20-102338-Geotechnical Report-06-09-2020-V1Earth Science + Technology
Geotechnical Engineering Services Report
Lakehaven Water and Sewer District
Maintenance Facility Improvements
Federal Way, Washington
for
Helix Design Group
June 9, 2020
Geotechnical Engineering Services Report
Lakehaven Water and Sewer District
Maintenance Facility Improvements
Federal Way, Washington
for
Helix Design Group
June 9, 2020
1101 South Fawcett Avenue, Suite 200
Tacoma, Washington 98402
253.383.4940
Geotechnical Engineering Services Report
Lakehaven Water and Sewer District
Maintenance Facility Improvements
Federal Way, Washington
File No. 4519-017-00
June 9, 2020
Prepared for:
Helix Design Group
6021 12th Street East, Suite 201
Tacoma, Washington 98424-1308
Attention: Jeff Blachowski
Prepared by:
GeoEngineers, Inc.
1101 South Fawcett Avenue, Suite 200
Tacoma, Washington 98402
253.383.4940
Stuart S. Thielman, PE
Geotechnical Engineer
Dennis (D.J.) Thompson, PE 6/9/2020
Associate
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Disclaimer: Any electronic form, facsimile or hard copy of the original document (email, text, table, and/or figure), if provided, and any attachments are only a
copy of the original document. The original document is stored by GeoEngineers, Inc. and will serve as the official document of record.
June 9, 2020| Page i
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Table of Contents
1.0 INTRODUCTION AND PROJECT UNDERSTANDING ........................................................................................ 1
2.0 SCOPE OF SERVICES ...................................................................................................................................... 1
3.0 SITE CONDITIONS ............................................................................................................................................ 2
3.1. Surface Conditions...................................................................................................................................... 2
3.2. Literature Review ........................................................................................................................................ 2
3.2.1. Geologic Setting .......................................................................................................................... 2
3.2.2. Natural Resources Conservation Service (NRCS) Description ................................................. 3
3.2.3. Well Log Review .......................................................................................................................... 3
3.3. Subsurface Conditions ............................................................................................................................... 3
3.3.1. Subsurface Explorations ............................................................................................................. 3
3.3.2. Surface Conditions...................................................................................................................... 4
3.3.3. Soil Conditions ............................................................................................................................ 4
3.3.4. Groundwater Conditions ............................................................................................................. 5
4.0 CONCLUSIONS AND RECOMMENDATIONS ................................................................................................... 6
4.1. General ........................................................................................................................................................ 6
4.2. Seismic Design Considerations .................................................................................................................. 7
4.2.1. Seismic Design Parameters ....................................................................................................... 7
4.3. Liquefaction, Lateral Spreading, and Surface Rupture ............................................................................ 7
4.3.1. Liquefaction................................................................................................................................. 7
4.3.2. Lateral Spreading Potential ........................................................................................................ 7
4.3.3. Surface Rupture Potential .......................................................................................................... 8
4.4. Site Development and Earthwork .............................................................................................................. 8
4.4.1. General ........................................................................................................................................ 8
4.4.2. Clearing and Stripping ................................................................................................................ 8
4.4.3. Erosion and Sedimentation Control ........................................................................................... 9
4.4.4. Temporary Excavations and Cut Slopes .................................................................................... 9
4.4.5. Permanent Cut and Fill Slopes ................................................................................................ 10
4.4.6. Temporary Groundwater Handling Considerations ................................................................ 10
4.4.7. Surface Drainage ..................................................................................................................... 11
4.4.8. Subgrade Preparation and Evaluation .................................................................................... 11
4.4.9. Subgrade Protection and Wet Weather Considerations ........................................................ 11
4.5. Fill Materials ............................................................................................................................................. 12
4.5.1. Structural Fill ............................................................................................................................ 12
4.5.2. Select Granular Fill .................................................................................................................. 12
4.5.3. Capillary Break ......................................................................................................................... 12
4.5.4. Crushed Surfacing ................................................................................................................... 13
4.5.5. Gravel Backfill for Walls and Drains ....................................................................................... 13
4.5.6. Pipe Bedding ............................................................................................................................ 13
4.5.7. Trench Backfill.......................................................................................................................... 13
4.5.8. Quarry Spalls ............................................................................................................................ 13
4.5.9. Recycled Materials ................................................................................................................... 13
4.5.10. On-Site Soil ............................................................................................................................... 14
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4.5.11. Topsoil Strippings ..................................................................................................................... 15
4.6. Fill Placement and Compaction .............................................................................................................. 15
4.6.1. General ..................................................................................................................................... 15
4.6.2. Area Fills and Pavement Bases .............................................................................................. 15
4.6.3. Backfill Behind Retaining Walls .............................................................................................. 15
4.6.4. Trench Backfill.......................................................................................................................... 15
4.6.5. Fill in Non-Structural Areas ...................................................................................................... 16
4.7. Shallow Foundations ............................................................................................................................... 16
4.7.1. General ..................................................................................................................................... 16
4.7.2. Footing Bearing Surface Overexcavation ............................................................................... 16
4.7.3. Footing Bearing Surface Preparation ..................................................................................... 17
4.7.4. Wet Weather Considerations .................................................................................................. 17
4.7.5. Foundation Design Parameters .............................................................................................. 17
4.7.6. Foundation Drains ................................................................................................................... 19
4.1. Slab-on-Grade Floors ............................................................................................................................... 20
4.1.1. General ..................................................................................................................................... 20
4.1.2. Slab-on-Grade Design Parameters ......................................................................................... 20
4.1.3. Underslab Drainage and Vapor Barrier .................................................................................. 20
4.2. Conventional Retaining Walls and Below Grade Structures ................................................................. 20
4.2.1. General ..................................................................................................................................... 20
4.2.2. Drainage ................................................................................................................................... 21
4.2.3. Design Parameters .................................................................................................................. 21
4.3. Retaining Wall at 1st Avenue South ........................................................................................................ 22
4.4. Stormwater Infiltration ............................................................................................................................. 23
4.4.1. General ..................................................................................................................................... 23
4.4.2. Stormwater Requirements ...................................................................................................... 23
4.4.3. Pilot Infiltration Tests ............................................................................................................... 24
4.4.4. Recommended Design Infiltration Rates ............................................................................... 26
4.4.5. Stormwater Treatment ............................................................................................................ 26
4.4.6. Discussion and Construction Considerations ........................................................................ 27
4.5. Asphalt Concrete Pavement Recommendations ................................................................................... 27
4.5.1. General Design Criteria ........................................................................................................... 27
4.5.2. Pavement Construction Considerations ................................................................................. 28
4.5.3. Asphalt Concrete Pavement Design ....................................................................................... 28
5.0 LIMITATIONS ................................................................................................................................................ 29
LIST OF FIGURES
Figure 1. Vicinity Map
Figure 2. Site Plan
Figures 3 and 4. PIT Results
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APPENDICES
Appendix A. Subsurface Explorations and Laboratory Testing
Figure A-1 – Key To Exploration Logs
Figures A-2 through A-7 – Logs of Borings
Figures A-8 and A-9 – Logs of Test Pits
Figure A-10 – Log of Hand Auger
Figures A-11 and A-12 – Sieve Analysis Results
Appendix B. Report Limitations and Guidelines for Use
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1.0 INTRODUCTION AND PROJECT UNDERSTANDING
This report presents the results of our geotechnical investigation and study performed for the Lakehaven
Water and Sewer District Maintenance Facility Improvements project located at 31627 1st Avenue South
in Federal Way, Washington. The approximate project boundaries are shown on the Vicinity Map, Figure 1.
Our understanding of the project is based on our discussions with members of the project team, which
includes Helix Design Group (project architect) and AHBL (project structural and civil engineer), and
provided project information, including a copy of recent architectural schematic design drawings prepared
by Helix Design Group and dated May 29, 2020.
The property is generally split into two areas and site development will be separated into two phases:
(1) Maintenance Facility (Phase 1 and Parcel 1) and (2) Oasis Area (Phase 2 and Parcel 2). The
Maintenance Facility occupies the southern area of the parcel and is the primary area of study for this
report. The Oasis Area consists of the northern portion of the parcel and occupies the remainder of the
property. The Oasis Area will be developed at a later date and is generally not a part of this study.
Overall Maintenance Facility improvements (Phase 1) consist of demolition or modification of existing
buildings, construction of new buildings and associated site improvements. Specifically, proposed
improvements include: demolition of the existing Administration and Lakehaven Center buildings and
construction of new Headquarters Administration Building (Building B1), Vehicle Storage Building
(Building B2), covered vehicle parking structure (Building B3), paved parking and driveway areas,
stormwater management infrastructure and off-site frontage improvements to 1st Avenue South. Existing
site access from 1st Avenue South will be maintained, driveway improvements will include construction of
sidewalk and retaining walls along the southern portion of driveway due to existing steep slopes.
Stormwater facilities at the site will be designed in accordance with the 2016 King County Surface Water
Design Manual (SWDM), which has been adopted by the City of Federal Way (City). Currently proposed
layouts of the new buildings are shown on the Site Plan, Figure 2. We understand preferred foundation
type for the proposed buildings is shallow foundations and slab-on-grade, with finish floor elevation
between approximately Elevation 334 and 337 feet. Elevations referenced in the provided drawings are
referenced to the North American Vertical Datum of 1988 (NAVD88). Accordingly, elevations referenced
within this report refer to NAVD88 and should be considered approximate.
2.0 SCOPE OF SERVICES
The purpose of our services is to evaluate subsurface conditions and provide geotechnical and earthwork
recommendations to support planning, design and construction of the proposed improvements. Our
specific scope of services can be reviewed in our agreement dated September 19, 2019 and signed
January 13, 2020.
Initial data from the Washington State Department of Ecology (Ecology) indicates the subject property is
located within and subject to the Tacoma Smelter Plume Model Remedies Map and Guidelines. We have
completed initial soil sampling at the site to address this issue, in accordance with our environmental
services scope (Tacoma Smelter Plume Sampling) included in our existing agreement. Our environmental
services and results will be provided in a separate report for this project. Please refer to the full
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environmental report, when it is available, for additional information that may affect site layout, design
and construction.
3.0 SITE CONDITIONS
3.1. Surface Conditions
The Lakehaven Water and Sewer District property consists of King County parcel number 0721049017
(denoted as Parcel 1 on provided project documents), totaling approximately 12 acres in area. The
property is generally bound by single- and multi-family residential housing developments to the north,
west and south and 1st Avenue South to the east.
Nearby properties in the project vicinity generally consist of single- and multi-family residential housing
developments. South King Fire and Rescue Station 62 (denoted as Parcel 3 on provided project
documents) is located just west of the existing maintenance facility, between the existing water shop
building and 1st Avenue South. French Lake Off-Leash Dog Park is located just northwest of the
maintenance facility.
The existing Maintenance Facility and proposed site development area occupies the southern area of the
parcel and totals approximately 7.6 acres. The existing facility generally consists of three structures:
(1) an approximate 7,440-square-foot two-story masonry Administration Building in the eastern portion of
the project area, (2) an approximate 760-square-foot wood-frame Maintenance Building located in the
northwest project area and (3) an approximate 15,000-square-foot masonry Watershop Building (Building
B4) in the western project area. Asphalt paved parking and driveway areas surround the existing
structures and provide access to 1st Avenue South.
The approximate southern 3.3 acres of the project area is undeveloped. The eastern site boundary
(adjacent to 1st Avenue South) is delineated as a wetland area. The remainder of this undeveloped area is
densely vegetated with brush and deciduous trees up to approximately 12 inches in diameter. The north-
central portion of this undeveloped area (just south of the existing pavement) consists of a grass lawn
area approximately 0.3 acres in size.
Based on survey included with the provided project drawings site grades vary between about Elevation
319 feet in the wetland adjacent to 1st Avenue South and as high as about Elevation 342 feet in the
undeveloped southern portion of the project area. Site grades for currently developed areas of the
existing maintenance facility generally increase from about Elevation 328 at the 1st Avenue South
driveway to Elevation 338 near Building B3.
3.2. Literature Review
3.2.1. Geologic Setting
We reviewed relevant in-house files and readily available geologic maps, including the Geologic Map of
King County (Booth, Troost and Wisher 2007) and the Geologic Map of the Poverty Bay 7.5’ Quadrangle,
Washington (Booth, Waldron and Troost 2004). According to both geologic maps, the site is underlain by
glacial till deposits (Qvt). Glacial till is typically described as an unstratified and very compact mixture of
clay, silt, sand and gravel deposited below glacial ice.
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Recessional outwash (Qvr) and occasional wetland (Qw) deposits are mapped to the west of the project
site. Glacial outwash soils are deposited by meltwater at the terminus of an advancing/receding glacier.
Recessional glacial outwash is typically described as variably sorted silt, clay, sand and gravel and is
typically less compact than underlying glacial till.
3.2.2. Natural Resources Conservation Service (NRCS) Description
According to the Natural Resources Conservation Service (NRCS) Web Soil Survey (accessed February 20,
2020), the site is underlain by Alderwood gravelly sandy loam (AgB and AgC). The literature describes
Alderwood soils as “nearly level to rolling, moderately well drained and somewhat excessively drained
soils that formed in glacial till and glacial outwash” and commonly found in upland areas. The literature
also describes these soils as having a weakly cemented substratum and are labeled “very slowly”
regarding permeability.
Seattle muck (Sk) and Shalcar muck (Sm) are occasionally mapped in the project vicinity, within what
appear to be low-lying wetland areas. Muck deposits are generally described as very poorly drained
organic-rich soils formed in decaying plant remains and alluvium within ponded basins.
3.2.3. Well Log Review
We reviewed readily available online boring and well logs from the Washington State Department of
Ecology (Ecology), Washington State Department of Natural Resources (DNR), Washington State
Department of Transportation (WSDOT) and United States Geological Survey (USGS) National Water
Information System (NWIS) for soil and groundwater information in the project vicinity.
Our review included four well logs and one groundwater site within ½ mile of the project site. Soil
conditions in the reviewed well logs are typically noted as “till” to depths of about 100 feet. The logs
include measured static groundwater levels between about 63 and 196 feet below top of well
(approximate Elevation 201 to 226 feet where ground surface elevations are provided). We also reviewed
available data from a USGS groundwater monitoring site, which appears to be located at the project site.
Eight groundwater readings are provided between 1979 and 2019, with groundwater measurements
between about Elevation 195 and 235 feet.
3.3. Subsurface Conditions
3.3.1. Subsurface Explorations
We explored subsurface conditions at the site by advancing six borings (designated B-1 through B-6), two
test pits (PIT-1 and PIT-2) and one hand auger (HA-1) at the approximate locations shown on Site Plan,
Figure 2. Explorations were completed between January 27 and February 11, 2020. The borings were
advanced to depths ranging from about 10.5 feet to 26.5 feet below existing ground surface (bgs). Test
pits were advanced to depths of approximately 12.5 and 17.5 feet bgs. Details regarding our subsurface
exploration program are provided in Appendix A. A key to the explorations logs is presented as Figure A-1
and summary logs are presented as Figure A-2 through Figure A-10.
Selected samples from the explorations were tested in the laboratory to evaluate engineering properties
and to confirm or modify field classifications. Our testing program consisted of particle-size gradation
analyses (sieves), percent fines content determinations, moisture content determinations, cation
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exchange capacity (CEC) analyses and organic content (OC) determinations. Details and the results of our
laboratory testing program are provided in Appendix A.
3.3.2. Surface Conditions
Four explorations (B-1, B-5, PIT-1 and PIT-2) were located in the existing grass lawn area just south of the
existing paved parking areas (north-central portion of the undeveloped project area). Immediate surface
conditions in the lawn area consisted of approximately 1 to 2 inches sod.
