HomeMy WebLinkAboutRS_Geology_Soils_Technical_Memo_TRIP_CA_171128_v1ATTACHMENT 6- GEOLOGY AND SOILS
TECHNICAL REPORT
I-405, Tukwila to Renton Improvement Project
(I-5 to SR 169 – Phase 2)
GEOLOGY AND SOILS
TECHNICAL MEMORANDUM
July 2007
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I-405, Tukwila to Renton Improvement Project (I-5 to SR 169 – Phase 2) Page i
Geology and Soils Technical Memorandum
July 2007
TABLE OF CONTENTS
SUMMARY..............................................................................................................................1
PROJECT DESCRIPTION......................................................................................................2
BUILD ALTERNATIVE...................................................................................................2
I-405 from I-5 to SR 181 Interchange....................................................................2
I-405 from East of SR 181 to SR 167 Interchange................................................3
SR 167 from I-405 to SW 43rd Street On-ramp ....................................................3
I-405 Interchange with SR 167..............................................................................3
I-405 from East of SR 167 Interchange to North of SR 169..................................4
NO BUILD ALTERNATIVE ............................................................................................4
BASELINE CONDITIONS.......................................................................................................5
WHAT ARE THE GEOLOGY AND SOILS OF THE STUDY AREA?.............................5
Soils.......................................................................................................................5
Geology.................................................................................................................5
Geologic Hazard Areas.........................................................................................6
POTENTIAL EFFECTS.........................................................................................................12
WILL THE PROJECT AFFECT SOILS OR GEOLOGY?.............................................12
WILL SOILS OR GEOLOGY AFFECT THE PROJECT CONSTRUCTION
OR OPERATION? .......................................................................................................12
Soils and Erosion ................................................................................................12
Landslide Hazard Areas......................................................................................12
Soft Ground Areas...............................................................................................13
Seismic Hazard Areas.........................................................................................13
Mine Subsidence Hazard Areas..........................................................................13
WHAT ARE THE UNAVOIDABLE ADVERSE EFFECTS?..........................................13
MEASURES TO AVOID OR MINIMIZE EFFECTS...............................................................13
WHAT WILL BE DONE TO AVOID OR MINIMIZE ADVERSE EFFECTS
FROM THE PROJECT? ..............................................................................................13
Vibration Effects of Construction Equipment.......................................................14
Erosion and Soils ................................................................................................14
Landslide Hazard Areas......................................................................................14
Soft Ground Areas...............................................................................................14
Seismic Hazard Areas.........................................................................................15
Mine Subsidence Hazard Areas..........................................................................15
ACRONYMS AND ABBREVIATIONS...................................................................................16
GLOSSARY..........................................................................................................................17
REFERENCES .....................................................................................................................20
GIS DATA SOURCES .................................................................................................20
TEXT REFERENCES ..................................................................................................21
APPENDIX A: METHODOLOGY........................................................................................22
HOW DID WE COLLECT INFORMATION ON GEOLOGY AND SOILS
FOR THIS REPORT? ..................................................................................................54
ii I-405, Tukwila to Renton Improvement Project (I-5 to SR 169 – Phase 2)
Geology and Soils Technical Memorandum
July 2007
Baseline Conditions Evaluation...........................................................................54
Potential Effects Evaluation.................................................................................54
List of Exhibits
Exhibit 1: Description of Soil Units.........................................................................................8
Exhibit 2: Description of Geologic Units...............................................................................11
Exhibit 3: Soil Units, Sheet 1................................................................................................22
Exhibit 4: Soil Units, Sheet 2................................................................................................24
Exhibit 5: Soil Units, Sheet 3................................................................................................25
Exhibit 6: Soil Units, Sheet 4................................................................................................26
Exhibit 7: Soil Units, Sheet 5................................................................................................27
Exhibit 8: Soil Units, Sheet 6................................................................................................28
Exhibit 9: Soil Units, Sheet 7................................................................................................29
Exhibit 10: Soil Units, Sheet 8..............................................................................................30
Exhibit 11: Surface Geologic Units, Sheet 1........................................................................31
Exhibit 12: Surface Geologic Units, Sheet 2........................................................................32
Exhibit 13: Surface Geologic Units, Sheet 3........................................................................33
Exhibit 14: Surface Geologic Units, Sheet 4........................................................................34
Exhibit 15: Surface Geologic Units, Sheet 5........................................................................35
Exhibit 16: Surface Geologic Units, Sheet 6........................................................................36
Exhibit 17: Surface Geologic Units, Sheet 7........................................................................37
Exhibit 18: Surface Geologic Units, Sheet 8........................................................................38
Exhibit 19: Geologic Hazard Areas, Sheet 1........................................................................39
Exhibit 20: Geologic Hazard Areas, Sheet 2........................................................................40
Exhibit 21: Geologic Hazard Areas, Sheet 3........................................................................41
Exhibit 22: Geologic Hazard Areas, Sheet 4........................................................................42
Exhibit 23: Geologic Hazard Areas, Sheet 5........................................................................43
Exhibit 24: Geologic Hazard Areas, Sheet 6........................................................................44
Exhibit 25: Geologic Hazard Areas, Sheet 7........................................................................45
Exhibit 26: Geologic Hazard Areas, Sheet 8........................................................................46
Exhibit 27: Soft Ground and Seismic Hazard Areas, Sheet 1..............................................47
Exhibit 28: Soft Ground and Seismic Hazard Areas, Sheet 2..............................................48
Exhibit 29: Soft Ground and Seismic Hazard Areas, Sheet 3..............................................49
Exhibit 30: Soft Ground and Seismic Hazard Areas, Sheet 4..............................................50
Exhibit 31: Soft Ground and Seismic Hazard Areas, Sheet 5..............................................51
Exhibit 32: Soft Ground and Seismic Hazard Areas, Sheet 6..............................................52
Exhibit 33: Soft Ground and Seismic Hazard Areas, Sheet 7..............................................53
Exhibit 34: Soft Ground and Seismic Hazard Areas, Sheet 8..............................................54
I-405, Tukwila to Renton Improvement Project (I-5 to SR 169 – Phase 2) Page 1
Geology and Soils Technical Memorandum
July 2007
Summary
The purpose of this technical memorandum is to present an assessment of the soils and geologic
conditions in the I-405, Tukwila to Renton Improvement Project (I-5 to SR 169 – Phase 2), referred to as
Tukwila to Renton Project. Describing the natural setting prior to construction is important because it can
be a major factor impacting project design (e.g., foundations, pavement sections, retaining walls, bridges,
etc.).
Identifying and evaluating possible impacts of the project on the geology and soils during the planning
stages allows the Washington State Department of Transportation (WSDOT) to develop mitigation
measures utilizing existing best management practices (BMPs) and procedures outlined in the WSDOT
Geotechnical Design Manual, dated December 2006, and the WSDOT Bridge Design Manual, dated
November 17, 2006. Possible mitigation measures include changing the alignment (avoidance),
designing project structures or components to accommodate the geologic and soils conditions, and
implementing protective measures and techniques that reduce impacts to environmental conditions.
The Tukwila to Renton Project lies in a heavily populated area located within the Green-Duwamish River
valley. The majority of the near-surface soil material in the study area along the I-405 and SR 167
corridors has been modified by the addition of fill material and is classified as Urban Land or Modified
Fill. The fill is underlain by relatively loose, soft soil with a shallow groundwater table. The local
surface geology in the study area also includes wetland deposits, glacial deposits, and sandstone bedrock.
The soils and geology in the project area combined with the topography result in several geologic hazards
along the corridor, including erosion, landslide, steep slope, soft ground, and coal mine subsidence
hazards.
The project will be constructed in a highly variable geologic environment. Potential project impacts on
the geology and soils during construction include disturbance of moisture sensitive soils, increased
erosion potential, and vibration effects of construction equipment; these issues are routinely encountered
by WSDOT and are resolved with the implementation of standard BMPs. The presence of erosion hazard
areas, soft ground areas, liquefaction-prone soils, and mine subsidence hazards may affect the project and
will be prominent design and construction considerations. WSDOT has managed these types of
conditions on several other projects, including the original construction of I-405. Once construction is
complete and the highway is in use, the built project will not affect the soils and geology.
The majority of potential adverse effects associated with the construction and operation of the project will
be avoided or minimized through the use of BMPs and by following the procedures outlined in the
WSDOT Geotechnical Design Manual, dated December 2006, and Bridge Design Manual, dated
November 17, 2006.
While WSDOT will avoid the majority of potential effects from the project on the geology and soils by
using standard WSDOT procedures and implementing BMPs, WSDOT will likely face a few unavoidable
adverse erosion effects.
2 I-405, Tukwila to Renton Improvement Project (I-5 to SR 169 – Phase 2)
Geology and Soils Technical Memorandum
July 2007
Project Description
WSDOT is proposing to construct the I-405, Tukwila to Renton Improvement Project (I-5 to SR 169 –
Phase 2), referred to as the Tukwila to Renton Project, to relieve congestion. Relieving congestion will
benefit the public by:
•Lowering the number of accidents, thus improving safety.
•Increasing overall speeds through this section of freeway.
•Improving response times for emergency service vehicles using I-405.
•Improving access to and from I-405 and local circulation.
The Tukwila to Renton Project extends approximately four and one-half miles along I-405, from I-5 to
SR 169, and approximately two miles along SR 167, from I-405 to SW 43rd Street. The project adds
capacity to both I-405 and SR 167; improves the SR 181 and SR 169 interchanges; reconstructs the
SR 167 interchange consisting of general-purpose direct-connector ramp from southbound I-405 to
southbound SR 167, HOV direct-connector ramps from northbound SR 167 to northbound I-405 and from
southbound I-405 to southbound SR 167, and a split-diamond interchange at Lind Avenue and Talbot
Road with connecting frontage roads. These improvements represent the second phase of the I-405
Corridor Program for this portion of I-405. The first phase consists of improvements in the Renton
Nickel Improvement Project, which is considered as the baseline condition for the Tukwila to Renton
Project.
The analysis in this technical memorandum describes the baseline conditions, how the project may affect
those conditions, and what measures will be taken to mitigate effects. To understand what improvements
are being proposed as part of this project, the following presents the main features of the Build
Alternative followed by a brief explanation of the No Build Alternative.
Build Alternative
The Tukwila to Renton Project improvements from west to east (northbound) along the study area are as
follows:
I-405 from I-5 to SR 181 Interchange
•Remove the existing northbound I-405 Tukwila Parkway on-ramp.
•Realign I-405 mainline slightly to the south beginning just west of the existing northbound I-405
Tukwila Parkway on-ramp to the SR 181 interchange.
•Improve the SR 181 interchange:
o Remove the existing SR 181 on-ramp to northbound I-405.
o Extend Tukwila Parkway from the intersection with 66th Avenue east over the Green River
to SR 181.
o Construct new northbound I-405 on-ramp from Tukwila Parkway just east of the new
crossing over the Green River (replaces the two existing on-ramps).
o Reconstruct the 66th Avenue S bridge over I-405 on a new alignment to the west and
reconstruct the intersections with Southcenter Boulevard and Tukwila Parkway.
o Reconstruct the off-ramp from northbound I-405 to SR 181.
o Improve local arterials within the interchange area such as Southcenter Boulevard and
Interurban Avenue.
I-405, Tukwila to Renton Improvement Project (I-5 to SR 169 – Phase 2) Page 3
Geology and Soils Technical Memorandum
July 2007
•Reconstruct five bridges and build one new bridge over the Green River.
•Lower the Duwamish-Green River Trail.
•Reconstruct the I-405 structures over SR 181.
•Realign the Interurban Trail.
I-405 from East of SR 181 to SR 167 Interchange
•Realign I-405 to provide a smooth transition onto the new Springbrook Creek/Oakesdale Avenue
bridge that was constructed under the Renton Nickel Improvement Project.
•Construct one additional general-purpose lane in each direction on I-405 from SR 181 through
SR 167.
•Stripe lanes to provide a buffer between HOV and general-purpose lanes along I-405.
•Reconstruct the I-405 structures over the Burlington Northern Santa Fe (BNSF) and Union
Pacific railroads.
•Stripe the bridges over Springbrook Creek/Oakesdale Avenue for five lanes in both directions.
SR 167 from I-405 to SW 43rd Street On-ramp
•Construct an auxiliary lane on northbound SR 167 from SW 43rd Street to I-405.
•Stripe lanes to provide a buffer between HOV and general-purpose lanes along SR 167.
•Reconstruct SR 167 between SW 27th Street and I-405 to accommodate the reconstructed SR 167
interchange.
•Reconstruct East Valley Road to the west of its current alignment between SW 23rd Street and
SW 16th Street to accommodate the reconstructed SR 167 interchange.
I-405 Interchange with SR 167
The interchange improvements affect both freeway to freeway access and local access.
Freeway to Freeway Access
•Construct a general-purpose direct-connector ramp from southbound I-405 to southbound
SR 167, replacing the existing loop ramp.
•Reconstruct exterior ramps from northbound I-405 to southbound SR 167 and from northbound
SR 167 to northbound I-405, replacing the existing ramps. This project will also add a general-
purpose lane to both ramps.
•Construct HOV direct-connector ramps from southbound I-405 to southbound SR 167 and from
northbound SR 167 to northbound I-405.
•Maintain existing loop ramp from northbound SR 167 to southbound I-405.
Local Access
Shift local access between I-405 and Renton from SR 167 to the Lind Avenue/Talbot Road split diamond
interchange. WSDOT will:
•Construct a new half-diamond interchange at Lind Avenue.
•Construct a new half-diamond interchange at SR 515 (Talbot Road).
•Construct southbound and northbound frontage roads connecting Lind Avenue to Talbot Road.
4 I-405, Tukwila to Renton Improvement Project (I-5 to SR 169 – Phase 2)
Geology and Soils Technical Memorandum
July 2007
•Remove exterior ramps to/from SR 167 north of I-405 and loop ramps south of I-405.
•Reconstruct the Lind Avenue bridge over I-405.
•Reconstruct I-405 structures over Talbot Road.
