### EXPLANATION OF SIGNIFICANT DIFFERENCES D&RGW Slag Pilesand Easement, Operable Unit 3

California Gulch Superfund Site Lake County, CO

August 2014

U.S. Environmental Protection Agency

Region 8 1595 Wynkoop Street Denver, CO 80202-1129

### Contents

1 Introduction 1.1 Site Name and Location 1.2 Lead and Support Agencies

. 1.3 Legal Authority for Explanation of Significant Differences 1.4 Summary ofPurpose 1 1.5 Administrative Record 1 2 Site History,Contamination, and Selected Remedy...........................................................1 2.1 Site History and Contamination * 2 2.2 Summary of SelectedRemedy » 4 3 Basis for and Description of Significant Differences 5 4 Support Agency Comments 5 5 Statutory Determinations. 5 6 Public Participation 6 7 Appendix -References 6

i

### 1 Introduction

1.1 Site Name and Location Site Name: California Gulch Superfund Site (Site) Operable Unit 3 (OU3) Site Location: Lake County, Colorado Site ID: COD980717938 1.2 Lead and SupportAgencies The United StatesEnvironmental Protection Agency (EPA) isthe lead agency.The Colorado Department ofPublic Health and Environment (CDPHE)is the support agency. 1.3 Legal Authority for Explanation of Significant Differences Under Section 117(c) ofthe Comprehensive Environmental Response, Compensation,and Liability Act of 1980 (CERCLA or Superfund), asamended by the Superfund Amendment and Reauthorization Act of1986 (SARA),the EPA isrequired to publishan Explanation of Significant Differences (ESD)when significant, butnot fundamental, changes areproposed to a previously selected siteremedy. Sections300.435(c)(2)(i) and 300.825(a)(2)oftheNational Contingency Plan (NCP) set forththe criteriafor issuingan ESDand requiring that an ESDbe published iftheremedy is modified in away that differs significantly ineither scope, performance, or cost from the remedy selected in the Record ofDecision (ROD) for the Site. 1.4 Summary of Purpose A Record ofDecision (1998ROD) was signed on May 6,1998 for Stockpiled Fine Slag

. Arkansas Valley Smelter (AV Smelter) Slag Pile, Operable Unit 3 (OU3), ofthe California Gulch Superfund Site (Site)in Lake County, CO. This ESDprovides abriefhistory ofthe Site, describes theOU3 remedy as selected in the 1998 ROD, and explainshow subsequentto the finalization ofthis decisiondocument, issues concerning institutional controls (ICs) have been identifiedfor tins OU. Due to the fact that residual slagremains onsite,this ESDaddresses theneed for ICs, and documents thedecision torequire ICs. In addition, theuse ofthe term "contingency" for fine slag utilization in the 1998 ROD is clarified. Fine slagcan be used for futurecommercial purposes by following the requirementsset out in the 1998 ROD. 1.5 Administrative Record This ESD and its supporting documentation hasbeen incorporated intothe Administrative Record asdirected in Section300.825(a)(2) ofthe NCP. The Administrative Record file is available forpublic review atthe follow location: Lake County Public Library 1115 Harrison Avenue Leadvillej, CO 80461 Or, by contacting Linda Kiefer,Project Manager, EPA-Region 8,303-312-6689, or

August 2014 Page 1kiefer.linda@ epa.gov.

