CHEYENNE - A recent federal court decision tossed out a rule exempting oil and gas construction sites from certain requirements under the Clean Water Act, prompting environmentalists to hail the ruling as a win for streams and rivers.

The U.S. Court of Appeals for the Ninth Circuit invalidated the U.S. Environmental Protection Agency rule last month in response to a lawsuit brought by the Natural Resources Defense Council and other environmental groups. The EPA rule exempted oil and gas construction sites from certain permitting requirements for discharging stormwater containing sediment.

Environmentalists said the decision requires oil and gas producers to prevent sediment-laden stormwater from washing off their construction sites. But if the ruling stands, it would not have an effect in states such as Wyoming, which have adopted requirements more stringent than the EPA rule.

In other major oil-and-gas states including Texas and Oklahoma, the EPA has permitting authority over stormwater discharges. Industry officials said the ruling could result in delays and confusion for developers trying to comply with environmental regulations.

In such states, the rule change could expose oil and gas developers to penalties if they misjudge the contamination from their projects, said Lee Fuller, vice president of government relations for the Independent Petroleum Association of America, which supported the EPA in the lawsuit.

"Now the operator would have to make a judgment of whether they're managing their activity without discharging contamination, without clarity of what contamination would be," Fuller said.

The EPA is reviewing the court's decision in consultation with the Department of Justice, said Benjamin H. Grumbles, the agency's assistant administrator for water. The agency has until July 7 to petition the California-based court for a rehearing.

"In the meantime, we'll continue to encourage best management practices to prevent stormwater runoff from oil and gas field activities and work to complete new regulatory guidelines and general permits for controlling stormwater runoff from construction and development sites," Grumbles said in a statement.

Environmental groups have argued sediment that washes off construction sites during rain or snow storms can harm fish, plants and other aquatic life - as well as increase the cost of water treatment for local governments.

The EPA exempted oil and gas construction sites from permitting rules for stormwater discharges at oil and gas construction sites in response to the Energy Policy Act of 2005, according to court records. The agency argued that Congress specifically ordered the exemption, regardless of sediment's impact on water quality, according to court records.

A majority of the appellate panel, however, found the EPA's rule change to be "arbitrary and capricious." The court found that prior to the 2005 Energy Policy Act, the EPA considered stormwater discharges "polluted with sediment" to have serious water quality impacts, the ruling said.

"The bottom line is it places the burden squarely on energy companies to take steps to ensure that their activities are not contributing to violations of water quality standards," said Sharon Buccino, senior attorney at the Natural Resources Defense Council. "The rule had essentially removed that obligation and basically given the companies a free pass to pollute."

In Oklahoma, oil and gas developers are required to use best management practices when it comes to retaining polluted stormwater at construction sites, said Michael Bernard, president of the Mid-Continent Oil and Gas Association of Oklahoma. He said the court's ruling could result in delays for developers.

"When you're drilling a well, time equals money," Bernard said. "It would slow down production. It would not only hurt the ability of oil and gas companies to drill wells and bring wells on line, it would hurt the consumer also because there would be less product getting to market."

In Wyoming, the state Department of Environmental Quality requires all construction activities that disturb at least one acre - including oil and gas projects - to have a stormwater pollution prevention plan, said Barb Sahl, the department's stormwater program coordinator.

"They're required to implement whatever practices are needed to control sediment or pollutants," Sahl said. "When we come out on an inspection, we make sure those practices are there and they are effective."

Earlier this month, the EPA and Justice Department announced that four of the nation's largest homebuilders had agreed to pay $4.3 million in fines for failing to control runoff at construction sites. The agency said the fines were part of a nationwide crackdown to find stormwater violations at construction sites.