United States Environmental Protection Agency · RECORD OF DECISION OPERABLE UNIT 6 CALIFORNIA...

SDMS Document ID

11111112008670

FINALRECORD OF DECISION

OPERABLE UNIT 6CALIFORNIA GULCH SUPERFUND SITE

LEADVILLE, COLORADO

September 2003

U.S. Environmental Protection Agency999 18th Street, Suite 500

Denver, CO 80202

RECORD OF DECISION

OPERABLE UNIT 6CALIFORNIA GULCH SUPERFUND SITE

LEADVILLE, COLORADO

The U.S. Environmental Protection Agency (EPA), with the concurrence of the ColoradoDepartment of Public Health and Environment (CDPHE), presents this Record ofDecision (ROD) for Operable Unit 6 (OU6) of the California Gulch Superfund Site (Site)in Leadville, Colorado. The ROD is based on the Administrative Record for OU6,including the Remedial Investigation/Feasibility Study (RI/FS), the Proposed Plan, thepublic comments received, and EPA responses. The ROD presents a brief summary ofthe RI/FS, past Response Actions, actual and potential risks to human health and theenvironment, and the Selected Remedy. EPA followed the ComprehensiveEnvironmental Response, Compensation, and Liability Act, as amended, the NationalContingency Plan (NCP), and EPA guidance (EPA, 1999a) in preparation of the ROD.The three purposes of the ROD are to:

1. Certify that the remedy selection process was carried out in accordance with therequirements of the Comprehensive Environmental Response, Compensation, andLiability Act, 42 U.S.C. 9601 et seq.. as amended by the Superfund Amendmentsand Reauthorization Act (collectively, CERCLA), and, to the extent practicable,the NCP;

2. Outline the engineering components and remediation requirements of the SelectedRemedy; and

3. Provide the public with a consolidated source of information about the history,characteristics, and risk posed by the conditions at OU6, as well as a summary ofthe cleanup alternatives considered, their evaluation, the rationale behind theSelected Remedy, and the agencies' consideration of, and responses to, thecomments received.

The ROD is organized into three distinct sections:

1. The Declaration Section functions as an abstract and data certification sheet forthe key information in the ROD and includes the formal authorizing signaturepage for the ROD.

2. The Decision Summary provides an overview of the characteristics of OU6,alternatives evaluated, and the analysis of those options. It also identifies theSelected Remedy and explains how the remedy fulfills statutory and regulatoryrequirements.

3. The Responsiveness Summary serves the dual purposes of: (1) presentingstakeholder concerns about OU6 and preferences regarding the remedialalternatives; and (2) explaining how those concerns were addressed and thepreferences were factored into the remedy selection process.

Final Record of DecisionOU6 California Gulch NPL Site

DECLARATION

DECLARATION

SITE NAME AND LOCATION

Operable Unit 6California Gulch Superfund SiteLeadville, ColoradoCERCLIS # COD980717938

STATEMENT OF BASIS AND PURPOSE

This decision document presents the Selected Remedy for OU6 of the Site in Leadville,Colorado. The Environmental Protection Agency selected the remedy in accordance withthe Comprehensive Environmental Response, Compensation, and Liability Act(CERCLA), as amended by the Superfund Amendments and Reauthorization Act(SARA), and to the extent practicable, the NCP. This decision is based on theAdministrative Record file for OU6. The State of Colorado concurs with the SelectedRemedy.

ASSESSMENT OF SITE

The Response Action selected in this Record of Decision is necessary to protect publichealth or welfare or the environment from actual or threatened releases of hazardoussubstances and pollutants or contaminants from OU6 which may present an imminent andsubstantial endangerment to public health or welfare.

DESCRIPTION OF SELECTED REMEDY

The Site was added to the National Priority List in 1983. In 1994 the Site was dividedinto 10 geographically-based areas, also called operable units. This was accomplishedthrough a Consent Decree with ASARCO and Resurrection Mining Company (themining companies). OU6 is one of these 12 operable units and covers approximately 3.4square miles in the northeastern portion of the Site. OU6 includes the Stray Horse Gulchwatershed and the upper and lower portions of the Evans Gulch watershed.

Investigation of the Site began in the mid-1980s and continues today. Most of theinvestigation in OU6 was performed as a part of broader studies of the entire Site. Acomplete list of investigative reports on OU6 can be found in the OU6 FocusedFeasibility Study (EPA, 2002a) in the Administrative Record.

Beginning in 1990, EPA and the mining companies began a series of Response Actionsto systematically cleanup the majority of the mine wastes causing contamination in OU6.A Response Action is a cleanup project that by itself may not achieve total site cleanup.However, taken together, all of the Response Actions performed to date in OU6 haveaddressed most of the mine wastes considered to be sources of contamination.

Final Record of Decision D-lOU6 California Gulch NPL Site

The major OU6 Response Actions have included:

• Consolidation and capping of selected mine waste piles.

• Collection and treatment of acid rock drainage (ARD) from mine waste piles.Treatment occurs at a facility operated by the US Bureau of Reclamation (BOR) atthe portal of the Leadville Mine Drainage Tunnel. BOR has cooperated with EPA totreat OU6 water on an interim basis to determine the feasibility of using its facility totreat OU6 water for the long-term.

• Diversion of clean surface water around mine wastes.

• Rehabilitation of Stray Horse Gulch and Starr Ditch.

Although these Response Actions have cleaned-up most of the mine wastes in OU6, it isnot certain that maintaining these remedies into the future is the most cost effective andreliable way to maintain the improvements achieved to date. Therefore, EPA willaugment portions of the work performed to date and/or use new kinds of cleanup methodsas presented in this ROD.

The cleanup plan for OU6 is one of the many remedies either completed or beingconsidered for each of the operable units in the Site. Pursuant to the agreement reachedbetween EPA, the State, ASARCO and Resurrection in the 1994 Consent Decree, theremedies for OUs 2 through 11 typically target the source materials such as mine wasterock and mill tailing. The remedies for all but OU6, OUS (AV/CZL Smelter), OU11(Arkansas River Floodplain), and OU12 (Site-Wide Surface and Groundwater) have beenconstructed.

EPA will monitor the improvements in surface and groundwater quality as the sourcecontrol remedies in each of the operable units are completed. If the remedies don'tsufficiently improve the quality of surface and groundwater, EPA and the State ofColorado may require further source control measures or other cleanup actions. OperableUnit 12 (OU12) will assess and address site-wide surface and ground water quality, ifnecessary. Unlike the other operable units, OU12 includes the entire Site.

The OU6 Focused Feasibility Study (FFS), Waste Rock Remedial Investigation Reportand other investigative reports describe those waste rock piles which generate acid rockdrainage (ARD) in quantities above a level of concern. Waste rock piles in OU6 havebeen addressed through prior Response Actions or will be addressed under the SelectedRemedy for OU6.

These prior Response Actions will be maintained under the Selected Remedy. In additionto maintaining prior Response Actions, the Selected Remedy will result in the removal ofadditional mine waste rock to an on-Site repository planned for the Site, thereby isolatingthe waste from the environment. Other components of the Selected Remedy address ARDderived from mine waste rock.

Final Record of Decision D-2OU6 California Gulch NPL Site

The major components of the Selected Remedy include:

• Continued collection and management of ARD with management by:

Treatment to remove contaminants at a water treatment facility operatedby the US Bureau of Reclamation (BOR).Discharge to surface water at a controlled rate to minimize impacts to theParkville Water District.Evaporation.

• Continued maintenance of consolidated and capped waste piles and surface watermanagement features constructed during prior Response Actions. Maintenancewill include inspections and repairs to caps and periodic cleaning/repairing ofsurface water management features. Wastes generated during maintenanceactivities will be disposed in an on-Site repository planned for the Site.

• Construction of a plug (bulkhead) in the Leadville Mine Drainage Tunnel(LMDT) to allow better management of groundwater in flooded undergroundmine workings connected to the LMDT (mine pool).

• Dewatering of the mine pool from a location upstream of the bulkhead anddelivery of pumped groundwater to the BOR's treatment plant via a buried gravitypipeline.

• Establishing a groundwater monitoring network to observe water level and qualityconditions in and around the mine pool.

• Relocation of additional mine waste rock (e.g., Ponsardine mine waste pile) to theon-Site repository planned for the Site.

• Stabilization of a retaining wall (crib wall) associated with the Emmet waste rockpile.

• Establishment of land use controls under an Institutional Control Overlay (ICO)District to ensure that any future changes in land use are consistent with the finalremedy.

STATUTORY DETERMINATIONS

The Selected Remedy is protective of human health and the environment, complies withfederal and State requirements that are applicable or relevant and appropriate to theremedial action, is cost effective, and utilizes permanent solutions and alternativetreatment technologies to'the maximum extent practicable. This remedy also satisfies thestatutory preference for treatment as a principal element of the remedy. Because thisremedy will result in hazardous substances, or pollutants or contaminants remaining inOU6 above levels that allow for unlimited use and unrestricted exposure, a statutoryreview will be conducted within five years after initiation of remedial action to ensure


that the remedy is, or will be, protective of human health and the environment. Thisremedy is acceptable to both the State of Colorado and the community of Leadville.

DATA CERTIFICATION CHECKLIST

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

• 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.• Current and reasonably anticipated future land use assumptions used in the

baseline risk assessment and ROD.• 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 costestimates are projected.

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

AUTHORIZING SIGNATURE

Max H. Dodson DateAssistant Regional AdministratorEcosystems Protection and RemediationU.S. Environmental Protection Agency, Region VIII


DECISION SUMMARY

TABLE OF CONTENTS

1.0 SITE NAME, LOCATION AND DESCRIPTION DS-12.0 SITE HISTORY AND ENFORCEMENT ACTIVITIES DS-23.0 COMMUNITIY PARTICIPATION DS-74.0 SCOPE AND ROLE OF OPERABLE UNIT OR RESPONSE ACTION DS-85.0 SITE CHARACTERISTICS DS-10

5.1 PHYSICAL SETTING DS-105.1.1 Site Physiology DS-105.1.2 Regional Geology DS-105.1.3 Climate DS-11

5.2 SURFACE WATER AND RELATED MEDIA DS-115.2.1 Surface Water Hydrology DS-115.2.2 Surface Water Chemistry : DS-125.2.3 Fluvial Tailing DS-135.2.4 Stream Sediments DS-13

5.3 GROUNDWATER DS-135.3.1 Hydrogeology DS-135.3.2 Groundwater Chemistry DS-15

5.4 MINE WASTE DS-155.4.1 Mine Waste Types DS-155.4.2 Mine Waste Locations DS-165.4.3 Mine Waste Quantities DS-19

6.0 SUMMARY OF SITE RISKS DS-206.1 HUMAN HEALTH RISKS DS-20

6.1.1 Contaminants of Concern DS-206.1.2 Exposure Assessment DS-216.1.3 Toxicity Assessment DS-216.1.4 Risk Characterization DS-22

6.2 ECOLOGICAL RISKS DS-236.2.1 Contaminant Identification DS-236.2.2 Exposure Assessment DS-246.2.3 Toxicity Assessment DS-246.2.4 Risk Characterization DS-25

7.0 REMEDIAL ACTION OBJECTIVES DS-267.1 INTRODUCTION DS-267.2 MEDIA OF CONCERN DS-277.3 MIGRATION PATHWAYS OF CONCERN DS-287.4 REMEDIAL ACTION OBJECTIVES DS-28

8.0 DESCRIPTION OF ALTERNATIVES DS-298.1 ALTERNATIVE 1: NO ACTION DS-298.2 ALTERNATIVE 2: MAINTAIN CURRENT REMEDIES W/LAND USE

CONTROLS DS-29

Final Record of Decision DS-iOU6 California Gulch NPL Site

8.3 ALTERNATIVE 4: IN-SITU CHEMICAL STABILIZATION ORRELOCATION (IN COMBINATION WITH ALTERNATIVE OPTIONS2A THROUGH 2H) DS-31

8.4 ALTERNATIVE 5: CONSOLIDATE AND CAP W/LAND USECONTROLS DS-32

8.5 ALTERNATIVE 6: EXCAVATE, TRANSPORT AND ON-SITEDICPOSAL W/LAND USE CONTROLS DS-32

9.0 SUMMARY OF COMPARATIVE ANALYSIS OF ALTERNATIVES DS-339.1 NCP CRITERIA DS-33

9.1.1 Overall Protection of Human Health and the Environment DS-339.1.2 Compliance with Applicable or Relevant and Appropriate

Requirements DS-339.1.3 Long-Term Effectiveness and Permanence DS-339.1.4 Reduction of Toxicity, Mobility, or Volume Through Treatment DS-349.1.5 Short-Term Effectiveness DS-359.1.6 Implementability DS-359.1.7 Cost DS-359.1.8 State Acceptance DS-369.1.9 Community Acceptance DS-36

9.2 WAMP CRITERIA DS-369.2.1 Surface Erosion Stability DS-369.2.2 Slope Stability DS-379.2.3 Flow Capacity and Stability DS-379.2.4 Surface Water and Groundwater Loading Reduction DS-389.2.5 Terrestrial Ecosystem Exposure DS-399.2.6 Non-Residential Soils DS-40

10.0 PRINCIPAL THREAT WASTES DS-4111.0 SELECTED REMEDY DS-42

11.1 DESCRIPTION OF THE SELECTED REMEDY DS-4211.2 SUMMARY OF ESTIMATED REMEDY COSTS DS-4411.3 CONTINGENCY MEASURES AND LONG-TERM MONITORING DS-45

12.0 STATUTORY DETERMINATIONS DS-4712.1 PROTECTION OF HUMAN HEALTH AND THE ENVIRONMENT DS-4712.2 COMPLIANCE WITH APPLICABLE OR RELEVANT AND

APPROPRIATE REQUIREMENTS DS-4712.3 COST-EFFECTIVENESS DS-4812.4 UTILIZATION OF PERMANENT SOLUTIONS AND ALTERNATIVE

TREATMENT (OR RESOURCE RECOVERY) TECHNOLOGIES TOTHE MAXIMUM EXTENT PRACTICABLE (MEP) DS-49

12.5 PREFERENCE FOR TREATMENT AS A PRINCIPAL ELEMENT DS-4912.6 FIVE-YEAR REVIEW REQUIREMENTS DS-49

13.0 DOCUMENTATION OF SIGNIFICANT CHANGES FROM PREFERREDALTERNATIVE OF PROPOSED PLAN DS-50

14.0 REFERENCES R-l

Final Record of Decision DS-iiOU6 California Gulch NPL Site

LIST OF TABLES

TABLE

1 1995 CONTAMINANT CONCENTRATIONS IN STREAM BED SEDIMENTS2 SUMMARY OF PILES IDENTIFIED AS CANDIATES FOR REMEDIAL

ACTTION3 ZINC AND CADMIUM CONCENTRATIONS AT SHG-08 AND SHG-094 ARD-GENERATING MINE WASTE VOLUMES5 HAZARD INDICES FOR SOLID SURFICIAL MEDIA BY RECEPTOR FOR

OU66 COMPARATIVE ANALYSIS USING NCP CRITERIA7 COMPARATIVE ANALYSIS USING ADDITIONAL CRITERIA8 SELECTED REMEDY COST ESTIMATE FOR ALTERNATIVE 2G AND 4B9 CHEMICAL-SPECIFIC ARARs10 LOCATION-SPECIFIC ARARs11 ACTION-SPECIFIC ARARs

Final Record of Decision DS-iiiOU6 California Gulch NPL Site

LIST OF FIGURES

FIGURE

1 LOCATION MAP CALIFORNIA GULCH SUPERFUND SITE2 SITE LOCATION MAP CALIFORNIA GULCH OU63 PREVIOUS REMOVAL ACTION AREAS4 STRAY HORSE GULCH SURFACE WATER MANAGEMENT REMEDIES5 SURFACE WATER FEATURES AND WETLAND AREAS6 PRE-REMEDIAL 1995 SURFACE WATER CONTAMINANT LOADING7 FLUVIAL TAILINGS LOCATIONS8 ALLUVIAL AQUIFER WATER TABLE CONTOURS9 POTENTIOMETRIC SURFACE CONTOURS OF BEDROCK AQUIFER10 BEDROCK AQUIFER GROUNDWATER CHEMISTRY NOV 1991 - JAN

199211 WASTE ROCK PILE LOCATIONS12 ARD-GENERATING SOURCE AREAS OF CONCERN13 AVIRIS MINERAL ASSEMBLAGES14 TOTAL CADMIUM LOADING TRENDS15 TOTAL ZINC LOADING TRENDS16 ALTERNATIVE 2G

Final Record of Decision DS-ivOU6 California Gulch NPL Site

1.0 SITE NAME, LOCATION AND DESCRIPTION

Site Name: Operable Unit 6California Gulch Superfund Site

Site Location: Leadville, ColoradoNational Superfund electronic database identification number: CERCLIS No.

COD980717938Lead Agency: US Environmental Protection AgencySupport Agency: Colorado Department of Public Health and Environment (CDPHE)

Cleanup funding: Superfund trust fund and matching funds provided by CDPHE.

Site Description:

The California Gulch Superfund Site (Site) is comprised of approximately 16.5 squaremiles of mountainous terrain in Lake County, Colorado, approximately 100 milessouthwest of Denver (Figure 1). The Site is divided into 12 Operable Units (Figure 2).Operable Unit No. 6 (OU6) covers approximately 3.4 square miles in the northeasternquadrant of the Site and includes the Stray Horse Gulch watershed and the upper andlower portions of the Evans Gulch watershed. Historic mining activities resulted inplacement of mine wastes on the land surface. Some of these mine wastes may containchemicals at concentrations posing an unacceptable human health risk as determined byEPA human health risk assessments. In addition, some of these mine wastes generate acidrock drainage (ARD) in concentrations toxic to aquatic organisms.

Final Record of Decision DS-1OU6 California Gulch NPL Site

2.0 SITE HISTORY AND ENFORCEMENT ACTIVITIES

The Site is located in a highly mineralized area of the Colorado Rocky Mountains.Mining, mineral processing, and smelting activities have produced gold, silver, lead andzinc for more than 140 years. Mining began in the Leadville area in 1859 whenprospectors working the channels of Arkansas River tributaries discovered gold at themouth of California Gulch. Initial activities consisted only of small-scale placer mininguntil 1868, when the first gold ore veins were discovered along California Gulch. By1872, however, problems with water, transportation and labor made ore removal sodifficult that most miners had left the area. In 1874, silver-bearing lead carbonate wasdiscovered, and mining in the Leadville district boomed.

Extensive replacement deposits of lead, silver and gold ores associated with fissure veinswere discovered and mined. Zinc and manganese, which were of little value in the earlydays, were later mined extensively. As surface veins diminished, miners tunneled deeperinto the mountains. Underground mines were developed east and southeast of Leadville.As mines were developed, waste rock was excavated along with the ore. The waste rockwas placed near the mine entrance, and the ore was transported to the mill. At the mill,ores were crushed and separated into metallic concentrates and waste products byphysical processes. The metallic concentrates were then shipped elsewhere or furtherprocessed at a smelter in the area. The waste products (mill tailing) were generally placednear the mill in a tailing pond. In the smelters, the high-grade ores were refined andconcentrated into higher-grade products. Waste products from the smelters included slagand dust, and off-gases. Forty-four known smelters were in the district (Woodward-Clyde, 1994a).

The EPA proposed adding the Site to the National Priorities List (NPL) on December 30,1982. The site was formally listed on September 8,1983. The following is a briefchronological summary of the major regulatory actions taken at the Site.

• 1982 - The Site is proposed for the NPL.

• 1983 - The Site is formally added to the NPL.

