HomeMy WebLinkAboutAppendix U - Soils, Geo, GW DR
I-405, Renton Nickel Improvement Project, I-5 to SR 169
SOILS, GEOLOGY, AND GROUNDWATER
DISCIPLINE REPORT
October 2005
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SOILS, GEOLOGY, AND GROUNDWATER
DISCIPLINE REPORT
I-405, Renton Nickel Improvement Project
Prepared for
Washington State Department of Transportation
Urban Corridors Office
And
Federal Highway Administration
Prepared by
Alexander McKenzie-Johnson, Bob Plum, and Doug Morell
Golder Associates
October 20, 2005
Title VI
WSDOT ensures full compliance with Title VI of the Civil Rights Act of 1964 by
prohibiting discrimination against any person on the basis of race, color, national
origin or sex in the provision of benefits and services resulting from its federally
assisted programs and activities. For questions regarding WSDOT's Title VI
Program, you may contact the Department's Title VI Coordinator at 360. 705.7098.
Americans with Disabilities Act (ADA) Information
If you would like copies of this document in an alternate format—large print, Braille,
cassette tape, or on computer disk, please call 360.705.7097. Persons who are deaf
or hard of hearing, please call the Washington State Telecommunications Relay
Service, or Tele-Braille at 7-1-1, Voice 1.800.833.6384, and ask to be connected to
360.705.7097.
Renton Nickel Improvement Project
Soils, Geology, and Groundwater Discipline Report i
T ABLE OF C ONTENTS
Glossary.............................................................................................................................................................................iv
Acronyms and Abbreviations Used in this Report ........................................................................................................vi
Introduction........................................................................................................................................................................1
What is the Renton Nickel Improvement Project? ...........................................................................................................1
What is the No Build Alternative?................................................................................................................................2
What is the Build Alternative?.....................................................................................................................................2
How will stormwater from the project be managed? .................................................................................................12
What environmental and utilities issues influenced the project design and what was done to avoid
and minimize project effects?....................................................................................................................................13
What is planned for wetland and stream mitigation?.....................................................................................................16
What benefits will the project provide?......................................................................................................................17
How will the project incorporate community design preferences?.............................................................................17
How will the project be constructed?.........................................................................................................................18
Why do we consider geology, soils, and groundwater as we plan this project? ............................................................19
What are the key points of this report?..........................................................................................................................20
Existing Conditions.........................................................................................................................................................21
How were the geology, soils, and groundwater information collected? .........................................................................21
What created the topography and geology of the Puget Sound Region and the study area?.......................................22
What is the geology of the study area?..........................................................................................................................24
Engineered Fill (m)....................................................................................................................................................25
Non-Engineered Fill (m)............................................................................................................................................25
Alluvium (Qyal)..........................................................................................................................................................26
Wetland Deposits (Qw).............................................................................................................................................27
Glacial Deposits (Qvt and Qvr)..................................................................................................................................28
Renton Formation Bedrock (Tpr) and Basalt (Ti)......................................................................................................28
Is the study area prone to seismic activity?...................................................................................................................29
Subduction zone and intraplate earthquake conditions.............................................................................................29
Crustal earthquake conditions...................................................................................................................................30
Historical earthquakes...............................................................................................................................................30
What are geologic hazards and do any occur in the study area?..................................................................................31
Liquefaction hazard areas.........................................................................................................................................32
Soft Ground Areas - Earthquake Shaking Amplification............................................................................................33
Soft Ground Areas – Compressible Soil....................................................................................................................36
Soft Areas – Poor Foundation Support .....................................................................................................................36
Mine Subsidence Hazard Areas................................................................................................................................38
Lahar hazard areas...................................................................................................................................................40
High erosion potential areas......................................................................................................................................40
Shallow groundwater areas.......................................................................................................................................42
What groundwater resources are located in the study area?.........................................................................................43
What aquifers are present in the study area?................................................................................................................44
Green-Duwamish Alluvial Aquifer..............................................................................................................................44
Cedar Valley Sole-Source Aquifer.............................................................................................................................45
What are the uses of groundwater in the study area?...................................................................................................46
Groundwater rights....................................................................................................................................................46
Groundwater wells ....................................................................................................................................................46
TABLE OF CONTENTS
Renton Nickel Improvement Project
ii Soils, Geology, and Groundwater Discipline Report
Are there critical/sensitive areas for groundwater protection?....................................................................................... 48
Critical recharge areas.............................................................................................................................................. 48
Cedar Valley sole-source aquifer.............................................................................................................................. 49
Are there specific ordinances to protect the Cedar Valley Aquifer?............................................................................... 51
Capture zones and travel times................................................................................................................................ 51
Aquifer protection ordinances................................................................................................................................... 52
What is the quality of groundwater in the study area?................................................................................................... 53
Potential Effects............................................................................................................................................................... 54
What methods were used to evaluate the project’s potential effects?........................................................................... 54
Could soils, geology, or groundwater affect project construction?................................................................................. 54
Could soils, geology, or groundwater affect project operation?..................................................................................... 55
Will project construction temporarily affect geology, soils, and groundwater?............................................................... 55
Moisture-sensitive soils............................................................................................................................................. 56
Increased erosion..................................................................................................................................................... 56
Vibration effects of construction equipment.............................................................................................................. 56
Will the project permanently affect geology, soils and groundwater?............................................................................ 57
Does the project have delayed or distant effects?......................................................................................................... 57
Measures to Avoid or Minimize Project Effects............................................................................................................ 58
What has been done to avoid or minimize negative effects from the project?............................................................... 58
Could the project compensate for unavoidable negative effects to soils, geology, and groundwater?.......................... 61
References....................................................................................................................................................................... 62
Appendix
A - Groundwater Rights Summary
TABLE OF CONTENTS
Renton Nickel Improvement Project
Soils, Geology, and Groundwater Discipline Report iii
E XHIBITS
Exhibit 1. Project Vicinity Map......................................................................................................................................... 1
Exhibit 2. Project Overview Section 1............................................................................................................................. 3
Exhibit 3. Project Overview Section 2............................................................................................................................. 4
Exhibit 4. Project Overview Section 3............................................................................................................................. 5
Exhibit 5. Project Overview Section 4............................................................................................................................. 6
Exhibit 6. Project Overview Section 5............................................................................................................................. 7
Exhibit 7. Project Overview Section 6............................................................................................................................. 8
Exhibit 8. Project Overview Section 7............................................................................................................................. 9
Exhibit 9. Project Overview Section 8............................................................................................................................10
Exhibit 10. Geologic Units in the Study Area..................................................................................................................26
Exhibit 11. Pacific Northwest Tectonic Setting...............................................................................................................29
Exhibit 12. Liquefaction Potential in the Study Area.......................................................................................................33
Exhibit 13. NEHRP Site Classes....................................................................................................................................34
Exhibit 14. NEHRP Site Classes in the Study Area......................................................................................................35
Exhibit 15. Soft Soil Locations in the Study Area...........................................................................................................37
Exhibit 16. Location of Coal Mine Workings near the Study Area.................................................................................39
Exhibit 17. Erosion Potential of Soil Units in the Study Area..........................................................................................41
Exhibit 18. Likely shallow Groundwater Areas in the Study Area...................................................................................42
Exhibit 19. 1-year, 5-year, and 10-year Groundwater Travel Times for the City of Renton’s Well Field
in the Delta Aquifer......................................................................................................................................46
Exhibit 20. Groundwater Wells in the Vicinity of the Study Area....................................................................................47
Exhibit 21. Critical Recharge Areas in the Vicinity of the Study Area.............................................................................49
Exhibit 22. Boundaries of the Cedar Valley Sole-Source Aquifer in the Vicinity of the Study Area................................51
Exhibit 23. Cedar Valley Sole-Source Aquifer Zone 1 and Zone 2 Groundwater Protection Zones..............................52
Renton Nickel Improvement Project
iv Soils, Geology, and Groundwater Discipline Report
GLOSSARY
Acceleration Measurement of strong ground shaking from an earthquake, commonly expressed as a
fraction of the acceleration of gravity (1g).
Active fault A fault that has had sufficiently recent displacements (i.e., movement) so that, in the opinion
of the user of the term, further displacements in the foreseeable future are likely. For
common engineering applications, any fault that has had one or more displacements in the
past 10,000 years is an active fault.
Admix A product, such as cement or kiln dust that is mixed into soil to improve the characteristics
of the soil during construction.
Alluvium Sediment deposited by flowing water, such as a river or stream.
Aquifer A unit of saturated geologic materials that is capable of producing useable quantities of
groundwater on a long-term, sustainable basis.
Aquitard Sediments or bedrock that restricts groundwater flow.
Compaction grouting A method of improving the soil by injecting a thick grout into the soil, causing the soil to
become denser and binding the soil together.
Continental crust That type of the earth’s crust which constitutes the continents and the offshore continental
shelves. Continental crust generally ranges from about 22 miles to 37 miles thick.
Critical Aquifer
Recharge Area
Aquifers which are considered more susceptible to groundwater contamination because the
depth to groundwater is shallow; a surficial low permeability protective layer is not present;
and the aquifers are critical for supply and use.
Crust The outermost layer or shell of the earth.
Fault A fracture or zone of fractures along which displacement has occurred parallel to the
fracture.
Fill Soil placed by humans, such as for roads or building foundations.
Glacier A major body of ice that moves under the influence of gravity. Examples of glaciers include
the numerous glaciers on Mount Rainier, or the continental ice sheet on Antarctica.
Group A Wells Groundwater wells that serve 15 or more households.
Group B Wells Groundwater wells that serve 2 to 14 households.
Hydrologically
Connected
Waterbodies or aquifers that are linked by the movement of water. For instance, an aquifer
that feeds water to a wetland is considered to be hydrologically connected to the wetland.
Lahar A rapidly flowing mixture of rock and water originating on a volcano.
Liquefaction (of soil) Transformation of a granular material from a solid state into a liquefied state as a
consequence of increased pore-water pressures, commonly induced by strong earthquake
shaking.
Outwash Sediment deposited by flowing water originating from a glacier, typically referring to
sediments deposited in the Pleistocene by large continental ice sheets. Outwash that is
deposited and then subsequently overrun by an advancing ice sheet is known as advance
outwash. Outwash that is not overrun is commonly called recessional outwash. Outwash
typically consists of sand (0.003 inches to 0.19 inches in diameter) and gravel sized
particles (0.19 inches to 2.9 inches in diameter).
GLOSSARY
Renton Nickel Improvement Project
Soils, Geology, and Groundwater Discipline Report v
Permeability A measure of how quickly a fluid (in this case water) can flow through a sediment or rock.
In this report, permeability is synonymous with hydraulic conductivity.
Plate tectonics A global theory of tectonics in which an outermost layer of a sphere (the crust) is divided
into a number of relatively rigid plates that collide with, separate from, and translate past
one another at their boundaries.
Recharge Well A well that pumps water into an aquifer, rather than taking water out of the aquifer.
Saturated The condition when all pore or open spaces in a geologic material are completely filled with
groundwater at or greater than atmospheric pressure.
Sedimentary Rock A rock type composed of sediments weathered from pre-existing rocks, from the chemical
precipitation of dissolved minerals, or the accumulation of living material. Examples of
sedimentary rocks include sandstone, shale, coal, and limestone.
Seismicity The occurrence of earthquakes in space and time.
Shallow Groundwater Groundwater encountered at depths of less than ten feet.
Sole-Source Aquifer U.S. Environmental Protection Agency designated aquifers where few or no reasonable
alternatives exist for acquiring drinking water.
Stereographic Aerial
Photographs
Overlapping photographs taken from an aircraft that when viewed using a stereoscope
produces a three-dimensional image.
Stratified Sediment deposited in layers.
Subduction The process of one crustal plate descending beneath another.
Subduction zone A long, narrow belt in which subduction takes place.
Subgrade The in-place material on which the pavement or embankment fills are placed.
Subsidence The collapse or excessive settlement of the ground into an underground void space.
Tectonics The study of earth and rock structure, structural forms, and their development and history
resulting from the deformation of the earth’s crust (e.g., faults, earthquakes, uplift and
subsidence).
Till An unsorted to poorly layered deposit of clay to boulder sized sediment deposited by a
glacier. Till deposited at the base of a glacier is usually hard or very dense, and is known
as lodgment till. Till deposited at the margins of a glacier is known as ablation till, and is
usually much less dense than lodgment till. Till is often referred to as hardpan.
Underdrain A drain installed at the base of a fill embankment or cut wall to control seepage and
eliminate water pressure against the wall.
Underpinning A method of increasing the foundation capacity of a structure by adding piles under the
structure.
Wellhead Protection
Area
The area surrounding a drinking water well that supplies groundwater to the well. The
Wellhead Protection Area is calculated by the time it takes potential contaminants to enter
the well.
Renton Nickel Improvement Project
vi Soils, Geology, and Groundwater Discipline Report
ACRONYMS AND
ABBREVIATIONS USED IN THIS REPORT
APA Aquifer Protection Area
BMPs Best Management Practices
EA Environmental Assessment
EIS Environmental Impact Statement
EPA U.S. Environmental Protection Agency
FHWA Federal Highway Administration
HOV High-occupancy Vehicle
LiDAR Light Distance and Ranging. An airborne laser surveying technique that can produce
high-quality digital topographic maps of the Earth’s surface with the overlying
vegetation removed.
MP Milepost
MTCA Model Toxics Control Act
NEHRP National Earthquake Hazard Reduction Program
NPDES National Pollutant Discharge Elimination System
NRCS National Resource Conservation Service
SPCC Spill Prevention Control and Countermeasures
TESC Temporary Erosion and Sediment Control
WDNR Washington Department of Natural Resources
WHPA Wellhead Protection Area
WSDOT Washington State Department of Transportation
Renton Nickel Improvement Project
Soils, Geology, and Groundwater Discipline Report 1
INTRODUCTION
What is the Renton Nickel Improvement Project?
The Renton Nickel Improvement Project is a highway expansion project that will
improve mobility and safety through Tukwila and Renton. On I-405, this project
begins just east of the I-5/I-405 interchange in Tukwila and extends north past the
Cedar River to the SR 169 (Maple Valley Highway) interchange. The project will build
an additional lane both northbound and southbound between I-5 and SR 169. On
SR 167, the project will extend the southbound high-occupancy vehicle (HOV) lane
north to I-405 and add a southbound auxiliary lane from I-405 to the SW 41st Street
off-ramp. These limits comprise the study area for the project.
