SOMS Document ID •niiii 

2008232 

Explanation of Significant Differences 

Upper California Gulch 

Operable Unit 4 

California Gulch Superfund Site 

Leadville, CO 

March 2004 

U.S. Environmental Protection Agency 

999 18* Street, Suite 500 

Denver, CO 80202 
1. Introduction 

This Explanation of Significant Differences (ESD) describes the removal of planned 

cleanup work from the construction schedule for Fluvial Tailing Site 4 (also known as Oro 

City) within the Operable Unit 4 of the California Gulch Superfund Site. This change to the 

remedy defers the reevaluation of the need for clean up at Fluvial Tailing Site 4/Oro city until 

after the review of site wide surface and groundwater post-construction monitoring data. This 

ESD provides information about this change and includes the site history, selected remedy, 

basis for the change, support agency comments, statutory determinations and documentation of 

public participation compliance. 

Interest in the cultural and historical values of Fluvial Tailing Site 4/Oro City has resulted 

in a change to the selected remedy and provides the basis for this ESD. Alternatives for the 

work planned at this area were initially discussed during a meeting on May 4,1999. The 

meeting included support staff from the Colorado Department of Public Health and 

Environment (CDPHE), the State Historical Society and interested parties. The U.S. 

Environmental Protection Agency (EPA) is the lead for this ESD. 

A formal public comment period is not required for an ESD. Comments from CDPHE are 

summarized in Section 5 of this document. EPA will publish a notice of availability and a brief 

description of the ESD in a major newspaper of general circulation (as required by Code of 

Federal Regulation 40, Section 300.435(c)(2)(i)(B). This ESD and supporting documents will 

become a part of the California Gulch Administrative Record file and information repository 

[as required by CFR 40, Section 300.435(c)(2)(i)(A) and 300.825(a)(2)]. 

Comprehensive information on the California Gulch Superftind site is available at: 

U.S. Environmental Protection Agency 

Region VIII 

Superfund Record Center 

999 18*Sfreet, 5*^Floor 

Denver, CO 80202 

(303)312-6473 

and 

Lake County Public Library 

1115 Harrison Avenue 

Leadville, CO 80461 

(719)486-0569 

On March 31,1998 the Record of Decision (ROD) for the Upper California Gulch, 

Operable Unit 4, was signed. Any significant, but non fimdamental, changes to the selected 

remedy must be publicly noticed under Section 117 of the Comprehensive Environmental 

Response Compensation and Liability Act of 1980 (CERCLA), as amended by the Superfund 

Amendment and Reauthorization Act of 1986 (SARA), and pursuant to CFR 40, Section 

300.435 (c)(2)(i), 55 Federal Register 8666, 8852 (March 8,1990). 
2. Site History and Contamination 

The California Gulch Superfund Site is located 100 miles southwest of Denver in Lake 

County, Colorado. The Site covers 16 '/a miles and includes the City of Leadville, various parts 

of the Leadville Historic Mining District and Stringtown. A section of the Arkansas River from 

the confluence of California Gulch to the confluence of Lake Fork Creek is also included. 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. 

The 1994 Consent Decree divided the Site into the 12 Operable Units (OUs) shown in 

Figure 1. OUs 2 through 11 were designated to facilitate source remediation and correspond 

with areas of responsibility. OU 12, which covers the entire Site, was designated to address 

Site-wide Surface and Groundwater. OU 12 will be addressed after completion of source 

remediation in OU 2 through 11. 

Upper California Gulch, OU 4, is a valley with an intermittent sfream that flows to the 

confluence with the Arkansas River. The subject of this ESD is Fluvial Tailing Site 4/Oro City, 

which is a sub-basin of Upper California Gulch, OU 4. Resurrection Mining Company is 

responsible for conducting all response actions at OU 4. The general location of the sub-basm 

is shown on Figure 2. 

