Amendment_0008_Attachment_-_best_practices.pdf

United States Office of OLEM 9200.3-118 Environmental Protection Land and July 2017 Agency Emergency Management

Superfund

Planning for Response Actions at Abandoned Mines with Underground Workings:

Best Practices for Preventing Sudden, Uncontrolled Fluid Mining Waste Releases www.epa.gov/aboutepa/about-office-land-and-emergency-management www.epa.gov/superfund/abandoned-mine-lands http://www.epa.gov/aboutepa/about-office-land-and-emergency-management http://www.epa.gov/superfund/abandoned-mine-lands

Best Practices for Preventing Sudden, Uncontrolled Fluid Mining Waste Releases i

NOTICE AND DISCLAIMER

This report provides topical information rather than guidance and does not impose legally binding requirements, nor does it confer legal rights, impose legal obligations, implement any statutory or regulatory provisions, or change or substitute for any statutory or regulatory provisions. Users are referred to applicable regulations, policies, and guidance documents. Selected references and additional resources are provided herein.

This report compiles and presents best practices and approaches for reducing the risk of sudden, uncontrolled releases of fluid mine waste prior to conducting response actions at abandoned mine sites with underground workings under the jurisdiction of the Comprehensive Environmental Response, Compensation, and Liability Act (CERCLA). The best practices presented in this report were selected based on research conducted by, and the practical experience of, Tetra Tech, Inc. and serves as a technical resource to guide response actions at abandoned mine sites with underground workings. Mention of specific products in this report does not constitute promotion of that product.

This best practices report was prepared by Tetra Tech, Inc. for the U.S. Environmental Protection Agency (EPA) under EPA Superfund Technical Assistance and Response Team (START) contract EP-S5-13-01.

ACKNOWLEDGEMENTS

EPA would like to acknowledge and thank the following organizations and individuals who contributed to the development and review of this report:

U.S. Environmental Protection Agency

• Shahid Mahmud, National Mining Team Leader

• Kirby Biggs, Contracting Officer’s Representative, National Optimization Coordinator

• Patrick Kelly, Office of Resource Conservation and Recovery

• Ed Hathaway, Remedial Project Manager, Region 1

• Bonnie Gross, Associate Director, Region 3

• Gary Baumgarten, Remedial Project Manager, Region 6

• Joy Jenkins, Remedial Project Manager, Region 8

• James Hanley, Remedial Project Manager, Region 8

• John Hillenbrand, Regional Mining Coordinator, Region 9

• Dan Shane, On-Scene Coordinator, Region 9

• Ken Marcy, Regional Mining Coordinator, Region 10

• Ed Moreen, Remedial Project Manager, Region 10

• Beth Sheldrake, Remedial Project Manager, Region 10

Tetra Tech, Inc.

• Kenyon A. Larsen, PMP, Project Manager and Lead Author

• Jody Edwards, P.G., Contributing Author and Senior Technical Reviewer

• Stephen Hoffman, Contributing Author and Senior Technical Reviewer

• William Balaz, P.E., P. Eng., Contributing Author and Senior Technical Reviewer

• Tom Gray, P.E., Contributing Author

• Eric Perry, Ph.D., Contributing Author

• Colin McCoy, P.E., Technical Reviewer

• Michelle Nolte, Technical Research and Reviewer Comment Support

• Carla Buriks, Quality Control Reviewer

• Kristen Jenkins, Production Specialist

Best Practices for Preventing Sudden, Uncontrolled Fluid Mining Waste Releases ii

Technical Reviewers

• Jay Hawkins, Office of Surface Mining Reclamation and Enforcement

• John Craynon, National Academy of Sciences, Virginia Tech

• Anne Marie Palmieri, Alaska Department of Environmental Conservation

• Paul Krabacher, U.S. Department of the Interior, Bureau of Land Management

• Scott Ludwig, U.S. Department of Agriculture, U.S. Forest Service

• John Stanton, Retired, U.S. Army Corps of Engineers, Nashville District

• John Hartley, U.S. Army Corps of Engineers, Omaha District

• Cory Kroger, U.S. Army Corps of Engineers, Sacramento District

Independent Peer Reviewers

• Richard Beam, P.G., Pennsylvania Department of Environmental Protection (Reviewed as an independent consultant)

• Jim Kuipers, P.E., Mining Engineer, Kuipers & Associates, LLC

• Dr. Glenn C. Miller, Ph.D., Professor, University of Nevada Reno (Reviewed on behalf of Earthworks)

• Dr. Michael A. Mooney, Ph.D., Director of the Center for Underground Construction and Tunneling and

Professor, Colorado School of Mines

• Ronald C. Rimelman, Vice President, NOVAGOLD Resources, Inc. and Board of American Exploration &

Mining Association (AEMA) (reviewed on behalf of AEMA)

• Andrew Nicholas Schaer, Lead Geologist, West Virginia Department of Environmental Protection

• Dr. Robert R. Seal II, Geologist, U.S. Geological Survey

Environmental Management Support, Inc.

