The US Clean Water Act was first passed in 1972 and regulates discharges of pollutants into the “waters of the United States.” For decades this federal legislation has been interpreted to apply to surface waters only and has not included groundwater. This week a Supreme Court ruling changed that and gave new emphasis to groundwater science in efforts to protect the nation’s waterbodies from pollution.

On April 23 the Supreme Court ruled that groundwater that flows into nearby lakes, streams, and bays should be included under Clean Water Act protections. This means that pollution entering groundwater that is hydrologically connected to surface water can be regulated just like pollution that directly enters surface water.

Under the Clean Water Act, “point sources” of pollution, such as effluent pipes that dump potentially polluted water directly to surface waters, must be regulated and operate only on the basis of a permit. Historically, those who dumped potentially polluted water into groundwater were not subject to the same scrutiny. With this week’s Supreme Court ruling, however, groundwater pollution is now subject to the same federal protections if the groundwater is connected to surface waters in a way that makes it “functionally equivalent” to direct discharge, such as from an effluent pipe.

The Supreme Court decision stemmed from a case in Hawaii, where a sewage treatment plant was dumping 15 million gallons a day of treated wastewater into underground wells adjacent to coastal beaches. Intensive scientific study of pollution in the adjacent ocean showed that the treated wastewater was in fact a source of water quality degradation and algal blooms because the groundwater receiving the wastewater was hydrologically connected to the ocean. In this way, dumping treated wastewater into the underground wells was “functionally equivalent” to discharging it into surface water (the ocean). Thus, the court ruled scenarios such as this should be subject to Clean Water Act regulations.

The new ruling will place a new emphasis on groundwater and its potential contribution to surface waters and surface water pollution. The ruling expands our list of potential factors that should be considered for regulation under the Clean Water Act.

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