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Civil Engineers ● Structural Engineers ● Landscape Architects ● Community Planners ● Land Surveyors
Preliminary
Technical Information Report
PREPARED FOR:
Gar Hansen and John Manuel
HHJ Inc.
601 St Helens Avenue
Tacoma, WA 98402
PROJECT:
Walker Subaru Service Center
Renton, WA
2240819.10
PREPARED BY:
Quinten Foster
Project Engineer
REVIEWED BY:
Scott T. Kaul, PE, LEED AP
Associate Principal
DATE:
March 2025
Preliminary
Technical Information Report
PREPARED FOR:
Gar Hansen and John Manuel
HHJ Inc.
601 St Helens Avenue
Tacoma, WA 98402
PROJECT:
Walker Subaru Service Center
Renton, WA
2240819.10
PREPARED BY:
Quinten Foster
Project Engineer
REVIEWED BY:
Scott T. Kaul, PE, LEED AP
Associate Principal
DATE:
March 2025
I hereby state that this Technical
Information Report for Walker Subaru
Service Center has been prepared by me
or under my supervision and meets the
standard of care and expertise that is
usual and customary in this community for
professional engineers. I understand that
City of Renton does not and will not
assume liability for the sufficiency,
suitability, or performance of drainage
facilities prepared by me.
03/06/2025
Preliminary Technical Information Report
Walker Subaru Service Center
2240819.10
Table of Contents
Section Page
1.0 Project Overview ............................................................................................................................ 1
1.1 Purpose and Scope............................................................................................................. 1
1.2 Predeveloped Conditions .................................................................................................... 1
1.3 Development Conditions ..................................................................................................... 1
2.0 Conditions and Requirements Summary .................................................................................... 2
2.1 Core Requirements ............................................................................................................. 2
2.1.1 CR 1 – Discharge at the Natural Location ............................................................. 2
2.1.2 CR 2 – Offsite Analysis .......................................................................................... 2
2.1.3 CR 3 – Flow Control Facilities ................................................................................ 2
2.1.4 CR 4 – Conveyance System .................................................................................. 2
2.1.5 CR 5 – Construction Stormwater Pollution Prevention .......................................... 2
2.1.6 CR 6 – Maintenance and Operations .................................................................... 2
2.1.7 CR 7 – Financial Guarantees and Liability ............................................................ 2
2.1.8 CR 8 – Water Quality Facilities .............................................................................. 2
2.1.9 CR 9 – Onsite Best Management Practices (BMPs) ............................................. 3
2.2 Special Requirements ......................................................................................................... 4
2.2.1 SR 1 – Critical Drainage Areas .............................................................................. 4
2.2.2 SR 2 – Flood Hazard Area Delineation .................................................................. 4
2.2.3 SR 3 – Flood Protection Facilities .......................................................................... 4
2.2.4 SR 4 – Source Controls ......................................................................................... 4
2.2.5 SR 5 – Oil Control .................................................................................................. 4
2.2.6 SR 6 – Aquifer Protection Area .............................................................................. 5
3.0 Offsite Analysis .............................................................................................................................. 5
3.1 Downstream Analysis.......................................................................................................... 5
3.2 Upstream Analysis .............................................................................................................. 5
4.0 Flow Control, Low Impact Development (LID), and Water Quality Facility Analysis and
Design ............................................................................................................................................. 5
4.1 Existing Site Hydrology ....................................................................................................... 5
4.2 Developed Site Hydrology .................................................................................................. 5
4.3 Performance Standards ...................................................................................................... 6
4.4 Flow Control System ........................................................................................................... 6
4.5 Water Quality System ......................................................................................................... 6
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5.0 Conveyance System Analysis and Design .................................................................................. 6
6.0 Special Reports and Studies ........................................................................................................ 6
7.0 Other Permits ................................................................................................................................. 6
8.0 Construction Stormwater Pollution Prevention Analysis and Design ..................................... 7
8.1 ESC Plan Analysis and Design ........................................................................................... 7
8.2 SWPPS Plan Design ........................................................................................................... 7
9.0 Bond Quantities, Facility Summaries, and Declaration of Covenant ....................................... 7
10.0 Operation and Maintenance Manual ............................................................................................ 7
11.0 Conclusion ...................................................................................................................................... 7
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Appendices
Appendix A
Figures
A-1 ............Vicinity Map
A-2 ............Soils Map
A-3 ............Existing Conditions Map
A-4 ............Developed Conditions Map
A-5 ............FEMA Flood Map
A-6 ............Aquifer Protection Map
Appendix B
Not Used
Appendix C
Hydrologic Analysis
C-1 ............Drainage Basin Map
C-2 ............Preliminary Basin Flows
Appendix D
Geotechnical Engineering Report
Appendix E
Non-Structural BMPs
A-1 ............Required Best Management Practices (BMPs) for all Properties with
Commercial Activities
A-8 ............Storage or Solid and Food Wastes (Including Cooking Grease)
A-45 ..........Maintenance of Public and Private Utility Corridors and Facilities
Appendix F
Not Used
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1.0 Project Overview
1.1 Purpose and Scope
This report accompanies the State Environmental Policy Act (SEPA) application for the Walker
Subaru Service Center.
The project site is located in the Southeast Quarter of the Northwest Quarter of Section 19,
Township 23 North, Range 5 East, Willamette Meridian, in the city of Renton, King County,
Washington. This site is located at 519 SW 12th Street (see Appendix A-1 for the Vicinity Map).
The Walker Subaru Service Center project is located on Parcels 3340404865 and 3340404870,
totaling approximately 2.28 acres, with the proposed disturbed area totaling approximately
0.84 acre. The proposed project is for a building addition of approximately 14,450 square feet
onto the existing Subaru Facility. The project also includes relocating stormwater, water, sanitary
sewer, and dry utilities.
The design for this project meets or exceeds the requirements of the 2022 City of Renton Surface
Water Design Manual (Storm Manual), which establishes the methodology and design criteria
used for this project.
1.2 Predeveloped Conditions
The existing condition is a developed site consisting of the Subaru Service Building and parking.
Existing Vegetation/Cover: The existing site is a majority impervious. The existing building and
paved parking make up a majority of the site. The existing stormwater swale and pond, along with
a few landscape islands, are the only vegetation cover. There are four driveways accessing the
site, two from the north end and two from the west end.
An existing sanitary 8-inch sewer main runs along the south side of the existing building with an
existing manhole located near the southeast corner of the building. There is an existing 8-inch
water main running along the south side of the existing building. Power and other utilities are also
running south of the existing building. There are several existing driveways at the north and west
end of the site.
The site is relatively flat and collects all stormwater via catch basins at low points. The site directs
stormwater to the existing bioswale/pond at the south end of the site. Refer to Appendix A-3 for
the Existing Conditions Map.
To our knowledge, no critical areas are located on or near the site.
1.3 Development Conditions
Approximately 0.84 acre of the 2.28-acre plot will be disturbed. Existing landscape trees within
the building addition footprint will be removed.
The proposed improvements are for a building addition and parking. The project also includes the
relocation of multiple utilities, including storm, water, sanitary sewer, and dry utilities.
The existing stormwater pond and bioswale will continue to mitigate the stormwater onsite
because there will not be an increase in impervious surfaces.
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2.0 Conditions and Requirements Summary
2.1 Core Requirements
2.1.1 CR 1 – Discharge at the Natural Location
Currently, runoff from the project site flows to an existing bioswale and stormwater pond. The
proposed addition will keep these facilities, so the discharge point will remain unchanged.
2.1.2 CR 2 – Offsite Analysis
A preliminary downstream analysis is included in Section 3.0 below. A full Level One Downstream
Analysis will be performed for the final Technical Information Report . The analysis will include:
• Defining and mapping the study area.
• Reviewing available information on the study area.
• Field inspecting the study area.
2.1.3 CR 3 – Flow Control Facilities
Per the Storm Manual, the project requires Flow Control Duration Standard – Match Existing
Condition. The existing system is proposed to remain to meet flow control requirements. The
proposed project will direct a portion of stormwater offsite into the City of Renton system. This
portion will produce less than 0.15 cfs in the 100-year peak flow and is an exception. The
remainder of the site will be directed toward the existing stormwater facilities .
2.1.4 CR 4 – Conveyance System
The project includes the construction of a new conveyance system to redirect stormwater around
the building addition and back into the existing system. Roof drains discharge into the
conveyance system. Conveyance calculations will be provided with the final site development
plans.
2.1.5 CR 5 – Construction Stormwater Pollution Prevention
An erosion and sediment control plan will be included with the site development submittal
package. A Construction Stormwater Pollution Prevention Plan will be included with the site
development submittal package.
2.1.6 CR 6 – Maintenance and Operations
A maintenance plan for the stormwater management system will be provided with the site
development permit.
2.1.7 CR 7 – Financial Guarantees and Liability
A bond, assignment of funds, or certified check will be provided, as required, prior to construction.
2.1.8 CR 8 – Water Quality Facilities
An existing Bioswale provides water quality treatment for areas subject to pollution generating
surfaces. A new StormFilter catch basin will also be installed in the northwest corner of the site to
treat stormwater being directed away from the site. A detailed discussion of the water quality
system is provided in Section 4.1.
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2.1.9 CR 9 – Onsite Best Management Practices (BMPs)
The project falls under the Large Lot BMP requirements, based on the size of the property. Core
Requirement 9 BMPs have been evaluated in the order described per the Storm Manual, with
infeasibility justification provided.
1. Full Dispersion
Infeasibility Justification: Full dispersion requires that a 100-foot minimum vegetated flow
path be provided. The small area and site plan do not allow for the required flow path. Full
dispersion also requires a maximum 15 percent of the site be impervious surfaces. The
project will convert approximately 76 percent of the site to impervious surfaces.
2. Full Infiltration of Roof Runoff
Infeasibility Justification: Full infiltration of Roof Runoff has been determined infeasible by
the geotechnical analysis performed by Migizi Group, Inc. The geotechnical analysis
recommends not using infiltration.
3. Option 1 - Full Infiltration
Infeasibility Justification: Full infiltration has been determined infeasible by the geotechnical
analysis performed by Migizi Group, Inc. The groundwater level is shallow and soils are not
suited for infiltration; therefore, infiltration was determined infeasible.
3. Option 2 - Limited Infiltration
Infeasibility Justification: Limited infiltration BMPs, per the Storm Manual, are the same as
full infiltration systems but located in poor infiltrative soils that are likely to clog and work
less effectively over time. Infiltration has been determined infeasible by the geotechnical
analysis performed by Migizi Group, Inc. Limited infiltration facilities would not adequately
provide infiltration.
3. Option 3 - Bioretention
The existing bioswale will continue to be used to meet the Onsite BMP and water quality
requirements. The bioswale facility is proposed to remain. All pollution generating
impervious surfaces will be directed to the bioswale.
3. Option 4 - Permeable Pavement
Permeable paving is considered infeasible. The geotechnical analysis has determined soils
in the area do not meet requirements and that all stormwaters should be managed onsite
through detention or diverted to the existing systems offsite.
4. Soil Amendment
All disturbed areas will be amended per the Soil Amendment BMP. The pollution
generating impervious surfaces will be provided with treatment and flow control.
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2.2 Special Requirements
2.2.1 SR 1 – Critical Drainage Areas
The project does not lie within a critical drainage area.
1. Master Drainage Plans (MDPs)
The project does not lie within an area covered by an approved Master Drainage Plan.
2. Basin Plans (BPs)
The project does not lie within an area with an adopted Basin Plan.
3. Salmon Conservation Plans (SCPs)
The project does not lie within an area with an adopted Salmon Conservation Plan.
4. Lake Management Plans
The project does not lie within an area with an adopted Lake Management Plan.
5. Hazard Mitigation Plan
The project does not lie within a flood hazard area and is not tributary to any identified
flooding per the City of Renton Hazard Mitigation Plan, April 2010.
6. Shared Facility Drainage Plans (SFDPs)
The project does not propose a Shared Facility Drainage Plan.
2.2.2 SR 2 – Flood Hazard Area Delineation
The proposed project is not within or adjacent to a flood hazard area, as identified by City of
Renton in the Hazard Plan per FEMA study.
2.2.3 SR 3 – Flood Protection Facilities
The project does not meet the any of the conditions requiring flood protection facilities.
2.2.4 SR 4 – Source Controls
Source control BMPs, as identified in the King County Stormwater Pollution Prevention Manual
and Renton Municipal Code, Title IV, have been incorporated into the layout and design of the
proposed stormwater management system. The site use will require non-structural BMPs to
maintain source control. BMPs A-01, A-08, and A-45 from the King County Stormwater Pollution
Prevention Manual shall be adhered to.
2.2.5 SR 5 – Oil Control
The proposed site is expected to meet the high-use site criteria. An oil-water separator (OWS) is
proposed to meet the oil control requirement. The existing OWS will be relocated and upsized , as
required for the additional service bays, as part of the project. Full OWS sizing will be provided
with final site development plans.
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2.2.6 SR 6 – Aquifer Protection Area
The project site is not within an aquifer protection zone. An existing bioswale will treat the
pollution generating surfaces onsite.
3.0 Offsite Analysis
3.1 Downstream Analysis
The site currently directs all runoff to the stormwater facilities in the southeast corner of the site.
The project improvements will not affect the discharge point, and the downstream will remain
unchanged.
3.2 Upstream Analysis
The project site does not receive any substantive runoff from offsite properties.
4.0 Flow Control, Low Impact Development (LID), and Water Quality Facility
Analysis and Design
An existing stormwater pond will remain to meet flow control requirements for Basin 1. The
existing bioswale will remain to provide water quality treatment for Basin 1. A small portion of the
existing site (Basin 2) will be redirected into the storm system within Seneca Avenue SW. The
purpose of this redirection is to prevent the stormwater system from running under the building
improvements. Preliminary design is based on the Appendix C-1 Drainage Basin Map and the
basin characteristics below.
Basin 1 is characterized as follows:
Total Area: 1.70 acres
Building Area: 0.80 acre
Asphalt Pavement Area: 0.90 acre
Basin 2 is characterized as follows:
Total Area: 0.20 acre
Landscaping: 0.01 acre
Asphalt Pavement Area: 0.19 acre
4.1 Existing Site Hydrology
The existing site is fully developed. The existing conveyance system directs runoff to a bioswale,
which treats stormwater before flowing into a detention pond. The existing facilities will remain to
mitigate runoff.
4.2 Developed Site Hydrology
All onsite improvements will redirect stormwater into existing facilities to mimic the existing
conditions. All onsite impervious surfaces will be conveyed to the existing systems to effectively
mitigate runoff.
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4.3 Performance Standards
The Area-Specific Flow Control Facility requirement for this project will be the Flow Control
Duration Standard – Match Existing Condition Areas. The City has identified the required flow
control standards per the City of Renton Flow Control Application Map.