Independent Peer Review Coordination Contractor

• Jen Rando, Peer Review Coordinator

• Diane Dopkin, Project Manager

Best Practices for Preventing Sudden, Uncontrolled Fluid Mining Waste Releases iii

TABLE OF CONTENTS

ACRONYMS AND ABBREVIATIONS .......................................................................................................................................... iiv

1.0 INTRODUCTION

1.1 Report Purpose

1.2 Background

1.3 Primary Resources

1.4 Report Organization

2.0 BEST PRACTICES AND APPROACHES OVERVIEW

3.0 CONDUCT INITIAL SCREENING

3.1 Review Available Documents and Data

3.2 Conduct a Site Visit

3.3 Potential Outcomes

4.0 DEVELOP MIW CONCEPTUAL SITE MODEL

4.1 Visualize and Assess Mine Workings

4.2 Evaluate Geotechnical, Hydrogeologic, Hydrologic and Hydraulic, and Geochemical Attributes of the MIW Pooling

4.2.1 Develop an Initial Water Balance

4.2.2 Conduct Additional Site Visits

4.2.3 Conduct Minimally Invasive Measurements

4.2.4 Conduct Invasive Measurement Activities: Drilling

4.2.5 Conduct Failure Modes and Effects Analysis

4.2.6 Plan for Invasive Measurement Activities: Contingency, Notification, and Emergency Action Planning

4.2.7 Use Monitoring Well Data to Determine Mine Pool Elevation

4.2.8 Hydraulic Head Prediction Modeling

4.2.9 Detailed Water Balance

4.3 Evaluate Data, Report Findings, and Determine Next Steps

5.0 MITIGATE POOLED MIW UNDER PRESSURE

5.1 Evaluate, Select and Implement Mitigation Options for Pressurized MIW Pools

6.0 QUALIFICATIONS OF THE TECHNICAL TEAM

7.0 BIBLIOGRAPHY

APPENDIX A. BEST PRACTICES CHECKLIST TOOL .......................................................................................................... A-1

APPENDIX B. GENERAL INFORMATION ON GROUNDWATER MODELS ................................................................ B-1

APPENDIX C. ADDITIONAL SOURCES OF CONCEPTUAL SITE MODEL INFORMATION .................................. C-1

APPENDIX D. REFERENCE MATERIALS MATRIX ............................................................................................................. D-1

Best Practices for Preventing Sudden, Uncontrolled Fluid Mining Waste Releases iv

ACRONYMS AND ABBREVIATIONS

3DVA 3-Dimensional Data Visualization and Analysis

AML Abandoned Mine Lands ASTM American Society for Testing and

Materials BOP Blowout Preventer BOPE Blowout Prevention Equipment BOR Bureau of Reclamation CBI Confidential business information CDMRS Colorado Division of Mining

Reclamation and Safety CERCLA Comprehensive Environmental

Response, Compensation, and Liability Act

CSoM Colorado School of Mines COC Contaminants of Concern CSM Conceptual Site Model DHS Department of Homeland Security DO Dissolved Oxygen DOE U.S. Department of Energy DOI U.S. Department of the Interior DOL U.S. Department of Labor DOT U.S. Department of Transportation DPT Direct Push Technologies EC Engineering Control EM Electromagnetics EPA U.S. Environmental Protection Agency ERI Electrical Resistivity Imaging ETA Event Tree Analysis FEMA Federal Emergency Management

Agency FHWA Federal Highways Administration FMEA Failure Modes and Effects Analysis FSP Field Sampling Plan GKM Gold King Mine GMS Groundwater Modeling System gpd Gallons Per Day GPR Ground Penetrating Radar GPS Global Positioning System HASP Health and Safety Plan HDD Horizontal Directional Drilling

HEM Helicopter Electromagnetic HP Heat Pulse HSA Hollow Stem Auger ICMM International Council on Mining and

Metals IP Induced Polarization LIDAR Light Imaging, Detection and Radar LLD Linear Leak Detection MALM Mise-a-la-Masse MIW Mining Influenced Water MSHA Mine Safety and Health Administration NCP National Oil and Hazardous Substances

Pollution Contingency Plan NMMR National Mine Map Repository ORCR Office of Resource Conservation and

Recovery ORP Oxidation/Reduction Potential OSRTI Office of Superfund Remediation and

Technology Innovation OSMRE Office of Surface Mining Reclamation and Enforcement PE Professional Engineer PG Professional Geologist QAPP Quality Assurance Project Plan RAB Rotary Air Blast RC Reverse Circulation SAP Sampling and Analysis Plan SC Specific Conductance SP Spontaneous Potential TDS Total Dissolved Solids UAV Unmanned Aerial Vehicle UNESCO United Nations Educational, Scientific and Cultural Organization UNEP United Nations Environment Program USACE U.S. Army Corps of Engineers USDA U.S. Department of Agriculture USFS U.S. Forest Service USGS U.S. Geological Survey VLF Very Low Frequency

Best Practices for Preventing Sudden, Uncontrolled Fluid Mining Waste Releases 1

1.0 INTRODUCTION

Under the Comprehensive Environmental Response, Compensation, and Liability Act (CERCLA), the U.S.

Environmental Protection Agency (EPA) may perform remedial and removal (known together as “response”) actions, including removal, pre-remedial and remedial activities at abandoned mine land (AML) sites where the potential exists for sudden, uncontrolled releases (commonly known as “blowouts”) of fluid mine wastes, such as impounded or “pooled” mining-influenced water (MIW) in underground mine workings. This report compiles, analyzes, and summarizes common best practices and approaches used or researched nationally and internationally by federal and state agencies, industry, and academic institutions to assess, reduce the risk of, or mitigate blowouts at AML sites as a result of response actions at mining sites with underground mine workings.

