Mississippi v. Tennessee

Background

Mississippi sued Tennessee, the City of Memphis, and the municipal utility MLGW, saying Memphis’s pumping took groundwater that once lay under Mississippi. The Middle Claiborne Aquifer lies under eight States, including Mississippi and Tennessee. Memphis pumps about 120 million gallons per day through more than 160 wells; those wells are drilled straight down and do not cross the state line. Mississippi sought at least $615 million in damages and asked for declaratory and injunctive relief while disavowing the fair-sharing remedy known as equitable apportionment. The Court appointed a Special Master, who recommended dismissing Mississippi’s complaint but allowing it to amend.

Reasoning

The key question was whether an interstate aquifer can be treated like other shared water resources and divided by the Court under equitable apportionment—a legal process to fairly allocate water use among States. The Court concluded the aquifer is a single, multistate hydrogeological unit; water naturally flows between the States; and Memphis’s pumping produced a cone of depression extending into Mississippi. The Court rejected Mississippi’s claim that it owned all groundwater beneath its lands and held that equitable apportionment applies to the Middle Claiborne Aquifer. Because Mississippi had not sought equitable apportionment, the Court dismissed its tort-based complaint and declined to grant leave to amend.

Real world impact

Mississippi cannot pursue the current tort damages claim as pleaded and will need to resort to an equitable apportionment action to seek an allocation or past relief. Any future fair-sharing case would require broader evidence, might involve other States that rely on the aquifer, and would determine how groundwater is allocated going forward.