MEMPHIS, Tenn. — Mississippi residents living near Memphis say that sewage could pollute the ground and water if the Tennessee city pulls out of a decadeslong treatment agreement.

In a newly filed federal lawsuit, the Mississippi sewer district for thousands of customers in the Memphis suburbs says it will have no way of treating their sewage for several years. If Memphis follows through on its plan to quit accepting their wastewater in 2023, it would result in sewage overflowing near the Mississippi-Tennessee line and causing “serious contamination” to soil and water in the area, the lawsuit states.

In 2018, Memphis Mayor Jim Strickland told mayors of the Mississippi cities of Southaven and Horn Lake that Memphis intends to quit providing wastewater treatment services in the fall of 2023. In its lawsuit, the Horn Lake Creek Basin Interceptor Sewer District says that will leave it with “no feasible way” of treating its customers’ wastewater. It calls Memphis’ decision a breach of contract.

“The consequences of the city’s breach are dire,” its lawsuit states. “The process of constructing a new wastewater treatment facility will likely take the District 10 years or more.”

Representatives of the Memphis mayor and city attorney did not immediately respond to requests for comment on Monday. But in court papers, lawyers for Memphis said the city continues to be in compliance with the agreement that began in 1975, and that it expires in 2023. They said city officials warned the sewage district that Memphis intended to end the arrangement in 2023.

The sewage district and the Mississippi suburbs have refused to accept that Memphis is able to end the agreement, city officials said in their court papers.

Both sides interpret the agreement differently, and are at odds over whether Memphis can legally quit treating sewage from the suburban areas.

It is of “paramount importance” that Memphis use its sewer system and treatment facilities for existing residents and to accommodate future growth, Memphis Director of Public Works Director Robert Knecht wrote in a letter to the suburban sewer district in 2018. The city “must remain in a position to attract and support the expansion of major industrial development within Memphis,” he said. The decision not to renew the contract is about putting “Memphis first,” Knecht told The Commercial Appeal in 2018.