PolychromeAreaImprovementsEA_20220113.pdf

National Park Service U.S. Department of the Interior

Denali National Park and Preserve Alaska Region

Denali National Park and Preserve Polychrome Area Improvements Environmental Assessment

NPS Photo / Emily Mesner

DENALI NATIONAL PARK AND PRESERVE POLYCHROME AREA IMPROVEMENTS

ENVIRONMENTAL ASSESSMENT

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As the nation's principal conservation agency, the Department of the Interior has responsibility for most of our nationally owned public lands and natural and cultural resources. This includes fostering the wisest use of our land and water resources, protecting our fish and wildlife, preserving the environmental and cultural values of our national parks and historical places, and providing for enjoyment of life through outdoor recreation. The department assesses our energy and mineral resources and works to assure that their development is in the best interests of all. The department also has a major responsibility for American Indian reservation communities and for people who live in island territories under U.S. administration.

If you wish to comment on this document:

Online at https://parkplanning.nps.gov/polychrome

Or via mail:

Superintendent, Denali National Park and Preserve P.O. Box 9 Denali Park, AK 99755-0009

Comments must be submitted or postmarked by February 13, 2022.

For additional information, please contact the National Park Service at: dena_planning@nps.gov

Before including your address, phone number, email address, or other personal identifying information in your comment, be aware that your entire comment—including your personal identifying information—may be made publicly available at any time. You can ask us to withhold your personal identifying information from public review, but we cannot guarantee that we will be able to do so.

ON THE COVER

The Denali Park Road winds its way along the Polychrome area.

Photo by Emily Mesner, National Park Service https://parkplanning.nps.gov/polychrome mailto:dena_planning@nps.gov

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TABLE OF CONTENTS

1 Introduction

1.1 Proposed Action

1.2 Purpose and Need

1.3 Background

1.4 Issues Selected for Detailed Analysis

1.5 Issues Considered but Dismissed

2 Alternatives

2.1 Alternative 1: No Action

2.2 Alternative 2: Pretty Rocks Bridge and Polychrome Road Improvements

2.2.1 Phase I

2.2.2 Phase II

2.3 Alternatives Considered but Dismissed

2.3.1 Alignment Options Considered

2.3.2 Removing the Upper Landslide

3 Affected Environment and Environmental Consequences

3.1 Approach to Analysis

3.1.1 General Approach

3.1.2 Reasonably Foreseeable Future Actions

3.2 Geology

3.2.1 Affected Environment

3.2.2 Environmental Consequences

3.3 Socioeconomics

3.3.1 Affected Environment

3.3.2 Environmental Consequences

3.4 Visual Resources

3.4.1 Affected Environment

3.4.2 Environmental Consequences

3.5 Visitor Use and Experience

3.5.1 Affected Environment

3.5.2 Environmental Consequences

3.6 Noise and Soundscape

3.6.1 Affected Environment

3.6.2 Environmental Consequences

3.7 Wildlife

3.7.1 Affected Environment

3.7.2 Environmental Consequences

3.8 Wetlands and Vegetation

3.8.1 Affected Environment

3.8.2 Environmental Consequences

3.9 Cultural Resources

3.9.1 Affected Environment

3.9.2 Environmental Consequences

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3.10 Wilderness

3.10.1 Affected Environment

3.10.2 Environmental Consequences

4 Consultation and Coordination

4.1 Civic Engagement

4.2 Agency Consultation

4.2.1 Endangered Species Act, Section 7

4.2.2 Migratory Bird Treaty Act and Golden Eagle Protection Act

4.2.3 National Historic Preservation Act, Section 106

4.3 Tribal Consultation

5 References

LIST OF APPENDICES

Appendix A—Alaska National Interest Lands Conservation Act Section 810(A) Subsistence—

Summary Evaluation and Findings Appendix B—Consultation Appendix C—Final Socioeconomic Analysis Report Appendix D—Visual Analysis Appendix E—Wilderness Act Minimum Requirements Analysis

LIST OF FIGURES

Figure 1-1. Regional Map Figure 1-2. Denali Park Road Looking West at the Pretty Rocks Landslide on September 28, 2021

(21-foot scarp on eastern side) Figure 1-3. Visitor Destinations Along the Denali Park Road Figure 1-4. Composite Image of the Pretty Rocks Landslide (Outlined in Red Dots) and the Perlite

Landslide (outlined in Green Dots) Figure 1-5. Illustration of the Pretty Rocks Landslide Figure 1-6. Three-Dimensional Imagery of the Bear Cave Landslide (Landslide Boundary Outlined in

Yellow Dots) Figure 2-1. Phase I and Phase II Project Areas Figure 2-2. Phase I Actions Figure 2-3. Digital Representation of the Proposed Pretty Rocks Bridge (Looking East) Figure 2-4. Phase II Actions Figure 2-5. Three Routes Considered in Addition to the Mainline Alignment (Proposed Action):

A Northern Alignment and Two Southern Alignments Figure 3-1. Conceptual Model of the Evolution of a Rock Glacier Figure 3-2. Geologic Illustration of the Pretty Rocks Area Figure 3-3. Wetland Study Area Figure 3-4. Cultural Study Survey Area

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LIST OF TABLES

Table 2-1. Comparison of Proposed Action to the Alternatives That Were Dismissed Table 3-1. Proposed Mitigation Measures Table 3-2. Reasonably Foreseeable Future Actions Along the Park Road Table 3-3. Wetlands by Cowardin Class Table 3-4. Approximate Wetland Impacts

