1167638-R8SDMS

Record of Decision Amendment

Operable Unit 6 - Stray Horse Gulch California Gulch Superfund Site Laiic County, Colorado

September 2010

U. S. Environmental Protection Agency 1595 Wynkoop Street Denver, CO 80202 Amendment to 2003 ROD September 2010 0U6 Stray Horse Gulch, California Gulch Superfund Site

DECLARATION

SITE NAME AND LOCATION

Operable Unit 6 California Gulch Superfund Site Lake County, Colorado CERCLIS #COD980717938

STATEMENT OF BASIS AND PURPOSE

This decision document presents the Selected Remedy Modification for Operable Unit 6 (0U6) of the Califomia Gulch Superfund Site (Site) in Lake County, Colorado. The Environmental Protection Agency selected the remedy modification in accordance with the Comprehensive Environmental Response, Compensation, and Liability Act (CERCLA), as amended by the Superfund Amendments and Reauthorization Act (SARA), and to the extent practicable, the National Contingency Plan (NCP). This decision is based on the Administrative Record for OU6. The State of Colorado (State) concurs with the Selected Remedy.

ASSESSMENT OF THE SITE

The Response Action selected in this Record of Decision (ROD) Amendment is necessary to protect public health or welfare or the environment from actual or threatened releases of hazardous substances and pollutants or contaminants from 0U6 which may present an imminent and substantial endangerment to public health or welfare.

DESCRIPTION OF THE SELECTED REMEDY MODIFICATION

The Califomia Gulch Superfund Site is located in Lake County, Colorado, approximately 100 miles southwest of Denver. About 18 square miles in size, the Site includes the City of Leadville, including Stringtown along with surrounding areas.

Added to the National Priority List (NPL) in 1983, the Site is divided into 12 operable units. 0U6, which is the subject of this ROD Amendment, includes approximately 3.4 square miles in the northeastem portion of the Site and includes the Stray Horse Gulch and Evans Gulch watersheds. This ROD Amendment only concerns the Stray Horse Gulch portion of OU6.

The 0U6 Record of Decision signed in 2003 combined two cleanup strategies to address acid rock drainage (ARD) from sources in Stray Horse Gulch: (1) consolidate and cap four mine waste rock piles and one tailing pile, and (2) manage surface water in Stray Horse Gulch.

The consolidation and capping performed to date effectively reduced or eliminated ARD generation at the mine waste rock piles and tailing pile that were consolidated and capped.

The surface water management strategy involved two components. The first was the construction of clean water diversion ditches uphill of the remaining ARD generating sources. A survey of the previously constructed clean water diversion structures revealed these structures may not capture and divert the maximum possible amount of clean water. Un-captured water may contribute to the generation of ARD. Amendment to 2003 ROD September 2010 OU6 Stray Horse Gulch, Califomia Gulch Superfund Site

The second component of the surface water management strategy involved the construction of diversion ditches and retention ponds to collect ARD generated from the uncapped mine waste rock piles within Stray Horse Gulch. When the ARD generated exceeds the volume of the retention ponds, the excess volume is diverted into the Marion Shaft where some portion (but not all) of the volume is delivered to the Leadville Mine Drainage Tunnel (LMDT). Water in the LMDT is delivered to the U.S. Bureau of Reclamation's (Reclamation) treatment plant where the water is treated and discharged into the Arkansas River. EPA and CDPHE are proposing to modify the surface water management portion of the 2003 remedy and perform additional capping of waste rock piles.

The Selected Remedy modifications include:

improving the clean water diversion components;

capping additional mine waste rock piles to decrease the volume of ARD generated;

enlarging and enhancing the current ARD collection system and retention ponds;

eliminating the use of the LMDT and Reclamation treatment plant from the OU6 remedy except in the case of emergencies;

siting and constructing a Site-wide repository in 0U6; and

implementing institutional controls.

STATUTORY DETERMINATIONS

The Selected Remedy Modification is protective of human health and the environment, complies with federal and state requirements that are applicable or relevant and appropriate to the remedial action, is cost effective, and utilizes permanent solutions and altemative treatment technologies to the maximum extent practicable. This remedy does not satisfy the statutory preference for treatment as a principal element of the remedy. Because this remedy modification will result in hazardous substances, or pollutants or contaminants remaining in 0U6 above levels that allow for unlimited use and unrestricted exposure, a statutory review will be conducted within five years after initiation of remedial action to ensure that the remedy will be protective of human health and the environment. Based on feedback from verbal discussions and written comments received, this remedy is acceptable to both the State of Colorado and the community in Lake County.

DATA CERTIFICATION CHECKLIST

The following information is included in the Decision Summary section of this Record of Decision Amendment. Additional information can be found in the Administrative Record file for this Site.

• Contaminants of concern (COCs) and their respective concentrations;

• Baseline risk represented by the COCs;

• Cleanup levels established for COCs and the basis for these levels; Amendment to 2003 ROD September 2010 OU6 Stray Horse Gulch, Califomia Gulch Superfund Site

• Current and reasonably anticipated future land use assumptions used in the baseline risk assessment and ROD Amendment;

• Potential land use that will be available at OU6 as a result of the Selected Remedy;

• Estimated capital, annual operation and maintenance (O&M), and total present worth costs, discount rate, and the number of years over which the remedy cost estimates are projected; and

• Key factor(s) that led to selecting the remedy.

AUTHORIZING SIGNATURE

Carol L. Campbell Date Assistant Regional Administrator Office of Ecosystems Protection and Remediation U.S. Environmental Protection Agency - Region 8 Amendment to 2003 ROD September 2010 OU6 Stray Horse Gulch, California Gulch Superfund Site

DECISION SUMMARY Amendment to 2003 ROD September 2010 OU6 Stray Horse Gulch, Califomia Gulch Superfiind Site

Table of Contents

Description Page No. 1.0 Introduction 8 1.1 Summary of Basis for ROD Amendment 8 2.0 Site History, Contamination and Selected Remedy 9 2.1 Site Background 9 2.1.1 OU6 - Stray Horse Gulch Background 10 2.2 0U6 Characteristics 10 2.3 Contaminants of Concern 11 2.4 Summary of Risks 11 2.4.1 Human Health Risks 11 2.4.2 Ecological Risks 12 2.4.3 Aquatic Ecological Risk Assessment 12 2.4.4 Terrestrial Ecological Risk Assessment 12 2.5 Scope and Role 12 2.6 Remedial Action Objectives 12 2.7 Prior Response Actions 13 2.8 Summary of Altematives from the 2002 Focused 14 Feasibility Study and 2003 Record of Decision 2.9 Selected Altemative in the 2003 ROD 15 2.10 Aspects ofthe 2003 ROD Not hnplemented 15 3.0 Basis for Document 16 4.0 Descriptionof Proposed Remedy Modification 16 4.1 Altematives Considered in the Proposed Plan 16 4.1.1 No Further Action /Implementation Steps 16 Necessary Alternative 4.1.2 Proposed Altemative 17 5.0 Evaluation of Altematives 18 5.1 Overall Protection to Human Health and 19 the Environment 5.2 Compliance with Applicable or Relevant and 20 Appropriate Requirements (ARARs) 5.3 Long-term Effectiveness and Permanence 21 5.4 Reduction in Toxicity, Mobility or Volume 21 Through Treatment 5.5 Short-term Effectiveness 22 5.6 Implementability 22 5.7 Cost 22 5.8 State Acceptance 22 5.9 Community Acceptance 22 5.10 Principal Threat Wastes 22 6.0 Summary of the Selected Remedy Modification/Alternative 23 7.0 Support Agency Comments 23 8.0 Affirmation of the Statutory Determinations 23 8.1 Protection of Human Health and the Environment 23 8.2 Compliance with Applicable or Relevant and Appropriate 24 Requirements 8.3 Cost-Effectiveness 24 8.4 Utilization of Permanent Solutions and Altemative Treatment 25 (or Resource Recovery) Technologies to the Maximum Extent Amendment to 2003 ROD September 2010 OU6 Stray Horse Gulch, Califomia Gulch Superfund Site

Practicable (MEP) 8.5 Preference for Treatment as a Principal Element 25 8.6 Five-Year Review Requirements 25 9.0 Public Participation and Historic Preservation 25 10.0 References Cited 26 11.0 Responsiveness Summary 27

List of Tables

Table 1 Evaluation Criteria for Superfiind Remedial Altematives 19 Table 2.0 Chemical-Specific ARARs 43 Table 2.1 Location-Specific ARARs 45 Table 2.2 Action-Specific ARARs 50 Amendment to 2003 ROD September 2010 OU6 Stray Horse Gulch, Califomia Gulch Superfiind Site

1.0 Introduction The purpose of this Record of Decision (ROD) Amendment is to explain modifications to the remedy selected for Operable Unit 6 (OU6), Stray Horse Gulch ofthe Califomia Gulch Superfund Site (Site) in Lake County, Colorado in the September 25,2003 Record of Decision (2003 ROD) (USEPA 2003). This ROD Amendment affects a portion ofthe existing remedy addressing environmental contamination in the Stray Horse Gulch area of OU6.

The lead agency for the Site is the U.S. Environmental Protection Agency (EPA), and the support agency is the Colorado Department of Public Health and the Environment (CDPHE or State). The lead agency is required to issue this ROD Amendment under CERCLA §117 and the National Contingency Plan (NCP) §300.435. This ROD Amendment and previously prepared Proposed Plan satisfy the public participation responsibilities under Section 117(c) ofthe Comprehensive Environmental Response, Compensation, and Liability Act of 1980, 42 U.S.C. Section 9601, et seq. (CERCLA, commonly known as "Superfund"), as amended by the Superfund Amendments and Reauthorization Act of 1986 (SARA), and 40 C.F.R. Section 300.435(c)(2)(ii), which is part ofthe National Oil and Hazardous Substances Pollution Contingency Plan (NCP). This document will be incorporated into the Administrative Record maintained for this Site, as required by NCP Section 300.825(aX2).

The 2003 ROD and supporting documentation incorporated by reference herein can be found in the Administrative Record for the Site. Copies ofthe Administrative Record are available at the following repositories:

U.S. EPA Region 8 Superfiind Records Center, 1595 Wynkoop Street Denver, CO 80202 (303) 312-6473 or toll free (800) 227-8917 Viewing hours: 8:00 a.m. to 4:00 p.m. Monday through Friday, excluding holidays and Lake County Public Library 1115 Harrison Avenue Leadville, CO 80461 (719)486-0569 Call for viewing hours

1.1 Summary of Basis for ROD Amendment The 2003 ROD combined two strategies to address acid rock drainage (ARD) from sources in Stray Horse Gulch: (1) consolidate and cap four mine waste rock piles and one tailing pile, and (2) manage surface water in Stray Horse Gulch.

Consolidation and capping effectively reduced or eliminated ARD generation at these ARD- generating sources. This portion ofthe 0U6 remedy is performing as expected with periodic maintenance.

The surface water management strategy involved two components. The first was the constmction of clean water diversion ditches uphill of these remaining ARD generating sources. A survey of the previously constructed clean water diversion stmctures revealed these structures are not Amendment to 2003 ROD September 2010 OU6 Stray Horse Gulch, Califomia Gulch Superfund Site capturing and diverting the maximum possible amount of clean water. Un-captured water may contribute to the generation of ARD.

The second component ofthe surface water management strategy involved the constmction of diversion ditches and retention ponds to collect ARD generated from uncapped mine waste rock piles within Stray Horse Gulch. When the ARD generated exceeds the volume ofthe retention ponds, this excess volume is diverted into the Marion Shaft where some portion (but not all) of the volume is delivered to the Leadville Mine Drainage Tunnel (LMDT). Several million gallons of ARD generated from the uncapped mine waste rock piles are annually diverted to the LMDT. Studies conducted before and after signing the 2003 ROD indicate that only a portion ofthe ARD introduced into the LMDT from the Marion Shaft arrives at the Reclamation plant for treatment. The portion ofthe ARD that is unaccounted for may migrate into mine workings and/or natural fractures/faults with the potential to discharge to alluvial groundwater and/or springs and seeps and eventually may enter a stream or river. (USEPA 2002a, USEPA 2006)

The 2003 ROD also called for constmction of bulkheads in the LMDT, selected development and adoption of an overlay district by Lake County, as the institutional control for this operable unit, and anticipated that a Site-wide repository would be constmcted under another operable unit to handle maintenance wastes from OU6 and wastes rock from the Ponsardine pile. The bulkheads within the LMDT have not been constmcted and are not expected to be constmcted due to disagreements between EPA, the State, and U.S. Bureau of Reclamation (Reclamation) over the need for such bulkheads. This amendment eliminates the bulkheads in the LMDT from EPA's remedy for OU6. The overlay district was adopted by the County in 2004 but was repealed by the County in 2005 due to County concerns over the lack of an on-site repository. Since wastes are to be left in place under either altemative under this amendment, institutional controls must be implemented for the remedy in OU6 to be protective. A Site-wide repository has not been constmcted and is not anticipated to be constmcted under any other operable unit at the Site, thus, the wastes from the Ponsardine Mine waste pile were placed near the RAM waste rock pile in 0U6 and maintenance work, on diversions ditches and the ponds, has been delayed while waiting for a place to deposit sediment and soils from these stmctures.

These uncertainties and missing components ofthe earlier remedy have convinced EPA and CDPHE that the remedy does not sufficiently meet the Remedial Action Objectives set forth in the 2003 ROD. In addition, the uncertainties regarding the ARD placed down the Marion Shaft raise significant doubts regarding the long-term effectiveness of this portion ofthe Selected Remedy.

2.0 Site History, Contamination and Selected Remedy 2.1 Site Background The Site is located in Lake County, Colorado, approximately 100 miles southwest of Denver. About 18 square miles in size, the Site includes the City of Leadville, including Stringtown along with surrounding areas.

Mining, mineral processing and smelting activities in the area produced gold, silver, lead and zinc for more than 130 years. Mining began in the Leadville area in 1859 when prospectors working the channels of Arkansas River tributaries discovered gold at the mouth of Califomia Gulch. Mine waste, which contains heavy metals and sulfide minerals generated during mining and ore processing, remains and poses a threat to human health and the environment. When water contacts the mine waste rock, acid is generated which lowers the pH ofthe water and mobilizes Amendment to 2003 ROD September 2010 0U6 Stray Horse Gulch, Califomia Gulch Superfund Site the heavy metals. This ARD is then transported to surface water and/or leached into the groundwater, which are exposure pathways for terrestrial and aquatic organisms.

Added to the National Priority List (NPL) in 1983, the Site is divided into 12 operable units. 0U6, which is the subject of this ROD Amendment, includes approximately 3.4 square miles in the northeastem portion ofthe Site and includes the Stray Horse Gulch and Evans Gulch watersheds. This ROD Amendment only concems the Stray Horse Gulch portion of OU6.

2.1.1 OU6 - Stray Horse Gulch Background Most of 0U6 is currently zoned by Lake County as industrial/mining. Although no active mines exist in 0U6, there is the potential for fijture mining activity. Other land uses within 0U6 include commercial activities which are limited to recreation and historic mine/heritage tourism, and residential home ownership. Only the Penrose Mine waste pile, which has been capped, and areas along Starr Ditch have residential uses. Recreational activities include biking, Nordic skiing, ATV use and hiking. Historic sites are within 0U6.

