Polychrome_Project Delivery Plan.pdf

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Table of Contents

EXECUTIVE SUMMARY

Background and Objective

Options

Considerations

Costs

Recommendation

PROJECT DELIVERY PLAN

INTRODUCTION

PURPOSE AND NEED

BACKGROUND

SUMMARY OF OPTIONS

Option 1 Mainline Alignment

Option 2 Northern Alignment

Options 3A and 3B Southern Alignment

DESIGN CONSIDERATIONS

ROADWAY STRUCTURE

CONSTRUCTION CONSIDERATIONS

Option 1: Mainline

Options 2 and 3: Northern and Southern Alignment

GEOTECHNICAL CONSIDERATIONS

EXPERT BASED RISK ASSESSMENT

VALUE ANALYSIS

AGGREGATE MATERIAL SOURCE CONSIDERATIONS

STRUCTURE CONSIDERATIONS

ENVIRONMENTAL CONSIDERATIONS

HYDRAULIC CONSIDERATIONS

GEOMATIC CONSIDERATIONS

SAFETY CONSIDERATIONS

SUMMARY OF COSTS

ALTERNATIVE CONTRACTING METHODS

POTENTIAL FUNDING SOURCES

Federal Lands Transportation Program

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NPS Funding Sources

Great American Outdoors Act 44Nationally Significant Federal Lands and Tribal Projects (NSFLTP) Program

Figures Figure 1. Park Map

Figure 2. Twelve month running mean temperatures at EVC (orange), Toklat (blue), and Denali Park HQ (grey) with 14-year linear trend (dashed lines) (National Park Service 2020a)

Figure 3. Denali Park Road at the Pretty Rocks Landslide. NPS photo (Date unknown)

Figure 4. Pretty Rocks Landslide scarp at the Denali Park Road in November 2019 (National Park Service 2020). The road had been displaced approximately 10 ft. since September 2019 (from red arrow to yellow arrow

Figure 5. The same location as Figure 3 at the Pretty Rocks Landslide in January 2020 (National Park Service, 2020). The road had been displaced approximately 15 ft. since September 2019..13

Figure 6. Options Locations Map

Figure 7. Shows a portion of the existing mainline road (Option 1) over Polychrome Pass where soil and rock unstable slopes rated higher than 400 points are located. These are the locations where roadway risk reduction improvements and reconstruction efforts are being focused for the comparison to the northern (Option 2) and southern (Option 3A and 3B) alignments are being considered. *(https://usmp.info/client/login.php, accessed on 4/2/2020 at 3:16 pm PST.)

Figure 8. Option 2

Figure 9. Option 3A and 3B

Figure 10. Typical Roadway Section

Figure 11. November 2019 Geomorphic Features Mapping by WFLHD

Figure 12. Choosing by Advantages Summary Table

Figure 13. Aggregate Sources

Figure 14. Future Maintenance Aggregate Source

Figure 15. Typical Section Single Lane Launchable Truss

Figure 16. Drainageways

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Tables Table 1. Summary of slope class along the existing alignment and the north and south alignments

Table 2. Summary of hazards along the existing alignment and the north and south alignments.25

Table 3. Estimated Impact Areas

Table 4. Option 1 Estimate

Table 5. Option 2 Estimate

Table 6. Option 3A Estimate

Table 7. Option 3B Estimate

Table 8. Bridge Estimates

Appendices Appendix A: REVISED Geotechnical Memorandum 03-20

Appendix B: Denali National Park Unstable Slope Corridor Assessment

Appendix C: Interim Geotechnical Summary Report of Existing Conditions

Appendix D: Environmental Feasibility Study Memo

Appendix E: Bridge TS&L Steel and Concrete Options

Appendix F: Polychrome Pass Alternative Analysis Hydraulics Memo

Appendix G: Polychrome Pass Alternatives Analysis Safety and Traffic Assessment Memo

Appendix H: Preliminary Structural Pavement Recommendation Memo

Appendix I: Earthwork feasibility memo

Appendix J: 2018 Geotechnical investigation reports

Appendix K: Expert Based Risk Assessment draft report (EBRA) Appendix L: Value Analysis Report

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EXECUTIVE SUMMARY

Background and Objective

Federal Highway Administration - Western Federal Lands Highway Division (WFLHD) is providing the National Park Service (NPS), our project management and technical staff to produce this Project Delivery Plan.

The Project Delivery Plan is in response to the road maintenance issues caused by the Pretty Rocks Landslide in the Polychrome Pass area of the Denali Park Road. Pretty Rocks Landslide is located at the midpoint of the 92-mile long road and impacts approximately 350 feet of the Denali Park Road. Accelerated landslide movement at this site is causing access to be cut off near MP 45.3;

having been displaced 15 ft. from last September 2019 to January 2020 and currently moves at an approximate rate of 2 inches per day. The rate of movement in the area is accelerating and is approaching the limit of the park’s ability to maintain access without significant additional resources. If the park staff is unable to maintain the road through Polychrome Pass, at least five major attractions within Denali National Park and the town of Kantishna would become inaccessible by motor vehicle.