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ACRONYMS AND ABBREVIATIONS

ADOLWD Alaska Department of Labor and Workforce Development ANCSA Alaska Native Claims Settlement Act ARC Alaska Road Commission BGEPA Bald and Golden Eagle Protection Act CFR Code of Federal Regulations COVID-19 Coronavirus Disease 2019 DENA Denali National Park and Preserve EA Environmental Assessment EBRA Expert-Based Risk Assessment FHWA Federal Highway Administration MBTA Migratory Bird Treaty Act National Register National Register of Historic Places NEPA National Environmental Policy Act NHPA National Historic Preservation Act NPS National Park Service PEPC Planning, Environment, and Public Comment PRHD&CL Park Road Historic District and Cultural Landscape RFFA Reasonably Foreseeable Future Action SHPO State Historic Preservation Officer U.S. United States USFWS United States Fish and Wildlife Service VA Value Analysis

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1 INTRODUCTION

1.1 PROPOSED ACTION

The National Park Service (NPS) proposes to implement a series of engineered solutions to address several geologic hazards impacting the Polychrome section of the Denali Park Road between Mile 44 and Mile 46 in Denali National Park and Preserve (DENA), including a 400-foot steel bridge spanning the Pretty Rocks Landslide at approximately Mile 45.4. The location of the proposed project in DENA is shown in Figure 1-1. Although Pretty Rocks Landslide is the highest priority and would be addressed first, the NPS is proposing a comprehensive approach with additional improvements along this 2-mile section of road to ensure that access through the Polychrome area wouldn't be subsequently jeopardized by another nearby hazard. In addition to the construction of a bridge, the Polychrome Area Improvements project would also include the following actions:

• Excavation of uphill slopes

• Placement of excavated material on the slope below the road

• Slight road realignment and temporary widening of the road

• Construction of retaining walls and drainage improvements

• Creation of rockfall ditches and benches

• Rock scaling and/or installation of rock bolts and dowels

• Construction of a temporary platform for bridge assembly

• Construction of a partially buried retaining wall along approximately 1,000 feet of road

The project would be implemented in two phases (Figure 2-1) to expedite the start date of the first phase and allow time to secure funding and finalize designs for secondary phases. Road access through Polychrome is not anticipated during Phase I, which would take approximately 2 years;

however, access would likely be allowed during Phase II with some delays or temporary restrictions expected.

The following assessment is intended to provide a detailed analysis of impacts for Phase I and a concept-level analysis of impacts for Phase II to fully disclose the overall impacts of current and future actions in the Polychrome area to the public. The NPS is the lead federal agency preparing this Environmental Assessment (EA) in compliance with the National Environmental Policy Act (NEPA;

40 Code of Federal Regulations [CFR] 1500 et seq.). The Federal Highway Administration (FHWA) is participating as a cooperating agency, which allows their adoption of this EA.

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FIGURE 1-1. REGIONAL MAP

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1.2 PURPOSE AND NEED

The purpose of the proposed action is to restore reliable access west of Polychrome for users of the Park Road, including visitors, staff, concessioners, and Kantishna property owners. Action is needed because the Pretty Rocks Landslide and other geohazards from Mile 44 through Mile 46 are threatening the integrity, safety, and continued viability of the Park Road as well as threatening access to 47 miles of the road west of the Pretty Rocks Landslide. As of September 2021, the NPS is no longer able to safely repair the road at Pretty Rocks and without action, that section of road would remain closed indefinitely. In addition, it is necessary to make other long-term improvements in the Polychrome area, including addressing Bear Cave Landslide, Perlite Landslide, and several rockfall areas because the safety of the road and reliable access to the 47 miles of the road west of the Pretty Rocks Landslide cannot be maintained without addressing all of these geohazards.

Landslide movement at Pretty Rocks has accelerated in recent years. The rate of road movement within the landslide evolved from a couple of inches per year prior to 2014, to inches per month in 2017, inches per week in 2018, and a few inches per day in 2019. Monitoring equipment used by DENA staff indicated that by the end of August 2021, the movement of the landslide had reached 13 to 15.5 inches per day and further acceleration is likely in the near future. The increasing movement of the landslide results in an increased risk of rockfall hazard as the loose material holding large rocks in place erodes away and the slope above the road becomes steeper. The current conditions require enhanced safety protocols, including the need for additional staff to serve as rockfall spotters during most maintenance activities in the area.

In recent years, the increased rate of movement has also required extraordinary maintenance efforts from the NPS in order to safely maintain access across the landslide. For example, over a 5-month period from fall 2020 to spring 2021, the Pretty Rocks Landslide section of the road slumped approximately 18 feet below the surrounding road grade, which required an emergency repair, the addition of about 6,000 cubic yards of material, and a delayed spring road opening. The slump required an additional 10,000 cubic yards of material and daily maintenance throughout the summer 2021 season. This limited the maintenance that the NPS could conduct on other parts of the Park Road and concerns grew about the rapid depletion of aggregate reserves. While these repairs were challenging, they were manageable until the acceleration of the slide in August 2021 proved that previous maintenance efforts would no longer be sustainable and the NPS was forced to close the Park Road at Mile 43 for the remainder of the season, 20 days earlier than scheduled. Without daily maintenance, the condition of the road quickly deteriorated and the landslide has displaced the road more than 30 feet below the surrounding road grade since September 2021. The condition of the road on September 28, 2021 is shown in Figure 1-2.

