The Quality of Our Groundwater—Progress on a National Survey

Groundwater—Our Invisible Critical Resource

By Water Resources Mission Area April 2, 2021

A U.S. Geological Survey study of groundwater quality across the nation that began in 2013 now includes water-quality information for 18 of the most heavily used aquifers in the nation.

In addition to summary fact sheets for 15 principal aquifers previously released, fact sheets are now available for the Edwards-Trinity aquifer system (primarily Texas, parts of Oklahoma and Arkansas), the Stream Valley aquifers in the western U.S. (Arkansas River, Missouri River, and Red River drainages in parts of Oklahoma, Nebraska, Kansas, Missouri, and Colorado), and the Colorado Plateaus aquifers in the western U.S. (SE Wyoming, E Utah, W Colorado, NW New Mexico, NE Arizona).

Untreated groundwater from nearly 1,300 deep public-supply wells has been sampled from the 18 aquifers. Overall, inorganic constituents with a geologic source—related to the interaction of groundwater and aquifer rocks and sediments—most commonly exceeded human-health benchmarks. Among the aquifers, from 3 to 50 percent of samples contained at least one inorganic constituent that exceeded a benchmark. Those constituents were primarily the trace elements arsenic, fluoride, manganese, and strontium. The most frequent trace element exceedances occurred in the Stream Valley aquifers (37 percent), Rio Grande aquifer system (27 percent), and the Glacial aquifer system (24 percent).

At least one radioactive constituent, which also have geologic sources, exceeded a human-health benchmark in a small percentage of samples (0 to 12 percent) in most of the 18 aquifers studied. The exceptions were the Piedmont and Blue Ridge crystalline-rock aquifers and the Cambrian-Ordovician aquifer system, where exceedances were 30 and 45 percent, respectively. The nutrient nitrate was the only constituent with a manmade source that exceeded the human-health benchmark, typically in a low percentage of samples (0 to 7 percent).

About half of the nation’s population relies on groundwater for drinking water. The U.S. Geological Survey is intensively studying principal aquifers that provide most of the nation’s groundwater pumped for public supply. Water-quality information for three remaining principal aquifers is slated for publication in 2021.