Determining whether shale gas production leads to tainted groundwater is tough, in part because predrilling water quality measurements are usually lacking. But thanks to tests done in the 1990s by the Texas Water Development Board, some predrilling data are available for aquifers atop the Barnett Shale in northern Texas. Researchers comparing samples from Barnett water wells with those predrilling data report that wells near natural gas production sites have elevated levels of arsenic, selenium, and strontium (Environ. Sci. Technol. 2013, DOI: 10.1021/es4011724). Brian E. Fontenot of the University of Texas, Arlington, and coworkers sampled 91 water wells in the current drilling area and analyzed them with mass spectrometry and gas chromatography methods. The average arsenic, selenium, and strontium concentrations in wells within 5 km of gas production sites significantly exceed predrilling values from the area, with some wells exceeding U.S. drinking-water standards for the toxic substances. Barium concentrations, meanwhile, fell. It’s unclear whether gas production activities caused these trends, the researchers say, but the trends were less remarkable or absent in reference water wells far from gas production sites. Some wells also had methanol and ethanol, which could have come from natural sources or drilling fluids, but the researchers lack predrilling data for those substances for comparison.