HomeMy WebLinkAbout32_RS_Geotechnical Engineering Services Report_20260506_v1
Geotechnical Engineering Services
Report
Renton Off Campus Emergency Department
Renton, Washington
for
KPFF Consulting Engineers
May 5, 2026
1145 Broadway, Suite 300
Tacoma, Washington 98402
253.383.4940
KPFF Consulting Engineers | May 5, 2026 Page i
File No. 2868-044-00
Table of Contents
1.0 Introduction and Project Understanding ......................................................................... 1
2.0 Site Conditions ............................................................................................................. 1
2.1 Project Vicinity and Site Limits ..................................................................................................... 1
2.2 Surface Conditions........................................................................................................................ 1
2.3 Literature Review .......................................................................................................................... 2
2.3.1 Geologic Mapping .............................................................................................................. 2
2.3.2 Structural Plan Review ...................................................................................................... 2
2.4 Subsurface Conditions ................................................................................................................. 3
2.4.1 Exploration Program .......................................................................................................... 3
2.4.2 Soil Conditions ................................................................................................................... 3
2.4.3 Groundwater Conditions ................................................................................................... 4
3.0 Conclusion and Recommendations ................................................................................ 4
3.1 Primary Geotechnical Considerations ......................................................................................... 4
3.2 Seismic Desing Considerations .................................................................................................... 5
3.2.1 Seismic Design Parameters .............................................................................................. 5
3.2.2 Liquefaction ....................................................................................................................... 6
3.2.3 Lateral Spread ................................................................................................................... 6
3.2.4 Surface Rupture Potential ................................................................................................ 7
3.3 Site Development and Earthwork ................................................................................................ 7
3.3.1 Clearing Stripping and Demolition .................................................................................... 7
3.3.2 Erosion and Sediment Control .......................................................................................... 7
3.3.3 Temporary Excavation ....................................................................................................... 8
3.3.4 Permanent Slopes ............................................................................................................. 8
3.3.5 Groundwater Handling Considerations ............................................................................ 8
3.3.6 Surface Drainage ............................................................................................................... 9
3.3.7 Subgrade Preparation ....................................................................................................... 9
3.3.8 Subgrade Protection and Wet Weather Considerations ................................................. 9
3.4 Fill Materials ................................................................................................................................ 10
3.4.1 Import Fill Materials ........................................................................................................ 10
3.4.2 Pipe Bedding .................................................................................................................... 10
3.4.3 Trench Backfill ................................................................................................................. 10
3.4.4 Capillary Break Material .................................................................................................. 10
3.4.5 Crushed Surfacing for Pavements and Sidewalks ........................................................ 11
3.4.6 On-Site Soil....................................................................................................................... 11
3.4.7 Fill Placement and Compaction ...................................................................................... 11
3.5 Foundation Support .................................................................................................................... 12
3.5.1 General ............................................................................................................................. 12
3.5.2 Bearing Resistance of Existing Footings ........................................................................ 12
3.5.3 Bearing Surface Preparation, Bearing Resistance and Settlement of New Footings . 13
3.5.4 Lateral Resistance of New and Existing Footings .......................................................... 14
3.5.5 Slab-on-Grade Floors ....................................................................................................... 14
3.5.6 Footing and Below-Slab Drainage .................................................................................. 15
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3.6 Below Grade Structures .............................................................................................................. 15
3.6.1 General ............................................................................................................................. 15
3.6.2 Drainage ........................................................................................................................... 17
3.7 Stormwater Infiltration ................................................................................................................ 17
3.7.1 General ............................................................................................................................. 17
3.7.2 Pilot Infiltration Test Results ........................................................................................... 18
3.7.3 Soil Physical and Chemical Suitability for Treatment .................................................... 18
3.7.4 Recommended Desing Infiltration Rate ......................................................................... 19
3.8 Pavement Design ........................................................................................................................ 19
3.8.1 General ............................................................................................................................. 19
3.8.2 Asphalt Concrete Pavement Sections ............................................................................ 20
3.8.3 Portland Cement Concrete Pavement Design ............................................................... 20
4.0 Limitations .................................................................................................................. 21
List of Figures
Figure 1. Vicinity Map
Figure 2. Site Plan
Appendices
Appendix A. Subsurface Explorations and Laboratory Testing
Figure A-1. Key to Explorations
Figure A-2 through A-8. Logs of Explorations
Figures A-9 and A-10. Sieve Analysis Results
Appendix B. Inflitration Testing
Figure B-1. PIT-1 Infiltration Testing
Figure B-2. PIT-2 Infiltration Testing
Appendix C. Report and Limitations and Guidelines for Use
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1.0 Introduction and Project Understanding
This report presents the results of our geotechnical engineering services for the MultiCare Renton Off
Campus Emergency Department (OCED) project. The project site is located at 3116 NE Sunset Boulevard
in Renton, Washington, and as shown in the attached Vicinity Map, Figure 1. Our understanding of the
project is based on communications with KPFF, review of the project “Geotechnical Report Requirements”
document prepared by PCS Structural and our prior involvement on MultiCare OCED projects in the Puget
Sound region.
The site is currently developed with a former Rite Aid building which we understand will be retrofitted for
use by MultiCare as an OCED. Construction of a new structure is not anticipated; however, we expect that
seismic retrofitting of the existing building and modifications to existing foundations or construction of
additional foundations may be needed. We understand that improvements to the existing parking lot, drive
areas and surrounding landscaping may be included in the project. Stormwater infiltration facilities, if
included, will be designed in accordance with the current version of the City of Renton Surface Water Design
Manual which references and is based on the King County 2021 Surface Water Design Manual.
The purpose of our services is to develop an understanding of soil and groundwater conditions at the site
as a basis for providing geotechnical design and construction recommendations to support the proposed
development. Our services have been provided in accordance with our signed agreement for this project
dated January 13, 2026 and executed on March 26, 2026
2.0 Site Conditions
2.1 PROJECT VICINITY AND SITE LIMITS
The project site is shown relative to surrounding physical features in Figure 2. Properties in the vicinity are
developed with urban construction, consisting of single- and two-story commercial buildings, multi-story
apartment complexes, paved city streets and sidewalks and paved driveway and parking areas. The
project site is bounded by a restaurant and residential buildings to the north, NE Sunset Boulevard
(State Route 900) to the east, NE 12th Street to south and Kirkland Avenue NE to the west.
2.2 SURFACE CONDITIONS
The former Rite Aid Building is located near the center of the site. The area surrounding the building is
paved with asphalt concrete. Landscape areas with deciduous trees and bushes line most of the eastern,
southern and western perimeters of the site. The site is generally flat with elevations ranging from 364 in
the northeast to 360 in the southwest (elevations in this report are referenced to the NAVD88 datum and
were determined from survey information provided by KPFF). A landscaped slope, between about 4 and
9 feet high with an approximate 2 horizontal to 1 vertical (2H:1V grade, separates NE Sunset Boulevard
from the lower grade of the eastern portion of the parking lot.
There are several existing retaining walls that border the site. The locations of the walls are shown in the
Site Plan Figure 2. A tiered concrete masonry block retaining wall is located along the western site boundary
and separates the site grade from the lower elevation of Kirkland Avenue NE. The wall has two tiers, the
bottom tier being about 3 feet tall and the upper tier being about 2 feet tall. The north end of the masonry
block wall intersects a cast in place concrete retaining wall in the northwest corner of the site. The cast in
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place wall is oriented east-west and runs about 150 feet to the east before intersecting a rockery wall that
runs north-south along the western edge of a parking area. The cast in place wall is on the order of 5 feet
tall and separates the site grade from the lower elevation residential parcels to the north. The rockery
appears to be on the order of a few feet tall, however because this wall appears to be constructed on the
adjacent parcel to the west and is not immediately visible from the site, we were not able to assess the
height along its full length.
2.3 LITERATURE REVIEW
2.3.1 Geologic Mapping
We reviewed published geologic information of the project vicinity, including the Geologic Map of Upper
Eocene to Holocene Volcanic and Related Rocks in the Cascade Range, Washington (Smith 1993) and the
Geologic Map of Surficial Deposits in the Seattle 30’ x 60’ Quadrangle, Washington (Youn 1993). Based
on our review, the site is mapped as Vashon Till (Qvt) and Glacial Deposits (Qg) with Vashon Recessional
Outwash (Qvr) mapped nearby.
2.3.2 Plan Review
We reviewed the 1998 structural plan set (1998 Structural Plans) for the existing structure at the site. The
structural plans show that the existing building is supported by conventional shallow foundations, with
some spread footings centered over pile caps with 6 inch diameter pipe piles below them. The structural
plans indicate that the building floor slab is 4 inches thick and is reinforced with welded wire.
The 1998 Structural Plans indicate that footings were designed assuming an allowable soil bearing
pressure between 2,000 and 3,000 pounds per square foot (psf). The capacity of the pipe piles is listed at
12 tons although the plans do not specify if this is an allowable or ultimate capacity. The design allowable
passive equivalent fluid density and allowable coefficient of friction values are not listed in the
1998 Structural Plans. The 1998 Structural Plans reference a geotechnical report that was prepared for
the original development; however, this report was not made available for our review. Construction
documentation from the original development including geotechnical field reports or pile installation
records are, to our knowledge, not available or do not exist.
The 1998 Structural Plans do not indicate if there were specific compaction requirements below footings
or slab on grade, or if structural fill was placed below foundations. The 1998 Structural Plans do not indicate
if footing drains were included around the perimeter of the building.
We understand that as built Civil Plans for the existing development are not currently available. We expect
that the original Civil Plans include details on the design of the retaining walls that surround the site. If
as built Civil Plans become available, we should be notified and will review the plans to confirm they are
consistent with the discussion and recommendations in this report.
2.3.3 Critical Areas Review
We completed a review of published City of Renton Critical Areas maps (accessed via the online City of
Renton Maps Viewer at https://maps.rentonwa.gov/Html5viewer/Index.html?viewer=CORMaps) and
reviewed the City of Renton’s Critical Areas Regulations presented in Section 4-3-050 of the Renton
Municipal Code. Our review of critical areas was specific to Geologically Hazardous Areas.
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Published critical areas maps do not indicate that there are landslide hazard areas or high erosion hazard
areas at the site or in the immediate site vicinity. Published maps indicate that there may be “regulated
slopes” with gradients greater than 25 percent (about 4H:1V) but less than 40 percent (about 2.5H:1V) at
the site. Based on our observations while onsite, with the exception of the previously mentioned retaining
walls, the only slope area within or abutting the site is the landscaped area along the eastern site boundary.
The height of this slope is between 4 and 9 feet, and the gradient of the slope is typically around 2H:1V
with occasional areas inclined around 1.5H:1V. This slope does not meet the minimum height requirement
to be classified as a steep slope (15 feet) per the Renton Municipal Code, and we did not observe any
indications of movement, instability or erosion on the slope. Accordingly, in our opinion no setback buffer
or special considerations are necessary for development around this slope. We recommend that the slope
not be disturbed or regraded as part of the development unless further assessments are made.
2.4 SUBSURFACE CONDITIONS
2.4.1 Exploration Program
We explored subsurface conditions at the site by advancing five borings (B-1 through B-8) to depths ranging
from about 16.5 to 41.5 feet below ground surface (bgs) and two test pits (PIT-1 and PIT-2) which extended
to about 8.5 feet bgs. Boring B-2 was completed as a monitoring well and a pressure transducer was
installed to measure and monitor groundwater levels at the site. Approximate locations of our explorations
are shown in Figure 2. Selected samples collected from the borings and test pits were tested in our
laboratory to confirm field classifications and to evaluate pertinent engineering properties. A detailed
description of our exploration and laboratory testing programs, summary exploration logs and laboratory
test results is provided in Appendix A.
We conducted two small-scale pilot infiltration tests (PITs) in test pits PIT-1 and PIT-2 at depths of
approximately 8.0 feet bgs. The PITs were completed to evaluate the infiltration capacity of the native soils
on site. Appendix B contains a description of the PIT testing procedures and test results.
2.4.2 Soil Conditions
Our explorations were advanced in areas surfaced with pavement sections consisting of 3 to 4 inches of
hot-mix asphalt overlying 4 to 8 inches of base coarse material. Underlying the pavement sections, we
observed what we interpret to be Recessional Outwash soils. Recessional Outwash soils were present until
the bottom of our explorations, which ranged in depth from 8.5 to 41.5 feet bgs. Observed Recessional
Outwash generally consisted of loose to dense sand with variable silt and gravel contents (USCS group
symbols, SP, SP-SM and SM). Generally speaking, Recessional Outwash soils in the upper portion of the
soil profile contained a higher percentage of silt than those encountered at depth. Soils in the upper portion
of the profile were loose to medium dense, and the relative consistency of their Recessional outwash
tended to increase with depth.
The transition between the upper Recessional Outwash soils (typically containing a higher fines content
with relative constancies between loose and medium dense) and the lower Recessional Outwash soils
(lower fines content and medium dense to dense) varied but typically occurred between depths of about
10 and 20 feet bgs.
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2.4.3 Groundwater Conditions
Our understanding of groundwater conditions at the site is based on observations during drilling, and
measurements collected from the installed monitoring well.
We did not observe groundwater or indications of wet soil during drilling of our borings. Minor seepage was
observed in test pit PIT-2 at a depth of 1.5 feet bgs but seepage stopped shortly after it was exposed. We
interpret the observed seepage to be isolated and discontinuous and the result of surface water infiltrating
into the near surface soil profile.
Groundwater measurements were made using a pressure transducer installed in the B-2 monitoring well
which was screened between 20 and 30 feet bgs (bottom elevation of about 332 NAVD88). Between April 2
and April 28, 2026, groundwater was not measured within monitoring well.
