20190604_Vista Place Geo Report.pdf
Geotechnical Investigation
Proposed Two Lot Subdivision
1736 Vista Place
Edmonds, Washington
May 31, 2019
GEOTECHNICAL INVESTIGATION
EDMONDS, WASHINGTON
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Table of Contents
1.0 INTRODUCTION ............................................................................................................. 1
2.0 PROJECT DESCRIPTION .............................................................................................. 1
3.0 SITE DESCRIPTION ....................................................................................................... 1
4.0 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
6.0 GEOLOGIC HAZARDS ................................................................................................... 3
6.1 Steep Slope Hazard .............................................................................................. 3
6.2 Erosion Hazard .................................................................................................... 6
6.3 Seismic Hazard .................................................................................................... 7
7.0 DISCUSSION ................................................................................................................... 7
7.1.1 General................................................................................................................. 7
8.0 RECOMMENDATIONS .................................................................................................. 8
8.1.1 Site Preparation ................................................................................................... 8
8.1.2 Temporary Excavations ........................................................................................ 8
8.1.3 Erosion and Sediment Control.............................................................................. 9
8.1.4 Foundation Design ............................................................................................... 9
8.1.5 Reinforced Concrete Retaining Walls ..................................................................10
8.1.6 Stormwater Management ....................................................................................12
8.1.7 Slab-on-Grade .....................................................................................................12
8.1.8 Utilities ...............................................................................................................13
8.1.9 Groundwater Influence on Construction .............................................................13
9.0 CONSTRUCTION FIELD REVIEWS ...........................................................................13
10.0 CLOSURE ...................................................................................................................14
LIST OF APPENDICES
Appendix A — Statement of General Conditions
Appendix B — Figures
Appendix C — Exploration Logs
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1.0 Introduction
In accordance with your authorization, Cobalt Geosciences, LLC (Cobalt) has completed a geotechnical
investigation for the proposed two lot subdivision located at 1736 Vist a Place in Edmonds, Washington
(Figure 1).
The purpose of the geotechnical investigation was to identify subsurface conditions and to provide
preliminary geotechnical recommendations for foundation design, retaining walls, earthwork, soil
compaction, and suitability of the on-site soils for use as fill. This report is based on our explorations and
recent borings performed by another consultant.
The scope of work for the geotechnical investigation 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 design , retaining walls, drainage,
and earthwork.
2.0 Project Description
The project includes subdivision of the parcel into two, followed by construction of a new residence in the
western portion of the site. An existing residence will remain in the central portion of the property and
access will be from an existing asphalt paved driveway. We anticipate that the new residence will
incorporate one or more daylight basement levels or larger stepped footings to generally fit the
topography of the new building lot.
We anticipate that structural loads will generally be light and site grading will include cuts and fills on the
order of 10 feet or less for daylight basement construction. We should be provided with the plans once
they become available so that we may update our recommendations, if necessary.
3.0 Site Description
The site is located at 1736 Vista Place in Edmonds, Washington (Figure 1). The property consists of one
rectangular shaped parcel (No. 00548900002201) with a total area of 0.92 acres.
The central portion of the property is developed with a multi-story residence with daylight basement level.
A paved driveway extends onto the property from the east. The driveway extends through the property to
near the southwest corner and along the west property line.
The site contains variable magnitude slopes ranging from nearly level up to about 45 percent west of the
existing residence. Most of the slopes extend downward from east to west although there are local slope s
that extend downward to the south from the existing residence. There are numerous modular block and
rockery walls within the property and near property lines. These walls are generally less than 3.5 feet in
height.
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The steepest slope area is the 30 to 45 percent slope west of the existing residence, which also comprises
much of the Lot 2 area where the residence may be located. This slope has a relief of about 28 feet. The
site is vegetated with grasses, bushes/shrubs, along with sparse trees.
The site is bordered on all sides by residential structures. The driveway extends onto the property from
the east through an easement between properties.
