As the oil and gas industry has turned increasingly to hydraulic fracturing to extract reserves, fears about groundwater contamination from the toxic chemicals used in "fracking" have intensified. And that's prompted a $747 million spending spree by major industry players in an effort to allay those fears and influence key energy committee members in Congress, according to a new report released by Common Cause.

The report, "Deep Drilling, Deep Pockets," suggests that the industry is pumping cash into the pockets of lawmakers in much the same way it pumps chemicals into tight shale formations to extract oil and gas. Only what it's extracting from Congress is loopholes in environmental controls, such as legislation in 2005 that exempted fracking from regulation under the Safe Drinking Water Act.

Common Cause calculates that gas industry leaders have spent $20 million on the campaigns of current members of Congress and another $726 million on lobbying efforts related to fracking over the past ten years. The campaign contributions have increased substantially in recent years, the report found.

Current members of the House Energy and Commerce Committee have been recipients of much of this largesse, with Representative Joe Barton of Texas, the former committee chairman, topping the list with $514,945 in contributions. Only three Colorado lawmakers show up in the top one hundred recipients -- Doug Lamborn clocks in at 63rd with a measly $96,600, followed by Michael Bennet (69th, $87,595) and Cory Gardner (79th, $77,500).

But with gas-friendly Governor John Hickenlooper insisting that contamination of groundwater from fracking is "almost inconceivable" and Colorado lagging behind other states in requiring disclosure of the chemicals used in fracking, look for more vigorous lobbying on the issue at a state level as the use of the controversial extraction method continues to expand.

The Common Cause report is only one volley in a counter-campaign by opponents. While the American Petroluem Institute has launched a new ad blitz suggesting that unfettered oil and gas exploration will generate a million new American jobs, the consumer advocacy organization Food & Water Watch is preparing to release a study next week that seeks to debunk those claims.

"Minor employment gains in the wake of shale gas development need to be weighed against the resulting costs to public health, public infrastructure and the environment," the group claims in a statement touting its study.

More weighing, less pumping? With the Environmental Protection Agency expected to release new findings about potential dangers from fracking next year, the debate is just going to get louder.

More from our Follow That Story archive: "Fracking primer: State seeks to address uproar over drilling process."