This Report summarizes an opinion issued on November 22, 2021 (Part I).

Cases Granted Review: Mississippi v. Tennessee, 143 Original

Mississippi v. Tennessee, 143 Original. The Court unanimously held that Mississippi’s objection to Tennessee’s pumping of groundwater from the Middle Claiborne Aquifer is subject to the remedy of equitable apportionment. The Middle Claiborne Aquifer underlies portions of eight states, including Mississippi and Tennessee. The City of Memphis, through its public utility, the Memphis Light, Gas & Water Division (MLGW), pumps about 120 million gallons of groundwater from the Middle Claiborne Aquifer each day. Although some of the wells MLGW uses are located just a few miles from the Mississippi-Tennessee border, none of the wells crosses the physical border between the states. A small amount of water naturally flows from the part of the aquifer beneath Mississippi to the part beneath Tennessee. But “Mississippi contends that MLGW’s pumping has substantially hastened this existing flow, allowing Memphis to take billions of gallons of groundwater that would otherwise have remained under Mississippi for thousands of years.” In 2014, Mississippi filed a bill of complaint against Tennessee, Memphis, and MLGW seeking to institute an original action in the Court based on MLGW’s pumping water from the aquifer. Mississippi disclaimed equitable apportionment, which traditionally has been the “exclusive remedy for interstate water disputes, unless a statute, compact, or prior apportionment controls.” Mississippi contended that equitable apportionment is premised on “each of the opposing States ha[ving] an equality of right to use the waters at issue”―but, Mississippi argued, it had “an absolute ‘ownership’ right to all groundwater beneath its surface.” Mississippi thus asserted that Tennessee’s pumping amounted to a tortious taking of property, and sought $615 million in damages. The Court appointed a Special Master, who recommended that equitable apportionment is the appropriate remedy, and that the Court grant Mississippi leave to amend its complaint to seek that remedy. In an opinion by Chief Justice Roberts, the Court agreed with the Special Master that equitable apportionment is the appropriate remedy, but declined to grant Mississippi leave to amend its complaint.

The Court found that whether equitable apportionment applies to interstate aquifers is an issue of first impression. The Court “resist[ed] general propositions” on that issue and instead focused its “analysis on whether equitable apportionment of the Middle Claiborne Aquifer would be ‘sufficiently similar’ to past applications of the doctrine to warrant the same treatment.” The Court concluded that it would. First, observed the Court, the “Middle Claiborne Aquifer’s ‘multistate character’ seems beyond dispute.” Second, “the Middle Claiborne Aquifer contains water that flows naturally between the States.” And third, “it is clear that actions in Tennessee ‘reach[] through the agency of natural laws’ to affect the portion of the aquifer that underlies Mississippi. . . . Such interstate effects are a hallmark of our equitable apportionment cases.”

The Court rejected Mississippi’s contention that “it has sovereign ownership of all groundwater beneath its surface, so equitable apportionment ought not apply.” The Court explained that it “ha[s] ‘consistently denied’ the proposition that a State may exercise exclusive ownership or control of interstate ‘waters flowing within her boundaries,’” and saw no reason why the Middle Claiborne Aquifer should be treated any differently. Indeed, noted the Court, “Mississippi’s ownership approach would allow an upstream State to completely cut off flow to a downstream one, a result contrary to our equitable apportionment jurisprudence.” Mississippi relied on Tarrant Regional Water Dist. v. Herrmann, 569 U.S. 614 (2013), but the Court distinguished that case as interpreting an interstate compact and as involving a state physically entering another state to take water. The Court closed by declining to decide whether Mississippi should be granted leave to file an amended complaint seeking equitable apportionment. The Court reasoned that Mississippi has never sought such relief and might not do so given the specific rules governing equitable apportionment cases.

[Editor’s note: Some of the language in the background section of the summary above was taken from the petition for writ of certiorari and brief in opposition.]