Three explorations (B-2 through B-4) were located with paved asphalt parking areas. Surface conditions
at paved areas consisted of approximately 2 inches asphalt concrete. We did not observe imported base
course material underlying the asphalt at the boring locations.
One exploration (B-6) was located just outside the curb area southeast of the existing Administration
Building. Surface soils consisted of approximately 3 inches forest duff.
One exploration (HA-1) was located adjacent to 1st Avenue South, mid-slope between the roadway and
wetland area. Surface conditions consisted of about 1 inch forest duff.
3.3.3. Soil Conditions
We observed what we interpret to be two general geologic units in our explorations, fill and glacial till
deposits. Brief descriptions of each soil unit observed in our explorations are provided below.
3.3.3.1. Fill
Due to relatively low blow counts during drilling, relatively low densities observed during test pit
excavations and our observations of soil type and organic matter, we interpret fill soils to be present at six
of the nine explorations locations (B-1, B-2, B-5, PIT-1, PIT-2 and HA-1). Fill soils generally consisted of
loose to medium dense silty sand and soft sandy silt. Variable gravel, cobble and organic material (roots
and wood debris) were also observed. Based on our observations, fill soils appear to consist of reworked
glacial till soils.
As described above, four explorations (B-1, B-5, PIT-1 and PIT-2) were located in the existing grass lawn
area just south of the paved parking. Fill soils at these locations were encountered to depths between
approximately 8.5 and 15.5 feet bgs (Elevation 332 to 324.5 feet). Organic-rich soils were observed
within three of the four explorations (B-5, PIT-1 and PIT-2) at depth, generally within about 1 to 2 feet of
the contact between the fill and underlying glacial till soils. Organics generally consisted of roots and
wood fragments up to about 1 inch in diameter. Based on our interpretation of soil type and likely
construction sequencing of the existing facility, we interpret these organic-rich soils to be topsoil and
vegetation from previous site clearing and grading activities.
Boring B-2 was located in paved parking area just north of the existing Building B3. Fill at this location
was observed to a depth of about 4.5 feet bgs.
Occasional asphalt concrete debris was also observed in HA-1, likely related to construction of the
roadway or subsequent utility trench backfill. Fill at this location was observed to the full depth explored,
approximately 1.75 feet bgs.
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3.3.3.2. Glacial Till
Soils we interpret to be undisturbed glacial till were noted in eight out of nine explorations (with the
exception of HA-1) underlying the surficial soils and/or fill described above. Glacial till typically consisted
of silty sand with variable gravel and cobble content. The upper 2 to 7 feet of till was generally brown to
gray and loose to medium dense, indicating a weathered condition. Glacial till graded to more gray and
very dense at depth, indicating an intact condition.
With the exception of HA-1, explorations were terminated within intact glacial till deposits at depths
between approximately 10.5 to 26.5 feet bgs.
3.3.4. Groundwater Conditions
We did not observe what we interpret to be static groundwater in our borings, which were terminated at
depths between 10.5 and 26.5 bgs (approximate Elevation 304.5 to Elevation 327 feet). Wet soils were
observed in five explorations (B-3, B-5, B-6, PIT-1 and PIT-2). In PIT-1 and PIT-2, slow groundwater
seepage, less than 1 gallon per minute, was observed entering the open test pit excavations at depths of
8.5 and 15 feet bgs, respectively. The observed wet soils and groundwater seepage were encountered
near the location of intact glacial till soils. We also observed occasional soil coloring and iron-oxide
staining in many of the explorations (as noted in the logs), which is an indication of presence of
groundwater seepage at various times of the year.
We interpret the water and groundwater seepage observed in our explorations to be intermittent seepage
of shallow perched groundwater from surface water infiltration present on top of the intact glacial till. It is
common for perched groundwater to be present near contacts where soil that is more permeable overlies
soil that is less permeable (i.e., fill or weathered glacial till over intact glacial till). The presence of perched
groundwater at the site is expected to occur from infiltration of surface water during rain events and is
expected to be discontinuous and intermittent. The amount of perched groundwater encountered will vary
depending on a variety of conditions including season, irrigation activities, installation of hardscaping and
rainfall events. We anticipate the likelihood for encountering perched groundwater will be lowest during
the dryer months of the year, typically between June and September in this region.
Based on our observations during subsurface explorations, our review of published groundwater data in
the area and our experience, it is our opinion regional static groundwater levels at the project site will not
come higher than the bottom of our explorations (as low as Elevation 305 feet) and are likely much
deeper; on the order of 100 feet or more bgs.
Groundwater levels, especially shallow perched groundwater, can fluctuate depending on soil conditions,
rainfall amounts, irrigation activities and other factors. Site grading, especially utility cuts into glacially
consolidated deposits that are backfilled with more permeable imported sands and gravels, can also
affect the quantity and location of perched groundwater. We anticipate the presence of shallow perched
groundwater and its location will generally be highest during the wet season, typically October through
May in western Washington.
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4.0 CONCLUSIONS AND RECOMMENDATIONS
4.1. General
Based on our understanding of the project, the explorations performed for this study and our experience,
it is our opinion that the proposed improvements can be constructed generally as envisioned with regard
to geotechnical considerations. A summary of the primary geotechnical considerations for the project is
provided below and is followed by our detailed recommendations.
■ For the purposes of design, we have identified two soil units in the area of the proposed
improvements: fill consisting of reworked glacial till underlain by undisturbed glacial till.
Fill depths vary across the site, but generally appear to be thickest in the area of the existing
grass lawn in the south-central portion of the project area.
Organic-rich soils are also present at the site, notably near the bottom of fill in the grass lawn
area and in wetland areas. If these soils are encountered during construction, additional
recommendations than those presented in this report may be required.
■ We anticipate perched groundwater may be encountered during site excavations and grading
depending on time of year. Intermittent perched groundwater should be able to be adequately
managed through the use of sumps, pumps and other shallow groundwater handling techniques
typically used in construction. We did not observe what we interpret to be regional groundwater in our
explorations. Based on our review of nearby boring and well logs, we anticipate regional groundwater
levels are greater than 100 feet bgs.
■ The site soils encountered in our explorations contain a significant percentage of fines (material
passing the U.S. No. 200 sieve). Soil with a higher fines content is more sensitive to small changes in
moisture content and may be difficult, if not impossible, to work and compact during wet weather
conditions. This material can also be susceptible to disturbance when wet or if earthwork is
performed during wet weather. Scheduling earthwork during periods of dry weather can lead to more
efficient management of on-site soil.
■ In our opinion shallow foundation support of the proposed structures is feasible. Loose fill was
encountered in the southern portion of the property, within the existing grass lawn. Due to the
potential for excessive differential settlement and potentially long-term settlement related to
consolidation and decomposition of the organic-rich soils observed, we recommend foundations not
bear directly on these relatively loose soils without improvements.
One option to reduce the risk of differential settlement is to overexcavate and replace
existing fill soils below foundations, depending on final foundation locations and elevations.
This option is discussed further in this report.
Alternatively, deep foundations (such as micropiles) or ground improvement (such as stone
columns or aggregate piers) may be more efficient for design to provide increased allowable
bearing pressures and mitigate the risk of settlements. Alternative foundation options are not
included as part of this report. We can provide additional recommendations upon request.
■ Due to the composition of on-site soils (dense fine-grained glacial till) and the presence of
groundwater seepage (which exceeded the infiltration rate of the soils), infiltration rates could not be
recorded in the PITs. Based on our observations, testing and experience with similar soils, it is our
opinion infiltration through intact glacial till soils at the site is generally infeasible.
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4.2. Seismic Design Considerations
4.2.1. Seismic Design Parameters
We understand seismic design of proposed structures will be performed using procedures outlined in the
2018 International Building Code (IBC). The 2018 IBC states structures shall be designed and
constructed to resist the effects of earthquake motions in accordance with American Society of Civil
Engineers (ASCE) 7-16.
We used map-based values available online as recommended by the USGS to determine the seismic
design spectrum in accordance with ASCE 7-16. Based on conditions observed in our explorations, our
review of geologic maps and our experience in the area, we anticipate soils below our explorations and
extending to depth are glacially consolidated and dense to very dense. For seismic design and analysis,
we recommend using a response spectrum for Site Class C. We recommend the parameters provided in
Table 1 below be used for design.
TABLE 1. SEISMIC DESIGN CRITERIA
2018 IBC (ASCE 7-16) Seismic Design Parameters
Spectral Response Acceleration at Short Periods (SS) 1.339g
Spectral Response Acceleration at 1-Second Periods (S1) 0.46g
Site Class C
Design Peak Ground Acceleration (PGAM) 0.679g
Design Spectral Response Acceleration at Short Periods (SDS) 1.071 g
Design Spectral Response Acceleration at 1-Second Periods (SD1) 0.46g
4.3. Liquefaction, Lateral Spreading, and Surface Rupture
4.3.1. Liquefaction
Liquefaction refers to a condition where vibration or shaking of the ground, usually from earthquake
forces, results in development of excess pore pressures in loose, saturated soils and subsequent loss of
strength in the deposit of soil so affected. In general, soils that are susceptible to liquefaction include
loose to medium dense sands to silty sands that are below the water table.
We reviewed readily available liquefaction susceptibility maps, including the Liquefaction Susceptibility
Map of King County, Washington (Palmer et al. 2004). According to the reviewed maps, the potential for
liquefaction at this site is very low. Based on the soil types and relative densities observed in our
explorations and our interpretation of the regional geology and groundwater table, it is also our opinion
the potential for liquefaction at this site is very low.
4.3.2. Lateral Spreading Potential
Lateral spreading related to seismic activity typically involves lateral displacement of large, surficial
blocks of non-liquefied soil when a layer of underlying soil loses strength during seismic shaking. Lateral
spreading usually develops in areas where sloping ground or large grade changes (including retaining
walls) are present. Based on our understanding of the proposed improvements and site grading,
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subsurface conditions, liquefaction risk and current site topography, it is our opinion that the risk of
lateral spreading is low.
4.3.3. Surface Rupture Potential
According to the Washington State DNR Interactive Natural Hazards Map (accessed February 20, 2020),
the nearest known seismogenic fault or fold is the Tacoma Fault zone, which is mapped approximately
1 mile from the project site. The Tacoma fault is designated a “Class-B” fault, indicating seismic activity is
suspected within the past 10,000 years. Paleoseismologic studies indicate the last event occurred
approximately 1,000 years ago. Information regarding recurrence interval and potential magnitude are
not available. Location of the Tacoma fault zone has been inferred from geophysical studies and there
are no known surface expressions of the fault. In addition, bedrock in the project area is covered by
several hundred feet of glacial soils. Based on this information, it is our opinion the risk for seismic
surface rupture at the site is low.
4.4. Site Development and Earthwork
4.4.1. General
We anticipate site development and earthwork will include clearing and stripping vegetated areas;
demolition of existing hardscaping; site grading; establishing subgrades for driveways, parking areas and
building foundations; and placing and compacting fill and backfill materials. We expect that the majority
of site grading and earthwork can be accomplished with conventional earthmoving equipment.
The following sections provide recommendations for stripping, erosion and sedimentation control,
excavation, temporary and permanent cut slopes, wet weather considerations, fill materials and fill
placement and compaction requirements.
4.4.2. Clearing and Stripping
Based on conditions observed in our explorations, minimum stripping depths at the site will likely be on
the order of 3 inches to remove organic-laden soil, topsoil, and sod, where located on site. However,
greater stripping depths could be required to remove localized zones of loose or organic-rich soil,
especially in areas of the site currently planted with trees and where fill is present in the south portion of
the site. During clearing and stripping, stumps and primary root systems of shrubs and trees should be
completely removed. Voids caused by removal of stumps and/or root systems should be backfilled with
compacted structural fill. Stripped material should be transported off site or processed and used as fill in
landscaping areas.
Based on our explorations, we anticipate that soils exposed will have a high fines content and thus be
susceptible to disturbance when wet. Care should be taken to avoid allowing these soils to become
saturated and disturbed. We provide recommendations for subgrade protection in Section 4.4.9
“Subgrade Protection and Wet Weather Considerations” of this report.
Cobbles were occasionally encountered in our explorations. In our experience, cobbles and boulders are
present in glacial deposits in the area. The contractor should be prepared for the presence of cobbles
and/or boulders in areas to be excavated or re-graded. Additionally, the contractor should be prepared to
separate cobbles and boulders from soils generated during excavation if excavated soils are to be reused
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as fill or backfill. Boulders may be removed from the site or used in landscape areas. Voids caused by
boulder removal should be backfilled with structural fill.
Structural elements of existing pavements and/or structures should be demolished and removed from
within the footprint of the proposed improvements. During demolition, excessive disturbance of surficial
soils may occur, especially if left exposed to wet conditions. Disturbed soils may require additional
remediation during construction and grading.
4.4.3. Erosion and Sedimentation Control
Erosion and sedimentation rates and quantities can be influenced by construction methods, slope length
and gradient, amount of soil exposed and/or disturbed, soil type, construction sequencing and weather.
Implementing an erosion and sedimentation control plan will reduce the project impact on erosion-prone
areas. The plan should be designed in accordance with applicable city, county and/or state standards.
The plan should incorporate basic planning principles, including:
■ Scheduling grading and construction to reduce soil exposure.
■ Re-vegetating or mulching denuded areas.
■ Directing runoff away from exposed soils.
■ Reducing the length and steepness of slopes with exposed soils.
■ Decreasing runoff velocities.
■ Preparing drainage ways and outlets to handle concentrated or increased runoff.
■ Confining sediment to the project site.
■ Inspecting and maintaining control measures frequently.
Some sloughing and raveling of exposed or disturbed soil on slopes should be expected. We recommend
that disturbed soil be restored promptly so that surface runoff does not become channeled.
Temporary erosion protection should be used and maintained in areas with exposed or disturbed soils to
help reduce erosion and reduce transport of sediment to adjacent areas and receiving waters. Permanent
erosion protection should be provided by paving, structure construction or landscape planting.
Until the permanent erosion protection is established and the site is stabilized, site monitoring may be
required by qualified personnel to evaluate the effectiveness of the erosion control measures and to
repair and/or modify them as appropriate. Provision for modifications to the erosion control system based
on monitoring observations should be included in the Erosion and Sedimentation Control Plan.
4.4.4. Temporary Excavations and Cut Slopes
Excavations deeper than 4 feet should be shored or laid back at a stable slope if workers are required to
enter. Shoring and temporary slope inclinations must conform to the provisions of Title 296 Washington
Administrative Code (WAC), Part N, “Excavation, Trenching and Shoring.” Regardless of the soil type
encountered in the excavation, shoring, trench boxes or sloped sidewalls will be required under
Washington Industrial Safety and Health Act (WISHA). The contract documents should specify that the
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contractor is responsible for selecting excavation and dewatering methods, monitoring the excavations
for safety and providing shoring, as required, to protect personnel and structures.
In general, temporary cut slopes should be inclined no steeper than about 1.5H:1V (horizontal to vertical).
Steeper slopes, on the order of 1H:1V may be attainable in the dense, undisturbed glacial till soils and
should be considered on a case-by-case basis with our review. These guidelines assume all surface loads
are kept a minimum distance of at least one-half the depth of the cut away from the top of the slope and
seepage is not present on the slope face. Flatter cut slopes will be necessary where seepage occurs or if
surcharge loads are anticipated. Temporary covering with heavy plastic sheeting should be used to
protect these slopes during periods of wet weather.
4.4.5. Permanent Cut and Fill Slopes
We recommend permanent slopes be constructed at a maximum inclination of 2H:1V. Where 2H:1V
permanent slopes are not feasible, protective facings and/or retaining structures should be considered.
