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DRAFT GEOTECHNICAL REPORT AND
INFILTRATION TEST RESULTS
PROPOSED TRUCK PARKING
600 Southwest 10th Street
Renton, Washington
PROJECT NO. 21-220
June 2021
Prepared for:
Elion Partners
Exhibit 9
RECEIVED
08/12/2021
AMorganroth
PLANNING DIVISION
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________________________________________________
3213 Eastlake Avenue E, Ste B
Seattle, WA 98102
Tel (206) 262-0370
Fax (206) 262-0374
Geotechnical & Earthquake
Engineering Consultants
June 10, 2021
Project No. 21-220
Mr. Michael Stellino
Elion Partners
3323 Northeast 163rd Street, Suite 600
Miami, Florida 33160
Subject: Draft Geotechnical Report and Infiltration Test Results
Proposed Truck Parking
600 Southwest 10th Street, Lakewood, Washington
Dear Mr. Stellino:
Attached please find our draft geotechnical report for the proposed truck parking at 600 Southwest
10th Street in Renton, Washington, Washington. In preparing the attached report, we performed a
reconnaissance of the site, observed and logged the excavation of eight test pits, conducted two
infiltration tests, and performed our engineering analyses.
This report is being provided as a draft pending the results of our laboratory testing. Our final
report will be issued the week of June 14 after the laboratory testing is completed, and after we
have received review comments from the design team.
In summary, based on the results of our study, it is our opinion the proposed truck parking
improvements may be constructed as planned. The near surface conditions in the project area
consist of fill comprised of poorly graded sand with silt overlying native medium stiff to stiff silt.
The fill should provide suitable support for the planned pavement improvements.
We conducted two infiltration tests to evaluate the feasibility of infiltrating stormwater at the site.
Based on the results of our tests, the site soils have limited infiltration capacity and the suitability
of infiltration would be subject to engineering feasibility.
We appreciate the opportunity to be of service. Please call if you have any questions.
Sincerely,
DRAFT
Scott D. Dinkelman, LEG
Principal Engineering Geologist
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21-220 600 SW 10th Avenue i PanGEO, Inc.
TABLE OF CONTENTS
..................................................................................................................................................... 1
1.0 INTRODUCTION................................................................................................................... 1
2.0 SITE AND PROJECT DESCRIPTION ............................................................................... 1
3.0 SUBSURFACE EXPLORATIONS ....................................................................................... 3
3.1 TEST PIT EXCAVATIONS ......................................................................................................... 3
3.2 LABORATORY TESTING .......................................................................................................... 3
3.2.1 Moisture Content and Grain Size Distribution Analysis ............................................... 3
3.2.2 Cation Exchange Capacity and Organic Content ......................................................... 4
4.0 SUBSURFACE CONDITIONS ............................................................................................. 4
4.1 SITE GEOLOGY ....................................................................................................................... 4
4.2 SOIL CONDITIONS................................................................................................................... 5
4.3 GROUNDWATER CONDITIONS ................................................................................................. 5
5.0 INFILTRATION TESTING AND RECOMMENDATIONS ............................................ 6
5.1 TEST METHOD ........................................................................................................................ 6
5.2 CORRECTION FACTORS .......................................................................................................... 7
5.3 LONG TERM INFILTRATION RATE FOR DESIGN ....................................................................... 7
5.4 CATION EXCHANGE CAPACITY TEST RESULTS ...................................................................... 8
5.5 ORGANIC CONTENT TEST RESULTS ........................................................................................ 9
5.6 CONSTRUCTION CONSIDERATIONS ......................................................................................... 9
6.0 PAVEMENT DESIGN ......................................................................................................... 10
6.1 DESIGN PARAMETERS .......................................................................................................... 10
6.2 PAVEMENT DESIGN .............................................................................................................. 11
6.2.1 Asphalt Pavement Sections .......................................................................................... 11
6.1.3 Portland Cement Concrete Pavements ........................................................................ 12
6.1.4 Subgrade Preparation .................................................................................................. 12
6.1.5 Construction of Cement Treated Base (CTB) .............................................................. 13
6.1.6 Placement of HMA ....................................................................................................... 14
6.1.7 Pavement Surface Drainage ........................................................................................ 14
6.1.8 Maintenance ................................................................................................................. 14
7.0 EARTHWORK CONSIDERATIONS ................................................................................ 14
7.1 TEMPORARY EXCAVATIONS ................................................................................................. 14
7.2 UNDERGROUND UTILITIES ................................................................................................... 15
7.2.1 Pipe Support and Bedding ........................................................................................... 15
7.2.2 Trench Backfill ............................................................................................................. 15
7.4 STRUCTURAL FILL AND COMPACTION .................................................................................. 16
DocuSign Envelope ID: 7DBCA7C0-8C41-4D51-AF13-689B38E87E3D
Geotechnical Report and Infiltration Assessment
Proposed Truck Parking: 600 Southwest 10th Street, Renton, Washington
June 10, 2021
21-220 600 SW 10th Avenue ii PanGEO, Inc.
7.5 MATERIAL REUSE ................................................................................................................ 16
7.6 PERMANENT CUT AND FILL SLOPES ..................................................................................... 17
7.7 WET WEATHER CONSTRUCTION .......................................................................................... 17
7.8 EROSION CONSIDERATIONS .................................................................................................. 17
8.0 LIMITATIONS ..................................................................................................................... 18
9.0 LIST OF REFERENCES ..................................................................................................... 20
DocuSign Envelope ID: 7DBCA7C0-8C41-4D51-AF13-689B38E87E3D
Geotechnical Report and Infiltration Assessment
Proposed Truck Parking: 600 Southwest 10th Street, Renton, Washington
June 10, 2021
21-220 600 SW 10th Avenue iii PanGEO, Inc.
LIST OF ATTACHMENTS
Figure 1 Vicinity Map
Figure 2 Site and Exploration Plan
Appendix A Summary Test Pit Logs
Figure A-1 Terms and Symbols for Boring and Test Pit Logs
Figure A-2 Log of Test Pit TP-1 (Infiltration Test)
Figure A-3 Log of Test Pit TP-2 (Infiltration Test)
Figure A-4 Log of Test Pit TP-3
Figure A-5 Log of Test Pit TP-4
Figure A-6 Log of Test Pit TP-5
Figure A-7 Log of Test Pit TP-6
Figure A-7 Log of Test Pit TP-7
Figure A-8 Log of Test Pit TP-8
Appendix B Geotechnical Laboratory Test Results
Figure B-1 Grain Size Distribution (Results Pending)
Appendix C Analytical Laboratory Test Results
Cation Exchange Capacity and Organic Matter Test Results (Results Pending)
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21-220 600 SW 10th Avenue PanGEO, Inc. 1
DRAFT GEOTECHNICAL REPORT AND INFILTRATION ASSESSMENT
PROPOSED TRUCK PARKING
600 SOUTHWEST 10TH AVENUE
RENTON, WASHINGTON
_______________________________________________________________________
1.0 INTRODUCTION
PanGEO has completed a geotechnical study and infiltration assessment for the proposed truck
parking at 600 Southwest 10th Avenue in Renton, Washington. Our scope of services included
conducting a site reconnaissance, excavating eight test pits, conducting two Small Pilot Infiltration
Tests, and developing the conclusions and recommendations presented in this report.
