ORRINGTON – Questions are expected to be answered soon concerning whether the Penobscot River and Penobscot Bay south of the former HoltraChem Plant in Orrington are contaminated with mercury from years of chlorine production at the factory.

A detailed 41-page plan to measure mercury levels in the river, air and soil between Veazie Dam and the southern point of Islesboro Island was approved by U.S. District Judge Eugene Carter on Aug. 10.

The study will look at the effects of mercury on aquatic organisms and food webs in the river and will study if the mercury levels are adversely affecting the organisms or creating a risk to human life. Samples will also be taken at locations above the Veazie Dam for comparison.

For years, environmentalists have said mercury dumped into the river by the chemical plant at the Orrington site contaminated the Penobscot River and waterways to the south.

“It doesn’t break down,” Nancy Marks, senior attorney who represents the Maine People’s Alliance and the Natural Resources Defense Council Inc., said Thursday. “It tends to end up miles and miles down the river.”

The Maine People’s Alliance and the Natural Resources Defense Council Inc. filed a lawsuit in April 2000 against Mallinckrodt Inc., in an attempt to force the company to address the downstream mercury contamination.

Mallinckrodt Inc., a St. Louis-based pharmaceutical company and owner of the facility from 1967 to 1982, has agreed to take some responsibility for the cleanup.

HoltraChem Manufacturing Co. LLC operated at the site between 1982 and 2000, when it declared bankruptcy. Mallinckrodt is the only former operator of the site still in existence.

Mallinckrodt hired Camp, Dresser & McKee Inc., an environmental firm based in Cambridge, Mass., to do a multimillion-dollar site cleanup in March 2003. Cleanup requirements, issued from the Maine Department of Environmental Protection, did not extend to the river or the estuary south of the plant, Marks said.

“We filed [the lawsuit] because we knew there was a mercury problem in the Penobscot and we knew this plant was responsible,” she said. “And we didn’t see the government addressing the issue down river.”

In July 2002, Judge Carter ordered the mercury contamination study be conducted. Since that date, a three-person panel was established and given the job of working out the details of the study plan.

As approved by Carter on Aug. 10, the study will determine:

. The extent of the harm resulting from mercury contamination to the Penobscot River-Bay system south of the HoltraChem plant site in Orrington.

. The need for and feasibility of a remediation plan to effectively address the present effects of such existing harm, if any.

. The elements of and timetable for the execution of the appropriate remediation plan to address the harm existing as a result of the mercury contamination.

The detailed study is expected to take three years to complete, with another year for planning and a fifth year for comparing the information and writing the final report.

“During the first year of the study, the whole ecosystem will be monitored in the river and the estuary to determine if concentrations of mercury in fish and wildlife are high enough to be of concern,” the study plan states.

The first year also will be used to compare mercury levels in air samples from the study area and from wetlands along the river and other sites outside that area where historically mercury has collected.

Studies on one or more additional waterways that have experienced no past or present discharge of industrial mercury will be completed for comparison.

“This study is very good,” Marks said. “It will answer where mercury is getting into the river, how it’s turning into methyl mercury, how that methyl mercury moves and how it gets into food, primarily fish that humans eat.”

The study is needed to determine what, if any, mercury cleanup is needed.

“It might be that you just have to remediate a couple wetlands along the river,” Marks said. “It allows you to determine a remediation to stop mercury from getting in the fish. [Right now] we don’t know for sure how the mercury is getting into the fish.”

The Aug. 10 court document also orders the selection of a project manager for the study, which is the first step in the process.