Groundwater monitoring with the pressure transducer is ongoing. Until more groundwater data is obtained
at the site, we recommend that a groundwater depth of 40 feet bgs, about Elevation 322, (equal to the
depth of the bottom of our deepest boring) be considered for design. In our opinion this is reasonable and
conservative considering the conditions observed in our explorations, our understanding of the regional
groundwater levels in the project vicinity and our experience. However, groundwater monitoring at the site
should continue to confirm this assumption. This is particularly important for design of stormwater
infiltration facilities. In the event that groundwater depth at the site is shallower than anticipated, it could
impact the design recommendations for infiltration facilities.
3.0 Conclusions and Recommendations
3.1 PRIMARY GEOTECHNICAL CONSIDERATIONS
A summary of key geotechnical considerations for the project is provided below and is followed by our
detailed recommendations.
■ The soil types and relative consistencies observed within the upper 20 feet of our explorations are
consistent with potentially liquefiable soils. However, these soils were not saturated and the limited
groundwater data we collected suggests that groundwater at the site is deeper than 40 feet bgs.
Accordingly, in our opinion the overall risk of liquefaction occurring at this site is low, however we
recommend that additional groundwater data be collected to confirm the design groundwater depth
and finalize our liquefaction hazard assessment.
■ Most of the soils observed in our explorations contain a significant percentage of fines and could be
difficult or impossible to work with when wet. If earthwork activities will take place during wet weather
months, we recommend that the contractor performing the work assume that onsite soils will not be
suitable for reuse and that imported, wet weather resilient structural fill materials will be required. We
also recommend that the overall project budget include contingencies for exporting site soils and
importing structural fill if construction will occur during wet weather months.
■ In our opinion existing footings for the structure should be evaluated using the originally prescribed
allowable soil bearing pressures outlined in the 1998 Structural Plans.
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■ In our opinion, new footings can be designed assuming an allowable soil bearing pressure of 2,500 psf
provided bearing surfaces are prepared as recommended in this report. This value is recommended to
help mitigate the risk of differential settlement between existing and new footings.
■ Based on the results of onsite infiltration testing, in our opinion, stormwater infiltration is feasible at
this site. Measured infiltration rates at the site varied between the two completed infiltration tests. We
recommend that the lower of the two measured rates be used for design due to the fine grained nature
of the onsite soils and the variability observed in our explorations.
■ The original plans detailing the design of existing retaining walls at the site were not available for review
at the time of this report. We recommend that the existing retaining walls be evaluated to confirm they
are suitable for integration with planned redevelopment and can support proposed traffic loads at the
site.
3.2 SEISMIC DESING CONSIDERATIONS
3.2.1 Seismic Design Parameters
Seismic design of the proposed improvements will be completed using procedures outlined in ASCE 41-17.
For the designated performance objectives outlined in ASCE 41-17, seismic design shall consider the
following earthquake levels:
■ BPON (Basic Performance Objective Equivalent to New Building Standards)
BSE-1N: Basic Safety Earthquake-1, taken as two-thirds of the BSE-2N at a site.
BSE-2N: Basic Safety Earthquake-2, taken as the ground shaking based on the Risk-Targeted
Maximum Considered Earthquake (MCER) at a site.
■ BPOE (Basic Performance Objective for Existing Buildings)
BSE-1E: Basic Safety Earthquake-1, taken as a seismic hazard with a 20 percent probability of
exceedance in 50 years (225-year return period).
BSE-2E: Basic Safety Earthquake-2, taken as a seismic hazard with a 5 percent probability of
exceedance in 50 years (975-year return period).
Per ASCE 41-17, seismic ground motion parameters and response spectra records are determined in
accordance with ASCE 7-16. Based on soils encountered in the borings, we recommend the site be
classified as Site Class D in accordance with ASCE 7-16.
Recommended seismic design parameters for code level seismic design in accordance with ASCE 41-17
are presented in Table 1 below
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TABLE 1. RECOMMENDED ASCE 41-17 SEISMIC DESIGN PARAMETERS1
ASCE 41-17 (ASCE 7-16) SEISMIC DESIGN PARAMETER2
RECOMMENDED VALUE1
BSE-1N
BSE-2N (MCER)
(2,475-YEAR)
BSE-1E
(225-YEAR)
BSE-2E
(975-YEAR)
Mapped Spectral Response Acceleration at Short
Period (0.2 second) (SS) n/a 1.425 g 0.484 g 1.041 g
Mapped Spectral Response Acceleration at
1 second Period (S1) n/a 0.488 g 0.15 g 0.351 g
Site Amplification Factor at 0.2 second period (Fa) n/a 1.0 1.413 1.084
Site Amplification Factor at 1.0 second period (Fv) n/a 1.812 2.3 1.949
Site Adjusted Spectral Response Acceleration at
Short Period (0.2 second) (SXS) 0.95 g 1.425 g 0.684 g 1.128 g
Site Adjusted Spectral Response Acceleration at
1 second Period (SX1) 0.589 g 0.884 g 0.345 g 0.683 g
Design Spectral Acceleration at 0.2 second period
(SDS) n/a 4.371 g n/a n/a
Design Spectral Acceleration at 1.0 second period
(SD1) n/a 1.628 g n/a n/a
Site amplification factor at PGA (FPGA) 0.607 0.607 0.607 0.607
Site Modified Peak Ground Acceleration (PGAM)3 0.668 g 0.668 g 0.668 g 0.2668
Notes:
1 Parameters developed based on Latitude 47.503557° and Longitude -122.178008 °
2 Parameters developed based on Site Class D,
3 Non-modified peak ground acceleration (PGA) is calculated as 0.4 times the site adjusted short-period response acceleration (SXS)
3.2.2 Liquefaction
Liquefaction refers to a condition where vibration or shaking of the ground, usually from earthquake forces,
results in development of excess pore pressures and subsequent loss of strength in the affected soil
deposit. In general, soils that are susceptible to liquefaction include loose to medium dense “clean” to silty
sands below the water table. According to the Washington State Department of Natural Resources (DNR)
Interactive Natural Hazards Map, the potential for liquefaction at this site is very low.
The soil types and relative consistencies observed within the upper 20 feet of our explorations are
consistent with potentially liquefiable soils. However, these soils were not saturated and the limited
groundwater data collected since the time our explorations were completed suggest that groundwater at
the site is deeper than 40 feet bgs. Accordingly, in our opinion the overall risk of liquefaction occurring at
this site is low. However, we recommend that additional groundwater data be collected to confirm the
design groundwater depth and finalize the conclusions of our liquefaction hazard assessment.
3.2.3 Lateral Spread
Lateral spreading related to seismic activity typically involves lateral displacement of large, surficial blocks
of non-liquefied soil when a layer of underlying soil loses strength during seismic shaking. Lateral spreading
usually develops in areas where sloping ground or large grade changes (including retaining walls) are
present. Based on our understanding of the liquefaction risk at the site, the proposed improvements and
the site topography, it is our opinion that the risk of lateral spreading at this site is very low.
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3.2.4 Surface Rupture Potential
According to the DNR Interactive Natural Hazards Map, the project site is in the vicinity of the Seattle fault
zone and approximately 1.1 miles away from Newcastle Hills fault trace. Considering the large distance
from the nearest trace, it is unlikely that movement of the fault would result in significant surface rupture
at the ground surface. In our opinion the risk for surface fault rupture occurring at this site is low.
3.3 SITE DEVELOPMENT AND EARTHWORK
We anticipate that site development and earthwork will include demolition of existing features, excavating
for shallow foundations and hardscaping and placing and compacting fill and backfill materials. We expect
that site grading and earthwork can be accomplished with conventional earthmoving equipment. The
following sections provide specific recommendations for site development and earthwork.
3.3.1 Clearing Stripping and Demolition
We recommend that existing pavements and hardscaping be completely removed from areas that will be
developed. During removal of these features, disturbance of surficial soils may occur, especially if left
exposed to wet conditions. Disturbed soils may require additional remediation during construction and
grading. If utilities exist beneath planned structures, they should be removed and backfilled or abandoned
in place.
While not observed in our explorations, cobbles and boulders could be present in the soils observed at this
site. The contractor should be prepared to remove boulders and cobbles if encountered during grading or
excavation. Boulders may be removed from the site or used in landscape areas. Voids caused by boulder
removal should be backfilled with structural fill.
3.3.2 Erosion and Sediment Control
Erosion and sedimentation rates and quantities can be influenced by construction methods, slope length
and gradient, amount of soil exposed and/or disturbed, soil type, construction sequencing and weather.
Implementing an Erosion and Sedimentation Control Plan will reduce the project impact on erosion-prone
areas. The plan should be designed in accordance with applicable city, county and/or state standards. The
plan should incorporate basic planning principles, including:
■ Scheduling grading and construction to reduce soil exposure;
■ Re-vegetating or mulching denuded areas;
■ Directing runoff away from exposed soils;
■ Reducing the length and steepness of slopes with exposed soils;
■ Decreasing runoff velocities;
■ Preparing drainage ways and outlets to handle concentrated or increased runoff;
■ Confining sediment to the project site; and
■ Inspecting and maintaining control measures frequently.
Some sloughing and raveling of exposed or disturbed soil on slopes should be expected. We recommend
that disturbed soil be restored promptly so that surface runoff does not become channeled.
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Temporary erosion protection should be used and maintained in areas with exposed or disturbed soils to
help reduce erosion and reduce transport of sediment to adjacent areas and receiving waters. Permanent
erosion protection should be provided by paving, structure construction or landscape planting.
Until the permanent erosion protection is established, and the site is stabilized, site monitoring may be
required by qualified personnel to evaluate the effectiveness of the erosion control measures and to repair
and/or modify them as appropriate. Provisions for modifications to the erosion control system based on
monitoring observations should be included in the Erosion and Sedimentation Control Plan.
3.3.3 Temporary Excavation
Excavations deeper than 4 feet must be shored or laid back at a stable slope if workers are required to
enter. Shoring and temporary slope inclinations must conform to the provisions of Title 296 Washington
Administrative Code (WAC), Part N, “Excavation, Trenching and Shoring.” Regardless of the soil type
encountered in the excavation, shoring, trench boxes or sloped sidewalls will be required under Washington
Industrial Safety and Health Act (WISHA). The contract documents should specify that the contractor is
responsible for selecting excavation and dewatering methods, monitoring the excavations for safety and
providing shoring, as required, to protect personnel and structures.
We recommend that, for planning purposes, temporary cut slopes be assumed to be inclined no steeper
than about 1½ H:1V. This guideline assumes that all surface loads are kept at a minimum distance of at
least one-half the depth of the cut away from the top of the slope and that seepage is not present on the
slope face. Flatter cut slopes will be necessary where seepage occurs or if surcharge loads are anticipated.
Temporary covering with heavy plastic sheeting should be used to protect slopes during periods of wet
weather. Ultimately the contractor is responsible for establishing and maintaining safe temporary slopes.
3.3.4 Permanent Slopes
We recommend permanent slopes be constructed at a maximum inclination of 2H:1V to limit erosion
potential. Where 2H:1V permanent slopes are not feasible, protective facings and/or retaining structures
should be considered.
To achieve uniform compaction, we recommend that fill slopes be overbuilt slightly and subsequently cut
back to expose well-compacted fill. Fill placement on slopes steeper than about 5H:1V should be benched
into the slope face. The configuration of benches depends on the equipment being used. Bench excavations
should be level and extend into the slope face.
Exposed areas should be re-vegetated as soon as practical to reduce the surface erosion and sloughing.
Temporary protection should be used until permanent protection is established.
3.3.5 Groundwater Handling Considerations
We do not anticipate that the regional groundwater table will be encountered in shallow excavations at the
site. We recommend that the contractor performing the work be prepared to encounter perched
groundwater seepage in excavations at the site. The interface between relatively more permeable and
relatively less permeable materials are likely locations for accumulation of perched groundwater.
Groundwater seepage handling needs will typically be lower during the late summer and early fall months.
We anticipate that perched groundwater, if encountered, can be handled with sumps, pumps and/or
diversion ditches, as necessary. Ultimately, we recommend that the contractor performing the work be
made responsible for controlling and collecting groundwater encountered.
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3.3.6 Surface Drainage
Surface water from roofs, pavements and landscape areas should be collected and controlled. Curbs or
other appropriate measures such as sloping pavements, sidewalks and landscape areas should be used
to direct surface flow away from buildings, erosion sensitive areas and from behind retaining structures.
Roof and catchment drains should not be connected to wall or foundation drains.
3.3.7 Subgrade Preparation
Subgrades that will support slab-on-grade floors, pavements and other site features should be thoroughly
compacted to a uniformly firm and unyielding condition on completion of stripping/excavation and before
placing structural fill. Prepared subgrades should be evaluated, as appropriate, to identify areas of yielding
or soft soil. Probing with a steel probe rod or proof-rolling with a heavy piece of wheeled construction
equipment are appropriate methods of evaluation.
If soft or otherwise unsuitable subgrade areas are revealed during evaluation that cannot be compacted to
a stable and uniformly firm condition, we recommend that: 1) the unsuitable soils be scarified (e.g., with a
ripper or farmer’s disc), aerated and recompacted, if practical; or 2) the unsuitable soils be removed and
replaced with compacted structural fill, as needed.
3.3.8 Subgrade Protection and Wet Weather Considerations
The wet weather season generally begins in October and continues through May in Western Washington;
however, periods of wet weather can occur during any month of the year. The soils encountered in our
explorations contain a significant amount of fines. Soil with high fines content is very sensitive to small
changes in moisture and is susceptible to disturbance from construction traffic when wet or if earthwork is
performed during wet weather. If wet weather earthwork is unavoidable, we recommend that the following
steps be taken.