As a result of extensive mining, the Stray Horse Gulch area contains numerous mine waste rock piles and at least one tailing impoundment. Investigations and studies identified many ofthe mine waste rock piles and the Hamm's tailing impoundment as ARD generating source areas. (USDOl 1997)

Part ofthe Stray Horse Gulch ARD collection system is connected to the LMDT via the Marion and Robert Emmet shafts. Completed in 1954, the LMDT conveys water to Reclamation's treatment plant which manages and treats groundwater before discharging it to the Arkansas River.

2.2 0U6 Characteristics 0U6 consists primarily of undeveloped land with cultural and historic resources including mining sites. Within OU6 are two drainage systems, Stray Horse Gulch and a small portion of Evans Gulch, which flow into the Arkansas River. This ROD Amendment addresses only a portion of the Stray Horse Gulch drainage within 0U6.

The mine wastes in Stray Horse Gulch are in the form of waste rock piles and mill tailing. These materials are the source of contaminants present in surface water in 0U6. Each waste type is discussed below:

• Waste Rock Piles

• Waste rock in OU6 contains many different types of chemicals that occur naturally (e.g. lead, zinc, cadmium, arsenic, sulfides). The chemicals in this waste rock are at levels that are toxic to humans, plants and animals. The different types of waste rock were ranked according to how much ofthe toxic chemicals are present in them and how easily the chemicals leach from the rock into surface water. (USDOl 1996a) The quantity of waste rock currently requiring attention within Stray Horse Gulch is approximately 300,000 cubic yards.

• Mill Tailing

• Mill tailing are wastes produced from the processing of ores. Mill tailing also contain chemicals that are toxic to humans, plants and animals (e.g., zinc and cadmium). One

10 Amendment to 2003 ROD September 2010 0U6 Stray Horse Gulch, Califomia Gulch Superfund Site

deposit of mill tailing (Hamm's Tailing Pile) exists in OU6 along the south side of Stray Horse Gulch. The Hamm's Tailing Pile was consolidated and capped as part of an earlier response action in 1999. (USEPA 1999)

The Stray Horse Gulch tailing/waste rock piles were characterized as part ofthe Mine Waste Piles Remedial Investigation (USDOl 1997). Surface soils demonstrated elevated levels of lead, cadmium and zinc, when compared to Preliminary Remediation Goals (PRGs). Subsurface and foundation soils contained elevated to significantly elevated levels of cadmium, lead and zinc, when compared to these same PRGs.

Contaminant levels on the surface in the Greenback, RAM, Old Mikado, New Mikado, and Adelaide waste rock piles measured in 1997 showed the following results: (USDOl 1997)

• The pH (a measure of acidity) results varied between 1 and 8. The areas where the pH is less than 7 (acidic to highly acidic) are of concern to EPA, due to their adverse impacts on surface water quality;

• The lead levels varied from 29 milligrams per kilogram (mg/kg) to 79,987 mg/kg;

• The cadmium levels varied from 9 mg/kg to 402 mg/kg;

• The zinc levels varied from 2 mg/kg to 31,663 mg/kg; and

2.3 Contaminants of Concern The contaminants of concem (COCs) with regard to human health are lead and arsenic. COCs with regard to aquatic life are aluminum, zinc, cadmium and copper. COCs with regard to terrestrial life are arsenic, antimony, barium, beryllium, cadmium, chromium, copper, lead, nickel, manganese, mercury, silver, thallium and zinc.

2.4 Summary of Risks Waste rock in 0U6 and consequently, ARD from this waste rock, contains high levels of acid producing compounds (sulfides) and heavy metals, which were identified as COCs in the human health and ecological risk assessments. (Weston 1991, Weston 1995a, Weston 1995b, Weston 1996a, Weston 1996b and Weston 1997).

As part ofthe Superfund remedial action process, EPA conducts studies, called baseline risk assessments, to assess potential risks to the public and/or the environment from site contaminants of concem and to evaluate risk, based on current and potential future land use. EPA assessed both ecological and human health risks at 0U6 in the mid-1990s.

2.4.1 Human Health Risks Of all the heavy metals found in mine waste rock in OU6, lead poses the greatest potential threat to humans. The magnitude of this threat, however, is related to the nature and duration ofthe exposure a person might experience at the Site. The Baseline Human Health Risk Assessment for the Califomia Gulch Superfiind Site (Weston 1996a and Weston 1996b), was started in 1995 and completed in 1996 and included an evaluation of recreational exposures to wastes present in 0U6. Recreational use is the current and anticipated predominant future use for this area ofthe

11 Amendment to 2003 ROD September 2010 OU6 Stray Horse Gulch, Califomia Gulch Superfund Site

Site. Based on the Baseline Human Health Risk Assessment, the 2003 ROD concluded that average lead levels in 0U6 were below the Recreational Action Level of 16,000 mg/kg. Therefore, recreationalists who visit the mining district on the east side of Leadville are not exposed to an unacceptable level of lead and are not expected to experience adverse health effects.

2.4.2 Ecological Risks The Baseline Aquatic and Terrestrial Ecological Risk Assessments concluded that the COCs may be a source of risk to aquatic areas downstream of OU6 and that the mine waste poses potential risk to both aquatic and terrestrial organisms.

2.4.3 Aquatic Ecological Risk Assessment The Baseline Aquatic Ecological Risk Assessment (Weston 1995a) identified the potential for contaminated surface water to impact aquatic species. The risk characterization indicated that mine waste has adversely impacted surface-water quality on the Site and consequently the water quality ofthe Arkansas River. More specifically, high levels of cadmium and zinc in surface water present the greatest risk to aquatic life.

2.4.4 Terrestrial Ecological Risk Assessment The Baseline Terrestrial Ecological Risk Assessment (Weston 1997) focused on certain exposed species and potential toxic effects resulting from their ingestion of mine waste and contaminated surface water. The risk characterization indicated potential risks to certain terrestrial species, due to exposure to contaminants in mine waste (i.e., elevated levels of cadmium, zinc, and other metals).

2.5 Scope and Role The primary purpose ofthe remedial actions in 0U6 is to reduce the potential load of heavy metals entering into the Arkansas River by preventing their release to surface water in the Sfray Horse Gulch area and to contain any contaminated waters in lined retention ponds.

The actions, outlined in this ROD Amendment, ensure that the 0U6 remedy is protective and effective in the long-term.

Three ofthe 12 operable units, 0U2, 0U8 and OUIO, as well as a portion of 0U9, have been deleted from the NPL. EPA completed field work in 2009 in 0U5, 0U9 and OUl 1 and is in the process of defining institutional controls and/or deletions for OU3, 0U4, 0U7 and the remaining portions of OU9. OUl is the Yak Tunnel and treatment plant operated by Resurrection Mining Company. The ROD for 0U12, Site-wide water quality, was signed in 2009. 0U12 is in the remedial design phase.

2.6 Remedial Action Objectives Remedial Action Objectives (RAOs) provide a general description of what a cleanup will accomplish. As stated above, the RAOs listed in the 2003 ROD for OU6 focused on preventing or controlling the release of contamination from source materials including mill tailing and mine waste rock. The only mill tailing deposit in 0U6, the Hamm's tailing pile, was consolidated and capped in 1999. The only source material that has not been remediated in its entirety in 0U6 is mine waste rock. Therefore, the remaining RAOs for this operable unit include controlling the erosion of mine waste rock into local streams and the leaching of metals from mine waste rock into streams and groundwater.

12 Amendment to 2003 ROD September 2010 OU6 Stray Horse Gulch, Califomia Gulch Superfund Site

The RAOs for this ROD Amendment are the same as those listed in the 2003 ROD. They are:

1. control erosion of mine waste rock and deposition into local water courses;

2. control leaching and migration of metals from mine waste rock into surface water;

3. control leaching of metals from mine waste rock into groundwater; and

4. prevent direct unacceptable exposures to elevated concentrations of contaminants in the soil and mine waste rock.

2.7 Prior Response Actions The response actions and remedies implemented at Stray Horse Gulch mainly addressed prevention of ARD generation and management and control of ARD that was generated by spring snowmelt and storm water mn-off.

A number of response actions were performed in the Stray Horse Gulch area prior to signing of the 2003 ROD:

• The Mahala, Wolftone, Maid of Erin, and Penrose Mine waste rock piles and the Hamm's Tailing Impoundment were consolidated and capped;

• Contaminated mnoff and seepage from mine waste piles were collected in retention ponds;

• In 2000, pursuant to an emergency removal action, ARD, collected in several retention ponds at risk of overtopping, was discharged into the Marion Shaft and diverted to the LMDT for conveyance to the Reclamation Treatment Plant. Reclamation agreed to allow use of its facilities on an interim basis;

• Studies were conducted to investigate the nature and magnitude ofthe hydraulic connection between the Marion Shaft and the LMDT. These studies were performed to assess the effectiveness ofthe 2000 emergency removal action and to assess the use of the LMDT as a long term component ofthe OU6 remedy. The studies concluded that while there is a connection between the Marion Shaft and the LMDT, not all ofthe water delivered into the Marion Shaft migrates to the LMDT;

• Clean sfream water was diverted around mine wastes; and

Sediment was removed from Stray Horse Gulch and the hydrology was improved.

After the 2003 ROD, EPA performed the following response actions:

• A portion ofthe Ponsardine Mine waste rock pile was relocated;

• Unstable cribbing associated with the Robert Emmet Mine Site was repaired;

• Additional hydrogeologic studies focused on the hydrology ofthe LMDT were conducted;

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• As part of data collection to support remedial design, monitoring wells were installed in the LMDT;

• In 2005, a non-time critical removal action was performed to constmct an engineered outlet for the Gaw Shaft. The Gaw Shaft is a discharge point for the bedrock groundwater and is hydraulically connected to the Pendery Fault;

• EPA negotiated with Reclamation concerning the use ofthe LMDT to convey ARD to the plant;

• During the spring of 2008, pursuant to a time critical removal action, a relief well was installed approximately 4,696 ft from the portal into the LMDT, along with a buried gravity-feed pipeline from the relief well to Reclamation's freatment plant; and

• In 2008, Reclamation completed a risk study which assessed the potential for a failure in the LMDT that could result in a sudden, uncontrolled release of contaminated water.

2.8 Summary of Altematives From the 2002 Focused Feasibility Study and 2003 Record of Decision In developing the cleanup plan, EPA, in consultation with the State, considered a wide range of remedial altematives identified in the 2002 0U6 Focused Feasibility Study (2002 FFS). Some of these altematives were eliminated during a preliminary screening step due to very high costs, concems over the effectiveness ofthe altematives, or the difficulty of implementing the altemative. Nine cleanup options remained viable after the preliminary screening steps and are listed below. The altematives are numbered in the same way as they appear in the 2002 FFS and 2003 ROD. (USEPA 2003) The altematives presented were:

1. No Action;

2. Maintain Current Remedies with Land Use Controls;

2a. Pressurized Pipeline to Yak Tunnel;

2b. Gravity Pipeline to Yak Water Treatment Plant with Storage;

2e. Gravity Pipeline to Existing Pumping Well along LMDT with Storage;

2g. Install Bulkhead in LMDT and Dewater Mine Pool with Gravity Pipeline to Reclamation's Treatment Plant (Selected Ahemative);

2h. Gravity Pipeline to Dedicated Water Treatment Plant;

4. In-situ Chemical Stabilization or Relocation (in Combination with Altematives Options 2a through 2h);

4a. In-Situ Chemical Stabilization;

4b. Relocation (Selected Altemative);

5. Consolidate and Cap with Land Use Controls; and

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6. Excavate, Transport and On-Site Disposal with Land Use Controls.

A complete description ofthe altematives considered is available in the 2002 0U6 Focused Feasibility Study. (USEPA 2002b)

2.9 Selected Altemative in the 2003 ROD After evaluating the altematives identified in the 2002 OU6 Focused Feasibility Study, EPA selected altematives 2g and 4b. Signed on September 25, 2003, the Record of Decision for 0U6 includes the following components:

• Continued collection and management of ARD through treatment to remove contaminants at a water treatment facility operated by Reclamation and evaporation in retention ponds;

• Continued maintenance of consolidated and capped waste piles and surface water management features constructed during prior response actions. Maintenance includes inspections and repairs to caps and periodic cleaning/repairing of surface water management features. Wastes generated during maintenance activities will be disposed of in a planned on-site repository;

• Constmction of a plug (bulkhead) in the LMDT to allow better management of groundwater in flooded underground mine workings connected to the LMDT mine pool;

• Dewatering ofthe LMDT from a location upsfream ofthe bulkhead and delivery of pumped groundwater to Reclamation's freatment plant via a buried gravity pipeline;

• Establishing a groundwater monitoring network to observe water level and quality conditions in and around the mine pool;

• Relocation of additional mine waste rock (e.g., Ponsardine Mine waste pile) to a planned on-site repository;

• Stabilization of a retaining wall (crib wall) associated with the Emmet waste rock pile; and

• Establishment of land use controls under an Institutional Control Overlay (ICO) Disfrict to ensure that any fiiture changes in land use are consistent with the final remedy.

The constmction, operation, and maintenance of an on-site repository is not part ofthe 2003 ROD, but EPA and the State anticipated that an on-site repository would be constmcted as part of another operable unit. This repository would be available for disposing of soils and sediments generated in maintaining the Selected Remedy in the 2003 ROD.

2.10 Aspects ofthe 2003 ROD Not Implemented Due to unsuccessful negotiations and lack of location for the repository, the following components ofthe Selected Remedy have not been implemented: • The bulkhead in the LMDT has not been constmcted.

• No on-site repository has been constmcted as part of another operable unit.

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• Land use controls under an ICO District are not in place.

The title of Section 11.3 ofthe 2003 ROD was Contingency Measures and Long-Term Monitoring. To the extent any ofthe measures described in that Section ofthe 2003 ROD are determined to be necessary at OU6, such measures will be implemented through minor Record of Decision Modifications, Explanations of Significant Differences, or Record of Decision Modifications, as appropriate. The measures listed under Section 11.3 were not meant to be and are not to be considered contingency remedial measures selected in the 2003 ROD.

3.0 Basis for Document See Section 1.1.

4.0 Description of Proposed Remedy Modification 4.1 Altematives Considered in the Proposed Plan In order to determine the next best step to complete the cleanup in OU6, two altematives: - the Proposed Altemative and the No Further Action Altemative - were evaluated based on the NCP's nine criteria. One was selected as the Preferred Altemative.

An estimated cost is provided for each altemative. The measure of cost used to compare the altematives is the 100-year present worth cost. This is the amount of money that, if invested today at a 7% interest rate, would adequately fund the remedy over 100 years.

4.1.1 No Further Action /Implementation Steps Necessary Alternative The No Further Action Altemative leaves waste rock in 0U6 in its current condition. Response actions that have already been completed would be left as-is. This altemative is presented as a begiiming point for comparison ofthe proposed altemative. Under this altemative, the bulkhead would not be installed and Reclamation would continue to treat the portion ofthe ARD that enters the Marion Shaft that actually makes it to the LMDT. The remaining ARD would remain in the LMDT and would have the potential to seep out. There would be no institutional confrols. The on-site repository would not be constmcted. Operation and maintenance (O&M) would be performed on the components ofthe remedy that are presently constmcted and operating.