Prior to planning this specific project, WSDOT created the I-405 Corridor Program.
This program provides a comprehensive strategy to reduce congestion and improve
mobility throughout the I-405 corridor. The corridor begins at the I-5 interchange in
the city of Tukwila and extends northward 30 miles to the I-5 interchange in the city of
Lynnwood. The program’s purpose is to provide an efficient, integrated, and
multimodal system of
transportation solutions.
Using the I-405 Corridor
Program’s Selected
Alternative as the Master
Plan to improve I-405,
WSDOT developed
relatively low cost,
congestion relief roadway
improvements as an interim
step in achieving the Master
Plan. As part of this effort,
WSDOT began to define
the Renton Nickel
Improvement Project. The
Renton Nickel Improvement
Project was developed as
part of a first step in
providing a focused strategy
to improve I-405 between
I-5 in Tukwila and SR 169 in
Renton and SR 167
southbound from I-405 to
SW 41st Street, see Exhibit
1. This discipline report
analyzes two project
alternatives: the No Build
Alternative and the Build
Alternative.
Exhibit 1. Project Vicinity Map
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SW 41st St
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INTRODUCTION
Renton Nickel Improvement Project
2 Soils, Geology, and Groundwater Discipline Report
What is the No Build Alternative?
The No Build Alternative assumes that only routine
activities such as road maintenance, repair, and safety
improvements would take place over the next 20 years.
This alternative does not include improvements to increase
roadway capacity or reduce congestion. For these
reasons, it does not satisfy the project’s purpose—improve
I-405 between I-5 in Tukwila and SR 169 in Renton and
SR 167 southbound from I-405 to SW 41st Street.
The No Build Alternative has been evaluated in this
discipline report to establish a baseline for comparing
the effects associated with the Build Alternative.
What is the Build Alternative?
The new lanes that will be built under this project are:
An I-405 northbound general-purpose (GP)
lane from I-5 to the SR 167 off-ramp.
An I-405 northbound auxiliary lane from the
SR 167 to I-405 on-ramp to the SR 169 off-ramp.
An I-405 southbound auxiliary lane from the
SR 169 to I-405 on-ramp to the SR 167 off-ramp.
An I-405 southbound GP lane from the SR 167
to I-405 on-ramp to the I-5 off-ramp.
A SR 167 southbound auxiliary lane from I-405 to the
SW 41st Street off-ramp. Also, the existing inside
HOV lane will be extended north to I-405 from its
present starting point in the vicinity of SW 21st Street.
See Exhibits 2 through 9 show the project features. In
addition to adding lanes to I-405 and SR 167, this project
will provide the following improvements.
Improve Interchanges
Minor modifications will be made to the ramps at the
SR 167 interchange:
The one-lane ramp from northbound I-405 to
SR 167 will be widened to a 2-lane off
connection, which provides a dedicated lane to
southbound SR 167 and a dedicated lane to
northbound Rainer Avenue. See Exhibit 5.
Traffic from two consecutive single-lane on-
ramps from southbound I-405 to SR 167 will be
separated by a concrete barrier. This will
provide a smoother transition to the mainline
and reduce congestion on the on-ramps.
What is an auxiliary lane?
An auxiliary lane is a lane added between
interchanges—from one on-ramp to the
next off-ramp. It is dedicated to traffic
entering and leaving the freeway and
provides motorists with more time and
extra room to accelerate or decelerate
and merge when getting on and off the
freeway.
89:P 89:T
Existing On-ramp On-ramp with
proposed auxiliary
lane
INTRODUCTION
Renton Nickel Improvement Project
Soils, Geology, and Groundwater Discipline Report 3
T u k w i l a P a r k w a y
I-405
Southern
Project Limit
at I-5
Gilliam Creek
Cottage Creek
Westfield
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I-405 Northboundbound Improvements:
A general-purpose lane will be added by restriping the existing
pavement and adding pavement up to 15 feet to the outside at
some locations.
I-405 Southbound Improvements:
A general-purpose lane will be added by restriping the existing
pavement and adding pavement up to 15 feet to the outside at
some locations. M0250500
Feet
I-405 NORTHBOUND
Existing
Proposed
I-405 SOUTHBOUND
Existing
Proposed
Renton
Renton
Piped River/Creek Channel
Open River/Creek Channel
Ecology EmbankmentÃÃÃÃÃÃÃÃÃÃÃÃ
Retaining Wall
Stormwater Flow Control
Facility
New Pavement
Easement Acquisition
Parcel Acquisition
Existing ROW
Areas of Construction
New ROW
Exhibit 2. Project Overview Section 1
INTRODUCTION
Renton Nickel Improvement Project
4 Soils, Geology, and Groundwater Discipline Report ÃÃÃÃÃÃÃÃÃÃÃÃÃÃÃÃÃÃÃÃÃÃÃÃInterurban TrailFort
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I-405 Northbound Improvements:
A general-purpose lane will be added by restriping the existing
pavement and adding pavement up to 15 feet to the outside at
some locations.
I-405 Southbound Improvements:
A general-purpose lane will be added by restriping the existing
pavement and adding pavement up to 15 feet to the outside at
some locations. M0250500
Feet
I-405 SOUTHBOUND
Existing
Proposed
Renton
Renton
I-405 NORTHBOUND
Existing
Proposed
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Piped River/Creek Channel
Open River/Creek Channel
ÃÃÃÃÃÃÃÃÃÃÃÃ Ecology Embankment
Stormwater Flow Control
Facility
New Pavement
Areas of Construction
Easement Acquisition
Parcel Acquisition
Existing ROW
New ROW
Exhibit 3. Project Overview Section 2
INTRODUCTION
Renton Nickel Improvement Project
Soils, Geology, and Groundwater Discipline Report 5
ÃÃÃÃÃÃÃÃÃÃÃÃÃÃÃÃÃÃ
SW 16th St
S W G r a d y W a y
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I-405 Northbound Improvements:
A general-purpose lane will be added by restriping the existing
pavement and adding pavement up to 15 feet to the outside at
some locations. The existing Springbrook Creek and Oakesdale
Avenue bridges will be replaced and the existing culvert will be
removed.
I-405 Southbound Improvements:
A general-purpose lane will be added by restriping the existing
pavement and adding pavement up to 70 feet to the outside at
some locations. The existing Springbrook Creek and Oakesdale
Avenue bridges will be replaced and the existing culvert will be
removed.M0250500
Feet
I-405 SOUTHBOUND
Existing
Proposed
Renton
Renton
I-405 NORTHBOUND
Existing
Proposed
Piped River/Creek Channel
Open River/Creek Channel
ÃÃÃÃÃÃÃÃÃÃÃÃ Ecology Embankment
Retaining Wall
Stormwater Flow Control
Facility
New Pavement
Areas of Construction
Easement Acquisition
Parcel Acquisition
Existing ROW
New ROW
Exhibit 4. Project Overview Section 3
INTRODUCTION
Renton Nickel Improvement Project
6 Soils, Geology, and Groundwater Discipline Report
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I-405 Northbound Improvements:
A general-purpose lane will be added up to the SR 167 interchange and an auxiliary lane
will be added from the SR 167 to I-405 on-ramp north. These lanes will be added by
restriping the existing pavement and adding pavement up to 15 feet to the outside at
some locations.
I-405 Southbound Improvements:
An auxiliary lane will be added up to the I-405 to SR 167 on-ramp and a general-purpose
lane will be added south of the interchange. These lanes will be added by restriping the
existing pavement and adding pavement up to 15 feet to the outside at some locations.
SR 167 Southbound Improvements:
An auxiliary lane will be added by restriping existing pavement and adding up to 19 feet
of pavement at the outside at some locations. The existing HOV lane will be extended
north from SW 21st Street to the interchange with I-405.M0250500
Feet
I-405 SOUTHBOUND
Existing
Proposed
Renton
Renton
I-405 NORTHBOUND
Existing
Proposed
SR 167 SOUTHBOUND
Existing
Proposed
Renton
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Open River/Creek Channel
Proposed Noise Wall
ÃÃÃÃÃÃÃÃÃÃÃÃ Ecology Embankment
Retaining Wall
Stormwater Flow Control
Facility
New Pavement
Areas of Construction
Easement Acquisition
Parcel Acquisition
Existing ROW
New ROW
Exhibit 5. Project Overview Section 4
INTRODUCTION
Renton Nickel Improvement Project
Soils, Geology, and Groundwater Discipline Report 7 ÃÃÃÃÃÃÃÃÃÃÃÃÃÃÃÃÃÃÃÃÃÃÃÃÃÃÃÃÃÃÃÃÃÃÃÃÃÃÃÃÃÃÃÃÃÃÃÃÃÃÃÃÃÃÃÃÃÃÃÃÃÃÃÃÃÃÃÃÃÃÃÃÃÃÃÃÃÃÃÃÃÃÃÃÃÃÃÃÃÃÃÃÃÃÃÃÃÃÃÃÃÃÃÃPanther
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SR 167 Improvements:
In addition to extending the HOV lane north from SW 21st
Street, an auxiliary lane will be added by restriping the existing
pavement and adding pavement up to 19 feet to the outside at
some locations.
M0250500
Feet
SR 167 SOUTHBOUND
Existing
Proposed
Renton
RentonÃÃÃÃÃÃÃÃÃÃÃÃÃÃÃÃÃÃÃÃÃÃÃÃÃÃÃÃÃÃÃÃÃÃÃÃÃÃÃÃÃÃÃÃÃÃÃÃÃÃÃÃÃÃÃÃÃÃÃÃÃÃÃÃÃÃÃÃÃÃÃÃÃÃÃÃÃÃÃÃÃÃÃÃÃÃÃÃÃÃÃÃÃÃ
Piped River/Creek Channel
Open River/Creek Channel
ÃÃÃÃÃÃÃÃÃÃÃÃ Ecology Embankment
Retaining Wall
Stormwater Flow Control
Facility
New Pavement
Areas of Construction
Easement Acquisition
Parcel Acquisition
Existing ROW
New ROW
Exhibit 6. Project Overview Section 5
INTRODUCTION
Renton Nickel Improvement Project
8 Soils, Geology, and Groundwater Discipline Report ÃÃÃÃÃÃÃÃÃÃÃÃÃÃÃÃÃÃSW 41st St
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An auxiliary lane will be added by restriping the existing
pavement and adding pavement up to 19 feet to the outside at
some locations. The new lane will tie into the existing ramp
connection to SW 41st Street.
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Retaining Wall
Stormwater Flow Control
Facility
New Pavement
Areas of Construction
Easement Acquisition
Parcel Acquisition
Existing ROW
New ROW
Exhibit 7. Project Overview Section 6
INTRODUCTION
Renton Nickel Improvement Project
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I-405 Northbound Improvements:
An auxiliary lane will be added by restriping the existing pavement
and adding pavement up to 15 feet to the outside at some locations.
I-405 Southbound Improvements:
An auxiliary lane will be added by restriping the existing pavement
and adding pavement up to 24 feet to the outside at some locations.
Benson Rd S Improvements:
The Benson Rd S overpass will be replaced and realigned to the
west of its current location. The new overpass will have 2 lanes with
5-foot bike lanes on both sides and a 6-foot sidewalk on the west
side.M0250500
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I-405 NORTHBOUND
Existing
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I-405 SOUTHBOUND
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Existing ROW
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Stormwater Flow Control
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Retaining Wall
ÃÃÃÃÃÃÃÃÃÃÃÃ Ecology Embankment
Proposed Noise Wall
Piped River/Creek Channel
Open River/Creek Channel
Exhibit 8. Project Overview Section 7
INTRODUCTION
Renton Nickel Improvement Project
10 Soils, Geology, and Groundwater Discipline Report
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I-405 Northbound Improvements:
An auxiliary lane will be added by restriping the existing
pavement and adding pavement up to 15 feet to the outside
at some locations.
I-405 Southbound Improvements:
An auxiliary lane will be added by restriping the existing
pavement and adding pavement up to 15 feet to the outside
at some locations. M0250500
Feet
I-405 NORTHBOUND
Existing
Proposed
I-405 SOUTHBOUND
Existing
Proposed
Renton
Renton
Piped River/Creek Channel
Open River/Creek Channel
ÃÃÃÃÃÃÃÃÃÃÃÃ Ecology Embankment
Retaining Wall
Stormwater Flow Control
Facility
New Pavement
Areas of Construction
Easement Acquisition
Parcel Acquisition
Existing ROW
New ROW
Exhibit 9. Project Overview Section 8
INTRODUCTION
Renton Nickel Improvement Project
Soils, Geology, and Groundwater Discipline Report 11
Improve Benson Road
The Benson Road overpass will be replaced and
realigned to accommodate the southbound auxiliary
lane on I-405 as well as future improvements to I-405
as shown on Exhibit 8. Improvements on Benson
Road include a 6-foot sidewalk on the west side and
5-foot bike lanes on both sides.
Widen and replace bridges
Several bridges within the study area will be widened
or replaced based on present location, cost, and
existing soil conditions. To construct the new lanes,
the project will:
Widen Talbot Road Bridge on both the
northbound and the southbound sides. See
Exhibit 8.
Replace Springbrook Creek Side Channel
Bridge and Oakesdale Avenue Bridge with new
southbound and northbound structures and
remove the Springbrook Creek box culvert.
See Exhibit 4.
Replace the rail on the I-405 bridges over
SR 181 and the Union Pacific and Burlington
Northern Santa Fe railroads.
The project will not affect the I-405 bridges over the
Green River, Lind Avenue, or the Cedar River. The
project will also not affect the Cedar Avenue or Renton
Avenue overpasses. The roadway will be restriped in
these areas to accommodate the new lanes.
Use retaining walls
Widening I-405 and SR 167 will require retaining walls
to minimize the construction footprint and right-of-way
acquisition. Retaining walls will also help avoid and
minimize effects to wetlands and other sensitive areas.
Improve culverts
WSDOT anticipates that construction will affect some
existing stormwater cross culverts and one stream
culvert. Associated culvert improvements include
extending the existing structures due to widening the
roadway and stabilizing culvert ends with rock or
retaining walls. The I-405 Team will conduct a hydraulic
analysis of the culverts to ensure that the modifications
will have no effect on the base flood elevations. See the
Fisheries and Aquatic Resources Discipline Report for
detailed discussion on fish passage.