•Improve local street intersections.
•Provide new connection to Grady Way from S Renton Village Place.
I-405 from East of SR 167 Interchange to North of SR 169
•Construct two additional general-purpose lanes in each direction on I-405 from SR 167 through
SR 169.
•Stripe lanes to provide a buffer between HOV and general-purpose lanes along I-405.
•Reconstruct S 14th Street south of its existing location.
•Cantilever the I-405 structures over Main Avenue.
•Reconstruct three bridges over the Cedar River: southbound and northbound I-405 and a
pedestrian bridge.
•Relocate the BNSF railroad bridge over the Cedar River west of its current alignment.
•Close off Houser Way as a cul-de-sac just south of the Cedar River and remove the bridge over
the river. Northbound traffic will be rerouted via Bronson Way, which will be striped to
accommodate the new traffic pattern. Two options are being considered for northbound traffic
between Houser Way and Bronson Way. The first option stripes Mill Avenue as a one-way street
to provide two lanes northbound from the intersection of Houser Way and Mill Avenue to
Bronson Way. Emergency vehicles will still be allowed to travel southbound on Mill Avenue
from 2nd Street to Houser Way. The second option leaves Mill Avenue as a two-way street up to
the intersection with 2nd Street where it will be striped for one-way traffic northbound and
reconfigures Main Avenue, a one-way street southbound, for two-way traffic. Main Avenue
would be widened and striped for two-way traffic to provide access from the south to Bronson
Way.
•Reconstruct the two local street accesses to Renton Hill. Two local access points will be
maintained by reconstructing the Renton Avenue bridge over I-405 and reconstructing Mill
Avenue as a stacked structure that also provides access to Renton Hill. The existing Cedar
Avenue bridge will be removed.
•Construct a pedestrian pathway from Renton Hill to City parks and trails.
No Build Alternative
The No Build Alternative assumes that the improvements associated with the Renton Nickel
Improvement Project are constructed as does the baseline condition. Only routine activities such as road
maintenance, repair, and safety improvements would be expected to take place between 2014 and 2030.
This alternative does not include improvements that would increase roadway capacity or reduce
congestion beyond baseline conditions. For these reasons, it does not satisfy the project’s purpose to
reduce congestion on I-405 between I-5 in Tukwila and SR 169 in Renton. The No Build Alternative has
been evaluated in this technical memorandum as a comparison for the effects associated with the Build
Alternative.
I-405, Tukwila to Renton Improvement Project (I-5 to SR 169 – Phase 2) Page 5
Geology and Soils Technical Memorandum
July 2007
Baseline Conditions
What are the geology and soils of the study area?
The Tukwila to Renton Project lies in a heavily populated area located within the Green-Duwamish River
and Cedar River valleys. These valleys are underlain by relatively loose geologic materials with a
shallow groundwater table. The geology of the study area consists of a variety of soil types and bedrock.
A more detailed description of the soil and geologic units is provided in Exhibits 1 and 2, respectively,
and maps of local soil and geologic conditions are presented on Exhibits 3 through 10 (soil units) and 11
through 18 (surface geologic conditions). The soils and geology in the area combined with the
topography result in several geologic hazards along the corridor, including erosion, landslide, steep slope,
soft ground, and coal mine subsidence hazards. These geologic hazard areas are shown on Exhibits 19
through 34. The baseline conditions presented in this section were gathered from a review of available
documents, including the Renton Nickel Improvement Project Soils, Geology and Groundwater
Discipline Report and the Geotechnical Baseline Report as referenced in Appendix A.
Soils
The majority of the near-surface soil material in the study area along the I-405 and SR 167 corridors has
been modified by the addition of fill material and is classified as Urban Land or Modified Fill. Naturally
occurring, undisturbed soils in the project area span from well drained, gravelly sandy loam to poorly
drained silty clay loam and muck. These materials have predominantly been derived from glacial till or
alluvial deposits. A description of these soil units is provided in Exhibit 1 and the mapped soil units
along the project corridor are depicted on Exhibits 3 through 10.
Geology
The I-405 project corridor is located within the central Puget lowland bordered by the Cascade mountains
to the east and the Olympic mountains to the west. The Puget lowland is a north-south trending trough
consisting of Holocene period deposits generally overlying a sequence of relatively unweathered glacial
and interglacial soil deposited during the ice ages of the Quaternary period. This region has experienced
at least six glaciations in the past 2 million years.
In the central Puget lowland, the most complete geologic record of the Quaternary period exists for the
most recent glaciation, the Vashon stade of the Fraser glaciation. The advance and retreat of the Vashon
age Puget glacial lobe, between roughly 13,000 to 18,000 years ago, deposited most of the near-surface
materials and sculpted most of the present landforms within the Puget lowland. The deposits of this
glacial episode reflect a wide range of glacial depositional environments. As the glacier advanced
southward, streams deposited sediment that formed a broad plain in front of the advancing glacier.
Gravel-size material was deposited close to the glacier, while silt and clay material was transported
farther from the glacier. The advance deposits, therefore, grade from coarse to fine with increasing depth,
with silts and clays (lake deposits) at the base, then coarse-grained sand and gravel at the top.
Lodgement till, consisting of a non-stratified, well-graded deposit of particle sizes ranging from clay to
large boulders, was deposited directly from the glacier itself. The most conspicuous aspect of glacial till
is its consolidation, the result of being overridden by the glacial ice. The maximum ice thickness was
roughly 3,000 feet in the project vicinity.
As the glacier retreated, the depositional sequence was repeated in the reverse order of the glacial
advance, with first coarse-grained gravel and sand, then fine-grained silts and clays. The retreat was rapid
relative to the advance of the glacier, and the recessional deposits are generally not as thick as the
advance deposits nor are they as densely compacted because they were not overridden by the glacial ice.
6 I-405, Tukwila to Renton Improvement Project (I-5 to SR 169 – Phase 2)
Geology and Soils Technical Memorandum
July 2007
Following the Fraser glaciation, Holocene period sediments were deposited over the glacial soils. These
deposits typically consist of alluvial soils in river valleys, beach and marine deposits along shorelines and
colluvial deposits (landslide materials) along slopes. Peat and other organic soils occur in numerous
depressional areas at the surface. Some of these Holocene period sediments have been modified by
human activity, including overexcavation and replacement beneath portions of the I-405 project corridor.
The majority of the bedrock in the study area is Renton Formation sandstone. Outcrops of this unit occur
along the project corridor in three areas: 1) along the north side of I-405 to just east of the Green River
(between I-405 milepost [MP] 0.3 to MP 0.6 and between MP 0.75 to MP 0.9), 2) at the southeast
interchange of SR 167 and I-405, and 3) along I-405 west of Benson Road (MP 2.8) to approximately
Cedar Avenue (MP 3.65). In the Green River valley (between the two outcrop areas) the bedrock is
located at depths greater than 100 feet below the existing ground surface (Yount et al., 1985).
The local surface geology in the study area is depicted on Exhibits 11 through 18 and includes engineered
and non-engineered fill, stream and river sediment (alluvial), wetland deposits, glacial deposits and
bedrock. Peat and other organic soils occur in numerous depressional areas at the surface. A description
of these geologic units is provided in Exhibit 2.
Geologic Hazard Areas
Geologic hazard areas in the vicinity of the study area include erosion hazards, mine subsidence hazards,
steep slope hazards, landslide hazards, seismic hazards, and soft ground areas. These hazard areas are
shown in Exhibits 19 through 34 and are described below.
•Erosion Hazard – The majority of the soils in the study area are classified as possessing a slight
to moderate erosion potential. Soils with high erosion potential include weathered sandstone and
glacial soils on slopes greater than 15 percent. Erosion hazard areas exist east of SR 167, along
Panther Creek1, near South 15th Street and Talbot Road, adjacent to I-405 from MP 3 to MP 3.15,
and along the Cedar River and SR 169, as shown on Exhibits 22, 23, 25 and 26.
•Landslide Hazard – There does not appear to be large-scale active landsliding within the project
area. As with most slopes in western Washington, shallow surficial sliding is possible,
particularly when the ground is saturated. Surficial slides typically occur in the upper 2 to 5 feet
of soil or weathered bedrock on steep slopes and movement occurs episodically, generally in
response to heavy rainfall. Earthquake shaking would tend to increase the size of the surficial
slide area as well as the frequency of movement.
•Steep Slope Hazard – Some areas along the I-405 project corridor have steep slopes that may be
associated with landslide and erosion hazards. Steep slopes are typically defined as areas
possessing slope inclinations greater than 40 percent with a vertical height of 10 feet or more.
Several steep slope hazard areas are mapped along the project corridor (see Exhibits 19 through
26). Their locations are presented below (GeoEngineers, 2006).
o Immediately west of the Green River at MP 0.8
o West of the Green River along the southern edge of Interurban Avenue
o Along both sides of I-405 between MP 1.0 and MP 1.4
o At the southeastern interchange between SR 167 (MP 27.5) and I-405 (MP 2.6)
o Along both sides of I-405 from Talbot Road (MP 2.8) to the Cedar River (MP 3.75)
1 Panther Creek is located east of SR 167 approximately 0.2 miles south of SR 167 MP 25, as shown on Exhibits 6
and 7.
I-405, Tukwila to Renton Improvement Project (I-5 to SR 169 – Phase 2) Page 7
Geology and Soils Technical Memorandum
July 2007
•Soft Ground Areas – Portions of the study area are underlain by soft ground areas that generally
consist of soft clay, silt, or highly organic soil such as peat. These areas are likely to be
encountered adjacent to younger alluvial or wetland deposits. Soft ground areas are located along
both sides of the project corridor on SR 167 from MP 26.1 to MP 27.3. The soft ground areas are
shown with respect to planned construction disturbance in Exhibits 30 through 32.
•Seismic Hazard – Seismic hazards are generally considered to be areas with a severe risk of
ground shaking or deformation during an earthquake. Loose sand areas below the groundwater
table can undergo a process called liquefaction2 during a seismic event.
Mapped seismic areas are located along the majority of the project area and areas planned to be
disturbed by construction, with the exception south of SW 41st Street on SR 167 and the I-405
corridor from SR 167 to 225 feet south of the Cedar River, as shown in Exhibits 27 though 34.
Areas with a high seismic hazard are located along I-405 south of MP 0.7 and from MP 1.7 to
MP 2.2.
•Coal Mine Subsidence Hazard – The Renton Formation has been mined for coal throughout the
Renton area since the late 1800s. Mine subsidence hazard areas within the project area are
located south of the I-405 interchange along the eastern side of SR 167 to approximately SW 23rd
Street. They are also located along I-405 near MP 3.0 as shown on Exhibits 22, 23, 24, 25 and
26. Two large retaining walls, which in some areas may be up to 70 to 80 feet tall, are located
along the cut walls of Thunder Creek and are associated with a new on-ramp from Talbot Road to
northbound I-405 (see MP 3.05 on Exhibit 25). This area is within a mine subsidence hazard
area. Recent borings and geophysical explorations indicate the upper 25 feet of the cut associated
with the retaining wall will be through coal mine spoils over a portion of the wall alignment.
Sandstone bedrock was encountered below the mine spoils in the explorations; however, a 3.5-
foot void was encountered within the sandstone about 35 feet below the ground surface in one
boring completed near the proposed wall alignment.
Based on historical maps available from the Washington State Department of Natural Resources
(DNR), a coal mine tunnel entrance (Renton Coal Mine) was situated near Benson Road, about 300
feet west of the I-405 right-of-way near MP 3. Field notes from the original construction of I-405
suggest the mine tunnel was encountered during grading operations for I-405 and that the tunnel was
backfilled. How much of the tunnel was backfilled is uncertain. The prevailing dip of the coal seams
in the area suggests that the mine workings likely dip downward toward the east at approximately 10
degrees. So the old mine workings would generally be expected to be below the level of the bottom
of the Thunder Creek retaining walls and the associated widening of I-405 to the east. However,
there is some uncertainty regarding the exact location of the old mine workings, and caving of the
open spaces from the mine workings may propagate upwards resulting in loosened rock and soils
above the mine workings and possible void spaces.
2 Liquefaction is a phenomenon where soils experience a rapid loss of internal strength as a consequence of strong
ground shaking.
8 I-405, Tukwila to Renton Improvement Project (I-5 to SR 169 – Phase 2)
Geology and Soils Technical Memorandum
July 2007
Exhibit 1: Description of Soil Units
Unit
Map
Symbol1 Description
Alderwood gravelly
sandy loam
AgC, AgD The Alderwood series is made up of moderately well drained soils that have a
weakly consolidated to strongly consolidated substratum at a depth of 24 to 40
inches. These soils are on uplands and formed under conifers, in glacial deposits.
Slopes are from 0 to 70 percent.
In a representative profile, the surface layer and subsoil are very dark brown, dark
brown and grayish-brown gravelly sandy loam about 27 inches thick. The
substratum is grayish-brown, weakly consolidated to strongly consolidated glacial
till that extends to a depth of 60 inches and more.
Alderwood and Kitsap
soils
AkF This unit is about 50 percent Alderwood gravelly sandy loam and 25 percent Kitsap
silt loam. Slopes are 25 to 70 percent.
Drainage and permeability vary. Runoff is rapid to very rapid, the erosion hazard
is severe to very severe, and the slippage potential is severe.
In a representative profile of Kitsap soils, the surface layer is dark grayish-brown,
dark yellowish-brown and dark brown silt loam to a depth of 33 inches. The
substratum extends to a depth of 60 inches or more and is light olive brown silty
clay loam.
The permeability of this Kitsap soil is moderate in the surface layer and slow
through the substratum. The available water capacity is moderate to high.
Increasing respectively with slope steepness, the runoff is slow to rapid and the
hazard of water erosion is slight to severe.
Arents, Alderwood
material
AmC Arents, Alderwood material consists of Alderwood soils that have been so
disturbed through urbanization that they no longer can be classified with the
Alderwood series. These soils, however, have many similar features. The upper
part of the soil, to a depth of 20 to 40 inches, is brown to dark brown gravelly sandy
loam. Below this is a grayish-brown, consolidated, and impervious substratum.