Capital Cost $0 Time to Implement 0 years 100-year Present Worth O&M Cost $2,748,258 100-year Present Worth Cost $2,748,258

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4.1.2 Proposed Altemative The Proposed Altemative included the following components:

• The current clean water diversion systems along the Mahala, Pyrenees, Greenback, RAM, Old Mikado, New Mikado, and Adelaide-Ward will be expanded and improved to increase the volume of clean water transported away from ARD-generating sources. Clean water will be collected and diverted into existing clean water systems such as Califomia Gulch, Sfray Horse Gulch and Starr Ditch;

• In order to prevent infilfration of snowmelt and rain into the mine waste and reduce the volume of ARD generated, EPA will cap, as determined in the design phase, all or parts ofthe Greenback, RAM, Old Mikado, New Mikado, and Adelaide-Ward Mine waste rock piles. Due to their historic value, the piles will be capped in a way that will maintain their current appearance to the greatest extent possible. In particular, the surfaces ofthe piles that are visible along the Mineral Belt Trail and county roads will be handled with great care. At the request of Lake County officials in 2009, EPA conducted a pilot capping study to demonsfrate various capping approaches that can achieve the environmental goals of ARD reduction while at the same time minimizing the alteration ofthe appearance ofthe piles;

• The existing ARD collection system including retention ponds (Pyrenees, Greenback, Marion, RAM, Old Mikado, New Mikado, Upper Adelaide and Lower Adelaide) would be enhanced, enlarged and lined to be able to hold spring mnoff flows ofthe minimized acidic, contaminated water. The specific sizing ofthe retention ponds will be determined in the design phase and will be based on a 100-year event design capacity with the option of constmcting 500-year event ponds where feasible;

• After this proposed remedy change is fiilly implemented, the use ofthe LMDT for conveyance of ARD to Reclamation's plant for freatment will be eliminated except for in the case of an exfreme weather event whereby the only other option would be to release unfreated ARD into Sfray Horse Gulch;

• Monitoring of groundwater and water levels in the LMDT will be shifted to the 0U12 Site-wide surface and groundwater remedy. The monitoring plan, which is part ofthe OUl 2 ROD, is being developed as part ofthe OUl 2 remedial design;

• A Site-wide repository will be constmcted in Sfray Horse Gulch as part ofthe 0U6 remedy. This repository will be made available for disposal of sediment or soils generated by periodic maintenance of remedy features by EPA or the State at 0U5, 0U6, OU7, OUl 1 and OUl2. Additionally, residential and non-residential mine wastes from soil removals in 0U9, as directed by the 0U9 Work Group, and soil excavations of commercial properties throughout the Site, up to a limit of 2,500 cubic yards per project, may be placed in the repository. The repository will meet applicable or relevant and appropriate requirements (ARARs). After constmction, the State and Lake County will operate and maintain the repository; and

• Institutional controls (ICs) are needed to protect engineered remedies and to reduce exposure to contaminants left in place. Lake County has enacted land use confrol ordinances for other OUs at the Site. EPA will work with Lake County to develop a similar land use control ordinance for OU6. These controls will protect existing

17 Amendment to 2003 ROD September 2010 OU6 stray Horse Gulch, Califomia Gulch Superfund Site

remedies, including caps and diversions, and will ensure that future changes in land use are protective of human health and the environment. In order for the remedy to comply with Colorado's Environmental Covenants Act (C.R.S. 25-15-317 to 327), Lake County will need to enter into an intergovernmental agreement (IGA) granting the State authority to enforce against violations ofthe land use control ordinance. If an IGA is not reached, areas affected by the amended remedy containing waste left in place or engineered features, including the repository, will need an environmental covenant or resfrictive notice as required by C.R.S. § 25-15-320.

EPA and CDPHE will develop a final cultural resource mitigation plan for this proposed work. The draft plan was available for review and comment as part ofthe Proposed Plan process. Generally, EPA will seek to avoid impacting identified cultural resources, but if avoidance is not possible, EPA will mitigate the impacts ofthe proposed remedial actions on historic features in the area. EPA may restore head frames and other stmctures, and provide interpretive signage and other features along the Mineral Belt Trail to support heritage tourism. The final plan will be based on community input regarding historic preservation and mitigation.

EPA plans to insure the integrity ofthe Greenback cribbing and the Pyrenees head frame while implementing the remedy modifications. Due to the potential impact of constmction equipment along the Mineral Belt Trail (MBT), EPA included the cost of repaying the MBT from the 5th Sfreet Bridge to south ofthe Pyrenees Mine site. EPA will finalize the draft cultural resource mitigation plan in concert with the design.

Capital Cost $ 18,000,000 Time to Implement 2 years 100-year Present Worth O&M Cost $45 8,043 100-year Present Worth Cost $ 18,45 8,043 5,0 Evaluation of Altematives EPA uses nine criteria to evaluate the proposed remedy change. This section discusses the performance ofthe Proposed Altemative and the No Further Action Altemative against the nine criteria, noting how the altenatives compare to the options under consideration.

To comply with the NCP, the EPA criteria must be applied to all remedial altematives. These criteria, outlined in Guidance for Conducting Remedial Investigations/Feasibility Studies under CERCLA (EPA 1988) and the NCP [40 CFR 300.430(f)(5)(i)], fall into three categories: threshold criteria; balancing criteria; and modifying criteria. Table 1 summarizes the nine criteria within these broad categories. The nine evaluation criteria follow.

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TABLE 1 - EVALUATION CRITERLV FOR SUPERFUND REMEDIAL ALTERNATIVES

SUPERFUND EVALUATION CRITERIA Threshold - Criteria must be met before an alternative can be selected as a remedy. 1. Overall protection to human health and the environment: addresses whether or not a remedy provides adequate protection and describes how risks posed through each pathway are eliminated or reduced. 2. Compliance with applicable or relevant and appropriate requirements (ARARs): addresses whether or not a remedy will meet all federal and state environmental laws or regulations. Balancing - Relative tradeoffs between different criteria are evaluated. 3. Long-term effectiveness and permanence: refers to the ability of a remedy to provide reliable protection of human health and the environment over time. 4. Reduction in toxicity, mobility or volume through treatment: refers to the preference for a remedy that reduces health hazards, the movement of contaminants, or the quantity of contaminants at the site. 5. Short-term effectiveness: addresses the period of time needed to complete the remedy and any adverse impacts during constmction and operation. 6. Implementability: refers to the technical and adminisfrative feasibility of a remedy. 7. Cost: evaluates the estimated capital, operation and maintenance costs. Modifying - Evaluate whether remedy is supported by state and community after public comment period. 8. Supporting agency acceptance: indicates whether the supporting agency agrees with, opposes, or has no comment. 9. Community acceptance: includes determining which components ofthe altemative interested persons in the community support, have reservations about or oppose.

5.1 Overall Protection of Human Health and the Environment Overall protection of human health and the environment addresses whether each altemative provides adequate protection of human health and the environment and describes how risks posed through each exposure pathway are eliminated, reduced, or controlled through treatment, engineering controls, and/or institutional controls.

The No Further Action Altemative is not protective of human health in the long-term because the ICO District in the Selected Remedy ofthe 2003 ROD is not implementable. In addition, it is uncertain whether this altemative is protective ofthe environment without implementation ofthe bulkhead and dewatering ofthe mine pool. The inability to account for all the ARD discharged down the Marion Shaft and the potential for heavy metals from this ARD to appear in seeps, springs or other surface water bodies also lowers the protectiveness of this altemative.

The Proposed Altemative would protect human health and the environment, and would result in further improvements in surface water and groundwater quality in all of Stray Horse Gulch. Capping select areas that have high potential for generating ARD materials with low-permeability covers would minimize the generation of ARD. Elimination ofthe discharge of ARD down the Marion Shaft would remove the uncertainty regarding protectiveness found in the 2003 remedy. The Proposed Altemative requires the development of ICs to ensure that any future changes in

19 Amendment to 2003 ROD September 2010 OU6 Stray Horse Gulch, Califomia Gulch Superfund Site land use are consistent with the final remedy, that engineered components ofthe remedy are protected and that human exposure to waste left in place is minimized.

5.2 Compliance with Applicable or Relevant and Appropriate Requirements (ARARs) Section 121(d) of CERCLA and NCP §300.430(f)(l)(ii)(B) require that remedial actions at CERCLA sites at least attain legally applicable or relevant and appropriate federal and state requirements, standards, criteria, and limitations which are collectively referred to as "ARARs," unless such ARARs are waived under CERCLA section 121(d)(4).

Applicable requirements are those cleanup standards, standards of confrol, and other substantive requirements, criteria, or limitations promulgated under federal environmental or state environmental or facility siting laws that specifically address a hazardous substance, pollutant, contaminant, remedial action, location, or other circumstance found at a CERCLA site. Only those state standards that are identified by a state in a timely manner and that are more stringent than federal requirements may be applicable.

Relevant and appropriate requirements are those cleanup standards, standards of control, and other substantive requirements, criteria, or limitations promulgated under federal environmental or.state environmental or facility siting laws that, while not "applicable" to a hazardous substance, pollutant, contaminant, remedial action, location, or other circumstance at a CERCLA site address problems or situations sufficiently similar to those encountered at the CERCLA site that their use is well-suited to the particular site. Only those state standards, which are identified in a timely manner and are more sfringent than federal requirements, may be relevant and appropriate.

Compliance with ARARs addresses whether a remedy will meet all of the applicable or relevant and appropriate requirements of federal and state environmental statues or provides a basis for an invokmg waiver.

The ARARs for this proposed action are found in Table 2. This list of ARARs is unchanged from those listed in the 2003 ROD.

ARARs related to specific standards for surface and groundwater are not considered in the source confrol operable units, such as OU6, but are included in the record of decision for OUl 2.

There are no chemical specific ARARs for this proposed action. Significant ARARs for the proposed altemative include: 1) the National Historic Preservation Act, due to the proposed capping of five additional waste rock piles; 2) the federal and State Solid Waste regulations regarding the constmction, operation, maintenance, and closure ofthe proposed Site-wide repository. The Colorado Envirorunental Covenant Act is a significant ARAR for each ofthe altematives.

In order for either altemative to comply with the Colorado's Environmental Covenant Act, Lake County will need to enter into an intergovernmental agreement (IGA) granting CDPHE authority to enforce against violations ofthe land use control ordinance. If an IGA is not reached, areas affected containing waste left in place or engineered features, including the repository, will need an environmental covenant or resfrictive notice as required by C.R.S. § 25-15-320 in order to comply with the ARAR.

20 Amendment to 2003 ROD September 2010 0U6 Stray Horse Gulch, Califomia Gulch Superfund Site

The present Lake County Board of County Commissioners has not yet agreed to an intergovernmental agreement with CDPHE regarding the ordinances adopted at the other operable units. However, the County and CDPHE have indicated their willingness to negotiate and conclude such an agreement. No other ARARs apply to the No Further Action Altemative. It is expected that the both altematives will meet all other ARARs.

5.3 Long- Term Effectiveness and Permanence Long-term effectiveness and permanence refers to expected residual risk and the ability of a remedy to maintain reliable protection of human health and the environment over time, once clean-up levels have been met. This criterion includes the consideration of residual risk that will remain onsite following remediation and the adequacy and reliability of confrols.

The No Further Action Altemative will not be effective in the long-term because it does not contain or freat the ARD that enters the LMDT. Hence, there is substantial uncertainty conceming the long-term effectiveness ofthe No Further Action Altemative. Studies show that only a portion ofthe ARD that EPA places down the Marion Shaft makes it to Reclamation's plant for freatment. It is known that there is a substantial mine pool behind blockages in the LMDT. It is a certainty that the LMDT and the various stopes, laterals, and shafts presently used to fransmit the ARD will continue to deteriorate and collapse. The uncertainties regarding where ARD placed in the Marion Shaft may ultimately migrate and the certainty regarding the ultimate failure ofthe LMDT as a conveyance system makes the long-term effectiveness ofthe No Further Action Altemative low.

The Proposed Altemative offers a higher level of long-term effectiveness and permanence. Capping and isolation ofthe source material responsible for contaminated mnoff and seepage are proven technologies widely used for mine waste material. In addition, clean water diversion ditches and collecting ARD in retention ponds has been shown to be effective at this Site and others in reducing substantially the levels of contaminants of concern in surface and groundwater. These potential remedy components are simple to maintain and are effective over the long-term.

The ICs proposed require that Lake County develop, adopt and maintain an ordinance restricting land use in 0U6 to protect human health and the environment as well as the engineered remedies. The OU6 ICs need to comply with the State's envfronmental covenant law. Pursuant to the Colorado Environmental Covenant Act, Lake County must enter into an intergovernmental agreement with CDPHE giving the department oversight and enforcement authority over the ordinance. Further negotiations between the present Board of County Commissioners and CDPHE are needed to reduce the uncertainty over long-term effectiveness ofthe Proposed Altemative.

In addition, even though the present board is supportive ofthe proposed institution confrols, the present Board of County Commissioners may not bind fiiture boards. Therefore, the long-term effectiveness ofthe IC retains some uncertainty.

5.4 Reduction in Toxicity, Mobility or Volume through Treatment Reduction of toxicity, mobility, or volume through freatment refers to the anticipated performance ofthe freatment technologies that may be included as part of a remedy.

Under the No Further Action Altemative, a portion ofthe ARD generated in Stray Horse Gulch is treated at Reclamation's treatment plant.

21 Amendment to 2003 ROD September 2010 OU6 Stray Horse Gulch, Califomia Gulch Superfund Site

The Proposed Altemative does not reduce toxicity, mobility or volume of contaminants through treatment. However, capping and isolating ARD-generating mine wastes will reduce the production of contaminated seepage, thereby reducing the mobility ofthe contaminants.

5.5 Short-Term Effectiveness Short-term effectiveness addresses the period of time needed to implement the remedy and any adverse impacts that may be posed to workers, the community and the environment during constmction and operation ofthe remedy until cleanup levels are achieved.

The No Further Action Altemative poses no adverse impacts in the short-term.

The Proposed Altemative involves moderate scale disturbance of mine wastes. Therefore, moderate short-term impacts would be expected.

5.6 Implementability Implementability addresses the technical and adminisfrative feasibility of a remedy from design through constmction and operation. Factors such as availability of services and materials, adminisfrative feasibility, and coordination with other governmental entities are also considered.

The No Further Action Altemative is taken as it stands today, so this criterion is not relevant because no components need to be implemented. The components ofthe Proposed Altemative are technically and adminisfratively implementable. Implementation ofthe proposed ICs requires the cooperation and willingness ofthe local government to develop and adopt ordinances. The Lake County Board of County Commissioners has indicated they are supportive of these proposed ICs.

5.7 Cost The estimated total 100-year Present Worth Cost for the altematives are $2,748,258 for the No Action Altemative and $18,458,043 for the Proposed Altemative. The cost ofthe No Further Action Altemative is about $2,748,258 over a hundred years for water freatment plus O&M costs ofthe diversion ditches and retention ponds.

The capital costs for the caps and upgraded diversion and retention system ofthe Proposed Altemative is approximately $18,000,000. Maintenance ofthe caps and clean water and ARD collection systems will be required in-perpetuity. The O&M costs for one hundred years are estimated to be $458,043. The total 100-year Present Worth Cost is estimated to be $18,458,043. The estimated cost ofthe Proposed Altemative has an expected accuracy of+50% to -30%.

5.8 State Acceptance The State concurs with this ROD Amendment.

5.9 Community Acceptance The community is generally supportive ofthe Proposed Altemative. However, a concem about balancing environmental protection and historic preservation was voiced.

5.10 Principal Threat Wastes The NCP establishes an expectation that EPA will use treatment to address the principal threats posed by a site wherever practicable (NCP 300.430(a)(l)(iii)(A)). Identifying principal threat

22 Amendment to 2003 ROD September 2010 0U6 Stray Horse Gulch, Califomia Gulch Superfiind Site wastes combines concepts of both hazard and risk. In general, principal threat wastes are those source materials considered to be highly toxic or highly mobile which generally cannot be contained in a reliable manner or would present a significant risk to human health or the environment should exposure occur. Conversely, non-principal threat wastes are those source materials that generally can be reliably contained and that would present only a low risk in the event of exposure. Typically, mine waste rock is not considered to be principal threat waste.