The NPS is no longer able to safely maintain the road through Pretty Rocks, without constructing a bridge that section of road would remain closed indefinitely. In addition, it is necessary for the NPS to make other long-term improvements in the Polychrome area, including addressing Bear Cave Landslide, Perlite Landslide, and several rockfall areas because without action to protect the road soon, these hazards will likely become bigger problems that would require more complex engineering solutions and be more difficult to mitigate in the future. The safety of the Polychrome section of road and access west of Mile 43 cannot be maintained without addressing all of these geohazards.

The Park Road—including the section through the Pretty Rocks Landslide and the Bear Cave Landslide—is the primary means by which most visitors experience DENA and inholders access their inholdings. The majority of park visitors use the Park Road, and most of those road users traverse the Pretty Rocks Landslide area. If left unaddressed, the Pretty Rocks Landslide and the Bear Cave Landslide would continue displacing the road, eliminating vehicular access to the western half of the Park Road and popular visitor destinations and NPS facilities including the Toklat Road

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Camp, Eielson Visitor Center, Wonder Lake, Kantishna, and the most iconic views of the Alaska Range and the Denali massif, as well as the easy wilderness access this section of road provides. As a result, the majority of visitors would lose the opportunity to experience the iconic views and recreational opportunities offered along the western half of the Park Road, NPS facilities would be abandoned, and concessioners and Kantishna businesses would suffer financial loss. Providing safe access through the Polychrome area would ensure access along the only overland route in DENA and allow visitors to continue experiencing and enjoying the entirety of the Park Road and the access it provides to other areas of the park.

Source: NPS

FIGURE 1-2. DENALI PARK ROAD LOOKING WEST AT THE PRETTY ROCKS LANDSLIDE ON SEPTEMBER 28, 2021

(21-FOOT SCARP ON EASTERN SIDE)

1.3 BACKGROUND

The Park Road was originally built by the Alaska Road Commission (ARC) in the 1920s and 1930s.

The 92-mile road is mostly gravel, with only the first 15 miles paved; private vehicles are restricted west of the Savage River (Mile 15) from May 20 to mid-September. The Park Road is connected to the Alaska State road system at Mile 0 and ends in Kantishna at Mile 92. In a typical visitor season, the Park Road opens to Mountain Vista (Mile 13) around mid-February, to the Teklanika Rest Stop (Mile 30) around April (after May 20, private vehicles are permitted to this point with a Teklanika River Campground permit), to the Toklat River Rest Stop (Mile 53) on May 20, to the Eielson Visitor Center (Mile 66) on June 1, and to Kantishna (Mile 89) on June 8. In the fall, the Park Road closes at the Teklanika Rest Stop before the second weekend after Labor Day, which is when DENA hosts winners of the road lottery for personal vehicle access to the Park Road. Following the road lottery, the Park Road is open to the Teklanika Rest Stop as long as weather permits (typically until mid- October). A map of visitor destinations along the Park Road is shown in Figure 1-3.

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FIGURE 1-3. VISITOR DESTINATIONS ALONG THE DENALI PARK ROAD

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The majority of the Park Road is listed on the National Register and is surrounded by designated wilderness, which begins 150 feet from the centerline of the original road alignment (Figure 1-1; it is important to note that the Park Road is not in designated wilderness). Halfway along the 92-mile route, the road cuts through the Polychrome area, which has several known unstable slopes including the Pretty Rocks Landslide at approximately Mile 45.4.

Often referred to as a landslide, Pretty Rocks is more appropriately termed a rock glacier. This rock glacier is composed of a thick (40- to 80-foot) layer of sediment and ice that is slowly sliding on top of frozen volcanic ash and clay. It flows perpendicular to the Park Road from its headscarp (i.e., the steep region of exposed soil and rock at the head of the landslide where the failure surface ruptures the ground surface) a few hundred feet upslope of the Park Road to its terminus on the valley floor, 1,400 feet downslope. Although it is more scientifically accurate to call Pretty Rocks a rock glacier, this EA will continue to refer to it as the Pretty Rocks Landslide to aid in public understanding. A composite image of the landslide area is shown in Figure 1-4.

The Pretty Rocks Landslide impacts the width of the road (approximately 20 feet in the project area) for approximately 300 linear feet. Movement at the Pretty Rocks Landslide has been observed since at least the 1980s but in 2014 NPS staff noticed a marked acceleration in landslide movement and maintenance needs at the landslide, which have continued to escalate since. Movement has been most noticeable in the areas at and above the current road grade, but activity continues into the substrate below the road grade and into the naturally deposited material piled up on the river bar below. The frozen volcanic ash and clay is thaw unstable, making it sensitive to changes in temperature and moisture. An illustration of the slumped road alignment is shown in Figure 1-5.

To the east of the Pretty Rocks Landslide there is an additional landslide area at approximately Mile 45.3 (known as the Perlite Landslide) that consists of rhyolite, perlite, and colluvium materials.

Slope failures at this location are triggered in part by a natural spring emitting from a geological contact between the impermeable perlite layer and the rhyolitic colluvium in the slope. The resulting debris flowing onto the road has caused traffic delays—a large event on August 26, 2015 affected 45 linear feet of the Park Road and blocked traffic for two hours, requiring the road to be closed overnight for additional cleanup. The Perlite Landslide is also shown in Figure 1-4.

