Research by the US Geological Survey may begin to help public well water managers identify how vulnerable their systems are to contamination, but the study that USGS released on Aug. 5 identified more variables than culprits. Essentially, it raised more questions than answers.
The study by USGS's National Water Quality Assessment Program certainly won't bolster arguments on either side of the debate over US unconventional oil and gas onshore supply development's possible impacts on drinking water supplies. Advocates on either side who are looking for easy answers will simply need to look elsewhere.
Everyone else will find new information about factors possibly affecting which contaminants in an aquifer might reach a public supply well, and when, how, and at what rates they might arrive, USGS said.
About one third of the US population gets its drinking water from such wells. The study examined supplies at or near Modesto, Calif.; Woodbury, Conn.; Tampa, Fla.; York, Neb.; Carson City and Sparks, Nev.; Glassboro, NJ; Albuquerque, NM; Dayton, Ohio; San Antonio, Tex.; and Salt Lake City, Utah.
"By examining 10 different aquifers across the nation, we have a more thorough and robust understanding of the complexities and factors affecting water quality in our public supplies," said Suzette Kimball, acting USGS director.
Measurements that are crucial for understanding public well supply vulnerability include: the sources of the water and contaminants in it that infiltrate the ground and are drawn into a well, the geochemical conditions encountered by the groundwater, and the age range of groundwater that enters a well.
Vulnerability differences
"Common sense might say that wells located near known contaminant sources would be the most vulnerable," said Sandra Eberts, who led the study. "But we found that even where contaminant sources are similar, there are differences in public well supply vulnerability to contamination."
USGS said its study found conditions in some aquifers enable contaminants to remain in the groundwater longer or travel more rapidly to wells than conditions in other aquifers.
Direct pathways, such as fractures in rock aquifers or wellbores of non-pumping wells, frequently affect groundwater and contaminant movement, making it difficult to identify which areas at land surface are the most important to protect from contamination, it indicated.
An unexpected finding was that human-induced changes in recharge and groundwater flow caused by irrigation and high-volume pumping for public supplies changed aquifer geochemical conditions in numerous study areas, according to USGS.
Changes in geochemical conditions often release naturally occurring drinking-water contaminants such as arsenic and uranium into the groundwater, increasing concentrations in public supply wells, it noted. The full study and additional information are available online at USGS's web site at www.usgs.gov.