■ The ground surface in and around the work area should be sloped so that surface water is directed
away from the work area. The ground surface should be graded so that areas of ponded water do not
develop. Measures should be taken by the contractor to prevent surface water from collecting in
excavations and trenches. Measures should be implemented to remove surface water from the work
area.
■ Earthwork activities should not take place during periods of heavy precipitation.
■ Slopes with exposed soils should be covered with plastic sheeting.
■ The contractor should take necessary measures to prevent on-site soils and other soils to be used as
fill from becoming wet or unstable. These measures may include the use of plastic sheeting and
controlling surface water with ditches, sumps with pumps and by grading. The site soils should not be
left uncompacted and exposed to moisture. Sealing the exposed soils by rolling with a smooth-drum
roller prior to periods of precipitation will help reduce the extent to which these soils become wet or
unstable.
■ Construction traffic should be restricted to specific areas of the site, preferably areas that are surfaced
with working pad materials not susceptible to wet weather disturbance.
■ Construction activities should be scheduled so that the length of time that soils are left exposed to
moisture is reduced to the extent practical.
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■ During periods of wet weather, concrete should be placed as soon as practical after preparation of the
footing excavations. Foundation bearing surfaces should not be exposed to standing water. If water
pools in the base of the excavation, it should be removed before placing structural fill or reinforcing
steel.
■ If footing excavations are exposed to extended wet weather conditions, a lean concrete mat or a layer
of clean crushed rock can be considered for foundation bearing surface protection.
3.4 FILL MATERIALS
3.4.1 Import Fill Materials
The workability of material for use as structural fill will depend on the gradation and moisture content of
the soil. Material used for structural fill should be free of debris, organic matter and rock fragments larger
than 6 inches. For most applications, we recommend that structural fill material consist of material similar
to “Select Borrow” or “Gravel Borrow” as described in Section 9-03.14 of the Washington State Department
of Transportation (WSDOT) Standard Specifications. Weather, material use, schedule, duration exposed
and site conditions should be considered when determining the type of import fill materials purchased and
brought to the site for use as structural fill. Structural fill used during periods of wet weather should consist
of material similar to WSDOT Specification 9-03.9 (Aggregates for Ballast and Crushed Surfacing), 9-03.10
(Aggregate for Gravel Base), or 9-03.14 (Borrow) provided that the fines content is less than 5 percent
(based on the minus ¾-inch fraction) and the maximum particle size is 6 inches. If prolonged dry weather
prevails during the earthwork phase of construction, materials with a somewhat higher fines content may
be acceptable.
3.4.2 Pipe Bedding
Trench backfill for the bedding and pipe zone should consist of well-graded granular material similar to
“gravel backfill for pipe zone bedding” described in Section 9-03.12(3) of the WSDOT Standard
Specifications. The material must be free of roots, debris, organic matter and other deleterious material.
Other materials may be appropriate depending on manufacturer specifications and/or local jurisdiction
requirements.
3.4.3 Trench Backfill
Trench backfill must be free of debris, organic matter and rock fragments larger than 6 inches.
We recommend that import trench backfill material consist of material similar to “Select Borrow” or “Gravel
Borrow” as described in Section 9-03.14 of the WSDOT Standard Specifications. Where water is present,
alternative materials may need to be considered.
3.4.4 Capillary Break Material
Structural fill placed as capillary break material below on-grade floor slabs should consist of ¾-inch coarse
aggregate with negligible sand or silt as described in Section 9-03.1(4)C Grading No. 67 of the WSDOT
Standard Specifications. WSDOT Specification 9-03.9 (Aggregates for Ballast and Crushed Surfacing,
Crushed Surfacing Base Course [CSBC]) may also be considered).
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3.4.5 Crushed Surfacing for Pavements and Sidewalks
Structural fill placed as CSBC below pavements and sidewalks should meet the requirements for Crushed
Surfacing Base Course, Section 9-03.9(3) of the WSDOT Standard Specifications.
3.4.6 On-Site Soil
Based on conditions observed in our subsurface explorations and experience, it is our opinion that existing
site soils may be considered for use as structural fill and trench backfill, provided they can be adequately
moisture conditioned, placed and compacted as recommended and do not contain organic or other
deleterious material. Recessional Outwash soils at the site contain significant amounts of silt and clay sized
particles and are extremely moisture sensitive. These soils will be difficult or impossible to properly compact
when wet and we do not recommend they be reused as structural fill during periods of wet weather.
It is possible that existing soils will be excavated at moisture contents above what is optimum for
compaction. In this case, the soils would need to be moisture conditioned (dried) prior to re-use. Space for
drying out material during dryer weather or covering on-site materials generated during wet weather should
be considered. During wetter or even slightly colder times of year, such as when temperatures get below
about 60 degrees, effectively drying out soils is very difficult and often is not possible. In these cases, it
should be assumed that over optimum soils would need to be exported from the site and imported
structural fill should be used.
It is our opinion that if earthwork activities will take place during wet weather months, the contractor
performing the work should assume that onsite soils will not be suitable for reuse and that imported, wet
weather resilient structural fill materials will be required for earthwork activities. We recommend that the
overall project budget include contingencies for exporting site soils and importing structural fill if
construction will occur during wet weather months.
3.4.7 Fill Placement and Compaction
To obtain proper compaction, fill soil should be compacted near optimum moisture content and in uniform
horizontal lifts. Lift thickness and compaction procedures will depend on the moisture content and
gradation characteristics of the soil and the type of equipment used. The maximum allowable moisture
content varies with the soil gradation and should be evaluated during construction. Generally, 12-inch loose
lifts are appropriate for steel-drum vibratory roller compaction equipment. Compaction should be achieved
by mechanical means. During fill and backfill placement, sufficient testing of in-place density should be
conducted by a representative of GeoEngineers to check that adequate compaction is being achieved.
3.4.7.1 AREA FILLS AND PAVEMENT BASES
Fill placed to raise site grades and materials under pavements and structural areas should be placed on
subgrades prepared as previously recommended. Fill material placed below structures and footings should
be compacted to at least 95 percent of the theoretical maximum dry density (MDD) per ASTM International
(ASTM) D 1557. Fill material placed shallower than 2 feet below pavement sections should be compacted
to at least 95 percent of the MDD. Fill placed deeper than 2 feet below pavement sections should be
compacted to at least 90 percent of the MDD. Fill material placed in landscaping areas should be
compacted to a firm condition that will support construction equipment, as necessary, typically around
85 to 90 percent of the MDD.
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3.4.7.2 BACKFILL BEHIND BELOW-GRADE STRUCTURES
Backfill directly behind retaining walls or below-grade structures should be compacted to between 90 and
92 percent of the MDD. Overcompaction of fill placed directly behind below-grade structures should be
avoided. We recommend use of hand-operated compaction equipment and maximum 6 inch loose lift
thickness when compacting fill within about 5 feet behind below-grade structures.
3.4.7.3 TRENCH BACKFILL
For utility excavations, we recommend that the initial lift of fill over the pipe be thick enough to reduce the
potential for damage during compaction but generally should not be greater than about 18 inches above
the pipe. In addition, rock fragments greater than about 1 inch in maximum dimension should be excluded
from this lift.
Trench backfill material placed below structures and footings should be compacted to at least 95 percent
of the MDD. In paved areas, trench backfill should be uniformly compacted in horizontal lifts to at least
95 percent of the MDD in the upper 2 feet below subgrade. Fill placed below a depth of 2 feet from
subgrade in paved areas must be compacted to at least 90 percent of the MDD. In non-structural areas,
trench backfill should be compacted to a firm condition that will support construction equipment, as
necessary.
3.5 FOUNDATION SUPPORT
3.5.1 General
In our opinion shallow foundations are appropriate for supporting improvements at this site. We expect that
shallow foundations will be constructed to support new improvements and as part of the existing building
retrofit. Additionally, we anticipate that the existing footings for the building will be evaluated by the
structural engineer as part of the building retrofit. The sections below provide recommendations for design
and construction of new shallow foundations and for evaluating the existing building footings.
Exterior footings should be established at least 18 inches below the lowest adjacent grade. Interior footings
can be founded a minimum of 12 inches below the top of the floor slab. Isolated column and continuous
wall footings should have minimum widths of 24 and 18 inches, respectively.
The recommended allowable bearing pressures provided below apply to the total of dead and long-term
live loads and may be increased by one-third when considering total loads, including earthquake or wind
loads. These are net bearing pressures. The weight of the footing and overlying backfill can be ignored in
calculating footing sizes.
3.5.2 Bearing Resistance of Existing Footings
Based on our interpretation of the boring logs, the existing footings at the site are likely supported on
Recessional Outwash. The near surface existing Recessional Outwash soils observed in our borings was
typically loose to medium dense. It is unclear what, if any, procedures were followed to compact bearing
surfaces below the existing structure foundations. If records of fill placement or bearing surface preparation
are available, they should be provided to us for review.
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The 1998 Structural Plans indicate that the existing structure was designed using an allowable bearing
resistance of 3,000 psf. The plans also indicate that select footings, primarily those along the east exterior
walls included 6 inch diameter steel pipe piles below them. The capacity of the pipe piles is listed at 12 tons
although the plans do not specify if this is an allowable or ultimate capacity or if the value is associated
with uplift or downward axial resistance. It is unclear on the reviewed plans why pipe piles were included
below some footings. It is also our understanding that records of pile installation are not available, and it is
unclear if the target capacities of the piles were verified during installation.
Based on the conditions observed in our explorations, we recommend that existing footings for the building
retrofit be evaluated using the same allowable soil being pressure as considered for the original design
(3,000 psf). In our opinion, it may be prudent to neglect or consider a reduced allowable resistance provided
by the steel pipe piles. At a minimum, if the resistance provided by the steel pipe piles is being considered
for design, we recommend that additional information regarding the design and construction of the piles
be obtained.
3.5.3 Bearing Surface Preparation, Bearing Resistance and Settlement of New
Footings
New footings can bear directly on compacted Recessional Outwash soils or structural fill extending to these
soils. We recommend that the base of all footing excavations be proof compacted to a uniformly firm and
unyielding condition prior to placement of structural fill, formwork or rebar.
If soft or otherwise unsuitable areas are observed at the base of the overexcavation that cannot be
compacted to a stable and uniformly firm condition the following options may be considered: 1) the exposed
soils be moisture conditioned and recompacted; or 2) the unsuitable soils be overexcavated to expose
competent soils and the overexcavation be backfilled with compacted structural fill. All structural fill placed
below footings must be compacted to 95 percent of the MDD.
It may also be acceptable to overpour the footings opposed to backfilling overexcavations with structural
fill; however, this practice should be approved by the structural engineer during construction. We expect
that overexcavation depths can be limited to 24 inches below design bottom of footing elevation. If
organic-rich soil or other deleterious material is encountered below footings, we recommend complete
removal of these materials so greater overexcavation depths could be necessary.
Foundation bearing surfaces should not be exposed to standing water. If water is present in the excavation,
it must be removed before placing structural fill, formwork and reinforcing steel. Protection of exposed soil
should be considered during the wetter times of the year. The amount of protection will depend, in part, on
prevailing weather, soil type exposed and duration exposed. Typically, a 3- to 4-inch lean concrete mat or a
6- to 8-inch crushed rock section is suitable for foundation bearing surface protection.
Prepared foundation bearing surfaces should be observed and evaluated by a member of our firm prior to
placement of structural fill, formwork or steel reinforcement. Our representative will confirm that the
bearing surfaces have been prepared in accordance with our recommendations and are suitable for
supporting the design footing load and provide recommendations for remediation, if necessary.
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New shallow foundations bearing on structural fill or proof compacted Recessional Outwash may be
designed using an allowable soil bearing pressure of 2,500 psf. The recommended design bearing
resistance for new foundations is less than what was used for design of the original building. In our opinion,
this is prudent to limit the potential for differential settlement between existing and new foundations, to
reduce the risk of loads from new footings inducing settlement of soils below existing foundations and
because there will be limited options for remediating or improving soils below new foundations that will be
constructed through the existing building slab.
Provided bearing surfaces are prepared as recommended, we estimate the total static settlement of
shallow foundations will be on the order of 1 inch or less for the bearing pressures presented above.
Differential settlements could be on the order of ½ inch between comparably loaded isolated column
footings or along 50 feet of continuous footing. Settlement is expected to occur rapidly as loads are applied.
Settlements could be greater than estimated if loose or disturbed soil is present beneath footings.
3.5.4 Lateral Resistance of New and Existing Footings
The ability of the soil to resist lateral loads is a function of frictional resistance, which can develop on the
base of footings and slabs and the passive resistance, which can develop on the face of below-grade
elements of the structure as these elements tend to move into the soil. The allowable frictional resistance
on the base of the footing may be computed using a coefficient of friction of 0.40 applied to the vertical
dead-load forces. The allowable passive resistance on the face of the footing or other embedded foundation
elements may be computed using an equivalent fluid density of 275 pounds per cubic foot (pcf) for
undisturbed site soils or structural fill extending out from the face of the foundation element a distance at
least equal to two and one-half times the depth of the element. These values include a factor of safety of
about 1.5.
The design allowable passive equivalent fluid density and allowable coefficient of friction values are not
listed in1998 Structural Plans. In our opinion the lateral resistance design parameters provided above can
also be used for evaluating the existing foundations.
The passive earth pressure and friction components may be combined provided that the passive
component does not exceed two-thirds of the total. The passive earth pressure value is based on the
assumptions that the adjacent grade is level, and that groundwater remains below the base of the footing
throughout the year. The top foot of soil should be neglected when calculating passive lateral earth pressure
unless the area adjacent to the foundation is covered with pavement or a slab-on-grade.
