HARLEYVILLE - Wood-burning power plants such as the facility operating near this town pollute more than coal-burning plants, an environmental group claims in a report due to be released today. But they are not held to the same emission controls and have been given clean energy subsidies.

Coming Monday

Read more about the biomass plant pollution controversy in an upcoming edition of The Post and Courier.

The group, Partnership for Policy Integrity, embargoed the report until midnight Tuesday but held a news conference. The plants, also called biomass plants, create electricity by burning wood products. A sister plant to the Harleyville plant is underway near Allendale.

The biomass company, EDF Renewable Energy, did not immediately return voice mail or email requests for comment. "Wood-waste biomass facilities like the ones we purchase power from in Allendale and Harleyville are carbon-neutral," said Mollie Gore, corporate communications manager for Santee Cooper, the utility that buys electricity from the plant. In other words, trees absorb carbon dioxide and decaying wood returns it to the air whether or not the wood is burned. Equipment at the plant captures other pollutants and the plant does not burn treated or painted wood, she said.

A staffer for the Coastal Conservation League, a Lowcountry environmental advocate, said the report appears to focus primarily on larger biomass plants than the Harleyville plant, and the league would not support that large of a plant.

The league "continues to qualify any support for biomass with concerns about the source material that would be used in these facilities and the size of these facilities," said Hamilton Davis, energy and climate director. "Biomass projects are evaluated on a case-by-case basis."

The Partnership for Policy Integrity based its findings on a megawatt-to-megawatt comparison of electricity produced. The plants compared are smaller than coal plants, but Mary Booth, partnership director, said the real question is the costs imposed on society for each of those megawatts. If you live in a community where one of the plants is proposed or operating, the pollution is significant, she said.

The regulation discrepancy "makes this industry even more polluting than it needs to be," she said.

The $46 million plant began operating in November 2013 in Harleyville, championed as "green energy" by Dorchester County leaders and Santee Cooper officials. The Harleyville plant was permitted in 2011 to burn nearly 300,000 tons of wood per year. County leaders gave fee-in-lieu-of tax incentives and contracted to supply the plant with 20 tons per year of wood debris from county operations.

Federal Environmental Protection Agency set pollutant emission rules for operations like the plant that are not as strict as the rules for the larger coal plants. State regulators followed the federal lead.

The EPA deferred a decision on toughening rules for three years until summer 2014, said Mark Plowden, S.C. Department of Health and Environmental Control communications director.

"The plant's air permit has stringent emission limits and stack test requirements to ensure these limits are being met," Plowden said.

Reach Bo Petersen at 937-5744, @bopete on twitter or Bo Petersen Reporting on Facebook.