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Source: BGC 2020

FIGURE 1-4. COMPOSITE IMAGE OF THE PRETTY ROCKS LANDSLIDE (OUTLINED IN RED DOTS) AND THE PERLITE

LANDSLIDE (OUTLINED IN GREEN DOTS)

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Source: NPS, Laurel Mundy

FIGURE 1-5. ILLUSTRATION OF THE PRETTY ROCKS LANDSLIDE

Between Mile 44 and Mile 46, there are also several unstable slopes that have been identified as high rockfall risk areas. Sight distance is limited through this section of road and the existing rockfall catchment areas are narrow, making the area a particular safety concern. Near the Perlite Landslide, a rocky slope above the road consists of decomposing rhyolite with intermittent layers of perlite. It has produced boulders up to 1 foot and has affected 550 linear feet of the Park Road. Farther to the east (around Mile 45.2), the existing road cut is over-steepened, causing instability on the lower slope. This has produced boulders up to 5 feet, as well as localized areas of raveling and undermining that has produced debris slide events up to about 9 cubic yards in volume and affected 230 linear feet of the Park Road. Around Mile 44.6, another area of loose rhyolitic rock has produced boulders up to 3 feet and affected 430 linear feet of the Park Road.

The Bear Cave Landslide (Mile 44.8) in the Polychrome area is also of concern. The unstable slope of the Bear Cave Landslide has the potential to affect the stability of approximately 1,000 feet of the Park Road. The landslide headscarp is just below the road (Figure 1-6) and erosion and regression continue to threaten the Park Road. In 1999, a project redirected subsurface and surface drainage away from the landslide area to a nearby culvert with the installation of a deep cutoff trench lined with geotextile in the uphill ditch. Although the rate of movement at Bear Cave Landslide has slowed since the drainage improvements in the 1990s, the landslide is still active. The upper edge of the

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landslide has continued to get closer to the road over the last two decades and is now within 10 feet of the road (BGC 2020). If the landslide becomes a bigger problem, it would likely require a more complex engineering solution and be more difficult to mitigate. As time passes, the risk of the landslide engulfing the roadway and catastrophic road failure occurring at this location also increases.

Source: NPS, Denny Capps, 2021; imagery from 2018 LiDAR survey

FIGURE 1-6. THREE-DIMENSIONAL IMAGERY OF THE BEAR CAVE LANDSLIDE (LANDSLIDE BOUNDARY OUTLINED IN

YELLOW DOTS)

1.4 ISSUES SELECTED FOR DETAILED ANALYSIS

This Environmental Assessment evaluates the following issues:

• Geology: Bridge construction and associated rock and scree excavation would disturb existing rock formations, scree slopes, and permafrost. Installing a bridge spanning the Pretty Rocks Landslide would allow the landslide and other associated processes to continue on to the toe of the landslide below the construction area without additional disturbance from road maintenance.

• Socioeconomics: Tourism in DENA primarily centers on travel along the Park Road and contributes substantially to the local, regional, and statewide economy. Providing continued safe vehicle access to the entirety of the Park Road would support the park’s role in the tourism

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economy inclusive of park concession contracts and privately owned businesses operating on the western end of the Park Road.

• Visual Resources: The addition of a bridge and retaining walls on the Park Road, as well as excavation and placement of material, would alter the visual setting of the road in the Pretty Rocks Landslide and Bear Cave Landslide areas.

• Visitor Use and Experience: Bridge construction and road maintenance projects would affect visitor experience by increasing long-term safety and reliability of park access. Bridge construction may temporarily disrupt recreation with loud noises and increased dust in the vicinity of the proposed project area. Project construction and operations may temporarily displace wildlife, decreasing wildlife viewing opportunities in the vicinity of the bridge. In addition, the project would be visible from the valley floor and high points in the surrounding landscape where hiking is permitted, including designated wilderness.

• Noise/Soundscape: The construction phase of the project would require earth movement and pile driving and/or drilling by heavy equipment that would temporarily disrupt the soundscape in the project area.

• Wildlife: The area provides important seasonal and year-round habitat for a variety of avian and mammalian species, especially golden eagles (Aquila chrysaetos), Dall’s sheep (Ovis dalli dalli), caribou (Rangifer tarandus), and grizzly bear (Ursus arctos horribilis). The proposed project would cause minor habitat loss and disturbance to wildlife from blasting, excavation, and material placement. Temporary localized disturbances to wildlife from project construction and operations may displace wildlife.

• Wetlands and Vegetation: The project area is mostly on steep rock slopes sparsely vegetated with species and vegetation communities that are common in the park. Less than 1 acre of wetlands is present in the project area, the majority of which is low quality wetlands and streams that are already disrupted by the Park Road or landslide activity. The project would remove or cover approximately 14 acres of vegetation during construction and would disturb some additional vegetation by driving over it with heavy machinery.

• Cultural Resources: The majority of the Park Road—including the project area—is part of a historic district listed in the National Register (Mount McKinley National Park Road Historic District). The majority of the Park Road is also in an identified Cultural Landscape (Mount McKinley National Park Road Cultural Landscape). Altering the road alignment and adding new constructed features would diminish the integrity of the historic character of the road. The proposed project would also maintain access, which would preserve the historic use of this resource.

