salem river crossing project geological resources ......salem river crossing project feis page 1-1...

F in a l T e chn i c a l Rep or t Add e ndum

Salem River Crossing Project Geological Resources

Technical Report Addendum

Prepared for

Oregon Department of Transportation September 2016

Prepared by

DRAFT

SALEM RIVER CROSSING PROJECT FEIS PAGE III GEOLOGICAL RESOURCES FINAL TECHNICAL REPORT ADDENDUM

Contents

Section Page

Acronyms and Abbreviations .......................................................................................................... v

1 Introduction ......................................................................................................................... 1-1 1.1 Summary of Project Purpose and Need .............................................................. 1-1 1.2 Description of the Preferred Alternative ............................................................. 1-2

1.2.1 National Environmental Policy Act ........................................................ 1-2 1.2.2 Crossing Location and Bridge Description ............................................ 1-2 1.2.3 Eastside Bridgehead and Distribution Network ................................... 1-2 1.2.4 Westside Bridgehead and Distribution Network ................................. 1-7 1.2.5 Bridge Type .............................................................................................. 1-13 1.2.6 Construction Activities ........................................................................... 1-15 1.2.7 River Traffic .............................................................................................. 1-16

2 Affected Environment ....................................................................................................... 2-1 2.1 Area of Potential Impact ........................................................................................ 2-1 2.2 Geologic Setting of Study Area ............................................................................ 2-1 2.3 Seismicity ................................................................................................................. 2-2 2.4 Geologic Hazards and Unique Geologic Features ............................................. 2-3

3 Data Sources and Data Collection Methods .................................................................. 3-1 3.1 Regulations and Standards ................................................................................... 3-1 3.2 Methods ................................................................................................................... 3-1 3.3 Data Gathering Methods ....................................................................................... 3-1

3.3.1 Analysis Methods ...................................................................................... 3-2 3.3.2 Guidance and Assumptions for Data Gathering and Analysis .......... 3-2

4 Impacts Analysis ................................................................................................................. 4-1 4.1 Overview of Impact Analysis ............................................................................... 4-1

4.1.1 Past and Present Actions .......................................................................... 4-1 4.1.2 Reasonably Foreseeable Future Actions................................................. 4-2

4.2 Direct Impacts ......................................................................................................... 4-2 4.2.1 New Bridge/Gravel Pit Area ................................................................... 4-2 4.2.2 OR 22 Eastbound Structure ...................................................................... 4-5 4.2.3 Bridge Scour/Erosion/Instability ........................................................... 4-6 4.2.4 West End of the New Bridge/Marine Drive Intersection.................... 4-7 4.2.5 Marine Drive Alignment .......................................................................... 4-8 4.2.6 Depletion of Geological Resources ....................................................... 4-10

4.3 Indirect Impacts .................................................................................................... 4-10 4.4 Cumulative Impacts ............................................................................................. 4-10 4.5 Construction Impacts ........................................................................................... 4-11 4.6 Mitigation Measures ............................................................................................ 4-11

5 Conclusions (Summary of Impacts) ................................................................................ 5-1

CONTENTS, CONTINUED

Section Page

GEOLOGICAL RESOURCES PAGE IV SALEM RIVER CROSSING PROJECT FEIS FINAL TECHNICAL REPORT ADDENDUM

5.1 Affected Environment ........................................................................................... 5-1 5.2 Summary of Impacts and Proposed Mitigation ................................................ 5-1 5.3 Findings ................................................................................................................... 5-4 5.4 Permits Likely Needed .......................................................................................... 5-4

6 References ........................................................................................................................... 6-1

Tables

2.4-1 Potentially Active Crustal Fault Summary ................................................................ 2-4 3.3-1 Data Collection Methods for Geological Resources Determinations ..................... 3-2 5.2-1 Summary of Anticipated Geological Resources Impacts of the Preferred

Alternative ...................................................................................................................... 5-2

Figures

1.2-1 Overview of Preferred Alternative .............................................................................. 1-3 1.2-2 Preferred Alternative Crossing Location .................................................................... 1-4 1.2-3 Cross-Section of Preferred Alternative New Bridge (Main Span) .......................... 1-5 1.2-4 Preferred Alternative – Eastside Bridgehead and Distribution Network.............. 1-6 1.2-5 Preferred Alternative – Westside Bridgehead and Distribution Network ............ 1-8 1.2-6 Preferred Alternative – Westside Distribution Network 1 of 4 ............................... 1-9 1.2-7 Preferred Alternative – Westside Distribution Network 2 of 4 ............................. 1-10 1.2-8 Preferred Alternative – Westside Distribution Network 3 of 4 ............................. 1-11 1.2-9 Preferred Alternative – Westside Distribution Network 4 of 4 ............................. 1-12 1.2-10 Visual Simulation of Segmental Precast Concrete Box Bridge Type .................... 1-14 1.2-11 Plan/Profile of Segmental Precast Concrete Box Bridge Type ............................. 1-14 2.2-1 Geology of the Affected Environment ........................................................................ 2-5 2.4-1 Potentially Active Crustal Faults ................................................................................. 2-6 2.4-2 Salem Area Geology Liquefaction Hazard Map ....................................................... 2-7 4.2-1 Overview of Geologic Areas of Concern .................................................................... 4-3 4.2-2 Bridge Piers Constructed Near Old Gravel Pit .......................................................... 4-4 4.2-3 Bridge Over Old Gravel Pit Filled with Water .......................................................... 4-4 4.2-4 Piers Constructed Near Willamette River Banks Subject to Erosion and Channel

Migration......................................................................................................................... 4-5 4.2-5 OR 22 Structure Along Outer Curve of Willamette River ....................................... 4-6 4.2-6 New Bridge Over the Willamette River ...................................................................... 4-7 4.2-7 New Intersection with Marine Drive on Soft Sediments with Very Shallow

Groundwater .................................................................................................................. 4-8 4.2-8 Marine Drive Crossing Low Terraces with Shallow Groundwater, Soft Sediments,

and Frequent Flooding .................................................................................................. 4-9

SALEM RIVER CROSSING PROJECT FEIS PAGE V GEOLOGICAL RESOURCES FINAL TECHNICAL REPORT ADDENDUM

Acronyms and Abbreviations

API area of potential impact

Commercial/Liberty couplet

Commercial Street/Liberty Street couplet (that is, paired one-way streets)

CSZ CSZ Cascadia Subduction Zone

DEIS Draft Environmental Impact Statement

FEIS Final Environmental Impact Statement

FHWA Federal Highway Administration

g acceleration of gravity

in./yr inches per year

ka kilo-annum

Ma mega-annum

mi miles

MSE mechanically stabilized earth

Mt. Mount

NEPA National Environmental Policy Act

NRCS Natural Resources Conservation Service

ODOT Oregon Department of Transportation

OR 22 Oregon State Route 22

PGA Peak Ground Acceleration

Pine/Hickory couplet Pine Street/Hickory Street couplet (that is, paired one-way streets)

project Salem River Crossing Project

Qal Recent river alluvium, described as unconsolidated cobbles, coarse gravel, sand, and some silt and clay

Qlg This unit, known as the Linn Gravel, consists of stratified fine to coarse fluvial gravels deposited on the east side of the Willamette River as an alluvial fan

Qth Higher terrace deposits described as semiconsolidated light-brown sand, silt, and clay

ACRONYMS AND ABBREVIATIONS

GEOLOGICAL RESOURCES PAGE VI SALEM RIVER CROSSING PROJECT FEIS FINAL TECHNICAL REPORT ADDENDUM

Qtlw Lower terrace deposits of the Willamette River, described as unconsolidated to semiconsolidated cobbles, gravel, sand, silt, clay, muck, and organic matter

Qtm Middle terrace deposits described as semiconsolidated gravel, sand, silt, that form flat terraces of major extent along the Willamette River

Tcr The hills west of Wallace Road are underlain by Columbia River Basalt, which is described as medium-gray to black, fine-grained, even-textured to slightly porphyritic basalt

USGS U.S. Geological Survey

SALEM RIVER CROSSING PROJECT FEIS PAGE 1-1 GEOLOGICAL RESOURCES FINAL TECHNICAL REPORT ADDENDUM

CHAPTER 1

Introduction

This addendum to the Draft Geological Resources Technical Report, which was submitted as an appendix of the Draft Environmental Impact Statement (Federal Highway Administration [FHWA], Oregon Department of Transportation [ODOT], and City of Salem, 2012; DEIS), that was published in April 2012, describes the Salem River Crossing Project Final Environmental Impact Statement (FEIS) preferred alternative, assesses geological resource impacts, and describes associated mitigation actions. Greater detail on the preferred alternative, including how it was selected, is provided in Chapter 2 of the FEIS.