4.0 Field Investigation
4.1.1 Site Investigation Program
The geotechnical field investigation program was completed on May 14, 2019 and included excavating one
test pit within the property for subsurface analysis. There was very limited space to excavate additional
test pits. The purpose of this test pit was to determine suitability for infiltration devices in the easte rn
portion of the property. We have been provided with three boring logs prepared by Zipper Geo. Zipper
Geo drilled the three borings in July 2018. These logs are attached in Appendix C.
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 test pit sampling are presented on the exploration log 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 regi onal 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 Composite Geologic Map of the Edmonds East and West Quadrangle, indicates that the site is located
near the contacts between Vashon Glacial Till and Esperance Sand.
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.
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Esperance Sand generally correlates to Vashon Advance Outwash. These materials consist of sand with
variable amounts of gravel which are generally dense to very dense and relatively permeable. Esperance
Sand often contains more gravel than typical advance outwash.
Test Pit TP-1
The test pit encountered approximately 6 inches of topsoil and grass underlain by approximately 4 feet of
loose to medium dense, silty-fine to medium grained sand with gravel (Fill). This layer was underlain by
approximately 4 feet of loose to medium dense, silty-fine to medium grained sand with gravel (Weathered
Glacial Till. This layer was underlain by dense, silty- fine to medium grained sand with gravel (Glacial
Till) which continued to the termination depth of the test pit.
The Zipper Geo borings encountered areas of fill overlying weathered glacial till and at depth, glacial till.
The soils encountered in their borings are consistent with our test pit and the mapped geologic unit in the
area.
5.1.2 Groundwater
Groundwater was not encountered during our investigation . Based on our observations and review of
nearby explorations, perched groundwater may be present between weathered and unweathered glacial
till. The depth to this contact likely varies between 8 and 15 feet below existing site elevations.
Groundwater was encountered in the Zipper Geo borings between 7 and 22 feet below grade. This
groundwater appears to have been perched between dense and very dense glacial till.
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.
6.0 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 up to 45 percent and relief of about 28 feet.
Based on borings by Zipper Geo, this slope is underlain by areas of fill, weathered glacial till, and at depth
by glacial till.
The site and adjacent areas appear stable at this time. The soils that underlie the fill are generally
medium dense to very dense and are relatively resistant to global instability. The steep slope west of the
residence meets the criteria described in items 4 and 8 (slopes greater than 40 percent and modified by
previous grading) from the Edmonds Municipal Code section 23.80.020 under heading B (items 1
through 8).
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.
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23.80.060 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 site is situated within a moderately steep slope area that was created over a time through natural
erosion and fill placement likely performed during construction of the existing residence. The site is not
situated within an active or historic landslide and the risk of landslide activity is relatively low. There is a
slight chance of sloughing of fill materials; however, the proposed development would remove most of the
fill from the slope area.
The proposed residence 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. The level of risk due to
the proposed development will be the same or lower than what is currently present provided temporary
and permanent runoff is fully controlled. This statement may be amended depending on the results of our
review of grading and foundation plans for the project. Temporary shoring may be required to maintain
stability of temporary excavations required for the foundation system. We must be provided with the
plans prior to confirmation of suitability.
23.80.070 Development standards – Specific hazards.
A. Erosion and Landslide Hazard Areas. Activities on sites containing erosi on or landslide hazards shall
meet the requirements of ECDC 23.80.060, 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;
A minimum effective building setback of 10 feet is required. This could require deeper foundation
embedment in order to create the setback.
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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;
No specific buffer is required from a geotechnical standpoint. We recommend that all site soils be
vegetated or protected from erosion through placement of surface landscaping materials/hardscapes.
3. Alterations. Alterations of an erosion or landslide hazard area, minimum buil ding 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
control, and periodic geotechnical oversight is performed, the development will not decrease slope
stability on adjacent properties, will not increase surface water discharge or 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 m eet 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 landslid e 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 cri tical
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;
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f. The use of retaining walls that allow the maintenance of ex isting natural slope area is preferred over
graded artificial slopes; and
g. Development shall be designed to minimize impervious lot coverage;
We can provide slope stability analyses and discussion of the above code items once we receive a final
grading and foundation plan.
