The U.S. Supreme Court recently ruled in favor of environmentalists six to three on a historic case involving the scope of the Clean Water Act. Maui County, Hawaii was sued by environmental groups over federal water quality permits because pollutants from the county’s wastewater treatment plants were seeping into the ocean, devastating local reefs. The county argued that it did not need permits because wastewater was pumped into groundwater wells, which they claimed did not count as being discharged directly into a “navigable water body” – such as oceans, lakes, and rivers – as specified by the Clean Water Act.

Scientists at University of Hawaii, Manoa performed a groundwater tracer study and concluded that 64% of wastewater from the plant was reaching the ocean through groundwater, with an average travel time of 15 months. 

The court’s ruling clarifies that permits are needed for indirect water contamination that is the “functional equivalent” of directly discharging contaminants into surface waters. Opponents claim that the ambiguity of what “functional equivalent” means can put businesses, counties, and homeowners in trouble for not acquiring permits.

On the other hand, the ruling has been considered a win for science. The application of the Clean Water Act to groundwater has been open to interpretation, and regulation often falls under the domain of states. But it’s challenging to draw boundaries between groundwater and surface water since the two systems are hydrologically connected, making it ambiguous where one set of regulations end and the others begin. 

This ruling closes a loophole in the Clean Water Act and broadens its definition of what counts as direct discharge into federal waters, emphasizing this hydrologic connection. Scientific evidence will now be central to future cases, giving federal waters more protection from pollutants.