The critical activities for assessing, reducing the risk of, and mitigating such releases include:

• Conducting an initial site screening;

• Developing a conceptual site model (CSM) of mine workings and pooled MIW risks;

• Collecting data by non-invasive, minimally invasive, and invasive1 (drilling) methods;

• Performing a Failure Modes and Effects Analysis (FMEA) of proposed work activities;

• Developing or revising plans for contingency, notifications, and emergency action; and

• Mitigating identified pooled MIW risks.

The best practices laid out in this report do not constitute guidance, rather they are best professional judgment on a range of approaches that can be applied on a site-specific basis to reduce the risks and uncertainty of sudden, uncontrolled releases of MIW. However, risk and uncertainty of MIW releases cannot be completely eliminated from many mine sites, particularly for those sites that have not been maintained or inspected for decades or longer, and given the often complex conditions that exist in underground mine workings with MIW pooling. Furthermore, the report does not provide best practices for conducting MIW remediation activities. Such actions are highly diverse and site-specific, and they are addressed in later project phases through existing EPA, state, and other agency guidance. Remediation activities require detailed planning and execution, the best practices for which are beyond the scope and intent of the report.

The term “fluid mine waste” is used in this report to describe one or a combination of MIW, sludge, and other fluidized or liquefiable mine wastes in mine workings that may be suddenly released during MIW pool blowouts.

The CERCLA response process is an established regulatory structure with major steps, and the best practices described in this document can be integrated into them. The best practices for preventing uncontrolled MIW releases can be applied at any phase of the CERCLA response process when planning is necessary to perform activities that may disturb pooled MIW in underground mine workings. Nothing in this report replaces or circumvents the National Oil and Hazardous Substances Pollution Contingency Plan (NCP) or any CERCLA guidance.

1 Non-invasive – work that does not disturb the subsurface, such as site reconnaissance, topographic surveys, and sampling, sonar imaging, and tracer dye testing of directly accessible MIW and surface water bodies.

Minimally invasive – work that minimally disturbs the subsurface, such as measurement or sampling using existing wells, boreholes, or other safely accessible surface openings; water elevation measurement and sampling; downhole assessment and monitoring using technologies such as video, downhole 3-dimensional laser mapping, pressure transducers, flow meters and surface geophysical surveys.

Invasive – work that disturbs the subsurface, such as drilling; probing; excavating; blasting; grading; and dewatering that may be conducted to assess or mitigate MIW pooling and discharge.

Best Practices for Preventing Sudden, Uncontrolled Fluid Mining Waste Releases 2

1.1 Report Purpose

This report provides EPA Regions and others with additional information to support site-specific decisions in addressing underground workings that may have pooled MIW. The goal of this report is to minimize the potential for sudden, uncontrolled releases of fluid mine waste from underground mine workings as a result of an EPA or other state or federal land management agencies’ response action. It is intended to inform practitioners and their managers on best practices to reduce the risk and uncertainty of blowouts of MIW from underground mine workings. It is important to note that application of these best practices depends on site-specific conditions that in limited cases may warrant the application of alternative technologies and approaches to those described in this report.

1.2 Background

On August 5, 2015, removal assessment activities being conducted by EPA triggered a sudden, uncontrolled release of approximately 3 million gallons of MIW from the Gold King Mine (GKM) into tributaries of the Animas River, located upstream of Silverton, Colorado. This incident drew widespread attention to the potential for sudden, uncontrolled releases of fluid mine wastes at other mine sites with underground workings.

EPA and the U.S. Department of the Interior (DOI) Bureau of Reclamation (BOR) both conducted reviews after the GKM incident, and produced the following reports:

1. Summary Report: EPA Internal Review of the August 5, 2015, Gold King Mine Blowout (EPA 2015a);

and

2. Technical Evaluation of the Gold King Mine Incident report (BOR 2015).

Both reports recommended applying best practices to help prevent future releases (EPA 2015a and BOR 2015). This best practices report was developed primarily in response to the following recommendations made in the two reports reviewing the GKM release incident:

The EPA report states:

“EPA should develop guidance to outline the steps that should be undertaken to minimize the risk of an adit blowout associated with investigation or cleanup activities.

“Even though the chance of encountering pressurized mine water was investigated in many ways at the Gold King Mine, the Gold King Mine blowout suggests that EPA should develop a toolbox of additional investigative tools such as remote sensing or drilling into the mine pool from the top or side that should be more seriously considered at similar sites. It’s important to recognize that underground mines may be extremely complex, making characterization of the internal hydraulic conditions and flow paths challenging. Adding to this complexity is that older mine workings are often not well mapped and that some underground mines may also be structurally unstable and prone to cave-ins and internal plugging making them very difficult to assess. The toolbox should identify techniques which could be used to minimize uncertainties associated with these types of mines. Site specific conditions may make certain investigative tools prohibitive or extremely challenging and costly. In the end, while additional information gathering may reduce the uncertainty, a complete understanding of the underground conditions may not be attainable.” (EPA 2015a)

The BOR report states:

“The standards of practice for reopening and remediating flooded inactive and abandoned mines are inconsistent from one agency to another. Various guidelines exist for this type of work, but there is little in actual written requirements that government agencies are required to follow when reopening an abandoned mine.” (BOR 2015)

Best Practices for Preventing Sudden, Uncontrolled Fluid Mining Waste Releases 3

This report incorporates many of the standards of practice referenced in the EPA and BOR reports. As noted previously, this report is not intended to be a guidance document but rather a toolbox which lays out techniques and approaches which can minimize MIW-related uncertainties associated with these types of mines. Exhibits 1 and 2 provide the complete recommendations from the EPA and BOR GKM review reports.

