Attachment_6_-_PPNM_Stabilization_-_Appendix_E.pdf

APPENDIX E:

ENVIRONMENTAL ASSESSMENT: POMPEYS PILLAR

NATIONAL MONUMENT

Pompeys Pillar National Monument Stabilization

DOI-BLM-MT-C010-2022-0002-EA

February 2022 Pompeys Pillar National Monument

3039 US Highway 312 Pompeys Pillar, MT 59064

Environmental Assessment

Table of Contents 1 Introduction

2 Alternatives

3 Affected Environment and Environmental Consequences

4. Consultation and Coordination

5. List of Appendices

A. Appendix A: List of Preparers

B. Appendix B: Table of Issues and Resources Considered

C. Appendix C: Acronyms and Abbreviations

D. Appendix D: List of References

E. Appendix E: Geotechnical Monitoring TARP

F. Appendix F: Remedial Measures Analyzed in Detail

G. Appendix G: Applied BMPs

H. Appendix H: Reclamation Plan

I. Appendix I: Remedial Measures Not Analyzed in Detail

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1. Introduction

1.1 Summary of Proposed Project

The Pompeys Pillar National Monument (PPNM) is undergoing natural processes that threaten the integrity of this National Historic Landmark (NHL) as well as the safety of the public who visits the location every year. The geologic makeup of the Pillar (sandstone, shale, and siltstone) lends itself to degradation through wind, moisture, and temperature changes.

Investigation into the stability of the Pillar led to its temporary closure in March of 2020 due to concerns for public safety. After contracting with a professional consulting firm, the site went through a comprehensive evaluation after which it was recommended all but the lower viewing deck of the Pillar be reopened. As part of the process a Trigger Action Response Plan (TARP) was developed which established pre-determined responses in the event of changes to the structure of the Pillar (see Appendix E). Further professional consulting has resulted in proposed measures to address the site’s issues. These measures include scaling, foliage removal, drainage controls, stabilization or environmental protection for the shale and siltstone layer, buttressing at Signature Block, underpinning of Turtle Rock, and rock bolting at both Signature Block and Turtle Rock.

1.2 Purpose and Need

The purpose and need of this project is to address ongoing natural destabilization and degradation of the Pompeys Pillar National Monument and National Historic Landmark through remediation measures designed to stabilize the rock formation, prevent future degradation, manage the risk to the public, and allow for future enjoyment while maintaining the character of the site.

1.3 Decision to be Made

This document will be used to select the remediation measures that when implemented will best fulfill the purpose and need of the project while minimizing adverse impacts to other affected resources.

1.4 Land Use Plan Conformance

This project is in conformance with the 2015 Billings Field Office and Pompeys Pillar National Monument Approved Resource Management Plan. The proposed action is in conformance with the following goals, objectives, and decisions listed in the RMP for the National Monument, Area of Critical Environmental Concern, Lewis and Clark National Historic Trail, and the Yellowstone River Corridor Special Management Area.

Goal REC-3: BLM’s goal is to develop and maintain appropriate recreational facilities, balancing public demand, protection of public land resources, and fiscal responsibility. (p. 3-29)

MD PPNM-1: Manage Pompeys Pillar NM (51) acres to protect the historical and cultural objects for which it was designated a National Monument.

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MD PPNM-14: Management Zones: Front Country Zone – includes all of the National Monument lands (51 acres) and 34 acres outside of and immediately adjacent to the National Monument 2. Use this zone area to develop new facilities, including structures and roads, where they are necessary for public health and safety, are required under law, are necessary for the exercise of valid existing rights or other non-discretionary uses, prevent impacts on fragile resources, or further the purposes for which the NM was designated.

MD PP ACEC-9: 4. Facilities would be designed to enhance visitor experiences.

General Management Zone – (347 acres)

MD PPMN-5: Visual Resource Management (VRM): Class II for the NHL (6 acres) for protection of the significant historical resource and VRM Class III for the remainder of the PPNM for consideration of potential facility development and public management concerns.

MD C&HR-5: Design and maintain facilities to preserve the visual integrity of cultural resources, settings, and cultural landscapes consistent with VRM objectives established in the RMP

Yellowstone River Corridor Special Recreation Management Area, Zone 1 (Billings Field Office RMP, Volume 2, Appendix N, page N-14)

Best Management Practices PPMN (PPMN RMP, Appendix B, page B-50)

1.5 Relationship to Statutes, Regulations, Other NEPA Documents Federal Land Policy and Management Act of 1976 (43 U.S.C. §§ 1701-1782, P.L. 94-

579, October 21, 1976, as amended 1978, 1984, 1986, 1988, 1990-1992, 1994 and 1996) National Historic Preservation Act (54 U.S.C. 300101 et seq.)

Federal Lands Recreation and Enhancement Act of 2004 (REA), P.L. 108-447 (16 U.S.C.

§ 6804.)

National Historic Landmarks Program of 1983 (54 USC 302102 et seq.)

