Between 2005 and 2009, the nation’s 14 leading natural gas drilling service companies used hydraulic fracturing fluids containing 29 different chemicals regulated under the Safe Drinking Water Act (SDWA) as potential human carcinogens, according to a new congressional report released Saturday.

Nationwide, the companies injected 11.4 million gallons of products containing at least one of the so-called BTEX chemicals (benzene, toluene, xylene, and ethylbenzene), according to the report produced by Democrats on the Energy and Commerce Committee, including Colorado’s Diana DeGette. Colorado, along with Oklahoma and Texas, ranked in the top three for the highest volume of fluids containing possible carcinogens.

“It is deeply disturbing to discover the content and quantity of toxic chemicals, like benzene and lead, being injected into the ground without the knowledge of the communities whose health could be affected,” DeGette said in a release.

“Of particular concern to me is that we learned that over the four-year period studied, over one and a half million gallons of carcinogens were injected into the ground in Colorado. Many companies were also unable to even identify some of the chemicals they were using in their own activities, unfortunately underscoring that voluntary industry disclosure is not enough to ensure the economic benefits of natural gas production do not come at the cost of our families’ health.”

The commonly used gas drilling practice of hydraulic fracturing, or fracking, frees up more natural gas by injecting mostly water and sand, along with undisclosed chemicals, deep into natural gas wells to fracture tight geological formations. The process has been increasingly scrutinized because of concerns about groundwater contamination.

DeGette and Colorado Rep. Jared Polis have introduced legislation that would compel companies to publicly disclose the types of chemicals being used in fracking fluids. Colorado is joining a national effort to set up a voluntary database for companies to disclose the chemical makeup of fracking fluids, but DeGette and Polis want to remove a Safe Drinking Water Exemption for the process that was granted during the Bush administration in 2005.

The latest report also comes from Democrats Henry Waxman, the ranking member of the House Energy and Commerce Committee, and Edward Markey, ranking member of the House Natural Resources Committee. DeGette, the ranking member of the House Oversight and Investigations Subcommittee, joined Waxman and Markey in releasing a report in late January revealing that the same oil and gas service companies injected more than 32 million gallons of diesel fuel into the ground between 2005 and 2009 – a possible violation of the Safe Drinking Water Act.

Colorado natural gas industry officials concurred with national industry representatives in countering that the U.S. Environmental Protection Agency (EPA) never has set any rules for the use of diesel fuel in fracking fluids.

Responding to the latest report, Matt Armstrong, an energy industry attorney, told The New York Times that the methodology of both congressional reports was flawed.

“This report uses the same sleight of hand deployed in the last report on diesel use — it compiles overall product volumes, not the volumes of the hazardous chemicals contained within those products,” Armstrong said. “This generates big numbers but provides no context for the use of these chemicals over the many thousands of frac jobs that were conducted within the timeframe of the report.”

Most oil and gas service companies insist they must maintain the secrecy of hydraulic fracturing ingredients for proprietary reasons. In Colorado, state rules that went into effect in 2009 compel companies to provide the chemical makeup of fracking fluids to regulatory officials and emergency workers upon request.