Slopes generally range from 0 to 15 percent.
Since these soils have been disturbed, there is no representative profile.
Arents, Everett
material
An Arents, Everett material consists mainly of Everett soils that have been so
disturbed through urbanization that they can no longer be classified with the
Everett series. The soil is level to gently sloping dark brown to olive brown gravelly
sandy loam.
Permeability is rapid in the soil and the erosion hazard is slight.
Since these soils have been disturbed, there is no representative profile.
Beausite gravelly
sandy loam
BeC, BeD The Beausite series is made up of well-drained gravelly sandy loam that was
underlain by sandstone at a depth of 20 to 40 inches. These soils formed in glacial
deposits and are rolling to very steep with Slopes ranging from 6 to 75 percent.
In a representative profile, the surface layer and the upper part of the subsoil are
dark brown.
1. The Map Symbol is an abbreviation of the unit as shown in the map exhibits.
I-405, Tukwila to Renton Improvement Project (I-5 to SR 169 – Phase 2) Page 9
Geology and Soils Technical Memorandum
July 2007
Exhibit 1: Description of Soil Units (Continued)
Unit
Map
Symbol1 Description
Everett gravelly
sandy loam
EvC and EvD This unit is made up of somewhat excessively drained soil that was formed by glacial
outwash and is located on terraces and outwash plains. Slopes range from 5 to 30
percent.
In a representative profile, the surface layer and subsoil are dark brown gravelly to
extremely gravelly sandy loam to a depth of 60 inches. Gravel content increases with
depth. In some areas the substratum is weakly cemented.
Permeability of the soil is rapid and available water capacity is low. Runoff is slow to
medium and the hazard of water erosion is slight to moderate, increasing with the
steepness of the slope.
Indianola loamy
sand
InC and InD This unit formed in sandy recessional stratified glacial drift and is composed of
somewhat excessively drained soil on terraces and outwash plains. Slopes are 4 to
15 percent.
In a representative profile, the surface is typically very dark grayish-brown loamy
sand with a 2-inch covering of forest duff. The subsoil is dark yellowish-brown loamy
fine sand to a depth of 26 to 30 inches. The substratum is light olive gray and
grayish-brown sand and extends to a depth of 60 inches or more.
Permeability of the soil is rapid and available water capacity is low to moderate.
Increasing respectively with slope steepness, the runoff is slow to medium, and the
hazard of water erosion is slight to severe. This unit is mainly used as woodland and
for urban development.
Newberg silty loam Ng The Newberg series is made up of well-drained soils that formed in alluvium in
stream valleys, and under grass, hardwoods, and conifers. Slopes are 0 to 2
percent.
In a representative profile, the surface layer is very dark grayish-brown silt loam and
very fine sandy loam about 20 inches thick. It is underlain, to a depth of 60 inches or
more, by stratified very fine sandy loam, loamy very fine sand, loamy sand and silt
loam.
Pilchuck loamy fine
sand
Pc The Pilchuck series is made up of excessively drained soils that formed in alluvium
on low stream terraces. Slopes are 0 to 2 percent.
In a representative profile, layers of very dark gray, dark grayish-brown, and dark
gray fine and loamy fine sand extend to a depth of about 38 inches. Below this is
black gravelly sand that extends to a depth of 60 inches or more.
Pits PITS These features consist of open pit mines some of which were used as hard-rock
quarries. None of the pits were underground mines.
Puget silty clay
loam
Pu The Puget series is made up of poorly drained soils that formed in alluvium in small
depressions of river valleys. Slopes are 0 to 1 percent.
In a representative profile, the soil is dominantly mottled dark grayish-brown and
grayish-brown silty clay loam to a depth of about 45 inches. The substratum is gray
silty clay that extends to a depth of 60 inches or more.
1. The Map Symbol is an abbreviation of the unit as shown in the map exhibits.
10 I-405, Tukwila to Renton Improvement Project (I-5 to SR 169 – Phase 2)
Geology and Soils Technical Memorandum
July 2007
Exhibit 1: Description of Soil Units (Continued)
Unit
Map
Symbol1 Description
Puyallup fine
sandy loam
Py The Puyallup series is made up of well-drained soils that formed in alluvium, under
grass, hardwoods, and conifers. These soils are on the natural levees adjacent to
streams in the river valleys. Slopes are 0 to 2 percent.
In a representative profile, very dark grayish-brown and dark grayish-brown fine
sandy loam and very fine sandy loam extend to a depth of about 34 inches. The
substratum, at a depth of 60 inches or more, is very dark grayish-brown, dark
grayish-brown, and dark brown medium sand, loamy sand, and sand.
Riverwash Rh Riverwash consists of long, narrow areas of sand, gravel, and stones along
channels of the larger streams. Some areas are barren of vegetation, and others
support scattered cottonwoods, willows, and other trees and shrubs. Overflow and
alteration by severe erosion and deposition are frequent.
Since these soils have been disturbed, there is no representative profile.
Seattle muck Sk The Seattle series is made up of very poorly drained organic soils that formed in
material derived primarily from sedges. These soils are in depressions and valleys
on the glacial till plain and also in the river and stream valleys. Slopes are 0 to 1
percent.
In a representative profile, the surface layer is black muck about 11 inches thick. It
is underlain by dark reddish-brown, black, very dark brown and dark brown muck
and mucky peat that extends to a depth of 60 inches or more.
Snohomish silt
loam
So The Snohomish series is made up of poorly drained soils that formed in alluvium in
stream valleys. Slopes are 0 to 2 percent.
In a representative profile, the surface layer and subsoil are very dark grayish-brown
and grayish-brown silt loam and clay loam about 17 inches thick. Below this is black
mucky peat about 10 inches thick. The substratum is dark gray loamy fine sand that
extends to a depth of 60 inches or more.
Tukwila muck Tu The Tukwila series is made up of very poorly drained organic soils that formed in
decomposing sedges, rushes, grasses, and shrubs. These soils are in wet basins of
upland depressions and on stream bottoms. Slopes are 0 to 1 percent.
In a representative profile, dominantly black to very dark brown muck extends to a
depth of 60 inches or more.
Urban land Ur Soil that has been modified by disturbance of the natural layers with additions of fill
material several feet thick to accommodate large industrial and housing installations.
In the Green River valley the fill ranges from about 3 to more than 12 feet in
thickness, and from gravelly sandy loam to gravelly loam in texture. The erosion
hazard is slight to moderate.
Since these soils have been disturbed, there is no representative profile.
Woodinville silt
loam
Wo The Woodinville series is made up of nearly level and gently undulating, poorly
drained soils that formed under grass and sedges, in alluvium, and on stream
bottoms. Slopes are 0 to 2 percent.
In a representative profile, gray silt loam, silty clay loam, and layers of peaty muck
extend to a depth of about 38 inches. This is underlain by greenish-gray silt loam
that extends to a depth of 60 inches and more.
1. The Map Symbol is an abbreviation of the unit as shown in the map exhibits.
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Geology and Soils Technical Memorandum
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Exhibit 2: Description of Geologic Units
Unit
Map
Symbol1 Description
Alluvium Qa Primarily composed of sand, silt and clay deposited by the Green River and sand and
gravel with thin beds of silt and clay deposited by the Cedar River. Locally, alluvial
deposits contain thin peat lenses.
Glacial Till Qgt Very dense, nonsorted mixture of clay, silt, sand, gravel, cobbles, and boulders. Upper
2 to 5 feet is often weathered and typically medium dense to dense.
Glaciolacustrine
Deposits
Qgl Clay, silt, silty clay, and silty fine sand with local dropstones; blue-gray or gray,
weathered to pale yellowish-brown; locally contains thick beds of structureless, clast-
rich diamicton that may be flow till or iceberg melt-out contact zones; also locally
contains lenses and beds of fine- to medium-grained sand; stiff or dense; well sorted.
Intrusive Rocks
(bedrock)
Oian Irregular masses of porphyritic andesite and basalt. Material is generally intersected
by numerous faults and joints, and by veins of montmorillonite, calcite, quartz and
other minerals.
Mass-wasting
Deposits
Qls Primarily landslide deposits, but locally includes talus, colluvium, protalus ramparts,
and rock glaciers.
Recessional
Outwash
Qgo Silty fine sand to clean coarse gravel with occasional cobbles and boulders. Due to
the fluvial nature of deposition of recessional outwash, materials are generally
stratified.
Renton Formation
(bedrock)
Ec(2r) Fine- to medium-grained arkosic and feldspathic, micaceous sandstone, but includes
some siltstone, sandy shale, and beds of coal and carbonaceous shale.
Sandstone is highly variable and ranges from completely weathered to fresh. Also
contains seams and zones, which are poorly lithified or even uncemented.
Tiger Mountain
Formation (bedrock)
Ec(2t) Light-colored, medium grained, micaceous feldspathic subquartzose sandstone
interbedded with siltstone, minor pebble conglomerate and coal beds.
Tukwila Formation
(bedrock)
Evc(t) Volcanic sedimentary rocks mostly composed of volcanic sandstone, siltstone, and
shale; also include some volcanic conglomerate, tuff, tuffaceous sandstone, and
siltstone, and a few carbonaceous shales. Fragments of wood and other plant remains
are common throughout. Most are various shades of brown; some of the finer grained
tuffs, however, are light gray to light dusky yellow, and a few are almost white. For the
most part, they are poorly sorted; some of the finer grained tuffaceous rocks, however,
are thinly bedded and well sorted. The sedimentary rocks are composed chiefly of
subangular to subrounded fragments of andesite and basaltic andesite, and grains of
plagioclase, pyroxene, and small amounts of quartz in a matrix of silt, iron oxide, and
clay minerals.
Undifferentiated
Glacial Drift
Qgpc Thin deposits of recessional outwash overlying glacial till (described above).
Wetland Deposits Qp Peat and organic material with minor amounts of silt and clay or mixtures of silt, clay,
sand, and peat. Some deposits also contain a thin layer of volcanic ash. Where
mapped, the peat and organic material is consistently 3 feet or more thick.
1. The Map Symbol is an abbreviation of the unit as shown in the map exhibits.
12 I-405, Tukwila to Renton Improvement Project (I-5 to SR 169 – Phase 2)
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Potential Effects
Will the project affect soils or geology?
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 are resolved with implementation of
standard BMPs. Relevant construction conditions along the study area include:
•Disturbance of moisture sensitive soils,
•Temporary cuts through landslide-prone areas,
•Increased erosion potential, and
•Vibration effects of construction equipment.
These effects will be avoided or minimized by using proper design and construction techniques.
Unavoidable effects to local soils and geology resulting from project construction will be mitigated by
following standard WSDOT construction practices and the I-405 Programmatic Commitments. Based on
WSDOT’s commitment in following these compliance measures, effects from soils and geology will be
few, if any. No substantial adverse affects to soils and geology are anticipated from either of the two
project build alternatives.
Will soils or geology affect the project construction or operation?
The project will be constructed in a highly variable geologic environment. The majority of the project is
located within the Green-Duwamish and Cedar River valleys, which are underlain by relatively loose soil
and a shallow groundwater table. The conditions along the alignment are not unusual for the Puget Sound
area and generally present conditions routinely encountered by WSDOT in their design, construction,
operation, and maintenance plans. However, the presence of erosion hazard areas and erosion susceptible
soils, soft ground areas, liquefaction-prone soils, and mine subsidence hazards may affect the project and
will be prominent design and construction considerations. WSDOT has managed these types of
conditions on several other projects, including the original construction of I-405. Once construction is
complete and the highway is in use, geology and soils should have essentially no affects on the built
project.
Soils and Erosion
Erosion risk is usually assessed by looking at the steepness of a slope in combination with the soil type.
However, since hillside cuts may create steep slope conditions during construction, cut areas, even if not
rated as having a high erosion risk, can become susceptible to erosion. Fill placed to widen existing
embankments may be susceptible to erosion during a storm event, particularly when stockpiled prior to
being placed during construction.
In addition, 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.
Landslide Hazard Areas
Cuts into landslide-prone slopes may destabilize slopes creating landslide hazard areas. Landslides,
should they occur, could exert lateral loads on retaining walls and other structures. Landslide debris, if
not properly contained, could also block the roadway.
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Soft Ground Areas
Soft, compressible soils will settle under new loads such as those imposed by new bridges, retaining walls
and fill embankments if they are not designed to account for the soft ground conditions. Soft
compressible soils underlying transportation corridors are common in the region and WSDOT has
considerable experience designing new improvements to accommodate these types of soils.
Seismic Hazard Areas
The majority of the project area is considered to be a seismic hazard area because soils in those areas are
prone to liquefaction. The project will widen, construct, or reconstruct numerous bridges. All of these
bridges (proposed and existing) may be underlain by soils considered to be moderately to highly
susceptible to liquefaction. New structures, such as bridges, retaining walls, and fill embankments,
supported above or within liquefiable soils can be subject to loss of bearing support and settlement should
the underlying soils liquefy during a seismic event. In addition, fill embankments such as approaches to
bridges are susceptible to lateral spreading (slope deformations) if soils below the embankments liquefy.
Lateral spreading of bridge approach fills could subsequently increase lateral loads to the adjacent bridge
piers.
Mine Subsidence Hazard Areas
Mine spoils near the top of the proposed cut for the Thunder Creek retaining walls are loose and would be
unstable if cut too steeply. Therefore, retaining wall designs and construction techniques must be able to
accommodate both loose soils along the top of the wall and dense sandstone in the lower half of the wall.
Voids associated with the previous mine workings could impact wall stability and result in long-term
settlement of the roadway.
What are the unavoidable adverse effects?
Unavoidable adverse effects include disturbance of moisture-sensitive soils, cuts in landslide-prone areas,
increased erosion potential, wall stability and long-term settlement of the roadway and vibration effects of
construction equipment. These effects will be minimal because standard WSDOT construction practices
will be followed.
Measures to Avoid or Minimize Effects
What will be done to avoid or minimize adverse effects from the project?