This project falls under the Large Lot BMP requirements. The existing bioswale and detention
pond will remain to meet onsite BMP requirements.
Because of site constraints and the elevation of the existing stormwater facilities. The new pipe
systems will match minimum slopes of the existing system to mimic existing conditions .
Basic Water Quality Treatment is required for pollution generating target surfaces . The pollution
generating surfaces from Basin 1 will be conveyed to the existing bioswale treatment before
entering the existing detention system. Basin 2 will treat runoff with a StormFilter before entering
the City’s conveyance system.
A commercial site development permit is required; therefore, source control BMPs are required.
Structural source controls will be provided based on the use of the site as commercial retail and
housing. Nonstructural source control measures will be provided per SR 4. Refer to Appendix E
for Non-Structural BMPs. The site will need an oil control facility due to vehicle maintenance
bays.
4.4 Flow Control System
The flow control system schematic layout can be found on the civil plan sheets . Refer to
Appendix C-2 for supporting documentation on the preliminary flows for each basin. Final
calculations to be provided with the site development plans.
4.5 Water Quality System
The existing bioswale will remain to treat runoff from Basin 1. The project proposes to direct less
runoff to the bioswale than it handles in the existing conditions. Therefore, the existing bioswale is
adequately sized. Basin 2 will direct runoff into a StormFilter catch basin , where runoff will be
treated before entering the City’s system.
5.0 Conveyance System Analysis and Design
Closed-pipe conveyance is provided to redirect runoff around the building improvements. Roof
drains are directed to the conveyance system.
A conveyance analysis will be provided with final site development plans .
6.0 Special Reports and Studies
A geotechnical engineering report has been prepared by Migizi Group, Inc. (see Appendix D).
7.0 Other Permits
This project will require a Building Permit and a Civil Construction Permit.
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8.0 Construction Stormwater Pollution Prevention Analysis and Design
8.1 ESC Plan Analysis and Design
A Construction Stormwater Pollution Prevention Plan will be provided for final site development
plans.
8.2 SWPPS Plan Design
A Temporary Erosion and Sediment Control Plan (TESC Plan) will be provided for the final site
development plans. A Construction Stormwater Pollution Prevention (CSWPP) supervisor will be
appointed by the Contractor at the time of construction to implement and update TESC plans , as
required. The CSWPP supervisor shall be a Certified Professional in Erosion and Sediment
Control or a Certified Erosion and Sediment Control Lead. The CSWPP supervisor will be
responsible for compliance with all City of Renton construction stormwater requirements .
9.0 Bond Quantities, Facility Summaries, and Declaration of Covenant
A bond quantities worksheet will be provided for the final site development permit.
All easement requests will be submitted to the City of Renton Community and Economic
Development (CED) Department.
10.0 Operation and Maintenance Manual
An Operation and Maintenance Manual will be provided for final site development.
11.0 Conclusion
This project is designed to meet the 2022 City of Renton Surface Water Design Manual
guidelines for stormwater management.
This analysis is based on data and records either supplied to or obtained by AHBL, Inc . These documents
are referenced within the text of the analysis. The analysis has been prepared using procedures and
practices within the standard accepted practices of the industry. We conclude that this project, as
proposed, will not create any new problems within the existing downstream drainage system.
AHBL, Inc.
Quinten Foster
Project Engineer
QF/lsk
March 2025
Q:\2024\2240819\WORDPROC\Reports\20250306 Rpt (Prelim TIR) 2240819.10.docx
Preliminary Technical Information Report
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Appendix A
Figures
A-1 .................... Vicinity Map
A-2 .................... Soils Map
A-3 .................... Existing Conditions Map
A-4 .................... Developed Conditions Map
A-5 .................... FEMA Flood Map
A-6 .................... Aquifer Protection Map
2215 North 30th Street
Suite 300
Tacoma, WA 98403
253.383.2422 TEL
253.383.2572 FAX
SUNSET HIGHLANDS MIXED USE 2190210.10
VICINITY MAP
A-1
NOT TO SCALE
VICINITY MAP
SUNSET HIGHLANDS - 2230621.10WALKER SUBARU SERVICE CENTER - 2240819.10
United States
Department of
Agriculture
A product of the National
Cooperative Soil Survey,
a joint effort of the United
States Department of
Agriculture and other
Federal agencies, State
agencies including the
Agricultural Experiment
Stations, and local
participants
Custom Soil Resource
Report for
King County
Area,
Washington
Natural
Resources
Conservation
Service
February 5, 2025
Preface
Soil surveys contain information that affects land use planning in survey areas.
They highlight soil limitations that affect various land uses and provide information
about the properties of the soils in the survey areas. Soil surveys are designed for
many different users, including farmers, ranchers, foresters, agronomists, urban
planners, community officials, engineers, developers, builders, and home buyers.
Also, conservationists, teachers, students, and specialists in recreation, waste
disposal, and pollution control can use the surveys to help them understand,
protect, or enhance the environment.
Various land use regulations of Federal, State, and local governments may impose
special restrictions on land use or land treatment. Soil surveys identify soil
properties that are used in making various land use or land treatment decisions.
The information is intended to help the land users identify and reduce the effects of
soil limitations on various land uses. The landowner or user is responsible for
identifying and complying with existing laws and regulations.
Although soil survey information can be used for general farm, local, and wider area
planning, onsite investigation is needed to supplement this information in some
cases. Examples include soil quality assessments (http://www.nrcs.usda.gov/wps/
portal/nrcs/main/soils/health/) and certain conservation and engineering
applications. For more detailed information, contact your local USDA Service Center
(https://offices.sc.egov.usda.gov/locator/app?agency=nrcs) or your NRCS State Soil
Scientist (http://www.nrcs.usda.gov/wps/portal/nrcs/detail/soils/contactus/?
cid=nrcs142p2_053951).
Great differences in soil properties can occur within short distances. Some soils are
seasonally wet or subject to flooding. Some are too unstable to be used as a
foundation for buildings or roads. Clayey or wet soils are poorly suited to use as
septic tank absorption fields. A high water table makes a soil poorly suited to
basements or underground installations.
The National Cooperative Soil Survey is a joint effort of the United States
Department of Agriculture and other Federal agencies, State agencies including the
Agricultural Experiment Stations, and local agencies. The Natural Resources
Conservation Service (NRCS) has leadership for the Federal part of the National
Cooperative Soil Survey.
Information about soils is updated periodically. Updated information is available
through the NRCS Web Soil Survey, the site for official soil survey information.
The U.S. Department of Agriculture (USDA) prohibits discrimination in all its
programs and activities on the basis of race, color, national origin, age, disability,
and where applicable, sex, marital status, familial status, parental status, religion,
sexual orientation, genetic information, political beliefs, reprisal, or because all or a
part of an individual's income is derived from any public assistance program. (Not
all prohibited bases apply to all programs.) Persons with disabilities who require
2
alternative means for communication of program information (Braille, large print,
audiotape, etc.) should contact USDA's TARGET Center at (202) 720-2600 (voice
and TDD). To file a complaint of discrimination, write to USDA, Director, Office of
Civil Rights, 1400 Independence Avenue, S.W., Washington, D.C. 20250-9410 or
call (800) 795-3272 (voice) or (202) 720-6382 (TDD). USDA is an equal opportunity
provider and employer.
3
Contents
Preface....................................................................................................................2
Soil Map..................................................................................................................5
Soil Map................................................................................................................6
Legend..................................................................................................................7
Map Unit Legend..................................................................................................8
Map Unit Descriptions..........................................................................................8
King County Area, Washington.......................................................................10
Ur—Urban land...........................................................................................10
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Soil Map
The soil map section includes the soil map for the defined area of interest, a list of
soil map units on the map and extent of each map unit, and cartographic symbols
displayed on the map. Also presented are various metadata about data used to
produce the map, and a description of each soil map unit.
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Custom Soil Resource Report
Soil Map
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558370 558390 558410 558430 558450 558470 558490 558510
558370 558390 558410 558430 558450 558470 558490 558510
47° 28' 8'' N
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N
Map projection: Web Mercator Corner coordinates: WGS84 Edge tics: UTM Zone 10N WGS84
0 45 90 180 270
Feet
0 10 20 40 60
Meters
Map Scale: 1:937 if printed on A portrait (8.5" x 11") sheet.
Soil Map may not be valid at this scale.
MAP LEGEND MAP INFORMATION
Area of Interest (AOI)
Area of Interest (AOI)
Soils
Soil Map Unit Polygons
Soil Map Unit Lines
Soil Map Unit Points
Special Point Features
Blowout
Borrow Pit
Clay Spot
Closed Depression
Gravel Pit
Gravelly Spot
Landfill
Lava Flow
Marsh or swamp
Mine or Quarry
Miscellaneous Water
Perennial Water
Rock Outcrop
Saline Spot
Sandy Spot
Severely Eroded Spot
Sinkhole
Slide or Slip
Sodic Spot
Spoil Area
Stony Spot
Very Stony Spot
Wet Spot
Other
Special Line Features
Water Features
Streams and Canals
Transportation
Rails
Interstate Highways
US Routes
Major Roads
Local Roads
Background
Aerial Photography
The soil surveys that comprise your AOI were mapped at
1:24,000.
Warning: Soil Map may not be valid at this scale.
Enlargement of maps beyond the scale of mapping can cause
misunderstanding of the detail of mapping and accuracy of soil
line placement. The maps do not show the small areas of
contrasting soils that could have been shown at a more detailed
scale.
Please rely on the bar scale on each map sheet for map
measurements.
Source of Map: Natural Resources Conservation Service
Web Soil Survey URL:
Coordinate System: Web Mercator (EPSG:3857)
Maps from the Web Soil Survey are based on the Web Mercator
projection, which preserves direction and shape but distorts
distance and area. A projection that preserves area, such as the
Albers equal-area conic projection, should be used if more
accurate calculations of distance or area are required.
This product is generated from the USDA-NRCS certified data as
of the version date(s) listed below.
Soil Survey Area: King County Area, Washington
Survey Area Data: Version 20, Aug 27, 2024
Soil map units are labeled (as space allows) for map scales
1:50,000 or larger.
Date(s) aerial images were photographed: Jul 31, 2022—Aug 8,
2022
The orthophoto or other base map on which the soil lines were
compiled and digitized probably differs from the background
imagery displayed on these maps. As a result, some minor
shifting of map unit boundaries may be evident.
Custom Soil Resource Report
7
Map Unit Legend
Map Unit Symbol Map Unit Name Acres in AOI Percent of AOI
Ur Urban land 2.6 100.0%
Totals for Area of Interest 2.6 100.0%
Map Unit Descriptions
The map units delineated on the detailed soil maps in a soil survey represent the
soils or miscellaneous areas in the survey area. The map unit descriptions, along
with the maps, can be used to determine the composition and properties of a unit.
A map unit delineation on a soil map represents an area dominated by one or more
major kinds of soil or miscellaneous areas. A map unit is identified and named
according to the taxonomic classification of the dominant soils. Within a taxonomic
class there are precisely defined limits for the properties of the soils. On the
landscape, however, the soils are natural phenomena, and they have the
characteristic variability of all natural phenomena. Thus, the range of some
observed properties may extend beyond the limits defined for a taxonomic class.
Areas of soils of a single taxonomic class rarely, if ever, can be mapped without
including areas of other taxonomic classes. Consequently, every map unit is made
up of the soils or miscellaneous areas for which it is named and some minor
components that belong to taxonomic classes other than those of the major soils.
Most minor soils have properties similar to those of the dominant soil or soils in the
map unit, and thus they do not affect use and management. These are called
noncontrasting, or similar, components. They may or may not be mentioned in a
particular map unit description. Other minor components, however, have properties
and behavioral characteristics divergent enough to affect use or to require different
management. These are called contrasting, or dissimilar, components. They
generally are in small areas and could not be mapped separately because of the
scale used. Some small areas of strongly contrasting soils or miscellaneous areas
are identified by a special symbol on the maps. If included in the database for a
given area, the contrasting minor components are identified in the map unit
descriptions along with some characteristics of each. A few areas of minor
components may not have been observed, and consequently they are not
mentioned in the descriptions, especially where the pattern was so complex that it
was impractical to make enough observations to identify all the soils and
miscellaneous areas on the landscape.
The presence of minor components in a map unit in no way diminishes the
usefulness or accuracy of the data. The objective of mapping is not to delineate
pure taxonomic classes but rather to separate the landscape into landforms or
landform segments that have similar use and management requirements. The
delineation of such segments on the map provides sufficient information for the
development of resource plans. If intensive use of small areas is planned, however,
onsite investigation is needed to define and locate the soils and miscellaneous
areas.
Custom Soil Resource Report
8
An identifying symbol precedes the map unit name in the map unit descriptions.
Each description includes general facts about the unit and gives important soil
properties and qualities.
Soils that have profiles that are almost alike make up a soil series. Except for
differences in texture of the surface layer, all the soils of a series have major
horizons that are similar in composition, thickness, and arrangement.
Soils of one series can differ in texture of the surface layer, slope, stoniness,
salinity, degree of erosion, and other characteristics that affect their use. On the
basis of such differences, a soil series is divided into soil phases. Most of the areas
shown on the detailed soil maps are phases of soil series. The name of a soil phase
commonly indicates a feature that affects use or management. For example, Alpha
silt loam, 0 to 2 percent slopes, is a phase of the Alpha series.
Some map units are made up of two or more major soils or miscellaneous areas.
These map units are complexes, associations, or undifferentiated groups.
A complex consists of two or more soils or miscellaneous areas in such an intricate
pattern or in such small areas that they cannot be shown separately on the maps.
The pattern and proportion of the soils or miscellaneous areas are somewhat similar
in all areas. Alpha-Beta complex, 0 to 6 percent slopes, is an example.
An association is made up of two or more geographically associated soils or
miscellaneous areas that are shown as one unit on the maps. Because of present
or anticipated uses of the map units in the survey area, it was not considered
practical or necessary to map the soils or miscellaneous areas separately. The
pattern and relative proportion of the soils or miscellaneous areas are somewhat
similar. Alpha-Beta association, 0 to 2 percent slopes, is an example.
An undifferentiated group is made up of two or more soils or miscellaneous areas
that could be mapped individually but are mapped as one unit because similar
interpretations can be made for use and management. The pattern and proportion
of the soils or miscellaneous areas in a mapped area are not uniform. An area can
be made up of only one of the major soils or miscellaneous areas, or it can be made
up of all of them. Alpha and Beta soils, 0 to 2 percent slopes, is an example.
Some surveys include miscellaneous areas. Such areas have little or no soil
material and support little or no vegetation. Rock outcrop is an example.