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 upstr eam 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;
b. Discharged at flow durations matching p redeveloped 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.
6.2 Erosion Hazard
The Natural Resources Conservation Services (NRCS) maps for Snohomish County indicate that the
property is underlain by Alderwood gravelly sandy loam (15 to 30 percent slopes). These soils have severe
to very severe erosion potential when exposed on slope magnitudes greater than about 15 percent. These
soils are included in the Edmonds Municipal Code section 23.80.020 under A1. It is our opinion that
typical erosion control measures will be suitable to limit/reduce erosion potential durin g construction.
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
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 100 feet.
We referenced the U.S. Geological Survey (USGS) Earthquake Hazards Program Website to obtain values
for SS, S1, Fa, and Fv. 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 125.80% of g
S1 49.00% of g
FA 1.00
FV 1.51
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 groundwate r table.
The relatively dense glacially consolidated materials that underlie the site have a low potential for
liquefaction.
7.0 DISCUSSION
7.1.1 General
It is our opinion that the proposed residence may be supported on a shallow foundation system bearing
on medium dense or firmer native soils. These soils will likely be encountered below the upper fill
materials which were locally encountered up to 7 feet below existing site elevations in the sloped area of
Lot 2.
The proposed residence should have a minimum effective setback of 10 feet from the slope face m easured
horizontally from the westernmost footing to the adjacent slope face. This will require additional footing
embedment. We should be provided with the grading plans to verify that temporary shoring, such as
gravity walls or soldier pile walls will not be required.
It is our opinion that the proposed development will not increase the potential for soil movement at the
property, and the risk of damage to the proposed development and adjacent properties will be minimal,
provided the work is performed in accordance with approved plans and our recommendations and is
monitored by the geotechnical engineer. A final review must be performed prior to confirmation of
suitability of the final development plan.
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8.0 Recommendations
8.1.1 Site Preparation
Trees, shrubs and other vegetation should be removed prior to stripping of surficial organic -rich soil.
Based on observations from the site investigation program, it is anticipated that the stripping depth will
range from 6 to 18 inches. Deeper excavations should be expected below larger vegetation and where
undocumented fill is present.
The near-surface soils consist of silty-sand with gravel. These soils are suitable for use as structural fill if
they are compacted when the moisture levels are within a few percent of optimum. This is typically only
possible during mid-late summer and early fall when there are extended periods of warm, dry weather.
All fill soils should be compacted when they are within 3 percent of the optimum moisture as determined
by the ASTM D 1557 proctor analysis test.
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 10 feet or less for basement foundation placement. These excavations should be
sloped no steeper than 1.5H:1V (horizontal to vertical) in fill, 1H:1V in medium dense native soils and
3/4H:1V in dense to very dense glacial till. If an excavation is subject to heavy vibration or surcharge
loads, we recommend that the excavations be sloped no steeper than 1.5H :1V, where room permits. The
geotechnical engineer should be on site during excavation work to determine safe temporary slope angles.
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.
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.
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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 complet ed
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 residence 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.
We anticipate that medium dense or firmer soils will be encountered following excavation for the daylight
basement level. Any remaining fill should be removed from within the building pad area. We should be
provided with the final grading and foundation plans to verify footing depth relative to fill and native soil
locations based on the Zipper Geo borings. Footings should bear on medium dense or firmer native soils
and embedded to a depth in order to create a minimum 10 feet effective setback. This is the horizontal
lateral distance between the westernmost footing and face of the nearest slope to the west.
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For shallow foundation support, we recommend widths of at least 18 and 24 inches, respe ctively, for
continuous wall and isolated column footings su pporting the proposed structures. 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 1 inch.
Differential settlement, along a 25-foot exterior wall footing, or between adjoining column footings,
should be less than ½ 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)
12H* (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 500 year seismic event (10 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 t he
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 90 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.
