ORRINGTON, Maine — Work began this week on the second phase of the multimillion-dollar cleanup of the former HoltraChem site on the banks of the Penobscot River.

HoltraChem, which operated from 1967 to 1982, produced 23,000 pounds of toxic mercury waste each year while making chemicals for papermaking and other industries until the adoption of significant hazardous waste disposal regulations.

Conducting and paying for the cleanup is Mallinckrodt Inc., the last remaining owner of HoltraChem still in existence. The cleanup effort could cost as much as $130 million, according to court documents filed in conjunction with litigation over the pollution.

Mallinckrodt has spent tens of millions of dollars over the years removing metallic mercury, mercury sludge and contaminated storage tanks and buildings from the site, according to company and town officials.

In addition, a court-ordered scientific study found that 6 to 12 tons of mercury were discharged from HoltraChem into the Penobscot River between 1967 and the early 1970s.

Smaller amounts have been released since then, and at least nine tons of the metal are still in sediments of the upper and lower Penobscot estuary, the study concluded. After hearing closing arguments in a lawsuit over the cleanup of the river, a federal judge on Wednesday said he would appoint a panel to recommend cost effective ways to rid the waterway of mercury.

Efforts to reach Mallinckrodt for comment on the cleanup were not successful on Wednesday.

The town acquired the land HoltraChem sat on several years ago through tax delinquency, but Mallinckrodt was deemed responsible for cleanup of the contaminated portion of the 235-acre property.

Previous work at the HoltraChem site included the installation of riprap on the riverbank next to one of the plant landfills to prevent erosion and river contamination, the addition of a groundwater collection system to capture contaminated groundwater discharging from the site for treatment, and the construction of a new wastewater plant for the treatment of contaminated groundwater.

The site cleanup began in 2014 and is expected to wrap up in early 2019, Stacy Ladner, an environmental specialist for DEP, said Wednesday.

It is a timeframe that Ladner said is feasible: “Yeah, I think if we can stay on track and don’t have any unexpected things happen.”

Orrington Town Manager Paul White agreed.

“Barring any setbacks, it is achievable,” he said.

The length of time it took to get to the environmental cleanup is not unusual, according to Ladner.

“In fact, it’s a pretty tight schedule,” she said. “What has taken so long is, of course, that it went through the whole court process. That took a very long time.”

Last year, most of the structures on the site were torn down to their concrete pads in anticipation of dealing with contaminated soils, according to the Maine Department of Environmental Protection’s web page for the former Holtrachem cleanup effort. In addition, the railroad tracks that will be used to remove waste from the site were improved.

This year, the focus turns to Southern Cove, which is adjacent to the former chemical plant. Testing of sediments is being done to determine which off-site disposal options would work best.

Over the next three years, two landfills are targeted for removal and caps will be upgraded on the remaining three landfills, according to a map that Mallinckrodt developed to illustrate the contamination removal timeline and the DEP’s website.

Contaminated soils will be removed as well as any remaining contaminated structures. Contaminated groundwater and surface water will be treated.

“There’s going to be ongoing operations and maintenance going on on that property for quite some time,” Ladner said.

Orrington Town Manager Paul White said earlier this month that the town hopes to redevelop the site once the cleanup is completed.

Last year, Mallinckrodt Inc. paid the town of Orrington $175,000 to buy back 63 acres of contaminated land under the chemical factory.

The payment was the final fulfillment of a 2010 deal between Orrington and St. Louis-based Mallinckrodt, which also provided the town $1.5 million for site monitoring and redevelopment.

Yet when any redevelopment can occur remains unclear.

“That I don’t know,” Ladner said when asked when redevelopment of the property can begin.

Environmental covenants on former HoltraChem land in Orrington not considered contaminated, about 170 acres, also must be lifted before the town can move forward, according to White. He said he has asked that those be lifted when practicable.

Ladner said last year that the covenant — which was placed by HoltraChem — means the town and state must collaborate on future redevelopment plans.

“Obviously the town can do some preliminary work on figuring out what it wants to do [with the site,] perhaps laying down roads and different things like that,” she said.

White said that there are no set plans for the former HoltraChem site.

The $1.5 million the town received from Mallinckrodt for redevelopment remains in a reserve account for the time being. The site doesn’t have a formal name.

“We refer to it as the Route 15 Industrial site and the reason I like that is that we want to get away from the stereotype of HoltraChem and the site itself,” he said.

Once the remediation is completed on the part of the property belonging to Mallinckrodt, the town has the right to buy it back for the $175,000 that Mallinckrodt paid for it, White said.

“It’s too early to tell what the town’s going to do. The town fathers will have to decide but that is an option,” he said.

“But finally, we are moving forward. That’s the important thing for the town of Orrington,” he said. “Progress is being made and we can see light at the end of the tunnel.”