The contamination of water supplies near U.S. gas fields appears to be the result of leaky cement wells and casings and not the controversial production technique of hydraulic fracturing, or "fracking," according to a study released Monday, The Associated Press reported.
Fracking is a method of extracting natural gas from deep layers of rock using high-pressure fluid injections, according to the AP. The method has triggered a surge in U.S. gas production, but raised fears that breaking up rock formations underground could allow gas to seep into drinking water.
Scientists from several universities, including Duke, Ohio State, Stanford and Dartmouth, analyzed more than 130 drinking-water well samples overlying the Marcellus and Barnett shale gas formations and attempted to trace the source of any contamination, according to the study, the AP reported.
The researchers found eight clusters of drinking-water wells that were tainted by hydrocarbons and linked them, using "gas geochemistry data," to leaky cement from three production casings and one underground well used by energy companies to extract the gas, according to the AP.
The study said the research data "appear to rule out gas contamination by upward migration from depth through overlying geological strata triggered by horizontal drilling or hydraulic fracturing," the AP reported.
"Determining the mechanisms of contamination will improve the safety and economics of shale-gas extraction," the study reported, according to the AP. It was published in the Proceedings of the National Academy of Sciences.
The U.S. Environmental Protection Agency is in the midst of a years-long study into the impacts of fracking on drinking water and is scheduled to release a draft this year, after reports of drinking water so badly contaminated that homeowners could light it on fire, the AP reported.
The DOE report will not be the final answer on the subject, according to the AP. The Energy Department monitored six wells at one site, but oil or gas drilling at other locations around the nation could show different results because of variations in geology or drilling practices, according to the AP.
Environmentalists and regulators have also documented numerous cases in which surface spills of chemicals or waste-water damaged drinking water supplies, the AP reported.