GEOTECHNICAL INVESTIGATION
EDMONDS, WASHINGTON
May 31, 2019
12
PO Box 82243
Kenmore, WA 98028
cobaltgeo@gmail.com
206-331-1097
8.1.6 Stormwater Management
The site is underlain by areas of fill, weathered glacial soils, and at depth by glacial till.
We performed a small-scale pilot infiltration test (PIT) in TP-1 at a depth of 5 feet below grade. Following
application of correction factors, the design infiltration rate was determined to be 0.3 inches per hour.
Any infiltration system should situated within the weathered glacial till and have overflow capability to
stormwater infrastructure.
We should be provided with the final plans to verify location suitability of any new systems.
8.1.7 Slab-on-Grade
We recommend that the upper 12 inches of the native soils within slab areas be re-compacted to at least
95 percent of the modified proctor (ASTM D1557 Test Method). If loose fill soils or deep topsoil/roots are
encountered, they should be removed and replaced with structural fill.
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 de tailing of
the vapor barrier below concrete slabs. Exterior slabs typically do not utilize vapor barriers.
The American Concrete Institutes ACI 360R-06 Design of Slabs on Grade and ACI 302.1R-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 180 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 to 6 inch thick capillary break may be placed over the subgrade. This should consist of
clean angular rock (5/8 inch) or pea gravel.
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 faci litate surface
water flow away from the building and preferably with a relatively impermeable surface cover
immediately adjacent to the building.
8.1.8 Groundwater Influence on Construction
Groundwater was not encountered in the test pit. In general, we do not expect groundwater to be
encountered in excavations at the site. Groundwater was encountered in the Zipper Geo borings at 22 feet
below grade in B-1, 10 feet below grade in B-2, and 7 feet below grade in B-3. These borings were lower in
elevation than our test pit. There is a slight chance that light volumes of perched groundwater could be
encountered between weathered and unweathered glacial till during late winter and spring months . This
would likely be between 8 and 15 feet below grade at our test pit location.
GEOTECHNICAL INVESTIGATION
EDMONDS, WASHINGTON
May 31, 2019
13
PO Box 82243
Kenmore, WA 98028
cobaltgeo@gmail.com
206-331-1097
If groundwater is encountered during construction, 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 ca n 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 suc h 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, sandy and silty soils were encountered at shallow depths in the explorations at this site. These
soils have variable cohesion and density and may 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.
9.0 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
Verify building setbacks
Monitor temporary excavation stability
Verify footing drain installation
Observe soil condition in stormwater facility locations
Observe bearing capacity at footing locations
Geotechnical design services should also be anticipated during the subse quent final design phase to
support the structural design and address specific issues arising during this phase. Field and engineering
GEOTECHNICAL INVESTIGATION
EDMONDS, WASHINGTON
May 31, 2019
14
PO Box 82243
Kenmore, WA 98028
cobaltgeo@gmail.com
206-331-1097
review services will also be required during the construction phase in order to provide a Final Letter for
the project.
10.0 Closure
This report was prepared for the exclusive use of Mark Langford 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 Langford who are 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:
Draft
Phil Haberman, PE, LG, LEG
Principal
PH/sc
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 ext ent 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.
