PHILADELPHIA, Aug 9 (Reuters) – Pennsylvania regulators are illegally allowing natural gas companies to withdraw water from rivers and streams for use in the Marcellus Shale drilling boom, an environmental group claims.

The Allegheny Defense Project says the state’s Department of Environmental Protection has no legal right to permit drillers, as it does, to take millions of gallons of water from rivers in the western part of the state.

That right belongs to owners of riparian land — that which borders waterways — but DEP has ignored the law in facilitating the industry’s demands, the group said in a letter sent to DEP Secretary John Hanger in late July.

The letter is the latest criticism by environmentalists who are concerned about the impact of the booming industry of drilling for natural gas in onshore shale formations.

DEP spokeswoman Helen Humphreys said the department would comment after it has studied the letter. “We have taken their concerns seriously and we are gathering all the information necessary to respond appropriately,” she said.

The Marcellus Shale Coalition, an industry group, did not respond to repeated requests for comment.

But at least one independent expert backed the project’s argument.

“While the DEP has some authority to regulate water withdrawals for public water supply facilities and power under the Clean Streams Act to regulate activities that impair water quality, neither of those authorities authorized DEP to give permission to withdraw water for Marcellus Shale use,” Joseph Dellapenna, a Villanova University law professor who specializes in water rights, said in an email.

Any attempt to prevent gas drillers from using the water would have to come in a lawsuit by owners of land bordering a waterway, Dellapenna said.

Outside of the Delaware and Susquehanna River watersheds in the eastern half of the state — where water withdrawals are regulated by two interstate commissions — water rights in Pennsylvania are governed by riparian rights common law, the Allegheny Defense Project says.

“Only those who live adjacent to the water can make reasonable use of the water on their land,” said Cathy Pedler of the project.

Energy companies use about 3 million gallons (11 million litres) of water for each well that is hydraulically fractured, or “fracked”, a process that pumps water mixed with sand and chemicals at high pressure to break open gas-bearing fissures in the shale about a mile underground.

The industry drilled 822 Marcellus wells in Pennsylvania in the first seven months of 2010, about 40 percent of which are in the western part of the state, according to the DEP.

The vast formation, underlying two-thirds of Pennsylvania and parts of surrounding states, is believed to contain enough gas to meet total U.S. energy needs for 20 years, and is expected to become the most productive U.S. shale gas field.