While gas companies refuse to identify the chemicals they use — claiming that is proprietary information — critics cite contamination problems in other natural gas drilling fields. They worry that unregulated fracking can taint drinking water, deplete aquifers and produce briny wastewater that can kill fish. In Dimock, Pa., about 40 miles west of the Matoushek well but outside the Delaware basin, state environmental regulators say that cracked casings on fracked wells have tainted residential water supplies with methane gas.
The Environmental Protection Agency announced last month that it will study the impact of fracking on the environment and human health. The EPA said in 2004 there was no evidence that fracking threatens drinking water quality, but critics, including a veteran engineer in the Denver regional EPA office, argued that report's methodology was flawed.
The industry contends environmental concerns are overblown. It says the drilling techniques are safe and that there has never been a proven case of groundwater contamination caused by fracking — in part because fracking occurs far below the water table.
Congress exempted hydraulic fracturing from federal oversight in 2005.http://www.usatoday.com/tech/science/2010-04-18-delaware-river-drilling_N.htm