• 1986 - EPA emergency response workers extended public water supplysystem lines to residences using private wells.

• 1987 - EPA began an investigation of mine wastes. Approximately 2,000mine waste piles within the Site were screened to identify those larger than100,000 cubic yards. Further screening was based on proximity to populatedareas, roadways, and surface water, and potential pile instability. Forty-fivewaste deposits were selected for field inspection and sampling based onaccess, size, waste type, stability, and proximity to residential areas and/orwatercourses. Eleven of these sites were mine waste piles, with the remainderbeing slag piles and tailing impoundments (Woodward-Clyde, 1994b).


• 1994 - The United States, the State of Colorado, and the PotentiallyResponsible Parties (PRPs) entered into a Consent Decree (CD). The CDdivided the Site into 12 Operable Units (OUs) for the cleanup ofgeographically based areas within the site (USDC, 1994). OU6 is one of theseOU's.

The EPA and ASARCO have implemented a number of Time Critical and Non-TimeCritical Response Actions within OU6. These Response Actions were conductedprimarily to prevent exposure of human populations to contaminants from mine wastesand to reduce leaching and migration of metals from the wastes into surface waters. Thissection briefly summarizes the Response Actions implemented to date in chronologicalorder (See Figure 3). Detailed descriptions of the individual Actions are available withinthe documents referenced.

1. In 1990, ASARCO performed improvements along 5th Street and Starr Ditchbetween East 5th Street and the Harrison Street slag pile. The improvementsinvolved converting existing open ditches to culverts along both sides of East 5th

Street, including the construction of the 5th Street headwall. Starr Ditch was alsofenced to restrict public access from just north of 5th Street to Monroe Street, justeast of the Harrison Street slag pile (USEPA, 1995a).

2. During the summer of 1994, the BOR, on behalf of EPA, implemented sedimentcontrol measures on Hamm's Tailing Impoundment as a Time Critical ResponseAction (USEPA, 1995a).

3. In 1995 and 1996 EPA implemented a Time Critical Response Action at Hamm'sTailing Impoundment. The Action involved removal of sediment fromsedimentation ponds, enlargement of selected sedimentation ponds, rehabilitationof straw dams and ponds, removal of sediment from culverts and associateddrainage structures, construction of an up-gradient run-on control ditch, andreestablishment of Starr Ditch at the base of Harrison Street slag pile (USEPA,1995a). The removed sediment was transported to the Hamm's TailingImpoundment for disposal (USEPA, 1996a).

4. Also in 1996, EPA conducted a Time Critical Response Action for the Hamm'sTailing Impoundment and the Penrose Mine Waste Pile. The majority of minewaste in the Penrose Pile was transported to the Hamm's Tailing Impoundment.The remaining waste at the Penrose Pile was graded to a 3:1 configuration,covered with a soil cap, and revegetated. The Hamm's Impoundment was thenconsolidated, compacted and graded to a stable 3:1 configuration, covered with asoil cap, and revegetated (USEPA, 1996b).


5. In 1997, EPA implemented Phase I of a five-phase OU6 Response Action. Thepurpose of the Non-Time Critical Response Action was to mitigate the majority ofthe source areas impacting water quality in the Stray Horse Gulch drainage(USEPA, 1997). The Phase I Action included (COM, 2000a):

• Capping of three, double-compartment mine shafts.• Construction of five crib walls.• Consolidation and capping of three waste rock piles.

> Wolftone> Maid of Erin> Mahala

Work on the waste rock piles consisted of excavating, transporting, placing,reshaping, and compacting contaminated mine waste rock from adjacent areasincluding approximately 5,900 cubic yards (CY) of acid generating waste rockfrom Stray Horse Gulch Road. A polyvinyl chloride (PVC) geomembrane incombination with a Mirafi geofabric was placed on top of each consolidated pile.A minimum of 8 ft of dolomite waste rock was then placed and compacted abovethe Mirafi geofabric at Wolftone and Maid of Erin at a 1.5:1 side slope. Whiteporphyry mixed with dolomite waste rock was used as a veneer material toprovide a more aesthetic appearance on the Wolftone Pile. At Mahala, the rockcap was constructed as described above with the exception of the top. The top ofthe pile was capped with 1-2 ft of white porphyry (Pacific Western, 2001).

The Ponsardine Pile and the source areas addressed in the 1998 Phase II ResponseAction (Ram, Mikado, Highland Mary, Adelaid and Pyrenees waste piles) wereinitially scheduled for Response Action during the Phase I work. The PonsardinePile, however, was eliminated due to state and local concerns about potentialadverse impacts to historic and cultural resources.

6. In 1998, EPA conducted Phase II of a Non-Time Critical Response Action tomitigate additional source areas impacting water quality in the Stray Horse Gulchdrainage (see Figure 4). The Phase II work involved surface water managementrather than consolidation and capping to address state and local concerns aboutpotential impacts to historic and cultural resources. The following majorcomponents were completed during Phase II (CDM, 2000b):

• Capping of one double-compartment mineshaft.• Construction of water run-on diversions at Highland Mary, Mikados,

RAM, Greenback, Pyrenees and Adelaide-Ward.• Construction of water runoff channels at Highland Mary, Mikados,

Pyrenees and Adelaide-Ward.• Construction of ARD retention basins at Highland Mary, Mikados,

Pyrenees and Adelaide-Ward.• Construction of detention basins in lower Stray Horse Gulch at Adelaide

Park and the Emmet waste rock pile.


• Construction of an interim water runoff collection channel and sedimentbasin at Fortune/Resurrection No. 1.

• Rehabilitation of Stray Horse Gulch and Starr Ditch.• Sediment removal at the 5th Street Headwall.

During Phase II, the Ponsardine Pile was considered for run-on/runoff control, butwas ultimately not included based on the small size of the pile and theinsignificant ARD it appeared to contribute based on available information. Inaddition, according to local observations runoff was believed to infiltrate beforereaching the east side of Leadville. Subsequent opportunistic data collected duringthe 1998 construction season showed that the Ponsardine pile can be a source ofARD and associated metals particularly during storm events (EPA, 1999b).

7. Phase III was implemented in 1999 as a continuation of the Phase II work. Thefollowing briefly describes the major work conducted (CDM, 2000b):

• Construction of water runoff collection channels at RAM and Greenback.• Construction of water runoff retention basins at RAM and Greenback.• Completion of water runoff collection channel and sediment basin at

Fortune/Resurrection No. 1.

8. In 2000, EPA conducted Phase IV of the OU6 Response Action. This phase of theNon-Time Critical Response Action involved removal and disposal of sedimentsalong Starr Ditch, rehabilitation and realignment of Starr Ditch, revegetation ofdisturbed areas, and slope stabilization at the RAM and Greenback areas (CDM,2000c).

During the spring runoff in 2000, the water collected in the retention basins atRAM, Greenback and Pyrenees nearly overtopped due to under design of theretention basins. In order to prevent overtopping, the water was collected at theGreenback Pond and siphoned to Stray Horse Gulch.

9. In the fall of 2000, as part of a Non-Time Critical Response Action, EPAconstructed a discharge to a lateral connecting the Marion and Emmet MineShafts to prevent the release of water into Stray Horse Gulch from the GreenbackRetention Pond during future spring runoff events. The current capacity of severalretention ponds does not accommodate a typical snowmelt event. The MarionShaft is tributary to the Leadville Mine Drainage Tunnel (LMDT) via the RobertEmmet Shaft. The LMDT then carries the collected runoff to the BOR's treatmentplant at the portal of the LMDT.

The connection between the Marion Shaft and the LMDT has been under analysis byEPA. A number of tracer studies were performed to determine the effectiveness of theLMDT as a conveyance structure for the Greenback Pond discharge. These studiesconfirm a hydraulic connection between the Marion Shaft and the LMDT portal.


This conclusion is based on information provided in Ground Water Hydrology Report onconditions near the LMDT (EPA, 2002b):

• Approximately 63% of the tracer injected in the Marion Shaft wasrecovered at the LMDT portal and additional dye was still being recoveredat the portal.

• A portion of the tracer remains in the Emmet Shaft.

• Tracer has not been detected at any other point where groundwaterdischarges to surface water.

10. During the 2001 construction season, EPA implemented Phase V of a Non-TimeCritical Response Action for surface water management and sediment control inthe Ibex/Irene area (USEPA, 2001). This phase involved constructing water run-on diversion ditches on the south side of Lake County Road 1A following the pathof the diverted Lincoln Gulch as well as additional ditches that direct surfacewater towards the Eclipse Mine and existing drainages, eventually leading toSouth Evans Gulch. Surface water runoff from ARD-generating sources isredirected to a detention basin, which ultimately discharges to Lincoln Gulch. Asecond detention basin was constructed in the Old Lincoln Gulch channel nearLake County Road 3B to collect sediment from erosion in Lincoln Gulch (CDM,200 la).

11. During the 2002 construction season, EPA completed the rehabilitation of Stan-Ditch as a Non-Time Critical Response Action. The project included theinstallation of 550 feet of culvert in the vicinity of Monroe Street.


3.0 COMMUNITIY PARTICIPATION

The Focused Feasibility Study (FFS), Proposed Plan and numerous other documents forOU6 were made available to the public over the course of investigative and remedialwork conducted in the Site since 1983. The FFS and Proposed Plan were made availablein September 2002 and April 2003, respectively. They can be found in the AdministrativeRecord file and the information repository maintained at the EPA Docket Room inRegion 8 and at the Lake County Public Library. The notice of the availability of thesetwo documents was published in the Lake County Herald on April 3,2003. A publiccomment period was held from April 3, 2003 to May 3, 2003. In addition, a publicmeeting was held on May 1, 2003 to present the Proposed Plan to a broader communityaudience than those that had already been involved at the Site. At this meeting,representatives from EPA, Bureau of Reclamation (BOR), and CDPHE answeredquestions about problems at the OU6 and the remedial alternatives. EPA's response to thecomments received during this period is included in the Responsiveness Summary, whichis part of this Record of Decision.

As part of past Response Actions, EPA conducted numerous public meetings and publiccomment periods to allow the public to comment on the Engineering Evaluations/CostAnalyses. EPA prepared responsiveness summaries related to various phases of Non-Time Critical Removal Actions.


4.0 SCOPE AND ROLE OF OPERABLE UNIT OR RESPONSE ACTION

EPA has organized work at the Site into 12 operable units. The operable units are listedbelow and grouped according to the status of remedial action:

Implemented Response Actions:

• OU1 - Yak Tunnel/Water Treatment Plant• OU2 - Malta Gulch Fluvial Tailing/Leadville Corporation Mill/Malta Gulch

Tailing Impoundment• OU3 - D&RGW Slag Piles/Railroad Easement/Railroad Yard and Stockpiled

Fine Slag• OU4 - Upper California Gulch• OU7 - Apache Tailing Impoundments• OU8 - Lower California Gulch• OU9 - Residential Populated Areas• OU10-Oregon Gulch

Activities Proposed Under this ROD:

• OU6 - Starr Ditch/Penrose Dump/Stray Horse Gulch/Evans Gulch

Future Response Plans:

• OU5 - ASARCO Smelter/Slag/Mill Sites and AV/CZL Smelters• OU11 - Arkansas River Valley Floodplain• OU12 - Site-Wide Water Quality

Pursuant to the August 26, 1994 Consent Decree (CD) at this Site (USDC, 1994), it wasagreed that the decision on remediation of Site-wide Surface Water and Groundwater(OU12) would be made only after remedies for source remediation were selected andimplemented at each OU. Therefore, prior and proposed Response Actions in OU1through OU11 are intended tu address mine wastes and features that are consideredsource materials. Remedies excluded Site-wide surface and groundwater as specifictargets for remediation in these OU's.

Source remedies were designed to minimize human exposure to mine wastes where thehuman health risk was outside the acceptable risk range and/or minimize the discharge ofARD to surface or groundwater within a given operable unit. The intent of this approachto remediation of the Site is to lower human health risks resulting from direct contactwith mine wastes to below a level of concern through remedial action within individualoperable units. In addition, the overall improvements in Site-wide surface andgroundwater (OU12) achieved through source remediation work in individual operableunits will be assessed against the remedial action objectives for OU12. Additional workwithin one or more operable units may be required if remedial action objectives for OU12are not met after source remediation is completed in OU1 through OU11.


Therefore, through the phases of work that utilize a water management approach, theSelected Remedy for OU6 minimizes the discharge of ARD to surface and groundwater.It also addresses human health risks outside of the acceptable risk range resulting fromdirect contact with mine wastes through removal or capping of mine waste, or throughthe ICO District.

The incremental improvement to Site-wide surface and groundwater quality (OU12)resulting from the implementation of the Selected Remedy in OU6 will be assessedagainst remedial action objectives for OU12. EPA and CDPHE will establish specificsurface and groundwater requirements at a later date under a ROD for OU-12. If furtherimprovement in water quality is required, consideration will be given to additional sourcecontrols or Site-wide water treatment.


5.0 SITE CHARACTERISTICS

5.1 PHYSICAL SETTING

5.1.1 Site Physiology

Operable Unit 6 lies in the Southern Rocky Mountain Physiographic Province of theUnited States, which is characterized by fault-block mountain ranges separated byintermontane valleys. Leadville is located on the east side of the Arkansas River Valleyat the base of Mount Evans near the confluence of Evans Gulch with the Arkansas River(see Figure 2). Evans Gulch is a large glacial valley that extends down the west slope ofMount Evans from elevations of 13,200 ft above mean sea level (MSL) to the ArkansasValley at approximately 9,900 ft above MSL. Evans Gulch is bordered on the north byProspect Mountain and on the south by Iron Hill, Breece Hill, and Ball Mountain. StrayHorse Gulch is a small ephemeral stream that lies in the south portion of the Evans GulchValley, separated by Yankee Hill and a lateral moraine from the former Evans glacier.

5.1.2 Regional Geology

The bedrock formations underlying OU6 are a series of sedimentary strata that range inage from Cambrian to Pennsylvanian and consist of quartzite, limestone, dolomite andshale. These Paleozoic sedimentary formations were intruded during the late Cretaceousor early Tertiary periods in several episodes by porphory in "blanket" sills and dikes.These porphyry intrusions created the major portion of the mineralized zones and oredeposits (BOR, 1997).

The entire sequence of intruded sedimentary formations and pre-Cambrian graniticbedrock was uplifted and faulted into a series of discrete bedrock blocks by north-southtrending normal faults that step downward in elevation from Mosquito Pass on the east tothe Arkansas Valley on the west. This series of faults largely controlled the distributionand depth of the ore bodies, as well as groundwater which entered the mines in largequantities prior to the construction of the drainage tunnels. Prior to the construction ofthe Yak Tunnel and the LMDT (see section on Surface Hydrology), pumping wasrequired to dewater the lower ore body levels throughout the mining district (BOR,1997).

Since the start of placer mining in 1859, the sedimentary bedrock units and intrusive oredeposits were mined, and wastes were deposited on the surface. These waste materialsbecome subject to weathering which oxidize, break down, and release remainingcontaminant metals into surface and ground water. Wastes containing significantamounts of metal sulfides generate acidic drainage further mobilizing soluble metals.

Throughout much of OU6, the bedrock is overlain by unconsolidated glacial depositsassociated with the Evans Gulch Glacier.


5.1.3 Climate

The topographic features of Lake County strongly influence the climatic variations in theLeadville area. The elevation of the City of Leadville is approximately 10,000 ft aboveMSL. Normal temperature extremes range from -30°F to 86°F, with an averageminimum temperature of 21.9°F. Average annual precipitation is 18 inches with thewettest months being July and August and the driest months being December andJanuary. Summer precipitation is usually associated with convective showers. Theannual peak snowmelt usually occurs in June. The average frost-free season is 79 days.The wind is predominantly from the northwest and ranges from calm to 30 miles per hour(Golder, 1996a).

The National Weather Service operates a meteorological station at the Leadville airporttwo miles southwest of Leadville. Additional weather observations were measured at theYak Tunnel meteorological station near the Yak Tunnel Water Treatment Plant. TheFinal Air Monitoring Report (Woodward-Clyde, 1992a) provides an evaluation of localmeteorological data.

5.2 SURFACE WATER AND RELATED MEDIA

5.2.1 Surface Water Hydrology f

Operable Unit 6 is made up of two main drainages that contribute surface water to theArkansas River: Stray Horse Gulch and Evans Gulch (see Figure 5). Stray Horse Gulchhas one main tributary, Little Stray Horse Gulch, and is routed through the easternportion of Leadville to its confluence with California Gulch via Starr Ditch. CaliforniaGulch is a tributary to the Arkansas River. Evans Gulch contains two sub-drainagebasins, Lincoln Gulch and South Evans Gulch. The majority of Evans Gulch lies outsideof OU6 (see Figure 5). ~

The BOR performed a three-phase water and sediment sampling and hydrologicmeasurement program during 1995 and 1996. Phase 1 consisted of water and sedimentsampling during the 1995 spring runoff season. Phase 2 involved sampling and analysisof mine wastes conducted in 1996. Phase 3 consisted of water and sediment samplingduring the 1996 spring runoff.

Stray Horse Gulch is an intermittent stream that flows only during spring runoff andintense and/or extended precipitation events. The drainage is approximately 12,300 feetlong with an elevation loss of 675 feet. The BOR collected flow rate data during the1995 (Phase 1) and 1996 (Phase 3) spring runoff periods. Four stations were monitoredwithin the Stray Horse Gulch Drainage during Phase 1: SHG-07, SHG-08, SHG-09 andSHG-10 (see Figure 5). An additional station, SHG-07A, was added during the Phase 3investigation. The flow measurements collected in 1995 and 1996 show that significantsurface water loss to the subsurface occurs in Stray Horse Gulch. The majority of theloss occurs between SHG07 and SHG09. There was no net effective gain to stream flowin this reach of the drainage (BOR, 1997). However, over the years of monitoring, Stray


Horse Gulch has been both a losing and gaining stream, therefore reversals are bothpossible and occurring. Flows in Stray Horse Gulch ranged from 0 to 3.76 cubic feet persecond (cfs) during the 1995 runoff event. Using United States Geological Survey(USGS) peak flow data from Station 07081200 (Arkansas River near Leadville, CO), aflood frequency analysis was performed using the HEC-FFA (Flood Frequency Analysis)program created by the US Army Corps of Engineers Hydrologic Engineering Center.Based on data from years 1968 - 2000,1995 was determined to be between a 10- and 20-year runoff event.

Evans Gulch is the longest continuous drainage within OU6 and serves as the municipalwater supply for the city of Leadville via the Parkville Water District. During Phase 1,BOR monitored eleven sampling stations within the Evans Gulch drainage: EG-01, EG-02, EG-03, WE-01, WE-02, SEG-01, SEG-02, SEG-03, SEG-04, SEG-05, and LG-01 asshown on Figure 5. The Evans Gulch Stations exhibited the highest runoff stream flowvolumes in OU6, up to 65.5 cfs (BOR, 1996a). The peak flow at the South Evans Gulchstations was 26.6 cfs. Lincoln Gulch exhibited relatively low flows for only a shortperiod of time during the sampling period and carries surface flows only during springrunoff or significant rain events. The Phase 3 sampling program showed similarcharacteristics to the Phase 1 results (BOR, 1997). Generally, surface flows from EvansGulch do not reach the confluence with the Arkansas River from late summer until thestart of spring runoff and are not considered a significant source of metals to theArkansas River.

A Wetlands Study was performed by Woodward-Clyde (1992b) to delineate the existingwetlands within the Site. The wetlands within OU6 are shown on Figure 5, and consistprimarily of the upper reach of Stray Horse Gulch at Adelaide Park and most of thefloodplain of the Evans Gulch drainage.

