Supreme Court Decision Finds Some Discharge to Groundwater Require Clean Water Act Permits

May 8, 2020

In a recent U.S. Supreme Court opinion in the Cty. of Maui v. Hawai’i Wildlife Fund (Maui) case, the Court expanded the U.S. Environmental Protection Agency’s (EPA) reading of its authority to regulate discharges to groundwater and created a new “functional equivalent” test that now leaves contractors confused about whether their stormwater storage ponds, basins and underground storage will require discharge permitting.

In the Maui case, the Court weighed the decision of whether discharges to groundwater that make their way to a waters of the United States require Clean Water Act National Pollutant Discharge Elimination System (NPDES) permits.  In its decision, the Supreme Court rejected the lower court’s “fairly traceable” test and remanded the case back to the Ninth Circuit to apply the new “functional equivalent” test.

The functional equivalent test will help decide whether a permit is needed and weighs several factors, but not all factors may be applicable in each circumstance.  According to the Court: “Many factors may be relevant to determining whether a particular discharge is the functional equivalent of one directly into navigable waters. Time and distance will be the most important factors in most cases, but other relevant factors may include, e.g., the nature of the material through which the pollutant travels and the extent to which the pollutant is diluted or chemically changed as it travels.”  The Court expects subsequent case law and U.S. EPA guidance to provide additional clarity on how to apply the test.

Pending the Supreme Court decision, U.S. EPA released an interpretive statement to try to provide clarity and regulatory certainty.  U.S. EPA’s statement concluded that “releases of pollutants to groundwater are categorically excluded from Clean Water Act’s permitting requirements…” because they are addressed by other statutes and programs.  The Court did not defer to U.S. EPA’s interpretive statement – and the majority rejected the agency’s position.  AGC expects U.S. EPA to release updated administrative guidance and additional information on its related Web page for discharges to groundwater.  At this time, there is no formal timeline for these actions to occur.

For more information, contact Melinda Tomaino at

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