Custom Soil Resource Report
9
King County Area, Washington
Ur—Urban land
Map Unit Composition
Urban land:100 percent
Estimates are based on observations, descriptions, and transects of the mapunit.
Description of Urban Land
Interpretive groups
Land capability classification (irrigated): None specified
Land capability classification (nonirrigated): 8
Hydric soil rating: No
Custom Soil Resource Report
10
2215 North 30th Street,
Suite 300,
Tacoma, WA 98403
253.383.2422 TEL
253.383.2572 FAX
JOB NO.
DATE:
WALKER SUBARU SERVICE CENTER
EXISTING CONDITIONS
A-3
2240819.10
2/5/2025
N
GRAPHIC SCALE
0 30 60
1" = 30 FEET
15
6
1
L
F
8
"
C
P
E
P
@
0
.
2
5
%
89 LF 8"
C
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P
@
0
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2
5
%
57 LF 8"
C
P
E
P
@
0
.
2
5
%
86 LF 8" CPEP @ 0.25%
34 LF 12" CPEP @ 2.14%
5 LF 12" CPEP @ 2.00%
29 LF 6" PVC @ 0.25%
SE
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A
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SW 12TH
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INTERSTATE 405
24 LF 8" CPEP @ 0.25%
5
7
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8
"
C
P
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@
0
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2
5
%
STORM PIPE
TO REMAIN
CAP AND
ABANDON
STORM PIPE
REDIRECT ROOF
DRAINS INTO CB #10
REDIRECT ROOF
DRAINS INTO CB #1
CAP AND
ABANDON
STORM PIPE
CAP AND
ABANDON
STORM PIPE
STORM PIPE
TO REMAIN
ROUTE NEW ROOF
DRAINS INTO CB #3
ROUTE NEW ROOF
DRAINS INTO CB #3
RECONNECT ROOF
DRAIN WITH NEW INVERT
BLDG ADDITION
FF: 21.95
EXISTING
BUILDING
29 LF 8" CPEP @ 0.49%
130 LF 6" PVC @ 0.27%
16 LF 6" PVC @ 0.25%
CB #4
N 173758.79
E 1296263.78
RIM: 21.60
IE: 18.72 8" (NW)
IE: 18.72 8" (E)
CB #2
N 173790.74
E 1296405.48
RIM: 21.60
IE: 18.64 8" (W)
IE: 18.64 8" (N)
CB #1
N 173874.77
E 1296386.65
RIM: 21.60
IE: 18.86 8" (S)
IE: 18.86 8" (NE)
CO #1
N 173976.34
E 1296194.85
RIM: 21.97
IE: 19.64 6" (W)
CB #8
N 173980.40
E 1296176.82
RIM: 21.26
IE: 18.80 12" (W)
IE: 18.80 12" (N)
CB #7
STORMFILTER CATCHBASIN
N 173985.44
E 1296176.98
RIM: 21.20
IE: 18.90 12" (S)
IE: 18.90 12" (NE)
CB #10
N 173835.29
E 1296174.69
RIM: 21.17
IE: 19.01 8" (SE)
IE: 19.18 6" (NE)
IE: 19.18 6" (NW)
CB #9
N 173981.17
E 1296143.14
RIM: 20.16
IE: 18.08 12" (E)
IE: 18.08 12" (N)
IE: 18.08 12" (S)
CB #6
N 173814.05
E 1296236.22
RIM: 21.41
IE: 18.92 8" (SW)
CB #5
N 173795.86
E 1296220.61
RIM: 21.56
IE: 18.86 8" (NW)
IE: 18.86 8" (SE)
IE: 18.86 8" (NE)CB #3
N 173778.29
E 1296350.24
RIM: 21.60
IE: 18.50 8" (W)
IE: 18.50 8" (E)
IE: 18.17 12" (SE)
EXIST. CB1
N 173898.95
E 1296401.89
RIM: 21.31
IE: 19.00 8" (SW)
IE: 19.00 8" (N)
CO #3
N 173847.01
E 1296163.19
RIM: 21.38
IE: 19.22 6" (N)
IE: 19.22 6" (SE)
CO #2
N 173976.94
E 1296166.26
RIM: 21.37
IE: 19.57 6" (E)
IE: 19.57 6" (S)
CITY OF
RENTON
IN COMPLIANCE WITH CITY OF RENTON STANDARDS
T A C O M A
2215 North 30th Street, Suite 300 Tacoma, WA 98403
253.383.2422TEL 253.383.2572FAX www.ahbl.comWEB
S E A T T L E
S P O K A N E T R I - C I T I E S
WALKER SUBARU SERVICE CENTER
SITE PLAN REVIEW
AHBL JOB #2240819.10
9
Know what's below.
before you dig.Call
R
R-____
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1" = 20 FEET
10
DRAINAGE PLAN
C4.1Q:
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HELD COMPUTED NAD 83/91, WASHINGTON STATE PLANE, NORTH ZONE,
GRID BEARING OF
NORTH 89°43'16" WEST BETWEEN A MONUMENT FOUND AT THE
INTERSECTION OF LIND AVE. SW AND SW 16TH ST., BEING CITY OF
RENTON CONTROL ID. 1895, TO A MONUMENT FOUND ON ALONG THE
NORTHERLY MARGIN OF SW 16TH ST. AT A BRIDGE CROSSING OF
SPRINGBROOK CREEK, BEING CITY OF RENTON CONTROL ID. 1891,
RESPECTIVELY.
NAD 83/91, WASHINGTON STATE PLANE, NORTH ZONE, AS DEFINED BY
THE CITY OF RENTON PUBLISHED HORIZONTAL CONTROL NETWORK
UNIT OF MEASUREMENT IS U.S. SURVEY FEET
ALL DISTANCES SHOWN ARE GROUND
A COMBINED GRID SCALE FACTOR OF 0.999987504615 (GRID TO GROUND)
WAS HELD AT CITY OF RENTON CONTROL ID. 1895
NAVD 88 (AS DEFINED BY THE PUBLISHED CITY OF RENTON VERTICAL
BENCHMARK NETWORK) (NGS2018 GEOID - USED)
PROJECT PRIMARY BENCHMARK:
CITY OF RENTON CONTROL ID. 1895
PUBLISHED ELEVATION: 25.702' NAVD 88
DESCRIPTION:
ENCASED 3" BRASS DISK W/PUNCH LOCATED AT THE INTERSECTION OF
LIND AVE. SW AND SW 16TH ST.
PROJECT SECONDARY BENCHMARK:
CITY OF RENTON CONTROL ID. 1891
PUBLISHED ELEVATION: 24.1568' NAVD 88
OBSERVED ELEVATION: 24.06' NAVD 88
DESCRIPTION:
MONUMENT FOUND ALONG THE NORTHERLY MARGIN OF SW 16TH ST. AT
A BRIDGE CROSSING OF SPRINGBROOK CREEK.
SITE BENCHMARK
OBSERVED ELEVATION: 27.41' NAVD 88
DESCRIPTION:
ENCASED 1 7/8" BRASS DISK W/PUNCH AT THE INTERSECTION OF SW
GRADY WAY AND SENECA AVE. SW
BASIS OF BEARING
HORIZONTAL DATUM
VERTICAL DATUM
STORM LINE TO
BE ABANDONED
STORM PIPE
TO REMAIN
DEVELOPED CONDITIONS A4
National Flood Hazard Layer FIRMette
0 500 1,000 1,500 2,000250
Feet
Ü
SEE FIS REPORT FOR DETAILED LEGEND AND INDEX MAP FOR FIRM PANEL LAYOUT
SPECIAL FLOOD
HAZARD AREAS
Without Base Flood Elevation (BFE)
Zone A, V, A99
With BFE or Depth Zone AE, AO, AH, VE, AR
Regulatory Floodway
0.2% Annual Chance Flood Hazard, Areas
of 1% annual chance flood with average
depth less than one foot or with drainage
areas of less than one square mile Zone X
Future Conditions 1% Annual
Chance Flood Hazard Zone X
Area with Reduced Flood Risk due to
Levee. See Notes.Zone X
Area with Flood Risk due to Levee Zone D
NO SCREEN Area of Minimal Flood Hazard Zone X
Area of Undetermined Flood Hazard Zone D
Channel, Culvert, or Storm Sewer
Levee, Dike, or Floodwall
Cross Sections with 1% Annual Chance
17.5 Water Surface Elevation
Coastal Transect
Coastal Transect Baseline
Profile Baseline
Hydrographic Feature
Base Flood Elevation Line (BFE)
Effective LOMRs
Limit of Study
Jurisdiction Boundary
Digital Data Available
No Digital Data Available
Unmapped
This map complies with FEMA's standards for the use of
digital flood maps if it is not void as described below.
The basemap shown complies with FEMA's basemap
accuracy standards
The flood hazard information is derived directly from the
authoritative NFHL web services provided by FEMA. This map
was exported on 2/5/2025 at 5:44 PM and does not
reflect changes or amendments subsequent to this date and
time. The NFHL and effective information may change or
become superseded by new data over time.
This map image is void if the one or more of the following map
elements do not appear: basemap imagery, flood zone labels,
legend, scale bar, map creation date, community identifiers,
FIRM panel number, and FIRM effective date. Map images for
unmapped and unmodernized areas cannot be used for
regulatory purposes.
Legend
OTHER AREAS OF
FLOOD HAZARD
OTHER AREAS
GENERAL
STRUCTURES
OTHER
FEATURES
MAP PANELS
8
B 20.2
The pin displayed on the map is an approximate
point selected by the user and does not represent
an authoritative property location.
1:6,000
122°13'49"W 47°28'18"N
122°13'11"W 47°27'54"N
Basemap Imagery Source: USGS National Map 2023
PROJECT SITE
Preliminary Technical Information Report
Walker Subaru Service Center
2240819.10
Appendix B
Not Used
Preliminary Technical Information Report
Walker Subaru Service Center
2240819.10
Appendix C
Hydrologic Analysis
C-1.................... Drainage Basin Map
C-2.................... Preliminary Basin Flows
SE
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SW 12TH
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1" = 30 FEET
15
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2215 North 30th Street,
Suite 300,
Tacoma, WA 98403
253.383.2422 TEL
253.383.2572 FAX
JOB NO.
DATE:
WALKER SUBARU SERVICE CENTER
DEVELOPED BASIN MAP
C-1
2240819.10
2/5/2025
BASIN 2
BASIN 1
BIOSWALE
STORMWATER POND
BASIN 1
AREA (ACRES)
ROOF 0.80
ROAD / PARKING 0.90
BASIN 2
AREA (ACRES)
ROAD / PARKING 0.19
LANDSCAPING 0.01
2215 North 30th Street
Suite 300
Tacoma, WA 98403
253.383.2422 TEL
253.383.2572 FAX
Walker Subaru Service Center
Basin Flows
EXHIBIT
C-2
Basin 1
Existing condition flows entering the bioswale
Devloped condition flows entering the bioswale
Basin 2
Developed condition flows directed offsite
Preliminary Technical Information Report
Walker Subaru Service Center
2240819.10
Appendix D
Geotechnical Engineering Report
Geotechnical Engineering Report
Walker’s Renton Subaru
519 SW 12th Street
Renton, WA 980057
P/N. 3340404265, 3340404148
December 11, 2024
prepared for:
HHJ Construction
Attention: John Manuel
601 St Helens Avenue
Tacoma, WA 98402
prepared by:
Migizi Group, Inc.
PO Box 44840
Tacoma, WA 98448
(253) 537-9400
MGI Project Z0816
i
TABLE OF CONTENTS
Page No.
1.0 SITE AND PROJECT DESCRIPTION .............................................................................................. 1
2.0 EXPLORATORY METHODS ............................................................................................................ 2
2.1 Auger Boring Procedures...................................................................................................... 3
3.0 SITE CONDITIONS ............................................................................................................................ 3
3.1 Surface Conditions ................................................................................................................. 3
3.2 Soil Conditions ....................................................................................................................... 4
3.3 Groundwater Conditions ...................................................................................................... 6
3.4 Infiltration Conditions ........................................................................................................... 6
3.5 Seismic Conditions ................................................................................................................. 6
3.6 Liquefaction Potential ........................................................................................................... 7
4.0 CONCLUSIONS AND RECOMMENDATIONS............................................................................ 8
4.1 Site Preparation ...................................................................................................................... 9
4.2 Spread Footings and Bearing Pads .................................................................................... 12
4.3 Slab-On-Grade-Floors .......................................................................................................... 13
4.4 Drainage Systems ................................................................................................................. 14
4.5 Asphalt Pavement ................................................................................................................. 14
4.6 Structural Fill ........................................................................................................................ 16
5.0 RECOMMENDED ADDITIONAL SERVICES ............................................................................. 17
6.0 CLOSURE ........................................................................................................................................... 18
List of Tables
Table 1. Approximate Locations and Depths of Explorations ............................................................................. 2
Table 2. Seismic Design Parameters ........................................................................................................................ 7
List of Figures
Figure 1. Topographic and Location Map
Figure 2. Site and Exploration Plan
Figure 3. Geologic Map of Immediate Project Area
Figure 2. Regional Liquefaction Susceptibility Map
APPENDIX A
Soil Classification Chart and Key to Test Data .................................................................................................. A-1
Logs of Auger Borings B-1 through B-5 .................................................................................................... A-2…A-6
Page 1 of 16
MIGIZI GROUP, INC.
PO Box 44840 PHONE (253) 537-9400
Tacoma, Washington 98448 FAX (253) 537-9401
December 11, 2024
HHJ Construction
601 St Helens Ave
Tacoma, WA 98402
Attention: John Manuel
Subject: Geotechnical Engineering Report
Walker’s Renton Subaru
519 SW 12th Street
Renton, WA 98057
Parcel Nos. 3340404265, -4148
MGI Project Z0816
Dear Mr. Manuel:
Migizi Group, Inc. (MGI) is pleased to submit this report describing the results of our geotechnical
engineering evaluation of the improvements proposed for the existing Walker’s Renton Subaru
facility located in Renton, Washington.
This report has been prepared for the exclusive use of HHJ Construction and their consultants for
specific application to this project, in accordance with generally accepted geotechnical engineering
practices.
1.0 SITE AND PROJECT DESCRIPTION
The project site consists of two contiguous tax parcels along the south side of SW 12th Street,
between Seneca Ave SW and Lind Ave SW, towards the western city limits of Renton,
Washington, as shown on the enclosed Topographic and Location Map (Figure 1). The larger
parcel incorporate the existing Subaru parts, service, and repair facility, while the smaller parcel
contains an outbuilding for additional parts and vehicle storage.
The existing Subaru facility consists of a 19,292-sf building, with a customer waiting area, parts
and services department and offices, and a large repair facility with multiple vehicle lifts for
servicing. The work area is irregularly shaped, encompassing a total area of approximately 2.30
acres. Asphalt pavement surrounds the primary building for vehicle storage and drive lanes, with
only asphalt parking in front of the ancillary parts building.