This EA was prepared to thoroughly examine the potential environmental impacts of the proposed action and alterative actions in order to support informed decision- EA is

Environmental Quality’s (CEQ) implementing NEPA regulations at 40 CFR Parts 1500-es including Secretary’s Order No. 3399 requiring bureaus and offices to use “the same application or level of NEPA that would have been applied to a proposed action before the 2020 Rule went into effect.”

1.6 Issues Identified for Analysis

Site specific resource concerns were identified by the BLM through the preliminary review process conducted during the internal and external scoping period. The BLM focuses its analysis on issues that are truly significant to the action in question. Issues have a cause-effect scientific analysis.

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1.6.1 How will the remediation measures affect the historic inscriptions on the Pillar, including those on the Turtle Rock area?

1.6.2 How will the visual integrity of the site be altered by the remediation measures?

1.6.3 How will public access and experience be affected by the remediation process?

1.6.4 How will the surface disturbing activities associated with the implementation of the project and the design feature of foliage removal affect native vegetation?

1.6.5 How will the remedial measures affect the geologic integrity of the National Monument?

1.7 Issues Identified but Eliminated from Further Analysis

1.7.1 Will public safety be affected during and after the construction process?

The interest of public safety is one of the key drivers behind the project. The site would normally plan to be opened and accessible by the public during most phases of the construction process.

However, there would be times when all or parts of the monument would be closed to public access for reasons such as public safety or the need to utilize places normally accessible for construction purposes. Due to the construction and design features listed in Appendix F, there is not expected to be an impact to public safety during the construction of this project.

Additionally, the Pillar is monitored by a Rock Block Monitoring System (RBMS) which consists of various monitoring devices at key points throughout the Pillar which will detect and automatically report movement in parts of the structure. There are protocols in place referred to as the Trigger Action Response Plan (TARP) that sets out predetermined courses of action if defined visual observations or monitoring thresholds are exceeded. See Appendix E for a full description of the plan. The Draft TARP and all associated RBMS pieces will remain in place both during and post construction. Once construction is complete a finalized TARP will be implemented taking into account the changes made to the Pillar. For these reasons, this issue is not carried forward for detailed analysis.

1.7.2 Will the surface disturbing activities associated with the implementation of the project cause soil erosion?

The project area is comprised of Haverson loam and Rock land soil units. These soils are loams, silt loams, very fine sandy loams, or sandy clay loams more than 20 inches deep. The secondary staging areas are mapped within the Rock land unit. The main construction staging area and staging area for crane to turtle rock are mapped within the Haverson loam unit. The main construction staging area and staging area for crane to turtle rock may be mowed prior to use.

Secondary staging areas will not have vegetation removed prior to the area will be used in its current state. All staging areas, except the main construction and crane staging area, are for daily use for equipment and material. The contractors shall removal all equipment and materials at the end of each day. The contractors will protect existing ground surface in all staging areas.

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All potential surface disturbing activities will be required to implement the Billings Field Office Approved Resource Management Plan (ARMP), Soil Best Management Practices (BMPs) (Appendix H). With the implementation of the BiFO ARMP Soil BMP’s, design features of the alternatives, and reclamation plan (Appendix H) soil erosion is not anticipated to occur.

Therefore, this issue was considered but eliminated from further analyses.

1.7.3 Would construction activities on and around the Pillar affect nesting raptors?

Two species of raptors are known to nest at PPNM. An active Bald Eagle nest lies >0.6 mi to the east of the Pillar. A pair of Great Horned Owls nests on the west side of the Pillar, moving nest sites year to year but typically nesting within 0.25 mi of the Pillar. The pair may in some years nest on the west face of the Pillar itself. Both species initiate courtship and nesting in the winter, some years as early as January. Typically, nest initiation takes place in February-March with fledging typically occurring by June for Great Horned Owls and July for Bald Eagles. Harsh winter conditions can delay nest initiation by several months.

The Bald Eagle nest is screened from view of the Pillar by trees. It is unlikely that construction activities at the Pillar would affect courtship, breeding, and nesting behaviors of Bald Eagles.

Most of the proposed construction activities are planned for the eastern face of the Pillar on the opposite side from the Great Horned Owl nest sites. Activities here would likely be suitably screened by the Pillar and would have little to no effect on nesting Great Horned Owls. However, work on Turtle Rock may affect nesting owls due to its location on the north face and near the west end of the Pillar. Effects to nesting owls would be mitigated by avoiding construction activities on Turtle Rock and the west/northwest side of the Pillar from February 1 through June 30.

Considering locations of raptor nest sites relative to proposed construction activities and timing limitations to mitigate effects of proposed activities, nesting raptors have not been carried forward for further analysis

1.7.4 Would construction activities on and around the Pillar affect nesting habitats for migratory birds?

The Pillar as a landform provides diverse nesting habitats for migratory bird species. Southerly rock faces show evidence of use by swallow species as nest sites. Silver buffaloberry, chokecherry, and other shrubs may support nesting birds where they grow on the Pillar. No construction activities are planned for rock faces containing past-years’ swallow nest sites.