This report is being provided in draft form for the preliminary use of the design team, pending the
results of our laboratory testing. We will provide a final version of this report when the laboratory
testing is completed. However, we do not anticipate the test results to affect the recommendations
contained herein.
2.0 SITE AND PROJECT DESCRIPTION
The subject site is located at 600 Southwest 10th Avenue in Renton, Washington and is
approximately as shown on Figure 1, Vicinity Map.
The project site is an approximately rectangular-shaped area on the north side of the existing
warehouse building at 600 Southwest 10th Avenue and comprises about 4½ acres. The project area
is surrounded to the north, south, east, and west by one-story warehouse buildings. The attached
Figure 2, Site and Exploration Plan shows the layout of the site. Plate 1 on the next page provides
an aerial view of the site while Plate 2 on the next page provides a ground level view of the site at
the time of this study.
The site is currently vacant of structures and is flat, with less than five feet of elevation change
across the length of the site. The north half of the site is vegetated with a thin covering of grass,
while the south portion of the site is surfaced with asphalt and gravel and is being used for outdoor
storage. The perimeter of the site is vegetated with alder trees.
We understand it is planned to develop the site for use as truck parking with spaces for 140 WB-
40 semi-trucks with trailers along with associated driving and turning lanes. At the time of this
study, it had not been determined how many trucks would use the facility on a daily basis. For
pavement design purposes, we have assumed 100 truck trips per day. We understand it is planned
DocuSign Envelope ID: 7DBCA7C0-8C41-4D51-AF13-689B38E87E3D
Geotechnical Report and Infiltration Assessment
Proposed Truck Parking: 600 Southwest 10th Avenue, Renton, Washington
June 10, 2021
21-220 600 SW 10th Avenue Page 2 PanGEO, Inc.
to use both concrete and asphalt pavements. The planned improvements will also include the
installation of underground utilities.
Surface water from the impervious surfaces will be directed to an infiltration trench below the
central portion of the site.
Plate 1: Aerial view of
the site looking toward
the north.
The warehouse at 600
Southwest 10th Street is in
the lower portion of the
photo.
The project area is
outlined in yellow.
Plate 2: Ground level view
of the site. View is looking
from west to east.
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Geotechnical Report and Infiltration Assessment
Proposed Truck Parking: 600 Southwest 10th Avenue, Renton, Washington
June 10, 2021
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3.0 SUBSURFACE EXPLORATIONS
3.1 TEST PIT EXCAVATIONS
Eight test pits (TP-1 through TP-8) were excavated at the site on May 27, 2021. The test pits were
excavated using a CAT 305E excavator. The approximate locations of our test pits were identified
in the field relative to site features and are shown on Figure 2, Site and Exploration Plan.
A geologist from PanGEO was present throughout the infiltration test program to observe the
excavation, assist in sampling, and to document the soil samples obtained from the excavation and
perform the tests. The relative in-situ density of cohesionless soils, or the relative consistency of
fine-grained soils, was estimated from the excavating action of the excavator, probing the sidewalls
of the test pits with a ½-inch diameter T-handle probe, and the stability of the test pit sidewalls.
Where soil contacts were gradual or undulating, the average depth of the contact was recorded in
the log.
Test Pits TP-1 and TP-2 were used for infiltration testing purposes. The infiltration testing process
consisted of initially excavating to about four feet below grade for testing. After the infiltration
tests were completed the test pits were excavated to a maximum depth of about ten feet below
grade. Details of our infiltration testing and discussion of the test results are included in Section 5
of this report.
The soils were logged in general accordance with ASTM D-2487 Standard Practice for
Classification of Soils for Engineering Purposes and the system summarized on Figure A-1, Terms
and Symbols for Boring and Test Pit Logs. The summary test pit logs are included in Appendix A.
3.2 LABORATORY TESTING
Representative soil samples have been submitted for laboratory testing, to verify or modify the field
soil classification and to evaluate the general physical properties and engineering characteristics of
the soil encountered. The test results are pending, and will be included in our final report.
3.2.1 Moisture Content and Grain Size Distribution Analysis
Moisture content tests and grain-size distribution analysis were performed on six soil samples
collected from the test pits. The tests were conducted in general accordance with ASTM D2216
Standard Test Methods for Laboratory Determination of Water (Moisture) Content of Soil and
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Geotechnical Report and Infiltration Assessment
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Rock by Mass and ASTM D-6913 Standard Test Methods for Particle-Size Distribution
(Gradation) of Soils Using Sieve Analysis. A summary of our test results is included in Appendix
B of this report.
3.2.2 Cation Exchange Capacity and Organic Content
Four samples were submitted to Kuo Testing Labs for cation exchange capacity (CEC) testing in
accordance with EPA Laboratory Method 9081. The CEC is a calculated value that estimates of
the soil’s ability to attract, retain, and exchange cation elements. It is reported in millequivalents
per 100 grams of soil (meq/100g). The results of the CEC tests are discussed in Section 5.4 of this
report and are provided in Appendix C.
3.2.3 Organics Content Testing
Four samples were also submitted to Kuo Testing Labs to determine the percent organics content.
The testing was performed in general accordance with the ASTM D-2974 Standard Test Methods
for Moisture, Ash, and Organic Matter of Peat and Other Organic Soils. Section 5.5 of this report
discusses the organics test results.
4.0 SUBSURFACE CONDITIONS
4.1 SITE GEOLOGY
Based on review of the Geologic Map of the Renton Quadrangle, King County, Washington
(Mullineaux, 1965) the geologic units in the vicinity of the site consist of Quaternary Alluvium
deposited by the Cedar River (Qac) and Quaternary Alluvium deposited by the White River (Qaw).
Quaternary Alluvium deposited by the Cedar River consists of sand and gravel deposited with thin
interbeds of silt, clay and peat and occurs along the edges of the Duwamish Valley.
Quaternary Alluvium deposited by the White River consists of clay, silt, and sand that locally
contains peat and gravel.
