Glacial sediment causing regional-scale elevated arsenic in drinking water.
In the upper Midwest, USA, elevated arsenic concentrations in public drinking water systems are associated with the lateral extent of northwest provenance late Wisconsin-aged drift. Twelve percent of public water systems located within the footprint of this drift (212 of 1764) exceed 10 microg/L arsenic, which is the U.S. EPA's drinking water standard. Outside of the footprint, only 2.4% of public water systems (52 of 2182) exceed 10 microg/L arsenic. Both glacial drift aquifers and shallow bedrock aquifers overlain by northwest provenance late Wisconsin-aged sediment are affected by arsenic contamination. Evidence suggests that the distinct physical characteristics of northwest provenance late Wisconsin-aged drift--its fine-grained matrix and entrained organic carbon that fosters biological activity--cause the geochemical conditions necessary to mobilize arsenic via reductive mechanisms such as reductive desorption and reductive dissolution of metal oxides. This study highlights an important and often unrecognized phenomenon: high-arsenic sediment is not necessary to cause arsenic-impacted ground water--when "impacted" is now defined as >10 microg/L. This analysis also demonstrates the scientific and economic value of using existing large but imperfect statewide data sets to observe and characterize regional-scale environmental problems.
Erickson
Melinda L
ML
Water Resources Science, University of Minnesota, Minneapolis 55455, USA. eric0984@umn.edu
Barnes
Randal J
RJ
D001151:Arsenic / Q000032:analysis*; D004784:Environmental Monitoring; D019015:Geologic Sediments; D046448:Ice Cover; D015146:Midwestern United States; D014874:Water Pollutants, Chemical / Q000032:analysis*; D014881:Water Supply / Q000032:analysis*
D014874:Water Pollutants, Chemical; D001151:Arsenic