• Wilderness: A portion of excavation and placement of materials would occur within designated wilderness adjacent to the road. Potential bolts installed for rockfall risk reduction at several sites would be in the surface and subsurface of the wilderness. Noise and visual impacts from construction activity temporarily would diminish opportunities for solitude in wilderness areas.

Maintaining road access through the Polychrome area would provide opportunities for unconfined wilderness recreation in wilderness areas accessed from the Park Road west of the project area.

1.5 ISSUES CONSIDERED BUT DISMISSED

The following issues were identified, considered, and dismissed from further analysis:

• Air Quality: Exhaust from large equipment would affect air quality but would be limited to a small number of machines operating during the construction period and localized in the vicinity of the project site.

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• Environmental Justice: There would be no socioeconomic, cultural, or health impacts to low income or minority communities.

• Hydrology: It is assumed that there would be no impact from the proposed project to the East Fork of the Toklat River, the streams below the project area, or other hydrologic systems because the limited amount of material to be placed on the toe of the landslide is unlikely to destabilize the landslide further.

• Floodplains: NPS completed a floodplain delineation and found that there are not any floodplains in the immediate project area. There is a delineated floodplain below the Pretty Rocks Landslide but material deposited adjacent to the floodplain is not expected to alter floodplain elevations or flood risk in the area.

• Subsistence: The proposed project would not permanently diminish abundance, availability, or access to subsistence resources (Appendix A).

• Threatened and Endangered Species: DENA does not have any documented threatened or endangered species (Appendix B).

• Other possible resources: Other resources not known to exist in the project area include paleontological resources, Indian Trust Resources, and Native grave sites.

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2 ALTERNATIVES

This section describes a No Action Alternative and the Action Alternative, and provides a description of alternatives considered but dismissed from further analysis.

2.1 ALTERNATIVE 1: NO ACTION

Under Alternative 1, the Park Road at Pretty Rocks would not be repaired and no bridge would be constructed; the Bear Cave Landslide, Perlite Landslide, and rockfall areas would not be addressed.

The NPS would not improve the Polychrome section of road and there would be no vehicle access through the Polychrome area to the 47 miles of road west of the landslide (Mile 45.4). Access to the Kantishna inholdings would be primarily via air, and visitor transportation would continue to be limited to Mile 43 of the Park Road, indefinitely. If no action is taken to restore road access to the west district of the park, further planning would be needed to determine if NPS roads and facilities west of Polychrome would be maintained, abandoned, or restored to a natural state.

2.2 ALTERNATIVE 2: PRETTY ROCKS BRIDGE AND POLYCHROME ROAD

IMPROVEMENTS

Alternative 2 is the NPS’s preferred action and environmentally preferred alternative. Alternative 2 would consist of two implementation phases (Figure 2-1). The project was broken into two phases for budgetary and scheduling reasons, with Phase I focusing on the highest priority sites. Phase I would restore access through the Polychrome area by constructing a bridge over the Pretty Rocks Landslide (approximately Mile 45.4) and undertaking risk reduction measures for the Perlite Landslide (approximately Mile 45.3) and rockfall hazards near the proposed bridge. The old road alignment through the Pretty Rocks Landslide would be abandoned after bridge construction, allowing landslide processes to continue and the road to degrade naturally.

Phase II would address several additional geologic hazards in the Polychrome area, including constructing a retaining wall at the Bear Cave Landslide and undertaking risk reduction measures in rockfall areas. For both phases, workers would be housed in existing areas in the park that have been previously disturbed, including the possible use of campgrounds. The Park Road would be used to transport materials and workers to work sites.

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FIGURE 2-1. PHASE I AND PHASE II PROJECT AREAS

2.2.1 Phase I

Phase I (Figure 2-2) would include the following:

• Excavation of uphill slopes at the western and eastern ends of the proposed bridge location and excavation of the “rock knob” on the eastern end

• Placement of excavated material on the slope below the road

• Slight road realignment near the west side of the bridge

• Construction of retaining walls, including possible earthwork and horizontal drains, on the east side of the bridge

• Rockfall risk reduction including rockfall ditches, cut benches, rock scaling, and/or installation of rock bolts and dowels

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• Construction of an approximately 400-foot steel bridge spanning the Pretty Rocks Landslide (including a temporary platform for bridge assembly on the eastern side and steel and concrete bridge abutments on both sides)

• Restriction of traffic through the project area (i.e., no visitor traffic would be allowed)

Construction equipment for Phase I may include the following:

• Excavators

• Dump trucks

• Bulldozers

• Motorized equipment

• Vibratory and/or impact hammer

• Generator

• Drill rig

• Mobile crane

• Forklifts

• Helicopter

FIGURE 2-2. PHASE I ACTIONS

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2.2.1.1 Excavation. Approximately 125,000 to 150,000 cubic yards of material would be excavated.

Excavation of the rock would be accomplished with heavy equipment and blasting. Areas east of the landslide, including the “rock knob” on the south side of the road and the slope on the north side of the road, would be excavated to provide space for bridge construction and equipment.

The slope above the west abutment would be excavated to provide space for construction of the bridge and to accommodate a slight road realignment for vehicles turning on and off the bridge. A portion of this excavation area (less than 1 acre) would be in designated wilderness. The excavation could include a bench cut into the rock partway down the rock face to serve as a rockfall catchment area. The excavation could also include a road-level rockfall ditch. Periodic maintenance of the bench using heavy machinery would be needed, a small portion of which would be in wilderness.

