595 U.S. 15
U.S.2021Background
- The Middle Claiborne Aquifer underlies eight States, including Tennessee and Mississippi, and supplies large-scale municipal pumping (Memphis/MLGW pumps ~120 million gallons/day).
- Mississippi sued Tennessee, Memphis, and MLGW claiming Tennessee’s pumping has “siphoned” groundwater formerly beneath Mississippi, seeking at least $615 million in tort damages and declaratory/injunctive relief.
- Mississippi expressly disclaimed any equitable-apportionment remedy, asserting sovereign ownership of groundwater beneath its surface.
- The Special Master found the aquifer is a single interstate hydrogeological unit, Tennessee’s pumping produces a cone of depression extending into Mississippi, and recommended dismissal of Mississippi’s complaint but with leave to amend to pursue equitable apportionment.
- The Supreme Court reviewed the Special Master’s report, held that equitable apportionment applies to the Middle Claiborne Aquifer, rejected Mississippi’s ownership theory, and dismissed the complaint without granting leave to amend (Mississippi had not sought amendment).
Issues
| Issue | Plaintiff's Argument | Defendant's Argument | Held |
|---|---|---|---|
| Applicability of equitable apportionment to the Middle Claiborne Aquifer | Mississippi: aquifer not subject to equitable apportionment; seeks tort/damages instead | Tennessee: aquifer is an interstate resource and equitable apportionment applies | Court: equitable apportionment applies to this interstate aquifer |
| Whether a State’s asserted sovereign ownership of subsurface water prevents apportionment | Mississippi: claims exclusive ownership of groundwater under its territory, so no apportionment | Tennessee: ownership claim cannot defeat equitable apportionment for shared waters | Court: rejected absolute sovereign-ownership claim; States lack exclusive control over interstate flowing waters |
| Remedy and procedural posture (dismissal; leave to amend) | Mississippi: sought damages and disavowed apportionment; did not request leave to amend | Tennessee: objected to granting leave to amend after dismissal | Court: dismissed the complaint; sustained Tennessee’s objection and did not grant leave to amend because Mississippi never sought it |
Key Cases Cited
- Kansas v. Colorado, 206 U.S. 46 (establishing equitable apportionment for interstate waters)
- Colorado v. New Mexico, 459 U.S. 176 (equitable-apportionment principles and guiding principle of reasonable use)
- Idaho ex rel. Evans v. Oregon, 462 U.S. 1017 (extending apportionment to migratory resources; burden for States)
- Hinderlider v. La Plata River & Cherry Creek Ditch Co., 304 U.S. 92 (States lack exclusive ownership/control of interstate flowing waters)
- Nebraska v. Wyoming, 515 U.S. 1 (groundwater pumping effects on interstate surface waters considered under apportionment)
- South Carolina v. North Carolina, 558 U.S. 256 (equitable apportionment among States)
- Tarrant Regional Water Dist. v. Herrmann, 569 U.S. 614 (interpreting interstate compact language; not a rejection of apportionment principles)