HHJ Const. – Walker’s Renton Subaru, 519 SW 12th Street, Renton, WA December 11, 2024
Geotechnical Engineering Report Z0816
Migizi Group, Inc. Page 2 of 18
Improvement plans involve the partial demolition of the existing Subaru facility, and expansion of
the existing service shop to provide additional vehicle bays. The western end of the building
addition will be a 2,380-sf, two story facility, constructed to expand the parts department. The
building will be a pre-engineering, metal-frame structure, with slab-on-grade at the existing
elevation of the current facility.
Plans also call for onsite stormwater to be retained and treated onsite in a new precast concrete
vault at the southeast corner of the parcel. This stormwater facility will be buried, with asphalt
pavement over top for additional vehicle parking.
2.0 EXPLORATORY METHODS
We explored surface and subsurface conditions at the project site on November 4-5, 2024. Our
exploration and evaluation program comprised the following elements:
• Surface reconnaissance of the site,
• Five auger boring explorations (designated B-1 through B-5), advanced on November 4-5,
2024, and
• A review of published geologic and seismologic maps and literature.
Table 1 summarizes the approximate functional locations and termination depths of our
subsurface explorations, and Figure 2 depicts their approximate relative locations. The following
sections describe the procedures used for excavation of borings.
TABLE 1
APPROXIMATE LOCATIONS AND DEPTHS OF EXPLORATIONS
Exploration Functional Location
Termination
Depth
(feet)
B-1
B-2
B-3
B-4
B-5
Parking Lot, Outbuilding; 47.468761, -122.224168
SE Property corner; 47.467968, -122.223976
SW Building corner; 47.468043, -122.225023
Southern parking lot; 47.468083, -122.224413
NW customer parking; 47.468596, -122.225141
21.5
31.5
31.5
31.5
31.5
The specific number and locations of our explorations were selected by your office, in relation to
the existing site features and underground utility conflicts.
It should be realized that the explorations performed and utilized for this evaluation reveal
subsurface conditions only at discrete locations across the project site and that actual conditions in
other areas could vary. Furthermore, the nature and extent of any such variations would not
become evident until additional explorations are performed or until construction activities have
begun. If significant variations are observed at that time, we may need to modify our conclusions
and recommendations contained in this report to reflect the actual site conditions.
HHJ Const. – Walker’s Renton Subaru, 519 SW 12th Street, Renton, WA December 11, 2024
Geotechnical Engineering Report Z0816
Migizi Group, Inc. Page 3 of 18
2.1 Auger Boring Procedures
Our exploratory borings were advanced through the soil with a hollow stem auger, using a track-
mounted drill rig operated by an independent drilling firm working under subcontract to MGI.
An engineering geologist from our firm continuously observed the borings, logged the subsurface
conditions, and collected representative soil samples. All samples were stored in watertight
containers and later transported to a laboratory for further visual examination. After the borings
were completed, they were backfilled with bentonite chips and topped with mixed concrete and
black dye to better match existing asphalt.
Throughout the drilling operation, soil samples were obtained at 2½ or 5-foot depth intervals by
means of the Standard Penetration Test (SPT) per ASTM:D-1586. This testing and sampling
procedure consists of driving a standard 2-inch-diameter steel split-spoon sampler 18 inches into
the soil with a 140-pound hammer free-falling 30 inches. The number of blows required to drive
the sampler through each 6-inch interval is counted, and the total number of blows struck during
the final 12 inches is recorded as the Standard Penetration Resistance, or "SPT blow count." If a
total of 50 blows are struck within any 6-inch interval, the driving is stopped, and the blow count
is recorded as 50 blows for the actual penetration distance. The resulting Standard Penetration
Resistance values indicate the relative density of granular soils and the relative consistency of
cohesive soils.
The enclosed boring logs (Appendix A) describe the vertical sequence of soils and materials
encountered in the borings, based primarily on our field classifications and supported by our
subsequent laboratory examination and testing. Where soil contact was observed to be
gradational, our logs indicate the average contact depth. Where a soil type changed between
sample intervals, we inferred the contact depth. Our logs also graphically indicate the blow
count, sample type, sample number, and approximate depth of each soil sample obtained from
the boring, as well as any laboratory tests performed on these soil samples. If any groundwater
was encountered in the borehole, the approximate groundwater depth is depicted on the boring
log. Groundwater depth estimates are typically based on the moisture content of soil samples, the
wet height on the drilling rods, and the water level measured in the borehole after the auger has
been extracted. The soils were classified visually in general accordance with the system described
in Figure A-1, which includes a key to the exploration logs. Summary logs of our explorations are
included as Figures A-2 through A-6.
3.0 SITE CONDITIONS
The following sections present our observations, measurements, findings, and interpretations
regarding surface, soil, groundwater, infiltration and seismic conditions, and liquefaction
potential.
3.1 Surface Conditions
As noted above, the project site consists of two contiguous tax parcels along the south side of SW
12th Street, between Seneca Ave SW and Lind Ave SW, towards the western city limits of Renton,
Washington. The larger parcel incorporates the existing Walker’s Renton Subaru facility, a 19,292-
sf building used for vehicle servicing, office space, and a customer waiting area. The smaller
HHJ Const. – Walker’s Renton Subaru, 519 SW 12th Street, Renton, WA December 11, 2024
Geotechnical Engineering Report Z0816
Migizi Group, Inc. Page 4 of 18
outbuilding is used for additional parts storage. The two parcels total 2.30 acres in size and create
an irregular-shaped project area. The service building is surrounded by asphalt pavement used
for customer parking, vehicle storage, and drive lanes, while the outbuilding has asphalt
pavement along the north side of the structure.
The site is situated south of the Bryn Mawr - Skyway highlands, in the valley between the Black
River 2,000 feet to the west and the Cedar River 1.4 miles to the east. Topographically, the project
area is flat, with minimal grade changes being observed across the paved areas. The topographic
low point of the site, sitting roughly 5 to 8 feet below adjacent asphalt, occurs at the southeast
corner of the property.
Site vegetation is limited to immature deciduous trees and some small flower planting areas
around the existing building and in small landscaping planters across the parking areas. In
addition, the open stormwater facility is moderately overgrown with thick grass, blackberries, and
small deciduous trees.
No natural hydrologic features were observed on site, such as seeps, springs, ponds, and streams,
nor were there indications of surface hydrology, such ripple marks or scouring present. The
property’s existing open stormwater retention facility is located at the southeast corner.
3.2 Soil Conditions
Subsurface conditions were observed through the advancement of five auger boring explorations,
with three located adjacent to the existing facility, and two located towards the perimeter of the
property. All five explorations revealed relatively consistent subgrade conditions, consisting of a
typical asphalt section, with loose to medium dense non-native asphalt subbase. The underlying
native soil consists of very soft silts and sands, grading to coarser, medium dense sands and
gravels at approximately 23 feet. The alluvial deposits encountered onsite are generally
associated with flood plain deposits and the historic Black River channel, which drained
Lake Washington until 1916, when the opening of the Lake Washington Ship Canal lowered the
lake level, causing this portion of the Black River to dry up.
All explorations encountered loose to medium dense imported gravely sand between 2 to 4 thick
beneath the asphalt base course. This layer of structural fill was observed to be somewhat thicker
in B-4, where the exploration was drilled adjacent to a located trench line, with the bottom of the
non-native soil being deeper than the surrounding gravel borrow section.
Native soils that underlie the project area consist of thick beds of silt and fine to medium sand in
varying amounts. This very soft and loose soil was relatively consistent across the project area
and were generally found to be on the order of 5 to 11 feet thick. Some organic content (i.e.
vegetation roots, small-diameter woody fibers) was also observed within thicker zones of silt-rich
soil. Soils were generally observed to increase in density with both depth and increased grain size.
Beginning approximately 20 feet below surrounding grade in all four of the deeper explorations
(B-2 through B-5), soils graded to more dense and coarse-grained sands with varying amounts of
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gravel. These soils were observed throughout the termination of the four noted auger bore holes
down to a maximum depth of 31.5 feet below grade.
In the Geologic Map of the Tacoma 1:100,000-scale Quadrangle, Washington, as prepared by the
Washington State Department of Natural Resources Division of Geology and Earth Resources
(WSDNR) (2015), the entire project area is mapped as containing Qa, or Holocene alluvium, which
is described as loose, stratified to massively bedded fluvial silt, sand, and gravel; typically, well
rounded and moderately to well sorted; locally includes sandy to silty estuarine deposits. An
excerpt of this map is shown below as Figure 3.
Fig. 3: Excerpt from the Geologic Map of the Tacoma 1:100,000-scale Quadrangle, Washington
(WSDNR) (2015)
The National Resources Conservation Services (NRCS) for King County classifies soils onsite as
Ur - Urban Land, indicating that the project site and surrounding areas have been significantly
modified through manmade activities. Our field observations generally correspond with the site
classifications performed by both the WSDNR and the NRCS. The enclosed exploration logs
(Appendix A) provide a detailed description of the soil strata encountered in our subsurface
explorations.
Project Site
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3.3 Groundwater Conditions
We encountered groundwater in four of the five subsurface explorations at a depth of
approximately 8 to 14 feet below existing grade. Given the fact that our explorations were
conducted within what is generally considered the rainy season in Western Washington
(November 1 to March 31), we anticipate that groundwater levels will rise somewhat higher than
that which we observed. Seasonally perched groundwater should be anticipated atop fine-
grained soil lenses in close proximity to existing grade. Groundwater levels will fluctuate with
localized geology and levels of precipitation.
3.4 Infiltration Conditions
As indicated in the Soil Conditions section of the report, the site is underlain by alluvial soils,
which can be readily subdivided into three soil horizons: upper fine-grained, intermediate fine-
grained sands, and deeper coarse sands and gravels. Given the fact that groundwater levels were
observed at between 8 to 14 feet below surrounding grades, the upper soil horizon is the only
horizon which could potentially support infiltration. However, these soils range in composition
from silty fine sand to silt, the latter of which should be considered relatively impermeable. Given
the hydrogeologic setting of the project area, we do not interpret infiltration as being feasible for
this project, and site produced stormwater should be managed through detention, and/or diverted
to an appropriate discharge location along SW 12th St.
3.5 Seismic Conditions
The site is in the Puget Sound basin which has experienced several earthquakes. A detailed
description of the regional seismicity is beyond the scope of this report; however, previous
regional earthquakes can be split into two general categories: 1.) large earthquakes with a moment
magnitude greater than 8.0 (MW > 8.0), and 2.) modest size earthquakes with a moment magnitude
generally less than 7.25 (MW < 7.25). In all cases, the thickness of the soil between the bedrock and
the ground surface can change (usually amplify) the seismically induced ground motions and
therefore the inertial loads acting on surface structures.
“Site Class” is a classification system used by the IBC and ASCE 7 to provide some insight to the
potential for ground motion amplification. The site class is based on the properties of the upper
100 feet of the soil and rock materials at the site. MGI used a combination of onsite explorations,
and our review of the geologic mapping of the site to derive a site class for the site. Based on
evaluation and the definitions of Site Class as provided in Table 20.3-1 of ASCE 7-16 (as required
by the 2018 International Building Code), the soil conditions on this site satisfy the definition of
Site Class D - Default. Our evaluation assumes the soil conditions encountered in the bottom of
our explorations, and those from nearby properties, is similar to or increasing in
density/consistency down to 100 feet below ground surface.
The 2018 IBC considers earthquake shaking to have a 2 percent probability of exceedance in
50 years (i.e. a 2475-year return period), as the code-based design requirement. Using the third-
party graphical user interface tools made available by the USGS at https://seismicmaps.org, MGI
derived the design ground motions to be used for design of the structures. Our evaluation used
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IBC 2018 as the code reference, Risk Category I/II/III, and Site Class D - Default. The results of our
evaluation are provided in Table 2 (below).
TABLE 2
SEISMIC DESIGN PARAMETERS
Parameter Value Basis
Site Class D - Default Table 20.3-1 of ASCE 7-16
SS 1.444 seismicmaps.org
Fa 1.2A seismicmaps.org
SMS 1.733 = Fa · SS, 2018 IBC Eqn. 16-36
SDS 1.155 = 2/3 SMS, 2018 IBC Eqn. 16-38
S1 0.492 seismicmaps.org
FV 1.808B, C 2018 IBC
SM1 0.889B, C = FV · S1, 2018 IBC Eqn. 16-37
SD1 0.593B, C = 2/3 SM1, 2018 IBC Eqn. 16-39
PGA 0.615g seismicmaps.org
PGAM 0.737g seismicmaps.org
T0 -- C Not applicable
TS -- C Not applicable
TL 6 sec. seismicmaps.org
Notes:
A. Use the value provided unless the simplified design procedure of ASCE 7 Section 12.14 is
used. If this occurs, please contact our office for more information.
B. Based on Table 1613.2.3(2) of the 2018 IBC – An ASCE 7-16 Chapter 21 analysis has not been
performed.
C. More detailed seismic design criteria are available upon request. Please contact MGI’s office
for more information.
3.6 Liquefaction Potential
Liquefaction is a sudden increase in pore water pressure and a sudden loss of soil shear strength
caused by shear strains, as could result from an earthquake. Research has shown that saturated,
loose, fine to medium sands with a fine (silt and clay) content of less than about 20 percent are most
susceptible to liquefaction. Subsurface explorations performed within the confines of the project
area revealed that native soils are comprised of soft silts and fine sands between 4 to 20 feet beneath
the project area. Based on observed groundwater at 8 to 14 feet, these native soils will generally
stay in a saturated condition.
Given the geologic/hydrogeologic conditions of the project area, we interpret this site as having a
moderate to high susceptibility to liquefaction. This interpretation corresponds to the findings by
the King County Flood Control map of Liquefaction Susceptibility. The liquefaction susceptibility
map of the immediate project area is shown in Figure 4.
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Figure 4: Excerpt of the Liquefaction Susceptibility map of King Co. (2010).
During large-scale seismic events, some degree of liquefaction and related post-construction
settlement should be anticipated.
To potentially mitigate these risks, we recommend constructing engineered structural fill bearing
pads beneath the foundation elements, as discussed in Section 4.2 of this report. Section 4.2
provides detailed recommendations on the design and implementation of these bearing pads,
including material specifications, compaction requirements, and thickness to improve load
distribution and reduce settlement potential. The use of structural fill bearing pads could help
improve the performance of the foundations in these challenging soil conditions, particularly
regarding liquefaction-related risks. These measures may provide a practical approach to
mitigating the identified challenges, depending on the specific site conditions and design
requirements.
