EXPLANATION OF SIGNIFICANT DIFFERENCES 

D&RGW Slag Piles and 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 of Purpose 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 Selected Remedy » 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 Support Agencies 

The United States Environmental Protection Agency (EPA) is the lead agency. The Colorado 

Department of Public Health and Environment (CDPHE) is the support agency. 

1.3 Legal Authority for Explanation of Significant Differences 

Under Section 117 (c) of the Comprehensive Environmental Response, Compensation, and 

Liability Act of 1980 (CERCLA or Superfund), as amended by the Superfund Amendment and 

Reauthorization Act of 1986 (SARA), the EPA is required to publish an Explanation of 

Significant Differences (ESD) when significant, but not fundamental, changes are proposed to a 

previously selected site remedy. Sections 300.435(c)(2)(i) and 300.825(a)(2) of the National 

Contingency Plan (NCP) set forth the criteria for issuing an ESD and requiring that an ESD be 

published if the remedy is modified in a way that differs significantly in either scope, 

performance, or cost from the remedy selected in the Record of Decision (ROD) for the Site. 

1.4 Summary of Purpose 

A Record of Decision (1998 ROD) was signed on May 6,1998 for Stockpiled Fine Slag . 

Arkansas Valley Smelter (AV Smelter) Slag Pile, Operable Unit 3 (OU3), of the California 

Gulch Superfund Site (Site) in Lake County, CO. 

This ESD provides a brief history of the Site, describes the OU3 remedy as selected in the 1998 

ROD, and explains how subsequent to the finalization of this decision document, issues 

concerning institutional controls (ICs) have been identified for tins OU. 

Due to the fact that residual slag remains onsite, this ESD addresses the need for ICs, and 

documents the decision to require ICs. In addition, the use of the term "contingency" for fine 

slag utilization in the 1998 ROD is clarified. Fine slag can be used for future commercial 

purposes by following the requirements set out in the 1998 ROD. 

1.5 Administrative Record 

This ESD and its supporting documentation has been incorporated into the Administrative 

Record as directed in Section 300.825(a)(2) of the NCP. The Administrative Record file is 

available for public review at the 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 1 
kiefer.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 is for informational purposes only regarding the EPA's response actions at the Site, 

and is not intended for any other purpose. 

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 of heavy 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 

of responsibility. 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 

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ballast. D&RGW purchased the La Plata Slag Pile from the Leadville Sanitation District 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 of Stringtown. The pile generally 

consists of slag produced by the AV smelter that operated from 1882 to i960. Based on aerial 

photography, the pile volume in the late 1950s was approximately 1.2 million cubic yards, 

whereas in 1998 approximately 422,000 Cubic yards of slag remained, of which, approximately 

190,000 cubic yards is stockpiled fine slag. 

The La Plata Slag Pile, located west of the city limits of Leadville on Elm Street, has a volume 

estimated at 105,000 cubic yards. 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 of Harrison Avenue and 

Elm Street, in a residential 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 Pile was removed to 

original grade and relocated to the AV Slag Pile in March 1998. 

Once a hot bed of transportation 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 of the Poverty Flats rail yard formerly owned by D&RGW is located near the north end 

of the City of Leadville, encompasses an area of roughly 43 acres, and is crossed by abandoned 

rail lines and access roads. Slag, which was used in the rail yard as ballast and as a road base to 

provide support for heavy vehicle traffic, was also deposited around the loading dock due to 

spillage during transportation activities. 

The rail easement includes the portion of railroad track that runs diagonally through Leadville 

and consists of approximately 25 feet on either side of the 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 of major lead 

slag piles and one zinc slag pile 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 of the 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 of an inch, was found to have elevated lead levels. 

In 1994, D&RGW entered into a Consent Decree (1994 D&RGW CD) with the EPA. In May 

1996, D&RGW submitted a Feasibility Study (FS) for the stockpiled fine slag at the AV Smelter 

Slag Pile, in accordance with the terms of the 1994 D&RGW CD. In addition, D&RGW 

identified-a small volume of fine slag in the rail yard (Poverty Flats). D&RGW prepared a plan 

which addressed removal of the fine slag from this area to the AV Smelter Slag Pile. 

As a result of the Union Pacific Railroad Company (UPRR) purchase of the Southern Pacific 

Transportation Company (surviving corporation from an earlier merger of D&RGW and 

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Southern Pacific Railroad), UPRR took ownership of all D&RGW property at the Site in 1996 

and assumed D&RGW's responsibilities under the 1994 D&RGW CD. 

