PORTER — The state Department of Environmental Conservation announced Thursday that it has granted CWM Chemical Services permission to use a thinner cap on its hazardous waste landfill here, increasing its capacity without increasing its size.

DEC spokeswoman Maureen Wren said the approval of the permit modification for CWM’s landfill adds 106,870 cubic yards, or 3 percent, to the 39-acre site’s capacity.

Before Thursday’s action, the landfill had a maximum permitted capacity of slightly less than 3.5 million cubic yards.

Foes of CWM’s operation as the only licensed hazardous waste disposal site in the northeastern U. S. weren’t pleased with the news.

Niagara County Legislature Vice Chairman Clyde L. Burmaster, RRansomville, said the county’s environmental attorneys are likely to head for court in Albany to seek an injunction preventing the ruling from going into effect.

“We have no opposition to the thinner liner, which is supposed to be better,” Burmaster said. “There’s nobody in the whole community who cares about the liner. . . . The issue is about the waste that goes into it. That’s what we’re afraid of.”

But CWM’s opponents haven’t done well in court so far. The county and Residents for Responsible Government, a local environmental group, filed suit earlier this year to try to block the DEC from approving the

thinner liner. The case was dismissed in State Supreme Court in Albany County, but Burmaster said that decision is being appealed.

Wren said the DEC’s approval of the thinner cap has no bearing on CWM’s application to dig a second landfill, a 36-acre site that could be used when the current landfill is full.

Wren said that request can’t be processed without adoption of a statewide hazardous waste siting plan and the creation of a state siting board.

But she said the DEC staff concluded that the thinner landfill cover wasn’t a change that required such a plan, because it would increase neither the height nor the acreage of the existing CWM landfill.

“It was determined by DEC staff that would not have an environmental impact,” Wren said.

Wren said the new cap will use geosynthetic clay, which includes a layer of fabric. It reduces the thickness of the cover from the current 4 1/4 feet to two feet.

“It’s more resistant to the freeze-thaw cycle than the technology they had, which was compacted clay,” Wren said. “It’ll be as good, if not better, as a barrier to [water].”

CWM spokeswoman Lori Caso said the new cap is “the environmentally responsible way to go.”

Lewiston activist Amy Witryol charged that the decision will ensure $25 million in additional revenue because CWM can stuff more waste into the landfill.

Caso acknowledged that more waste equals more money, but she said, “There’d be no way to estimate the revenue.”

She said that would be dependent on the type of waste and the type of cleanup and disposal contracts that come CWM’s way. The company does not have a standard per-ton fee, Caso said.

Steven J. Doleski, regional permit administrator for the DEC, wrote in his letter to CWM announcing the decision that the agency had reviewed all materials sent during a 79-day public comment period, and the transcript of a Jan. 21 public hearing.

“Based on this review, the department has not identified any substantive and significant issues specifically related to the CWM permit modification application,” Doleski wrote.

CWM submitted the request for the thinner cap in April 2008 and modified the request two months later.