5.2.2 Surface Water Chemistry

During the Phase 1 and Phase 3 surface water sampling events, Stray Horse Gulchexhibited acidic, sulfate-rich water indicative of ARD. The exception was at theupstream station SHG-07, directly downgradient of the Adelaide wetlands, where thewater had a near-neutral pH (see Figure 6). The pH decreased at each downstreamstation while zinc and cadmium loadings increased (BOR, 1996a).

Figure 6 provides the 1995 zinc and cadmium loading values for OU6 during springrunoff as calculated by the BOR in their Phase 1 report (BOR, 1996a). Zinc andcadmium are shown, as they are generally good indicators of water quality and arecontaminants of concern (Weston, 1995a). The BOR calculated flow-weighted metalloading using the following equation:

[(flow, cfs) x (28.3168 L/cf) x (6.048xl05 s/wk) x.(metal cone, ug/L)] / (l.OxlO9 ug/kg)

The reported value was then converted to pounds per day for use in this document.


5.2.3 Fluvial Tailing

The Mine Waste Piles and Tailing Disposal Area Remedial Investigations (Woodward-Clyde, 1994a and b) identified the fluvial tailing within the Site and evaluated whethersurface and/or groundwater had been affected. Fluvial tailings were categorized assuspected source areas and are shown on Figure 7. Note, however, that no fluvial tailingexist within OU6.

5.2.4 Stream Sediments

Stream sediments are naturally occurring throughout drainages of OU6 and havehistorically been disturbed due to placer mining. Table 1 presents a summary of themedian concentration of various analytes at multiple stations within each watershed forthe 1995 spring runoff.

Median stream bed sediment contaminant metal concentrations were highest in StrayHorse Gulch, followed by Lincoln Gulch, Evans Gulch, and then finally by South EvansGulch where median concentrations were the lowest. Contaminant metal concentrationstypically increased with decreasing station elevation. This is consistent with the greatercontributing watershed at lower surface water monitoring stations (BOR, 1996a).

5.3 GROUNDWATER

5.3.1 Hydrogeology

No hydrogeologic study existed at the time the OU6 Focused Feasibility Study wasprepared. Therefore, relevant information from the California Gulch Site HydrogeologicRI (Golder, 1996a) is used in this document to describe the hydrogeology of the area.This information is supplemented with the results of a recent study of the hydrogeologyin the vicinity of the LMDT (EPA, 2002b).

The Site contains two hydrogeologic units: one consists of unconsolidated sediments andthe other is a series of igneous and sedimentary bedrock formations. The unconsolidatedsediment unit includes a saturated section (alluvial aquifer) and several perchedgroundwater zones. The bedrock aquifer is the saturated portion of the bedrock unit.Groundwater recharge to the hydrologic units is from infiltration of precipitation,including snowmelt and surface water (Golder, 1996a).

The alluvial aquifer is largely contiguous and primarily under unconfined conditionsalthough perched groundwater can occur locally. Depth to groundwater varies from lessthan one foot near California Gulch to approximately 250 feet at higher elevations, andsaturated thickness ranges from 0 to over 1,000 feet in the alluvial aquifer above thebedrock contact. The average groundwater flow direction of the alluvial aquifer is east towest (S88°W) with a 0.03 foot/foot (ft/ft) hydraulic gradient. Lithologic variability,variable recharge rates, and interactions with surface water and/or groundwater cause


local variation in the groundwater flow direction and hydraulic gradient (Golder, 1996a).Alluvial aquifer water table contours from 1992 are provided in Figure 8.

The bedrock aquifer refers to the areas of granitic, metamorphic and sedimentary bedrockthrough which groundwater flows. This groundwater flow is primarily controlled byfracture zones associated with faults, solution features associated with calcareoussedimentary rocks, and mine workings. The bedrock aquifer is primarily underunconfined conditions in the eastern third of the Site and confined or partially confinedconditions in the western two-thirds of the Site. Depth to groundwater in the bedrockaquifer ranges from approximately 28 feet to 796 feet below ground surface (Golder,1996a). Groundwater levels and flow directions indicate that the bedrock aquifer isflowing into-both the Yak Tunnel and the LMDT. The hydraulic gradient near the YakTunnel ranges from 0.54 ft/ft to 0.13 ft/ft (Golder, 1996a). Near the LMDT, thehydraulic gradient is estimated to be 0.04 ft/ft. Outside of the influence of these drainagetunnels, the groundwater flow direction is west-northwest with a hydraulic gradient of0.02 ft/ft (Golder, 1996a). Potentiometric surface contours for the bedrock aquifer, basedon water level measurements taken in 1992, are provided in Figure 9.

Limited information concerning the alluvial/bedrock aquifer interaction is available fromthe Hydrogeologic RI. Groundwater level data was collected from alluvial aquiferpiezometer/bedrock monitoring well pairs PZ-4/BMW-1, PZ-6/BMW-2, PZ-10/BMW-3(see Figure 9). At PZ-4/BMW-1 AND PZ-6/BMW-2, an upward gradient of 0.26 and0.07 ft/ft was observed, respectively. The well pair PZ-10/BMW-3 exhibited adownward gradient of 0.39 ft/ft between the aquifers (Golder, 1996a). Subsurfacedrainage of bedrock aquifer groundwater by the LMDT may cause the relatively lowhydraulic head exhibited in the third well pair. There is no direct evidence of flowbetween bedrock and alluvial aquifer groundwater at this location.

The Yak Tunnel was developed to reduce mine-flooding problems experienced in theIron Hill region during hard-rock mining for lead ores in the late 1800's. Yak Tunnelconstruction began in 1895 at a bottom elevation of 10,330 ft. The tunnel proved soeffective at draining the Iron Hill area that it was extended to connect with the Ibex andResurrection mines (CDM, 1997). Construction began on a second tunnel, the LMDT, in1943 to drain mine workings below 10,063 ft including the lower parts of the Iron Hilibasin and the Downtown, Fryer Hill, and Carbonate Hill basins. The LMDT wascompleted in 1952.Recent studies of the LMDT and vicinity (EPA, 2002b) suggest that collapses in theLMDT have impounded substantial amounts of water in the LMDT and hydraulicallyconnected underground workings (mine pool). The specific locations of the collapses arenot known, and warrant further investigation. These collapses have resulted in changes inthe groundwater levels or conditions in the vicinity of the LMDT, OU6, California Gulch,and possibly other locations throughout the Leadville area. Collapses are suspected nearthe LMDT portal and near the Robert Emmet Shaft, approximately 10,000 feet from thetunnel portal (EPA, 2002b).


The increased hydraulic head associated with flooded mine workings (mine pool) in thevicinity of the Robert Emmet Shaft has caused recharge from the bedrock aquifer to thealluvial aquifer via local fault systems (Pendry Fault) resulting in rising groundwaterlevels in the alluvium of Lower California Gulch.

Dye tracer testing in the Marion and Robert Emmet Shafts has not substantiated concernsover migration of mine pool water away from the LMDT. Dye tracers introduced at theMarion and Robert Emmet Shafts have been recovered only at the LMDT portal. Otherthan this detection, dye has not been detected at any other surface water or groundwatermonitoring location (EPA, 2002b).

5.3.2 Groundwater Chemistry

Only limited information is available regarding groundwater quality in OU6. Figure 10illustrates the groundwater pH values as well as dissolved zinc and cadmiumconcentrations for November 1991 through January 1992 as reported in theHydrogeologic RI (Golder, 1996a). Background water quality was also investigated inthe Hydrogeologic RI. The investigation showed that both the alluvial and bedrockaquifers are of the calcium-magnesium-carbonate/sulfate type with a pH range from 7.3to 8.0. Dissolved metals were rarely above the detection limits.

The wells within OU6 (Figure 10) have been monitored periodically by CDPHE forchemicals other than zinc and cadmium. A comprehensive summary of thesegroundwater quality data for the Site can be found in RMC, 200la. Concentrations ofcadmium, iron, magnesium, zinc and sulfate are elevated. Low pH values are alsocommon.

Recent unpublished data (Tetra Tech-RMC, 2003) suggests that shallow alluvialgroundwater is being impacted by infiltration of ARD stored in some of the detentionponds constructed during prior Response Actions (Section 2.0). Elevated levels of arsenicand cadmium have been observed in monitoring wells proximal to the detention ponds.

Access to the flooded mine workings under OU6 is very limited and water qualitysampling has been limited to a single sample collected from the Robert Emmet Shaftlocated just north of the Marion Mineshaft illustrated on Figure 3. The sample contained2.66 ug/1 of cadmium, 18.5 ug/1 of copper, 22.5 ug/1 of lead, 185,150 ug/1 of manganeseand 164,850 ug/1 of zinc. The sample was collected in 1999 and represents conditionsprior to the introduction of ARD into the Marion mineshaft.

5.4 MINE WASTE

5.4.1 Mine Waste Types

Two types of mine wastes are present within OU6: waste rock and tailing. Mine wasterock piles are usually located near adit and shaft entrances and are comprised of rockexcavated during mine development, gangue (un-mineralized rock), and low-grade ores


(Water, Waste and Land, 1990). Gangue consists of material such as chert, limestone,quartzite, and minor quantities of rock with metal sulfide mineralization including pyrite,chalcopyrite, sphalerite, and galena. Surface exposure and weathering of these mineralsmay lead to pyrite oxidation resulting in the production of ARD with elevated metalsconcentrations.

Mill tailing is the waste generated during the processing of ore. When ores were taken tothe mill they were first crushed and separated into metallic concentrates and wasteproducts. These waste products were generally placed near the mill in a tailing pond.Tailing occurrence in OU6 is limited to the Hamms Tailing. Mine wastes in the OU6area are illustrated on Figure 11.

5.4.2 Mine Waste Locations

As part of the FFS, a number of mine waste areas were identified as candidates forpossible remedial action (see Figure 12 and Table-2). These areas were identified fromavailable surface water quality data, Airborne Visible and Infra-Red ImagingSpectroscopy (AVIRIS) data (Figure 13), surface soil chemical data, and fieldobservations of mineralogy. In addition, any mine waste area that was subjected to aprior Response Action resulting in mine waste exposed at the surface (i.e. that were notcapped) was considered to be a candidate for remedial action without further analyses.

Surface water quality data was obtained from investigations conducted by the BOR aswell as 2000 and 2001 synoptic sampling events by the Colorado Mountain College(CMC) and Rocky Mountain Consultants (RMC). Synoptic sampling is the sampling of aslug of water as it moves through a hydrologic system (RMC, 2001b). The surface waterdata was first analyzed to identify drainages that contribute significant loadingdownstream. When a potential source drainage was identified, the contaminant loadingtrends between individual surface water monitoring stations were evaluated to isolatesub-drainages of concern.

The sub-drainages were then analyzed with respect to surface mineralogy obtained fromremote sensing analysis of OU6 to map the distribution of surface minerals (AVIRIS).The AVIRIS instrument collects data from a NASA ER-2 aircraft at an altitude of 65,000ft with resolution of approximately 17 meters (BOR, 1997). The data is presented byshowing the predominant mineral in each 17 x 17 meter pixel as illustrated in Figure 13.

These data were used extensively to help prioritize ARD-generating source areas forResponse Actions implemented in OU6. The key indicators of ARD, as determined bythe BOR investigation are pyrite and its secondary minerals as listed below.


Mineral Chemical Formula ARD-Generation

Pyrite FeS2 HighCopiapite FeFe4(S04)60(OH)-20H20Jarosite (Na,K)Fe3(SO4)2(OH)6

Goethite alpha-FeO(OH)Hematite alpha-FeÔa Low

The last set of screening tools for identification of ARD-generating mine waste areas issurface soil chemical data and field observations of mineralogy. This information wasprimarily obtained from the Mine Waste Piles RI (Woodward-Clyde, 1994a). Based onfield reconnaissance, the Mine Waste Piles RI categorized the inventoried mine wastepiles into five groups:

ARD-Generation• Group 1: No observed minerals of concern. Low• Group 3: Minor amounts of sulfide minerals such as pyrite,

sphalerite and chalcopyrite, but no galena.• Group 2: Predominantly manganese and carbonate minerals

with occasional traces of pyrite.Group 4: Abundant amounts of sulfide minerals (except

galena) and occasional manganese and carbonateminerals.

• Group 5: Similar to Group 4 piles, but contain visible galena. High

The results of this screening identified mine waste areas in Stray Horse, Little StrayHorse and Upper Lincoln Gulch (Ibex/Irene Area). The general areas containing ARD-generating mine wastes-are illustrated on Figure 12.

The individual mine waste piles identified as candidates for remedial action are listedbelow. Those that have already been addressed by prior Response Actions are boldfaced.

• Greenback• RAM• Old Mikado• New Mikado• Highland Mary• Adelaide/Ward• Pyrenees• Fortune/Resurrection• Ponsardine• Emmet• Evans F&G


After further analysis, several portions of the Emmet mine waste area and the Evans F &G waste piles were dropped from consideration for additional remedial action asdiscussed below.

The Emmet mine area consists of five piles as identified in the Final Mine Waste Piles RI(Woodward-Clyde, 1994a). Two of these piles were directly associated with the EmmetMine, while the other three are located in the vicinity. The 2001 synoptic sampling datacollected by the Colorado Mountain College demonstrates a significant increase incontaminant concentrations between stations SHG-08 and SHG-09, as shown in Table 3,which lie just up- and down-stream of the Emmet Pile (see Figure 5). While this increasemay be attributable in part to the loading contribution from the Emmet Pile, it should benoted that there is uncertainty as to what portion of the loading is from the Emmet Pileand what portion may be from remediated source areas on the south side of Stray HorseGulch or in-channel seeps/springs. These areas (including Maid of Erin, Wolftone andMahala) have been consolidated and capped. However, the soils underlying the wastepiles may continue to discharge ARD as the remedies stabilize.

Based on a Group 5 categorization assigned by the Mine Waste Piles RI as well as visualobservations, two of the five piles in the Emmet Mine area were identified as ARD-generating (see Figure 12).

The final potential source area of concern identified during this process is referred to asEvans F&G. This area was delineated as two areas (Evans F & Evans G) in the DraftBOR Value Analysis Report (BOR, 1996b). The labeling scheme for these areas wasretained from the report for continuity. The Evans F&G area was initially identified dueto significant contaminant concentration increases between stations SEG-03, SEG-04 andSEG-05 during the 2000 spring run-off sampling event. In addition, AVIRIS data showedARD-generating mineralogies present in Evans areas F&G.

However, 1995 BOR water chemistry data showed that South Evans Gulch had thelowest median flow-weighted metal loading in OU6 (BOR, 1996a). Subsequent workidentified Lincoln Gulch as the largest source for loading to the Evans Gulch watershed.This was the basis for the Ibex/Irene Response Action documented in an ActionMemorandum (EPA, 2001). Based on this information, and the fact that Evans Gulch isnot considered to be a major loading source to the Arkansas River, the Evans F&G areawas not retained as a candidate for remedial action. However, long-term water qualitymonitoring will be performed as part of the remedy to observe any changes that mayaffect the Parkville Water Supply. As data are collected, and during the five-year remedyreview, changes in water quality will be assessed to determine if further work isnecessary

Table 2 provides a summary of the screening process used to define each of the candidatepiles identified in this document.


5.4.3 Mine Waste Quantities

The volume of each mine waste area identified in Figure 12 is listed in Table 4. Thevolumes were obtained from the Draft Value Analysis Report (BOR, 1996b) exceptwhere otherwise noted.

Since the Emmet mine area was not identified during the Value Analysis, an estimatedvolume for the two Emmet piles of concern was obtained using GIS topographic and pilelocation data obtained from the Leadville area GIS database provided by EPA Region 8.Initially, a Triangulated Irregular Network (TIN) model was created using currenttopographic information. A pre-mining TIN model was then produced by estimatingcontour locations before mine waste piles began to influence topographic features. Thesetwo TIN models were subtracted from one another to obtain approximate pile volumes.This volume is given in Table 4.

Recent studies of the LMDT and vicinity (EPA, 2002b) suggest that collapses in theLMDT have impounded substantial amounts of contaminated groundwater in the LMDTand hydraulically connected underground workings (mine pool). Although not supportedby recent dye tracer studies (EPA, 2002b) the potential or this impounded water tomigrate in the subsurface and/or to discharge to surface water remains. Therefore, themine pool will be addressed under the Selected Remedy. The volume of waterimpounded in the mine pool was estimated to range from 539,000,000 gallons to1,465,000,000 gallons (EPA, 2002b).


6.0 SUMMARY OF SITE RISKS

The Baseline Risk Assessment (BRA) estimates what risks site contaminants pose if noaction is taken. It provides the basis for taking action and identifies the contaminants andexposure pathways that need to be addressed by the remedial action. This section of theROD summarizes the results of the BRA for the Site as they apply to OU6.

6.1 HUMAN HEALTH RISKS

Although a BRA was not prepared specifically for OU6, a number of BRAs werecompleted for the Site. These are listed and briefly described below:

• Preliminary Human Health Baseline Risk Assessment for the California GulchNPL Site (Weston, 1991).

• Baseline Human Health Risk Assessment for the California Gulch SuperfundSite. Part C: Screening Level Soil Concentrations for Workers andRecreational Site Visitors Exposed to Lead and Arsenic (Weston, 1995b).

> Baseline Human Health Risk Assessment for the California GulchSuperfund Site. Part C: Evaluation of Worker Scenario.

> Baseline Human Health Risk Assessment for the California GulchSuperfund Site. Part C: Evaluation of Recreational Scenarios.

• Baseline Human Health Risk Assessment for the California Gulch SuperfundSite. Part A - Risks to Residents from Lead (Weston, 1996a).

• Baseline Human Health Risk Assessment for the California Gulch SuperfundSite. Part B - Risks to Residents from Contaminants other than Lead (Weston,1996b).

The findings of the BRAs regarding contaminants of concern, completed and significantexposure pathways and numerical clean-up goals are relevant to OU6.

6.1.1 Contaminants of Concern

Historic mining, milling and smelting operations typically contaminated the environmentwith a number of metals. This includes many of the metals which were the main objectiveof historic mining and refining activities (copper, lead, silver, zinc), as well as a varietyof other metals that exist in the ore body (arsenic, antimony, barium, beryllium,cadmium, chromium, nickel, manganese, mercury, thallium). Essentially, all of thesechemicals occur at elevated concentrations (compared to background) in on-Site media(including soil, mine wastes, surface water and groundwater), and all of these metals arecapable of causing adverse effects in humans if exposure is high enough (Weston 1996b).


Even though many metals occur at elevated concentrations in the environment aroundLeadville, experience at other sites, as well as the results of preliminary calculations atthis site indicate that lead and arsenic are the "risk drivers". Thus, the Baseline HumanHealth Risk Assessment for the California Gulch Superfund Site. Part C: Evaluation ofWorker and Recreational Scenarios focuses on these two chemicals (Weston, 1995b).

6.1.2 Exposure Assessment

The non-residential areas of OU6 are currently zoned Industrial Mining. However, thecurrent land use is primarily recreational. Risks associated with direct contact with minewaste and contaminated soils by the recreational adult and adult worker were evaluated inthe BRA. .

Human exposure to contaminants in surface water through direct contact with water orsediment is considered to be sufficiently minor across the Site that quantitative evaluationwas not warranted (Weston, 1995b).