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Geotechnical Report and Infiltration Assessment
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4.2 SOIL CONDITIONS
For a detailed description of the subsurface conditions encountered at each exploration location,
please refer to our test pit logs provided in Appendix A. The stratigraphic contacts indicated on
the logs represent the approximate depth to boundaries between soil units. Actual transitions
between soil units may be more gradual or occur at different elevations. The descriptions of
groundwater conditions and depths are likewise approximate. The following is a generalized
description of the soils encountered in the test pits.
Topsoil – A surficial layer of topsoil and sod was encountered at our test pit locations. The
topsoil was about six inches thick and consisted of dark brown sand with silt and organics.
Fill – Below the topsoil, we encountered fill. The fill ranged from two to four feet thick and
consisted of poorly graded fine to medium sand with silt and a trace of gravel. Based on the
extent of the fill encountered at our exploration locations, it is likely the pavement subgrade
soils will consist of fill.
Quaternary Alluvium (Qaw) – Directly below the fill, we encountered medium stiff to stiff
gray silt with a trace to some sand. Based on the relatively fined grained nature of this soil,
we classified this soil as Quaternary Alluvium deposited by the White River. This soil was
encountered to the maximum exploration depth of 10 feet below grade.
Our test pits were backfilled after completion of our logging and testing. The backfill was not
compacted. We recommend the backfill in the test pits be overexcavated during clearing and
grading and backfilled with properly-compacted structural fill.
Our subsurface descriptions are based on the conditions encountered at the time of our exploration.
Soil conditions between our exploration locations may vary from those encountered. The nature
and extent of variations between our exploratory locations may not become evident until
construction. If variations do appear, PanGEO should be requested to reevaluate the
recommendations in this report and to modify or verify them in writing prior to proceeding with
earthwork and construction.
4.3 GROUNDWATER CONDITIONS
Light groundwater seepage was encountered at 8 to 8½ feet below grade in all of our test pits
except Test Pits TP-4, TP-5, and TP-7 located along the north side of the site. With the planned
DocuSign Envelope ID: 7DBCA7C0-8C41-4D51-AF13-689B38E87E3D
Geotechnical Report and Infiltration Assessment
Proposed Truck Parking: 600 Southwest 10th Avenue, Renton, Washington
June 10, 2021
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improvements to be constructed at or near existing site grade, we do not anticipate that
groundwater seepage will result in construction related issues. However, groundwater could be
encountered in utility trenches, especially deep utilities, if planned.
It should also be noted that groundwater elevations may vary depending on the season, local
subsurface conditions, and other factors. Groundwater levels are normally highest during the
winter and early spring (typically October through May).
The planned infiltration systems will need to be set at least five feet above the wet season high
groundwater elevation. We installed shallow two-inch diameter standpipe piezometers in Test Pits
TP-4, TP-6, and TP-7 to allow for monitoring of groundwater levels during the wet season to allow
for establishing the wet season high groundwater elevation.
5.0 INFILTRATION TESTING AND RECOMMENDATIONS
Two infiltration tests were conducted in TP-1 and TP-2 at the locations indicated on the attached
Figure 2. The test method and the results are discussed below.
5.1 TEST METHOD
The field infiltration tests were conducted in general accordance with the procedure for Small Pilot
Infiltration Test (PIT) as outlined in the King County Surface Water Design Manual (KCSWDM)
(King County, 2016). In general, the test consisted of the following procedure:
• A test pit was excavated to the approximate design bottom of the proposed infiltration
facilities with a minimum bottom area of 12 square feet.
• The test pit was pre-soaked by maintaining a water level of at least 12 inches above the
bottom of the pit.
• After the pre-soak period, an electronic flow meter was used to monitor the amount of
water needed to maintain a constant head of 12 inches for at least one hour and until at least
a constant volume of water per time unit was achieved.
• At the end of the constant head test, we measured the falling head infiltration rate by
shutting off the water flow and recorded the drop in water level over regular time intervals
for one hour or until all of the water was completely infiltrated.
The field infiltration rate was calculated based on the final measured volume per time unit, and the
surface area of the holes.
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Geotechnical Report and Infiltration Assessment
Proposed Truck Parking: 600 Southwest 10th Avenue, Renton, Washington
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5.2 CORRECTION FACTORS
The KCSWDM requires the infiltration rates measured in the field be reduced by applying
correction factors to account for uncertainties in the test method used, depth to the water table or
impervious strata, the geometry of the infiltration facility, and degree of influent control to prevent
siltation and bio-buildup. We used the simplified method outlined in the King County Surface
Water Design Manual (KCSWDM, 2016) to estimate the maximum design infiltration rate. The
simplified method equation is provided below:
Idesign = Imeasured x Ftesting x Fgeometry x Fplugging (KCSWDM Eq 5-11)
where, Fgeometry = 4 D/W + 0.05 (KCSWDM Eq 5-12)
(where D = the 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, a value between 0.25 and 1.0 should be used)
The following values were used to reduce the field infiltration rate and provide a long-term design
infiltration rate:
Ftesting = 0.5 for large-scale testing
Fgeometry = 1.0 (D=4 feet*, W=4 feet)
Fplugging = 0.7 (loams and sandy loams)
*To determine Fgeometry, we estimated D to be 4 feet based on an assumed infiltration system depth
of four feet and used a groundwater elevation of eight feet below grade.
5.3 LONG TERM INFILTRATION RATE FOR DESIGN
Table 1, below, details the infiltration data collected during the tests and the long-term design rates
calculated for each tested location.
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Geotechnical Report and Infiltration Assessment
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TABLE 1: Small Pilot Infiltration Test Data Corrected for Long Term Design Rate
Test
Location
(depth)
Pre-Soak
Duration
(hours)
Test
Stage
Test
Duration
Field
Measured
Rate
(in/hour)
Correction Factors Long
Term
Design
Rate
(in/hour) Ftesting Fgeometry Fplugging
TP-1
(4 feet) 6 Constant
Head 1 hour 0.7 0.5 1 0.7 0.25
TP-2
(4 feet) 6 Constant
Head 1 hour 0.4 0.5 1 0.7 0.14
Infiltration provided in Table 2 are relatively low and the soils may not be feasible to use for
infiltration. The KCSWDM does not specify a minimum infiltration rate for infiltration system
design except a requirement that any ponding be drawn down with 24 hours. The infiltration
system feasibility should be determined by the civil engineer.
5.4 CATION EXCHANGE CAPACITY TEST RESULTS
The KCSWDM specifies that soils used for treatment and infiltration should have a CEC of greater
than or equal to 5 milliequivalents per 100 grams of dry soil (meq/100g). CEC testing was
performed on two representative samples from our test pits. Table 2, below, provides a summary
of the CEC test results.
