The Environmental Protection Agency has issued letters to nine natural gas drilling companies requesting “cooperation in a scientific study” of hydraulic fracturing and how it affects drinking water and public health, the agency announced on Thursday. Buried further down in the document, however, is a veiled threat to take legal action if the information isn’t provided (Read a copy of the letter [PDF]):

EPA is requesting that you provide this information voluntarily; however, to the extent that EPA does not receive sufficient data in response to this letter, EPA will be exploring legal alternatives to compel submission of the needed information.

The agency seems to be taking names with this latest request. The letter calls for a corporate officer to certify that the information provided is, to the best of his or her knowledge, “true, accurate and complete,” and it requires the company to specify the source of each piece of information by name, position and title. These two requirements could be important, should the information provided prove to be insufficient or inaccurate.

Chemicals used in the hydrofracking process, as we’ve noted, have generally been treated as trade secrets. The EPA said it would honor companies’ claims to confidentiality as long as it is explicitly requested at the time the information is submitted.

It’s also worth noting that in the letter, the agency requested that companies turn over not only the formulation of the companies’ fracking fluids, but also “all data and studies in the Company’s possession relating to the human health and environmental impacts and effects of all products and constituents” in it. (Information on certain chemicals’ effect on human health, aside from industry data, is likely to be scarce.)

The EPA also called for far more information than is currently known about specific sites at which hydrofracking fluids have been used, and the companies for which these services were performed. From the letter:

Identify all sites where, and all persons to whom, the Company:

i.   provided hydraulic fracturing fluid services that involve the use of hydraulic fracturing fluids for the year prior to the date of this letter, and

ii.   plans to provide hydraulic fracturing fluid services that involve the use of hydraulic fracturing fluids during one year after the date of this letter.

According to the letter, companies have seven days to provide notice as to whether they will submit the requested information, and 30 days for the full response.

Stephanie Meadows, a policy adviser for the American Petroleum Institute — an industry trade group — told The New York Times she was “disappointed with the threats” from the agency.

“I’m not sure how they would do that, or if they even have the authority to do that,” Meadows said. “I thought we’d made it clear all along that we want to be helpful.”

A spokeswoman for Halliburton, one of nine companies sent a letter, told the Times that the company planned to cooperate fully with the EPA:

“Halliburton supports and continues to comply with state, local and federal requirements promoting the forthright disclosure of the chemical additives that typically comprise less than one-half of 1 percent of our hydraulic fracturing solutions,” Ms. [Cathy G. Mann] said by e-mail. “We view this both as a means of enhancing public safety, and as a way to engage the public in a straightforward manner.”

If this attitude is genuine, it would be quite a shift. Halliburton hasn’t always acted cooperatively when asked to reveal the chemicals in its fracking fluid. When state regulators in Colorado demanded that the company hand over its recipe, the company threatened to end its natural-gas operations in the state, before eventually reaching a compromise to disclose some ingredients to regulators, but not to the public.

The EPA had concluded in 2004 that hydrofracking did not pose a threat to drinking water. That report, as we’ve noted, was used to justify legislation exempting the natural gas extraction process from oversight under the Safe Drinking Water Act — an exemption that is now being re-examined as awareness and public concern have grown over the potential risks that fracking can pose to water supplies.