6.0 Summary ofthe Selected Remedy Modification/Alternative The selected altemative is the Proposed Altemative because, even though the costs are greater, it eliminates the uncertainties in the present remedy and is expected to be more effective over the long-term and thereby provide greater protection of human health and the environment.

Based on current information, the EPA believes the Selected Remedy change meets the threshold criteria and provides the best balance of fradeoffs with respect to the balancing and modifying criteria. The EPA expects the preferred altemative to satisfy the following statutory requirements of CERCLA § 121(b): 1) be protective of human health and the environment; 2) comply with ARARs; 3) be cost-effective; 4) utilize permanent solutions and altemative freatment technologies to the maximum extent practical; and 5) justify the reason for not selecting a freatment technology due to the volume and historic nature ofthe waste.

7.0 Support Agency Comments The State concurs with the Selected Remedy but will ensure compliance with the Environmental Covenant Law through entering into an IGA with Lake County, or, absent an IGA, requiring a covenant or restrictive notice on 0U6 property with waste in place or engineered features.

8.0 Affirmation ofthe Statutory Determinations Under CERCLA Section 121 and the NCP, EPA must select a remedy that is protective of human health and the environment; that complies with ARARs; is cost-effective; and utilizes permanent solutions, altemative freatment technologies, or resource recovery technologies to the maximum extent practicable. In addition, CERCLA includes a preference for remedies that employ freatment that permanently and significantly reduces the volume, toxicity, or mobility of hazardous wastes as a principal element and a bias against off-site disposal of unfreated wastes. The following sections discuss how the Selected Remedy meets these statutory requirements.

8.1 Protection of Human Health and the Environment \n accordance with CERCLA Section 121, 42 U.S.C. § 9621, EPA believes the Selected Remedy will adequately protect human health and the environment.

Land use confrols with ICs will minimize the likelihood of human health risk above a level of concem from exposure to non-residential soils and mine wastes.

The Selected Remedy is protective ofthe terrestrial ecology ofthe Site through selected consolidation and capping of mine wastes. The caps break the exposure pathway for terresfrial receptors thereby reducing risks to the terrestrial ecology. In addition, unremediated mine waste piles typically are devoid of vegetation rendering them poor habitat for terrestrial receptors resulting in limited exposure to Site wastes.

The Selected Remedy includes the continued use of small detention and retention ponds constructed at the base of several mine waste piles as part of previous Response Actions. These ponds collect and store ARD. Although it is possible that these ponds will attract terrestrial

23 Amendment to 2003 ROD September 2010 0U6 Stray Horse Gulch, Califomia Gulch Superfund Site receptors, their combined area is limited. In addition, these ponds have existed since 1998 and EPA has received no reports of terresfrial receptor contact with ponded ARD or acute impacts to wildlife.

8.2 Compliance With Applicable or Relevant and Appropriate Requirements The Selected Remedy satisfies the requirements that are applicable or relevant and appropriate to this remedial action. The Selected Remedy will comply with all ARARs identified in Tables 2.0 through 2.2. No waiver of ARARs will be necessary.

Chemical Specific ARARs There are no chemical specific ARARs associated with the Selected Remedy.

Location Specific ARARs The Selected Remedy will comply with all location specific ARARs. Several regulations pertaining to the preservation of historic features have been identified as ARARs. Compliance will be achieved through implementation of procedures to preserve historical and archeological data should qualifying historical features be affected by the remedy.

Action Specific ARARs The Selected Remedy will comply with all action specific ARARs. Environmental covenants are required whenever contamination is left in place, such as mine waste. Compliance with this ARAR will be achieved through ICs.

8.3 Cost-Effectiveness In EPA's judgment, the Selected Remedy is cost-effective and represents a reasonable value for the money to be spent. In making this determination, the following definition was used: "A remedy shall be cost-effective if its costs are proportional to its overall effectiveness (NCP 300.430(f)(l)(ii)(D))". This was accomplished by evaluating the "overall effectiveness" of those altematives that satisfied the threshold criteria (i.e., were both protective of human health and the environment and ARAR-compliant). Overall effectiveness was evaluated by assessing three of the five balancing criteria in combination (long-term effectiveness and permanence; reduction in toxicity, mobility, and volume through freatment; and short-term effectiveness). Overall effectiveness was then compared to costs to determine cost-effectiveness. The relationship ofthe overall effectiveness of this remedial altemative was determined to be proportional to its costs and hence this altemative represents a reasonable value for the money to be spent. The estimated present worth cost ofthe Selected Remedy is $18,458,043.

8.4 Utilization of Permanent Solutions and Alternative Treatment (or Resource Recovery) Technologies to the Maximum Extent Practicable (MEP) EPA has determined that the Selected Remedy represents the maximum extent to which permanent solutions and freatment technologies can be utilized in a practicable manner at OU6.

The basic premise ofthe Selected Remedy is to keep clean water clean and prevent the generation of acid rock drainage. The preference is for contaminant reduction and not freatment. A reduction of toxicity and mobility would be achieved with this remedy.

EPA has determined that the Selected Remedy provides the best balance of frade-offs in terms of the five balancing criteria, while also considering the statutory preference for freatment as a

24 Amendment to 2003 ROD September 2010 OU6 Stray Horse Gulch, Califomia Gulch Superfund Site principal element and bias against off-site disposal and considering State and community acceptance.

A large volume of mine wastes precludes treatment or off-Site disposal as a viable option. In addition, the mine waste and related ARD do not contain resources that may be recovered economically at the present time. However, the potential remains for reprocessing of mine waste in the fiiture should it become economically viable.

8.5 Preference for Treatment as a Principal Element The Selected Remedy includes preventing the generation of ARD as a principal element. Capping and isolating ARD-generating mine wastes will reduce the production of contaminated seepage, thereby reducing the mobility ofthe contaminants resulting in further improvements in surface water and groundwater quality in all of Stray Horse Gulch.

8.6 Five- Year Review Requirements Because this remedy will result m hazardous substances, pollutants, or contaminants remaining in OU6 above levels that allow for unlimited use and unresfricted exposure, a statutory review will be conducted within five-years after initiation of remedial action to ensure the remedy remains protective of human health and the environment.

9.0 Public Participation and Historic Preservation EPA recognizes the historical value of this area to the Leadville Community. In the fall of 2009, EPA conducted a pilot study to demonstrate several iimovative capping techniques to determine how we might help preserve the historic character ofthe mine waste rock piles. The community, through public meetings, one on ones, the Virtual Fomm, websites and letters, has provided EPA with comments and preferences regarding the demonsfrated capping approaches and ideas for mitigation of impacts to historic features.

Additionally EPA, in consultation with the State Historical Preservation Office, conducted a re- evaluation of our previous cultural resource mventory ofthe affected area. (URS 2010)

EPA has drafted a plan of procedures to mitigate impacts to historic features in 0U6. The public was notified ofthe availability of this plan and asked to comment.

EPA and the State will continue to provide information regarding the cleanup of 0U6 to the public through public meetings, fact sheets, the Administrative Record for the Site, our website www.epa.gov/region8/superfund/co/calgulch. and through announcements in the Leadville Herald Democrat. EPA and the State encourage the public to gain a more comprehensive understanding of 0U6 and the Superfund activities conducted at the Site.

In accordance with 40 CFR Section 300.435(c)(2)(ii), EPA published a Proposed Plan on June 10, 2010 and was available for comment until July 12, 2010. The comment period was then extended to August 11, 2010 at the request of a community member. A public meeting was held on June 24, 2010 in Leadville, CO.

EPA received comments from one federal agency and eleven community members. Five community members commented on the Capping Pilot study.

25 Amendment to 2003 ROD September 2010 OU6 Stray Horse Gulch, Califomia Gulch Superfund Site

10.0 References Cited All of the documents referenced can be found in the Administrative Record.

United States Department ofthe Interior, (USDOl) Bureau of Reclamation, 1996a. Phase I: Feasibility Study, Water and Sediment Sampling and Hydrologic Measurement Program, Results and Findings, 1995 Spring Runoff for Operable Unit 6, California Gulch NPL Site, Leadville, Colorado, November 1996.

USDOl, Bureau of Reclamation, 1997. Draft Environmental Geology of Operable Unit 6, Removal Action Design Data, California Gulch Superfund Site, Leadville, Colorado, Febmary 1997.

USDOl, Bureau of Reclamation, 2008. Leadville Mine Drainage Tunnel Risk Assessment, Leadville Mine and Drainage Tunnel Project, Colorado Great Plains Region, November 2008

USDOl, U. S. Geological Survey, 2008a. Memorandum: To: Jeff Deckler, Colorado Department of Public Health and Environment, Canterbury Investigation, November 1, 2008

URS, 2Q\Q.Cultural Resource Reevaluation of Cultural Resources in Potentially Affected Areas of Stray Horse Gulch, California Gulch Superfund Site Operable Unit 6, January 28,2010

USEPA, 1999. Final Pollution Report, Time Critical Removal Action at the Hamm 's Tailing Impoundment and the Penrose Mine Waste Pile 0U6, Califomia Gulch Site, Leadville, Lake County, Colorado, October 4, 1999

USEPA, 2002a. Draft Groimdwater Hydrology in the Vicinity ofthe Leadville Mine Drainage Tunnel, Operable Unit 6 and Affected Areas, California Gulch Superfund Site, August 2002

USEPA, 2002b. Final Focused Feasibility Study for Operable Unit 6, California Gulch Superfund Site, 2002

USEPA, 2003. Record of Decision, Operable Unit 6, California Gulch Superfund Site, Lake County, Colorado, September 25, 2003

USEPA, 2006. Hydrogeologic Characterization ofthe Ground Waters, Mine Pools and the Leadville Mine Drainage Tunnel, Leadville, Colorado, 2006

Weston, Inc., 1991. Preliminary Human Health Baseline Risk Assessment for the California Gulch NPL site, Leadville, Colorado, December 1991.

Weston, Inc., 1995a. Final Baseline Aquatic Ecological Risk Assessment for the California Gulch NPL Site, September 1995.

Weston, Inc., 1995b. Baseline Human Health risk Assessment for the Califomia Gulch Superfund Site, Part C —Evaluation of Worker and Recreational Scenarios, April 1995.

26 Amendment to 2003 ROD September 2010 OU6 Stray Horse Gulch, Califomia Gulch Superfund Site

Weston, Inc., 1996a. Baseline Human Health Risk Assessment, Califomia Gulch Superfund Site, Leadville, Colorado, Part A - Risks to Residents from Lead, January 1996.

Weston, Inc., 1996b. Baseline Human Health Risk Assessment, California Gulch Superfund Site, Leadville, Colorado, Part B - Risks to Residents ft-omContaminant s other than Lead, January 1996.

Weston, Inc., 1997. Ecological Risk Assessment for the Terrestrial Ecosystem, Califomia Gulch NPL Site, Leadville, Colorado, January 1997

11.0 Responsiveness Summary

RESPONSIVENESS SUMMARY FOR THE RECORD OF DECISION AMENDMENT OU6, STRAY HORSE GULCH, CALIFORNIA GULCH SUPERFUND SITE

Summary of Comments

The comments below were received via email or letter. At the Public Meeting, no formal comments were given by the attendees. A copy ofthe comments received during the Public Comment Period and the Verbatim Transcript ofthe Public Meeting ofthe Matter of: Califomia Gulch Superfund Site Operable Unit 6, Leadville, Colorado can be found in the Administrative Record.

EPA received comments from one federal agency, the Bureau of Reclamation and eleven community members. Five community members commented on the Capping Pilot Study.

Comments are presented in italics. Responses are provided in standard type.

Agency Responses and Public Comments

Agency Responses Received from the Bureau of Reclamation:

1. Comment: Reclamation supports actions identified in the plan that will reduce the generation and movement of acid rock drainage (ARD), including capping waste rock piles, expanding clean water diversion systems, and enhancing contaminated water impoundment/retention facilities. The design ofthe impoundment/retention facilities is critical to the success of the proposal and significant consideration should be given to the appropriate sizing of these facilities to capture a probable maximum precipitation/runoff event as well as to the consequences of facility failure of capacity exceedance.

Response: Noted.

2. Comment: On page 9, the last bullet point ofthe "Prior Response Actions " provides information related to Reclamation's 2008 analysis ofthe potential for a failure within the LMDT and the potential for a sudden, uncontrolled release of contaminated water and includes a statement that the study determined the risk was "fairly low.' Reclamation completed a scientific, peer-reviewed risk assessment and found that it was highly unlikely that a sudden release of water could occur from either blockage in the LMDT or through the engineered bulkheads

11 Amendment to 2003 ROD September 2010 0U6 Stray Horse Gulch, Califomia Gulch Superfund Site installed in the tunnel near the portal. Please amend the statement to accurately reflect the type of analysis completed as well as its findings.

Response: Noted and the statement was modified.

3. Comment: Please clarify the definition of "extreme weather event" as described in the "Proposed Altemative " on page 13, when ARD would be conveyed to Reclamation's plant for treatment, as well as the method for this conveyance. As provided in the proposal, should the retention facilities exceed their capacity, the overflow ARD would be conveyed to Reclamation's facility through the existing hydrologic connection between the Marion Shaft and the LMDT.

Response: As mentioned in the Proposed Plan in the Proposed Altemative section on page 13, the "specific sizing ofthe retention ponds will be determined in the design phase and will be based on a 100-year event design capacity with the option of constmcting 500-year event ponds where feasible." In the event of unexpected weather event where the capacity ofthe drainage system and retention ponds is exceeded and the ARD could potentially flow down Starr Ditch through town and into the Arkansas River system, ARD may be diverted into the Marion Shaft.

4. Comment: It is also recognized that only a portion of ARD introduced into the LMDT arrives at the plant for treatment and that the long-term hydrologic connection between the Marion Shaft and the LMDT is unlikely to be sustainable. The physical stability ofthe connection between the Marion Shaft and the LMDT will likely deteriorate with time. Consideration should be given to the development of an altemative that does not rely upon the use of this hydrologic connection.

Response: This remedy does not rely on the hydrologic connection.

5. Comment: In the "No Further Action" section on page 12 and again on page 15, it is unclear if the cost information provided includes Reclamation's costs for operation ofthe water treatment plant. Does the Proposed Alternative include Reclamation's costs? If they are not included. Reclamation believes they should be so the total cost to the government is shown. Please include the assumptions and values used for the calculations either in the proposal or as supporting documentation.

Response: Yes, EPA and Reclamation have an Interagency Agreement through which EPA has been and will continue to reimburse Reclamation for the agreed to cost of freating the ARD from the 0U6 area that is infroduced into the LMDT. Independent Govemment Cost Estimates, prepared by EPA and Reclamation using historical data, have projected future costs to be about $130,000 per year. For estimating purposes, the water freatment plant annual cost represented, as $150,000, along with an annual cost of operations and maintenance ofthe remedy of $30,000, were used to calculate the 100-year Present Worth Operation and Maintenance Costs ofthe "No Further Action" Altemative.

6. Comment'. Reclamation is the largest wholesale water supplier and the second largest producer of hydroelectric power in the United States, with operations and facilities in the 17 Western States. As such, we have significant technical expertise in the design and construction of water impoundment and conveyance facilities. We are available to assist EPA in the design and/or technical peer review as implemented (sic) of the proposed plan moves forward.

Response: Noted.