3.5.5 Slab-on-Grade Floors
We anticipate that the existing building slab on grade will be reused. However, portions of the slab on grade
will likely be replaced or reconstructed as a result of new utility and footing installation within the building.
Bearing surfaces for slab on grade floors should be prepared in accordance with Section “3.3.7 Subgrade
Preparation” of this report. Slab on grade floors can be supported on existing site soils. The exposed
subgrade should be evaluated after site grading is completed by a member of our firm. Disturbed areas
should be compacted, if possible, or removed and replaced with compacted structural fill.
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We recommend slab-on-grade floors be underlain by a minimum 6-inch-thick capillary break consisting of
material similar to what is recommended in Section “3.4.4 Capillary Break Material”. The presence and
condition of capillary break material below the existing building slab on grade has not been confirmed. We
expect that it will not be practical to replace or install a capillary break section below the existing slab as
part of construction. We recommend that portions of the capillary break section exposed during
construction be observed and evaluated by a member from our firm. If during construction, areas of damp
or wet slabs are observed, it could be necessary to remove the existing slab and replace the capillary break
section in those areas.
Provided that loose soil is removed, and the subgrade is prepared as recommended, we recommend slabs-
on-grade be designed using a modulus of subgrade reaction of 250 pounds per cubic inch (pci). We
estimate that settlement for slabs-on-grade constructed as recommended will be less than ¾ inch for a
floor load of 500 psf.
3.5.6 Footing and Below-Slab Drainage
It is unclear if the existing building has a perimeter or underslab drainage system. Based on the conditions
observed in our explorations, in our opinion a foundation or below-slab drainage system is not necessary
to maintain structural support. However, a perimeter foundation drainage system will help maintain dry
conditions below the building and should be considered by the project team from a building serviceability
and maintenance perspective.
Foundation drains should be designed to collect and direct water away from the perimeter of the building.
The drains should be provided with cleanouts and should consist of at least 4-inch-diameter perforated
pipe. The pipe should be placed on a 3-inch bed of, and surrounded by, 6 inches of drainage material. A
nonwoven geotextile fabric should be placed between the drain rock and existing site soils to prevent fine
soil from migrating into the drain material. We recommend that the drainpipe consist of either heavy-wall
solid pipe or rigid corrugated smooth interior polyethylene pipe. We do not recommend using flexible tubing
for footing drainpipes. The drain material should consist of pea gravel or material similar to “Gravel Backfill
for Drains” per Washington State Department of Transportation (WSDOT) Standard Specifications
Section 9-03.12(4). The drains should be sloped to drain by gravity, if practical, to a suitable discharge
point. Water collected in roof downspout lines must not be routed to the perimeter footing drains.
If an existing drainage system is present, we recommend that existing systems around the building be
inspected during construction. The inspection should confirm that the drains are intact and have not
become plugged or otherwise compromised. We also recommend that the existing drainage system, if
present, be reviewed by the project Civil Engineer to verify that the existing system has adequate capacity
for the currently envisioned improvements. We recommend that damaged portions of drainage systems be
repaired or replaced, as necessary.
3.6 RETAINING WALLS AND BELOW GRADE STRUCTURES
3.6.1 Existing Retaining Walls
As described previously, there are several existing retaining walls at the site and existing plans or design
information pertaining to the walls were not available for review. We were not able to make a detailed visual
assessment of these walls while we were onsite for our field activities as they were either overgrown with
vegetation (portions of the concrete masonry block retaining wall) or were not fully visible from the parcel
and access permissions to inspect the walls from adjacent parcels had not been coordinated (cast in place
wall and rockery). However, during our site reconnaissance activities we did not observe any obvious signs
of wall distress or failure.
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We recommend that the internal stability of the existing walls at the site be evaluated to confirm that they
are suitable for continued use. This should include a structural evaluation using the lateral soil earth
pressures provided below (unless the earth pressures that were originally used for design of the walls are
found and confirmed to be appropriate for continued use) as well as the seismic and traffic surcharge loads
discussed below. We also recommend that the drainage system associated with the cast in place wall be
further investigated to confirm if it is functional and suitable for continued use. If a drainage system is not
present or is not functioning properly, it should be confirmed that the cast in place retaining wall can resist
pressures associated with undrained soil conditions, or the drainage system should be repaired/replaced.
We completed limit equilibrium slope stability analyses to assess the global stability of the existing concrete
masonry block retaining wall and cast in place retaining walls. Since full details regarding wall design and
construction were not available for our review, our slope stability models reflected conservative
assumptions with regards to soil conditions behind the walls and wall dimensions that have an impact on
global stability (e.g. foundation embedment depth). Our slope stability analyses results indicate that the
existing masonry block retaining wall and cast in place retaining wall meet minimum factory of safety
requirements outlined in the Washington State Department of Transportation Geotechnical Design Manual
for global slope stability considering static and pseudo static conditions, 1.5 and 1.1, respectively.
If the as-built plans or additional design information regarding the existing retaining walls at the site are
obtained, they should be provided for our review and we will complete updated global slope stability
assessments, if necessary.
3.6.2 General
We recommend the following lateral earth pressures be used for design of conventional retaining walls and
below-grade structures. Our design pressures assume that the ground surface around the retaining
structures will be level or near level. If drained design parameters are used, drainage systems must be
included in the design in accordance with the recommendations presented in Section 3.6.3 below.
■ Active soil pressure may be estimated using an equivalent fluid density of 35 pcf for the drained
condition.
■ Active soil pressure may be estimated using an equivalent fluid density of 80 pcf for the undrained
condition; this value includes hydrostatic pressures.
■ At-rest soil pressure may be estimated using an equivalent fluid density of 56 pcf for the drained
condition
■ At-rest soil pressure may be estimated using an equivalent fluid density of 88 pcf for the undrained
condition; this value includes hydrostatic pressures.
■ For seismic considerations, a uniform lateral pressure of 16H psf (where H is the depth of a structure
bgs) should be added to the lateral earth pressure.
■ A typical traffic surcharge of 250 psf should be included if vehicles are allowed to operate within ½ the
height of the retaining walls. Other surcharge loads should be considered on a case-by-case basis. We
can provide additional surcharge loads for specific loading conditions once known.
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The active soil pressure condition assumes the wall is free to move laterally 0.001H, (where H is the wall
height). The at-rest condition is applicable where walls are restrained from movement. The above-
recommended lateral soil pressures do not include other surcharge loads than described, or the effects of
sloping backfill surfaces. We should be consulted if other surcharge loads are anticipated or if sloping
backfill conditions are planned, this may change the lateral pressure values provided.
Overcompaction of fill placed directly behind below-grade structures must be avoided. We recommend use
of hand-operated compaction equipment and maximum 6-inch loose lift thickness when compacting fill
within about 5 feet of retaining walls and below-grade structures.
Below grade structure bearing surfaces should be prepared following Section 3.5.3 of this report. Provided
bearing surfaces are prepared as recommended, below grade structures may be designed using the
allowable soil bearing values and lateral resistance values presented above. We estimate settlement of
below grade structures will be similar to the values previously presented for spread foundations.
3.6.3 Drainage
If below-grade structures are designed using drained parameters, a drainage system behind the structure
must be constructed to collect water and prevent the buildup of hydrostatic pressure against the structure.
We recommend the drainage system includes a zone of free-draining backfill a minimum of 18 inches in
width against the back of the wall. The drainage material should consist of coarse sand and gravel
containing less that 5 percent fines based on the fraction of material passing the ¾-inch sieve. Material
similar to “Gravel Backfill for Drains” per WSDOT Standard Specifications Section 9-03.12(4) is also
suitable. Waffle board-type drainage mats may be considered instead of gravel, provided they are protected
from accumulating silt and discharge appropriately.
A perforated, rigid, smooth-walled drainpipe with a minimum diameter of 4 inches should be placed along
the base of the structure within the free-draining backfill and extend for the entire wall length. The drain
pipe should be metal or rigid polyvinyl chloride (PVC) pipe and be sloped to drain by gravity. Discharge
should be routed to appropriate discharge areas and designed to reduce erosion potential. Cleanouts
should be provided to allow routine maintenance. We recommend roof downspouts or other types of
drainage systems not be connected to retaining wall drain systems.
We recommend GeoEngineers be retained to review the retaining wall design calculations and plans to
confirm design meets the recommendations provided in this report.
3.7 STORMWATER INFILTRATION
3.7.1 General
We understand that the design of the proposed infiltration management facility has not been finalized and
will, in part, be informed by the results of infiltration testing herein. Preliminary plans to manage stormwater
at the site include below-grade infiltration facilities such as StormTech chambers. We understand that the
infiltration facility will be designed according to the City of Renton Surface Water Design Manual which
references and is based on the King County 2021 Surface Water Design Manual (2021 KCSWDM).
Two PITs were completed at the site to evaluate stormwater infiltration potential. Both PITs were completed
within Recessional Outwash soils at depths of around 8 feet below existing site grades. The target testing
depth for our PITs was selected in coordination with KPFF.
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Based on the subsurface conditions observed in our explorations and the results of our onsite infiltration
testing, it is our opinion that stormwater infiltration into the native Recessional Outwash soils at the site is
feasible. The sections below provide recommendations for preliminary design of infiltration facilities.
Appendix B includes a detailed description of the infiltration testing procedures and results.
3.7.2 Pilot Infiltration Test Results
Table 2 summarizes the measured infiltration rates determined from the PITs.
TABLE 2: STORMWATER INFILTRATION RATE TESTING RESULTS
TEST LOCATION SOIL TYPE AT TEST DEPTH ELEVATION OF INFILTRATION TEST
(FEET, NAVD88)
MEASURED INFILTRATION RATE
(IN/HR)
PIT-1 Recessional Outwash
(SM, 25 percent fines) 354 3.3
PIT-2 Recessional Outwash
(SM, 21 percent fines) 353 1
Notes:
in/hr = inches per hour
1 Elevations are based on survey by KPFF, dated February 2026 and should be considered approximate
3.7.3 Soil Physical and Chemical Suitability for Treatment
According to the 2021 KCSWDM, for infiltration facilities that intend to use the native soil to provide runoff
treatment:
■ The CEC of the treatment soil must be greater than or equal to 5 milliequivalents per 100 grams of soil
(meq/100g),
■ An organic content of 1.0 percent or greater is necessary, and
■ Waste fill materials shall not be used as infiltration soil media.
The Table below summarizes the results of the CEC testing conducted on samples taken from the bottom
of each of our PIT locations:
TABLE 3. RESULTS OF ORGANIC CONTENT AND CATION EXCHANGE CAPACITY TESTING
LOCATION SAMPLE DEPTH (FEET BGS) ORGANIC CONTENT (%)
CATION EXCHANGE CAPACITY,
CEC (MEQ/100G)
PIT-1 8.5 0.9 4.6
PIT-2 8.5 2.2 7.9
Notes:
feet bgs = feet below ground surface
% = percent by weight of organic matter in the soil
meq/100g = milliequivalents per 100 grams of soil
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3.7.4 Recommended Desing Infiltration Rate
Based on the results of onsite infiltration testing, in our opinion stormwater infiltration is feasible at this
site. Measured infiltration rates at the site varied between the two completed infiltration tests. We
recommend that the lower of the two measured rates (1 inch per hour) be used to establish the design
infiltration rate due to the fine-grained nature of the onsite soils and the variability observed in our
explorations.
The design infiltration rate is determined by applying correction factors to the infiltration rate measured
during testing. The correction factors account for uncertainties in testing, depth to the water table or
impervious strata, infiltration facility geometry and long-term reductions in permeability due to biological
activity and accumulation of fines. As described in Appendix B we currently recommend that a total
correction factor of 0.35 be used to determine the design infiltration rate. This total correction factor
assumes that the geometry factor will be equal to 1.0, which could change based on the final facility
geometry.
Based on the recommended infiltration rate determined during field testing (1 inch per hour) and the
currently recommended total correction factor (0.35), we recommend that infiltration facilities be evaluated
considering a preliminary design infiltration rate of 0.35 inches per hour.
Once the final facility dimensions are known and additional groundwater data is collected, the geometry
factor should be recalculated using the equation in Appendix B and applied so a final design infiltration rate
can be determined. The final infiltration rate used for design of facilities should be reviewed and confirmed
by GeoEngineers.
3.8 PAVEMENT DESIGN
3.8.1 General
New paving areas are expected to include improvements to the parking areas, driveways and sidewalks.
We provide recommended conventional asphalt concrete pavement (ACP) and Portland cement concrete
(PCC) sections below. These sections are based on our experience as no specific traffic loading was
available at the time of our report. Standard duty pavement sections are intended for automobile parking.
Heavy duty pavement sections are intended for occasional heavy truck use such as the route used by
garbage trucks.
These pavement sections may not be adequate for heavy construction traffic loads such as those imposed
by concrete transit mixers, dump trucks or cranes. Additional pavement thickness may be necessary to
prevent pavement damage during construction if other loading types are planned. The recommended
sections assume that final improvements surrounding the pavements will be designed and constructed
such that stormwater or excess irrigation water from landscape areas does not accumulate below the
pavement section or pond on pavement surfaces.
Existing pavements, hardscaping or other structural elements should be removed prior to placement of new
pavement sections. Pavement subgrade should be prepared as recommended in Section 3.3.7 of this
report. Crushed surfacing base course and subbase should be moisture conditioned to near optimum
moisture content and compacted to at least 95 percent of the theoretical MDD per ASTM D 1557.
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CSBC and crushed surfacing top course (CSTC) should conform to applicable sections of 4-04 and 9-03.9(3)
of the WSDOT Standard Specifications. The top approximate 2 inches of the CSBC sections provided may
consist of CSTC as a leveling layer and for more precise grade development.
