BANGOR – Environmental officials plan to brief the public next week on the city’s effort to get to the bottom of a sticky problem that has plagued the Bangor waterfront for decades.

The findings of an investigation into a coal tar deposit on the Penobscot River bottom – and options for remediation – will be explored during a public informational meeting Wednesday, Sept. 24 at City Hall.

During the session, which begins at 7 p.m., the results of an investigation into the tar deposit at Dunnett’s Cove will be presented by representatives of the Maine Department of Environmental Protection and RMT Inc. of Madison, Wis., the private environmental contractor the city hired to conduct ecological and health assessments of the affected area.

The investigation focused on the nature and extent of the tar deposit, which covers roughly a 10-acre area. Impacts on human health and the environment also were assessed.

Initial studies of the area determined that the now-defunct Bangor Gas Works was the source of the plume-shaped deposit, which begins at a former sewage outlet known locally as the “old stone” or Davis Brook sewer, and extends 1,400 feet downstream from the Bangor landing. The sewage outlet once began at the gas plant that operated on the city’s west side from 1881 to 1963 and emptied into the river.

While not believed to be harmful to humans, the sticky, black residue found at the site sometimes bubbles up to the surface, sticking to boat hulls and creating an oily sheen on the river surface when temperatures rise.

“This has been an issue for a long time,” City Engineer Jim Ring said Tuesday. “It is a nuisance condition and it’s something that we want to see resolved.

“I can’t say whether it’s caused boat owners to [move to other docking facilities],” he said, adding, “We have enjoyed for a number of years greater demand for dock space than we have been able to accommodate.”

According to Ring, the presence of petroleum waste is not uncommon where historically there have been working harbors like Bangor’s.

“It’s not technically our responsibility, but Bangor has had a history of wanting to do the right thing,” he said. “That’s why we’re pursuing this.”

Regardless of the outcome of the studies, city officials have said that the mere existence of the substance is troubling and must be addressed.

Last fall, the city filed a federal lawsuit against the former owner of the Bangor Gas Works. The lawsuit aims to compel Stamford, Conn.-based Citizens Communications to pay a share of the estimated $10 million price tag for cleaning up the polluted area.

In turn, Citizens Communications has filed about a dozen third-party lawsuits against companies, some from Maine, it alleges also share responsibility for the pollution and the cleanup, City Solicitor Norman Heitmann said Tuesday. The case is still in the discovery phase and likely won’t go to trial until next fall, he said.

Presenters at next week’s public information meeting will include Eugene McLinn, a senior project manager for RMT, and Kathy Niziolek, DEP project manager. Other DEP representatives expected to attend are Deborah Rice, toxicologist; Troy Smith, staff geologist; and Hank Aho, acting director of the department’s remediation division. Ring will provide an introduction and brief project background statement before the presentations.

The city first hired RMT in 1999 to study the former site of the Bangor Gas Works, which generated the coal tar as a waste product of its gas manufacturing operations, officials believe, near what is now Second Street Park. Those studies confirmed the presence of coal tar in the river and linked the pollution to the plant.

Two years ago, Second Street Park underwent its own cleanup after studies revealed higher than allowed levels of Benzo(a)pyrene, a waste product of factories that produce coal tar.

A suspected carcinogen, the hydrocarbon was discovered during shallow soil tests designed to identify the point of origin of coal tar in the nearby Penobscot River. After a review of the city’s manufacturing history and several tests of the area, the gas works was deemed the most likely source of the hydrocarbon.

The discovery prompted neighborhood meetings, at which city officials outlined a $35,000 plan to treat the area, where five of the 10 soil samples tested had concentrations of the substance above the 2 parts per million level allowed by the DEP. Although the levels were higher than allowed in residential areas, state officials categorized the contamination as “very low,” stressing that it did not present a significant danger to people using the park.