The 2020 Supreme Court case County of Maui v. Hawaii Wildlife Fund considered whether pollutant point discharges to groundwater that flows to surface waters of the United States (WOTUS) require a permit under the CWA. In a 6-3 ruling, the Court held that a permit is required if the discharge could be considered the “functional equivalent” of a direct discharge to a WOTUS.

The Lahaina Wastewater Reclamation Facility treats domestic wastewater for the County of Maui in Hawaii. Reclaimed (partially treated) wastewater is injected into a series of injection wells at a rate of 3 to 5 million gallons per day. Because Maui’s geology is naturally highly permeable, more than 60 percent of this injected wastewater eventually ends up in the coastal waters around Maui. The treated wastewater contains high levels of nutrients and has caused significant environmental damage to local coral reefs and beaches through algal blooms and contamination by fecal bacteria.

The Supreme Court rejected as too broad the Ninth Circuit’s “fairly traceable” standard and as too narrow the County of Maui’s bright line rule limiting the jurisdiction of the CWA for any pollutants entering groundwater. Instead, the Court set forth a test for determining when a discharge into groundwater was functionally equivalent to a direct discharge into a WOTUS and thus required a permit. The Court enumerated a nonexhaustive list of seven relevant factors, including:

1. transit time that it takes for the pollutant to reach the navigable waters
2. distance traveled by the pollutant
3. nature of the material through which the pollutant travels
4. extent to which the pollutant is diluted or chemically changed as it travels
5. amount of pollutant entering the navigable waters relative to the amount that leaves the point source
6. manner by or area in which the pollutant enters the navigable waters
7. degree to which the pollutant has maintained its specific identity as it moved from the point source to the navigable waters

More information on County of Maui v. Hawaii Wildlife Fund and the science of groundwater can be found here.