4.0 CONCLUSIONS AND RECOMMENDATIONS
Improvement plans involve the partial demolition of the existing Walker’s Renton Subaru facility,
expansion of the existing vehicle service area, and construction of a new 2-story addition on the
Project Site
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western end of the building. The building addition plans to be metal-framed, with a slab-on-
grade at existing elevation. This addition will serve as a customer waiting area and include office
space for employees. Construction plans also call for the existing asphalt around the building to
be removed and replaced with a new asphalt surface.
Plans call for stripping and grading the existing stormwater facility, and installation of a new
concrete, pre-cast stormwater vault in the southeast corner of the property. After installation of
the new facility, the vault will be filled around and over, with new asphalt pavement placed over
top for expanded parking. We offer these recommendations:
• Feasibility: Based on our field explorations, research and analyses, the proposed
structures and pavements appear feasible from a geotechnical standpoint.
• Foundation Options: Over-excavation of spread footing subgrades, to a depth of 3 to
5 feet, and the construction of structural fill bearing pads will be necessary for foundation
support of the new structure. If foundation construction occurs during wet conditions, it
is likely that a geotextile fabric, placed between bearing pads and native soils, will also be
necessary. Recommendations for spread footings are provided in Section 4.2.
• Floor Options: We recommend over-excavation of slab-on-grade floor subgrades to a
minimum depth of 2 feet, then placement of properly compacted structural fill as a floor
subbase. If floor construction occurs during wet conditions, it is likely that a geotextile
fabric, placed between the structural fill floor subbase and native soils, will be necessary.
Recommendations for slab-on-grade floors are included in Section 4.3. Fill underlying
floor slabs should be compacted to 95 percent (ASTM:D-1557).
• Pavement Sections: We recommend over-excavation of pavement subgrades to a
minimum depth of 12 inches, then placement of properly compacted structural fill as
pavement subbase. We recommend a conventional pavement section comprised of an
asphalt concrete pavement over a crushed rock base course over a properly prepared
(compacted) subgrade or a granular subbase, depending on subgrade conditions during
pavement subgrade preparation.
All soil subgrades should be thoroughly compacted, then proof-rolled with a loaded
dump truck or heavy compactor. Any localized zones of yielding subgrade disclosed
during this proof-rolling operation should be over-excavated to a depth of 2 feet and
replaced with a suitable structural fill material.
• Infiltration Conditions: As indicated in the Soil Conditions section of the report, the site is
underlain by shallow, fine-grained alluvial soils. Given the fact that groundwater levels
are likely to rise higher than 8 feet below existing grade, which was the shallowest
groundwater encountered during explorations, the upper fine-grained soil horizon would
be the only horizon which could potentially support infiltration. However, this material
ranges in compositions from silty fine sand to silt, the latter of which should be considered
relatively impermeable. Given the hydrogeologic setting of the project area, we do not
interpret infiltration as being feasible for this project, and site produced stormwater
should be managed onsite through detention, or diverted to a suitable discharge location
along SW 12th St.
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The following sections of this report present our specific geotechnical conclusions and
recommendations concerning site preparation, spread footings, slab-on-grade floors, subgrade
and retaining walls, asphalt pavement, and structural fill. The Washington State Department of
Transportation (WSDOT) Standard Specifications and Standard Plans cited herein refer to
WSDOT publications M41-10, Standard Specifications for Road, Bridge, and Municipal Construction,
and M21-01, Standard Plans for Road, Bridge, and Municipal Construction, respectively.
4.1 Site Preparation
Preparation of the project site should involve erosion control, temporary drainage, clearing,
stripping, excavations, cutting, subgrade compaction, and filling.
Erosion Control: Before new construction begins, an appropriate erosion control system should
be installed. This system should collect and filter all surface water runoff through silt fencing. We
anticipate a system of berms and drainage ditches around construction areas will provide an
adequate collection system. Silt fencing fabric should meet the requirements of WSDOT Standard
Specification 9-33.2 Table 6. In addition, silt fencing should embed a minimum of 6 inches below
existing grade. An erosion control system requires occasional observation and maintenance.
Specifically, holes in the filter and areas where the filter has shifted above ground surface should
be replaced or repaired as soon as they are identified.
Temporary Drainage: We recommend intercepting and diverting any potential sources of surface
or near-surface water within the construction zones before stripping begins. Because the selection
of an appropriate drainage system will depend on the water quantity, season, weather conditions,
construction sequence, and contractor's methods, final decisions regarding drainage systems are
best made in the field at the time of construction. Based on our current understanding of the
construction plans, surface, and subsurface conditions, we anticipate that curbs, berms, or ditches
placed around the work areas will adequately intercept surface water runoff. As the existing site
is covered by non-permeable asphalt, sediment-laden stormwater will quickly flow into the
existing stormwater system; preventing stormwater from leaving the project area should be done
well ahead of any forecasted heavy precipitation events.
Clearing and Stripping: After surface and near-surface water sources have been controlled, sod,
topsoil, and root-rich soil should be stripped from the site. Our subsurface explorations indicate
that there are no organic-rich soils onsite below the existing asphalt pavement in the vicinity of
the proposed site development. Stripping is best performed during a period of dry weather.
Site Excavations: Based on our explorations, we expect that the vast majority of project
excavations will encounter a layer of non-native structural fill under the existing structure and
asphalt pavements, underlain by soft, poorly consolidated fine-grained alluvial soils. Both soil
types can be readily excavated utilizing standard excavation equipment.
Dewatering: Our explorations encountered groundwater in four of five subsurface boring, with
the shallowest groundwater being encountered approximately 8 feet below surrounding grades.
We anticipate that an internal system of ditches, sump holes, and pumps will be adequate to
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temporarily dewater shallow excavations. In order to dewater deeper explorations below the
regional water table, expensive dewatering equipment, such as well points will need to be
utilized.
Temporary Cut Slopes: At this time, final designs and construction sequencing have not been
completed. To facilitate project planning we provide the following general comments regarding
temporary slopes:
• All temporary soil slopes associated with site cutting or excavations should be adequately
inclined to prevent sloughing and collapse,
• Temporary cut slopes in site soils should be no steeper than 1½H:1V, and
• Temporary slopes should conform to Washington Industrial Safety and Health Act
(WISHA) regulations.
These general guidelines are necessarily somewhat conservative (steeper temporary slopes may be
possible). As the project progresses, temporary grading plans are developed, final site features are
better defined, and a contractor is engaged, MGI may modify these general guidelines to allow
steeper slopes.
Subgrade Compaction: Exposed subgrades for the foundation of the proposed structure should
be compacted to a firm, unyielding state before new concrete or fill soils are placed. Any localized
zones of loose granular soils observed within a subgrade should be compacted to a density
commensurate with the surrounding soils. In contrast, any organic, soft, or pumping soils
observed within a subgrade should be overexcavated and replaced with suitable structural fill
material.
Site Filling: Our conclusions regarding the reuse of onsite soil and our comments regarding wet-
weather filling are presented subsequently. Regardless of soil type, all fill should be placed and
compacted according to our recommendations presented in the Structural Fill section of this
report. Specifically, building pad fill soil should be compacted to a uniform density of at least
95 percent (based on ASTM:D-1557).
Onsite Soils: We offer the following evaluation of these onsite soils in relation to potential use as
structural fill:
• Non-native Gravelly Sand: Non-native gravelly sand structural fill underlies existing
pavement, and most likely the existing Subaru building. This soil may be reused for
structural fill, but a geotechnical engineer should first observe the soil prior to reuse. This
soil may become difficult to reuse if placed in an over-optimum moisture condition and
should be protected with plastic sheeting during forecasted wet weather.
• Alluvial Silt and Silty Fine Sand: The alluvial silt and silty sand that underlies the site is
highly moisture sensitive and will likely become impossible to reuse during most weather
conditions. As observed, soils are currently above optimum moisture content and will not
compact adequately unless aerated or cement treated. Reuse is not recommended, and
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this material should only be used for non-structural purposes, such as in landscaping
areas.
• Coarse-Grained Alluvial Sands and Gravels: Native coarse-grained sands and sands with
gravel were encountered at significant depths (greater than 20 feet) below ground surface
in most explorations. Coarse-grained soils which underlie the site are relatively
impervious to moisture content variations and can be reused as structural fill under most
weather conditions.
Permanent Slopes: All permanent cut slopes and fill slopes should be adequately inclined to
reduce long-term raveling, sloughing, and erosion. We generally recommend that no permanent
slopes be steeper than 2H:1V. For all soil types, the use of flatter slopes (such as 2½H:1V) would
further reduce long-term erosion and facilitate revegetation.
Slope Protection: We recommend that a permanent berm, swale, or curb be constructed along the
top edge of all permanent slopes to intercept surface flow. Also, a hardy vegetative groundcover
should be established as soon as feasible, to further protect the slopes from runoff water erosion.
Alternatively, permanent slopes could be armored with quarry spalls or a geosynthetic erosion
mat.
4.2 Spread Footings and Bearing Pads
In our opinion, conventional spread footings built atop structural fill bearing pads will provide
adequate support for the proposed structures if the subgrade is properly prepared. We offer the
following comments and recommendations for spread footing design.
Footing Depths and Widths: For frost and erosion protection, the bases of all exterior footings
should bear at least 18 inches below adjacent outside grades, whereas the bases of interior footings
need bear only 12 inches below the surrounding slab surface level. To reduce post-construction
settlements, continuous (wall) and isolated (column) footings should be at least 18 and 24 inches
wide, respectively.
Bearing Subgrades: Given the poor consolidation of near surface soils in the immediate vicinity of
the project area, structural fill bearing pads 3 to 5 feet thick and compacted to a density of at least 95
percent (based on ASTM:D-1557), should underlie all foundation elements on this site. If
foundation construction occurs during wet conditions, a geotextile fabric may be necessary between
the bearing pad and native soils. We should be consulted if any new foundations are to be placed
adjacent to existing foundations. Refer to the Structural Fill section of this report for more detail.
In general, before footing concrete is placed, any localized zones of loose soils exposed across the
footing subgrades should be compacted to a firm, unyielding condition, and any localized zones
of soft, organic, or debris-laden soils should be over-excavated and replaced with suitable
structural fill.
Lateral Over excavations: Because foundation stresses are transferred outward as well as
downward into the bearing soils, all structural fill placed under footings, should extend
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horizontally outward from the edge of each footing. This horizontal distance should be equal to
the depth of placed fill. Therefore, placed fill that extends 3 feet below the bottom elevation of the
foundation should also extend 3 feet outward, in both directions, from the footing edges.
Subgrade Observation: All footing subgrades should consist of firm, unyielding, native soils, or
structural fill materials that have been compacted to a density of at least 95 percent (based on
ASTM:D-1557). Footings should never be cast atop loose, soft, or frozen soil, slough, debris,
existing uncontrolled fill, or surfaces covered by standing water.
Bearing Pressures: For static loading purposes, footings that bear on dense, properly prepared
structural fill bearing pads can be designed for maximum allowable soil bearing pressures listed in
the table on the following page:
Bearing Pad Thickness (feet) Allowable Bearing Pressure (psf)
3 1,500
4 2,000
5 2,500
A one-third increase in allowable soil bearing capacity may be used for short-term loads created by
seismic or wind related activities.
Footing Settlements: Assuming that structural fill soils are compacted to a medium dense or denser
state, we estimate that total post-construction settlements of properly designed footings bearing on
properly prepared subgrades will not exceed 1 inch under static conditions. Differential
settlements for comparably loaded elements may approach one-half of the actual total settlement
over horizontal distances of approximately 50 feet.
Footing Backfill: We recommend all footing excavations be backfilled on both sides of the footings
and stem walls after the concrete has been cured. This will provide erosion protection and lateral
load resistance. Only imported structural fill should be used for this purpose, contingent on
suitable moisture content at the time of placement. Onsite native fine-grained soils should not be
used. Regardless of soil type, all footing backfill soil should be compacted to a density of at least 90
percent (based on ASTM:D-1557).
4.3 Slab-On-Grade Floors
In our opinion, soil-supported slab-on-grade floors can be used for the planned structures if the
subgrades are properly prepared. We offer the following comments and recommendations
concerning slab-on-grade floors.
Floor Subbase: Given the poor consolidation of near surface soil observed across the project area,
we recommend over-excavation of slab-on-grade floor subgrades to a minimum depth of 2 feet,
with placement and thorough compaction of structural fill as a floor subbase. If floor construction
occurs during wet conditions, it is likely that a geotextile fabric, placed between the structural fill
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floor subbase and native soils, will be necessary. All subbase fill should be compacted to a density
of at least 95 percent (based on ASTM:D-1557).
Capillary Break and Vapor Barrier: To retard the upward wicking of moisture beneath the floor
slab, we recommend that a capillary break be placed over the floor subbase and beneath the slab
vapor barrier. Ideally, this capillary break would consist of a 4-inch-thick layer of pea gravel or
other clean, uniform, well-rounded gravel, such as “Gravel Backfill for Drains” per WSDOT
Standard Specification 9-03.12(4), but clean angular gravel can be used if it adequately prevents
capillary wicking. A manufactured product, such as 5/8 inch minus crushed rock, should not be
used as cap break, as the “minus” component of the crushed rock facilitates moisture wicking
beneath a poured slab.
In addition, a layer of plastic sheeting (such as Crosstuff, Visqueen, or Moistop) should be placed
over the capillary break to serve as a vapor barrier. During subsequent casting of the concrete slab,
the contractor should exercise care to avoid puncturing this vapor barrier.
4.4 Drainage Systems
In our opinion, the proposed structure should be provided with a permanent drainage system to
reduce the risk of future moisture problems, given the low permeability nature of the shallow non-
native soils which underlie the project area. We offer the following recommendations and
comments for drainage design and construction purposes.
Perimeter Drains: We recommend that the structure be encircled with a perimeter drain system to
collect seepage water. This drain should consist of a 6-inch-diameter perforated pipe within an
envelope of pea gravel or washed rock, extending at least 6 inches on all sides of the pipe, and the
gravel envelope should be wrapped with filter fabric to reduce migration of fines from the
surrounding soils. Ideally, the drain invert would be installed no more than 8 inches above the base
of the perimeter footings.
Discharge Considerations: If possible, all perimeter drains should discharge to a sewer system, the
proposed stormwater facility, or other suitable location by gravity flow. Check valves should be
installed along any drainpipes that discharge to a sewer system to prevent sewage backflow into
the drain system. If gravity flow is not feasible, a pump system is recommended to discharge any
water that enters the drainage system.
Runoff Water: Roof- and surface-runoff water should not discharge into the perimeter drain
system. Instead, these sources should discharge into separate tightline pipes and be routed away
from the structure to a storm drain or other appropriate location.
