21-104105-Geotechnical Report-10-06-2021-V1EarthSolutionsNWLLC
EarthSolutions
NW LLC
15365 N.E. 90th Street, Suite 100 Redmond, WA98052
(425) 449-4704 Fax (425) 449-4711
www.earthsolutionsnw.com
Geotechnical Engineering
Construction Observation/Testing
Environmental Services
PRELIMINARY GEOTECHNICAL ENGINEERING STUDY
TWIN TRAILS RESIDENTIAL SUBDIVISION
1605 SOUTHWEST 341ST PLACE
FEDERAL WAY, WASHINGTON
ES-7961
PREPARED FOR
PROSPECT DEVELOPMENT, LLC
August 23, 2021
Updated September 13, 2021
__________________________
Scott S. Riegel, L.G., L.E.G.
Senior Project Manager
__________________________
Kyle R. Campbell, P.E.
Principal Engineer
PRELIMINARY GEOTECHNICAL ENGINEERING STUDY
TWIN TRAILS RESIDENTIAL SUBDIVISION
1605 SOUTHWEST 341ST PLACE
FEDERAL WAY, WASHINGTON
ES-7961
Earth Solutions NW, LLC
15365 Northeast 90th Street, Suite 100
Redmond, Washington 98052
Phone: 425-449-4704 | Fax: 425-449-4711
www.earthsolutionsnw.com
09/13/2021
Geotechnical-Engineering Report
Important Information about This
Subsurface problems are a principal cause of construction delays, cost overruns, claims, and disputes.
While you cannot eliminate all such risks, you can manage them. The following information is provided to help.
The Geoprofessional Business Association (GBA)
has prepared this advisory to help you – assumedly
a client representative – interpret and apply this
geotechnical-engineering report as effectively as
possible. In that way, you can benefit from a lowered
exposure to problems associated with subsurface
conditions at project sites and development of
them that, for decades, have been a principal cause
of construction delays, cost overruns, claims,
and disputes. If you have questions or want more
information about any of the issues discussed herein,
contact your GBA-member geotechnical engineer.
Active engagement in GBA exposes geotechnical
engineers to a wide array of risk-confrontation
techniques that can be of genuine benefit for
everyone involved with a construction project.
Understand the Geotechnical-Engineering Services
Provided for this Report
Geotechnical-engineering services typically include the planning,
collection, interpretation, and analysis of exploratory data from
widely spaced borings and/or test pits. Field data are combined
with results from laboratory tests of soil and rock samples obtained
from field exploration (if applicable), observations made during site
reconnaissance, and historical information to form one or more models
of the expected subsurface conditions beneath the site. Local geology
and alterations of the site surface and subsurface by previous and
proposed construction are also important considerations. Geotechnical
engineers apply their engineering training, experience, and judgment
to adapt the requirements of the prospective project to the subsurface
model(s). Estimates are made of the subsurface conditions that
will likely be exposed during construction as well as the expected
performance of foundations and other structures being planned and/or
affected by construction activities.
The culmination of these geotechnical-engineering services is typically a
geotechnical-engineering report providing the data obtained, a discussion
of the subsurface model(s), the engineering and geologic engineering
assessments and analyses made, and the recommendations developed
to satisfy the given requirements of the project. These reports may be
titled investigations, explorations, studies, assessments, or evaluations.
Regardless of the title used, the geotechnical-engineering report is an
engineering interpretation of the subsurface conditions within the context
of the project and does not represent a close examination, systematic
inquiry, or thorough investigation of all site and subsurface conditions.
Geotechnical-Engineering Services are Performed
for Specific Purposes, Persons, and Projects,
and At Specific Times
Geotechnical engineers structure their services to meet the specific
needs, goals, and risk management preferences of their clients. A
geotechnical-engineering study conducted for a given civil engineer
will not likely meet the needs of a civil-works constructor or even a
different civil engineer. Because each geotechnical-engineering study
is unique, each geotechnical-engineering report is unique, prepared
solely for the client.
Likewise, geotechnical-engineering services are performed for a specific
project and purpose. For example, it is unlikely that a geotechnical-
engineering study for a refrigerated warehouse will be the same as
one prepared for a parking garage; and a few borings drilled during
a preliminary study to evaluate site feasibility will not be adequate to
develop geotechnical design recommendations for the project.
Do not rely on this report if your geotechnical engineer prepared it:
• for a different client;
• for a different project or purpose;
• for a different site (that may or may not include all or a portion of
the original site); or
• before important events occurred at the site or adjacent to it;
e.g., man-made events like construction or environmental
remediation, or natural events like floods, droughts, earthquakes,
or groundwater fluctuations.
Note, too, the reliability of a geotechnical-engineering report can
be affected by the passage of time, because of factors like changed
subsurface conditions; new or modified codes, standards, or
regulations; or new techniques or tools. If you are the least bit uncertain
about the continued reliability of this report, contact your geotechnical
engineer before applying the recommendations in it. A minor amount
of additional testing or analysis after the passage of time – if any is
required at all – could prevent major problems.
Read this Report in Full
Costly problems have occurred because those relying on a geotechnical-
engineering report did not read the report in its entirety. Do not rely on
an executive summary. Do not read selective elements only. Read and
refer to the report in full.
You Need to Inform Your Geotechnical Engineer
About Change
Your geotechnical engineer considered unique, project-specific factors
when developing the scope of study behind this report and developing
the confirmation-dependent recommendations the report conveys.
Typical changes that could erode the reliability of this report include
those that affect:
• the site’s size or shape;
• the elevation, configuration, location, orientation,
function or weight of the proposed structure and
the desired performance criteria;
• the composition of the design team; or
• project ownership.
As a general rule, always inform your geotechnical engineer of project
or site changes – even minor ones – and request an assessment of their
impact. The geotechnical engineer who prepared this report cannot accept
responsibility or liability for problems that arise because the geotechnical
engineer was not informed about developments the engineer otherwise
would have considered.
Most of the “Findings” Related in This Report
Are Professional Opinions
Before construction begins, geotechnical engineers explore a site’s
subsurface using various sampling and testing procedures. Geotechnical
engineers can observe actual subsurface conditions only at those specific
locations where sampling and testing is performed. The data derived from
that sampling and testing were reviewed by your geotechnical engineer,
who then applied professional judgement to form opinions about
subsurface conditions throughout the site. Actual sitewide-subsurface
conditions may differ – maybe significantly – from those indicated in
this report. Confront that risk by retaining your geotechnical engineer
to serve on the design team through project completion to obtain
informed guidance quickly, whenever needed.
This Report’s Recommendations Are
Confirmation-Dependent
The recommendations included in this report – including any options or
alternatives – are confirmation-dependent. In other words, they are not
final, because the geotechnical engineer who developed them relied heavily
on judgement and opinion to do so. Your geotechnical engineer can finalize
the recommendations only after observing actual subsurface conditions
exposed during construction. If through observation your geotechnical
engineer confirms that the conditions assumed to exist actually do exist,
the recommendations can be relied upon, assuming no other changes have
occurred. The geotechnical engineer who prepared this report cannot assume
responsibility or liability for confirmation-dependent recommendations if you
fail to retain that engineer to perform construction observation.
This Report Could Be Misinterpreted
Other design professionals’ misinterpretation of geotechnical-
engineering reports has resulted in costly problems. Confront that risk
by having your geotechnical engineer serve as a continuing member of
the design team, to:
• confer with other design-team members;
• help develop specifications;
• review pertinent elements of other design professionals’ plans and
specifications; and
• be available whenever geotechnical-engineering guidance is needed.
