GARDINER — Excavators at work along Cobbosseecontee Stream on either side of Bridge Street are cleaning up decades of industrial pollution in conjunction with the state bridge replacement project that’s now underway.

A Maine Department of Environmental Protection employee, left, inspects rocks cleaned Tuesday by contractors on Arcade Street in Gardiner. The DEP is overseeing the cleanup of pollutants uncovered as part of the Maine Department of Transportation’s replacement of two bridges spanning Cobbosseecontee Stream in Gardiner. Kennebec Journal photo by Andy Molloy

Work under the supervision of the Maine Department of Environmental Protection to clear contaminants on the work sites started last week and is expected to continue for a couple weeks more, but it’s not expected to affect the timeline of the bridge replacement project.

“They have been moving some of the large rocks and granite blocks to clean,” said Molly King, DEP senior environmental hydrogeologist. “They were scrubbing them with solution and spraying them down.”

For the last several years, city and state transportation officials have been meeting over the details of a $12 million project, the replacement of both the Bridge Street and Maine Avenue bridges that cross Cobbosseecontee Stream, which runs along the north edge of the city’s downtown area.

Both of the bridges have reached the end of their useful life and are scheduled to be replaced. In addition, a pedestrian bridge next to the Maine Avenue bridge is expected to be installed.

As a part of that project, some environmental cleanup work had been expected.

Tony LaPlante, director of public works in Gardiner, said city officials have been aware of the contaminants for several years.

Gardiner city officials were able to secure both state and federal grants to assess sites with suspected contaminants, and to clean up the Summer Street site of the former T.W. Dick Co., which the city had acquired for redevelopment.

The stream has been the focus of planning efforts in Gardiner for years. The Cobbossee Corridor, the section of the stream from the New Mills Dam to the Kennebec River, was identified in Cobbossee Corridor Master Plan, which city officials adopted in 2005. It envisioned commercial, residential and mixed-use development and recreational options.

Two specific projects — building a trail along the stream and redeveloping the Summer Street area — were identified as long-range goals in a 1999 downtown revitalization plan the city also had adopted.

The replacement of the Bridge Street and Maine Avenue bridges also will affect the corridor. Over the last several years, as transportation and city officials worked out details of what the bridges would look like and how two intersections, where Water Street crosses Bridge Street and Brunswick Avenue, and where Water Street crosses Church Street and Maine Avenue, would be changed to accommodate traffic through downtown Gardiner.

The project also will incorporate construction of the Cobbossee Trail, which includes the new pedestrian bridge.

“We found (contamination) first a couple of years ago doing some brownfields assessment stuff, and we did some more along the bridge,” LaPlante said. “Then the DEP came in and did some more tests for us to see what the extent was, and they are cleaning it up for us.”

For more than two centuries, the stream corridor has been home to a range of industries, which have left their mark.

A boom deployed by the Department of Environmental Protection collects fluids leaking from Arcade Street on Tuesday in Gardiner. The DEP is overseeing the cleanup of pollutants uncovered as part of the Maine Department of Transportation’s construction project to replace two bridges spanning Cobbossee Stream in Gardiner. Kennebec Journal photo by Andy Molloy

“This is not a surprise,” said David Madore, DEP’s director of communications. “Maine has located a lot of industries along rivers and streams, so this is not unusual.”

Testing has shown that the contaminants are petroleum products, probably from businesses that have long since closed, Madore said.

The DOT provides site assessments of its projects to the DEP for review if there is any inkling of contamination, King said, as part of a longstanding agreement between the two departments.

“We saw there was potential for some petroleum contamination here,” she said. “I said, ‘Can we jump on board?’ They were doing some earthwork there, but not as much as we are doing.”

Over the course of the remediation, work is expected to take place in the roadway starting under the Bridge Street bridge and working out in both directions.

Containment and absorbent booms have been deployed in the stream to keep pollutants contained. There is a skimmer in the excavation hole to collect the petroleum products that are floating on the water in the hole and store in a tank on site.

“It’s an internally drained excavation,” she said. “Nothing has gotten into the stream.”

“Those are all the protocols we follow to make sure (the petroleum product) is as contained as we possibly can make it and removing it as quickly as we can,” Madore said.

The contaminated soil has been tested to identify the nature of the contamination, and it’s being taken to the landfill in Norridgewock. It’s not clear yet how much contamination will be found. The screening and testing will continue for the duration of the project.

Some of the boulders will be returned to the site and some are likely to be turned into asphalt once they’re cleaned to the satisfaction of the DEP, King said.

Paul Merrill, public information officer for Department of Transportation, said the $220,000 project cost will be split between the two departments; and if the costs exceed that, the Department of Environmental Protection is expected to pick up the tab for the additional cost.

“This work is not delaying the project at all,” Merrill said. “The end date is late 2020.”

“It worked out. It’s good for the community and it worked out for the DEP,” LaPlante said. “It’s nice when there’s a win-win.”