State environmental officials have asked Red Shield Environmental LLC in Old Town for more information on the company’s pollution control plans following tests this summer on the amount of lead coming from the facility’s stacks.

Red Shield Environmental, which operates the former Georgia-Pacific Co. mill, conducted emissions tests over a three-day period at the end of June and beginning of July, as required under state permits.

Lead emissions were higher than allowed for two out of the three days. But because the emissions are averaged over the three-day period for the purposes of the state permit, the facility’s lead output was within the limits allowed under Red Shield’s operating license.

State and federal environmental regulatory agencies often use averages, rather than snapshots from a particular moment, in order to adjust for temporary fluctuations.

But in a letter to Red Shield, Maine Department of Environmental Protection staff point out that if a fourth batch of emissions data had been averaged in, the facility would have been out of compliance. As a result, the DEP asked for more information on the company’s lead-control plans.

“This situation has the department concerned about ongoing lead emissions,” Ted Perkins, environmental specialist with the DEP’s Bureau of Air Quality, wrote in the Sept. 6 letter. “The department requests a report of the steps that Red Shield will take to ensure that the lead emissions limit is met on a continuous basis.”

Bryce Sproul, who handles licensing and compliance with the Bureau of Air Quality, said Wednesday that Red Shield’s emissions limit for lead is already very low. The department would like more specific information on emissions variations and the performance of some of the complex pollution-control devices at the plant.

“They have an emissions rate that they met, and that emissions rate is very protective of public health,” Sproul said.

Dick Arnold, Red Shield’s environmental manager, said the company changed some of the parameters in the fourth emissions test as an experiment as part of their license agreement. Arnold said he is confident the company is meeting its emissions requirements overall.

“We’ve demonstrated that we are in compliance and we will address the DEP’s concerns within a week or so,” Arnold said.

Arnold acknowledged, however, that Red Shield likely will face additional public scrutiny on lead emissions because of an earlier high-profile soot problem at the facility.

Earlier this year, Red Shield had problems with toxic levels of lead in ash samples taken from the facility’s biomass boiler. On two separate occasions, soot also fell onto homes and yards in the neighboring town of Bradley.

Those problems have since been resolved, according to company and DEP officials.

About 45 percent of the fuel burned in the facility’s biomass boiler is wooden construction and demolition debris. Although a cheaper fuel source than green wood chips, wooden debris contains more lead, arsenic and other contaminants than raw wood.

Red Shield has approximately 180 employees at the pulp mill. Officials hope to eventually produce ethanol and other products at the former G-P facility.