Excavation may also require heavy equipment to drive up the vegetated slope from the western edge of the project area, which would require temporary access of motorized vehicles through designated wilderness. Measures would be implemented to protect the vegetation from damage by heavy machinery and tracked vehicles. If feasible, equipment may be placed for excavation by helicopter, eliminating the need to drive over vegetation in wilderness. Actions are intended to produce rough irregular rock faces that resemble the surrounding natural rock outcrops while maintaining the integrity of the finished rock cut face to minimize rockfall and rock instability.

2.2.1.2 Material Placement. After swell is accounted for, the volume of material that would need to be disposed of would be slightly larger than the volume that was excavated. Excavated material that is of sufficient quality for maintenance use would be trucked off site and stored in existing DENA material storage locations (such as the Toklat pit) for use on future projects. As shown in Figure 2-2, the majority of the excavated material would be disposed of on site on the slope below the road.

Approximately 10 acres of that area would be in wilderness and 0.6 acre in streams or wetlands.

Some vegetation toward the toe of the landslide would be covered by excavated material. Excavated material would consist of rock and soil similar to what currently exists at the site and would be expected to look similar to existing rock/soil at the landslide. Motorized equipment would be used to move material off the roadway and into the material placement area, which would require temporary use in wilderness.

2.2.1.3 Road Realignment. On the west side of the bridge, a short section of the road would be realigned slightly to create space for an appropriate turning radius for vehicles entering and exiting the bridge. The realignment would also include shifting an additional section of road away from the eroding road edge. The realigned road corridor would be entirely outside of designated wilderness;

the wilderness boundary would not shift with this realignment.

2.2.1.4 Retaining Walls. A retaining wall near the east abutment of the Pretty Rocks Bridge would be installed on the slope above the road to reduce the risk of rockfall from the excavated slope. A combination of earthwork, horizontal drains, and possibly a retaining wall would also be required to address the Perlite Landslide on the east side of the Pretty Rocks Landslide. These structures would be outside of wilderness.

2.2.1.5 Rockfall Risk Reduction. Rockfall areas above the road to the east and west of Pretty Rocks Landslide would be addressed using a combination of rock scaling (i.e., the removal of loose or potentially unstable rocks), installation of rock bolts or dowels, and/or the creation of rockfall ditches. Rock scaling would be designed to match existing surroundings and would be conducted by workers on ropes and performed by hand using prybars; no blasting would be necessary. Installation of rock bolts would include 1-inch diameter bolts or dowels drilled into the surface and subsurface rock of the cliff face to secure hazardous rocks and would be designed to match surroundings by either staining the bolts or cutting them flush with the rock and grouting over them. Rock scaling and installation of rock bolts would occur in wilderness and would be repeated every 5 to 10 years, or as needed to reduce additional rockfall hazards.

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2.2.1.6 Pretty Rocks Bridge Construction. A bridge spanning the Pretty Rocks Landslide site would be installed (Figure 2-3). The bridge would be approximately 400 feet long and have an overall width of approximately 24 feet and would be supported by two abutments, one on either end.

Abutments would be steel pilings with ground anchors, which would be drilled or driven into the bedrock and fortified with concrete. The bridge would be one lane and traffic would stop at existing pullouts at either end, yielding to vehicles on the bridge.

A temporary platform would be constructed near the east abutment for use as a bridge assembly location. The platform would extend 150 feet from the south side of the road. The bridge components would be trucked to the site and stored at the temporary platform until assembly. A large crane would be used to assemble the bridge on site. Temporary platform construction would require some pile driving and concrete placement, with several dozen piles needed.

After bridge construction, the temporary platform would be removed, the staging areas would be recontoured, and the road would be restored to its historic road width where possible. Space would be preserved at both abutments for future maintenance needs.

The landscape of this area is changing due to climate change causing permafrost melt. These changing conditions may affect the longevity of the design (approximately 50 years). Currently, the overall synergy between climate change and effects on the engineered solution is unknown and unpredictable. Additional maintenance projects to retrofit the bridge may be needed in response to climate change. Future design considerations to address the possibility of melting permafrost under the bridge abutments, such as the use of thermal siphons, would be researched and evaluated to ensure longevity.

Note: The darker areas on each side of the bridge show where excavation would take place. The dark area under the bridge depicts the shadow of the bridge.

Source: FHWA 2021

FIGURE 2-3. DIGITAL REPRESENTATION OF THE PROPOSED PRETTY ROCKS BRIDGE (LOOKING EAST)

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2.2.1.7 Traffic. Road access through Polychrome is not anticipated during Phase I. For safety reasons, only construction traffic would be allowed in the Pretty Rocks area during most construction activities. Incidental traffic may be facilitated as conditions permit. Visitor transportation would continue to be limited to Mile 43 of the Park Road and buses would turn around at the East Fork Bridge or the East Fork cabin site. Access to Kantishna inholdings would be primarily via air until the bridge is completed.