Hot mix asphalt should conform to applicable sections of 5-04, 9-02 and 9-03 of the WSDOT Standard
Specifications.
PCC mix design should conform with Section 5-05.3(1) of the WSDOT Standard Specifications. Aggregates
for PCC should conform to applicable sections of 9-03.1 of the WSDOT Standard Specifications.
Some areas of pavement may exhibit settlement and subsequent cracking over time. Cracks in the
pavement will allow water to infiltrate to the underlying base course, which could increase the amount of
pavement damage caused by traffic loads. To prolong the effective life of the pavement, cracks should be
sealed as soon as possible.
3.8.2 Asphalt Concrete Pavement Sections
Recommended minimum ACP sections are provided below.
3.8.2.1 STANDARD-DUTY – AUTOMOBILE DRIVEWAYS AND PARKING AREAS
■ Two (2) inches of hot mix asphalt, class ½ inch, PG 58-22
■ Four (4) inches of compacted CSBC
■ Native soil, existing fill or structural fill prepared as recommended in Section 3.3.7 of this report
3.8.2.2 HEAVY DUTY ACP – AREAS SUBJECT TO OCCASIONAL HEAVY TRAFFIC
■ Three (3) inches of hot mix asphalt, class ½ inch, PG 58-22
■ Six (6) inches of compacted CSBC
■ Native soil, existing fill or structural fill prepared as recommended in Section 3.3.7 of this report
3.8.3 Portland Cement Concrete Pavement Design
Recommended minimum PCC pavement sections are provided below. In our opinion steel reinforcement
does not need to be included in PCC pavements that will be primarily used in landscaping and pedestrian
areas (areas not subjected to heavy vehicle traffic). Reinforcement could be considered to reduce the
potential for cracking in areas where the concrete slabs have irregular shapes or where new slabs abut
existing concrete slabs, and the joint layout between the slabs cannot be matched. If reinforcement is
considered, we are available to discuss typical steel reinforcement volumes with the project structural
engineer, who ultimately designs the location, size and layout of reinforcement.
3.8.3.1 SIDEWALK PCC PAVEMENT – PEDESTRIAN AREAS NOT SUBJECTED TO VEHICLE LOADING
■ Four (4) inches of PCC with a minimum 14-day flexural strength of 650 pounds per square inch (psi)
■ Two (2) inches of compacted CSBC
■ Native subgrade or structural fill prepared in accordance with Section 3.3.7 of this report
KPFF Consulting Engineers | May 5, 2026 Page 21
File No. 2868-044-00
3.8.3.2 STANDARD PCC PAVEMENT – AUTOMOBILE DRIVEWAYS AND PARKING AREAS
■ Six (6) inches of PCC with a minimum 14-day flexural strength of 650 psi
■ Four (4) inches of compacted CSBC
■ Native subgrade, existing fill or structural fill prepared in accordance with Section 3.3.7 of this report
3.8.3.3 HEAVY DUTY PCC PAVEMENT – AREAS SUBJECT TO OCCASIONAL HEAVY TRAFFIC
■ Nine (9) inches (minimum) of PCC with a minimum 14-day flexural strength of 650 psi
■ Four (4) inches of compacted CSBC
■ Native subgrade, existing fill or structural fill prepared in accordance with Section 3.3.7 of this report
4.0 Limitations
We have prepared this report for KPFF Consulting Engineers for the Renton Off Campus Emergency
Department project located in Renton, Washington. KPFF Consulting Engineers may distribute copies of
this report to owner and owner’s authorized agents and regulatory agencies as may be required for the
project.
Within the limitations of scope, schedule and budget, our services have been executed in accordance with
generally accepted practices for geotechnical engineering in this area at the time this report was prepared.
The conclusions, recommendations and opinions presented in this report are based on our professional
knowledge, judgment and experience. No warranty, express or implied, applies to the services or this report.
Please refer to Appendix C titled “Report Limitations and Guidelines for Use” for additional information
pertaining to use of this report.
Figures
LOT 1 (R2)
SUBJECT PARCEL
B-1
B-2
B-3
B-4
B-5
PIT-2
PIT-1
Figure 2
Site Plan
N
N
P:
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Renton Off Campus Emergency Department
Renton, Washington
Legend
40
Source(s):
·Survey by KPFF, dated February 2026.
·Proposed site features from KPFF.
Coordinate System: WA State Plane, N Zone, NAD83, US Foot
Disclaimer: This figure was created for a specific purpose and project. Any use of this figure for
any other project or purpose shall be at the user's sole risk and without liability to GeoEngineers.
The locations of features shown may be approximate. GeoEngineers makes no warranty or
representation as to the accuracy, completeness, or suitability of the figure, or data contained
therein. The file containing this figure is a copy of a master document, the original of which is
retained by GeoEngineers and is the official document of record.
Feet
0
N
Site Boundary
B-X Boring by GeoEngineers, 2026
Existing Building
PIT-X Pilot Infiltration Test, 2026
NE
S
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NE 12th Street
Ki
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Site Boundary
Existing Building
B-X Monitoring Well by GeoEngineers, 2026
Tie
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Cast in Place Concrete Retaining Wall
Ro
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Appendices
Appendix A
Subsurface Explorations and Laboratory Testing
KPFF Consulting Engineers | May 5, 2026 Page A-1
File No. 2868-044-00
Appendix A
Subsurface explorations and Laboratory Testing
SUBSURFACE EXPLORATIONS
Exploration Program
Soil conditions at the project site were explored by advancing five borings (B-1 through B-5) between April 2
and 3, 2026 and two test pits (PIT-1 and PIT-2) on April 16,2026. Approximate locations of our explorations
are shown in the Site Plan, Figure 2. The explorations were located in the field using a handheld global
positioning system (GPS) device. Locations and elevations of the explorations presented herein should be
considered approximate.
Boring B-4 was completed as a groundwater monitoring well to observe groundwater conditions at the site.
Borings
Borings extended to approximate depths between 11.5 and 41.5 feet bgs. Borings were advanced using
hollow-stem auger drilling methods and a Diedrich D-70 Turbo track-mounted drill rig provided and
operated by Holt Services, Inc. under subcontract to GeoEngineers. Standard Penetration Tests (SPTs) were
completed using a 1.4-inch-inner-diameter split-barrel sampler driven into the soil using a 140-pound
hammer free-falling a distance of 30 inches. The number of blows required to drive the sampler the last
12 inches, or other indicated distance is recorded on the logs as the blow count. SPTs were advanced at
2.5- to 5-foot intervals.
The drilling was continuously monitored by an engineer from our firm who maintained a detailed log of
subsurface explorations, visually classified the soil encountered and obtained representative soil samples
from the borings. Recovered soil samples were visually classified in the field in general accordance with
ASTM International (ASTM) D 2488 and the classification chart listed in Key to Exploration Logs, Figure A-1.
The logs of the borings are presented in Figures A-2 through A-6. The log is based on interpretation of the
field and laboratory data and indicates the depth at which subsurface materials, or their characteristics,
change although these changes might actually be gradual.
Observations of groundwater conditions were made during drilling and are presented on the boring logs.
Groundwater conditions observed during drilling represent a short-term condition and may or may not be
representative of the long-term groundwater conditions at the site. Groundwater conditions observed
during drilling should be considered approximate.
Borings were backfilled by the driller in accordance with Washington State Department of Ecology (Ecology)
requirements.
Groundwater Monitoring Well
The monitoring well at boring B-2 was completed to a depth of approximately 30 feet bgs with a screened
interval between approximately 20 and 30 feet bgs. The well was completed with a steel monument, flush
with the surrounding grade. An electronic data logger was installed in the well to record groundwater levels
on a regular interval. We plan to return to the site on a quarterly basis to retrieve groundwater data. We will
KPFF Consulting Engineers | May 5, 2026 Page A-2
File No. 2868-044-00
provide updated groundwater information as an addendum to this report once it is available. It is not
currently in our budget to decommission the well after our groundwater monitoring period is complete. We
assume the contractor performing the work will be responsible for coordinating monitoring well
decommissioning. Wells must be decommissioned by a licensed well driller. The reference well Department
of Ecology Well ID number is BOT828.
Test Pits
Test pits were continuously observed by a geologist from our firm who evaluated and classified the soils
encountered, obtained representative soil samples and maintained a detailed log of each test pit. Density
was estimated from difficulty of digging and difficulty of sample collection using a hand-held trowel. In
addition, pertinent information including soil sample depths, stratigraphy and groundwater seepage was
recorded.
The soils encountered during excavation were visually classified in general accordance with the system
summarized in Figure A-1. The logs of the test pits are presented in Figures A-7 through A-8. The logs are
based on our interpretation of the field and laboratory data and indicate the various soils encountered.
They also indicate the approximate depths at which the soils or their characteristics change; although the
change may be gradual. Representative soil samples were obtained from the test pits, logged, sealed in
plastic bags and transported to our laboratory. Laboratory testing is described in Appendix B.
The test pits were backfilled with the excavated soils and compacted to the extent practical with the bucket
of the excavator. The backfill was not compacted to the requirements of structural fill. Once backfill was
complete the test pit area was surfaced with the base coarse gravel that we were able to segregate from
the rest of the excavated soils.
LABORATORY TESTING
Soil samples obtained from the explorations were retained in sealed plastic bags and transported to the
GeoEngineers’ laboratory. Representative soil samples were selected for laboratory tests to evaluate
pertinent geotechnical engineering characteristics of the soils and refine our field classification, as
necessary. The tests were performed in general accordance with test methods of ASTM International
(ASTM) or other applicable procedures. The following paragraphs provide a description of the tests
performed.
Moisture Content (MC)
Selected samples were oven dried to estimate the percentage of water (on a mass basis) in the soil.
Moisture content tests were completed in general accordance with ASTM Test Method D 2216. The results
of these tests are presented on the exploration logs at the depths at which the samples were obtained.
Percent Fines (%F)
Selected samples were “washed” through the U.S. No. 200 sieve to estimate the relative percentages of
coarse- and fine-grained particles in the soil. The percent passing value represents the percentage by
weight of the sample finer than the U.S. No. 200 sieve (fines). Tests were conducted in general accordance
with ASTM D 1140. Test results are presented on the exploration logs at the respective sample depths.
KPFF Consulting Engineers | May 5, 2026 Page A-3
File No. 2868-044-00
Particle Size Gradation - Sieve Analysis (SA)
Sieve analyses were performed on selected samples in general accordance with ASTM Test
Method D 6913. This test method covers the quantitative determination of the distribution of particle sizes
in soils. Typically, the distribution of particle sizes larger than 75 micrometers (µm) is determined by sieving.
Figures A-10 and A-11 present the results of our sieve analyses.
Organic Content
Organic content testing was completed on one representative sample of the Recessional Outwash from
each test pit using the ASTM D 2974 test method. This test method evaluates the percentage by weight of
organic matter in the soil. The test results are summarized in Table 3 of this report and in Table A-1 below.
Cation Exchange Capacity (CEC)
CEC testing was performed on a representative sample of the Recessional Outwash from each test pit
following the U.S. Environmental Protection Agency (EPA) 9081 test method. CEC testing was performed by
Northwest Agricultural Consultants, Inc. under subcontract to GeoEngineers. This test evaluates the total
capacity of a soil to hold exchangeable cations. The results of the CEC testing are summarized in Table A-1
below.
TABLE A-1. RESULTS OF ORGANIC CONTENT AND CATION EXCHANGE CAPACITY TESTING
LOCATION SAMPLE DEPTH (FEET BGS) ORGANIC CONTENT (%)
CATION EXCHANGE CAPACITY,
CEC (MEQ/100G)
PIT-1 8.5 0.9 4.6
PIT-2 8.5 2.2 7.9
Notes:
feet bgs = feet below ground surface
% = percent by weight of organic matter in the soil
meq/100g = milliequivalents per 100 grams of soil
Measured groundwater level in exploration,well, or piezometer
Measured free product in well or piezometer
Distinct contact between soil strata
Approximate contact between soil strata
Contact between geologic units
SYMBOLS TYPICAL
DESCRIPTIONS
GW
GP
SW
SP
SM
FINEGRAINED
SOILS
SILTS ANDCLAYS
NOTE: Multiple symbols are used to indicate borderline or dual soil classifications
MORE THAN 50%RETAINED ONNO. 200 SIEVE
MORE THAN 50%PASSINGNO. 200 SIEVE
GRAVEL
ANDGRAVELLYSOILS
SC
LIQUID LIMITLESS THAN 50
(APPRECIABLE AMOUNTOF FINES)
(APPRECIABLE AMOUNTOF FINES)
COARSEGRAINEDSOILS
MAJOR DIVISIONS GRAPH LETTER
GM
GC
ML
CL
OL
SILTS AND
CLAYS
SANDS WITHFINES
SANDANDSANDY
SOILS
MH
CH
OH
PT
(LITTLE OR NO FINES)
CLEAN SANDS
GRAVELS WITHFINES
CLEAN GRAVELS
(LITTLE OR NO FINES)
WELL-GRADED GRAVELS, GRAVEL -SAND MIXTURES
CLAYEY GRAVELS, GRAVEL - SAND -CLAY MIXTURES
WELL-GRADED SANDS, GRAVELLYSANDS
POORLY-GRADED SANDS, GRAVELLYSAND
SILTY SANDS, SAND - SILT MIXTURES
CLAYEY SANDS, SAND - CLAYMIXTURES
INORGANIC SILTS, ROCK FLOUR,CLAYEY SILTS WITH SLIGHTPLASTICITY
INORGANIC CLAYS OF LOW TOMEDIUM PLASTICITY, GRAVELLYCLAYS, SANDY CLAYS, SILTY CLAYS,LEAN CLAYS
ORGANIC SILTS AND ORGANIC SILTYCLAYS OF LOW PLASTICITY
INORGANIC SILTS, MICACEOUS ORDIATOMACEOUS SILTY SOILS
INORGANIC CLAYS OF HIGHPLASTICITY
ORGANIC CLAYS AND SILTS OFMEDIUM TO HIGH PLASTICITY
PEAT, HUMUS, SWAMP SOILS WITHHIGH ORGANIC CONTENTSHIGHLY ORGANIC SOILS
SOIL CLASSIFICATION CHART
MORE THAN 50%OF COARSEFRACTION RETAINEDON NO. 4 SIEVE
MORE THAN 50%OF COARSEFRACTION PASSINGON NO. 4 SIEVE
SILTY GRAVELS, GRAVEL - SAND -SILT MIXTURES
POORLY-GRADED GRAVELS,GRAVEL - SAND MIXTURES
LIQUID LIMIT GREATERTHAN 50
Contact between soil of the same geologicunit
Material Description Contact
Graphic Log Contact
NOTE: The reader must refer to the discussion in the report text and the logs of explorations for a proper understanding of subsurface conditions.Descriptions on the logs apply only at the specific exploration locations and at the time the explorations were made; they are not warranted to berepresentative of subsurface conditions at other locations or times.