During the summer and fall of 1997, UPRR removed 1,264 cubic yards of 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 of lead. Soils samples, taken before and after removal of the 

slag, showed levels of lead in soil that exceed the Site-wide residential action level of 3500 

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 of their ballast operations, UPRR relocated approximately 104,000 cubic yards of slag to 

the AV Slag Pile in March 1998 to bring the Harrison Street Slag Pile to grade. Soils samples 

taken after removal of the slag showed levels of lead in soils, both under where the slag pile was 

located and otherwise on the Harrison Avenue property, that exceed the residential action level 

for lead in soils of 3500 mg/kg. Thus lead in the soils on the Harrison Avenue property may 

create the potential for unacceptable human health risks should the property be developed for 

residential use. To date, the land remains vacant. Sections along the highway are zoned 

Commercial, and the remaining sections are zoned Transitional Commercial by the City of 

Leadville. 

In July 1998, UPRR submitted a Work Plan for the Consolidation of Fine Slag at the Railroad 

Easement Near McWethy Drive to 12th Street, Leadville, Colorado, July 20,1998. The work 

plan provided for the easement to be converted into a segment of the Mineral Belt Trail. 

Consistent with the plan, fine slag from the rail easement was used as base material on the 

Mineral Belt Trail. More specifically, the fine slag was consolidated and covered with a 

compacted gravel sub-base of six inches and 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 of Decision for OU3. The completion of the consolidation work was approved in 

September 1998. The conversion of the 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 of Understanding between EPA, UPRR, 

and Lake County, Lake County completed these projects, and UPRR provided funding for the 

sub-base, culverts, and asphalt in 2000. Ownership of the easement has been transferred to Lake 

County via quitclaim deed. 

2.2 Summary of Selected Remedy 

The EPA issued the Stockpiled Fine Slag - Arkansas Valley Smelter Slag Pile ROD (1998 ROD) 

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 No Action alternative leaves the 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 of the slag, if it is encapsulated prior to its use or 

reuse. The 1998 ROD also provides a provision to use the slag in the fixture if regional market 

demand exists for the material as a component in construction materials. 

The 1998 ROD did not require maintenance of the fine slag piles. Any future use of the slag 

would require encapsulation prior to reuse. Encapsulation can include the use of fine slag in 

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concrete 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 of a different material). 

3 Basis for and Description of Significant Differences 

Sampling in the Poverty Flats rail yard property and the Harrison Avenue 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 on the former railroad easement, acts as a 

cap for fine slag. Thus, ICs are needed at OU3 because the remedial action results in hazardous 

substances, pollutants, or contaminants remaining at the Site above levels that allow for 

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 of a local ordinance, 

environmental covenant, and/or restrictive notice as part of the OU3 remedy. 

The objectives of the ICs are to reduce or control human exposure to contaminants of concern. 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 the City of Leadville on May 7,2013 

and Lake County on March 3,2009, passed ordinances that established ICs for OU3. Under these 

ordinances, a building permit will not be issued for any activity on a property within OU3 that 

contains a designated engineered remedy unless the permit applicant has secured approval for 

those activities from the CDPHE. For all other portions of OU3 not designated as part of an 

engineered remedy, the ordinance provides that any excavation or other earth removal 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 provides that 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 clarifying the use of the term "contingency" set out in the 1998 ROD. The 

use of the term contingency was not meant to establish a contingency remedy. It was meant in 

the sense that, if the owner of the fine slag wanted to use the fine slag in the future, the 

requirements set out in the 1998 ROD are the requirements that must be followed for use of the 

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 with the statutory requirements 

of Section 121 of CERCLA such that the remedy remains protective of human health and the 

environment and complies with Federal and State requirements that 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 of the remedial action to 

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ensure that the remedy is, or will be, protective of human health and the environment. 

6 Public Participation 

All of the public participation requirements set forth in Sections 117(c) and (d) of CERCLA, as 

well as Section 300.435(c)(2)(i) of the 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 

of this ESD are contained in the Administrative Record for the California Gulch Superfund Site. 

The EPA will also publish a notice of availability and a brief description of the 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 Consent for Remedial Investigation/Feasibility Study. CERCLAVIII-92-06. California Gulch Superfund Site, Denver and Rio Grande Western Railroad. 