Potential nest sites for species such as Rock Wren which prefer to nest in rock crevices and cavities may be covered by stabilizing materials on a portion of the southeastern side of the Pillar under all action alternatives. Most migratory birds do not return to the same nest site annually, and rock faces at the Pillar are not unique along the Yellowstone River. Avoidance of construction activities from April 15 through July 15 would mitigate most effects to current year breeding and nesting migratory birds. Mowing of staging areas prior to and frequently throughout the breeding and nesting season would reduce suitable nesting habitat and reduce the likelihood of birds attempting to nest at these high use sites. Some potential nest sites in vegetation and on rock faces would be permanently removed or altered. Relative to the amount of nesting habitat available to birds along the Yellowstone River bottom and sandstone bluffs, loss of habitat at the Pillar is expected to have negligible effects to breeding and nesting

P a g e | 5 migratory birds. Nesting habitats for migratory birds are therefore not carried forward for further analysis.

1.7.5 Will attempts to stabilize the Pillar inadvertently alter the characteristics for which the Pillar is listed as a National Historic Landmark (NHL)

The NHL status of Pompeys Pillar was granted in 1965 because of William Clark's 1806 signature on his return trip after reaching the Pacific Ocean with the Corps of Discovery. The presence of Clark’s signature at this location is well documented, so will remain special and significant regardless of the proposed stabilization work.

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2. Alternatives Alternatives for the Pompeys Pillar Stabilization Project were selected from a range of remedial measures developed by the engineering firm Itasca. Aside from the No Action Alternative, most remediation measures are carried forward throughout Alternatives A and B. However, some remediation measures utilize different approaches in achieving, relatively, the same outcome and constitute the differences between all of the action alternatives. A description of all remediation measures can be found in Appendix F. Alternatives were developed both in order to examine the impact of differing measures as well as provide alternatives for completing the project in the even on the ground issues arose during construction.

For the alternatives that were considered in detail, below is a table which illustrates which remedial measures were considered in each alternative.

Table 1: Comparison of Alternatives

Remedial Measure No Action

Alternative Alternative A Alternative B Scaling Excluded Analyzed Analyzed

Foliage Removal Excluded Analyzed Analyzed Top of Sandstone Drainage Control Excluded Analyzed Analyzed

Shale and Siltstone Stabilization Excluded Analyzed Excluded Shale and Siltstone Environmental Protection Excluded Excluded Analyzed

Buttressing at Signature Block Excluded Analyzed Excluded Rock Bolting at Signature Blocks 2a, 2b, and 2c Excluded Excluded Analyzed

Rock Bolting at Signature Block 1a Excluded Analyzed Analyzed Underpinning at Turtle Rock Excluded Analyzed Analyzed Rock Bolting at Turtle Rock Excluded Analyzed Analyzed

2.1 No Action Alternative

Under the No Action Alternative, the BLM would take no action in stabilizing Pompeys Pillar National Monument. The natural degradation would be allowed to continue to occur. Monitoring of the site utilizing previously installed instrumentation would continue. If such monitoring indicates that an issue may arise, the appropriate steps to protect public safety would be implemented in accordance with the TARP. Selection of the No Action Alternative would not preclude future implementation of these, or other stabilization measures accompanied by the appropriate level of NEPA analysis. See Table 1: Comparison of Alternatives below for a breakdown of which remedial measures are included in each alternative.

2.2 Alternative A

Alternative A utilizes the following remedial measures to achieve protection of the Pillar:

Scaling Foliage Removal Top of Sandstone Drainage Control

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Shale and Siltstone Stabilization Buttressing at Signature Block Rock Bolting at Signature Block 1a Underpinning at Turtle Rock Rock Bolting at Turtle Rock

Alternative A reflects the recommended remedial actions from Itasca Consulting that would enact the soundest stabilization and protection measures. After careful study, these measures are expected to be able to be applied to the Pillar notwithstanding its distinct geologic makeup. All remedial measures are described in detail in Appendix F.

2.3 Alternative B

Alternative B utilizes the following remedial measures to achieve protection of the Pillar:

Scaling Foliage Removal Top of Sandstone Drainage Control Shale and Siltstone Environmental Protection Rock Bolting at Signature Blocks 2a, 2b, and 2c Rock Bolting at Signature Block 1a Underpinning at Turtle Rock Rock Bolting at Turtle Rock

Alternative B may be enacted if there are issues with the applicability of Alternative A. This measure differs from Alternative A in two ways. First, it analyzes the Shale and Siltstone Environmental Protection as opposed to Shale and Siltstone Stabilization. This is being examined in the event that during construction it is found that places of the shale and siltstone are not conducive to receive stabilization treatment, in which case environmental protection would be utilized. Next, in the event that underpinning is not feasible at the Signature Blocks 2a, 2b, and 2c, applying rock bolts in a limited capacity are a reasonable option to address some of the same concerns. All remedial measures are described in detail in Appendix F.

2.4 Alternatives Considered but not Analyzed in Detail

The design of the project was provided by Itasca, a private consulting firm specializing in geotechnical project. The alternatives being considered are based upon expert opinion of what are the best methods for achieving the project’s purpose and need. Alternatives that were considered were based upon differences in achieving the purpose and need in the faces of differing resource concerns and on-site factors which may necessitate altering courses of action.