Grading and Capping: Final site grades should slope downward away from the structure so that
runoff water will flow by gravity to suitable collection points, rather than ponding near the
building. Ideally, the area surrounding the building will be capped with concrete, asphalt, or low-
permeability (silty) soils to minimize or preclude surface-water infiltration.
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4.5 Asphalt Pavement
Plans call for the eventual replacement of existing asphalt across the project area after major
construction operations have been completed. We offer the following comments and
recommendations for pavement design and construction.
Subgrade Preparation: We recommend over-excavation of pavement subgrades to depths of 12 or
24 inches, based on geotechnical observation, then placement of properly compacted structural fill
as pavement subbase. If construction occurs during wet conditions, it is likely that a geotextile
fabric, placed between the structural fill pavement subbase and native soils, will be necessary. We
recommend a conventional pavement section comprised of an asphalt concrete pavement over a
crushed rock base course over a properly prepared (compacted) subgrade or a granular subbase,
depending on subgrade conditions during pavement subgrade preparation.
All soil subgrades should be thoroughly compacted, then proof-rolled with a loaded dump truck
or heavy compactor. Any localized zones of yielding subgrade disclosed during this proof-rolling
operation should be over-excavated to a depth of 2 feet and replaced with a suitable structural fill
material. All structural fill should be compacted according to our recommendations given in the
Structural Fill section. Specifically, the upper 2 feet of soils underlying pavement section should
be compacted to at least 95 percent (based on ASTM D-1557), and all soils below 2 feet should be
compacted to at least 90 percent.
Pavement Materials: We recommend using imported washed crushed rock, such as "Crushed
Surfacing Base Course” per WSDOT Standard Specification 9-03.9(3) but with a fines content of
less than 5 percent passing the No. 200 Sieve for the asphalt sections base course. Observations
made during explorations do not indicate a need for a pavement subbase. We recommend using
imported, clean, well-graded sand and gravel such as “Ballast” or “Gravel Borrow” per WSDOT
Standard Specifications 9-03.9(1) and 9-03.14, respectively, should a subbase course be needed
based on geotechnical observations.
Conventional Asphalt Sections: A conventional pavement section typically comprises an asphalt
concrete pavement over a crushed rock base course. We recommend using the following
conventional pavement sections:
Minimum Thickness
Pavement Course Parking Areas High Traffic Driveways
Asphalt Concrete Pavement 3 inches 4 inches
Crushed Rock Base 6 inches 8 inches
Granular Fill Subbase (if needed) 12 inches 24 inches
Compaction and Observation: All subbase and base course material should be compacted to at
least 95 percent of the Modified Proctor maximum dry density (ASTM D-1557), and all asphalt
concrete should be compacted to at least 92 percent of the Rice value (ASTM D-2041). We
recommend that an MGI representative be retained to observe the compaction of each course
before any overlying layer is placed. For the subbase and pavement course, compaction is best
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observed by means of frequent density testing. For the base course, methodology observations
and hand-probing are more appropriate than density testing.
Pavement Life and Maintenance: No asphalt pavement is maintenance-free. The above-described
pavement sections present our minimum recommendations for an average level of performance
during a 20-year design life; therefore, an average level of maintenance will likely be required.
Furthermore, a 20-year pavement life typically assumes that an overlay will be placed after about
10 years. Thicker asphalt and/or thicker base and subbase courses would offer better long-term
performance but would cost more initially; thinner courses would be more susceptible to
“alligator” cracking and other failure modes. As such, pavement design can be considered a
compromise between a high initial cost and low maintenance costs versus a low initial cost and
higher maintenance costs.
4.6 Structural Fill
The term "structural fill" refers to any material placed under foundations, retaining walls, slab-on-
grade floors, sidewalks, pavements, and other structures. Our comments, conclusions, and
recommendations concerning structural fill are presented in the following paragraphs.
Materials: Typical structural fill materials include clean sand, gravel, pea gravel, washed rock,
crushed rock, well-graded mixtures of sand and gravel (commonly called "gravel borrow" or "pit-
run"), and miscellaneous mixtures of silt, sand, and gravel. Import materials meeting WSDOT
Standard Specification 9-03.14(1) gravel borrow will be satisfactory for use as structural fill during
dry weather. Recycled asphalt, concrete, and glass, which are derived from pulverizing the
parent materials, are also potentially useful as structural fill in certain applications. Soils used for
structural fill should not contain any organic matter or debris, nor any individual particles greater
than about 6 inches in diameter.
Fill Placement: Clean sand, gravel, crushed rock, soil mixtures, and recycled materials should be
placed in horizontal lifts not exceeding 8 inches in loose thickness, and each lift should be
thoroughly compacted with a mechanical compactor.
Compaction Criteria: Using the Modified Proctor test (ASTM:D-1557) as a standard, we
recommend that structural fill used for various onsite applications be compacted to the following
minimum densities:
Fill Application Minimum
Compaction
Footing subgrade and bearing pad
Foundation backfill
Asphalt pavement base
Asphalt pavement subgrade (upper 2 feet)
Asphalt pavement subgrade (below 2 feet)
95 percent
90 percent
95 percent
95 percent
90 percent
Subgrade Observation and Compaction Testing: Regardless of material or location, all structural
fill should be placed over firm, unyielding subgrades prepared in accordance with the Site
HHJ Const. – Walker’s Renton Subaru, 519 SW 12th Street, Renton, WA December 11, 2024
Geotechnical Engineering Report Z0816
Migizi Group, Inc. Page 17 of 18
Preparation section of this report. The condition of all subgrades should be observed by
geotechnical personnel before filling or construction begins. Also, fill soil compaction should be
verified by means of in-place density tests performed during fill placement so that adequacy of
soil compaction efforts may be evaluated as earthwork progresses.
Soil Moisture Considerations: The suitability of soils used for structural fill depends primarily on
their grain-size distribution and moisture content when they are placed. As the "fines" content
(that soil fraction passing the U.S. No. 200 Sieve) increases, soils become more sensitive to small
changes in moisture content. Soils containing more than about 5 percent fines (by weight) cannot
be consistently compacted to a firm, unyielding condition when the moisture content is more than
2 percentage points above or below optimum. For fill placement during wet-weather site work,
we recommend using "clean" fill, which refers to soils that have a fines content of 5 percent or less
(by weight) based on the soil fraction passing the U.S. No. 4 Sieve.
5.0 RECOMMENDED ADDITIONAL SERVICES
Because the future performance and integrity of the structural elements will depend largely on
proper site preparation, drainage, fill placement, and construction procedures, monitoring and
testing by experienced geotechnical personnel should be considered an integral part of the
construction process. Subsequently, we recommend that MGI be retained to provide the
following post-report services:
• Review all construction plans and specifications to verify that our design criteria
presented in this report have been properly integrated into the design,
• Prepare a letter summarizing all review comments (if required),
• Check all completed subgrades for footings and slab-on-grade floors before concrete is
poured, in order to verify their bearing capacity, and,
• Prepare a post-construction letter summarizing all field observations, inspections, and test
results (if required).
HHJ Const. – Walker’s Renton Subaru, 519 SW 12th Street, Renton, WA December 11, 2024
Geotechnical Engineering Report Z0816
Migizi Group, Inc. Page 18 of 18
6.0 CLOSURE
The conclusions and recommendations presented in this report are based, in part, on the
explorations that we observed for this study; therefore, if variations in the subgrade conditions are
observed at a later time, we may need to modify this report to reflect those changes. Also, because
the future performance and integrity of the project elements depend largely on proper initial site
preparation, drainage, and construction procedures, monitoring and testing by experienced
geotechnical personnel should be considered an integral part of the construction process. MGI is
available to provide geotechnical monitoring of soils throughout construction.
We appreciate the opportunity to be of service on this project. If you have any questions
regarding this report or any aspects of the project, please feel free to contact our office.
Respectfully submitted,
MIGIZI GROUP, INC.
Randall V. Conger-Best, L.G. James E. Brigham, P.E.
Senior Staff Geologist Senior Principal Engineer
APPROXIMATE SITE
LOCATION
P.O. Box 44840
Tacoma, WA 98448
Location Job Number Figure
DateTitle
519 SW 12th Street
Renton, WA 98057
Topographic and Location Map
1
12/01/24
Z0816
222000mmm
666000fffttt
+–
47.46835 -122.22446 Degrees
JOB NO.
PROJECT:
SHEET TITLE:
FILE:
FIGURE:
SCALE:
DATE:
CHECKED BY:
DRAWN BY:
DESIGNER:
Migizi Group, Inc.
PO Box 44840
Tacoma, WA 98448
253-537-9400
253-537-9401 fax
www.migizigroup.com
519 SW 12th Street
Renton, WA 98057
Site and Exploration Plan
Nov. 08, 2024
JEB
RVCB
RVCB Z0816
NTS
2
Fig2.dwg
APPENDIX A
SOIL CLASSIFICATION CHART AND
KEY TO TEST DATA
LOGS OF BORINGS
CLAYEY GRAVELS, POORLY GRADED GRAVEL-SAND-CLAY
MIXTURES
SILTS AND CLAYS
CO
A
R
S
E
G
R
A
I
N
E
D
S
O
I
L
S
Mo
r
e
t
h
a
n
H
a
l
f
>
#
2
0
0
s
i
e
v
e
LIQUID LIMIT LESS THAN 50
LIQUID LIMIT GREATER THAN 50
CLEAN GRAVELS
WITH LITTLE OR
NO FINES
GRAVELS WITH
OVER 15% FINES
CLEAN SANDS
WITH LITTLE
OR NO FINES
MORE THAN HALF
COARSE FRACTION
IS SMALLER THAN
NO. 4 SIEVE
MORE THAN HALF
COARSE FRACTION
IS LARGER THAN
NO. 4 SIEVE
INORGANIC SILTS, MICACEOUS OR DIATOMACIOUS FINE
SANDY OR SILTY SOILS, ELASTIC SILTS
ORGANIC CLAYS AND ORGANIC SILTY CLAYS OF LOW
PLASTICITY
OH
INORGANIC SILTS AND VERY FINE SANDS, ROCK FLOUR,
SILTY OR CLAYEY FINE SANDS, OR CLAYEY SILTS WITH
SLIGHT PLASTICITY
CH
SILTY GRAVELS, POORLY GRADED GRAVEL-SAND-SILT
MIXTURES
SANDS
SILTS AND CLAYS
Figure A-1
INORGANIC CLAYS OF LOW TO MEDIUM PLASTICITY,
GRAVELLY CLAYS, SANDY CLAYS, SILTY CLAYS,
LEAN CLAYS
E3RA
R-Value
Sieve Analysis
Swell Test
Cyclic Triaxial
Unconsolidated Undrained Triaxial
Torvane Shear
Unconfined Compression
(Shear Strength, ksf)
Wash Analysis
(with % Passing No. 200 Sieve)
Water Level at Time of Drilling
Water Level after Drilling(with date measured)
RV
SA
SW
TC
TX
TV
UC
(1.2)
WA
(20)
Modified California
Split Spoon
Pushed Shelby Tube
Auger Cuttings
Grab Sample
Sample Attempt with No Recovery
Chemical Analysis
Consolidation
Compaction
Direct Shear
Permeability
Pocket Penetrometer
CA
CN
CP
DS
PM
PP
PtHIGHLY ORGANIC SOILS
TYPICAL NAMES
GRAVELS
ORGANIC CLAYS OF MEDIUM TO HIGH PLASTICITY,
ORGANIC SILTS
WELL GRADED GRAVELS, GRAVEL-SAND MIXTURES
MAJOR DIVISIONS
PEAT AND OTHER HIGHLY ORGANIC SOILS
WELL GRADED SANDS, GRAVELLY SANDS
POORLY GRADED SANDS, GRAVELLY SANDS
SILTY SANDS, POOORLY GRADED SAND-SILT MIXTURES
CLAYEY SANDS, POORLY GRADED SAND-CLAY MIXTURES
POORLY GRADED GRAVELS, GRAVEL-SAND MIXTURES
SOIL CLASSIFICATION CHART AND KEY TO TEST DATA
GW
GP
GM
GC
SW
SP
SM
SC
ML
FI
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G
R
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2
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L
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B
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G
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1
1
/
4
/
0
5
INORGANIC CLAYS OF HIGH PLASTICITY, FAT CLAYS
CL
OL
MH
SANDS WITH
OVER 15% FINES
Migizi Group, Inc.
SS
S-1
SS
S-2
SS
S-3
SS
S-4
20.8
20.3
16.8
14.0
12.0
11.5
5-3-2
(5)
1-2-8
(10)
5-7-9
(16)
3-3-5
(8)
GP
SP
ML
SP
GP
SP
0.3
0.7
4.3
7.0
9.0
9.5
Asphalt
(GP) 5/8 inch minus crushed rock (Moist, Dense)
Imported crushed surfacing base course
(SP) Brown gravelly sand (Moist, Medium Dense)
Imported asphalt section subbase
(ML) Gray silt with gravel and sand (Moist, Very Soft)
(SP) Brown gravelly sand (Moist, Medium Dense)
(GP) Gray gravel with sand (Moist, Medium Dense)
Coarse-grained lens
(SP) Dark gray medium to coarse sand with fine gravel (Moist, Loose)
NOTES
LOGGED BY RVCB
DRILLING METHOD Track Mounted Drill Rig
DRILLING CONTRACTOR Holocene Drilling GROUND WATER LEVELS:
CHECKED BY JEB
DATE STARTED 11/4/24 COMPLETED 11/4/24
AT TIME OF DRILLING 10.00 ft / Elev 11.00 ft
AT END OF DRILLING ---
AFTER DRILLING ---
HOLE SIZE 4.25" HSAGROUND ELEVATION 21 ft
SA
M
P
L
E
T
Y
P
E
NU
M
B
E
R
DE
P
T
H
(f
t
)
0.0
2.5
5.0
7.5
10.0
(Continued Next Page)
PAGE 1 OF 2
Figure A-2
BORING NUMBER B-1
CLIENT HHJ Construction
PROJECT NUMBER Z0816
PROJECT NAME Walker's Renton Subaru
PROJECT LOCATION 519 SW 12th Street, Renton WA
CO
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Migizi Group, Inc.
PO Box 44840
Tacoma, WA 98448
Telephone: 253-537-9400
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(
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(R
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BL
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(N
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U.
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C
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S
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GR
A
P
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I
C
LO
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MATERIAL DESCRIPTION
SS
S-5
SS
S-6
5.0
3.0
-0.5
1-0-1
(1)
11-10-7
(17)
SP
ML
SP
16.0
18.0
21.5
(SP) Dark gray medium to coarse sand with fine gravel (Moist, Loose) (continued)
Grades to medium to coarse sand
(ML) Gray fine sandy silt (Moist, Very Soft)
(SP) Gray coarse sand with fine gravel (Moist, Medium Dense)
Observed zone of heaving sands
Bottom of borehole at 21.5 feet.