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Received from Bob Elder

7. Comments: I believe that the EPA is now taking a measured and planned approach to alleviating the Acid Mine Drainage situation in the Stray Horse Gulch area.

Your test remediation effort at the Denver City waste dump was effective in demonstrating acceptable techniques for dealing with the problems at the larger, more challenging sulfide waste dumps at the Old and New Mikado, Greenback, RAM and Adelaide sites. All ofthe altemative techniques demonstrated were shown to be usable under applicable circumstances.

In particular, the use ofthe timber cribs can be particularly valuable in dealing with the steep existing slopes ofthe two Mikado dumps. Minor cribs are already present at the north base of the New Mikado dump. By extending the cribbed section across the base of both dumps and markedly increasing the crib height, the EPA could greatly reduce the unstable dump slopes and make it possible to stabilize your planned geotextile barrier and overlying benign rock cover.

As we have discussed before, I believe that interception and diversion ofthe existing near-surface water flow from the Graham Park wetlands into the Mahala and Greenback dumps will be critical in minimizing generation of AMD from both of these high-sulfide piles. Either French drains and/or shallow curtain walls may prove effective in diverting the existing water flow.

I certainly appreciate the work that you and the other EPA personnel have devoted to your new OU6plan.

Response: Noted.

Received from Salem Minerals, Inc.

8. Comment (Summaiy): One property owner is concerned that capping would prevent future ability to reprocess the waste rock to recover metals using an oxidation-reduction technology developed by Leadville Silver & Gold.

Response: Capping would not prevent land owners from accessing the waste rock in the future as long as they follow all applicable laws.

Received from Richard Silkey

9. Comment: I am in agreement with the new proposed plan for the cleanup of OU6. Allowing highly contaminated water to enter the LMDT is a bad idea and needs to be stopped. The LMDT is compromised and if we have a few good snow years with high runoffs, we might start seeing seeps of really nasty water running through our town or streams. The less water that goes in there the better. I think lining the retention ponds will also help lower the amount of water entering the LMDT. I feel like many ofthe piles need to be capped as well. If we can keep the chemical reaction that creates ARD from occurring we should. I feel it is important to maintain the historical aesthetics by keeping the head frames, and using the alternative capping techniques. The alternative capping types look very realistic and should be used to keep the historical setting. I don't seem to have a preference, I looked at them the other day and they all looked good to me.

Response: Noted.

29 Amendment to 2003 ROD September 2010 OU6 Stray Horse Gulch, Califomia Gulch Superfund Site

Received from Ben Arndt

10. Comment: Based on discussions with the County Commissioners, one ofthe main issues driving the proposed tailings pile cap and consolidation option is due to the political conflict between the Bureau of Reclamation (BOR) and the Environmental Protection Agency (EPA). The BOR apparently wants to limit treatment of mine waste water through the Marian Shaft per the previous 2003 ROD. Presently there is congressional legislation so the two agencies will cooperate in some manner.

Response: Noted.

11. Comment: The EPA June 2010 information sheet summarizes alternatives from a 2002 Focused Feasibility Study that is very similar to a HDR Study from September 2002 which outlines in Section 7.3 - Detailed Analysis of Remediation Alternatives for OU 6 which include: a. Alt 1. No Further Action b. Alt 2. Acid Rock Drainage Conveyance Storage and Treatment options to either in-place YAK or LMDT treatment facilities. c. Alt 3. In-situ Chemical Stabilization d. Alt 4. Cap and Consolidate (No Shotcrete Option is provided) e. Alt 5. Excavate, Transport and Dispose

The HDR Study describes many altematives. It seems the community at this time has been given variations of Alternative 4 - Capping and Consolidation.

Response: Noted. The 2002 Focused Feasibility Study and the HDR Study are the same document. The numbering ofthe altematives does differ in the 2002 Feasibility Study and the 2003 ROD.

12. Comment: Greenback crib walls and Pyrenees Head Frame. The greenback crib walls are a very important historic feature when biking or skiing along the mineral belt trail. Initially I was told these walls are not in the current OU 6 remediation plan, but based on the EPA 2009 and 2010 Fact Sheets they appear to be at the center of the proposed mitigation for the Greenback Area. The crib walls represent history to me. I can bike with my 7 year old and see, touch, smell and really have a connection to the mining past. If these walls are removed and replaced with cribbing that was recently constructed near the Denver City, then the Leadville Community will have lost even more of its mining heritage, and in my opinion, will degrade its historic importance.

Response: Noted.

13. Comment: What is the extent ofthe problem ofthe ARD introduced into the LMDT?

Response: The only significant source in 0U6 is the leachate generated by infilfration of snowmelt and rain thm the piles in the proposed work area. Since the waste rock piles were constmcted this leachate has infiltrated into shallow mine workings in upper Sfray Horse Gulch and in Evans Gulch. Once m the shallow mine workings -some ofthe leachate finds its way to the LMDT and mixes with the main inflows to the LMDT -bedrock groundwater. Groundwater in the bedrock formations that underlie upper Stray Horse Gulch and the adjacent part of Evans of Evans Gulch is typically good quality with near neufral pH. Groundwater in the mine pools below Graham Park - (immediately SE of RES) is also fairly neutral.

30 Amendment to 2003 ROD September 2010 0U6 Stray Horse Gulch, Califomia Gulch Superfund Site

14. Comment: What evidence is there that ARD materials may discharge into streams or rivers as alleged in the EPA June 2010 Sheet? a. The Groimd Water Hydrology Report goes on to further say "Other than the detection of tracer at the Robert Emmet Shaft and LMDT portal, dye has not been detected at any other surface water or ground water monitoring locations including well NW5D in the Pendery Fault (consistent with the estimated ground water travel time along the fault) ".

Response: Several years ago when the LMDT mine pool was it highest, EPA saw evidence that the LMDT mine pool is hydraulically connected with the GAW shaft. Several seeps and springs in Califomia Gulch occurred due to the increased flow from seeps and springs.

15. Comment: Why can't the surface water runoff be conveyed and treated by surface means as outlined in Alternative 2 ofthe HDR report by one oftwo in-place treatment facilities that were specifically constructed for treating mine water waste (does this involve the federal agency conflict and/or unwillingness to negotiate with the treatment operators)?

Response: Each ofthe altematives suggested by this commenter would require the constmction of a substantial retention pond to hold all the contaminated water generated during spring mnoff or substantial storm event. This component of these altematives, on balance, made these altematives less implementable. At this point in time, EPA believes preventing the generation of ARD is the most sustainable option.

16. Comment: Will the pending congressional legislation to have the BOR and EPA cooperate make it possible to treat ARD surface discharge at the LMDT Treatment Plant?

Response: EPA does not comment on pending legislation.

17. Comment: If the in-place treatment plants cannot be used, then temporary portable mine water treatment plants are available that can treat for a designated time period, in this case typically between April and June. Has a cost comparison been done of portable treatment vs. the proposed tailings options? I am aware of one such portable treatment plant that is being proposed for mitigation of mine waste water during construction ofSH119 south ofBlackhawk in North Clear Creek?

Response: EPA prefers a more permanent solution with lower future operations and maintenance costs. In addition, there is the problem that the contaminated water cannot be treated as fast as it is generated during this time of year, so some means of storage ofthe many millions of gallons of contaminated water generated must be constructed.

18. Comment: Have other options been reviewed as outlined in Altemative 3 ofthe HDR report, such as treating the surface ofthe tailings with neutralizing modifiers? The EPA apparently contracted a small business to study the use of thiocyanate as an agent to control or prevent ARD (EPA contract number 68D00276). The study is found on an EPA web site http://cfpub.epa.gov/ncer_abstracts/index.cfm and reads as a quite promising solution "Final Report: A Novel Approach to Prevention of Acid Rock Drainage (ARD) ". Did anything come out of this EPA funded study that could be used at OU 6?

Response: EPA is concemed about using thiocyanate on a project of this scale/volume and the toxicity of thiocyanate to fish. There may be other situations at this Site (smaller scale, experimental projects) in the future where the use of thiocyanate may be appropriate.

31 Amendment to 2003 ROD September 2010 OU6 Stray Horse Gulch, Califomia Gulch Superfiind Site

Additionally, chemical stabilization would have a greater impact on historic waste piles in Sfray Horse Gulch than the capping proposed by EPA because the stabilizing agent would have to be completely mixed into the piles. This would entail plowing up the piles, probably repeatedly. Additionally, there is no guarantee that initial freatment would be effective so long-term effectiveness may be limited.

19. Comment: If no other option is found and the capping consolidation is pushed through, I would definitely vote for the Altemative 1: Natural Face with Partial Cap as a preferred altemative. As for Alternative 2: Shotcrete with no liner, in my opinion, the shotcrete option will create significant problems in the future for the community leaders due to cracking, staining, efflorescence, and degrading ofthe shotcrete in a low pH environment, even with concrete admixtures and modifiers. Additionally, the shotcrete option appears to be a recent proposal so it is unclear how effective this option would be.

Response: Noted.

20. Comment: Is the Pyrenees Mine Area going to be affected? The EPA Fact Sheet (June 2010) indicates it will not be affected, but a sentence near the end states "EPA plans to insure the integrity ofthe Greenback Cribbing and Pyrenees Head Frame ". Does this mean the Pyrenees Tailings will be affected also?

Response: Work may be conducted on the retention pond at the Pyrenees. No work is plarmed for the waste rock pile or the head frame.

21. Comment: Where is the site-wide repository going to be located at for OU 6? Will this be in an area of historical significance?

Response: The site-wide repository will be located where the current Borrow Area is just east ofthe Denver City Mine Site and north of Stray Horse Gulch Road. This area was excavated as part ofthe soil remediations for Operable Unit 9 Residential Soils.

22. Comment: Has a cost comparison be done between the capping alternatives? An $18 Million value is used but it is unclear which option?

Response: Each of the five waste rock piles varies in topography and geology. EPA believes that one capping altemative will not be appropriate in all situations. A combination of capping materials will be used. The estimate of $18 million takes this into consideration.

Received from Becca Katz

23. Comment: As a citizen of Leadville, I certainly support the desire to maintain mining heritage, especially as it serves to increase tourism and economic opportunities. I do not, however, support maintaining the appearance of mine waste at a cost to the environment, let alone to human health and safety. I also recognize that remediation to the piles (i.e. capping the piles or reducing their toxicity through in-situ chemical stabilization) is not mutually exclusive of maintaining their "historical" appearance.

Response: Noted

32 Amendment to2003ROD September2010 0U6 Stray Horse Gulch, Califomia Gulch Superfund Site

Received from Bill Klauber

24. Comment: Reason for the ROD Amendment The EPA reasoning hinges primarily on the uncertainty of contaminant transport from Mine Pool to LMDT treatment plant. I disagree with this reasoning.

Response: EPA and the State are seeking a permanent solution to the problem ofthe generation of acid rock drainage. EPA and the State believe that allowing the perpetual generation of millions of gallons of ARD that require perpetual treatment is not a sound, cost effective altemative that is protective of human health and the environment.

25. Comment: First, the various dye tests have shown that the overwhelming majority ofthe dye does arrive in a short period of time at the plant. There should be a reasonable expectation of dilution and adsorption/absorption affecting the remainder ofthe dye en route.

Response: Dye test have shown that 40 to 60 % ofthe dye reaches the portal.

26. Comment: Second, the collapse ofthe tunnel and the failure to bulkhead it at the margins of the stoped areas ofOU6 are the primary reasons for dilution and impeded drainage and dye retardation or adsorption. These are engineering problems that need to be addressed rather than run away from.

Response: EPA acknowledges that collapses exist in the tunnel and acknowledges that there may be engineering fixes to issues with the LMDT. However, even if bulkheads were placed in the LMDT, there would still be concems with using the LMDT mine pool as the storage facility for ARD from OU6. EPA and the State believe that the prevention of ARD generation is the best long-term altemative with the fewest long-term uncertainties.

27. Comment: Third, the statement that the existing remedy in 0U6 has been mostly successful is not true. Shallow groundwater, both influent to and effluent from the waste piles and engineered remedies is completely ignored in the current fix.

Response: The existing remedy has been successful in reducing the release ofthe contaminants of concem into Stray Horse Gulch.

28. Comment: Enhancement ofthe Clean Water Diversion System

Control of surface water flows (overlandflows), both influent and effluent, is cheap, and should always be implemented first. It is unlikely that overlandfiows are responsible for much ofthe ARD, however, since most ofthe soils are quite permeable and infiltrate water easily. Overland flows are relatively rare in most undisturbed soil areas in Lake County, except briefly when the ground is frozen and saturated.

The Mahala is a good example of what is actually most important relative to ARD from the waste piles. Although capped by the EPA, the Mahala continues to visibly seep ARD. The water source is not through infiltration, but through shallow groundwater flow intercepting the base ofthe pile. Virtually all ofthe capped and uncapped piles are on hillslopes, where shallow groundwater can flow into and through their lower portions. Shallow groundwater flow is not limited by the direct infiltration area above, but by the area ofthe entire upstream watershed, which may be orders of magnitude greater.

33 Amendment to 2003 ROD September 2010 OU6 Stray Horse Gulch, Califomia Gulch Superfund Site

Just because the Maid of Erin or Wolftone or Hamms do not show visual surface seepage does not mean that they are not contaminating the shallow aquifer. It just means that any groundwater-caused ARD continues on beneath the ground surface, instead of being forced to the surface by a local impermeable layer as imder the Mahala. Absence of visual surface seepage does not indicate success ofthe remedy.

Similarly, the uncapped waste piles to the east are also on slopes in formerly marshy areas. They probably generate almost all of their ARD from groundwater flow during spring runoff, when perched water tables are high. The principal solution there is also through control of shallow groundwater flow, not through surface capping methods.

Response: The proposed modification to the remedy will be prioritized and sequenced in the following manner. First, clean water will be kept clean. The existing diversion system will be examined and redesigned to maximize the amount of water that is kept away from the waste rock piles and divert clean water into existing natural drainage systems in the area. Next, based on the results ofthe clean water diversion and testing of waste rock for heavy metal concentrations, the areas with the highest contamination would be capped. The need to maintain the historic appearance and natural topography ofthe waste rock piles would be taken into consideration. Third, the retention ponds and the contaminated diversion system would be designed based on the anticipated results ofthe capping. This is a phased approach.

29. Comment: Shallow Groundwater Control Shallow groundwater control may be achieved through horizontal drains, through vertical pumped wells, through deep cutoff trenches, or through combinations of those methods. Trench drains would be most effective, and may also incorporate infiltrating surface swales

Response: Noted.

30. Comment: Capping of Waste Piles Capping ofthe OU6 waste piles, which are the most accessible examples for mining heritage tourists, should only be considered as a last resort, where no other method will work and where the ARD is volumetrically significant. I do not believe that any ofthe OU6 piles will meet those criteria after technically rational methods (shallow groundwater control) are implemented. The entire effort should be redirected toward the implementation of shallow groundwater control, monitoring ofthe results over a period of years, and only then evaluating the results and deciding if further action is necessary. Capping should be absolutely a last consideration, only after several years of monitoring ofthe effectiveness of all other remedies and finding none to be effective, and only with the concurrence ofthe County.

Areas that have been fouled by EPA dumping of Ponsardine wastes should be buried in the repository rather than capped. The Ponsardine removal was an ill-considered action that created additional ARD problems in the RAM area.

Response: See Response to Comment 28.