Groundwater Contact
Blowcount is recorded for driven samplers as the number ofblows required to advance sampler 12 inches (or distance noted).See exploration log for hammer weight and drop.
"P" indicates sampler pushed using the weight of the drill rig.
"WOH" indicates sampler pushed using the weight of thehammer.
Key to Exploration LogsFigure A-1 -
ADDITIONAL MATERIAL SYMBOLS
SYMBOLS
Asphalt Concrete
Cement Concrete
Crushed Rock/Quarry Spalls
Topsoil
GRAPH LETTER
AC
CC
SOD Sod/Forest Duff
CR
DESCRIPTIONS
TYPICAL
TS
No Visible SheenSlight SheenModerate SheenHeavy Sheen
Laboratory / Field Tests
%F%GALCACPCSDDDSHAMCMDMohsOCPMPIPLPPSATXUCUUVS
Sheen Classification
NSSSMSHS
Percent finesPercent gravelAtterberg limitsChemical analysisLaboratory compaction testConsolidation testDry densityDirect shearHydrometer analysisMoisture contentMoisture content and dry densityMohs hardness scaleOrganic contentPermeability or hydraulic conductivityPlasticity indexPoint load testPocket penetrometerSieve analysisTriaxial compressionUnconfined compressionUnconsolidated undrained triaxial compressionVane shear
Continuous Coring
Bulk or grab
Direct-Push
Piston
Shelby tube
Standard Penetration Test (SPT)
Sampler Symbol Descriptions
Modified California Sampler (6-inch sleeve) or Dames & Moore
Rev. 03/2024
Project: Renton Off Campus Emergency Department
Project Location: Renton, Washington
Project Number: 2868-044-00
15
22
9
8
Approximately 3 inches of asphalt concrete
Approximately 4 inches of base course
Silty Sand (SM), medium dense, brown-gray, moist;medium sand; fine gravel. [Recessional Outwash]
Becomes loose
Silty Sand (SM), medium dense, brown, moist; fine tomedium sand; trace fine to rounded gravel.
Becomes loose
Becomes medium dense and gray-brown
Silty Sand with Gravel (SM), medium dense, brown,moist; fine to coarse gravel.
Poorly Graded Sand with Silt (SP-SM), very dense,gray-brown, moist; fine to medium sand.
1
2
3
4
5%F
6SA
8
3
13
13
15
14
9
17
10
24
20
AC
CR
SM
SM
SM
SP-SM
Notes:
41.5 EV
LML Holt Services, Inc. Hollow-stem Auger
Truck-mounted D-58DrillingEquipmentAutohammer140 (lbs) / 30 (in) Drop
WA State Plane NorthNAD83 (feet)1307985.91186575.11
362NAVD88
Easting (X)Northing (Y)
Start TotalDepth (ft)
Logged By
Checked By
End
Surface Elevation (ft)Vertical Datum
Drilled
HammerData
SystemDatum
Driller DrillingMethod
Groundwater not observed at time of exploration
4/2/20264/2/2026
Note: See Figure A-1 for explanation of symbols.Coordinates Data Source: Horizontal approximated based on Locational Survey. Vertical approximated based on Locational Survey.
Sheet 1 of 2Project Number:
Project Location:
Project:
2868-044-00
Log of Boring B-1
Figure A-2
Renton Off Campus Emergency Department
Renton, Washington
Da
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FIELD DATA
MATERIALDESCRIPTION
Sa
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Gr
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355
350
345
340
Poorly Graded Sand (SP), dense, gray, moist; fine tomedium sand.
Becomes very dense
7
8
9
10
13
10.5
16
10
52
43
50
53
SP
Sheet 2 of 2Project Number:
Project Location:
Project:
2868-044-00
Log of Boring B-1 (continued)
Figure A-2
Renton Off Campus Emergency Department
Renton, Washington
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P
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(
%
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(
%
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FIELD DATA
MATERIALDESCRIPTION
Sa
m
p
l
e
N
a
m
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Te
s
t
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Re
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(
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Bl
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S
a
m
p
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De
p
t
h
(
f
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)
25
30
35
40
Gr
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h
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El
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a
t
i
o
n
(
f
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t
)
335
330
325
Approximately 3 inches of asphalt concrete
Approximately 4 inches of base course
Silty Sand with Gravel (SM), loose, brown, moist;trace subangular gravel.
Becomes with no gravel
Poorly Graded Sand with Silt (SP-SM), mediumdense, brown-yellow, moist.
Silty Sand with Gravel (SM), dense, yellow-brown,moist; little, subangular gravel.
1
2
3
4
5SA
6
7
12
11
3
9
4
8
10
16
4
16
34
AC
CR
SM
SP-SM
SM
Concrete surfaceseal
2-inch Schedule 40PVC well casing
3/8-inch bentoniteseal
2-inch Schedule 40PVC screen,0.010-inch slotwidth
Construction sandbackfill
3
18
20
6 8
StartDrilled4/2/2026
HammerData
Date MeasuredHorizontalDatum
Vertical Datum
Easting (X)Northing (Y)
DrillingEquipment
Top of CasingElevation (ft)
Elevation (ft)
Groundwater Depth toWater (ft)
Notes:
Surface Elevation (ft)
Logged By
Truck-mounted D-58
361.67362.5NAVD88
1308051.81186658.8 WA State Plane NorthNAD83 (feet)Dry
41.5 DrillingMethod4/2/2026
End
Checked By DrillerTotalDepth (ft)
Autohammer140 (lbs) / 30 (in) Drop
EV
LML Holt Services, Inc.Hollow-stem Auger/Cal Mod
DOE Well I.D.: BOT828A 2-in well was installed on 4/2/2026 to a depth of 30 ft.
Note: See Figure A-1 for explanation of symbols.Coordinates Data Source: Horizontal approximated based on Locational Survey. Vertical approximated based on Locational Survey.
Surface
Monument
El
e
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(
f
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)
360
355
350
345
340
De
p
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(
f
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t
)
0
5
10
15
20
25
FIELD DATA
MATERIALDESCRIPTION
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WELL LOG
Mo
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Fin
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(
%
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Sheet 1 of 2Project Number:
Project Location:
Project:
2868-044-00
Log of Boring with a Monitoring Well B-2
Figure A-3
Renton Off Campus Emergency Department
Renton, Washington
Da
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4
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0
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2
6
P
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D
_
U
S
_
J
U
N
E
_
2
0
1
7
.
G
L
B
/
G
E
I
8
_
G
E
O
T
E
C
H
_
W
E
L
L
_
%
F
Poorly Graded Sand with Silt (SP-SM), very dense,gray-brown, moist.
Becomes very dense
Grades to dense
7SA
8%F
9
10
14
10
10
12
38
50
51
49
SP-SM
30
7
5
13
7
El
e
v
a
t
i
o
n
(
f
e
e
t
)
335
330
325
De
p
t
h
(
f
e
e
t
)
25
30
35
40
FIELD DATA
MATERIALDESCRIPTION
Sa
m
p
l
e
N
a
m
e
Te
s
t
i
n
g
Wa
t
e
r
L
e
v
e
l
In
t
e
r
v
a
l
Re
c
o
v
e
r
e
d
(
i
n
)
Bl
o
w
s
/
f
o
o
t
Co
l
l
e
c
t
e
d
S
a
m
p
l
e
Gr
a
p
h
i
c
L
o
g
Gr
o
u
p
Cl
a
s
s
i
f
i
c
a
t
i
o
n
WELL LOG
Mo
i
s
t
u
r
e
Co
n
t
e
n
t
(
%
)
Fi
n
e
s
Co
n
t
e
n
t
(
%
)
Sheet 2 of 2Project Number:
Project Location:
Project:
2868-044-00
Log of Boring with a Monitoring Well B-2 (continued)
Figure A-3
Renton Off Campus Emergency Department
Renton, Washington
Da
t
e
:
4
/
3
0
/
2
6
P
a
t
h
:
P
:
\
2
\
2
8
6
8
0
4
4
\
G
I
N
T
\
2
8
6
8
0
4
4
0
0
.
G
P
J
D
B
L
i
b
r
a
r
y
/
L
i
b
r
a
r
y
:
G
E
O
E
N
G
I
N
E
E
R
S
_
D
F
_
S
T
D
_
U
S
_
J
U
N
E
_
2
0
1
7
.
G
L
B
/
G
E
I
8
_
G
E
O
T
E
C
H
_
W
E
L
L
_
%
F
25
27
9
10
Approximately 3 inches of asphalt concrete
Approximately 4 inches of base course
Silty Sand (SM), medium dense, gray, moist; fine tomedium sand. [Recessional Outwash]
Silty Sand (SM), medium dense, gray-brown, moist;medium to coarse sand; trace gravel.
Poorly Graded Sand with Silt (SP-SM), dense,gray-brown, moist; medium to coarse sand; few totrace gravel; few silt.
1%F
2
3SA
4
5
15
17
12
13
15
25
19
22
25
42
AC
CR
SM
SM
SP-SM
Notes:
16.5 EV
LML Holt Services, Inc. Hollow-stem Auger
Truck-mounted D-58DrillingEquipmentAutohammer140 (lbs) / 30 (in) Drop
WA State Plane NorthNAD83 (feet)1308240.92186651.61
364NAVD88
Easting (X)Northing (Y)
Start TotalDepth (ft)
Logged By
Checked By
End
Surface Elevation (ft)Vertical Datum
Drilled
HammerData
SystemDatum
Driller DrillingMethod
Groundwater not observed at time of exploration
4/3/20264/3/2026
Note: See Figure A-1 for explanation of symbols.Coordinates Data Source: Horizontal approximated based on Locational Survey. Vertical approximated based on Locational Survey.
Sheet 1 of 1Project Number:
Project Location:
Project:
2868-044-00
Log of Boring B-3
Figure A-4
Renton Off Campus Emergency Department
Renton, Washington
Da
t
e
:
4
/
3
0
/
2
6
P
a
t
h
:
P
:
\
2
\
2
8
6
8
0
4
4
\
G
I
N
T
\
2
8
6
8
0
4
4
0
0
.
G
P
J
D
B
L
i
b
r
a
r
y
/
L
i
b
r
a
r
y
:
G
E
O
E
N
G
I
N
E
E
R
S
_
D
F
_
S
T
D
_
U
S
_
J
U
N
E
_
2
0
1
7
.
G
L
B
/
G
E
I
8
_
G
E
O
T
E
C
H
_
S
T
A
N
D
A
R
D
_
%
F
_
N
O
_
G
W
REMARKS
Fi
n
e
s
Co
n
t
e
n
t
(
%
)
Mo
i
s
t
u
r
e
Co
n
t
e
n
t
(
%
)
FIELD DATA
MATERIALDESCRIPTION
Sa
m
p
l
e
N
a
m
e
Te
s
t
i
n
g
Re
c
o
v
e
r
e
d
(
i
n
)
In
t
e
r
v
a
l
Bl
o
w
s
/
f
o
o
t
Co
l
l
e
c
t
e
d
S
a
m
p
l
e
De
p
t
h
(
f
e
e
t
)
0
5
10
15
Gr
a
p
h
i
c
L
o
g
Gr
o
u
p
Cl
a
s
s
i
f
i
c
a
t
i
o
n
El
e
v
a
t
i
o
n
(
f
e
e
t
)
360
355
350
3213
Approximately 3 inches of asphalt concrete
Approximately 4 inches of base course
Poorly Graded Sand with Silt (SP-SM), loose, brown,moist; fine to medium sand. [RecessionalOutwash]
Silty Sand (SM), medium dense, brown, moist.
Silty Sand (SM), dense, gray-brown, moist; fine tomedium sand.
Poorly Graded Sand with Silt (SP-SM), dense,gray-brown, moist.
1
2%F
3
4
5
10.5
15
14
13
14
7
17
15
31
41
AC
CR
SP-SM
SM
SM
SP-SM
Notes:
20 EV
LML Holt Services, Inc. Hollow-stem Auger
Truck-mounted D-58DrillingEquipmentAutohammer140 (lbs) / 30 (in) Drop
WA State Plane NorthNAD83 (feet)1308174.88186543.85
362NAVD88
Easting (X)Northing (Y)
Start TotalDepth (ft)
Logged By
Checked By
End
Surface Elevation (ft)Vertical Datum
Drilled
HammerData
SystemDatum
Driller DrillingMethod
Groundwater not observed at time of exploration
4/3/20264/3/2026
Note: See Figure A-1 for explanation of symbols.Coordinates Data Source: Horizontal approximated based on Locational Survey. Vertical approximated based on Locational Survey.