2.2.2 Phase II

Phase II (Figure 2-4) would include the following:

• Construction of a partially buried retaining wall along approximately 1,000 feet of road above the Bear Cave Landslide, including excavation of materials, installation of drainage improvements, and temporary widening of the road

• Rockfall risk reduction (rock bolts or dowels, rock scaling, and/or rockfall ditches)

• Visitor traffic allowed through the project area, with delays and temporary restrictions possible

Construction equipment for Phase II may include the following:

• Excavators

• Graders

• Front-end loaders

• Dump trucks

• Vibratory and/or impact hammer

• Generator

• Drill rig

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FIGURE 2-4. PHASE II ACTIONS

2.2.2.1 Retaining Wall. At the Bear Cave Landslide area, Phase II would include excavation of materials and construction of a retaining wall on the south side of the Park Road. The retaining wall would be buried approximately 30 to 60 feet deep and run approximately 1,000 feet along the road to stabilize the road edge, and would potentially require several hundred piles. The north side of the Park Road would be temporarily widened to allow traffic to pass around the construction site. Road work would also include subsurface and surface drainage improvements. The retaining wall and road widening/improvements would not be in the wilderness area. After construction of the wall, the area on the north side of the road would be recovered and the road would be returned to the existing roadway centerline and width. Disturbed areas would be revegetated to match the surrounding area.

The retaining wall would be minimally visible from the surrounding area, including from backcountry areas south of the road. Equipment and materials for Bear Cave work would be stored at existing staging areas in DENA.

2.2.2.2 Rockfall Risk Reduction. Rockfall areas above the road to the east and west of Bear Cave Landslide would be addressed during Phase II (Figure 2-4) using a combination of rock scaling (i.e., the removal of loose or potentially unstable rocks), installation of rock bolts or dowels, and/or the

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creation of rockfall ditches. Rock scaling would be designed to match existing surroundings and would be conducted by workers on ropes and performed by hand using prybars; no blasting would be necessary. Installation of rock bolts would include 1-inch diameter bolts or dowels drilled into the surface and subsurface rock of the cliff face to secure hazardous rocks and would be designed to match surroundings by either staining the bolts or cutting them flush with the rock and grouting over them. Rock scaling and installation of rock bolts would occur in wilderness and would be repeated every 5 to 10 years, or as needed to reduce additional rockfall hazards.

2.2.2.3 Traffic. Road access through the Polychrome area is anticipated during Phase II. Visitor transportation to destination points west of Pretty Rocks and regular traffic to Kantishna inholdings would be allowed. There may be some traffic delays due to single-lane use or temporary restrictions at the project sites. There could also be scheduled nighttime road restrictions for work to occur.

Because rock scaling and bolting cannot occur in the dark due to safety concerns, road restrictions would be needed during some daylight hours as well.

2.3 ALTERNATIVES CONSIDERED BUT DISMISSED

2.3.1 Alignment Options Considered

In addition to the proposed project described as Alternative 2, the NPS considered the construction of a new road to bypass the Pretty Rocks Landslide. Three routes were considered in addition to the mainline alignment (proposed action): a northern alignment and two southern alignments (Figure 2-5). The FHWA conducted an Expert-Based Risk Assessment (EBRA) (BGC 2020) and the NPS developed a Value Analysis (VA) (DG&A 2020) to compare the alignments. The EBRA considered the risk associated with geohazards for each alignment and determined that the two southern alignments had the least long-term risk of road closures or road failure associated with geohazards. The EBRA analysis also revealed that improvements to the proposed correction at the Bear Cave Landslide would likely result in the mainline alignment performing as well as the southern alignments. Therefore, the mainline option (proposed action) was revised to include those improvements. The VA determined that the mainline alignment would offer the greatest value to stakeholders when weighing factors such as providing safe visits, protecting natural and cultural resources, improving visitor enjoyment, improving park operations, and providing cost-effective and environmentally responsible development. DENA leadership, along with support from the Alaska Region of the NPS and the FHWA, concluded that impacts to visitors and park resources from the northern and southern alignments would be too great to consider further. A summary of factors that went into the decision process to dismiss the reroute alternatives is provided in Table 2‑1. Note that the long construction duration estimates are partially due to the short construction seasons in this area of the park.

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Source: DG&A 2020

FIGURE 2-5. THREE ROUTES CONSIDERED IN ADDITION TO THE MAINLINE ALIGNMENT (PROPOSED ACTION): A

NORTHERN ALIGNMENT AND TWO SOUTHERN ALIGNMENTS

TABLE 2-1. COMPARISON OF PROPOSED ACTION TO THE ALTERNATIVES THAT WERE DISMISSED

Factor South Alignments North Alignment Proposed Action

Construction duration 11 to 13 years 12 to 14 years 1 to 2 years

Number of new bridges 5-8 8 1

Length of new road 5 to 6 miles 6 miles 600 feet

Designated wilderness 780 to 830 acres 748 acres 11 acres

Cost $255-$275 million $186 million $91 million

Maintenance gravel need over 50-year design life 1 million cubic yards 1 million cubic yards 25,000 cubic yards

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2.3.2 Removing the Upper Landslide

The NPS considered removing the upper landslide material at the Pretty Rocks Landslide from above the road, and shifting the roadway into the hillside. This alternative would require the excavation of a substantial portion of the mountain (approximately 1.1 million cubic yards), mostly from federally designated wilderness. Considering that the large volume of excavated waste material would swell to approximately 1.3 million cubic yards (approximately 10 times the amount anticipated for the proposed action) and require over 100,000 dump truck loads to haul off site, the material would need to be deposited on site below the road. The material would be placed on the toe of the landslide and immediately to the east of the landslide, in wilderness. Given the presence of permafrost and an active landslide in the area, drainage issues would cause localized instabilities contributing to unsafe conditions for operating heavy equipment on the slope. Safety hazards and the unpredictable nature of the project area during construction would not allow for reliable traffic access through the site for potentially 3 years. Due to the geology of the project area (described in Section 3.2), it was determined that this alternative would only provide a temporary solution, because excavation to reach competent bedrock to permanently reestablish a road is unachievable.