1.1 Summary of Project Purpose and Need The purpose of the Salem River Crossing Project (project) is to improve mobility and safety for people and freight for local, regional, and through travel across the Willamette River in the Salem-Keizer metropolitan area while alleviating congestion on the Center Street and Marion Street Bridges and on the connecting highway and arterial street systems.

Primary measures to satisfy the purpose statement include the following:

• Reducing congestion levels at the existing bridgeheads

• Remediating safety and operational deficiencies on the existing bridges and in the study area in locations where crash rates are higher than average

The following statements identify the need for the project:

• Need Statement #1. Based on available data, the existing river crossing facilities and local bridge system in Salem are inadequate for current and future traffic demand, resulting in a need to improve traffic operations in the study area over the No Build Alternative conditions.

• Need Statement #2. Based on available data, the existing river crossing facilities and local bridge connections in Salem are inadequate for current and future users (vehicles, freight, bicycles, and pedestrians) with regard to safety conditions, resulting in a need to improve traffic safety for all these users.

• Need Statement #3. Based on available data, the existing river crossing facilities and local bridge system in Salem are inadequate for current and future freight-vehicle capacity, resulting in a need to improve freight mobility in the area of the Center Street and Marion Street Bridges.

• Need Statement #4. Congestion levels on the existing river crossing facilities result in unreliable public transportation service, thereby necessitating an improvement in transit travel time and reliability from/to West Salem.

• Need Statement #5. The existing river crossing options in Salem are inadequate to accommodate emergency response vehicles in the event of restricted access to and/or

CHAPTER 1 INTRODUCTION

GEOLOGICAL RESOURCES PAGE 1-2 SALEM RIVER CROSSING PROJECT FEIS FINAL TECHNICAL REPORT ADDENDUM

closure of the existing bridges because of an emergency or other incident, resulting in the need to provide improved crossings or an additional crossing in case the Center Street and Marion Street Bridges are closed or limited because of an incident.

1.2 Description of the Preferred Alternative This section describes the project preferred alternative evaluated in the FEIS. An overview of the preferred alternative is shown on Figure 1.2-1.

1.2.1 National Environmental Policy Act Compliance with the National Environmental Policy Act (NEPA) is required because the proposed action intends to satisfy a transportation need and is funded or partially funded with FHWA funds. NEPA provides the overall regulatory setting for this section. With regard to traffic forecasts, in general, the design traffic year should be set so as to accommodate a 20‐year period from the expected date of completion of the facility (Title 23, United States Code [U.S.C.], Highways Section 109 Standards).

1.2.2 Crossing Location and Bridge Description Under the preferred alternative, a new bridge would be constructed. The bridge would connect to Hope Avenue at Wallace Road on the west, cross Wallace Marine Park at its northern tip, cross the Willamette River and McLane Island, and cross over a realigned Front Street (see Figure 1.2-2). The bridge would connect to Pine and Hickory Streets at Commercial Street on the east. The bridge could be constructed as a single structure or two side-by-side structures.

In order to ensure adequate right-of-way to accommodate all modes, the new bridge would include, in each direction of travel:

• Two 12-foot-wide travel lanes

• 8-foot-wide left-hand shoulders

• 10-foot-wide right-hand shoulders

• 10‐foot‐wide multi-use paths on outermost part of both sides of the bridge that would be separated from the paved roadway raised by a barrier

The new bridge span would also have a 16-foot-wide center median. The cross-section of the proposed new bridge main span is shown on Figure 1.2-3. The existing Center Street and Marion Street Bridges would remain in service, without modification.

1.2.3 Eastside Bridgehead and Distribution Network This subsection describes the preferred alternative on the east side of the new bridgehead and on the road network east of the Willamette River (see Figure 1.2-4).



Figure 1.2-1: Overview of Preferred Alternative



Figure 1.2-2: Preferred Alternative Crossing Location



Figure 1.2-3: Cross-Section of Preferred Alternative New Bridge (Main Span)



Figure 1.2-4: Preferred Alternative – Eastside Bridgehead and Distribution Network



The preferred alternative new bridge would have an eastbound connection at Commercial Street (via an exit ramp aligned with Pine Street) and a westbound connection (via an entrance ramp aligned with Hickory Street). Entrance and exit ramps would connect at‐grade to a proposed short Pine Street/Hickory Street couplet (that is, paired one-way streets) just east of Front Street. This couplet would be only two blocks in length, extending from the bridge ramps to Liberty Street, including the respective Pine and Hickory Street intersections with Commercial Street. Bridge access to and from Salem Parkway would be via the existing north-south Commercial/Liberty couplet. The new bridge would also be accessible from the north from River Road (via Commercial Street).

A portion of Front Street would be reconstructed closer to the river below the bridge ramps in the segment between Columbia Street and a point approximately 540 feet south of Tryon Street to maintain Front Street’s north‐south connectivity. The remnant segments of Front Street in this area would allow access to existing businesses (on both sides of the bridge approaches). The former segment of Front Street below the bridge approaches would be closed to vehicles.

Commercial Street would be widened in its segment between Tryon Avenue and Hickory Street to provide enough space for the installation of two right turn-only lanes from southbound Commercial Street to the westbound bridge approach on Hickory Street. The segment of Pine Street between Liberty Street and 4th Street would be widened slightly to accommodate the proposed double-right turn lane from westbound Pine Street to northbound Liberty Street.

1.2.4 Westside Bridgehead and Distribution Network This subsection describes the preferred alternative on the west side of the new bridgehead and on the road network west of the Willamette River (see Figures 1.2-5 through 1.2-9).

The westside bridgehead approaches would combine into a single roadway at the intersection with Marine Drive (which would be constructed as part of the preferred alternative). This roadway (“Hope Avenue Extension”) would then continue to the Wallace Road intersection at Hope Avenue. There would be no driveway access to the Hope Avenue Extension roadway (either westbound or eastbound) from Wallace Road eastward; all existing driveway access to Wallace Road and Hope Avenue (west of Wallace Road) would be maintained.

The Wallace Road/Hope Avenue intersection would be widened to accommodate the additional traffic traveling to and from the new bridge. There would also be a widening of the Wallace Road/Orchard Heights Road intersection to accommodate increased traffic volumes, including widening along Wallace Road between Taybin Road and Narcissus Court to accommodate the additional turn lanes; Orchard Heights Road would remain in its current alignment. See Figures 1.2-5 and 1.2-7.



Figure 1.2-5: Preferred Alternative – Westside Bridgehead and Distribution Network



Figure 1.2-6: Preferred Alternative – Westside Distribution Network 1 of 4



Marine Drive would be constructed at-grade from River Bend Road in the north to Glen Creek Road in the south. South of Glen Creek Road, Marine Drive would ramp up to an elevated structure that would cross over the existing pedestrian/bicycle multi-use trail as well as the existing Marion Street Bridge exit ramp before descending back to grade near its connection with Oregon State Route 22 (OR 22). Marine Drive would contain one through-lane in each direction of travel with turn lanes at intersections1. A 12-foot-wide paved multi-use path would be constructed adjacent to the east side of Marine Drive from River Bend Road to Glen Creek Road (a 5-foot buffer strip would separate the multi-use path from the northbound Marine Drive travel lane). The proposed alignment of Marine Drive, as well as all new proposed roadway connections from Marine Drive to Wallace Road, is consistent with the Salem Transportation System Plan (TSP).