So, while there were no specific alternatives that were not considered for analysis, there were various remediation measures first considered by Itasca but eventually dismissed due to feasibility concerns. These are all outlined in Appendix I.

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3. Affected Environment and Environmental Consequences

3.1 General Setting

Pompeys Pillar National Monument lies 30 miles east of Billings, MT and less than one-mile north of I-94 and is adjacent to the Yellowstone River. The area is surrounded by agricultural development with associated housing and infrastructure including a United Grain silo facility which lies between the monument and the highway. While the setting is generally rural, its proximity to the highway and railroad further south, as well as the silo facility, take away from any true sense of solitude.

The site itself has been developed to accommodate the large number of visitors and provide them with a safe and rewarding experience. To host the large crowds that tour the area during peak season, there is a paved parking lot, interpretive center, and amphitheater. Most importantly, there is a large boardwalk wrapping around the Pillar that allows visitors to view such sites to include Clark’s signature, Turtle Rock, and the surrounding landscape from the top of the Pillar.

Additionally, the site contains various safety and monitoring devices to ensure the well-being of visitors and the Landmark itself.

3.2 How will the remediation measures affect the historic inscriptions of the Pillar, including those on the Turtle Rock area?

3.1.1 Affected Environment

After Clark left his name on the rock, various other travelers from fur trappers to homesteaders to soldiers and travelers on the Steamship Josephine, one of the last such boats to travers as far west as the Pillar, left their own inscriptions on the sandstone. Due to the nature of the sandstone, most, if not all, of the petroglyphs and pictographs postdate the 1700s, and even more visible elements postdate 1900. Inscriptions from solders and travelers on Josephine are primarily found on Turtle Rock.

Before Europeans reached Pompeys Pillar, generations of Native Americans made use of the rock and surrounding landscape, to leave pictographs on the rock face, only traces of which are still visible. These are found primarily on the same rock face bearing Clark’s signature.

The Billings Field Office archaeologist documented PPNM extensively at the time the BLM took over management of the Monument, designated as such in 2001. John Taylor’s 1990 site form created the basis for the alphanumeric numbering system used to note where rock art panels are located on the Pillar. In 2001, the Billings Field Office contracted representatives of the Art Department at Minot State University in North Dakota to provide baseline documentation of the signatures and rock art at the Monument. The project was led by Linda Olson, who expanded on Taylor’s earlier numbering system to document rock art in detail. The project recorded over 2,000 separate names, dates and initials on 147 separate panels from the 11 sections of the butte, as well as a sampling of Native American petroglyphs and pictographs. Rock art and historic graffiti of varying age were documented all over the Pillar, on every accessible rock surface, although not all inscriptions contribute to the significance of the site.

3.1.2 Environmental Effects —No Action Alternative

The No Action alternative would result in continual, natural erosion at the site. No inscriptions

P a g e | 9 would be at risk by application of remediation measures. The inscriptions at the Pillar would continue their natural degradation.

3.1.3 Environmental Effects—Alternative A

The shale and siltstone stabilization component of Alternative A could result in over spraying of shotcrete/concrete onto historic inscriptions located on the sandstone above the area to be treated.

A Design Feature in Appendix F specifies that measures shall be taken to prevent over spraying of these materials

The underpinning at Turtle Rock could result in the covering of significant historic inscriptions.

To prevent this, a Design Feature is included in Appendix F specifying no shotcrete, concrete, resin or any other materials will be applied over the inscriptions found to the left and center left of the Turtle Rock neck/chin areas. See Figure 26 in Appendix F.

The proposed bolting of Turtle Rock carries risk that the bolting procedure damages the inscriptions found on the Rock. To mitigate this, drilling shall commence at a speed unlikely to created vibrations that could damage the Rock. A Design Feature specifying this requirement can be found in Appendix F. Potential mitigation measures should historic inscriptions be damaged includes such things as creating replica inscriptions to house in the visitor center and other forms of public education regarding any lost inscriptions.

3.1.4 Environmental Effects—Alternative B

Some of the Environmental Effects of Alternative B are the same as in Alternative A, with the substitution of shale and siltstone environmental protections rather than shale and siltstone stabilization. Both actions include the application of shotcrete, concrete, resin, sodium silicate, and other materials which could over spray onto historic inscriptions without preventative measures. Stabilization measures for Turtle Rock are the same in both alternatives.

Rock bolting of blocks 2a, 2b, and 2c would replace underpinning at the Signature Block, if it is determined to be unfeasible. Potential effects created by rock bolting includes vibration created by drilling and installation of the rock bolts, possibly disturbing historic inscriptions located on the outside of these rocks. Design Features found in Appendix F serve to prevent this kind of damage.