You should also confront the risk of constructors misinterpreting this
report. Do so by retaining your geotechnical engineer to participate in
prebid and preconstruction conferences and to perform construction-
phase observations.
Give Constructors a Complete Report and Guidance
Some owners and design professionals mistakenly believe they can shift
unanticipated-subsurface-conditions liability to constructors by limiting
the information they provide for bid preparation. To help prevent
the costly, contentious problems this practice has caused, include the
complete geotechnical-engineering report, along with any attachments
or appendices, with your contract documents, but be certain to note
conspicuously that you’ve included the material for information purposes
only. To avoid misunderstanding, you may also want to note that
“informational purposes” means constructors have no right to rely on
the interpretations, opinions, conclusions, or recommendations in the
report. Be certain that constructors know they may learn about specific
project requirements, including options selected from the report, only
from the design drawings and specifications. Remind constructors
that they may perform their own studies if they want to, and be sure to
allow enough time to permit them to do so. Only then might you be in
a position to give constructors the information available to you, while
requiring them to at least share some of the financial responsibilities
stemming from unanticipated conditions. Conducting prebid and
preconstruction conferences can also be valuable in this respect.
Read Responsibility Provisions Closely
Some client representatives, design professionals, and constructors do
not realize that geotechnical engineering is far less exact than other
engineering disciplines. This happens in part because soil and rock on
project sites are typically heterogeneous and not manufactured materials
with well-defined engineering properties like steel and concrete. That
lack of understanding has nurtured unrealistic expectations that have
resulted in disappointments, delays, cost overruns, claims, and disputes.
To confront that risk, geotechnical engineers commonly include
explanatory provisions in their reports. Sometimes labeled “limitations,”
many of these provisions indicate where geotechnical engineers’
responsibilities begin and end, to help others recognize their own
responsibilities and risks. Read these provisions closely. Ask questions.
Your geotechnical engineer should respond fully and frankly.
Geoenvironmental Concerns Are Not Covered
The personnel, equipment, and techniques used to perform an
environmental study – e.g., a “phase-one” or “phase-two” environmental
site assessment – differ significantly from those used to perform a
geotechnical-engineering study. For that reason, a geotechnical-engineering
report does not usually provide environmental findings, conclusions, or
recommendations; e.g., about the likelihood of encountering underground
storage tanks or regulated contaminants. Unanticipated subsurface
environmental problems have led to project failures. If you have not
obtained your own environmental information about the project site,
ask your geotechnical consultant for a recommendation on how to find
environmental risk-management guidance.
Obtain Professional Assistance to Deal with
Moisture Infiltration and Mold
While your geotechnical engineer may have addressed groundwater,
water infiltration, or similar issues in this report, the engineer’s
services were not designed, conducted, or intended to prevent
migration of moisture – including water vapor – from the soil
through building slabs and walls and into the building interior, where
it can cause mold growth and material-performance deficiencies.
Accordingly, proper implementation of the geotechnical engineer’s
recommendations will not of itself be sufficient to prevent
moisture infiltration. Confront the risk of moisture infiltration by
including building-envelope or mold specialists on the design team.
Geotechnical engineers are not building-envelope or mold specialists.
Copyright 2019 by Geoprofessional Business Association (GBA). Duplication, reproduction, or copying of this document, in whole or in part, by any means whatsoever, is strictly
prohibited, except with GBA’s specific written permission. Excerpting, quoting, or otherwise extracting wording from this document is permitted only with the express written permission of
GBA, and only for purposes of scholarly research or book review. Only members of GBA may use this document or its wording as a complement to or as an element of a report of any kind.
Any other firm, individual, or other entity that so uses this document without being a GBA member could be committing negligent or intentional (fraudulent) misrepresentation.
Telephone: 301/565-2733
e-mail: info@geoprofessional.org www.geoprofessional.org
August 23, 2021
Updated September 13, 2021
ES-7961
Prospect Development, LLC
2913 – 5th Avenue Northeast, Suite 201
Puyallup, Washington 98372
Attention: Mr. Justin Holland
Dear Mr. Holland:
Earth Solutions NW, LLC (ESNW) is pleased to present this preliminary report that supports the
current project. Based on the results of our investigation, construction of the proposed residential
subdivision is feasible from a geotechnical standpoint. Our study indicates the site is underlain
primarily by glacially consolidated soils with areas of outwash type deposits. This update includes
the current site plan.
In general, typical residences up to three stories in height may be supported on conventional
continuous and spread footing foundations bearing on competent native soil, recompacted native
soil, or new structural fill placed directly on competent native soil. In general, competent native
soil, suitable for support of the new foundations, will likely be encountered beginning at depths of
about two to four feet below the existing ground surface. Where loose or unsuitable soil
conditions are exposed at foundation subgrade elevations, compaction of soils to the
specifications of structural fill, or overexcavation and replacement with suitable structural fill, will
be necessary. Because no design details were available at the time of this report, ESNW should
review the project details to confirm the recommendations in this report are applicable.
Infiltration is feasible in the northeastern portion of the site (TP-1 through TP-3) where outwash
type soils were encountered at depth. Infiltration facilities planned for this site must expose the
clean outwash sand and gravel soils across the entirety of the system.
We appreciate the opportunity to be of service to you on this project. If you have questions
regarding the content of this geotechnical engineering study, please contact us.
Sincerely,
EARTH SOLUTIONS NW, LLC
Scott S. Riegel, L.G., L.E.G.
Senior Project Manager
15365 N.E. 90th Street, Suite 100 • Redmond, WA 98052 •(425) 449-4704 • FAX (425) 449-4711
Earth Solutions NW LLC
Geotechnical Engineering, Construction
Observation/Testing and Environmental Services
Earth Solutions NW, LLC
Table of Contents
ES-7961
PAGE
INTRODUCTION ................................................................................. 1
General..................................................................................... 1
Project Description ................................................................. 1
SITE CONDITIONS ............................................................................. 2
Surface ..................................................................................... 2
Subsurface .............................................................................. 2
Topsoil and Fill ............................................................. 2
Native Soil ..................................................................... 3
Geologic Setting ........................................................... 3
Groundwater ................................................................. 3
GEOLOGICALLY HAZARDOUS AREAS ........................................... 3
DISCUSSION AND RECOMMENDATIONS ....................................... 3
General..................................................................................... 3
Site Preparation and Earthwork ............................................. 4
Temporary Erosion Control ......................................... 4
Stripping ....................................................................... 5
Excavations and Slopes .............................................. 5
In-situ and Imported Soils ........................................... 5
Wet-Season Grading .................................................... 6
Structural Fill ................................................................ 6
Foundations ............................................................................ 6
Seismic Design ....................................................................... 7
Slab-on-Grade Floors ............................................................. 8
Retaining Walls ....................................................................... 8
Landscape Retaining Walls ......................................... 9
Drainage................................................................................... 9
Infiltration Evaluation ................................................... 9
Utility Support and Trench Backfill ....................................... 10
Preliminary Pavement Sections ............................................. 10
LIMITATIONS ...................................................................................... 11
Additional Services ................................................................. 11
Earth Solutions NW, LLC
Table of Contents
Cont’d
ES-7961
GRAPHICS
Plate 1 Vicinity Map
Plate 2 Test Pit Location Plan
Plate 3 Retaining Wall Drainage Detail
Plate 4 Footing Drain Detail
APPENDICES
Appendix A Subsurface Exploration
Test Pit Logs
Appendix B Laboratory Test Results
Earth Solutions NW, LLC
PRELIMINARY GEOTECHNICAL ENGINEERING STUDY
TWIN TRAILS RESIDENTIAL SUBDIVISION
1605 SOUTHWEST 341ST PLACE
FEDERAL WAY, WASHINGTON
ES-7961
INTRODUCTION
General
This preliminary geotechnical engineering study (study) was prepared for the proposed
residential development to be constructed off the south side of Southwest 341st Place near 16th
Avenue Southwest in Federal Way, Washington. The purpose of this study was to develop
geotechnical recommendations for the proposed project. The scope of services for completing
this study included the following:
Subsurface exploration consisting of test pit excavations;
Laboratory testing of soil samples collected at the test pit locations;
Engineering analyses and recommendations for the proposed development, and;
Preparation of this report.
