24-100687-Civil Conceptual TIR-02.22.241
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GEOTECHNICAL REPORT
Dash Point Palisades
5101 Southwest 316th Place
Federal Way, Washington
Project No. T-8926-1
Prepared for:
JKM Holdings, LLC
Puyallup, Washington
January 22, 2024
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TABLE OF CONTENTS
Page No.
1.0 Project Description .......................................................................................................... 1
2.0 Scope of Work ................................................................................................................. 1
3.0 Site Conditions ................................................................................................................ 2
3.1 Surface ................................................................................................................ 2
3.2 Subsurface .......................................................................................................... 2
3.3 Groundwater ....................................................................................................... 3
3.4 Geologic Hazards ............................................................................................... 3
3.4.1 Erosion Hazard Areas ............................................................................... 3
3.4.2 Landslide Hazard Areas ........................................................................... 4
3.4.3 Seismic Hazard Areas ............................................................................... 5
3.5 Seismic Site Class .............................................................................................. 5
4.0 Discussion and Recommendations .................................................................................. 6
4.1 General ............................................................................................................... 6
4.2 Site Preparation and Grading .............................................................................. 6
4.3 Excavations ........................................................................................................ 8
4.4 Foundation Support ............................................................................................ 8
4.5 Slab-on-Grade Floors ......................................................................................... 9
4.6 Lateral Earth Pressures for Wall Design ............................................................ 9
4.7 Infiltration Feasibility ....................................................................................... 10
4.8 Drainage ........................................................................................................... 11
4.9 Utilities ............................................................................................................. 12
4.10 Pavements ......................................................................................................... 12
5.0 Additional Services ....................................................................................................... 13
6.0 Limitations ..................................................................................................................... 13
Figures
Vicinity Map ......................................................................................................................... Figure 1
Exploration Location Plan .................................................................................................... Figure 2
Typical Wall Drainage Detail ............................................................................................... Figure 3
Appendix
Field Exploration and Laboratory Testing ........................................................................ Appendix A
Determination of Infiltration Rate .................................................................................... Appendix B
Cation Exchange Capacity, pH, and Organic Content Test Results ................................. Appendix C
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Geotechnical Report
Dash Point Palisades
5101 Southwest 316th Place
Federal Way, Washington
1.0 PROJECT DESCRIPTION
The project consists of redeveloping the approximately 4.21-acre site with single-family residential lots
along with associated access and utilities. Grading and development plans were not available at the time of this
report. Based on existing topography, we would expect grading to be minor, with cuts and fills between one and
five feet.
We would expect that the residential structures will be two- to- three-story, wood-frame buildings with the main
floors constructed over a crawl space with attached garages constructed at grade. Foundation loads are expected
to be relatively light, in the range of 2 to 3 kips per foot for bearing walls and 50 to 75 kips for isolated columns.
The recommendations in the following sections of this report are based on our understanding of the
preceding design features. We should review design drawings as they become available to verify our
recommendations have been properly interpreted and to supplement them, if required.
2.0 SCOPE OF WORK
Our work was completed in accordance with our authorized proposal dated August 2, 2023. Accordingly, on
September 19, 2023, we observed soil and groundwater conditions at 13 soil test pits excavated with a mini track-
mounted excavator to maximum depths of approximately 10 to 14 feet below existing grades. Using the
information obtained from the subsurface exploration, we performed analyses to develop geotechnical
recommendations for project design and construction.
Specifically, this report addresses the following:
Soil and groundwater conditions.
Geologic Hazards per the City of Federal Way Municipal Code
Seismic design parameters per the current International Building Code (IBC).
Site preparation and grading.
Excavations.
Foundation support.
Slab-on-grade floors.
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Lateral earth pressures for wall design.
Infiltration Feasibility.
Drainage.
Utilities.
Pavements.
It should be noted, recommendations outlined in this report regarding drainage are associated with soil strength,
design earth pressures, erosion, and stability. Design and performance issues with respect to moisture as it relates
to the structure environment are beyond Terra Associates, Inc.s purview. A building envelope specialist or
contactor should be consulted to address these issues, as needed.
3.0 SITE CONDITIONS
3.1 Surface
The project site consists of three tax parcels (King County Parcel #s: 1021039001, 1021039016, and 1021039040)
totaling approximately 4.21 acres located at and south of 5101 Southwest 316th Place in Federal Way,
Washington. The approximate site location is shown on Figure 1.
The site is currently developed with a single-family residence, and associated access and landscaping in the
northern portion of the site. The remainder of the site south of the existing residence is undeveloped and covered
with a moderate forest and associated understory. Site topography consists of a gentle slope that descends from
the southwest corner of the site towards the northeast with an overall relief of approximately 30 feet.
3.2 Subsurface
In general, the soil conditions at the site consist of approximately four to nine inches of grass, forest duff and/or
organic topsoil overlying approximately two to six feet of medium dense silty sand with gravel, occasional
cobbles, and occasional boulders overlying medium dense to dense stratified sand and gravel with variable silt
content, occasional cobbles, and occasional boulders to the termination of the test pits. Exceptions to this general
condition were observed in Test Pits TP-7, TP-9, TP-11, and TP-13 where sand and gravel to sand with silt and
variable gravel content was observed underlying the surficial topsoil and in Test Pit TP-13 where the upper
approximately four feet of the soil formation was observed in a loose condition.
The Geologic Map of the Tacoma 1:100,000-scale quadrangle, Washington by J.E. Schuster, A.A. Cabibbo, J.F.
Schilter, and I.J. Hubert (2015) maps the site as being underlain by Recessional Outwash (Qgo). The soils we
observed in our test pits are generally consistent with the regional geology mapping.
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The preceding discussion is intended to be a general review of the soil conditions encountered. For more detailed
descriptions, please refer to the Test Pit Logs in Appendix A. The approximate location of the test pits are shown
on Figure 2, the Exploration Location Plan.
3.3 Groundwater
Groundwater seepage was not observed in any of our test pits. Mottling was observed within the upper portion of
the outwash soil formation in all of the Test Pits. Mottling is typically an indication that shallow groundwater
seepage develops within this mottled zone. We would expect that shallow groundwater seepage develops during
the normally wet winter and spring months within the siltier portions of the outwash formation. This occurs as a
result of rainfall that infiltrates through the upper surficial soils and becomes perched on siltier soils beneath.
Groundwater seepage levels will fluctuate seasonally with the highest levels occurring during the normally wet
winter to late spring months (November through May).
3.4 Geologic Hazards
We evaluated site conditions for the presence of Geologically Hazardous Areas as defined in Chapter 19 of the
City of Federal Way Revised Code (FWRC). Discussions related to erosion, landslide, and seismic hazards are
given below.
3.4.1 Erosion Hazard Areas
Chapter 19.05.070(1) of the FWRC defines Erosion Hazard Areas as those areas identified by the U.S.
Department of Agricultures Natural Resource Conservation Service as having a moderate to severe or severe to
very severe rill and inter-rill erosion hazard due to natural agents such as wind, rain, splash, frost action or stream
flow; those areas containing the following group of soils when they occur on slopes of 15 percent or greater:
Alderwood-Kitsap (AkF), Alderwood gravelly sandy loam (AgD), Kitsap silt loam (KpD), Everett
(EvD), and Indianola (InD); and those areas impacted by shore land and/or stream bank erosion.
The soils observed onsite are classified as Alderwood gravelly sandy loam, 8 to 15 percent slopes by the United
States Department of Agriculture Natural Resources Conservation Service (NRCS). Across the site, with the
existing slope gradients, these soils will have a moderate potential for erosion when exposed. Therefore, the site
does not meet the above criteria for an erosion hazard area as defined by the FWRC in our opinion.
Regardless, the site soils would be susceptible to some erosion when exposed during construction. In our opinion,
proper implementation, and maintenance of Best Management Practices (BMPs) for erosion prevention and
sediment control would adequately mitigate the erosion potential in the planned development area. Erosion
protection measures, as required by the City of Federal Way, will need to be in place prior to and during grading
activities at the site.