Two small portions of OU6 are either zoned residential or adjoin residential areas. Theseinclude the Penrose Mine Waste Pile and Starr Ditch. The Penrose Mine Waste Pile iszoned residential and was capped with a soil cover during a prior Response Action.Therefore, the human exposure pathway has been interrupted at this location. Starr Ditchwas remediated under a prior Response Action by removing contaminated sediments. Inaddition, an extensive education and intervention program to manage lead exposure at theSite is included in the Lake County Community Health Program (LCCHP) implementedunder the Record of Decision for OU9. The LCCHP combines blood lead monitoring,education, community awareness, and residence-specific Response Actions to reduce therisk of lead exposure to children in Leadville and surrounding residential areas. Theprogram addresses lead from soil and dust, interior and exterior paint, leaded plumbingfixtures, and other potential sources beyond an individual residence. An extensiveeducation and intervention program to manage exposure at the site is an integral part ofthe program. For these reasons, it is believed that there are no known residentialexposures to unacceptable levels of contamination.

6.1.3 i oxiciry Assessment

EPA and CDPHE have identified many chemicals at the Site that pose unacceptable riskto human health and the environment. Of these chemicals of concern, the two chemicalsdescribed below are of primary concern at the Site.

Lead is present mostly in the waste rock, slag, and soil. Lead can accumulate in the bodyover time if exposure is frequent or continuous. It can cause harm if present abovecertain levels in the human body. Lead can affect the development of the nervoussystem, including impaired learning ability and hearing, and the reproductive system.Children are especially vulnerable to lead contamination for the following reasons: Theirbodies and brains are still developing and they absorb more lead than adults, and childrenoften play outside where they are more likely to be exposed to lead in the soil. They aremore likely to put dirty fingers and toys in their mouths.


Arsenic is also present in mine waste rock, slag, soil and groundwater at the Site. Arsenicdoes not easily accumulate in the body. Most arsenic that is absorbed into the body isefficiently passed in the urine. Harmful health effects related to long-term exposure totoo much arsenic include lung and skin cancer and digestive tract problems. Oralexposure to high doses of arsenic produces marked acute irritation of the gastrointestinaltrack, leading to nausea and vomiting.

6.1.4 Risk Characterization

Weston (1995b) developed risk-based action levels for lead and arsenic rather thancalculating risks for all areas of the Site. Action levels were developed for recreationaland worker scenarios. The action levels represent risk-based concentrations protective ofhuman health and may be used to identify soils (or mine waste) of potential concern torecreational visitors or workers.

For the recreational scenario, lead action levels ranged from as low as 5,000 mg/kg to85,000 mg/kg, depending upon which input parameters were used (Weston, 1995b). Alead concentration of 16,000 mg/kg was selected for comparison to soil concentrationsfor lead (Weston 1995b). For arsenic, action levels ranged from 1,400 to 3,200 mg/kgbased on carcinogenic and systemic effects, respectively (Weston, 1995b). An arsenicconcentration of 1,400 mg/kg was selected for comparison to soil arsenic concentrations,based on the potential carcinogenic health effects (Weston, 1995b). The recreationalscenario considered all appropriate age groups.

For the worker scenario, plausible action levels for lead ranged from as low as 2,200mg/kg to as high as 19,100 mg/kg. The central tendency values include 6,100 and 7,700mg/kg (geometric and arithmetic mean, respectively; Weston, 1995b). Leadconcentrations in this range are likely to be protective with a reasonable degree ofconfidence (Weston, 1995b). For arsenic the plausible action levels range from 330mg/kg to 1,300 mg/kg. The central tendency values include 610 and 690 mg/kg(geometric and arithmetic mean, respectively, Weston, 1995b).

For the residential scenario, the lead action level, as identified in the OU9 ROD, is 3,500mg/kg (USEPA, 1999c). For arsenic, PRGs ranged from 120 mg/kg to 340 mg/kg(Weston, 1996b). Action levels for arsenic and lead are likely exceeded in some locationswithin OU6 and will be addressed through implementation of the ICO District.

In order to identify areas where action levels might be exceeded, the action levels werecompared to soil concentration values presented in previous Remedial Investigations(RIs). Note that it is the average lead level and 95% upper confidence limit of the meanarsenic level over an area that should be compared to the soil action level. Occasionalmeasurements of concentrations above the action level do not necessarily constituteevidence that an area is unsafe (Weston, 1995b).


Inspection of prior Site-wide RIs (containing data from OU6) shows that average leadlevels are generally well below the action level of 16,000 parts per million (ppm) forareas where recreational scenarios are considered likely (Weston, 1995b). For the workerscenario, the average lead levels are mostly below the central-tendency range of plausibleaction levels (6100-7700 ppm) for most areas zoned for commercial land use, with thepossible exception of some areas in the historic mining area east of town (includingportions of OU6) (Weston, 1995b). Therefore, the potential exists for action levels to beexceeded under the worker scenario in portions of OU6.

In accordance with the 1994 Consent Decree (USDC, 1994), remedial action objectives(RAO's) for OU6 do not include achieving numerical water quality goals. Achievementof quantitative water quality goals will be addressed under the RAO's for OU12.

6.2 ECOLOGICAL RISKS

Although an assessment of ecological risks was not prepared specifically for OU6, anumber of ecological risk assessments (ERA's) were completed for the Site. These arelisted below:

• Final Baseline Aquatic Ecological Risk Assessment for the California GulchNPL Site (Weston, 1995a).

• Ecological Risk Assessment for the Terrestrial Ecosystem, California GulchNPL Site (Weston, 1997).

6.2.1 Contaminant Identification

The Aquatic ERA (Weston, 1995a) identifies the impact of mine waste contamination onthe aquatic ecosystem at the Site. The media of concern were surface water andsediments. The contaminants evaluated included aluminum, arsenic, barium, cadmium,copper, iron, lead, manganese, nickel, selenium, and zinc. Further assessment has lead toa refinement of this initial list to the following chemicals of potential concern for surfacewater:

• Aluminum• Cadmium• Copper• Lead• Zinc

Media evaluated in the Terrestrial ERA (Weston, 1997) included soil, slag, waste rock,and tailing in upland areas, and fluvial tailing and sediments in riparian areas. Only datafrom the top two inches of these media were evaluated. Adverse impacts on the terrestrialecosystem from exposure to contaminants in surface water were also evaluated.Contaminants evaluated included arsenic, antimony, barium, beryllium, cadmium,chromium, copper, lead, nickel, manganese, mercury, silver, thallium, and zinc.


6.2.2 Exposure Assessment

The Aquatic ERA evaluated ecological receptors typical of those present or historicallypresent at the Site, consisting of aquatic plants, benthic macroinvertebrates, and fish(primarily trout species). The potential exposure pathways for aquatic receptors wereingestion of surface water, sediments, and dietary items, and direct contact with surfacewater, sediments, and modeled concentrations of dissolved contaminants in sedimentpore water.

Aquatic risks were assessed by sampling station rather than by OU. Sampling stations ofconcern in OU6 were in the Stray Horse Gulch and Starr Ditch drainages. However, thephysical limitations of these and other OU6 tributaries preclude the support of aquaticlife. Therefore, risk evaluations were focused on California Gulch and the Arkansas River(CDM, 1997).

Receptors evaluated in the Terrestrial ERA were representative of those found at OU6;upland and riparian vegetation communities, birds, and herbivorous and predatorymammals. Contaminant intakes were estimated for these receptors based on assumptionsregarding exposure, such as food ingestion rates and body weight. Exposure pathwaysevaluated included direct exposure to contaminated media, ingestion of contaminatedponded water or surface runoff, incidental ingestion of contaminated media, and indirectexposure through the food chain (Weston, 1995b).

The Aquatic ERA used the 95% upper confidence limit (UCLgs) as the exposure pointconcentration (EPC) for chronic exposure. If the UCL^s was greater than the maximumcontaminant concentration, the maximum was used as the chronic EPC. The maximumcontaminant concentration was used to represent the acute exposure (Weston, 1995a).

The Terrestrial ERA used the UCLgj as the EPC to evaluate risk by OU. If the maximumcontaminant concentration was less than the UCL95, the maximum was used as thechronic EPC. Risks were also characterized by sampling station. The maximumcontaminant concentrations were used to calculate risks at individual sampling stationsdue to limited data quantities per station.

6.2.3 Toxicity Assessment

The toxicity assessment in the Aquatic ERA discusses the toxicity of inorganic elementsto aquatic species. However, the toxicity varies so widely that it is not practical to listspecific concentrations that cause effects under conditions of acute or chronic exposurefor all species. The Aquatic ERA reaches the general conclusion that concentrationsbelow the Ambient Water Quality Criteria (AWQC) or state standards are unlikely toadversely affect populations of fish or macro invertebrates.

The lexicological, literature was reviewed in the Terrestrial ERA to obtain acceptablechemical concentrations in the environment for plants and soil fauna, as well asacceptable intakes for birds or mammals. The goal of the literature review was todocument No Adverse Effect Levels (NOAELs) for each receptor and chemical. Because


literature values for any given wildlife species are often lacking, there was typically onlyone good study for birds, and one for mammals, which was used to represent the avianand mammalian receptors, respectively. One study was selected to represent the plants,and one study selected to represent soil fauna. Even this distillation of available literatureinformation is too large for inclusion in this ROD. The relevant toxicological informationis provided in the Terrestrial ERA (Tables 4-4 and 4-5, Weston 1977).

6.2.4 Risk Characterization

The Aquatic ERA used EPA AWQC as well as standards developed by the State ofColorado to evaluate the toxicity of contaminants in surface water to aquatic receptors.Sediment toxicity values were derived from the toxicological literature. Sediment andsurface water toxicity criteria were compared to contaminant EPCs to determine risk toaquatic receptors. The resulting value is termed a hazard quotient (HQ). An HQ less thanone indicates there is little potential for adverse effects to occur. An HQ greater than oneindicates a potential for risk but does not necessarily mean that adverse effects will occur.The sum of the HQ's is the hazard index (HI).

HQs and Hi's specific to OU6 were not presented in the ERA's. Therefore, this summarydoes not provide quantitative risks associated with surface water in OU6. Results of theAquatic RA indicate that mine waste poses potential risk to all aquatic species.

In accordance with the 1994 Consent Decree (USDC, 1994), remedial action objectives(RAO's) for OU6 do not include achieving numerical water quality goals. Achievementof quantitative water quality goals will be considered under the RAO's for OU12.

To quantify terrestrial risks, exposure intakes were estimated for upland and wetlandreceptors and hazard quotients (HQs) were calculated by analyte for each receptor. Dueto the large number of analytes, receptors and media evaluated, Hazard Indices (His)were estimated by summing the HQs for each exposure pathway for all analytes. TheOU6 His are given in Table 5. A review of this table reveals ecological risks above alevel of concern for several birds and mammal. Species with Hi's above 20 include Bluegrouse, Mountain Bluebird and Least Chipmunk.


7.0 REMEDIAL ACTION OBJECTIVES

7.1 INTRODUCTION

The objectives of the Response Actions taken to date in OU6 and documented in thisROD are very specific and originate in a Consent Decree (CD; USDC, 1994). TheUnited States, the State of Colorado, and the Potentially Responsible Parties entered intothe CD in 1994. The objectives set forth in the CD were to:

1. Protect public health, welfare, and the environment from releases or threatenedreleases of waste material at or from the Site;

2. To divide the Site into areas of responsibility among the parties;

3. To improve the quality of Site-wide Surface and Ground Waters through SourceRemediation;

4. To reimburse the Past and Future Response Costs of the Plaintiffs;

5. To resolve the liabilities of the Settling Defendants at the Site

6. To resolve the claims of the Settling Defendants against the United States and theState.

The CD defines Source Remediation (mentioned in Item 3, above) as:

"Response Actions designed to prevent or control the release or threatenedrelease ofwaste^materialfrom sources of contamination such as tailingsimpoundments, fluvial tailings, waste rock piles and soils into all pathways ofmigration, but shall not include any treatment of Site-wide Surface or GroundWaters."

Item 3, above, provides the most specific direction for remedial measures in OU6. Therequirement to improve water quality through source remediation presents an inherentlimitation in the scope of the remedial alternatives and remedial objectives. Restrictingremedial action to source remediation may preclude the achievement of any specificnumerical water quality objectives for surface or groundwater in OU6. This is due to:

• The presence of non-point source pollution.• The discharge of contaminated groundwater to surface water.• Natural background contaminant levels.

These limitations coupled with the specific exclusion of Site-wide surface or groundwater treatment leads to the conclusion that remedial action objectives should not, at thistime, include chemical-specific numerical water quality standards applied within OU6boundaries. Rather, the objective is to reduce metal loading to the watershed to the


extent practicable. Although this is a subjective standard, the effectiveness of existingand proposed remedial actions can be measured or estimated as a relative improvement inwater quality from pre-remedial conditions.

Chemical-specific water quality standards will be formally addressed under OU12. TheParties to the 1994 Consent Decree agreed the OU was established to determine finalSite-wide surface and groundwater quality standards and a process for achieving thosestandards after source remediation is completed.

7.2 MEDIA OF CONCERN

Before setting the Remedial Action Objective (RAO's) for OU6, consideration was givento the specific environmental media that constitute a source for metals in the watershedand therefore should be targeted for remedial action.

The CD suggests materials that may be considered sources:

"Response Actions designed to prevent or control the release or threatenedrelease of waste material from sources of contamination such as tailingsimpoundments, fluvial tailings, waste rock piles and soils into all pathways ofmigration, but shall not include any treatment of Site-wide Surface or GroundWaters."

As discussed in Section 2.0 the only fluvial or impounded tailing in OU6 is the formerHamm's Tailing Impoundment. These mine wastes were consolidated and capped in1996. No tailing remain exposed at the surface in OU6. Native soils are not consideredto be a significant source of ARD.

Although not specifically identified in the CD's definition of Source Remediation, streamsediments were also considered as a medium of potential concern. Most of the priorResponse Actions included the removal of stream sediments, construction of sedimentbasins and the re-routing of stream channels around ARD-generating mine wastes. Inareas of OU6 where stream sediments have not been physically removed (Evans Gulch),metal loading at the OU6 boundary has been relatively low and is not believed tosignificantly contribute to human or ecological risk. Therefore, stream sediments are notconsidered a medium of concern and are not targeted for remedial action throughphysical removal.

Mine waste rock remains the primary source for metal loading to surface and groundwater in OU6.


7.3 MIGRATION PATHWAYS OF CONCERN

Before setting the RAO's for OU6, consideration was given to the potential contaminantpathways of concern. As a starting point, the migration pathways of concern listed in theScreening Feasibility Study (SFS) (EPA, 1993) were considered including:

• Control wind erosion of waste rock materials from the source locations.• Control water erosion of waste rock materials from the source locations.• Control leaching and migration of metals from waste rock into surface water.• Control leaching of metals from waste rock into groundwater.

The first migration pathway (airborne transport) was determined to present a humanhealth risk below a level of concern. The Baseline Human Health Risk Assessment -Part A: Risks to Residents from Lead (Weston, 1996a) concluded that "inhalationexposure to lead is minimal at this site, and the inhalation exposure was not consideredfurther in this assessment. " Based on this conclusion, airborne transport of contaminantswas not considered further.

The second, third and fourth migration pathways relate to the release of metals fromsource material (mine waste rock, in the case of OU6) to surface and ground water.These migration pathways were considered relevant.

7.4 REMEDIAL ACTION OBJECTIVES

Based on the forgoing, the RAO's for OU6 include:

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.4. Prevent direct unacceptable exposures to elevated concentrations of contaminants

in the soil and waste rock.


8.0 DESCRIPTION OF ALTERNATIVES

This section provides a brief explanation of the remedial alternatives developed for OU6.Remedial alternatives described below were retained after preliminary screening andwere evaluated using the nine criteria required by the NCP and six additional criteriarequired by the Work Area Management Plan (WAMP) as part of the CD. Alternative 3(Expand Surface Water Management) was not retained and is not discussed further.

8.1 ALTERNATIVE 1: NO ACTION

Estimated capital and operating cost: $0Implementation time: Immediate

This alternative leaves waste rock in OU6 in its current condition. Remedies previouslyimplemented as Response Actions would be abandoned as-is with no monitoring ormaintenance. The current discharge of contaminated surface water to the LMDT(introduction into the Marion Shaft) would be abandoned and the flows allowed to enterthe Stray Horse Gulch channel when the collection ponds overtop.

8.2 ALTERNATIVE 2: MAINTAIN CURRENT REMEDIES W/LAND USECONTROLS

This alternative involves maintaining the prior Response Actions and the addition of landuse controls through an ICO District. Maintenance of capped mine waste materials wouldrequire periodic inspection, repair of erosional features and other minor repairs.Maintenance of the water management remedies would require sediment removal fromretention ponds and other catch basins, and the conveyance, storage, and treatment ofcollected ARD.

Alternative 2 includes seven ARD conveyance, storage and treatment options, detailedbelow. ARD considered under the conveyance/treatment options includes only thecurrent discharge to the Marion Shaft. Treatment options include the Yak and BORtreatment plants or a new, dedicated treatment facility. Cost estimates for each of theoptions under Alternative 2 assume that an on-Site waste repository would be developedwithin the Site and would accept wastes generated under this alternative.

Land use controls would be implemented as part of this remedy and would limit access toor use of the areas remediated through prior Response Actions. EPA will work with LakeCounty on the ICO District for the unremediated portions of OU6, including exposedmine wastes and contaminated soils remaining in-place. These controls will protectexisting remedies including caps and diversions and would ensure that future changes inland use are protective of human health and the environment.


• Alternative 2a - Pressurized Pipeline to Yak Tunnel

Estimated capital and operating cost: $12,589,648Implementation time: 2-years

This alternative involves the construction of a lift station at the Greenback Pondto deliver ARD via a pressure line to a vertical bore advanced into the Yak Tunnelat a location up-stream of the existing bulkhead. The subsurface mine workingswould be used to store contaminated water that would be metered out and treatedat the Yak Treatment Plant.

• Alternative 2b - Gravity Pipeline to Yak Water Treatment Plant w/Storage


This alternative involves delivering ARD to the Yak surge pond via a gravitypipeline. A 10 million gallon lined impoundment would be constructed along thepipeline alignment to permit water to metered out to the Yak surge pond.

• Alternative 2e - Gravity Pipeline to Existing Pumping Well along LMDTw/Storage


This alternative-involves delivering ARD to the existing extraction well along thelower portion of the LMDT. The existing pipeline between the extraction well andthe BOR treatment plant would be used to convey OU6 ARD to the BOR's plant.A 10-million gallon lined impoundment would be constructed along the pipelinealignment to permit water to be metered out to the BOR's plant.

• Alternative 2g - Install Bulkhead in LMDT and Dewater Mine Poolw/Gravitv Pipeline to BOR Treatment Plant (Selected Alternative)


This alternative involves continuing the introduction of ARD into the MarionShaft. A bulkhead would be constructed in the LMDT where it passes throughcompetent rock. The ground water upstream of the bulkhead (mine pool) wouldbe pumped and delivered to the BOR treatment plant via a gravity pipeline.Significant plant upgrades would be needed in order for this alternative to beselected. This alternative would result in the treatment of collected ARD as well


as the accelerated treatment of contaminated groundwater filling the mineworkings in OU6.

• Alternative 2h - Gravity Pipeline to Dedicated Water Treatment Plant


This alternative involves the construction of an independent water treatmentfacility to treat ARD collected in OU6. The water would be conveyed to thetreatment facility from the Greenback Pond via a gravity pipeline and returned toStray Horse Gulch after treatment. The alternative would result in the long-termtreatment of collected ARD.

8.3 ALTERNATIVE 4: IN-SITU CHEMICAL STABILIZATION ORRELOCATION (IN COMBINATION WITH ALTERNATIVES OPTIONS2A THROUGH 2H)

This alternative involves maintaining the existing remedies (identical to Alternative 2) inaddition to selecting one of two options for addressing waste rock piles that areconsidered to be sources for ARD that have not been previously addressed throughResponse Actions. These include the Ponsardine and Emmet waste rock piles.

