Fifty-six private wells, 20 public wells and 38 monitoring wells in ten counties in southeastern Michigan were sampled to determine the concentration of naturally-occurring arsenic and specific geochemical parameters. The majority of ground water samples were analyzed for pH, dissolved oxygen, oxidation/reduction potential, specific conductance, major ions, dissolved and suspended organic carbon, and arsenic. Selected samples were analyzed for minor elements, nutrients, the isotope ratio of carbon and the concentration of tritium. The Mississippian Marshall Sandstone comprises a major aquifer in southeastern Michigan. To compare the lithology of the Marshall Aquifer to water chemistry, two new wells were drilled through the Marshall Sandstone to the underlying Coldwater Shale. Depth-specific bedrock and water samples were collected from these wells. For public and private drinking-water wells, the lowest concentration detected by USGS analysis was <1 microgram per liter and the highest was 220 micrograms per liter. Arsenic concentrations near or exceeding the current USEPA standard of 50 micrograms per liter occurred in ground water from each of the major aquifers in the study area. In the two newly-drilled wells, the lowest concentration detected by the USGS was <1 microgram per liter at about 350 ft below land surface and the highest concentration of 140 micrograms per liter was detected at around 50 ft below land surface. The data from this study may be used to indicate well characteristics and water chemistry factors that are related to arsenic in ground water in southeastern Michigan.