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3.4.2 Landslide Hazard Areas
Landslide Hazard Areas are defined in Chapter 19.05.070(2) of the FWRC as those areas potentially subject to
episodic downslope movement of a mass of soil or rock including, but not limited to, the following areas:
(a) Any area with a combination of:
(i) Slopes greater than 15 percent.
(ii) Permeable sediment, predominately sand and gravel, overlying relatively impermeable
sediment or bedrock, typically silt and clay; and
(iii) Springs or groundwater seepage.
(b) Any area that has shown movement during the Holocene epoch, from 10,000 years ago to the present,
or that is underlain by mass wastage debris of that epoch.
(c) Any area potentially unstable as a result of rapid stream incision, stream bank erosion or undercutting
by wave action.
(d) Any area located in a ravine or on an active alluvial fan, presently or potentially subject to inundation
by debris flows or flooding.
(e) Those areas mapped as Class U (unstable), UOS (unstable old slides), and URS (unstable recent
slides) by the Department of Ecologys Coastal Zone Atlas.
(f) Areas designated as quaternary slumps, earthflows, mudflows, lahars, or landslides on maps published
by the U.S. Geological Survey or Washington State Department of Natural Resources.
(g) Slopes having gradients greater than 80 percent subject to rockfall during seismic shaking.
(h) Any area with a slope of 40 percent or steeper and with a vertical relief of 10 or more feet except areas
composed of consolidated rock. A slope is delineated by establishing its toe and top and is measured
by averaging the inclination over at least 10 feet of vertical relief.
None of the above conditions were observed at the site and the site is not mapped as a potential landslide hazard
area by the King County iMap, nor is it designated as a landslide hazard area on the Washington State Department
of Natural Resources King County Landslide Hazard Areas Map dated May 2010. Review of the Department of
Ecologys Coastal Atlas Map shows that the site is mapped as having a slope stability of Stable and is
approximately 1,100 feet from the nearest mapped Unstable coastal bluff. Therefore, in our opinion, the site
does not contain a landslide hazard area as defined by the FWRC.
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3.4.3 Seismic Hazard Areas
Chapter 19.05.070(3) of the FWRC defines Seismic Hazard Areas as those areas subject to severe risk of
earthquake damage as a result of seismically induced ground shaking, slope failure, settlement or soil
liquefaction, or surface faulting. These conditions occur in areas underlain by cohesionless soils of low density
usually in association with a shallow groundwater table.
Liquefaction is a phenomenon where there is a reduction or complete loss of soil strength due to an increase in
water pressure induced by vibrations. Liquefaction mainly affects geologically recent deposits of fine-grained
sands underlying the groundwater table. Soils of this nature derive their strength from intergranular friction. The
generated water pressure or pore pressure essentially separates the soil grains and eliminates this intergranular
friction, thus eliminating the soils strength.
The site is currently mapped on the Washington State DNRs King County Liquefaction Susceptibility Map, dated
May 2010, as having very low liquefaction potential.
Based on the soil conditions and the lack of significant groundwater we observed, in our opinion, the risk for
liquefaction to occur at the site during an earthquake and its associated impacts is low.
The closest known Class A fault (existence of Quaternary fault of tectonic origin demonstrated by geologic
evidence) to the project site is the Tacoma Fault. The Tacoma Fault is described as a west-trending (average
strike N89°E), thrust fault that extends more than 24 kilometers across the south-central Puget Lowland from the
Tacoma region to Hood Canal. The subject site is located about 31 to 32 kilometers east-southeast of the
approximate eastern termini of the fault strand mapped by the USGS; however, it is reported that the fault could
continue more than 55 kilometers farther to the east-southeast along the flanks of moderately constrained gravity
anomalies. A 50-kilometer projection of one of the inferred fault strands to the southeast crosses very near to the
northern extent of the subject site. The USGS online mapping tool (U.S. Quaternary Faults) shows that the
nearest of these inferred fault traces, categorized as Class B, is located approximately 350 feet northeast of the
site. We did not observe any indications of faulting or surface rupture at the project site and are unaware of any
reported documentation of surface rupture due to past movement along the TFZ in the project area. Considering
this, it is our opinion that the potential for ground rupture at the project site, during a severe seismic event, is low.
Based on the site topography, the soil conditions observed, and the lack of significant groundwater, it is our
opinion that the risk for damage resulting from earthquake-induced slope failure, settlement, lateral spreading,
surface failure, or soil liquefaction is negligible. Therefore, in our opinion, unusual seismic hazard areas do not
exist at the site, and design in accordance with local building codes for determining seismic forces would
adequately mitigate impacts associated with ground shaking.
3.5 Seismic Site Class
Based upon the site soil conditions observed in the test pits and our knowledge of the area geology, per the current
International Building Code (IBC), site class D should be used in structural design.
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4.0 DISCUSSION AND RECOMMENDATIONS
4.1 General
Based on our study, there are no geotechnical considerations that would preclude development of the site, as
currently planned. The residential buildings can be supported on conventional spread footings bearing on
competent inorganic native soils observed below the organic surface horizon or on structural fill placed and
compacted above the native soils. Pavement and floor slabs can be similarly supported.
Some of the upper site soils were observed in a loose condition. Depending upon the condition of the material at
the time of construction the contractor should be prepared to scarify the upper 12 inches of material and re-
compacted to a firm condition.
The silty sand with gravel and sand with silt with gravel soils encountered at the site contain a sufficient amount
of soil fines that will make them difficult to compact as structural fill when too wet. The ability to use these
native soils from site excavations as structural fill will depend upon its moisture content and the prevailing
weather conditions at the time of construction. If grading activities will take place during winter, the owner
should be prepared to import clean granular material for use as structural fill and backfill.
While not observed in our test pits completed for this study, existing fill material may be present in other areas
where we did not explore near the existing residence in the northern portion of the site.
The following sections provide detailed recommendations regarding the preceding issues and other geotechnical
design considerations. These recommendations should be incorporated into the final design drawings and
construction specifications.
4.2 Site Preparation and Grading
To prepare the site for construction, all vegetation, organic surface soils, and other deleterious material should be
stripped and removed from the site. Surface stripping depths of approximately four to nine inches should be
expected to remove the organic surface soils and vegetation. In the developed portion of the site, demolition of
existing structures should include complete removal of foundations, floor slabs, pavements, and hardscape
surfaces from areas of new construction. Existing buried utilities that will be abandoned should be excavated and
removed or sealed to prevent intrusion of groundwater seepage and soil. Abandoned utilities beneath new
foundations should be removed. Organic surficial soils will not be suitable for use as structural fill but may be
used for limited depths in nonstructural areas.
As noted above, some of the upper site soils were observed in a loose condition. The contractor should be
prepared to scarify the upper 12 inches of soil and re-compact to a firm condition. The lateral extent of the re-
compaction should be determined in the field during grading.
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Once clearing and stripping operations are complete, cut and fill operations can be initiated to establish desired
building grades. Prior to placing fill, all exposed bearing surfaces should be observed by a representative of
Terra Associates, Inc. to verify soil conditions are as expected and suitable for support of new fill or building
elements. Our representative may request a proofroll using heavy rubber-tired equipment to determine if any
isolated soft and yielding areas are present. If excessively yielding areas are observed and they cannot be
stabilized in place by compaction, the affected soils should be excavated and removed to firm bearing and grade
restored with new structural fill. If the depth of excavation to remove unstable soils is excessive, the use of
geotextile fabrics, such as Mirafi 500X or an equivalent fabric can be used in conjunction with clean granular
structural fill. Our experience has shown, in general, a minimum of 18 inches of a clean, granular structural fill
placed and compacted over the geotextile fabric should establish a stable bearing surface.
The silty sand with gravel and sand with silt and gravel soils encountered at the site contain a sufficient amount of
soil fines that will make them difficult to compact as structural fill when too wet or too dry. The ability to use
these native soils from site excavations as structural fill will depend upon its moisture content and the prevailing
weather conditions at the time of construction. If wet soils are encountered, the contractor will need to dry the
soils by aeration during dry weather conditions. Alternatively, the use of an additive, such as Portland cement,
cement kiln dust (CKD), or lime to stabilize the soil moisture can be considered. If the soil is amended, additional
Best Management Practices (BMPs) addressing the potential for elevated pH levels will need to be included in the
Storm Water Pollution Prevention Program (SWPPP) prepared with the Temporary Erosion and Sedimentation
Control (TESC) plan for the project.
