You are here:
BOUNDS ON SUBSURFACE MERCURY FLUX FROM THE SULPHUR BANK MERCURY MINE, LAKE COUNTY, CALIFORNIA
Citation:
Jewett*, D G., E. Manges, G. J. Reller, AND E R. Bates*. BOUNDS ON SUBSURFACE MERCURY FLUX FROM THE SULPHUR BANK MERCURY MINE, LAKE COUNTY, CALIFORNIA. Presented at U.S. EPA Workshop, San Francisco, CA, 11/28-30/2000.
Description:
The Sulphur Bank Mercury Mine (SBMM) in Lake County, California has been identified as a significant source of mercury to Clear Lake. The mine was operated from the 1860s through the 1950's. Mining started with surface operations, progressed to shaft mining, and later to open pit techniques. Open pit mining created Herman Pit, a 20 ac, 90 ft deep pit located approximately 750 ft from the shore of Clear Lake to the west of the SBMM. During the last 15 years various investigations have resulted in estimates of flow from Herman Pit to Clear Lake, ranging from approximately 20 to 1.66 x 106 ft3 day-1 (0.1 to 8,600 gpm). The U. S. EPA recently completed a hydrogeologic characterization of the SBMM to better understand ground water flow and contaminant transport pathways from the SBMM to Clear Lake. The hydrogeologic investigation was based on the synthesis of available information (regional structural maps, historical site descriptions from the literature, geologic maps of the site, site-specific surface geophysics, and existing bore hole logs, etc.) and new field activities (drilling, logging visual cuttings and borehole geophysics, well construction, hydraulic testing, and water quality sampling and analysis). Results of the hydrogeologic investigation were used to estimate ground water discharge rates from Herman Pit to Clear Lake. The discharge varies throughout the year as a function of fluctuations in Clear Lake and Herman Pit water surface elevations. The estimated average subsurface discharge during a dry period monitoring event was 4,264 ft3 day-1 (22 gpm) and 3,133 ft3 day-1 (16 gpm) during a wet period event. Approximately 65% of the discharge is transmitted through the uppermost geologic horizon (waste rock and post-andesite lake sediments). Using these results and the average total mercury concentration in ground water samples, subsurface mercury loading from the SBMM to Clear Lake was estimated. The subsurface mercury flux is approximately 3.23 lbs yr-1 (1.47 kg yr-1) and 2.40 lbs yr-1 (1.09 kg yr-1) during dry and wet periods, respectively. Over 99% of the mercury transported to Clear Lake via the subsurface is through the waste rock/upper lake sediments unit.