Primary contaminant source areas wdthin Fluvial Tailing Site 4/Oro City include seven 

waste rock piles and Fluvial Tailing Site 4. Waste rock surface samples show elevated 

concentrations of cadmium and lead. Fluvial Tailing Site 4 contains an estimated 102,000 

cubic yards of tailing (intermixed v^dth alluvial sediments) and extends for 1.5 miles along 

Upper California Gulch. Fluvial Tailing Site 4 samples show elevated concentrations for 

arsenic, cadmium, copper, lead and zinc. Since residential, commercial and industrial uses do 

not occur in OU 4, recreational visitors were selected as the focus of the Risk Assessment. 

Results of this study indicated that risks to visitors from exposure to contaminants in waste 

rock and surface tailing did not exceed EPA levels of concern. 

EPA's 5-Year Review of the California Gulch Site concluded that there is a continued 

presence of metal and atypical pH contamination within the Upper California Gulch surface 

water despite completion of most of the response actions. Remedial action at Oro City may 

ultimately be necessary. EPA will continue monitoring the site. 

Storm event data collected by EPA for a storm that occurred in July 2003 indicated an 84% 

increase in zinc loading in California Gulch between sample locations up and downstream of 

Oro City. EPA will continue to collect storm event data to better understand actual impacts to 

the environment. 

Sediment sampling conducted by EPA in August of 2001 indicated that sediments at Oro 

City exceeded (EPA) ECOTOX threshold values for all metals except manganese and arsenic 

(and zinc in one instance) thus indicating that the erosion of these sediments during storm 

events could adversely impact water quality in California Gulch. The erosion and subsequent 
deposition of these metal laden sediments may also serve to re-contaminate down stream 

reaches of the gulch that have already been remediated. EPA will continue to monitor sediment 

erosion, resulting from storm events and annual spring runoff, to determine their actual impacts 

on the environment. 

3. Selected Remedy 

The ROD for Upper California Gulch presented the selected remedy for the sub-basin 

Fluvial Tailing Site 4/Oro City. The selected remedy for this sub-basin involved reconstructing 

the Upper California Gulch stream channel, regrading the channel spoil material and regrading 

selected fluvial tailing areas. Specific elements included: 

Channelization of approximately 8,600 feet of Upper California Gulch 

Regrading and blending of channelization spoil material into adjacent areas 

Regrading of side slopes along channel 

Minor surface regrading to enhance positive runoff 

Amending and revegetating approximately 16 acres 

Construction of approximately eight sediment dams 

Construction of approximately 1.5 acres of wetlands 

The ROD did not identify water quality goals for surface streams and heavy metal 

contamination. Therefore, EPA agreed to establish surface and groundwater requirements 

when EPA and CDPHE have determined allowable water quality standards under OU 12. This 

is pursuant to the 1994 Consent Decree, which designated 0U12 to address Site-wide surface 

and groundwater. In addition, the Consent Decree states that OU 12 wiU be addressed only 

after completion of source remediation in OUs 2 through 11. The Consent Decree also 

recognized that additional source remediation of other appropriate response actions related to 

surface or groundwater could occur as part of OU 12 anywhere within the Site. 

4. Basis for and Description of Significant Differences 

Due to the presence of historical properties within OU 4, the ROD specified that remedial 

design occur in consultation with the State Historic Preservation Officer. Historical sites 

identified as eligible for listing on the National Register of Historic Places are identified as 

contributing to the Leadville Historic District. These are the subject of the Cultural Resource 

Inventory of Select Mine Waste Rock Piles and Fluvial Tailing Locations in Operable Unit 4 of 

the California Gulch CERCLA Site, Lake County, Colorado. Fluvial Tailing Site 4/Oro City is 

identified as a contributing element of the historic Leadville Mining District. 

During the remedial design process, a demonstrated interest in the cultural and historical values 

of Fluvial Tailing Site 4/Oro City was expressed. This information triggered the consideration of 

altematives to the selected remedy and provides the basis for this ESD. In 1998, Colorado 

Preservation Inc. (CPI) placed the Leadville Mining District on its list of "most endangered" places. 

CPI's 1998 site tour, and the opinions expressed by local and state government representatives who 

took part in the tour, were instrumental in EPA's decision to defer clean-up work at Oro City. 

