The U.S. Navy, Northrop Grumman Corp. and other defendants being sued for groundwater pollution that forced the closing of some Levittown water wells have asked a federal judge to dismiss the litigation.

The Town of Hempstead, which provides public water, on June 30 filed the multimillion-dollar lawsuit in U.S. District Court in Central Islip, claiming that toxic chemicals it discovered in three wells in July 2013 were released into the groundwater by current and former businesses that operated near the town-run Levittown water district.

Northrop Grumman, in its written application of Dec. 2, asked U.S. District Court Judge Joseph F. Bianco to dismiss the lawsuit on several grounds — including that Hempstead had three years to sue for cleanup and related costs from the time it discovered the contamination, and that window of time has closed.

The aerospace and defense company said its contractor hired to test the groundwater notified Hempstead on July 12, 2012, that its water well at Wantagh Avenue and Entry Lane contained the chemical Freon and volatile organic chemicals, a year before the town said it first became aware of the contamination.

Northrop Grumman also said Hempstead knew that the other two wells, both on Bowling Lane, between Bellows and Tanners lanes, were polluted on Feb. 7, 2013, five months before the town said it first became aware of the contamination.

Mike Deery, a spokesman for Hempstead, declined to address the litigation. “The town is confident in its position in this matter,” Deery said.

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Hempstead is seeking at least $50 million to pay for cleanup and related costs that the town said it has incurred and will incur in future years.

The lawsuit focuses on sites in Bethpage, Hicksville and Levittown where contamination was released and mixed together, flowing into the drinking water supply area for Levittown. That water district serves 50,000 residents.

Some of the contamination at issue stems from a more than 600-acre parcel in Bethpage, where the Navy and what is now Northrop Grumman manufactured, tested and developed airplanes and space equipment from the 1940s until 1998. A complex series of underground plumes is part of several cleanup plans under supervision by the state Department of Environmental Conservation.

One cleanup agreement, Northrop Grumman and the Navy contend, required Hempstead to first discuss a treatment solution with them and come to an agreement on the funding.

“Instead, the Town unilaterally designed a ‘packed tower aeration system’ to treat the water and began construction of that system,” according to court documents.

Afterward, on April 24, 2015, the Navy said Hempstead sent a letter announcing its decision and asking the Navy to compensate the town for the cost of designing, constructing and operating the treatment system.

In response, the Navy asked Hempstead for various data so the Navy could evaluate the town’s claim for funding for the treatment systems for the three wells.

“The Town ignored these requests,” said the Navy.