SA
M
P
L
E
T
Y
P
E
NU
M
B
E
R
DE
P
T
H
(f
t
)
12.5
15.0
17.5
20.0
PAGE 2 OF 2
Figure A-2
BORING NUMBER B-1
CLIENT HHJ Construction
PROJECT NUMBER Z0816
PROJECT NAME Walker's Renton Subaru
PROJECT LOCATION 519 SW 12th Street, Renton WA
CO
P
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O
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R
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B
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1
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6
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4
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:
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Migizi Group, Inc.
PO Box 44840
Tacoma, WA 98448
Telephone: 253-537-9400
RE
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(
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GR
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P
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I
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LO
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MATERIAL DESCRIPTION
SS
S-1
SS
S-2
SS
S-3
SS
S-4
29.8
29.3
28.0
23.0
21.0
3-2-1
(3)
1-0-0
(0)
15-9-9
(18)
13-7-2
(9)
GP
SP
ML
SP
SP
0.3
0.7
2.0
7.0
9.0
Asphalt
(GP) 5/8 inch minus crushed rock (Moist, Dense)
Imported crushed surfacing base course
(SP) Brown gravelly sand (Moist, Medium Dense)
Imported asphalt section subbase
(ML) Mottled brown/gray silt with fine sand (Moist, Very Soft)
(SP) Brown/gray sand with gravel (Moist, Loose)
(SP) Gray fine to medium sand (Moist, Loose)
NOTES
LOGGED BY RVCB
DRILLING METHOD Track Mounted Drill Rig
DRILLING CONTRACTOR Holocene Drilling GROUND WATER LEVELS:
CHECKED BY JEB
DATE STARTED 11/4/24 COMPLETED 11/4/24
AT TIME OF DRILLING 14.00 ft / Elev 16.00 ft
AT END OF DRILLING ---
AFTER DRILLING ---
HOLE SIZE 4.25" HSAGROUND ELEVATION 30 ft
SA
M
P
L
E
T
Y
P
E
NU
M
B
E
R
DE
P
T
H
(f
t
)
0.0
2.5
5.0
7.5
10.0
(Continued Next Page)
PAGE 1 OF 3
Figure A-3
BORING NUMBER B-2
CLIENT HHJ Construction
PROJECT NUMBER Z0816
PROJECT NAME Walker's Renton Subaru
PROJECT LOCATION 519 SW 12th Street, Renton WA
CO
P
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O
F
G
E
N
E
R
A
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B
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/
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Migizi Group, Inc.
PO Box 44840
Tacoma, WA 98448
Telephone: 253-537-9400
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(
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(R
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.
GR
A
P
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I
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MATERIAL DESCRIPTION
SS
S-5
SS
S-6
15.0
6.0
1-0-1
(1)
2-1-2
(3)
SP
ML
SP
15.0
24.0
(SP) Gray fine to medium sand (Moist, Loose) (continued)
(ML) Gray organic-rich silt with fine sand (Moist, Very Soft)
(SP) Gray fine to medium gravelly coarse sand (Moist, Medium Dense)
SA
M
P
L
E
T
Y
P
E
NU
M
B
E
R
DE
P
T
H
(f
t
)
12.5
15.0
17.5
20.0
22.5
25.0
(Continued Next Page)
PAGE 2 OF 3
Figure A-3
BORING NUMBER B-2
CLIENT HHJ Construction
PROJECT NUMBER Z0816
PROJECT NAME Walker's Renton Subaru
PROJECT LOCATION 519 SW 12th Street, Renton WA
CO
P
Y
O
F
G
E
N
E
R
A
L
B
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/
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L
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.
G
P
J
Migizi Group, Inc.
PO Box 44840
Tacoma, WA 98448
Telephone: 253-537-9400
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(
i
n
)
(R
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.
S
.
GR
A
P
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I
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MATERIAL DESCRIPTION
SS
S-7
SS
S-8
1.0
-1.0
-1.5
12-10-20
(30)
16-21-21
(42)
SP
SP
GP
29.0
31.0
31.5
(SP) Gray fine to medium gravelly coarse sand (Moist, Medium Dense) (continued)
(SP) Gray medium to coarse sand (Moist, Dense)
(GP) Gray medium gravel (Moist, Dense)
Bottom of borehole at 31.5 feet.
SA
M
P
L
E
T
Y
P
E
NU
M
B
E
R
DE
P
T
H
(f
t
)
27.5
30.0
PAGE 3 OF 3
Figure A-3
BORING NUMBER B-2
CLIENT HHJ Construction
PROJECT NUMBER Z0816
PROJECT NAME Walker's Renton Subaru
PROJECT LOCATION 519 SW 12th Street, Renton WA
CO
P
Y
O
F
G
E
N
E
R
A
L
B
H
/
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P
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Migizi Group, Inc.
PO Box 44840
Tacoma, WA 98448
Telephone: 253-537-9400
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MATERIAL DESCRIPTION
SS
S-1
SS
S-2
SS
S-3
SS
S-4
29.8
29.3
28.0
19.0
4-2-2
(4)
2-2-1
(3)
1-0-0
(0)
0
GP
SP
ML
SP
0.3
0.7
2.0
11.0
Asphalt
(GP) 5/8 inch minus crushed rock (Moist, Dense)
Imported crushed surfacing base course
(SP) Brown gravelly sand (Moist, Medium Dense)
Imported asphalt section subbase
(ML) Gray silt with fine sand (Moist, Very Soft)
(SP) Gray fine to medium sand (Moist, Loose)
NOTES
LOGGED BY RVCB
DRILLING METHOD Track Mounted Drill Rig
DRILLING CONTRACTOR Holocene Drilling GROUND WATER LEVELS:
CHECKED BY JEB
DATE STARTED 11/4/24 COMPLETED 11/4/24
AT TIME OF DRILLING 10.00 ft / Elev 20.00 ft
AT END OF DRILLING ---
AFTER DRILLING ---
HOLE SIZE 4.25" HSAGROUND ELEVATION 30 ft
SA
M
P
L
E
T
Y
P
E
NU
M
B
E
R
DE
P
T
H
(f
t
)
0.0
2.5
5.0
7.5
10.0
(Continued Next Page)
PAGE 1 OF 3
Figure A-4
BORING NUMBER B-3
CLIENT HHJ Construction
PROJECT NUMBER Z0816
PROJECT NAME Walker's Renton Subaru
PROJECT LOCATION 519 SW 12th Street, Renton WA
CO
P
Y
O
F
G
E
N
E
R
A
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B
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L
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.
G
P
J
Migizi Group, Inc.
PO Box 44840
Tacoma, WA 98448
Telephone: 253-537-9400
RE
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V
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R
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(
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n
)
(R
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U
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T
S
(N
V
A
L
U
E
)
U.
S
.
C
.
S
.
GR
A
P
H
I
C
LO
G
MATERIAL DESCRIPTION
SS
S-5
SS
S-6
10.0
7.0
3-2-3
(5)
1-1-0
(1)
SP
ML
SP
20.0
23.0
(SP) Gray fine to medium sand (Moist, Loose) (continued)
(ML) Gray organic-rich silt (Moist, Very Soft)
(SP) Gray fine to medium gravelly coarse sand (Moist, Loose)
SA
M
P
L
E
T
Y
P
E
NU
M
B
E
R
DE
P
T
H
(f
t
)
12.5
15.0
17.5
20.0
22.5
25.0
(Continued Next Page)
PAGE 2 OF 3
Figure A-4
BORING NUMBER B-3
CLIENT HHJ Construction
PROJECT NUMBER Z0816
PROJECT NAME Walker's Renton Subaru
PROJECT LOCATION 519 SW 12th Street, Renton WA
CO
P
Y
O
F
G
E
N
E
R
A
L
B
H
/
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P
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O
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S
-
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U
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E
.
G
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-
1
1
/
2
6
/
2
4
1
2
:
4
0
-
C
:
\
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R
S
\
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I
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A
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S
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\
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I
T
S
A
N
D
B
O
R
I
N
G
S
-
G
I
N
T
\
Z
0
8
1
6
\
Z
0
8
1
6
B
O
R
I
N
G
L
O
G
.
G
P
J
Migizi Group, Inc.
PO Box 44840
Tacoma, WA 98448
Telephone: 253-537-9400
RE
C
O
V
E
R
Y
(
i
n
)
(R
Q
D
)
BL
O
W
CO
U
N
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S
(N
V
A
L
U
E
)
U.
S
.
C
.
S
.
GR
A
P
H
I
C
LO
G
MATERIAL DESCRIPTION
SS
S-7
SS
S-8
3.0
-1.0
-1.5
7-2-7
(9)
7-16-20
(36)
SP
SP
SP
27.0
31.0
31.5
(SP) Gray fine to medium gravelly coarse sand (Moist, Loose) (continued)
Soils grade to medium dense
(SP) Gray medium to coarse sand (Moist, Dense)
(SP) Brown coarse sandy fine to medium gravel (Moist, Dense)
Bottom of borehole at 31.5 feet.
SA
M
P
L
E
T
Y
P
E
NU
M
B
E
R
DE
P
T
H
(f
t
)
27.5
30.0
PAGE 3 OF 3
Figure A-4
BORING NUMBER B-3
CLIENT HHJ Construction
PROJECT NUMBER Z0816
PROJECT NAME Walker's Renton Subaru
PROJECT LOCATION 519 SW 12th Street, Renton WA
CO
P
Y
O
F
G
E
N
E
R
A
L
B
H
/
T
P
L
O
G
S
-
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G
U
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E
.
G
D
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-
1
1
/
2
6
/
2
4
1
2
:
4
0
-
C
:
\
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R
S
\
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I
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\
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S
A
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D
B
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I
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S
-
G
I
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\
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0
8
1
6
\
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0
8
1
6
B
O
R
I
N
G
L
O
G
.
G
P
J
Migizi Group, Inc.
PO Box 44840
Tacoma, WA 98448
Telephone: 253-537-9400
RE
C
O
V
E
R
Y
(
i
n
)
(R
Q
D
)
BL
O
W
CO
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(N
V
A
L
U
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)
U.
S
.
C
.
S
.
GR
A
P
H
I
C
LO
G
MATERIAL DESCRIPTION
SS
S-1
SS
S-2
SS
S-3
SS
S-4
29.8
29.3
26.5
23.5
19-22-13
(35)
6-5-5
(10)
2-0-1
(1)
1-0-0
(0)
GP
SP
SP
ML
0.3
0.7
3.5
6.5
Asphalt
(GP) 5/8 inch minus crushed rock (Moist, Dense)
Imported crushed surfacing base course
(SP) Brown gravelly sand (Moist, Medium Dense)
Imported asphalt section subbase
(SP) Brown gravelly sand (Moist, Loose)
Imported trench backfill soils
(ML) Gray silt with fine sand (Moist, Very Soft)
Soils grade to fine sandy silt
NOTES
LOGGED BY RVCB
DRILLING METHOD Track Mounted Drill Rig
DRILLING CONTRACTOR Holocene Drilling GROUND WATER LEVELS:
CHECKED BY JEB
DATE STARTED 11/5/24 COMPLETED 11/5/24
AT TIME OF DRILLING ---
AT END OF DRILLING ---
AFTER DRILLING ---
HOLE SIZE 4.25" HSAGROUND ELEVATION 30 ft
SA
M
P
L
E
T
Y
P
E
NU
M
B
E
R
DE
P
T
H
(f
t
)
0.0
2.5
5.0
7.5
10.0
(Continued Next Page)
PAGE 1 OF 3
Figure A-5
BORING NUMBER B-4
CLIENT HHJ Construction
PROJECT NUMBER Z0816
PROJECT NAME Walker's Renton Subaru
PROJECT LOCATION 519 SW 12th Street, Renton WA
CO
P
Y
O
F
G
E
N
E
R
A
L
B
H
/
T
P
L
O
G
S
-
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G
U
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E
.
G
D
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-
1
1
/
2
6
/
2
4
1
2
:
4
0
-
C
:
\
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R
S
\
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\
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S
T
P
I
T
S
A
N
D
B
O
R
I
N
G
S
-
G
I
N
T
\
Z
0
8
1
6
\
Z
0
8
1
6
B
O
R
I
N
G
L
O
G
.
G
P
J
Migizi Group, Inc.
PO Box 44840
Tacoma, WA 98448
Telephone: 253-537-9400
RE
C
O
V
E
R
Y
(
i
n
)
(R
Q
D
)
BL
O
W
CO
U
N
T
S
(N
V
A
L
U
E
)
U.
S
.
C
.
S
.
GR
A
P
H
I
C
LO
G
MATERIAL DESCRIPTION
SS
S-5
SS
S-6
16.0
9.0
5.0
0
0-0-5
(5)
ML
ML
SP-
SM
SP
14.0
21.0
25.0
(ML) Gray silt with fine sand (Moist, Very Soft) (continued)
(ML) Gray organic-rich silt with fine sand (Moist, Very Soft)
Soils grade to firm
(SP-SM) Fine to coarse sand with silt (Moist, Medium Dense)
(SP) Gray medium to coarse sand with fine gravel (Moist, Dense)
SA
M
P
L
E
T
Y
P
E
NU
M
B
E
R
DE
P
T
H
(f
t
)
12.5
15.0
17.5
20.0
22.5
25.0
(Continued Next Page)
PAGE 2 OF 3
Figure A-5
BORING NUMBER B-4
CLIENT HHJ Construction
PROJECT NUMBER Z0816
PROJECT NAME Walker's Renton Subaru
PROJECT LOCATION 519 SW 12th Street, Renton WA
CO
P
Y
O
F
G
E
N
E
R
A
L
B
H
/
T
P
L
O
G
S
-
F
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U
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E
.
G
D
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-
1
1
/
2
6
/
2
4
1
2
:
4
0
-
C
:
\
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E
R
S
\
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S
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A
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A
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\
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S
T
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I
T
S
A
N
D
B
O
R
I
N
G
S
-
G
I
N
T
\
Z
0
8
1
6
\
Z
0
8
1
6
B
O
R
I
N
G
L
O
G
.
G
P
J
Migizi Group, Inc.
PO Box 44840
Tacoma, WA 98448
Telephone: 253-537-9400
RE
C
O
V
E
R
Y
(
i
n
)
(R
Q
D
)
BL
O
W
CO
U
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T
S
(N
V
A
L
U
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)
U.
S
.
C
.
S
.
GR
A
P
H
I
C
LO
G
MATERIAL DESCRIPTION
SS
S-7
SS
S-8 -1.0
-1.5
1-7-17
(24)
10-21-30
(51)
SP
GP
31.0
31.5
(SP) Gray medium to coarse sand with fine gravel (Moist, Dense) (continued)
Soils grade to medium to coarse gravel
(GP) Gray/brown coarse sandy fine to coarse gravel (Moist, Dense)
Bottom of borehole at 31.5 feet.