Altematives for the work planned at Oro City were discussed during a meeting on May 4,1999. The 
meeting included CDPHE, representatives of the Advisory Council on Historic Preservation, the 

State Historical Society and interested parties. Interested parties recommended various alternative 

methods to address contamination in the Oro City area. 

In response to the cultural and historical values expressed in that meeting, EPA has removed the 

clean up work planned for Fluvial Tailing Site 4/Oro City from the construction schedule for OU 4. 

Therefore, this sub-basin is not subject to any remediation at this time. The need for clean up in the 

area will be reevaluated after reviewing Site-wide surface and groundwater post-construction 

monitoring data. The Consent Decree recognizes that additional source remediation or other 

appropriate response actions related to surface or groundwater could occur as part of OU 12 

anywhere within the Site. Consequently, this ESD does not alter the possibility for future response 

actions within Fluvial Tailings Site 4/Oro City. 

Included in this ESD determination are current groundwater and surface water 

analyses from the site. A recent assessment, dated June 11*, 2002, summarizes the surface 

water metal concentrations and loads in the historic Oro City area. Overall, flows, 

concentration and calculated loads of the key metal parameters (except dissolved lead) decrease 

in Upper California Gulch across the entire reach of the Oro City area. 

Specific trends of the key parameters include the decrease of arsenic, cadmium, 

copper and manganese concentrations across the Printer Boy fluvial tailings area during both 

baseflow and high flow. During baseflow, there is an increase in iron, sulfate and zinc 

concenfrations, however, the concentrations decrease across the segment during high flow. In 

addition, though there is an increase of the metal load, it is relatively minor and accounts for 

less than 10 percent of the metal load across the entire area. 

In response to the information contained in the water quality assessment, no further 

remediation will take place in OU4/Oro City at this time. With this information and the 

information from the cultural and historic preservation meeting, no action will be taken in the 

OU4/Oro City area. Further source remediation may be required under OU 12, which covers 

the entire site surface and groimdwater. OU 12 wall be addressed after source remediation is 

completed in OU 2 through 11. 

5. Support Agency Comments 

The Colorado Department of Public Health and Environment (CDPHE) supports EPA's decision 

to defer remedial action at the Oro City site, under the OU 4 Record of Decision, while the agencies 

gather additional water quality data to determine whether remediation of the Oro City site is 

necessary to protect human health and the environment. However, CDPHE believes that some sort of 

remedy may ultimately be necessary to address contamination emanating from the Oro City site. 

6. Statutory Determinations 

Under CERCLA Section 121, EPA must select a remedy that is protective of human 

health and the environment that complies with ARAR's and is cost effective. EPA believes that 

the new alternative to the ROD for Fluvial Tailing Site 4/Oro City is appropriate and the remedy 
will remain protective of human health and the environment. The selected remedy will continue 

to comply with federal and state requirements that are applicable and relevant and appropriate to 

the remedial action. This ESD does not fundamentally change the remedy and is cost effective. 

Section 121 also states that EPA must select a remedy that uses permanent solutions, 

alternative treatment technologies, or resource recovery technologies to the maximum extent 

practicable. In addition, CERCLA prefers remedies that include treatment that permanently and 

significantly reduces the volume, toxicity, or mobility of hazardous wastes as a principal element 

of the remedy. In the Final Focused Feasibility Study, it was determined that treatment of the 

Upper California Gulch waste rock and fluvial tailing material was impracticable. 

7. Public Participation Compliance 

EPA will publish a notice in the Herald Democrat newspaper that describes the ESD and 

its availability for review (under Section 117(c) of CERCLA, 42 U.S.C. Section 9617). A formal 

public comment period is not required when issuing an ESD. This ESD and all documents that 

support the changes and clarifications are contained in the Administrative Record of the 

California Gulch Superftind Site (under CFR 40, Section 300.435(c)(2)(i)). 

Dated MaxjLDodson ' 

Assistant Regional Administrator 

US EPA Region 8