Nevada Division of Environmental Protection, Comstock Mine

EPA Superfund Record of Decision: CARSON RIVER MERCURY SITE
EPA ID: NVD980813646 OU 01 DAYTON, NV 03/30/1995

Mercury Contamination — The contaminants of potential concern (COPCs) for the CRMS are mercury, arsenic and lead. Mercury was imported to the region during the Comstock era (1859-1900) to process ore. Although mercury is also naturally occurring in the region, such sources are not considered important relative to the large amount of mercury imported to the region during the Comstock era. Arsenic and lead are naturally occurring trace metals in the region which were concentrated in the environment by natural and anthropogenic processes. The highest concentrations of the COPCs are found at and around historic millsites and extant tailing piles. The COPCs also occur in areas where discharged tailings and other eroded material from historic millsites have come to be deposited. These areas include: the alluvial fan below Sixmile Canyon, the flood plain of the Carson River below New Empire, the active channel of the Carson River below New Empire, Lahontan Reservoir, Carson Lake, Stillwater, Indian Lakes and Washoe Lake.

Long-term Sampling and Response Plan — With exception for Alternative 1, certain institutional controls were considered to be an additional part of each of the described alternatives. These institution controls, which will be known as the "Long-term Sampling and Response Plan," are to manage impacted areas that will not be remediated as part of this operable unit. The FS did not evaluate remediation alternatives for impacted areas in Sixmile Canyon and adjacent to the Carson River between New Empire and Dayton because these areas do not pose health risks with the current land use (non-residential). In the event that residential development is proposed in these areas or other areas where mercury levels may exceed 80 mg/kg, then certain procedures described in the Long- term Sampling and Response Plan will be followed.

The Long-term Sampling and Response Plan will set forth specific sampling guidelines for characterizing mercury levels in surface soils and for addressing impacted areas. The areas where any residential development will be subject to the guidelines prescribed in this plan are generally described as follows:

In instances where residential development is proposed within these defined areas, Nevada Division of Environmental Protection (NDEP) will provide the interested parties with the Long-term Sampling and Response Plan Guidelines. The guidelines will provide specific instructions for sampling an area to assess mercury levels in surface soils, instructions for interpreting and reporting results, instructions for follow-up sampling, and instructions for addressing impacted areas.

The Long-term Sampling and Response Plan Guidelines will be developed by EPA as part of the remedial design for this operable unit. The guidelines will be administered through NDEP's Bureau of Corrective Actions. However, development within the boundaries of the specified areas will be monitored through NDEP's Bureau of Water Pollution Control which reviews sewerage facility plans for new developments made up of five or more subdivisions. For smaller developments, the county planning offices will notify NDEP of proposed developments, and NDEP will contact the developer. The Long-term Sampling and Response Plan does not provide for NDEP to enforce the implementation of the guidelines. Rather, NDEP will notify EPA of any recalcitrant parties and EPA will have the discretion of using the Comprehensive Environmental Response, Compensation, and Liability Act (CERCLA), Sections 104 and 106 authorities to enforce compliance with the guidelines.

Source: USEPA Carson River Mercury Site

Print ROD — EPA Superfund Record of Decision: CARSON RIVER MERCURY SITE EPA ID: NVD980813646 OU 01, DAYTON, NV 03/30/1995