SA
M
P
L
E
T
Y
P
E
NU
M
B
E
R
DE
P
T
H
(f
t
)
27.5
30.0
PAGE 3 OF 3
Figure A-5
BORING NUMBER B-4
CLIENT HHJ Construction
PROJECT NUMBER Z0816
PROJECT NAME Walker's Renton Subaru
PROJECT LOCATION 519 SW 12th Street, Renton WA
CO
P
Y
O
F
G
E
N
E
R
A
L
B
H
/
T
P
L
O
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S
-
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D
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-
1
1
/
2
6
/
2
4
1
2
:
4
0
-
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:
\
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\
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A
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B
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I
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G
S
-
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I
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\
Z
0
8
1
6
\
Z
0
8
1
6
B
O
R
I
N
G
L
O
G
.
G
P
J
Migizi Group, Inc.
PO Box 44840
Tacoma, WA 98448
Telephone: 253-537-9400
RE
C
O
V
E
R
Y
(
i
n
)
(R
Q
D
)
BL
O
W
CO
U
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T
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(N
V
A
L
U
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)
U.
S
.
C
.
S
.
GR
A
P
H
I
C
LO
G
MATERIAL DESCRIPTION
SS
S-1
SS
S-2
SS
S-3
SS
S-4
29.8
29.3
27.5
22.0
20.0
1-1-1
(2)
1-2-1
(3)
1-1-1
(2)
1-0-1
(1)
GP
SP
ML
ML
SP-
SM
0.3
0.7
2.5
8.0
10.0
Asphalt
(GP) 5/8 inch minus crushed rock (Moist, Dense)
Imported crushed surfacing base course
(SP) Brown gravelly sand (Moist, Medium Dense)
Imported asphalt section subbase
(ML) Mottled brown/gray silt with fine sand (Moist, Very Soft)
(ML) Mottled brown fine sandy silt (Moist, Very Soft)
(SP-SM) Gray medium to coarse sand with silt (Moist, Loose)
NOTES
LOGGED BY RVCB
DRILLING METHOD Track Mounted Drill Rig
DRILLING CONTRACTOR Holocene Drilling GROUND WATER LEVELS:
CHECKED BY JEB
DATE STARTED 11/5/24 COMPLETED 11/5/24
AT TIME OF DRILLING 8.00 ft / Elev 22.00 ft
AT END OF DRILLING ---
AFTER DRILLING ---
HOLE SIZE 4.25" HSAGROUND ELEVATION 30 ft
SA
M
P
L
E
T
Y
P
E
NU
M
B
E
R
DE
P
T
H
(f
t
)
0.0
2.5
5.0
7.5
10.0
(Continued Next Page)
PAGE 1 OF 3
Figure A-6
BORING NUMBER B-5
CLIENT HHJ Construction
PROJECT NUMBER Z0816
PROJECT NAME Walker's Renton Subaru
PROJECT LOCATION 519 SW 12th Street, Renton WA
CO
P
Y
O
F
G
E
N
E
R
A
L
B
H
/
T
P
L
O
G
S
-
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U
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E
.
G
D
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-
1
1
/
2
6
/
2
4
1
2
:
4
0
-
C
:
\
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R
S
\
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A
B
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A
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\
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S
A
N
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B
O
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I
N
G
S
-
G
I
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T
\
Z
0
8
1
6
\
Z
0
8
1
6
B
O
R
I
N
G
L
O
G
.
G
P
J
Migizi Group, Inc.
PO Box 44840
Tacoma, WA 98448
Telephone: 253-537-9400
RE
C
O
V
E
R
Y
(
i
n
)
(R
Q
D
)
BL
O
W
CO
U
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(N
V
A
L
U
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)
U.
S
.
C
.
S
.
GR
A
P
H
I
C
LO
G
MATERIAL DESCRIPTION
SS
S-5
SS
S-6
17.0
9.0
0
2-8-16
(24)
SP-
SM
ML
SP
13.0
21.0
(SP-SM) Gray medium to coarse sand with silt (Moist, Loose) (continued)
(ML) Gray/brown organic-rich silt with fine sand (Moist, Very Soft)
(SP) Gray fine gravelly coarse sand (Moist, Medium Dense)
SA
M
P
L
E
T
Y
P
E
NU
M
B
E
R
DE
P
T
H
(f
t
)
12.5
15.0
17.5
20.0
22.5
25.0
(Continued Next Page)
PAGE 2 OF 3
Figure A-6
BORING NUMBER B-5
CLIENT HHJ Construction
PROJECT NUMBER Z0816
PROJECT NAME Walker's Renton Subaru
PROJECT LOCATION 519 SW 12th Street, Renton WA
CO
P
Y
O
F
G
E
N
E
R
A
L
B
H
/
T
P
L
O
G
S
-
F
I
G
U
R
E
.
G
D
T
-
1
1
/
2
6
/
2
4
1
2
:
4
0
-
C
:
\
U
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E
R
S
\
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A
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A
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\
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T
P
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S
A
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D
B
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I
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G
S
-
G
I
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\
Z
0
8
1
6
\
Z
0
8
1
6
B
O
R
I
N
G
L
O
G
.
G
P
J
Migizi Group, Inc.
PO Box 44840
Tacoma, WA 98448
Telephone: 253-537-9400
RE
C
O
V
E
R
Y
(
i
n
)
(R
Q
D
)
BL
O
W
CO
U
N
T
S
(N
V
A
L
U
E
)
U.
S
.
C
.
S
.
GR
A
P
H
I
C
LO
G
MATERIAL DESCRIPTION
SS
S-7
SS
S-8
4.0
3.0
0.0
-1.0
-1.5
7-5-13
(18)
7-14-21
(35)
SP
SP
SP
SP
GP
26.0
27.0
30.0
31.0
31.5
(SP) Gray fine gravelly coarse sand (Moist, Medium Dense) (continued)
(SP) Gray medium to coarse sand (Moist, Medium Dense)
(SP) Gray coarse sand with trace fine gravel (Moist, Dense)
(SP) Gray medium to coarse sand (Moist, Dense)
(GP) Gray coarse sandy fine gravel (Moist, Dense)
Bottom of borehole at 31.5 feet.
SA
M
P
L
E
T
Y
P
E
NU
M
B
E
R
DE
P
T
H
(f
t
)
27.5
30.0
PAGE 3 OF 3
Figure A-6
BORING NUMBER B-5
CLIENT HHJ Construction
PROJECT NUMBER Z0816
PROJECT NAME Walker's Renton Subaru
PROJECT LOCATION 519 SW 12th Street, Renton WA
CO
P
Y
O
F
G
E
N
E
R
A
L
B
H
/
T
P
L
O
G
S
-
F
I
G
U
R
E
.
G
D
T
-
1
1
/
2
6
/
2
4
1
2
:
4
0
-
C
:
\
U
S
E
R
S
\
J
E
S
S
I
C
A
B
I
Z
A
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\
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S
K
T
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\
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T
P
I
T
S
A
N
D
B
O
R
I
N
G
S
-
G
I
N
T
\
Z
0
8
1
6
\
Z
0
8
1
6
B
O
R
I
N
G
L
O
G
.
G
P
J
Migizi Group, Inc.
PO Box 44840
Tacoma, WA 98448
Telephone: 253-537-9400
RE
C
O
V
E
R
Y
(
i
n
)
(R
Q
D
)
BL
O
W
CO
U
N
T
S
(N
V
A
L
U
E
)
U.
S
.
C
.
S
.
GR
A
P
H
I
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LO
G
MATERIAL DESCRIPTION
Preliminary Technical Information Report
Walker Subaru Service Center
2240819.10
Appendix E
Non-Structural BMPs
A-1 .................... Required Best Management Practices (BMPs) for all Properties with
Commercial Activities
A-8 .................... Storage or Solid and Food Wastes (Including Cooking Grease)
A-45 .................. Maintenance of Public and Private Utility Corridors and Facilities
Stormwater Pollution Prevention Manual • King County 27
A-1 Required Best Management Practices for all Properties with Commercial Activities
The following Best Management Practices (BMPs) are required for all commercial, industrial,
agricultural, public, or residential properties with commercial activities in unincorporated King County.
Best Management Practices (BMPs) are required by King County Code 9.12. If the BMPs included here
are not enough to prevent contamination of stormwater, you will be required to take additional
measures.
Required BMPs:
Clean and Maintain Storm Drainage System
• Evaluate the condition of the catch basin by checking the amount of sediment in the bottom of the sump.
Catch basins must be cleaned out when the solids, trash, and debris in the sump reaches one–half of the
depth between the bottom of the sump and the bottom of the lowest inflow or outflow pipe connected to
the catch basin or is at least 6 inches below this point.
• Hire a professional drainage contractor to inspect and maintain your system or clean the system yourself. If
there is sediment or other debris in the drainage pipes, then a professional contractor must be hired to flush
or jet out the pipes.
• Small amounts of floating oil can be soaked up with oil absorbent pads, bagged and disposed of as solid
waste.
• Up to one cubic yard of nonhazardous solid material may be disposed of as solid waste in your regular
garbage. If you exceed this threshold hire a professional drainage contractor. All of the solids and stagnant
water collected from catch basin sumps must be disposed of properly. None of the sump contents can
be flushed into the catch basin outflow pipe. Depending on the nature of the pollutants in the sump, and
the associated types of activities taking place on the site, the sump contents may need to be handled
as contaminated waste. Contractors who perform catch basin clean–out services are required to follow
appropriate disposal requirements.
• Clean and maintain catch basins annually. Sites with activities generating a lot of sediments and other debris
will have to inspect and clean out their catch basins more often. Frequent sweeping of paved parking and
storage areas will save time and money in maintaining the drainage system.
• Other components of drainage systems such as ponds, tanks, and bioswales must also be maintained. If this
maintenance is beyond your ability, contractors are available to complete this work.
Label All Storm Drain Inlets on Your Property
• Stencil or apply storm drain markers adjacent to storm drains to help prevent the improper disposal of
pollutants. If the storm drain grate is stamped with warnings against polluting, then additional marking may
not be required if there is no evidence of pollutants being dumped or washed into the storm drain.
Stormwater Pollution Prevention Manual • King County28
Eliminate Illicit Connections to the Storm Drainage System
• Connections to the storm drainage system that convey substances other than stormwater are prohibited.
Examples are connections from internal floor drains, HVAC systems, industrial processes, sinks, and toilets.
• Illicit connections must be immediately removed, permanently plugged or re–plumbed.
• The discharge must be re–plumbed so that it goes to the sanitary sewer, a septic system, an on–site
treatment system, or a holding tank for off–site disposal. There are restrictions on what can be disposed of
to the sanitary sewer and septic systems. You may be required to do additional investigation to determine
where all stormwater and non–stormwater discharges go. This may include smoke, dye, and chemical
testing or closed circuit television inspection.
Additional Information:
• Drainage System Maintenance Contractors Information Sheet
• For stencils and instructions or to determine if you have an illicit connection, contact King County
Stormwater Services at 206–477–4811 or kingcounty.gov/stormwater.
Stormwater Pollution Prevention Manual • King County 35
A-8 Storage or Solid and Food Wastes (Including Cooking Grease)
This refers to garbage dumpsters and outdoor waste containers such as cooking oil/grease receptacles.
Best Management Practices (BMPs) are required by King County Code 9.12. If the BMPs included here
are not enough to prevent contamination of stormwater, you will be required to take additional
measures.
Required BMPs:
• Store wastes in leak–proof containers with solid lids.
• Keep dumpsters closed except when adding waste.
• Used cooking oil/grease containers should be labeled with their contents.
• Clean up any spills immediately using dry methods. Grease cannot be left on the ground.
• Have spill cleanup materials nearby.
• Use a lid or cover when transporting cooking oil/grease containers from kitchens to outside grease
containers.
• Ensure that drip pans or absorbent materials are used whenever grease containers are emptied by vacuum
trucks or other means.
• Dispose of collected cooking oil/grease as garbage if it is not being recycled. Do not dispose of fats, oils or
grease (FOG) into the sanitary sewer or septic system.
Required Routine Maintenance:
• Keep the area around the grease container clean and free of debris.
• Check storage containers frequently for leaks and to ensure that lids are on securely.
• Replace leaking or damaged containers. Contact waste hauler for replacements.
• Sweep and clean the storage area as needed if it is paved. Do not hose down waste storage areas.
• When cleaning or rinsing waste containers, dispose of all wastewater into a sanitary sewer. If no sewer is
available, store in a holding tank, dead end sump, or truck o site to an approved disposal location.
Additional Information:
• Disposal Information Sheet
For more information or assistance contact the King County Stormwater Services at 206–477–4811 and
visit kingcounty.gov/stormwater.
Stormwater Pollution Prevention Manual • King County 77
A-45 Maintenance of Public and Private Utility Corridors and Facilities
This covers maintenance activities associated with the transmission and distribution of public and
private utilities such as petroleum products, natural gas, water, sewage, and electrical power. This
includes the maintenance of underground utility vaults, pump stations, and similar facilities.
Best Management Practices (BMPs) are required by King County Code 9.12.
If the BMPs included here are not enough to prevent contamination of stormwater, you will be required
to take additional measures.
Required BMPs:
• Minimize the amount of herbicides and other pesticides used to maintain access roads and facilities.
• Stabilize access roads or areas of bare ground with gravel, crushed rock, or another method to prevent
erosion. Use and manage vegetation to minimize bare ground/soils that may be susceptible to erosion.
• Provide stormwater drainage for roads and maintenance areas. Grade roads with a crown or slope to
minimize the potential for erosion from runo. Provide ditches, swales, and culverts to convey stormwater
runo.
• Keep ditches and culverts clear to reduce the possibility of the drainage becoming plugged or blocked,
causing overows and erosion.
• Check utility vaults or other underground structures for oil prior to pumping out any collected water.
Contaminated water must be collected for proper disposal. Small amounts of oil may be captured with
absorbent material. Never discharge contaminated water, including high or low pH, to storm drainage
facilities or surface waters.
• When removing water and/or sediment from electrical transformer vaults, determine from records or testing
if the transformers contain PCBs.
• Clean up any debris or spilled material immediately after completing maintenance and repair activities.
Additional Information:
• Landscaping Activities and Vegetation Management – Activity Sheet A-26
• Erosion and Sediment Control Standards – King County Surface Water Design Manual, Appendix D
• Work in public road right of ways requires permission from King County Utility Inspection Program
(206) 296–8122.
Preliminary Technical Information Report
Walker Subaru Service Center
2240819.10
Appendix F
Not Used