2 Site History, Contamination, and Selected Remedy
OU3 Location Map

Disclaimer: This map and any boundary lines within the map are approximate and subject to change. The map is not a survey. The map isfor informationalpurposes only regarding the EPA's response actions at the Site, and is not intendedfor any otherpurpose. 2.1 Site History and Contamination The Site is located 100 miles southwest of Denver in Lake County, Colorado. The Site covers 18 square miles and includes the City of Leadville, various parts of the Leadville Historic Mining District, and Stringtown. The Site also includes a section of the Arkansas River from the confluence of California Gulch to the confluence of Two-Bit Gulch. The Site was placed on the National Priorities List due to concerns about the impact of mine drainage on surface waters in California Gulch and the impact ofheavy metals loading in the Arkansas River. Pursuant to a 1994 Consent Decree, the EPA divided the Site into the 12 operable units (OUs). OU1 through OU11 were designated to facilitate source remediation and correspond with areas ofresponsibility. OU12, which covers the entire Site, was designated to address site-wide surface and groundwater. The cleanup strategy at the Site entailed conducting source remediation response actions at OU1-OU11, then OU12 would look at how well these source remediation response actions reduced or eliminated the release of contaminants of concern such that the surface and groundwater RAOs and ARARs selected in the OU12 ROD will be met. Additional
source remediation may be selected as part of the OU12 remedy. OU3 includes three slag piles (Arkansas Valley (AV), La Plata, and Harrison Street), approximately 12 acres at Harrison Avenue and Monroe Street which contained the Harrison Street slag pile, an easement that runs diagonally through the City of Leadville, and a portion of the rail yard known as Poverty Flats (see OU3 Location Map) all owned by the Denver & Rio Grande Western Railroad Company (D&RGW) when OU3 was designated in 1994. In 1961, D&RGW purchased the AV Slag Pile from ASARCO, Incorporated for use as railroad

August 2014 Page 2ballast. D&RGW purchased the La Plata Slag Pile from the Leadville SanitationDistrict in 1970.

Additionally, D&RGW purchased the Harrison Street Slag Pile and Harrison Avenue property from NL Industries in 1983. The AV Slag Pile covers approximately 40 acres just west ofStringtown. The pile generally consists of slag produced by the AV smelterthat operated from 1882 to i960. Based on aerial photography, the pile volume in the late 1950swas approximately 1.2 million cubic yards, whereas in 1998 approximately 422,000 Cubic yards of slag remained, ofwhich, approximately 190,000 cubic yards is stockpiled fine slag. The La Plata Slag Pile, located west ofthecity limits of Leadvilleon Elm Street, has a volume estimated at 105,000 cubicyards. Bimetallic Smelting Company leased the La Plata Smelter Works in OU3 from 1892 to 1900 for pyritic smelting of low-grade ores. The Harrison Reduction Works was located near the northeast comer ofHarrison Avenue and Elm Street, in aresidential area. The Harrison Street Slag Pile ranged from 20 to 50 feet in height and covered an area of approximately 3 acres. The Harrison Street Slag Pilewas removed to original grade and relocated to the AV Slag Pile in March 1998. Once a hot bed oftransportation activities mostly related to mining,the Poverty Flats rail yard, located between 12th Street, Highway 24,17th Street and County Road 8, is now vacant. The portion ofthe Poverty Flatsrail yard formerly owned by D&RGW is located near the north end ofthe City of Leadville, encompasses an area ofroughly 43 acres, and is crossed by abandoned rail lines and access roads. Slag, which was used inthe rail yard as ballast and asa road base to provide support for heavy vehicletraffic, was also deposited around the loading dock due to spillage during transportation activities. The rail easement includesthe portion ofrailroad track that runs diagonally through Leadville and consists of approximately 25 feet on either side ofthe track centerline. Slag was used as a road base to provide support for heavy vehicle traffic. Slag was also deposited as spillage from passing rail cars. EPA and D&RGW entered into an Administrative Order on Consent (D&RGW AOC) on December 3,1991, which required D&RGW to perform remedial investigations ofmajor lead slag piles and one zinc slagpile within the Site. D&RGW completed the slag remedial investigation (1992 Slag RI)in 1992. It was concluded that the fine fraction of slag was the only part ofthe slag that may present an unacceptable risk. Slag was found to have elevated levels of zinc, lead, arsenic and cadmium along with a low acid-generating potential, and a neutral to basic pH. Fine slag, which is less than 3/8 ofan inch, was found to have elevated lead levels. In 1994, D&RGW entered into a Consent Decree (1994 D&RGW CD) withthe EPA. In May 1996, D&RGW submitted aFeasibility Study (FS) for the stockpiled fine slag at the AV Smelter Slag Pile, in accordance with theterms ofthe 1994 D&RGW CD. In addition, D&RGW identified-a small volume offine slag in the rail yard (Poverty Flats). D&RGW prepared a plan which addressed removal ofthe fine slag from this areato the AV Smelter Slag Pile. As a result ofthe Union Pacific Railroad Company (UPRR)purchase ofthe Southern Pacific Transportation Company (surviving corporation from an earlier merger ofD&RGW and