Why rebuild Benson Road on a new
alignment over I-405?
By building the new overpass to the west
on a new alignment, the new structure
can be constructed while the existing
structure remains open to traffic. Traffic
can then be shifted onto the new
structure, while the old overpass is
demolished.
What does a “rail” replacement involve?
Typically, a bridge rail replacement
project consists of making minor
adjustments to the width of the bridge
deck and replacing the guard rail or
barrier. This type of project does not
include adding new bridge columns or
footings.
INTRODUCTION
Renton Nickel Improvement Project
12 Soils, Geology, and Groundwater Discipline Report
Build a noise wall
One noise wall will be built on the northbound side of
the freeway as shown on Exhibits 5 and 8. The wall
will begin at the intersection of South 14th Street and
South 15th Street and follow South 14th Street east to
Talbot Road. This wall will be approximately 2,150
feet long and 18 feet tall.
How will stormwater from the project be
managed?
Stormwater from the project will be managed for both
quality and peak flows using currently accepted best
management practices (BMPs). The I-405 Team has
designed the stormwater management facilities to
comply with the following guidelines and procedures:
WSDOT Highway Runoff Manual M 31-16
WSDOT Hydraulics Manual M 23-03
Stormwater treatment facilities
The project will add new impervious surface within the
study area, most of which will be within the Springbrook
Creek basin. This project will treat runoff for an area
equal to 100 percent of these new surfaces.
The project will use BMPs that the HRM lists as
enhanced treatment facilities. The I-405 Team has
proposed that stormwater be treated using a
combination of these facilities. In most of the study
area, ecology embankments will be used to capture
runoff from the edge of the
pavement and provide water
quality treatment. Ecology
embankments also serve to
convey treated runoff to
receiving waters or to flow
control facilities as required.
The project also includes a
combined stormwater quality
wetland and detention facility
that addresses water quality
and flow control in one facility.
Exhibits 2 through 9 show the
location of stormwater facilities
that will be built for this project. Ecology Embankment Cross-Section
What are the guidelines for stormwater
management facilities?
Water quality treatment will be provided
for an area equal to the new impervious
surfaces created on the project.
Impervious surfaces, such as pavement,
are those that do not allow water to
penetrate into the ground. Stormwater
from new impervious surfaces or an equal
area will be controlled in detention
facilities. This process allows water to
be held (detained) and thus released at
rates that are equal to existing
conditions.
INTRODUCTION
Renton Nickel Improvement Project
Soils, Geology, and Groundwater Discipline Report 13
Drainage Collection and Conveyance
Some changes to existing drainage will be necessary
to provide flow control and water quality treatment to
address the new impervious area added by the
project. However, existing storm drainage systems
will be kept to the greatest extent possible and existing
flow patterns will be maintained. Where roadway
widening affects drainage ditches that convey water
from adjacent private properties, the project design will
assure that existing conveyance capacities are
maintained.
What environmental and utilities issues
influenced the project design and what
was done to avoid and minimize project
effects?
Throughout the development of the Renton Nickel
Improvement Project design, environmental elements
were reviewed and design features were modified to
avoid or minimize negative effects to the environment.
Influence on the project design came from:
Soil Conditions: the soils in the project area are
highly prone to accentuate earthquake
shaking, which influences how bridges can be
widened or replaced.
Noise: highway noise in the project area
already exceeds acceptable levels, which
means that including noise walls as part of the
project had to be considered.
Wetland Locations: many wetlands are located
along the edges of the highway, which
influence whether the widened sections will
use retaining walls or fill slopes.
Historical Sites: some historic sites exist within
the study area, so the project design was
coordinated to avoid these properties.
Because the I-405 Team planned for these
environmental considerations, several design features
have the benefit of avoiding or minimizing potential
effects due to the project. These design features are
described from south to north below.
I-405, I-5 to SR 167
WSDOT will construct a retaining wall from west of the
68th Avenue structure over I-405 at Tukwila Parkway
to the Green River. This wall avoids the need to
What are detention facilities?
These facilities control stormwater runoff
so that it can be released at a controlled
rate. Two types are commonly used:
Ponds.
Vaults. Similar to a pond, but with a
hard-sided construction. These
concrete structures function like a
pond but also provide detention
storage.
INTRODUCTION
Renton Nickel Improvement Project
14 Soils, Geology, and Groundwater Discipline Report
The proposed design modifications allow
the additional lanes to be added over the
Green River by restriping instead of
bridge widening. This avoids effects on
the river, stream habitat, floodplain, and
Interurban Trail.
construct a fill slope that would extend into Gilliam
Creek. See Exhibit 2.
WSDOT will provide a narrower outside shoulder on
northbound I-405 at the Green River Bridge. The
shoulder will vary from 10 to just over 3 feet at the west
abutment of the existing bridge. Narrowing the
shoulder avoids modifications to the existing bridge. As
a result, the design also avoids effects to the river, the
100-year floodplain, the ordinary high water level, and
adjacent riparian zones.
At the SR 181 interchange, the bridge and ramp will
be restriped to provide the new general-purpose lane
and ramp improvements. This approach minimizes
the need to widen the existing SR 181 Bridge,
reconstruct the SR 181 interchange, or modify the
Southcenter Boulevard crossing of the Green River.
This in turn avoids relocating or diverting the
Interurban Trail, which goes under the bridge. See
Exhibit 3.
Near the Westfield Shoppingtown Mall, a large Seattle
Public Utilities water transmission line parallels I-405.
WSDOT will line this pipe so that is can support the
loads from the new roadway embankment. This
approach allows the line to stay in its present location.
WSDOT will remove the existing I-405 bridges over
the Springbrook Creek side channel and Oakesdale
Avenue and replace them with a single northbound
and a single southbound bridge. This approach will
allow for the removal of the Springbrook Creek box
culvert. Construction of the new bridges will be
phased with the southbound bridge built slightly to the
north of the existing roadway. This phasing minimizes
the need to construct temporary roadway to maintain
traffic operations. WSDOT also evaluated the location
of the new bridge piers and selected locations that will
minimize the effect on the existing stream, stream
buffer, and trail that crosses under the bridge.
WSDOT will construct a narrower exit gore from I-405
to the northbound ramp at the SR 167 interchange as
shown in Exhibit 5. By building a narrower exit gore,
the project can be constructed within the existing right-
of-way. This has the benefit of avoiding right-of-way
acquisition, avoiding effects to the wetland outside the
right-of-way, and avoiding effects to the existing Lind
Avenue Bridge.
What is an exit gore?
An exit gore is a roadway feature that
separates an exiting lane from the main
lanes. An exit gore can be defined either
by paint stripes, raised buttons, physical
barriers, or a combination of these.
INTRODUCTION
Renton Nickel Improvement Project
Soils, Geology, and Groundwater Discipline Report 15
Retaining walls will help to avoid and
minimize effects on the Panther Creek
wetlands along SR 167
SR 167, southbound from I-405 to SW 41st Street
WSDOT will build a retaining wall along a large portion
of the west edge of SR 167 southbound instead of an
earth fill slope. See Exhibits 6 and 7. The retaining
wall minimizes effects on three wetlands. The
retaining wall has the added benefit of minimizing
right-of-way needs and reduces the effect on existing
utility crossings, in particular, the City of Seattle’s 60-
inch water line and Olympic Petroleum’s two high
pressure pipelines, which all cross under SR 167.
I-405, SR 167 to SR 169
WSDOT will add a lane by restriping I-405 northbound
next to the Talbot Hill retaining wall immediately east
of the SR 167 interchange. Restriping instead of
widening avoids the need to reconstruct the existing
Talbot Hill retaining wall and avoids effects on
properties south of I-405 in this area. Between Talbot
Road and the “S-Curves”, northbound I-405 will be
widened to achieve standard lane and shoulder
widths. Most of this length will be supported by
retaining walls to minimize effects to Thunder Hills
Creek, adjacent properties, and the existing cut slope
south of I-405.
To support the fill required to widen the roadway on
the north side of I-405 next to the outfall for the
original Rolling Hills Creek culvert, the design uses a
retaining wall. By using the retaining wall, the project
improvements at this location can be constructed
without affecting the existing culvert.
WSDOT will use a non-standard design for the I-405
to SR 167 exit ramp. The changes from the design
standards include not providing a recovery lane,
narrowing the distance between the through lane and
ramp, and providing narrower shoulders. While these
changes deviate from WSDOT design standards they
are an improvement over existing conditions. These
features will avoid effects to the existing Rolling Hills
Creek/Thunder Hills Creek channel located between
I-405 and the Renton Cinema complex as shown in
Exhibit 5. Using retaining walls along the west side of
Benson Road avoids effects to Rolling Hills Creek and
the wetlands east of Talbot Road.
WSDOT will use retaining walls to support widening
southbound I-405 south of the Cedar Avenue
overpass. Using retaining walls versus a fill slope,
avoids encroaching on Cedar Avenue and Main
Avenue in Renton.
What is a recovery lane?
A recovery lane is a paved area adjacent
to an off-ramp. This area gives drivers,
who find themselves exiting the freeway
unintentionally, room to maneuver back
onto the freeway.
INTRODUCTION
Renton Nickel Improvement Project
16 Soils, Geology, and Groundwater Discipline Report
WSDOT also plans to replace the existing Benson
Road overpass on a new alignment. The new bridge
will be located slightly to the west of the existing
bridge. This will allow traffic to continue to use the
existing overpass until the new one is completed. This
will minimize disruption for local traffic and to
emergency response vehicles.
Where northbound and southbound I-405 passes
under the Renton Avenue and Cedar Avenue
overpasses, WSDOT will add lanes by restriping. This
design avoids replacing the two overpasses; however,
the available area does not allow the standard
shoulder and lane widths.
WSDOT shifted a proposed stormwater facility to
avoid effects to the existing Renton Coal Mine Hoist
Foundation site south of Benson Road. This site is on
the Washington Historic Register.
What is planned for wetland and stream mitigation?
WSDOT will compensate for unavoidable effects to
wetlands with credits from the Springbrook Creek
Wetland and Habitat Mitigation Bank. Mitigation is
needed for 1.66 acres of wetlands.
The Springbrook Creek Wetland and Habitat Mitigation
Bank is being developed as a joint effort between
WSDOT and the City of Renton. This ‘bank’ will
construct a new high quality wetland complex that will
serve to replace other wetlands that are filled in by
projects such as the Renton Nickel Improvement
Project. The location of the bank is shown to the left.
In addition to wetland mitigation, the site will also
provide flood storage mitigation. The Springbrook
Creek Wetland and Habitat Mitigation Bank will be one
of the first urban mitigation banks to be certified in
Washington.
To mitigate project effects on streams, WSDOT will
remove the existing Springbrook Creek box culvert.
With the new I-405 southbound and northbound
bridges that will span both Springbrook Creek and
Oakesdale Avenue, the box culvert is no longer
needed. After the new bridges are in place, the box
culvert will be removed and the streambed in that area
will be restored. This will improve fish habitat within
Springbrook Creek. Any additional stream mitigation
required to offset project effects will be accommodated
within the project vicinity.
Renton Coal Mine Hoist Foundation site
looking west
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Study Area Limits
Springbrook Creek Wetland and Habitat
Mitigation Bank
INTRODUCTION
Renton Nickel Improvement Project
Soils, Geology, and Groundwater Discipline Report 17
What benefits will the project provide?
The Build Alternative will benefit the area by reducing
congestion at chokepoints, reducing the duration of
congestion during peak commuter travel hours, and
improving freight movement.
This section of I-405, from the I-5 interchange to
SR 169, is congested due to large traffic volumes and
merging and diverging traffic. The new lanes will help
relieve congestion by adding roadway capacity. This
in turn will improve safety by providing drivers with
more time and extra room to accelerate or decelerate
and move into and out of the stream of traffic when
getting on and off the freeway. This provides a
smoother transition for motorists as they get on and off
I-405 in Tukwila and Renton and helps decrease rear-
end and sideswipe collisions.
The project reduces congestion approaching the
SR 167 interchange, and it complements the
completed southbound I-405 to southbound SR 167
flyover ramp.
This project will construct one noise wall along
northbound I-405 from the intersection of South 14th
Street and South 15th Street east to Talbot Road. This
wall will benefit residents in that area by lowering the
overall noise levels.
Another benefit of this project is that it continues the
application of the Context Sensitive Solutions (CSS)
design choices made by the communities within the
I-405 corridor. The Benson Road realignment will
reflect the most comprehensive application of these
design choices as explained further in the next section.
How will the project incorporate
community design preferences?
The Renton Nickel Improvement Project is being
planned, developed, and designed according to CSS
guidelines. These guidelines establish the community
design preferences used to design the project
features. Working within the framework for the overall
I-405 corridor, the Urban Design Guidelines will be
adapted to incorporate the communities’ design
preferences. These preferences will be included in
the contract documents prepared for the Renton
Nickel Improvement Project. The selected I-405
theme of “Culture, Nature, and Progress,” with nature
being the dominant theme, will be carried into corridor-
wide and local I-405 designs.
This rendering shows the new Benson
Road overpass with the CSS Guidelines
applied
INTRODUCTION
Renton Nickel Improvement Project
18 Soils, Geology, and Groundwater Discipline Report
The new Benson Road overpass is the main project
feature that will receive CSS treatment. The new
southbound and northbound bridges over Springbrook
Creek and Oakesdale Avenue will also receive CSS
treatments. The rest of the project elements will be
designed to match in color and vegetation type only, as
many of these elements will be affected by construction
of future Master Plan projects. During future Master
Plan phases for the overall I-405 corridor, the approved
CSS guidelines will be applied throughout.
How will the project be constructed?
Construction of the entire Renton Nickel Improvement
Project is expected to take two years, beginning in
early 2008 and being completed in late 2010.
However, construction activity will not be constant for
the entire study area throughout this time, and in some
locations, the work will take substantially less time
than two years. Construction will pose some minor
inconveniences because of localized travel delays due
to temporary lane closures and narrowed lanes and
shoulders.
