Naturally Occurring Contaminants in "Ancient" Groundwater of the Atlantic and Gulf Coastal Plain aquifers

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Groundwater in the Atlantic and Gulf Coastal Plain aquifers is old—more than 21,300 years old in more than half of 252 public-supply wells sampled. That ancient groundwater is more likely to contain concentrations of fluoride, arsenic, and polonium-210 that exceed human-health benchmarks than is younger groundwater, reports a new study from the USGS National Water Quality Program.

The study investigated the occurrence of “geogenic” contaminants—those that occur in groundwater naturally because of its contact with aquifer rocks—in untreated water from 252 public-supply wells in the Atlantic and Coastal Plain aquifers. At least one of four geogenic constituents—fluoride, arsenic, lead-210, or polonium-210—exceeded a human-health benchmark for drinking water in 12% of the wells sampled.

The Atlantic and Gulf Coastal Plain aquifers provide more than 2 billion gallons of water per day for public supply and 250 million gallons per day for domestic supply, more than 15 percent and 10 percent of the national use of groundwater for those purposes, respectively. The aquifers are located along the Gulf of Mexico coast from Texas to Florida, inland along an ancient coastline in Kentucky, Tennessee, Mississippi, Alabama and Georgia, and along the Atlantic Ocean coast from Georgia up to Long Island, New York.

The authors of the study found that concentrations of these four geogenic constituents were related to the amount of dissolved oxygen present, other dissolved constituents in the water, and pH, all of which evolve as groundwater moves through an aquifer. Understanding these relations will aid water-resource managers to better determine where elevated concentrations of these geogenic contaminants are likely to occur in this aquifer system.

 

Citation: The relation of geogenic contaminants to groundwater age, aquifer hydrologic position, water type, and redox conditions in Atlantic and Gulf Coastal Plain aquifers, eastern and south-central USA. 2020. Degnan, J.R., Lindsey, B.D., Levitt, J., Szabo, Z. Science of the Total Environment. https://doi.org/10.1016/j.scitotenv.2020.137835

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