August 2014 Page 3Southern Pacific Railroad), UPRR took ownership ofall D&RGW property at the Site in 1996

and assumed D&RGW's responsibilities underthe 1994 D&RGW CD. During the summer and fall of 1997, UPRR removed 1,264 cubic yardsof slag, including fine slag, from the rail yard and placed it onto the AV Slag Pile. As a result, soils were exposed containing elevated concentrations oflead. Soils samples, taken before and after removal ofthe slag, showed levels oflead in soil that exceed the Site-wide residential action level of3500 mg/kg lead, thus lead in the soils on this property may create the potential for unacceptable human health risks should the property be developed for residential use. To date, the land remains vacant, and is zoned Business by Lake County, As part oftheirballast operations, UPRR relocated approximately 104,000 cubic yards ofslag to the AV Slag Pile in March 1998 to bringthe Harrison Street Slag Pile to grade. Soils samples taken after removal ofthe slag showed levels of lead in soils, both under wherethe slag pile was located and otherwise on the HarrisonAvenue property, that exceed the residential action level for lead in soils of3500 mg/kg. Thus lead in the soilson the Harrison Avenue property may create the potential for unacceptable human healthrisks should the property be developed for residential use. To date,the land remains vacant. Sections alongthe highway are zoned Commercial, and the remaining sections are zoned Transitional Commercial by the City of Leadville. In July 1998, UPRR submitted a Work Planfor the Consolidation ofFine Slag at the Railroad Easement Near McWethy Drive to 12th Street, Leadville, Colorado, July20,1998. The work plan provided for the easement to be converted into a segment ofthe Mineral Belt Trail. Consistent with the plan, fine slag from the rail easementwas used as base material onthe Mineral Belt Trail. More specifically,the fine slag was consolidated and covered with a compacted gravel sub-base of six inchesand then two one-inch layers of asphalt to encapsulate it. This resource utilization was consistent with the requirements for resource utilization set out in the Record ofDecision for OU3. The completion ofthe consolidation work was approved in September 1998. The conversion ofthe railroad easement to the Mineral Belt Trail was completed with the installation of a sub-base, culverts, asphalt, signs, centerline striping, and revegetation. In accordance with a 1998 Memorandum ofUnderstanding between EPA, UPRR, and Lake County, Lake County completed these projects, and UPRR provided funding for the sub-base, culverts, and asphalt in 2000. Ownershipofthe easement hasbeen transferred to Lake County via quitclaim deed. 2.2 Summary of Selected Remedy The EPA issuedthe Stockpiled Fine Slag-Arkansas Valley Smelter Slag Pile ROD (1998ROD) for OU3 on May 6,1998. Based on consideration of CERCLA requirements, detailed analyses of alternatives, and public comments, the EPA determined that a No Action alternative was the appropriate remedy. The NoAction alternative leavesthe stockpiled fine slag in its existing condition with no control or cleanup planned. The No Action alternative includes a provision, denoted as a contingency, for future utilization ofthe slag, if it isencapsulated prior to its use or reuse. The 1998 ROD also provides a provision to usethe slag in the fixture ifregional market demand exists forthe material as a component in construction materials. The 1998 ROD did not requiremaintenance ofthe fine slag piles. Any future use ofthe slag would require encapsulation prior to reuse. Encapsulation can include the use of fine slag in

August 2014 Page 4concrete or asphalt aggregate,as a road base, or as backfill (so long as the slag is chemically

bound or physically separated from an exposure by a barrier consisting ofa different material).