10.2
PO Box 82243
Kenmore, WA 98028
cobaltgeo@gmail.com
206-331-1097
APPENDIX B
Figures: Vicinity Map, Site Plan
SITE
N
Project
Location
Edmonds
WASHINGTON
SITE PLAN
FIGURE 1
Cobalt Geosciences, LLC
P.O. Box 82243
Kenmore, WA 98028
(206) 331-1097
www.cobaltgeo.com
cobaltgeo@gmail.com
Proposed Two Lot Subdivision
1736 Vista Place
Edmonds, Washington
N
Cobalt Geosciences, LLC
P.O. Box 82243
Kenmore, WA 98028
(206) 331-1097
www.cobaltgeo.com
cobaltgeo@gmail.com
SITE PLAN
FIGURE 2
TP-1
Loose Yard Waste & Other Fills
Proposed Two Lot Subdivision
1736 Vista Place
Edmonds, Washington
TP-1
Subject Property
Approximate Location of
Addition
B-1
B-2
B-3
General
Area of
Proposed
Residence
B-1
APPENDIX C
Exploration Logs
PT
Well-graded gravels, gravels, gravel-sand mixtures, little or no fines
Poorly graded gravels, gravel-sand mixtures, little or no fines
Silty gravels, gravel-sand-silt mixtures
Clayey gravels, gravel-sand-clay mixtures
Well-graded sands, gravelly sands, little or no fines
COARSE
GRAINED
SOILS
(more than 50%
retained on
No. 200 sieve)
Primarily organic matter, dark in color,
and organic odor Peat, humus, swamp soils with high organic content (ASTM D4427)HIGHLY ORGANIC
SOILS
FINE GRAINED
SOILS
(50% or more
passes the
No. 200 sieve)
MAJOR DIVISIONS SYMBOL TYPICAL DESCRIPTION
Gravels
(more than 50%
of coarse fraction
retained on No. 4
sieve)
Sands
(50% or more
of coarse fraction
passes the No. 4
sieve)
Silts and Clays
(liquid limit less
than 50)
Silts and Clays
(liquid limit 50 or
more)
Organic
Inorganic
Organic
Inorganic
Sands with
Fines
(more than 12%
fines)
Clean Sands
(less than 5%
fines)
Gravels with
Fines
(more than 12%
fines)
Clean Gravels
(less than 5%
fines)
Unified Soil Classification System (USCS)
Poorly graded sand, gravelly sands, little or no fines
Silty sands, sand-silt mixtures
Clayey sands, sand-clay mixtures
Inorganic silts of low to medium plasticity, sandy silts, gravelly silts,
or clayey silts with slight plasticity
Inorganic clays of low to medium plasticity, gravelly clays, sandy clays,
silty clays, lean clays
Organic silts and organic silty clays of low plasticity
Inorganic silts, micaceous or diatomaceous fine sands or silty soils,
elastic silt
Inorganic clays of medium to high plasticity, sandy fat clay,
or gravelly fat clay
Organic clays of medium to high plasticity, organic silts
Moisture Content Definitions
Grain Size Definitions
Dry Absence of moisture, dusty, dry to the touch
Moist Damp but no visible water
Wet Visible free water, from below water table
Grain Size Definitions
Description Sieve Number and/or Size
Fines <#200 (0.08 mm)
Sand
-Fine
-Medium
-Coarse
Gravel
-Fine
-Coarse
Cobbles
Boulders
#200 to #40 (0.08 to 0.4 mm)
#40 to #10 (0.4 to 2 mm)
#10 to #4 (2 to 5 mm)
#4 to 3/4 inch (5 to 19 mm)
3/4 to 3 inches (19 to 76 mm)
3 to 12 inches (75 to 305 mm)
>12 inches (305 mm)
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 0 to 5 percent of the soil
(i.e., slightly silty SAND, trace gravel).
