Are you one of 30 million Americans whose drinking-water supply relies on groundwater from the glacial aquifer system? A new USGS study assesses the quality of untreated groundwater from this critical water resource, which underlies parts of 25 northern U.S. states.
Contaminants in Glacial Aquifer Groundwater
Where do contaminants occur and why?
The study reports that naturally occurring inorganic constituents—trace metals, iron, sulfate, and dissolved solids—occur in untreated groundwater at high concentrations (that is, exceeding a human-health benchmark or non-health guideline) across 20 to 50% of the glacial aquifer system, depending on the constituent. In particular, more than 4 million people may be relying on drinking water whose source is groundwater with high concentrations of the trace metals manganese and/or arsenic.
Anthropogenic contaminants—those related to human activities—occur in smaller proportions of the glacial aquifer system but still could affect large numbers of people. Groundwater with a high concentration of one or more organic contaminants such as pesticides and volatile organic compounds is a source of drinking water for an estimated 870,000 people, and about 740,000 people are estimated to obtain their drinking water from groundwater with high concentrations of nitrate.
The study analyzed the hydrogeologic settings where high concentrations of contaminants and inorganic constituents in groundwater are most likely to occur. For example, high manganese and arsenic concentrations occur at a range of depths and primarily in areas underlain by thick, stratigraphically complex, fine-grained glacial sediment, where groundwater has low concentrations of dissolved oxygen (“reducing conditions”). In contrast, high concentrations of anthropogenic contaminants more commonly occur at shallow groundwater depths and tend to be limited to areas near where people live and use or release such chemicals.
The untreated groundwater assessed for this study is a source for both public-supply and domestic (private) wells. Water from public-supply wells is required to be tested by the well operator on a routine basis, and—if necessary—treated, to help assure that the water provided to consumers meets Federal and State water-quality standards. Routine testing of water from domestic wells is typically not required. Homeowners are responsible for testing, maintenance, or treatment of the water from their domestic well.
For more information, contact Mindy Erickson.
Citation: Erickson, M.L., Yager, R.M., Kauffman, L.J.,and Wilson, J.T. Drinking water quality in the glacial aquifer system, northern USA. Science of the Total Environment, vol. 694: 133735. https://doi.org/10.1016/j.scitotenv.2019.133735.
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