The majority of potential adverse effects associated with the construction and operation of the project will
be avoided or minimized through the use of BMPs, from following the procedures outlined in the
WSDOT Geotechnical Design Manual (GDM) and Bridge Design Manual, and from following the I-405
Programmatic Commitments. Avoidance measures are discussed below in the following sections.
The effects described in the previous section will be avoided or minimized by using proper design and
construction techniques. Unavoidable effects to local soils and geology resulting from project
construction will be mitigated by following standard WSDOT construction practices and the I-405
Programmatic Commitments. Based on WSDOT’s commitment in following these compliance measures,
effects from soils and geology will be few, if any. No substantial adverse affects to soils and geology are
anticipated from the project build alternative.
BMPs and other measures will be incorporated into construction specifications to control or reduce
construction related erosion and sedimentation, increase infiltration (where appropriate), reduce seismic
and soft ground hazards, improve safety in landslide hazard areas, and address collapsed mine openings
or underground rooms associated with historic mining activities. Design solutions to avoid, minimize, or
mitigate disturbance to geologic, seismic, and mine hazard areas will be implemented.
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Gravel from imported sources outside of the study area will be required. Standard WSDOT contract
language requires imported materials to come from approved sources whose operations comply with all
applicable laws.
Vibration Effects of Construction Equipment
The impacts of construction vibrations can be mitigated by restricting the hours of construction or
operation of certain types of equipment to times least likely to disturb nearby residences or businesses and
increase the distance between source and receptor. For example, a drilled pile could be substituted for a
driven pile to reduce vibrations in some instances. Potential impacts to structures and people will be
evaluated on a site-specific basis during design.
Erosion and Soils
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, use of temporary or permanent
erosion control blankets, mulching, or soil amendment to promote plant growth, and avoiding
unnecessary vegetation clearing. Structural measures consist of the construction of temporary structures
to reduce the transport of sediment, such as detention ponds, ditches, silt fences, or sediment traps.
Should any BMP or other operation not function as intended, WSDOT will take additional action to
minimize erosion.
WSDOT will reduce degradation of moisture-sensitive soils by maintaining proper surface drainage to
avoid surface water ponding; 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. Soil admixtures such as
lime or cement may also be mixed into the subgrade to add strength and stabilize the ground.
Landslide Hazard Areas
Analyses of slope stability and design of mitigation measures, such as retaining walls, buttresses, and
groundwater control, will be performed during the design of excavations or embankments on hillsides.
WSDOT will design retaining walls for undercut and potentially unstable slopes. Cleared slopes will be
covered per permit requirements in the rainy season.
Facilities in landslide hazard areas can be designed to be safely constructed and operated. Cuts through
landslide-prone materials could be limited in height or avoided, requiring the use of special retaining wall
systems for earth retention. Walls could be designed for higher lateral pressures to limit soil movement.
Subsurface drainage may be needed to increase slope stability. Light-weight fill, bridging structures, or
realignment and relocation of improvements could be used to avoid loading slopes.
WSDOT will have earthwork and wall placement sequencing plans, construction drainage plans, and a
slope monitoring program. During construction, areas of observed or suspected groundwater seepage will
be drained to reduce the risk of landslide and surface sloughing through the use of gravel drainage
blankets, French drains, horizontal drains and/or placement of a surface rock facing or similar methods.
Soft Ground Areas
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 by supporting
them on deep foundations gaining support below the compressible soils and protecting or relocating
utilities. Other techniques that may be employed are to stage construction of embankments so the soil has
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time to gain strength; wick drains to hasten consolidation and strength gain; construct embankments of
light-weight materials to minimize loading; reinforce embankments with geosynthetics to add strength
and minimize the footprint; induce settlement of the underlying soils through the use of preloads prior to
constructing the infrastructure; construct on pile supports; and increase grades to keep pavement above
groundwater. Soft ground hazards at bridge locations will be mitigated by founding the structures on
deep foundations.
Seismic Hazard Areas
Bridges constructed on liquefaction-prone soils will be founded on deep foundations and/or the soil under
the bridges will be improved so that they are no longer susceptible to liquefaction. Soil improvement
measures will likely consist of stone columns, compaction grouting, or similar soil densification
techniques. Approach embankments within 100 feet of bridge abutments will also be designed for
seismic conditions, including liquefaction. These measures will be implemented to minimize damage
during an earthquake. WSDOT will select measures that will minimize the effect on adjacent properties.
In accordance with the WSDOT GDM, retaining walls will be designed to remain stable under seismic
loading conditions and anticipated displacements associated with liquefaction. Mitigation, such as
founding walls on deep foundations or improving the underlying soils, to achieve overall stability may be
required. Likewise, bridge structures and approach embankments within 100 feet of bridge abutments
will be designed for seismic loading and to resist or accommodate liquefaction-induced displacements,
according to the WSDOT GDM. WSDOT will select measures that will minimize the effect on adjacent
properties.
Mine Subsidence Hazard Areas
WSDOT will design the project to avoid adverse settlement or subsidence effects from abandoned mine
workings. If necessary, avoiding settlement or subsidence may be accomplished by bridging over these
areas with a structural slab or by backfilling the voids. If an opening or surface depression is found or
develops after construction, it will be filled with soil or grout, or bridged. Suspect areas along WSDOT
facilities will be monitored by maintenance crews.
For design of the Thunder Creek retaining walls and the adjacent widened I-405 lanes, design standards
will be followed to ensure the soils will retain enough bearing to accept the load of the wall and roadway.
If there appears to be a possibility of a collapsed mine opening or underground room near the proposed
facilities, the design will include measures to bridge over these areas, fill them in, or otherwise mitigate
the subsidence potential.
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Acronyms and Abbreviations
Acronym Meaning
BMPs Best management practices
BNSF Burlington Northern Santa Fe Railway
DNR Washington State Department of Natural Resources
Ecology Washington State Department of Ecology
EPA U.S. Environmental Protection Agency
HOV High-occupancy vehicle
LiDAR Light Distance and Ranging
MP Milepost
SR State Route
TESC Temporary Erosion and Sediment Control
USGS United States Geological Survey
WSDOT Washington State Department of Transportation
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Glossary
Term Meaning
admix A product, such as cement or kiln dust that is mixed into soil to improve the characteristics of
the soil during construction.
advance outwash Layered and sorted sediments (chiefly sand and gravel) washed out from an advancing
glacier by melt-water streams and deposited beyond the margin of the glacier. The coarser
material is deposited nearer to the glacier.
alluvium Sediment deposited by a stream or river, either along the stream bed or in the floodplain.
bedrock Bedrock is referred to as the rock underlying gravel and/or soil and is sometimes visible on
the surface as outcrops.
best management
practice (BMP)
Innovative and improved environmental protection tools, practices, and methods that have
been determined to be the most effective, practical means of avoiding or reducing
environmental impacts.
colluvium Loose, heterogeneous mass of soil and/or rock fragments deposited on the ground surface
by rain wash, sheet wash, or soil creep.
effect Something brought about by a cause or agent; a result. This may include ecological,
aesthetic, historic, cultural, economic, social, health or other effects, whether direct, indirect,
or cumulative. Effects may include those resulting from actions that may have both
beneficial and detrimental effects.
erosion The wearing away of soil or rock by the action of running water, wind, ice, or geologic
agents. For this analysis, erosion relates primarily to stormwater runoff.
fault A fracture or zone of fractures of the earth’s crust along which displacement has occurred
parallel to the fracture.
fill Any material placed in an area to increase surface elevation.
geographic
information system
(GIS)
A digital computer mapping system that can overlay a wide variety of data such as land use,
utilities, and vegetative cover, and provide a spatial analysis.
glacial till The mass of rocks and finely ground material carried by a glacier and then deposited when
the glacial ice melts. This creates an unstratified material of varying composition.
glaciation The process of ice growth and retreat within a glacier.
glacier A major body of ice that moves under the influence of gravity.
general-purpose lane A freeway or arterial lane available for use by all traffic.
groundwater That portion of the water below the ground surface that is free flowing within the soil
particles. Groundwater typically moves slowly, generally at a downward angle because of
gravity, and eventually enters into streams, lakes, and oceans.
high-occupancy
vehicle (HOV)
High-occupancy vehicle is a special designation for a bus, carpool, or vanpool provided as
an encouragement to increase ride-sharing. Specially designated HOV lanes and parking
are among the incentives for persons to pool trips, use fewer vehicles, and make the
transportation system more efficient. HOV lanes are generally inside (left-side) lanes, and
are identified by signs and a diamond on the pavement. Currently, two or more (2+)
occupants are required to use the I-405 HOV lanes. Motorcycles are allowed to use freeway
HOV lanes as well.
impervious surface Pavement, roofs, and other compacted or hardened areas that do not allow the passage of
rainfall or runoff into the ground.
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infiltration The passage of water through the soil surface into the subsoil.
liquefaction Transformation of a granular soil material from a solid state into a liquefied state, often as a
consequence of strong earthquake shaking.
loam Soil that contains a combination of sand, silt, organic matter, and clay.
mitigation An effort to: (1) avoid the impact altogether by not taking a certain action or parts of an
action; (2) minimize the impact by limiting the magnitude of the action and its
implementation, by using technology or by taking affirmative steps; (3) rectify the impact by
repairing, rehabilitating, or restoring the affected environment; (4) reduce or eliminate the
impact over time by preservation and maintenance operations; (5) compensate for the
impact by replacing, enhancing or providing substitute resources or environments; and/or (6)
monitor the impact and taking appropriate corrective measures.
outwash Sediment deposited by flowing water originating from glacial meltwaters. 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 and gravel sized particles.
permeability A measure of how quickly a fluid (in this case, water) can move through sediment or other
subsurface material.
programmatic
commitments
These are assurances or obligations identified in the Environmental Impact Statement for
the overall I-405 Corridor Program and intended for implementation by WSDOT and/or the
other project sponsors, as appropriate.
reconnaissance-level
field survey
A qualitative investigation, where the biologist walks the site, photographs key areas, and
makes observations of plants and wildlife, to assess overall site conditions.
retaining wall A structure used to hold earth in place where the natural grade cannot be maintained.
right-of-way Land purchased prior to the construction of transportation improvements along with land for
sound walls, retaining walls, stormwater facilities, and other project features. This also
includes permanent or temporary easements for construction and maintenance. Vacant
land may also be set aside for future highway expansion under certain circumstances.
runoff Rainwater or snowmelt that leaves an area as a surface drainage.
saturated soil
conditions
A condition in which all easily drained voids (pores between soil particles) in the root zone
are filled with water to the soil surface.
sediment Material that originates from weathering and erosion of rocks, dirt, or unconsolidated
deposits and organic material. Sediment is carried and deposited by wind, ice or water. It is
often transported by stormwater runoff and may be suspended within the water.
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.
seep A spot where water trickles out of the ground to form a pool or wet area.
seismicity The frequency or magnitude of earthquake activity in a given area.
silty loam A type of soil that is rich in organic materials mixed with fine clay-like particles.
slope The change in elevation over a distance, or an inclined land form.
stade A period within glacial retreat marked by a glacial re-advance.
stormwater The portion of precipitation that does not naturally percolate into the ground or evaporate,
but flows overland, in channels, or in pipes into a defined surface water channel or a
constructed stormwater facility.
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stratified Arranged or deposited in layers.
study area The area specifically evaluated for environmental effects.
sub-basin A smaller portion, or sub-area, of a watershed or catchment area.
subgrade The in-place material on which pavement or embankment fills are placed.
till An unsorted and non-stratified 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. Till is often
referred to as hardpan.
topography The physical features of a geographic area taken collectively; especially, the variations in
elevation of the earth's surface.
underpinning A method of increasing the load-bearing capacity of a foundation by adding piles under the
structure.
Vashon Stade The most recent Pleistocene glacial advance and retreat in the Puget Sound region,
occurring approximately 14,000 years ago.
vehicle Any car, truck, van, motorcycle, or bus designed to carry passengers or goods. Bicycles
and other pedestrian-oriented vehicles are not included in this definition.
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References
GIS Data Sources
Exhibits 3 thru 10
NRCS (Natural Resources Conservation Service, United States Department of Agriculture).
2005 Soils. Soil Survey Geographic (SSURGO) Database for King, County. May 2005.
Washington State Department of Transportation (WSDOT).
2006 – 2007. I-405 Staff; project limits.
Exhibits 11 thru 18
Washington State Department of Natural Resources (WSDNR), Geology and Earth Resources Division.
2003 Surface Geology.
WSDOT.
2006 – 2007. I-405 Staff; project limits.
Exhibits 19 thru 26
King County Standard GIS Data Disk, extract June 2006:
1997 Coal Mine Hazards
1997 Erosion Hazards.
2003 Landslide Hazard Areas.
Puget Sound LiDAR Consortium, LiDAR,
2002 http://pugetsoundlidar. ess. washington. edu/About_PSLC. htm
2006 Steep Slopes. Adapted by GeoEngineers, Inc. using the Puget Sound LiDAR Consortium
data.
WSDNR, Geology and Earth Resources Division.
2004 Liquefaction.
WSDOT.
2006 – 2007. I-405 Staff; project limits.
Exhibits 27 thru 34
King County Standard GIS Data Disk, extract:
2006 Seismic Hazard Areas. June 2006
WSDNR, Geology and Earth Resources Division.
2003 Surface Geology.
2007. Soft Ground Areas. Adapted by GeoEngineers, Inc. using the WSDNR Geology data.
WSDOT.
2006 – 2007. I-405 Staff; project limits and area of disturbed soil.
Base Data
All GIS exhibits contain one or more of the following as base layers:
Geographic Data Technology, Inc. (GDT).
2005 GDT – Dynamap Transportation. April 2005.
I-405, Tukwila to Renton Improvement Project (I-5 to SR 169 – Phase 2) Page 21
Geology and Soils Technical Memorandum
July 2007
King County Standard GIS Data Disk, extract June 2006:
2004 Cities with annexations.
2005 Open Water.
2006 Parks in King County. Data updated by I-405 staff to match data from cities of Renton and
Tukwila.
