The controversial practice of hydraulic fracturing used to release underground reserves of natural gas has no direct connection to groundwater contamination, a new study says.

Hydraulic fracturing -- colloquially called "fracking" -- involves massive amounts of water, sand and chemicals injected at high pressures to fracture rock and release the stored gas.

Critics say the practice leaves groundwater supplies vulnerable to harmful chemicals in fracking fluid.

The study, "Fact-Based Regulation for Environmental Protection in Shale Gas Development," by the Energy Institute at the University of Texas at Austin says that many problems attributed to fracking have other causes, such as "casing failures or poor cement jobs."

Study authors say the report stems from a self-funded initiative at the Energy Institute and no industry funds paid for the study.

"Our goal was to provide policymakers a foundation for developing sensible regulations that ensure responsible shale-gas development," Charles Groat, an Energy Institute associate director who led the research, told the Fort Worth Star-Telegram.

"What we've tried to do is separate fact from fiction."

The research team looked at reports of groundwater contamination in three shale plays: the Barnett Shale in north Texas, Marcellus Shale in Pennsylvania and the Haynesville Shale in Louisiana and eastern Texas.

A lack of baseline studies in areas of shale gas development, the study says, makes it difficult to evaluate long-term, cumulative effects and risks associated with fracking.

Still, the study said that "natural gas found in water wells within some shale-gas areas ... can be traced to natural sources and probably was present before the onset of shale-gas operations."

Surface spills in gas development pose greater risks to groundwater than fracking itself, the study says.

Justin Furnace, president of the Texas Independent Producers and Royalty Owners Association, welcomed the study, telling the Houston Chronicle that it "echoes what we as an association have been saying: The process is very safe and has been in place for 60 years."

Scott Anderson, a senior policy adviser for the Environmental Defense Fund, in a posting on his blog said the study "does not mean such contamination is impossible or that hydraulic fracturing chemicals can't get loose in the environment in other ways (such as through spills of produced water)."

EDF helped develop the scope of work and methodology for the study.

"In fact," Anderson continued, "the study shines a light on the fact that there are a number of aspects of natural gas development that can pose (a) significant environmental risk."