Some discharges of pollutants from point sources to groundwater will require an NPDES permit.
On April 23, 2020, the U.S. Supreme Court held in a 6-3 decision that a discharge of a pollutant from a point source to groundwater that ultimately reaches navigable waters may fall under the permit requirements of the Clean Water Act.
Under the court's decision, the NPDES requirements apply when the discharge of a pollutant from a point source into groundwater that reaches a navigable water is the "functional equivalent" of discharging that pollutant from a point source directly into navigable waters.
An NPDES permit is required for the addition of a pollutant from any point source into navigable waters. 33 U.S.C. §§ 1311(a), 1362(12)(A), 1342.
County of Maui
The court's decision addressed a wastewater reclamation facility operated by the County of Maui, in the State of Hawaii, that pumps partially treated wastewater into underground wells. The partially treated wastewater travels a half mile through groundwater to the Pacific Ocean.
In determining that the County of Maui's wastewater facility discharge constitutes a discharge for which an NPDES permit is required, the court specified examples of discharges that would and would not trigger the permitting requirements. A pollutant discharged from a pipe located a few feet from a navigable water that travels a short distance through groundwater to navigable waters would be subject to NPDES permitting requirements. On the other hand, a pollutant discharged from a pipe ending many miles from navigable waters that travels through groundwater for "many years" before reaching the navigable water likely would not require an NPDES permit.
In addition to the factors of time and distance, the court enumerated other aspects of point source pollutant travel through groundwater that are relevant in determining whether the ultimate discharge to navigable waters is subject to the CWA.
These include:
the type of material the pollutant travels through;
whether, and how much, the pollutant is diluted or changed by travel;
how much of the pollutant reaches and enters the navigable water, compared to the amount of the pollutant that leaves the point source;
where and through what means the pollutant enters a navigable water; and
what is retained of the pollutant's identity at the time it reaches the navigable water.
The court further stated that the CWA language underlying the NPDES permitting requirements and future EPA administrative guidance are among the tools that regulated parties may rely on to determine whether a discharge constitutes the "functional equivalent of a direct discharge."
The full decision, Maui v. Hawaii Wildlife Fund et. al., case 18-260, is available here.