Sheet 1 of 1Project Number:
Project Location:
Project:
2868-044-00
Log of Boring B-4
Figure A-5
Renton Off Campus Emergency Department
Renton, Washington
Da
t
e
:
4
/
3
0
/
2
6
P
a
t
h
:
P
:
\
2
\
2
8
6
8
0
4
4
\
G
I
N
T
\
2
8
6
8
0
4
4
0
0
.
G
P
J
D
B
L
i
b
r
a
r
y
/
L
i
b
r
a
r
y
:
G
E
O
E
N
G
I
N
E
E
R
S
_
D
F
_
S
T
D
_
U
S
_
J
U
N
E
_
2
0
1
7
.
G
L
B
/
G
E
I
8
_
G
E
O
T
E
C
H
_
S
T
A
N
D
A
R
D
_
%
F
_
N
O
_
G
W
REMARKS
Fi
n
e
s
Co
n
t
e
n
t
(
%
)
Mo
i
s
t
u
r
e
Co
n
t
e
n
t
(
%
)
FIELD DATA
MATERIALDESCRIPTION
Sa
m
p
l
e
N
a
m
e
Te
s
t
i
n
g
Re
c
o
v
e
r
e
d
(
i
n
)
In
t
e
r
v
a
l
Bl
o
w
s
/
f
o
o
t
Co
l
l
e
c
t
e
d
S
a
m
p
l
e
De
p
t
h
(
f
e
e
t
)
0
5
10
15
20
Gr
a
p
h
i
c
L
o
g
Gr
o
u
p
Cl
a
s
s
i
f
i
c
a
t
i
o
n
El
e
v
a
t
i
o
n
(
f
e
e
t
)
360
355
350
345
25
35
24
12
14
10
Approximately 4 inches of asphalt concrete
Approximately 4 inches of base course
Silty Sand (SM), medium dense, gray, moist; fine tomedium sand. [Recessional Outwash]
Trace gravel
Becomes brown
Poorly Graded Sand with Silt (SP-SM), loose, brown,moist.
1%F
2
3SA
4%F
5
15
7
14
13
7
20
19
9
18
9
AC
CR
SM
SP-SM
Notes:
16.5 EV
LML Holt Services, Inc. Hollow-stem Auger/Cal Mod
Truck-mounted D-58DrillingEquipmentAutohammer140 (lbs) / 30 (in) Drop
WA State Plane NorthNAD83 (feet)1308075.46186513.6
362NAVD88
Easting (X)Northing (Y)
Start TotalDepth (ft)
Logged By
Checked By
End
Surface Elevation (ft)Vertical Datum
Drilled
HammerData
SystemDatum
Driller DrillingMethod
Groundwater not observed at time of exploration
4/3/20264/3/2026
Note: See Figure A-1 for explanation of symbols.Coordinates Data Source: Horizontal approximated based on Locational Survey. Vertical approximated based on Locational Survey.
Sheet 1 of 1Project Number:
Project Location:
Project:
2868-044-00
Log of Boring B-5
Figure A-6
Renton Off Campus Emergency Department
Renton, Washington
Da
t
e
:
4
/
3
0
/
2
6
P
a
t
h
:
P
:
\
2
\
2
8
6
8
0
4
4
\
G
I
N
T
\
2
8
6
8
0
4
4
0
0
.
G
P
J
D
B
L
i
b
r
a
r
y
/
L
i
b
r
a
r
y
:
G
E
O
E
N
G
I
N
E
E
R
S
_
D
F
_
S
T
D
_
U
S
_
J
U
N
E
_
2
0
1
7
.
G
L
B
/
G
E
I
8
_
G
E
O
T
E
C
H
_
S
T
A
N
D
A
R
D
_
%
F
_
N
O
_
G
W
REMARKS
Fi
n
e
s
Co
n
t
e
n
t
(
%
)
Mo
i
s
t
u
r
e
Co
n
t
e
n
t
(
%
)
FIELD DATA
MATERIALDESCRIPTION
Sa
m
p
l
e
N
a
m
e
Te
s
t
i
n
g
Re
c
o
v
e
r
e
d
(
i
n
)
In
t
e
r
v
a
l
Bl
o
w
s
/
f
o
o
t
Co
l
l
e
c
t
e
d
S
a
m
p
l
e
De
p
t
h
(
f
e
e
t
)
0
5
10
15
Gr
a
p
h
i
c
L
o
g
Gr
o
u
p
Cl
a
s
s
i
f
i
c
a
t
i
o
n
El
e
v
a
t
i
o
n
(
f
e
e
t
)
360
355
350
Approximately 4 inches of asphalt concrete
Silty Gravel with Sand (GM), medium dense, gray-brown, moist. [BaseCourse]
Silty Sand with Gravel (SM), medium dense, gray-brown, moist; mostlyfine sand; few to little gravel; ocassionally weakly cemented.[Recessional Outwash]
Test pit terminated at approximately 8½ feet
AC
GM
SM
S-1
S-2
S-3
S-4SA
8 Infiltration test completed at 8 feet25
Notes: See Figure A-1 for explanation of symbols.The depths on the test pit logs are based on an average of measurements across the test pit and should be considered accurate to ½ foot.Coordinates Data Source: Horizontal approximated based on Locational Survey. Vertical approximated based on Locational Survey.
Da
t
e
:
4
/
3
0
/
2
6
P
a
t
h
:
P
:
\
2
\
2
8
6
8
0
4
4
\
G
I
N
T
\
2
8
6
8
0
4
4
0
0
.
G
P
J
D
B
L
i
b
r
a
r
y
/
L
i
b
r
a
r
y
:
G
E
O
E
N
G
I
N
E
E
R
S
_
D
F
_
S
T
D
_
U
S
_
J
U
N
E
_
2
0
1
7
.
G
L
B
/
G
E
I
8
_
T
E
S
T
P
I
T
_
1
P
_
G
E
O
T
E
C
_
%
F
Sheet 1 of 1Project Number:
Project Location:
Project:
2868-044-00
Log of Test Pit PIT-1
Figure A-7
Renton Off Campus Emergency Department
Renton, Washington
El
e
v
a
t
i
o
n
(
f
e
e
t
)
361
360
359
358
357
356
355
354
De
p
t
h
(
f
e
e
t
)
1
2
3
4
5
6
7
8
Te
s
t
i
n
g
S
a
m
p
l
e
Gr
a
p
h
i
c
L
o
g
SAMPLE
MATERIALDESCRIPTION
Gr
o
u
p
Cla
s
s
i
f
i
c
a
t
i
o
n
Sa
m
p
l
e
N
a
m
e
Te
s
t
i
n
g
Mo
i
s
t
u
r
e
Co
n
t
e
n
t
(
%
)
REMARKS
Fin
e
s
Co
n
t
e
n
t
(
%
)
DateExcavated
Surface Elevation (ft)Vertical Datum Coordinate SystemHorizontal DatumEasting (X)Northing (Y)
TotalDepth (ft)4/16/2026 8.5
362NAVD88 1308186.05186593.09 WA State Plane NorthNAD83 (feet)
EV
Checked By LML
Groundwater not observed
Caving not observedEquipment John Deere 356
Logged By Excavator Holt Services, Inc.
Approximately 4 inches of asphalt concrete
Silty Gravel with Sand (GM), medium dense, gray, moist; concretetreated base course.
Silty Sand with Gravel (SM), medium dense. gray-brown, moist; mostlyfine sand; few gravel; organics (wood debris). [RecessionalOutwash]
Becomes gray
Silty Sand with Gravel and Cobbles (SM), medium dense, lightgray-brown, moist; mostly fine sand; few gravel; trace cobbles.
Test pit terminated at approximately 8½ feet
AC
GM
SM
SM
S-1
S-2
S-3
S-4SA
7
Minor groundwater seepage observed at 1½ feet
Infiltration test completed at 8 feet21
Notes: See Figure A-1 for explanation of symbols.The depths on the test pit logs are based on an average of measurements across the test pit and should be considered accurate to ½ foot.Coordinates Data Source: Horizontal approximated based on Locational Survey. Vertical approximated based on Locational Survey.
Da
t
e
:
4
/
3
0
/
2
6
P
a
t
h
:
P
:
\
2
\
2
8
6
8
0
4
4
\
G
I
N
T
\
2
8
6
8
0
4
4
0
0
.
G
P
J
D
B
L
i
b
r
a
r
y
/
L
i
b
r
a
r
y
:
G
E
O
E
N
G
I
N
E
E
R
S
_
D
F
_
S
T
D
_
U
S
_
J
U
N
E
_
2
0
1
7
.
G
L
B
/
G
E
I
8
_
T
E
S
T
P
I
T
_
1
P
_
G
E
O
T
E
C
_
%
F
Sheet 1 of 1Project Number:
Project Location:
Project:
2868-044-00
Log of Test Pit PIT-2
Figure A-8
Renton Off Campus Emergency Department
Renton, Washington
El
e
v
a
t
i
o
n
(
f
e
e
t
)
360
359
358
357
356
355
354
353
De
p
t
h
(
f
e
e
t
)
1
2
3
4
5
6
7
8
Te
s
t
i
n
g
S
a
m
p
l
e
Gr
a
p
h
i
c
L
o
g
SAMPLE
MATERIALDESCRIPTION
Gr
o
u
p
Cla
s
s
i
f
i
c
a
t
i
o
n
Sa
m
p
l
e
N
a
m
e
Te
s
t
i
n
g
Mo
i
s
t
u
r
e
Co
n
t
e
n
t
(
%
)
REMARKS
Fin
e
s
Co
n
t
e
n
t
(
%
)
DateExcavated
Surface Elevation (ft)Vertical Datum Coordinate SystemHorizontal DatumEasting (X)Northing (Y)
TotalDepth (ft)4/16/2026 8.5
361NAVD88 1308038.26186499.18 WA State Plane NorthNAD83 (feet)
EV
Checked By LML
Groundwater not observed
Caving not observedEquipment John Deere 356
Logged By Excavator Holt Services, Inc.
MEDIUM FINE
3/8”3” 1.5”#4 #10 #20 #40 #60 #1003/4”
02868-044-00 Date Exported: 04/29/2026
Soil Description
Boring
Number
Depth
(feet)
B-1
B-2
B-2
B-3
20
15
25
7.5
Silty sand with gravel (SM)
Poorly graded sand with silt (SP-SM)
Silty sand (SM)
Silty sand (SM)
Symbol
Moisture
(%)
8
6
7
10
Note: This report may not be reproduced, except in full, without written approval of GeoEngineers, Inc. Test results are applicable only to the
specific sample on which they were performed, and should not be interpreted as representative of any other samples obtained at other
times, depths or locations, or generated by separate operations or processes.
The grain size analysis results were obtained in general accordance with ASTM D 6913.
Figure A9
Sieve Analysis Results
Renton off Campus Emergency Department
Renton, Washington
#200
0
10
20
30
40
50
60
70
80
90
100
0.0010.010.11101001000
PE
R
C
E
N
T
P
A
S
S
I
N
G
B
Y
W
E
I
G
H
T
GRAIN SIZE IN MILLIMETERS
U.S. STANDARD SIEVE SIZE
SAND SILT OR CLAYCOBBLESGRAVEL
COARSECOARSE FINE
MEDIUM FINE
3/8”3” 1.5”#4 #10 #20 #40 #60 #1003/4”
02868-044-00 Date Exported: 04/29/2026
Soil Description
Boring
Number
Depth
(feet)
B-4
B-5
PIT-1
PIT-2
5
7.5
8
8
Silty sand (SM)
Silty sand (SM)
Silty sand with gravel (SM)
Silty sand with gravel (SM)
Symbol
Moisture
(%)
13
14
8
7
Note: This report may not be reproduced, except in full, without written approval of GeoEngineers, Inc. Test results are applicable only to the
specific sample on which they were performed, and should not be interpreted as representative of any other samples obtained at other
times, depths or locations, or generated by separate operations or processes.
The grain size analysis results were obtained in general accordance with ASTM D 6913.
Figure A10
Sieve Analysis Results
Renton off Campus Emergency Department
Renton, Washington
#200
0
10
20
30
40
50
60
70
80
90
100
0.0010.010.11101001000
PE
R
C
E
N
T
P
A
S
S
I
N
G
B
Y
W
E
I
G
H
T
GRAIN SIZE IN MILLIMETERS
U.S. STANDARD SIEVE SIZE
SAND SILT OR CLAYCOBBLESGRAVEL
COARSECOARSE FINE
Appendix B
Infiltration Testing
KPFF Consulting Engineers | May 5, 2026 Page B-1
File No. 2868-044-00
Infiltration Testing
PILOT INFILTRATION TESTS
We conducted small-scale pilot infiltration tests (PITs) in test pits PIT-1 and PIT-2 on April 16, 2026.
Figure 2, Site Plan, shows the approximate location of the test pits where the PITs were performed. The
infiltration tests were completed in general accordance with the guidelines provided in the City of Renton
Surface Water Design Manual which references and is based on the King County 2021 Surface Water
Design Manual (2021 KCSWDM). The following is a summary of test methods, field measured infiltration
rates and correction factors used for developing the design soil infiltration rate for the site.
METHODOLOGY AND TESTING PROCEDURES
Test pits PIT-1 and PIT-2 were initially excavated with a John Deere 35G excavator to approximately 8 feet
below the ground surface. We selected PIT locations and depths based on conversations with the project
team and utility access considerations. We performed both small-scale PITs in the native Recessional
Outwash soils.