1.3 Primary Resources

The best practices and approaches presented in this report were developed from a variety of resources, including (1) review of existing technical resources and publications, (2) compilation of lessons learned from similar incidents, and (3) technical contributions from expert professionals with relevant experience in mine waste characterization and mitigation. In developing this report, EPA’s contractor conducted interviews with, or received material contributions from, federal and state government agencies, international organizations, and academic experts in MIW pool blowout assessment and prevention.

The following federal agencies were consulted or contributed materials to the development of this report:

• Department of the Interior:

o Office of Surface Mining Reclamation and Enforcement (OSMRE);

o U.S. Geological Survey (USGS); and o Bureau of Reclamation.

• U.S. Environmental Protection Agency.

• Department of Labor, Mine Safety and Health Administration (MSHA).

• Federal Highways Administration, Interstate (FHWA) Technical Group on Abandoned

Underground Mines.

• U.S. Army Corps of Engineers.

• Department of Homeland Security, Federal Emergency Management Agency (FEMA).

• U.S. Department of Agriculture (USDA), U.S. Forest Service (USFS).

The Agency’s contractor also consulted with the International Council on Mining and Metals (ICMM), the National Academy of Sciences Committee on Subsurface Characterization, the University of Nevada Reno, the West Virginia University and Virginia Tech, and the Colorado Division of Mining Reclamation and Safety (CDMRS).

1.4 Report Organization

This report is organized into six sections, a bibliography and four appendices, as follows:

Section 1: introduces this report.

Section 2: provides an overview of the best practices and approaches presented in this report.

Section 3: describes the initial site screening.

Section 4: describes the CSM of mine workings and pooled MIW risks, including planning and execution of data collection to develop a more comprehensive CSM.

Section 5: describes mitigation measures for pooled MIW.

Section 6: describes the qualifications of individuals on the technical team.

Bibliography: provides references for material used in the development of this report as well as additional resources available for referral; where applicable, web site addresses (URLs) are provided for additional resources available on the Internet.

Appendix A: provides a checklist tool for applying the best practices described in this report.

Appendix B: presents general resources and information on groundwater modeling.

Appendix C: presents additional resources for developing an MIW CSM.

Appendix D: is a topical matrix associating bibliographic sources with report topics.

Best Practices for Preventing Sudden, Uncontrolled Fluid Mining Waste Releases 4

Exhibit 1 Recommendations Summarized from EPA’s Internal Review of GKM Incident (EPA 2015a)

1. EPA should develop guidance to outline the steps that should be undertaken to minimize the risk of an adit blowout associated with investigation or cleanup activities. The guidance, at a minimum, should:

a Identify a tiered approach that requires increased detail regarding the proposed action based on the complexity of the site conditions or the potential nature of any release.

b Provide criteria to identify whether a proposed investigation or cleanup action presents a low, moderate, or high risk with respect to the potential for an adit blowout and significant release of acid mine drainage or mine waste.

c Require that a management review meeting(s), including the key state (and other federal agencies when appropriate) be held to determine whether sufficient information exists to meet the criteria established in the guidance or whether additional information is necessary before undertaking the investigation or cleanup activity.

d Outline the outreach activities to inform the local community and stakeholders.

e Identify the contingency planning that may be appropriate based upon the risk of blowout and the nature of the potential release.

2. Even though the chance of encountering pressurized mine water was investigated in many ways at the

Gold King Mine, the Gold King Mine blowout suggests that EPA should develop a toolbox of additional investigative tools such as remote sensing or drilling into the mine pool from the top or side that should be more seriously considered at similar sites. It’s important to recognize that underground mines may be extremely complex, making characterization of the internal hydraulic conditions and flow paths challenging. Adding to this complexity is that older mine workings are often not well mapped and that some underground mines may also be structurally unstable and prone to cave-ins and internal plugging making them very difficult to assess. The toolbox should identify techniques which could be used to minimize uncertainties associated with these types of mines. Site specific conditions may make certain investigative tools prohibitive or extremely challenging and costly. In the end, while additional information gathering may reduce the uncertainty, a complete understanding of the underground conditions may not be attainable.

3. Emergency Action Plans should include protocols should a blowout occur at those mine sites where there is a potential for such an event to occur.

4. Information and rationale developed by a site team in anticipation of an investigation or cleanup action for sites where an adit blowout could be a concern (e.g., available pressure information, a reasonable estimate of the volume of water within the mine workings, or adit drainage flow rate data) should be critically reviewed by a qualified and experienced Regional Mining engineer and or Mining Hydrologist/Geologist. The Region may want to consider getting assistance from qualified outside parties such as other federal agencies, state agencies, or outside consultants in conducting this critical review.