• Alternative 4a - In-Situ Chemical Stabilization

Estimated capital and operating cost: $400,000Implementation time: 1-year

This alternative would involve the injection and dispersion of buffering agentsinto the Ponsardine waste pile so that a final equilibrium is reached that inhibitsacid generation. Chemically stabilized systems are susceptible to weathering andchemical decomposition therefore the potential for contact by surface water run-on or runoff during storm events should be minimized. This process wouldmaintain the general integrity of the waste piles for cultural and historicalaesthetics. However, some disturbance of the pile would be expected, asequipment will need to access all portions of the pile.

• Alternative 4b - Relocation (Selected Alternative)

Estimated capital and operating cost: $292,236Implementation time: 1-year

This alternative involves the relocation of the Ponsardine waste pile to the on-Siterepository planned for the Site as discussed under Alternative 2. A four-mile hauldistance is assumed for costing purposes. This alternative includes repairs


(physical stabilization) of a retaining crib wall on the south side of the Emmetwaste rock pile.

8.4 ALTERNATIVE 5: CONSOLIDATE AND CAP W/LAND USECONTROLS


This alternative involves consolidating and capping of waste rock piles that areconsidered to be sources for ARD. This alternative excludes those mine wastes that havealready been consolidated and capped. The cap design would follow that implementedduring prior Response Actions including a geomembrane and an 8-foot thick dolomitewaste rock cap. Cap material other than dolomite may be considered equally effective.

8.5 ALTERNATIVE 6: EXCAVATE, TRANSPORT AND ON-SITE DISPOSALW/LAND USE CONTROLS


This alternative would involve the excavation, transport, and disposal in an wasterepository (constructed within the OU6 boundaries) of waste rock piles (and underlyingsoils to a depth of 1-foot) that are considered to be sources for ARD. This alternativeexcludes those mine wastes that have already been consolidated and capped. The pilefootprint would be vegetated after removal. The repository is not associated with the on-Site waste repository discussed in Alternative 2. Rather, it would be located within OU6and would meet most of the requirements for an industrial solid waste landfill cellincluding a geomembrane bottom liner and cover, or appropriate alternatives.


9.0 SUMMARY OF COMPARATIVE ANALYSISOF ALTERNATIVES

Section 300.430(e)(9) of the NCP requires that the EPA evaluate and compare theremedial cleanup alternatives using the nine criteria listed below. The first two criteria,(1) overall protection of human health and the environment and (2) compliance withapplicable or relevant and appropriate requirements (ARAR), are threshold criteria thatmust be met for the Selected Remedies. The Selected Remedies must then consider theremaining 5 balancing and 2 acceptance criteria. In addition, the cleanup alternativeswere evaluated using six performance criteria specified in the WAMP (USDC, 1994) toassist in evaluating the effectiveness of each alternative. A summary of the comparativeanalysis is presented on Tables 6 and 7.

9.1 NCP CRITERIA

9.1.1 Overall Protection of Human Health and the Environment

Overall protection of human health and the environment addresses whether eachalternative can adequately protect human health and the environment, in both the short-and long-term, from unacceptable risks posed by hazardous substances, pollutants, orcontaminants present at the site by eliminating, reducing, or controlling human andenvironmental exposures.

The range of alternatives provides the full spectrum of protectiveness from No Action(Alternative 1) through alternatives that result in the isolation of source material fromhumans and the environment (Alternative 5 and 6). The intermediate alternative(Alternative 2) offers protectiveness equal or somewhat greater than that alreadyachieved through prior Response Actions.

All of the alternatives (except Alternative 1) require institutional controls under the ICODistrict to minimize the likelihood of human health risks above a level of concern.

9.1.2 Compliance with Applicable or Relevant and Appropriate Requirements

Compliance with ARARs addresses whether a remedy will meet all of the applicable orrelevant and appropriate requirements under federal environmental laws and stateenvironmental or facility siting laws or provide grounds for invoking waivers.

There are no chemical-specific ARARs for OU6. All of the alternatives are expected tocomply with action- and location-specific ARARs.

9.1.3 Long-Term Effectiveness and Permanence

Long-term effectiveness and permanence refers to expected residual risk and the abilityof a remedy to maintain reliable protection of human health and the environment overtime, once cleanup levels have been met. This criterion includes the consideration of


residual risk that will remain on-Site following remediation and the adequacy andreliability of controls.

The variations on Alternative 2 require perpetual operation of ARD collection,conveyance and treatment facilities. Therefore, while these alternatives are effective inthe long-term they are less permanent. Alternatives 4b, 5 and 6 offer equal or greaterlong-term effectiveness when compared with the other alternatives. Alternatives 4b, 5and 6 also offer greater permanence than the other alternatives. The isolation of ARD-generating source material either under engineered caps or through placement in a landfillcell provides a greater level of permanence with low maintenance.

Within the variations on Alternative 2, the Selected Remedy (Alternative 2g - constructbulkhead in LMDT) offers some additional long-term effectiveness when compared withthe other Alternative 2 options. Under option 2g, the likelihood of untreated ARD beingdischarged to surface water is minimized through the use of the LMDT mine pool to storeARD even during high runoff years. Groundwater entering the LMDT downstream of thebulkhead is expected to eventually be relatively clean. This may permit discharge ofLMDT portal flows without treatment thereby improving the efficiency of the BOR'swater treatment program. In addition, dewatering of the mine pool over time will reducethe potential for contaminated groundwater to discharge to surface water through seeps,springs and flowing mine shafts.

The degree of effectiveness and permanence realized through implementation ofAlternative 2g depends, in part, on the competency of the LMDT and flooded mineworkings connected to the LMDT. The area of the LMDT targeted for bulkheadconstruction is considered to be competent bedrock. However, the current and potentialfuture conditions in the LMDT are not well understood.

In order to help assess long-term effectiveness, a monitoring program will beimplemented to observe groundwater quality, flows and hydraulic head levels. This isdiscussed further in section 11.3 (Contingency Measures and Long-Term Monitoring)

9.1.4 Reduction of Toxicity, Mobility, or Volume Through Treatment

Reduction of toxicity, mobility, or volume through treatment refers to the anticipatedperformance of the treatment technologies that may be included as part of a remedy.Alternatives are assessed for the degree to which they employ recycling or treatment thatreduces toxicity, mobility, or volume, including how treatment is used to address theprincipal threats posed by the site.

Treatment of source materials is provided only under Alternative 4, In-situ ChemicalStabilization. This technology, if effective, will reduce the mobility of the contaminantsthrough chemical and possibly physical fixation. Alternative 2 will treat collected ARDand convert the dissolved metals to solid metal complexes thereby reducing the mobilityof the contaminants. Alternatives 5 and 6 will minimize the generation of ARD, thereby


reducing the mobility of the contaminants. None of the alternatives affect contaminantvolume or toxicity.

9.1.5 Short-Term Effectiveness

Short-term effectiveness addresses the period of time needed to implement the remedyand any adverse impacts that may be posed to workers, the community and theenvironment during construction and operation of the remedy until cleanup levels areachieved.

Alternatives 1, 2, and 4a do not require significant disturbance of mine wastes.Alternatives-4b, 5 and 6 involve moderate to large-scale disturbance of mine wastes.Therefore, relatively greater short-term impacts would be expected.

9.1.6 Implementability

Implementability addresses the technical and administrative feasibility of a remedy fromdesign through construction and operation. Factors such as availability of services andmaterials, administrative feasibility, and coordination with other governmental entitiesare also considered.

All of the alternatives are technically and administratively implementable. However, pastcommunity objection to remedies that result in significant disturbance to mine wastesmay render Alternatives 5 and 6 not implementable.

The variations on Alternatives 2 require a range of operation and maintenance activitiesincluding long-term water treatment. The implementation of Alternative 2, including theSelected Remedy (2g) will require the development of long-term operating agreementsbetween the State of Colorado, USEPA and the Bureau of Reclamation. Therefore, theimplementability of Alternative 2 is considered to be moderate.

Land use controls would be implemented under an overlay district planned for the Site.Implementability of the overlay district is considered to be moderate.

9.1.7 Cost

The costs of Alternatives 2g and 4b (the Selected Remedy) are difficult to quantify at thistime given uncertainties regarding water treatment plant upgrades that may be needed. Inaddition, the BOR plant replacement costs are also uncertain and impact Alternatives 2eand2g.

Despite these uncertainties, it is possible to rank the alternatives by cost. Alternative 1has no costs associated with it. The options under Alternative 2 are all expected have alower present worth cost than Alternatives 5 and 6. Alternative 6 is less costly thanAlternative 5. All costs are summarized on Table 8.


9.1.8 State Acceptance

The State has been consulted throughout this process and concurs with the SelectedRemedy.

9.1.9 Community Acceptance

Public comment on the FFS and Proposed Plan was solicited during a formal publiccomment period extending from April 3 through May 3, 2003. The community isgenerally supportive of the selected remedial alternatives. Written comments andcomments received during the public meeting pertained to clarification of specific issuesassociated with the selected remedial alternatives. One comment objecting to therelocation of the Ponsardine mine waste pile was received from a private citizen whoresided near OU6. A private citizen who owns property within OU6 submitted onecomment expressing concern over the proposed use of the Black Cloud TailingImpoundment as the location for an on-Site repository. Otherwise, there were noobjections to the selected remedial alternatives and questions posed during the publicmeeting appeared to be satisfactorily addressed during the meeting. The ResponsivenessSummary addresses all comments received during the public comment period.

9.2 WAMP CRITERIA

WAMP Criteria are based on a Draft Work Area Management Plan prepared by USEPAin 1995. The plan identifies criteria to be used to evaluate the effectiveness of remedialalternatives developed in an FS. These criteria were included in the OU6 FFS to ensureconsistency in remedial design and construction at all operable units as described in the1994 Consent Decree. The description of the criteria follows EPA, 1995b.

9.2.1 Surface Erosion Stability

Remedial alternatives for source material were assessed for surface erosion stability.Erosion stability would be achieved through the development of surface configurationsand implementation of erosion protection measures. Predictions of erosion stability anderosion protective measures include:

a) Erosional releases of waste material will be predicted by use of all or some of thefollowing procedures: the Revised Universal Soils Loss Equation (RUSLE), winderosion soil loss equation and the procedures set forth in the U.S. NuclearRegulatory Commission's Staff Technical Position on the Design of ErosionProtection Cover For Stabilization of Uranium Mill Tailing Sites for site specificstorm flow condition set forth in (b), below or other standard recognizedengineering methods.

b) Remediated surfaces located within the 500-year floodplain shall be stable under500-year, 24-hour and 2-hour storm events. Remediated surfaces located outsidethe 500-year floodplain shall be stable under 100-year, 24-hour and 2-hour storm


events. On source area embankments or where the slope of the reconstructedsource is steeper that 5:1, surface flow shall be concentrated by a factor of 3 forpurposes of evaluating erosion stability.

Alternatives 1, 2, and 4A do not require significant disturbance of mine wastes. Wastepiles consolidated and capped under Alternative 5 and 6 will comply with this WAMPcriterion. Alternative 4B will result in the removal of the Ponsardine waste pile andAlternative 6 leave none of the ARD-generating mine waste targeted for remediationexposed at the surface.

9.2.2 Slope Stability

Source remediation alternatives were assessed for geotechnical stability. Geotechnicalstability would be ensured through the development of embankments or slope contours.The remedial design would meet the following:

a) Impounding embankments shall be designed with a Factor of Safety (SafetyFactor) of 1.5 for static conditions and 1.0 for pseudo-static conditions.

b) Recontoured slopes shall be designed with a Safety Factor of 1.5 for staticconditions and 1.0 for pseudo-static conditions.

c) Analysis of geotechnical stability shall be performed using an acceptable model.Material and geometry input parameters would be obtained from available data.

Alternatives 1, 2, and 4A do not require significant disturbance of mine wastes. Wastepiles consolidated and capped under Alternative 5 and 6 will comply with this WAMPcriterion. Alternative 4B will result in the removal of the Ponsardine waste pile andAlternative 6 leave none of the ARD-generating mine waste targeted for remediationexposed at the surface.

9.2.3 Flow Capacity and Stability

Remedial alternatives were assessed for conformance with flow capacity and stabilityrequirements. The remedial design would meet the following criteria:

a) Capacity: Diversion ditches shall be sized to convey the 100-year, 24-hour and 2-hour storm events. Reconstructed stream channels shall be sized to convey flowequal to or greater than the flow capacity immediately upstream of thereconstruction.

b) Stability: Erosional releases of Waste Material from ditches, stream channels, orretaining structures as determined by all or some of the following models andengineering methods: U.S. Army Corps of Engineers Hydrologic EngineeringCenter HEC-1 and HEC-2 models or by other recognized engineering erosionalmodels.


1. Diversion Ditches and Reconstructed Stream Channels: Remedialconstruction located within the 500-year floodplain shall be designed to bestable under flows resulting from a 500-year, 24-hour and 2-hour stormevents. Remedial construction outside of the 500-year floodplain shall bedesigned to withstand flows resulting from 100-year, 24-hour and 2-hourstorm events. Reconstructed stream channels shall be configured to the extentpracticable to replicate naturally occurring channel patterns.

2. Retaining structures: Structures such as gabions, earth dikes, or riprap shall bedesigned to be stable under the conditions stated above in item (a) for thediversion ditch or stream channel with which the structure is associated. Ifriprap is to be placed in stream channels or ditches, the riprap will be sizedutilizing one of the following methods:

> U.S. Army Corps of Engineers> Safety Factor Method> Stephenson Method> Abt/CSU Method

Selection of one of these methods will be based on the site-specific flow and slopeconditions encountered.

None of the alternatives involve the construction of channels with the possible exceptionof Alternative 6, which may involve the diversion of storm water around and off of theon-Site repository.

9.2.4 Surface Water_and Groundwater Loading Reduction

Remedial alternatives were assessed for reduction of mass loading of Contaminants ofConcern (COCs), including Total Suspended Solids (TSS) and sulfate, as defined in theAquatic Ecosystem Risk Assessment, and change in pH, resulting from run-on, runoffand infiltration from source areas. This criterion incorporates the following:

• For each source of contamination evaluated, the present mass loading of COCs(including TSS and sulfate) and present pH measurements should be calculatedfor both surface water and ground water using scientifically accepted methods.

• For each source of contamination evaluated, the net loading reduction of COCs(including TSS and sulfate) and change in pH resulting from implementation ofeach remedial alternative should be calculated for surface water and groundwater.Scientifically accepted methods for calculating mass loading shall be used.

Alternative 1 is expected to achieve little reduction in surface and groundwater loading.Alternative 2 maintains existing improvements in metal loading. Therefore, actual ratherthan modeled reductions in mass loading of cadmium and zinc to surface water are


provided on Figures 14 and 15. It is possible that ARD detention ponds included underAlternative 2 will result in an increase in loading to groundwater. Section 11.3 discussescontingencies should long-term monitoring demonstrate an increase in loading togroundwater under Alternative 2.

Significant reduction in mass loading is expected under Alternative 4a. However, themagnitude of the reduction is a function of the effectiveness of the chemical/physicalstabilization process. Reduction in mass loading under Alternative 4b is expected to becomplete for the Ponsardine waste pile. Stabilization of the Emmet crib wall is expectedto achieve some reduction in mass loading to surface water. Water quality monitoring ofthis portion of Stray Horse Gulch will be needed to assess the degree of loadingreduction. Reduction in mass loading under Alternatives 5 and 6 is expected to be nearlycomplete as these alternatives result in the isolation of the waste rock from theenvironment..

9.2.5 Terrestrial Ecosystem Exposure

Remedial alternatives were assessed with respect to reduction of risk to the terrestrialecosystem within OU6. This assessment was based on area-wide estimations of risk toreceptor populations. Exposure estimations for assessing this risk considered factors thataffect frequency and duration of contact with contaminated media, such as (1) theconcentrations and horizontal extent of contamination; and, (2) the effect of home rangeon the amount of time a given species will spend in contact with contaminated media. Foreach source of contamination, the reduction of the potential exposure predicted to resultfrom the implementations of each remedial action alternative should be compared to thepresent potential exposure predicted by the Terrestrial Risk Assessment as follows:

a) For each source of contamination evaluated, the present risk due to exposure asdefined in the Terrestrial Ecosystem Risk Assessment should be calculated forsoil, each source of contamination, and ponded surface water associated with eachsource of contamination.

b) For each source of contamination evaluated, reduction of exposure and ecologicalrisk resulting from implementation of each RA alternative should be calculatedfor soil and other media described above. The potential exposure predicted toresult from implementation of each RA alternative should be compared to thepresent potential baseline exposure predicted by the Terrestrial Ecosystem RiskAssessment.

The options under Alternative 2 through 6 involve the maintenance of existingconsolidated and capped mine wastes. The caps break the exposure pathway forterrestrial receptors thereby reducing risks to the terrestrial ecology. Mine wasteexcavation and disposal under Alternative 4b further reduces exposure of terrestrialreceptors to mine waste. In addition, unremediated mine waste piles typically are devoidof vegetation rendering them poor habitat for terrestrial receptors resulting in limitedexposure to Site wastes.


Some variations on Alternative 2 involve the construction of large lined impoundments tostore ARD prior to treatment. These impoundments would have to be monitored to assurethey are not attractive to terrestrial receptors (the Selected Remedy does not include suchimpoundments). All variations under Alternative 2 involve the continued use of smalldetention and retention ponds constructed at the base of several mine waste piles as partof previous Response Actions (Figure 4). These ponds collect and store ARD. Althoughit is possible that these ponds attract terrestrial receptors, their combined area is limited.In addition, these ponds have existed since 1998 and EPA has received no reports ofterrestrial receptor contact with ponded ARD or acute impacts to wildlife such as animalcarcasses in or proximal to the ponds.

Alternatives-5 and 6 result in the isolation of ARD-generating mine wastes from theenvironment eliminating the terrestrial exposure pathway. Non-ARD generating minewastes will not be addressed under any of the alternatives.

9.2.6 Non-Residential Soils

Non-residential areas were addressed in the FFS. These nonresidential soils are in areaszoned agricultural/forest, and industrial mining. The nonresidential areas within OU6were evaluated in the ecological risk assessments and FFS consistent with current andlikely future land use. Given existing zoning and land use development patterns, EPAexpects that current agricultural/forest, and industrial/mining land uses will not changesubstantially.

All of the alternatives (except Alternative 1) include institutional controls under the ICODistrict to minimize the likelihood of unacceptable human health risks from non-residential soils. Alternatives 5 and 6 will result in the isolation of ARD-generating minewastes from humans.


10.0 PRINCIPAL THREAT WASTES

The NCP establishes an expectation that EPA will use treatment to address the principalthreats posed by a site wherever practicable (NCP 300.430(a)(l)(iii)(A)). Identifyingprincipal threat wastes combines concepts of both hazard and risk. In general, principalthreat wastes are those source materials considered to be highly toxic or highly mobilewhich generally cannot be contained in a reliable manner or would present a significantrisk to human health or the environment should exposure occur. Conversely, non-principal threat wastes are those source materials that generally can be reliably containedand that would present only a low risk in the event of exposure.

Mine waste rock is not considered to be principal threat waste.


11.0 SELECTED REMEDY

11.1 DESCRIPTION OF THE SELECTED REMEDY

The Selected Remedy for OU6 includes Alternatives 2g and 4b.

