BELFAST, Maine — A company that wants to raise Atlantic salmon in huge tanks in Belfast is inching closer to that reality — but its opponents are not backing down.

The Maine Board of Environmental Protection has issued draft permits to Nordic Aquafarms Inc., saying its pollutant, wastewater discharge and air emissions plans comply with federal guidelines.

The Belfast Planning Board, which has spent more than a year reviewing Nordic’s lengthy permit application, also has advanced it for a final vote.

“We’re happy,” Marianne Naess, Nordic Aquafarms’ commercial director, said Friday, noting that regulators did a thorough assessment.

Nordic’s plan to build a $500-million indoor fish farm on the southern edge of Belfast has been controversial since it was proposed two and a half years ago, and critics have opposed just about every facet of the plan. The question of who owns the mudflat where the company wants to lay intake and outflow pipes, which has slowed the project, ultimately will be decided by a judge.

Upstream Watch, an environmental nonprofit that’s been critical of Nordic Aquafarms, slammed the integrity of the data submitted to regulators. It filed a memorandum to the Maine Board of Environmental Protection, claiming that Nordic’s air emissions are likely to exceed the allowable limits because its modeling did not consider the company’s fish hatchery, fish rearing tanks, slaughterhouse, fish packaging and storage area, cement plant, heating and ventilation and more.

“Any one of those sources is likely to push total air emissions over the maximum limits of the Clean Air Act,” Upstream Watch said.

That federal law required the Environmental Protection Agency to set national air quality standards for common pollutants in order to protect public health and welfare.

In its draft permit, environmental regulators said staff conducted air quality impact modeling for the project because of significant public concerns. Typically, a project of this scale would not even require modeling because any emissions would be minor.

Regulators concluded in December 2019 that Nordic’s operations would not be expected to exceed limits on six pollutants set by the Environmental Protection Organization under the authority of the Clean Air Act.

During a public hearing this February, regulators noted inconsistencies between modeling parameters and testimony from Nordic’s witnesses. So the Maine Board of Environmental Protection directed a second round of modeling using the updated inputs and parameters. The additional testing also concluded Nordic would not exceed federal air emissions standards for pollutants including sulfur dioxide, particulate matter and nitrogen dioxide.

Nevertheless, Maine regulators need more information to accurately evaluate the project, according to Upstream Watch, which said regulators should especially scrutinize air quality emissions because the farm will be built on an “unsuitable site.”

The project will be located in Belfast’s Route 1 south business park district, but abuts a residential neighborhood with a public conservation trail where some could be sensitive to air quality, according to Upstream.

Despite those fears, Naess said she is confident that Nordic will not exceed the threshold for pollution and will remain in compliance with state and federal rules.

“We have minor air emissions,” she said. “I think what they don’t get is that if you exceed the limits of the permit, you have to reduce your levels. It’s actually fairly simple.”