TABLE 2: Cation Exchange Capacity Test Results
Location Soil Sample Depth
(feet) CEC (meq/100g)
TP-1 4 PENDING
TP-2 4 PENDING
The results of the analytical testing are provided in Appendix C.
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Geotechnical Report and Infiltration Assessment
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5.5 ORGANIC CONTENT TEST RESULTS
Two representative samples collected from our infiltration test pits were submitted to determine
the percent of organic material in the soils at our infiltration test locations. The testing procedure
was performed in general accordance with the ASTM D2974-13 Standard Test Methods for
Moisture, Ash, and Organic Matter of Peat and Other Organic Soils. Table 5, below, provides a
summary of the organic material test results.
TABLE 3: Organic Matter of Organic Soils Test Results
Location Soil Sample Depth
(feet)
Organic Content
(%)
PIT-1 4 PENDING
PIT-2 4 PENDING
A summary of the analytical testing is provided in Appendix C.
5.6 CONSTRUCTION CONSIDERATIONS
Infiltration facilities are post-construction facilities which are designed to improve the quality and
manage the volume of stormwater runoff by encouraging natural infiltration on-site. In order to
protect the infiltration receptor soils from becoming clogged with sediment and/or becoming
compacted during construction, we recommend the following measures be implemented during
construction:
• The infiltration facilities should be constructed as late in the schedule as feasible and
should not be constructed until after the upstream areas are stabilized.
• Heavy equipment traffic on prepared subgrades should be limited, especially during wet
weather.
• If fine grained sediment is deposited or tracked onto the infiltration system subgrade, it
should be removed using an excavator with a grade plate, a small dozer or a vacuum
truck.
• The subgrade should be scarified prior to placing fill to prevent sealing of the receptor
soils.
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Geotechnical Report and Infiltration Assessment
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• Structural fill and aggregate base materials should be end-dumped at the edge of the fill
area and the material pushed out over the subgrade.
• Grading of the infiltration galleries should be accomplished using low-impact earth-
moving equipment to prevent compaction of the underlying soils. Wide tracked vehicles
such as excavator, small dozers and bobcats are suggested.
• The infiltration system subgrade soils should be reviewed after excavation to verify the
soils encountered are as anticipated.
• The infiltration system should not be brought on-line until after earthwork is completed
and the site is permanently stabilized with vegetation and hardscaping.
6.0 PAVEMENT DESIGN
6.1 DESIGN PARAMETERS
Our pavement analysis was performed using the 1993 AASHTO pavement design methodology.
Our analysis included evaluating hot mix asphalt (HMA) and Portland Cement Concrete (PCC)
pavement sections. For the HMA pavement section, it is our opinion that the HMA may be used
in conjunction with crushed surfacing base course (i.e., 1 ¼ inch minus crushed rock), or cement
treated base. The principal benefit of CTB is the use of on-site soils and the reduction and possible
elimination of the need for crushed rock base for pavement.
We understand traffic will consist of 40-WB semi-trucks with trailers. The number of daily truck
trips was not available at the time this study was prepared. Therefore, for our design we assumed
100 trucks per day.
The parameters summarized in Table 4 on the next page were used in our design.
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TABLE 4: Pavement Design Parameters
Parameter
Value
HMA PCC
Pavement Design life 20 years 20 years
Reliability 85% 85%
Overall Standard Deviation 0.45 0.45
Initial Serviceability 4.2 4.2
Terminal Serviceability 2.5 2.5
Design Serviceability Loss (∆PSI) 1.7 1.7
Drainage Coefficient 1.0 1.0
Layer Coefficients:
Hot Mix Asphalt
Crushed Surfacing Base/Top Course
Cement Treated Base
0.44
0.14 0.14
0.11 0.11
Design Resilient Modulus for Subgrade 15,000 psi 15,000 psi
Average Annual Daily Traffic 100 100
Percent Heavy Trucks 100 100
ESAL 1,145,000 1,145,000
The performance of the pavement designs provided below and using the design period assumed in
our analysis would depend on a number of factors, including the actual traffic loading conditions
and performance of regular maintenance. The recommended pavement sections will need to be
revised if the anticipated truck traffic varies from our assumptions.
6.2 PAVEMENT DESIGN
6.2.1 Asphalt Pavement Sections
We recommend the following minimum pavement sections be used in new asphalt paved areas:
Light Traffic Areas – truck parking areas and passenger vehicle areas:
• Three inches of Class ½ inch Hot Mix Asphalt (HMA) over six inches crushed surfacing
top/base course (CSTC/CSBC); or
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Geotechnical Report and Infiltration Assessment
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• Three inches of Class ½ inch HMA over 12 inches cement treated base (see detailed
discussion on cement treated base in Section 6.5.1)
Heavy Traffic Areas – drive aisles subjected to truck traffic:
• Four inches of Class ½ inch Hot Mix Asphalt (HMA) over six inches crushed surfacing
top/base course (CSTC/CSBC); or
• Four inches of Class ½ inch HMA over 12 inches cement treated base
The asphalt binder should consist of pavement grade (PG) PG64-22.
6.1.3 Portland Cement Concrete Pavements
• Eight inches of Portland cement concrete (plain butt jointed) over six inches of crushed
surfacing base course; or
• Eight inches of Portland cement concrete (plain butt jointed) over 12 inches of cement
treated base.
The design is based on using concrete that will achieve a minimum 28-day compressive strength
(f’c) of 4,000 psi. The transverse joints in the pavement should be spaced 15 feet apart or less and
should be in accordance with WSDOT Standard Specifications for Road, Bridge and Municipal
Construction (WSDOT, 2021).
6.1.4 Subgrade Preparation
Based on the conditions encountered in our test pits, the pavement subgrade will consist of existing
fill comprised of poorly graded sand with silt and a trace of gravel.
Site preparation for new pavement areas should begin with removal of the existing topsoil,
vegetation, roots, debris, deleterious material, and unsuitable soil from the area of the proposed
improvements and excavating to the design subgrade elevation, where applicable. Following the
stripping operation and excavations necessary to achieve construction subgrade elevations, the
ground surface where structural fill, or pavements are to be placed should be observed by PanGEO.
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The test pits for this study were backfilled with the site soils after completion of our logging and
testing. The backfill was not compacted to the requirements of structural fill. The test pit locations
should be identified during grading and the fill overexcavated and backfilled with properly-
compacted structural fill.
Proofrolling should be performed to identify soft or unstable areas. Soft or yielding areas identified
during proofrolling should be moisture conditioned as needed and re-compacted in place. If the
soft areas are still yielding after re-compaction, they should be overexcavated and replaced with
structural fill to a depth that will provide a stable pavement base. The optional use of a geotextile
subgrade stabilization fabric, such as Mirafi 600X, or an equivalent product placed directly on the
overexcavated surface may help to bridge excessively unstable areas. The need for geotextile can
be determined during construction, based on the actual conditions encountered, but should be
included in the construction budget.