At its northern terminus, Marine Drive would intersect with River Bend Road via a three-legged roundabout (see Figure 1.2-6). The segment of Marine Drive between River Bend Road and the Hope Avenue Extension would include a connection to existing Harritt Drive. South of the Hope Avenue Extension, a new roadway would be built between Marine Drive and Wallace Road (“Beckett Street”) as well as between Marine Drive and the Cameo Street/5th Avenue intersection (“5th Avenue”). There would be a new full intersection at Marine Drive and Glen Creek Road (at the entrance to Wallace Marine Park).

Eastbound OR 22 would need to be widened out onto the riverbank (not into the river itself) to allow for the installation of the flyover ramp from OR 22 to Marine Drive. When the Marine Drive-OR 22 connection ramps are installed, the existing Rosemont Avenue westbound exit-ramp would be closed (see Figure 1.2-9). This closure would be done for safety reasons – the existence of both a Marine Drive-to-OR 22 ramp and a westbound Rosemont exit-ramp at its current location would result in undesirable weaving conditions; the potential for conflict would occur during all periods of the day, but would likely be more severe during the off-peak periods when speeds are higher. With the closure of the Rosemont Avenue exit-ramp, it is forecasted that former Rosemont Avenue-bound traffic wishing to access West Salem neighborhoods would shift to the Wallace Road exit (either to access Edgewater Street or to continue north on Wallace Road) or would continue west on OR 22 to Rosewood Drive, College Drive, or Doaks Ferry Road. The eastbound on-ramp from Rosemont Avenue to OR 22 would continue to function as it does today, but would not have access to the eastbound ramps exiting to northbound Marine Drive.

1.2.5 Bridge Type In September 2014, the project Oversight Team identified a segmental precast concrete box as the recommended bridge type for the preferred alternative new bridge over the Willamette River. A visual simulation and engineering plan/ profile drawing of this bridge type are provided on Figures 1.2-10 and 1.2-11.

1 Between Hope Avenue and the new Beckett Street, Marine Drive would have two southbound lanes to receive traffic going from the bridge south onto Marine Drive. This additional lane would drop as a right-turn lane at Beckett Street.



Figure 1.2-10: Visual Simulation of Segmental Precast Concrete Box Bridge Type

Figure 1.2-11: Plan/Profile of Segmental Precast Concrete Box Bridge Type

This bridge type would have 300-foot spans between piers across the river, thereby allowing for full navigational clearance in both channels of the river astride McLane Island (see the orange pier symbols on Figure 1.2-11). This bridge type would have a vertical clearance of 45 feet over mean high water and 53 feet over mean low water.

On the east side of the river at Commercial Street, the new bridge would connect to a realigned Pine Street with a three-lane exit ramp for eastbound traffic, and to Hickory Street with a two-lane entrance ramp for westbound traffic. Construction of these two bridge ramps would require the realignment of Front Street closer to the riverfront. The east leg of the Hickory Street/Liberty Street intersection would be converted to a right-in only configuration. Pine Street between Commercial and Liberty streets would be realigned to



connect to the new bridge exit ramp. Bicycles on Commercial Street would be directed to a separated multi-use path from Taylor Street to south of Pine Street.

1.2.6 Construction Activities The estimated total project cost of the preferred alternative is $424.6 million (in 2020 dollars); this includes the cost associated with purchasing right-of-way. If built as a single project, the preferred alternative would take approximately 4 years to construct.

1.2.6.1 Construction Impacts on East Side of Willamette River Construction staging on the east side of the river would be relatively minor due to the localized nature of the work. Modifications of the Commercial Street/Liberty Street and Pine Street/Liberty Street intersections would interrupt traffic for one construction season and would include lane closures. Front Street would be out of service for at least two construction seasons due to overhead bridge construction and realignment of the street. Other construction activities on the east side of the river would primarily be offline of the existing transportation system. Temporary construction impacts to properties in the immediate four-block area such as noise, dust, and traffic delays could be high for at least one construction season. Alternate routes for impacted traffic include Broadway Street and Cherry Avenue.

1.2.6.2 Construction Impacts on West Side of Willamette River Construction staging of the preferred alternative on the west side of the river would consists of work both online and offline of the existing transportation system. Offline work would include the construction of Marine Drive from Glen Creek Road to River Bend Road, the new river crossing and its connection to Marine Drive, the extension of 5th Avenue to Marine Drive, and Beckett Street between Wallace Road and Marine Drive.

Online work would include the intersection construction work on Wallace Road, Orchard Heights Road, Glen Creek Road, and River Bend Road. Construction activities on Wallace Road would entail widening for additional turn lanes at Hope Avenue and Orchard Heights Road. On River Bend Road, activities would entail the construction of a roundabout at the new intersection with the proposed Marine Drive. On Glen Creek Road, activities would entail a new intersection with proposed Marine Drive.

A major component of the preferred alternative is the construction of a new elevated flyover roadway connection from proposed Marine Drive to OR 22 in the Edgewater Street area. This work would cause disruptions to OR 22 and Edgewater Street for at least two to three construction seasons.

If built as a single project, the duration of construction activities on the west side of the river would be completed in two to three construction seasons.

1.2.6.3 Construction Mitigation Measures The preferred alternative creates opportunities to implement best practices for construction staging. Many measures can be implemented to mitigate temporary impacts caused by construction, including the following:



• Minimize construction duration using alternative delivery methods that place a high emphasis on an accelerated construction schedule.

• Implement a highly effective public involvement/public relations plan to educate travelers about the project and keep them regularly informed of construction activities.

• Place a high priority on maintaining regional mobility during construction; the existing Marion/Center Street Bridge river crossing is pivotal and must continue to operate during construction.

• Develop high-quality construction staging and traffic control plans that balance the needs of the construction contractor with the ongoing needs of the traveling public and local landowners.

• Demonstrate strong community leadership in the planning, design, and construction of the project.

1.2.7 River Traffic No impacts to river traffic (e.g., recreational boating, Willamette River Queen tours) in the Willamette River are anticipated as a result of the preferred alternative. The preferred alternative new bridge would have full navigational clearance in both channels of the river around McLane Island and it is located far north of the boat ramp.


CHAPTER 2

Affected Environment

This section defines the area of potential impact (API) and describes the geologic setting, seismicity, geologic hazards, and unique geologic features in the study area.

2.1 Area of Potential Impact Geologic impacts are tied to construction in geologically-sensitive areas. The API for the preferred alternative consists of the approaches on each side of the proposed bridges, the bridge alignments across the river, and the bridge abutments. The major impacts will be to the resources at the approaches and abutments. The primary geologic issues include the following:

• Potential for increased erosion because of excavations and fills

• Placement of structures and fills

• Seismic shaking and liquefaction

• Embankment foundation stability

• Flooding and scour of embankments near the river and piers in river

• Instability of steep river banks

• Current and future gravel operations impacting the project by undermining fills or foundations

2.2 Geologic Setting of Study Area The geology of the site consists primarily of Holocene to Pleistocene-age fluvial deposits of the Willamette River, with bedrock hills in the extreme western part of the project area. Figure 2.2-1 shows a geologic map of the API, adapted from Bela (1981). That geologic map shows the following units:

• Qal. Recent river alluvium, described as unconsolidated cobbles, coarse gravel, sand, and some silt and clay within active channels of the Willamette River. This unit is generally 15 to 45 feet thick and consists of stratified sands and well-rounded pebbles, gravels and cobbles that are primarily basaltic and andesitic in origin. Often, 3 to 15 feet of light brown sand and silt overlie this unit. This unit is subject to major flooding, critical streambank erosion, and lateral channel migration.