This guideline assumes all surface loads are kept at a minimum distance of at least one-half the height of
the slope away from the top of the slope and seepage is not present on the slope face. Flatter cut slopes
or additional drainage measures could be necessary where seepage occurs or if surface surcharge loads
are anticipated.
To achieve uniform compaction, we recommend that fill slopes be overbuilt and subsequently cut back to
expose well-compacted fill. Fill placement on slopes steeper than 5H:1V should be benched into the slope
face. The configuration of benches depends on the equipment being used and inclination of the existing
slope. Bench excavations should be level and extend into the slope face at least half the width of the
compaction equipment used.
Exposed areas should be re-vegetated as soon as practical to reduce the surface erosion and sloughing.
Temporary protection should be used until permanent protection is established.
4.4.6. Temporary Groundwater Handling Considerations
We did not encounter what we interpret to be static groundwater in our explorations. Indications of
groundwater in our explorations appear to be consistent with perched groundwater, as previously
discussed in Section “3.3.4 Groundwater Conditions” of this report. Based on our explorations and review
of available data in the project area, we do not expect static groundwater to be a significant factor during
shallow excavations and earthwork activities.
We expect some perched groundwater could be encountered depending on the time of year of
construction. Perched groundwater is likely near contacts where soil that is more permeable overlies soil
that is less permeable (e.g., fill or weathered glacial till overlying intact glacial till).
Groundwater handling needs will typically be lower during the late summer and early fall months. We
anticipate shallow perched groundwater can typically be handled adequately with sumps, pumps and/or
diversion ditches, as necessary. Perched groundwater at relatively shallow depths is typically surface
water that has recently infiltrated nearby. Proactive handling of surface water (e.g., grading to reduce
ponding) can reduce groundwater handling needs. Ultimately, we recommend the contractor performing
the work be made responsible for controlling and collecting groundwater encountered.
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4.4.7. Surface Drainage
Surface water should be collected and controlled. Curbs or other appropriate measures such as sloping
pavements, sidewalks and landscape areas should be used to direct surface flow away from subgrades,
excavations, erosion sensitive areas and from behind retaining structures. Roof and catchment drains
should not be connected to wall or foundation drains.
4.4.8. Subgrade Preparation and Evaluation
Subgrades that will support structural fill, structures and/or paving should be thoroughly compacted to a
uniformly firm and unyielding condition on completion of stripping and demolition, prior to placing fill or
structures. We recommend subgrades be evaluated to identify areas of yielding or soft soil. Evaluation
methods such as probing with a steel probe rod or proof-rolling with a heavy piece of wheeled
construction equipment are appropriate methods of evaluation.
If soft or otherwise unsuitable subgrade areas are revealed during evaluation that cannot be compacted
to a stable and uniformly firm condition, we recommend: (1) the unsuitable soils be scarified (e.g., with a
ripper or farmer’s disc), aerated and recompacted, if practical; or (2) the unsuitable soils be removed and
replaced with compacted structural fill, as needed.
Specific recommendations for bearing surface and pavement subgrade preparation are also provided in
this report.
4.4.9. Subgrade Protection and Wet Weather Considerations
The soils encountered in our explorations contain a significant amount of fines and will be susceptible to
disturbance during periods of wet weather. Soil with high fines content is very sensitive to small changes
in moisture and is susceptible to disturbance from construction traffic when wet or if earthwork is
performed during wet weather. The wet weather season generally begins in October and continues
through May in western Washington; however, periods of wet weather can occur during any month of the
year. In our opinion, earthwork will be most efficient during the summer months or during periods of
extended dry weather. If wet weather earthwork is unavoidable, we recommend that the following steps
be taken.
■ The ground surface in and around the work area should be sloped so that surface water is directed
away from the work area. The ground surface should be graded so that areas of ponded water do not
develop. Measures should be taken by the contractor to prevent surface water from collecting in
excavations and trenches. Measures should be implemented to remove surface water from the work
area.
■ Earthwork activities should not take place during periods of heavy precipitation.
■ Slopes with exposed soils should be covered with plastic sheeting.
■ The contractor should take necessary measures to prevent on-site soils and other soils to be used as
fill from becoming wet or unstable. These measures may include the use of plastic sheeting, sumps
with pumps and grading. The site soils should not be left uncompacted and exposed to moisture.
Sealing the exposed soils by rolling with a smooth-drum roller or other appropriate compaction
equipment prior to periods of precipitation will help reduce the extent to which these soils become
wet or unstable.
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■ Construction traffic should be restricted to specific areas of the site, preferably areas that are
surfaced with working pad materials not susceptible to wet weather disturbance.
■ Construction activities should be scheduled so that the length of time that soils are left exposed to
moisture is reduced to the extent practical.
■ Protective surfacing such as placing asphalt-treated base (ATB), cement treated subgrades, or haul
roads made of quarry spalls or a layer of free-draining material such as well-graded pit-run sand and
gravel may be necessary to protect completed areas from construction traffic. Typically, minimum
gravel thicknesses on the order of 18 inches are necessary to provide adequate subgrade protection
for repeated construction traffic. Maintaining the existing asphalt surfacing is also an adequate
method of protection; however, asphalt could become distressed and may need repairs depending on
the amount of heavy truck traffic.
■ Foundation bearing surface protection should also be considered. We provide additional
recommendations in Section 4.7 “Shallow Foundations” of this report.
4.5. Fill Materials
Our recommendations on various earthwork materials for use on site are presented below. We
recommend GeoEngineers review contractor submittals for earthwork materials to be used on site.
4.5.1. Structural Fill
Material used for structural fill should be free of rock fragments larger than 6 inches in maximum
dimension, debris and organics. As the percentage of fines increases, fill materials become increasingly
sensitive to changes in moisture. Typically, soil containing more than about 5 percent fines becomes
more sensitive to changes in moisture and will become difficult to compact when just a few percent
above the optimum moisture content.
For imported material, we recommend crushed rock or select granular fill (described below) be used for
structural fill during the wet season. If prolonged dry weather prevails during the earthwork phase of
construction, materials with a somewhat higher fines content such as “Select Borrow” or “Gravel Borrow”
as described in Section 9-03.14 of the 2020 WSDOT Standard Specifications may be acceptable.
4.5.2. Select Granular Fill
Select granular fill should consist of well-graded sand and gravel or crushed rock with a maximum particle
size of 6 inches and less than 5 percent fines by weight based on the minus ¾-inch fraction. Organic
matter, debris or other deleterious material should not be present. In our opinion, material with gradation
characteristics similar to 2020 WSDOT Specification 9-03.9 “Aggregates for Ballast and Crushed
Surfacing”, or 9-03.14 “Borrow” is suitable for use as select granular fill, with the additional requirement
that the fines content is limited as described above and the exception that the maximum particle size can
be up to 6 inches.
4.5.3. Capillary Break
Capillary break material should consist of a well-graded sand and gravel, crushed rock or washed rock
with a maximum particle size of ¾ inch and less than 5 percent fines. Alternatively, 1¼-inch minus base
course in accordance with WSDOT Specification 9-03.9 “Aggregates for Ballast and Crushed Surfacing”
may also be considered.
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4.5.4. Crushed Surfacing
Crushed surfacing base course (CSBC) and crushed surfacing top course (CSTC) should conform to
applicable sections of 4-04 and 9-03.9(3) of the 2020 WSDOT Standard Specifications.
4.5.5. Gravel Backfill for Walls and Drains
We recommend material used for footing drains and in wall drainage zones be of approximately the same
quality as 2020 WSDOT Standard Specification 9-03.12(2) “Gravel Backfill for Walls”. Alternative
materials, such as washed rock, may also be considered provided the fines content is limited to that
similar to “Gravel Backfill for Walls.”
4.5.6. Pipe Bedding
Trench backfill for the bedding and pipe zone should consist of well-graded granular material similar to
2020 WSDOT Standard Specification 9-03.12(3) “Gravel Backfill for Pipe Zone Bedding”. The material
must be free of roots, debris, organic matter and other deleterious material. Other materials may be
required depending on pipe manufacturer specifications and/or jurisdictional requirements where utilities
extend off the property and into the public right-of-way.
4.5.7. Trench Backfill
On-site soils can be considered for trench backfill as discussed below. Trench backfill must be free of
debris, organic material and rock fragments larger than 6 inches. Imported trench backfill material may
be required if material generated from the trench excavation is above optimum moisture content and
cannot be dried out. We recommend imported trench backfill material consist of material similar to 2020
WSDOT Standard Specification 9-03.14 “Gravel Borrow” or “Select Borrow”. During wet weather, select
granular fill may be required as trench backfill. Deeper excavations close to or below groundwater
seepage may require other backfill materials and base stabilization materials such as a clean ballast
and/or quarry spalls, which are relatively self-compacting.
Pipe manufacturer and jurisdictional requirements should also be considered when choosing trench
backfill material.
4.5.8. Quarry Spalls
We recommend that quarry spalls consist of 2- to 4-inch washed, crushed stone similar to that described
in Section 9-13 of the 2020 WSDOT Standard Specifications. Alternative stone size ranges may be
considered, depending on the application.
4.5.9. Recycled Materials
In our opinion, recycled material (such as existing asphalt and concrete) may be considered as fill
material on site provided the material is in accordance with 2020 WSDOT Standard Specification 9-03.21
“Recycled Material” and meets requirements for its end use. Recycled asphalt should not be considered
for use within building areas or below foundations. We recommend we review material submittals prior to
using recycled materials on site. The use of recycled asphalt and/or concrete may also need approval for
use from the City or other jurisdictional authority in regard to metals content.
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Recycled materials may be blended, provided the recycled material component included in a blended
product meets the specification requirements for the specified material. We recommend the amount of
recycled material generally not exceed percentages presented in WSDOT Specification Table 9-03.21(1)E.
Higher percentages may be allowed on a case-by-case basis and can be accepted or rejected in the field
during construction based on quality and performance. Blending may be achieved as recycled material is
processed in-place, windrowing with a bulldozer, or other suitable methods.
For instance, WSDOT Specification Table 9-03.21(1)E allows a maximum 25 percent by weight of hot mix
asphalt for recycled material to be used as “Gravel Borrow”. Accordingly, we recommend a 3-inch thick
section of hot mix asphalt be blended with about 9 inches of aggregate. The final blended product
(including the hot mix asphalt component) shall meet the specification requirements for “Gravel Borrow”.
4.5.10. On-Site Soil
Based on our experience, the silty soils encountered in our explorations are moisture sensitive and will be
very difficult or impossible to properly compact when wet. In addition, it is possible existing soils will be
excavated at moisture contents above optimum moisture content. In our experience undisturbed glacial
till is often at or near the optimum moisture content when first excavated. Once disturbed it can quickly
become wet and over the optimum moisture content. In addition, soils located just above the glacial till in
the perched groundwater zone are more likely to have moisture contents above optimum. For reference,
moisture content test results are presented on the boring logs for selected samples from our
explorations.
In general, on-site soils can be considered for use as structural fill and trench backfill provided that the
material:
■ Is used during extended periods of dry weather,
■ Can be adequately moisture conditioned and placed and compacted as recommended in this report,
■ Does not contain organic or other deleterious material, and
■ Meets any special requirements related to its end use
If earthwork occurs during a typical wet season, or if the soils are persistently wet and cannot be dried
back to near optimum due to prevailing wet weather conditions, we recommend the use of imported
structural fill or select granular fill as described above. Budgets should include provisions for import
granular fill, especially if construction is planned during the wet weather season.
Depending on the cut-fill balance at the site it may be necessary to import structural fill material in
addition to using fill soils generated at the site. If this is the case, we recommend existing site soils be
reserved for use as fill in non-structural areas or as the initial lifts in structural areas. If practical, imported
structural fill should be reserved for use below footings and when near design subgrade within structural
areas.
Additional considerations for use of on-site material should include review of our environmental report
and the presence of heavy metal soils contamination in the form of lead and arsenic. Please refer to our
full environmental report, when it is available, during site layout and design and prior to beginning any
earthwork activities and determination on the use of on-site material as fill.
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4.5.11. Topsoil Strippings
Topsoil strippings may be placed on site provided they are placed in non-structural areas that can tolerate
significant long-term total and differential settlements. Settlements of organic-rich soils are highly
variable and difficult to quantify. Settlement could continue for several years after construction is
completed as the organics break down and decompose. Alternatively, topsoil strippings can be hauled off
site.
4.6. Fill Placement and Compaction
4.6.1. General
To obtain proper compaction, fill material should be compacted near optimum moisture content and in
uniform horizontal lifts. Lift thickness and compaction procedures will depend on the moisture content
and gradation characteristics of the soil and the type of equipment used. The maximum allowable
moisture content varies with the soil gradation and should be evaluated during construction. Compaction
should be achieved by mechanical means. In general, 12-inch-thick loose lifts are appropriate for steel-
drum vibratory roller compaction equipment. During fill and backfill placement, regular testing of in-place
density should be conducted to verify adequate compaction is being achieved.
4.6.2. Area Fills and Pavement Bases
Fill placed to raise site grades and materials under pavements and structural areas should be placed on
subgrades prepared as previously recommended. Fill material placed below structures and footings must
be compacted to at least 95 percent of the theoretical maximum dry density (MDD) per ASTM
International (ASTM) D 1557. Fill material placed less than 2 feet below pavement sections must be
compacted to at least 95 percent of the MDD. Fill placed deeper than 2 feet below pavement sections
must be compacted to at least 90 percent of the MDD. Fill material placed in landscaping areas should
be compacted to a firm condition that will support construction equipment, as necessary, typically around
85 to 90 percent of the MDD.
4.6.3. Backfill Behind Retaining Walls
Backfill behind retaining walls should be compacted to between 90 and 92 percent of the MDD.
Overcompaction of fill placed directly behind retaining walls should be avoided. We recommend use of
hand-operated compaction equipment and maximum 6-inch loose lift thickness when compacting fill
within about 5 feet behind retaining walls.
4.6.4. Trench Backfill
For utility excavations, we recommend the initial lift of fill over the pipe be thick enough to reduce the
potential for damage during compaction but generally should not be greater than about 18 inches. In
addition, rock fragments greater than about 1 inch in maximum dimension should be excluded from this
lift.
Trench backfill material placed below structures and footings must be compacted to at least 95 percent
of the MDD. In paved areas, trench backfill must be compacted to at least 95 percent of the MDD in the
upper 2 feet below subgrade. Fill placed below a depth of 2 feet from subgrade in paved areas must be
compacted to at least 90 percent of the MDD. In non-structural areas, trench backfill should be
compacted to a firm condition that will support construction equipment as necessary.
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4.6.5. Fill in Non-Structural Areas
4.6.5.1. General
Areas that will not support buildings or pavements and can tolerate moderate total and differential
settlements will not require structural fill. To limit long-term settlements that could affect site drainage,
we recommend fill placed in these non-structural areas be compacted to at least 85 to 90 percent of the
MDD and generally contain no more than 10 percent organic material by weight.
4.6.5.2. Topsoil Strippings
If topsoil strippings are placed in on-site excavations, the sidewalls of the excavation should be sloped at
3H:1V or flatter. This will help provide a transition between the thick layer of compressible soil in the
center of the excavation and the on-site soil surrounding the excavation. Similarly, the top of the fill
should be crowned to allow for future settlement.
Organic soils should be placed in moderate lifts and tracked or back-bladed into place with a bulldozer or
similar equipment. A sheep’s foot type roller will likely be more effective for breaking up and compacting
sod than a smooth drum roller.
4.7. Shallow Foundations
4.7.1. General
Proposed structures can be founded on continuous wall and isolated column footings; however,
settlements may need to be considered for final design as discussed below. Alternatively, deep
foundations (such as micropiles) or ground improvement (such as stone columns or aggregate piers) may
be more efficient for design to provide increased allowable bearing pressures and/or reduced
settlements.