### 3 Basis for and Description of Significant Differences Sampling in the Poverty Flats rail yard property and the HarrisonAvenue property shows levels of lead in soils above levels that would allow for unlimited use and unrestricted exposure. In addition, the Mineral Belt Trail,which was constructed onthe former railroad easement,acts as a cap for fine slag. Thus, ICs are needed at OU3 because the remedialaction results in hazardous substances, pollutants, or contaminants remaining at the Site above levels that allowfor unlimited use and unrestricted exposure to soils. The remedial action, selected in the 1998 ROD, does not include ICs. As a result,this ESD requires ICs in the form ofa local ordinance, environmental covenant, and/or restrictive notice aspart ofthe OU3 remedy. The objectives ofthe ICs are to reduceor control human exposureto contaminants ofconcern. In the event that a change in land use is approved by local governments, procedures are in place,for notification to the EPA and the CDPHE. Additionally, both theCity of Leadville on May 7,2013 and Lake County on March 3,2009,passed ordinances that established ICs for OU3.Under these ordinances, a buildingpermit will not be issued for any activity ona property within OU3that contains a designated engineered remedy unless the permit applicant has secured approval for those activities from the CDPHE.For all otherportions of OU3 not designated as part of an engineered remedy, the ordinance providesthat any excavation or other earthremoval activity that exceeds 10 cubic yards requires CDPHE approval for such activity as a condition precedent to the City or County granting a permit. Finally, the ordinance providesthat all permit applicants shall be provided with information regarding best management practices regarding potentially contaminated soils and the applicant must certify they have received and reviewed this information before a permit will be issued. Additionally, EPA is clarifyingthe use ofthe term "contingency" setout in the 1998 ROD. The use ofthe term contingency was not meant to establish a contingency remedy. It was meant in the sense that, ifthe ownerofthe fine slag wanted to use the fine slag in the future,the requirements set out in the 1998ROD are the requirementsthat must be followed for use ofthe fine slag.


### 4 Support Agency Comments CDPHE supports the EPA's decision to modify the remedy for OU3.


### 5 Statutory Determinations The EPA has determined that these significant changes comply withthe statutory requirements of Section 121 of CERCLA suchthat the remedy remains protectiveofhuman health and the environment and complies withFederal and State requirementsthat are applicable or relevant and appropriate to this remedial action. Because this remedy will result in hazardous substances, pollutants, or contaminants remaining on site above levels that allow for unlimited use and unrestricted exposure, a statutory review will be conducted no less often than each five years after the initiation ofthe remedial actionto

August 2014 Page 5ensure that theremedy is, or will be, protective ofhuman health and the environment.



### 6 Public Participation All ofthe public participationrequirements set forth in Sections 117(c) and (d) ofCERCLA, as well as Section 300.435(c)(2)(i) ofthe NCP will be met. Although a formal public comment period is not required when issuing an ESD, this ESD and all documents that serve as the basis ofthis ESD are contained in the Administrative Record for the California Gulch Superfund Site. The EPA will also publish a notice ofavailability and a brief description ofthe ESD in the Leadville Herald Democrat.

Assistant Regional Administrator Office of Ecosystems Protection and Remediation U.S. EPA, Region 8



### 7 Appendix - References

• Administrative Order on Consentfor Remedial Investigation/Feasibility Study. CERCLAVIII-92-06. California GulchSuperfund Site, Denver and Rio Grande Western Railroad. SDMS #1020621. December 3,1991.

• Baseline Human Health RiskAssessmentfor the California GulchSuperfund Site - Draft Final - Part A - Risks toResidentsfrom Lead,prepared by Roy F. Weston, Inc. SDMS #319625. U.S. Environmental Protection Agency. January 2,1996.

• Baseline Human Health RiskAssessmentfor the California Gulch Superfund Site -Part B

-Risks to Residentsfrom Contamination Other than Leadpreparedby Roy F. Weston, Inc. SDMS #319626. U.S. Environmental Protection Agency. January 2,1996.

• Baseline Human Health RiskAssessmentfor the California GulchSuperfund Site - Part C - Evaluation ofRecreational and Worker Scenariosprepared by Roy F. Weston, Inc. SDMS #316598. U.S. Environmental Protection Agency. April 17, 1995.

• Baseline Aquatic Ecological RiskAssessment - Final. California GulchNPL Site. Prepared by Roy F. Weston, Inc. SDMS #320591. U.S.Environmental Protection Agency. September, 1995.

• Consent Decree with Denver and Rio Grande Western Railroad Civil Action No. 83-C2388. California Gulch SuperfundSite, Denver and Rio Grande Western Railroad. SDMS #318593. U.S. District Court. December 15,1993. Martin Hestmark

August 2014 Page 6• Ecological RiskAssessmentfor the Terrestrial Ecosystem. California Gulch NPL

Super fund Site, Leadville, Colorado,preparedby Roy F. Weston, Inc. SDMS #321677. U.S. Environmental Protection Agency. January 1997.

