AUGUSTA – Members of Maine’s Board of Environmental Protection expressed concern Thursday about how a proposal to allow power plants to burn more wood waste could affect air quality and the state’s landfills.

Two companies have filed paperwork with the state for authorization to generate steam or electricity by burning wooden construction or demolition debris, or CDD, in biomass boilers.

Georgia-Pacific Corp. also hopes to burn wood debris at its Old Town plant, but residents have appealed the permit.

Those projects could be affected by rule changes proposed by the Department of Environmental Protection that could open the door for the cleanest-burning plants to use more wood debris, the vast majority of which is trucked into Maine from out of state. The state adopted the current regulations in 1999 to deal with growing interest in burning CDD in biomass boilers, which traditionally have burned timber industry waste.

DEP officials said the staff had been planning to update the wood debris rules for some time before the recent permit requests.

During Thursday’s work session, board members peppered department staff with questions about why Maine is the only New England state to allow CDD biomass boilers and the potential environmental implications of allowing more burning.

Ash from the burned debris can contain mercury, arsenic and other toxins, although the state has standards to minimize use of wood containing hazardous chemicals.

The board requested another work session to grapple with the environmental issues before voting to approve or amend the department’s proposed rules.

“My sense is there is going to be an awful lot of this stuff burned in the state … and this is a much more significant rulemaking than we normally embark on,” said board member Ernest Hilton.

Four biomass boilers located in Greenville, Livermore Falls, Stratton and Sherman burned more than 300,000 tons – or 600 million pounds – of construction and demolition debris in 2004.

More than 52,000 tons of the waste came from within Maine.

“It does allow us to reuse this material and not put it in the landfill,” said Paula Clark, director of DEP’s Division of Solid Waste.

The remaining 82 percent of the CDD fuel that year, however, came from outside Maine and resulted in more than 25,000 tons of potentially toxic ash deposited in Maine landfills.

State law allows biomass plants to use up to 50 percent CDD content in boilers. The new standards proposed by the DEP would allow plants to burn solely construction and demolition debris, but only if the plant uses the latest pollution-control technology.

No existing plants would qualify to exceed 50 percent without major, costly modifications, Clark said. A new plant proposed for Athens by power company GenPower likely would qualify under the new standards.

But board members were obviously uncomfortable with the prospect of permitting higher CDD burn rates without more information on the potential environmental costs.

“If we are going to go down this road, I think it is very important for us to have a clear understanding of the numbers” under a 100 percent scenario, said board member Elizabeth Ehrenfeld.

Member Nancy Ziegler also questioned repeatedly whether the state needs additional monitoring to ensure that out-of-state wood waste does not contain hazardous materials that will end up airborne in soot or deposited in landfills as ash.

The board had been tentatively scheduled to vote on DEP’s proposals during its January meeting. Under the new timeline, the board will reconvene for another work session in January before deciding whether to proceed with the proposed changes.