SDMS #1020621. December 3,1991. 

• Baseline Human Health Risk Assessment for the California Gulch Superfund Site - Draft 

Final - Part A - Risks to Residents from Lead, prepared by Roy F. Weston, Inc. SDMS 

#319625. U.S. Environmental Protection Agency. January 2,1996. 

• Baseline Human Health Risk Assessment for the California Gulch Superfund Site - Part B 

- Risks to Residents from Contamination Other than Lead prepared by Roy F. Weston, 

Inc. SDMS #319626. U.S. Environmental Protection Agency. January 2,1996. 

• Baseline Human Health Risk Assessment for the California Gulch Superfund Site - Part 

C - Evaluation of Recreational and Worker Scenarios prepared by Roy F. Weston, Inc. 

SDMS #316598. U.S. Environmental Protection Agency. April 17, 1995. 

• Baseline Aquatic Ecological Risk Assessment - Final. California Gulch NPL 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 Superfund Site, Denver and Rio Grande Western Railroad. 

SDMS #318593. U.S. District Court. December 15,1993. 

Martin Hestmark 

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• Ecological Risk Assessment for the Terrestrial Ecosystem. California Gulch NPL 

Super fund Site, Leadville, Colorado, prepared by Roy F. Weston, Inc. SDMS #321677. 

U.S. Environmental Protection Agency. January 1997. 

• Feasibility Study Work Plan for Stockpiled Fine Slag at the California Gulch Site 

Leadville, Colorado, prepared for Denver & Rio Grande Western Railroad. SDMS 

#316702. Morrison Knudsen Corporation. March 15,1994. 

• Final Screening Feasibility Study for Remediation Alternatives at the California Gulch 

NPL Site, Leadville, CO. SDMS #301445. U.S. Environmental Protection Agency. 

September 1993. 

• Findings of Metal Speciation Investigations- Draft Final- at the 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 of Leadville, May 7,2013 . 

• Preliminary Human Health Baseline Risk Assessment for the California Gulch NPL 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 Plan for Stockpiled Fine Slag, Arkansas Valley Smelter Slag Pile, 

California Gulch Superfund 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 Yard Area, prepared for Denver & 

Rio Grande Western Railroad. SDMS #316699. Morrison Knudsen Corporation. 

February 8,1995 

• Record of Decision Stockpiled Fine Slag Arkansas Valley Smelter Slag Pile, California 

Gulch Superfund Site, Operable Unit 3, 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, prepared by CH2MHill. SDMS#U.S. 

Environmental Protection Agency. May 1989. 

• Remedial Investigation Report for Lead Slag Pile at the California Gulch Site Leadville, 

Colorado, preparedfor Denver & Rio Grande Western Railroad. SDMS #s 305053, 

305054, 307275. Morrison Knudsen Corporation. December 11,1992. 

• Request for Certification of Closure, California Gulch Superfund Site, preparedfor 

Union Pacific Railroad Company. SDMS #485982. Environmental Resources 

Management. February 25, 1999. 

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

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• Stockpiled Fine Slag Feasibility Study - Final, prepared for 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 of Fine Slag Denver & Rio Grande Western Rail Yard 

State Highway 24 and 12th Street Leadville, CO. SDMS # . Environmental Resources 

Management. November 19,1997. 

• Work Plan Consolidation of Fine Slag, preparedfor Denver & Rio Grande Western 

Railroad. SDMS #321511. Terranext. November 12,1996. 

• Work Plan Consolidation of Fine Slag Railroad Easement Near Mc Wethy Drive to 12th 

Street Leadville, CO, prepared for Union Pacific Railroad Company. SDMS # . 

Environmental Resources Management. July 20,1998, 

• Work Plan for Slag Pile Remedial Investigation at California Gulch Site, Leadville, CO, 

prepared for Denver & Rio Grande Western Railroad Company. SDMS #316309. 

Morrison Knudson Corporation. October 1991. 

• Work Plan Harrison Street Slag Pile Closure Intersection of Harrison and Monroe 

Streets Leadville, CO, prepared for Union Pacific Railroad Company. SDMS #323870. 

Environmental Resources Management. November 12,1998. 

• Zinc Slag Pile Investigation Report, California Gulch Site, Leadville, CO, prepared for 

Denver & Rio Grande Western Railroad Company. SDMS #s 318849, 307409, 317059 

and 305592. Morrison Knudsen Corporation. December 11,1992. 

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