Range Resources also did not immediately comment on the letter. The company has denied it contaminated Texas water, saying the gas in the water was from a different rock formation and does not originate in the Barnett shale.
In the letter, the environmental groups also question whether by not releasing Thyne's report, the EPA denied the public "access to information that could be useful for preventing negative impacts" associated with hydraulic fracturing, also called fracking.
Fracking combined with horizontal drilling has allowed drillers to extract once out-of-reach gas and oil by pumping large volumes of chemical-laced water at high pressure into thick, impermeable rock formations. The process cracks the dense rock, releasing the oil and gas.
The industry contends the method is safe. Critics, however, say it contaminates water, and demand greater federal oversight.
In the case near Fort Worth, the EPA never said how the drilling operation contaminated the groundwater in that area.
Plushnick-Masti can be followed on Twitter at https://twitter.com/RamitMastiAP
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