Based on the materials observed in our borings, the site topography, and the proposed site layout we
anticipate shallow foundations will likely be founded on one of three typical soils profiles: glacial till,
structural fill extending to glacial till or structural fill overlying existing fill soils. Existing fill soils
encountered in our explorations generally consisted of loose to medium silty sand and soft sandy silt with
variable gravel, cobble and organic material (roots and wood debris). In addition, fill soils in the existing
grass lawn area (B-1, B-5, PIT-1 and PIT-2) appear to indicate organic-rich soils present at depth; within
1 to 2 feet of the underlying undisturbed glacial till soils. We interpret these organic-rich soils to be topsoil
and vegetation from previous site clearing and grading activities and were once filled over.
Due to the potential for excessive differential settlement, we recommend foundations not bear directly on
relatively loose soils (including existing fill) without improvements. Overexcavation and replacement of
existing fill soils below foundations is required but will ultimately depend on final foundation locations and
elevations. Overexcavation is also recommended to address long-term settlements related to
consolidation and decomposition of the organic-rich soils observed between the fill and glacial till at
depth.
4.7.2. Footing Bearing Surface Overexcavation
Our specific overexcavation recommendations for the typical soils profile described above are as follows:
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■ Bearing surfaces for footings bearing directly on dense to very dense glacial till deposits soils should
be proof-compacted as necessary to a uniformly firm and unyielding condition. For this condition,
overexcavation is not anticipated. We estimate that this will occur in the approximate northern
1/3 area of proposed location of Building B1 footprint.
■ Structural fill overlying glacial till should extend laterally beyond the edge of the footings a distance
equal to the thickness of the fill or 2 feet, whichever is less.
■ Bearing surfaces where relatively loose and/or organic-rich soils are present should be overexcavated
at least 2 feet below footings, proof compacted to a uniformly firm and unyielding condition and
replaced with select granular compacted structural fill. If dense glacially consolidated soils are
encountered prior to removal of the 2 feet of soil, then overexcavation can be limited. Structural fill
should extend 2 feet laterally beyond the edges of the footings. We expect that this will occur in the
majority of the foundation footprint areas below Buildings B1 (approximate southern 2/3), B2 and
B-3.
4.7.3. Footing Bearing Surface Preparation
Prepared foundation bearing surfaces should be evaluated by the geotechnical engineer during
construction to confirm bearing surfaces have been prepared in accordance with our recommendations.
There may also be conditions observed during construction where fill or weathered glacial till soils are
relatively dense, avoiding overexcavation and replacement. The geotechnical engineer can help verify and
provide additional direction on this during construction.
Footing excavations should be performed using a smooth-edged bucket to limit bearing surface
disturbance. The foundation bearing surface must be confirmed or compacted as necessary to a firm,
nonyielding condition. Loose, disturbed, or organic-rich materials present at the base of footing
excavations should be removed or compacted as discussed above. If soft or otherwise unsuitable areas
are revealed during evaluation that cannot be compacted to a stable and uniformly firm condition the
following options may be considered: (1) the exposed soils be moisture conditioned and recompacted; or
(2) the unsuitable soils be overexcavated and replaced with compacted structural fill, as needed; or (3) it
may be possible to push, seat, and compact quarry spalls into the soft soils to stabilize the surface.
4.7.4. Wet Weather Considerations
During periods of wet weather, concrete should be placed as soon as practical after preparation of the
footing excavations. Foundation bearing surfaces should not be exposed to standing water. If water pools
in the base of the excavation, it should be removed before placing structural fill or reinforcing steel. If
footing excavations are exposed to extended wet weather conditions, a 3- to 4-inch thick layer of lean mix
concrete or control density fill (CDF) can be considered for subgrade protection. Alternatively, 6 to
8 inches of crushed rock can also be considered for subgrade protection.
4.7.5. Foundation Design Parameters
4.7.5.1. Minimum Footing Depths and Dimensions
Exterior footings should be established at least 18 inches below the lowest adjacent grade. Interior
footings should be founded a minimum of 12 inches below the top of the floor slab. Continuous footings
should have a minimum width of 18 inches. Isolated column footings should have a minimum width of
24 inches.
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4.7.5.2. Allowable Soil Bearing Pressure
We provide different bearing capacity values for two generalized soil profiles: (1) bearing surfaces where
relatively loose and/or organic-rich soils are present and (2) bearing surfaces for footings bearing directly
on dense to very dense glacial till deposits or structural fill extending to these deposits. Lower allowable
soil bearing pressures are appropriate for foundations bearing on relatively loose and/or organic-rich
soils. For this project, we expect that this is the case for the majority of proposed structures. For higher
bearing capacity values, we recommend foundations bear on dense to very dense intact glacially
consolidated deposits or structural fill extending to these deposits. In some instances, this may require
complete removal of the existing fill (up to 15.5 feet bgs in our explorations) present below buildings.
Our specific bearing capacity recommendations for the generalized soil profiles described above are as
follows:
■ We recommend an allowable downward soil bearing pressure of 2,500 pounds per square foot (psf)
be used for design of footings bearing on 2 feet of structural fill overlying existing fill soils, or if
footings span between relatively loose fill or weathered soil with the 2 feet of structural fill and dense
glacial till soils.
■ We recommend an allowable downward soil bearing pressure of 5,000 psf be used for design of
footings bearing entirely on dense to very dense glacial till deposits or structural fill extending to
these deposits.
The recommended allowable bearing pressures provided above apply to the total of dead and long-term
live loads and may be increased by one-third when considering total loads, including earthquake or wind
loads. These are net bearing pressures. The weight of the footing and overlying backfill can be ignored in
calculating footing sizes.
4.7.5.3. Footings Near Slopes
The allowable soil bearing pressures provided above are suitable for foundations bearing on level ground.
For the purposes of this report, we define level ground as areas with slopes less than about 6H:1V. If
foundations are located within a distance of about 25 feet from the top of slopes steeper than about
6H:1V, we recommend we be contacted to determine if a reduced allowable soil bearing pressure may be
appropriate or to provide alternative recommendations on embedment depths.
4.7.5.4. Foundation Settlement Estimates
In our opinion, the organic-rich soil layers observed at depth in our explorations are compressible and will
consolidate when subjected to new loads. These soils can also experience decomposition of organic
material, secondary compression and may continue to settle over time (in some cases several years). The
amount of settlement that could occur during and after construction is dependent on three major factors:
(1) the thickness and nature of the compressible soil layers; (2) the loading of the site, including fill
placement; and (3) the loading history of the site.
For footings designed and constructed as recommended in this report, we provide the following
settlement estimates:
■ We estimate total settlement (including consolidation) of footings bearing on at least 2 feet of
structural fill overlying existing fill soils could be on the order of 1 to 2 inches for a 2,500 psf long-
term load at the bottom of footing. We estimate differential settlements of about or ½ to 1 inch (half
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the total settlement) between comparably loaded isolated column footings or along 50 to 100 feet of
continuous footing. At least half of the estimated settlement is expected to occur rapidly as loads are
applied. The remainder of the estimated settlement is expected to occur over the long-term due to
consolidation of the underlying organic-rich soils and may take several years to complete.
■ We estimate settlement of footings bearing entirely on dense to very dense glacial till deposits or
structural fill extending to these deposits will be less than 1 inch, with differential settlements of less
than ½ inch between comparably loaded isolated column footings or along 50 to 100 feet of
continuous footing. Settlement is expected to occur rapidly as loads are applied.
Settlements could be greater than the estimates provided above if loose or disturbed soil is present
beneath footings. These estimates are based on footings under a design load of about 5,000 lbs per
lineal foot or 50,000 lbs per column and proportioned using the recommended allowable bearing
pressures above. We should be notified if foundation loads exceed those presented above so we can
review and revise our settlement estimates, if necessary.
4.7.5.5. Lateral Resistance
The ability of the soil to resist lateral loads is a function of frictional resistance, which can develop on the
base of footings and slabs and the passive resistance, which can develop on the face of below-grade
elements of the structure as these elements tend to move into the soil. For footings founded in
accordance with the recommendations presented above, the allowable frictional resistance on the base
of the footing may be computed using a coefficient of friction of 0.40 applied to the vertical dead-load
forces. The allowable passive resistance on the face of the footing or other embedded foundation
elements may be computed using an equivalent fluid density of 250 pounds per cubic foot (pcf) for
undisturbed site soils or structural fill extending out from the face of the foundation element a distance at
least equal to two and one-half times the depth of the element. These values include a factor of safety of
about 1.5.
The passive earth pressure and friction components may be combined provided that the passive
component does not exceed two-thirds of the total. The passive earth pressure value is based on the
assumptions that the adjacent grade is level and that groundwater remains below the base of the footing
throughout the year. The top foot of soil should be neglected when calculating passive lateral earth
pressure unless the area adjacent to the foundation is covered with pavement or a slab-on-grade.
4.7.6. Foundation Drains
Based on our interpretation of the regional groundwater table, groundwater seepage conditions observed
in our explorations and subsurface soil conditions, it is our opinion footing drains are not necessary to
maintain bearing support. However, because of the potential for near-surface seepage during wetter
times of the year and potential addition of water from irrigation and landscaping, perimeter footing drains
are strongly encouraged to maintain drier conditions around the structure and intercept water that could
accumulate below the slab. We can provide specific recommendations for design of foundation drains, if
requested.
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4.1. Slab-on-Grade Floors
4.1.1. General
Exposed slab subgrades should be evaluated after site grading is complete. In general, the building slab
can be supported on the existing fill; however, we have increased the typical capillary break material
thickness described below to provide subgrade uniformity. Subgrade soils could be variable and range
from existing fill to weathered and intact glacial till. Disturbed and excavated areas should be compacted,
if possible, or removed and replaced with compacted structural fill. In all cases, the exposed soil should
be proof compacted to a uniformly dense, firm and unyielding condition.
4.1.2. Slab-on-Grade Design Parameters
In our opinion, a modulus of subgrade reaction of 250 pounds per cubic inch (pci) can be used for
designing building floor slabs, provided the slab subgrade consists of firm and unyielding existing site
soils or compacted structural fill and has been prepared in accordance with Section 4.4.9 “Subgrade
Protection and Wet Weather Considerations” of this report.
We recommend slab-on-grade floors be underlain by a minimum 8-inch thick capillary break layer to
provide uniform support within fill or between fill and glacial till soil and to reduce the potential for
moisture migration into the slab. This minimum section thickness is recommended, in part, to assist in
bridging areas and to provide uniform support where the existing fill and/or weathered glacial deposits
may cross through denser glacial deposits. The capillary break material should conform to
recommendations provided in Section 4.5 “Fill Materials” of this report. The material should be placed as
recommended in Section 4.6 “Fill Placement and Compaction” of this report.
We estimate settlement for slabs-on-grade constructed as recommended will be less than ¾ inch for a
floor load of 400 psf. We estimate differential settlement of floor slabs will be ½ inch or less over a span
of 50 feet.
4.1.3. Underslab Drainage and Vapor Barrier
Based on our review of groundwater conditions, it is our opinion an underslab drain system is not
necessary. However, if dry slabs are required (e.g., where adhesives are used to anchor carpet or tile to
slab), a waterproof liner may be placed as a vapor barrier below the slab.
4.2. Conventional Retaining Walls and Below Grade Structures
4.2.1. General
Based on our review of the provided drawings, we understand retaining walls will be constructed adjacent
to the existing wetland to achieve proposed site grades. If final site slopes elsewhere on site are to
exceed recommendations presented in Section 4.4.5 “Permanent Cut and Fill Slopes” of this report,
protective facings and/or retaining structures should be considered.
We have assumed retaining walls will be less than about 10 feet tall, will not be tiered and will not be
located within about 25 feet (above or below) slopes steeper than about 6H:1V. If these conditions exist,
we should be contacted to evaluate if a more detailed global stability analysis is required.
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File No. 4519-017-00
4.2.2. Drainage
Positive drainage is imperative behind retaining walls unless they are designed to resist hydrostatic
forces. We recommend a zone of free-draining material behind the retaining structure with perforated
pipes to collect seepage water. Most of the site soils encountered in our explorations contain a significant
percentage of fines (material passing the U.S. No. 200 sieve). Fine soils are susceptible to particle
migration, potentially clogging the drainage. We recommend one of the following options for drainage
behind retaining walls:
■ Drainage material consisting of “Gravel Backfill for Walls and Drains” described in Section 4.5 “Fill
Materials” of this report and Section 9-03.12(2) of the 2020 WSDOT Standard Specifications. The
drainage zone should extend horizontally at least 24 inches from the back of the retaining structure.
■ Drainage material consisting of material similar to “Gravel Backfill for Drains” described in Section
9-03.12(4) of the 2020 WSDOT Standard Specifications. The drainage zone should extend
horizontally at least 12 inches from the back of the retaining structure. A filter fabric designed for
separation should be placed between the gravel backfill and native site soils to prevent soil migration.
■ Waffle boards or drainage mats specifically designed for this application are also appropriate. We
recommend we review drainage mat submittals and plan details if drainage mats are to be used. In
below-grade areas where dry interiors are critical, drainage mats can also be combined with gravel
backfill.
A perforated, smooth-walled, rigid PVC pipe with a minimum diameter of 4 inches should be placed at the
bottom of the drainage zone along the entire length of the retaining structure with the pipe invert at or
below the elevation of the base of the footing. The drainpipes should collect water and direct it to a
tightline leading to an appropriate disposal system. Cleanouts should be incorporated into the design of
the drains in order to provide access for regular maintenance. Roof downspouts, perimeter drains or
other types of drainage systems must not be connected to drain systems for retaining walls or below-
grade structures.
4.2.3. Design Parameters
Footings for retaining structures should be designed in accordance with Section 4.7 “Shallow
Foundations” of this report. Frictional wall resistance, including coefficient of friction along the base of
the wall and allowable passive resistance on the face of the wall, should be computed using
recommendations provided in Section 4.7.5.5 “Lateral Resistance” of this report. Fill material placed
behind retaining walls should be placed and compacted as described in Section 4.6 “Fill Placement and
Compaction” of this report.
We recommend retaining structures that are free to deflect at least 0.001H, where H is the height of the
retaining structures, be designed for active earth pressures. If the retaining structures are restrained
against deflection, we recommend they be designed for at-rest earth pressures. The following table
provides recommended lateral soil pressure parameters suitable for design of retaining walls and
subsurface structures. These recommended values do not include hydrostatic forces.
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File No. 4519-017-00
TABLE 2. LATERAL SOIL PRESSURE PARAMETERS FOR PERMANENT RETAINING WALLS AND
SUBSURFACE STRUCTURES
Soil Parameter Structural Fill Intact Glacial Till
Soil Unit Weight Total Weight = 130 pcf Total Weight = 135 pcf
Friction Angle 34 degrees 38 degrees
Cohesion 0 psf 100 psf
Active Earth Pressure
(Level Backfill Condition)
Ka = 0.28
Equivalent Fluid Pressure:
Ka*Unit Weight = 37 pcf
Ka = 0.24
Equivalent Fluid Pressure:
Ko*Unit Weight = 32 pcf
Active Earth Pressure
(Backfill Sloping Upward Behind
Wall at 2H to 1V or less)
Ka = 0.40
Equivalent Fluid Pressure:
Ka*Unit Weight = 52 pcf
Ka = 0.33
Equivalent Fluid Pressure:
Ko*Unit Weight = 45 pcf
At-rest Earth Pressure
(Level Backfill Condition)
Ko = 0.44
Equivalent Fluid Pressure:
Ko*Unit Weight = 57 pcf
Ko = 0.38
Equivalent Fluid Pressure:
Ko*Unit Weight = 52 pcf
If permanent retaining walls or subsurface structures are to be designed for seismic forces, we
recommend the seismic loading be approximated using a uniform lateral pressure equal to 12*H psf,
where H is the height (in feet) of the structure. This is based on Mononobe-Okabe method and one-half of
the design Peak Ground Acceleration (PGAM). This seismic lateral pressure is in addition to the static soil
load and any anticipated hydrostatic or surcharge pressures. This assumes that the structure is free to
yield somewhat during a seismic event. Where restrained conditions are used, but the wall may move
slightly (as indicated for the active condition) during an earthquake, the uniform seismic pressure may be
combined with the active earth pressure value for earthquake considerations.