Alternative 2g involves continued maintenance of consolidated and capped waste pilesincluding the Wolftone, Maid of Erin and Mahala. This alternative also involvesmaintenance of surface water management features constructed during prior ResponseActions at Ram, Mikado, Highland Mary, Adelaide, Pyrenees and Ibex/Irene mine wastepiles/areas as well as portions of the Stray Horse Gulch channel. Maintenance willinclude inspections and repairs to caps and periodic cleaning/repairing of surface watermanagement features. Wastes generated during maintenance activities will be disposed inan on-Site repository planned for the Site.

Alternative 2g also includes continued collection of ARD with management by:

Discharge to surface water at a controlled rate to minimize impacts to theParkville Water District (detention pond constructed at Ibex/Irene area(Figure 3) under prior Response Action).Evaporation (detention ponds constructed at New and Old Mikado,Highland Mary and Adelaide/Ward area (Figure 3) under prior ResponseActions).Treatment to remove contaminants at a water treatment facility operatedby the BOR. This portion of the remedy includes most new componentsto be constructed under this ROD as discussed below.

Alternative 2g continues the introduction of ARD into the Marion Shaft. A plug would beconstructed in the LMDT where it passes through competent rock (See Figure 16). Theresulting impounded groundwater (mine pool) would be pumped from a location upstream of the concrete plug and delivered to the BOR treatment plant via a gravitypipeline. Groundwater entering the LMDT below the plug would ultimately be allowed toexit the tunnel portal and flow downstream without treatment. EPA anticipates that thewater quality would improve over time to a level complying with discharge permitscurrently held by the BOR. Water treatment would be required until the water qualityreached the level required by discharge permits.

The total estimated ARD discharged to the Marion Shaft in 2001 is 9,600,000 gallonswith an estimated peak flow of 550 gpm. The anticipated available capacity of the BORTreatment Plant is not known with certainty. However, the plant is believed to havecurrent excess capacity of at least 50 gpm of typical OU6 ARD. This quantity is the basisfor sizing remedial designs involving the BOR facilities.

The estimated volume of water in the mine pool above the elevation of the LMDT is 750million gallons. A pumping rate of 3,000 gpm was estimated in order to dewater the minepool in less than two years to the elevation of the LMDT. After dewatering the mine pool,an equilibrium-pumping rate would be maintained in perpetuity. The actual pumping rate

Final Record of Decision . DS-42OU6 California Gulch NPL Site

will be determined during remedial design. However, for the purposes of developing acost for this alternative a pump system and pipeline capable of delivering 3,000 gpm isassumed.

The BOR plant does not have the capacity to treat water at an initial pumping rate of3,000 gpm. As discussed above, the actual pumping rate and treatment capacity will bedetermined during remedial design. If the selected pumping rate exceeds the existingBOR plant capacity, plant upgrades will be necessary. The type of plant upgradesdepends not only on the pumping rate but also on the quality of the water in the minepool. At the present time the mine pool water chemistry is not fully characterized. As analternative, the mine pool may be dewatered at a much lower pumping rate for a longerperiod of time. In either case, an equilibrium-pumping rate will have to be maintained inperpetuity. The pipeline alignment and locations of the proposed bulkhead in the LMDTis shown on Figure 16.

Alternative 4b involves the relocation of the Ponsardine Waste Pile to an on-Siterepository planned for the Site in addition to stabilization of the Emmet Waste Pile cribwall. Relocation of the Ponsardine Waste Pile will minimize ARD runoff and infiltration.Stabilization of the Emmet Waste Pile crib wall will reduce the amount of contaminatedseepage originating from the current crib wall and minimize the likelihood of a structuralcollapse of the portion of the waste pile retained by the existing crib wall.

Controls on land use would be implemented as part of this remedy. Land Use Controlswould limit access to or use of the areas remediated through prior Response Actions.These include capped and consolidated waste piles, areas with clean water diversion andARD collection structures. Permanent measures to be considered would include legal orinstitutional mechanisms to provide notification that a Superfund remedy is in place andestablish restrictions/requirements for future activities to maintain the integrity andeffectiveness of the remedies. Modifications to county and/or city zoning ordinanceswould involve the creation of an "overlay district" to provide a screening process toidentify properties where special precautions or requirements may be needed. Land useand plans/proposals for future land use would be monitored and evaluated as part of thefive-year review process.

EPA will work with Lake County on an ICO District that would be implemented as partof this remedy and would limit access to or use of the areas remediated through priorResponse Actions. These controls will protect existing remedies including caps anddiversions and would also ensure that future changes in land use are protective of humanhealth and the environment.

Groundwater monitoring will include but not be limited to water quality and elevationmonitoring of the mine pool impounded behind the bulkhead to be installed in theLMDT. The purpose of the mine pool monitoring is to determine to what degree pumpingof groundwater from the LMDT has arrested or retarded the migration of mine pool wateraway from OU6.


The remedy would consist of the following elements:

• 375-feet of 2.4 meter diameter vertical shaft.• Concrete bulkhead in LMDT.• Pump system capable of delivering 3,000 gpm.• 7,287- feet of 18-inch I.D., PVC pipe buried below frost depth (including a pipe

"pig" and launcher for pipeline maintenance)• Treatment at the BOR's plant of 50 gpm of piped mine pool water in addition to

existing waters collected at the portal and dewatering wells, assuming no plantupgrades.

• Periodic cleaning of retention ponds and sediment basins.• Transport of water treatment residuals, and pond and sediment basin deposits to

an on-Site repository.• Operation and maintenance of new and existing remedy components.• Groundwater monitoring to observe water level and quality conditions in and

around the mine pool, the Emmet waste piles, and retention ponds.• Removal of Ponsardine and disposal to an on-Site Repository.• Construction of Emmet Waste Pile crib wall.• Institutional controls under an ICO District.

11.2 SUMMARY OF ESTIMATED REMEDY COSTS

The detailed cost estimate and present worth analysis for the Selected Remedy ispresented in Table 8. The present worth value of the estimated capital and operating costfor a 100-year period is approximately $13,605,227. The present worth of implementingthis remedy over 100-years is based on a 7 percent discount rate. The construction costof the BOR's plant is not available for use in calculating the periodic replacement costsfor this facility. Therefore, the actual construction cost of the Yak water treatment plantis used for developing a cost estimate for this alternative.

For costing purposes, the quantity of mine pool water treated annually is based on thecurrent estimated minimum excess capacity of 50 gpm. It is assumed that a minimum of50 gpm of mine pool water would be delivered to the BOR treatment plant continuouslythroughout the year. However, pumping and conveyance equipment proposed under thisalternative is sized for a maximum pumping rate of 3,000 gpm.

Costing of operation and maintenance wastes assumes that an on-Site repository will bedeveloped within the Site and will be able to accept wastes generated under the SelectedRemedy. The wastes include water treatment residuals and sediment periodicallyremoved from detention ponds.

For costing the relocation of the Ponsardine Waste Pile, a four-mile haul distance isassumed.


11.3 CONTINGENCY MEASURES AND LONG-TERM MONITORING

Specific water quality goals for surface streams and heavy metals contamination have notbeen established at this time. EPA and CDPHE will establish specific surface andgroundwater requirements at a later date under a Record of Decision for OU12.

Pre-remedial data will be compared to water quality data collected after the SelectedRemedy has been implemented. EPA and CDPHE will make an evaluation of the degreeof surface water quality improvement at that time. If the improvement in OU6 surfacewater is not considered sufficient to meet OU12 water quality standards, additionalResponse Actions may be required under an OU12 record of decision.

Additional Response Actions will be considered in the event that groundwater underARD detention ponds becomes adversely affected by infiltration from the detentionponds. The additional Response Actions may include:

• Construct liners or abandon existing ARD detention ponds associated with theGreenback, RAM and Pyrenees mine waste piles (Figure 3) and allow ARD todrain to the Marion Mineshaft without detention.

• Construct liners in existing ARD detention ponds associated with the New andOld Mikado, Highland Mary and Adelaide/Ward mine waste piles (Figure 3).

• Construct a gravity pipeline to convey ARD from the New and Old Mikado,Highland Mary and Adelaide/Ward mine waste pile detention ponds (Figure 3) tothe Marion Mineshaft.

If monitoring indicates that significant surface loading between SHG-08 and SHG-09continues, and is not attributable to infiltration from impoundments, remedial alternativesfor addressing ARD from the Emmet piles will be evaluated.

Because most mine wastes will remain in-place, the Selected Remedy will require a five-year review under Section 12 (c) CERCLA and Section 300.430(f)(4)(ii) of the NCP. Thefive-year review includes a review of groundwater and surface water monitoring data,inspection of the integrity of the covers, diversion channels and impoundments and howwell the Selected Remedy is achieving the remedial action objectives and ARAR's that itwas designed to meet. Groundwater monitoring will include but not be limited to waterquality and elevation monitoring of the mine pool impounded behind the bulkhead to beinstalled in the LMDT. The purpose of the mine pool monitoring is to determine to whatdegree pumping of groundwater from the LMDT has arrested or retarded the migration ofmine pool water away from OU6. A monitoring plan specific to the mine pool will bedeveloped during the remedial design phase of remedy implementation. The monitoringplan will define ambient conditions to ensure that if conditions change in the LMDT orattendant mine workings they will not go undetected.


In the event that conditions in the mine pool change beyond certain thresholds, as definedby the monitoring plan, EPA will consider such changes as constituting a "RemedyFailure". At such time EPA will implement all monitoring and remedial ResponseActions required to address the failure in a timely manner. Allocation of the USEPA,USBOR, and State of Colorado costs and responsibilities will be subject to agreementsthat will be defined in Long-Term Operation & Maintenance Agreements between theparties and in the EPA-CDPHE State Superfund Contract (SSC).

Portions of the Phase II Response Action (the consolidation and capping of waste rockpiles) may not have achieved the 1.5 slope stability factor of safety for static conditionsand 1.0 for psuedo-static conditions specified in the Work Area Management Plan(WAMP). If slope failure should occur, EPA will consider the event a "Remedy Failure",and at such time implement all remedial Response Action required (and monitoring ifneeded) to address the failure in a timely manner.


12.0 STATUTORY DETERMINATIONS

Under CERCLA Section 121 and the NCP, EPA must select a remedy that is protectiveof human health and the environment; that complies with ARARs; is cost-effective; andutilizes permanent solutions, alternative treatment technologies, or resource recoverytechnologies to the maximum extent practicable. In addition, CERCLA includes apreference for remedies that employ treatment that permanently and significantly reducesthe volume, toxicity, or mobility of hazardous wastes as a principal element and a biasagainst off-site disposal of untreated wastes. The following sections discuss how theSelected Remedy meets these statutory requirements.

12.1 PROTECTION OF HUMAN HEALTH AND THE ENVIRONMENT

The Selected Remedy will protect human health and the environment through themaintenance of prior Response Actions and the perpetual treatment of ARD. Dewateringof the mine pool will result in a reduction in bedrock water table potentially reducing thenumber of springs in the area discharging contaminated groundwater. Long-term surfaceand groundwater monitoring will be used to assess the effects of ARD discharge to theMarion Shaft as well as dewatering of the mine pool. The details of the long-termmonitoring will be developed during remedial design. Land use controls under an ICODistrict will minimize the likelihood of human health risk above a level of concern fromexposure to non-residential soils and mine wastes.

The Selected Remedy is protective of terrestrial ecology through the maintenance ofexisting consolidated and capped mine wastes and the removal of the Ponsardine minewaste pile. The caps break the exposure pathway for terrestrial receptors thereby reducingrisks to the terrestrial ecology. In addition, unremediated mine waste piles typically aredevoid of vegetation rendering them poor habitat for terrestrial receptors resulting inlimited exposure to Site wastes.

The Selected Remedy includes the continued use of small detention and retention pondsconstructed 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 attractterrestrial receptors, their combined area is limited. In addition, these ponds have existedsince 1998 and EPA has received no reports of terrestrial receptor contact with pondedARD or acute impacts to wildlife such as animal carcasses in or proximal to the ponds.

12.2 COMPLIANCE WITH APPLICABLE OR RELEVANT ANDAPPROPRIATE REQUIREMENTS

The Selected Remedy will comply with all ARARs identified in Tables 9 through 11. Nowaiver of ARARs will be necessary. Final performance standards will not includeARARs for Site-Wide Surface and Ground Water or require a specified decrease inconcentrations of COCs to Site-Wide Surface and Ground Water (USCD, 1994). It wasagreed that the decision on remediation of Site-Wide Water Quality (OU12) would be


made only after remedies for source remediation were selected and implemented at eachOU (USDC, 1994). As a result, specific water quality goals for surface streams andgroundwater have not been established at this time.

Chemical Specific ARAR's. There are no chemical specific ARAR's associated with theSelected Remedy.

Location Specific ARAR's The selected remedy will comply with all location specificARAR's. Several regulations pertaining to the preservation of historic features have beenidentified as ARARs. Compliance will be achieved through implementation ofprocedures to preserve historical and archeological data should qualifying historicalfeatures be affected by the remedy.

Action Specific ARAR's. The selected remedy will comply with all action specificARAR's. Environmental covenants are.required whenever contamination is left in place,such as mine waste. Compliance with this ARAR will be achieved through the creation ofan institutional control overlay (ICO) district. Underground injection control (UIC)regulations are triggered by the introduction of collected ARD into the Marion mineshaftvia a class 5 well. The UIC regulation requires that injected waters not degrade drinkingwater sources. Current data indicate degradation of groundwater outside of the LMDTand Marion mineshaft resulting from the injection of ARD into the Marion Shaft has notoccurred (Section 2.0). Similarly the State PDES and CBGS are applicable and requirethat there be no degradation of ground water from the introduction of the collected ARDwater in the Marion mine shaft. Points of Compliance for this ARAR will be establishedand monitored through the implementation of long-term groundwater quality monitoringprogram.

12.3 COST-EFFECTIVENESS

In EPA's judgment, the Selected Remedy is cost-effective and represents a reasonablevalue for the money to be spent. In making this determination, the following definitionwas used: "A remedy shall be cost-effective if its costs are proportional to its overalleffectiveness (NCP 300.430(f)(l)(ii)(D))". This was accomplished by evaluating the"overall effectiveness" of those alternatives that satisfied the threshold criteria (i.e., wereboth protective of human health and the environment and ARAR-compliant). Overalleffectiveness was evaluated by assessing three of the five balancing criteria incombination (long-term effectiveness and permanence; reduction in toxicity, mobility,and volume through treatment; and short-term effectiveness). Overall effectiveness wasthen compared to costs to determine cost-effectiveness. The relationship of the overalleffectiveness of this remedial alternative was determined to be proportional to its costsand hence this alternative represents a reasonable value for he money to be spent.

The estimated present worth cost of the Selected Remedy is $13,998,431.


12.4 UTILIZATION OF PERMANENT SOLUTIONS AND ALTERNATIVETREATMENT (OR RESOURCE RECOVERY) TECHNOLOGIES TOTHE MAXIMUM EXTENT PRACTICABLE (MEP)

EPA has determined that the Selected Remedy represents the maximum extent to whichpermanent solutions and treatment technologies can be utilized in a practicable manner atOU6. Of those alternatives that are protective of human health and the environment andcomply with ARARs, EPA has determined that the Selected Remedy provides the bestbalance of trade-offs in terms of the five balancing criteria, while also considering thestatutory preference for treatment as a principal element and bias against off-site disposaland considering State and community acceptance.

The large volume of mine wastes precludes treatment or off-Site disposal as a viableoption. In addition, the mine waste and related ARD do not contain resources that may berecovered economically at the present time. However, the potential remains forreprocessing of mine waste in the future should it become economically viable.

12.5 PREFERENCE FOR TREATMENT AS A PRINCIPAL ELEMENT

The Selected Remedy includes treatment of ARD as a principal element.

12.6 FIVE-YEAR REVIEW REQUIREMENTS

Because this remedy will result in hazardous substances, pollutants, or contaminantsremaining in OU6 above levels that allow for unlimited use and unrestricted exposure, astatutory review will be conducted within five-years after initiation of remedial action toensure that the remedy remains protective of human health and the environment.


13.0 DOCUMENTATION OF SIGNIFICANT CHANGESFROM PREFERRED ALTERNATIVE

OF PROPOSED PLAN

The Proposed Plan for OU6 was released for public comment in April 2003. TheProposed Plan identified Alternative 2g and 4b as the Preferred Alternative for wasterock. EPA reviewed all written and verbal comments submitted during the publiccomment period. It was determined that no significant changes to the remedy, asoriginally identified in the Proposed Plan, were necessary or appropriate.


14.0 REFERENCES

CDM, 1997. Engineering Evaluation/Cost Analysis for Stray Horse Gulch, OperableUnit 6, California Gulch NPL Site, Leadville, Colorado, June 1997.

CDM, 2000a. Final Phase I Removal Action Completion Report for the California GulchSuperfund Site, Lake County, Colorado, Operable Unit 6, December 11, 2000.

CDM, 2000b. Final Phase II/IH Removal Action Completion Report for the CaliforniaGulch Superfund Site, Lake County, Colorado, Operable Unit 6, December 2000.

CDM, 2000e. Final Phase IV Removal Action Completion Report for the CaliforniaGulch Superfund Site, Lake County, Colorado, Operable Unit 6, December 2000.

CDM, 200la. Final Technical Memorandum Response Action Alternative Evaluation ofIbex/Irene Site at Operable Unit 6, California Gulch Superfund Site, Lake County,Colorado, July 2001.

Golder Associates, Inc., 1996a. Hydrogeologic Remedial Investigation Report, CaliforniaGulch Site, Leadville, Colorado, Volume I, May 1996.

Pacific Western Technologies, Ltd., 2001. Evaluation of Mahala Waste Pile, Stray HorseGulch, Removal Action for the California Gulch Superfund Site, OU6, June 27, 2001.

Rocky Mountain Consultants, Inc., 2001 a. Summary of Groundwater Quality Data,California Gulch NPL Site, Lake County, Colorado, March 26, 2001.

Rocky Mountain Consultants, Inc., 2001 b. California Gulch Superfund Site, SynopticSampling of Stray Horse Gulch, Starr Ditch, and Lower California Gulch (OU6), Spring2000, January 2001.

Roy F. Weston, Inc., 1991. Preliminary Human Health Baseline Risk Assessment for theCalifornia Gulch NPL site, Leadville, Colorado, December 1991.

Roy F. Weston, Inc., 1995a. Final Baseline Aquatic Ecological Risk Assessment for theCalifornia Gulch NPL Site, September 1995.

Roy F. Weston, Inc., 1995b. Baseline Human Health risk Assessment for the CaliforniaGulch Superfund Site, Part C —Evaluation of Worker and Recreational Scenarios, April1995.

Roy F. Weston, Inc., 1996a. Baseline Human Health Risk Assessment, California GulchSuperfund Site, Leadville, Colorado, Part A - Risks to Residents from Lead, January1996.

Final Record of Decision R-lOU6 California Gulch NPL Site

Roy F. Weston, Inc., 1996b. Baseline Human Health Risk Assessment, California GulchSuperfund Site, Leadville, Colorado, Part B - Risks to Residents from Contaminantsother than Lead, January 1996.

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

United States Department of the Interior, 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 NPLSite, Leadville, Colorado, November 1996.

United States Department of the Interior, Bureau of Reclamation, 1996b. Value Analysis,Draft-Presentation Report, Project: California Gulch OU6 Removal Action Evaluationand Decision Phase, Leadville, Colorado, April 1996.

United States Department of the Interior, Bureau of Reclamation, 1997. DraftEnvironmental Geology of Operable Unit 6, Removal Action Design Data, CaliforniaGulch Superfund Site, Leadville, Colorado, February 1997.