Relative Density Consistency
(Coarse Grained Soils) (Fine Grained Soils)
N, SPT, Relative
Blows/FT Density
0 - 4 Very loose
4 - 10 Loose
10 - 30 Medium dense
30 - 50 Dense
Over 50 Very dense
N, SPT, Relative
Blows/FT Consistency
Under 2 Very soft
2 - 4 Soft
4 - 8 Medium stiff
8 - 15 Stiff
15 - 30 Very stiff
Over 30 Hard
Cobalt Geosciences, LLC
P.O. Box 82243
Kenmore, WA 98028
(206) 331-1097
www.cobaltgeo.com
cobaltgeo@gmail.com
Soil Classification Chart Figure C1
Test Pit
Logs
Cobalt Geosciences, LLC
P.O. Box 82243
Kenmore, WA 98028
(206) 331-1097
www.cobaltgeo.com
cobaltgeo@gmail.com
Proposed Development
1736 Vista Place
Edmonds, Washington
Test Pit TP-1
Date: May 14, 2019
Contractor: Jim
Depth: 10’
Elevation:Logged By: PH Checked By: SC
Groundwater: None
Material Description
Moisture Content (%)Plastic
Limit
Liquid
Limit
10 20 30 400 50
1
2
3
4
5
6
DCP Equivalent N-Value
7
8
9
10
Loose to medium dense, silty-fine to medium grained sand with gravel,
mottled yellowish brown, moist. (Weathered Glacial Till)
SM
Dense to very dense, silty-fine to medium grained sand with gravel,
grayish brown, moist. (Glacial Till)
SM
End of Test Pit 10’
Topsoil/Grass
SM Loose to medium dense, silty-fine to medium grained sand with
gravel, dark yellowish brown, moist. (Fill)
280
EL
E
V
A
T
I
O
N
I
N
F
E
E
T
DISTANCE IN FEET
40
270
250
260
A A'
240
230
0 10 20 30 50 60 70
EL
E
V
A
T
I
O
N
I
N
F
E
E
T
B-1
(OFFSET 17' S)
B-2
(OFFSET 11' S)
11
73/11"
60
8
TD=16.5'
4
26
22
(OFFSET 27' N)
B-3
TD=30.5'
220
210
280
270
250
260
240
230
220
210
EXISTING POOL
VERY DENSE
GLACIAL TILL
WD
WD
WD
PROB
A
B
L
E
F
I
L
L
3
14
50/6"
16
28
30
TD=21.5'
36
34
65
16
14
50/6"
MEDIUM DENSE
GLACIAL TILL
32
B-1
STANDARD PENETRATION TEST (SPT) BLOWCOUNT
(INTERPOLATED BETWEEN EXPLORATIONS)
APPROXIMATE SOIL UNIT BOUNDARY
EXPLORATION NUMBER
APPROXIMATE GROUND WATER LEVEL WHILE DRILLING
OR DATE NOTED
GENERALIZED CROSS SECTION LEGEND : FIGURE 3
WD
TD=35.5 TOTAL DEPTH OF EXPLORATION IN FEET
(OFFSET 15' W)BORING OFFSET DISTANCE & DIRECTION FROM SECTION LINE
SCALE IN FEET
010 105
FIGURE
Job No.
Zipper Geo Associates, LLC
19019 36th Ave. W.,Suite E
Lynnwood, WA SHT. of 11
GENERALIZED A-A' CROSS SECTION
2034.01JULY 2018
2
LANGFORD RESIDENCE
1136 VISTA PLACE
EDMONDS, WA
Drilling Company:Bore Hole Dia.:
Top Elevation:Drilling Method:Hammer Type:
Drill Rig:Logged by:
Standard Penetration Test
Hammer Weight and Drop:
SAMPLE LEGEND GROUNDWATER LEGEND % Fines (<0.075 mm)
2-inch O.D. split spoon sample Clean Sand % Water (Moisture) Content
3-inch I.D. Shelby tube sample Bentonite Liquid Limit
Grout/Concrete
Screened Casing
TESTING KEY Blank Casing
GSA = Grain Size Analysis
200W = 200 Wash Analysis Date:Project No.:
Consol. = Consolidation Test
Att. = Atterberg Limits
Boring Location:
Sa
m
p
l
e
N
u
m
b
e
r
SA
M
P
L
E
S
Re
c
o
v
e
r
y
De
p
t
h
(
f
t
)
SOIL DESCRIPTION
Date Drilled:
The stratification lines represent the approximate boundaries
between soil types. The transition may be gradual. Refer to
report text and appendices for additional information.Gr
o
u
n
d
W
a
t
e
r
PENETRATION RESISTANCE (blows/foot)
B-1
B-1
2034.01
Bl
o
w
C
o
u
n
t
s
Langford Residence
1136 Vista Place
Zipper Geo Associates
19023 36th Ave. W, Suite D
Lynnwood, WA
Edmonds, Washingon
Page 1 of 2
BORING
LOG:
Te
s
t
i
n
g
Plastic Limit
Groundwater level at
time of drilling (ATD) or
on date of
measurement.