The following documents and maps were reviewed as part of preparing this study:
Preliminary Site Plan, Sheet PP-03 and PP-04, prepared by ESM Consulting Engineers
dated September 3, 2021;
Geologic Map of the Poverty Bay 7.5’ Quadrangle, King County, Washington, prepared by
Tabor, et al, 2014;
Federal Way Municipal Code (FWMC) section19.145 Environmentally Critical Areas, and;
Web Soil Survey (WSS), provided by the United States Department of Agriculture (USDA),
Natural Resources Conservation Service.
Project Description
Based on review of the referenced site plan, the subject site will be developed with 38 detached
residential lots, access roadways, a stormwater detention tract and utility improvements. The
stormwater tract will be located in the northern portion of the site.
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Earth Solutions NW, LLC
Based on existing grades, we anticipate mass grading activities will include minor cuts and fills
of up to about seven feet. Perimeter footing loads will likely be 1 to 2 kips per lineal foot. Slab-
on-grade loading is anticipated to be approximately 150 pounds per square foot (psf).
The referenced plan indicates a stormwater infiltration pond will be constructed in the northern
portion of the site where outwash soils were encountered during our fieldwork. The pond base
will be excavated at least seven feet below existing grade to expose outwash soils and will use a
combination of cut and fill berms.
If the above design assumptions are incorrect or change, ESNW should be contacted to review
the recommendations provided in this report. ESNW should review final designs to confirm that
our geotechnical recommendations have been incorporated into the plans.
SITE CONDITIONS
Surface
The subject site is located off the south side Southwest 341st Place in Federal Way, Washington.
The approximate location of the property is illustrated on Plate 1 (Vicinity Map). The site consists
of two adjoining tax parcels (King County Parcel Numbers 2421039051 and the east half of
2421039008). The property at 1605 Southwest 341 st Place is occupied by a residence,
outbuildings and landscaping in the northeastern portion of the site, but is otherwise forested.
The site topography generally descends gently to the west and north from the southeastern
portion of the property with about 30 feet of total elevation change.
Subsurface
A representative of ESNW observed, logged, and sampled eight test pits excavated across the
overall project area, on May 28, 2021 using a trackhoe and operator provided by the client. The
test pits were completed for purposes of assessing soil conditions, classifying site soils, and
characterizing near-surface groundwater conditions within the overall development area. The
approximate locations of the test pits are depicted on Plate 2 (Test Pit Location Plan). Please
refer to the test pit logs provided in Appendix A for a more detailed description of subsurface
conditions. Representative soil samples collected at the test pit locations were analyzed in
general accordance with Unified Soil Classification System (USCS) and USDA methods and
procedures.
Topsoil and Fill
Topsoil (where encountered) generally extended to depths of ranging from about two to eight
inches below the existing ground surface (bgs). The topsoil was characterized by the observed
dark brown color, the presence of fine organics, and root intrusions extending into the shallow,
weathered soils.
Fill was not encountered during our exploration; however, fill is likely present near the existing
development areas of the site.
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Earth Solutions NW, LLC
Native Soil
Underlying topsoil, native soils encountered on the subject site were consisting primarily of silty
sand with gravel (USCS: SM) that extended to the maximum exploration depth of about nine and
one-half feet except test pit locations TP-1 through TP-3. At test pit locations TP-1 through TP-
3, underlying about five to six feet of silty sand, we encountered medium dense to dense,
outwash-type sand and gravel deposits (USCS: SP and GW-GM) that extended to the termination
depths of the test pits.
Geologic Setting
The referenced geologic map resource identifies ice contact (Qvi) deposits as the primary
geologic unit underlying the site and surrounding areas. The referenced WSS map resource
identifies Alderwood gravelly sandy loam (Map Unit Symbol: AgC) across the property. The
Alderwood series soils formed in glacial till plains.
Based on our field observations, the majority of the native soils encountered during our fieldwork
are consistent with ice contact deposits, and the sandy soils encountered below the glacially
consolidated cap within test pit locations TP-1 through TP-3 are consistent with outwash deposits.
Groundwater
During our subsurface exploration completed on May 2021, groundwater seepage was not
encountered at the test pit locations. However, perched seepage should be expected within the
weathered zone of soils on this site depending on the time of year grading occurs. In general,
groundwater flow rates and elevations are higher during the winter, spring, and early summer
months.
GEOLOGICALLY HAZARDOUS AREAS
Based on our review of the referenced Federal Way municipal code section and site conditions
encountered during our fieldwork, there are no geologic hazard areas (erosion, landslide, seismic,
or mine hazards) on or within 300 feet of the subject site. Standard development BMPs may be
used for this site development plans.
DISCUSSION AND RECOMMENDATIONS
General
Based on the results of our investigation, construction of typical single-family residences on this
site is feasible from a geotechnical standpoint. The primary geotechnical considerations
associated with the proposed development include site grading, infiltration facility construction,
foundation support, slab-on-grade subgrade support, and the suitability of using on-site soils as
structural fill.
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Earth Solutions NW, LLC
Typical single-family residences may be supported on conventional continuous and spread
footing foundations bearing on competent native soil, recompacted native soil, or new structural
fill placed directly on competent native soil. In general, competent native soil, suitable for support
of the new foundations, will likely be encountered beginning at depths of about two to four feet
bgs. Where loose or unsuitable soil conditions are exposed at foundation subgrade elevations,
compaction of soils to the specifications of structural fill, or overexcavation and replacement with
suitable structural fill, will be necessary. ESNW should review the proposed plans to confirm the
recommendations in this report remain applicable.
The relatively clean sand and gravel deposits encountered at test pit locations TP-1 through TP-
3 are suitable for infiltration but in-situ testing will be required to determine the infiltration rate for
formal designs. Due to the low infiltration capacity of the glacially consolidated soils on this site,
infiltration is not recommended for the southern portion of the development area.
This study has been prepared for the exclusive use of Prospect Development, LLC, and their
representatives. A warranty is neither expressed nor implied. This study has been prepared in
a manner consistent with the level of care and skill ordinarily exercised by other members of the
profession currently practicing under similar conditions in this area.
Site Preparation and Earthwork
Initial site preparation activities will consist of installing temporary erosion control measures,
establishing grading limits, removing structural improvements, and clearing and stripping the site.
Subsequent earthwork activities will involve site grading and related infrastructure improvements.
