The Dynamics and Speciation of Arsenic in Drinking Water Wells in Eastern Wisconsin

Abstract

Arsenic typically develops in Eastern Wisconsin groundwater as a result of oxidation of sulfide bearing minerals in the limestone bedrock (Schreiber et al. 2000). Naturally occurring arsenic exists in groundwater as oxyanions which have two oxidation states, As(III) and As(V). Under ambient pH conditions As(V) is primarily present as an anion (i.e., H2AsO4-) while As(III) tends to be uncharged (i.e., H3AsO3), making it much more difficult to remove through the existing treatment techniques such as adsorption and reverse osmosis (RO). Although many studies exist establishing arsenic concentrations across Wisconsin, there is a lack of investigations into the concentrations of each arsenic species as well as minute-scale arsenic dynamics, which is essential for establishing a removal technique. The primary goals of this research were to establish baseline concentrations of each arsenic species, accounting for seasonal variations, and determine how these concentrations could be affected by strenuous water usage. Private drinking water wells were selected at 16 locations across Eastern Wisconsin. The wells were screened at various depths, in multiple geologic units, and contained a wide-range of total arsenic concentrations. Analysis of the speciation data indicated that As(III) was the dominant species of arsenic in all of the wells sampled. Data from the 11 pumping tests that were conducted, showed 9 exhibiting a downward trend in As(III) concentration and an upward trend in As(V) concentration as volume purged increased. The pumping tests also showed a substantial increase in total arsenic in many of the wells as volume purged increased. The results of this study suggest that there is an elevated health risk of consuming water following short-term strenuous water usage and an increased necessity for proper filtration due to dominant As(III) concentrations.