2005 Streams and Rivers. Data updated by I-405 staff to match fieldwork, 2002 LiDAR, and
orthorectified aerial photography.
2005 Trails in King County. Data updated by I-405 staff to match fieldwork, 2002 LiDAR and
orthorectified aerial photography.
United States Geological Survey (USGS).
2002 Color Aerial Photography. June 2002. http://edc.usgs. gov/products/aerial/hiresortho.html
Washington State Department of Transportation (WSDOT).
2001 Aerial photography program. March 2001.
1997 Spatial Data Catalog, Railroads.
Text References
Bates L, Robert and Jackson A., Julia,
1984 “Dictionary of Geologic Terms, Third Edition.” Anchor Books, New York.
GeoEngineers Inc.
2005 “Geotechnical Baseline Report, I-405 Renton Nickel Improvement Project, Renton and
Tukwila, Washington.” October 14, 2005
Golder Associates
2005 “Soils, Geology, and Groundwater Discipline Report, I-405, Renton Nickel Improvement
Project.” October 20, 2005.
Washington State Department of Transportation (WSDOT)
2006 Geotechnical Design Manual, M 46-03. December 2006.
2006 Bridge Design Manual. November 17, 2006.
Yount, J.C., Dembroff, G.R., and Barats, G.M.
1985 Map Showing Depth to Bedrock in the Seattle 30’ by 60’ Quadrangle, Washington.
22 I-405, Tukwila to Renton Improvement Project (I-5 to SR 169 – Phase 2)
Geology and Soils Technical Memorandum
July 2007
Exhibit 3: Soil Units, Sheet 1
S
o
u
t
h
c
e
n
t
e
r
P
a
r
k
w
a
y
Klickitat
Dr
Western
Project
Limit
Tukwila Parkway
Westfield
Shoppingtown
Mall
Southcenter Blvd
C
o
t
t
a
g
e
C
r
e
e
k
G i l l i a m C r e e k
Tukwila
City
Hall
MP 0.4
MP 0.3
MP 0.2
MP 0.1
MP 0.0
MP 0.5
Gilliam Creek
Sheet
8
Sheet
1
Sheet
4
Sheet
5
Sheet
2
Sheet
3 Sheet
6
Sheet
7
TUKWILA RENTON
Project Area
Water Body
Stream - Open Channel
Stream - Pipe
Railroad
Trail
Other Roads
Local Road
Freeway
Municipality 0250500
Feet
TRIP_GEO_SOILS.mxd Updated: 10-5-07
Soils Units
AgC (Alderwood gravelly sandy loam)
AgD (Alderwood gravelly sandy loam)
AkF (Alderwood and Kitsap soils)
AmC (Arents, Alderwood material)
An (Arents, Everett material)
BeC (Beausite gravelly sandy loam)
BeD (Beausite gravelly sandy loam)
EvC (Everett gravelly sandy loam)
EvD (Everett gravelly sandy loam)
InC (Indianola loamy fine sand)
InD (Indianola loamy fine sand)
Ng (Newberg silty loam)
PITS
Pc (Pilchuck loamy fine sand)
Pu (Puget silty clay loam)
Py (Puyallup fine sandy loam)
Rh (Riverwash)
Sk (Seattle muck)
So (Snohomish silt loam)
Tu (Tukwila muck)
Ur (Urban land)
Wo (Woodinville silt loam)
I-405, Tukwila to Renton Improvement Project (I-5 to SR 169 – Phase 2) Page 23
Geology and Soils Technical Memorandum
July 2007
Exhibit 4: Soil Units, Sheet 2
I
n
t
e
r
u
r
b
a
n
T
r
a
i
l
W
V
a
l
l
e
y
H
w
y
Interurba
n
A
ve
S
R
E
N
T
O
N
C
I
T
Y
L
I
M
I
T
S
T
U
K
W
I
L
A
C
I
T
Y
L
I
M
I
T
S
S o u t h c e n t e r B l v d
M
o
n
ster
R
d
S
W
Westfield
Shoppingtown
Mall
6
5
t
h
A
v
e
S
BN
SF
G r e e n R i ver
C
o
t
t
a
g
e
C
r
e
e
k
G i l l i a m C r e e k
G r e e n R i v e r T r a i l
Tukwila
City
Hall
D
u
w
a
m
i
s
h
-
G
r
e
e
n
R
i
v
e
r
T
r
a
i
l
U
n
i
o
n
P
a
c
i
f
i
c
MP
MP 1.2
MP 1.1
MP 1.0
MP 0.9
MP 0.8
MP 0.7
MP 0.6
P 0.4
MP 0.5
D
u
w
a
m
i
s h
-G r e e n R i v e r
T
r
i
a
l
T u k w i l a P a r k w a y
A
n
d
o
v
e
r
P
a
r
k
E
G
r
e
e
n
R
i
v
e
r
Sheet
8
Sheet
1
Sheet
4
Sheet
5
Sheet
2
Sheet
3 Sheet
6
Sheet
7
TUKWILA RENTON
Project Area
Water Body
Stream - Open Channel
Stream - Pipe
Railroad
Trail
Other Roads
Local Road
Freeway
Municipality 0250500
Feet
TRIP_GEO_SOILS.mxd Updated: 10-5-07
Soils Units
AgC (Alderwood gravelly sandy loam)
AgD (Alderwood gravelly sandy loam)
AkF (Alderwood and Kitsap soils)
AmC (Arents, Alderwood material)
An (Arents, Everett material)
BeC (Beausite gravelly sandy loam)
BeD (Beausite gravelly sandy loam)
EvC (Everett gravelly sandy loam)
EvD (Everett gravelly sandy loam)
InC (Indianola loamy fine sand)
InD (Indianola loamy fine sand)
Ng (Newberg silty loam)
PITS
Pc (Pilchuck loamy fine sand)
Pu (Puget silty clay loam)
Py (Puyallup fine sandy loam)
Rh (Riverwash)
Sk (Seattle muck)
So (Snohomish silt loam)
Tu (Tukwila muck)
Ur (Urban land)
Wo (Woodinville silt loam)
24 I-405, Tukwila to Renton Improvement Project (I-5 to SR 169 – Phase 2)
Geology and Soils Technical Memorandum
July 2007
Exhibit 5: Soil Units, Sheet 3
SW 16th St
S W G r a d y W a y
O
a
k
e
s
d
a
l
e
A v
e
S
W
SW 16th St
L
i
n
d
A
v
e
S
W
BN
SF
S
p
ringbrook
C
r
e
e
k
S
p
i
n
g
b
r
o
o
k
T
r
a
i
l
MP 2MP 2.0MP 1.9MP 1.8MP 1.7MP 1.6
MP 1.5
MP 1.4
MP 1.3
Sheet
8
Sheet
1
Sheet
4
Sheet
5
Sheet
2
Sheet
3 Sheet
6
Sheet
7
TUKWILA RENTON
Project Area
Water Body
Stream - Open Channel
Stream - Pipe
Railroad
Trail
Other Roads
Local Road
Freeway
Municipality 0250500
Feet
TRIP_GEO_SOILS.mxd Updated: 10-5-07
Soils Units
AgC (Alderwood gravelly sandy loam)
AgD (Alderwood gravelly sandy loam)
AkF (Alderwood and Kitsap soils)
AmC (Arents, Alderwood material)
An (Arents, Everett material)
BeC (Beausite gravelly sandy loam)
BeD (Beausite gravelly sandy loam)
EvC (Everett gravelly sandy loam)
EvD (Everett gravelly sandy loam)
InC (Indianola loamy fine sand)
InD (Indianola loamy fine sand)
Ng (Newberg silty loam)
PITS
Pc (Pilchuck loamy fine sand)
Pu (Puget silty clay loam)
Py (Puyallup fine sandy loam)
Rh (Riverwash)
Sk (Seattle muck)
So (Snohomish silt loam)
Tu (Tukwila muck)
Ur (Urban land)
Wo (Woodinville silt loam)
I-405, Tukwila to Renton Improvement Project (I-5 to SR 169 – Phase 2) Page 25
Geology and Soils Technical Memorandum
July 2007
Exhibit 6: Soil Units, Sheet 4
MP 25.3
MP 25.2
MP 25.1
MP 25.0
MP 24.9
MP 24.8
MP 24.7
MP 24.6
MP 24.5
MP 24.4
SW 41st St
S W 3 3rd S t
Southern
Project
Limit
SW 43rd St
E
a
s
t
V
a
l
l
e
y
R
d
T
a
l
b
o
t
R
d
S
P a n ther
C
reek
KENT CITY
LIMIT
RENTON
CITY
LIMIT
RENTON
CITY
LIMIT
UNINCORPORATED
KING COUNTY
Valley
Medical
Center
Sheet
8
Sheet
1
Sheet
4
Sheet
5
Sheet
2
Sheet
3 Sheet
6
Sheet
7
TUKWILA RENTON
Project Area
Water Body
Stream - Open Channel
Stream - Pipe
Railroad
Trail
Other Roads
Local Road
Freeway
Municipality 0250500
Feet
TRIP_GEO_SOILS.mxd Updated: 10-5-07
Soils Units
AgC (Alderwood gravelly sandy loam)
AgD (Alderwood gravelly sandy loam)
AkF (Alderwood and Kitsap soils)
AmC (Arents, Alderwood material)
An (Arents, Everett material)
BeC (Beausite gravelly sandy loam)
BeD (Beausite gravelly sandy loam)
EvC (Everett gravelly sandy loam)
EvD (Everett gravelly sandy loam)
InC (Indianola loamy fine sand)
InD (Indianola loamy fine sand)
Ng (Newberg silty loam)
PITS
Pc (Pilchuck loamy fine sand)
Pu (Puget silty clay loam)
Py (Puyallup fine sandy loam)
Rh (Riverwash)
Sk (Seattle muck)
So (Snohomish silt loam)
Tu (Tukwila muck)
Ur (Urban land)
Wo (Woodinville silt loam)
26 I-405, Tukwila to Renton Improvement Project (I-5 to SR 169 – Phase 2)
Geology and Soils Technical Memorandum
July 2007
Exhibit 7: Soil Units, Sheet 5
MP 26.0
MP 25.9
MP 25.8
MP 25.7
MP 25.5
MP 25.4
MP 25.3
MP 25.2
MP 25.1
MP 25.6
S W 27th S t
SW 19th St
E
a
s
t
V a
l
l
e
y
R
d
SW 23rd St
T a l b o t
R d
S
P
a
n
t
h
e
r
C
r
e
e
k
Sheet
8
Sheet
1
Sheet
4
Sheet
5
Sheet
2
Sheet
3 Sheet
6
Sheet
7
TUKWILA RENTON
Project Area
Water Body
Stream - Open Channel
Stream - Pipe
Railroad
Trail
Other Roads
Local Road
Freeway
Municipality 0250500
Feet
TRIP_GEO_SOILS.mxd Updated: 10-5-07
Soils Units
AgC (Alderwood gravelly sandy loam)
AgD (Alderwood gravelly sandy loam)
AkF (Alderwood and Kitsap soils)
AmC (Arents, Alderwood material)
An (Arents, Everett material)
BeC (Beausite gravelly sandy loam)
BeD (Beausite gravelly sandy loam)
EvC (Everett gravelly sandy loam)
EvD (Everett gravelly sandy loam)
InC (Indianola loamy fine sand)
InD (Indianola loamy fine sand)
Ng (Newberg silty loam)
PITS
Pc (Pilchuck loamy fine sand)
Pu (Puget silty clay loam)
Py (Puyallup fine sandy loam)
Rh (Riverwash)
Sk (Seattle muck)
So (Snohomish silt loam)
Tu (Tukwila muck)
Ur (Urban land)
Wo (Woodinville silt loam)
I-405, Tukwila to Renton Improvement Project (I-5 to SR 169 – Phase 2) Page 27
Geology and Soils Technical Memorandum
July 2007
Exhibit 8: Soil Units, Sheet 6
MP 26.5
MP 26.4
MP 26.3
MP 26.2
MP 26.1
MP 26.0
MP 25.9
MP 25.8
SW 16th St
SW 19th St
L
a
k
e
A
v
e
S
L
i
n
d
A
v
e
S
W
SGr a d y W a y
R a i n i e r A v e S
S 15th St
M
MP 2.7
MP 2.6
MP 2.5MP 2.4MP 2.3MP 2.2MP 2.1MP 2.0
Sheet
8
Sheet
1
Sheet
4
Sheet
5
Sheet
2
Sheet
3 Sheet
6
Sheet
7
TUKWILA RENTON
Project Area
Water Body
Stream - Open Channel
Stream - Pipe
Railroad
Trail
Other Roads
Local Road
Freeway
Municipality 0250500
Feet
TRIP_GEO_SOILS.mxd Updated: 10-5-07
Soils Units
AgC (Alderwood gravelly sandy loam)
AgD (Alderwood gravelly sandy loam)
AkF (Alderwood and Kitsap soils)
AmC (Arents, Alderwood material)
An (Arents, Everett material)
BeC (Beausite gravelly sandy loam)
BeD (Beausite gravelly sandy loam)
EvC (Everett gravelly sandy loam)
EvD (Everett gravelly sandy loam)
InC (Indianola loamy fine sand)
InD (Indianola loamy fine sand)
Ng (Newberg silty loam)
PITS
Pc (Pilchuck loamy fine sand)
Pu (Puget silty clay loam)
Py (Puyallup fine sandy loam)
Rh (Riverwash)
Sk (Seattle muck)
So (Snohomish silt loam)
Tu (Tukwila muck)
Ur (Urban land)
Wo (Woodinville silt loam)
28 I-405, Tukwila to Renton Improvement Project (I-5 to SR 169 – Phase 2)
Geology and Soils Technical Memorandum
July 2007