Options Three alignment options are proposed in this report. Option 1 (Mainline Option) is the proposed work on the existing Polychrome Pass alignment and calls for a bridge constructed over the active Pretty Rocks Landslide and a quarter mile long roadway shift with drainage improvements, upslope and away from the retrogressing Bear Cave Landslide. The realignment was considered for the Bear Cave Landslide but during the expert-based risk assessment, the findings pointed out that the Bear Cave Landslide would still be one of the riskier road way sections along this option and the proposed realignment would not necessarily preserve access without a moderate to high risk over a 50-year design life. With this in mind, a more robust option was proposed, with a higher initial cost, WFLHD proposed to construct a buried cylinder pile wall to reinforce the existing roadway and upslope area above the active Bear Cave Landslide for approximately 900 feet in length. For the perlite landslide, adjacent to the proposed east bridge approach to the Pretty Rocks Landslide, a cut side retaining wall and horizontal drains are proposed to reduce the risk of future failure. The other work identified in Option 1 is improving the condition and reducing the risk of five other highly rated (poor condition) unstable rock slopes along the existing Polychrome Pass road corridor that require slope scaling and reinforcement of loose rock and unsupported rock mass features. This option will need 3 years for preliminary and final engineering (geotechnical analysis, survey design), permitting, procurement and 2 to 4 years to construct.

Option 2 reroutes Denali Park Road to the north, near the existing East Fork Toklat River Bridge site at MP 43, then westerly through approximately 6-miles of mountainous terrain, and includes up to 8 bridges with spans ranging from 225 to 1,175 feet, with the largest bridge crossing the East Fork Toklat River. This potential roadway traverses large areas of discontinuous permafrost and landslide features with differing levels of observed activity and rejoins the road near MP 48.

This option will need 4 to 6 years for preliminary and final engineering and 12 to 14 years to construct.

Option 3 reroutes Denali Park Road to the south and has two potential start points, which are

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identified as Options 3A and 3B. Option 3A begins just west of the Ghiglione Bridge near MP 42.1 and Option 3B begins west of the existing East Fork Toklat River Bridge at MP 44.3 (6 miles and

5.3 miles, respectively). Both alignments meet up after crossing the East Fork Toklat river. The road alignment then traverses a broad valley, known as the Plains of Murie, with wide floodplains, discontinuous permafrost, and muskeg. Bridges or causeways will be required to bridge several active, braided river and stream channels. This option crosses large open drainage areas, which may require 5 to 8 bridges with over 9,000 feet of total bridge length with individual bridge spans ranging from 450 to 3,000 feet. Both of these options will need 4 to 6 years for preliminary and final engineering and 11 to 13 years to construct.

Considerations Construction logistics associated with the mainline option will be similar to previous road and bridge projects completed in Denali N.P. Northern and Southern Route Options are much larger in scope and scale than the mainline option and for this reason will require more space for staging equipment, material and personnel than is currently available at existing Denali N.P. facilities and staging areas.

There is a considerable difference in the amount of geotechnical information available for each of the alignments. The performance of the existing alignment has been observed for nearly 100 years and there have been several investigations targeted at understanding the geological and geotechnical issues along the road. In contrast, there is very little known about the geological and geotechnical conditions along the north and south alignments. BGC Engineering is in the process of investigating the impacts of the geomorphic and geotechnical issues on these options.

Sources of aggregate from within the park have been identified and are recommended for

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construction of the project and for the next 50-years of road maintenance. Areas near the East Fork River bridge and the tributaries of the East Fork River have been identified as potential sources of aggregate for construction, but quality of the aggregate is yet to be verified. . The currently permitted area at the Toklat River (north of the causeway) and at the East Fork River scrape area are available to supply quality aggregate for maintenance of the existing Park Road and Option 1 (if chosen), but likely contain insufficient volumes to balance scraping and environmental compliance techniques required to support the aggregate needs for the next 50 years of maintenance for Options 2, 3A, and 3B in the Polychrome Pass area therefore, an area south of the Toklat River Causeway is proposed for aggregate scrape to potentially augment the quality aggregate required for maintenance of Polychrome Pass Options 2, 3A, and 3B over the course of the next 50 years.

The acreage within Denali National Park to be impacted by each alignment option and associated aggregate source is defined in the table below. Due to potential significant impacts of the proposed reroute alternatives, including impacts to federally designated Wilderness, an Environmental Impact Study (EIS) will likely by required. Completion of the EIS under One Federal Decision timelines and pre-NEPA field work will take approximately 3 to 4 years.

The table below provides estimated impact acres for the roadway corridor and for the aggregate source areas with the approximate aggregate needs assumed. Figures 14 and 15 illustrate the proposed roadway corridors and aggregate source areas and are contained in the aggregate material source section of this report.

