|Map from study; click on the image to enlarge it.|
The U.S. groundwater supply is smaller than originally thought, much of it is old (meaning such groundwater is unlikely to replenish itself), and hydraulic fracturing wells may be contaminating it, according to a newly published study from researchers at the University of California Santa Barbara, the University of Arizona, and the University of Saskatchewan. Groundwater is the primary source of domestic water supply for half the U.S. population, and about 40 percent of water used for agricultural irrigation comes from groundwater.
Potable groundwater doesn't go as deep as previously thought, too, so drilling deeper wells may not be a long-term solution for increasing demand for fresh water. Moreover, the study found that some fracking wells are so shallow that they can contaminate fresh water instead of going deeper to where the more brackish (saline) water is.
Previous studies suggested that fresh groundwater can go down to 6,500 feet below the surface, but the new research found that the average depth of transition from fresh to brackish water is about 1,800 feet. Aquifers tend to be especially shallow in parts of the eastern U.S., with the transition from fresh to brackish water occurring at less than 1,000 feet.