Project Description:

1)      Rathburn and Rathburn-Petray Mines are located in the Sulphur Creek Mining District. The Rathburn and Rathburn-Petray mercury mines were worked prior to 1892, with the greatest activity reported between 1892 and 1893 for use in gold mining operations in California. Minor production also occurred in the late 1960's and early 1970's when Homestake Mining Company, Yellow Strike Exploration, Cypress Gold Exploration, and the Petray Family operated the mines.

2)   Mercury-bearing material is exposed in cuts, slopes, open pits, mine waste piles, and storm water retention ponds. Ash from a brick retort at the Rathburn mine also contains elevated levels of mercury. Waste piles at Rathburn and Rathburn-Petray Mines collectively contain approximately 101,500 cubic yards of mercury-bearing waste material.

3)   Surface water runoff during storm events erodes waste and tailings piles, overflows retention ponds, and transports mercury-laden sediment into drainage swales and unnamed tributaries of Bear Creek. Bear Creek is a tributary of Cache Creek and contributes an estimated 17% of methylmercury and 4% of total mercury load to Cache Creek. Mercury loads from upper Bear Creek range from 6.8 to 53.1 kg/year.

4)   Monitoring of surface water, sediment and aquatic life containing mercury and methyl mercury in the Bear Creek watershed has been conducted by the Central Valley Water Board, the California Geological Survey, and various consultants. Test results show mercury concentrations in the tissue of fish taken from Bear Creek ranged up to 6.0 ppm. USEPA guidelines for the consumption of locally caught fish corresponds to a safe concentration of mercury in fish tissue of 0.3 ppm.

5)   Mine waste present at the mine sites contains mercury that may pose a threat to human health due to exposure (dermal, ingestion, and inhalation) through recreation (hiking, camping, fishing, and hunting) or work at the mine sites.  Mercury contamination has been found in the water, sediment and biota downstream of the Rathburn and Petray mine sites. Mercury is a toxic substance, which can cause damage to the brain, kidneys and to a developing fetus. Young children are particularly sensitive to mercury exposure. Methylmercury, the organic form of mercury that has entered the biological food chain, is of particular concern, as it accumulates in fish tissue and in the wildlife and people that eat fish.

6)   Section 303(d) of the Federal Clean Water Act requires states to identify waters not attaining water quality standards (referred to as the 303(d) list). Bear Creek has been identified by the Central Valley Water Board as an impaired water body due to the high levels of mercury in fish and water sampled from Bear Creek. Bear Creek has been on the 303-(d) list since 1988.

Proposed CERCLA actions include compilation of a PRP search, SI Removal and EE/CA reports in order to conduct removal and disposal operations on approximately 15,000 cubic yards of mercury calcines and related mine wastes from the mercury retort site within the Sulpher Creek subwatershed, tributary to Cache Creek and the Sacramento River watershed.

Benefits/Results:

The removal of mercury mine wastes from the Molina Mine site will reduce the downstream transport of mercury into Carlos Creek Creek and thence the San Joaquin River River watershed. These water courses are used each year by migrating salmon and steelhead trout and provide spawning habitat

Feasibility/Implementation:

An engineering evaluation/cost analysis (EE/CA) was prepared in 2008, prior to the development of final cleanup and design plans.

External Support/Partners:

Developed partnerships include the CA Water Resouces Division, California Regional Water Quality Control Board, and USGS-Geologic Division. Local watershed stakeholder groups also support the project. The California Regional Water Quality Control Board (CRWQCB) is supportive of this project. There is no known opposition to the project.

Rathburn Mine

Rathburn waste rock piles

Rathburn Mine pit