Temporary Erosion Control
The following temporary erosion control measures are offered:
Temporary construction entrances and drive lanes, consisting of at least six inches of
quarry spalls, should be considered to both minimize off-site soil tracking and provide a
stable access entrance surface. Placing geotextile fabric underneath the quarry spalls will
provide greater stability, if needed.
Silt fencing should be placed around the site perimeter.
When not actively graded, soil stockpiles should be covered or otherwise protected.
Temporary measures for controlling surface water runoff, such as interceptor trenches,
sumps, or swales, should be installed prior to beginning earthwork activities.
Dry soils disturbed during construction should be wetted to minimize dust and airborne soil
erosion.
Additional Best Management Practices (BMPs), as specified by the project civil engineer and
indicated on the plans, should be incorporated into construction activities. Temporary erosion
control measures should be actively managed and may be modified during construction as site
conditions require, to ensure proper performance.
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Earth Solutions NW, LLC
Stripping
Topsoil was generally encountered within the upper approximately four to eight inches at the test
pit locations. The organic-rich topsoil should be stripped and segregated into a stockpile for later
use on site or to haul off site. The material remaining immediately below the topsoil may have
some root zones and will likely be variable in composition, density, and/or moisture content. The
material exposed after initial topsoil stripping will likely not be suitable for direct structural support
as is and will likely need to be compacted in place or stripped and stockpiled for reuse as fill;
depending on the time of year stripping occurs, the soil exposed below the topsoil may be too
wet to compact and may need to be aerated or treated. ESNW should observe initial stripping
activities to provide recommendations regarding stripping depths and material suitability.
Excavations and Slopes
Based on the soil conditions observed at the subsurface exploration locations, the maximum
allowable temporary slope inclinations provided below may be used. The applicable Federal
Occupation Safety and Health Administration and Washington Industrial Safety and Health Act
soil classifications are also provided.
Areas exposing groundwater seepage 1.5H:1V (Type C)
Loose soil; fill 1.5H:1V (Type C)
Medium dense to dense native soil 1H:1V (Type B)
Permanent slopes should be planted with vegetation to both enhance stability and minimize
erosion. The presence of perched groundwater may cause localized sloughing of temporary
slopes. An ESNW representative should observe temporary and permanent slopes to confirm
the slope inclinations are suitable for the exposed soil conditions and to provide additional
excavation and slope recommendations as necessary. If the recommended temporary slope
inclinations cannot be achieved, temporary shoring may be necessary to support excavations.
In-situ and Imported Soils
The majority of the near-surface soils encountered during our subsurface exploration have a high
sensitivity to moisture and were generally in a damp to moist condition at the time of the
exploration (May 2021). Exposed soils will degrade rapidly if exposed to wet weather and/or
construction traffic. In general, soils encountered during site excavations that are excessively
over the optimum moisture content will require aeration or treatment prior to placement and
compaction. Conversely, soils that are substantially below the optimum moisture content will
require moisture conditioning through the addition of water prior to use as structural fill. A
representative of ESNW should determine the suitability of in-situ soils for use as structural fill at
the time of construction.
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Imported soil intended for use as structural fill should consist of a well-graded, granular soil with
a moisture content that is at (or slightly above) the optimum level. During wet weather conditions,
imported soil intended for use as structural fill should consist of a well-graded, granular soil with
a fines content of 5 percent or less (where the fines content is defined as the percent passing the
Number 200 sieve, based on the minus three-quarter-inch fraction).
Wet-Season Grading
Because the site soils are highly sensitive to moisture, grading during the rainy season will be
very difficult. If grading takes place during the winter, spring, or early summer months, a
contingency in the project budget should be included to allow for export of native soil and import
of structural fill.
Structural Fill
Structural fill is defined as compacted soil placed in foundation, slab-on-grade, roadway,
permanent slope, retaining wall, utility trench, and vault backfill areas. Soils placed in structural
areas should consist of a granular material devoid of deleterious debris and organics, placed in
loose lifts of 12 inches or less and compacted to a relative compaction of 95 percent, based on
the laboratory maximum dry density as determined by the Modified Proctor Method (ASTM D-
1557).
Foundations
Typical two to three story residential structures may be supported on conventional spread and
continuous footings bearing on competent native soil, recompacted native soil, or new structural
fill placed directly on competent native soil. In general, competent native soil suitable for the
support of foundations will likely be encountered at depths of about two to four feet bgs. ESNW
should evaluate the design subgrade conditions to confirm suitable conditions are exposed and
to provide additional preparation recommendations, where necessary. Where loose, organic, or
otherwise unsuitable soil conditions are observed at foundation subgrade elevations, compaction
of the soils to the specifications of structural fill, or overexcavation and replacement with granular
structural fill, will likely be necessary.
Provided residential structures will be supported as described above, the following parameters
can be used for design of the new foundations:
Allowable soil bearing capacity 2,500 psf
Passive earth pressure 300 pcf (equivalent fluid)
Coefficient of friction 0.40
The passive earth pressure and coefficient of friction values include a safety factor of 1.5. A one-
third increase in the allowable soil bearing capacity may be assumed for short-term wind and
seismic loading conditions. With structural loading as expected, total settlement in the range of
1 inch is anticipated, with differential settlement of about 0.5 inch. The majority of settlement
should occur during construction, as dead loads are applied.
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Earth Solutions NW, LLC
Seismic Design
The 2018 International Building Code (2018 IBC) recognizes the most recent edition of the
Minimum Design Loads for Buildings and Other Structures manual (ASCE 7-16) for seismic
design, specifically with respect to earthquake loads. Based on the soil conditions encountered
at the boring locations, the parameters and values provided below are recommended for seismic
design per the 2018 IBC.
Parameter Value
Site Class D*
Mapped short period spectral response acceleration, S S (g) 1.336
Mapped 1-second period spectral response acceleration, S 1 (g) 0.459
Short period site coefficient, Fa 1
Long period site coefficient, Fv 1.86
Adjusted short period spectral response acceleration, S MS (g) 1.336
Adjusted 1-second period spectral response acceleration, S M1 (g) 0.854
Design short period spectral response acceleration, S DS (g) 0.891
Design 1-second period spectral response acceleration, S D1 (g) 0.569
* Assumes medium dense soil conditions, encountered to a maximum depth of nine and one-half feet bgs during
the May 2021 field exploration, remain medium dense or better to at least 100 feet bgs. Based on our experience
with the project geologic setting (glacial till) across the Puget Sound region, soil conditions are likely consistent
with this assumption.
Further discussion between the project structural engineer, the project owner (or their
representative), and ESNW may be prudent to determine the possible impacts to the structural
design due to increased earthquake load requirements under the 2018 IBC. ESNW can provide
additional consulting services to aid with design efforts, including supplementary geotechnical
and geophysical investigation, upon request.
Liquefaction is a phenomenon where saturated or loose soil suddenly loses internal strength and
behaves as a fluid. This behavior is in response to increased pore water pressures resulting from
an earthquake or another intense ground shaking. In our opinion, site susceptibility to liquefaction
may be considered negligible. The absence of a shallow groundwater table and the relative
density of the native soil were the primary bases for this opinion.
