Environmental groups are pressing the state of Tennessee to regulate "fracking," a controversial method of fracturing underground rock formations to release natural gas for drilling. The practice has been blamed for numerous cases of drinking water contamination nationwide.

The Tennessee Oil and Gas Board held a public hearing yesterday to discuss proposed changes to gas drilling rules. But those changes fail to address fracking, which involves drilling a well and pumping in fluids to free the gas.

To draw attention to fracking's risks, a coalition of environmental and public-interest groups including United Mountain Defense, Sierra Club, Statewide Organizing for Community eMpowerment and the League of Women Voters rallied at the Tennessee Department of Environment and Conservation Office in Knoxville before the hearing, where citizens spoke out about the need for fracking oversight.

"Although our state regulators assure us that fracking, if it is done at all here, is perfectly safe under the proposed regulations, experience in other states has shown that when the natural gas bandwagon gets to Tennessee -- and it will -- we will need far stronger regulations than what is being offered us," said Axel Ringe with the Sierra Club's Tennessee chapter.

The fluids used in the fracking process are often proprietary compounds containing toxic ingredients such as cancer-causing hydrocarbons and solvents, and there is concern over the lack of disclosure requirements. Diesel fuel has also been used as a fracking fluid.

In addition, fracking involves pumping large quantities of water underground, which can bring to the surface potentially harmful contaminants such as brine and naturally occurring radioactive materials.

TDEC reports that there are already more than 15,000 gas and oil wells in the state, and Chevron Corp. recently purchased 120,000 acres in Tennessee for gas drilling.

The evening before Tuesday's rally and hearing, Knoxville residents got a chance to attend a free showing of "Gasland." The award-winning documentary by Josh Fox features stories about communities from Pennsylvania to Texas where water supplies have been damaged by fracking. Watch the trailer here:

(Photo of Tennessee rally for safer gas drilling regulations courtesy of United Mountain Defense.)