The relatively clean outwash sand and gravel observed have a low percentage of soil fines and should be suitable
for use as structural fill in most weather conditions. The availability of the relatively clean outwash soils may be
limited due to site grading requirements. If there is insufficient clean sand and gravel available, the contractor
should be prepared to import free-draining granular material for use as structural fill and backfill during the wet
season.
If there are insufficient clean outwash sand and gravel soils available due to grading requirements and grading
activities are planned during the wet winter months, or if they are initiated during the summer and extend into fall
and winter, then the contractor should be prepared to import wet-weather structural fill. For this purpose, we
recommend importing a granular soil that meets the following grading requirements:
U.S. Sieve Size Percent Passing
6 inches 100
No. 4 75 maximum
No. 200 5 maximum*
* Based on the 3/4-inch fraction.
Prior to use, Terra Associates, Inc. should examine and test all materials imported to the site for use as structural
fill.
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Structural fill should be placed in uniform loose layers not exceeding 12 inches and compacted to a minimum of
95 percent of the soils maximum dry density, as determined by American Society for Testing and Materials
(ASTM) Test Designation D-1557 (Modified Proctor). The moisture content of the soil at the time of compaction
should be within two percent of its optimum, as determined by this ASTM standard. In nonstructural areas, the
degree of compaction can be reduced to 90 percent.
4.3 Excavations
All excavations at the site associated with confined spaces, such as those for utility construction, must be
completed in accordance with local, state, or federal requirements. Based on current Washington Industrial Safety
and Health Act (WISHA) regulations, the sites soils would be classified as Type C soils.
Accordingly, temporary excavations in Type C soils should have their slopes laid back at an inclination of 1.5:1
(Horizontal: Vertical) or flatter, from the toe to the crest of the slope. If there is insufficient space to complete the
excavations in this manner, or if excavations greater than 20 feet in depth are planned, then temporary shoring to
support the excavations may be required. Properly designed and installed shoring trench boxes can be used to
support utility trench excavations where required. All exposed temporary slope faces that will remain open for an
extended period of time should be covered with a durable reinforced plastic membrane during construction to
prevent slope raveling and rutting during periods of precipitation.
The above information is provided solely for the benefit of the owner and other design consultants and should not
be construed to imply that Terra Associates, Inc. assumes responsibility for job site safety. It is understood that
job site safety is the sole responsibility of the project general contractor.
4.4 Foundation Support
The residential buildings may be supported on conventional spread footing foundations bearing on competent
inorganic native soils or on structural fill placed above competent inorganic native soils. Foundation subgrade
should be prepared as recommended in Section 4.2 of this report. Perimeter foundations exposed to the weather
should bear a minimum depth of one and one-half feet below final exterior grades for frost protection. Interior
foundations can be constructed at any convenient depth below the floor slab.
The native soils that will be exposed at the expected foundation elevations are moisture sensitive and will be
easily disturbed by normal construction activity when wet. As a measure to protect the soils from disturbance
during construction, consideration should be given to placing a four-inch layer of clean crushed rock or lean mix
concrete over the foundation subgrade to serve as a working surface.
Foundations bearing on competent soils can be dimensioned for a net allowable bearing capacity of 2,500 pounds
per square foot (psf). For short-term loads, such as wind and seismic, a one-third increase in this allowable
capacity can be used. With structural loading as anticipated and this bearing stress applied, estimated total
settlements are less than one inch.
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For designing foundations to resist lateral loads, a base friction coefficient of 0.35 can be used. Passive earth
pressures acting on the side of the footing and buried portion of the foundation stem wall can also be considered.
We recommend calculating this lateral resistance using an equivalent fluid weight of 350 pcf. We recommend not
including the upper 12 inches of soil in this computation because they can be affected by weather or disturbed by
future grading activity. This value assumes the foundation will be constructed neat against competent existing
fill, native soil, or backfilled with structural fill as described in Section 4.2 of this report. The values
recommended include a safety factor of 1.5.
4.5 Slab-on-Grade Floors
Slab-on-grade floors may be supported on subgrade prepared as recommended in Section 4.2 of this report.
Immediately below the floor slab, we recommend placing a four-inch-thick capillary break layer composed of
clean, coarse sand or fine gravel that has less than five percent passing the No. 200 sieve. This material will
reduce the potential for upward capillary movement of water through the underlying soil and subsequent wetting
of the floor slab. Installation of a capillary break layer will not be necessary where the floor subgrade is
composed of the clean native outwash or structural fill comprised of the clean outwash. A representative of Terra
Associates should observe the subgrade at the time of construction to verify this condition and determine if an
imported capillary break layer is required.
The capillary break layer will not prevent moisture intrusion through the slab caused by water vapor transmission.
Where moisture by vapor transmission is undesirable, such as covered floor areas, a common practice is to place a
durable plastic membrane on the capillary break layer and then cover the membrane with a layer of clean sand or
fine gravel to protect it from damage during construction and to aid in uniform curing of the concrete slab. It
should be noted, if the sand or gravel layer overlying the membrane is saturated prior to pouring the slab, it will
not be effective in assisting uniform curing of the slab and can actually serve as a water supply for moisture
bleeding through the slab, potentially affecting floor coverings. Therefore, in our opinion, covering the
membrane with a layer of sand or gravel should be avoided if floor slab construction occurs during the wet winter
months and the layer cannot be effectively drained. We recommend floor designers and contractors refer to the
current American Concrete Institute (ACI) Manual of Concrete Practice for further information regarding vapor
barrier installation below slab-on-grade floors.
4.6 Lateral Earth Pressures for Wall Design
The magnitude of earth pressure development on engineered retaining walls will partly depend on the quality of
the wall backfill. We recommend placing and compacting wall backfill as structural fill as described in Section
4.2 of this report. To guard against the build-up of hydrostatic pressure, wall drainage must also be installed. A
typical wall drainage detail is provided as Figure 3. All drains should be routed to an approved point of
discharge.
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With backfill placed and compacted as recommended and drainage properly installed, we recommend designing
restrained (not free to deflect) retaining walls for an at-rest earth pressure equivalent to a fluid weighing 50 pcf. A
value of 35 pcf may be used for the case where the wall is unrestrained. To account for seismic loading an
additional lateral load equivalent to 8H psf where H is the below-grade height of the wall should be applied.
These values do not include other surcharge loading such as from fill backslopes, adjacent footings, or traffic
surcharge loading that may act on the wall. If such conditions will exist, then the imposed loading must be
included in wall design. Values of friction at the base of wall foundations and passive earth pressure that are used
in design to resist lateral loads are provided in Section 4.4 of this report.
4.7 Infiltration Feasibility
Our evaluation of feasibility for site infiltration as a means for site stormwater disposal was based on review of
the Test Pit Logs and laboratory grain size distribution testing. Based on our evaluation of soil conditions,
discharge of development stormwater by use of infiltration may be feasible for facilities that are founded in the
cleaner sand and gravel portion of the soil formation typically observed about two to seven feet below current site
grades or near current site grades in the vicinity of Test Pits TP-7, TP-9, and TP-11 in the southwest portion of the
site.
We used the Soil Grain Size Analysis Method as outlined in Volume V, Section 5.4 of the 2019 Washington State
Department of Ecology Stormwater Management Manual for Western Washington (SMMWW), to determine a
preliminary long-term design infiltration rate. This method correlates the saturated hydraulic conductivity with
the D10, D60, and D90 particle sizes determined from gradation testing of the soils in accordance with ASTM Test
Designation D-422. The D10 particle size represents the grain size below which ten percent of the soil is smaller
in size. The D60 particle size represents the grain size below which 60 percent of the soil is smaller in size. The
D90 particle size represents the grain size below which 90 percent of the soil is smaller in size. The particle sizes
are put in the Massman formula to determine the saturated hydraulic conductivity. Gradation curves from
laboratory testing on the soils are attached in Appendix A. Based on the results of the testing, a
long-term design infiltration rate of 1.3 inches per hour can be used. This preliminary design infiltration rate
incorporates correction factors recommended in the 2019 SMMWW. The calculations are attached in Appendix
B.