Prospect Development, LLC ES-7961
August 23, 2021 Page 8
Updated September 13, 2021
Earth Solutions NW, LLC
Slab-on-Grade Floors
Slab-on-grade floors should be supported on a firm and unyielding subgrade consisting of
competent native soil or new structural fill. Unstable or yielding areas of the subgrade should be
recompacted or overexcavated and replaced with suitable structural fill prior to construction of
the slab. A capillary break, consisting of a minimum of four inches of free-draining crushed rock
or gravel, should be placed below the slab. The free-draining material should have a fines content
of 5 percent or less defined as the percent passing the number 200 sieve based on the minus
three-quarters inch fraction. In areas where slab moisture is undesirable, installation of a vapor
barrier below the slab should be considered. If used, the vapor barrier should consist of a material
specifically designed to function as a vapor barrier and should be installed in accordance with the
manufacturer’s specifications.
Retaining Walls
Retaining walls must be designed to resist earth pressures and applicable surcharge loads. The
following parameters may be used for design:
Active earth pressure (unrestrained condition) 35 pcf (equivalent fluid)
At-rest earth pressure (restrained condition) 55 pcf
Traffic surcharge (passenger vehicles) 70 psf (rectangular distribution) *
Passive earth pressure 300 pcf (equivalent fluid)
Coefficient of friction 0.40
Seismic surcharge 8H psf**
* Where applicable
** Where H equals the retained height (in feet)
The above design parameters are based on a level backfill condition and level grade at the wall
toe. Revised design values will be necessary if sloping grades are to be used above or below
retaining walls. Additional surcharge loading from adjacent foundations, sloped backfill, or other
relevant loads should be included in the retaining wall design, where applicable. A safety factor
of 1.5 is included in the passive earth pressure and coefficient of friction values.
Retaining walls should be backfilled with free-draining material or suitable sheet drainage that
extends along the height of the wall and a distance of at least 18 inches behind the wall. The
upper 12 inches of the wall backfill can consist of a less permeable soil, if desired. A perforated
drainpipe should be placed along the base of the wall and connected to an approved discharge
location. A typical retaining wall drainage detail is provided on Plate 3. If drainage is not provided,
hydrostatic pressures should be included in the wall design.
Prospect Development, LLC ES-7961
August 23, 2021 Page 9
Updated September 13, 2021
Earth Solutions NW, LLC
Landscape Retaining Walls
Based on the existing site grades, retaining walls may be used along the portions of the lots to
raise grades for new building pads. Final wall heights, alignments and facing materials have not
been determined at the time of this report. Walls over four feet in total height, including toe
embedment will require building permits supported by an engineered design. ESNW can prepare
and engineered retaining wall design, upon request. ESNW should review the final grading plans
to confirm the recommendations are incorporated and to provide additional recommendations
where appropriate.
Drainage
Groundwater seepage was not encountered during our exploration; however, groundwater
seepage will likely be encountered within site excavations, particularly utility trenches and deeper
excavations such as detention vault/pond areas. Temporary measures to control surface water
runoff and groundwater during construction would likely involve passive elements, such as
interceptor trenches and sumps. ESNW should be consulted during preliminary grading to
identify areas of groundwater and to provide recommendations to reduce the potential for
instability related to groundwater effects. Depending on the flow volumes encountered during
grading, an interceptor trench drain system may be warranted along the up-slope perimeter of
the work area to help mitigate or otherwise control shallow perched groundwater flows.
Finish grades must be designed to direct surface water away from the new structures and/or
slopes for a distance of at least 10 feet or as setbacks allow. Water must not be allowed to pond
adjacent to the new structures and/or slopes. A typical foundation drain detail is provided on
Plate 4.
Infiltration Evaluation
Outwash type soils were encountered at depth within test pits TP-1 through TP-3 with
corresponding fines content of about 5 percent. The outwash soils may be suitable for infiltration
pending in-situ infiltration testing. Based on textural analyses and using the DOE saturated
hydraulic conductivity calculation, for feasibility considerations, a preliminary infiltration rate of 10
inches per hour was recommended to the project civil engineer for the relatively clean outwash
sand and gravel deposits such as those encountered at test pit locations TP-1 through TP-3. The
facility illustrated on the referenced preliminary plans were developed based on information
provided by ESNW during the early phase of design. ESNW should conduct targeted infiltration
testing to better characterize the infiltration potential for the outwash type soils. Based on the
conditions observed during our fieldwork and anecdotal information provided by the project civil
engineer, groundwater separation will likely be feasible. We understand projects nearby to the
north also use infiltration systems and these are functioning as intended.
The native soils in the southern portion of the site consist predominately of silty sand with gravel,
glacially consolidated deposits that exhibit fines contents ranging from about 33 to 49 percent
(passing the U.S. No. 200 sieve), and are not suitable for infiltration.
Prospect Development, LLC ES-7961
August 23, 2021 Page 10
Updated September 13, 2021
Earth Solutions NW, LLC
Utility Support and Trench Backfill
The native soils observed at the test pit locations are generally suitable for support of utilities;
however, the native soils may not be suitable for use as structural backfill in the utility trench
excavations unless the soil is at or near the optimum moisture content at the time of placement
and compaction. Moisture conditioning or cement treatment of the soils may be necessary at
some locations prior to use as structural fill. If utility backfill occurs during wet weather, cement
treatment of native soils or import of a suitable material will be necessary. Utility trench backfill
should be placed and compacted to the specifications of structural fill provided in this report, or
to the applicable requirements of presiding jurisdiction.
Preliminary Pavement Sections
The performance of site pavements is largely related to the condition of the underlying subgrade.
To ensure adequate pavement performance, the subgrade should be in a firm and unyielding
condition when subjected to proofrolling with a loaded dump truck. Structural fill in pavement
areas should be compacted to the specifications detailed in the Site Preparation and Earthwork
section of this report. It is possible that soft, wet, or otherwise unsuitable subgrade areas may
still exist after base grading activities. Areas of unsuitable or yielding subgrade conditions may
require remedial measures such as overexcavation and replacement with structural fill or thicker
crushed rock sections prior to pavement.
For lightly loaded pavement areas subjected primarily to passenger vehicles such as driveways,
the following preliminary pavement sections may be considered:
A minimum of two inches of hot mix asphalt (HMA) placed over four inches of crushed
rock base (CRB), or;
A minimum of two inches of HMA placed over three inches of asphalt treated base (ATB).
Heavier traffic areas generally require thicker pavement sections depending on site usage,
pavement life expectancy, and site traffic. For preliminary design purposes, the following
pavement sections for occasional truck traffic areas may be considered:
Three inches of HMA placed over six inches of crushed rock base (CRB), or;
Three inches of HMA placed over four-and-one-half inches of ATB.
The HMA, CRB and ATB materials should conform to WSDOT specifications.
If pavement areas will include a reverse crown, additional drainage should be used to effectively
convey water that may enter the subgrade toward the storm drainage system. ESNW can provide
recommendations for enhanced drainage upon request.
Prospect Development, LLC ES-7961
August 23, 2021 Page 11
Updated September 13, 2021
Earth Solutions NW, LLC
LIMITATIONS
The recommendations and conclusions provided in this study are professional opinions
consistent with the level of care and skill that is typical of other members in the profession
currently practicing under similar conditions in this area. A warranty is neither expressed nor
implied. Variations in the soil and groundwater conditions observed at the test locations may
exist and may not become evident until construction. ESNW should reevaluate the conclusions
provided in this study if variations are encountered.
Additional Services
ESNW should have an opportunity to review final project plans with respect to the geotechnical
recommendations provided in this report. ESNW should also be retained to provide testing and
consultation services during construction.
