BRUNSWICK, Maine — A day after Gov. Paul LePage wrote to the Federal Rail Administration requesting a “significant and thorough review” of the location of a proposed train layover facility in Brunswick, the organization planning to construct the controversial building defended the process by which that site was selected.

The Northern New England Passenger Rail Authority, which operates the Downeaster service for Amtrak, plans to build a $12 million train layover facility on tracks between Church Road and Stanwood Street in Brunswick.

The 60,000-square-foot building would allow trains to idle during the day and power down overnight instead of returning to Portland late at night only to arrive early the next day to pick up more southbound passengers, rail authority executive director Patricia Quinn has said. The building also is designed to reduce noise and pollution by allowing trains to power down during the day.

In the past, rail authority officials have said the facility would make it possible to add trips to and from Brunswick, enhancing the value and cost-effectiveness of the passenger rail service that returned to Brunswick in 2012.

However, since the site for the facility first was proposed, neighbors have vigorously opposed it. They have cited noise pollution and other negative environmental effects as well as diminished property values and quality of life in fighting the proposal.

In a letter to Joseph Szabo, administrator of the Federal Railroad Administration, LePage echoed those concerns, which have been most aggressively voiced by the Brunswick West Neighborhood Coalition, an organization formed to oppose the proposed location.

LePage questioned whether rail officials had done appropriate “due diligence” to gauge potential threats the facility could pose to the health of residents who live nearby. He also said an alternative site previously proposed for the facility, across town in east Brunswick, would better stimulate economic growth at the former Brunswick Naval Air Station.

In response, Quinn on Tuesday said her organization has conducted a transparent process and collaborated with the community as much as possible.

“I think we’ve acted in accordance with the requirements and I think we tried to go above and beyond, to have public meetings and engage in discussions with the neighborhood group,” she said. “We listened carefully to their concerns and incorporated a lot of their concerns into the proposed design facility.”

In fact, Quinn said, changes to the proposed facility since the environmental assessment was conducted were made in order to address and mitigate those concerns, including shifting the site 20 feet to allow a tree buffer on one side and eliminating a track to allow “switching” inside the building.

The governor also called for “thoroughly vett[ing]” the determination that as a federal railroad project, the proposed facility is exempt from the Maine Department of Environmental Protection Site Law process and local zoning regulations.

The Federal Railroad Administration is reviewing an initial environmental assessment that determined the proposed project would not hurt the neighborhood, and will determine whether a full environmental impact study will be required.

According to the Northern New England Passenger Rail Authority, construction cannot begin until the federal agency determines that the project complies with the National Environmental Policy Act.

With three members of the BWNC on the advisory committee for the environmental assessment, their voice has been heard, said Jeff Reynolds, a supporter of the project who lives not far from the tracks.

“I don’t know what more they could want,” he said.

Reynolds said the BWNC is “the poster child for NIMBY [Not in My Backyard]” and said their request for a new environmental study was a delaying tactic designed to eventually end the project altogether.

But Sen. Stan Gerzofsky, D-Brunswick, on Tuesday objected to what he called “NNEPRA’s continued arrogance at trying to site something where it’s not wanted.”

Gerzofsky said he also wrote to the FRA urging more transparency “so we don’t have an environmental mistake happen because we didn’t ask questions. … This is the single most important event happening in Brunswick that could negatively impact our environment. NNEPRA is a creation of the state and it’s taxpayer funded. They should take into consideration what the taxpayers want.”

Gerzofsky supports an alternative location in east Brunswick near the former Navy base.

That site would benefit companies at the former Brunswick Naval Air Station, as well as all companies in the area, from L.L. Bean to Bath Iron Works, that transport significant freight, according to Steve Levesque, executive director of the Midcoast Regional Redevelopment Authority, which is redeveloping the former base.

However, Quinn said NNEPRA looked at that site several years ago and concluded that the currently proposed site was preferable for several reasons, “mostly in support of the [Downeaster] service, but also [because of] cost and impact.”

Asked Tuesday whether LePage’s letter would affect whether the FRA requires an additional environmental impact statement, FRA spokesman Kevin Thompson replied by email, “The Federal Railroad Administration takes our responsibility under the National Environmental Policy Act very seriously and we will consider the concerns Gov. LePage has pointed out seriously as well.”