5. The Team also recommends that subsequent reviews of the Gold King Mine Adit Blowout by an Independent External Review Group or the Office of Inspector General consider the possibility of assembling a panel of experts consisting of mining industry experts, other federal and state mining experts, academia, consultants, non-governmental organizations and tribal governments to further analyze the situation encountered at this site and come up with recommendations on additional safeguard measures to reduce the risk and minimize the consequences of such incidents in the future.

Exhibit 2 Recommendations from the BOR Technical Evaluation of the GKM Incident (BOR 2015)

1. “Because of the complexity of reopening a flooded abandoned mine, a potential failure modes analysis should be incorporated into project planning.

2. Before opening an abandoned mine adit, review mine maps, production records, dump size, and local history about the mine to evaluate the potential volume of mine workings. If the volume is large, consider what would happen if there were an accidental release and what could be done to protect against it. A downstream-consequences analysis should be a part of every complex mine remediation.

3. Water conditions within the mine should be directly measured prior to opening a blocked mine. Indirect evidence is insufficient if the potential for a blowout exists.

4. Where significant consequences of failure are possible, independent expertise should be obtained to review project plans and designs prior to implementation.”

Best Practices for Preventing Sudden, Uncontrolled Fluid Mining Waste Releases 5

2.0 BEST PRACTICES AND APPROACHES OVERVIEW

Underground workings of abandoned mines experience infilling by groundwater, surface water, and by communication with interconnected underground mine workings, including continuous “mine pools.”

MIW can subsequently discharge from the mine workings via openings to the ground surface, including but not limited to, adit and tunnel portals, open shafts, air vents, bedrock fractures, bore holes, and springs or seeps. When mine workings are blocked or drainage is impeded, mine pools can form and undergo increasing pressurization as water levels increase. MIW pooling can form as a result of natural and anthropogenic conditions. Example causes of mine pooling include:

• Structural geologic conditions dictating mine void shape (for example, doubly plunging synclinal basins);

• Natural blockages or man-made seals (for example, seismic events, collapses, subsidence events, clogged pipes, bulkheads, and coffer dams);

• Down dip direction horizontal openings;

• Opening locations below the water table or surface drainage; and

• Changes in subsurface hydraulic conductivity.

The presence and extent of mine pools can be difficult to identify and evaluate because of limited physical and visual access. Seasonal variations in precipitation, runoff, and snow melt, as well as remote locations, limit worker and equipment access for field investigations. Sudden, uncontrolled releases of MIW pools can occur as a result of changing conditions in the mine caused by natural or anthropogenic mechanisms.

A range of investigation and remediation activities undertaken during CERCLA response actions at mine sites could impair the stability of MIW pooling. Example activities include, but are not limited to, drilling, earth work, mine workings stabilization, debris removal, backfilling, flow-through bulkhead installation, plugging, and road construction/maintenance.

An overarching best practice is not to initiate such “invasive” activities at underground mine sites unless sufficient information is available or collected to determine whether MIW pooling exists, is likely to exist, or may be caused by activities. If MIW pooling is confirmed or suspected, a better understanding of the cause and extent of MIW pooling should be developed before undertaking such site activities. See Exhibit 3 for a site-specific best practice example.

This report presents best practices and approaches compiled from, (1) lessons learned from past MIW pool releases, and (2) best practices used in similar industries (for example, coal mining), where MIW in underground workings is present under atmospheric or confined pressure (and may discharge as a result of sudden, uncontrolled releases). While this report uses the terms “MIW pool” and “MIW pooling” generally to describe water or fluids accumulating within mine workings, conditions in underground

Exhibit 3 Best Practice Example:

Leadville Mine Drainage Tunnel Risk Assessment The DOI BOR performed a risk assessment for the Leadville Mine Drainage Tunnel in Colorado at EPA’s request. The Leadville risk assessment evaluated the likelihood of mine tunnel failures and potential water buildup. A key feature at the Leadville site is that the workings had a higher degree of physical access than typically exists at many abandoned mine sites. For less accessible workings, risk assessment must rely more on data derived from invasive investigations and best professional judgement. While the Leadville risk assessment provides a number of best practices that apply to AML sites, this best practices report also includes considerations to address MIW pooling in sites with limited physical access.

Source: BOR 2008. The full Leadville Mine Drainage Tunnel Risk Assessment can be found at:

https://www.usbr.gov/gp/ecao/leadville/combined_risk_assessment.pdf

Best Practices for Preventing Sudden, Uncontrolled Fluid Mining Waste Releases 6 workings can result in multiple MIW pools within the same workings. Separate pools are commonly hydraulically connected and thus behave as a unified pool similar to groundwater aquifers; however, hydraulically separate MIW pool conditions can also occur. The overall objective of this document is to provide site teams with a broad range of information and techniques to support site specific planning to prevent the sudden, uncontrolled releases of fluids from MIW pools as a result of site activities.

3.0 CONDUCT INITIAL SCREENING

Before any invasive activities associated with the underground workings of an AML site are undertaken, an initial screening should generally be performed to document whether potential exists for MIW pooling and how the MIW pooling relates to planned activities. The initial screening typically involves collection and review of existing site information, a site visit or visits, interviewing individuals familiar with the site, and an initial determination of the potential for MIW pooling.

