ORRINGTON, Maine — Nearly 60 rail cars, each carrying approximately 98 tons of mercury-contaminated soil, were hauled away from Orrington in December as part of the multimillion-dollar environmental cleanup at the former HoltraChem Manufacturing Co. site.

The contaminated dirt dug up on the banks of the Penobscot River was destined for Republic Services’ hazardous waste disposal facility in Niagara Falls, New York, according to the most recent monthly progress report on the cleanup submitted to the Maine Department of Environmental Protection.

“The [consent] order requires the bulk of it to go by rail as much as possible but there is some that has gone by truck,” Stacy Ladner, an environmental specialist for the Department of Environmental Protection, said in a recent interview.

Ladner said last week it’s not clear how much soil will need to be excavated and disposed of at the Republic facility and at Stablex Canada Inc. in Blainville, Quebec.

“They’re actually in the process of trying to define the extent of the contamination,” Ladner said. “It’s open ended at this point, and it’s primarily because each area seems to be wider and more in area than what was originally expected.”

That doesn’t necessarily mean there is more mercury onsite than anticipated, Ladner said, just that it spread farther than expected.

“The plan is proceeding the way it’s expected to proceed. The contamination is the same kind of concentrations that we were expecting, it’s just that the areas are wider. The testing indicates that they need to go out farther around the areas to get the contamination.”

Ladner said uncontaminated waste, including demolition debris from the removal of buildings at the site, was sent earlier to Juniper Ridge Landfill in Old Town.

HoltraChem, which operated from 1967-1982, 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.

Work on the second phase of the cleanup, which is under way, began in June.

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 9 tons of the metal still are 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 said in June 2015 he would appoint a panel to recommend cost-effective ways to rid the waterway of mercury.

In September, U.S. District Court Judge John Woodcock issued a ruling ordering that an engineering firm be hired to develop a plan to clean up mercury deposited in the Penobscot River.

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 land cleanup began in 2014 and is expected to wrap up in 2018 or early 2019, according to Ladner.

In 2014, 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 being used to remove waste from the site were improved. Pan Am Railway is transporting the contaminated soil.

Last summer, the focus turned to Southern Cove, which is adjacent to the former chemical plant. Testing of sediments is being done to determine what off-site disposal options would work best.

By the time all is said and done, two on-site landfills will be removed and caps will be upgraded on the remaining three landfills, according to a map that Mallinckrodt developed to illustrate the contamination removal timeline.

“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 that the town hopes to redevelop the site once the cleanup is completed.

In 2014, Mallinckrodt 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.

But when redevelopment can occur remains unclear.

Environmental covenants on former HoltraChem land in Orrington not considered contaminated, about 170 acres, 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 covenants, which were placed by HoltraChem, means the town and state must collaborate on future redevelopment plans.

White said recently there are no set plans for the former HoltraChem site. He said the funds the town received from Mallinckrodt for redevelopment remain in a reserve account for the time being.

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.