Options & Aggregate Source Agg Source

(CUYD)

Estimated Impacts

(ACRES)

Mainline (1) Road Corridor 45 North Alignment (2) Road Corridor 362 North Alignment (2) Agg Source 1,863,000 385 South Alignment (3A) Road Corridor 365 South Alignment (3B) Road Corridor 318 Southern Agg Source 1 651,000 135 Southern Agg Source 2 443,000 92 Southern Agg Source 3 399,000 82 Southern Agg Source 4 756,000 156

Future Maintenance Agg (1)1 90,000 0 Future Maintenance Agg (2, 3A, 3B)2,3 150,000 31

Costs

*Total project costs is the total to construct the options and includes 4 years of inflation at 1.9% per year

Preliminary Engineering Construction Engineering Total Project Costs* Option #1 $ Option #2 $

Option #3A $ Option #3B $

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Recommendation

Based on all the factors outlined in this report, WFLHD recommends proceeding with design and NEPA for Option 1. This option provides the most benefit with the least amount of risks and will allow the park road to operate for many years to come.

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PROJECT DELIVERY PLAN

INTRODUCTION

This Project Delivery Plan (PDP) documents alignment options considered to reroute Denali

Park Road to the north, south, or improve resiliency of the existing alignment, which includes constructing safe and reliable access across the Pretty Rocks Landslide. The need to keep the road open and safe, and the increasing landslide movement at Pretty Rocks Landslide over Polychrome Pass has led to the consideration of these optional routes.

PURPOSE AND NEED

The Denali Park Road over Polychrome pass is vital and serves as the sole road access to the western regions of the park, including Kantishna. Pretty Rocks Landslide (Figure 1) impacts approximately 350 feet of the Denali Park Road near Mile Post (MP) 45.3. While private vehicles of Park visitors are only allowed access up to MP 15, and on a limited basis during road lottery in September each year from MP 15 to MP 92, professionally trained drivers provide bus access for the vast majority of visitors to the park between MP 15 to MP 92. The exception to general road access rules, between MP 15 and MP 92, is the private vehicles and commercial deliveries for Kantishna land owners and residents that use the Park Road to the Park Boundary (MP 87.5); where the road continues to MP 92, but is under the jurisdiction of the State of Alaska Department of Transportation and Public Facilities to the town of Kantishna.

The Pretty Rocks Landslide (Figures 3, 4, and 5) at MP 45.3 is one of several known (soil and rock) unstable slopes along the route. If access at Pretty Rocks is cutoff by landslide movement, the following major attractions will no longer be accessible by road:

□ Toklat Rest Stop (MP 53)

□ Stony Hill Overlook (MP 62)

□ Eielson Visitor Center (MP 66)

□ Wonder Lake Campground (MP 85)

□ Kantishna (MP 89 to 92)

Iconic, scenic views beyond Milepost 43 of the park would be inaccessible by road to park visitors should these sites become unreachable. Furthermore, a primary aggregate source and west end Park housing facilities would not be accessible by road at the Toklat Rest Area and Camp (MP 53).

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Figure 1. Park Map

Along the Denali Park Road are over 140 unstable slopes with varying degrees of operational impact potential. There are two significant landslides within the Polychrome Pass area: Bear Cave Landslide (Mile Post (MP) 44.8), Pretty Rocks Landslide (MP 45.3). The Pretty Rocks Landslide’s rate of movement has increased in recent years. In Spring 2018, the road movement was measured at approximately 0.2 to 0.3 inches per day and it was difficult to maintain through the summer season by Park maintenance crews. From September 2018 to March 2019, road surface movement measurements had increased to 0.4 inches per day. Following record warm average temperatures in the summer of 2019 and record breaking rain events in August 2019, the rate of road subsidence has increased significantly at the Pretty Rocks Landslide. From August 2019 to January 2020, landslide surface change measurements have been, on average, 2 inches per day.

Denali National Park has also experienced warming temperatures over the last 14 years. A temperature analysis was conducted by the National Park Service (2020a) to best characterize the changing conditions at the Pretty Rocks Landslide from 2006 to 2019. Figure 2 illustrates the increase in 12-month running mean temperatures at the Eielson Visitor Centre (EVC), Denali HQ and at the Toklat River. This warming has changed the climatic regime to one where temperatures are now greater than 0 °C. Climate and soil conditions control permafrost stability and it tends to degrade at air temperatures greater than 0 °C (NPS, 2020a). The trend from past data and climate models indicate that most years will experience average mean annual temperatures over 0°C.

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Figure 5. The same location as Figure 3 at the Pretty Rocks Landslide in January 2020 (National Park Service, 2020). The road had been displaced approximately 15 ft. since September 2019.

To ensure that the accessibility is both safer and more sustainable for the long term, NPS with technical support from the Western Federal Lands Highway Division (WFLHD) have evaluated three options for a more resilient roadway corridor in the Polychrome Pass area between MP 43 and 48.3. These options, explained in this report, focus on roadway improvement in the Polychrome Pass area along this critical transportation corridor. Figure 6 shows a plan view of the options.

□ Option 1: Mainline (Existing Alignment)

□ Option 2: Northern route

□ Options 3A and 3B: Southern route – o 3A begins to the west of the existing Ghiglione Bridge and, o 3B begins to the west of the existing East Fork Toklat River Bridge.