United States District Court for the District of Colorado. Consent Decree with AsarcoIncorporated, Resurrection Mining Company, Newmont Mining Corporation, and theRes-Asarco Joint Venture, Civil Action No. 83-C-2388, August 25, 1994.

USEPA, 1993. Final Screening Feasibility Study for Remediation Alternatives at theCalifornia Gulch NPL Site, Leadville, Colorado, September 1993.

USEPA, 1995a. Action Memorandum. Subject: Request for Removal (Response) Actionat the California Gulch National Priorities List Site, Leadville, Colorado: ACTIONMEMORANDUM for an Emergency Removal Action for Rehabilitation andConstruction of Drainage and Sediment Control Features, Hamm's TailingImpoundment. Ref: 8HWM-SR, November 6,1995.

USEPA, 1995b. Work Area Management Plan for the California Gulch Superfund Site,Implementation by the U.S. Environmental Protection Agency (draft), June 14, 1995.

USEPA, 1996a. Action Memorandum. Subject: Request for Removal (Response) Actionat the California Gulch National Priorities List Site, Leadville, Colorado: ACTIONMEMORANDUM for an Emergency Response Removal for the removal of sedimentsfrom the 5th Street Drainage Ditch and Starr Ditch, Operable Unit 6, (OU6). Ref: EPR-SR, May 1,1996.

Final Record of Decision R-2OU6 California Gulch NPL Site

USEPA, 1996b. Action Memorandum. Subject: Request for Removal (Response) Actionat the California Gulch National Priorities List Site, Leadville, Colorado: ACTIONMEMORANDUM for Time Critical Removal Actions for Hamm's TailingsImpoundment and the Penrose Mine Waste Pile. Ref: 8EPR-SR, July 26, 1996.

USEPA, 1997. Work Area Management Plan for the California Gulch Superfund Site,Implementation by the U.S. Environmental Protection Agency: ACTIONMEMORANDUM for Non-Time Critical Removal Actions for Source Control Activitiesat Designated Mine Waste Piles (Operable Unit VI). Ref: 8EPR-SR, June 24,1997.

USEPA, 1999a A Guide to Preparing Superfund Proposed Plans, Records of decision,and Other Remedy Selection Decision Documents, OSWER 9200.1-23P, EPA 540-R-98-031, July 30, 1999.

USEPA, 1999b Action Memorandum. Subject: Request for Removal (Response) Action atthe California Gulch National Priorities List Site, Leadville, Colorado: ACTIONMEMORANDUM AMENDMENT for subsequent Non-Time Critical Removal Actionsfor Surface Water Management at Designated Mine Waste Piles. Ref: 8EPR-SR, June 2,1999.

USEPA, \999cRecordofDecision, Residential Populated Areas, Operable Unit 9,September 1999.

USEPA, 2001. Action Memorandum. Subject: Request for Removal (Response) Action atthe California Gulch National Priorities List Site, Leadville, Colorado: ACTIONMEMORANDUM for a Non-Time Critical Removal Action for Water ManagementActivities at the Ibex/Irene Mine Waste Pile at the upper end of Lincoln Gulch. (Aportion of Operable Unit 6)(Phase V) Ref: 8EPR-SR, June 25, 2001.

USEPA, 2002a, Final Feasibility Study, Operable Unit 6, California Gulch NPL Site,September 11, 2002.

USEPA, 2002b. Draft Groundwater Hydrology in the Vicinity of the Leadville MineDrainage Tunnel, Operable Unit 6 and Affected Areas, August 2002.

Water, Waste and Land, Inc., 1990. California Gulch Hydrologic Investigation,Leadville, Colorado, August 1990.

Woodward-Clyde Consultants, 1992a. Final Air Monitoring Report, California GulchSite, Leadville, Colorado, Volume I, May, 1992.

Woodward-Clyde Consultants, 1992b. Wetlands Map for California Gulch RI/FS StudyArea, September 1992.


Woodward-Clyde Consultants, 1994a. Final Mine Waste Piles Remedial InvestigationReport, California Gulch Site, Leadville, Colorado, January 1994.

Woodward-Clyde Consultants, 1994b. Final Tailings Disposal Area RemedialInvestigation Report, California Gulch Site, Leadville, Colorado, January 1994.


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Table 2Summary of Piles Identified as Candidates for Remedial Action

Pile/Area - :GreenbackRAMOld MikadoNew MikadoHighland MaryAdelaide/WardPyreneesFortune/ResurrectionPonsardineEmmettEvans F&G

PreviousResponse

Action(Y/N).'

YYYYYYYYN*NN

AVIRISNANANANANANANANANAYY

'..Mine£Waste;.PHeRI

NANANANANANANANANAY

NA

ry • Water|£Quality • :

NANANANANANANANANAYN

u Candidate for '•%.^-•Furiher^B^Remedial Actions^•^(Y/Srf^?

YYYYYYYYY*YN

* Although the Ponsardine Pile has not been part of a prior Response Action, it was scheduled forResponse Action activities, and therefore identified as ARD-generating.

NA - Not applicable. Sources identified during prior Response Actions were not analyzed further. TheMine Waste Pile RI only encompassed the populated areas of Leadville and therefore did notinventory the Evans area.

AVIRIS - airborn visible and infrared imaging spectroscopy

Table 3Zinc and Cadmium Concentrations at SHG-08 and SHG-09

Station -SHG-08SHG-09

SHG-08SHG-09

SHG-08SHG-09

SHG-08SHG-09

Date

5/15/015/15/01

5/15/015/15/01

5/23/015/23/01

5/23/015/23/01

Analyte

Total Cadmium^,Total Cadmium

Total ZincTotal Zinc

Total CadmiumTotal Cadmium

Total ZincTotal Zinc

Units

wsflng/i"g/1JJig/1ug/1

Ug/1Hg/1Ug/1

:• Result/19.8155

2,20020,400

35376

3,08048,100

(RMC, 2001)

Table 4ARD-Generating Mine Waste Volumes

v Pile/Area ; :GreenbackRAMOld MikadoNew MikadoHighland MaryAdelaide/WardPyreneesFortune/ResurrectionIbex/IrenePonsardineEmmett

Total:

Volume (Cyy44,00024,80042,00044,00027,00054,00060,500

200,000223,000*

11,00011,800**742,100

Volumes obtained from the Value Analysis Report(BOR, 1996b) unless otherwise noted.

*Used sum of volumes reported in Value Analysis forareas Ibex-H and Ibex-I

**Calculated by HDR during FFS process.

Table 5Hazard Indices for Solid Surficial Media by Receptor for OU6

Operable Unit :

Blue GrouseMountain BluebirdAmerican KestrelRed-tailed HawkBald EagleLeast ChipmunkMule DeerRed Fox

;•*.. ' -'. " ''V

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Responses to Comments Received on the Proposed PlanOperable Unit No. 6

California Gulch NPL Site

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

Comments received during May 1.2003 Public Meeting

1. Brian Pearson of the US Bureau of Reclamation (BOR) expressed support for thepreferred alternative but recognized the need to confirm that BOR has theauthority to treat OU6 water over the long-term.

EPA appreciates the BOR's support for the preferred alternative and recognizesits need to formalize within its own organization the decision to treat OU6 waterover the long-term.

2. Russ Allen of the Colorado Department of Public Health and Environment(CDPHE) expressed support for the preferred alternative but recognized the needfor EPA and CDPHE to reach agreement on the CDPHE's operation andmaintenance responsibilities. CDPHE also requested more technical assuranceregarding the technical implementability of the remedy.

EPA has identified in Section 11.3 (Contingencies), those remedy elements thatwould be the responsibility of EPA. Remaining operation and maintenanceactivities will be defined through discussions with CDPHE during remedialdesign. Technical implementability will also be further evaluated during remedialdesign.

3. What happens to the water that is collected at the Greenback settlement pond?

This collection pond discharges through a culvert and the water flows in aconstructed channel to the Marion collection pond. The water collected in theMarion pond is discharged through a borehole to an underground mine workingconnecting the Marion and Emmet mine shafts and the Leadville Mine DrainageTunnel (LMDT). Water flowing through the LMDT is treated in a facilityoperated by the U.S. Bureau of Reclamation.

Responsiveness SummaryOU6 California Gulch NPL SitePage 2

The connection between the Marion Shaft and the LMDT has been under analysisby EPA. A number of tracer studies were performed to determine the effectivenessof the LMDT as a conveyance structure for the Greenback Pond discharge. Thesestudies confirm a hydraulic connection between the Marion Shaft and the LMDTportal. This conclusion is based on information contained in the August 2002Ground Water Hydrology in the Vicinity of the Leadville Mine Drainage Tunnel,Operable Unit 6 and Affected Areas including:

• Approximately 60% of the tracer injected in the Marion Shaft wasrecovered at the LMDT portal as of the summer of 2003 andadditional dye was still being recovered at the portal.

• A portion of the tracer remains in the Marion Shaft.

• Tracer has not been detected at any other point where groundwaterdischarges to surface water.

4. Are the collection ponds lined?

The collection ponds are underlain with interbedded "Lake Bed" deposits tovarying degrees. These Lake Bed deposits serve somewhat as a natural (clay)barrier. Additional Response Actions will be considered in the event thatgroundwater under ARD detention ponds becomes adversely affected byinfiltration from the detention ponds. The additional response actions mayinclude:

• Abandon existing ARD detention ponds associated with the Greenback,RAM and Pyrenees mine waste piles and allow ARD to drain to theMarion Mineshaft without detention.

• Construct liners in existing ARD detention ponds associated with the Newand Old Mikado, Highland Mary and Adelaide/Ward mine waste piles.

• Construct a gravity pipeline to convey ARD from the New and OldMikado, Highland Mary and Adelaide/Ward mine waste pile detentionponds to the Marion Mineshaft.

5. What happens to water coming off of the Emmet?

Surface water coming into contact with rock in back of the Emmet crib wall isproducing acid rock drainage and will be mitigated under the OU6 ResponseActions.

Responsiveness SummaryOU6 California Gulch NPL SitePageS

6. What is the plan for relocation of mine waste?

We are considering development of an on-Site waste repository at the BlackCloud tailing pond area in Iowa Gulch.

1. How will EPA develop the bulkhead?

We are currently surveying the tunnel and analyzing water levels. Plans willlikely involve drilling down 380 feet offset of the shaft to develop a temporaryplug, dewatering the area, then placing a permanent plug. Specific plans for theplug will be finalized during the Remedial Design phase.

8. What is the maximum capacity of the Leadville Mine Drainage Tunnel?

The plant is designed to handle about 2200 gallons of water per minute, althoughin reality it is probably more like 1,900 gallons per minute.

9. What happens to the sludge derived from treated water?

Hazardous waste is transported to hazardous waste sites; non hazardous waste isplaced in a solid waste landfill.

10. How will institutional controls affect companies that are interested in conductingfuture mining activities here?

Institutional controls are not designed to prevent mining, which would beregulated by the State of Colorado Division of Minerals and Geology. Anyactivities that might compromise the effectiveness of current remedies will needEPA approval. Excavation activities may require county approval.

Comments received from Resurrection Mining Company

11. The Proposed Plan issued by EPA describes and summarizes the evaluation of sixremedial alternatives for cleanup of Operable Unit No. 6 (OU6). The EPA intendsto select a final remedy for OU6 following review and consideration ofinformation received during the public comment period. As described in theProposed Plan, the preferred alternative consists of Alternatives 2g and 4b, whichincludes the following principal components:

• continued operation and maintenance of remedial actions previouslycompleted by the EPA;

• continued collection of contaminated runoff and seepage from mine wasterock piles within a portion of the OU6 area and delivery of the water to the


LMDT via the Marion Shaft for eventual treatment at the BOR's watertreatment plant;

• construction of a bulkhead in the LMDT for hydraulic head control of themine water pool in the underground mine workings connected to the LMDT;

• pumping of mine water stored behind the bulkhead in a pipeline to the BOR'swater treatment plant;

• removal of the Ponsardine waste rock pile to a yet to be determined on-Siterepository; and

• physical stabilization of the existing crib wall at the Robert Emmet waste rockpile.

Resurrection Mining Company (Resurrection) has reviewed the remedialalternatives described in the OU6 Proposed Plan from the perspective of theexpected reduction that will be achieved in the metal loading currently beingcontributed by Stray Horse Gulch to lower California Gulch and ultimately to theArkansas River. EPA previously completed considerable response actions in OU6for mill tailing and selected mine waste rock piles. It is unlikely, however, that thepreferred alternative described in the OU6 Proposed Plan will achieve any furthermeasurable reduction in metal loading from Stray Horse Gulch, as the alternativeessentially maintains existing conditions. Resurrection suggests that the EPAconsider remedial actions that provide further reduction in metal loading beingcontributed by Stray Horse Gulch.

The Focused Feasibility Study for OU6 estimated a 90% reduction in zinc andcadmium loading at the downstream boundary ofOU6 (Stations SHG-09A andSD-3) between 1995 and 2001 (OU6 FFS, Figure 4-5 and 4-6). Most of the ARD-generating mine wastes in OU6 have already been addressed through sourcecontrol measures implemented during eleven time-critical and non-time criticalremoval actions performed between 1990 and 2001. Additional reductions inmetal loading through source control measures are expected to be small.Nevertheless, the selected remedy includes the physical removal of over 10,000rubic yards of ARD-generating mine waste (Ponsardine waste rock pile).

Dewatering of the mine pool is a major component of the selected remedy. Thisportion of the remedy is intended to further reduce metal loading to surface waterthrough reducing discharge of contaminated water at springs and seeps and frombedrock to alluvium and ultimately to surface water. These improvements areexpected not only in OU6 but also in other OU's.

Further remedial action in OU6 would be implemented under OU12, Site- WideSurface and Groundwater.


12. Metal Loading in Lower Stray Horse Gulch - Based on past evaluation of surfacewater quality data for OU6, a significant increase in metal loading and decrease inpH was observed in the reach of Stray Horse Gulch from approximately theRobert Emmet mine downstream to below Hamm's Mill Tailing Impoundment, asrepresented by the water quality data collected at sampling station SHG-09A.Previous response actions completed by EPA in the drainage area contributing tothis reach were beneficial in reducing metal loading. However, based on initialreview of recent water quality data collected at SHG-09 A, this reach continues tobe a source of metal loading. Specifically, as identified during the public meetingof May 1, 2003, evidence suggests the Robert Emmet waste rock pile iscontributing metals to Stray Horse Gulch. The proposed plan does not proposeany response actions that would result in any further reduction in metal loading inthis reach. The previously completed surface water management activities, whichintercept and transfer water into the Marion Shaft, are in areas upstream of thisreach. Resurrection suggests that EPA evaluate the Robert Emmet waste rock pileand other potential sources of surface water metal loading and consider additionalremedial actions to mitigate the loading sources in this lower reach of Stray HorseGulch.

Available data are insufficient to determine the magnitude of the metal loadcontribution from the Robert Emmet waste pile, if any. A large volume of ARD-generating mine waste exists between surface water monitoring stations SHG-08and SHG-09A. The vast majority of these wastes have been remediated throughin-place capping and surface water management including collection andtreatment of ARD. The Emmet waste rock pile may be contributing to metalloading in this teach of Stray Horse Gulch. However, grouting and stabilizationof the Emmet crib wall is expected to achieve some reduction in mass loading tosurface water. Water quality monitoring of this portion of Stray Horse Gulch willbe needed to assess the degree of loading reduction.

13. Location of Proposed LMDT Bulkhead in Relation to Pendrv Fault - The specificlocation of the proposed bulkhead in the LMDT is not identified in the ProposedPlan or in the Focused Feasibility Study. Several faults intersect the LMDTincluding the Pendry Fault, which has been shown to provide a groundwater flowpathway to California Gulch alluvium under high hydraulic head conditions in theLMDT. Rising groundwater levels in California Gulch alluvium have beenattributed to the migration of groundwater flow along the Pendry Fault uponincreased head in the LMDT. Based on mapping provided in Draft GroundwaterHydrology in the Vicinity of the Leadville Mine Drainage Tunnel, Operable Unit6 and Affected Areas (EPA, August, 2002), the Pendry Fault crosses the LMDTapproximately 5,000 feet from the portal. Information provided in the FocusedFeasibility Study suggests that the bulkhead be located between 4,000 and 6,000feet from the portal. Resurrection recommends that the bulkhead be located incompetent rock upgradient of the Pendry fault to minimize the potential for


groundwater flow to migrate from the LMDT mine pool via the Pendry Fault tothe California Gulch Alluvium.

Information should also be presented by the EPA regarding management of the.mine pool behind the proposed LMDT bulkhead. The management plan woulddefine the normal operation parameters, including the proposed operating headbehind the bulkhead. As part of the remedial design for the selected OU6 remedy,EPA should develop a management and contingency plan for conditions that maypotentially exceed normal operating parameters.

The location, design, normal and contingency operation and method ofconstruction for the proposed bulkhead will be determined during remedialdesign. The placement of the bulkhead up-stream of the Pendry Fault is one ofseveral considerations when selecting a suitable location. EPA agrees that it isdesirable to place the bulkhead upstream of the Pendry Fault.

14. Existing Surface Water Management Activities

a) As described in the Proposed Plan, the preferred alternative includes thecontinuation of the collection of runoff and seepage from mine waste rockpiles within a portion of the OU6 area and delivery of the water to the LMDTvia the Marion Shaft for eventual treatment at the BOR's water treatmentplant. The details of the collection and delivery systems are not described inthe Proposed Plan.

j

Details of the collection and deliver system is provided the Final PhaseII/III Removal Action Completion Report (CDM, 20001) and summarizedon Figure 4-3 of the OU6 FFS.

b) The long-term effectiveness of the existing retention and overflow system isobviously dependent on the criteria used in the design of the storage capacitiesof the basins and the sizing of the conveyance features. Presumably, flow inexcess of the design criteria will return untreated into Stray Horse Gulch.

The design of collection and delivery systems to Marion Pond areconsistent with Work Area Management Plan criteria. Construction wasdesigned to withstand flows resulting from 100-year, 24-hour and 2-hourstorm events.

1 CDM, 2000. Final Phase II/III Removal Action Completion Report for the California Gulch SuperfundSite, Lake Coun'.y, Colorado, Operable Unit 6, December 2000.

Responsiveness SummaryOU6 California Gulch NPL SitePage 7 '

c) The Focused Feasibility Study states that EPA was forced to siphon waterfrom the retention basins during the Spring 2000 due to inadequate sizing ofthe basins. In the Focused Feasibility Study, an estimate of the water volumeand peak flow discharged during 2001 from the retention basin into theMarion Shaft is used for conceptual sizing of remedial alternatives. The datacollected in 2001 was only for part of the year and runoff conditions in 2001were below average. Sizing of facilities based on partial data from one below-average year is highly uncertain.

Diversion of Greenback Pond overflows to the Marion Pond and finally tothe LMDT via Emmet Shaft mitigated the inadequate sizing of the basinsin that ARD collection area. The FFS used an estimate of 2001 flows inorder to develop comparable cost estimates among the variousalternatives involving water treatment. Given Alternative 2g employsunderground mine workings to store collected ARD, the ability exists tocollect, store and treat ARD in excess of the 2001 flows. The actualcapacity of the remediation system will be determined during remedialdesign.

d) The design criteria for the existing water management system or the preferredalternative are not specified in the Proposed Plan or in the Focused FeasibilityStudy and it is unclear whether the existing system will be upgraded as part ofthe preferred plan. EPA should provide additional information with regard tothe design and operation of the current and proposed water managementsystems in order to allow a thorough evaluation of the proposed alternative.