The recommended lateral soil pressure parameters provided above do not include surcharge loads. For
typical traffic surcharge, an additional 2 feet of fill representing a typical traffic surcharge of 250 psf
should be included if vehicles are allowed to operate within ½ the height of the retaining walls. Other
surcharge loads such as stockpiles, point loads, other equipment, etc. should be considered on a case-by-
case basis. We should review surcharge loading conditions where different than typical traffic surcharge
described. We can provide additional recommendations considering location and geometry of the load as
the design progresses.
4.3. Retaining Wall at 1st Avenue South
Proposed frontage improvements along 1st Avenue South generally consist of roadway widening to
include an additional traffic lane, sidewalk, curb and gutter and landscaping. We understand a retaining
wall will be necessary along the western edge of 1st Avenue South to accommodate the frontage
improvements and existing steep slopes in the area. Because these frontage improvements are still in the
conceptual design phase proposed wall details (including wall type, geometry and grading elevations) are
not available at this time.
Based on our observations during a reconnaissance of the area (including HA-1), we anticipate existing fill
soils are present along the western edge of 1st Avenue South. Footings for retaining structures should be
designed in accordance with Section 4.7 “Shallow Foundations” of this report. We recommend
contingency for overexcavation of loose soils below footings be included in project plans and budget. For
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File No. 4519-017-00
preliminary design, we recommend lateral soil pressures are estimated in accordance with “Structural
Fill” as presented in Table 2 above.
Depending on proposed final elevations, time of year and water levels in the adjacent wetland,
excavations may extend below the perched groundwater zone. Alternative construction methods and
materials may be appropriate. We can provide additional recommendations for this wall as the design is
progressed.
Upon request we can provide further assistance with determining wall type, complete wall design, develop
wall plans and specifications and/or review wall design. We recommend that, at a minimum, we review
the wall design to ensure the designer has interpreted our geotechnical report correctly and to provide
additional recommendations, as necessary.
4.4. Stormwater Infiltration
4.4.1. General
At this time, we understand preliminary plans to manage stormwater at the site include underground
detention vaults consisting of subsurface chambers and aggregate backfill or similar construction.
Proposed depths of detention systems are about 7 to 12 feet below existing grade (approximate Elevation
319 to 325 feet). The chamber systems are designed and constructed to provide the option for
stormwater infiltration into underlying soils. Based on our explorations, the site appears to be underlain
by intact glacial till soils where stormwater detention vaults will be constructed, which typically have low
infiltration potential.
Stormwater facilities on site will be designed in accordance with the 2016 King County Surface Water
Design Manual (SWDM), which has been adopted by the City of Federal Way (City). According to the
SWDM, measured infiltration rates shall be determined using a PIT or single-ring percolation test. The
manual does not allow the use of soil grain-size analysis to determine design infiltration rates.
The sections below provide our interpretation of the suitability of site soils for infiltration, an estimate of
soil infiltration rates that may be possible based on empirical correlations and a discussion about further
studies that might be needed to design infiltration facilities.
4.4.2. Stormwater Requirements
Per the SWDM, the infiltration rate of underlying soils shall be determined with a PIT. The SWDM specifies
PIT excavations shall be located within the footprint of proposed infiltration facilities, with a minimum of
two tests for each proposed infiltration facility location. As final locations and sizes of the infiltration
facilities were not fully determined at the stage of subsurface explorations, additional PITs beyond those
performed in this study could be necessary. The SWDM also states performance testing and verification
shall be conducted for infiltration facilities before final construction approval and may be requested by
regulating agencies.
Groundwater mounding analysis is generally not required for infiltration facilities with at least 5 feet of
vertical separation between the bottom of the proposed facility and the maximum seasonal groundwater
table or low permeability layer. As described in our “Groundwater Conditions” section, in our opinion it is
unlikely seasonal high groundwater levels will come within 50 feet of the ground surface at the project
site and are likely much deeper. The intact glacial till soils encountered in our explorations could be
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File No. 4519-017-00
considered a low permeability layer; however, based on the proposed design elevations and the results of
our explorations and testing, it is our opinion that a groundwater mounding analysis will not be necessary
for this condition as the stormwater facility it is not expected to be developed in a more permeable
material overlying a less permeable material.
Additional limitations to those referenced above might be required for infiltration on site. Other
requirements (including setback distances) set forth by the SWDM, King County, Environmental
Protection Agency (EPA) or other appropriate agencies should be evaluated as required.
4.4.3. Pilot Infiltration Tests
4.4.3.1. Methodology
Two small-scale PITs were completed at the site following GeoEngineers’ standard methodology for
stormwater facilities in Western Washington. Our methodology is a synthesis of standard practices and
current local jurisdictional procedures set forth by King County and Ecology. GeoEngineers’ PIT procedure
has been developed to provide increased confidence that fully saturated conditions have been achieved
and that the infiltration rate measured at the end of the test is representative of the saturated hydraulic
conductivity of the soil. In our opinion, the GeoEngineers’ PIT procedure meets the intent of procedures
set forth in the SWDM.
Approximate dimensions at the base of the PIT excavations were 4 feet by 4 feet. Upon reaching the
target excavation depth (12 feet for PIT-1 and 17 feet for PIT-2), a graduated yard stick was driven into
the floor of the test pit as a visual reference for monitoring water levels during testing. A piezoelectric
pressure transducer was secured to the bottom of the yard stick to provide accurate water-level
measurements at 30-second intervals throughout the duration of the test.
GeoEngineers’ PIT procedure consists of a minimum 6-hour saturation period (pre-soak) where the water
depth in the PIT is maintained above about 12 inches. During the saturation period, the water depth is
raised and lowered in a series of falling-head stages over an approximate 2- to 4-inch interval. The
approximate depths to which water is filled and allowed to drain are based on the minimum PIT water
depth requirements in the SWDM, anticipated water depths in the proposed facilities and the soil
conditions present in the excavations. Water level measurements collected by the pressure transducer
during each falling-head stage are used to calculate the apparent infiltration rate for each stage. The
falling-head stage methodology is intended to fully saturate the soils below the base of the PIT while
allowing for a direct measurement of when saturated or near-saturated conditions have been achieved.
This is usually manifested by a progressive decline in the apparent infiltration rate until the rate
approximately stabilizes. The stabilized rate corresponds to the saturated infiltration rate of the soil.
Once the minimum 6-hour saturation time has elapsed and a stabilized infiltration rate is observed during
the falling-head stages, the PIT is left undisturbed until the water drains away completely. The final
draindown period shows how infiltration changes over a continuous range of declining water depths.
According to the SWDM, infiltration rates should be determined based on a water depth in the PIT equal
to 6 inches.
After the PITs are complete, the test pits are excavated deeper to obtain samples, observe for indications
of lateral water flow and characterize the underlying soils.
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File No. 4519-017-00
4.4.3.2. PIT Analysis
Infiltration rates calculated from the transducer data are representative of the measured (uncorrected)
infiltration rate of the soils at the test location. Per the SWDM, the design infiltration rate is determined by
applying correction factors to the measured infiltration rate. The correction factors account for
uncertainties in the testing method (Ftesting), the influence of facility geometry and depth to water table or
impervious soils (Fgeometry) and long-term reductions in permeability due to accumulation of fines and
biological activity (Fplugging). Section 5.2.1 in the 2016 SWDM outlines the correction factors appropriate
for design and provides recommended values. The total correction factor (Ftotal) is calculated with the
equation
Ftotal = Ftesting * Fgeometry * Fplugging
We selected appropriate correction factors based on our project understanding, observed soil conditions,
requirements presented in the SWDM and our discussions with the project team during the design
process. According to the SWDM, Ftesting = 0.5 for small- and large-scale PITs. The correction factor Fgeometry
accounts for the influence of facility geometry and depth to water table or impervious strata. Per the
SWDM, Fgeometry must be between 0.25 and 1.0 as determined by the equation
Fgeometry = 4 D/W + 0.05 (Equation 5-12)
Where D = depth from the bottom of the proposed facility to the maximum wet-season water table or
nearest impervious layer, whichever is less, and W = width of the facility. As facilities have not been
designed at this stage, facility dimensions are not available and geometry calculations cannot be
performed at this time. Based on our understanding of subsurface conditions and proposed facility
depths, we have assumed facilities will be designed such that the correction factor for facility geometry is
equal to 0.25. Glacial till soils exposed at the PIT depths consisted of silty sand with variable gravel and
generally classify as “silt loam” within the USDA Textural Triangle. According to the SWDM Fplugging = 0.7
for loams, the lowest recommended value.
Equation 5-11 of the 2016 SWDM was developed to account for these correction factors. This equation
estimates the maximum design infiltration rate (Idesign) by multiplying the initial saturated hydraulic
conductivity, or measured infiltration rate (Imeasured), by the appropriate correction factors.
𝐼ௗ௦ ൌ𝐼௦௨ௗ ∗𝐹௧௦௧ ∗𝐹௧௬ ∗𝐹௨ (Equation 5-11)
We selected appropriate correction factors based on our project understanding, observed soil conditions
and our experience assisting in the design of stormwater infiltration facilities. Table 3 below summarizes
the partial and total correction factor(s) that, in our opinion, are suitable for preliminary design. We should
be contacted once facilities have been designed to confirm these correction factors are still appropriate.
TABLE 3. PIT CORRECTION FACTOR SUMMARY
Issue Partial Correction Factor
Test Method (Ftesting) 0.5
Geometry/Depth to Groundwater (Fgeometry) 0.251
Long-Term Plugging (Fplugging) 0.7
Total Correction Factor = Ftesting x Fgeometry x Fplugging CF = 0.09
Note:
1 Correction factor for geometry assumed and must be verified for final design.
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File No. 4519-017-00
4.4.3.3. PIT Results
PITs were located in the southern project area and targeted undisturbed glacial till soils near the
proposed elevation of stormwater facilities. We observed slow groundwater seepage (less than 1 gallon
per minute) from excavation sidewalls just above the bottom of the excavations. PIT-1 and PIT-2 were
filled with 19 and 18 inches of water, respectively, to initially saturate the soils. However, we observed
water levels increased within the PITs even after the hose was turned off, indicating the rate of seepage
from the perched layers exceeded the infiltration rate of the soils. PITs were left overnight to record water
levels, however, no movement in water levels was recorded. Therefore, measured and design infiltration
rates could not be calculated for the PITs. Recorded water level data from the PITs are presented in PIT
Results, Figures 3 and 4.
Table 4 below summarizes the measured (short-term) and design (long-term) infiltration rates for each
PIT.
TABLE 4. INFILTRATION RATE SUMMARY
Pilot
Infiltration
Test Number
Approx. PIT
Depth
(feet bgs)
Approx. PIT
Elevation
(feet)1 Geologic Unit Soil Type
Percent
Fines
Measured
(Short-Term)
Infiltration
Rate (in/hr)2
Design
(Long-Term)
Infiltration
Rate (in/hr)3
PIT-1 12 327 Glacial Till SM 25 n/a4 n/a4
PIT-2 16 324 Glacial Till SM 35 n/a4 n/a4
Notes:
1 Elevations based on provided survey documents and should be considered approximate.
2 Measured (short-term) infiltration rate based on a water depth of 12 inches and must be verified for design.
3 Design (long-term) infiltration rate with appropriate correction factors applied.
4 Measured and design infiltration rates could not be calculated for PIT-1 and PIT-2.
4.4.4. Recommended Design Infiltration Rates
Based on soil conditions observed during explorations and proposed depths of stormwater facilities, we
anticipate the proposed stormwater detention systems will be established within intact glacial till soils.
Intact glacial till soils typically consisted of silty sand with varying gravel and cobble content and were
observed in each of the borings and test pits, at proposed infiltration depths, completed throughout the
site. Based on the explorations for this study (including laboratory test results) it is our opinion the intact
glacial till soils encountered throughout the site have similar gradation and hydraulic conductivity
characteristics.
In some cases, groundwater seepage nearly exceeded the infiltration rate of the soils. In our observed
test results of both infiltration and grain-size analysis, design infiltration rates could not be calculated for
the PITs. Based on our observations and experience with similar soils, it is our opinion infiltration through
intact glacial till soils at proposed stormwater vault depths at the site is generally infeasible.
4.4.5. Stormwater Treatment
Section 5.2.1 of the 2016 SWDM provides minimum soil properties required for groundwater protection.
Based on our review of data available online via King County iMap (accessed February 19, 2020), the
project site is mapped within a wellhead protection area. According to the SWDM, within groundwater
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File No. 4519-017-00
protection areas the first 2 feet or more of the soil beneath an infiltration facility must meet the following
requirements:
■ Cation exchange capacity (CEC) greater than 5 milliequivalents per 100 grams (meq/100g) dry soil
■ Organic content (OC) of 1 percent or greater
■ Measured (initial) soil infiltration rate of 2.4 inches per hour or less, or meet specific gradation
requirements
Chemical laboratory results for selected samples from the PITs are summarized in the table below and
are also presented on the test pit logs, as appropriate.
TABLE 5. CHEMICAL LABORATORY TESTING RESULTS
Pilot
Infiltration
Test Number
Approx. Sample
Depth
(feet bgs)
Approx. Sample
Elevation
(feet)1 Geologic Unit Soil Type
Cation
Exchange
Capacity
(meq/100g)
Organic
Content
(%)
B-2 10 327 Glacial Till SM 7.3 0.9
B-6 7.5 318 Glacial Till SM 3.0 1.4
PIT-1 12 327 Glacial Till SM 5.0 1.5
Note:
1 Elevations based on provided survey documents and should be considered approximate.
Based on the results of our PITs and laboratory analysis, it appears the site soils may not readily meet the
required cation exchange capacity and/or organic content criteria for treatment. Therefore, an imported
soil treatment layer may be required as part of the stormwater system design and should be verified in
the SWDM, which will be based, in part, on proposed application and use.
4.4.6. Discussion and Construction Considerations
We recommend we review the proposed stormwater infiltration facilities if the location, size or elevation
of the proposed infiltration area(s) change to confirm our recommendations are appropriate or provide
revised recommendations, as necessary. We can be retained during construction to observe soil
conditions at the base of the infiltration facilities and verify exposed soils are consistent with our
assumptions described above.
4.5. Asphalt Concrete Pavement Recommendations
4.5.1. General Design Criteria
Pavements for the proposed improvements will likely include parking areas, driveways and service areas.
We have assumed driveway areas for this project will consist of general light-duty traffic and occasional
heavy-duty traffic for service deliveries and other larger maintenance vehicles. Based on our experience,
we provide recommended conventional asphalt concrete pavement (ACP) sections below.
The recommended pavement sections below may not be adequate for heavy construction traffic loads
such as those imposed by concrete transit mixers, dump trucks or cranes, or interstate or highway truck
traffic frequencies. Additional pavement thickness may be necessary to prevent pavement damage during
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File No. 4519-017-00
construction. An asphalt treated base (ATB) section can also be used during construction to protect
partially constructed pavement sections and pavement subgrades. The recommended sections assume
final improvements surrounding the pavement areas will be designed and constructed such that
stormwater or excess irrigation water from landscape areas does not accumulate below the pavement
section or pond on pavement surfaces. If pavements in parking areas slope inward (toward the center of
the parking area) full depth curbs or other measures should be used to prevent water from entering and
ponding on the subgrade and within the underlying base section.