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Figure 6. Options Locations Map

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BACKGROUND

Denali National Park is home to the tallest peak in North America, measuring 20,310 feet in elevation, and is the home to an abundance of wildlife. Tourism is the critical driver of the regional economy. In 2017, 400,000 people visited Denali National Park and Preserve and spent $632 million in the local region. That spending supported over 8,100 jobs in the local area and had a cumulative benefit to the local economy of nearly $924 million, according to a National Park Service Report.

The existing alignment traverses a precipitous section of road known as Polychrome Pass.

Built in the 1920s and 1930s as a scenic high-line route that overlooks the Plains of Murie, this section of road between about MP 43 and MP 48 is approximately mid-way on the 92-mile long road. The roadway through Polychrome Pass is critical to the park as it is the only access to major viewing sites, campgrounds, and in holder owned private land.

SUMMARY OF OPTIONS

An interdisciplinary team of employees at WFLHD and Denali National Park developed the alignment options described in this section.

Option 1: Mainline (Existing Alignment)

For this evaluation, the proposed work on the existing Polychrome Pass alignment calls for a bridge constructed over the active Pretty Rocks Landslide and a quarter mile long roadway shift with drainage improvements, upslope and away from the retrogressing Bear Cave Landslide. The realignment was considered for the Bear Cave Landslide but during the expert-based risk assessment, the findings pointed out that the Bear Cave Landslide would still be one of the riskier road way sections along this option and the proposed realignment would not necessarily preserve access without a moderate to high risk over a 50-year design life. With this in mind, we proposed a more robust, higher initial cost, buried cylinder pile wall in the existing roadway to reinforce the existing roadway and upslope area above the active Bear Cave Landslide for approximately 900 feet in length. For the perlite landslide, adjacent to the proposed east bridge approach to the Pretty Rocks Landslide, a cut side retaining wall and horizontal drains are proposed to reduce the risk of future failure at this location. The other work identified in Option 1 is improving the condition and reducing the risk of five other highly rated (poor condition) unstable rock slopes along the existing Polychrome Pass road corridor that require slope scaling and reinforcement of loose rock and unsupported rock mass features (see Appendix B).

Several highly rated (poor condition) unstable slopes are identified along this corridor and are shown in red in Figure 7. Site specific hazard and risk ratings are detailed in the Denali National Park Unstable Slope Management Program (USMP), adopted from the USMP for Federal Land Management Agencies (FLMA) publication and website tools (FLH, January 2019) (Appendix B).

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Figure 7. Option 1

Figure 7 shows a portion of the existing mainline road (Option 1) over Polychrome Pass where soil and rock unstable slopes rated higher than 400 points are located. These are the locations where roadway risk reduction improvements and reconstruction efforts are being focused for the comparison to the northern (Option 2) and southern (Option 3A and 3B) alignments being considered. The USMP ratings of nearly 2500 unstable slopes across the United States over time have provided a consistent site condition range of points that correspond to the road/slope condition being generally in a good, fair, and poor condition. The range for good conditioned slopes is typically between 0 and 200 points; fair condition ranges from 200 to 400 points; and a poor condition is generally higher than 400 points, respectively. Although the proposed north and south alignments would be new and assumed to be initially in good condition, the presence of landslides and permafrost will likely result in a good to fair condition road section;

therefore, the mainline option comparison has only been brought up to a fair condition for comparison. *(https://usmp.info/client/login.php, accessed on 4/2/2020 at 3:16 pm PST.)

The Pretty Rocks Landslide site within Option 1 has been the location of most geologic and geotechnical studies since 2016, where several options were considered for risk reduction and mitigation of the accelerating landslide movement. The current practice, which requires filling in the subsiding roadway to bring it back to grade required an emergency contract to place approximately 5,000 cubic yards of fill and aggregate in 2020 as the movement of the landslide has significantly increased since 2014. This was removed from further consideration as a long-term solution since the movement of the landslide continues to increase and Denali maintenance forces are beginning to struggle to keep up with the releveling of the roadway.

We also conceptualized and considered several risk reduction efforts for the Pretty Rocks Landslide since the 2018 geotechnical drilling investigation, instrumentation, and laboratory testing provided adequate information to characterize the landslide and begin analyzing its stability. Four broader categories with conceptual considerations were brainstormed by FHWA

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and NPS in February 2019:

Avoidance:

• Realignment away from the landslide (Options 2, 3A, 3B)

• Remove the landslide – earthwork option

• Bridge the landslide

• Short and long tunnel

Reduce Driving Forces of the Landslide:

• Minor shift in roadway alignment upslope with terracing

• Reduce weight in upper portion of the landslide (redistribute loads, lightweight fill options) – combine with earthwork option where appropriate

• Improve drainage (surface and subsurface) – combine with all alternatives, if feasible

Increase Resisting Forces (external loads):

• Shear key buttress and/or counter berm at landslide toe, or rock-filled shafts to increase shear resistance

• Structural wall with tie-back anchor systems – combine with minor roadway shift and upslope terracing large, pre-cast or cast-in-place anchor pads on the surface of the landslide

Increase Resisting Forces (internally):

• Large area of rock-filled shafts with drainage improvements in the lower landslide – combine with earthwork option

• Ground freezing technology (keep permafrost frozen)

Out of these conceptual alternatives, the avoidance alternatives were moved forward for proof in concept and constructability considerations along with the light weight fill replacement of the roadway embankment with minor earthwork and large pre-cast or cast-in-place anchor pads on the surface of the landslide. The short list of conceptual alternatives moved forward are detailed in the 2018 Geotechnical Investigation and Conceptual Design Considerations Report contained in Appendix J. After presenting this short list of conceptual alternatives with a list of pro’s and con’s under the proof of concept stage, the NPS selected moving forward with the realignment options (2, 3A, 3B), remove the landslide earthwork option (Appendix I), and bridging the landslide option (Appendix A) in June 2019.