Drwn.MRS
Checked SSR Date Aug.2021
Date 08/13/2021 Proj.No.7961
Plate 1
Earth Solutions NWLLC
Geotechnical Engineering,Construction
EarthSolutionsNWLLC
EarthSolutions
NW LLC Observation/Testing and Environmental Services
Vicinity Map
Twin Trails
Federal Way,Washington
Reference:
King County,Washington
OpenStreetMap.org
NORTH
NOTE:This plate may contain areas of color.ESNW cannot be
responsible for any subsequent misinterpretation of the information
resulting from black &white reproductions of this plate.
SITE
MRS
SSR
09/13/2021
7961
2TestPitLocationPlan TwinTrailsFederalWay,WashingtonNORTH
NOT -TO -SCALE
NOTE:This plate may contain areas of color.ESNW cannot be
responsible for any subsequent misinterpretation of the information
resulting from black &white reproductions of this plate.
NOTE:The graphics shown on this plate are not intended for design
purposes or precise scale measurements,but only to illustrate the
approximate test locations relative to the approximate locations of
existing and /or proposed site features.The information illustrated
is largely based on data provided by the client at the time of our
study.ESNW cannot be responsible for subsequent design changes
or interpretation of the data by others.
LEGEND
Approximate Location of
ESNW Test Pit,Proj.No.
ES-7961,May 2021
Subject Site
Existing Building
Proposed Lot Number
TP-1
19
S.W.341ST PLACE
S.W.342ND PLACE
S.W.344TH STREET 19THavenueS.W.road a
road B
1
2
3
4
5678
9
10
11
12 13 14 15
16
17
18192021
2223
24
25
26
27
28 29
30
31
32
33
34
35 36
3738
Tract A
Tract B
Tract C
Tract D
Tract E
Tract F340338336334Close-Up of Tract A with Pond
TP-1
TP-2
TP-3
TP-4TP-5
TP-6
TP-7
TP-8
Plate
Proj.No.
Date
Checked By
Drwn.ByEarthSolutionsNWLLCGeotechnicalEngineering,ConstructionObservation/TestingandEnvironmentalServicesEarthSolutionsNWLLCEarthSolutionsNWLLC
Drwn.MRS
Checked SSR Date Aug.2021
Date 08/13/2021 Proj.No.7961
Plate 3
Earth Solutions NWLLCEarthSolutionsNWLLC
EarthSolutions
NW LLC Geotechnical Engineer ing,C onstr uction
Observation/Testing and Environmental Services
Retaining Wall Drainage Detail
Twin Trails
Federal Way,Washington
NOTES:
Free-draining Backfill should consist
of soil having less than 5 percent fines.
Percent passing No.4 sieve should be
25 to 75 percent.
Sheet Drain may be feasible in lieu
of Free-draining Backfill,per ESNW
recommendations.
Drain Pipe should consist of perforated,
rigid PVC Pipe surrounded with 1-inch
Drain Rock.
LEGEND:
Free-draining Structural Backfill
1-inch Drain Rock
18"Min.
Structural
Fill
Perforated Rigid Drain Pipe
(Surround in Drain Rock)
SCHEMATIC ONLY -NOT TO SCALE
NOT A CONSTRUCTION DRAWING
Drwn.MRS
Checked SSR Date Aug.2021
Date 08/13/2021 Proj.No.7961
Plate 4
Earth Solutions NWLLC
Geotechnical Engineering,Construction
Observation/Testing and Environmental Services
EarthSolutionsNWLLC
EarthSolutions
NW LLC
Footing Drain Detail
Twin Trails
Federal Way,Washington
Slope
Perforated Rigid Drain Pipe
(Surround in Drain Rock)
18"Min.
NOTES:
Do NOT tie roof downspouts
to Footing Drain.
Surface Seal to consist of
12"of less permeable,suitable
soil.Slope away from building.
LEGEND:
Surface Seal:native soil or
other low-permeability material.
1-inch Drain Rock
SCHEMATIC ONLY -NOT TO SCALE
NOT A CONSTRUCTION DRAW ING
Earth Solutions NW, LLC
Appendix A
Subsurface Exploration
Test Pit Logs
ES-7961
Subsurface conditions at the subject site were explored on May 28, 2021 by excavating eight test
pits using a mini-trackhoe and operator provided by the client. The approximate locations test
pits are illustrated on Plate 2 of this study. The test pit logs are provided in this Appendix. The
maximum exploration depth was approximately nine and one-half feet bgs and were terminated
in firm native soils.
The final logs represent the interpretations of the field logs and the results of laboratory analyses.
The stratification lines on the logs represent the approximate boundaries between soil types. In
actuality, the transitions may be more gradual.
GRAVEL
AND
GRAVELLY
SOILS
CLAYEY GRAVELS, GRAVEL - SAND -
CLAY MIXTURES
WELL-GRADED SANDS, GRAVELLY
SANDS, LITTLE OR NO FINES
POORLY-GRADED SANDS,
GRAVELLY SAND, LITTLE OR NO
FINES
SILTY SANDS, SAND - SILT
MIXTURES
CLAYEY SANDS, SAND - CLAY
MIXTURES
INORGANIC SILTS AND VERY FINE
SANDS, ROCK FLOUR, SILTY OR
CLAYEY FINE SANDS 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 SAND OR
SILTY SOILS
INORGANIC CLAYS OF HIGH
PLASTICITY
SILTS
AND
CLAYS
MORE THAN 50%
OF MATERIAL IS
LARGER THAN
NO. 200 SIEVE
SIZE
MORE THAN 50%
OF MATERIAL IS
SMALLER THAN
NO. 200 SIEVE
SIZE
MORE THAN 50%
OF COARSE
FRACTION
PASSING ON NO.
4 SIEVE
MORE THAN 50%
OF COARSE
FRACTION
RETAINED ON NO.
4 SIEVE
SOIL CLASSIFICATION CHART
(APPRECIABLE
AMOUNT OF FINES)
(APPRECIABLE
AMOUNT OF FINES)
(LITTLE OR NO FINES)
FINE
GRAINED
SOILS
SAND
AND
SANDY
SOILS
SILTS
AND
CLAYS
ORGANIC CLAYS OF MEDIUM TO
HIGH PLASTICITY, ORGANIC SILTS
PEAT, HUMUS, SWAMP SOILS WITH
HIGH ORGANIC CONTENTS
LETTERGRAPH
SYMBOLSMAJOR DIVISIONS
COARSE
GRAINED
SOILS
TYPICAL
DESCRIPTIONS
WELL-GRADED GRAVELS, GRAVEL -
SAND MIXTURES, LITTLE OR NO
FINES
POORLY-GRADED GRAVELS,
GRAVEL - SAND MIXTURES, LITTLE
OR NO FINES
SILTY GRAVELS, GRAVEL - SAND -
SILT MIXTURES
CLEAN
GRAVELS
GRAVELS WITH
FINES
CLEAN SANDS
(LITTLE OR NO FINES)
SANDS WITH
FINES
LIQUID LIMIT
LESS THAN 50
LIQUID LIMIT
GREATER THAN 50
HIGHLY ORGANIC SOILS
DUAL SYMBOLS are used to indicate borderline soil classifications.
The discussion in the text of this report is necessary for a proper understanding of the nature
of the material presented in the attached logs.
GW
GP
GM
GC
SW
SP
SM
SC
ML
CL
OL
MH
CH
OH
PT
Earth Solutions NW LLC
MC = 13.3%
MC = 4.5%
Fines = 5.3%
MC = 4.8%
TPSL
SM
GW-
GM
Dark brown TOPSOIL, minimal root intrusions
Brown silty SAND with gravel, medium dense, moist (Weathered Till)
-becomes gray, dense
Gray well-graded GRAVEL with silt and sand, dense, damp
[USDA Classification: extremely gravelly loamy coarse SAND]
Test pit terminated at 9.0 feet below existing grade. No groundwater encountered during
excavation. No caving observed.
