Arsenic speciation and quality of groundwater in a lead-zinc mine, Idaho

The variations of As(V)/As(III) ratio, with respect to metal contents and pH in groundwater of a major lead-zinc mine in the Coeur d'Alene Mining District, Idaho were studied. A wide range of arsenic concentrations and As(V)/As(III) ratios were observed in the groundwaters collected from this mine. Samples with high As(V)/As(III) ratios were generally acidic (pH 3, and its chemical behavior appears to be controlled by iron hydroxide precipitate. In comparison with Eh measurement by a platinum electrode, the As(V)/As(III) ratio seems to be a more sensitive indicator for evaluating redox status of a groundwater system. Arsenic species in surface waters collected from the Coeur d'Alene River were also measured for comparison.