Additional test boring, instrumentation, and laboratory testing was initiated in September 2019 to conduct viability and constructability for the earthwork and bridging options. The Earthwork Option is feasible and constructible and would impair access on the road and would require more than one field season to complete. However, based on our findings, it would likely only be an intermediate risk reduction measure because it would require ongoing and possibly significant work to arrest erosion and failures from newly exposed, very weak rock over the next 50 years initiating from the high, new cut slope above the road. In this option, over one million cubic yards of material (including permafrost rich soils) will need to be removed from the upper hillside to reach the very weak bedrock material to build the road upon. The excavated material will be partially placed on the landslide toe at the base of the slope and to the east on the edge of the valley floor flood plain. The impacts, design, and construction considerations for this option are contained in the Pretty Rocks Landslide Earthwork Feasibility and

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Constructability Geotechnical Memorandum 14-20 in Appendix I.

The bridging option is feasible and constructible but will have impacts to existing road access in order to be completed in two construction seasons. Constructing the bridge will take longer if only shoulder season road closures and work are allowed. The Pretty Rocks bridging option discussion and details is further discussed in the REVISED Geotechnical Memorandum 03-20 in Appendix A. Preliminary discussions with NPS in early 2020 resulted in moving forward with the bridging option for this Polychrome Pass Alternatives analyses and cost estimating for Option 1 (Mainline).

Option 2: Northern Alignment This alignment reroutes Denali Park Road, near the existing East Fork Toklat River Bridge site at MP 43, then westerly through approximately 5.7 miles of mountainous terrain, crossing rivers and several drainages, and includes up to 8 bridges with spans ranging from 225 to 1,175 feet, with the largest bridge crossing the East Fork Toklat River (Figure 8). Option 2 roadway traverses large areas of discontinuous permafrost and landslide features with differing levels of observed activity and rejoins the road near MP 48.

Figure 8. Option 2

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Options 3A and 3B: Southern Alignment Option 3A begins just west of the Ghiglione Bridge near MP 42.1 and Option 3B begins west of the existing East Fork Toklat River Bridge at MP 44.3 (6.3 miles and 5.3 miles long, respectively), per Figure 9. Both alignments meet up after crossing the East Fork Toklat river.

The road alignment then traverses a broad valley, known as the Plains of Murie, with wide floodplains, discontinuous permafrost, and muskeg (wetlands). The road reconnects to the existing mainline road at MP 48.5.

Bridges will be required to bridge several active, braided river and stream channels. This option crosses large open drainage areas, which may require bridges between 450 and 3000 feet long, with one of the most substantial ones crossing the East Fork Toklat River at the beginning of Option 3B at 2,500 feet-long and 200 ft. tall.

Figure 9: Options 3A and 3B

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DESIGN CONSIDERATIONS

The project development process, no matter which option is chosen, will be quite challenging. While significant efforts have been made to inventory construction needs, development of project plans will require additional field evaluations and geological reconnaissance. This is a critical factor to ensure the success of the project.

Estimated time required for project development for Option 1 (Mainline) is 3 years.

Depending on the complexity of the project, estimated project development for Options 2 (North) and 3 (South) routes will need 4 to 6 years. This time factors in preliminary and final engineering (geological analysis, survey design), permitting and procurement.

ROADWAY STRUCTURE

Typical roadway structure for these options will require eight inches of roadway aggregate to be applied to areas that do not cross over permafrost and muskeg, per Figure 9.

Figure 10. Typical Roadway Section

A considerable amount of material will be needed for Options 2, 3A, and 3B, since these alignments cross through permafrost and muskeg. Due to the anticipated prevalence of permafrost in the northern and southern alignments, excavation was minimized in the profile grades and road locations where possible and embankment sections were kept 3-feet high to maintain drainage. Initial excavation estimates, per typical sections shown in Figures 10 and 11, were calculated and every effort was made to avoid permafrost and muskeg areas during the preliminary design of the alignments. A more in-depth analysis will determine the soil types in the areas and the plan for the analysis is further discussed in the Interim Geotechnical Summary Report of Existing Conditions, Appendix C. Alignments can be further refined as more information is collected.

Initial approximations for Option 2 will require over 4 miles of typical thermal section and under a quarter mile of typical muskeg section, while Option 3 will require approximately 3 to 4 miles of a typical thermal section and 0.5 mile of a typical muskeg section.

When crossing permafrost ground the park has determined that they would like to go with a standard aggregate section rather than a typical thermal section that would contain Styrofoam. The standard section will accelerate permafrost degradation approximately in the first 10 years of life.