During testing, a graduated grade rod or tape measure was placed at the base of the excavation as a visual
reference for monitoring water levels during testing. A piezoelectric pressure transducer was placed at the
base of the excavation to provide accurate water level records in 5-second intervals throughout the duration
of the tests. Water used for the infiltration tests in PIT-1 and PIT-2 was provided by water trucks using 2½
and 2-inch hoses.
Initial filling and maintaining of the water level in the PITs was performed by monitoring the declining water
level in a series of stages. The excavation was filled to a predetermined depth (approximately 14 inches)
for the 6-hour pre-soak period. During the pre-soak, the water level was allowed to drain approximately
2 inches before the pit was refilled to the initial level again to maintain a constant minimum depth of
12 inches. This draining and refilling process was repeated as needed in succession (stages). At the end of
the 6-hour pre-soak period, the successive filling and draining was repeated at the same 12 and 14 inches
of water depth for an additional hour, which is considered the testing period.
By periodically refilling the excavation to the starting level, then allowing the water level to drop between
two predetermined levels, the apparent infiltration rate for each cycle was determined accurately using
measurements from the pressure transducer. The rate of decline in the falling water levels recorded after
each filling cycle was used to calculate the apparent infiltration rate for each stage of the test. The overall
testing process for each PIT took approximately 8 hours with water levels measured continuously
(every 5 seconds). The water-level measurements for the PITs and plots of the measured infiltration rates
calculated during each stage of the small-scale PIT in test pits PIT-1 and PIT-2 are shown in Figures B-1
and B-2.
After completing the PITs, the test pits were excavated an additional ½ foot below the infiltration testing
depth to observe and sample the soils below the level of the infiltration testing.
KPFF Consulting Engineers | May 5, 2026 Page B-2
File No. 2868-044-00
CORRECTION FACTORS
The design infiltration rate is determined by applying correction factors to the saturated infiltration rate
measured during testing. The correction factors account for uncertainties in testing, depth to the water
table or impervious strata, infiltration receptor geometry and long-term reductions in permeability due to
biological activity and accumulation of fines. Equation 5-11 of the 2021 KCSWDM was developed to
account for these factors. This equation estimates the maximum design infiltration rate (Idesign). 𝐼𝐼𝑑𝑑𝑑𝑑𝑑𝑑𝑑𝑑𝑑𝑑𝑑𝑑=𝐼𝐼𝑚𝑚𝑑𝑑𝑚𝑚𝑑𝑑𝑚𝑚𝑚𝑚𝑑𝑑𝑑𝑑∗𝐹𝐹𝑡𝑡𝑑𝑑𝑑𝑑𝑡𝑡𝑑𝑑𝑑𝑑𝑑𝑑∗𝐹𝐹𝑑𝑑𝑑𝑑𝑔𝑔𝑚𝑚𝑑𝑑𝑡𝑡𝑚𝑚𝑔𝑔∗𝐹𝐹𝑝𝑝𝑝𝑝𝑚𝑚𝑑𝑑𝑑𝑑𝑑𝑑𝑑𝑑𝑑𝑑 (Equation 5-11)
Ftesting accounts for uncertainties in the testing method. For small and large-scale PITs, Ftesting = 0.5.
Fgeometry accounts for the influence of facility geometry and depth to the water table or impervious strata on
the actual infiltration rate. Fgeometry must be between 0.25 and 1.0 as determined by Equation 5-12:
Fgeometry = 4 D/W + 0.05 (Equation 5-12)
Where D = depth from the bottom of the proposed facility to the maximum wet-season water table or
nearest impervious layer, whichever is less, and W = width of the facility.
We did not observe what we interpret to be an impervious layer in our explorations. Until additional
groundwater data is collected at the site we recommend assuming a design depth to groundwater of 40 feet
below existing site grades (about Elevation 322 feet). While the dimensions of the proposed infiltration
facilities are not known, we anticipate that the recommended design groundwater depth/elevation will
correspond to a calculated geometry factor of 1.0. As discussed in Section 3.7.4, a final geometry factor
should be calculated once more groundwater data is collected and the facility dimensions are known. The
design infiltration rate used for the facility should consider the finalized geometry factor.
Fplugging accounts for reductions in infiltration rates over the long term due to plugging of soils. We
recommend a correction factor Fplugging of 0.7 because the soils encountered were loams and sandy loams.
All currently recommended correction factors and the total correction factor are provided in Table B-1.
TABLE B-1. RECOMMENDED INFILTRATION CORRECTION FACTORS
FTESTING FGEOMETRY FPLUGGING
TOTAL CORRECTION
FACTOR
0.5 1.0 0.7 0.35
Notes:
Fgeometry = must be verified once final facility dimensions are known and additional groundwater data is collected.
Figure B-1
PIT-1 Infiltration Testing
Renton Off Campus Emergency Department
Renton, Washington
02868-044-00 Date Exported: 4/22/2026
Notes:
1. The small-scale PIT was completed on April 16, 2026.
2. The testing head range was analyzed during the 1-hour testing period.
3. Measured infiltration rates are corrected according to a correction factor of 0.35 outlined in
Appendix B.
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Figure B-2
PIT-2 Infiltration Testing
02868-044-00 Date Exported: 4/22/2026
Notes:
1. The small-scale PIT was completed on April 16, 2026.
2. The testing head range was analyzed during the 1-hour testing period.
3. Measured infiltration rates are corrected according to a correction factor of 0.35 outlined in
Appendix B.
Renton Off Campus Emergency Department
Renton, Washington
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Appendix C
Report Limitations and Guidelines for Use
KPFF Consulting Engineers | May 5, 2026 Page C-1
File No. 2868-044-00
Appendix C
Report Limitations and Guidelines for Use1
This appendix provides information to help you manage your risks with respect to the use of this report.
READ THESE PROVISIONS CLOSELY
It is important to recognize that the geoscience practices (geotechnical engineering, geology and
environmental science) rely on professional judgment and opinion to a greater extent than other
engineering and natural science disciplines, where more precise and/or readily observable data may exist.
To help clients better understand how this difference pertains to our services, GeoEngineers includes the
following explanatory “limitations” provisions in its reports. Please confer with GeoEngineers if you need to
know more how these “Report Limitations and Guidelines for Use” apply to your project or site.
GEOTECHNICAL SERVICES ARE PERFORMED FOR SPECIFIC PURPOSES, PERSONS AND
PROJECTS
This report has been prepared for KPFF Consulting Engineers and for the Project(s) specifically identified
in the report. The information contained herein is not applicable to other sites or projects.
GeoEngineers structures its services to meet the specific needs of its clients. No party other than the party
to whom this report is addressed may rely on the product of our services unless we agree to such reliance
in advance and in writing. Within the limitations of the agreed scope of services for the Project, and its
schedule and budget, our services have been executed in accordance with our signed agreement for this
project executed on March 26, 2026, and generally accepted geotechnical practices in this area at the time
this report was prepared. We do not authorize, and will not be responsible for, the use of this report for any
purposes or projects other than those identified in the report.
A GEOTECHNICAL ENGINEERING OR GEOLOGIC REPORT IS BASED ON A UNIQUE SET OF
PROJECT-SPECIFIC FACTORS
This report has been prepared for the Renton Off Campus Emergency Department project in Renton,
Washington. GeoEngineers considered a number of unique, project-specific factors when establishing the
scope of services for this project and report. Unless GeoEngineers specifically indicates otherwise, it is
important not to rely on this report if it was:
■ Not prepared for you,
■ Not prepared for your project,
■ Not prepared for the specific site explored, or
■ Completed before important project changes were made.
1 Developed based on material provided by GBA, GeoProfessional Business Association; www.geoprofessional.org.
KPFF Consulting Engineers | May 5, 2026 Page C-2
File No. 2868-044-00
For example, changes that can affect the applicability of this report include those that affect:
■ The function of the proposed structure;
■ Elevation, configuration, location, orientation or weight of the proposed structure;
■ Composition of the design team; or
■ Project ownership.
If changes occur after the date of this report, GeoEngineers cannot be responsible for any consequences
of such changes in relation to this report unless we have been given the opportunity to review our
interpretations and recommendations. Based on that review, we can provide written modifications or
confirmation, as appropriate.
ENVIRONMENTAL CONCERNS ARE NOT COVERED
Unless environmental services were specifically included in our scope of services, this report does not
provide any environmental findings, conclusions, or recommendations, including but not limited to, the
likelihood of encountering underground storage tanks or regulated contaminants.
INFORMATION PROVIDED BY OTHERS
GeoEngineers has relied upon certain data or information provided or compiled by others in the
performance of our services. Although we use sources that we reasonably believe to be trustworthy,
GeoEngineers cannot warrant or guarantee the accuracy or completeness of information provided or
compiled by others.
SUBSURFACE CONDITIONS CAN CHANGE
This geotechnical or geologic report is based on conditions that existed at the time the study was performed.
The findings and conclusions of this report may be affected by the passage of time, by man-made events
such as construction on or adjacent to the site, new information or technology that becomes available
subsequent to the report date, or by natural events such as floods, earthquakes, slope instability or
groundwater fluctuations. If more than a few months have passed since issuance of our report or work
product, or if any of the described events may have occurred, please contact GeoEngineers before applying
this report for its intended purpose so that we may evaluate whether changed conditions affect the
continued reliability or applicability of our conclusions and recommendations.
GEOTECHNICAL AND GEOLOGIC FINDINGS ARE PROFESSIONAL OPINIONS
Our interpretations of subsurface conditions are based on field observations from widely spaced sampling
locations at the site. Site exploration identifies the specific subsurface conditions only at those points where
subsurface tests are conducted or samples are taken. GeoEngineers reviewed field and laboratory data
and then applied its professional judgment to render an informed opinion about subsurface conditions at
other locations. Actual subsurface conditions may differ, sometimes significantly, from the opinions
presented in this report. Our report, conclusions and interpretations are not a warranty of the actual
subsurface conditions.
KPFF Consulting Engineers | May 5, 2026 Page C-3
File No. 2868-044-00
GEOTECHNICAL ENGINEERING REPORT RECOMMENDATIONS ARE NOT FINAL
We have developed the following recommendations based on data gathered from subsurface
investigation(s). These investigations sample just a small percentage of a site to create a snapshot of the
subsurface conditions elsewhere on the site. Such sampling on its own cannot provide a complete and
accurate view of subsurface conditions for the entire site. Therefore, the recommendations included in this
report are preliminary and should not be considered final. GeoEngineers’ recommendations can be
finalized only by observing actual subsurface conditions revealed during construction. GeoEngineers
cannot assume responsibility or liability for the recommendations in this report if we do not perform
construction observation.
We recommend that you allow sufficient monitoring, testing and consultation during construction by
GeoEngineers to confirm that the conditions encountered are consistent with those indicated by the
explorations, to provide recommendations for design changes if the conditions revealed during the work
differ from those anticipated, and to evaluate whether earthwork activities are completed in accordance
with our recommendations. Retaining GeoEngineers for construction observation for this project is the most
effective means of managing the risks associated with unanticipated conditions. If another party performs
field observation and confirms our expectations, the other party must take full responsibility for both the
observations and recommendations. Please note, however, that another party would lack our project-
specific knowledge and resources.
A GEOTECHNICAL ENGINEERING OR GEOLOGIC REPORT COULD BE SUBJECT TO
MISINTERPRETATION
Misinterpretation of this report by members of the design team or by contractors can result in costly
problems. GeoEngineers can help reduce the risks of misinterpretation by conferring with appropriate
members of the design team after submitting the report, reviewing pertinent elements of the design team’s
plans and specifications, participating in pre-bid and preconstruction conferences, and providing
construction observation.
DO NOT REDRAW THE EXPLORATION LOGS
Geotechnical engineers and geologists prepare final boring and testing logs based upon their interpretation
of field logs and laboratory data. The logs included in a geotechnical engineering or geologic report should
never be redrawn for inclusion in architectural or other design drawings. Photographic or electronic
reproduction is acceptable but separating logs from the report can create a risk of misinterpretation.
GIVE CONTRACTORS A COMPLETE REPORT AND GUIDANCE
To help reduce the risk of problems associated with unanticipated subsurface conditions, GeoEngineers
recommends giving contractors the complete geotechnical engineering or geologic report, including these
“Report Limitations and Guidelines for Use.” When providing the report, you should preface it with a clearly
written letter of transmittal that:
■ Advises contractors that the report was not prepared for purposes of bid development and that its
accuracy is limited; and
■ Encourages contractors to confer with GeoEngineers and/or to conduct additional study to obtain the
specific types of information they need or prefer.
KPFF Consulting Engineers | May 5, 2026 Page C-4
File No. 2868-044-00
CONTRACTORS ARE RESPONSIBLE FOR SITE SAFETY ON THEIR OWN CONSTRUCTION
PROJECTS
Our geotechnical recommendations are not intended to direct the contractor’s procedures, methods,
schedule or management of the work site. The contractor is solely responsible for job site safety and for
managing construction operations to minimize risks to on-site personnel and adjacent properties.
BIOLOGICAL POLLUTANTS
GeoEngineers’ Scope of Work specifically excludes the investigation, detection, prevention or assessment
of the presence of Biological Pollutants. Accordingly, this report does not include any interpretations,
recommendations, findings or conclusions regarding the detecting, assessing, preventing or abating of
Biological Pollutants, and no conclusions or inferences should be drawn regarding Biological Pollutants as
they may relate to this project. The term “Biological Pollutants” includes, but is not limited to, molds, fungi,
spores, bacteria and viruses, and/or any of their byproducts.
A Client that desires these specialized services is advised to obtain them from a consultant who offers
services in this specialized field.