Mississippi v. Tennessee is not only the Supreme Court’s first oral argument of the 2021-22 term, but it is also the first time that states have asked the court to weigh in on how they should share an interstate aquifer. The court’s decision could fundamentally restructure interstate groundwater law in the United States for decades — or the case could be dismissed immediately on the grounds that Mississippi has failed to allege the proper cause of action.
The case will be argued on Monday, and it will be the court’s first in-person argument in a year and a half. In March 2020, the justices stopped meeting in person due to the coronavirus pandemic, and since then, all arguments have been conducted by phone. But the justices are returning to the bench for the start of their new term (though the courtroom will remain mostly empty aside from attorneys, members of the press, and the justices themselves).
Like most original jurisdiction water cases, Mississippi v. Tennessee has taken a few years to wend its way to Supreme Court oral argument, and that argument will be keyed to the parties’ objections to the report of a court-appointed special master. Mississippi first came to the court in 2014. Its complaint alleged that Tennessee is stealing Mississippi’s groundwater by allowing the Memphis Light, Gas & Water Division to pump large amounts of groundwater from the Memphis Sand Aquifer that straddles the Mississippi-Tennessee border, pulling Mississippi’s groundwater across the border and to the surface for use in Memphis. Mississippi has asked the Supreme Court to enter a declaratory judgment “establishing Mississippi’s sovereign right, title and exclusive interest in the groundwater stored naturally in the Sparta Sand formation” of the aquifer, which lies entirely under Mississippi and would not, according to Mississippi, ever flow into Tennessee absent the pumping in Memphis. Mississippi is also seeking over $600 million in damages.
Mississippi’s request for a declaration of groundwater ownership is simultaneously an argument that the “equitable apportionment” rules that the Supreme Court has used for over a century to resolve interstate surface water disputes do not apply to groundwater — or, at least, do not apply to this groundwater. Equitable apportionment cases started with Kansas v. Colorado, in which Kansas argued that upstream Colorado was taking too much of the Arkansas River. The doctrine of equitable apportionment is founded upon the equality of rights of all states, as well as the importance of fresh water to the sovereignty of each. As refined in its later jurisprudence, the court emphasizes four principles when engaged in an equitable apportionment analysis. First, as co-equal sovereigns, the states sharing a waterbody have co-equal rights to make reasonable use of that waterbody, but not to use the water inefficiently or wastefully. Second, the court seeks to equitably apportion the water based on the realities of the conflict in front of it, “without quibbling about formulas.” Third, as the court emphasized again earlier this year, the complaining state — almost always the downstream state — has a higher burden of proof than normal to show injury sufficient to induce the court to intervene. Finally, if the complaining state meets that burden, the court will consider all relevant factors (such as physical and climate conditions, the “consumptive use” of the water, the availability of storage water, among many others) in apportioning the waterbody.
The key legal issue in Mississippi v. Tennessee, therefore, is whether the equitable apportionment doctrine (automatically) applies to groundwater resources. Notably, the Supreme Court has already made it clear that the equitable apportionment doctrine is not limited to surface water. In 1983, for example, it upheld the special master in Idaho ex rel. Evans v. Oregon in using equitable apportionment law to decide a dispute among Idaho, Oregon, and Washington over salmon in the Columbia River/Snake River system. However, the logic of that case cuts both ways for Mississippi v. Tennessee. For example, the court emphasized that “[t]he doctrine of equitable apportionment is neither dependent on nor bound by existing legal rights to the resource being apportioned” and that “although existing legal entitlements are important factors in formulating an equitable decree, such legal rights must give way in some circumstances to broader equitable considerations.” These statements suggest that Mississippi cannot avoid the equitable apportionment doctrine simply because it asserts a state law ownership claim to the groundwater beneath its territory. At the same time, however, the Idaho v. Oregon court also emphasized the flow of resources among states as the main reason that the equitable apportionment doctrine was applicable to salmon:
Although that doctrine has its roots in water rights litigation, … the natural resource of anadromous fish is sufficiently similar to make equitable apportionment an appropriate mechanism for resolving allocative disputes. The anadromous fish at issue travel through several States during their lifetime. Much as in a water dispute, a State that overfishes a run downstream deprives an upstream State of the fish it otherwise would receive. A dispute over the water flowing through the Columbia-Snake River system would be resolved by the equitable apportionment doctrine; we see no reason to accord different treatment to a controversy over a similar natural resource of that system.
Importantly, from the beginning of Mississippi v. Tennessee, Mississippi has sought to distinguish the equitable apportionment line of cases on precisely this flow logic, arguing that “[e]quitable apportionment principles have only been applied by this Court to those disputes in which two or more states possessed a claim to water available within each state under natural conditions such as rivers and other surface waters, and the watersheds supplying them.” Mississippi advances instead a territorial property rights theory, claiming that it owns all the groundwater that would have remained under Mississippi under natural conditions.
Of course, like rivers, groundwater aquifers often flow naturally across state lines. That reality gives rise to the key factual issue in Mississippi v. Tennessee, which will become relevant only if Mississippi wins the legal one: Would groundwater in the Sparta Sand portion of the Memphis Sound Aquifer ever reach Tennessee absent groundwater pumping? This issue led to an interim battle among the parties to exclude various expert witnesses regarding the aquifer’s hydrogeology and a five-day evidentiary hearing before Special Master Eugene Siler in May 2019.
The two defendants (Tennessee and Memphis Light, Gas, & Water) argued that Mississippi has failed to plead a legally available cause of action. Notably, both sets of amici — the United States and three water law professors — agreed with the defendants.
So did Siler in the report he filed with the court in fall 2020. As he summarized, “Mississippi’s claims are simple: Tennessee has, by pumping in Shelby County, Tennessee, taken groundwater that would have remained in Mississippi for centuries. … Mississippi thinks Tennessee has stolen and continues to steal its water. Easy enough.” With respect to the hydrogeology battles, Siler concluded that the aquifer is indeed a resource that flows between the two states. Thus, he recommended three findings to the Supreme Court: (1) that the relevant resource in dispute is the groundwater in the Middle Claiborne Aquifer; (2) that that groundwater is an interstate resource; and (3) that the equitable apportionment doctrine applies. He also recommended that the court dismiss Mississippi’s complaint with leave to amend.
As might be expected, in briefing to the court, Mississippi has taken exception to almost everything in the special master’s report. In contrast, the only exception Tennessee raised was against the recommendation that the court should give Mississippi leave to amend its complaint. Notably, Siler’s factual finding that the aquifer is a flow resource gives the court the opportunity to conclude that equitable apportionment applies in this case without categorically deciding whether that doctrine applies to all groundwater. However, eight states subject to interstate water sharing, led by Colorado, filed an amicus brief with the court to resist what they see as Mississippi’s attempt to upend interstate water law, which might sway a majority of justices to announce a broader conclusion.
The Supreme Court granted the motion of the acting solicitor general of the United States to participate in the 65-minute oral argument on Monday. Mississippi will have 30 minutes to argue, the two defendants 20 minutes, and the solicitor general 15 minutes. In addition to the return to in-person arguments, Monday will also be the debut of a slightly modified argument format that will give each justice designated time at the end of an advocate’s presentation to ask final questions.