3.3 How will the visual integrity of the site be altered by the remediation measures?

3.3.1 Affected Environment

The Bureau of Land Management (BLM) is entrusted with the care of 264 million acres of public lands containing many outstanding scenic landscapes. By law, BLM is responsible for managing these public lands for multiple uses. But BLM is also responsible for ensuring that the scenic values of these public lands are considered before allowing uses that may have negative visual impacts. BLM accomplishes this through its Visual Resource Management (VRM) system, a system which involves inventorying scenic values and establishing management objectives for those values through the resource management planning process, and then evaluating proposed activities to determine whether they conform to the management objectives. BLM has established VRM coordinators in each state and provides training in VRM so that this system is implemented effectively and consistently throughout the Bureau. The Bureau’s VRM system

P a g e | 10 helps to ensure that the actions taken on the public lands today will benefit the landscape and adjacent communities in the future.

Visual Resources are inventoried using procedures established in the BLM Handbook H-8410-1 and are managed under the guidelines in BLM Handbook H-8431. A class is based on the physical and sociological characteristics of any given homogeneous area and serves as a management objective. Categories assigned to public lands are based on scenic quality, sensitivity level, and distance zones. Each class has an objective that prescribes the amount of change allowed in the characteristic landscape (from H-1601-1, BLM Land Use Planning Handbook). The four classes are described below:

Class I provides for natural ecological changes with very little management activity.

This class includes primitive areas, some natural areas, some wild and scenic rivers, and other similar areas where landscape modification activities should be restricted.

Class II areas are those areas where changes in any of the basic elements (form, line, color, or texture) caused by management activity should not be evident in the characteristic landscape. The goal is to retain the existing landscape character.

Class III includes areas where changes in the basic elements (form, line, color, or texture) caused by a management activity may be evident in the characteristic landscape.

The level of change from an activity should not dominate the landscape but may attract attention of the casual observer. Changes should repeat the basic landscape elements.

Class IV applies to areas where changes may subordinate the original composition and he characteristic landscape, if possible. The level of change to the existing landscape can be high and may dominate the view. This class provides for management activities which require modification to the existing landscape character.

Pompeys Pillar National Monument RMP/EIS established visual management objectives to minimize adverse impacts to the visual resources on the landscape, and maintain the overall integrity of VRM classes, while allowing for modifications to landscapes in those classes, consistent with the established management objectives. The six acres of the National Historic Landmark where the remedial measures are proposed to be performed are Class II in order to protect historic and cultural resources. The remaining acres of the monument come under Class

III.

3.3.2 Environmental Effects—No Action Alternative

Under the No Action Alternative, the BLM would take no action in stabilizing Pompeys Pillar National Monument. The natural degradation would continue to occur. Water and wind would continue to erode away the signature rocks deepening cracks and undermining the stability of the Signature Block area and Turtle Rock.

3.3.3 Environmental Effects—Alternative A

Under Alternative A, actions would be carried out within the six acres of the National Historic Landmark managed as Class II. The actions described would comply with the Best Management Practices outlined in the PPMN RMP stating site design elements shall be integrated with the surrounding landscape. Elements to address include minimizing the profile of any structures and making sure they blend with the surrounding landscape.

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In this case the topsoil drainage system would be designed so as not to draw the eye of the casual observer. Rocks removed by scaling could be used to conceal the drainage system. Shale and Siltstone Stabilization, underpinning at the Signature block and Turtle rock would be done by in the contractor in a manner that maintains the existing landscape character. A metal post would be utilized for underpinning at Turtle Rock. The post would be designed in a manner to match the natural forms surrounding turtle rock. The post would flare at the top and bottom eliminating potential concerns of a straight metal pipe being the solution, the surface shall be textured, and the surface shall be finished to appear like the shale and siltstone. The rock surfaces shall be protected against permanent damage, especially in areas the public would be able to see. The Signature Block rock bolting would be concealed with shotcrete matching the existing surface avoiding the eye of the casual observer. Detailed descriptions for all above actions can be found in Appendix F.

3.3.4 Environmental Effects—Alternative B

Actions under Alternative B would include all actions under Alterative A except Shale and Siltstone Environmental Protection would replace Shale and Siltstone Stabilization, and Rock bolting would replace underpinning at the Signature Block, if each are determined to be unfeasible. Substituting Environmental Protection and rock bolting would look the same to the casual observer upon project completion. Environmental protection would encompass the same area as the stabilization method but would not utilize shotcrete and would instead allow the existing rock to show through a thin layer of hardening material. Rock bolting would also not use shotcrete and would instead utilize hidden bolts with minimal and easily covered access points.

3.4 How will public access and experience be affected by the

remediation process?

3.4.1 Affected Environment

After acquiring Pompeys Pillar National Landmark in 1991, the BLM constructed a wooden boardwalk in 1992 to provide visitors access to the sandstone butte. This walkway provides access via a walkable path from the base of the Pillar to the very top of the Pillar. The walkway also includes a few viewing platforms at Clark’s signature and at the very top west side of the Pillar. The ability for visitors to access the boardwalk and Pillar is a main draw for the site and is very important to the visitors’ experience in seeing the inscriptions on the sandstone and having a 360-degree view of the Yellowstone Valley landscape. Providing a safe experience and safe access to the Pillar is the top priority.

The boardwalk was temporarily closed in March 2020 until May 2021 while a comprehensive assessment was conducted to address safety concerns about the stability of the rock formation.