At-grade construction
At-grade construction, which occurs on the same
elevation as the existing lanes, will be staged to
minimize traffic delays and detours. Typically, lanes
are shifted toward the median. WSDOT then places a
concrete barrier to close off the shoulder. Staging
allows construction to occur safely without closing
lanes for the duration of construction. Access to
construction areas will occur from the roadway side to
minimize property effects.
Bridge construction
Construction of the I-405 bridges will occur in multiple
stages to minimize traffic delays and detours. The
following describes typical staging for bridge
construction. As the first stage, traffic is shifted toward
the I-405 median and the existing lanes and shoulders
are narrowed slightly to allow widening of the existing
structure or construction of the new bridge depending
on the design. In the next stage, traffic is shifted onto
the new bridge area. If the bridge is being replaced
rather than simply widened, the old structure is
demolished after traffic is shifted to the new bridge.
The new Benson Road overpass will also be staged.
The new structure will be built to the west, while the
existing overpass remains in service. After traffic has
At-grade construction for this project will
likely be staged similar what is shown
above. Here, the southbound lanes of I-5
were shifted toward the median and a
concrete barrier closed off the shoulder to
provide crews a safe work area.
INTRODUCTION
Renton Nickel Improvement Project
Soils, Geology, and Groundwater Discipline Report 19
been shifted onto the new overpass, the existing
structure will be demolished.
Staging areas
Construction staging areas along I-405 and SR 167
will be within the WSDOT right-of-way. Potential
staging areas have been identified as shown on
Exhibits 2 through 9.
Traffic control
Detour agreements with the local agencies will be
obtained after WSDOT awards the contract. A traffic
control plan will be approved by WSDOT prior to starting
construction. The plan’s primary objectives will be to
provide a safe facility, to streamline the construction
schedule, and to minimize reductions to existing traffic
capacity. To lessen effects on traffic, the duration of
activities will be minimized and reductions in capacity will
be limited and will be targeted to a period when they will
have the least effect.
Why do we consider geology, soils, and groundwater as
we plan this project?
We consider soils, geology, and groundwater because
they are major factors in determining the types of
foundations, pavement sections, subsurface drainage,
retaining walls, and bridges required for the project.
When we refer to soils and geology, we mean the
physical material that makes up the ground. These
physical characteristics also determine the risk of
landslides, liquefaction, erosion, and other types of
behavior, which can affect the environment.
Groundwater pertains to the water contained in the
soil and bedrock below the ground’s surface. We
consider groundwater quality and quantity because
changes to quality and quantity can affect water
supplies for drinking water, and water available for
surface waterbodies such as lakes, streams, and
wetlands. When reviewing potential effects to
groundwater quality and quantity in the project area
we considered federal, state and local regulations,
including: State of Washington Water Resource
regulations (WAC Title 508 and WAC 173-500), Model
Toxics Control Act regulations (WAC 173-340),
Groundwater Quality regulations (WAC 173-200),
Federal (40 CFR 141 and 149) and State Drinking
Water regulations (WAC 246-290), and applicable
INTRODUCTION
Renton Nickel Improvement Project
20 Soils, Geology, and Groundwater Discipline Report
sections within the City of Renton municipal code
pertaining to protection of the Cedar Valley Sole-
Source Aquifer (RMC Chapters 4-3, 4-4, 4-5 and 4-9)
What are the key points of this report?
The following key points are discussed in this report:
The project will be constructed in a highly
variable geologic environment. The majority of
the project is located within the Green-
Duwamish River valley, underlain by relatively
loose sediment with a shallow groundwater
table. This loose sediment has the potential to
cause damage to the project during an
earthquake. Consequently, we have changed
the design of several bridges that will be
constructed for the project, as discussed under
the Effects section. The rest of the project is
generally located on a hillside underlain by
bedrock.
Potential effects from the project to soils,
geology, and groundwater will likely include
temporarily increased erosion, disturbance to
moisture-sensitive soils, and construction-
related vibration. These effects will be avoided
or minimized by using proper design and
construction techniques.
Unavoidable effects from the project will be
minimal, as standard WSDOT construction
practices are followed. Unavoidable effects
include the effects discussed in the preceding
paragraph. The unavoidable effects discussed
in the preceding paragraph are common to
large highway projects.
Renton Nickel Improvement Project
Soils, Geology, and Groundwater Discipline Report 21
EXISTING CONDITIONS
How were the geology, soils, and groundwater
information collected?
The Renton Nickel Improvement Project (hereafter
referred to as the project) lies in a heavily-populated
area that has been investigated thoroughly over the
years for projects such as the initial construction and
subsequent upgrades of I-405 and SR 167. For this
reason, considerable information related to the
geology, soils, and groundwater along the proposed
alignment is readily available. To compile this report,
we reviewed the following data sources:
Previous investigations along I-405 and
SR 167 conducted by WSDOT and others,
including the borehole logs for these
investigations.
Public data such as LiDAR, stereographic
aerial photographs, soil conservation service
(now known as the National Resource
Conservation Service) soil maps, geologic
maps, coal mine maps, liquefaction
susceptibility maps, and sensitive groundwater
areas, e.g., Sole Source Aquifers and Group A
and B Wellhead Protection Areas.
Published articles from the U.S. Geological
Survey (USGS); local purveyor reports;
Washington State Department of Ecology
(Ecology); U.S. Environmental Protection
Agency (EPA); King County, and other
agencies.
Agency web sites for geology, soils, and
groundwater conditions and identified sensitive
areas, as well as databases on wells and water
rights.
Applicable WSDOT Standards, such as those
contained in the revised WSDOT Geotechnical
Design Manual.
Please see the References section for a complete list
of the sources we reviewed for this report.
Following our compilation of this information, we
evaluated existing conditions within the study area. In
some cases, existing conditions were evaluated
directly from the data sources. For instance, we were
What is LiDAR?
LiDAR is an acronym for Light Distance
and Ranging. In the context of this
report, LiDAR refers to an airborne laser
surveying technique that can produce
high-quality topographic data of the
earth’s surface with the overlying
vegetation removed. The topographic
data can be used for many purposes such
as to produce images like the one
displayed below, or topographic maps.
LiDAR image of the study area
EXISTING CONDITIONS
Renton Nickel Improvement Project
22 Soils, Geology, and Groundwater Discipline Report
able to determine the erosion potential of soils along
the study area from the erosion hazard rating
previously determined by the U.S. Department of
Agriculture Soil Conservation Service soil survey map.
In most cases, however, we determined existing
conditions by evaluating information from multiple
sources using standard geologic and hydrogeologic
principles. For example, we evaluated areas that will
likely be underlain by soft soils by reviewing and
compiling published information and evaluating boring
logs from previous investigations.
What created the topography and geology of the Puget
Sound Region and the study area?
The existing topography and surface geology of the
Puget Sound region are largely the result of
Pleistocene glacial, Holocene river, and volcanic
processes. During the last century, human activities
caused large-scale landscape modifications, such as
the lowering of Lake Washington in the early 1900s
and widespread topographic changes associated with
urbanization. Bedrock is generally covered with
glacial and alluvial sediments, so that bedrock
outcrops are rare in the Puget Sound lowland area.
However, several outcroppings of bedrock can be
found in the study area.
The oldest geologic units exposed in the study area
are the Eocene to Oligocene aged Renton and
Tukwila Formations, both sedimentary formations
composed primarily of sandstone, siltstone, and coal.
Geologists have concluded that the sediments
composing the Renton and Tukwila Formations were
deposited by streams on a slowly-subsiding coastal
plain.1
During the Pleistocene, glaciers advanced southward
from Canada into the Puget Sound region at least four
times, each time retreating back into Canada.2
Scouring from these glaciers formed deep troughs in
some areas, such as Lake Washington and Lake
1 Waldron, 1962, Geology of the Des Moines Quadrangle, King County, Washington.
2 Easterbrook, 1994, Stratigraphy and Chronology of Early to Late Pleistocene Glacial and Interglacial Sediments in the
Puget Lowland, Washington; Troost, 2001, Conceptual Stratigraphic Column, Central Puget Lowland Area, an Overview
of Puget Lowland Geology.
Geologic timeline for the last 65 million
years
What are boring logs?
Boring logs are a record of the soil and/or
rock conditions encountered in holes
drilled as part of the investigation for
projects such as road construction or
land development.
EXISTING CONDITIONS
Renton Nickel Improvement Project
Soils, Geology, and Groundwater Discipline Report 23
Sammamish. Melting of the glaciers deposited thick
accumulations of sediment in other areas. In the
study area, the glacial ice was more than 3,000 feet
thick.3
The retreat or melting of the most recent glaciation
began about 13,000 years ago. During the retreat of
the glacial ice, water and sediment flowed off the
melting ice into large drainage channels created or
enhanced by the high volume of water. In the study
area, the Green-Duwamish River Valley and the
Cedar River Valley appear to have been meltwater
channels for the retreating glacial ice.4
Following the retreat of the glacial ice from the study
area, erosion, river processes, and volcanic mudflows
(i.e., lahars) have dominated the shaping of the
geology and topography of the study area. The
Green-Duwamish River Valley is likely to have been a
marine bay that gradually filled with sediment
deposited by the Green River.5
Approximately 5,000 years ago, the Osceola Mudflow,
a lahar originating on Mount Rainier, flowed down the
Green River at least as far as the current location of
the City of Kent.5 Sediment originating from the lahar
filled the current Green-Duwamish River Valley.6
Another lahar may have flowed down the Green-
Duwamish River Valley about 2,600 years ago.7 After
the lahars, the rivers and streams flowing down the
Green-Duwamish River Valley migrated back and forth
across the valley, depositing thick deposits of well-
sorted silt, sand, and gravel. In wetlands adjacent to
the streams and rivers, decaying vegetation
accumulated and formed thick layers of organic silt
and peat.8 The constant migration of the rivers and
the continual deposition of sediment formed the flat
bottom of the Green-Duwamish River Valley.
3 Galster and Laprade, 1991, Geology of Seattle, Washington, United States of America.
4 Mullineaux, 1965, Geologic Map of the Renton Quadrangle, King County, Washington.
5 Dragovich et al., 1994, Extent and Geometry of the Mid-Holocene Osceola Mudflow in the Puget Lowland –
Implications for Holocene Sedimentation and Paleogeography.
6 Dragovich et al., 1994, see footnote 5; Pringle and Scott, 2001, Postglacial Influence of Volcanism on the Landscape
and Environmental History of the Puget Lowland, Washington: A Review of Geologic Literature and Recent Discoveries,
with Emphasis on the Landscape Disturbances Associated with Lahars, Lahar Runouts, and Associated Flooding.
7 Pringle and Scott, 2001, see footnote 6.
8 Mullineaux, 1965, see footnote 4.
How can a glacier deposit sediment?
Aren’t glaciers just flowing ice?
When a glacier covers a land surface, the
material on that surface, such as gravel
or bedrock, can freeze to the base of the
glacier and become part of the glacier. If
a glacier is confined in a valley, then
landslides from the valley sides may fall
on the glacier, and this debris might also
become part of the glacier.
The sediment moves within the ice
toward the front of the glacier where it
melts, and is deposited either at the base
or margin of the glacier. These deposits
are called till. If the deposits are from
flowing streams originating at the
glacier, they are called outwash.
EXISTING CONDITIONS
Renton Nickel Improvement Project
24 Soils, Geology, and Groundwater Discipline Report
The most recent agent of topographic change has
been human activity. For example, in the late 1800s
and early 1900s, coal seams in the Renton Formation
bedrock were mined, leaving several abandoned coal
mines near the study area.9 In addition, the
construction of the Lake Washington Ship canal from
1911 to 1916 lowered Lake Washington by about 10
feet, essentially eliminating the Black River, which
used to drain Lake Washington south to the
Duwamish River. As part of the ship canal project, the
Cedar River, which used to flow into the Black River in
Renton, was diverted into Lake Washington.10 The
construction of I-405, SR 167 and the extensive
development of the cities of Renton and Tukwila have
further altered the topography in the vicinity of the
study area.
What is the geology of the study area?
The geology of the study area consists of a variety of
soil types and bedrock. Soil types include engineered
and non-engineered fill, stream and river sediment,
wetland deposits, and glacial deposits. Bedrock
primarily consists of Renton Formation sandstone,
siltstone, and coal. For the purposes of our
discussion, we refer to these soil and bedrock types
as geologic units. In the following paragraphs, we
discuss each of the geologic units that will most likely
be encountered. A geologic map depicting the surface
geologic units in the study area is presented in
Exhibit 10. The abbreviation for the geologic units
shown on Exhibit 10 follows the heading in
parentheses, such as (m) for engineered and non-
engineered fill or (Qyal) for alluvium. Geologic units
shown on Exhibit 10 that are not intersected by the
project are not described below.
9 Walsh and Logan, 1989, Land subsidence in Washington; Walsh and Bailey, 1989, Coal Mine Subsidence at Renton,
Washington; Galster and Laprade, 1991, see footnote 3.
10 Galster and Laprade, 1991, see footnote 3.
Why do engineering geologists use words
like ‘soft and hard’ or ‘loose and dense’ to
describe soils and other material
deposits?
Words like soft, hard, loose, and dense
have very specific meanings to
engineering geologists. The words soft
and hard refer to the consistency of
cohesive soils, like silts and clays. The
words loose and dense refer to the
density of cohesionless soils, like sand
and gravel. The consistency or density of
the soil refers to the amount of weight
the soil can support, and helps predict
how the soil will behave. Hard or dense
soils can support much heavier loads
than soft or loose soils.
EXISTING CONDITIONS
Renton Nickel Improvement Project
Soils, Geology, and Groundwater Discipline Report 25
Engineered Fill (m)
Except for the bridges, engineered roadbed fill
underlies the entire existing I-405 and SR 167
roadways in the study area. Engineered fill is soil that
is placed and compacted according to designed
specifications for the construction of roads, structures,
or buildings. The fill ranges in thickness from a few
feet in areas of the road that have been cut into
hillsides, such as between SR 167 and the Cedar
River, to more than 50 feet thick in some areas along
I-405 in the Green-Duwamish River Valley, and about
15 feet thick along SR 167. The fill generally consists
of well-graded silty sand with varying gravel content
and scattered cobbles and boulders. Based on the
reviewed borehole logs, the fill is generally dense to
very dense, and it appears to have been placed to
design specifications for constructing roads.
