Arsenic in southeastern Michigan

Arsenic levels exceeding 10 μg/L are present in hundreds of private supply wells distributed over ten counties in eastern and southeastern Michigan. Most of these wells are completed in the Mississippian Marshall Sandstone, the principal bedrock aquifer in the region, or in Pleistocene glacial or Pennsylvanian bedrock aquifers. About 70% of ground water samples taken from more than 100 wells, have arsenic contents ≥10 μg/L with a maximum value of 220 μg/L. Water samples and continuous cores were taken from two test wells. Arsenic content of core samples ranges from