Exhibit 9: Soil Units, Sheet 7
T
a
l
b
o
t
R
d
S
B
e
a
c
o
n
W
a
y
S
S 7t h St
B e n s o n
R d
S
W
i
l
l
i
a
m
s
A
v
e
S
S Gr a d y W a y
R
o
l
l
i
n
g
H
i
l
l
s
C
r
e
e
k
S 15th St
S
P
u
g
e
t
D
r
B
e
n
s
o
n
R
d
S
T
h
u
n
d
e
r
H
i
l
l
s
C
r
e
e
k
S 5th St
S 6th St
B N S F
Renton
City
Hall
MP 3.4
MP 3.3
MP 3.2
MP 3.1
MP 2.9
MP 2.8
MP 2.7
MP 2.6
MP 3.0
Sheet
8
Sheet
1
Sheet
4
Sheet
5
Sheet
2
Sheet
3 Sheet
6
Sheet
7
TUKWILA RENTON
Project Area
Water Body
Stream - Open Channel
Stream - Pipe
Railroad
Trail
Other Roads
Local Road
Freeway
Municipality 0250500
Feet
TRIP_GEO_SOILS.mxd Updated: 10-5-07
Soils Units
AgC (Alderwood gravelly sandy loam)
AgD (Alderwood gravelly sandy loam)
AkF (Alderwood and Kitsap soils)
AmC (Arents, Alderwood material)
An (Arents, Everett material)
BeC (Beausite gravelly sandy loam)
BeD (Beausite gravelly sandy loam)
EvC (Everett gravelly sandy loam)
EvD (Everett gravelly sandy loam)
InC (Indianola loamy fine sand)
InD (Indianola loamy fine sand)
Ng (Newberg silty loam)
PITS
Pc (Pilchuck loamy fine sand)
Pu (Puget silty clay loam)
Py (Puyallup fine sandy loam)
Rh (Riverwash)
Sk (Seattle muck)
So (Snohomish silt loam)
Tu (Tukwila muck)
Ur (Urban land)
Wo (Woodinville silt loam)
I-405, Tukwila to Renton Improvement Project (I-5 to SR 169 – Phase 2) Page 29
Geology and Soils Technical Memorandum
July 2007
Exhibit 10: Soil Units, Sheet 8
CedarRiverTrail
M
a
p
l
e
V
a
ll
e
y
H
w
y
Northern
Project
Limit
H o u s e r W a y S
N 3 r d S t
B r o ns on
W
ay N
NE 3 r d S t
R
e
n
t
o
n
A
v
e
S
C e
d
a r
A v e S
B NS F
S 3 r d S t
N 4th St
C e d a r R i v e r
N 2nd St
MP 4.4
MP 4.3
MP 4.2
MP 4.0
MP 3.4
MP 4.1
MP 3.9
MP 3.8
MP 3.7
MP 3.6
MP 3.5
W
i
l
l
i
a
m
A
v
e
S
M
a
i
n
A
v
e
S
W
e
l
l
s
A
v
e
S
M
i
l
l
A
v
e
S
Sheet
8
Sheet
1
Sheet
4
Sheet
5
Sheet
2
Sheet
3 Sheet
6
Sheet
7
TUKWILA RENTON
Project Area
Water Body
Stream - Open Channel
Stream - Pipe
Railroad
Trail
Other Roads
Local Road
Freeway
Municipality 0250500
Feet
TRIP_GEO_SOILS.mxd Updated: 10-5-07
Soils Units
AgC (Alderwood gravelly sandy loam)
AgD (Alderwood gravelly sandy loam)
AkF (Alderwood and Kitsap soils)
AmC (Arents, Alderwood material)
An (Arents, Everett material)
BeC (Beausite gravelly sandy loam)
BeD (Beausite gravelly sandy loam)
EvC (Everett gravelly sandy loam)
EvD (Everett gravelly sandy loam)
InC (Indianola loamy fine sand)
InD (Indianola loamy fine sand)
Ng (Newberg silty loam)
PITS
Pc (Pilchuck loamy fine sand)
Pu (Puget silty clay loam)
Py (Puyallup fine sandy loam)
Rh (Riverwash)
Sk (Seattle muck)
So (Snohomish silt loam)
Tu (Tukwila muck)
Ur (Urban land)
Wo (Woodinville silt loam)
30 I-405, Tukwila to Renton Improvement Project (I-5 to SR 169 – Phase 2)
Geology and Soils Technical Memorandum
July 2007
Exhibit 11: Surface Geologic Units, Sheet 1
S
o
u
t
h
c
e
n
t
e
r
P
a
r
k
w
a
y
KlickitatDr
Western
Project
Limit
Tukwila Parkway
Westfield
Shoppingtown
Mall
Southcenter Blvd
C
o
t
t
a
g
e
C
r
e
e
k
G i l l i a m C r e e k
Tukwila
City
Hall
MP 0.4
MP 0.3
MP 0.2
MP 0.1
MP 0.0
MP 0.5
Gilliam Creek
Qgl
Qa
Qgt
Qgo Qgo
Oian
Ec(2r)
Qgt
Qgt
Ec(2r)
Oian
Oian
Qgo
Sheet
8
Sheet
1
Sheet
4
Sheet
5
Sheet
2
Sheet
3 Sheet
6
Sheet
7
TUKWILA RENTON
Project Area
Water Body
Stream - Open Channel
Stream - Pipe
Railroad
Trail
Other Roads
Local Road
Freeway
Municipality
0250500
Feet
TRIP_GEO_GEOLOGY.mxd Updated: 10-5-07
Surficial Geologic Units
Ec(2r) (Renton Formation)
Ec(2t) (Tiger Mountain Formation)
Evc(t) (Tukwila Formation)
Oian (intrusive andesite)
Qa (alluvium)
Qgl (glaciolacustrine deposits, Fraser-age)
Qgo (continental glacial outwash, Fraser-age)
Qgpc (continental glacial drift, pre-Fraser, and nonglacial deposits)
Qgt (till)
Qls (mass-wasting deposits, mostly landslides)
Qp (peat deposits)
I-405, Tukwila to Renton Improvement Project (I-5 to SR 169 – Phase 2) Page 31
Geology and Soils Technical Memorandum
July 2007
Exhibit 12: Surface Geologic Units, Sheet 2
I
n
t
e
r
u
r
b
a
n
T
r
a
i
l
W
V
a
l
l
e
y
H
w
y
Interurb
a
n
A
ve
S
R
E
N
T
O
N
C
I
T
Y
L
I
M
I
T
S
T
U
K
W
I
L
A
C
I
T
Y
L
I
M
I
T
S
S o u t h c e n t e r B l v d
M
o
n
ster
R
d
S
W
Westfield
Shoppingtown
Mall
6
5
t
h
A
v
e
S
BN
SF
G r e e n R i v er
C
o
t
t
a
g
e
C
r
e
e
k
G i l l i a m C r e e k
G r e e n R i v e r T r a i l
Tukwila
City
Hall
D
u
w
a
m
i
s
h
-
G
r
e
e
n
R
i
v
e
r
T
r
a
i
l
U
n
io
n
P
a
c
i
f
ic
MP
MP 1.2
MP 1.1
MP 1.0
MP 0.9
MP 0.8
MP 0.7
MP 0.6
P 0.4
MP 0.5
D
u
w
a
m
i
s h
-G r e e n R i v e r
T
r
i
a
l
T u k w i l a P a r k w a y
A
n
d
o
v
e
r
P
a
r
k
E
G
r
e
e
n
R
i
v
e
r
Qa
Oian
Ec(2r)
Qgt
Ec(2r)
Evc(t)
Oian
Qgt
Oian
Sheet
8
Sheet
1
Sheet
4
Sheet
5
Sheet
2
Sheet
3 Sheet
6
Sheet
7
TUKWILA RENTON
Project Area
Water Body
Stream - Open Channel
Stream - Pipe
Railroad
Trail
Other Roads
Local Road
Freeway
Municipality
0250500
Feet
TRIP_GEO_GEOLOGY.mxd Updated: 10-5-07
Surficial Geologic Units
Ec(2r) (Renton Formation)
Ec(2t) (Tiger Mountain Formation)
Evc(t) (Tukwila Formation)
Oian (intrusive andesite)
Qa (alluvium)
Qgl (glaciolacustrine deposits, Fraser-age)
Qgo (continental glacial outwash, Fraser-age)
Qgpc (continental glacial drift, pre-Fraser, and nonglacial deposits)
Qgt (till)
Qls (mass-wasting deposits, mostly landslides)
Qp (peat deposits)
32 I-405, Tukwila to Renton Improvement Project (I-5 to SR 169 – Phase 2)
Geology and Soils Technical Memorandum
July 2007
Exhibit 13: Surface Geologic Units, Sheet 3
SW 16th St
S W G r a d y W a y
O
a
k
e
s
d
a
l
e
A v
e
S
W
SW 16th St
L
i
n
d
A
v
e
S
W
BN
SF
S
p
ringbrook
C
r
e
e
k
S
p
i
n
g
b
r
o
o
k
T
r
a
i
l
MP 2MP 2.0MP 1.9MP 1.8MP 1.7MP 1.6
MP 1.5
MP 1.4
MP 1.3
Qa
Qp
Qa
Ec(2r)
Evc(t)
Sheet
8
Sheet
1
Sheet
4
Sheet
5
Sheet
2
Sheet
3 Sheet
6
Sheet
7
TUKWILA RENTON
Project Area
Water Body
Stream - Open Channel
Stream - Pipe
Railroad
Trail
Other Roads
Local Road
Freeway
Municipality
0250500
Feet
TRIP_GEO_GEOLOGY.mxd Updated: 10-5-07
Surficial Geologic Units
Ec(2r) (Renton Formation)
Ec(2t) (Tiger Mountain Formation)
Evc(t) (Tukwila Formation)
Oian (intrusive andesite)
Qa (alluvium)
Qgl (glaciolacustrine deposits, Fraser-age)
Qgo (continental glacial outwash, Fraser-age)
Qgpc (continental glacial drift, pre-Fraser, and nonglacial deposits)
Qgt (till)
Qls (mass-wasting deposits, mostly landslides)
Qp (peat deposits)
I-405, Tukwila to Renton Improvement Project (I-5 to SR 169 – Phase 2) Page 33
Geology and Soils Technical Memorandum
July 2007
Exhibit 14: Surface Geologic Units, Sheet 4
MP 25.3
MP 25.2
MP 25.1
MP 25.0
MP 24.9
MP 24.8
MP 24.7
MP 24.6
MP 24.5
MP 24.4
SW 41st St
S W 3 3rd S t
Southern
Project
Limit
SW 43rd St
E
a
s
t
V
a
l
l
e
y
R
d
T
a
l
b
o
t
R
d
S
P a n ther
C
re
ek
KENT CITY
LIMIT
RENTON
CITY
LIMIT
RENTON
CITY
LIMIT
UNINCORPORATED
KING COUNTY
Valley
Medical
Center
Qgt
Qp
Qa
Qgpc
Ec(2r)
Ec(2r)
Ec(2r)Ec(2r)
Oian
Sheet
8
Sheet
1
Sheet
4
Sheet
5
Sheet
2
Sheet
3 Sheet
6
Sheet
7
TUKWILA RENTON
Project Area
Water Body
Stream - Open Channel
Stream - Pipe
Railroad
Trail
Other Roads
Local Road
Freeway
Municipality
0250500
Feet
TRIP_GEO_GEOLOGY.mxd Updated: 10-5-07
Surficial Geologic Units
Ec(2r) (Renton Formation)
Ec(2t) (Tiger Mountain Formation)
Evc(t) (Tukwila Formation)
Oian (intrusive andesite)
Qa (alluvium)
Qgl (glaciolacustrine deposits, Fraser-age)
Qgo (continental glacial outwash, Fraser-age)
Qgpc (continental glacial drift, pre-Fraser, and nonglacial deposits)
Qgt (till)
Qls (mass-wasting deposits, mostly landslides)
Qp (peat deposits)
34 I-405, Tukwila to Renton Improvement Project (I-5 to SR 169 – Phase 2)
Geology and Soils Technical Memorandum
July 2007
Exhibit 15: Surface Geologic Units, Sheet 5
MP 26.0
MP 25.9
MP 25.8
MP 25.7
MP 25.5
MP 25.4
MP 25.3
MP 25.2
MP 25.1
MP 25.6
S W 27th S t
SW 19th St
E
a
s
t
V a
l
l
e
y
R
d
SW 23rd St
T a l b o t
R d
S
P
a
n
t
h
e
r
C
r
e
e
k
Qp
Qgt
Qa
Ec(2r)
Qa
Ec(2r)
Ec(2t)
Oian
Sheet
8
Sheet
1
Sheet
4
Sheet
5
Sheet
2
Sheet
3 Sheet
6
Sheet
7
TUKWILA RENTON
Project Area
Water Body
Stream - Open Channel
Stream - Pipe
Railroad
Trail
Other Roads
Local Road
Freeway
Municipality
0250500
Feet
TRIP_GEO_GEOLOGY.mxd Updated: 10-5-07
Surficial Geologic Units
Ec(2r) (Renton Formation)
Ec(2t) (Tiger Mountain Formation)
Evc(t) (Tukwila Formation)
Oian (intrusive andesite)
Qa (alluvium)
Qgl (glaciolacustrine deposits, Fraser-age)
Qgo (continental glacial outwash, Fraser-age)
Qgpc (continental glacial drift, pre-Fraser, and nonglacial deposits)
Qgt (till)
Qls (mass-wasting deposits, mostly landslides)
Qp (peat deposits)
I-405, Tukwila to Renton Improvement Project (I-5 to SR 169 – Phase 2) Page 35
Geology and Soils Technical Memorandum
July 2007
Exhibit 16: Surface Geologic Units, Sheet 6
MP 26.5
MP 26.4
MP 26.3
MP 26.2
MP 26.1
MP 26.0
MP 25.9
MP 25.8
SW 16th St
SW 19th St
L
a
k
e
A
v
e
S
L
i
n
d
A
v
e
S
W
SGr a d yWa y
R a i n i e r A v e S
S 15th St
M
MP 2.7
MP 2.6
MP 2.5MP 2.4MP 2.3MP 2.2MP 2.1MP 2.0
Qa
Qp
Ec(2r)
Qgt
Qgo
Qa
Sheet
8
Sheet
1
Sheet
4
Sheet
5
Sheet
2
Sheet
3 Sheet
6
Sheet
7
TUKWILA RENTON
Project Area
Water Body
Stream - Open Channel
Stream - Pipe
Railroad
Trail
Other Roads
Local Road
Freeway
Municipality
0250500
Feet
TRIP_GEO_GEOLOGY.mxd Updated: 10-5-07
Surficial Geologic Units
Ec(2r) (Renton Formation)
Ec(2t) (Tiger Mountain Formation)
Evc(t) (Tukwila Formation)
Oian (intrusive andesite)
Qa (alluvium)
Qgl (glaciolacustrine deposits, Fraser-age)