The initial screening includes a review of available site information and a site visit by a qualified technical team to assess whether or not MIW pooling exists. If pooling is known or suspected to be present, the initial screening also considers the possibility of conditions that pose risk of a blowout. If MIW pooling is confirmed not to be present within the hydraulically connected area of proposed response activities, there likely will be no potential to cause a blowout. Similarly, if MIW pooling is present but stable, and diligent assessment indicates no activities threaten this stability, then proposed response activities will likely have little potential to cause a blowout.

When the results of an initial screening indicate that there is limited potential for a blowout, an informed decision to proceed with the CERCLA response action can be made. Further evaluations are warranted if any uncertainty regarding the existence of MIW pooling or the potential for a sudden, uncontrolled release is identified. Table 1 shows the focus area and potential outcomes associated with an initial screening.

3.1 Review Available

Documents and Data

The technical team should review pertinent site documentation including, but not limited to, reports on operational history; past investigation and remediation efforts; mine working maps and drawings; and historical MIW discharge information and lists of local mine experts.

It is recommended that former site workers and nearby land owners be interviewed during a site visit. The technical team should also consider consulting with applicable state and federal agencies to

Table 1: Initial Screening Focus Areas and Potential Outcomes

Focus Areas Potential Outcomes

1. Understanding underground and above ground mine workings (including interconnection with other mine workings and hydrogeologic conditions connected with, but potentially distant from the mine)

2. Gathering information on hydrology and hydrogeology (including a geologic and surface hydrology assessments to determine inter-connections between the mine workings, surface water, surface openings and groundwater)

3. Understanding proposed response actions and their potential to impact the subsurface

4. Evaluating downstream surface water bodies and their uses (for example, public water supply), considering loss of human life, infrastructure disruption, environmental and ecological damage, and economic loss

• Finding of Limited Potential for Release (analysis and documentation of the absence of pooled MIW or that MIW pooling is present but stable and that any proposed actions will not adversely affect the mine pooling) OR

• Finding of Uncertainty or Potential for Release (data indicate a potential exists for a mine pool blowout or data gaps that leave uncertainty about the MIW pool and the risk for a blowout). Best practices for further study are warranted.

Best Practices for Preventing Sudden, Uncontrolled Fluid Mining Waste Releases 7 determine if any studies were conducted at the site or for other sites in the area that can provide insight into site conditions related to MIW pooling and discharge.

After reviewing available site-specific information, the technical team should identify data gaps and collect additional information, as needed. Gathering information that is as location-specific as possible will improve the understanding of site MIW pooling. However, regional information can provide important supporting perspectives. For example, it may be useful to review USGS maps of the site with overlays generated using satellite imagery, such as Google Maps. OSMRE also operates the National Mine Map Repository (NMMR), which collects and maintains mine map information and images for the entire country (including data and maps of hardrock mines in the west). Searching the NMMR’s Mine Map Index could identify workings maps for sites. NMMR has more than 180,000 maps of closed or abandoned mines (http://mmr.osmre.gov/MultiPub.aspx). Caution should be used when reviewing historical mine maps, as they may not be accurate, current, or complete; thus, information on mine conditions key to formation of MIW pooling may be absent in site documents or missing from site files.

Historical aerial photography and overlays from on-line databases at the USGS and USDA can provide useful information on mine workings and conditions. Stereo-paired aerial photography dating back to the late 1930s is typically available at 10-year intervals. Often, surface features (such as shafts, drifts, slope entries, waste piles, seeps, and discharges) are visible on these photos that may no longer be recognizable or present at the site.

After collecting and reviewing desktop information, it is recommended that the technical team consult with site experts and others with general site knowledge, including:

• Nearby land owners, local miners, mine operators, experts, and historians;

• Local government personnel;

• Local document repositories (libraries, municipal records departments, non-profit organizations);

• State experts, including geologists, state engineers, mining offices, geological surveys, and AML programs;

• DOI’s BOR, USGS, and BLM State Office experts; and

• Regional USFS experts.

This initial screening step ensures that the available information about an AML site is identified for the assessment of geotechnical, hydrogeologic, hydrologic, hydraulic, and geochemical attributes as early in the review process as possible. This information can be used to focus the site visit on areas of interest such as potential MIW pools or to resolve related data gaps. See Appendix D for examples of additional sources of information.

3.2 Conduct a Site Visit

The purpose of the site visit is to further familiarize the technical team with the mine workings and other important features of the site, to evaluate current conditions, and to resolve data gaps identified during document and data review. The site visit should generally include, but not be limited to:

• Identifying relevant features in the area of interest;

• Documenting all impounded water, both natural and man-made;

• Noting differing conditions from reviewed information, such as collapsed workings, recent vegetation die-off/stress, or changed MIW discharge conditions;

• Measuring MIW discharge rates;

• Collecting non-invasive field measurements (for example, pH, conductivity, dissolved oxygen);

• Photo-documenting key features and conditions;

• Taking global positioning system (GPS) coordinates for all salient features;

• Inspecting easily and safely accessible open portions of mine workings;

http://mmr.osmre.gov/MultiPub.aspx

Best Practices for Preventing Sudden, Uncontrolled Fluid Mining Waste Releases 8

• Identifying any time-sensitive conditions posing potential risk; and

• Identifying conditions that might impede access or future work.