31. Comment: Enlargement of Evaporation Ponds Evaporation ponds are a negative feature of the Draft OU6 ROD amendment. If influent overland flow and shallow groimdwater are fully controlled, then they may be properly sized, but otherwise, the effluent flow may exceed their capacity. Sludge would have to be periodically removed and taken to the repository. Their presence would have a negative effect on the mining heritage area. Negative effects on the local

34 Amendment to 2003 ROD September 2010 0U6 Stray Horse Gulch, Califomia Gulch Superfund Site tourism economy should be an integral part ofthe economic and social cost analysis of such a system. County wishes should be honored in this respect.

The large evaporation pond concept seems destructive and poorly considered. A small out ofthe way pond, as is currently in place, with overflow to the Mine Pool, should be adequate for process holding requirements.

Response: See Response for Comment 28.

32. Comment: If the Mine Pool and/or surface runoff from 0U6 are not adequately drained by the LMDT, the water source for much ofthe county population may be contaminated through the alluvial aquifer. Yet there is no provision for the EPA enforcing the continued operation ofthe LMDT and its treatment plant. This is a serious shortcoming that should be addressed by the 0U6 ROD amendment. The LMDT and its treatment plant should be annexed into 0U6 or OUl2 to ensure its future operation, although its configuration should change.

It is clear that the LMDT and its treatment plant are in need of improvement As it stands now, the upper portions ofthe tunnel, above the bulkhead and pump, are mostly collapsed and may soon be fully collapsed, as indicated by the pressure and flow data from the tunnel. When collapse is complete, the BOR will either have to make the above adjustment itself, or be forced to do so by the EPA. This future certainty should be addressed now instead of on an emergency basis.

Response: The water source for much ofthe county population comes from the Canterbury Tunnel. In 2008, a study conducted by the U. S. Geological Survey for the State determined that there is not a substantial hydrological connection between the Canterbury Tunnel and the LMDT. (USDOl 2008a)

Additionally, discharges from the LMDT and the freatment plant are subject to regulation under the Clean Water Act. The current discharges from the freatment plant are subject to a National Pollution Discharge Elimination System permit issued by EPA's Water Program.

33. Comment: If the current plant is to be maintained, the collapsed and collapsing portions of the upper tunnel need to be bypassed, and Mine Pool water pumped directly from the area ofthe Robert Emmett and Marian to the treatment plant. This would result in much smaller volumes of water to process, and allow most ofthe uncontaminated water tofiow on by gravity flow to the river. The contaminated water would have much higher metal contents, undiluted by the runoff flows, and probably require a modification in the treatment process.

Response: EPA agrees that the BOR should seek to eliminate as much clean water as possible from its freatment plant influent and agrees that if the characteristics ofthe influent changed the freatment process would probably need modification.

34. Comment: The use of LMDT treatment ofOU6 contaminants on an emergency overflow basis only, instead of a routine basis, is a major waste of time and money and resources. The large evaporation pond will create an eyesore at a critical tourism location, and continue to depress the local economy. The evaporation pond will have to be cleaned of its poly-metallic sludge on a regular basis, ensuring it will always be ugly.

Since treatment of a more concentrated but lower volume wastewater stream would require a significant change in the LMDT process, a unique opportunity would arise. Why not build a new

35 Amendment to 2003 ROD September 2010 0U6 Stray Horse Gulch, Califomia Gulch Superfund Site plant right in OU6, and eliminate the existing plant and most ofthe tunnel altogether. OU6 contaminants could be processed directly at the surface as the first priority, with seasonal overflows to the Mine Pool. Mine Pool water would be pumped up to the surface for treatment as a second priority. The plant could be located a few hundred yards away back in the trees near the repository. No worries about the red herring complaints of losses enroute to the portal And the sludge could be put to rest a few yards away in the proposed repository. All it takes is aUAO from EPA to BOR

Response: Noted.

35. Comment: I am very concerned that BOR will gradually try to disengage from their treatment plant process, perhaps by simply sealing the tunnel at some time in the future, or by letting it completely collapse and doing nothing about it. I totally disagree with the stated concept of Carol Campbell that long term functioning ofthe LMDT plant is undesirable or untenable. The plant needs to be relocated and updated into the 21"' century, downsized, automated, and improved. The jurisdictional squabbles among EPA, BOR and CDPHE regarding the future operation ofthe LMDT constitute a failure in leadership by those agencies. This issue should be taken up at the highest levels ofthe departments to overstep the petty concerns ofthe regional bureaucrats who are currently making the remedial and operational decisions.

Response: Noted.

36. Comment: Treatment System The LMDT treatment plant is the current treatment method. It treats a volume of water which is huge because the majority ofthe influent is clean runoff from the annual spring melt. This system should be modified to collect only the Mine Pool effluent plus whatever contaminated effluent comes from the OU6 waste piles and engineered remedies. This low volume, high concentration ARD would require a modified system, and the precipitated sludge from that system should be studied for potential economic recovery of metals, since it constitutes, in effect, an in situ leaching mining process.

The construction of a new treatment plant of smaller hydraulic capacity but greater contaminant removal capacity in the repository area would be ideal. During periods of high effluent flow from the waste piles, it would treat the waste pile effluent as highest priority, achieving full capacity by filling in with Mine Pool water pumped from very nearly right below. During periods of extreme effluent flow exceeding plant capacity, the excess effluent would go down to Mine Pool. During periods of low effluent flow from the waste piles, the plant would process mainly Mine Pool water. The old treatment plant and the LMDT north of station 66+00 could be abandoned completely, and the tunnel plugged in that area. The area between 66+00 and the Robert Emmett may be separately bulkheaded and monitored for ARD accumulation, and then pumped to the treatment plant if necessary.

Response: Noted.

37. Comment: Monitoring of Results via OUl 2 Monitoring Plan Monitoring should be greatly expanded, so that everyone can really understand the actual physical situation, rather than guessing, which seems to be currently in vogue at the EPA.

Response: Noted. EPA will continue to evaluate monitoring data and remedy protectiveness through the five-year review process, although there will always be come uncertainties in a landscape as complex as the Sfray Horse Gulch area.

36 Amendment to 2003 ROD September 2010 0U6 Stray Horse Gulch, Califomia Gulch Superfund Site

38. Comment:. ROD Amendment should not be finalized until more information is gathered after clear water diversions are in place.

Response: EPA, through Sourcewater Consulting, is conducting a hydrological investigation during the spring seasons of 2010 and 2011 with the option of a third year in 2012. The results will be used in the design phase. Additionally the design/implementation will follow a prioritized, phase approach, as described in Comment 28.

39. Comment: Site-wide Repository in OU6 It's about time. And it should be positioned above the Marion area, so that any leakage would be collected right back into the system.

Response: The site-wide repository will be located where the current Borrow Area is just east of the Denver City Mine Site and north of Sfray Horse Gulch Road. This area was excavated as part ofthe soil remediations for Operable Unit 9 Residential Soils.

40. Comment: Least cost or cost/benefit decisions The EPA finds it very easy to make their decisions on a least cost (to the EPA) basis, rather than a total societal cost that includes the economic well-being ofthe local citizens of Lake County. This approach is morally wrong, and should be corrected. Coimty Commissioners should be much more important partners in these decisions than at present. The draft ROD Amendment should reflect an approach that is acceptable to all parties before it is even presented as a draft.

Response: CERCLA and its implementing regulations, the NCP, provide the legal parameters that EPA is required to consider in making a remedy decision. Under this legal framework, EPA may have to choose and move forward with remedy decisions that are not acceptable to some members ofthe community. Acceptance of a proposed plan by all community members is a goal that is rarely, if ever, achieved.

41. Comment: Community Involvement The EPA Citizens Advisory Group, as implemented by the EPA in Lake County, was eye candy that was configured to subvert the genuine involvement process and to rubber stamp whatever the EPA wanted to do. It was used to conduct an end run around the truly involved citizens who had substantive comments and opinions that differed from those ofthe EPA. This effort should be completely abandoned, the contract with Meridian terminated, and the biased results completely ignored. Keep the PR people (EPA's community involvement people) out of the project. The best community involvement is when the technical EPA people, like Stan Christensen before, and like yourself now, talk directly with the local knowledgeable citizens and commissioners, then sit down around a big table and work out an acceptable plan together, and finally publish a well-rounded draft for the entire community to comment on.

Response: EPA is required to publish a public notice, conduct a public meeting, provide a public comment period, obtain a meeting transcript and develop a responsiveness summary as part of a proposed plan process. EPA met these requirements. Given the site history, EPA also engaged the community using fact sheets, regular community visits, one-on-one meetings, speaking at civic groups and regularly briefing local officials and opinion leaders. At the request of local officials, EPA provided administrative support for the community to consider a Community Advisory Group (CAG). Due to divisions within the community, it was not possible to form a CAG so EPA developed a web site which was the basis for the "Virtual Fomm," a means of providing comments via the Intemet, and held numerous public input sessions.

37 Amendment to 2003 ROD September 2010 0U6 Stray Horse Gulch, Califomia Gulch Superfund Site

42. Comment: Technical Advisory Group (TAG) No technical advisory funds were made available for the local citizens to conduct their own independent review ofthe 0U6 problems. This created a one-sided process in which the citizens had no effective voice. It is hard to fashion alternatives when the only budget is for data collection to support a solely EPA-contrived plan. The absence of a funded TAG renders substantive community involvement a fantasy.

Response: The TAG grant process is available for all active Superfiind sites. EPA shared information about Technical Assistance Grants (TAG) at public meetings to discuss formation of a Community Advisory Group in summer 2009. Information about the grants was also provided to local elected officials. No organizations applied for a grant.

43. Comment: Mitigation for Historical Site Disturbances and Tourism Effects In my opinion, any mitigation should be directly related to the problem at hand and not just thrown out as a sop to the community as a bone is thrown for a dog. Stabilization and accurate restoration of remaining historical 0U6 structures would be a reasonable undertaking. None ofthe mitigation work should be Disney-ish or artificial or glitzy or diorama-like, in my opinion.

I believe that construction of access structures, such as paved walking paths with explanatory signs among some ofthe historically accurate remains would serve a dual purpose. It would allow tourists to experience the area in a directed and controlled and educational manner, and it would reduce the inclination of tourists toward random or uncontrolled exploration of other, potentially dangerous, remains in other areas. The OU6 area is a prime candidate for such work.

Response: Noted.

44. Comment: I have reconsidered the issue of making the current engineered wedding cakes more realistic in coloration and I now feel that that is a very secondary mitigation priority. After all, they are not original, and they reflect a distinctly modern era of EPA remediation efforts, so their standout nature is not troubling to me.

Response: Noted.

45. Comment: I strongly support a well-done effort, even if the EPA needs to stay another 10 years to accomplish it.

Response: Noted.

Received from Greg Race

46. Comment: I'd first like to state that I firmly agree with the intention ofthe Proposed Plan to eliminate the use ofthe LMDT for water treatment except in the case of an extreme flooding event. Improving the clean water diversions and enhancing the retention ponds below the identified waste piles seem to be a logical step as is constructing a permanent site-wide repository, although I haven't been able to ascertain where that repository might be constructed. My primary concern though, is how exactly the four waste piles will be capped and consolidated.

Response: Noted. The site-wide repository will be located where the current Borrow Area is just east ofthe Denver City Mine Site and north of Sfray Horse Gulch Road. This area was excavated as part ofthe soil remediations for Operable Unit 9 Residential Soils. Also see response to Comment 28.

38 Amendment to 2003 ROD September 2010 0U6 stray Horse Gulch, Califomia Gulch Superfund Site

47. Comment: As an athlete and outdoor person with a general disdain for environmental destruction, whether through large-scale development, road building, intensive extractive industrial processes, etc. I see a very real benefit to the environment, and the flora and fauna that inhabit it- including us humans- to fully prevent ARD from occurring by consolidating and capping the indentified mine waste piles completely. As a historian and conservationist, however I see a unique opportunity to not only preserve the historic scars of mining- waste piles and built structures alike- to tell the story of unsustainable extractive practices to fixture generations. We live in a culture that continues to revere unrestrained consumption without regard for any potential deleterious impacts that might be created through the unmitigated process of plodding full-steam ahead. Culturally we 've inherited that mindset from our laissez-faire capitalistic Victorian-era industrialist predecessors, and though we 're less genocidal than our forebears we 're outdoing them in the abuse of our earth herself.

Response: Noted.

48. Comment: I see two alternatives. A no-holds-barred remedial approach where mine waste piles are entirely reclaimed using the best practices available including re-grading and re- vegetating with native trees to a pre-mining condition. The other approach is to remediate with a mind toward accurate historic preservation. Falling somewhere in between seems to compromise the goal of preserving the environment from further contamination, or conversely destroying historical treasures. A contentious example of the folly of attempting to unite such disparate objectives is typified by the wedding cakes. I lived in Leadville when the haul trucks were halted by the Clouber-Miller show live on 9News and the politically negotiated settlement lead to a remedy that serves no historical purpose. While it is a solid, maintainable solution, the capping could have been achieved much more economically, with less drama, and in a much more aesthetically pleasing way if the original construction plan were followed. It makes no sense in my mind to use shotcrete or, inert materials with or without a liner to attempt to recreate something that never existed, and consequently has no real significant cultural value- the waste piles were sulfides, not dolomite. I sure hope that we don't re-create another wedding cake type remedy for the four waste piles identified in the Proposed Plan.

Response: Noted.

49. Comment: The Greenback waste pile and crib walls, as well as the Pyrenees waste pile and head frame are the most important historic features within the project area to the character ofthe Mineral Belt Trail and to the expectation of visitors to the mining district looking for clues and remnants of archaic industrialism. These features should be preserved to the greatest extent possible. If the least visible parts ofthe waste piles need to be lined and capped they should done with as little disruption as possible to the site. It seems to me that if the goal is to preserve the historic integrity ofthe site, larger clean water diversions and retaining ponds ought to be the primary engineering objective. If the ARD cannot be managed through diversions and evaporative retaining ponds, only then should capping be implemented.

Response: Noted.

50. Comment: Historic Mitigation I have some very specific suggestions about mitigation for consideration for the Procedural Guide, all of which relate to the Mineral Belt Trail. As previously mentioned, interpretive signs which convey the process of mine site reclamation are completely missing from the MBT narrative. The current interpretive elements only allude topre- WWII history. Consequently, visitors to the Leadville Historic Mining District don't know about the rich EPA Superfund story itself, which represents a significant component ofthe history ofthe

39 Amendment to 2003 ROD September 2010 0U6 Stray Horse Gulch, Califomia Gulch Superfund Site mining district. The story needs to be told, either through additional signage or in combination with additional paved spur pathways off the main trail alignment.

The trail grade running up to the j"" street bridge abutments we not properly compacted when the trail was originally constructed, and consequently the trail surface has subsided over time leaving hazardous lips on both the north and south approaches to the bridge. Since repaving is proposed from this bridge to the south, please consider repairing the north approach as well.

The westerly Greenback crib wall doesn 't fully contain the mine waste from falling onto the MBT, especially during spring when the soil is super-saturated. Mud fiows onto the trail from both the north and south side of this westerly wall. In addition, there is no drainage to speak of along the base ofthe crib wall which makes this section of trail very maintenance intensive. The easterly wall has a similar issue along its southern edge. Additional cribbing is needed.