Non-Engineered Fill (m)
Non-engineered fill, consisting of coal mine tailings
(crushed rock and coal) and concrete blocks underlies
I-405 approximately at milepost (MP) 3.1, near a
tunnel associated with the abandoned Renton Coal
Mine.11 Non-engineered fill, presumably derived from
local alluvial sediment, underlies much of the Cedar
River Valley and the valley floor to the west of the
study area between MP 2.8 and the northern end of
the project. These fills were likely not compacted to
design specifications for constructing roads.
11 Walsh and Bailey, 1989, see footnote 9; Walsh and Logan, 1989, see footnote 9.
You keep talking about clay, silt, sand,
gravel, and cobbles. What do these
terms mean?
In the context of this report, clay, silt,
sand, gravel, and cobbles refer to the size
of grains in soil, as shown below. Gravel
and sand are shown to scale. Silt and
clay sized particles are not visible with
the human eye. Boulders are larger than
this page.
EXISTING CONDITIONS
Renton Nickel Improvement Project
26 Soils, Geology, and Groundwater Discipline Report
Exhibit 10. Geologic Units in the Study Area
Modified from Booth et. al., (2002).
Alluvium (Qyal)
The most commonly-encountered surface native
geologic unit in the study area is alluvium. Alluvium is
loosely defined as sediment deposited by flowing
water. Alluvium deposited by the Green-Duwamish
River and associated tributary streams and the Cedar
River, underlies the majority of the study area.
Alluvium in the Green-Duwamish River Valley
EXISTING CONDITIONS
Renton Nickel Improvement Project
Soils, Geology, and Groundwater Discipline Report 27
generally consists of relatively loose, fine to coarse
sand with varying gravel content, interlayered with soft
silt and clay, which becomes denser with depth.12
Most of the alluvium contains a trace of organic
material. Boreholes previously drilled in the valley
also have encountered scattered, laterally-
discontinuous deposits of peat and soil containing a
high percentage of organic material within the Green-
Duwamish River Valley. The deposits of peat and
highly-organic soil are generally less than 5 feet thick.
The alluvium in the Green-Duwamish River Valley
may be more than 150 feet thick.13 Alluvium may also
be interbedded with lahar deposits originating on
Mount Rainier.14 The water table in the Green-
Duwamish River alluvium is very shallow, typically less
than 10 feet. The water table may be at the surface in
the winter months. Alluvium encountered in the Cedar
River Valley generally consists of sand and gravel,
with a much lower organic content than that
encountered in the Green-Duwamish River Valley.
Wetland Deposits (Qw)
Bronson (1989) notes that a thick deposit of soft,
compressible organic soil, ranging in thickness from 5
to 16.5 feet underlies SR 167, between approximately
MP 25.9 and MP 24.8. Most likely, this organic soil
was deposited in a wetland environment similar to the
wetlands currently bordering SR 167. Loose to
medium-dense sand with varying silt, clay, and gravel
content underlies the organic soil.15 The winter water
table in the wetland deposits is likely to be at or near
the surface.
12 WSDOT borehole logs; Bronson, 1989, Geotechnical Impacts on Construction of State Route 167, The Valley
Freeway; Galster and Laprade, 1991, see footnote 3.
13 Galster and Laprade, 1991, see footnote 3.
14 Pringle and Scott, 2001, see footnote 6.
15 Bronson, 1989, see footnote 12.
How do thick deposits of organic soil
form?
Thick deposits of organic soils, such as
peat, usually form in a wetland or
backwater area of a stream or lake.
Plant material falls into the water and
accumulates on the bottom of the
wetland or backwater area. If the water
is low in oxygen, then decay of the plant
material occurs very slowly, and more
and more material can accumulate.
EXISTING CONDITIONS
Renton Nickel Improvement Project
28 Soils, Geology, and Groundwater Discipline Report
Glacial Deposits (Qvt and Qvr)
Soil deposited by Pleistocene continental glaciers
underlie the study area near the I-5/I-405 interchange,
south of the Benson Road overpass, and south of the
Cedar River. The glacial deposits near the I-5/I-405
interchange consist of glacial till, an unsorted, crudely-
stratified mix of very dense silt, sand, gravel, and
cobbles. Glacial till is deposited at the base of the
glacier. The weight of the glacier compacts the till,
causing the till to become very dense.
Recessional outwash, sediment deposited by flowing
water from a glacier, underlies the study area near
Benson Road; and south of the Cedar River. This
sediment generally consists of stratified sand,
interbedded with thin silt layers, and scattered gravel-
rich layers. These deposits, unlike till, were not
overridden by the weight of the glacial ice and,
therefore, have typical densities ranging from loose to
medium dense.
Renton Formation Bedrock (Tpr) and
Basalt (Ti)
Renton Formation bedrock underlies the study area
between the SR 181/I-405 and the I-5/I-405
interchanges as well as between the SR 167/I-405
interchange and the Cedar River. The Renton
Formation generally consists of weathered sandstone
with siltstone and coal interbeds and scattered
conglomerate (i.e., gravel-rich sandstone) layers.
Near the SR 181 interchange, the Renton Formation
sandstone is intruded by basalt.
What are sandstone, siltstone, and coal?
Sandstone and siltstone are sedimentary
rocks composed of sand and silt-sized
particles that have become compressed
and cemented until they form a rock.
Coal is formed from peat that has been
compressed and heated.
Why are organic soils an important
concern to geologists and engineers?
Organic soils are important because they
are more prone to settlement and
typically experience much stronger
shaking than other soils, such as till,
during an earthquake. Therefore,
structures or roads built on organic soils
need to be designed to accommodate the
settlement and the strong shaking that
occurs during a seismic event.
EXISTING CONDITIONS
Renton Nickel Improvement Project
Soils, Geology, and Groundwater Discipline Report 29
Is the study area prone to seismic activity?
The study area is located in a region of active
tectonics where earthquakes occur because of the
interaction of tectonic plates. Tectonic plates are
pieces of the Earth’s crust that move independently of
each other. Offshore of Washington, Oregon, and
British Columbia, the Juan de Fuca oceanic crustal
plate is moving northeastward toward, and converging
with the North American continental crustal plate, as
shown on Exhibit 11.16 The study area is located on
the North American plate.
Subduction zone and intraplate
earthquake conditions
The Juan de Fuca plate intersects with the North
American continental coastal plate along an oceanic
trench located offshore. At this intersection, the
denser Juan de Fuca plate dives, or subducts,
beneath the less dense North American plate.
Earthquakes can occur where the two plates
converge, known as the subduction zone interface
region. Earthquakes within this region can be as large
as M 9.017, which was the size of the recent
earthquake in Indonesia. The most recent large
earthquake in the subduction zone is thought to have
occurred in 1700 A.D.18
Earthquakes can also occur in the subducted Juan de
Fuca plate beneath Puget Sound. Earthquakes
generally occur at depths of 25 to 37 miles in what is
known as the intraplate region. Intraplate earthquakes
can have maximum magnitudes of about M 7.5, and
these are the most frequent type of earthquake that
affects the Puget Sound region.19 Specific examples
16 Yeats et al., 1997, The Geology of Earthquakes.
17 Weaver and Shedlock, 1996, Estimates of Seismic Source Regions from the Earthquake Distribution and Regional
Tectonics in the Pacific Northwest; Stanley et al, 1999, Subduction Zone and Crustal Dynamics of Western Washington:
A Tectonic Model for Earthquake Hazards Evaluation.
18 Leonard et al., 2004, Coseismic subsidence in the 1700 great Cascadia earthquake: Coastal estimates versus elastic
dislocation models.
19 McCrumb et al., 1989, Tectonics, Seismicity, and Engineering Seismology in Washington; Weaver and Shedlock,
1996, see footnote 17.
Exhibit 11. Pacific Northwest
Tectonic Setting
Source: Troost, 2003
How is the size of an earthquake
measured?
Seismologists generally measure the
size, or magnitude (M), of an earthquake
by taking the largest ground motion
recorded during the arrival of a particular
seismic wave type at a recording station,
then applying a standard correction for
the distance to the earthquake source.
An increase of magnitude by 1, such as
from M 5 to M 6, equals an increase in the
energy released by 32.
EXISTING CONDITIONS
Renton Nickel Improvement Project
30 Soils, Geology, and Groundwater Discipline Report
of such earthquakes include the M 6.9 1949 Olympia
earthquake, the M 6.7 1965 Seattle earthquake, and
the M 6.8 2001 Nisqually earthquake.
Crustal earthquake conditions
Convergence along the Cascadia subduction zone
also causes active faulting within the crust of the North
American plate. Crustal earthquakes are generally
less than 25 miles deep. Earthquakes on crustal
faults could be as large as M 7.0 to M 7.5. The largest
historical earthquake reported (M 6.8 to 7.4) in
Washington happened in 1872 on a crustal fault near
Lake Chelan.20
The Seattle fault zone that runs east-west through
Seattle is an example of a crustal fault. The Seattle
fault is more than 42 miles long and extends from west
of Bremerton, across southern Bainbridge Island,
through southern Seattle and southern Mercer Island,
to east of Issaquah.21 The fault forms a zone that
ranges from about three to four miles wide. The
southern mapped limit of the fault zone is located
about three miles north of the study area. Geologic
studies of the Seattle fault indicate that the most
recent large earthquake on the Seattle fault was an
M 7.0+ event about 1,100 years ago.22 The fault may
have had at least five more major earthquakes in the
prior 12,000 years.23
Historical earthquakes
The historical record shows that earthquake
magnitude and frequency is moderate to high in the
vicinity of the study area.24 Between 1891 and 2005,
twenty-six major earthquakes occurred within about 95
miles of the study area.
20 U.S. Geological Survey, 2003, Largest Earthquake in Washington, Near Lake Chelan, Washington, 1872 12 15 05:40
UTC (local (12/14), Magnitude 7.3.
21 Blakely et al., 2002, Location, structure, and seismicity of the Seattle fault zone, Washington: Evidence from
aeromagnetic anomalies, geologic mapping, and seismic-refection data.
22 Bucknam et al., 1992, Abrupt Uplift Within the Past 1700 Years at Southern Puget Sound, Washington.
23 Sherrod, 2003, Update on Active Holocene Faults: U.S. Geological Survey National Earthquake Program, Update on
Current USGS Earthquake Hazards Studies in Puget Sound.
24 U.S. Geological Survey, 2005, NEIC: Earthquake Search Results for 1568-2005, 150 km Radius About 47.468N and
122.224W.
Why does the source of an
earthquake matter?
The deeper an earthquake occurs,
the less energy reaches the surface.
Thus crustal earthquakes will tend to
cause much stronger shaking than
deep, intraplate earthquakes. For
example, the 2001 M 6.8 Nisqually
earthquake occurred in the intraplate
region, and it caused relatively little
damage. In contrast, the 1995 M 6.9
Kobe, Japan earthquake occurred on
a crustal fault similar to the Seattle
fault. The Kobe earthquake resulted
in the deaths of over 5,000 people
and about $200 billion in property
damage.
EXISTING CONDITIONS
Renton Nickel Improvement Project
Soils, Geology, and Groundwater Discipline Report 31
The largest historical earthquake within about 95 miles
of the study area was the 1949 intraplate M 6.9
Olympia earthquake. The closest major historical
earthquake to the site was the 1965 M 6.7 Seattle
earthquake, which was also a deep, intraplate event.
What are geologic hazards and do any occur in the study
area?
In the context of this discipline report, a geologic
hazard is a geologic condition that can adversely
affect project design or construction. It also includes
conditions that can cause the project construction or
operation to result in an adverse effect on adjacent
properties or resources. Two examples of such an
event might include: a large earthquake inducing
loose, saturated soil to liquefy, causing settlement and
damage to the highway; or pumping water out of a
trench dug for utility work in compressible ground
causing settlement of adjacent properties.
As will be discussed later in this report, WSDOT
practices routinely deal with these hazards to
eliminate or mitigate adverse construction and
operation effects.
Based on our data review, we identified the following
geologic hazards that may be encountered within the
study area:
Liquefaction hazard areas.
Soft ground areas (seismic amplification, high
settlement potential, poor foundation support).
Potential settlement in abandoned mine areas.
Lahar hazard areas.
Areas of high erosion potential.
Areas of shallow groundwater.
We also assessed the potential for landslide hazard
areas by reviewing stereographic aerial photographs,
LiDAR, WSDOT borehole logs, geologic maps and the
WSDOT slope stability database. We did not identify
any potential landslide hazard areas from our review.
In addition, the proposed project does not involve
substantial cuts. Thus, landslides are not considered
a geologic hazard for this project.
EXISTING CONDITIONS
Renton Nickel Improvement Project
32 Soils, Geology, and Groundwater Discipline Report
Liquefaction hazard areas
Under the influence of strong earthquake shaking, soil
liquefaction can occur in saturated, loose, granular soil
(sand, silty sand, and sandy silt). These soils occur
within the alluvium and non-engineered fill in the study
area. The effects of liquefaction can be loss of
foundation support, excessive settlement, buoyancy
(floating) of underground utilities and facilities, and
lateral spreading. Lateral spreading is a process
where liquefied ground cannot support ground slopes
or embankments. The ground literally flows downhill,
resulting in large lateral movements and ground
cracking.
A study conducted in the spring of 2005 to evaluate
the liquefaction potential specifically for the project
concluded that liquefaction prone soils underlay the
majority of the project.25 Exhibit 12 depicts the relative
potential of soils underlying the study area to liquefy.26
The highest potential for liquefaction is found in
alluvial soil, especially in filled former stream
channels, such as the former stream channels that
cross I-405 at approximately MP 1.75, MP 1.8, and
MP 2.1. The majority of the study area is underlain by
soils with a “moderate to high” potential for
liquefaction. Other geologic units underlying the study
area, such as till, bedrock, or organic soils have a very
low potential to liquefy.
25 GeoEngineers, 2005, Geotechnical Engineering Services; South Renton Liquefaction Evaluation; I-405 South Renton
Segment; Renton, Washington.
26 Palmer et al., 2004, Liquefaction Susceptibility Map of King County. Washington Division of Geology and Earth
Resources.
Liquefaction and lateral spreading of soil
near Olympia caused by the 1965 Seattle
earthquake
What is liquefaction?
Liquefaction usually occurs in
saturated, loose, granular soil such
as sand, silty sand, and sandy silt.
During a strong earthquake, these
soils lose their grain-to-grain contact
and essentially become slurry with
characteristics like quicksand.
