Sulphur Bank Mercury Mine

Investigation and Cleanup Activities

EPA is addressing the site in three phases: emergency actions to prevent short-term harm to the lake and nearby residents, and two long-term remedial phases, called "operable units". In Operable Unit-1 EPA will develop and implement a cleanup plan to address the Herman Impoundment and the mine waste piles located on the mine property. In Operable Unit-2 EPA will develop and implement a cleanup plan to address the contaminated sediments in Clear Lake and the resulting mercury accumulation in the biota.

Initial Actions

Erosion control emergency response. In 1992, EPA cut back the slope of the mine waste pile located along the shore of Clear Lake and then reseeded this area. These measures were taken to eliminate the erosion of mine wastes containing mercury and arsenic into Clear Lake. In 1996, EPA raised a small earthen dam at the Herman Impoundment as as a temporary flood control measure.

Initial Actions

Soil removal from residential yards. In 1997, EPA removed up to 18 inches of the mercury and arsenic-contaminated mine wastes from 17 residential yards at the Elem Tribal Colony, which is located adjacent to the mine property. EPA placed clean fill material and top soil in the residential yards. Varying amounts of contaminated mine waste remained at depth in the residential yards.

Initial Actions

Surface Water Diversion. In 1999-2000, EPA constructed surface water diversions on the mine site to prevent contaminated sediments and water from flowing into Clear Lake. The diversion work included the construction of a 4,000' pipeline which allows clean storm water from up gradient surrounding hills to flow around the site without being contaminated by mine wastes or causing an overflow of the Herman Impoundment.

Initial Actions

Well closure emergency response. During the 1970's owners of the mine had allowed exploration companies to drill some exploratory geo-thermal wells near the Herman Impoundment. EPA was concerned that the wells were not properly abandoned and that they might be subject to a violent release of geo-thermal gases. EPA conducted an emergency action in late 2000 and early 2001 to investigate the closure of all of the historic wells, and took action to properly close three wells that had not been properly abandoned.

Site Studies

Operable Unit-1: Herman Impoundment and Waste Piles Investigation. In 1990, EPA began an investigation into the nature and extent of contamination associated with the Herman Impoundment and mine waste piles. EPA initially completed a remedial investigation and feasibility study (RI/FS) and issued a proposed cleanup plan for Operable Unit-1 in 1994. Following the plan's release, the seven-year drought ended with severe flooding, revealing a major acid mine drainage problem affecting Clear Lake. EPA decided to re-open the RI/FS to identify sources of the discharge of mercury-rich acid mine drainage into Clear Lake and to identify appropriate control strategies. In late 2000, the Department of Energy completed an aerial survey of geological resistivity at the site to help define the pathways of contaminated groundwater movement from the mine property to Clear Lake. In early 2001, EPA's contractors completed a hydrogeological study of groundwater movement through the site. EPA has completed the remedial investigation and is currently performing a feasibility study to develop and evaluate cleanup alternatives for the Herman Impoundment and mine waste piles in Operable Unit-1.

Site Studies

Operable Unit-2: Lake Sediments and North Wetland Investigation. In 1991, EPA began an investigation into the nature and extent of contamination in the lake sediments, but put this study on hold in order to focus on the sources of the contaminant discharges at the mine property. Meanwhile, other entities, notably the University of California - Davis, have continued to study the processes affecting bioavailability of mercury in Clear Lake. In 2000, EPA convened a conference of national experts on mercury contamination. EPA is currently conducting a number of additional studies to characterize the nature and extent of mine waste contaminants in the lake sediments and in the North Wetland. EPA is also conducting studies to define the baseline conditions of water quality and the biota in the North Wetland and Clear Lake prior to the performance of the cleanup to provide data to assess the effectiveness of the cleanup.

Initial Actions

Soil removal from Elem Indian Colony. In June 2006, EPA began work to remove 28,000 cubic yards of mercury and arsenic contaminated mine waste from the Elem Indian Colony residential area. EPA removed mine wastes from 14 residential yards, several inactive gravel roadways, and from beneath the entire paved roadway system. Clean fill was imported and used to prepare foundations and clean topsoil was brought in for all yards and open areas. EPA installed five new homes, refurbished seven existing homes, repaved the roadway, installed new curbs, sidewalks, water system and storm drains, and improved the sewer system. All Elem residents participated in the Temporary Transitional Housing Program during the mine waste removal action. In December 2006, 15 of 17 households returned to their permanent homes at the Elem Indian Colony. EPA completed the installation of two additional trailers and completed several roadway improvements in June 2007. The remaining two households have returned to their permanent homes.

Initial Actions

Mine Waste Removal from Sulphur Bank Mine Road. In January 2008, EPA began work to remove mercury and arsenic contaminated mine waste from the gravel roadways and adjacent areas in a residential area located to the south of Sulphur Bank Mercury Mine along Sulphur Bank Mine Road. EPA completed the mine waste removal action in April 2008.

Initial Actions

Mine Waste Capping on BIA Route 120. In late 2010, EPA completed a removal action to re-build Route 120, the main access road to the residential area of the Elem Colony. The re-construction eliminates potential human exposure to mine waste by containing the waste used to construct the original road.