The developer of the Echelon Seaport luxury residential complex in Boston's Seaport District and the Massachusetts Department of Revenue have each made their case for a pretrial win in a long-running dispute over a tax credit for an environmental cleanup.

The developer, Boston Seaport M1&2 Land LLC, and the state filed dueling motions for judgment on the pleadings Monday ahead of a Nov. 19 hearing before a Suffolk County Superior Court judge.

Boston Seaport said it spent more than $30 million to clean up the site, which once served as a waterfront industrial district and had significant contamination. That, it said, entitles it to a 50% tax credit, or about $15 million.

But state officials said the developer is trying to get the state to include costs that were related to construction of two underground garages, "far deeper than any contaminates that needed cleaning up." A consultant hired by the state said the work should have cost no more than $9 million, and the state has offered a $4.5 million credit.

Boston Seaport, in turn, said the law does not give the state authority to substitute the judgment of its consultant for that of the one who designed and oversaw the original cleanup.

The developer sued the DOR in January, alleging that the agency had been dragging its feet for more than four years on its application for the brownfields tax credit.

The brownfields program allows a property owner or developer to recoup, via a tax credit, up to half the cost of permanently remediating a contaminated site. That incentive is intended to help address a number of environmental concerns that otherwise might fall to the government to fix.

Under the state's environmental regulations, most site cleanups are required to be designed and managed by a licensed site professional.

The area where the complex was built, former tidal flats that were filled in during the mid-19th century and then used for rail freight terminals, warehouses and industrial plants, was later acquired by the Massachusetts Bay Transportation Authority for construction of a dedicated busway.

The contamination was found during construction of that busway, known as the Silver Line, in the 1990s.

The plaintiffs purchased unused portions of the site in 2015.

Boston Seaport M1&2 said the agency's staff initially denied the entire application based solely on its own opinion and by relying on inapplicable regulations. It sought reconsideration.

Despite providing records from Haley & Aldrich, the licensed site professional it had hired to oversee the cleanup, along with a tax credit consultant and attorneys explaining the Brownfields Act, the developer said the DOR again proposed denying the entire credit.

Boston Seaport M1&2 said the DOR is now attempting to rely on "objectively erroneous" conclusions by its own consultant, Verdantas LLC, a licensed site professional the agency said it hired to help it in evaluating the appeal.

Verdantas concluded last fall that far less soil would need to have been removed to clean up the site, at a cost of $5.7 million, plus another $3.3 million in other allowable costs. That led the DOR to offer the $4.5 million tax credit in July.

The state said in its cross-motion for judgment that it is entitled to deference as to its interpretation of the brownfields law.

The Massachusetts DOR declined to comment Thursday. Messages seeking comment from counsel for the developer did not immediately receive responses Thursday.

Boston Seaport M1&2 Land LLC is represented by Bruce E. Falby, Charles Baker, Michael R. Walsh and George Lilov of DLA Piper LLP.

The Commissioner of Revenue is represented by Meredith Fierro of the Office of the Attorney General of the Commonwealth of Massachusetts.

The case is Boston Seaport M1&2 Land LLC v. Commissioner of Revenue, case number 2584CV00039, in the Suffolk County Superior Court of the Commonwealth of Massachusetts.