EXISTING CONDITIONS
Renton Nickel Improvement Project
Soils, Geology, and Groundwater Discipline Report 33
Exhibit 12. Liquefaction Potential in the Study Area
Source: Palmer et al., 2004
Soft ground areas - earthquake shaking
amplification
Strong seismic ground shaking can be made more
damaging to structures by the effects of deep, soft
ground. Soft ground can act like a “bowl of jello”
increasing ground acceleration and movement at the
surface. Geologists have long observed that
earthquake-induced ground shaking is much stronger
in areas underlain by thick soft or loose soil, than in
areas underlain by shallow, firm ground or bedrock.
EXISTING CONDITIONS
Renton Nickel Improvement Project
34 Soils, Geology, and Groundwater Discipline Report
National Earthquake Hazard Reduction Program
(NEHRP) ratings range from A to F, with A
representing hard bedrock, and F representing loose,
liquefiable soil or soft organic soil such as peat, as
summarized in Exhibit 13. The anticipated ground
shaking increases from A to F.
Exhibit 13. NEHRP Site Classes
Site Class Average Shear Wave Velocity in the upper
100 feet Rock or Soil Category
A Greater than 5,000 feet per second Hard bedrock
B 2,500 to 5,000 feet per second Soft bedrock
C 1,200 to 2,500 feet per second Very stiff soil (such as till) or soft rock
D* 600 to 1,200 feet per second Stiff soil
E* Less than 600 feet per second Soft
F Soils susceptible to failure under seismic
loading conditions, such as liquefiable soils,
sensitive clays, peat, organic clay, and thick
clay deposits
Special category indicating a geotechnical evaluation
should be performed to assess liquefaction potential
Modified from Palmer at al., 2004
* In the project area, class D and E soils should also be considered susceptible to liquefaction, based on GeoEngineers, 2005, and as shown on Exhibit 14
EXISTING CONDITIONS
Renton Nickel Improvement Project
Soils, Geology, and Groundwater Discipline Report 35
As shown on Exhibit 14, NEHRP class D to E soils
underlie the majority of the I-405 portion of the study
area, and NEHRP class F soils underlie the majority of
the SR 167 portion of the study area.27 Areas
underlain by class E or F are considered strongly
susceptible to severe ground shaking during an
earthquake.
Exhibit 14. NEHRP Site Classes in the Study Area
Source: Palmer et al., 2004
27 Palmer et al., 2004, see footnote 26.
EXISTING CONDITIONS
Renton Nickel Improvement Project
36 Soils, Geology, and Groundwater Discipline Report
Soft ground areas – compressible soil
Areas underlain by soft clay, silt, or highly-organic soil
such as peat can experience substantial settlements
near foundation or embankment loads. Exhibit 15
identifies areas of soft soils that are susceptible to
settlement.
The most highly-compressible soils underlie the
SR 167 portion of the study area. The combined
thickness of peat and organic silt underlying SR 167 in
the study area can exceed 15 feet. Embankment fills
placed for SR 167 south of the study area experienced
up to several feet of settlement.
The sediment underlying I-405 between SR 181 and
SR 167 generally consists of loose silt to gravel, with
scattered, relatively thin deposits of organics.
Scattered areas of the soil underlying I-405 between
SR 181 and SR 167 may be compressible, but are
likely to be much less compressible than the soil
underlying SR 167.
Soft areas – poor foundation support
Areas underlain by soft clay, silt, or highly-organic soil
such as peat are not suitable for supporting bridge or
wall loads. Areas of loose to compact granular soils
may not be suitable for supporting heavy foundation
loads such as those used for bridges. Thick fill
embankments placed on soft clay or highly-organic
soil, such as peat, can cause the embankment to fail.
Exhibit 15 identifies areas of soft soils that are
susceptible to settlement. Generally the soft clay, silt,
or highly-organic soils fall into the “Soft” areas on the
map. The loose to compact alluvial soils fall into the
“Moderately Soft” areas.
EXISTING CONDITIONS
Renton Nickel Improvement Project
Soils, Geology, and Groundwater Discipline Report 37
Exhibit 15. Soft Soil Locations in the Study Area
Based on Booth et. al., (2002), WSDOT borehole logs, and Bronson (1989).
EXISTING CONDITIONS
Renton Nickel Improvement Project
38 Soils, Geology, and Groundwater Discipline Report
Mine subsidence hazard areas
In the context of this discipline report, mine
subsidence is the collapse or excessive settlement of
the ground into an underground void space.
Settlement can occur rapidly, in a few minutes, or it
may manifest itself over months or years as a gradual
downwarping of the area above the void. Subsidence
typically occurs in areas underlain by shallow
abandoned coal mine workings. Methods historically
used in Washington State to mine coal often left
underground voids when the mine was abandoned.28
Considerable portions of the study area are underlain
by the Renton Formation which contains coal.
Commercial coal mining of the Renton Formation
began in 1874 with the opening of the Renton Coal
Mine and largely ceased in 1922, when the mine was
closed.29 Exhibit 16 depicts the approximate location
of the workings associated with the Renton Coal Mine.
Mr. William Strain reportedly continued to mine at this
location until 1933.29
Access to the mine was gained through a now
abandoned tunnel that underlies the current I-405 near
the Benson Road overpass. The tunnel was
encountered during the initial construction of I-405.
The tunnel opening at I-405 appeared to be at least
10-15 feet high, and it was partially filled with water.
The tunnel reportedly extended horizontally at least
another 1,000 feet underneath I-405, before dipping to
the east at about 15 degrees.30 According to
construction notes, the tunnel entrance was backfilled
with gravel and concrete.31 The construction notes do
not detail how far into the tunnel fill was placed (i.e.,
just at the entrance, 100 feet back, 200 feet back,
etc.). Based on our knowledge, the current I-405
roadway through this area has not experienced any
problems associated with the old mine tunnel.
28 Walsh and Logan, 1989, see footnote 9.
29 Walsh and Bailey, 1989, see footnote 9.
30 Renton Herald-Chronicle, 1962, Shovel uncovers Ancient Coal Mine Shaft: Mine Closed 45 Years Uncovered by
Road Men; October 2, 1963.
31 Washington State Department of Transportation, 1963, Construction notes from September 20 to October 7, 1963;
Contract # 0 07155.
Sample coal mining methods in Washington
Walsh and Logan, 1989
Entrance to the Renton Coal Mine, looking
east from the Benson Way Bridge, 1907.
Used by permission of the Renton Historical
Society.
EXISTING CONDITIONS
Renton Nickel Improvement Project
Soils, Geology, and Groundwater Discipline Report 39
Exhibit 16. Location of Coal Mine Workings near the Study Area
Modified from Walsh and Logan, 1989
EXISTING CONDITIONS
Renton Nickel Improvement Project
40 Soils, Geology, and Groundwater Discipline Report
Lahar hazard areas
A lahar is a rapidly flowing mixture of rock and water
originating at a volcano. A lahar hazard area is the
area that may be affected by a lahar. Lahars can
potentially cause catastrophic damage. The May,
1980 eruption of Mount St. Helens in southern
Washington State triggered lahars that destroyed 185
miles of roads and highways, 15 miles of railways, and
damaged or destroyed 27 bridges and 200 homes.32
Twice in the last 5,000 years, lahars have swept off
Mount Rainier and down the Green-Duwamish River
Valley.33 Rapid sediment deposition following the
Osceola mudflow approximately 5,000 years ago may
have advanced the shoreline of the Green-Duwamish
River bay as much as 31 miles.34
The probability of a lahar occurring during the design
lifetime of the Renton Nickel Improvement Project is
very low, since only two are thought to have occurred
within the study area in the last 5,000 years.
However, in the unlikely event of a large lahar, the
area that will be most likely affected is in the vicinity of
the Green River.
High erosion potential areas
A variety of surface soil types will be encountered in
the study area. While all soils have the potential to
erode, some soils have a much higher potential and,
consequently, require more effort to minimize erosion
during and after construction. Within the context of
this report, we consider erosion-prone soils (i.e., soils
that will require additional work to minimize erosion)
as soils rated as having a severe or very severe
erosion potential.35
The Soil Conservation Service rated the majority of the
soil units in the study area as having a slight to moderate
erosion potential. Soil units encountered in the study
area with a severe to very severe erosion potential
32 Topinka, 1997, Eruption Summary – May 18, 1980 Eruption of Mount St. Helens.
33 Pringle and Scott, 2001, see footnote 6.
34 Dragovich et al., 1994, see footnote 5; Pringle and Scott, 2001, see footnote 6.
35 USDA, 1973, Soil Survey, King County Area, Washington.
Dredging the Toutle River after the lahar
triggered by the May 18, 1980 eruption of Mt.
St. Helens
EXISTING CONDITIONS
Renton Nickel Improvement Project
Soils, Geology, and Groundwater Discipline Report 41
consist of weathered sandstone and glacial soils on
slopes of greater than 15 percent. Such occurrences are
found between the SR 167/ I-405 interchange and the
Cedar River. The relative erosion potential of near
surface soils in the study area is shown in Exhibit 17.
In areas where the project will involve moderate to deep
cuts, the data in Exhibit 17 have limited application
since they are based on the soils within the upper few
feet of the current ground surface. Areas where cuts
may encounter weathered rock and loose, granular
alluvium should be considered to have a high erosion
potential.
Exhibit 17. Erosion Potential of Soil Units in the Study Area
U.S. Department of Agriculture Soil Conservation Service, 1973
EXISTING CONDITIONS
Renton Nickel Improvement Project
42 Soils, Geology, and Groundwater Discipline Report
Shallow groundwater areas
The presence of shallow groundwater can require
additional construction measures, such as dewatering
trenches that will be dug for utilities and highway cuts. It
can be reasonably expected that excavations will
encounter shallow groundwater between the SR 181/I-405
interchange and the SR 167/ I-405 interchange on I-405,
and between the SR 167/ I-405 interchange and SW 41st
Street on SR 167. Areas that have been previously filled,
such as those where previous construction of I-405 or
nearby buildings has taken place may have a deeper
water table, depending on the thickness of the fill. Exhibit
18 displays areas where shallow groundwater is likely to
be encountered in the study area.
Exhibit 18. Likely shallow Groundwater Areas in the Study Area
Modified from Booth et al., 2002
What is shallow groundwater?
In the context of this report, shallow
groundwater is fully saturated soil
encountered at depths of less than 10
feet.
EXISTING CONDITIONS
Renton Nickel Improvement Project
Soils, Geology, and Groundwater Discipline Report 43
What groundwater resources are located in the study area?
Groundwater aquifers in the study area occur primarily
in shallow alluvial sediments. Alluvial sediments in the
study area consist primarily of sand, silt, and gravel.
Renton Formation bedrock underlies the alluvial
sediments. The bedrock is saturated and contains
groundwater, but it is considered to be an area
aquitard, or low permeability basement to the
overlying aquifers within the glacial and alluvial
sediments. Locally, bedrock can yield useable
quantities of water where substantial weathering or
fracturing has occurred. Depth to bedrock varies
considerably. Bedrock outcrops in the study area
along the south bluffs of the Cedar River and along
the north side of the study area between the Green-
Duwamish River and I-5. The bedrock is more than
100 feet deep between SR 167 and SR 181.36
Bedrock, overlain by alluvial sediments, may be
encountered at relatively shallow depths near the
western portion of the study area.
Groundwater, from the Renton Formation bedrock,
accumulates in the abandoned Renton Coal Mine
tunnel. The groundwater discharges to a wetland
below Benson Road.
Groundwater can be encountered in glacial deposits.
The coarse-grained and less consolidated sediments
commonly associated with recessional outwash
deposits typically have a relatively high permeability
and can be productive aquifers. Recessional outwash
deposits underlie the study area near Benson Road
and south of the Cedar River. However, the relatively
small area and thickness of the recessional deposits
within the study area limit the amount of available
groundwater. Glacial till is a highly consolidated
deposit that typically has a low permeability and is not
considered to be an aquifer.
Wetland deposits are present in the study area
adjacent to SR 167. These wetland deposits are fine-
grained and contain high amounts of organic material.
Wetland deposits can be relatively thick, but they
36 Galster and Laprade, 1991, see footnote 3.
What is an aquifer?
An aquifer is a unit of saturated geologic
materials that are capable of producing
useable quantities of groundwater on a
long-term, sustainable basis.
What do you mean by saturated?
Saturated means that all pore or open
spaces in a geologic material are
completely filled with groundwater at or
greater than atmospheric pressure.
Saturated thickness is an indication of
the amount of water that may be
available. The greater the saturated
thickness for a geologic material, the
greater the potential amount of
groundwater that may be available.
What is permeability?
Permeability is a measure of a soil or
rock’s ability to transmit water. Soils
such as clean sands and gravel have a
high permeability. Excavations below the
groundwater table in these types of
materials will encounter heavy seepage
flows requiring high capacity pumps to
dewater. At the other extreme, soils
such as clay and silty, very dense tills
have a low permeability. Excavations
below the groundwater table in these
types of materials will encounter little, if
any seepage.
EXISTING CONDITIONS
Renton Nickel Improvement Project
44 Soils, Geology, and Groundwater Discipline Report
typically do not produce large quantities of
groundwater and, thus, are not considered aquifers.
What aquifers are present in the study area?
Most of the groundwater resources in the study area
exist within sediment deposits along the Cedar River
and Green-Duwamish River valleys. The extent of
shallow aquifers closely correlates with the extent of
shallow groundwater, as is shown in Exhibit 18.
Green-Duwamish alluvial aquifer
The Green-Duwamish River Valley Aquifer is an
unconfined aquifer system consisting of interbedded
loose to dense silty sand with organics and scattered
gravel layers, soft peat, organic silt, soft to stiff silt,
and clay.37 Thickness of these sediments vary but can
be over 100 feet.
Groundwater is shallow in this aquifer, often at less
than 10 feet below ground surface, but varies
considerably with surface topography and season. In
many places, the water table is at or near land surface
and is hydrologically connected to wetlands. The
permeability of this aquifer is variable. Locally, where
silt or clay-rich layers have accumulated, the aquifer
has a low permeability and may not yield much
groundwater. No Group A or Group B groundwater
supply wells are receiving water from this aquifer
within 0.5 miles of the study area.38
Groundwater flow in the Green-Duwamish River
Valley Aquifer is complex. The presence of wetlands
and drainage ditches locally influences groundwater
flow patterns. The primary discharge is to the Green-
Duwamish River, but some groundwater may also
discharge to the Delta Aquifer and Lake Washington.