4.5.2. Pavement Construction Considerations
Existing pavements, hardscaping or other structural elements should be removed prior to placement of
new pavement sections. Pavement subgrade should be prepared to a uniformly firm, dense and
unyielding condition as previously described. Crushed surfacing base course and subbase should be
moisture conditioned to near optimum moisture content and compacted to at least 95 percent of the
MDD (ASTM D 1577).
Crushed surfacing base course should conform to applicable sections of 4-04 and 9-03.9(3) of the
2020 WSDOT Standard Specifications. Subbase should conform to applicable sections of 4-02 “Gravel
Base” and 9-03.10 “Aggregate Gravel for Base” of the WSDOT Standard Specifications. Hot mix asphalt
should conform to applicable sections of 5-04, 9-02 and 9-03 of the WSDOT Standard Specifications.
Some areas of pavement may exhibit cracking over time. Cracks in the pavement will allow water to
infiltrate to the underlying base course, which could increase the amount of pavement damage caused by
traffic loads. To prolong the effective life of the pavement, cracks should be sealed as soon as possible.
4.5.3. Asphalt Concrete Pavement Design
We provide recommended conventional ACP sections below.
4.5.3.1. Standard-Duty ACP – Automobile Driveways and Parking Areas
■ 2 inches of hot mix asphalt, class ½-inch, PG 58-22 or PG64-22 (depending on availability)
■ 4 inches of CSBC
■ 6 inches of subbase consisting of select granular fill, previously described, to provide a uniform
grading surface, to provide pavement support, to maintain drainage, and to provide separation from
fine-grained subgrade soil
■ Subgrade consisting of proof-compacted firm and unyielding conditions or structural fill prepared in
accordance with Section 4.4.8 “Subgrade Preparation and Evaluation” of this report
4.5.3.2. Heavy-Duty ACP –Areas Subject to Occasional Heavy Truck Traffic
■ 4 inches of hot mix asphalt, class-½ inch, PG 58-22 or PG64-28 (depending on availability)
■ 6 inches of CSBC
■ 6 inches of subbase consisting of select granular fill, previously described, to provide a uniform
grading surface, to provide pavement support, to maintain drainage, and to provide separation from
fine-grained subgrade soil
■ Subgrade consisting of proof-compacted firm and unyielding conditions or structural fill prepared in
accordance with Section 4.4.8 “Subgrade Preparation and Evaluation” of this report
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4.5.3.3. Temporary Construction Surfacing
A temporary surfacing of ATB can be used to protect partially constructed ACP sections and subgrades
during construction. This can provide a relatively clean working surface, prevent construction traffic from
damaging final paving surfaces and reduce subgrade repairs required for final paving. A 2-inch thick
section of ATB can be substituted for the upper 3 inches of CSBC in either the light-duty or heavy-duty ACP
sections. Prior to placement of the final pavement surface sections, we recommend that any areas of ATB
pavement failure be removed and the subgrade repaired. If ATB is used and is serviceable when final
pavements are constructed, the design ACP thickness can be placed directly over properly prepared ATB
surfaces. In addition, if ATB is used as a substitute for CSBC, we still recommend the subbase select
granular fill layer be included below the ATB and subgrades be prepared as recommended.
5.0 LIMITATIONS
We have prepared this report for Helix Design Group and the proposed Lakehaven Water and Sewer
District Maintenance Facility Improvements project in Federal Way, Washington. Helix Design Group may
distribute copies of this report to the owner, owner’s authorized agents and regulatory agencies as may
be required for the project.
Within the limitations of scope, schedule and budget, our services have been executed in accordance
with generally accepted practices for geotechnical engineering services in this area at the time this report
was prepared. The conclusions, recommendations, and opinions presented in this report are based on
our professional knowledge, judgment and experience. No warranty, express or implied, applies to the
services or this report.
Please refer to Appendix B titled “Report Limitations and Guidelines for Use” for additional information
pertaining to use of this report.
µ
SITE
Vicinity Map
Figure 1
Lakehaven Water & Sewer DistrictMaintenance Facility Improvements Federal Way, Washington
2,000 2,0000
Feet
Data Source: Mapbox Open Street Map, 2016
Notes:1. The locations of all features shown are approximate.2. This drawing is for information purposes. It is intended to assist in showing features discussed in an attached document. GeoEngineers, Inc. cannot guarantee the accuracy and content of electronic files. The master file is stored by GeoEngineers, Inc. and will serve as the official record of this communication.
Projection: NAD 1983 UTM Zone 10N
P:\4\4519017\GIS\MXD\451901700_F01_VicinityMap.mxd Date Exported: 02/14/20 by mwoods
Building B2
Parcel 1
Parcel 3
B-1 (26.5 ft)
B-2 (10.9 ft)
B-3 (11 ft)
B-4 (11 ft)
B-5 (25.2 ft)
B-6 (21.5 ft)
PIT-1 (12.5 ft)PIT-2 (17 ft)
Building B1
Building B3Parcel 2
HA-1 (1.75 ft)
Figure 2
Lakehaven Water & Sewer District
Maintenance Facility Improvements
Federal Way, Washington
Site Plan
W E
N
S
P:\4\4519017\CAD\00\Geotech\451901700_F02_Site Plan.dwg TAB:F02 Date Exported: 03/31/20 - 14:23 by mwoodsNotes:
1.The locations of all features shown are approximate.
2.This drawing is for information purposes. It is intended to assist in showing
features discussed in an attached document. GeoEngineers, Inc. cannot
guarantee the accuracy and content of electronic files. The master file is stored
by GeoEngineers, Inc. and will serve as the official record of this communication.
Data Source: Aerial from Google Earth Pro dated 7/1/2018.
Projection: NAD83 Washington State Planes, North Zone, US Foot
Feet
080 80
Legend
Boring and depth by GeoEngineers, Inc., 2020B-1 (26.5 ft)
Hand Auger and depth by GeoEngineers, Inc., 2020HA-1 (1.75 ft)
Test Pit and depth by GeoEngineers, Inc., 2020PIT-1 (12.5 ft)1st Ave SS 317th Pl
Proposed Building
Site Boundary
0
5
10
15
20
25
30
35
40
45
50
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24Water Depth (inches)Test Duration (hour)
PIT-1
Measured Water Levels
Figure 3
PIT-1 Results
Lakehaven Water & Sewer District
Maintenance Facility Improvements
Federal Way, Washington
04519-017-00 Date Exported: 02/27/20Notes:
1.This drawing is for information purposes. It is intended to
assist in showing features discussed in an attached
document. GeoEngineers, Inc. cannot guarantee the accuracy
and content of electronic files. The master file is stored by
GeoEngineers, Inc. and will serve as the official record of this
communication.
2.Water levels increased within the PIT even after the hose was
turned off, indicating the rate of groundwater seepage
exceeded the infiltration rate of the soils. Therefore,
measured infiltration rate could not be calculated for the PIT.
0
0.5
1
1.5
0 1Measured Infiltration Rate (in/hr)Test Duration (hour)
PIT-1
Measured (Short-Term)Infiltration Rates
0
5
10
15
20
25
30
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18Water Depth (inches)Test Duration (hour)
PIT-2
Measured Water Levels
Figure 4
PIT-2 Results
Lakehaven Water & Sewer District
Maintenance Facility Improvements
Federal Way, Washington
04519-017-00 Date Exported: 02/27/200
0.5
1
1.5
0 1Measured Infiltration Rate (in/hr)Test Duration (hour)
PIT-2
Measured (Short-Term)Infiltration Rates
Notes:
1.This drawing is for information purposes. It is intended to
assist in showing features discussed in an attached
document. GeoEngineers, Inc. cannot guarantee the accuracy
and content of electronic files. The master file is stored by
GeoEngineers, Inc. and will serve as the official record of this
communication.
2.Water levels increased within the PIT even after the hose was
turned off, indicating the rate of groundwater seepage
exceeded the infiltration rate of the soils. Therefore,
measured infiltration rate could not be calculated for the PIT.
APPENDIX A
Subsurface Explorations and Laboratory Testing
June 9, 2020| Page A-1
File No. 4519-017-00
APPENDIX A
SUBSURFACE EXPLORATIONS AND LABORATORY TESTING
Subsurface Explorations
Soil and groundwater conditions at the project site were explored by advancing borings, advancing hand
augers and excavating test pits. Approximate locations of the explorations are shown on the Site Plan,
Figure 2. Locations of the explorations were determined in the field using and electronic tablet with global
positioning system (GPS) software. Elevations are based on the provided “Concept Site Plan” prepared by
Helix Design Group and dated September 6, 2019. The locations and elevations of the explorations
should be considered approximate. Exploration locations were constrained to some degree by existing
buildings, site infrastructure, utilities and vegetation.
The explorations were continuously monitored by an engineer from our firm who examined and classified
the soil encountered, obtained representative soil samples, maintained a detailed log of the explorations
and observed groundwater conditions. Samples were retained in sealed plastic bags to prevent moisture
loss. The soils were classified visually in general accordance with ASTM International (ASTM) D 2488.
Figure A-1 includes a Key to the Exploration Logs.
Brief descriptions of the explorations are provided below.
Soil Borings
Borings were completed using drilling equipment provided and operated by Holocene Drilling, Inc. under
subcontract to GeoEngineers. Borings were advanced using hollow-stem auger drilling methods to depths
between approximately 10.5 and 26.5 feet below existing ground surface (bgs). Borings were backfilled
by the driller in accordance with Washington State Department of Ecology requirements.
Soil samples were obtained from the borings using a 1.4-inch inner diameter split-barrel sampler driven
into the soil using a 140-pound hammer free-falling a distance of 30 inches in general accordance with
ASTM D 1586 Standard Penetration Test (SPT). The number of blows required to drive the sampler the
last 12 inches or other indicated distance is recorded on the logs as the blow count. Our field
representative made sample attempts at 2.5- to 5-foot depth intervals. Summary logs of the borings are
presented as Figures A-2 through A-7. The logs are based on our interpretation of the field and laboratory
data and indicate the depth at which we interpret subsurface materials or their characteristics to change,
although these changes might actually be gradual.
Test Pits
Test pit excavations were performed using a tracked excavator provided and operated by Kelly’s
Excavating, Inc. PIT-1 and PIT-2 were advanced to an intermediate depth of about 12 feet for PIT-1 and
17 feet for PIT-2, at which point a Pilot Infiltration Test (PIT) was performed. After infiltration testing was
complete, the test pits were advanced to depths of approximately 12.5 and 17.5 feet bgs, respectively.
After each test pit was complete the excavation was backfilled using the generated material and
compacted using the bucket of the excavator. Summary logs of the test pits are presented as Figures A-8
and A-9. The densities noted on the test pit exploration logs are based on the difficulty of excavation,
observations of caving and our experience and judgment.
June 9, 2020| Page A-2
File No. 4519-017-00
Hand Auger
A hand auger exploration was advanced using hand-operated equipment and techniques by a
GeoEngineers representative. Soil samples were obtained using a 3-inch diameter sampler. The hand
auger was advanced to a depth of approximately 1.75 feet bgs. Soil cuttings generated from the hand
auger were left on site. Summary log of the hand auger is presented as Figure A-10.
Laboratory Testing
Soil samples obtained from the explorations were transported to the GeoEngineers laboratory.
Representative soil samples were selected for laboratory tests to evaluate the pertinent geotechnical
engineering characteristics of the soils and to confirm or modify our field classification. The following
paragraphs provide a description of the tests performed.
Moisture Content (MC)
The moisture content of selected samples was determined in general accordance with ASTM Test Method
D 2216. The test results are used to aid in soil classification and correlation with other pertinent
engineering soil properties. The test results are presented on the exploration logs, as indicated for the
sample tested.
Percent Fines (%F)
Selected samples were “washed” through the U.S. No. 200 sieve to estimate the relative percentages of
coarse- and fine-grained particles in the soil. The percent passing value represents the percentage by
weight of the sample finer than the U.S. No. 200 sieve (fines). Tests were conducted in general
accordance with ASTM D 1140. Test results are presented on the exploration logs at the respective
sample depths.
Sieve Analysis (SA)
Sieve analyses were performed on selected samples in general accordance with ASTM Test Method D
6913. This test method covers the quantitative determination of the distribution of particle sizes in soils
using sieve analysis. Typically, the distribution of particle sizes larger than 75 micrometers (m) is
determined by sieving. Figures A-11 and A-12 present the results of our sieve analyses.
Cation Exchange Capacity (CEC)
Cation exchange capacity (CEC) is a measure of the soil’s ability to hold positively charged ions. It
influences soil structure stability, nutrient availability, soil pH and the soil’s reaction to fertilizers and
provides a buffer against soil acidification. CEC tests were completed at an off-site laboratory (Anatek
Labs, Inc. located in Spokane, Washington) under subcontract to GeoEngineers. Test results are indicated
on the exploration logs, as appropriate.
Organic Content (OC)
Organic content (OC) is the fraction of the soil that consists of plant or animal tissue in various stages of
decomposition. It influences a soil’s water infiltration characteristics and water holding capacity and
provides a buffer against soil acidification. OC tests were completed at an off-site laboratory (Anatek
Labs, Inc. located in Spokane, Washington) under subcontract to GeoEngineers. Test results are indicated
on the exploration logs, as appropriate.
Measured groundwater level in exploration,
well, or piezometer
Measured free product in well or piezometer
Distinct contact between soil strata
Approximate contact between soil strata
Contact between geologic units
SYMBOLS TYPICAL
DESCRIPTIONS
GW
GP
SW
SP
SM
FINE
GRAINED
SOILS
SILTS AND
CLAYS
NOTE: Multiple symbols are used to indicate borderline or dual soil classifications
MORE THAN 50%
RETAINED ON
NO. 200 SIEVE
MORE THAN 50%
PASSING
NO. 200 SIEVE
GRAVEL
AND
GRAVELLY
SOILS
SC
LIQUID LIMIT
LESS THAN 50
(APPRECIABLE AMOUNT
OF FINES)
(APPRECIABLE AMOUNT
OF FINES)
COARSE
GRAINED
SOILS
MAJOR DIVISIONS GRAPH LETTER
GM
GC
ML
CL
OL
SILTS AND
CLAYS
SANDS WITH
FINES
SAND
AND
SANDY
SOILS
MH
CH
OH
PT
(LITTLE OR NO FINES)
CLEAN SANDS
GRAVELS WITH
FINES
CLEAN GRAVELS
(LITTLE OR NO FINES)
WELL-GRADED GRAVELS, GRAVEL -SAND MIXTURES
CLAYEY GRAVELS, GRAVEL - SAND -CLAY MIXTURES
WELL-GRADED SANDS, GRAVELLYSANDS
POORLY-GRADED SANDS, GRAVELLYSAND
SILTY SANDS, SAND - SILT MIXTURES
CLAYEY SANDS, SAND - CLAYMIXTURES
INORGANIC SILTS, ROCK FLOUR,CLAYEY SILTS WITH SLIGHTPLASTICITY
INORGANIC CLAYS OF LOW TOMEDIUM PLASTICITY, GRAVELLYCLAYS, SANDY CLAYS, SILTY CLAYS,LEAN CLAYS
ORGANIC SILTS AND ORGANIC SILTYCLAYS OF LOW PLASTICITY
INORGANIC SILTS, MICACEOUS ORDIATOMACEOUS SILTY SOILS
INORGANIC CLAYS OF HIGHPLASTICITY
ORGANIC CLAYS AND SILTS OFMEDIUM TO HIGH PLASTICITY
PEAT, HUMUS, SWAMP SOILS WITHHIGH ORGANIC CONTENTSHIGHLY ORGANIC SOILS
SOIL CLASSIFICATION CHART
MORE THAN 50%
OF COARSE
FRACTION RETAINED
ON NO. 4 SIEVE
MORE THAN 50%
OF COARSE
FRACTION PASSING
ON NO. 4 SIEVE
SILTY GRAVELS, GRAVEL - SAND -SILT MIXTURES
POORLY-GRADED GRAVELS,GRAVEL - SAND MIXTURES
LIQUID LIMIT GREATER
THAN 50
Continuous Coring
Bulk or grab
Direct-Push
Piston
Shelby tube
Standard Penetration Test (SPT)
2.4-inch I.D. split barrel
Contact between soil of the same geologic
unit
Material Description Contact
Graphic Log Contact
NOTE: The reader must refer to the discussion in the report text and the logs of explorations for a proper understanding of subsurface conditions.