• Qtlw. Lower terrace deposits of the Willamette River, described as unconsolidated to semiconsolidated cobbles, gravel, sand, silt, clay, muck, and organic matter with a thickness between 30 and 50 feet. This unit is on flood plain and lowland terraces immediately above the recent river alluvium (unit Qal). Typically, this unit has 5 to 20 feet of light brown silt and clay or very fine sand overlying 10 to 45 feet of moderately

CHAPTER 2 AFFECTED ENVIRONMENT


well sorted sand and locally cemented gravel. The surface topography of this unit is characterized by a low, undulating fluvial surface with abandoned channels, meander scrolls, oxbow lakes, and sloughs. This unit is subject to major and local flooding, some catastrophic channel migration of major scale, ponding, and high groundwater.

• Qtm. Middle terrace deposits described as semiconsolidated gravel, sand, silt, that form flat terraces of major extent along the Willamette River, with a thickness typically 40 to 50 feet. This unit generally has 10 to 30 feet of light brown silty clay and interbedded very fine sand and silt surficial material that is believed to be primarily related to the Willamette Silts, which were deposited during the glacial Lake Missoula floods.

• Qlg. This unit, known as the Linn Gravel, consists of stratified fine to coarse fluvial gravels deposited on the east side of the Willamette River as an alluvial fan in the area by the ancestral Santiam River. This thickness of this unit ranges from 30 to 300 feet.

• Qth. Higher terrace deposits described as semiconsolidated light-brown sand, silt, and clay with a thickness typically between 3 and 15 feet. Near the foothills, this unit contains colluvium, slope wash, and alluvial fan deposits. This unit is located along the western part of the study area along Wallace Road and is adjacent to foothills underlain by basalt bedrock.

• Tcr. The hills west of Wallace Road are underlain by Columbia River Basalt, which is described as medium-gray to black, fine-grained, even-textured to slightly porphyritic basalt. The thickness of this unit is as much as 400 to 600 feet, with the thickness highly modified by erosion and weathering in many places.

Based on soil borings conducted for the construction of the Marion Street Bridge, the subsurface conditions in the vicinity of the bridge consist of inter-layered sediments including silty sand, fine sand with loose gravel, loose to compact medium blue sand, stiff sandy red clay, medium red and brown clay, and loose to compact gravel.

Based on observations from the site visit in 2009, in the vicinity of the gravel mining operations, the subsurface consists of 10 to 15 feet of silt and fine sand overlying rounded river gravels to a depth of approximately 50 to 60 feet (Figure 2.2-1). The bottom of this gravel layer is harder, and has some cementation. Below the gravel layers is a hard silt or siltstone. The gravel-pit operators have attempted to penetrate this layer by excavation with a large backhoe, but it is apparently deeper than the reach of the backhoe.

2.3 Seismicity The understanding of the seismic setting of western Oregon is continually being updated as new information is gathered on existing faults, new faults are mapped, and earthquakes occur. The principal tectonic feature of the Pacific Northwest is the active Cascadia Subduction Zone (CSZ), where the Juan de Fuca Plate subducts beneath the North American Plate along the Pacific coast. This subduction zone begins off the coast of Oregon and dips downward beneath western Oregon. In addition, shallow crustal sources resulting from built-up tectonic stresses within the North American Plate can also generate earthquakes. Crustal sources are shallow earthquakes occurring in the North American plate.



For preliminary design purposes, the geological resources analysts performed a limited evaluation of seismic ground motion parameters at the project site. The analysts obtained firm rock horizontal Peak Ground Acceleration (PGA) from national maps prepared by the U.S. Geological Survey (USGS) National Seismic Hazard Mapping Project (USGS, 2008).

The ODOT Geotechnical Design Manual (ODOT, 2015a) defines two levels of seismic design loading for bridge design.

• The ODOT 1,000-year “no collapse” criterion requires that bridges must be designed for a level of shaking that has a 1,000-year return period under a “no collapse” criterion. “…the bridge, bridge foundation, and bridge approach fills within 100 feet of the bridge must be able to withstand the forces and displacements without collapse of any portion of the structure” (ODOT, 2015a). No requirements for serviceability or other limits on the extent of damage are defined for this earthquake.

• The ODOT 500-year “serviceable” criterion requires that bridges must remain “serviceable” for a level of shaking that has a 500-year return period. “… the bridge and bridge approach fills within 100 feet of the bridge are designed to remain in service shortly after the event” (ODOT, 2015b).

Using the location of the site (latitude of 44.95 degrees north and longitude of 123.04 degrees west), the PGA on a rock/stiff soil site (National Earthquake Hazards Reduction Program B-C Boundary) is estimated to be 0.28g (g=acceleration of gravity) for an earthquake with a 5 percent probability of being exceeded in 50 years (an approximately 1,000-year return period) and 0.19g for an earthquake with a 10 percent probability of being exceeded in 50 years (an approximately 500-year return period).

2.4 Geologic Hazards and Unique Geologic Features Geologic hazards that could potentially impact a project of this type would typically include earthquakes and associated hazards, volcanic eruptions, floods, channel migration, landslides, and subsidence/settlement on weak soils. The geologic terrain that underlies the study area is generally low relief, but locally steep slopes are present along the east side of the Willamette River that could be subject to local slope failures.

The site, which is located in a seismically active region (the CSZ), could be subject to large, regionally occurring earthquakes. Portions of the site are underlain by soft-saturated soils that may be subject to liquefaction and lateral spread or settlement during an earthquake. Seismic activity can also cause settlement, heave, or lateral movement, which could damage project structures.

Figure 2.4-1 (from USGS) and Table 2.4-1 show the mapped potentially active faults within 20 miles of the project site. No known potentially active faults have been mapped within the project boundaries or the immediate vicinity. The Eola Hills Homocline is approximately 4 miles away at the closest, and this structure is classified as a Quaternary-age fault, with the last movement within the last 1.6 million years. Therefore, impacts to the project from fault surface ruptures within the project boundaries are anticipated to be low.



TABLE 2.4-1 Potentially Active Crustal Fault Summary Geological Resources Technical Report Addendum, Salem River Crossing Project FEIS

Fault No.a

USGS Fault

Classb Fault Name

Distance to Site (mi) Movementc

Mapped Length

(mi) Most Recent Deformation

Slip Rate (in./yr)

719 A Salem-Eola Hills Homocline

4.1 RL/R 19.4 <1.6 Ma <0.008

872 A Waldo Hills Fault 5.3 N 7.3 <1.6 Ma <0.008

871 A Mill Creek Fault 8.7 RL 11.4 <1.6 Ma <0.008

873 A Mount Angel Fault 14.0 T/RL 18.5 <15 ka <0.008

a Faults are identified by number in Figure 2.4-2. b USGS Fault Class:

A: Geologic evidence demonstrates the existence of a Quaternary fault of tectonic origin, whether the fault is exposed by mapping or inferred from liquefaction or other deformational features.

c Fault type notation: R (Reverse), N (Normal), LL (Left Lateral), RL (Right Lateral), T (Thrust). in./yr = inches per year ka = kilo-annum Ma = mega-annum mi = miles Source: USGS, 2006.

Soils that underlie portions of the project area are anticipated to be susceptible to liquefaction during a seismic event. Liquefaction is defined as the loss of soil strength due to an increase in pore pressure. Loose, water-saturated, sandy and silty soils could liquefy during earthquake shaking and could cause extensive damage. In the project area, the liquefaction hazard has been divided into four categories. These categories range from Category 2, which means “>6-12 feet of liquefiable material,” up to Category 5, which indicates “>24 feet estimated thickness of liquefiable material” (Wang and Leonard, 1996).

The areas subject to the highest liquefaction hazards are typically low-lying areas of sandy soils and shallow groundwater along the Willamette River (where bridge embankments and piers would be built). Impacts could include structural and foundation failures (because of differential movement in the vertical direction between the structure and the ground) and lateral spreading (which is horizontal movement of surface soil layers down gentle slopes or towards free faces, such as river banks). Figure 2.4-2 (from Wang and Leonard, 1996) shows the liquefaction hazard in the project area.

The nearest volcanoes are Mount (Mt.) Hood, Mt. Jefferson, and Mt. St. Helens in the Cascade Range. These volcanoes are more than 70 miles from the site and are not anticipated to pose direct volcanic hazards. No unique paleontological features have been recognized within the study area. A review of the paleontological resources map indicated that no recognized fossil localities are within the project area.

