Updated September 2, 2011
About 20% of untreated water samples from public, private, and monitoring wells across the nation contain concentrations of at least one trace element, such as arsenic, manganese and uranium, at levels of potential health concern, according to a new study by the U.S. Geological Survey.
"In public wells these contaminants are regulated by the U.S. Environmental Protection Agency, and contaminants are removed from the water before people drink it," said Joe Ayotte, USGS hydrologist and lead author on the study. "However, trace elements could be present in water from private wells at levels that are considered to pose a risk to human health, because they aren’t subject to regulations. In many cases people might not even know that they have an issue."
Trace elements in groundwater exceed human health benchmarks at a rate that far outpaces most other groundwater contaminants, such as nitrate, pesticides, and volatile organic compounds (VOCs). Most trace elements, including manganese and arsenic, get into the water through the natural process of rock weathering. Radon, derived from naturally occurring uranium in aquifers, also occurs frequently at high levels in groundwater. Human activities like mining, waste disposal, and construction also can contribute to trace elements in groundwater.
These findings are based on over 5,000 samples collected primarily from public and private wells nationwide. This study is part of efforts by the U.S. Geological Survey's National Water-Quality Assessment Program to monitor the quality of the nation’s groundwater and surface water. Details can be found online.
Human health benchmarks used in this study include U.S. Environmental Protection Agency Maximum Contaminant Levels for regulated contaminants and Health Based Screening Levels (HBSLs) for unregulated contaminants. HBSLs are unenforceable contaminant threshold guidelines developed by the USGS in collaboration with EPA, and the New Jersey Department of Environmental Protection. and Oregon Health Sciences University.
Treated drinking water from public wells is regulated under the Safe Drinking Water Act. Water utilities, however, are not required to treat water for unregulated contaminants. The EPA uses USGS information on the occurrence of unregulated contaminants to identify contaminants that may require drinking-water regulation in the future.
Links and contacts within this release are valid at the time of publication.