Colorado Department of Public Health and Environment

Colorado Department of Public Health and Environment

CENTRAL CITY/CLEAR CREEK SUPERFUNB SITE Amendment to the Operable Unit 4 Record of Decision for the Active Treatment of the

National Tunnel, Gregory Incline and Gregory Gulch

Prepared hi Cooperation with the United States Environmental Protection Agency Region VIII

Denver, Colorado

PRO"^?

DECLARATION

SITE NAME AND LOCATION

The Central City/Clear Creek Superfund Site (Site) is located approximately 30 miles west of Denver, Colorado within Clear Creek and Gilpin counties. The Comprehensive Environmental Response, Compensation, and Liability Information System (CERCLIS) Site Identification Number is COD980717557. The Central City/Clear Creek area was one of the most heavily mined areas in Colorado during the late 1800s, producing large quantities of metals such as gold, silver, copper, lead, nickel and zinc. The Study Area for the Site is located within the Clear Creek watershed, which spans approximately 400 square miles. The U.S. Environmental Protection Agency (EPA) listed the Site on the National Priorities List (NPL) in 1983.

STATEMENT OF BASIS AND PURPOSE

This decision document amends the Record of Decision (ROD) for the Central City/Clear Creek Superfund Site, Operable Unit 4 (OU4), signed Sept. 29, 2004. The Colorado Department of Public Health and Environment (CDPHE) as lead agency on the Site, and EPA have jointly selected the amended remedy.

This ROD amendment has been developed in accordance with the requirements of the Comprehensive Environmental Response, Compensation, and Liability Act of 1980, 42 USC ?9601 et. seq., as amended by the Superfund Amendments and Reauthorization Act (collectively, CERCLA) and to the extent practicable, the National Oil and Hazardous Substance Pollution Contingency Plan (NCP), 40 CFR Part 300. Upon signature, this decision document will become pant of the Administrative Record for the Central City/Clear Creek Superfund Site.

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This ROD Amendment was prepared to change the water treatment component of the remedy from a combination of passive treatment and active treatment at a privately owned facility to active treatment of all waters at a new water treatment plant.

ASSESSMENT OF THE SITE

The response action selected in this ROD amendment protects public health and the environment from actual or threatened releases of hazardous substances into the environment. Such release, or threat of release, may present an imminent and substantial endangerment to public health or welfare or the environment.

The remains of historical mining operations in the Central City/Clear Creek Superfund Site include mine drainages that discharge acidic, metal-laden water into the North Fork of Clear Creek. The high concentrations of metals adversely impact aquatic life and potentially pose a risk to water supplies in Clear Creek and the North Fork of Clear Creek.

DESCRIPTION OF THE SELECTED REMEDY The amended remedy for OU4 changes the location of active water treatment for the Gregory Incline and Gregory Gulch alluvial ground water, and replaces passive treatment of the National Tunnel discharge with active treatment. A new water treatment plant will be constructed to treat these sources. The sediment control remedy selected in the OU4 ROD will not change.

The major components of the amended OU4 selected remedy include: the collection, conveyance and active treatment of the Gregory Incline discharge, Gregory Gulch ground water, and the National Tunnel discharge at a new water treatment plant.

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STATUTORY DETERMINATtONS The selected remedy attains the mandates of CERCLA Section 121 and, to the extent practical, the NOP. Specifically, the amended remedy is protective of human health and the environment, complies with federal and state requirements that are applicable or relevant and appropriate for the remedial action, is cost effective, and utilizes permanent solutions. The selected remedy in this amendment satisfies the statutory preference for treatment as a principal element. Because surface water restoration is a component of the remedy, the water treatment plant will be subject to Long-Term Response Action provisions. The remedies will result in hazardous substances or pollutants or contaminants remaining at the Site above levels that allow for unlimited use and unrestricted exposure, therefore a statutory review will be conducted within five years after initiation of the remedial action and every five years thereafter to ensure that the remedies continue to provide adequate protection of human health and the environment. In addition, institutional controls, identified in the OU4 ROD, are included as requirements to ensure the integrity of the remedy.

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AUTHORIZING SIGNATURES

Gary W. Baughman

Director Hazardous Materials and Waste Management Division

Colorado Department of Public Health and Environment

y/21/20/0 Date

Q )ifoUtuL - s?UAA^

Eddie A. Sierra Acting Assistant Regional Administrator Office of Ecosystems Protection and Remediation U.S. Environmental Protection Agency, Region VIII

afh^j ZOlto

Date

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