Overexcavated areas should be backfilled with WSDOT 9-03.9(3) Crushed Surfacing Base
Course, or WSDOT 9-03.14 (1) Gravel Borrow (WSDOT, 2021) compacted to the requirements
of structural fill. The subgrade preparation should be observed by PanGEO during construction,
to verify the adequacy of the prepared subgrade.
6.1.5 Construction of Cement Treated Base (CTB)
If cement treated base pavement option is used, the cement treatment should be performed using
Portland concrete cement. The cement should be applied at a rate of at least 10 pounds of cement
per square foot of area to be treated to a depth of 12 inches.
The cement treatment operation should be performed in general accordance with the following
recommendations:
• For every square foot of treated area, mix minimum 10 pounds of cement into the upper 12
inches of the subgrade soils. A road reclaimer/stabilizer, or similar piece of equipment,
should be used to thoroughly mix the cement into the soil to the recommended treatment
depth.
• The treated subgrade should then be graded and compacted using a smooth-drum vibratory
roller to at least 95 percent maximum dry density in accordance with ASTM D 1557,
Modified Proctor.
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• Heavy truck traffic should be kept off the treated area for at least 3 days after treatment to
allow the cement treated soils to cure; passenger vehicles may use the CTB treated surface
two hours after its completion.
6.1.6 Placement of HMA
Placement of HMA should be in accordance with Section 5-04 of the WSDOT Standard
Specifications for Road and Bridge Construction (WSDOT, 2021).
6.1.7 Pavement Surface Drainage
The pavement surface should be sloped to provide drainage of surface water to the storm drain
system. Wherever possible, the grades around the perimeter of the parking log should be sloped
so surface water will drain away from the pavement. Water that ponds on or adjacent to pavement
surfaces could penetrate or seep under the pavement, saturate the subgrade and contribute to
premature pavement deterioration.
6.1.8 Maintenance
Cracking in asphalt pavement is typical and should be expected over the life of the pavement.
These require routine maintenance to prevent accelerated deterioration. Accordingly, it is highly
recommended to establish a maintenance program where the cracks are routinely filled as they
appear beginning at about the second year of life. It is also recommended that surface fog seal
coats be considered beginning at about year five and every five years after. This will help preserve
the pavements, extending the pavement service life.
It should be anticipated that a functional overlay will be required at between 20 and 30 years.
7.0 EARTHWORK CONSIDERATIONS
7.1 TEMPORARY EXCAVATIONS
Temporary excavations should be made in accordance with Part N of WAC (Washington
Administrative Code) 296-155. The contractor is responsible for maintaining safe excavation
slopes and/or shoring. It is contractor’s responsibility to maintain safe working conditions,
including temporary excavation stability and, if needed, dewatering.
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Based on the encountered fill and fine grained soils underlying the project area, temporary
excavations should be inclined no steeper and 1½H:1V (Horizontal:Vertical). Temporary
excavations should be evaluated in the field during construction based on actual observed soil
conditions. If seepage is encountered, temporary excavation slope inclinations may need to be
reduced. During wet weather, the cut slopes may need to be flattened to reduce potential erosion
or should be covered with plastic sheeting.
7.2 UNDERGROUND UTILITIES
Underground utilities planned as part of the road improvements can be installed using conventional
excavation methods. Excavations in excess of 4 feet in depth should be sloped in accordance with
the recommendations in Section 8.2 of this study.
7.2.1 Pipe Support and Bedding
Utility installation should be conducted in accordance with the 2021 WSDOT Standard
Specifications or other applicable specifications for placement and compaction of pipe bedding
and backfill. In general, pipe bedding should be placed in loose lifts not exceeding 6 inches in
thickness and compacted to a firm and unyielding condition. Bedding materials and thicknesses
provided should be suitable for the utility system and materials installed, and in accordance with
any applicable manufacturers' recommendations. Pipe bedding materials should be placed on
relatively undisturbed native soil.
Based on our field explorations, we anticipate relatively coarse-grained soils comprised of poorly
graded gravel with cobbles. Some overexcavation and removal of cobbles should be anticipated
at the pipe invert elevation to maintain a uniform grade for the utility installation. Where
overexcavation is needed, additional pipe bedding should be placed to restore the grade.
7.2.2 Trench Backfill
Utility trench backfill is a primary concern in reducing the potential for settlement along utility
alignments, particularly in pavement areas. It is important that each section of utility line be
adequately supported in the bedding material. The material should be hand tamped to ensure
support is provided around the pipe haunches.
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Fill should be carefully placed and hand tamped to about 12 inches above the crown of the pipe
before heavy compaction equipment is brought into use. The trench backfill should be placed in
8- to 12-inch-thick loose lifts and compacted to at least 95 percent maximum dry density, per
ASTM D1557 Standard Test Methods for Laboratory Compaction Characteristics of Soil Using
Modified Effort.
In order to reduce the potential for damaging the utilities, heavy compaction equipment should not
be permitted to operate directly over utilities until a minimum of two feet of backfill has been
placed.
7.4 STRUCTURAL FILL AND COMPACTION
Structural fill should be properly moisture conditioned, placed in loose, horizontal lifts less than 8
inches in thickness, and compacted to at least 95 percent maximum density, determined using
ASTM D 1557 (Modified Proctor). The procedure to achieve proper density of a compacted fill
depends on the size and type of compacting equipment, the number of passes, thickness of the lifts
being compacted, and certain soil properties. If the excavation is constricted and limits the use of
heavy equipment, smaller equipment can be used, but the lift thickness will need to be reduced to
achieve the required relative compaction.
Generally, loosely compacted soils are a result of poor construction technique or improper
moisture content. Soils with high fines contents are particularly susceptible to becoming too wet
and coarse-grained materials easily become too dry, for proper compaction. Silty or clayey soils
with a moisture content too high for adequate compaction should be dried as necessary, or moisture
conditioned by mixing with drier materials, or other methods.
7.5 MATERIAL REUSE
The existing fill may be used as structural fill, provided earthwork is conducted during dry weather
and the fill is free of topsoil and organics. If it is planned to use the existing fill as structural fill
the excavated soil should be stockpiled and protected with plastic sheeting to prevent it from
becoming saturated by precipitation or runoff.
The native silt underlying the site will not be suitable for reuse as structural fill due to the high
percent of fines and relatively high natural moisture content.
