BANGOR – A federal judge has concluded that a Connecticut-based owner of the former Bangor Gas Works is responsible for 60 percent of the cost of cleaning up the coal-tar deposit in the Penobscot River along the city’s waterfront redevelopment area.

U.S. District Judge George Singal assigned 40 percent of the responsibility for the pollution in Dunnett’s Cove to the city of Bangor. He also limited the area of the cleanup from the 10 acres proposed by the city to a small section of the river where the tar deposits have been seen.

Singal issued his 86-page ruling Wednesday afternoon, six months after hearing closing arguments in the case.

The total cost of the cleanup is estimated to run between $12 million and $20 million.

” … [The city and Citizens Communications Co.] bear responsibility for the same exact tar,” Singal wrote. “Tar that was produced and discharged from the Bangor manufactured gas plant by Citizens was carried into Dunnett’s Cove by sewers that were constructed and maintained by the city.”

The judge’s ruling concluded the first step in a two-part process. In September, he conducted a 12-day, jury-waived trial in U.S. District Court in Bangor and Portland. Dozens of witnesses testified and both sides presented more than 1,000 pieces of evidence combined.

Singal will hold a second trial to determine the appropriate remedy that should be used to clean up the river before issuing a final judgment.

A date for that trial has not been set.

“The city is pleased that the court assigned a majority share of the responsibility to Citizens,” William Devoe, the Bangor attorney who represents the city in the case, said Wednesday.

Citizens also said it was happy with the decision.

“We are pleased that the court has both recognized that the alleged contamination that needs to be remediated is limited to a small section of the river, and that the city also has significant responsibility for the remediation,” Hillary Glassman, senior vice president and general counsel for Citizens, said Wednesday in a prepared statement.

The legal battle began in 2002 when the city sued the Stamford, Conn.-based Citizens Communications Co., the successor of a series of corporate entities that owned and operated Bangor Gas Works, claiming that the plant was the sole cause of the pollution.

Citizens denied it was responsible for the pollution in the section of the river known as Dunnett’s Cove. It filed a dozen third-party lawsuits alleging that others, including the city, should pay for the cleanup because they, not Citizens, were responsible for the plume-shaped coal-tar deposit.

Shaw’s Supermarket on Main Street now sits on a portion of the site where Bangor Gas Works once removed usable gas from coal, supplying the gas to the city.

The residue left after the gasification was a tar substance stored in tanks at the facility. The plant also extended into what is now Second Street Park, which was cleaned up several years ago.

City Solicitor Norman Heitmann said Wednesday that the judge’s ruling still is being reviewed in-house and by Devoe.

The City Council probably will discuss the decision early next month, Heitmann said.

As of Wednesday, it was too early to determine what the city’s share of the cleanup cost would be or if the city would consider appealing Singal’s final judgment, according to the city solicitor.

“It’s too early for that conversation,” Heitmann said.

Although the city is responsible for 40 percent of the cleanup, the judge actually assigned 5 percent of the responsibility for the pollution to the city-owned sewer system, Devoe said Wednesday.

Singal also concluded that the other 35 percent was caused by other entities along the river, including a former railroad bed, he said.

Bangor purchased the Maine Central Railroad yard in 1995 and the city assumed responsibility for the pollution it might have caused during its years of operation, Devoe said.

It could not be determined Wednesday what kind of a cleanup the city or Citizens would recommend to court.

The Department of Environmental Protection has offered a proposed remedy, but it has not yet been approved by the judge or the parties.

The DEP plan includes isolating the contaminated area, filling in a portion of the river to prevent migration of contaminants and stabilizing the sediment permanently.

Bangor Daily News reporter Dawn Gagnon contributed to this report.