Tucked inside the Senate bill aimed at cracking down on oil drillers after the Gulf spill is a long-sought measure to protect groundwater from natural gas drilling.

The bill, called The Clean Energy Jobs and Oil Company Accountability Act, would require that drilling companies make public a complete list of chemicals injected underground in proprietary formulas to break up rock deep underground and extract natural gas, a process called hydraulic fracturing.

It would not, however, reverse the exemption that prohibits the Environmental Protection Agency from regulating the fracturing process like other forms of underground injection, another important regulatory change that was initially proposed in House and Senate bills last June along with the chemical disclosure.

That bill, called the Frac Act, was sponsored by Sen. Bob Casey, D-Pa., who pushed for its inclusion in the accountability bill now being considered.

"Proper regulation is another essential element in protecting drinking water and public health. That is a battle that we still need to fight," Casey told ProPublica in an e-mail. But he emphasized that disclosing the chemical names "is an important step toward informing the public and building accountability for oil and gas companies."

A push for disclosure and stricter regulation of the fracturing process began in earnest last year after a series of articles by ProPublica reported more than a thousand cases of ground and surface water contamination in drilling areas where the process was being used. The articles examined drilling records in more than seven states, and found both a consistent pattern of water contamination in drilling areas, and a gap in scientific knowledge about the way hydraulic fracturing affects underground layers of rock and aquifers.

Problems were severe in Casey's home state, where fast-paced development of the Marcellus Shale natural gas deposit quickly led to dozens of reports of drinking water well contamination in places where hydraulic fracturing had been employed. Residents reported flammable tap water, and state investigations found that methane had seeped into water supplies underground as a result of the drilling activity.

Investigating the cause of such incidents has been difficult in part because the EPA does not have the jurisdiction to regulate fracturing the way it does other injection processes, and because the chemical makeup of the fracturing fluids has been guarded as a trade secret.

Several states, including New York, Colorado and Wyoming, have recently passed disclosure laws of their own, and industry representatives have begun to support the notion. But the language of the Senate bill is the most specific, and would apply to all of the states where oil and gas is produced.

The disclosure proposed today would still allow companies to withhold the exact recipes they use, meaning they wouldn't have to disclose the concentrations to the public. But they would -- in case of emergencies -- be required to share that information on a confidential basis with doctors and hospitals responding to an accident.

It's not clear how far the bill will get in the face of Republican opposition. Sen. Harry Reid, D-Nev., who added the disclosure component to the accountability bill, has said he hoped to bring the bill to a vote next week. Even if it passes, it will need to be reconciled with a House version that does not include the fracturing disclosure language.

Update: Politico notes that Reid may have added the disclosure language as a note to environmentalists, who have been upset that the Senate has moved away from a bill on global warming.