In the absence of a groundwater mounding analysis, the 2021 King County Surface Water Design Manual
(KCSWDM) requires a minimum five-foot separation between the bottom of the infiltration facility and the
seasonal-high groundwater elevation. A separation of three feet may be considered if a groundwater mounding
analysis demonstrated the facility would function and not overflow. Groundwater was not observed at the time of
exploration. For preliminary design purposes, we recommend placing the groundwater at 20 feet below current
site grades.
We should review the stormwater infiltration facility plans, when available, to confirm the facility design and
locations are consistent with the ground conditions observed at the site. Our analysis included size factors that
were assumed based on our experience. Once facilities have been sized and located, we will need to perform
onsite infiltration tests in accordance with the 2021 KCSWDM to confirm design infiltration rates.
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The permeability of the native sand and gravel soils will be significantly impacted by the intrusion of soil fines
(silt- and clay-sized particles). Even a relatively minor amount of soil fines can reduce the permeability of the
formation by a factor of ten. The greatest exposure to soil fines contamination will occur during mass grading
and construction. Therefore, we recommend that the Temporary Erosion and Sedimentation Control (TESC)
plans route construction stormwater to a location other than the permanent infiltration trenches.
We recommend a representative of Terra Associates, Inc. observe the subgrade of the infiltration facility during
construction to ensure the soils exposed are as expected and suitable for infiltration of development stormwater.
Groundwater Protection
To assess soil properties in relation to the King County groundwater protection criteria and specifications for
amended soils per the Washington State Department of Ecology SMMWW, Cation Exchange Capacity (CEC),
pH, and organic matter content testing was performed by an analytical testing lab on soil samples obtained from
Test Pits TP-2, TP-4, TP-6, TP-8, TP-10, and TP-12 at depths of four to four and one-half feet below current site
grades. The results of the CEC, pH, and organic matter content testing are summarized in the table below and
attached in Appendix C. Based on the results of the testing, the soil at Test Pits TP-2, TP-6, TP-10, and TP-12 did
not meet the CEC portion of the criteria and the soil at Test Pits TP-2 and TP-10 did not meet the organic matter
content criteria. Soils that do not meet groundwater protection criteria will likely require some admixture to meet
treatment requirements.
Test Pit
#
Depth
(ft.)
Cation Exchange Capacity
(meq/100g) pH Organic Matter
(%)
TP-2 4 4.6 4.8 0.9
TP-4 4 8.8 4.1 1.8
TP-6 4 3.8 4.2 1.0
TP-8 4 6.2 4.2 2.0
TP-10 4 3.9 4.2 0.8
TP-12 4.5 3.7 4 1.0
ft Feet below ground surface
4.8 Drainage
Surface
Final exterior grades should promote free and positive drainage away from the site at all times. Water must not be
allowed to pond or collect adjacent to foundations or within the immediate building areas. We recommend
providing a positive drainage gradient away from the building perimeter. If this gradient cannot be provided,
surface water should be collected adjacent to the structures and directed to appropriate storm facilities.
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Subsurface
We recommend installing perimeter foundation drains adjacent to shallow foundations. The drains can be laid to
grade at an invert elevation equivalent to the bottom of footing grade. The drains can consist of four-inch
diameter perforated PVC pipe enveloped in washed pea gravel-sized drainage aggregate. The aggregate should
extend six inches above and to the sides of the pipe. Roof and foundation drains should be tightlined separately to
the storm drains. All drains should be provided with cleanouts at easily accessible locations.
4.9 Utilities
Utility pipes should be bedded and backfilled in accordance with American Public Works Association (APWA) or
the local jurisdictional specifications. At a minimum, trench backfill should be placed and compacted as
structural fill as described in Section 4.2 of this report. Soils excavated onsite should generally be suitable for use
as backfill material. However, some of the upper site soils contain moderate to high percentages of fines and are
moisture sensitive; therefore, moisture conditioning may be necessary to facilitate proper compaction. The
relatively clean outwash sand and gravel at the site have a low percentage of soil fines and should be suitable for
use as structural fill in most weather conditions. If utility construction takes place during the winter and there is
insufficient clean sand and gravel available, the contractor should be prepared to import suitable wet weather fill
for utility trench backfilling.
4.10 Pavements
Pavement subgrades should be prepared as described in Section 4.2 of this report. Regardless of the degree of
relative compaction achieved, the subgrade must be firm and relatively unyielding before paving. The subgrade
should be proofrolled with heavy rubber-tired construction equipment such as a loaded ten-yard dump truck to
verify this condition.
The pavement design section is dependent upon the supporting capability of the subgrade soils and the traffic
conditions to which it will be subjected. For residential access, we expect traffic will consist mainly of cars and
light trucks, with occasional heavy traffic in the form of moving trucks and trash/recycle vehicles. With a stable
subgrade prepared as recommended, we recommend the following pavement sections:
Light Traffic and Parking:
Two inches of hot mix asphalt (HMA) over four inches of crushed rock base (CRB).
Three and one-half inches of full depth HMA.
The paving materials used should conform to the current Washington State Department of Transportation
(WSDOT) specifications for one-half-inch hot mix asphalt HMA and CRB.
Long-term pavement performance will depend upon surface drainage. A poorly drained pavement section will be
subject to premature failure as a result of surface water infiltrating into the subgrade soils and reducing their
supporting capability. For optimum pavement performance, we recommend surface drainage gradients of at least
two percent. Some degree of longitudinal and transverse cracking of the pavement surface should be expected
over time. Regular maintenance should be planned to seal cracks when they occur.
A-22
January 22, 2024
Project No. T-8926-1
Page No. 13
5.0 ADDITIONAL SERVICES
Terra Associates, Inc. should review the final design drawings and specifications in order to verify earthwork and
foundation recommendations have been properly interpreted and implemented in project design. We should also
provide geotechnical service during construction to observe compliance with our design concepts, specifications,
and recommendations. This will allow for design changes if subsurface conditions differ from those anticipated
prior to the start of construction.
6.0 LIMITATIONS
We prepared this report in accordance with generally accepted geotechnical engineering practices. No other
warranty, expressed or implied, is made. This report is the copyrighted property of Terra Associates, Inc. and is
intended for specific application to the Dash Point Palisades project in Federal Way, Washington. This report is
for the exclusive use of JKM Holdings, LLC, and their authorized representatives.
The analyses and recommendations presented in this report are based on data obtained from the subsurface
explorations completed onsite. Variations in soil conditions can occur, the nature and extent of which may not
become evident until construction. If variations appear evident, Terra Associates, Inc. should be requested to
reevaluate the recommendations in this report prior to proceeding with construction.
A-23
A-24
A-25
A-26
Project No. T-8926-1
APPENDIX A
FIELD EXPLORATION AND LABORATORY TESTING
Dash Point Palisades
5101 Southwest 316th Place
Federal Way, Washington
On September 19, 2023, we completed our site exploration by observing soil conditions at 13 test pits. The test
pits were excavated using a mini track-mounted excavator to maximum depths of approximately 10 to 14 feet
below existing site grades. Test pit locations were approximately determined in the field using GPS tracking and
by pacing and sighting from existing site features. The approximate location of the test pits is shown on the
attached Exploration Location Plan, Figure 2. Test Pit Logs are presented on Figures A-2 through A-14.
A geologist from our office conducted the field exploration. Our representative classified the soil conditions
encountered, maintained a log of each test pit, obtained representative soil samples, and recorded water levels
observed during excavation. All soil samples were visually classified in accordance with the Unified Soil
Classification System (USCS) described on Figure A-1.
Representative soil samples obtained from the test pits were placed in sealed plastic bags and taken to our
laboratory for further examination and testing. The moisture content of selected samples was measured and is
reported on the corresponding Test Pit Logs. Grain size analyses were also performed on select samples. The
results are shown on Figures A-15 and A-21.
