Annie Snider, E&E reporter
Published: Monday, January 26, 2015
Farming practices, urban sprawl and groundwater pumping and recharge are dramatically changing the aquifers that supply drinking water to 130 million Americans, according to a new federal report.
Over the last two decades, two-thirds of groundwater areas studied in the new U.S. Geological Survey report saw upward trends in key man-made contaminants. At the top of the list are nitrates — a fertilizer byproduct that can cause blue baby syndrome and breathing problems in adults — and dissolved solids and chlorides — salts that can harm aquatic ecosystems.
Overall, the report, which summarized more than 230 groundwater studies that took water samples from 6,600 wells between 1991 and 2010, found 1 in 5 drinking water wells with at least one contaminant at levels higher than federal standards.
Most of those contaminants came from geologic sources, but the study found that people’s use of water — through irrigation, pumping, artificial recharge and other activities — can cause naturally occuring contaminants from aquifer rocks and sediments to be released.
To be sure, detecting pollution in drinking water wells does not necessarily indicate human health concerns at the tap. The samples were taken before water was treated by municipal utilities. But private residential wells are not subject to federal standards, and treatment is up to homeowners.
Man-made contaminants were most concentrated in the shallow groundwater beneath agricultural and urban land, the report found, rather than the deeper parts of aquifers that are tapped for drinking water.
While that may be a relief in the near term, it could pose problems over the long term, according to the report.
Groundwater moves slowly; the health of many aquifers today is the result of activities and contaminants from 30 years ago.
“Over time, the changes that we see in shallow groundwater are likely to appear in the deeper parts of aquifers, as the shallow groundwater moves downward,” the report states. “This change in quality of deeper aquifers is a concern for the future because the restoration of groundwater supplies that have become contaminated is difficult, is costly, and can take decades.”