Direct infiltration from precipitation recharges this
aquifer, but recharge can also occur from higher
elevation areas within the Green-Duwamish River
drainage, and from overland flow from the bordering
valley hills.
37 GeoEngineers, 2005, Geotechnical Baseline Report; I-405, I-5 to SR 169; Nickel Package (South Renton); Renton,
Washington.
38 King County, 2005, IMAP Web Site.
What is an unconfined aquifer?
An unconfined aquifer is usually a
relatively shallow aquifer that can be
recharged directly by downward seepage.
An unconfined aquifer is called this
because the aquifer is not overlain by a
thick, low permeability layer, such as a
thick deposit of clay.
A simplified view of the water cycle showing
how infiltration recharges groundwater
EXISTING CONDITIONS
Renton Nickel Improvement Project
Soils, Geology, and Groundwater Discipline Report 45
Cedar Valley sole-source aquifer
The most important aquifer in the study area exists
along the Cedar River, known as the Cedar Valley
Aquifer. The Cedar Valley Aquifer is an EPA-
designated “Sole-Source Aquifer.”
This aquifer has been subdivided into several smaller
aquifer units. The Delta Aquifer subunit is located
along the lower drainage of the Cedar River and is the
closest to the I-405 project. The Delta Aquifer is
unconfined and composed of alluvial sediments
deposited by the lower Cedar River. Other
subdivisions of this system include the Cedar Valley
Alluvial Aquifer, the Marblewood Production Aquifer
and other aquifers further upvalley (i.e., the “Deep
Aquifer”). These other subdivisions are not discussed
in this report.
The Delta Aquifer occurs within the Cedar River Valley
between bedrock exposures to the south of the Cedar
River and glacial uplands along the north side of the
valley. Its western boundary in the study area is Lake
Washington, and the eastern boundary is located
upriver from the study area. The depth to the water
table varies, but it is generally shallow (less than 25
feet) in the vicinity of the study area. The Delta
Aquifer has a saturated thickness of between 65 and
90 feet.39 The Delta Aquifer is recharged by infiltration
from the flow of surface water and groundwater
originating at the bordering hills within its drainage
basin and groundwater flow from underlying bedrock.
The Delta Aquifer discharges to groundwater supply
wells, to the Cedar River, and to Lake Washington.
Groundwater flow in the Delta Aquifer is predominantly
along the valley from east to west. Local drawdown
depressions around the City of Renton production
wells exist and capture most of the groundwater
flowing through the aquifer. Exhibit 19 shows
modeled groundwater capture zones in the Delta
Aquifer for 1-year, 5-year, and 10-year travel times
(City of Renton, 1999).
39 RH2 and Pacific Groundwater Group, 1993, Renton Groundwater Model Design, Development, and Calibration Final
Draft Report.
What are Sole-Source Aquifers?
Sole Source Aquifers are U.S. EPA-
designated aquifers where few or no
reasonable alternatives exist for
acquiring drinking water.
EXISTING CONDITIONS
Renton Nickel Improvement Project
46 Soils, Geology, and Groundwater Discipline Report
Exhibit 19. 1-year, 5-year, and 10-year Groundwater Travel Times for the City of
Renton’s Well Field in the Delta Aquifer
City of Renton, 1999
What are the uses of groundwater in the study area?
Groundwater within the study area has multiple uses,
such as groundwater rights and groundwater wells.
Specific uses are discussed below.
Groundwater rights
Groundwater is extracted and used for water supply
along the study area. Groundwater certificates and
permits for use that have a point of withdrawal within
0.5 miles of the Renton Nickel Improvement Project
are listed Appendix A.40 Appendix A does not list
surface water rights, but it does include water
certificates and permits for springs, since springs
represent groundwater discharges.
Groundwater wells
Many documented water supply wells exist within 0.5 miles
of the study area. Existing groundwater wells in the study
40 Ecology, 2005, Washington State Department of Ecology Water Rights Application Tracking System (WRATS)
Database, January 2005.
What are Group A and B wells?
Group A wells serve 15 or greater
households. Group B groundwater supply
wells serve between 2 and 14
households.
EXISTING CONDITIONS
Renton Nickel Improvement Project
Soils, Geology, and Groundwater Discipline Report 47
area are shown on Exhibit 20 and identify Group A, Group
B, and other types of groundwater wells.41 The “other”
types of wells are primarily monitoring wells, dewatering
wells used for construction, and decommissioned wells, as
identified in Ecology’s database.
Exhibit 20. Groundwater Wells in the Vicinity of the Study Area
King County, 2005
The location of all Group A and Group B classified
groundwater supply wells within the study area is
illustrated on Exhibits 19 and 20.42 No Group B-
41 King County, 2005, see footnote 39.
42 King County, 2005, see footnote 39.
EXISTING CONDITIONS
Renton Nickel Improvement Project
48 Soils, Geology, and Groundwater Discipline Report
designated wells in the study area will be affected by
the proposed project. All Group A wells in the study
area are owned and operated by the City of Renton.
Six Group A wells within 0.5 miles of the I-405
Corridor extract groundwater from the Delta Aquifer.
The Delta Aquifer is the primary aquifer Renton uses
for municipal purposes.
The Green-Duwamish River Valley Aquifer near the
study area is not used for water supply by water
purveyors for Group A or Group B wells systems. The
wells shown on Exhibit 20 in the “other” category
consist primarily of decommissioned wells,
environmental monitoring wells not used for potable
supply, and dewatering wells used on a temporary
basis during construction. According to a search of
Ecology’s database, none of the “other” wells within
the project right-of-way are used for domestic water
supply or irrigation purposes.
Are there critical/sensitive areas for groundwater
protection?
One of the primary purposes of this report is to identify
areas that are particularly susceptible to groundwater
contamination. These areas are identified because
they currently supply or can supply water for drinking
and industrial uses, and they are hydrologically
connected to bodies of surface water, such as lakes or
rivers. Specific areas and their conditions are
discussed below.
Critical recharge areas
King County designates certain areas of aquifers as
“critical aquifer recharge areas.” These areas are
more susceptible to groundwater contamination
because the depth to groundwater is shallow; a
surficial low permeability protective layer does not
exist; and the aquifers are critical for supply and use.
Exhibit 21 shows critical aquifer recharge areas within
the study area. These areas are subdivided by their
relative susceptibility to contamination into
designations of low, medium, and high.43
43 King County, 2005, see footnote 39.
EXISTING CONDITIONS
Renton Nickel Improvement Project
Soils, Geology, and Groundwater Discipline Report 49
Exhibit 21. Critical Recharge Areas in the Vicinity of the Study Area
King County, 2005
Cedar Valley sole-source aquifer
The City of Renton petitioned the U.S. Environmental
Protection Agency (EPA) for designating the aquifer
along the Cedar River as a sole-source aquifer in
March 1988.44 The petition was submitted because
44 CH2M Hill, 1988b, Final Sole-Source Aquifer Petition for The Cedar River Aquifer.
EXISTING CONDITIONS
Renton Nickel Improvement Project
50 Soils, Geology, and Groundwater Discipline Report
the City’s water supply to the public is dependent on
this aquifer. The Cedar Valley Aquifer was designated
a sole-source aquifer on October 17, 1988 by the
EPA, supporting the goals of aquifer protection
previously initiated by the City.45 The EPA states the
reasons for designation as follows:
The Cedar Valley Aquifer supplies at least 80
percent of the drinking water used in the
aquifer service area.
No economically feasible alternative drinking
water sources exist.
Contamination of the aquifer would pose a
substantial hazard to public health.
The Cedar Valley Aquifer boundary within the study
area is shown in Exhibit 22. As discussed previously,
the Delta Aquifer subunit is most relevant to potential
effects from the I-405 project.
The City of Renton has a well system for the
extraction of groundwater for public supply. Exhibit 19
shows the City’s production wells, which include: wells
1, 2, 3, PW 8, and PW 9. In addition, Renton has
emergency production wells designated as EW. The
City has numerous groundwater monitoring wells
surrounding its production wells for aquifer testing and
water quality monitoring. All production wells are
located within the designated sole-source aquifer.
45 U.S. Environmental Protection Agency, 1988, Sole Source Aquifer Designation of the Cedar Valley Aquifer, King
County, WA.
EXISTING CONDITIONS
Renton Nickel Improvement Project
Soils, Geology, and Groundwater Discipline Report 51
Exhibit 22. Boundaries of the Cedar Valley Sole-Source Aquifer in the Vicinity of the
Study Area
City of Renton, 2003 and Federal Register, October 3, 1988
Are there specific ordinances to protect the Cedar Valley
Aquifer?
The Cedar Valley Aquifer (known as the Delta Aquifer
in the study area) supplies drinking water to the City of
Renton. Because the aquifer is highly susceptible to
contamination, the City has conducted studies and
passed ordinances designed to protect the Cedar
Valley Aquifer. These studies and ordinances are
discussed below.
Capture zones and travel times
The City of Renton conducted a study of groundwater
travel times being captured by its production wells to
formulate wellhead protection areas for its wells. The
results are presented in Exhibit 19 for 1-year, 5-year
and 10-year groundwater capture zones.
Groundwater capture travel times are used for aquifer
protection planning.
What are Wellhead Protection Areas?
Wellhead Protection Areas (WHPA) are
the areas surrounding a drinking water
well that supply groundwater to the well.
The boundary of the WHPA is determined
by the distance a contaminant travels in
a designated time period. For instance, a
5-year WHPA is the distance from a well
where a contaminant released into the
groundwater would take 5 years to reach
the well.
EXISTING CONDITIONS
Renton Nickel Improvement Project
52 Soils, Geology, and Groundwater Discipline Report
Aquifer protection ordinances
The City of Renton established Aquifer Protection
Zones for the Sole-Source Cedar Valley Aquifer and
its production well fields. Exhibit 23 presents the
Cedar Valley Aquifer Protection Zone 1 and 2
boundaries. Renton enacted local ordinances
specifically for the protection of its sole-source aquifer
and production well fields within the Zone 1 and 2
boundaries. The ordinances are specific to the aquifer
protection zones and are in the Renton Municipal
Code.46 The code specifies construction requirements
for stormwater facilities and pipelines, sewer pipelines,
storage limitations for hazardous/toxic substances and
other requirements for activities within the aquifer
protection zones.
Exhibit 23. Cedar Valley Sole-Source Aquifer Zone 1 and Zone 2 Groundwater
Protection Zones
City of Renton, 1999
46 Renton, City of, 2005, Renton Municipal Codes (RMC) http://www.ci.renton.wa.us/.
EXISTING CONDITIONS
Renton Nickel Improvement Project
Soils, Geology, and Groundwater Discipline Report 53
What is the quality of groundwater in the study area?
The Delta Aquifer portion of the designated Sole-
Source Cedar Valley Aquifer produces good quality
water for potable use. The groundwater meets all
Washington State Department of Health water quality
criteria.
The seep discharge of groundwater from the
abandoned Renton Coal Mine tunnel adjacent to the
study area has a “sulfur type” smell and is of
questionable quality. We have not found a report that
contains water quality analysis of the discharge from
the coal mine tunnel.
Renton Nickel Improvement Project
54 Soils, Geology, and Groundwater Discipline Report
POTENTIAL EFFECTS
What methods were used to evaluate the project’s
potential effects?
The methods used to evaluate the project’s potential
effects included:
Reviewing the proposed project design
concept and likely construction methods.
Evaluating the potential effects of the geology,
soils and groundwater on the project, based on
the existing site conditions and standard
WSDOT practices, including the avoidance
measures listed in the Measures to Avoid or
Minimize Project Effects section.
Evaluating the potential effects of the project
on the geology, soils and groundwater, based
on the existing site conditions and standard
WSDOT practices, including the avoidance
measures listed in the Measures to Avoid or
Minimize Project Effects section.
The evaluations are based primarily on our
experience, our expert judgment, and WSDOT
practices and sound engineering principles.
WSDOT’s 2005 Geotechnical Design Manual (GDM)
discusses many WSDOT design and construction
practices.
Could soils, geology, or groundwater affect project
construction?
The presence of liquefaction prone soils (see Exhibit
12) under the majority of the project, in combination
with current requirements as set forth in the WSDOT
GDM and Bridge Design Manual, have caused us to
redesign the project. Our original plan for the Renton
Nickel Improvement Project involved adding additional
lanes over six bridges between Lind Avenue and the
Green River. These six bridges are underlain by
liquefaction prone soils. Existing bridges underlain by
liquefaction prone soils would require extensive
modifications if they are widened. Because of the cost
and difficulty in replacing or widening all six bridges to
add additional lanes, the design of the project has
been revised.
POTENTIAL EFFECTS
Renton Nickel Improvement Project
Soils, Geology, and Groundwater Discipline Report 55
We have redesigned the project to eliminate or
minimize the number of bridges that will be widened.
Additional lanes will be provided over some of these
existing bridges by reducing the width of the traffic
lanes and the width of the shoulders on the existing
bridges. These bridges will be restriped instead of
widened.
Some of the bridges will be replaced instead of
widened. The new bridges will be designed to current
seismic standards and founded on deep piles to avoid
damage from soil liquefaction during an earthquake.
In accordance with the WSDOT GDM, if a retaining
wall is greater than 10 feet in height and within 10 feet
of the roadway, then the wall will be founded on deep
piles or the soils under the wall will be improved using
measures such as compaction grouting. Because of
the design changes to the project, the presence of
liquefaction-prone soils constitutes a substantial effect
on the project.
Other conditions along the alignment are not unusual for
the Puget Sound area and generally present construction
conditions WSDOT routinely encounters. WSDOT has
managed these types of conditions on other projects,
including the original construction of I-405.
Could soils, geology, or groundwater affect project
operation?
The conditions along the alignment are not unusual for
the Puget Sound area and generally present
conditions routinely encountered by WSDOT in their
design, operation and maintenance plans. Once
construction is complete and the highway is in use,
soils, geology, and groundwater should have
essentially no effects on the project.
Will project construction temporarily affect geology, soils,
and groundwater?
The anticipated construction conditions along the
alignment are not unusual for the Puget Sound area.