0.5
5.0
9.0
NOTES Depth of Topsoil & Sod 6": grass
LOGGED BY SES
EXCAVATION METHOD
EXCAVATION CONTRACTOR Client Provided
CHECKED BY SSR
DATE STARTED 5/28/21 COMPLETED 5/28/21
GROUND WATER LEVEL:
GROUND ELEVATION
LONGITUDE -122.35659 LATITUDE 47.29579
AT TIME OF EXCAVATION
SAMPLE TYPENUMBERDEPTH(ft)0
5
PAGE 1 OF 1
TEST PIT NUMBER TP-1
PROJECT NUMBER ES-7961 PROJECT NAME Twin Trails
GENERAL BH / TP / WELL - 7961.GPJ - GRAPHICS TEMPLATE.GDT - 9/13/21Earth Solutions NW, LLC
15365 N.E. 90th Street, Suite 100
Redmond, Washington 98052
Telephone: 425-449-4704
Fax: 425-449-4711
TESTS
U.S.C.S.MATERIAL DESCRIPTION
GRAPHICLOG
MC = 10.1%
MC = 5.3%
TPSL
SM
GW-
GM
Dark brown TOPSOIL, minimal root intrusions
Brown silty SAND with gravel, medium dense, damp (Weathered Till)
-becomes gray, dense
Gray well-graded GRAVEL with silt and sand, dense, damp (Unweathered Till)
Test pit terminated at 8.0 feet below existing grade. No groundwater encountered during
excavation. No caving observed.
0.5
5.5
8.0
NOTES Depth of Topsoil & Sod 4": grass
LOGGED BY SES
EXCAVATION METHOD
EXCAVATION CONTRACTOR Client Provided
CHECKED BY SSR
DATE STARTED 5/28/21 COMPLETED 5/28/21
GROUND WATER LEVEL:
GROUND ELEVATION
LONGITUDE -122.35649 LATITUDE 47.29516
AT TIME OF EXCAVATION
SAMPLE TYPENUMBERDEPTH(ft)0
5
PAGE 1 OF 1
TEST PIT NUMBER TP-2
PROJECT NUMBER ES-7961 PROJECT NAME Twin Trails
GENERAL BH / TP / WELL - 7961.GPJ - GRAPHICS TEMPLATE.GDT - 9/13/21Earth Solutions NW, LLC
15365 N.E. 90th Street, Suite 100
Redmond, Washington 98052
Telephone: 425-449-4704
Fax: 425-449-4711
TESTS
U.S.C.S.MATERIAL DESCRIPTION
GRAPHICLOG
MC = 7.3%
MC = 6.6%
TPSL
SM
SP
Dark brown TOPSOIL, minimal root intrusions
Brown silty SAND with gravel, medium dense, damp
-large cobbles 1.5' diameter
Brown poorly graded SAND with gravel, medium dense, damp
Test pit terminated at 8.5 feet below existing grade. No groundwater encountered during
excavation. No caving observed.
0.5
6.0
8.5
NOTES Depth of Topsoil & Sod 8": grass
LOGGED BY SES
EXCAVATION METHOD
EXCAVATION CONTRACTOR Client Provided
CHECKED BY SSR
DATE STARTED 5/28/21 COMPLETED 5/28/21
GROUND WATER LEVEL:
GROUND ELEVATION
LONGITUDE -122.35591 LATITUDE 47.29502
AT TIME OF EXCAVATION
SAMPLE TYPENUMBERDEPTH(ft)0
5
PAGE 1 OF 1
TEST PIT NUMBER TP-3
PROJECT NUMBER ES-7961 PROJECT NAME Twin Trails
GENERAL BH / TP / WELL - 7961.GPJ - GRAPHICS TEMPLATE.GDT - 9/13/21Earth Solutions NW, LLC
15365 N.E. 90th Street, Suite 100
Redmond, Washington 98052
Telephone: 425-449-4704
Fax: 425-449-4711
TESTS
U.S.C.S.MATERIAL DESCRIPTION
GRAPHICLOG
MC = 15.7%
Fines = 49.1%
MC = 12.0%
SM
Gray silty SAND with gravel, medium dense, moist
[USDA Classification: gravelly LOAM]
-becomes dense, damp
-weakly cemented
Test pit terminated at 8.0 feet below existing grade. No groundwater encountered during
excavation. No caving observed.
8.0
NOTES Depth of Topsoil & Sod 2": duff
LOGGED BY SES
EXCAVATION METHOD
EXCAVATION CONTRACTOR Client Provided
CHECKED BY SSR
DATE STARTED 5/28/21 COMPLETED 5/28/21
GROUND WATER LEVEL:
GROUND ELEVATION
LONGITUDE -122.35622 LATITUDE 47.29358
AT TIME OF EXCAVATION
SAMPLE TYPENUMBERDEPTH(ft)0
5
PAGE 1 OF 1
TEST PIT NUMBER TP-4
PROJECT NUMBER ES-7961 PROJECT NAME Twin Trails
GENERAL BH / TP / WELL - 7961.GPJ - GRAPHICS TEMPLATE.GDT - 9/13/21Earth Solutions NW, LLC
15365 N.E. 90th Street, Suite 100
Redmond, Washington 98052
Telephone: 425-449-4704
Fax: 425-449-4711
TESTS
U.S.C.S.MATERIAL DESCRIPTION
GRAPHICLOG
MC = 10.5%
MC = 13.2%
Fines = 33.5%
SM
Gray silty SAND, medium dense, damp
-increasing sand content
[USDA Classification: slightly gravelly sandy LOAM]
Test pit terminated at 9.5 feet below existing grade. No groundwater encountered during
excavation. No caving observed.
9.5
NOTES Depth of Topsoil & Sod 3": duff
LOGGED BY SES
EXCAVATION METHOD
EXCAVATION CONTRACTOR Client Provided
CHECKED BY SSR
DATE STARTED 5/28/21 COMPLETED 5/28/21
GROUND WATER LEVEL:
GROUND ELEVATION
LONGITUDE -122.35755 LATITUDE 47.29382
AT TIME OF EXCAVATION
SAMPLE TYPENUMBERDEPTH(ft)0
5
PAGE 1 OF 1
TEST PIT NUMBER TP-5
PROJECT NUMBER ES-7961 PROJECT NAME Twin Trails
GENERAL BH / TP / WELL - 7961.GPJ - GRAPHICS TEMPLATE.GDT - 9/13/21Earth Solutions NW, LLC
15365 N.E. 90th Street, Suite 100
Redmond, Washington 98052
Telephone: 425-449-4704
Fax: 425-449-4711
TESTS
U.S.C.S.MATERIAL DESCRIPTION
GRAPHICLOG
MC = 14.7%
MC = 13.2%
Fines = 33.3%
SM
Brown silty SAND, medium dense, moist
-becomes gray
-becomes dense
-iron oxide staining
[USDA Classification: gravelly sandy LOAM]
Test pit terminated at 8.0 feet below existing grade. No groundwater encountered during
excavation. No caving observed.