Following this assessment, the majority of the Pillar was reopened to the public. However, the lower viewing platform at Clark’s signature remains closed at this time due to ongoing safety concerns.

Pompeys Pillar National Monument receives approximately 30,000 visitors annually. A large percentage of these visitors use the boardwalk to experience the Pillar during the months of May through September.

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3.4.2 Environmental Effects—No Action Alternative

Under the No Action Alternative, access to the boardwalk may continue until it is determined that the conditions present are not safe enough to allow for public access. Techniques used to monitor the conditions could be visual inspection, data collected through the rock block monitoring system, and data analysis. The lower platform, currently closed, would remain closed indefinitely.

3.4.3 Environmental Effects—Alternative A

Under Alternative A, access to the boardwalk may continue and access could be temporarily restricted during the construction period which could be during the summer months where visitation is at the highest. The boardwalk is near some of the work areas at the signature block and turtle rock. There may be times where construction activities (scaling, top of sandstone foliage removal, drainage protection, shale and siltstone stabilization, buttressing at Signature block, underpinning at Turtle rock and rock bolting at Turtle rock) could present a safety issue with public access to the boardwalk and the boardwalk would need to be temporarily closed.

Construction activities could produce additional noise from construction equipment and tools.

Construction personnel would use the boardwalk to access work areas. Areas off the boardwalk, not accessible to the public, may be used by construction personnel to access the work areas.

These activities may be a distraction to visitors during their visit.

Prior to construction activities, the BLM will attempt to alert potential visitors about the timeline for the project and temporary closures that are planned so we can lessen any impact to visitors’ enjoyment of the Monument. A combination of press releases, social media posts, website postings, and phone messages as well as on-site information will be available.

In Alternative A, once construction activities are completed, access to the boardwalk would continue and the lower viewing platform would reopen and would ensure that public access continues at the Pillar.

3.4.4 Environmental Effects—Alternative B

Under Alternative B, like under Alternative A, access to the boardwalk may continue and access could be temporarily restricted during the construction period which could be during the summer months where visitation is at the highest. The boardwalk is near some of the work areas at the signature block and turtle rock. There may be times where construction activities (scaling, foliage removal, top of sandstone drainage control, shale and siltstone environmental protection, underpinning at Turtle rock, rock bolting at Signature block and Turtle rock) could present a safety issue with public access to the boardwalk and the boardwalk would need to be temporarily closed. Construction activities could produce additional noise from construction equipment and tools. Construction personnel would use the boardwalk to access work areas. Areas off the boardwalk, not accessible to the public, may be used by construction personnel to access the work areas. These activities may be a distraction to visitors during their visit.

Prior to construction activities, the BLM will attempt to alert potential visitors about the timeline for the project and temporary closures that are planned so we can lessen any impact to visitors’ enjoyment of the Monument. A combination of press releases, social media posts, website postings, and phone messages as well as on-site information will be available.

In Alternative B, once construction activities are completed, access to the boardwalk would

P a g e | 13 continue and the lower viewing platform would reopen and would ensure that public access continues at the Pillar.

3.5 How will the surface disturbing activities associated with the implementation of the project and the design feature of foliage removal affect native vegetation?

3.5.1 Affected Environment

The project area is within the Major Land Resource Area (MLRA) (as defined by the United States Department Agriculture (USDA) Natural Resources Conservation Service (NRCS)) Sedimentary Plains, Central 58 AC. The major Ecological Site Description (ESD) is Silty (Si) RRU 11–14-inch precipitation zone (R058AC040MT) and Rock Outcrop.

The Silty ESD is grassland dominated by cool and warm season grasses, with forbs and shrubs occurring in smaller percentages. Approximately 75-80% of the annual production by weight is from grasses and sedges, 5-15% is from forbs, and 1-5% is from shrubs, half-shrubs, and cacti.

Canopy cover of shrubs is typically 1-5%. Trees are not significant on this site. Dominant species include bluebunch wheatgrass (Pseudoroegneria spicata), green needlegrass (Nassella viridula), western or thickspike wheatgrass (Pascopyrum smithii), needleandthread (Hesperostipa comata ssp. comata), and short grasses such as Sandberg bluegrass (Poa secunda) and prairie junegrass (Koeleria macrantha). There are abundant forbs (purple and/or white prairie clover (Dalea purpurea and Dalea candida), prairie coneflower (Rudbeckia fulgida), dotted gayfeather (Liatris puncatata) which occur in smaller percentages. Shrubs such as Wyoming big sagebrush (Artemisia tridentata ssp. wyomingensis) and winterfat (Krascheninnikovia lanata) are common. There are no reasonably foreseeable future actions within this project area.

3.5.2 Environmental Effects—No Action Alternative

Under the No Action Alternative, the BLM would not authorize any action which would cause surface disturbing activities. Therefore, the native vegetation would remain in its current state and potential effects to vegetation would not occur.

