BRUNSWICK — The neighborhood group that fought construction of an Amtrak maintenance and layover facility in West Brunswick will not challenge the facility’s stormwater permit in Superior Court.

The decision means construction of the estimated $12.7 million terminal, which proponents say is needed to provide more efficient and possibly expanded passenger rail service in Maine, can proceed. Construction has been underway since fall, and is expected to continue through September, according to the Amtrak Downeaster website.

The Brunswick West Neighborhood Coalition last July appealed to the Board of Environmental Protection to block the permit issued to the Northern New England Passenger Rail Authority by the Department of Environmental Protection. The panel is the department’s citizen oversight board.

But the board unanimously upheld the permit for the project on Nov. 19, 2015.

The complainants had 30 days to file an appeal of that decision with the state Attorney General’s Office. BEP spokeswoman Cynthia Bertocci confirmed Monday that no appeal had been filed.

“So ends a multiyear struggle to obtain the final permit necessary for the facility,” Wayne Davis, chairman of the rail advocacy group TrainRiders/Northeast, said in a news release.

“Although many in the Brunswick area supported the authority’s proposed location for the facility,” he said, “a group of neighbors who had purchased property next to what has historically been a rail yard … objected, claiming that the facility should be located elsewhere.”

The fact that there has been no further appeal is “good news,” Davis said in a phone interview Monday.

In an interview Wednesday, Brunswick West Neighborhood Coalition spokesman Charles Wallace said the group ran out of money to continue the appeal process.

“That whole nasty affair was fought with taxpayer dollars,” he said, referring to the fact that the Northern New England Passenger Rail Authority, which operates the Downeaster, is a public transportation authority.

“You can’t continue to fight an unlimited source of your own money,” Wallace said.

He maintained that despite the end of the appeal process, he still believes the permitting process was fundamentally flawed because a state agency, the DEP, was regulating another quasi-public body.

“It was a very seriously botched public process, and it’s always going to be a botched public process when you have people who meet … behind the scenes,” Wallace said.

The result is “putting cancer-causing diesel (emissions) in the middle of a residential neighborhood,” he said.

The World Health Organization classifies diesel engine exhaust as carcinogenic to humans, although the levels of exposure associated with cancer risk have not been determined.

The Brunswick facility’s steel structure and framework were erected on the site as of Dec. 16, 2015, a photo gallery on the Northern New England Passenger Rail Authority’s website shows.

The construction has received a positive reaction from others in town.

“We’re behind the world in terms of transportation,” Councilor Kathy Wilson said in an interview on Wednesday. “Public transportation is the only answer.”