The Environmental Protection Agency on Nov. 9 issued a subpoena to oil-field services contractor Halliburton for failing to provide information the agency needs to complete its congressionally mandated study on hydraulic fracturing, or “hydrofracking.”

Eight other hydrofracking firms that received voluntary information requests in September agreed to submit “timely and complete information” to EPA, the agency said.

But Houston-based Halliburton took another tack, refusing to give EPA full data on the company’s hydraulic fracturing operations over the past five years. “Because the agency’s request was so broad, potentially requiring the company to prepare approximately 50,000 spreadsheets, we have met with the agency and had several additional discussions with EPA personnel in order to help narrow the focus of their unreasonable demands,” Halliburton said. The company said it had posted on its website information about many of the chemicals used.

Hydraulic fracturing, a technique that has been in use since the 1940s, involves pumping fluids—generally water and chemical additives—into geologic formations at a high pressure to open fractures in the rock to get at otherwise difficult-to-reach gas and oil reserves. Although the specific chemicals vary from company to company, the additives typically used include sand; acids; N, n-dimethylformamide, which prevents pipe corrosion; petroleum distillates and glutaraldehyde, which eliminates bacteria in water.

Its proponents say the practice is a way to boost production of dwindling energy resources, particularly in North America. But some environmental advocates say the practice could pose a threat to human health by contaminating drinking-water supplies. The Pennsylvania Dept. of Environmental Protection banned a drilling contractor earlier this year after a well blowout spilled 35,000 gallons of hydraulic chemicals in Clearfield County.

At the request of U.S. lawmakers, EPA has embarked on a study to evaluate the effects of the practice on drinking-water supplies and human health. EPA says it is in the midst of collecting data and designing the scope of the study; it plans to complete the study some time in 2012

Industry sources say they believe the practice is safe and point to a 2004 EPA study that found no harmful effects from hydraulic fracturing. Lindsay Link, president of Houston-based Baker Hughes’ pressure-pumping business segment, says, “I’m not concerned that it has caused groundwater contamination because of the steps that are taken” in the hydraulic fracturing process to ensure that hydrocarbons are isolated from sources of groundwater.

Gary Flaharty, vice president of investor relations for Baker Hughes, adds, “Hydraulic fracturing has a really solid safety track record.”

But Myron Arnowitt, Pennsylvania state director of Clean Water Action, says, “There certainly have been lots of reports around Pennsylvania about project well contamination from folks living near recent drilling of Marcellus Shale.”

He says it is hard to distinguish whether drinking-water contamination results from hydraulic fracturing itself or from the natural-gas extraction process. “From our perspective, studying fracturing by itself doesn’t really make sense. You need to look at the entire procedure of natural-gas extraction, from cradle to grave, so that you’re studying the full scope of what the potential sources of drinking-water contamination could be,” Arnowitt say.