Aggregate needs will therefore be increased in the first 10 years to maintain the roadway elevation and drainage.

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CONSTRUCTION CONSIDERATIONS

Option 1: Mainline

The logistics associated with the mainline option will be similar to previous road and bridge projects completed in the Denali N.P. backcountry and will require 2 to 4 years to construct. Toklat Road Camp is of sufficient size to be used for aggregate material production and most of the space required for construction equipment, materials and project office trailers.

Toklat Road Camp also has enough RV trailer spaces to house the contractor’s core work force.

Additional housing or material storage needs can be met in existing park staging areas and campgrounds.

Although the Mainline Option is smaller in scope and scale than the other Options, it has a greater likelihood of impacting public traffic with construction work occurring immediately adjacent to and within the existing Park Road alignment. Some of these impacts can be mitigated by scheduling work that cannot be completed under public traffic during the shoulder seasons, or at night, when public traffic volumes are lower. However, limiting the work window will extend the overall duration and cost to complete the project.

Options 2 and 3: Northern and Southern Alignment

The Northern and Southern Route Options are much larger in scope and scale than the mainline option and for this reason will require more space for staging equipment, material and personnel than is currently available at existing Denali N.P. facilities and staging areas. Option 2 will require 12 to 14 years and Options 3A and 3B will require 11 to 13 years. These estimates are based on the limited information currently available.

Space for staging should be provided along the proposed routes, or as close as possible, to limit public traffic conflicts and to reduce the travel time between the staging location and active construction. Staging for the Northern and Southern Alignments includes space necessary to perform the following; production and stockpiling of processed roadway material, construction equipment, construction materials, field offices, and lodging for the contractor’s work force.

At a minimum, 7 to 10 acres will be required to produce and store aggregate material for roadway construction. For comparison, the portion of Toklat currently used for processing and storing aggregate is approximately 7 acres.

Another 7 to 10 acres of space is needed to stage equipment and miscellaneous construction materials (culverts, geotextile, insulating board, containers for small tool storage, etc.) and field offices for the contractor and subcontractors.

In addition to the staging areas outlined above, each bridge will require a lay down area outside of the proposed alignment to store bridge materials and equipment. Additional space is also required immediately adjacent to the bridge abutments for construction of the bridge foundations and to provide adequate space for crane support. The amount of space will vary depending on the size and complexity of the bridge.

The number of workers supporting the field project work will vary significantly depending on the type and number of construction activities. The anticipated crew size for large bridge and road construction operations is typically 15 to 30 individuals for each operation.

Although it’s not necessary to house all the workers on-site, as many are transient and only involved with the work for days or weeks at a time; there is an advantage to housing those

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workers that will remain with the project for longer durations. The commute from potential housing locations in Healy, AK to the project site requires 1.5 to 2 hours each direction. If housing options are not provided near the project, it would lead to a shorter work shift (longer construction duration) and higher costs. Housing accommodations for the construction staff only requires providing sufficient space for the contractor to organize a work camp. This camp would likely consist of recreational vehicles with the contractor providing essential services such as water, electricity and waste water disposal.

Although both the Northern and Southern alignment work will be performed outside of the existing alignment, the work will require a significant amount of construction traffic on the first 43 miles of the existing Park Road. To the extent possible, roadway materials (waste, fill and processed material) will be sourced, produced, stored and wasted along the proposed alignments.

However, there is still a large volume of material and equipment that will be transported across the existing Park Road including all bridge materials and miscellaneous road construction items.

Most of these shipments can be scheduled outside of peak visitation hours. Additional maintenance will be required along the gravel section of the Park Road as a result of the additional construction traffic.

The arctic weather conditions in Denali National Park presents one of the biggest challenges to construction. The months of December and January are too cold to efficiently complete any item of work with low temperatures routinely dropping below -20℉.

Temperatures during the months of November and February are generally warmer but can still drop to levels that would prevent construction from occurring. Snow is also prevalent during this time of year and can block access to the work sites. Practically, construction for most operations would begin in March and conclude in October, providing an 8-month construction season.

Although the weather in March and October is still marginal for construction with the potential for temperatures to drop below 0℉ and snow fall events that block access to and from the work sites.

The topography of the Northern and Southern alignments and distance from the existing Park Road requires a linear sequential approach to road construction. There is not an opportunity to access the proposed alignments at any point other than the beginning and end of the routes where they tie in with the existing Park Road. Temporary bridges may be used to span depressions or drainages that cannot otherwise be traversed until the permanent structures are completed. This will allow construction to proceed at multiple sites concurrently and reduce the overall duration of construction.

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GEOTECHNICAL CONSIDERATIONS

There is a considerable difference in the amount of geotechnical information available for each of the alignments. The performance of the existing alignment has been observed for nearly 100 years and there have been several investigations targeted at understanding the geological and geotechnical issues along the road. In contrast, there is very little known about the geological and geotechnical conditions along the north and south alignments; so far, knowledge is limited to what can be synthesized from the following:

• Review of air photos and satellite imagery.