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7.6 PERMANENT CUT AND FILL SLOPES
Based on the anticipated soil that will be exposed in the planned excavation, we recommend
permanent cut and fill slopes be constructed no steeper than 2H:1V (Horizontal:Vertical). Cut
slopes should be observed by a qualified professional during excavation to verify that conditions
are as anticipated. Supplementary recommendations can then be developed, if needed, to improve
stability, including flattening of slopes or installation of surface or subsurface drains.
Permanently exposed slopes should be seeded with an appropriate species of vegetation to reduce
erosion and improve stability of the surficial layer of soil.
7.7 WET WEATHER CONSTRUCTION
General recommendations relative to earthwork performed in wet weather or in wet conditions are
presented below. The following procedures are best management practices recommended for use
in wet weather construction:
• Earthwork should be performed in small areas to minimize subgrade exposure to wet
weather. Excavation or the removal of unsuitable soil should be followed promptly by
the placement and compaction of clean structural fill. The size and type of construction
equipment used may have to be limited to prevent soil disturbance.
• During wet weather, the allowable fines content of the structural fill should be reduced
to no more than 5 percent by weight based on the portion passing the 0.75-inch sieve.
The fines should be non-plastic.
• The ground surface within the construction area should be graded to promote run-off
of surface water and to prevent the ponding of water.
• Bales of straw and/or geotextile silt fences should be installed at strategic locations
around the site to control erosion and the movement of soil.
• Excavation slopes and soils stockpiled on site should be covered with plastic sheeting.
7.8 EROSION CONSIDERATIONS
Surface water runoff can be controlled during construction by careful grading practices. Typically,
this includes the construction of shallow, upgrade perimeter ditches or low earthen berms in
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conjunction with silt fences to collect runoff and prevent water from entering excavations or to
prevent runoff from the construction area leaving the immediate work site. Temporary erosion
control may require the use of hay bales on the downhill side of the project to prevent water from
leaving the site and potential storm water detention to trap sand and silt before the water is
discharged to a suitable outlet. All collected water should be directed under control to a positive
and permanent discharge system.
Permanent control of surface water should be incorporated in the final grading design. Adequate
surface gradients and drainage systems should be incorporated into the design such that surface
runoff is collected and directed away from the reservoir structure to a suitable outlet. Potential
issues associated with erosion may also be reduced by establishing vegetation within disturbed
areas immediately following grading operations.
8.0 LIMITATIONS
We have prepared this report for Elion Partners and the project design team. Recommendations
contained in this report are based on a site reconnaissance, a subsurface exploration program,
review of pertinent subsurface information, and our understanding of the project. The study was
performed using a mutually agreed-upon scope of work.
Variations in soil conditions may exist between the locations of the explorations and the actual
conditions underlying the site. The nature and extent of soil variations may not be evident until
construction occurs. If any soil conditions are encountered at the site that are different from those
described in this report, we should be notified immediately to review the applicability of our
recommendations. Additionally, we should also be notified to review the applicability of our
recommendations if there are any changes in the project scope.
The scope of our work does not include services related to construction safety precautions. Our
recommendations are not intended to direct the contractors’ methods, techniques, sequences or
procedures, except as specifically described in our report for consideration in design. Additionally,
the scope of our work specifically excludes the assessment of environmental characteristics,
particularly those involving hazardous substances.
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June 10, 2021
21-220 600 SW 10th Avenue Page 19 PanGEO, Inc.
This report has been prepared for planning and design purposes for specific application to the
proposed project in accordance with the generally accepted standards of local practice at the time
this report was written. No warranty, express or implied, is made.
This report may be used only by the client and for the purposes stated, within a reasonable time
from its issuance. Land use, site conditions (both off and on-site), or other factors including
advances in our understanding of applied science, may change over time and could materially
affect our findings. Therefore, this report should not be relied upon after 24 months from its
issuance. PanGEO should be notified if the project is delayed by more than 24 months from the
date of this report so that we may review the applicability of our conclusions considering the time
lapse.
It is the client’s responsibility to see that all parties to this project, including the designer,
contractor, subcontractors, etc., are made aware of this report in its entirety. The use of information
contained in this report for bidding purposes should be done at the contractor’s option and risk.
Any party other than the client who wishes to use this report shall notify PanGEO of such intended
use and for permission to copy this report. Based on the intended use of the report, PanGEO may
require that additional work be performed and that an updated report be reissued. Noncompliance
with any of these requirements will release PanGEO from any liability resulting from the use this
report.
We appreciate the opportunity to be of service.
Sincerely,
DRAFT DRAFT
Scott D. Dinkelman, LEG Siew L. Tan, P. E.
Principal Engineering Geologist Principal Geotechnical Engineer
SDinkelman@pangeoinc.com STan@pangeoinc.com
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Geotechnical Report and Infiltration Assessment
Proposed Truck Parking: 600 Southwest 10th Avenue, Renton, Washington
June 10, 2021
21-220 600 SW 10th Avenue Page 20 PanGEO, Inc.
9.0 LIST OF REFERENCES
Mullineaux, D.R., 1965, Geologic Map of the Renton Quadrangle, King County,
Washington: U.S. Geological Survey, Geologic Quadrangle Map GQ-405, scale
1:24000.
King County, 2016, King County Surface Water Design Manual, Department of Natural
Resources and Parks.
WSDOT, 2021, Standard Specifications for Road, Bridge and Municipal Construction, M 41-10.
DocuSign Envelope ID: 7DBCA7C0-8C41-4D51-AF13-689B38E87E3D
VICINITY MAP
21-220 1
Reference: ArcGIS Online Terrain Map
Not to Scale
PROJECT
SITE
Proposed Truck Parking
600 Southwest 10th Avenue
Renton, WA
DocuSign Envelope ID: 7DBCA7C0-8C41-4D51-AF13-689B38E87E3D
Project No.Figure No.
SITE AND EXPLORATION PLAN
21-220 213
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Approximate Boring Location,
PanGEO, Inc., December 2014
LEGEND:
Approx. Scale
(feet)Note: Site plan modified from Concept Plan #2 prepared by Innova Architects, dated October 20, 2015.
B-1
Project Boundary
0 200 400
NORTH
SECOND AVE S.