Chapter 4, Impacts Analysis, discusses potential impacts to the project from these geologic hazards in detail.



Figure 2.2-1. Geology of the Affected Environment

Source: Bela, 1981.



Figure 2.4-1. Potentially Active Crustal Faults

Source: U. S. Geological Survey http://earthquake.usgs.gov/hazards/qfaults/map/#qfaults

.

http://earthquake.usgs.gov/hazards/qfaults/map/#qfaults



Figure 2.4-2. Salem Area Geology Liquefaction Hazard Map

Source: Wang and Leonard, 1996.


CHAPTER 3

Data Sources and Data Collection Methods

3.1 Regulations and Standards The geological resources analysts used the following design standards for the geological resources technical report:

• American Association of State Highway and Transportation Officials, LRFD Bridge Design Specifications, 7th Edition (2014)

• ODOT Geotechnical Design Manual (2015a)

3.2 Methods The analysts researched the following information for the geological resources technical report:

• Published Geologic Mapping (from Oregon Department of Geology and Mineral Industries, USGS)

• Soil Maps from the U.S. Department of Agriculture, Natural Resources Conversation Service (NRCS, 2008)

• Data reports from previous geotechnical investigations

• USGS National Earthquake Information Center

• Bridge drawings with soil borings from original Center Street and Marion Street Bridge design

• Bridge drawings and scour repair information from the adjacent Union Street Pedestrian Bridge.

3.3 Data Gathering Methods The analysts used the following data collection methods to obtain data regarding the geologic setting of the site and potential impacts of the project:

• Aerial photographic review

• Review of previous geologic/geotechnical investigations

• Review of existing geologic mapping

• Review of geologic hazard maps that describe specific hazards such as landslides, liquefaction, faulting, and seismic shaking

• Discussions with ODOT personnel

CHAPTER 3 DATA SOURCES AND DATA COLLECTION METHODS


• Site reconnaissance to observe the site geologic conditions

3.3.1 Analysis Methods The proposed project would create impacts to geological resources if:

• Project features and structures would require mitigation measures

• Project structures would require specific geologic/geotechnical investigations and geotechnical analyses

• Project features would require specific construction techniques or geotechnical monitoring

The analysts used the following methods to evaluate impacts:

• Identified areas that could potentially be underlain by soft, compressible soils or erodible soils on geologic maps and NRCS soil maps and compared the locations of project structures (such as bridges) on these areas to determine the potential impacts.

• Identified areas potentially prone to geologic hazards such as seismic shaking, liquefaction potential, and landslides using existing geologic hazard maps and site observations.

• Identified areas with scour or flood potential and compared to the locations of project structures on these areas to determine the potential for impacts.

• Identified working, future, and abandoned gravel pits and their proximity to project structures.

• Evaluated the earthquake potential of the study area using published USGS earthquake hazard maps and probabilistic analysis.

3.3.2 Guidance and Assumptions for Data Gathering and Analysis Table 3.3-1 shows the data collection methods used to make geological resource determinations. Research and analysis methods and data collection tools are detailed.

TABLE 3.3-1 Data Collection Methods for Geological Resources Determinations Geological Resources Technical Report Addendum, Salem River Crossing Project FEIS

Research and Analysis Methods Data Collection Tools (Office and Field)

Review published geologic mapping (from Oregon Department of Geology and Mineral Industries, USGS)

Review aerial photographs

Review data reports and boring logs from previous geotechnical investigations

Review previous geologic/geotechnical investigations

Review USGS National Earthquake Information Center maps

Review existing geologic mapping

Review bridge drawings with soil borings from original Marion Street Bridge design

Review geologic hazard maps that describe specific hazards such as landslides, liquefaction, and seismic shaking

CHAPTER 3 DATA SOURCES AND DATA COLLECTION METHODS


TABLE 3.3-1 Data Collection Methods for Geological Resources Determinations Geological Resources Technical Report Addendum, Salem River Crossing Project FEIS

Research and Analysis Methods Data Collection Tools (Office and Field)

Analyze structures/ project features that would require mitigation measures due to adverse geologic conditions

Engage in discussions and conduct a field visit with ODOT personnel

Identify areas of specific geologic/geotechnical investigations and geotechnical analyses

Perform a site reconnaissance to observe the site geologic conditions

Identify needs for specific construction techniques or geotechnical monitoring based on geologic conditions

Review geologic hazard maps, existing borings, and site conditions


CHAPTER 4

Impacts Analysis

This chapter contains an analysis of the direct, indirect, cumulative, and temporary impacts related to the project preferred alternatives. This chapter also discusses measures to mitigate anticipated negative impacts from preferred alternative actions.

4.1 Overview of Impact Analysis Direct, indirect, cumulative, and temporary impacts are defined as follows for the project:

• Direct impacts are defined as those permanent impacts that are caused by preferred alternative actions and occur at the same time and place as those actions. For the purpose of the geological resources report, direct impacts are considered to be primarily those related to the impacts caused by geologic hazards on project features.

• Indirect impacts are defined as those permanent impacts that are caused by preferred alternative actions and are later in time or farther removed in distance but are still reasonably foreseeable.

• Cumulative impacts are defined as impacts on the environment resulting from the incremental impact of the proposed action when added to other past, present, and reasonably foreseeable future actions. A number of actions have been (or are likely to be) undertaken that, when combined with any of the alternatives, would have cumulative impacts on the social and natural environment in the study area. To evaluate cumulative impacts, the project team established a time frame of reference for evaluating how past actions have shaped the social and natural environment of the study area, and how future actions might further change the conditions resulting from these past actions. The “past” runs from the 1840s (settlement of the Salem area) to the present.

• Temporary construction impacts are defined as those short-term impacts that are caused by constructing the preferred alternative action.

4.1.1 Past and Present Actions The following list summarizes key historic events that provide a basis for analysis of past and present actions that have helped shape current geological resources conditions (Salem Public Library, 2006).

• A wooden truss bridge was built over the Willamette River at Center Street (1886), and was washed out and replaced with a steel bridge at that location (1891)

• A railroad bridge was built across the Willamette River (1913)

• Third Center Street Bridge was constructed (1917–18)

• Dams constructed along the Willamette River reduced flooding and allowed development in low-lying areas, such as Keizer (1950s)

CHAPTER 4 IMPACTS ANALYSIS


• Marion Street Bridge was constructed; Center Street Bridge was modified (1952)

• Park and open space areas were acquired and developed, including Minto-Brown Island Park (early 1970s), Salem Riverfront Park (late 1990s), and Wallace Marine Park (1950s–70s)

• Marion Street Bridge was widened to four lanes (1982)

• Center Street Bridge was reconstructed to include four lanes (1983)

• Union Street railroad bridge was converted to a bicycle/pedestrian facility (2009)

• Gravel mining operations were conducted adjacent to the site in the Willamette River floodplain, which modified the Willamette River floodplain (these operations began within the last 40 to 50 years and continue into the present)

4.1.2 Reasonably Foreseeable Future Actions Future actions that might affect conditions in the API with respect to geological resources would include:

• The likely continuance of development in floodplain areas and areas adjacent to the Willamette River

• Continued expansion and mining of the gravel pits

4.2 Direct Impacts Figure 4.2-1 provides an overview of the geologic areas of concern in the APE. The inset boxes and numbering (e.g., 4.2-2, 4.2.-3) refer to subsequent figures that provide more detailed close-ups of specific geologic concerns in each area described.

4.2.1 New Bridge/Gravel Pit Area Proposed layouts indicate that five to six of the bridge piers, or “bents” would be constructed in the gravel pit, or near the steep side slopes of the pit. The pit has filled with water, which could also make construction more difficult and require cofferdams and dewatering. Figure 4.2-2 shows where the bridge piers would be constructed near the old gravel pit (see Figure 4.2-1 for the location in the APE).