8.0
NOTES Depth of Topsoil & Sod 3": duff
LOGGED BY SES
EXCAVATION METHOD
EXCAVATION CONTRACTOR Client Provided
CHECKED BY SSR
DATE STARTED 5/28/21 COMPLETED 5/28/21
GROUND WATER LEVEL:
GROUND ELEVATION
LONGITUDE -122.35822 LATITUDE 47.2944
AT TIME OF EXCAVATION
SAMPLE TYPENUMBERDEPTH(ft)0
5
PAGE 1 OF 1
TEST PIT NUMBER TP-6
PROJECT NUMBER ES-7961 PROJECT NAME Twin Trails
GENERAL BH / TP / WELL - 7961.GPJ - GRAPHICS TEMPLATE.GDT - 9/13/21Earth Solutions NW, LLC
15365 N.E. 90th Street, Suite 100
Redmond, Washington 98052
Telephone: 425-449-4704
Fax: 425-449-4711
TESTS
U.S.C.S.MATERIAL DESCRIPTION
GRAPHICLOG
MC = 14.4%
MC = 14.1%
TPSL
SM
Dark brown TOPSOIL, shallow root intrusions
Brown silty SAND with gravel, medium dense, moist
-becomes gray, dense
-weakly cemented
-becomes gray
-iron oxide staining
Test pit terminated at 8.5 feet below existing grade. No groundwater encountered during
excavation. No caving observed.
0.5
8.5
NOTES Depth of Topsoil & Sod 6": duff
LOGGED BY SES
EXCAVATION METHOD
EXCAVATION CONTRACTOR Client Provided
CHECKED BY SSR
DATE STARTED 5/28/21 COMPLETED 5/28/21
GROUND WATER LEVEL:
GROUND ELEVATION
LONGITUDE -122.3571 LATITUDE 47.29438
AT TIME OF EXCAVATION
SAMPLE TYPENUMBERDEPTH(ft)0
5
PAGE 1 OF 1
TEST PIT NUMBER TP-7
PROJECT NUMBER ES-7961 PROJECT NAME Twin Trails
GENERAL BH / TP / WELL - 7961.GPJ - GRAPHICS TEMPLATE.GDT - 9/13/21Earth Solutions NW, LLC
15365 N.E. 90th Street, Suite 100
Redmond, Washington 98052
Telephone: 425-449-4704
Fax: 425-449-4711
TESTS
U.S.C.S.MATERIAL DESCRIPTION
GRAPHICLOG
MC = 10.8%
Fines = 39.2%
MC = 10.4%
SM
Gray silty SAND with gravel, medium dense, damp
-becomes dense
-weakly cemented
[USDA Classification: slightly gravelly sandy LOAM]
-becomes very dense
Test pit terminated at 6.5 feet below existing grade due to refusal on very dense soils. No
groundwater encountered during excavation. No caving observed.
6.5
NOTES Depth of Topsoil & Sod 3": duff
LOGGED BY SES
EXCAVATION METHOD
EXCAVATION CONTRACTOR Client Provided
CHECKED BY SSR
DATE STARTED 5/28/21 COMPLETED 5/28/21
GROUND WATER LEVEL:
GROUND ELEVATION
LONGITUDE -122.35624 LATITUDE 47.29431
AT TIME OF EXCAVATION
SAMPLE TYPENUMBERDEPTH(ft)0
5
PAGE 1 OF 1
TEST PIT NUMBER TP-8
PROJECT NUMBER ES-7961 PROJECT NAME Twin Trails
GENERAL BH / TP / WELL - 7961.GPJ - GRAPHICS TEMPLATE.GDT - 9/13/21Earth Solutions NW, LLC
15365 N.E. 90th Street, Suite 100
Redmond, Washington 98052
Telephone: 425-449-4704
Fax: 425-449-4711
TESTS
U.S.C.S.MATERIAL DESCRIPTION
GRAPHICLOG
Earth Solutions NW, LLC
Appendix B
Laboratory Test Results
ES-7961
0
5
10
15
20
25
30
35
40
45
50
55
60
65
70
75
80
85
90
95
100
0.0010.010.1110100
3
D100
140
Specimen Identification
1
fine
6
HYDROMETER
304
5.3
1.7
49.1
33.5
33.3
101/2
COBBLES
Specimen Identification
4
coarse
20 401.5 8 14
USDA: Brown Extremely Gravelly Loamy Coarse Sand. USCS: GW-GM with Sand.
USDA: Brown Very Gravelly Coarse Sand. USCS: SP with Gravel.
USDA: Gray Gravelly Loam. USCS: SM.
USDA: Gray Slightly Gravelly Sandy Loam. USCS: SM.
USDA: Gray Gravelly Sandy Loam. USCS: SM.
6 60
PERCENT FINER BY WEIGHTD10
2.869
0.663
15.214
2.435
0.233
0.256
0.324
GRAIN SIZE DISTRIBUTION
100
50.84
7.83
LL
TP-01
TP-03
TP-04
TP-05
TP-06
0.299
0.311
3/4
U.S. SIEVE OPENING IN INCHES U.S. SIEVE NUMBERS
GRAVEL SAND
37.5
19
19
19
37.5
%Silt
1.81
0.58
TP-01
TP-03
TP-04
TP-05
TP-06
2 2003
Cc CuClassification
%Clay
16
PID60 D30
coarse SILT OR CLAYfinemedium
GRAIN SIZE IN MILLIMETERS
3/8 50
6.0ft.
8.5ft.
2.5ft.
9.5ft.
8.0ft.
6.00ft.
8.50ft.
2.50ft.
9.50ft.
8.00ft.
PL
PROJECT NUMBER ES-7961 PROJECT NAME Twin Trails
GRAIN SIZE USDA ES-7961 TWIN TRAILS.GPJ GINT US LAB.GDT 6/4/21Earth Solutions NW, LLC
15365 N.E. 90th Street, Suite 100
Redmond, Washington 98052
Telephone: 425-449-4704
Fax: 425-449-4711
0
5
10
15
20
25
30
35
40
45
50
55
60
65
70
75
80
85
90
95
100
0.0010.010.1110100
3
D100
140
Specimen Identification
1
fine
6
HYDROMETER
304
39.2
101/2
COBBLES
Specimen Identification
4
coarse
20 401.5 8 14
USDA: Gray Slightly Gravelly Sandy Loam. USCS: SM.
6 60
PERCENT FINER BY WEIGHTD10
0.224
GRAIN SIZE DISTRIBUTION
100
LL
TP-08
3/4
U.S. SIEVE OPENING IN INCHES U.S. SIEVE NUMBERS
GRAVEL SAND
19
%Silt
TP-08
2 2003
Cc CuClassification
%Clay
16
PID60 D30
coarse SILT OR CLAYfinemedium
GRAIN SIZE IN MILLIMETERS
3/8 50
3.0ft.
3.00ft.
PL
PROJECT NUMBER ES-7961 PROJECT NAME Twin Trails
GRAIN SIZE USDA ES-7961 TWIN TRAILS.GPJ GINT US LAB.GDT 6/4/21Earth Solutions NW, LLC
15365 N.E. 90th Street, Suite 100
Redmond, Washington 98052
Telephone: 425-449-4704
Fax: 425-449-4711
Earth Solutions NW, LLC
Report Distribution
ES-7961
EMAIL ONLY Prospect Development, LLC
2913 – 5th Avenue Northeast, Suite 201
Puyallup, Washington 98372
Attention: Mr. Justin Holland
EMAIL ONLY Mr. Clay Loomis