��
•.ti:
9
End of Test Pit 10'
Cobalt Geosciences, LLC
•G
_
E 0 S C I
E N C E S
Proposed Residence
18711 88th Avenue West
Edmonds, Washington
Test Pit
Logs
P.O. Box 82243
Kenmore, 09 98028
www.cobaltgeo.com
cobaltgeoogmail.com