A-27
A-28
Sample No.Depth (ft)PROJECT NAME:PROJ. NO:LOGGED BY:
LOCATION:
DATE LOGGED:
APPROX. ELEV:
DEPTH TO CAVING:
FIGURE
DEPTH TO GROUNDWATER:
SURFACE CONDITIONS:
Description Consistency/
Relative Density W (%)interpreted as being indicative of other locations at the site.
NOTE: This subsurface information pertains only to this test pit location and should not be
0
1
2
3
4
5
6
7
8
9
10
11
12
13
A-2
T-8926-1 TG
Federal Way, Washington Grass
September 19, 2023
Dash Point Palisades
LOG OF TEST PIT NO. TP-1
~230'
NA NA
7.6
3.4
5.2
11.9
4.6
Medium Dense
(4 inches of Grass and Topsoil)
Light Brownish Gray, silty SAND with gravel, fine to coarse sand, fine to coarse gravel,
dry to moist, lightly mottled, occasional cobbles, small roots and rootlets (SM)
(Recessional Outwash)
*Soil contains increased moisture at 4 feet
Brown to Light Reddish Brown, SAND with gravel to gravelly SAND, fine to coarse sand,
fine to coarse gravel, moist, trace silt, lightly mottled to 7 feet, occasional cobbles,
stratified (SP)
*Color turns Brownish Gray to Gray at 7 feet
*Soil contains less gravel and increased moisture at 8 feet
*Soil contains increased gravel at 9.5 feet
Test pit terminated at approximately 10.5 feet.
No groundwater seepage observed.
No caving observed.
A-29
Sample No.Depth (ft)PROJECT NAME:PROJ. NO:LOGGED BY:
LOCATION:
DATE LOGGED:
APPROX. ELEV:
DEPTH TO CAVING:
FIGURE
DEPTH TO GROUNDWATER:
SURFACE CONDITIONS:
Description Consistency/
Relative Density W (%)interpreted as being indicative of other locations at the site.
NOTE: This subsurface information pertains only to this test pit location and should not be
0
1
2
3
4
5
6
7
8
9
10
11
12
13
A-3
T-8926-1 TG
Federal Way, Washington Grass
September 19, 2023
Dash Point Palisades
LOG OF TEST PIT NO. TP-2
~230'
NA NA
4.2
3.7
6.0
6.2
7.5
Medium Dense
Medium Dense
to Dense
(4 inches of Grass and Topsoil)
Light Brownish Gray, silty SAND with gravel, fine to coarse sand, fine to coarse gravel,
dry to moist, lightly mottled, occasional cobbles, occasional boulders up to ~18"
diameter, small roots and rootlets (SM) (Recessional Outwash)
Brownish Gray to Light Reddish Brown, SAND with silt and gravel to gravelly SAND with
silt, fine to coarse sand, fine to coarse gravel, moist, lightly mottled to 8 feet, occasional
cobbles, stratified (SP-SM)
*Color turns Brownish Gray to Gray at 8 feet
*Soil contains increased moisture at 9.5 feet
Test pit terminated at approximately 10 feet.
No groundwater seepage observed.
No caving observed.
A-30
Sample No.Depth (ft)PROJECT NAME:PROJ. NO:LOGGED BY:
LOCATION:
DATE LOGGED:
APPROX. ELEV:
DEPTH TO CAVING:
FIGURE
DEPTH TO GROUNDWATER:
SURFACE CONDITIONS:
Description Consistency/
Relative Density W (%)interpreted as being indicative of other locations at the site.
NOTE: This subsurface information pertains only to this test pit location and should not be
0
1
2
3
4
5
6
7
8
9
10
11
12
13
A-4
T-8926-1 TG
Federal Way, Washington Forest Duff
September 19, 2023
Dash Point Palisades
LOG OF TEST PIT NO. TP-3
~230'
NA NA
14.1
5.8
13.0
10.5
12.8
Medium Dense
(4 inches of Forest Duff and Topsoil)
Light Brownish Gray, silty SAND with gravel, fine to coarse sand, fine to coarse gravel,
dry to moist, lightly mottled, small roots and rootlets to ~3' (SM) (Recessional Outwash)
Brown to Light Reddish Brown, SAND with silt and gravel to gravelly SAND with silt, fine
to coarse sand, fine to coarse gravel, moist, lightly mottled, occasional cobbles,
occasional boulders up to ~24" diameter (SP-SM)
*Soil contains increased moisture, increased sand, less silt, and becomes stratified at 6
feet
Gray, SAND with gravel, fine to coarse sand, fine to coarse gravel, moist, trace silt,
stratified (SP)
*Soil contains increased gravel at 9.5 feet
Test pit terminated at approximately 10.5 feet.
No groundwater seepage observed.
No caving observed.
A-31
Sample No.Depth (ft)PROJECT NAME:PROJ. NO:LOGGED BY:
LOCATION:
DATE LOGGED:
APPROX. ELEV:
DEPTH TO CAVING:
FIGURE
DEPTH TO GROUNDWATER:
SURFACE CONDITIONS:
Description Consistency/
Relative Density W (%)interpreted as being indicative of other locations at the site.
NOTE: This subsurface information pertains only to this test pit location and should not be
0
1
2
3
4
5
6
7
8
9
10
11
12
13
A-5
T-8926-1 TG
Federal Way, Washington Forest Duff
September 19, 2023
Dash Point Palisades
LOG OF TEST PIT NO. TP-4
~230'
NA NA
8.5
4.9
4.8
8.4
10.6
Medium Dense
(4 inches of Forest Duff and Topsoil)
Light Brownish Gray, silty SAND with gravel to silty gravelly SAND, fine to coarse sand,
fine to coarse gravel, dry to moist, lightly mottled, occasional cobbles, small roots and
rootlets (SM) (Recessional Outwash)
Brown to Light Reddish Brown, SAND with gravel, fine to coarse sand, fine to coarse
gravel, moist, trace silt, lightly mottled to 8 feet, occasional cobbles, stratified (SP)
*Color turns Brownish Gray to Gray and contains less gravel at 8 feet
*Soil contains increased moisture at 9.5 feet
Test pit terminated at approximately 10 feet.
No groundwater seepage observed.
No caving observed.
A-32
Sample No.Depth (ft)PROJECT NAME:PROJ. NO:LOGGED BY:
LOCATION:
DATE LOGGED:
APPROX. ELEV:
DEPTH TO CAVING:
FIGURE
DEPTH TO GROUNDWATER:
SURFACE CONDITIONS:
Description Consistency/
Relative Density W (%)interpreted as being indicative of other locations at the site.
NOTE: This subsurface information pertains only to this test pit location and should not be
0
1
2
3
4
5
6
7
8
9
10
11
12
13
A-6
T-8926-1 TG
Federal Way, Washington Forest Duff
September 19, 2023
Dash Point Palisades
LOG OF TEST PIT NO. TP-5
~230'
NA NA
6.5
2.1
5.8
11.9
Medium Dense
(6 inches of Forest Duff and Topsoil)
Light Brownish Gray, silty SAND with gravel, fine to coarse sand, fine to coarse gravel,
dry to moist, lightly mottled, small roots and rootlets to ~3' (SM) (Recessional Outwash)
Brown to Light Reddish Brown, gravelly SAND, fine to coarse sand, fine to coarse gravel,
moist, trace silt, lightly mottled, occasional cobbles, stratified (SP)
*Color turns Gray and sand is stratified with layers that contain less gravel at 7.5 feet
*Soil contains increased moisture at 9 feet
Test pit terminated at approximately 10 feet.
No groundwater seepage observed.
No caving observed.
A-33
Sample No.Depth (ft)PROJECT NAME:PROJ. NO:LOGGED BY:
LOCATION:
DATE LOGGED:
APPROX. ELEV:
DEPTH TO CAVING:
FIGURE
DEPTH TO GROUNDWATER:
SURFACE CONDITIONS:
Description Consistency/
Relative Density W (%)interpreted as being indicative of other locations at the site.