• Observations collected by WFLHD in September of 2019 while walking along the proposed alignment corridors. This includes photos, geological hazard observation (e.g.

landslides and permafrost) which is presented as geomorphic mapped units produced by WFLHD (Figure 13), and scattered ground temperature measurements along the south alignment.

• Review of existing geological maps.

• Satellite Interferometric synthetic aperture radar (InSAR) collected and processed by

TRE ALTAMiRA in March of 2020.

Note: All mapping and data tables discussed in these bullets are contained in Appendix C in the interim geotechnical summary report of existing conditions

For comparison between the alignments, the slopes have been classified into three categories: less than 20 degrees inclination (less likely to have unstable slopes), 20 to 34 degrees (moderate likelihood of having unstable slopes), and greater than 34 degrees (higher probability of having unstable slopes and initiating snow avalanches). When the preliminary roadway intersection are analyzed with natural slope inclinations, most of the terrain that the alignments intersect is less than 20 degrees in slope (measured in any direction) (Table 2), ranging from approximately 51 percent of the total alignment length for the north alignment to greater than 80 percent of slope intersections greater than 34 degrees. The north alignment has the largest percentage of slope intersections greater than 20 degrees. The south alignments do not have as much intersection with steep slopes, but they do intersect a higher percentage of 20 to 34-degree slopes when compared to the existing alignment

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Figure 11. November 2019 Geomorphic Features Mapping by WFLHD

Table 1. Summary of slope class along the existing alignment and the north and south alignments.

For reference, please note the Northern Alignment_AB is Option 2, South Alignment_AD is Option 3B, South Alignment_CED is Option 3A, and Existing Alignment is Option 1.

The distribution in slope inclination intersections and the hazard mapping intersections shown in Figure 13 provide an objective measure for developing comparisons and describing the general character of the alignments and associated geologic hazards. For instance, the existing alignment has more length intersecting steep slopes than other alignments (Table 2) and has more length intersecting landslides (Table 3); the south alignments cross a larger percentage of flatter terrain with permafrost, muskeg, and flood/erosion hazards, and the north alignment is

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more of a mixture of geomorphic characteristics with permafrost, flood/erosion hazards, and mapped landslides (Table 3).

Table 2. Summary of hazards along the existing alignment and the north and south alignments.

For reference, please note the Northern Alignment_AB is Option 2, South Alignment_AD is Option 3B, South Alignment_CED is Option 3A, and Existing Alignment is Option 1.

Knowledge of the existing conditions on the proposed north and south alignments is based on mapping, a traverse performed on foot in 2019, and InSAR collected in 2020. These data sources and mapping efforts have informed the proposed preliminary investigation plan for the potential new alignments. The InSAR data mapping provides satellite image comparisons that identify areas of ground surface movement to focus efforts for further investigation when looking at long alignment section in potentially unstable geologic settings.

BGC Engineering has prepared a conceptual scope of the preliminary geotechnical investigation, along with a conceptual cost estimate for the contracted exploration services. The preliminary plan along the alternative alignments will include subsurface explorations at the abutments of proposed bridges, three identified landslides, 5.2 miles of earthwork on the north alignment and 4.5 miles on the south alignment. The proposed investigation scope also includes:

□ geotechnical drilling,

□ sampling and testing,

□ temperature subsurface profiles

□ geophysical surveys, and

□ instrumentation and monitoring.

The locations and quantities of these are shown in Appendix D.

Preliminary drilling for the structures will identify the conditions for foundation design, including material type and frost depth. Given the need to establish site variability and subsurface conditions for type, size, and location (TSL) plans, it is proposed to drill each abutment of each bridge to a depth that would be required for final design. Until bridge TSL plans are complete, no intermediate pier foundations are recommended for drilling under this

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preliminary phase of investigation.

Preliminary drilling for the landslides will characterize the subsurface materials and temperatures, denote the presence of groundwater and/or ice, depth of potential landslide movement, and current level of activity. The field exploration program will help develop an understanding of how climate or proposed construction could affect landslide activity. The drilling will also provide insight into whether the landslides could be mitigated, would need to be avoided, or will likely be an ongoing maintenance or safety issue throughout the 50-year design life of the alignment.

Preliminary drilling for the earthwork will provide a better understanding of the spatial variation of permafrost, the depth of seasonal ice, and distribution of subsurface materials and presence of seasonal groundwater conditions. Note that there are means and methods for this work that would cause a relatively high degree of disturbance, such as pioneering roads to provide access to locations for rubber tire or track rigs. To limit disturbance, these methods are not recommended given the long-lasting impacts, and helicopter access is specified for the boring location plan in Drawing 01 of the Conceptual Geotechnical Investigation and Instrumentation Plan in Appendix D.

An alternative approach for accessing sensitive drilling locations, or a combination of the two approaches, would be to use lightweight equipment that can be carried by a team of people, such as the Talon drill by Kryotek. This type of lightweight equipment will not likely be as successful at drilling to depths greater than about 20 feet, may more often hit refusal on cobbles and boulders, and would not provide SPT results, but it would allow for more holes to be drilled, and better characterization of depth of seasonal ice, presence of permafrost, and frost susceptibility variability along the alignments. An alternate plan of test hole locations using this lightweight equipment is proposed in Drawing 02 of the Conceptual Geotechnical Investigation and Instrumentation Plan in Appendix D.