The site visit is conducted to assess site conditions for the locations of the proposed activities relative to mine features, with a focus on identifying and locating features that are commonly associated with blockages and MIW pooling. Observe site conditions, such as seeps or springs with cloudy or low pH water, or discharges from mine openings that may indicate the presence of internal blockages that are not visible during surface inspection. The site visit should include viewing maps of adjacent mine site workings with known or potential interconnections. Consider participation of key federal, local, and state experts and reviews of local file repositories as part of the site visit.

3.3 Potential Outcomes

The technical team evaluates the available documents and data to determine if the proposed activity poses no blowout risk (for example, no MIW pooling, or stable MIW pooling that the response action will not impact). The team also evaluates whether further study is needed to make this determination (for example, unknown potential for MIW pooling; or potential that MIW is not stable; or that response actions can make the MIW pool unstable). The quality of the data is evaluated to assess its usability for making these determinations. If further study is needed, the technical team develops a CSM of the pooled MIW risks (see Section 4.0) and identifies additional data needs.

The certainty of any decision to proceed with a proposed response action must be based on sound scientific data and analysis informed by current conditions, and made by qualified personnel. Therefore, initial screenings are advised to be performed by qualified mining engineers, civil/environmental engineers, geologists, hydrogeologists, and geochemists with experience in assessing and addressing MIW pooling (see Section 6.0).

4.0 DEVELOP MIW CONCEPTUAL SITE MODEL

Updating the existing CSM with data and information specific to the MIW pool, or creating an MIW CSM if a CSM has not been developed, is a best practice for integrating site information and identifying key data gaps. This section presents the common best practices for developing an MIW CSM to identify and assess risks and uncertainty regarding the potential for MIW blowout. It is critical that this CSM focus on the physical structure of mine workings, regional and local structural geology, regional and local meteorology and hydrology, and defining the nature and the extent of MIW pooling, including known and suspected blockages and conditions for future potential workings collapse and blockage. It is recommended that the technical team develop graphical depictions of the CSM (for example, maps of workings, cross-sections and 3-dimensional visualizations) that show the physical structure, areal extent, cross-sectional area, and condition of mine workings and related features. The MIW CSM supplements the environmentally focused site CSM prepared for the site cleanup.

The MIW CSM integrates geotechnical data about the mine workings with hydrogeologic, hydrologic, hydraulic, and geochemical data to assess the risk of a sudden, uncontrolled release in relation to planned response actions. Given the specialized focus of these assessments on MIW pooling, the use of “geotechnical, hydrogeologic, hydrologic, hydraulic and geochemical assessment” in this report is not intended to equate with any traditional site assessment, remedial investigation, or other characterization stage in the CERCLA pipeline.

The stated “problem” for which the MIW CSM is developed is:

What is the nature and extent of MIW pooling and what are the potential failure modes for an MIW blowout?

Best Practices for Preventing Sudden, Uncontrolled Fluid Mining Waste Releases 9

A variety of references support the best practices for performing an FMEA are described in this report.

The BOR’s Risk Assessment of the Leadville Mine Drainage Tunnel (BOR 2008) contains many best practices for conducting geotechnical assessments and FMEA. Appendix A of the EPA and Hardrock Mining: A Source Book for Industry in the Northwest and Alaska (EPA 2003) addresses geologic, hydrogeologic, hydrologic, and geochemical assessment practices, which are necessary to quantify the nature and extent of mine pooling and develop a water balance. The USDA, USFS Investigative Methods for Controlling Groundwater Flow to Underground Mine Workings provides another resource for developing the hydrogeologic elements of the MIW pool CSM (USFS 2006). These and other important references are provided in the bibliography at the end of this report. Appendix D comprises a Reference Materials Matrix that maps specific best practice topics to references listed in the bibliography.

MIW CSM development begins by defining the area of interest and the watershed/aquifer boundary of that area. Boundary conditions may include definitions of flow or hydraulic conditions across the boundary.

The subsequent steps are described in the following subsections. The MIW CSM should generally be updated or developed, as applicable, in conjunction with the performance of a FMEA on proposed or potential actions, to identify potential failure modes that could affect MIW pooling (BOR 2008). The discussion below includes common components of a CSM for MIW pooling.

4.1 Visualize and Assess Mine Workings

A critical element of visualizing and assessing the CSM for MIW pooling is understanding the extent, features, and geospatial orientations of the mine workings. This element should include any mine openings or surface expressions and any known or suspected blockages or collapses. This step is best performed through a comprehensive assessment of available mineral exploration planning and final development maps, geologic maps, cross-sections, reports, models, and other information that illustrate the historical evolution and operation of the mine workings. Similar information should be collected for other mines near the mine site of concern, particularly where there are known or suspected interconnections between mines. Any information or reports on known or suspected locations of blockages, zones of known collapse, or zones of potential instability are also important. The MIW CSM should clearly indicate where information is generated from direct observations, the level of uncertainty, and where assumptions have been made, to clarify for other users the level the information being relied on in assessing the potential for fluid hazards. Attributes of mine workings to consider as a part of developing the CSM of MIW are discussed in Section 4.2. Figure 1 provides an example CSM visualization of mine workings and adit flows, with notes on MIW flow direction and uncertainties.

Active interest in re-starting operations for some mines for additional mineral extraction may have resulted in consolidation of information on past mine workings and collection of additional data. These efforts may provide the best and most current information on mine workings and should generally be identified and reviewed. However, because these data are frequently considered confidential business information (CBI), they may not be readily available. It is recommended that technical teams specifically inquire about such information and recognize that gaining access to this information may require confidentiality or may not be possible.