3.5.3 Environmental Effects—Alternative A

Under Alternative A, the BLM would authorize actions that would potentially have a short-term effect on vegetation from the use of the staging areas. The main construction staging area and staging area for crane to turtle rock may be mowed prior to use. The secondary staging areas will not have vegetation removed prior to use the area will be used in its current state. Disturbance may occur to vegetation within the staging areas by trampling of vegetation by workers, equipment and material storage. All staging areas, except the main construction and crane staging area, are for daily use for equipment and material. The contractors shall removal all equipment and materials at the end of each day. The contractors will protect existing ground surface in all staging areas.

The BLM would also authorize an action that would have a long-term effect on approximately 900 square feet of vegetation. The long-term effects would be from the design feature of the permeant removal of foliage within the upper signature construction area (refer to Figure 7 and Figure 8 in Section F.4). Removal would consist of a BLM approved herbicide application

P a g e | 14 and/or physical removal of foliage (refer to Section F.4 for details).

All potential surface disturbing activities would be required to implement the Billings Field Office Approved Resource Management Plan (ARMP), Vegetation, Vegetation Rangeland, and Soils Best Management Practices (BMPs) (Appendix G.). With the implementation of the BiFO ARMP BMP’s, design features of the alternative, and reclamation plan (Appendix H) effects to vegetation within the staging areas would be short-term and minimal. The design feature of foliage removal would be long-term for approximately 900 square feet of vegetation.

3.5.4 Environmental Effects—Alternative B

Under Alternative B, the BLM would authorize actions that would potentially have a short-term effect on vegetation from the use of the staging areas. The main construction staging area and staging area for crane to turtle rock may be mowed prior to use. The secondary staging areas will not have vegetation removed prior to the area will be used in its current state. Disturbance may occur to vegetation within the staging areas by trampling of vegetation by workers, equipment and material storage. All staging areas, except the main construction and crane staging area, are for daily use for equipment and material. The contractors shall removal all equipment and materials at the end of each day. The contractors will protect existing ground surface in all staging areas.

The BLM would also authorize an action that would have a long-term effect on approximately 900 square feet of vegetation. The long-term effects would be from the design feature of the permeant removal of foliage within the upper signature construction area (refer to Figure 7 and Figure 8 in Section F.4). Removal would consist of a BLM approved herbicide application and/or physical removal of foliage (refer to Section F.4 for details).

All potential surface disturbing activities would be required to implement the Billings Field Office Approved Resource Management Plan (ARMP), Vegetation, Vegetation Rangeland, and Soils Best Management Practices (BMPs) (Appendix G). With the implementation of the BiFO ARMP BMP’s, design features of the alternative, and reclamation plan (Appendix H) effects to vegetation within the staging areas would be short-term and minimal. The design feature of foliage removal would be long-term for approximately 900 square feet of vegetation.

3.6 How will the remedial measures affect the geologic integrity of the National Monument?

3.6.1 Affected Environment

The Hell Creek (floodplain/fluvial) and the Lance (fluvial) are laterally equivalent formations.

Depending on the preferences of the geographic state or the author, they are often considered the same formation and the formation names are interchangeable. Montana and North Dakota tend to favor use of the term Hell Creek, and Lance is preferred in Wyoming.

The Hell Creek Formation in the Pompeys Pillar/Billings area is composed of light-colored, fine-grained, cliff-forming massive sandstones separated by beds of darker shale and siltstone, with minor thin beds of coal. The upper and lower sandstone layers forming the Monument are friable (porous and crumbly) and separated by an easily erosible member of shales, siltstones, and thin sandstones (shortened to “siltstone” in this issue section. The basal layer of the monument is similar to the middle siltstone. The siltstone beds were subjected to faster weathering and erosion where Pompeys Pillar Creek enters the floodplain, and the Yellowstone River channel probably

P a g e | 15 avulsed at this point during a flood or ice jam event. This process left behind the erosional remnant and prominent geological feature now known as Pompeys Pillar. Temperature changes, wind, ice, water, salts, acids, biological inputs, gravity, and other factors combine to naturally weather the sandstone and siltstone layers of the pillar. The slope-forming siltstone layers are generally more susceptible to weathering and erosion, destabilizing the massive cliff-forming sandstone beds and causing rock falls and topples.

The Hell Creek Formation is locally abundant, and generally doesn’t possess the mineralization or physical qualities typical of locatable building or decorative stone. It also isn’t suitable for most salable mineral material uses such as road construction or maintenance, being chosen for that use only when there is nothing else available. Due to the physical properties and the National Monument designation, there are no mining claims or rock quarries on or near Pompeys Pillar. The visual, paleontological, and cultural qualities that have made Pompeys Pillar a geological landmark will be addressed in other resource sections, as will most safety questions.

3.6.2 Environmental Effects—No Action Alternative

Weathering and erosion of the siltstones and subsequent fracturing and destabilization of the massive sandstones are natural processes which will continue without the remedial measures.

The Signature Blocks and Turtle Rock appear most susceptible to cracking and rock falls/slides due to the loss of support. It cannot be stated with certainty when the unstable blocks will topple from the pillar if no effort is made to restore support.

