3-D Models of High Concentrations of As and Mn in Glacial Aquifer Groundwater

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New 3-dimensional models predict where high concentrations of arsenic and manganese are likely to occur in the glacial aquifer system, reports a new study from the U.S. Geological Survey National Water Quality Program. The glacial aquifer system, which underlies parts of 25 states across the northern U.S., supplies groundwater for about 30 million people.

Predictions of the occurrence of high concentrations of arsenic and manganese in the glacial aquifer system are based in part on new models of oxidation-reduction conditions, which are related to the amount of dissolved oxygen in the water, and pH.

Elevated concentrations of arsenic and manganese—elements with a geologic source—limit drinking water availability in aquifers worldwide. Exposure to arsenic is linked to increased risk of cancer and other adverse health outcomes. Manganese is an essential element for human health, but exposure of infants and children to elevated concentrations of manganese in drinking water can harm brain development, causing problems with memory, attention, and motor skills and affecting learning and behavior.

High concentrations of arsenic are predicted to occur primarily in the Midwest, extending from Ohio into Minnesota and the Dakotas. That’s because glacial sediment in this part of the U.S. is very thick, so the wells used to supply drinking water tend to be deep. Well depth is associated with many of the characteristics that affect arsenic concentration, such as the oxidation-reduction conditions, pH, and groundwater age. High manganese concentrations are predicted to occur at aquifer depths used for domestic and public supply mostly in the Midwest and Northeast, and over a larger part of the glacial aquifer system than high arsenic.

Maps showing the results of the models are useful for identifying areas, such as Michigan’s Upper Peninsula, where there is little information on groundwater quality but where physical and geochemical conditions could contribute to high arsenic or high manganese concentrations. These results can be used to identify where water suppliers and well owners might want to test their water supply for high arsenic and high manganese concentrations and take appropriate actions if necessary.

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