USGS study find contaminants in private wells

More than one in every five private domestic wells sampled nationwide contain at least one contaminant at levels of potential health concern, according to a new study by the U.S. Geological Survey.
The study was released this morning.
USGS scientists sampled about 2,100 private wells between 1991 and 2004 in 48 states and found that the contaminants most frequently measured at concentrations of potential health concern were inorganic contaminants, including radon and arsenic. These contaminants are mostly derived from the natural geologic materials that make up the aquifers from which well water is drawn.
Nitrate was the most common inorganic contaminant derived from man-made sources-such as from fertilizer applications and septic-tanks-that was found at concentrations greater than the Federal drinking-water standard for public-water supplies (10 parts per million). Nitrate was greater than the standard in about 4 percent of sampled wells.
The study shows that the occurrence of selected contaminants varies across the country, often following distinct geographic patterns related to geology, geochemical conditions, and land use. For example, elevated concentrations of nitrate were largely associated with intensively farmed land, such as in parts of the Midwest Corn Belt and the Central Valley of California. Radon was found at relatively high concentrations in crystalline-rock aquifers in the Northeast, in the central and southern Appalachians, and in central Colorado.
“The results of this study are important because they show that a large number of people may be unknowingly affected,” Matt Larsen, the USGS Associate Director for Water, said in a news release.