Qgo (continental glacial outwash, Fraser-age)
Qgpc (continental glacial drift, pre-Fraser, and nonglacial deposits)
Qgt (till)
Qls (mass-wasting deposits, mostly landslides)
Qp (peat deposits)
36 I-405, Tukwila to Renton Improvement Project (I-5 to SR 169 – Phase 2)
Geology and Soils Technical Memorandum
July 2007
Exhibit 17: Surface Geologic Units, Sheet 7
T
a
l
b
o
t
R
d
S
B
e
a
c
o
n
W
a
y
S
S 7t h St
B e n s o n
R d
S
W
i
l
l
i
a
m
s
A
v
e
S
S Gr a d y W a y
R
o
l
l
i
n
g
H
i
l
l
s
C
r
e
e
k
S 15th St
S
P
u
g
e
t
D
r
B
e
n
s
o
n
R
d
S
T
h
u
n
d
e
r
H
i
l
l
s
C
r
e
e
k
S 5th St
S 6th St
B N S F
Renton
City
Hall
MP 3.4
MP 3.3
MP 3.2
MP 3.1
MP 2.9
MP 2.8
MP 2.7
MP 2.6
MP 3.0
Qa
Qgt
Ec(2r)
Ec(2r)
Qgo
Qgo
Qgo
Qgpc
Ec(2r)
Sheet
8
Sheet
1
Sheet
4
Sheet
5
Sheet
2
Sheet
3 Sheet
6
Sheet
7
TUKWILA RENTON
Project Area
Water Body
Stream - Open Channel
Stream - Pipe
Railroad
Trail
Other Roads
Local Road
Freeway
Municipality
0250500
Feet
TRIP_GEO_GEOLOGY.mxd Updated: 10-5-07
Surficial Geologic Units
Ec(2r) (Renton Formation)
Ec(2t) (Tiger Mountain Formation)
Evc(t) (Tukwila Formation)
Oian (intrusive andesite)
Qa (alluvium)
Qgl (glaciolacustrine deposits, Fraser-age)
Qgo (continental glacial outwash, Fraser-age)
Qgpc (continental glacial drift, pre-Fraser, and nonglacial deposits)
Qgt (till)
Qls (mass-wasting deposits, mostly landslides)
Qp (peat deposits)
I-405, Tukwila to Renton Improvement Project (I-5 to SR 169 – Phase 2) Page 37
Geology and Soils Technical Memorandum
July 2007
Exhibit 18: Surface Geologic Units, Sheet 8
CedarRiverTrail
M
a
p
l
e
V
a
ll
e
y
H
w
y
Northern
Project
Limit
H o u s e r W a y S
N 3 r d S t
B r o ns on
W
a y N
NE 3 r d S t
R
e
n
t
o
n
A
v
e
S
C e
d
a r
A v e S
B NS F
S 3 r d S t
N 4th St
C e d a r R i v e r
N 2nd St
MP 4.4
MP 4.3
MP 4.2
MP 4.0
MP 3.4
MP 4.1
MP 3.9
MP 3.8
MP 3.7
MP 3.6
MP 3.5
W
i
l
l
i
a
m
A
v
e
S
M
a
i
n
A
v
e
S
W
e
l
l
s
A
v
e
S
M
i
l
l
A
v
e
S
Qa
Qgo
Qgo
Ec(2r)
Ec(2r)
Qgpc
Qgpc
Qls
Qgpc
Sheet
8
Sheet
1
Sheet
4
Sheet
5
Sheet
2
Sheet
3 Sheet
6
Sheet
7
TUKWILA RENTON
Project Area
Water Body
Stream - Open Channel
Stream - Pipe
Railroad
Trail
Other Roads
Local Road
Freeway
Municipality
0250500
Feet
TRIP_GEO_GEOLOGY.mxd Updated: 10-5-07
Surficial Geologic Units
Ec(2r) (Renton Formation)
Ec(2t) (Tiger Mountain Formation)
Evc(t) (Tukwila Formation)
Oian (intrusive andesite)
Qa (alluvium)
Qgl (glaciolacustrine deposits, Fraser-age)
Qgo (continental glacial outwash, Fraser-age)
Qgpc (continental glacial drift, pre-Fraser, and nonglacial deposits)
Qgt (till)
Qls (mass-wasting deposits, mostly landslides)
Qp (peat deposits)
38 I-405, Tukwila to Renton Improvement Project (I-5 to SR 169 – Phase 2)
Geology and Soils Technical Memorandum
July 2007
Exhibit 19: Geologic Hazard Areas, Sheet 1
S
o
u
t
h
c
e
n
t
e
r
P
a
r
k
w
a
y
Klickitat
Dr
Western
Project
Limit
Tukwila Parkway
Westfield
Shoppingtown
Mall
Southcenter
B
lvd
C
o
t
t
a
g
e
C
r
e
e
k
G i l l i a m C r e e k
Tukwila
City
Hall
MP 0.4
MP 0.3
MP 0.2
MP 0.1
MP 0.0
MP 0.5
Gilliam Creek
Sheet
8
Sheet
1
Sheet
4
Sheet
5
Sheet
2
Sheet
3 Sheet
6
Sheet
7
TUKWILA RENTON
Project Area
Erosion Hazard
Steep Slope (Greater than 40%)
Mine Subsidence Hazard
Landslide Hazard
Stream - Open Channel
Stream - Pipe
Water Body
Railroad
Trail
Other Roads
Local Road
Freeway
Municipality
0250500
Feet
TRIP_GEO_HAZARD.mxd Updated: 10-5-07
I-405, Tukwila to Renton Improvement Project (I-5 to SR 169 – Phase 2) Page 39
Geology and Soils Technical Memorandum
July 2007
Exhibit 20: Geologic Hazard Areas, Sheet 2
I
n
t
e
r
u
r
b
a
n
T
r
a
i
l
W
V
a
l
l
e
y
H
w
y
Interurban
A
v
e
S
R
E
N
T
O
N
C
I
T
Y
L
I
M
I
T
S
T
U
K
W
I
L
A
C
I
T
Y
L
I
M
I
T
S
S o u t h c e n t e r B l v d
M
o
n
ster
R
d
S
W
Westfield
Shoppingtown
Mall
6
5
t
h
A
v
e
S
BN
SF
G r e e n R iver
C
o
t
t
a
g
e
C
r
e
e
k
G i l l i a m C r e e k
G r e e n R i v e r T r a i l
Tukwila
City
Hall
D
u
w
a
m
i
s
h
-
G
r
e
e
n
R
i
v
e
r
T
r
a
i
l
Un
io
n
P
a
c
i
f
ic
MP
MP 1.2
MP 1.1
MP 1.0
MP 0.9
MP 0.8
MP 0.7
MP 0.6
P 0.4
MP 0.5
D
u
w
a
m
i
s h
-G r e e n R i v e r
T
r
i
a
l
T u k w i l a P a r k w a y
A
n
d
o
v
e
r
P
a
r
k
E
G
r
e
e
n
R
i
v
e
r
Sheet
8
Sheet
1
Sheet
4
Sheet
5
Sheet
2
Sheet
3 Sheet
6
Sheet
7
TUKWILA RENTON
Project Area
Erosion Hazard
Steep Slope (Greater than 40%)
Mine Subsidence Hazard
Landslide Hazard
Stream - Open Channel
Stream - Pipe
Water Body
Railroad
Trail
Other Roads
Local Road
Freeway
Municipality
0250500
Feet
TRIP_GEO_HAZARD.mxd Updated: 10-5-07
40 I-405, Tukwila to Renton Improvement Project (I-5 to SR 169 – Phase 2)
Geology and Soils Technical Memorandum
July 2007
Exhibit 21: Geologic Hazard Areas, Sheet 3
SW 16th St
S W G r a d yWa y
O
a
k
e
s
d
a
l
e
A v
e
S
W
SW 16th St
L
i
n
d
A
v
e
S
W
BN
SF
S
pringbrook
C
r
e
e
k
S
p
i
n
g
b
r
o
o
k
T
r
a
i
l
MP 2MP 2.0MP 1.9MP 1.8MP 1.7MP 1.6
MP 1.5
MP 1.4
MP 1.3
Sheet
8
Sheet
1
Sheet
4
Sheet
5
Sheet
2
Sheet
3 Sheet
6
Sheet
7
TUKWILA RENTON
Project Area
Erosion Hazard
Steep Slope (Greater than 40%)
Mine Subsidence Hazard
Landslide Hazard
Stream - Open Channel
Stream - Pipe
Water Body
Railroad
Trail
Other Roads
Local Road
Freeway
Municipality
0250500
Feet
TRIP_GEO_HAZARD.mxd Updated: 10-5-07
I-405, Tukwila to Renton Improvement Project (I-5 to SR 169 – Phase 2) Page 41
Geology and Soils Technical Memorandum
July 2007
Exhibit 22: Geologic Hazard Areas, Sheet 4
MP 25.3
MP 25.2
MP 25.1
MP 25.0
MP 24.9
MP 24.8
MP 24.7
MP 24.6
MP 24.5
MP 24.4
SW 41st St
S W 33rd S t
Southern
Project
Limit
SW 43rd St
E
a
s
t
V
a
l
l
e
y
R
d
T
a
l
b
o
t
R
d
S
P a n ther
C
reek
KENT CITY
LIMIT
RENTON
CITY
LIMIT
RENTON
CITY
LIMIT
UNINCORPORATED
KING COUNTY
Valley
Medical
Center
Sheet
8
Sheet
1
Sheet
4
Sheet
5
Sheet
2
Sheet
3 Sheet
6
Sheet
7
TUKWILA RENTON
Project Area
Erosion Hazard
Steep Slope (Greater than 40%)
Mine Subsidence Hazard
Landslide Hazard
Stream - Open Channel
Stream - Pipe
Water Body
Railroad
Trail
Other Roads
Local Road
Freeway
Municipality
0250500
Feet
TRIP_GEO_HAZARD.mxd Updated: 10-5-07
42 I-405, Tukwila to Renton Improvement Project (I-5 to SR 169 – Phase 2)
Geology and Soils Technical Memorandum
July 2007
Exhibit 23: Geologic Hazard Areas, Sheet 5
MP 26.0
MP 25.9
MP 25.8
MP 25.7
MP 25.5
MP 25.4
MP 25.3
MP 25.2
MP 25.1
MP 25.6
S W 27t h S t
SW 19th St
E
a
s
t
V
a
l
l
e
yR
d
SW 23rd St
T a l b o t
R d
S
P
a
n
t
h
e
r
C
r
e
e
k
Sheet
8
Sheet
1
Sheet
4
Sheet
5
Sheet
2
Sheet
3 Sheet
6
Sheet
7
TUKWILA RENTON
Project Area
Erosion Hazard
Steep Slope (Greater than 40%)
Mine Subsidence Hazard
Landslide Hazard
Stream - Open Channel
Stream - Pipe
Water Body
Railroad
Trail
Other Roads
Local Road
Freeway
Municipality
0250500
Feet
TRIP_GEO_HAZARD.mxd Updated: 10-5-07
I-405, Tukwila to Renton Improvement Project (I-5 to SR 169 – Phase 2) Page 43
Geology and Soils Technical Memorandum
July 2007
Exhibit 24: Geologic Hazard Areas, Sheet 6
MP 26.5
MP 26.4
MP 26.3
MP 26.2
MP 26.1
MP 26.0
MP 25.9
MP 25.8
SW 16th St
SW 19th St
L
a
k
e
A
v
e
S
L
i
n
d
A
v
e
S
W
S G r a d yWa y
R a i ni e r A v e S
S 15th St
M
MP 2.7
MP 2.6
MP 2.5MP 2.4MP 2.3MP 2.2MP 2.1MP 2.0
Sheet
8
Sheet
1
Sheet
4
Sheet
5
Sheet
2
Sheet
3 Sheet
6
Sheet
7
TUKWILA RENTON
Project Area
Erosion Hazard
Steep Slope (Greater than 40%)
Mine Subsidence Hazard
Landslide Hazard
Stream - Open Channel
Stream - Pipe
Water Body
Railroad
Trail
Other Roads
Local Road
Freeway
Municipality
0250500
Feet
TRIP_GEO_HAZARD.mxd Updated: 10-5-07
44 I-405, Tukwila to Renton Improvement Project (I-5 to SR 169 – Phase 2)
Geology and Soils Technical Memorandum
July 2007
Exhibit 25: Geologic Hazard Areas, Sheet 7
T
a
l
b
o
t
R
d
S
B
e
a
c
o
n
W
a
y
S
S 7 th St
B e n s o n
R d
S
W
i
l
l
i
a
m
s
A
v
e
S
S G r a d y W a y
R
o
l
l
i
n
g
H
i
l
l
s
C
r
e
e
k
S 15th St
S
P
u
g
e
t
D
r
B
e
n
s
o
n
R
d
S
T
h
u
n
d
e
r
H
i
l
l
s
C
r
e
e
k
S 5th St
S 6th St
B N S F
Renton
City
Hall
MP 3.4
MP 3.3
MP 3.2
MP 3.1
MP 2.9
MP 2.8
MP 2.7
MP 2.6
MP 3.0
Sheet
8
Sheet
1
Sheet
4
Sheet
5
Sheet
2
Sheet
3 Sheet
6
Sheet
7
TUKWILA RENTON
Project Area
Erosion Hazard
Steep Slope (Greater than 40%)
Mine Subsidence Hazard
Landslide Hazard
Stream - Open Channel
Stream - Pipe
Water Body
Railroad
Trail
Other Roads
Local Road
Freeway
Municipality
0250500
Feet
TRIP_GEO_HAZARD.mxd Updated: 10-5-07
I-405, Tukwila to Renton Improvement Project (I-5 to SR 169 – Phase 2) Page 45
Geology and Soils Technical Memorandum
July 2007
Exhibit 26: Geologic Hazard Areas, Sheet 8
CedarRiverTrail
M
a
p
l
e
V
a
ll
e
y
H
w
y
Northern
Project
Limit
H o u s e r W a y
S
N 3 r d S t
B r o ns on
W a y N
NE 3 r d S t
R
e
n
t
o
n
A
v
e
S
C e d a r
A v e S
B N S F
S 3 r d S t
N 4th St
C e d a r R i v e r
N 2nd St
MP 4.4
MP 4.3
MP 4.2
MP 4.0
MP 3.4
MP 4.1
MP 3.9
MP 3.8
MP 3.7
MP 3.6
MP 3.5
W
i
l
l
i
a
m
A
v
e
S
M
a
i
n
A
v
e
S
W
e
l
l
s
A
v
e
S
M
i
l
l
A
v
e
S
Sheet
8
Sheet
1
Sheet
4
Sheet
5
Sheet
2
Sheet
3 Sheet
6
Sheet
7
TUKWILA RENTON
Project Area
Erosion Hazard
Steep Slope (Greater than 40%)
Mine Subsidence Hazard
Landslide Hazard
Stream - Open Channel
Stream - Pipe
Water Body
Railroad
Trail
Other Roads
Local Road
Freeway
Municipality
0250500
Feet
TRIP_GEO_HAZARD.mxd Updated: 10-5-07
46 I-405, Tukwila to Renton Improvement Project (I-5 to SR 169 – Phase 2)
Geology and Soils Technical Memorandum
July 2007