See response to comment nos. 12b and c.

e) The long-term effectiveness of the surface water management system is alsodependent on the hydraulic connection between the Marion Shaft and theLMDT, which is used to convey the OU6 surface water to the LMDT minepool for eventual treatment at the existing BOR plant. EPA commissioned astudy to evaluate the connection as described in the Draft GroundwaterHydrology in the Vicinity of the Leadville Mine Drainage Tunnel, OperableUnit 6 and Affected Areas (EPA, August, 2002). The results of that studyindicate a hydraulic connection exists between the Marion and Robert EmmetShafts and the LMDT portal, but that only limited discharge occurs from themine pool impounded in the Robert Emmet Shaft to the LMDT portal. Assuch, the EPA should include a long-term comprehensive groundwatermonitoring and detection program as part of the preferred plan to ensure thatthe OU6 water delivery system and the LMDT remains functional.


A long-term comprehensive groundwater monitoring and detectionprogram to ensure that the OU6 water delivery system and the LMDTremains functional will be developed during remedial design.

f) Under the preferred alternative, the Marion Shaft will receive water overflowfrom only three of the eight retention basins constructed by the EPA in OU6according to information presented in the Focused Feasibility Study. Anywater overflow from the five additional retention basins (including HighlandMary, New and Old Mikado, Adelaid/Ward group, and Stray Horse Gulch atRobert Emmet) will presumably report to Stray Horse Gulch. Periodicoverflows from these ponds would potentially affect water quality in StrayHorse and California Gulch. Again, the design criteria or as built informationfor the existing water management systems are not identified in the ProposedPlan or in the Focused Feasibility Study. EPA should provide the designcriteria for these ponds and address the long-term management of potentialoverflows from these retention basins as well as the potential impact toshallow groundwater resulting from impoundment of contaminant forextended periods.

The watershed served by the three retention basins mentioned in thecomment is the largest of the water management areas in Stray HorseGulch. While it is likely the remaining retention basins will overflow in thefuture, the frequency and volume of such overflows is expected to be farless than occurs on a regular basis at the Greenback pond. The decision toexclude the remaining retention basins from the Marion Pond collectionsystem was based on: .

• The low frequency and magnitude of anticipated overflows fromthe remaining retention ponds.

• The difficulties in plumping multiple remotely located basins to acommo^ discharge point.

Also, see response to comment nos. 12a, b and c.

15. Water Treatment Cost for the Preferred Remedy - In reviewing the estimatedcosts presented in the Proposed Plan and Focused Feasibility Study for thepreferred alternative, it appears that the treatment costs may have beenunderestimated. The proposed Plan indicated that continued treatment of OU6water may require an expansion of the BOR treatment plant. The FocusedFeasibility Study states that the existing capacity of the BOR treatment plant isinsufficient to treat the volume of water estimated for this alternative an thatsignificant plant upgrades would be required. However, costs associated withexpansion of the BOR treatment plant have not been included. The cost of watertreatment for the preferred alternative should be more fully evaluated by the EPA,


as the cost for this alternative may be significantly greater than that presented inthe Proposed Plan.

Alternative 2g may be implemented using only the current excess capacity at theBOR's facility. The volume of collected ARD during the 2001 runoff season wasestimated to be 9,600,000 gallons. The estimated 50 gpm of existing excesscapacity of the BOR's facility equates to 26,280,000 gallon per year. Therefore, itwill be possible to de-water the mine pool and treat collected ARD withoutexpansion of the BOR's facility. More rapid dewatering of the mine pool (ifdesirable) may require plant expansion.

16. Relocation of the Ponsardine Waste Rock Pile - As part of the preferredalternative, the Ponsardine waste rock pile in Little Stray Horse Gulch will berelocated to a proposed on-Site repository. As described in the Focused FeasibilityStudy, the Ponsardine waste pile was previously identified as a candidate forremedial action due to potential ARD-generation, high lead concentrations, andpotential degradation to downgradient water quality. Given the limitedinformation presented in the Focused Feasibility Study and the Proposed Plan,including the apparent absence of data demonstrating an impact to surface waterquality, relocation of the pile does not appear to be cost effective. The only otheralternative described for this pile in the Proposed Plan was in-situ chemicalstabilization. Resurrection recommends that the EPA evaluate other alternativesfor the pile, specifically in-situ stabilization by placement of a cover. It isanticipated that the pile could be regraded and covered with a relatively thin cap(earthen, or possibly rock in conjunction with a geosynthetic liner) to achieve theremedial action objectives. Placement of an 8-foot thick cover, as was completedduring the previous response actions for consolidation and capping of selectedwaste rock piles, does not appear to be warranted based on specific siteconditions. In-situ stabilization would eliminate the need to excavate andtransport the waste rock, and to construct a repository.

EPA has assessed in place capping and water management for the Ponsardine,and determined removal of the pile to be the most effective due to the location ofthe pile adjacent to 7th Street and the lack of adequate space for capping or watermanagement techniques. The proposed on-Site repository is intended to receiveSuperfund wastes from many sources including treatment plant sludges,residential soils, and other wastes. Therefore, an alternative remedy for thePonsardine waste rock pile would not preclude the Repository.

Comments from Peter G. MoIIer

17.1 have studied the "Proposed Plan for Operable Unit No. 6 of the California GulchNational Priority List Site" and would like to indicate my support for the"Preferred Alternative" 2g and 4b. I was glad to see that this alternative "willensure that all the prior source control measures are maintained and that treatment


of contaminated runoff and seepage continues indefinitely." I would think thatmaintenance of existing sediment ponds and ditches diverting clean water aroundcontaminated sites would be a concern.

Comment Acknowledged

18.1 do have a couple of questions. First, where will the planned site-wide repositorybe located?

The Black Cloud tailing impoundment is the most likely candidate location for theon-Site repository.

19. Second, in what ways have you been able to utilize results of the revegtation plotson pyritic waste rock at the "Denver City" mine site? I believe you have a copy ofthe report I prepared on the project, which was published in June, 1996"Proceedings: High Altitude Revegetation Workshop No. 12". I have spoken withKarmen King of the Natural Resource Management program at CMC here inLeadville about the importance of having the NRM program continue with themonitoring of the plots and expanding upon the project. I would be interested ingetting your feedback.

EPA will continue to support Colorado Mountain College's monitoring of theplots in anyway possible. EPA recognizes the importance of long-termmonitoring of the plots to determine the effectiveness of establishing vegetation inhigh metal soils.

Comments from James Tiffany

20.1 favor alternative 4, chemical stabilization of the Ponsardine and Emmet wastepiles plus stabilization of the crib wall on the south side of the Robert Emmet.This plan maintains a bit of the "flavor of the mining camp" and is a low costsolution. Monitoring over a relatively short time should indicate if this solution issuccessful. If not corrections could be implemented.

Chemical stabilization has several drawbacks including:

• Disturbance of the crusted surface of the waste pile by track-mountedequipment used to inject the proprietary agent. This can lead tosubsequent erosion.

• Unknown effectiveness of the stabilization process. EPA is reluctant toperform a demonstration project at a time when the final remedies shouldbe completed. The prospect of having to implement a contingency remedyat a later date is undesirable.


• The stabilization process (if effective) would not prevent mechanicalerosion of the mine waste rock during storm events and snow melt.

21. It is obvious that the BOR and Yak tunnels need to be kept open and draining.Bulkheading and flooding mine workings above the tunnel levels will cause themto collapse much quicker than if they were free draining. It also makes repairs tothe tunnels difficult and costly at best. Seasonal storage would be betteraccommodated in surface ponds. Consider the problems caused by multiple cavedsections with water backed up behind each. Alternative 2a will surely collapse theYak at the point where water enters the tunnel.

Alternative 2g does not address the Yak tunnel (the commenter mentions the YakTunnel).

The LMDT is not believed to currently be open and free draining. Suspectedblockages currently impound water in flooded mine workings. The intent ofAlternative 2g is to install the bulkhead in competent rock and to dewater themine pool up-stream of the bulkhead. This approach would dewater mineworkings that currently are flooded. Seasonal storage of collected ARD in surfaceponds as several disadvantages including:

• Eliminates the portion of Alternative 2g intended to mitigate the adverseenvironmental impacts of the mine pool.

• Increases the likelihood of discharge of untreated ARD during high runoffyears. It is impractical to construct an impoundment to contain runoffduring very high precipitation conditions.

• A large impoundment would be visually unattractive and would result insignificant evaporative losses requiring mitigation.

22.1 also favor option 2g due to the bulkhead proposal. In locations where miningoccurred below the tunnel level; would it be possible to install a well or wellsdrilled from the surface into these areas and dewater the mine pool? If it werepossible to discharge the wells directly into the BOR tunnel the power requiredwould be far less than pumping to the surface. This might permit the mine pool tobe used for storage below the tunnel level. Options 2b, 2e and 2h are viable. I amassuming that long term operating and maintenance costs, including tunnelmaintenance, ar« included in the present worth numbers. Without tunnelmaintenance all systems fail to be viable.

The LMDT was designed to drain mine workings at or above its level. It isunlikely tht&jpumpingfrom a single mine working below the level of the LMDTwould affect a large area. In addition, discharge of pumped water to the LMDTwould require the well to be vertically aligned with both the LMDT and the


deeper flooded mine working. This scenario is unlikely and would be difficult ifnot impossible to implement.

23. My choice for the use of the LMDT is a variation of 2g. Pipe the contaminatedwater from the Marion Shaft area to a new dedicated treatment plant or to theBOR plant. Keep the LMDT free draining and perhaps pump ground water frombelow the tunnel level.

See response to comments 21 and 22.

Comments from Bob Calder:

24. My first choice would be Alt. 1, but we all know that will not happen.

Comment Acknowledged

25. Alt.2:1 think that the most critical point now would be to have ASARCO Calif,gulch treatment plant, working and on line, to aid the LMDT in the volume ofwater they are unable to handle. Any and all chances of water from Iron Hillshould be sent out the Yak Tunnel. The LMDT treatment plant should beupgraded itself as opposed to a shaft, bulkhead, and miles of pipeline. When themetals from Iron Hill might better be processed and treated at the Yak plant.Possibly selling reduced materials. Pipelines to the new bulkhead/Shaft, willcause eco-damage that will take a lifetime to recover. Motorized vehicles nowalso go everywhere, and they will follow these work areas and make moreproblems. I would please ask that all attempts to upgrade the LMDT plant be afirst consideration, along with more thoughts towards drainage towards the YakPlant.

Tlie selection of the BOR's Water Treatment Plant were driven by costs. Watertreatment costs are significantly lower at the BOR's facility than at the Yak watertreatment facility. In addition, treatment at the Yak facility would require a newpipeline (either to the plant itself or to a location where water could beintroduced into the Yak Tunnel). The installation of the bulkhead in the LMDT isto facilitate the dewatering of the flooded mine workings Treatment plant sludgedoes not contain economically recoverable metals.

26. Alt.4 I am absolutely opposed to the removal of the Posardine Mine pile. Thecontamination of water, from this pile, and down 7th street will not cease becauseof the removal of this pile. Next, it will come again from the east of the Pons., andthen east of that etc.etc..I also believe that the Ponsardine dump, truly givesvisitors to Lake County of the great mining history we have, as the road leads intothe mining district. Other piles that were removed a few years ago, took awaymuch of Leadville's unique mining character. The Pons. removal will just takeaway more history. I have designed an idea that I believe will keep the Pons.


dump intact, and also filter the runoff from this area, as well as historically andaesthetically appeal to all. I also have drawings that will aid in my proposal.

The idea is a drain along the toe of the dump, and 7th street, to a settle pond onthe west of the pile, which will also catch any seepage from the old rail grade. Thedrain will be along the idea of a french drain, ie. to allow seepage to the pond.This pond will be excavated to the west, N.west of the main dump, and into thehillside south ifnecessary. Along with a small patch of existing aspen trees and a few lodgepolepines, the plan asks for a crib wall to hide the drain system and settle pond. Ibelieve that this might look very good, and serve well the intended purpose. Ihave done an artist's rendition of what I think it will look like. The top of thePons. dump will also be graded lightly to drain towards the shaft subsidence.

There could be a possibly be a core hole drain, easterly, looking towards theHayden workings which have a connection to the LMDT. I really like this idea,and although I am not an engineer, I worked in and around mines for many years,and I think it can be done, and done historically appealing.

As mentioned previously, due to the lack of space between the County road andthe toe of the pile in-place stabilization and surface water management featureswould be difficult to implement.

Comments from Bob Elder

27. Both the EPA and State of Colorado have chosen to combine Alternatives 2g and4b as the preferred action from among the several alternatives evaluated. Ibelieve that this selection is the correct one, as it will satisfactorily address thelong-term water quality issues remaining in Operable Unit 6.

Comment acknowledged

28. Alternative 2g - Install Bulkhead in LMDT and Dewater Mine Pool, with GravityPipeline to BOR Treatment Plant.

This alternative uniquely includes the important goal of lowering the level of thepresently elevated water pool in the mine workings beneath Fryer Hill, CarbonateHill and Graham Park. Implementation of this alternative will greatly lessen theability of the metals laden water in the elevated pool to migrate into adjacentground water resources. It will also eliminate the possibility of a catastrophicrelease of impounded mine water from the caved LMDT.

Alternative 2g will eventually eliminate the unavoidable mixing of contaminatedmine water and clean alluvial ground water in the discharge from the LMDT. At


the present time, pumping of the mixture of mine water and alluvial water fromthe shallow well system near the LMDT portal draws down the level of alluvialwater in the area.

When Alternative 2g allows discontinuance of this well pumping, restoration ofthe local alluvial water table may significantly increase the domestic water flowthat issues form Parkville Water District's nearby Canterbury Tunnel portal.


29. There is a potential maintenance problem to be addressed under Alternative 2g.This is in regard to the planned use of a dewatering well and gravity pipeline todeliver mine water to the BOR treatment Plant at LMDT portal. We recognizedat the Climax mine that the continued pumping of heavy metals laden watertended to build up hard deposits in the pump columns and delivery lines involved.

The build up of hard deposits stems from the air entrained in the water during thepumping process. The contained oxygen tends to precipitate the iron andmanganese sulfates contained in the acid mine drainage (AMD) as the basicsulfate, jarosite. The jarosite deposits reduce and constrict the cross section of thepipelines, and can completely block water flow if neglected.

Timely inspection of the lines and removal of the hard deposits with rotary cutterswill be necessary to insure delivery of water through the planned system.Providing sufficient manholes along the gravity line to allow equipment access topipe runs of workable lengths will be important for long-term maintenance of thesystem.

Alternative 2g includes the cost of a pipe pig and launcher for regular removal ofscale.

30. Alternative 4b - Relocation of the Ponsardine waste dump to the on-Siterepository and physical stabilization of the retaining wall on the south side of theRobert Emmet waste dump.

Alternative 4b will certainly be a more compatible solution to the Ponsardine andRobert Emmet environmental conditions than the alternative actions studied. Theother actions considered included either in-situ chemical stabilization orconsolidation and capping of the waste deposits.

hi situ chemical stabilization is not only expensive to implement, but is alsouncertain in its effectiveness in each specific application. Consolidation andcapping of the waste deposits requires a large capital expenditure. It also has theunfavorable effect of greatly altering the historic aspect of the Mining District.


The existing historic landscape is highly prized not only by the local citizens butalso by Lake County's touring visitors.

The Robert Emmet dump cribbing has not been repaired or replaced since themine plant was last reconstructed by ASARCO in 1951-52. Stabilization of thedeteriorated cribbing will prevent future collapse of the retained dump materialdown slope onto County Road 1. Possible exposure of additional mineralizedmaterial to run off water will thus be avoided.

Removal of the Ponsardine waste material to the planned on-Site repository willeliminate the sulfide-bearing waste rock presently being subjected to run off waterin Little Stray Horse Gulch. The sulfide bearing material may prove to be mainlyat the surface of this waste deposit, and the underlying portion of the dump mayconsist of surficial moraine and unmineralized bedrock placed on the dump in thefirst stages of the shaft operation.

In any case, the Ponsardine dump will furnish a considerable volume of coarsewaste rock that can beneficially layered and mixed with the water plant sludges tobe routinely placed in the on-Site repository.


31. The Proposed Plan does not specify a preferred site for the Site-Wide Repository.I understand that the existing Black Cloud tailing pond is being considered for useas this repository.

It would be a serious mistake for the EPA and the State of Colorado to becomeresponsible for the integrity of this tailing pond as a result of the repository use.The Black Cloud pond has severe environmental problems that will only becomeworse as time passes.

I was very familiar with the surface area now underlying the pond prior to 1970,when the pond construction was commenced. The area consisted entirely of adeep wetland, and the water feeding the area was not drawn from Iowa GulchCreek. Instead, the wetland was well fed from springs and seeps contained in thelandslide topography to the immediate south, on the steep north-facing slope ofLong & Deny HiH.

The springs and seeps are associated with the Weston Fault branches exposed onLong & DerryHilL The fault branches connect with the extensive manganesemineralization present in the Leadville dolomite. The black manganese oxidemineralization can be seen hi outcrop on the cliff further west along the Long &Derry ridge, and also is evident on the dumps of the old Doris and Frank mineworkings down dip to the east beneath the prominent rock glacier.


This prevalent manganese mineralization accounts for the high manganesecontent of the water issuing from the springs and seeps, and has necessitated thespecial effort of the Black Cloud water treatment plant to lower manganesecontent of the plant effluent by employment of liquid oxygen.

The wetland water must account for most of the flow that exits at the western toeof the tailing dam. Unless an extraordinary effort to contain this flow isundertaken, such as a cofferdam, it will probably continue in perpetuity.

The landslide in contact with the south abutment of the tailing pond dam is acontinuing threat to the integrity of the pond. This landslide extends severalhundred feet up the steep slope of Long & Derry Hill. It has been activelymoving in recent time. This is evidenced by the pronounced slant of the stillliving evergreen trees rooted in the slide. They stand at all angles from vertical tohorizontal, a result of the gradual descent of the slide.

The landslide material is saturated with water, and crossed by many collapsefissures. Continued downward movement of the slide is exerting lateral pressureupon the south abutment of the tailing dam. At sometime in the future, thispressure will be relieved by a failure of the west face of the dam. The dam isconstructed of deposited tailing sand and faced with Rock, and does not have thestructural cohesion necessary to resist the lateral pressure.

The Black Cloud Mine (BCM) operator installed a toe-drain system to dewaterthe tailing dam. This dewatering system was built in part to address the seepsassociated with-the Long and Derry hillside, and is a major source of the seepwater historically treated by the Black Cloud facility.

The Black Cloud operator and DMG also regularly monitored the movement ofthe hillside south of the impoundment during the course of tailing pond operation.The hillside monitoring did indicate small amounts of lateral and verticalmovement. The tailing dam did not show signs of movement, cracking, buckling orother adverse local conditions. The hillside monitoring was performed to predicthillside movement that might have caused displacement of tailing pond water intoIowa Gulch. There was no indication of tailing dam failure associated withhillside creep.

The Administrative Record indicate that the tailing dam is an earthen damconstructed of rolled earth and rock fill with centerline raises constructed asnecessary. The dam was analyzed for slope stability under both static anddynamic loading conditions as well as a Probable Maximum Flood Eventanalysis. The extensive evaluation of the tailing facility required under DMGclosure requirements revealed no shortcomings in the long-term structuralperformance and integrity of the impoundment.


As a result, EPA will require the following items, should the BCM tailingimpoundment be selected as the On-Site Repository.

• Evaluate failure due to rock slide during design of the on-Site repository.

• Re-institute hillside monitoring and inspection as part of the on-Siterepository operation and maintenance.

EPA appreciate Mr. Elder's comments because they will keep the public attentionfocused on safe design and monitoring systems,

Date post:	06-Oct-2020
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