WA
S
H
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T
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B
L
V
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B-1
Proposed Residence
Existing Structures B-3
B-4 B-5
B-6
Approximate Extent of 40 Percent
and Steeper Slopes
SOUTHW
E
S
T
1
0
T
H
S
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Existing Structures
SENECA AVE
TP-1
(2')
TP-2
(2')
TP-3
(4')
TP-4
(2')
TP-5
(2.5')TP-7
(2.5')
TP-6
(2')
TP-8
(2')
TP-1 Approximate Test Pit Location,
PanGEO, Inc., May 2021
(Approximate Fill Thickness in Feet)
- Infiltration tests were conducted in TP-1 and TP-2
- Ellipse around symbol indicates shallow standpipe
piezometer location
Proposed Truck Parking
600 Southwest 10th Avenue
Renton, WA
Proposed Infiltration System
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APPENDIX A
SUMMARY TEST PIT LOGS
DocuSign Envelope ID: 7DBCA7C0-8C41-4D51-AF13-689B38E87E3D
MOISTURE CONTENT
2-inch OD Split Spoon, SPT
(140-lb. hammer, 30" drop)
3.25-inch OD Spilt Spoon
(300-lb hammer, 30" drop)
Non-standard penetration
test (see boring log for details)
Thin wall (Shelby) tube
Grab
Rock core
Vane Shear
Dusty, dry to the touch
Damp but no visible water
Visible free water
Terms and Symbols for
Boring and Test Pit Logs
Density
SILT / CLAY
GRAVEL (<5% fines)
GRAVEL (>12% fines)
SAND (<5% fines)
SAND (>12% fines)
Liquid Limit < 50
Liquid Limit > 50
Breaks along defined planes
Fracture planes that are polished or glossy
Angular soil lumps that resist breakdown
Soil that is broken and mixed
Less than one per foot
More than one per foot
Angle between bedding plane and a planenormaltocoreaxis
Very Loose
Loose
Med. Dense
Dense
Very Dense
SPT
N-values
Approx. Undrained Shear
Strength (psf)
<4
4 to 10
10 to 30
30 to 50
>50
<2
2 to 4
4 to 8
8 to 15
15 to 30
>30
SPT
N-values
Units of material distinguished by color and/orcomposition frommaterial unitsabove andbelow
Layers of soil typically 0.05 to 1mm thick, max. 1 cm
Layer of soil that pinches out laterally
Alternating layers of differing soil material
Erratic, discontinuous deposit of limited extent
Soil with uniform color and composition throughout
Approx. Relative
Density (%)
Gravel
Layered:
Laminated:
Lens:
Interlayered:
Pocket:
Homogeneous:
Highly Organic Soils
#4 to #10 sieve (4.5 to 2.0 mm)
#10 to #40 sieve (2.0 to 0.42 mm)
#40 to #200 sieve (0.42 to 0.074 mm)
0.074 to 0.002 mm
<0.002 mm
UNIFIED SOIL CLASSIFICATION SYSTEM
MAJOR DIVISIONS GROUP DESCRIPTIONS
Notes:
MONITORING WELL
<15
15 - 35
35 - 65
65 - 85
85 - 100
GW
GP
GM
GC
SW
SP
SM
SC
ML
CL
OL
MH
CH
OH
PT
TEST SYMBOLS
50%or more passing #200 sieve
Groundwater Level at time of drilling (ATD)Static Groundwater Level
Cement / Concrete Seal
Bentonite grout / seal
Silica sand backfill
Slotted tip
Slough
<250
250 - 500
500 - 1000
1000 - 2000
2000 - 4000
>4000
RELATIVE DENSITY / CONSISTENCY
Fissured:
Slickensided:
Blocky:
Disrupted:
Scattered:
Numerous:
BCN:
COMPONENT DEFINITIONS
Dry
Moist
Wet
1. Soil exploration logs contain material descriptions based on visual observation and field tests using a systemmodified from the Uniform Soil Classification System (USCS). Where necessary laboratory tests have beenconducted (as noted in the "Other Tests" column), unit descriptions may include a classification. Please refer to thediscussions in the report text for a more complete description of the subsurface conditions.
2. The graphic symbols given above are not inclusive of all symbols that may appear on the borehole logs.Other symbols may be used where field observations indicated mixed soil constituents or dual constituent materials.
COMPONENT SIZE / SIEVE RANGE COMPONENT SIZE / SIEVE RANGE
SYMBOLS
Sample/In Situ test types and intervals
Silt and Clay
Consistency
SAND / GRAVEL
Very Soft
Soft
Med. Stiff
Stiff
Very Stiff
Hard
Phone: 206.262.0370
Bottom of BoringBoulder:
Cobbles:
Gravel
Coarse Gravel:
Fine Gravel:
Sand
Coarse Sand:
Medium Sand:
Fine Sand:
Silt
Clay
> 12 inches
3 to 12 inches
3 to 3/4 inches
3/4 inches to #4 sieve
Atterberg Limit Test
Compaction Tests
Consolidation
Dry Density
Direct Shear
Fines Content
Grain Size
Permeability
Pocket Penetrometer
R-value
Specific Gravity
Torvane
Triaxial Compression
Unconfined Compression
Sand
50% or more of the coarse
fraction passing the #4 sieve.
Use dual symbols (eg. SP-SM)
for 5% to 12% fines.
for In Situ and Laboratory Testslisted in "Other Tests" column.
50% or more of the coarse
fraction retained on the #4
sieve. Use dual symbols (eg.
GP-GM) for 5% to 12% fines.
DESCRIPTIONS OF SOIL STRUCTURES
Well-graded GRAVEL
Poorly-graded GRAVEL
Silty GRAVEL
Clayey GRAVEL
Well-graded SAND
Poorly-graded SAND
Silty SAND
Clayey SAND
SILT
Lean CLAY
Organic SILT or CLAY
Elastic SILT
Fat CLAY
Organic SILT or CLAY
PEAT
ATT
Comp
Con
DD
DS
%F
GS
Perm
PP
R
SG
TV
TXC
UCC
LO
G
KE
Y
09
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1
1
8
LO
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11
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/1
3
Figure A-1
DocuSign Envelope ID: 7DBCA7C0-8C41-4D51-AF13-689B38E87E3D
Test Pit TP-1 (Infiltration Test)
Location: 47.471510, -122.225836 (WGS84)
Approximate ground surface elevation: 23 feet (NAVD88)
Depth (ft) Material Description
0 – ½ Sod with loose fine to medium SAND with organics (Topsoil)
½ – 2
Loose to medium dense, brown, fine to medium SAND with silt, trace
gravel, trace organic material (rootlets), minor iron-oxide staining; moist
(Fill)
2 – 10 Medium stiff to stiff, gray to brown, SILT, trace to some sand, trace clay,
minor iron-oxide staining; moist to wet (Alluvium)
Image of soils encountered at approximately 4 feet (testing depth). After testing, the test pit was
excavated to approximately 10 feet below the existing ground surface. Light groundwater
seepage was encountered at approximately 8 feet at the time of exploration.