• Feasibility Study Work Plan for Stockpiled Fine Slagat the California Gulch Site Leadville, Colorado,preparedfor Denver & Rio Grande Western Railroad. SDMS #316702. Morrison Knudsen Corporation. March 15,1994.

• Final Screening Feasibility Studyfor Remediation Alternativesat the California Gulch NPL Site, Leadville, CO. SDMS #301445. U.S. Environmental Protection Agency. September 1993.

• Findings ofMetal Speciation Investigations- Draft Final- atthe California Gulch NPL Site,prepared by John W. Drexler and Roy F. Weston, Inc. SDMS #319693. U.S. Environmental Protection Agency. October 1995.

• Ordinance s,Series 20IS. SDMS # 1265522. City ofLeadville, May 7,2013

. • Preliminary Human Health Baseline RiskAssessmentfor the California GulchNPL Site, Leadville, Colorado. Prepared by Roy F. Weston, Inc.for the U.S. EPA. SDMS #303951. U.S. Environmental Protection Agency. December 1991.

• Proposed No Action Planfor StockpiledFine Slag, Arkansas Valley Smelter Slag Pile, California GulchSuperfund Site, Leadville, Colorado. SDMS#321484. U.S. Environmental Protection Agency. September 1996.

• Reconnaissance Report California Gulch Railroad Easement,prepared for Denver & Rio Grande Western Railroad. SMDS #316700. Morrison Knudsen Corporation. February 8, 1995.

• Reconnaissance Report California Gulch Railroad YardArea,preparedfor Denver & Rio Grande Western Railroad. SDMS #316699. Morrison Knudsen Corporation. February 8,1995

• Record ofDecisionStockpiled Fine Slag Arkansas Valley Smelter Slag Pile, California GulchSuperfund Site, Operable Unit3, Leadville, Colorado. SDMS # 323545. U.S. Environmental Protection Agency. May 1,1998.

• Remedial Investigation Draft Phase II Technical Memorandum 1986-1987. California Gulch Site, Leadville, Colorado, U.S. EPA,preparedby CH2MHill. SDMS#U.S. Environmental Protection Agency. May 1989.

• Remedial Investigation Reportfor Lead Slag Pile at the CaliforniaGulch Site Leadville, Colorado,preparedfor Denver & Rio Grande Western Railroad. SDMS#s 305053, 305054, 307275. Morrison Knudsen Corporation. December 11,1992.

• Requestfor Certification ofClosure, California GulchSuperfund Site,preparedfor Union Pacific Railroad Company. SDMS#485982. Environmental Resources Management. February 25, 1999.

• Resolution 2009. SDMS #1100390. Lake County Commissioners. March 3,2009.

August 2014 Page 7• Stockpiled Fine Slag Feasibility Study - Final,preparedfor Denver & Rio Grande

Western Railroad. SDMS #320758. Terranext. May 13,1996.

• Terrestrial Ecosystem Evaluation Report - Draft. California Gulch Site, Leadville, Colorado. SDMS #303424. Woodward Clyde Consultants. April 1993.

• Verification Report Consolidation ofFine Slag Denver & Rio Grande Western Rail Yard State Highway 24 and 12th Street Leadville, CO. SDMS #

. Environmental Resources Management. November 19,1997.

• Work Plan ConsolidationofFine Slag,preparedfor Denver & Rio Grande Western Railroad. SDMS #321511. Terranext. November 12,1996.

• Work Plan ConsolidationofFine Slag Railroad Easement Near McWethy Drive to 12th Street Leadville, CO,preparedfor Union PacificRailroad Company. SDMS #

. Environmental Resources Management. July 20,1998,

• Work Planfor Slag Pile Remedial Investigation at California GulchSite, Leadville, CO, preparedfor Denver & Rio Grande Western Railroad Company. SDMS #316309. Morrison Knudson Corporation. October 1991.

• Work Plan Harrison Street Slag Pile Closure Intersection ofHarrison and Monroe Streets Leadville, CO,preparedfor UnionPacific Railroad Company. SDMS #323870. Environmental Resources Management. November 12,1998.

• Zinc Slag Pile Investigation Report, California GulchSite, Leadville, CO,preparedfor Denver & Rio Grande Western Railroad Company. SDMS #s 318849, 307409, 317059 and 305592. Morrison Knudsen Corporation. December 11,1992.

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