These types of conditions are routinely encountered
by WSDOT and resolved with implementation of
standard BMPs (best management practices).
Relevant construction conditions along the study area
include:
Disturbance of moisture sensitive soils.
What are BMPs?
BMPs stand for Best Management
Practices. BMPs is a generic term for
practices which are considered to be
the industry standard, and which have
a proven track record of success.
What are soil improvements?
Soil improvements are measures which
increase the density and/or cohesion of
soil. Soil improvements are usually
conducted to lower the risk that
structures will be damaged by
liquefaction during an earthquake or from
settlement of soft, compressible soils.
POTENTIAL EFFECTS
Renton Nickel Improvement Project
56 Soils, Geology, and Groundwater Discipline Report
Increased erosion potential. and,
Vibration effects of construction equipment.
Moisture-sensitive soils
Most of the soils that will be encountered during
construction are moisture sensitive. These soils
include alluvium, till, weathered bedrock, and existing
embankment fills.
Heavy earthmoving equipment tracking on moisture-
sensitive soils during wet weather, in areas of
seepage, or in areas of shallow groundwater will tend
to degrade the subgrade into a soft, unstable material.
WSDOT and the local earthmoving contractors are
aware of these types of conditions and routinely use a
variety of methods to minimize adverse effects. These
methods are described in the Measures to Avoid or
Minimize Project Effects section.
Increased erosion
The majority of the soil types in the study area are
susceptible to erosion, as discussed previously.
Erosion risk is usually assessed by looking at the
steepness of a slope in combination with the soil type.
The relative potential for soils to erode is shown on
Exhibit 17. However, since hillside cuts create a steep
slope during construction, cut areas, even if not rated
as having a high erosion risk, can become susceptible
to erosion.
In addition, fill placed to widen existing embankments
may also be susceptible to erosion. Fill, particularly
when stockpiled prior to being placed during
construction, can be eroded during a storm event.
Erosion will be minimized, but not completely
eliminated, through the implementation of BMPs.
BMPs to reduce erosion are described in more detail
in the Measures to Avoid or Minimize Project Effects
section.
Vibration effects of construction
equipment
Any large construction project will cause ground
vibrations due to the use of heavy equipment.
Sources of construction ground vibrations might
include:
Heavy earthmoving equipment including
trucks, and
What do you mean by subgrade?
The subgrade is the in-place material on
which the pavement or embankment fills
are placed.
A scraper stuck in the mud demonstrates a
negative effect of working in moisture-
sensitive soils if BMPs are not properly
implemented
POTENTIAL EFFECTS
Renton Nickel Improvement Project
Soils, Geology, and Groundwater Discipline Report 57
Large cranes used to install deep foundations,
particularly driven piles.
Will the project permanently affect geology, soils and
groundwater?
In general, there will be essentially no adverse
permanent effects from the project related to soils,
geology or groundwater, except for a slight increase in
impervious surfaces. The planned increase in
impervious surfaces are small and will not
substantially affect the total amount of recharge to the
shallow alluvial aquifers in the vicinity of the project,
since the vast majority of recharge to these aquifers
are derived from upgradient drainage areas. No new
construction will take place over the Cedar Valley
Aquifer APA Zone 1 or Zone 2, and thus there should
be no effects on the aquifer from this project.
Does the project have delayed or distant effects?
Based on our review, there will not likely be any
delayed or distant effects to soils, geology, or
groundwater caused by the project.Were cumulative effects looked at for
this discipline?
The team did not evaluate cumulative
effects for this discipline report. A report
of cumulative effects is not needed for
every discipline studied for NEPA and
SEPA documentation. The disciplines
that were studied for cumulative effects
are Air Quality, Surface Water and Water
Quality, Fisheries and Aquatic Habitat,
and Wetlands. The cumulative effects for
these disciplines are presented in the
Cumulative Effects Analysis Discipline
Report.
Renton Nickel Improvement Project
58 Soils, Geology, and Groundwater Discipline Report
MEASURES TO AVOID OR
MINIMIZE PROJECT EFFECTS
What has been done to avoid or minimize negative effects
from the project?
The majority of potential negative effects associated
with the construction and operation of the project will
be avoided or minimized through the use of BMPs and
from following the procedures outlined in the WSDOT
GDM and Bridge Design Manual. Contractors and
consultants associated with this project will follow
these procedures. A brief summary of these
procedures is listed below:
WSDOT will prepare and implement a
temporary erosion and sedimentation control
(TESC) plan. A TESC plan consists of
operational and structural measures to control
the transport of sediment. Operational
measures consist of good housekeeping
practices, such as removing mud and dirt from
trucks before they leave the site, covering fill
stockpiles or disturbed areas, or avoiding
unnecessary vegetation clearing. Structural
measures consist of the construction of
temporary structures to reduce the transport of
sediment, such as silt fences or sediment
traps. Should any BMP or other operation not
function as intended, WSDOT will take
additional action to minimize erosion and
maintain water quality.
WSDOT will reduce degradation of moisture-
sensitive soils by maintaining proper surface
drainage to avoid ponding of surface water or
groundwater; by minimizing ground
disturbance through limiting the use of heavy
equipment, limiting turns, and/or not tracking
directly on the subgrade; and by covering the
final subgrade elevation with a working mat of
crushed rock and/or geotextile for protection.
A soil admix such as cement may also be
mixed into the subgrade to add strength and
stabilize the ground.
If WSDOT identifies areas where dewatering
will be necessary for utility work, then WSDOT
will take steps to minimize the potential
What is a silt fence? Sediment trap?
A silt fence consists of a temporary
sediment barrier made of synthetic fabric
stretched between posts, with a shallow
trench located upslope. The silt fence is
“keyed” into the ground to prevent water
from running under the fence. A
sediment trap consists of a temporary
ponding area formed by an earthen
embankment or an excavation. Both silt
fences and sediment traps are designed
to slow the flow of water, allowing
sediment to settle out.
What is an admix?
An admix is a product, such as cement or
kiln dust, that is mixed into soil to
improve the characteristics of the soil,
such as workability and compactability.
MEASURES TO AVOID OR MINIMIZE PROJECT EFFECTS
Renton Nickel Improvement Project
Soils, Geology, and Groundwater Discipline Report 59
settlement effects. These steps may include
recharge wells and/or cut-off shoring walls, as
well as surveying adjacent properties to
monitor for settlement.
Many areas of the project may be underlain by
soft ground conditions. During the design
process, WSDOT will assess potential
settlement problems associated with existing
utilities or structures and design appropriate
solutions, such as underpinning of structures
or relocation of utilities.
We identified a coal mine tunnel near Benson
Road. WSDOT will design the project to avoid
adverse settlement or subsidence effects from
the tunnel. If necessary, avoiding settlement
or subsidence may be accomplished by
bridging over the tunnel with a structural slab
or by adding fill to the tunnel.
Large construction projects will cause ground
vibrations as a result of heavy equipment use.
WSDOT will determine acceptable limits for
off-site construction related vibration before the
beginning of construction. WSDOT will
demonstrate that off-site ground vibrations are
within the limits set for the project through the
use of vibration monitoring equipment.
New bridges underlain by liquefaction prone
soils will be designed to current seismic
standards. The bridges will be founded on
deep piles and/or the soil under the bridges will
be improved. Soil improvement measures will
likely consist of compaction grouting. These
measures will be implemented to minimize
damage during an earthquake. WSDOT will
select measures that will minimize the effect on
adjacent properties.
Retaining walls that will be constructed in the
Green-Duwamish River Valley (all of SR 167
and I-405 between SR 181 and Lind Avenue)
are planned for locations underlain by
liquefaction-prone soils. In accordance with
the WSDOT GDM, if a retaining wall is greater
than 10 feet in height and within 10 feet of the
roadway, then the wall will be founded on deep
piles or the soils under the wall will be
improved using measures such as compaction
grouting. WSDOT will select measures that
will minimize the effect on adjacent properties.
What is compaction grouting?
Compaction grouting is a method of
improving the soil by injecting a thick
grout into the soil, causing the soil to
become denser. The higher density of
the soil causes it to be less susceptible
to liquefaction and shaking during an
earthquake.
MEASURES TO AVOID OR MINIMIZE PROJECT EFFECTS
Renton Nickel Improvement Project
60 Soils, Geology, and Groundwater Discipline Report
A large earthquake can damage existing
roads, utilities, and structures near new
embankment fills. WSDOT will identify these
areas and mitigate risks using ground
modifications or other procedures identified in
the WSDOT GDM.
Fuel and chemical storage and fueling
operations for construction vehicles and
equipment during construction will be located
within secondary containment areas. A spill
prevention control and countermeasures
(SPCC) plan will be established for
construction activities and will also detail the
procedures that will be followed in the event of
a spill to prevent or minimize effects. The
SPCC plan will specifically address potential
fuel spills from vehicles and potential spills of
chemicals that are commonly used during
construction. Spill response equipment will be
located at regular and specified intervals within
the project area for minimizing countermeasure
response times.
WSDOT will only import and place clean fill for
the project. Contaminated fill brought from
outside sources can contaminate shallow
aquifers. WSDOT will require documentation
for fill brought onto the site from the supplier
that the fill does not exceed Washington State
soil cleanup standards. If documentation is not
available, then WSDOT will require testing of
imported fill soils prior to placement. WSDOT
will test suspect soils encountered during
project construction. Where necessary,
WSDOT will require their removal from the site
and proper disposal in accordance with
Washington State regulations.
WSDOT will identify and develop staging areas
for equipment repair and maintenance away
from all drainage courses. WSDOT will require
that washout from concrete trucks not be
dumped into storm drains or onto soil or
pavement that carries stormwater runoff.
Thinners and solvents will not be used to wash
oil, grease, or similar substances from heavy
machinery or machine parts. WSDOT will
designate a washdown area for equipment and
concrete trucks.
WSDOT will be required to obtain a NPDES
(National Pollutant Discharge Elimination
System) permit. WSDOT will ensure that
MEASURES TO AVOID OR MINIMIZE PROJECT EFFECTS
Renton Nickel Improvement Project
Soils, Geology, and Groundwater Discipline Report 61
water encountered during construction meets
the standards specified in the NPDES permit
prior to the discharge of the encountered water
to a surface waterbody. If necessary, water
quality will be improved, such as by using
sediment ponds to allow sediment to settle out
prior to discharge.
WSDOT may need to install underdrains to
control seepage for retaining walls and fill
embankments. These underdrains may lower
the groundwater table in the immediate vicinity
of the project. In the unlikely scenario that the
effects from this drawdown could be adverse,
WSDOT will include special provisions in the
design, such as discharging drain flow back
into affected wetlands.
The new Southbound and northbound bridges
over Springbrook Creek and Oakesdale
Avenue will be configured to minimize the
impact of construction and columns on the
ordinary high water channel and the 100-year
flood channel of Springbrook Creek.
Could the project compensate for unavoidable negative
effects to soils, geology, and groundwater?
While WSDOT will avoid the majority of potential
effects from the project by standard WSDOT
procedures and implementation of BMPs, WSDOT will
likely face a few unavoidable negative effects, as
identified on pages 55 and 56. As discussed above,
WSDOT can reduce and largely control these effects,
however, WSDOT will not be able completely to
eliminate them.
Renton Nickel Improvement Project
62 Soils, Geology, and Groundwater Discipline Report
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APPENDIX A
Groundwater Rights Summary
Renton Nickel Improvement Project Soils, Geology, and Groundwater Discipline Report A-1 Exhibit A-1. Groundwater Rights Summary DOCUMENT NUMBER DOCUMENT TYPE PURPOSE LIST NAME PRIORITY DATE GPM ACRE FEET OLD CERTIFICATE NUMBER TRS G1-082020CL Claim Short Form DG JACK A. MCMILLEN T23N/R04E-13 G1-084194CL Claim Short Form DG PATRICIA E. PAOLINO T23N/R04E-14 G1-053628CL Claim Short Form DG EUGENE W. IVES T23N/R04E-14 G1-155270CL Claim Long Form DG IR CHARLES A FOX T23N/R04E-23 G1-155271CL Claim Long Form DG CHARLES A FOX T23N/R04E-23 G1-154945CL Claim Short Form DG DONALD A BUCKINGHAM T23N/R04E-23 G1-160407CL Claim Short Form IR FREDERICK J II PACK T23N/R04E-26 G1-160408CL Claim Short Form IR FREDERICK J II PACK T23N/R04E-26 G1-24191C Certificate MU Renton City 18-Oct-82 1,300 1,040 T23N/R05E-17 G1-*09985C Certificate MU Renton City 21-Jan-69 500 800 6776 T23N/R05E-17 G1-*09349C Certificate MU Renton City 01-Apr-68 3,000 4,839 6775 T23N/R05E-17 G1-*08040C Certificate MU Renton City 14-Apr-66 1,600 2,560 5835 T23N/R05E-17 Source: Washington State Department of Ecology Water Rights Application Tracking System Database, January 2005 GPM: gallons per minute TRS: Township-Range-Section DG: Domestic General IR: Irrigation MU: Municipal
APPENDIX A Renton Nickel Improvement Project Soils, Geology, and Groundwater Discipline Report A-2 Exhibit A-1. Groundwater Rights Summary (continued) DOCUMENT NUMBER DOCUMENT TYPE PURPOSE LIST NAME PRIORITY DATE GPM ACRE FEET OLD CERTIFICATE NUMBER TRS G1-*08041C Certificate MU Renton City 14-Apr-66 1,960 3,136 5836 T23N/R05E-17 G1-*08042C Certificate MU Renton City 14-Apr-66 960 1,536 5838 T23N/R05E-17 G1-*00816S Certificate MU Renton City 01-Jan-44 1,040 1,676 886 T23N/R05E-17 G1-*00817S Certificate MU Renton City 01-Jan-44 1,040 838 887 T23N/R05E-17 G1-134169CL Claim Short Form IR EDWARD PLUTE T23N/R05E-17 G1-155174CL Claim Short Form DG IR JAMES J ELVES T23N/R05E-19 G1-108233CL Claim Short Form IR MRS J R BUTLER T23N/R05E-19 Source: Washington State Department of Ecology Water Rights Application Tracking System Database, January 2005 GPM: gallons per minute TRS: Township-Range-Section DG: Domestic General IR: Irrigation MU: Municipal