3.6.3 Environmental Effects—Alternative A

If successful, the engineered interventions of the Proposed Action may slow down the weathering and erosion of the pillar and strengthen and stabilize vulnerable rock blocks. It cannot be guaranteed that any single remedial measure or combination thereof will completely stabilize the Pillar. If there is a failure during the construction or afterwards, the impacts would be similar to the No Action Alternative, just hastened.

Scaling – potentially unstable, small boulders will be manually removed from the sandstone above and adjacent to the viewing platforms. These small boulders on or near the tops of the massive sandstone tend to bounce further away, and more randomly, than the larger blocks.

While removing these unstable boulders is mostly intended to improve the safety of people on the viewing platforms, the removal can enhance the stability of the pillar by decreasing the weight load on top of the Signature Blocks. The scaled rocks may be repurposed to conceal other remedial treatments, landscaping, or for other purposes designated by the BLM.

Foliage Control – plants can physically and chemically weather rock, processes collectively termed biological weathering. For example, roots can create fractures, or salts/acids/decay products secreted by plants may dissolve mineral grains or the cement bonding them. Controlling foliage by removal and preventing future growth in joints above the Signature Block is expected to decrease the input of biological factors and to slow the formation of new fractures. Removing a portion of the foliage could allow water/ice to flow faster in the existing fractures – faster flowing water is more erosive. Another remedial measure, installing a top of sandstone drainage control, should divert most of the precipitation before it flows into the cracks.

Top of Sandstone Drainage Control – precipitation drains from the top of the pillar through joints in the upper sandstone and flows out the middle siltstone layers. The siltstone layers differentially weather and erode faster than the upper sandstone, creating voids and piping

P a g e | 16 beneath the Signature Block. If the water in the joints freezes, frost wedging may also increase joint dimensions. Controlling drainage on the top sandstone by diverting water away from the joints is expected to decrease the volume of water flowing into the joints and then out the middle siltstone. Sedimentary rock is naturally porous and permeable, so water diversion will not stop all water input to the existing joints. However, most of the water that does flow through the upper sandstone should be slower and therefore less abrasive to the siltstone below.

Shale & Siltstone Stabilization – the siltstone layers are deteriorated and weathered, threatening the stability of the Signature Blocks on top of them. Rock bolts are a common method to increase the strength of rock – when properly installed, there is a resistance to movement along the length of the bolt shaft. The proposed drainage channels and reinforced shotcrete will limit future weathering and erosion by shielding the remaining siltstone from wind, water, and temperature differentials. The drainage channels built into the shotcrete would also allow the release of water that naturally flows through permeable sedimentary rock. Strengthened siltstones, subject to much slower weathering and erosion, are expected to provide a more stable support for the Signature Blocks.

Buttressing at Signature Block – in the Signature Blocks area the middle siltstone is significantly eroded, leaving large overhangs of the massive sandstone. These sandstone blocks are unsupported and have prominent cracks along bedding planes. Under the proposed action, the overhanging blocks would have reinforced shotcrete forms constructed beneath them, in direct contact with a constructed base and the bottom of the overhanging blocks. The structure would be similar to the siltstone stabilization, but thicker. If successful, the buttressing will provide support to the currently unstable massive sandstone blocks and decrease the chances of a rockfall/slide.

Signature Block 1a Rock Bolting – rock bolts would be inserted from the top of Signature Block 1a, which is a perpendicular angle to the sandstone bedding planes most susceptible to splitting. The tension provided by the bolt shaft is intended to increase the resistance of the sandstone to further horizontal cracking. This action is required for worker safety prior to building the shale and siltstone stabilization feature and is not a stand-alone action.

Underpinning at Turtle Rock – a post would be installed, anchored to the bottom of the Turtle Head and the surface of the sandstone below. The sandstone block supporting the Turtle Head is cracked and eroding, and the Turtle Head will tumble from the Pillar if the supporting block becomes too weak. The post should provide support to the Turtle Head, which seems to be moving along joints and fractures. It may ease some of the pressure on the supporting sandstone block underneath. The Turtle Head feature is probably less suited to buttressing due to its relatively small size, and inscriptions present on the bottom.

Turtle Head Rock Bolting – rock bolts would be inserted from the top back area of the Turtle Head, which is a perpendicular angle to the sandstone bedding planes most susceptible to splitting. The tension provided by the bolt shaft is intended to increase the resistance of the sandstone to further horizontal cracking. This remedial action should arrest movement of the Turtle Head occurring at joints and fractures.

3.6.4 Environmental Effects—Alternative B

All effects will be the same as those discussed in Alternative A other than the replacement of Shale and Siltstone Stabilization with Shale and Siltstone Environmental Protection and

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Buttressing at Signature Block with Signature Block 2a, 2b, and 2c Rock Bolting. The impacts of the two replacement measures are discussed below.

Shale & Siltstone Environmental Protection – sodium silicate or other treatment sprays would be applied to the surface of the siltstone layers and/or at the edges of the siltstone stabilization structure. The treatment spray fills in voids and pores, cements grains together, and acts as an impermeable barrier. This increases the hardness of the rock to which it applied, increasing its resistance to weathering or preparing a rock surface for other repairs. Treatment spray would have to be reapplied as needed, including constructing a work area for each reapplication procedure.