Evidence of Mercurial Contamination and Denundation Downstream of New Idria Mercury Mine, San Benito County, California

Thursday, 18 December 2014
Haley E Letsinger1, Rohit kumar Sharma2 and Beth Weinman1, (1)California State University Fresno, Fresno, CA, United States, (2)South Dakota School of Mines & Technology, COALINGA, CA, United States


California’s Central Valley water quality and soils are essential to the survival of the valley’s communities and agriculture. Therefore, detection of possible contaminants within the valley streams and soils are paramount to the protection of this land and the people that depend upon it. Here we explore the impact of the contaminated stream beds near the New Idria Mercury Mine site, San Benito County, California. Previous work by Ganguli et al. (2000) has been done in this area to determine the mercury levels associated with the water that flows near the ghost town of New Idria. We performed geochemical analyses on the finer bed sediments from channels draining the area, as well as the coarser sediments taken from along the channel banks, to determine mercury transport downriver from the source. Using a novel application of tau, a mass transfer coefficient typically used in critical zone studies or  soil production and weathering rates, we determine downstream weathering, accumulation, and transport of mercury. Our initial geochemical data showed higher tau values upstream as well as within the banks of the contaminated streambed and a greater accumulation of mercury near the pollution source (i.e.,  mine tailings, (τ ~ 103)). Tau results also show elevated mercurial levels existing downstream, with accumulations in mid- (τ ~ 102) and down-stream (τ ~ 10) reaches. Combining tau results with more traditional indices of chemical weathering (CIA) support  consistent overall Hg-weathering processes with low levels of chemical weathering and higher dominance of coupled physical-anthropogenic weathering.