I understand that EPA typically only entertains mitigation suggestions within the OU that the remediation is affecting historic resources, but I urge you to consider mitigating other trail issues which actually lie within OU 4. When the trail was initially constructed by EPA contractors along the northern side of California Gulch- through the A. Y. and Minnie Mines- the steep slopes were not adequately prepared. Presently, two sections of trail, approximately one hundred feet long are in imminent danger of sliding off the mountain side. There is no shoulder left in these areas, and the asphalt is crumbling away down the embankment. Not only is this a hazard to trail users, but it is also a considerable construction undertaking that the Lake County govemment could not have foreseen when it took responsibility for maintaining the trail. Additional concerns along this same quarter mile stretch of trail are that the northerly retaining walls do not contain rockfall and mudslides in the winter months which make grooming the trail for skiers damaging to CMC's and Lake County's grooming equipment- snow cats aren 't designed to groom rocks and mud. Lastly, the trail has an erosion/drainage issue at the bottom of this section on the north side ofthe trail, about 100' to the west of mile marker six. Again, I understand that these maintenance issues are in OU4, however, the continued functioning ofthe trail in its entirety is directly related to mitigating resource disruption a little over a mile down the trail in OU 6. If the EPA wishes to analyze these concems, I'm happy to guide a site visit with members ofthe MBT Committee. -

I'd like to make a final comment about mitigation. While I appreciate the suggestion of stabilizing built structures as a component of mitigation, the continual loss of myriad structures in Finntown and elsewhere in the mining district due to vandalism and arson leads me to believe that money is better spent on the ground, so to speak. Once Lake County has sufficient law enforcement capabilities and an active group of historic preservationists to care for such amenities then perhaps enhancing these structures will make sense. Presently, neither the property owners nor our elected officials seem to have any ability to provide enduring security for these structures.

Response: Noted.

51. Comment: Institutional Controls Lake County doesn't regulate OHV use, quite the contrary. In fact, the commissioners recently adopted resolution 10-13, which encourages the use of unlicensed vehicles on all roads in Lake County, excepting state highways. This means that OHV's are allowed on un-postedprivate lands within the county, which obviously include EPA remediated projects that don't have posted signs on them. Most ofthe signs that EPA has installed in the past have been ripped down. With this in mind, institutional controls should deal with this issue, including performance and enforcement provisions. There seems to always be talk about allowing development on the east side of Leadville. Strong institutional controls should be

40 Amendment to 2003 ROD September 2010 OU6 Stray Horse Gulch, Califomia Gulch Superfund Site adopted, to not only prevent the disruption of EPA's remedies, but also to prevent ill-considered development which will put an uninformed public at risk. As more mine workings collapse, the area's hydrology will continue to change. Providing water and sanitation to service whatever type of development might occur in the future should be incorporated into any institutional controls, the EPA should help facilitate this process.

Response: Noted.

Received from WilHam H. MacFaden

52. Comment: In your paragraph titled "Historic Mitigation", I would prefer you use "shall" rather than "may restore head frames, etc.". The word "may" intimates you have no intention of any restoration.

Response: Noted.

Comments regarding Pilot Study of Capping Techniques received during Public Comment Period

Received from Becca Katz

53. Comment: With the understanding the capping the mine tailings piles is the best option (based on EPA analysis) and that all 5 alternatives are feasible, I believe that the order of priorities should be as follows: 1) Most EFFECTIVE capping solution, 2) appearance 3) cost. With this in mind, I think both the shotcrete and the inert rock look fine, and I believe they would be more effective/secure w/a liner. However, my opinion on which option I like is not well informed. As someone who would like to evaluate the options based on the three criteria mentioned above, I would like to see more available information comparing and contrasting the different capping alternatives on a basis of efficacy and cost. I can obviously go look at the Denver City Mine Tailings Pile and figure out which option I think looks the best, but I do not know which option *works* the best, which is the most important thing to me.

Response: Noted. A final report ofthe Pilot Study at the Denver City Mine Site will contain technical data on the efficiency and cost of each capping technique.

Received from Marci Stassi

54. Comment: I believe that if one of the four listed altematives is used, it should be U4. Rustic looking cribbing done well is beautiful. The original wood structures would have looked as nice when they were installed 100+ yrs ago. Surface areas are a different ball game. You could use surface decking in wood or cement. Recycled, green friendly!! Top that surface with historical, interactive, and healthy exhibits. A place people can lock up their bike and engage in some sort of physical activity. Solar powered lights that could be used to illuminate a basketball court, picnic area, covered structures for outside classes or meditation that could resemble the old structures with a modem twist. Something different that the tourists will come to see and that the locals can use!

Response: Noted.

41 Amendment to 2003 ROD September 2010 0U6 Stray Horse Gulch, Califomia Gulch Superfund Site

Received from Barb Arnett

55. Comment: The shotcrete used at the Denver City is about as unnatural a covering as I have seen. I would be interested in someone from the EPA coming to Leadville and driving me to ANY other mine dump in the mining district that is as smooth as those are. If that is what is used, that will destroy forever the mining district in Leadville. Some ofthe other remedies are more palatable, if indeed a remedy is needed. I am still looking for specific evidence that anything needs to be done. Is there a study indicating that water is being contaminated from the runoff NOT going into the Marion? Where do I find that?

Response: There is visual evidence (staining ofthe drainage ditches) ofthe Marion Pond overflowing and going into the Starr Ditch drainage system.

56. Comment: The cribbing is also out of place at the Denver City. It is quite obvious that it was recently put into place. That does not accurately portray the mining district. If you must put cribbing in, why don't you weather the wood? Mother nature does an outstanding job up here and wood left out for several winters would much more easily fit into the district. That cribbing is an eyesore on the Mineral Belt Trail and should be removed or replaced with something that is more accurately a product of our mining heritage.

Response: EPA has seen weathering occur in the past nine months. Weathering will continue to occur.

Received from Audrey Kruse

57. Comment: I went and saw the potential capping approaches on the Mineral Belt Trail. I feel that the most important approach to this process is to do whatever most effectively stops the acid mine run-off from going down toward Leadville and into our water system. Therefore, I think that the shotcrete option is the best option.

On another note, I have an altemative suggestion: I think many ofthe piles along the Mineral Belt (those which are less-historically important) can be capped with shotcrete and then, rather than painting them to mimic tailings and waste rock piles, commission local artists to paint their work on the piles.

Response: Noted.

Received from Richard Silkey

58. Comment: The altemative capping types look very realistic and should be used to keep the historical setting. I don't seem to have a preference, I looked at them the other day and they all looked good to me.

Response: Noted.

42 1 Tabic 2.0 1 1 Chemical-Specific ARARs _|

Relevant and Standard, Requirement or Criteria Description Applicable Comment Appropriate

FEDERAL | Clean Water Act (33 USC Sect. 1351-1376) Requires EPA and states to establish ambient Federal (or State) fi-eshwater AWQCs are not considered to be ARAR as the remedial 1 Ambient Water Qiialily Criteria (40 CFR Part 131; water quality control criteria (AWQC) and action objectives for 0U6 as identified in the CD requires reducfion in metal loading Quality Criteria for Water, 1976, 1980, 1985, 1987; standaids, respectively, for surface water to the watershed from source areas. Specific numerical performance standards within Ambient Water Quality Criteria for Seleniiun, 1987) based on use classifications and the criteria No No the OU are not part ofthe RAO's. Achievement of chemical-specific numerical 1 stated under Sections 304(a) and 303 ofthe performance standards will be addressed under the site-wide surface and groundwater Clean Water Act. operable unit (12). Clean Air Act (42 USC Sect. 7401-7642) National Establishes ambient air quality standards for National ambient air quality standards (NAAQS) are implemented through the New 1 Ambient Air Quality Standards (40 CFR Part 50) certain "criteria pollutants" to protect public Source Review Program and State Implementation Plans (SIPs). The federal New health and welfare Source Review program address only major sources. Current air emissions from No No undisturbed mine waste are below a level of concem per EPA's Baseline Human 1 health Risk Assessment, Part A (1996). Emissions associated with remedial action are addressed under Action-specific ARARs. National Emissions Standards for Hazardous Air Establishes emission standards for certain NESHAPs are a subset ofthe Clean Air Act. NESHAP's is not considered to be 1 No No Pollutants (40 CFR Part 61) industrial pollutants and sources. ARAR. 1 iNational Primary Drinking Water Standards Establishes maximum contaminant levels MCLs are applicable for drinking water at the tap and may be relevant and 1 40 CFR Part 141 (MCLs) for specific contaminants which are appropriate for drinking water sources. However, remedial action objectives for 0U6 FR 8750(1990) health-based standards for public drinking as identified in the CD requires reduction in metal loading to the watershed fi-om water systems. source areas. Specific numerical perfonnance standards within the OU are not part of No No the RAO's. Achievement of chemical-specific numerical perfonnance standards will be addressed under the site-wide surface and groundwater operable imit (12). Further, the Leadville water supply located in the Evan's Gulch watershed consistently meets MCL's. 1 National Secondary Drinking Water Standards 40 Establishes secondary maximum contaminan SMCLs may be applicable for drinking water at the tap and relevant and appropriate 1 CFR Part 143 levels (SMCLs) which are non-enforceable for drinking water sources. However, remedial action objectives for 0U6 as identified guidelines for public drinking water systems in the CD requires reducfion in metal loading to the watershed from source areas. to protect the aesthetic quality ofthe water. No No Specific numerical performance standards within the OU are not part ofthe RAO's. Achievement of chemical-specific numerical performance standards will be addressed under the site-wide surface and groundwater operable unit (12).

1 Maximum Contaminant Level Goals (MCLGs) Establishes drinking water quality goals set MCLGs set above zero levels may be relevant and appropriate at the tap. However, 1 PL No. 99-339, 100 Stat. 642 (1986), FR 8750 at a level at which no adverse health effects remedial action objectives for 0U6 as identified in the CD requires reduction in metal 1 (1990) may arise with an adequate margin of safety. loading to the watershed fi"om source areas. Specific numerical performance standards No No witliin the OU are not part ofthe RAO's. Achievement of chemical-specific niunerical performance standards is addressed under OUl 2 Site-wide surface and groundwater quality. | RCRA LDRs are not applicable to mine wastes because the materials have been identified as extraction or beneficiafion wastes that are specifically exempted from the RCRA Land Disposal Restrictions (LDRs) (40 CFR Prohibits land disposal of RCRA hazardous No No definirion of a hazardous waste. Further, waste placement pre-dates the RCRA. A Part 258) waste without treatment. discussion of LDR's as ARAR for treatment residuals (water plant sludge and impoundment sediment) is provided under Action-Specific ARAR's. 1 Identification and Listing of Hazardous Wastes 40 Identifies those solid wastes which are Mine wastes are not hazardous wastes because the materials have been identified as 1 CFR Part 251 subject to regulation as hazardous wastes extraction or beneficiation wastes that are specifically exempted from the definition ol 1 imder Parts 262 through 265, 268, and Parts a hazardous waste. Further, waste placement pre-dates the RCRA. A discussion of 1 270, 271, and 124, and which are subject to LDR's as ARAR for treatment residuals (water plant sludge and impoundment 1 No No the notification requirements of Section 3010 sediment) is provided imder Action-Specific ARAR's. 1 of Resource Conservation and Recovery Act of 1976 (RCRA). Table 2.0 ChemicakSpecific ARARs .. .

Relevant and standard, Requirement or Criteria Description Applicable Comment Appropriate STATE 1 Colorado Water Quality Control Act C.R.S 25-8- Establishes Statewide Water Quality State freshwater WQSs are not considered to be ARAR as the remedial action 101 et seq., 5-CCR-1002.3I - Basic Standards and Standards objectives for 0U5 as identified in the CD requires reduction in metal loading to the Metliodologies for Surface Water watershed from source areas. Specific numerical perfonnance standards within the No No OU are not part ofthe RAO's. Chemical-specific numerical perfonnance standards are addressed under 0UI2 Site-wide surface and groimdwater quality.

Cunent air emissions from imdisturbed mine waste are below a level of concem per Provides authority to the Air Quality Control EPA's Baseline Human health Risk Assessment, Part A (1995). Emissions associated Commission to establish ambient air quality Colorado Air Pollution Prevention and Control Act with remedial action are addressed under Action-specific ARARs. standards, and to the Air Pollution Control No No C.R.S. 25-7-101 Division to establish emission limitations to ensure good health in the public at large. 1 Table 2.1 1 Location-Specific ARARs |

Relevant and Standard, Requirement or Criteria Description Applicable Comment Appropriate

FEDERAL | Appendix A (E.G.. 11988 Protection of Requires federal agencies to evaluate the potential Portions of 0U6 lie within a 100-year floodplain,! Floodplains) effects of actions they may take in a floodplain to however, implementation of the selected remedy avoid, to the extent possible, adverse effects for 0U6 will not result in any development in the associated with direct or indirect development of a floodplain that will result in direct or indirect floodplain. Yes adverse impacts.

Appendix A (E.G.. 11990 Protection of Requires federal agencies conducting certain Wetlands are present in portions of OU6 as 1 Wetlands) activities to avoid, to the extent possible, the defined in a 1992 study by Woodward Clyde, adverse impacts associated with the destruction or however implementation of the selected remedy Yes loss of wetlands and to avoid support of new for 0U6 will not result in any construction or construction in wetlands if a practicable activities in any identified wetlands. altemative exists Clean Water Act Section 404 (33 USC 1251, et Requires Federal agencies to avoid, to the extent Wetlands are present in portions of 0U6 as seq; 40 CFR 230, 231) possible, adverse impacts associated with defined in a 1992 study by Woodward Clyde and destruction or loss of wetlands. Regulates the Stray Horse Gulch is considered "waters ofthe discharge of dredged or fill material into waters of Yes United States", implementation ofthe selected U.S. Consultation with the Regional Response remedy will not result in the discharge of dredge Team required. or fill material into waters ofthe United States.

Endangered Species Act (16 USC 1531 et seq; Protects endangered species and threatened Provides protection for threatened and 1 50 CFR 200, 50 CFR 402 species and preserves their habitat. Requires endangered species and their habitats. However, coordination with federal agencies for mitigation site-specific studies did not document the of impacts. presence of threatened or endangered species. If Yes threatened or endangered species are encountered during remedial activities in OU6, then requirements ofthe Act would be applicable. Migratory Bird Treaty Act (16 USC 703-712) Protects migratory birds, their nests, and eggs. If it appears that remedial activities may impact wildlife resources, EPA will coordinate with both Yes the U.S. Fish and Wildlife Service and the Colorado Department of Natural Resources. Fish and Wildlife Coordination Act (16 USC Requires coordination with federal and state If it appears that remedial activities may impact 1 661 etseq) agencies on activities affecting/modifying streams wildlife resources, EPA will coordinate with both or rivers if the activity has a negative impact on the U.S. Fish and Wildlife Service and the fish or wildlife. Requires coordination with federa Colorado Department of Natural Resources. and state agencies to provide protection offish Yes TMo and wildlife in water resource development programs.

Rivers and Harbors Act of 1899; Section 10 (33 Section 10 permit required for structures or work Stray Horse Gulch, Evans Gulch and Starr Ditch No No use 403, 33 CFR 320-330) in or affecting navigable waters. are not considered "navigable rivers." I Table 2.1 Location-Specific ARARs

Relevant and Standard, Requirement or Criteria Description Applicable Comment Appropriate

|National Historic Preservation Act (NHPA) (16 Requires the preservation of historic properties This Act is applicable as parts of OU6 are on the lUSC 470 et seq.; 36 CFR Part 63, Part 65, Part included in or eligible for the National Register of National Register and parts may lie within the 800) Historic Places and to minimize harm to National Leadville National Historic Landmark District. Historic Landmarks. Currently there are discussions about the development of a revised Programmatic Yes Agreement between the EPA, the Advisory Council on Historic Preservation, and the Colorado State Historic Preservation Officer in accordance with Sections 106 and 110(f) of NHPA. The Historic and Archeological Data Establishes procedures to provide for preservation A cultural resource survey was coinpleted in Preservation Act of 1974 (16USC 469) of historical and archeological data which might OU6 to identify historic properties which may be be destroyed through alteration of terrain as a affected by removal activity. EPA will preserve Yes result of a federal construction project or a historical and archaeological data encountered federally licensed activity program. during implementation ofthe remedy.

