PORTLAND — The Maine Board of Environmental protection will permit the Dragon Cement plant in Thomaston to operate under federal emissions standards that raise the amount of mercury the plant could release into the air by 68 percent, as production increases.

Marc Cone, head of the Department of Environmental Protection’s Bureau of Air Quality, said the citizen board voted unanimously Thursday morning to approve allowing the plant to operate under federal standards.

Michael Martunas, Dragon’s environmental manager, said in a phone interview Thursday that application of the federal standards effectively increases the possible production at the plant, which has been limited by a 2008 state law specifically targeting mercury emissions. That law capped the mercury the plant could release at 25 pounds per year.

The federal limit does not set an overall cap on air emissions but limits them based on production.

Dragon’s state license permits production of up to 766,500 tons of clinker, a powder created in the process of making cement. Under the federal limit, the plant could release up to 42 pounds of mercury into the air at that production level.

The decision drew sharp criticism from the Natural Resources Council of Maine, which said the state is “effectively surrendering [its] ability to limit mercury emissions at Dragon, allowing the plant to pollute at the highest level permitted nationwide,” noting mercury is hazardous to humans and the environment.

“Dragon Cement Company’s request flies in the face of Maine’s law to limit mercury and the state’s Mercury Action Plan, too. Maine joined with the Conference of New England Governors and Eastern Canadian Premiers in adopting the action plan, the goal of which is the virtual elimination of anthropogenic mercury emissions,” NRCM said in a response to the decision.

Cone said the state statute permits alternative mercury emissions limits to be approved and factors in what is “economically feasible” for the company.

NRCM criticized that aspect of the decision as well, saying there are technologies Dragon could use to reduce its mercury emissions to meet the state’s 25-pound-per-year emissions standard as production increases.

At current production levels, Cone said the plant is not emitting more than its now-former limit, but it’s also producing less clinker than its state license allows.

“We’re still coming out of the recession, and we’ve not yet returned to 2006 levels, which was our best year of production,” Martunas said.

The plant produced 600,000 tons of clinker in 2004. Last year, it emitted 13 pounds of mercury into the air. Martunas could not immediately say how much clinker the plant produced in 2013.

The company requested the change in February, seeking to operate under one federally issued emissions license rather than separate licenses from the state and federal government.

The company is Thomaston’s largest property taxpayer and employs around 100 people around the state. It pays Thomaston and neighboring Rockland more than $830,000 in property taxes each year.

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