Portions of the bridge structure would overlie an area of continued gravel mining. This could result in poor foundation conditions, or lateral loading from unstable side slopes that could impact the structures (Figure 4.2-3; see Figure 4.2-1 for the location in the APE).

The project would be required to acquire sufficient adjoining ground so that stable slopes could be maintained during future gravel-mining operations. The property acquisition might also include placing deed restrictions on the adjacent mining operations to limit the slope angles and depth of excavation next to the acquired right-of-way.



Figure 4.2-1: Overview of Geologic Areas of Concern



Figure 4.2-2. Bridge Piers Constructed Near Old Gravel Pit

Figure 4.2-3: Bridge Over Old Gravel Pit Filled with Water



4.2.2 OR 22 Eastbound Structure The piers for the new OR 22 structure (Figure 4.2-4) would be placed very near the edge of the Willamette River on unconsolidated deposits that consist of gravel, sand, silt, clay and organic matter. The piers for the new entrance ramp would be constructed on recent alluvial deposits that consist of sands and gravels. The new bridge piers would be constructed primarily on geologic units that are subject to major flooding, critical streambank erosion, lateral channel migration, liquefaction, and seismic slope instability. This is along the “outer” bend of the Willamette River, which would be more likely to experience erosion rather than deposition during high water (Figure 4.2-5). Figure 4.2-1 shows the location in the APE.

Figure 4.2-4. Piers Constructed Near Willamette River Banks Subject to Erosion and Channel Migration



Figure 4.2-5. OR 22 Structure Along Outer Curve of Willamette River

4.2.3 Bridge Scour/Erosion/Instability Potential scour and erosion of the new bridge piers would need to be addressed and mitigated. The bridge embankments and piers would be constructed primarily on geologic units, including recent alluvial deposits and lower terrace deposits that consist of gravel, sand, silt, clay, and organic matter. The recent alluvium unit on the west side of the bridge is subject to major flooding, critical streambank erosion, lateral channel migration, liquefaction, and seismic slope instability. The lower terrace unit is subject to major and local flooding, some catastrophic channel migration of major scale, ponding, and high groundwater (Figure 4.2-6; see Figure 4.2-1 for the location in the APE).

The analysts observed scour and damage to the existing bridge piers during the site visit in 2009. Bridge embankments or mechanically stabilized earth (MSE) retaining walls constructed near the river’s edge (such as for the Front Street underpass on the east side of the river) or in flood-prone areas would be susceptible to scour and erosion from high water and channel migration, which could lead to slope failures. Potential for bridge pier scour, which would be modeled using hydraulic models, is discussed in the Hydraulics Technical Report (CH2M HILL, 2012a; CH2M, 2016a).

Steep river banks along the east side of the Willamette River are up to 30 feet high and may be susceptible to local landslides and slope instability due to streambank erosion and seismic shaking. In 2009, the analysts observed bent and leaning trees on this slope, which could indicate long-term slope creep. Shallow failures on steep slopes that line the east side



of the Willamette River could impact bridge abutments or piers or MSE wall construction, such as the Front Street Underpass.

Figure 4.2-6. New Bridge Over the Willamette River

Note: The west side could be subject to liquefaction, channel migration, and streambank erosion. The east side could be subject to slope failures and instability.

4.2.4 West End of the New Bridge/Marine Drive Intersection The intersection with Marine Drive would overlie a floodplain underlain by sand, silt, clay, organic matter, standing water in a slough (Figure 4.2-7; see Figure 4.2-1 for the location in the APE). Portions of the roadway across this area would be built on MSE retaining walls. The retaining wall could be constructed on weak, soft sediments, and shallow groundwater with poor foundation conditions that could lead to impacts such as settlement and liquefaction.

The preferred alignment would be constructed through the American Storage property (300 Musgrove Ave NW) which for several decades was a lumber mill (including a wigwam burner). Across the Union Pacific Railroad roadbed there was a 3-acre wood waste/sawdust storage area that also existed for multiple decades (1930s to 1960s). No geological impacts are anticipated as a result of project actions at these two sites aside from potential need for overextraction/replacement with suitable subgrade.



Figure 4.2-7. New Intersection with Marine Drive on Soft Sediments with Very Shallow Groundwater

4.2.5 Marine Drive Alignment The new Marine Drive alignment would cross an area with an old abandoned river channel and water-filled slough. This area is underlain by lower terrace deposits of the Willamette River described as unconsolidated to semiconsolidated cobbles, gravel, sand, silt, clay, muck, and organic matter. Flooding, settlement, and liquefaction could potentially impact this portion of the new road (Figure 4.2-8; see Figure 4.2-1 for the location in the APE).



Figure 4.2-8. Marine Drive Crossing Low Terraces with Shallow Groundwater, Soft Sediments, and Frequent Flooding



4.2.6 Depletion of Geological Resources Other direct impacts would include the irreversible and irretrievable depletion of geological resources. Construction of the roadways and bridges would deplete geological resources and consume raw materials, either alone or as components of common construction elements. These would include earth materials for embankment; durable rock for rip-rap; steel for reinforcing bars and structural members; stone aggregate and Portland cement for concrete; steel and copper for electrical cables and wires; fuel oil, gasoline, and diesel fuel; and other raw materials used in constructing a project. The quantities of materials that would be required for the preferred alternative are estimated and addressed in the Energy Technical Report (CH2M HILL, 2012b; CH2M, 2016b).

4.3 Indirect Impacts Indirect impacts could include damage from long-term erosion, future large precipitation events, and future earthquakes. Grading fill slopes too steeply or establishing high-maintenance exposed soil slopes could lead to long-term erosion problems. Large precipitation events could lead to flooding, scouring of walls and structures, slope failures, and erosion on slopes that would be constructed as part of the Build alternatives.

A future seismic event (earthquake) could lead to indirect impacts including localized slope failures, lateral movement, and damage to bridge foundations and retaining walls. The steep river banks near the east abutments of the new Bridge and Front Street underpass could become unstable due to the seismic shaking.

Soils that underlie portions of the project area are anticipated to be susceptible to liquefaction during a seismic event. The areas subject to the highest liquefaction hazards are typically low-lying areas of sandy soils and shallow groundwater along the Willamette River floodplain, where bridge embankments and piers would be built (Figures 2.4-2, 4.2-5, and 4.2-6). The geologic unit “recent alluvium,” which would underlie much of the new bridge, is ranked in a liquefaction Category of 4 or 5. This category indicates that the “recent alluvium” unit is highly susceptible to liquefaction. Impacts could include structural and foundation failures because of differential movement in the vertical direction between the structure and the ground and lateral spreading, which is horizontal movement of surface soil layers down gentle slopes or toward free faces such as river banks.

4.4 Cumulative Impacts The following cumulative impacts from the preferred alternative are anticipated:

Alterations to the Willamette River. The possibility that construction of the project would add to flood or scour potential by the Willamette River in conjunction with other projects that might alter the hydraulics of the river, place fill in the floodway, constrict the channel opening, and increase the amount of impermeable area (which would increase the volume of stormwater runoff). This is discussed in more detail in the Hydraulics Technical Report (CH2M HILL, 2012a; CH2M, 2016a).

Materials required and proximity to gravel pits. Additional cumulative impacts could occur due to a larger quantity of materials required and construction of bridge structures close to the working gravel pits. Construction of the project, in conjunction with ongoing



mineral lease activities (gravel pits) and potentially other existing mineral leases, could lead to increased depletion of geological resources

4.5 Construction Impacts During construction of the preferred alternative, the following impacts to the geologic environment could include the following:

• Surficial soil erosion. Surficial soil erosion might occur during project construction due to site fills and grading, temporary excavations for footings and retaining walls and devegetation.

• Erosion, dust generation, and sedimentation. Temporary access roads and staging areas would be built for constructing bridges and roads to move equipment and materials. These roads would temporarily expose surficial soils, which could lead to erosion, dust generation, and sedimentation.

