Natural sources of arsenic in Southeastern Michigan groundwater

In Southeastern Michigan, arsenic concentrations in well waters range from 1 to 1310 μg/1, with most common levels being 5-50 μg/L. Arsenopyrite is common in Marshall Sandstone, the primary aquifer in the study area, and is the only known arsenic-containing mineral in the region. While it is hypothesized that oxidation of arsenic-rich pyrite in the till fragments is the primary mechanism for arsenic release into the groundwater, the underlying geochemical processes are still unclear. Four mechanisms for arsenic release into the environment have been hypothesized. These include pyrite oxidation, carbonation of arsenic sulfide minerals, reduction of arsenic-containing iron-oxyhydroxides, and reduction of arsenic sorbed to the aquifer [1,2]. Each of these theories is discussed.