E.O.. 11593 Protection and Enhancement ofthe Federal agencies directed to institute procedures to This Act is applicable as parts of 0U6 are on the Cultural Environment (16 USC 470) ensure programs contribute to the preservation and National Register and parts may lie within the enhancement of non-federally owned historic Leadville National Historic Landmark District. resources. Consultation with the Advisory Council Currently there are discussions about the on Historic Preservation required. development of a revised Programmatic Yes Agreement between the EPA, the Advisory Council on Historic Preservation, and the Colorado State Historic Preservation Officer in accordance with Sections 106 and 110(f) of NHPA. The Archeological Resources Protection Act of Requires a permit for any excavation or removal If any remedial activity involves removal of 1979(16USC470aa-47011) of archeological resources from public lands or No Yes archeological resources; EPA will comply with Indian lands. the substantive requirements ofthe Act. The Historic Sites Act of 1935 (16 USC 461- Enables the National Park Service to preserve There are no features within 0U6 that are No No 467) historic resources for public use. eligible under the Act. Wilderness Act (16 USC 1311,16 USC 668; 50 Limits activities within areas designated as The site is not within a federally-owned area CFR 53, 50 CFR 27) wilderness areas or National Wildlife Refuge Yes designated as a wilderness area or a National Systems. Wildlife Refuse System. Wild & Scenic Rivers Act (16 USC 1271) Protects rivers that are designated as wild, scenic, The Arkansas River is not listed as a Wild and No No or recreational. Scenic River. Resource Conservation and Recovery Act Municipal Solid Waste Landfill (MSWLF) No MSWLF is included in the selected remedy. (RCRA), Subtitle D (40 CFR 258.10-15) Facilities where treatment, storage, or disposal of The selected remedy assumes that an on-site solid waste will be conducted must meet certain repository will be sited. Such a facility is not location standards. These include location No No being selected as part of this remedy. restrictions on proximity to airports, floodplains, wetlands, fault areas, seismic impact zones, and 1 Table 2.1 1 1 Location-Specific ARARs |

Relevant and Standard, Requirement or Criteria Description Applicable Comment Appropriate

IsTATE 1 IColorado Historical, Prehistorical and Establishes procedures and requires a permit for Archeological Resources Act (Colorado Revised investigation, excavation, gathering, or removal Statutes, Title 24, Article 80, Sections 401-411) from the natural state of any historical, prehistorical, or archeological resources on state lands for the benefit of recognized scientific or No No No State lands included. educational institutions. Also requires an excavation permit and notification if human remains are found on state land. [Register of Historic Places (Colorado Revised Establishes requirements for protecting properties No properties listed on the Registry of Historic Statues, Title 24, Article 80, Sections 101-108) of historical significance. No No Places will be impacted by the selected remedy. [Colorado Non-game, Endangered, or Threatened Protects endangered and threatened species and Standards for regulation of non-game wildlife [ Species Act (Colorado Revised Statutes, Title preserves their habitats. Requires coordination and threatened and endangered species. Site- 33, Article 2, Secfions 101-108) with the Division of Wildlife if remedial activities specific studies did not document the presence of impact on state-listed endangered/threatened threatened or endangered species. If threatened Yes species or their habitat. or endangered species are encountered during remedial activities at OU6, then requirements of Act will be applicable.

[Colorado Species of Special Concem and Protects animals listed on the Colorado Division Species of Undetermined Status (Colorado of Wildlife generated list. Coordination with the Protects species listed on the Colorado Division Division of Wildlife Administrative Directive E Division of Wildlife is strongly urged if animal of Wildlife generated list. Urges coordination 1, 1985, modified) species are to be impacted. with the Division of Wildlife if wildlife species | are to be impacted. No evidence of species of special concem have been identified at this site. No* No EPA will coordinate with the Division if it encounters listed wildlife species. •This is not a promulgated standard or regulation and is therefore a policy or guidance to be considered (TBC) and not an ARAR.

Colorado Natural Areas (Colorado Revised The Colorado Natural Areas Program maintains a EPA will coordinate with the Division if it [ Statutes, Title 33, Article 33, Section 104) list of plant species of special concern for the encounters plant species of special concem. State. Although not required by State statute, Yes coordination with Division of Parks and Outdoor Recreation is recommended if activities will impart listed sner.ies [state Solid Waste Disposal Sites and Facilities Establishes location standards for solid waste Act (Colorado Revised Statutes, Title 30, Article management facilities The selected remedy does include the siting of a Yes No 20, Sections 101-118; 6 CCR 1007-2) Site-wide repository.

Colorado Wildlife Act (Colorado Revised Establishes provisions governing the taking, Remedial actions being considered will not 1 Statutes, Title 33, Article 1, Sections 101-120) possession, and use of wildlife and migratory No No involve any taking, possession, or use of wildlife birds. and migratory birds. 1 Table 2.2 Action-Specific ARARs Relevant and Standard, Requirement or Criteria Description Applicable Comment Appropriate FEDERAL | Clean Water Act (33 USC Sect 1351-1376) Federal water quality criteria (FWQC) are Federal WQCs may be relevant and appropriate to discharges 1 Ambient Water Quality Criteria (40 CFR Part guidance established by EPA for from water treatment facilities if they are a part ofthe remedial 131; Quality Criteria for Water, 1976, 1980, evaluating toxic effects on human health action in OU6, however, the selected remedy does not include 1986, 1987; Ambient Water Quality Criteria for and aquatic organisms. FWQC are used any such discharges. The U.S. Bureau of Reclamation water No No Selenium, 1987) or considered by the States in setting their treatment facility is part ofthe selected remedy, however the water quality standards. discharge from this facility is off-site and is therefore subject toaNDPESpermit.

Clean Air Act (42 USC Sect. 7401-7642) New Establishes emission standards for certain National ambient air quality standards (NAAQS) are Source Performance Standards (40 CFR 60) categories of industrial stationary sources. implemented through the New Source Review Program and State Implementation Plans (SIPs). The federal New Source Review program address only major sources. Emissions associated with the proposed remedial action in 0U6 will be limited to fugitive dust emissions associated with earth moving activities during construction and will occur in isolated areas No No over a short period of time. Remedial work in 0U6 will be completed in industrial zoned areas significant distances from residential areas. These remedial activities will not constitute a major source. Therefore, attainment and maintenance of NAAQS pursuant to the New Source Review Program are not ARARs. See Colorado Air Pollution Prevention and Control Act conceming the applicability of requirements implemented through the SIP. Solid Waste Disposal Act (SWDA) as amended Solid Waste Disposal Act - Provides The selected remedy includes the construction of a Site-wide by the Resource Conservation and Recovery Act substantive requirements to ensure the repository. The selected remedy also includes the operation of 1976 (RCRA) (42 USC Sect. 6901-6987) appropriate management of solid waste. and maintenance of retention ponds that collect stormwater Criteria for Classification of Solid Waste Disposal The regulations in 40 CFR Part 257 from Mine wastes that are acid generating. The collected Yes No Facilities and Practices (Subtitle D) provide substantive criteria to be met by stormwater is considered an industrial discharge which is a (40 CFR Part 257) solid waste disposal facilities. point source subject to permits under section 402 ofthe Clean Water Act, so it is by definition (see 40 CFR 257.2) not a solid wa«tp Solid Waste Closure (40 CFR 258.60 b, c, h, 1, J) Provides methods and standards for The selected remedy does not include the construction of a 1 proper closure of municipal solid waste municipal solid waste landfill facility. The potential No No landfills facilities. construction and siting ofthe on-site repository is not part of the selected remedy. Identification and Listing of Hazardous Wastes Defines those solid wastes which are The State is authorized to implement this portion of RCRA and (Subtitle C) subject to regulation as hazardous wastes therefore, the potential ARARs arise under the State No No 40 CFR part 261 under 40 CFR Parts 262-265 and Parts regulations. 124. 270. and 271. Standards Applicable to Generators of Hazardous Establishes standards for generators of The State is authorized to implement this portion of RCRA and Waste (Subtitle C) hazardous waste. No No therefore, the potential ARARs arise under the State 40 CFR Part 262 regulations. Table 2.2 1 • Action-Specific ARARs | Relevant and Standard, Requirement or Criteria Description Applicable Comment Appropriate Standards Applicable to Transporters of Establishes standards which apply to The State is authorized to implement this portion of RCRA andl Hazardous Waste (Subtitle C) persons transporting hazardous waste therefore, the potential ARARs arise under the State 40 CFR Part 263 within the US if the transportation No No regulations. requires a manifest under 40 CFR Part 262. Standards for Owners and Operators of Hazardous Establishes minimum national standards The State is authorized to implement this portion of RCRA andl Waste Treatment, Storage, and Disposal Facilities which define the acceptable management therefore, the potential ARARs arise under the State (Subtitle C) of hazardous waste for owners and regulations. No No 40 CFR Part 264 operators of facilities which treat, store, or dispose hazardous waste. iLand Disposal Restrictions Prohibits land disposal of RCRA No hazardous wastes will be land disposed on-site under the 40 CFR Part 268 hazardous waste without treatment. No No selected remedy. Nothing in these regulations are relevant and aooroDriate to the selected remedy. Hazardous Materials Transportation Act (49 USC Regulates transportation of hazardous Applicable to the transportation of water treatment residuals 1 Sect. I801-I8I3; 49 CFR Parts 107, 171-177) materials. Yes and consolidation of waste rock on-site under the selected remedy. lUnderground Injection Control Regulations, 42 Provides for protection of underground The selected remedy includes emergency injection of collected 1 U.S.C. Sect. 300h-300h-8, 40 CFR 144-147 sources of drinking water. stormwater down the Marion shaft. This injection well would Yes be classified as a Class V well. This injecfion will not adversely impact underground sources of drinking water.

National Pollutant Discharge Elimination System Requires permits for the discharge of The State of Colorado has an approved program, so the State 1 40 CFR parts 122, 125 pollutants from any point source into No No program provides any potential applicable or relevant and waters ofthe United States appropriate provisions. | Table 2.2 Action-Specific ARARs Relevant and Standard, Requirement or Criteria Description Applicable Comment Appropriate iSTATE 1 Environmental Covenants (CRS 25-15-317-327) Requires environmental covenant Applicable to the selected remedy. Compliance will be whenever contamination left in place Yes achieved through institutional controls. requires restrictions on land use. Colorado Water Quality Control Act, CRS 25-8- Establishes program for permitfing The substantive provisions ofthe CPDES program are 101 et seq., and Colorado Discharge Permit discharges of contaminates into waters of potentially applicable to point source discharges under the System Regulations (5-CCR-1002.6I) the United States within Colorado selected remedy, (i.e., potential discharges from treatment facilities or stormwater discharges to groundwater that is hydraulically connected to waters ofthe U.S.). The U.S. Bureau of Reclamation water treatment facility is part ofthe Yes selected remedy during times of emergency. However, the discharge from this facility is off-site and is therefore subject to a NDPES permit. Stormwater and non-point source discharges during construction would be mitigated through an Erosion Control Plan. The emergency injection of stormwater into the Marion shaft will comply with the Colorado Basic Standards for Groundwater sections, see below. 5-CCR-1002.31 - Basic Standards for Surface Establishes basic State-wide surface State freshwater WQSs may be applicable to discharges from Water Water Quality Standards (WQS), specific point sources if they are a part ofthe remedial action in 0U6. surface WQSs, and an antidegradation The U.S. Bureau of Reclamation water treatment facility is rule. part ofthe selected remedy during times of emergency. Yes However, the discharge from this facility is off-site and is therefore subject to a NDPES permit. Stormwater and non- point source discharges during construction would be mitigated through an Erosion Control Plan.

Colorado Water Quality Control Act, CRS 25-8- Establishes basic State-wide Water The selected remedy includes emergency injection of collected 101 etseq., 5-CCR-1002.41.5 and 41.6 - Basic Quality Standards for groundwater, stormwater down the Marion shaft. This emergency injection Standards for Ground Water specific water quality standards for will not adversely impact underground sources of drinking groundwater, and an antidegradation Yes water. An extensive groundwater monitoring network will be rule. designed and the points of compliance will be determined during remedial design.

State Solid Waste Disposal Sites and Facilities Establishes policy for licensing, locafing, The selected remedy does include the construction of a Site- Act (CRS 30-20-101 to 118) Colorado Solid constructing, and operating of solid waste wide repository. The selected remedy also includes the Waste Management Regulations (6CCR 1007-2) facilities. operation and maintenance of retention ponds that collect stormwater from Mine wastes that are acid generating. The Yes No collected stormwater is considered an industrial discharge which is a point source subject to permits under the provisions ofthe Colorado Water Quality Control Act, so it is by definition not a solid waste. 1 Table 2.2 1 1 Action-Specific ARARs [ Relevant and Standard, Requirement or Criteria Description Applicable Comment Appropriate [Colorado Mined Land Reclamation Act (CRS 34- Regulates all aspects of land use for The reclamation provisions of these regulations are relevant 32-101 to 125) Mineral Rules and Regulations (2 mining, including the location of mining and appropriate to remedial activities involving plugging of CCR 407-1) operations and related reclamation adits, water control measures and treatment and disposal of No Yes activities and other environmental and waste piles. Permit not required for CERCLA sites. socio-economic impacts.

Colorado Air Quality Control Act (5CCR 1001-1, Establishes emissions standards for PMIO Yes Compliance with applicable provisions ofthe Colorado air 1 3,8, 10) and lead. Pursuant to the Colorado Air quality requirements will be achieved by adhering to a fugitive Pollution Prevention and Control Act, emissions control plan prepared in accordance with Regulation applicants for construction permits are No. 1. The proposed remedial action in OU6 is not projected required to evaluate whether the proposed to exceed the emission levels for lead, although some lead source will exceed NAAQS. Applicants emissions may occur. The substantive are also required to evaluate whether the requirements of Regulation 3 are potentially applicable and proposed activities would cause the these requirements will be met by submitting an APEN. Colorado ambient standard for PMIO to Remedial work in OU6 will be completed in industrial zoned be exceeded. Colorado regulates fugitive areas significant distances from residential areas. emissions through Regulation No. 1.

Colorado Noise Abatement Act (CRS 25-12-101 Establishes maximum permissible noise Applicable to remedial activities involving construction 1 to 108) levels for particular time periods and land Yes activities. The selected remedy will be implemented so as not use zones. to violate noise limits. Regulations on the Collection of Aquatic Life Requirements governing the collection of Remedial actions will not trigger the need for biological [ No No (2CCR 406-8, Ch.l3, Article IIL Section 1316) wildlife for scientific purposes. monitoring. [Colorado Hazardous Waste Regulations (6 CCR Establishes requirements regarding The wastes have been determined to be Beville exempt and 1 1007-3, Part 264: storage, treatment and disposal of therefore the hazardous waste regulations are not applicable. hazardous waste. Specific provisions ofthe hazardous waste regulations may be relevant and appropriate in certain circumstances regarding response actions involving mining wastes that are Beville No Yes exempt. Specific provisions regarding run-on and run-off control (See Section 264.301 (g),(h), &(i)) are relevant and appropriate to the operation and maintenance ofthe stormwater detention basins to be operated and maintained under the selected remedy.