• Landslides or slumps. Small landslides or slumps could occur during construction activities such as grading, excavating, changing drainage that would lead to saturation, altering existing slopes, or surcharging slopes by constructing embankments. In addition, construction of the new bridge would cause more disturbance to the east and west banks of the Willamette River.

4.6 Mitigation Measures Potential measures to mitigate the preferred alternative direct impacts related to soil erosion and disturbance; settlement; stability; lateral loading; earthquake hazards (such as liquefaction and seismic shaking); channel migration and scour; and construction across existing gravel pits could include the following:

• Gravel Mining Right-of-Way: Mitigation measures for impacts of gravel mining could include wide right-of-way berths around embankments and piers; coordination with gravel-pit operators to avoid working too close to the bridge and jeopardizing structures; placing deed restrictions on adjacent mining operations to limit slope angles and depth of excavation next to acquired right-of-way; excavating the gravel pits at safe slopes that would avoid slope failures; and closing or providing grading for abandoned gravel-pit operations that would stabilize the slopes for long-term conditions.

• Gravel Pit instability/construction issues: Mitigation measures for building across existing and open/unstable gravel pits within the proposed alignment could include backfilling the gravel pit with compacted fill materials to create suitable slope conditions that would not impact pier locations; and constructing deep foundations below the impacted area on geologically-suitable material.

• Poor Foundation Conditions: Given the potentially poor foundation conditions, future geologic and geotechnical investigations would be conducted for final design. These investigations would evaluate foundation conditions for bridges, roadways, retaining walls, and other structures to adequately characterize the subsurface soils for designing stable structures, and assess lateral loading from unstable side slopes that could impact the structures.



• Soil Erosion: Mitigation measures for soil erosion and disturbance during construction would include standard erosion control techniques described in the ODOT Erosion Control Manual (ODOT, 2005). Mitigation measures would include, but not be limited to, installing straw bales and wattles; setting up sediment fences; hydroseeding and revegetation; minimizing the size of disturbed areas; providing dust control for exposed areas; diverting stormwater runoff away from cut and fill slopes; and maintaining erosion control devices used on the slopes. Erosion control and sedimentation mitigation are also discussed in the Water Resources Technical Report (CH2M HILL, 2012c; CH2M, 2016c).

• Stability Monitoring. Embankment and fill stability would be monitored during construction by using inclinometers to measure movement or settlement, and vibrating wire piezometers to determine changes in pore pressures that could lead to instability. Mitigation measures for embankment instability would include using ground improvement methods or dewatering to improve foundation soil strength.

• Settlement Monitoring. Settlement would be measured during construction of embankment fills and MSE walls using settlement plates or horizontal inclinometers. Mitigation for settlement includes using staged construction techniques where the embankment is built in lifts and allowed to settle, ground improvements (such as stone columns), or overexcavating and replacing weak soils.

• Streambank erosion/channel migration. Mitigation techniques for streambank erosion and channel migration would include, but not be limited to, using rip-rap, jet grouting, sheet piling, and bank-stabilizing vegetation.

• Scour. Mitigation techniques to prevent scour of bridge supports would include extending deep foundations below the depth of anticipated scour, or avoiding locating structures or embankments too close to areas with high scour potential.

• Flooding. Mitigation of flooding hazards for this project would include primarily constructing new roadway on piers and as bridge structures to avoid roads and embankments in flood-prone areas, which are extensive throughout the project area. Mitigation of flooding and scour impacts are also discussed in the Hydraulics Technical Report (CH2M HILL, 2012a; CH2M, 2016a).

• Seismic Hazards/Earthquakes. Mitigation measures for a seismic event would include conducting stability analyses using standard computer software to evaluate the effects of earthquake shaking when designing safe slope angles and embankments. Mitigation measures for liquefaction and seismic shaking would include proper earthquake-resistant engineering of structures such as drilled shafts founded on competent materials, ground improvements to increase foundation strength, and dewatering using wick drains or other means to reduce pore pressure and increase soil strength to avoid liquefaction.


CHAPTER 5

Conclusions (Summary of Impacts)

This chapter summarizes the affected environment, anticipated project impacts, proposed mitigation, findings, and permits that would likely be needed.

5.1 Affected Environment The geology of the site consists primarily of Holocene- to Pleistocene-age fluvial deposits of the Willamette River, with bedrock hills in the extreme western part of the project area. The fluvial deposits include recent river alluvium, terrace deposits of the Willamette River, and the Linn Gravel. The hills west of Wallace Road are underlain by Columbia River Basalt.

The fluvial deposits are typically described as unconsolidated cobbles, coarse gravel, sand, and some silt and clay. These deposits are overlain by silty deposits, and also include muck and organic matter. The surface topography of the fluvial deposits closest to the Willamette River is characterized by a low, undulating surface with abandoned channels, meander scrolls, oxbow lakes, and sloughs. These units are subject to major and local flooding, some catastrophic channel migration of major scale, critical streambank erosion, ponding, and high groundwater.

The seismic setting of western Oregon is dominated by the active CSZ, where the Juan de Fuca Plate subducts beneath the North American Plate along the Pacific Coast. The CSZ has the potential to generate large regional earthquakes in the vicinity.

The PGA on a rock/stiff soil site is estimated to be 0.28g for an earthquake with a 5 percent probability of being exceeded in 50 years (an approximately 1,000-year return period) and 0.19g for an earthquake with a 10 percent probability of being exceeded in 50 years (an approximately 500-year return period).

Seismic shaking from a large, subduction-zone earthquake could impact bridge and roadway structures. Soils that underlie portions of the project area are anticipated to be susceptible to liquefaction during a seismic event. The areas subject to the highest liquefaction hazards are typically low-lying areas of sandy soils and shallow groundwater along the Willamette River (where bridge embankments and piers would be built).

5.2 Summary of Impacts and Proposed Mitigation Table 5.2-1 summarizes potential direct, indirect, cumulative and construction (temporary) impacts to geological resources by alternative and lists potential mitigation measures.

CHAPTER 5 CONCLUSIONS (SUMMARY OF IMPACTS)


TABLE 5.2-1 Summary of Anticipated Geological Resources Impacts of the Preferred Alternative Geological Resources Technical Report Addendum, Salem River Crossing Project FEIS

Element Preferred Alternative

Direct Impacts

Bridge/Ramps/ MSE Walls – Stability and Settlement

Settlement of the new bridge piers, bridge embankments, and MSE walls, plus instability of MSE walls on weak, low-strength sediments. Roadway at Marine Drive intersection would be built on an MSE retaining wall constructed on weak, soft soils, and poor foundation conditions. Impacts could include settlement and instability.

Bridge Embankments and Piers – Scour and Erosion

The new roadway across the alluvial floodplain would have to be a long bridge structure constructed on deep foundations; could be impacted by flood and scour. Scour could impact new eastbound OR 22 piers.

River Banks – Erosion and Instability

New structures near steep river banks along the east side of the Willamette River might be impacted by local landslides and slope failures. Shallow water, flooding potential, erosion, and potentially soft soils could impact the north-south Marine Drive construction.

Gravel-Pit Operation Impacts

The new bridge alignment would cross over existing gravel-mining operations. This could result in poor foundation conditions, or lateral loading from unstable side slopes that could impact the structures. Mitigation measures could include backfilling the gravel pit with compacted fill materials to create suitable slope conditions that would not impact pier locations; and constructing deep foundations below the impacted area on geologically-suitable material.

Resource Depletion Depletion of geological resources and consumption of raw materials, either alone or as components of common construction would occur because of the new bridge, roadway, and MSE wall construction.

Indirect Impacts

Long-Term Erosion/ Slope Maintenance

Steep fill slopes or high-maintenance exposed soil slopes could lead to long-term erosion problems. Any slopes in floodplains or adjacent to the river’s edge would be especially subject to impacts.

Flooding, Channel Migration, Bank Erosion

New bridge over Willamette River, construction on floodplain, elevated OR 22 ramp, and Marine Drive, could be impacted by future flooding and bank erosion because of structures close to the river and in the floodplain.