Natural Water Content
7/1/2018
0 20 40 60
4
14
9
14
18
18
S-1
S-2
S-3
S-4
S-5
S-6
0
5
10
15
20
25
See Figure 1, Site and Exploration Plan
267 FT
6/20/2018
Geologic Drill
Hollow Stem Auger
Mini Bobcat
4"
Cat Head
11
/
2
/
1
2
8
4
26
16
22
14
SPS
A.
T
.
D
.
Grass surface over approximately 8 inches of organics
Loose, moist, brown, silty SAND, trace gravel and organics
(Probable Fill)
Very loose, moist, red-brown, silty SAND, trace to some gravel
(Possible Fill)
Medium dense, moist, mottled red-brown, silty SAND, trace to
some gravel (weathered glacial till)
grades to gray-brown
interbedded 2-12" layers of SAND some silt observed from 13
to 25 feet (Sand Eskers)
22' -perched water observed during drilling
Drilling Company:Bore Hole Dia.:
Top Elevation:Drilling Method:Hammer Type:
Drill Rig:Logged by:
Standard Penetration Test
Hammer Weight and Drop:
SAMPLE LEGEND GROUNDWATER LEGEND % Fines (<0.075 mm)
2-inch O.D. split spoon sample Clean Sand % Water (Moisture) Content
3-inch I.D. Shelby tube sample Bentonite Liquid Limit
Grout/Concrete
Screened Casing
TESTING KEY Blank Casing
GSA = Grain Size Analysis
200W = 200 Wash Analysis Date:Project No.:
Consol. = Consolidation Test
Att. = Atterberg Limits
Boring Location:
B-1
Date Drilled:
De
p
t
h
(
f
t
)
SOIL DESCRIPTION
Sa
m
p
l
e
N
u
m
b
e
r
SA
M
P
L
E
S
Re
c
o
v
e
r
y
Gr
o
u
n
d
W
a
t
e
r
PENETRATION RESISTANCE (blows/foot)
Bl
o
w
C
o
u
n
t
s
Te
s
t
i
n
g
1136 Vista Place
The stratification lines represent the approximate boundaries
between soil types. The transition may be gradual. Refer to
report text and appendices for additional information.
Plastic Limit
Natural Water Content
Langford Residence
Groundwater level at
time of drilling (ATD) or
on date of
measurement.
Edmonds, Washingon
2034.01
Zipper Geo Associates
19023 36th Ave. W, Suite D
Lynnwood, WA
BORING
LOG:B-1
Page 2 of 2
7/1/2018
18S-7
6S-8
0 20 40 60
25
30
35
40
45
50
See Figure 1, Site and Exploration Plan
267 FT
6/20/2018
Geologic Drill
Hollow Stem Auger
Mini Bobcat
4"
Cat Head
11
/
2
/
1
2
65
50/6"
SPS
Very dense, gray, moist, silty SAND with gravel (Glacial Till)
Boring terminated at 30.5 feet.
Drilling Company:Bore Hole Dia.:
Top Elevation:Drilling Method:Hammer Type:
Drill Rig:Logged by:
Standard Penetration Test
Hammer Weight and Drop:
SAMPLE LEGEND GROUNDWATER LEGEND % Fines (<0.075 mm)
2-inch O.D. split spoon sample Clean Sand % Water (Moisture) Content
3-inch I.D. Shelby tube sample Bentonite Liquid Limit
Grout/Concrete
Screened Casing
TESTING KEY Blank Casing
GSA = Grain Size Analysis
200W = 200 Wash Analysis Date:Project No.:
Consol. = Consolidation Test
Att. = Atterberg Limits
Groundwater level at
time of drilling (ATD) or
on date of
measurement.