In addition, the handling, transport, and placement of excavated material would be far greater than that anticipated for Alternative 2. Therefore, given the unreasonable operational and safety challenges and the insufficiency of this alternative to fulfill the purpose of restoring reliable access, the NPS dismissed removing the upper landslide from further consideration.

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3 AFFECTED ENVIRONMENT AND ENVIRONMENTAL CONSEQUENCES

3.1 APPROACH TO ANALYSIS

3.1.1 General Approach

The impact analysis for the EA includes the issues selected for detailed analysis as identified in Chapter 2. These issues include Geology, Socioeconomics, Visual Resources, Visitor Use and Experience, Noise/Soundscape, Wildlife, Wetlands and Vegetation, Cultural Resources, and Wilderness. Consistent with 40 CFR Part 1501.3(b), impacts for each resource are described in terms of affected area; degree of effect (i.e., extent to which the effect would result in a measurable change to the resource); short-term (generally construction-related) and long-term (operations-related) effects; and beneficial or adverse effects. Impacts are quantified wherever possible, and the analysis considers the timing and duration of the impacts. Additive impacts from Reasonably Foreseeable Future Actions (RFFAs) that consider the contribution of the project are discussed in a separate section following the issue-specific analyses.

The proposed action would incorporate best management practices to proactively minimize environmental impacts and comply with applicable environmental regulatory requirements.

Additional mitigation measures are proposed to further reduce impacts (Table 3-1).

TABLE 3-1. PROPOSED MITIGATION MEASURES

Resource Area Proposed Mitigation Measures

Socioeconomics Section 3.3

• Construction workers would be housed in DENA at previously disturbed locations

Visual Resources Section 3.4

• The bridge would be designed to be nonreflective and in a neutral color to reduce contrast with surroundings.

• The width of the bench cut along the west abutment excavation area would be minimized and have a rough texture.

• The retaining walls at the east end of the bridge and Perlite Landslide would resemble natural materials and blend into the landscape, if possible.

• Excavation and rock scaling would produce rough, irregular rock faces that resemble the surrounding natural rock

• Revegetation of disturbed areas would be implemented with plants salvaged from the project area and native seeds.

• Shielding on construction lighting would be required to eliminate light trespass.

Visitor Use and Experience Section 3.5

• Dust management measures would be employed during Phase II.

Noise and Soundscape Section 3.6

• Broadband amplitude-adjusting backup alarms would be used on construction vehicles to reduce the noise intensity and audible distances.

• Vibratory hammers would be used for pile driving, instead of impact hammers, whenever possible

• The driving surface of the bridge would be a closed metal deck topped with a high-friction surface to reduce the noise of vehicles on the bridge

• Approach pavement would be included on both ends of the bridge to limit the noise of vehicles coming onto the bridge and driving over the bridge

Wildlife Section 3.7

• If ground disturbing activities are conducted during the bird breeding and nesting season, measures would be implemented to avoid disturbance to active nests.

• All construction activities would comply with the Migratory Bird Treaty Act and Executive Order 13186.

• Construction would halt when certain wildlife are within limits established in the Code of Federal Regulations Section 13.920 to reduce disturbance.

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Resource Area Proposed Mitigation Measures

• Nest deterrents would be included in the bridge design

• Vehicles that encounter wildlife on the road or proposed bridge would be required to comply with NPS regulations, which give wildlife the right of way.

Wetlands and Vegetation Section 3.8

• Dust management measures would be employed.

• Revegetation of disturbed areas would be implemented with plants salvaged from the project area and native seeds.

• Stormwater and erosion control best management practices would be implemented to protect wetlands and waters during construction, including vegetation buffers and erosion control fencing

• Measures would be implemented to protect the vegetation from damage by heavy machinery and tracked vehicles.

• Construction vehicle and equipment inspection would be done prior to entering DENA to ensure invasive/nonnative plant species are not introduced.

• Wetland areas within 100 feet of the project area would be flagged and avoided. A

0.01 acre wetland area above the road in the Phase I project area would be avoided.

Cultural Resources Section 3.9

• The above measures to reduce visual impacts would be implemented.

• Mitigation for adverse effects has not been finalized and would be included in the amended Denali Park Road Programmatic Agreement.

• The road realignment on the west side of the proposed bridge would be consistent with the curvilinear design of the existing road.

• The historic road width (16 to 24 feet) would be restored once construction is complete

Wilderness Section 3.10

• Wilderness areas within 100 feet of the established project area would be identified and avoided.

• Measures would be implemented to protect the wilderness areas from damage by heavy machinery and tracked vehicles.

• The above measures to reduce visual impacts, as well as impacts to visitor experience, soundscape, wildlife, and vegetation in wilderness areas would be implemented

Notes:

DENA = Denali National Park and Preserve NPS = National Park Service

3.1.2 Reasonably Foreseeable Future Actions

Descriptions of the RFFAs that were considered for analysis to determine if the proposed project would have additive impacts to projects planned for the next 5 years are provided in Table 3-2. All projects would occur during the summer months (April through October).

TABLE 3-2. REASONABLY FORESEEABLE FUTURE ACTIONS ALONG THE PARK ROAD

Project Description Timeframe

Road and Facility Maintenance, Research…