One of the largest gas drillers in the Marcellus Shale has announced that it will disclose the chemicals it uses in its Pennsylvania wells. The company, Range Resources, said it will display the list on its website, giving regulators and landowners an account of the hazardous chemicals injected into each well.

Last month, Pennsylvania's Department of Environmental Protection made public a list of more than 80 chemicals used by the drilling industry. But the Range list, first reported by the Wall Street Journal on Tuesday night, goes a step further because it includes the volume, concentration and purpose of the chemicals.

Range's disclosure will help health specialists and regulators determine whether the drilling is polluting drinking-water supplies, said Deborah Goldberg, an attorney at Earthjustice, a nonprofit environmental law firm. But she said the list is just a first step, because it will include only chemicals that are deemed hazardous to workplace safety by federal authorities. She said it won't necessarily include chemicals that may harm aquatic ecosystems or drinking water.

"It does not by any stretch of the imagination cover what most people would consider to be hazardous," Goldberg said.

The drilling industry combines chemicals with water and sand and injects the mixture into wells to break apart shale and release natural gas, a process called hydraulic fracturing, or fracking. Drilling companies have been slow to disclose the chemicals they use, which sometimes include toxic chemicals such as toluene and naphthalene, which is listed by the EPA as a possible carcinogen.

In September, Range CEO John Pinkerton joined another drilling executive in calling on his industry to release this information. The executives blamed the companies that produce the chemical mixes for preventing such disclosure out of proprietary concerns.

In recent years, landowners around the country have grown increasingly concerned that gas drilling is polluting their water, but scientists say it's difficult to determine the source of the pollution without knowing which chemicals are being injected into the earth. Drilling companies have stressed that the chemicals are highly diluted; Range said they account for only about 0.14 percent of the fracking fluid.

The exact percentage of chemicals used in each of Range's Pennsylvania wells will be available on the website, the company said, and each report will be posted within 30 days of a well's completion. A sample report (PDF) from the company shows the components of the fluid in a "typical Marcellus well." It lists four additives that contain a number of chemicals, including ethanol and glutaraldehyde, a toxic pesticide. Range spokesman Matt Pitzarella said these four additives are what the company generally uses in its Marcellus wells.