NOTE: This subsurface information pertains only to this test pit location and should not be
0
1
2
3
4
5
6
7
8
9
10
11
12
13
A-7
T-8926-1 TG
Federal Way, Washington Forest Duff
September 19, 2023
Dash Point Palisades
LOG OF TEST PIT NO. TP-6
~230'
NA NA
9.3
4.3
4.4
7.0
8.5
Medium Dense
Medium Dense
to Dense
(9 inches of Forest Duff and Topsoil)
Light Brownish Gray, silty SAND with gravel, fine to coarse sand, fine gravel, dry to
moist, lightly mottled, small roots and rootlets (SM) (Recessional Outwash)
Brown to Light Reddish Brown, SAND with silt and gravel, fine to coarse sand, fine to
coarse gravel, moist, lightly mottled, occasional cobbles, stratified (SP-SM)
Brown to Light Reddish Brown, SAND with gravel, fine to coarse sand, fine to coarse
gravel, moist, trace silt, lightly mottled, occasional cobbles, stratified (SP)
*Soil contains increased moisture at 9 feet
Test pit terminated at approximately 10 feet.
No groundwater seepage observed.
No caving observed.
A-34
Sample No.Depth (ft)PROJECT NAME:PROJ. NO:LOGGED BY:
LOCATION:
DATE LOGGED:
APPROX. ELEV:
DEPTH TO CAVING:
FIGURE
DEPTH TO GROUNDWATER:
SURFACE CONDITIONS:
Description Consistency/
Relative Density W (%)interpreted as being indicative of other locations at the site.
NOTE: This subsurface information pertains only to this test pit location and should not be
0
1
2
3
4
5
6
7
8
9
10
11
12
13
A-8
T-8926-1 TG
Federal Way, Washington Forest Duff
September 19, 2023
Dash Point Palisades
LOG OF TEST PIT NO. TP-7
~230'
NA NA
4.0
2.7
3.3
5.0
Medium Dense
(6 inches of Forest Duff and Topsoil)
Light Brownish Gray to Brown, gravelly SAND with silt, fine to coarse sand, fine to
coarse gravel, dry to moist, lightly mottled, occasional cobbles, stratified, small roots and
rootlets to ~2.5' (SP-SM) (Recessional Outwash)
Brown to Brownish Gray, SAND with gravel to gravelly SAND, fine to coarse sand, fine to
coarse gravel, moist, trace silt, somewhat stratified (SP)
*Soil contains slightly increased moisture and color turns more gray at 8 feet
Test pit terminated at approximately 10 feet.
No groundwater seepage observed.
No caving observed.
A-35
Sample No.Depth (ft)PROJECT NAME:PROJ. NO:LOGGED BY:
LOCATION:
DATE LOGGED:
APPROX. ELEV:
DEPTH TO CAVING:
FIGURE
DEPTH TO GROUNDWATER:
SURFACE CONDITIONS:
Description Consistency/
Relative Density W (%)interpreted as being indicative of other locations at the site.
NOTE: This subsurface information pertains only to this test pit location and should not be
0
1
2
3
4
5
6
7
8
9
10
11
12
13
A-9
T-8926-1 TG
Federal Way, Washington Forest Duff
September 19, 2023
Dash Point Palisades
LOG OF TEST PIT NO. TP-8
~235'
NA NA
4.7
4.0
3.3
7.7
10.7
Medium Dense
(6 inches of Forest Duff and Topsoil)
Light Brownish Gray, silty SAND with gravel, fine to coarse sand, fine to coarse gravel,
dry to moist, lightly mottled, small roots and rootlets (SM) (Recessional Outwash)
Brown to Brownish Gray, SAND with silt and gravel to gravelly SAND with silt, fine to
coarse sand, fine to coarse gravel, moist, somewhat stratified (SP-SM)
*Color turns more Gray at 6 feet
*Soil contains increased moisture at 9 feet
Test pit terminated at approximately 10 feet.
No groundwater seepage observed.
No caving observed.
A-36
Sample No.Depth (ft)PROJECT NAME:PROJ. NO:LOGGED BY:
LOCATION:
DATE LOGGED:
APPROX. ELEV:
DEPTH TO CAVING:
FIGURE
DEPTH TO GROUNDWATER:
SURFACE CONDITIONS:
Description Consistency/
Relative Density W (%)interpreted as being indicative of other locations at the site.
NOTE: This subsurface information pertains only to this test pit location and should not be
0
1
2
3
4
5
6
7
8
9
10
11
12
13
A-10
T-8926-1 TG
Federal Way, Washington Forest Duff
September 19, 2023
Dash Point Palisades
LOG OF TEST PIT NO. TP-9
~240'
NA NA
2.3
2.5
2.6
4.1
Medium Dense
(6 inches of Forest Duff and Topsoil)
Brown to Light Reddish Brown, SAND with gravel, fine to coarse sand, fine to coarse
gravel, dry to moist, trace silt, lightly mottled, occasional cobbles, somewhat stratified,
small rootlets to ~2' (SP) (Recessional Outwash)
*Soil contains slightly increased moisture and color turns more gray at 4 feet
*Soil contains less gravel at 9 feet
Test pit terminated at approximately 10 feet.
No groundwater seepage observed.
No caving observed.
A-37
Sample No.Depth (ft)PROJECT NAME:PROJ. NO:LOGGED BY:
LOCATION:
DATE LOGGED:
APPROX. ELEV:
DEPTH TO CAVING:
FIGURE
DEPTH TO GROUNDWATER:
SURFACE CONDITIONS:
Description Consistency/
Relative Density W (%)interpreted as being indicative of other locations at the site.
NOTE: This subsurface information pertains only to this test pit location and should not be
0
1
2
3
4
5
6
7
8
9
10
11
12
13
A-11
T-8926-1 TG
Federal Way, Washington Forest Duff
September 19, 2023
Dash Point Palisades
LOG OF TEST PIT NO. TP-10
~240'
NA NA
6.8
4.1
10.9
9.7
Medium Dense
(6 inches of Forest Duff and Topsoil)
Light Brownish Gray, silty SAND with gravel, fine to coarse sand, fine to coarse gravel,
dry to moist, lightly mottled, occasional cobbles, small roots and rootlets (SM)
(Recessional Outwash)
Brown to Light Reddish Brown, SAND with silt and gravel to gravelly SAND with silt, fine
to coarse sand, fine to coarse gravel, moist, lightly mottled, occasional cobbles, stratified
(SP-SM)
Brownish Gray to Gray, SAND with gravel, fine to coarse sand, fine to coarse gravel,
moist, trace silt, somewhat stratified (SP)
Test pit terminated at approximately 10.5 feet.
No groundwater seepage observed.
No caving observed.
A-38
Sample No.Depth (ft)PROJECT NAME:PROJ. NO:LOGGED BY:
LOCATION:
DATE LOGGED:
APPROX. ELEV:
DEPTH TO CAVING:
FIGURE
DEPTH TO GROUNDWATER:
SURFACE CONDITIONS:
Description Consistency/
Relative Density W (%)interpreted as being indicative of other locations at the site.
NOTE: This subsurface information pertains only to this test pit location and should not be
0
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
A-12
T-8926-1 TG
Federal Way, Washington Forest Duff
September 19, 2023
Dash Point Palisades
LOG OF TEST PIT NO. TP-11
~250'
NA NA
1.8
2.3
1.7
3.1
6.3
4.9
Medium Dense
(6 inches of Forest Duff and Topsoil)
Light Brown to Brownish Gray, gravelly SAND to sandy GRAVEL, fine to coarse sand,
fine to coarse gravel, dry to moist, trace silt, lightly mottled, occasional cobbles,
somewhat stratified, small rootlets to ~4' (SP) (Recessional Outwash)
*Soil contains slightly more moisture and color turns more gray at 3 feet
*Soil contains increased gravel from 6 to 7 feet
*Soil contains less gravel at 9.5 feet
Test pit terminated at approximately 14 feet.
No groundwater seepage observed.
No caving observed.
A-39
Sample No.Depth (ft)PROJECT NAME:PROJ. NO:LOGGED BY:
LOCATION:
DATE LOGGED:
APPROX. ELEV:
DEPTH TO CAVING:
FIGURE
DEPTH TO GROUNDWATER:
SURFACE CONDITIONS:
Description Consistency/
Relative Density W (%)interpreted as being indicative of other locations at the site.
