Transport and natural attenuation of Cu, Zn, As, and Fe in the acid mine drainage of Leviathan and Bryant Creeks

Abstract

The Leviathan and Bryant Creek (LBC) drainage system, on the border of California and Nevada, flows through overburden and waste from a former open-pit sulfur mine. The drainage contains acid mine waters with high concentrations of several trace elements, including Cu, Zn, and As, derived from oxidative weathering of sulfides in the wastes and altered bedrock. In June and October, 1982, the mainstream and tributary flows of the LBC drainage were measured and the waters sampled and analyzed for major and trace elements. Empirical mass flow and metal attenuation rates were determined, and chemical models were used to examine mechanisms of trace element removal during downstream transport. In June the flow in the mainstream was 2-5 times greater than in October, and with higher contributions from the acid mine effluent. Seasonal variations in the attenuation rates of Cu, Zn, and As were directly related to this increase in acid mine-effluent production, and to the consequent increase in the acidity of the mainstream drainage. Although As concentrations immediately below the mine site were high in June, As was readily removed from solution by adsorption onto an assumed iron(III) oxyhydroxysulfate precipitate, whereas Cu was incompletely adsorbed and Zn remained unaffected by adsorption. In October, the smaller discharge of acidic LBC drainage waters were more readily diluted (and neutralized) by other regional tributaries. Arsenic concentrations remained low, and both Cu and Zn were removed from solution by adsorption onto iron(III) oxyhydroxysulfate in the lower regions of the LBC drainage system.