Mine workings information is best synthesized using current off-the-shelf 3-dimensional data visualization and analysis (3DVA) software, which include those designed for use as active mine planning tools and those adapted to support environmental evaluations. The resulting visualizations can serve as the basis for a project life cycle CSM (EPA 2011), wherein the CSM is updated as new data are generated from overall site assessment, investigation, and response actions.

Best Practices for Preventing Sudden, Uncontrolled Fluid Mining Waste Releases 10

Figure 1. Example CSM visualization: Standard Mine adit levels and underground workings. Note: The angle of view exaggerates the apparent dip of the adits beyond their actual 1 percent grade. (EPA 2015f)

To the maximum extent practicable, representations of the mine workings should be as geospatially accurate in three dimensions as possible. Geo-referencing the underground mine workings to the surface (vertically and horizontally) is essential, as well as ensuring that the volumetric measurements of the workings dimensions are reasonable, given the general uncertainty commonly associated with mine development maps and measurements. Estimates of MIW volume within workings are dependent on the accuracy of these maps and measurements. The vertical dimension is also particularly important because elevation differences are critical to determining hydrostatic connectivity and MIW conditions. Achieving this accuracy may require focused topographic surveys to locate reference points during additional site visits.

4.2 Evaluate Geotechnical, Hydrogeologic, Hydrologic and Hydraulic, and Geochemical Attributes of the MIW Pooling

Understanding MIW pooling requires evaluating the geotechnical, hydrogeologic, hydrologic, hydraulic, and geochemical attributes of the mine, evidence of MIW pooling, and underground workings and adjacent surroundings. Specifically, the team should generally evaluate:

1. The geotechnical conditions of the mine workings, including attributes that influence collapses, blockages, releases, or potential slope instability;

2. The hydrogeologic conditions that create inflow into, and outflow (discharge) from the workings;

3. Hydrologic and hydraulic conditions of the MIW pooling and the surface water features (including water management infrastructures) that receive or influence MIW; and

Best Practices for Preventing Sudden, Uncontrolled Fluid Mining Waste Releases 11

4. The geochemical characteristics of the MIW quality and acid generating/neutralizing characteristics of the ore zones and adjacent rock.

These attributes inform the risk assessment and contingency planning. The information available for each site will vary and the data collection should be related to the proposed specific site activity. Below are some of the mine workings and MIW pooling attributes to consider in assessing MIW pool blowout risks.

Geotechnical Attributes Geotechnical attributes evaluated as a common best practice in assessing MIW pooling risks include, but are not limited to (BOR 2008, EPA 2000, EPA 2003, EPA 2015f, USFS 2006):

• Dimensions and extent of mine workings, including adits, drifts, cross-cuts, haulage routes, shafts, raises, winzes, manways, air vents;

• Types and conditions of support/rehabilitation structures such as timbering, beams, cribbing, square sets, ribs, pillars, crossbars, steel beams, pinning, bolts, concrete;

• Workings storage – volume of mine workings above and below mine potential blockage locations to estimate MIW pooling volume;

• Mine working openings at the surface that serve or could potentially serve as MIW inflow or outflow locations, as well as air inflow locations, key contributors to MIW acidification;

• Portal or other mine opening stability assessment;

• Known or suspected mine workings interconnections between mines;

• Presence of faults, joints, folding or other geologic features that could affect mine stability;

• Thickness and integrity of overburden cover above the mine workings (for example, fracturing is typically more prevalent and fractures have wider aperture at shallower depths);

• Types, strengths, and competency of bedrock and other strata;

• Location, composition, and dimensions of known or suspected flow blockages, and the forces acting on the blockages;

• Surface expressions of underground workings such as structure failure subsidence and slope collapses;

• Potential for liquefaction of soils near mine openings or comprising blockages; and

• Slope stability: physical, mechanical, and seismic properties (for possible naturally occurring slope failure or failure as a result of drilling and/or construction equipment).

Hydrogeologic Attributes Hydrogeologic attributes evaluated as a common best practice in assessing MIW pooling risks include, but are not limited to (BOR 2008, EPA 2000, EPA 2003, EPA 2015f, USFS 2006):

• Types and nature of hydrogeologic units (unconsolidated deposits, bedrock);

• Hydraulic properties of hydrogeologic units (hydraulic conductivity, transmissivity, storability, porosity, dispersity);

• Thickness and areal extent of hydrogeologic units;

• Type of porosity (primary, such as intergranular pore space in unconsolidated deposits or porous bedrock matrices; or secondary, such as bedrock discontinuities, fractures, or solution cavities);

• Groundwater flow through faults, joint fractures, mineral veins;

• Presence or absence of confining or semi-confining lithologic units;

• Depth to water table and seasonal variation, thickness of vadose zone, potentiometric surface, and confined, unconfined, or leaky confined conditions;

• Groundwater flow directions (hydraulic gradients, both horizontal and vertical), volumes (specific discharge), rate (average linear velocity);

• Catchment area and groundwater recharge zones;

Best Practices for Preventing Sudden, Uncontrolled Fluid Mining Waste Releases 12

• Groundwater/surface water interactions, areas of groundwater discharge to surface water (gaining), and surface water recharge of groundwater (losing); and

•…