NOTE: This subsurface information pertains only to this test pit location and should not be
0
1
2
3
4
5
6
7
8
9
10
11
12
13
A-13
T-8926-1 TG
Federal Way, Washington Forest Duff
September 19, 2023
Dash Point Palisades
LOG OF TEST PIT NO. TP-12
~250'
NA NA
4.9
3.4
4.2
4.0
5.3
Medium Dense
(9 inches of Forest Duff and Topsoil)
Light Brownish Gray, silty SAND with gravel, fine to coarse sand, fine to coarse gravel,
dry to moist, lightly mottled, small roots and rootlets (SM) (Recessional Outwash)
Brownish Gray to Light Reddish Brown, gravelly SAND to sandy GRAVEL, fine to coarse
sand, fine to coarse gravel, moist, trace silt, lightly mottled, stratified, occasional cobbles
(SP/GP)
*Color turns Brown to Brownish Gray and soil contains less gravel at 5.5 feet
Test pit terminated at approximately 10.5 feet.
No groundwater seepage observed.
No caving observed.
A-40
Sample No.Depth (ft)PROJECT NAME:PROJ. NO:LOGGED BY:
LOCATION:
DATE LOGGED:
APPROX. ELEV:
DEPTH TO CAVING:
FIGURE
DEPTH TO GROUNDWATER:
SURFACE CONDITIONS:
Description Consistency/
Relative Density W (%)interpreted as being indicative of other locations at the site.
NOTE: This subsurface information pertains only to this test pit location and should not be
0
1
2
3
4
5
6
7
8
9
10
11
12
13
A-14
T-8926-1 TG
Federal Way, Washington Forest Duff
September 19, 2023
Dash Point Palisades
LOG OF TEST PIT NO. TP-13
~255'
NA NA
3.3
3.3
3.4
3.5
Loose
Medium Dense
(6 inches of Forest Duff and Topsoil)
Light Brownish Gray, SAND with silt and gravel, fine to coarse sand, fine to coarse
gravel, dry to moist, lightly mottled, occasional cobbles, occasional boulders up to ~18"
diameter, small roots and rootlets to ~3' (SP-SM) (Recessional Outwash)
Gray to Brownish Gray, SAND with gravel to SAND with silt and gravel, fine to coarse
sand, fine to coarse gravel, moist, lightly mottled, occasional cobbles, stratified, lightly
cemented layers within formation (SP/SP-SM)
Gray, SAND with gravel, fine to coarse sand, fine to coarse gravel, moist, trace silt,
stratified (SP)
Test pit terminated at approximately 10 feet.
No groundwater seepage observed.
No caving observed.
A-41
Tested By: KJ
LL PL D85 D60 D50 D30 D15 D10 Cc Cu
Material Description USCS AASHTO
Project No.Client:Remarks:
Project:
Location: TP-1 Depth: 1.5'
Location: TP-1 Depth: 5'
Location: TP-2 Depth: 4'
Terra Associates, Inc.
Kirkland, WA Figure
5.1536 0.5321 0.3034
16.5713 7.1315 4.5827 0.7502 0.3277 0.2484 0.32 28.71
13.3985 5.2100 2.9626 0.5893 0.2887 0.1823 0.37 28.58
silty SAND with gravel SM
gravelly SAND SP
gravelly SAND with silt SP-SM
T-8926-1 JKM Holdings, LLC
A-15PERCENT FINER0
10
20
30
40
50
60
70
80
90
100
GRAIN SIZE - mm.
0.0010.010.1110100
% +3"Coarse
% Gravel
Fine Coarse Medium
% Sand
Fine Silt
% Fines
Clay
0.0 0.0 16.0 11.6 16.4 19.1 36.9
0.0 11.4 37.9 12.0 18.5 17.2 3.0
0.0 7.1 34.9 12.2 23.5 14.9 7.46 in.3 in.2 in.1½ in.1 in.¾ in.½ in.3/8 in.#4#10#20#30#40#60#100#140#200Particle Size Distribution Report
Dash Point Palisades Federal Way, WA Tested on 9/25/2023
Tested on 9/25/2023
Tested on 9/25/2023
A-42
Tested By: KJ
LL PL D85 D60 D50 D30 D15 D10 Cc Cu
Material Description USCS AASHTO
Project No.Client:Remarks:
Project:
Location: TP-2 Depth: 8'
Location: TP-3 Depth: 5'
Location: TP-4 Depth: 4'
Terra Associates, Inc.
Kirkland, WA Figure
12.9274 4.0723 2.3831 0.6888 0.3357 0.2416 0.48 16.86
8.2456 1.4492 0.5899 0.2728 0.1637
20.6990 3.6222 0.6176 0.2185
gravelly SAND with silt SP-SM
SAND with silt and gravel SP-SM
silty gravelly SAND SM
T-8926-1 JKM Holdings, LLC
A-16PERCENT FINER0
10
20
30
40
50
60
70
80
90
100
GRAIN SIZE - mm.
0.0010.010.1110100
% +3"Coarse
% Gravel
Fine Coarse Medium
% Sand
Fine Silt
% Fines
Clay
0.0 8.8 27.9 16.1 27.5 13.9 5.8
0.0 6.0 18.7 13.0 19.8 32.4 10.1
0.0 16.7 20.5 6.7 11.5 23.9 20.76 in.3 in.2 in.1½ in.1 in.¾ in.½ in.3/8 in.#4#10#20#30#40#60#100#140#200Particle Size Distribution Report
Dash Point Palisades Federal Way, WA Tested on 9/25/2023
Tested on 9/25/2023
Tested on 9/25/2023
A-43
Tested By: KJ
LL PL D85 D60 D50 D30 D15 D10 Cc Cu
Material Description USCS AASHTO
Project No.Client:Remarks:
Project:
Location: TP-4 Depth: 6.5'
Location: TP-5 Depth: 4.5'
Location: TP-6 Depth: 1.5'
Terra Associates, Inc.
Kirkland, WA Figure
9.7064 1.8237 0.8289 0.4835 0.2915 0.2216 0.58 8.23
18.7517 7.0837 4.0893 0.9852 0.5146 0.4002 0.34 17.70
3.0079 0.4293 0.2625
SAND with gravel SP
gravelly SAND SP
silty SAND with gravel SM
T-8926-1 JKM Holdings, LLC
A-17PERCENT FINER0
10
20
30
40
50
60
70
80
90
100
GRAIN SIZE - mm.
0.0010.010.1110100
% +3"Coarse
% Gravel
Fine Coarse Medium
% Sand
Fine Silt
% Fines
Clay
0.0 2.5 26.1 10.8 35.3 21.1 4.2
0.0 14.6 32.8 13.5 28.1 8.6 2.4
0.0 0.0 6.6 15.5 18.1 28.0 31.86 in.3 in.2 in.1½ in.1 in.¾ in.½ in.3/8 in.#4#10#20#30#40#60#100#140#200Particle Size Distribution Report
Dash Point Palisades Federal Way, WA Tested on 9/25/2023
Tested on 9/25/2023
Tested on 9/25/2023
A-44
Tested By: KJ
LL PL D85 D60 D50 D30 D15 D10 Cc Cu
Material Description USCS AASHTO
Project No.Client:Remarks:
Project:
Location: TP-6 Depth: 4'
Location: TP-7 Depth: 1.5'
Location: TP-8 Depth: 2.5'
Terra Associates, Inc.
Kirkland, WA Figure
6.5984 1.4336 0.9575 0.5270 0.2608 0.1500 1.29 9.56
17.2255 7.0818 4.5939 0.6976 0.2759 0.1662 0.41 42.60
8.6328 0.9082 0.6638 0.3915 0.1914 0.1045 1.62 8.69
SAND with silt and gravel SP-SM
gravelly SAND with silt SP-SM
SAND with silt and gravel SP-SM
T-8926-1 JKM Holdings, LLC
A-18PERCENT FINER0
10
20
30
40
50
60
70
80
90
100
GRAIN SIZE - mm.