Exhibit 27: Soft Ground and Seismic Hazard Areas, Sheet 1
S
o
u
t
h
c
e
n
t
e
r
P
a
r
k
w
a
y
Klickitat
Dr
Western
Project
Limit
Tukwila Parkway
Westfield
Shoppingtown
Mall
Southcenter
B
lvd
C
o
t
t
a
g
e
C
r
e
e
k
G i l l i a m C r e e k
Tukwila
City
Hall
MP 0.4
MP 0.3
MP 0.2
MP 0.1
MP 0.0
MP 0.5
Gilliam Creek
Sheet
8
Sheet
1
Sheet
4
Sheet
5
Sheet
2
Sheet
3 Sheet
6
Sheet
7
TUKWILA RENTON
Project Area
Areas of Disturbed Soil
Soft Ground
Seismic Hazard Area
High
Moderate to High
Stream - Open Channel
Stream - Pipe
Water Body
Railroad
Trail
Other Roads
Local Road
Freeway
Municipality
0250500
Feet
TRIP_GEO_SFTGRND.mxd Updated: 10-5-07
I-405, Tukwila to Renton Improvement Project (I-5 to SR 169 – Phase 2) Page 47
Geology and Soils Technical Memorandum
July 2007
Exhibit 28: Soft Ground and Seismic Hazard Areas, Sheet 2
I
n
t
e
r
u
r
b
a
n
T
r
a
i
l
W
V
a
l
l
e
y
H
w
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Interurban
A
v
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S
R
E
N
T
O
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C
I
T
Y
L
I
M
I
T
S
T
U
K
W
I
L
A
C
I
T
Y
L
I
M
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T
S
S o u t h c e n t e r B l v d
M
o
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ster
R
d
S
W
Westfield
Shoppingtown
Mall
6
5
t
h
A
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S
BN
SF
G r e e n R iver
C
o
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t
a
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C
r
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k
G i l l i a m C r e e k
G r e e n R i v e r T r a i l
Tukwila
City
Hall
D
u
w
a
m
i
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h
-
G
r
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e
n
R
i
v
e
r
T
r
a
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l
Un
io
n
P
a
c
i
f
ic
MP
MP 1.2
MP 1.1
MP 1.0
MP 0.9
MP 0.8
MP 0.7
MP 0.6
P 0.4
MP 0.5
D
u
w
a
m
i
s h
-G r e e n R i v e r
T
r
i
a
l
T u k w i l a P a r k w a y
A
n
d
o
v
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r
P
a
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k
E
G
r
e
e
n
R
i
v
e
r
Sheet
8
Sheet
1
Sheet
4
Sheet
5
Sheet
2
Sheet
3 Sheet
6
Sheet
7
TUKWILA RENTON
Project Area
Areas of Disturbed Soil
Soft Ground
Seismic Hazard Area
High
Moderate to High
Stream - Open Channel
Stream - Pipe
Water Body
Railroad
Trail
Other Roads
Local Road
Freeway
Municipality
0250500
Feet
TRIP_GEO_SFTGRND.mxd Updated: 10-5-07
48 I-405, Tukwila to Renton Improvement Project (I-5 to SR 169 – Phase 2)
Geology and Soils Technical Memorandum
July 2007
Exhibit 29: Soft Ground and Seismic Hazard Areas, Sheet 3
SW 16th St
S W G r a d yWa y
O
a
k
e
s
d
a
l
e
A v
e
S
W
SW 16th St
L
i
n
d
A
v
e
S
W
BN
SF
S
pringbrook
C
r
e
e
k
S
p
i
n
g
b
r
o
o
k
T
r
a
i
l
MP 2MP 2.0MP 1.9MP 1.8MP 1.7MP 1.6
MP 1.5
MP 1.4
MP 1.3
Sheet
8
Sheet
1
Sheet
4
Sheet
5
Sheet
2
Sheet
3 Sheet
6
Sheet
7
TUKWILA RENTON
Project Area
Areas of Disturbed Soil
Soft Ground
Seismic Hazard Area
High
Moderate to High
Stream - Open Channel
Stream - Pipe
Water Body
Railroad
Trail
Other Roads
Local Road
Freeway
Municipality
0250500
Feet
TRIP_GEO_SFTGRND.mxd Updated: 10-5-07
I-405, Tukwila to Renton Improvement Project (I-5 to SR 169 – Phase 2) Page 49
Geology and Soils Technical Memorandum
July 2007
Exhibit 30: Soft Ground and Seismic Hazard Areas, Sheet 4
SW 41st St
S W 33rd S t
Southern
Project
Limit
SW 43rd St
E
a
s
t
V
a
l
l
e
y
R
d
T
a
l
b
o
t
R
d
S
P a n ther
C
reek
KENT CITY
LIMIT
RENTON
CITY
LIMIT
RENTON
CITY
LIMIT
UNINCORPORATED
KING COUNTY
Valley
Medical
Center
Sheet
8
Sheet
1
Sheet
4
Sheet
5
Sheet
2
Sheet
3 Sheet
6
Sheet
7
TUKWILA RENTON
Project Area
Areas of Disturbed Soil
Soft Ground
Seismic Hazard Area
High
Moderate to High
Stream - Open Channel
Stream - Pipe
Water Body
Railroad
Trail
Other Roads
Local Road
Freeway
Municipality
0250500
Feet
TRIP_GEO_SFTGRND.mxd Updated: 10-5-07
50 I-405, Tukwila to Renton Improvement Project (I-5 to SR 169 – Phase 2)
Geology and Soils Technical Memorandum
July 2007
Exhibit 31: Soft Ground and Seismic Hazard Areas, Sheet 5
S W 27t h S t
SW 19th St
E
a
s
t
V
a
l
l
e
yR
d
SW 23rd St
T a l b o t
R d
S
P
a
n
t
h
e
r
C
r
e
e
k
Sheet
8
Sheet
1
Sheet
4
Sheet
5
Sheet
2
Sheet
3 Sheet
6
Sheet
7
TUKWILA RENTON
Project Area
Areas of Disturbed Soil
Soft Ground
Seismic Hazard Area
High
Moderate to High
Stream - Open Channel
Stream - Pipe
Water Body
Railroad
Trail
Other Roads
Local Road
Freeway
Municipality
0250500
Feet
TRIP_GEO_SFTGRND.mxd Updated: 10-5-07
I-405, Tukwila to Renton Improvement Project (I-5 to SR 169 – Phase 2) Page 51
Geology and Soils Technical Memorandum
July 2007
Exhibit 32: Soft Ground and Seismic Hazard Areas, Sheet 6
SW 16th St
SW 19th St
L
a
k
e
A
v
e
S
L
i
n
d
A
v
e
S
W
S G r a d yWa y
R a i ni e r A v e S
S 15th St
M
MP 2.7
MP 2.6
MP 2.5MP 2.4MP 2.3MP 2.2MP 2.1MP 2.0
Sheet
8
Sheet
1
Sheet
4
Sheet
5
Sheet
2
Sheet
3 Sheet
6
Sheet
7
TUKWILA RENTON
Project Area
Areas of Disturbed Soil
Soft Ground
Seismic Hazard Area
High
Moderate to High
Stream - Open Channel
Stream - Pipe
Water Body
Railroad
Trail
Other Roads
Local Road
Freeway
Municipality
0250500
Feet
TRIP_GEO_SFTGRND.mxd Updated: 10-5-07
52 I-405, Tukwila to Renton Improvement Project (I-5 to SR 169 – Phase 2)
Geology and Soils Technical Memorandum
July 2007
Exhibit 33: Soft Ground and Seismic Hazard Areas, Sheet 7
T
a
l
b
o
t
R
d
S
B
e
a
c
o
n
W
a
y
S
S 7 th St
B e n s o n
R d
S
W
i
l
l
i
a
m
s
A
v
e
S
S G r a d y W a y
R
o
l
l
i
n
g
H
i
l
l
s
C
r
e
e
k
S 15th St
S
P
u
g
e
t
D
r
B
e
n
s
o
n
R
d
S
T
h
u
n
d
e
r
H
i
l
l
s
C
r
e
e
k
S 5th St
S 6th St
B N S F
Renton
City
Hall
MP 3.4
MP 3.3
MP 3.2
MP 3.1
MP 2.9
MP 2.8
MP 2.7
MP 2.6
MP 3.0
Sheet
8
Sheet
1
Sheet
4
Sheet
5
Sheet
2
Sheet
3 Sheet
6
Sheet
7
TUKWILA RENTON
Project Area
Areas of Disturbed Soil
Soft Ground
Seismic Hazard Area
High
Moderate to High
Stream - Open Channel
Stream - Pipe
Water Body
Railroad
Trail
Other Roads
Local Road
Freeway
Municipality
0250500
Feet
TRIP_GEO_SFTGRND.mxd Updated: 10-5-07
I-405, Tukwila to Renton Improvement Project (I-5 to SR 169 – Phase 2) Page 53
Geology and Soils Technical Memorandum
July 2007
Exhibit 34: Soft Ground and Seismic Hazard Areas, Sheet 8
CedarRiverTrail
M
a
p
l
e
V
a
ll
e
y
H
w
y
Northern
Project
Limit
H o u s e r W a y
S
N 3 r d S t
B r o ns on
W a y N
NE 3 r d S t
R
e
n
t
o
n
A
v
e
S
C e d a r
A v e S
B N S F
S 3 r d S t
N 4th St
C e d a r R i v e r
N 2nd St
MP 4.4
MP 4.3
MP 4.2
MP 4.0
MP 3.4
MP 4.1
MP 3.9
MP 3.8
MP 3.7
MP 3.6
MP 3.5
W
i
l
l
i
a
m
A
v
e
S
M
a
i
n
A
v
e
S
W
e
l
l
s
A
v
e
S
M
i
l
l
A
v
e
S
Sheet
8
Sheet
1
Sheet
4
Sheet
5
Sheet
2
Sheet
3 Sheet
6
Sheet
7
TUKWILA RENTON
Project Area
Areas of Disturbed Soil
Soft Ground
Seismic Hazard Area
High
Moderate to High
Stream - Open Channel
Stream - Pipe
Water Body
Railroad
Trail
Other Roads
Local Road
Freeway
Municipality
0250500
Feet
TRIP_GEO_SFTGRND.mxd Updated: 10-5-07
54 I-405, Tukwila to Renton Improvement Project (I-5 to SR 169 – Phase 2)
Geology and Soils Technical Memorandum
July 2007
Appendix A: Methodology
How did we collect information on geology and soils for this report?
The I-405 Corridor Team collected information for this technical memorandum by reviewing the
following data sources:
•Previous investigations along I-405 and SR 167 conducted by Washington State Department of
Transportation (WSDOT) and others, including the borehole logs for these investigations.
•I-405, Renton Nickel Improvement Project, Geotechnical Baseline Report.
•I-405, Renton Nickel Improvement Project, Soils, Geology and Groundwater Discipline Report.
•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, and liquefaction susceptibility maps.
•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 and soil conditions.
•Applicable WSDOT Standards, such as those contained in the revised WSDOT Geotechnical
Design Manual.
A complete list of the sources that were reviewed for this report is provided in the References section. In
addition to the literature review, we completed a site reconnaissance to observe physical features to aid
with interpreting subsurface conditions and to “field truth” the information gleaned from the literature
review to the extent possible.
Baseline Conditions Evaluation
Following our compilation of this information, we evaluated baseline conditions within the study area.
Baseline conditions were evaluated directly from the data sources and by evaluating information from
multiple sources using standard geologic and geotechnical principles. For example, identifying areas that
will likely be underlain by soft soils by reviewing and compiling published information and evaluating
boring logs from previous investigations.
Potential Effects Evaluation
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 and soils on the project based on the baseline site
conditions and standard WSDOT practices.
•Evaluating the potential effects of the project on the geology and soils based on the baseline site
conditions and standard WSDOT practices.
The evaluations are based primarily on our experience, our expert judgment, and WSDOT practices and
sound engineering principles. WSDOT’s 2006 Geotechnical Design Manual discusses many WSDOT
design and construction practices for various geological conditions.