Figure A-2
DocuSign Envelope ID: 7DBCA7C0-8C41-4D51-AF13-689B38E87E3D
Test Pit TP-2 (Infiltration Test)
Location: 47.471547, -122.226891 (WGS84)
Approximate ground surface elevation: 22 feet (NAVD88)
Depth (ft) Material Description
0 – ½ Sod with loose fine to medium SAND with organics (Topsoil and Sod)
½ – 2
Loose to medium dense, brown, fine to medium SAND with silt, trace
gravel, trace organic material (rootlets), minor iron-oxide staining; moist
(Fill)
2 – 10 Medium stiff to stiff, gray, SILT, trace to some sand, trace clay, minor
iron-oxide staining; moist to wet (Alluvium)
Image of soils encountered at approximately 4 feet (testing depth). After testing, the test pit was
excavated to approximately 10 feet below the existing ground surface. Light groundwater
seepage was encountered at approximately 8 feet at the time of exploration.
Figure A-3
DocuSign Envelope ID: 7DBCA7C0-8C41-4D51-AF13-689B38E87E3D
Test Pit TP-3
Location: 47.471558, -122.227340 (WGS84)
Approximate ground surface elevation: 22 feet (NAVD88)
Depth (ft) Material Description
0 – ½ Sod with loose fine to medium SAND with organics (Topsoil and Sod)
½ – 4
Loose to medium dense, brown, fine to medium SAND with silt, trace
gravel, trace organic material (rootlets), minor iron-oxide staining; moist
(Fill)
4 – 10
Medium stiff to stiff, gray, SILT, trace to some sand, trace clay, trace
organic material (wood), minor iron-oxide staining; moist to wet
(Alluvium)
- Wood debris encountered between approximately 6 and 8 feet.
Image of soils encountered approximately 10 feet below the existing ground surface. Light
groundwater seepage was encountered at approximately 8 feet at the time of exploration.
Figure A-4
DocuSign Envelope ID: 7DBCA7C0-8C41-4D51-AF13-689B38E87E3D
Test Pit TP-4
Location: 47.471783, -122.227372 (WGS84)
Approximate ground surface elevation: 22 feet (NAVD88)
Depth (ft) Material Description
0 – ½ Sod with loose fine to medium SAND with organics (Topsoil and Sod)
½ – 2
Loose to medium dense, brown, fine to medium SAND with silt, trace
gravel, trace organic material (rootlets), minor iron-oxide staining; moist
(Fill)
2 – 10 Medium stiff to stiff, gray, clayey SILT to silty CLAY, trace to some
sand, minor iron-oxide staining; moist to very moist (Alluvium)
Image of soils encountered approximately 10 feet below the existing ground surface.
Groundwater was not encountered at the time of exploration. However, an increase in moisture
was noted below approximately 8 feet.
Figure A-5
DocuSign Envelope ID: 7DBCA7C0-8C41-4D51-AF13-689B38E87E3D
Test Pit TP-5
Location: 47.471793, -122.226299 (WGS84)
Approximate ground surface elevation: 23 feet (NAVD88)
Depth (ft) Material Description
0 – ½ Sod with loose fine to medium SAND with organics (Topsoil and Sod)
½ – 2½
Topsoil over loose to medium dense, brown, fine to medium SAND with
silt, trace gravel, trace organic material (rootlets), minor iron-oxide
staining; moist (Fill)
2½– 10 Medium stiff to stiff, brown to gray, SILT, trace to some sand, trace clay,
minor iron-oxide staining; moist to very moist (Alluvium)
Image of soils encountered approximately 10 feet below the existing ground surface.
Groundwater was not encountered at the time of exploration.
Figure A-6
DocuSign Envelope ID: 7DBCA7C0-8C41-4D51-AF13-689B38E87E3D
Test Pit TP-6
Location: 47.471551, -122.226204 (WGS84)
Approximate ground surface elevation: 22 feet (NAVD88)
Depth (ft) Material Description
0 – ½ Sod with loose fine to medium SAND with organics (Topsoil and Sod)
½ – 2
Topsoil over loose to medium dense, brown, fine to medium SAND with
silt, trace gravel, trace organic material (rootlets), minor iron-oxide
staining; moist (Fill)
2 – 10
Medium stiff to stiff, gray, SILT, trace to some sand, trace to some clay,
minor iron-oxide staining; moist to wet (Alluvium)
- Transitions to SAND with silt and clay at approximately 6 feet.
Image of
soils
encountered
approximately 10 feet below the existing ground surface. Light groundwater seepage was
observed at approximately 8½ feet at the time of exploration.
Figure A-7
DocuSign Envelope ID: 7DBCA7C0-8C41-4D51-AF13-689B38E87E3D
Test Pit TP-7
Location: 47.471761, -122.224953 (WGS84)
Approximate ground surface elevation: 24 feet (NAVD88)
Depth (ft) Material Description
0 – ½ Sod with loose fine to medium SAND with organics (Topsoil and Sod)
½ – 2½
Loose to medium dense, brown, fine to medium SAND with silt, trace
gravel, trace organic material (rootlets), minor iron-oxide staining; moist
(Fill)
2½ – 10 Medium stiff to stiff, brown to gray, SILT, trace to some sand, trace clay,
minor iron-oxide staining; moist to very moist (Alluvium)
Image of soils encountered approximately 10 feet below the existing ground surface.
Groundwater was not encountered at the time of exploration.
Figure A-8
DocuSign Envelope ID: 7DBCA7C0-8C41-4D51-AF13-689B38E87E3D
Test Pit TP-8
Location: 47.471200, -122.225226 (WGS84)
Approximate ground surface elevation: 22 feet (NAVD88)
Depth (ft) Material Description
0 – ½ Sod with loose fine to medium SAND with organics (Topsoil and Sod)
½ – 2½
Loose to medium dense, brown, gravelly fine to medium SAND with
silt, trace organic material (rootlets), minor iron-oxide staining; moist
(Fill)
2½ – 10
Medium stiff to stiff, gray, SILT, trace to some sand, trace clay, minor
iron-oxide staining; moist to wet (Alluvium)
- Sand lens (1½-feet) observed at approximately 8 feet
Image of soils encountered approximately 10 feet below the existing ground surface. Light
groundwater seepage encountered at approximately 8 feet at the time of exploration.
Test Pit Explorations: Test pits were excavated on May 27, 2021 using a CAT 305.5E2 rubber
tracked excavator.
Test Pits Logged by: Christian Venturino
Figure A-9
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APPENDIX B
GEOTECHNICAL LABORATORY TEST RESULTS
(RESULTS PENDING)
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APPENDIX C
ANALYTICAL LABORATORY TEST RESULTS
(RESULTS PENDING)
DocuSign Envelope ID: 7DBCA7C0-8C41-4D51-AF13-689B38E87E3D