0.0010.010.1110100
% +3"Coarse
% Gravel
Fine Coarse Medium
% Sand
Fine Silt
% Fines
Clay
0.0 0.0 18.8 14.5 43.1 15.0 8.6
0.0 12.5 36.8 12.9 16.9 13.3 7.6
0.0 2.0 22.2 10.1 33.2 23.6 8.96 in.3 in.2 in.1½ in.1 in.¾ in.½ in.3/8 in.#4#10#20#30#40#60#100#140#200Particle Size Distribution Report
Dash Point Palisades Federal Way, WA Tested on 9/25/2023
Tested on 9/26/2023
Tested on 9/26/2023
A-45
Tested By: KJ
LL PL D85 D60 D50 D30 D15 D10 Cc Cu
Material Description USCS AASHTO
Project No.Client:Remarks:
Project:
Location: TP-8 Depth: 4'
Location: TP-9 Depth: 1.5'
Location: TP-10 Depth: 4'
Terra Associates, Inc.
Kirkland, WA Figure
11.7386 3.2772 1.2402 0.4942 0.2128 0.1376 0.54 23.82
9.4441 1.2461 0.8374 0.5649 0.3981 0.2959 0.87 4.21
6.7209 1.7571 0.8682 0.5473 0.2788 0.1766 0.96 9.95
gravelly SAND with silt SP-SM
SAND with gravel SP
SAND with silt and gravel SP-SM
T-8926-1 JKM Holdings, LLC
A-19PERCENT FINER0
10
20
30
40
50
60
70
80
90
100
GRAIN SIZE - mm.
0.0010.010.1110100
% +3"Coarse
% Gravel
Fine Coarse Medium
% Sand
Fine Silt
% Fines
Clay
0.0 5.9 27.4 13.3 27.3 17.7 8.4
0.0 7.3 16.8 12.0 46.9 14.6 2.4
0.0 2.6 20.2 16.1 40.6 14.3 6.26 in.3 in.2 in.1½ in.1 in.¾ in.½ in.3/8 in.#4#10#20#30#40#60#100#140#200Particle Size Distribution Report
Dash Point Palisades Federal Way, WA Tested on 9/26/2023
Tested on 9/26/2023
Tested on 9/26/2023
A-46
Tested By: KJ
LL PL D85 D60 D50 D30 D15 D10 Cc Cu
Material Description USCS AASHTO
Project No.Client:Remarks:
Project:
Location: TP-11 Depth: 1.5'
Location: TP-11 Depth: 9'
Location: TP-12 Depth: 1.5'
Terra Associates, Inc.
Kirkland, WA Figure
21.8658 9.2614 5.5931 0.7727 0.5187 0.4448 0.14 20.82
4.8601 0.6342 0.4392 0.1489
4.8601 0.6342 0.4392 0.1489
sandy GRAVEL GP
sandy GRAVEL GP
silty SAND with gravel SM
T-8926-1 JKM Holdings, LLC
A-20PERCENT FINER0
10
20
30
40
50
60
70
80
90
100
GRAIN SIZE - mm.
0.0010.010.1110100
% +3"Coarse
% Gravel
Fine Coarse Medium
% Sand
Fine Silt
% Fines
Clay
0.0 19.0 33.4 7.3 31.5 8.4 0.4
0.0 2.3 13.0 10.0 25.5 24.2 25.0
0.0 2.3 13.0 10.0 25.5 24.2 25.06 in.3 in.2 in.1½ in.1 in.¾ in.½ in.3/8 in.#4#10#20#30#40#60#100#140#200Particle Size Distribution Report
Dash Point Palisades Federal Way, WA Tested on 9/26/2023
Tested on 9/26/2023
Tested on 9/26/2023
A-47
Tested By: KJ
LL PL D85 D60 D50 D30 D15 D10 Cc Cu
Material Description USCS AASHTO
Project No.Client:Remarks:
Project:
Location: TP-12 Depth: 4.5'
Location: TP-13 Depth: 1.5'
Location: TP-13 Depth: 4'
Terra Associates, Inc.
Kirkland, WA Figure
20.0385 9.1676 5.3671 0.9092 0.3539 0.2366 0.38 38.74
7.8214 0.7776 0.5872 0.3238 0.1705 0.1124 1.20 6.92
10.1147 0.8586 0.6604 0.4061 0.1934 0.1403 1.37 6.12
sandy GRAVEL GP
SAND with silt and gravel SP-SM
SAND with silt and gravel SP-SM
T-8926-1 JKM Holdings, LLC
A-21PERCENT FINER0
10
20
30
40
50
60
70
80
90
100
GRAIN SIZE - mm.
0.0010.010.1110100
% +3"Coarse
% Gravel
Fine Coarse Medium
% Sand
Fine Silt
% Fines
Clay
0.0 16.5 35.3 11.8 18.6 13.2 4.6
0.0 5.3 15.3 8.6 32.9 28.8 9.1
0.0 6.3 17.6 8.6 36.1 24.2 7.26 in.3 in.2 in.1½ in.1 in.¾ in.½ in.3/8 in.#4#10#20#30#40#60#100#140#200Particle Size Distribution Report
Dash Point Palisades Federal Way, WA Tested on 9/26/2023
Tested on 9/26/2023
Tested on 9/27/2023
A-48
APPENDIX B
DETERMINATION OF INFILTRATION RATE
A-49
Test pit TP-1 TP-2 TP-2 TP-3 TP-4 TP-5 TP-6 TP-7 TP-8 TP-8 TP-9 TP-10 TP-11 TP-11 TP-12 TP-13 TP-13
Depth 2.5 4 8 5 6.5 4.5 4 1.5 2.5 4 1.5 4 1.5 9 4.5 1.5 4
D10 (mm)0.2484 0.1823 0.2416 0.07 0.2216 0.4002 0.15 0.1662 0.1045 0.1376 0.2959 0.1766 0.4448 0.425 0.2366 0.1124 0.1403
D60 (mm)7.1315 5.21 4.0723 1.4492 1.8237 7.0837 1.4336 7.0818 0.9082 3.2772 1.2461 1.7571 9.2614 12.7479 9.1676 0.7776 0.8586
D90 (mm)16.5713 13.3985 12.9274 8.2456 9.7064 18.7517 6.5984 17.2255 8.6328 11.7386 9.4441 6.7209 21.8658 22.5215 20.0385 7.8214 10.1147
fines (decimal value)0.03 0.074 0.058 0.101 0.042 0.024 0.086 0.076 0.089 0.084 0.024 0.062 0.004 0.049 0.046 0.091 0.072
KSAT = 2835*10(-1.57+1.90(D10)+0.015(D60)-0.013(D90)-2.08(%fines))
KSAT (ft/day)152.64 95.27 130.01 52.48 131.04 285.43 84.02 83.67 62.72 73.42 195.33 106.69 374.99 306.60 129.85 65.59 75.99
Average Hydraulic Conductivity
Test pits
d(total soil column)
dn (thickness of layer)
Kn (Ksat of layer n)
KEQUIV=d/(dn/Kn)#DIV/0!#DIV/0!#DIV/0!#DIV/0!KEQUIV (ave) =141.51
Hydraulic Gradient (i)i =(D wt + D pond )CF size /138.62(K 0.1 )
Dwt(Depth to High GW/Barrier Layer) (fe 10 (assumed)
Dpond(Depth of pond) (feet)3 (assumed)
Pond Length (feet)150 (assumed)
Pond Width (feet)50
Apond (acres)0.172176309
CFsize=0.73(Apond)-0.76 1 2.77960499
K (KEQUIV)141.51
Hydraulic Gradient (i)0.057152829
f = KEQUIV *i (ft/day)8.1
f (inches/hour)4.0
Facility-design Infiltration Rate fdesign = f*CF plugging*CF testing*CF geometry (Correction factors per 2019 DOE SMMWW)
CF*site variability 0.9
CF*test method 0.4
CF *plugging 0.9
fdesign (inches/hour)1.3
Potential Hydraulic Conductivity
Determination of Initial Design Infiltration Rate per Ecology 5.4 Vol. V (Grain Size Method)
A-50
APPENDIX C
CATION EXCHANGE CAPACITY, PH, AND ORGANIC CONTENT TEST RESULTS
A-51
A-52
A-53
A-54
A-55