Descriptions on the logs apply only at the specific exploration locations and at the time the explorations were made; they are not warranted to be
representative of subsurface conditions at other locations or times.
Groundwater Contact
Blowcount is recorded for driven samplers as the number of
blows required to advance sampler 12 inches (or distance noted).
See exploration log for hammer weight and drop.
"P" indicates sampler pushed using the weight of the drill rig.
"WOH" indicates sampler pushed using the weight of the
hammer.
Key to Exploration Logs
Figure A-1
Sampler Symbol Descriptions
ADDITIONAL MATERIAL SYMBOLS
NS
SS
MS
HS
No Visible Sheen
Slight Sheen
Moderate Sheen
Heavy Sheen
Sheen Classification
SYMBOLS
Asphalt Concrete
Cement Concrete
Crushed Rock/
Quarry Spalls
Topsoil
GRAPH LETTER
AC
CC
SOD Sod/Forest Duff
CR
DESCRIPTIONS
TYPICAL
TS
Percent fines
Percent gravel
Atterberg limits
Chemical analysis
Laboratory compaction test
Consolidation test
Dry density
Direct shear
Hydrometer analysis
Moisture content
Moisture content and dry density
Mohs hardness scale
Organic content
Permeability or hydraulic conductivity
Plasticity index
Point lead test
Pocket penetrometer
Sieve analysis
Triaxial compression
Unconfined compression
Vane shear
%F
%G
AL
CA
CP
CS
DD
DS
HA
MC
MD
Mohs
OC
PM
PI
PL
PP
SA
TX
UC
VS
Laboratory / Field Tests
Reworked glacial till
Somewhat cemented
Drill chatter at 13 feet bgs
Drill chatter approximately 22 to 25 feet bgs
18
12 50
Approximately 1 inch sod
Dark brown silty fine to coarse sand with gravel and
trace organic matter (fine roots) (loose, moist) (fill)
Gray and tan with iron oxide staining silty fine to
medium sand (medium dense, moist) (weathered
glacial till)
Gray with iron oxide staining silty fine to medium sand
with gravel (very dense, moist) (intact glacial till)
1
MC
2
3
4
5
6
7SA
8
3
2
16
10
10
17
7
8
33
77/17"
50/5"
50/4"
50/6"
SOD
SM
SM
SM
Notes:
26.5 SAH
SST Holocene Drilling, Inc. Hollow-stem Auger
Diedrich D50 Track MountedDrilling
EquipmentAuto Hammer
140 (lbs) / 30 (in) Drop
WA State Plane North
NAD83 (feet)
119475.6
1267524.71
337
NAVD88
Easting (X)
Northing (Y)
Start Total
Depth (ft)
Logged By
Checked By
End
Surface Elevation (ft)
Vertical Datum
Drilled
Hammer
Data
System
Datum
Driller Drilling
Method
Groundwater not observed at time of exploration
1/27/20201/27/2020
Note: See Figure A-1 for explanation of symbols.
Coordinates Data Source: Horizontal approximated based on USGS Topo. Vertical approximated based on USGS Topo.
Sheet 1 of 1Project Number:
Project Location:
Project:
Federal Way, Washington
4519-017-00
Log of Boring B-1
Figure A-2
Lakehaven Water & Sewer District Maintenance Facility Improvements
Date:4/1/20 Path:P:\4\4519017\GINT\451901700.GPJ DBLibrary/Library:GEOENGINEERS_DF_STD_US_JUNE_2017.GLB/GEI8_GEOTECH_STANDARD_%F_NO_GWREMARKS
MoistureContent (%)FinesContent (%)FIELD DATA
MATERIAL
DESCRIPTION
Sample NameTestingRecovered (in)IntervalBlows/footCollected SampleDepth (feet)0
5
10
15
20
25 Graphic LogGroupClassificationElevation (feet)335330325320315
No base course observed
No recovery, sample collected from cuttings,
reworked glacial till
Somewhat cemented
16
8 37
2 inches asphalt concrete
Dark brown silty fine to medium sand with trace
organic matter (fine roots) (medium dense, moist)
(fill)
Gray with iron oxide staining silty fine to medium sand
with gravel (medium dense, moist) (weathered
glacial till)
Gray silty fine to medium sand with gravel (very dense,
moist) (intact glacial till)
1
MC
2
3
4
SA
0
16
6
11
16
26
50/6"
50/5"
AC
SM
SM
SM
Notes:
11 SAH
SST Holocene Drilling, Inc. Hollow-stem Auger
Diedrich D50 Track MountedDrilling
EquipmentAuto Hammer
140 (lbs) / 30 (in) Drop
WA State Plane North
NAD83 (feet)
119730.55
1267445.17
337
NAVD88
Easting (X)
Northing (Y)
Start Total
Depth (ft)
Logged By
Checked By
End
Surface Elevation (ft)
Vertical Datum
Drilled
Hammer
Data
System
Datum
Driller Drilling
Method
Groundwater not observed at time of exploration
1/27/20201/27/2020
Note: See Figure A-1 for explanation of symbols.
Coordinates Data Source: Horizontal approximated based on USGS Topo. Vertical approximated based on USGS Topo.
Sheet 1 of 1Project Number:
Project Location:
Project:
Federal Way, Washington
4519-017-00
Log of Boring B-2
Figure A-3
Lakehaven Water & Sewer District Maintenance Facility Improvements
Date:4/1/20 Path:P:\4\4519017\GINT\451901700.GPJ DBLibrary/Library:GEOENGINEERS_DF_STD_US_JUNE_2017.GLB/GEI8_GEOTECH_STANDARD_%F_NO_GWREMARKS
MoistureContent (%)FinesContent (%)FIELD DATA
MATERIAL
DESCRIPTION
Sample NameTestingRecovered (in)IntervalBlows/footCollected SampleDepth (feet)0
5
10 Graphic LogGroupClassificationElevation (feet)335330
No base course observed
Somewhat cemented
Groundwater observed at 7.2 feet bgs
Observed 4-inch diameter cobble in cuttings
3
9
19
44
2 inches asphalt concrete
Light brown and gray silty fine to coarse sand with
gravel (very dense, moist) (weathered glacial till)
Gray with iron oxide staining silty fine to medium sand
with gravel (very dense, moist) (intact glacial till)
Grades to wet
Grades to moist
1
%F
2
3
4
SA
6
6
4
12
87
50/6"
50/4"
50/6"
AC
SM
SM
Notes:
11 SAH
SST Holocene Drilling, Inc. Hollow-stem Auger
Diedrich D50 Track MountedDrilling
EquipmentAuto Hammer
140 (lbs) / 30 (in) Drop
WA State Plane North
NAD83 (feet)
119863.25
1267590.93
338
NAVD88
Easting (X)
Northing (Y)
Start Total
Depth (ft)
Logged By
Checked By
End
Surface Elevation (ft)
Vertical Datum
Drilled
Hammer
Data
System
Datum
Driller Drilling
Method
See "Remarks" section for groundwater observed
1/27/20201/27/2020
Note: See Figure A-1 for explanation of symbols.
Coordinates Data Source: Horizontal approximated based on USGS Topo. Vertical approximated based on USGS Topo.
Sheet 1 of 1Project Number:
Project Location:
Project:
Federal Way, Washington
4519-017-00
Log of Boring B-3
Figure A-4
Lakehaven Water & Sewer District Maintenance Facility Improvements
Date:4/1/20 Path:P:\4\4519017\GINT\451901700.GPJ DBLibrary/Library:GEOENGINEERS_DF_STD_US_JUNE_2017.GLB/GEI8_GEOTECH_STANDARD_%F_NO_GWREMARKS
MoistureContent (%)FinesContent (%)FIELD DATA
MATERIAL
DESCRIPTION
Sample NameTestingRecovered (in)IntervalBlows/footCollected SampleDepth (feet)0
5
10 Graphic LogGroupClassificationElevation (feet)335330
No base course observed
Somewhat cemented
9
2 inches asphalt concrete
Gray with iron oxide staining silty fine to medium sand
with gravel (medium dense, moist) (weathered
glacial til)
Grades to dense
Gray with iron oxide staining silty fine to medium sand
with gravel (very dense, moist) (intact glacial till)
1
2
MC
3
4
12
14
11
12
28
30
50/5"
50/5"
AC
SM
SM
Notes:
11 SAH
SST Holocene Drilling, Inc. Hollow-stem Auger
Diedrich D50 Track MountedDrilling
EquipmentAuto Hammer
140 (lbs) / 30 (in) Drop
WA State Plane North
NAD83 (feet)
119620.9
1267643.33
337
NAVD88
Easting (X)
Northing (Y)
Start Total
Depth (ft)
Logged By
Checked By
End
Surface Elevation (ft)
Vertical Datum
Drilled
Hammer
Data
System
Datum
Driller Drilling
Method
Groundwater not observed at time of exploration
1/27/20201/27/2020
Note: See Figure A-1 for explanation of symbols.
Coordinates Data Source: Horizontal approximated based on USGS Topo. Vertical approximated based on USGS Topo.
Sheet 1 of 1Project Number:
Project Location:
Project:
Federal Way, Washington
4519-017-00
Log of Boring B-4
Figure A-5
Lakehaven Water & Sewer District Maintenance Facility Improvements
Date:6/9/20 Path:P:\4\4519017\GINT\451901700.GPJ DBLibrary/Library:GEOENGINEERS_DF_STD_US_JUNE_2017.GLB/GEI8_GEOTECH_STANDARD_%F_NO_GWREMARKS
MoistureContent (%)FinesContent (%)FIELD DATA
MATERIAL
DESCRIPTION
Sample NameTestingRecovered (in)IntervalBlows/footCollected SampleDepth (feet)0
5
10 Graphic LogGroupClassificationElevation (feet)335330
Sampler on rock, reworked glacial till
Organic-rich soil
Somewhat cemented
Drill chatterapproximately 21 to 25 feet bgs
19
10
8 37
Approximately 2 inches sod
Light brown sandy silt with gravel (stiff, wet) (fill)
Dark brown silty fine to medium sand with gravel and
trace organic matter (fine roots) (medium dense,
moist)
Gray iron oxide staining silty fine to medium sand with
gravel and trace organic matter (fine roots)
(medium dense, moist)
Grades to loose with trace wood fragments
Gray silty fine to medium sand with gravel (very dense,
wet) (intact glacial till)
Grades to light gray, moist
1
2
MC
3
4
5
MC
6
SA
7
8
10
12
12
8
6
2
14
10
11
6
88
50/6"
50/2"
SOD
ML
SM
SM
SM
Notes:
25 SAH
SST Holocene Drilling, Inc. Hollow-stem Auger
Diedrich D50 Track MountedDrilling
EquipmentAuto Hammer
140 (lbs) / 30 (in) Drop
WA State Plane North
NAD83 (feet)
119446.57
1267696.51
342
NAVD88
Easting (X)
Northing (Y)
Start Total
Depth (ft)
Logged By
Checked By
End
Surface Elevation (ft)
Vertical Datum
Drilled
Hammer
Data
System
Datum
Driller Drilling
Method
Groundwater not observed at time of exploration
1/27/20201/27/2020
Note: See Figure A-1 for explanation of symbols.
Coordinates Data Source: Horizontal approximated based on USGS Topo. Vertical approximated based on USGS Topo.
Sheet 1 of 1Project Number:
Project Location:
Project:
Federal Way, Washington
4519-017-00
Log of Boring B-5
Figure A-6
Lakehaven Water & Sewer District Maintenance Facility Improvements
Date:6/9/20 Path:P:\4\4519017\GINT\451901700.GPJ DBLibrary/Library:GEOENGINEERS_DF_STD_US_JUNE_2017.GLB/GEI8_GEOTECH_STANDARD_%F_NO_GWREMARKS
MoistureContent (%)FinesContent (%)FIELD DATA
MATERIAL
DESCRIPTION
Sample NameTestingRecovered (in)IntervalBlows/footCollected SampleDepth (feet)0
5
10
15
20
25 Graphic LogGroupClassificationElevation (feet)340335330325320
Fewer organics
Somewhat cemented
Groundwater observed at 9.3 feet bgs
Relatively low fines content
Relatively coarser than above
Cemented
11 31
Approximately 3 inches forest duff
Dark brown silty fine to coarse sand with occasional
gravel and trace organic matter (fine roots) (loose,
moist) (weathered glacial till)
Grades to light brown
Light gray with iron oxide staining silty fine to medium
sand with gravel (dense, moist) (intact glacial till)
Gray silty fine to coarse sand with gravel (dense, wet)
Light gray with iron oxide staining silty fine to medium
sand with gravel (very dense, moist)
1
2
3
SA
4
5
6
14
12
12
8
12
14
6
2
46
31
50
90
SOD
SM
SM
SM
SM
Notes:
21.5 SAH
SST Holocene Drilling, Inc. Hollow-stem Auger
Diedrich D50 Track MountedDrilling
EquipmentAuto Hammer
140 (lbs) / 30 (in) Drop
WA State Plane North
NAD83 (feet)
119554.91
1267896.63
326
NAVD88
Easting (X)
Northing (Y)
Start Total
Depth (ft)
Logged By
Checked By
End
Surface Elevation (ft)
Vertical Datum
Drilled
Hammer
Data
System
Datum
Driller Drilling
Method
See "Remarks" section for groundwater observed
1/27/20201/27/2020
Note: See Figure A-1 for explanation of symbols.
Coordinates Data Source: Horizontal approximated based on USGS Topo. Vertical approximated based on USGS Topo.
Sheet 1 of 1Project Number:
Project Location:
Project:
Federal Way, Washington
4519-017-00
Log of Boring B-6
Figure A-7
Lakehaven Water & Sewer District Maintenance Facility Improvements
Date:4/1/20 Path:P:\4\4519017\GINT\451901700.GPJ DBLibrary/Library:GEOENGINEERS_DF_STD_US_JUNE_2017.GLB/GEI8_GEOTECH_STANDARD_%F_NO_GWREMARKS
MoistureContent (%)FinesContent (%)FIELD DATA
MATERIAL
DESCRIPTION
Sample NameTestingRecovered (in)IntervalBlows/footCollected SampleDepth (feet)0
5
10
15
20 Graphic LogGroupClassificationElevation (feet)325320315310305
Approximately 2 inches sod
Brown silty fine to medium sand with gravel and trace organic matter
(fine roots) (medium stiff, wet) (fill)
Gray silty fine to medium sand with occasional gravel (loose, moist)
Dark brown sandy silt with occasional organic matter (wood
fragments) (soft, moist)
Gray with iron oxide staining silty fine sand (medium dense, moist)
(weathered glacial till)
Gray silty fine to medium sand with occasional gravel (dense, moist)
(intact glacial till)
SOD
SM
SM
ML
SM
SM
1%F
2
3MC
4
5
SA
17
59
14
Reworked glacial till
Reworked organic-rich topsoil; slow groundwater
seepage at 8½ feet
3-inch thick lens of gray silt at 9½ feet bgs
PIT completed at 12 feet bgs; moist soil conditions
observed with continued excavation
27
25
Notes: See Figure A-1 for explanation of symbols.