Natural Water Content
7/3/2018
B-2
B-2
2034.01
Bl
o
w
C
o
u
n
t
s
Langford Residence
1136 Vista Place
Zipper Geo Associates
19023 36th Ave. W, Suite D
Lynnwood, WA
Edmonds, Washingon
Page 1 of 1
BORING
LOG:
Te
s
t
i
n
g
Plastic Limit
Boring Location:
Sa
m
p
l
e
N
u
m
b
e
r
SA
M
P
L
E
S
Re
c
o
v
e
r
y
De
p
t
h
(
f
t
)
SOIL DESCRIPTION
Date Drilled:
The stratification lines represent the approximate boundaries
between soil types. The transition may be gradual. Refer to
report text and appendices for additional information.Gr
o
u
n
d
W
a
t
e
r
PENETRATION RESISTANCE (blows/foot)
0 20 40 60
1
14
6
4
12
14
S-1
S-2
S-3
S-4
S-5
S-6
0
5
10
15
20
25
See Figure 1, Site and Exploration Plan
251 FT
6/20/2018
Geologic Drill
Hollow Stem Auger
Mini Bobcat
4"
Cat Head
11
/
2
/
1
2
3
14
50/6"
16
28
30
SPS
A.
T
.
D
.
Grass surface over approximately 12 inches of topsoil
Very loose, moist, dark brown, silty SAND, with organics
(Possible Fill)
Medium dense, moist, brown, silty SAND, some gravel
(weathered Glacial Till)
(blowcount overstated on gravel)
grades to gray
10' -perched groundwater observed while drilling
interbedded 2-4" layers of SAND some silt observed from 11
feet to end of boring (Sand Eskers)
grades to with gravel
Boring terminated at 21.5 feet.
Drilling Company:Bore Hole Dia.:
Top Elevation:Drilling Method:Hammer Type:
Drill Rig:Logged by:
Standard Penetration Test
Hammer Weight and Drop:
SAMPLE LEGEND GROUNDWATER LEGEND % Fines (<0.075 mm)
2-inch O.D. split spoon sample Clean Sand % Water (Moisture) Content
3-inch I.D. Shelby tube sample Bentonite Liquid Limit
Grout/Concrete
Screened Casing
TESTING KEY Blank Casing
GSA = Grain Size Analysis
200W = 200 Wash Analysis Date:Project No.:
Consol. = Consolidation Test
Att. = Atterberg Limits
Groundwater level at
time of drilling (ATD) or
on date of
measurement.
Natural Water Content
7/3/2018
B-3
B-3
2034.01
Bl
o
w
C
o
u
n
t
s
Langford Residence
1136 Vista Place
Zipper Geo Associates
19023 36th Ave. W, Suite D
Lynnwood, WA
Edmonds, Washingon
Page 1 of 1
BORING
LOG:
Te
s
t
i
n
g
Plastic Limit
Boring Location:
Sa
m
p
l
e
N
u
m
b
e
r
SA
M
P
L
E
S
Re
c
o
v
e
r
y
De
p
t
h
(
f
t
)
SOIL DESCRIPTION
Date Drilled:
The stratification lines represent the approximate boundaries
between soil types. The transition may be gradual. Refer to
report text and appendices for additional information.Gr
o
u
n
d
W
a
t
e
r
PENETRATION RESISTANCE (blows/foot)
0 20 40 60
18
18
18
17
18
S-1
S-2
S-3
S-4
S-5
0
5
10
15
20
25
See Figure 1, Site and Exploration Plan
243 FT
6/20/2018
Geologic Drill
Hollow Stem Auger
Mini Bobcat
4"
Cat Head
11
/
2
/
1
2
36
34
11
73/11"
60
SPS
A.
T
.
D
.
Grass surface over approximately 4 inches of topsoil
Dense, moist, brown, silty fine SAND (weathered Glacial Till)
7' -perched groundwater encountered while drilling
Medium dense, gray, wet, silty fine SAND (sand esker)
Very dense, gray, moist, silty SAND with gravel (Glacial Till)
Boring terminated at 16.5 feet.