Earthquake Impacts (Liquefaction, Shaking)

New bridge over Willamette River, construction on floodplain, elevated OR 22 ramp, and Marine Drive could be impacted by future earthquakes.

Cumulative Impacts

Alterations to Willamette River Floodplain

Previous projects (such as dams constructed in the Willamette River drainage area and bridges constructed in the river) have reduced flooding, channel migration, and bank erosion potential. Previously constructed bridges have contributed to channel constrictions. Project could add to the Willamette River’s flood or scour potential in conjunction with other projects that might alter the hydraulics of the Willamette River; place fill in the floodway; constrict the channel opening, and increase the amount of impermeable area (which would increase the volume of stormwater runoff).

Depletion of Geological Resources

Continued gravel mining for future construction projects in the floodplain area would eventually deplete the gravel resources, changing geological resources within the project area. Could lead to increased depletion of geological resources.



TABLE 5.2-1 Summary of Anticipated Geological Resources Impacts of the Preferred Alternative Geological Resources Technical Report Addendum, Salem River Crossing Project FEIS

Element Preferred Alternative

Construction (Temporary) Impacts

Surficial Soil Erosion Future road improvement/excavation projects could contribute to soil erosion during construction excavations, site grading, and temporary access road construction. Surficial soil erosion during project construction because of site fills; temporary excavations; and grading.

Dust/Sedimentation Construction of temporary access road and staging areas would expose surficial soils, which could lead to erosion, dust generation, and sedimentation. Additional access road construction along the new proposed bridge alignment in the floodplain and for Marine Drive and the new OR 22 ramp.

Slides/slumping/ slope instability

Construction activities such as grading, excavating, changing drainage that would lead to saturation, altering existing slopes, or surcharging slopes by constructing embankments could cause small landslides or slumps, plus additional excavation in floodplain and construction work in Willamette River to construct new bridge.

Mitigation Measures

Poor foundation conditions

Conducting specific geologic and geotechnical investigations to characterize soils and identify constraints; more bridge structure and construction in floodplain areas would require additional investigations. Delineating thickness extent of soft soils.

Soil erosion and disturbance

Using the standard erosion control techniques described in the ODOT Erosion Control Manual (ODOT, 2005). Mitigation measures could include installing straw bales and wattles; setting up sediment fences; hydroseeding and revegetation; minimizing the size of disturbed areas; providing dust control for exposed areas; diverting stormwater runoff away from cut and fill slopes; and maintaining erosion control devices used on the slopes. Larger construction areas would require more mitigation.

Settlement, stability, lateral loading

Performing geotechnical stability analyses; using staged construction techniques; improving foundation soil strength using ground improvements such as stone columns or over-excavating and replacing weak soils; and constructing bridge piers on stable foundation materials identified during previous and future investigations.

Earthquake hazards (liquefaction and seismic shaking)

Using proper earthquake-resistant engineering of structures such as drilled shafts founded on competent materials, using ground improvements to increase foundation strength, and dewatering using wick drains to reduce pore pressure and increase soil strength.

Channel migration, streambank erosion

Using riprap, jet grouting, sheet piling, and bank-stabilizing vegetation.

Flooding and scouring hazards

Constructing new roadway on piers and bridge structures to avoid flood-prone areas; conducting hydraulic analyses to determine scour potential. Avoiding channel constriction (same area before and after).

Building across existing gravel pit

Backfilling with suitable foundation materials; constructing deep foundations; spanning the gravel pit with a bridge structure to avoid foundation and stability issues.

Impacts of gravel mining

Establishing wide right-of-way berths around embankments and piers; coordinating with gravel-pit operators to avoid working too close to the bridge and jeopardizing structures; acquiring future right-of-way; excavating the gravel pits at safe slopes that would avoid slope failures; and closing or providing grading for abandoned gravel operations that would stabilize the slopes for long-term conditions.



5.3 Findings • The geologic conditions and geological resources in the project vicinity could pose

challenges to project construction. The preferred alternative could negatively impact the local geological resources and could potentially be impacted by geologic hazards in the project vicinity, both directly and indirectly.

• The project could contribute to impacts in the floodplain including scour, flood potential, and local slope failures. The presence of loose, soft soils, scour, streambank erosion, and earthquake-related issues (such as seismic shaking and liquefaction) could impact the project and require special construction techniques and monitoring during construction.

• The preferred alternative could lead to depletion of geological resources such as earth materials for embankment; durable rock for rip-rap; steel for reinforcing bars and structural members; stone aggregate and Portland cement for concrete; steel and copper for electrical cables and wires; and fuel oil, gasoline, and diesel fuel.

• The preferred alternative would require mitigation measures to ensure safe construction and long-term performance. However, by conducting proper geotechnical investigations, adequate site characterization, and proper engineering design, the project structures could be constructed safely.

5.4 Permits Likely Needed It is likely that the project would need the following permits:

• Right-of-way permit to conduct geotechnical investigations along existing roadways for preliminary and final design, obtained from ODOT/City of Salem and Polk County

• Right-of-entry permits for private property.

• Oregon Department of State Lands Removal-Fill and Section 404 permits from U.S. Army Corps of Engineers for geotechnical investigations and construction in floodplain areas

• National Pollutant Discharge Elimination System permit and Stormwater Pollution Prevention Plan for construction


CHAPTER 6

References

American Association of State Highway and Transportation Officials. 2014. LRFD Bridge Design Specifications, 7th Edition.

Bela, J.L. 1981. Geology of Rickreall, Salem W, Monmouth, and Sidney Quadrangles, Marion, Polk, and Linn Counties. Oregon Department of Geology and Mineral Industries GMS 18. Scale 1:24,000.

CH2M HILL. 2012a. Hydraulics Technical Report for the Salem River Crossing Project DEIS.

CH2M HILL. 2012b. Energy Technical Report for the Salem River Crossing Project DEIS.

CH2M HILL. 2012c. Water Resources Technical Report for the Salem River Crossing Project DEIS.

CH2M. 2016a. Hydraulics Technical Report Addendum for the Salem River Crossing Project FEIS.

CH2M. 2016b. Energy Technical Report Addendum for the Salem River Crossing Project FEIS.

CH2M. 2016c. Water Resources Technical Report Addendum for the Salem River Crossing Project FEIS.

City of Salem. 1998, updated in 2016. Transportation System Plan. Adopted August 24, 1998, last amended February 8, 2016. http://www.cityofsalem.net/Departments/PublicWorks/TransportationServices/TransporationPlan/Pages/default.aspx.

Oregon Department of Transportation (ODOT). 2005. ODOT Erosion Control Manual. April 2005.

Oregon Department of Transportation (ODOT). 2015a. Geotechnical Design Manual.

Oregon Department of Transportation (ODOT). 2015b. Highway Design Manual.

Salem Public Library. 2006. Salem Online History. http://www.salemhistory.net/.

U.S. Department of Agriculture, Natural Resources Conservation Service (NRCS). 2008. Web Soil Survey. http://websoilsurvey.nrcs.usda.gov/. Accessed August 2008.

U.S. Geological Survey (USGS). 2006. Earthquake Hazard Program, Quaternary Fault and Fold Database of the United States. http://earthquake.usgs.gov/regional/qfaults/.

U.S. Geological Survey (USGS). 2008. National Seismic Hazard Mapping Project. http://earthquake.usgs.gov/hazards/.

Wang, Y., and W.J. Leonard. 1996. Relative Earthquake Hazard Maps of Salem East & Salem West quadrangles, Marion & Polk Cos. Oregon Department of Geology and Mineral Industries GMS 105. Scale 1:24,000.

http://www.cityofsalem.net/Departments/PublicWorks/TransportationServices/TransporationPlan/Pages/default.aspx

http://www.cityofsalem.net/Departments/PublicWorks/TransportationServices/TransporationPlan/Pages/default.aspx

http://www.salemhistory.net/

http://websoilsurvey.nrcs.usda.gov/

http://earthquake.usgs.gov/regional/qfaults/

http://earthquake.usgs.gov/hazards/

salem river crossing project geological resources ......salem river crossing project feis page 1-1...

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