Last Thursday, the U.S. Supreme Court held that the Clean Water Act (“CWA”) requires a permit to discharge pollutants that reach “navigable waters” through groundwater, but only if the discharge is the “functional equivalent of a direct discharge” to the navigable water.1 In reaching this decision, the Court took the middle ground. It rejected both the Ninth Circuit’s interpretation that the CWA requires a source to obtain a permit whenever pollutants found in a navigable water are “fairly traceable” to that source, and arguments by Environmental Protection Agency (“EPA”) and others that a permit is never required for discharges of pollutants that reach a navigable water through groundwater.

The CWA prohibits “any addition of any pollutant to navigable waters from any point source” without a permit. For discharges of pollutants in wastewater or stormwater, the relevant permit is a National Pollutant Discharge Elimination System (“NPDES”) permit from EPA or a delegated state agency. The CWA defines a “point source” as “any discernible, confined and discrete conveyance . . . from which pollutants are or may be discharged,” including but not limited to any “pipe, ditch, . . . [or] well.” Thus, any addition of pollutants from any of these point sources to navigable waters requires a permit. Because the CWA defines “navigable waters” only as “waters of the United States,” much controversy surrounds what waters constitute waters of the United States. There is general agreement, however, that waters of the United States do not include groundwater. Accordingly, a discharge of pollutants from a point source to groundwater does not itself require an NPDES permit. But the lower federal courts have for many years reached different and inconsistent decisions regarding whether a permit is required if the groundwater containing the discharged pollutants flows into a surface water that is a water of the United States.

By declining to adopt one of the opposing “bright line” interpretations of the permit requirement advanced by the Ninth Circuit and the EPA, the Court attempted to reach a result that would be more faithful to what it understood to be the CWA’s dual objectives of protecting navigable waters while leaving the protection of groundwater to the states. The decision, however, will necessitate case-by-case evaluations of the permit requirement, which in many instances will involve difficult questions of fact and policy. The Court acknowledged these difficulties and offered several factors to consider when determining whether a discharge to groundwater requires a permit. These factors will help dischargers evaluate the risk that a permit is required, but, except at the extremes, they offer little certainty. Much more litigation is sure to follow, as will lobbying of EPA and Congress—whatever the results of the next election—to clarify or revise the results of the Court’s decision.

The Court identified the following non-exclusive factors to consider when determining functional equivalency and whether a permit is required:

  • Factors identified by the Court as “most important”:
    • The time required for the pollutants to reach waters of the United States after they are discharged.
    • The distance traveled by the pollutants to reach waters of the United States.
  • Other factors:
    • The “nature of the material through which the pollutant travels.”
    • The “the extent to which the pollutant is diluted or chemically changed as it travels.”
    • The “amount of pollutant entering [waters of the United States] 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.”
    • The “degree to which the pollution (at that point) has maintained its specific identity.”



1 County of Maui, Hawaii v. Hawaii Wildlife Fund, Docket No. 18-260 (Apr. 23, 2020), available here.