The Supreme Court ruled on April 23, 2020 that wastewater treatment operations and other dischargers of pollution cannot avoid permitting requirements under the CWA based on the new "functional equivalent" test. In County of Maui v. Hawaii Wildlife Fund, SCOTUS found that the discharge of polluted water into the ground which reaches a nearby jurisdictional water still requires the discharger to comply with the CWA. But the Court rejected the broader standard embedded in the decision of the Ninth Circuit Court that permits are required when pollutants are "fairly traceable," and sent the case back to the Ninth Circuit Court for further proceedings consistent with its decision.

Under the "functional equivalent" test several factors can be considered, such as: transit time, distance traveled, the nature of the material through which the pollutant travels, the extent to which the pollutant is diluted or changed, the amount of the pollutant entering the navigable waters relative to the amount of the pollutant that leaves the point source, the manner by or area in which the pollutant enters the navigable waters, etc. Time and distance are the most important factors.

The Maui decision will have immediate impacts on similar cases now pending in other US Circuit Courts. EPA is expected to craft implementation guidance documents based on the Maui decision.