The Sulphur Bank Mercury Mine Injection Evaluation covers about 200 acres along the eastern shore of Clear Lake, the former mine is a United States EPA Superfund site. The Sulphur Bank mine was mined for sulphur and mercury from 1865 to 1957. Mercury contamination leaked from the unlined water-filled former mine open pit (the 23-acre Herman Pit) into the adjacent Clear Lake (the largest natural freshwater lake totally within California). The mine is noted for being an area of active thermal features (fumaroles and hot springs) with active mercury precipitation. The mine site was drilled and explored for geothermal potential since 1961 with limited success.

Earth Systems provided consulting services to our client who, working under contract to the US EPA, evaluated various options to mitigate the mercury contamination issue. One option developed was to pump and inject acidic mercury-contaminated water from the Herman Pit into the deep subsurface in the geothermal reservoir adjacent to the mine. Our task was to complete a peer review of technical reports on the injection concept, to evaluate the geothermal exploration completed in the area, comment on the technical pros and cons of such injection (well bore and formation stability, incompatible fluid chemistry, etc.) and to propose an exploration and drilling strategy to test the viability of the injection concept.