The depths on the test pit logs are based on an average of measurements across the test pit and should be considered accurate to ½ foot.
Coordinates Data Source: Horizontal approximated based on USGS Topo. Vertical approximated based on USGS Topo.Date:4/1/20 Path:P:\4\4519017\GINT\451901700.GPJ DBLibrary/Library:GEOENGINEERS_DF_STD_US_JUNE_2017.GLB/GEI8_TESTPIT_1P_GEOTEC_%FSheet 1 of 1Project Number:
Project Location:
Project:
Federal Way, Washington
4519-017-00
Log of Test Pit PIT-1
Figure A-8
Lakehaven Water & Sewer District Maintenance Facility ImprovementsElevation (feet)338337336335334333332331330329328327Depth (feet)1
2
3
4
5
6
7
8
9
10
11
12 Testing SampleGraphic LogSAMPLE
MATERIAL
DESCRIPTION
GroupClassificationSample NameTestingMoistureContent (%)REMARKS
FinesContent (%)Date
Excavated
Surface Elevation (ft)
Vertical Datum
Coordinate System
Horizontal Datum
Easting (X)
Northing (Y)
Total
Depth (ft)2/10/2020 12.5
339
NAVD88
119475.85
1267585.43
WA State Plane North
NAD83 (feet)
SAH
Checked By SST
See "Remarks" section for groundwater observed
Caving not observedEquipment Komatsu PC120
Logged By Excavator Kelly's Excavating
Approximately 2 inches sod
Gray with iron oxide staining silty fine to medium sand with gravel and
occasional cobbles (medium dense, moist) (fill)
Brown silty fine to medium sand with gravel and trace organic matter
(fine roots and wood fragments) (medium dense, moist)
Gray silty fine sand with gravel and occasional cobbles (medium
dense, moist)
Brown and gray silty fine to medium sand with gravel and occasional
cobbles and trace organic matter (fine roots and wood fragments)
(medium dense, moist)
Gray silty fine to coarse gravel with sand (dense, moist) (intact glacial
till)
SOD
SM
SM
SM
SM
GM
1
%F
2
3
4
MC
5SA
10
11
11
3- to 4-inch diameter cobbles
Reworked glacial till
3- to 6-inch diameter cobbles
Wood fragments to approximately 1-inch diameter
Organic-rich soils at 14½ feet
Slow groundwater seepage at 15 feet
PIT completed at 17 feet bgs
32
35
Notes: See Figure A-1 for explanation of symbols.
The depths on the test pit logs are based on an average of measurements across the test pit and should be considered accurate to ½ foot.
Coordinates Data Source: Horizontal approximated based on USGS Topo. Vertical approximated based on USGS Topo.Date:4/1/20 Path:P:\4\4519017\GINT\451901700.GPJ DBLibrary/Library:GEOENGINEERS_DF_STD_US_JUNE_2017.GLB/GEI8_TESTPIT_1P_GEOTEC_%FSheet 1 of 1Project Number:
Project Location:
Project:
Federal Way, Washington
4519-017-00
Log of Test Pit PIT-2
Figure A-9
Lakehaven Water & Sewer District Maintenance Facility ImprovementsElevation (feet)339338337336335334333332331330329328327326325324323Depth (feet)1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17 Testing SampleGraphic LogSAMPLE
MATERIAL
DESCRIPTION
GroupClassificationSample NameTestingMoistureContent (%)REMARKS
FinesContent (%)Date
Excavated
Surface Elevation (ft)
Vertical Datum
Coordinate System
Horizontal Datum
Easting (X)
Northing (Y)
Total
Depth (ft)2/10/2020 17.5
340
NAVD88
119487.86
1267712.72
WA State Plane North
NAD83 (feet)
SAH
Checked By SST
See "Remarks" section for groundwater observed
Caving not observedEquipment Komatsu PC120
Logged By Excavator Kelly's Excavating
Dark brown silty fine to medium sand with trace organic matter
(roots) (loose, moist) (fill)
Gray and tan with iron oxide staining silty fine to medium sand with
gravel, occasional debris (asphalt) and trace organic matter
(roots) (dense, moist)
SM
SM
1 Reworked glacial till; root up to ½ inch diameter
Notes: See Figure A-1 for explanation of symbols.
The depths on the hand-augered boring logs are based on an average of measurements across the hand-auger and should be considered accurate to ½ foot.
Coordinates Data Source: Horizontal approximated based on USGS Topo. Vertical approximated based on USGS Topo.Date:4/1/20 Path:P:\4\4519017\GINT\451901700.GPJ DBLibrary/Library:GEOENGINEERS_DF_STD_US_JUNE_2017.GLB/GEI8_TESTPIT_1P_GEOTEC_%FSheet 1 of 1Project Number:
Project Location:
Project:
Federal Way, Washington
4519-017-00
Log of Hand Auger HA-1
Figure A-10
Lakehaven Water & Sewer District Maintenance Facility ImprovementsElevation (feet)Depth (feet)1 Testing SampleGraphic LogSAMPLE
MATERIAL
DESCRIPTION
GroupClassificationSample NameTestingMoistureContent (%)REMARKS
FinesContent (%)Date
Excavated
Surface Elevation (ft)
Vertical Datum
Coordinate System
Horizontal Datum
Easting (X)
Northing (Y)
Total
Depth (ft)1/30/2020 1.75
Undetermined
NAVD88
119607.79
1267993.99
WA State Plane North
NAD83 (feet)
SAH
Checked By SST
Groundwater not observed
Caving not observedEquipment Hand Auger
Logged By Excavator GeoEngineers, Inc.
0
10
20
30
40
50
60
70
80
90
100
0.0010.010.11101001000PERCENT PASSING BY WEIGHT GRAIN SIZE IN MILLIMETERS
U.S. STANDARD SIEVE SIZE
2”
SAND SILT OR CLAYCOBBLESGRAVEL
COARSE MEDIUM FINECOARSEFINE
Boring Number Depth(feet)Soil Description
B-1
B-2
B-3
B-5
25
10
10
20
Silty fine to medium sand with gravel (SM)
Silty fine to medium sand with gravel (SM)
Silty fine to medium sand with gravel (SM)
Silty fine to medium sand with gravel (SM)
Symbol Moisture(%)
12
8
9
8
3/8”3”1.5”#4 #10 #20 #40 #60 #1003/4”Figure A-11Sieve Analysis ResultsLakehavenWater & Sewer Maintenance Facility ImprovementsFederal Way, Washington4519-017-00 Date Exported: 2/26/20
Note:This report may not be reproduced,except in full,without written approval of GeoEngineers,Inc.Test results are applicable only to the specific sample on which they were
performed,and should not be interpreted as representative of any other samples obtained at other times,depths or locations,or generated by separate operations or processes.
The grain size analysis results were obtained in general accordance with ASTM C 136.GeoEngineers 17425 NE Union Hill Road Ste 250,Redmond,WA 98052
#2001”#140
0
10
20
30
40
50
60
70
80
90
100
0.0010.010.11101001000PERCENT PASSING BY WEIGHT GRAIN SIZE IN MILLIMETERS
U.S. STANDARD SIEVE SIZE
2”
SAND SILT OR CLAYCOBBLESGRAVEL
COARSE MEDIUM FINECOARSEFINE
Boring Number Depth(feet)Soil Description
B-6
PIT-1
PIT-2
7.5
12
17
Silty fine to medium sand with gravel (SM)
Silty fine to medium sand with gravel (SM)
Silty fine to coarse gravel with sand (GM)
Symbol Moisture(%)
11
14
11
3/8”3”1.5”#4 #10 #20 #40 #60 #1003/4”Figure A-12Sieve Analysis Results4519-017-00 Date Exported: 2/26/20
Note:This report may not be reproduced,except in full,without written approval of GeoEngineers,Inc.Test results are applicable only to the specific sample on which they were
performed,and should not be interpreted as representative of any other samples obtained at other times,depths or locations,or generated by separate operations or processes.
The grain size analysis results were obtained in general accordance with ASTM C 136.GeoEngineers 17425 NE Union Hill Road Ste 250,Redmond,WA 98052
#2001”#140
LakehavenWater & Sewer Maintenance Facility ImprovementsFederal Way, Washington
APPENDIX B
Report Limitations and Guidelines for Use
June 9, 2020| Page B-1
File No. 4519-017-00
APPENDIX B
REPORT LIMITATIONS AND GUIDELINES FOR USE1
This appendix provides information to help you manage your risks with respect to the use of this report.
Read These Provisions Closely
It is important to recognize that the geoscience practices (geotechnical engineering, geology and
environmental science) rely on professional judgment and opinion to a greater extent than other
engineering and natural science disciplines, where more precise and/or readily observable data may
exist. To help clients better understand how this difference pertains to our services, GeoEngineers
includes the following explanatory “limitations” provisions in its reports. Please confer with GeoEngineers
if you need to know more how these “Report Limitations and Guidelines for Use” apply to your project or
site.
Geotechnical Services are Performed for Specific Purposes, Persons and Projects
This report has been prepared for Helix Design Group and for the Project(s) specifically identified in the
report. The information contained herein is not applicable to other sites or projects.
GeoEngineers structures its services to meet the specific needs of its clients. No party other than the
party to whom this report is addressed may rely on the product of our services unless we agree to such
reliance in advance and in writing. Within the limitations of the agreed scope of services for the Project,
and its schedule and budget, our services have been executed in accordance with our Agreement with
Helix Design Group dated September 19, 2019 (signed January 13, 2020) and generally accepted
geotechnical practices in this area at the time this report was prepared. We do not authorize, and will not
be responsible for, the use of this report for any purposes or projects other than those identified in the
report.
A Geotechnical Engineering or Geologic Report is based on a Unique Set of Project-Specific
Factors
This report has been prepared for the proposed Lakehaven Water and Sewer District Maintenance Facility
Improvements project in Federal Way, Washington. GeoEngineers considered a number of unique,
project-specific factors when establishing the scope of services for this project and report. Unless
GeoEngineers specifically indicates otherwise, it is important not to rely on this report if it was:
■ not prepared for you,
■ not prepared for your project,
■ not prepared for the specific site explored, or
■ completed before important project changes were made.
For example, changes that can affect the applicability of this report include those that affect:
■ the function of the proposed structure;
1 Developed based on material provided by ASFE, Professional Firms Practicing in the Geosciences; www.asfe.org.
June 9, 2020| Page B-2
File No. 4519-017-00
■ elevation, configuration, location, orientation or weight of the proposed structure;
■ composition of the design team; or
■ project ownership.
If changes occur after the date of this report, GeoEngineers cannot be responsible for any consequences
of such changes in relation to this report unless we have been given the opportunity to review our
interpretations and recommendations. Based on that review, we can provide written modifications or
confirmation, as appropriate.
Environmental Concerns are Not Covered
Unless environmental services were specifically included in our scope of services, this report does not
provide any environmental findings, conclusions, or recommendations, including but not limited to, the
likelihood of encountering underground storage tanks or regulated contaminants.
Information Provided by Others
GeoEngineers has relied upon certain data or information provided or compiled by others in the
performance of our services. Although we use sources that we reasonably believe to be trustworthy,
GeoEngineers cannot warrant or guarantee the accuracy or completeness of information provided or
compiled by others.
Subsurface Conditions Can Change
This geotechnical or geologic report is based on conditions that existed at the time the study was
performed. The findings and conclusions of this report may be affected by the passage of time, by
man-made events such as construction on or adjacent to the site, new information or technology that
becomes available subsequent to the report date, or by natural events such as floods, earthquakes, slope
instability or groundwater fluctuations. If more than a few months have passed since issuance of our
report or work product, or if any of the described events may have occurred, please contact GeoEngineers
before applying this report for its intended purpose so that we may evaluate whether changed conditions
affect the continued reliability or applicability of our conclusions and recommendations.
Geotechnical and Geologic Findings are Professional Opinions
Our interpretations of subsurface conditions are based on field observations from widely spaced sampling
locations at the site. Site exploration identifies the specific subsurface conditions only at those points
where subsurface tests are conducted or samples are taken. GeoEngineers reviewed field and laboratory
data and then applied its professional judgment to render an informed opinion about subsurface
conditions at other locations. Actual subsurface conditions may differ, sometimes significantly, from the
opinions presented in this report. Our report, conclusions and interpretations are not a warranty of the
actual subsurface conditions.
Geotechnical Engineering Report Recommendations are Not Final
We have developed the following recommendations based on data gathered from subsurface
investigation(s). These investigations sample just a small percentage of a site to create a snapshot of the
subsurface conditions elsewhere on the site. Such sampling on its own cannot provide a complete and
accurate view of subsurface conditions for the entire site. Therefore, the recommendations included in
June 9, 2020| Page B-3
File No. 4519-017-00
this report are preliminary and should not be considered final. GeoEngineers’ recommendations can be
finalized only by observing actual subsurface conditions revealed during construction. GeoEngineers
cannot assume responsibility or liability for the recommendations in this report if we do not perform
construction observation.
We recommend that you allow sufficient monitoring, testing and consultation during construction by
GeoEngineers to confirm that the conditions encountered are consistent with those indicated by the
explorations, to provide recommendations for design changes if the conditions revealed during the work
differ from those anticipated, and to evaluate whether earthwork activities are completed in accordance
with our recommendations. Retaining GeoEngineers for construction observation for this project is the
most effective means of managing the risks associated with unanticipated conditions. If another party
performs field observation and confirms our expectations, the other party must take full responsibility for
both the observations and recommendations. Please note, however, that another party would lack our
project-specific knowledge and resources.
A Geotechnical Engineering or Geologic Report Could Be Subject to Misinterpretation
Misinterpretation of this report by members of the design team or by contractors can result in costly
problems. GeoEngineers can help reduce the risks of misinterpretation by conferring with appropriate
members of the design team after submitting the report, reviewing pertinent elements of the design
team’s plans and specifications, participating in pre-bid and preconstruction conferences, and providing
construction observation.
Do Not Redraw the Exploration Logs
Geotechnical engineers and geologists prepare final boring and testing logs based upon their
interpretation of field logs and laboratory data. The logs included in a geotechnical engineering or
geologic report should never be redrawn for inclusion in architectural or other design drawings.
Photographic or electronic reproduction is acceptable, but separating logs from the report can create a
risk of misinterpretation.
Give Contractors a Complete Report and Guidance
To help reduce the risk of problems associated with unanticipated subsurface conditions, GeoEngineers
recommends giving contractors the complete geotechnical engineering or geologic report, including these
“Report Limitations and Guidelines for Use.” When providing the report, you should preface it with a
clearly written letter of transmittal that:
■ advises contractors that the report was not prepared for purposes of bid development and that its
accuracy is limited; and
■ encourages contractors to confer with GeoEngineers and/or to conduct additional study to obtain the
specific types of information they need or prefer.
Contractors are Responsible for Site Safety on Their Own Construction Projects
Our geotechnical recommendations are not intended to direct the contractor’s procedures, methods,
schedule or management of the work site. The contractor is solely responsible for job site safety and for
managing construction operations to minimize risks to on-site personnel and adjacent properties.
June 9, 2020| Page B-4
File No. 4519-017-00
Biological Pollutants
GeoEngineers’ Scope of Work specifically excludes the investigation, detection, prevention or assessment
of the presence of Biological Pollutants. Accordingly, this report does not include any interpretations,
recommendations, findings or conclusions regarding the detecting, assessing, preventing or abating of
Biological Pollutants, and no conclusions or inferences should be drawn regarding Biological Pollutants as
they may relate to this project. The term “Biological Pollutants” includes, but is not limited to, molds,
fungi, spores, bacteria and viruses, and/or any of their byproducts.
A Client that desires these specialized services is advised to obtain them from a consultant who offers
services in this specialized field.