BANGOR – Who will pay to clean up a coal-tar deposit in the Penobscot River along the city’s waterfront redevelopment area is now up to a federal judge in Portland.

U.S. District Judge George Singal heard closing arguments last week in the jury-waived trial that pits the city of Bangor against the owner of the former Bangor Gas Works.

The cost of the remediation is estimated to run between $12 million and $20 million, no matter whom the court orders to pay for it.

In September, the judge conducted a three-week 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.

There is no timetable under which the judge must issue his verdict, although both sides have said they expect it within the first three months of the new year.

The legal battle began in 2002 when the city sued 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 10-acre, 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.

“The evidentiary paths traced by history and science come together in the sediments at the bottom of Dunnett’s Cove,” the city’s attorney, William Devoe of Bangor, wrote in his 50-page post-trial brief. “Investigations show that the tar-contaminated sediment is thickest at the outfall of the Davis Brook Sewer. The evidence shows that the tar closest to the sewer outfall is stratified, with the kind of tar made in the earliest days of the [plant] located at the bottom, and the more recent type of tar located at or near the top.

“The evidence,” he continued, “reveals that both of the tar types made by the [gas works] and found in the sediments of Dunnett’s Cove permeate the original streambed or ‘floor’ of the Davis Brook Sewer, as near to the former [plant] as investigators could go, thus marking the trail traveled by the tar on its way from the plant to the river.”

Martha Gaythwaite, Citizens’ Portland attorney, countered in her equally long post-trial brief that “the city’s theories amount to nothing more than speculation.” She argued that the evidence presented at trial showed that none of the city’s records “depict a physical connection between the gas works and the sewer” and the state Department of Environmental Protection failed to find a sewer when it excavated the site in 1980.

More credible sources of the pollution, according to Gaythwaite, include the former Maine Central Railroad yard, the city’s coal-tar tanks operated on the riverbank, fires on the coal docks in the late 1940s and the bulkhead adjacent to the cove that was discovered in spring 2005.

“During the era when Bangor was one of the busiest ports in the United States, the granite bulkhead portion of the cove was known as the Maine Central Railroad wharf,” the attorney stated in her brief. “Given the amount of tar and other material loaded and unloaded every year in Bangor Harbor, there must have been hundreds, if not thousands of ships docking in the cove on a yearly basis. Considering the volume of tar and [similar] materials loaded and unloaded in Bangor Harbor, common sense alone indicates that at least some spills in the cove occurred.”

If Singal were to rule that both the city and Citizens were partially responsible for the pollution, the judge would determine in his written verdict:

. The amount and toxicity of the waste contributed by Citizens and the city compared with any other parties.

. The degree to which the city and Citizens each have cooperated in the effort to investigate the tar deposit.

. The degree of care exercised by Citizens and the city toward the hazardous substance now lying at the bottom of the river.

. Citizens’ and the city’s abilities to pay for remediation and other costs associated with the case.

The recommended remedy, approved in August by the DEP but not yet approved by the judge or the parties, would consist of isolating the contaminated area, filling in a portion of the river to prevent migration of contaminants and stabilizing the sediment permanently.

The second phase of the trial, which would determine the remedy, and the third phase, which would determine what portion of the cleanup costs third parties would have to pay for, won’t be scheduled until after the verdict in the city’s case against Citizens is issued. The lawsuits against the third parties would be dismissed if Singal determined the city and-or Citizens were the only parties responsible for the pollution.