The USGS (U.S. Geological Survey) published a new report on the vulnerability of public-supply wells to contamination. The report, produced by the National Water-Quality Assessment Program (NAWQA), and titled “Factors affecting public-supply-well vulnerability to contamination: understanding observed water quality and anticipating future water quality,” describes a number of key factors found to be significant in understanding the vulnerability of public-supply wells to contamination.
Among other things, the report discusses “which contaminants in an aquifer might reach a well and when, how and at what concentration they might arrive.” It identifies measures that are essential for understanding vulnerability to contamination in public-supply wells. These measures include: “1) the sources of the water and contaminants in the water that infiltrate the ground and are drawn into a well; 2) the geochemical conditions encountered by the groundwater; and 3) the range of ages of the groundwater that enters a well.”
The report examines ten different study areas across the country: Modesto, California; Woodbury, Connecticut; near Tampa, Florida; York, Nebraska; near Carson City and Sparks, Nevada; Glassboro, New Jersey; Albuquerque, New Mexico; Dayton, Ohio; San Antonio, Texas; and Salt Lake City, Utah.
An important point made in the report is that “common sense” doesn’t always rule when it comes to understanding how vulnerable a well is to contamination. One may think that a well located near an identified source of contamination would be the most susceptible to contamination, but the reality is more nuanced. As Sandra Eberts, the scientist who led the study, notes “Common sense might say that wells located near known contaminant sources would be the most vulnerable, but this study found that even where contaminant sources are similar, there are differences in public-supply-well vulnerability to contamination.”
Because factors apart from proximity to sources of contamination contribute to the vulnerability of a well, it is difficult to identify ways to protect them from contamination. According the USGS, “The study found that 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.”
The study also assess human impact on public-supply wells. The USGS reports that “an unexpected finding” of the report is that “human-induced changes in recharge and groundwater flow caused by irrigation and high-volume pumping for public supply changed aquifer geochemical conditions in numerous study areas.” These changes “often release naturally occurring drinking-water contaminants such as arsenic and uranium into the groundwater, increasing concentrations in public-supply wells.”
As the USGS points out, it is extremely important to understand human impact on groundwater. Around one third of Americans source their drinking water from public-supply wells. Reports such as this are important in that they give scientists insight and tools to assess, and hopefully mitigate or prevent, future impact of contamination of groundwater.
The full report is available here.