Electrical resistivity tomography (ERT) geophysical surveys will be coupled with boreholes and downhole instrumentation to provide additional insight into the spatial variability of ground ice conditions at bridge, landslide, and earthwork locations along each alignment.

Other geophysical methods may be used in conjunction with ERT.

Although the existing alignment has had more study, there are some areas where additional investigation is desired to understand current ground movement or the potential for future ground movement. These six holes will be located between MP 43 and MP 48. Five holes will be drilled from the existing road and one will be drilled below the road and will require helicopter access.

Prior investigations at the Polychrome Overlook have focused on landsliding impacting the road.

However, the lidar, orthophotos, and InSAR presented in Appendix C along with recent changes in landslide movement at the edge of the parking area since 2018-2019 suggest we should pay close attention to this area as it shows sign of deterioration and has the attributes of the other big landslides on the existing Polychrome Pass. The imagery suggests that there may be two existing landslides lower on the slope. These landslides have a toe at the river elevation or below and while they have not apparently impacted the road yet, if they are active landslides or were to reactivate, they could impact the road in the future. We acknowledge that this unstable slope does not currently rate higher than 400 points in the unstable slope management program, but it would be wise and proactive to characterize the lower landslide features and the risk of potential impact to the Polychrome parking area since this is high value view point and parking area for the visitor experience before additional landslide activity is observed.

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reduced to be more in line with the Option 3 alternatives.

VALUE ANALYSIS

A Value Analysis was conducted in July 2020 to evaluate additional criteria that were not considered during the EBRA. These criteria included providing safe visits and working conditions for vehicles and pedestrians, protecting natural and cultural resources, improving the efficiency, reliability and sustainability of park operations, and providing cost-effective, environmentally responsible and otherwise beneficial development to the nation park system. The VA team gave each of these criteria a score based on the advantages and disadvantages of each alignment, these scores are summarized in Figure 12-choosing by advantages. Option 1 (mainline alignment) scored the highest and provided the best value based on importance and initial costs as well as total lifecycle costs. The full draft value analysis report is located in appendix L.

FACTOR OPTION 1

(Mainline)

Option 2 Option 3A Option 3B

Provide safe visits and working conditions for vehicles and pedestrians

82 30 119 116

Protect natural and cultural resources 342 29 28 47 Improve visitor enjoyment through better service and educational and recreational opportunities

238 84 97 100

Improve the efficiency, reliability and sustainability of park operations

188 0 29 53

Provide cost-effective, environmentally responsible and otherwise beneficial development to the national park system

72 66 0 6

Total Importance of advantages (benefits) 922 209 273 322

Figure 12: Choosing by advantages summary table note: for full table with sub-factors for each category refer to appendix L.

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AGGREGATE MATERIAL SOURCE CONSIDERATIONS

Proposed Construction and Maintenance Aggregate Areas

To avoid importing considerable embankment and quality aggregate materials into the Park, we recommend considering aggregate needs for the initial construction and for up to 50 years of maintenance. For the south alignment option, the preliminary embankment and aggregate surfacing needed to build the roadway sections between drainages from the East Fork Bridge to the west are shown in the white polygons with the estimated volume of aggregate noted for each. The northern alignment option preliminary aggregate needs is illustrated in yellow polygons, and the absence of drainages for aggregate production along the northern alignment requires the use of two large areas identified in the East Fork River drainage to build the northern alignment option, per Figure 13.

Figure 13. Aggregate Sources. North alignment (yellow polygon) preliminary road aggregate construction needs is approximately 1.86 million cubic yards (CY), and the south alignments preliminary road construction aggregate needs is about 2.25 million CY

For all the alignments, the assumptions for the aggregate scraping process is the average depth of scraping, 3 feet deep, in one mining entry for constructing the initial alignments. The assumed loss of material during aggregate production is 10%, based on Toklat River Scrap Aggregate Processing measurements over the years. Due to the unknown mix of embankment

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materials and bridge spans for stream crossing designs at this time, we have assumed that embankments will be used for the width of the drainage rather than bridges to estimate the aggregate needs. This allows for additional aggregate area and capacity in the preliminary planning because the quality of the aggregate in each of these drainages, originating from differing geologic formations, is unknown until a material investigation confirms quality aggregate products in each drainage. We are hopeful these areas will be reduced as the material investigation confirms quality aggregate materials for road building and it becomes clearer what combination of bridge lengths and embankments may be used for the drainage crossings.

Maintenance for 50 years on the new alignments (Option 2, 3A, 3B) would require more aggregate than the currently permitted Toklat (north of the causeway) and East Fork River scrape areas can provide. In an effort to minimize the impact on the landscape following initial road building needs, an area of the Toklat River (south of the causeway) could be considered as a new source of aggregate for the realignment options. See Figure 14 for the location of the proposed maintenance aggregate source for the new alignments and an estimated area for the gravel portion of the Denali Park Road for the next 100 years.