Atmospheric mercury concentrations above mercury contaminated mill tailings in the Carson River Drainage Basin, NV

During processing of the historic Comstock Ore, Virginia City, NV, an estimated 5.5 x 10 super(9) g of metallic mercury (Hg) were released into the Carson River Drainage Basin. The Bessels Mill site is one of at least 75 locations where Hg was used to amalgamate the gold and silver from the ore. Although the mill is no longer standing, Hg contaminated tailings attest to its past location. Mercury concentrations in samples of tailings from the Bessels Mill site are as high as 1570 mu g/g. Mercury concentrations vary spatially over the site. Total Hg concentrations in air measured directly over the site are well above regional background levels (1 to 7.1 ng/m super(3)). The highest average atmospheric Hg concentration measured at the site was 240 ng/m super(3) for October 1993. The estimated range of Hg flux to the atmosphere from the site was 37 to 500 ng/m super(2) hr. Atmospheric Hg concentrations varied seasonally, diurnally and spatially. Atmospheric Hg concentrations varied as a function of Hg concentration, soil and air temperature, wind speed and surface morphology.