U.S. Supreme Court Splits the Difference: Clean Water Act Permits Are Required for Some, But Not All, Discharges to Groundwater

Legal Alert

The U.S. Supreme Court held on Thursday 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 the lower court’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. But it also rejected 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.

By declining to adopt one of the opposing “bright line” interpretations of the permit requirement, 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, which are described below, 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 Issue

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, with the Federal Register publishing just this week EPA’s new and soon-to-be-litigated definition.2 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.

The Case

The case before the Court involved Maui County’s sewage treatment plant, which daily pumps up to several million gallons of treated wastewater into the ground through four wells. The wastewater then flows through groundwater about a half mile to the Pacific Ocean, which is a water of the United States. The treatment plant did not have an NPDES permit for the discharge, and several environmental advocacy organizations brought a CWA citizen suit against the County for discharging without a permit. The lower courts rejected arguments that a permit was not required because the discharge was to groundwater rather than directly to a water of the United States, with the Ninth Circuit Court of Appeals holding that a permit is required whenever pollutants in a water of the United States are “fairly traceable” to a point source. In this instance, because the pollutants discharged from the sewage treatment plant could be found in the ocean, and thus were “fairly traceable” to the plant, the Ninth Circuit held that a permit was required.

The Supreme Court’s Decision

The Supreme Court held that the Ninth Circuit’s “fairly traceable” interpretation was too broad because it would allow CWA regulation of discharges to groundwater, which is not protected by the CWA, based on the most tenuous of effects on surface waters. On the other hand, the Court rejected, as inconsistent with the text and purpose of the CWA, arguments by the County, EPA, and others that a point source discharge of pollutants that reaches a water of the United States through any amount of groundwater is, for that reason, excluded from the permit requirement. The Court held that the interpretation that best captures the text and purpose of the CWA is that a permit is required whenever a point source discharge to groundwater is the “functional equivalent of a direct discharge” to a water of the United States. According to the Court, this interpretation both protects waters of the United States as Congress intended without interfering with the states’ authority over the protection of land and groundwater.

As the Court acknowledged, its decision does not provide a bright line for determining whether a permit is needed. Additional guidance will need to be developed by EPA and the courts through the litigation of future cases. The Court did identify, however, the following non-exclusive factors to consider when determining functional equivalency:

  • 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.”

The Court vacated and remanded the Ninth Circuit’s decision so that the lower courts could reevaluate whether Maui County’s treatment plant requires a permit in light of the Court’s opinion.


The Court’s decision will certainly reduce the number of facilities that would have been required to obtain a permit under the Ninth Circuit’s decision. But to what degree remains to be seen, as NPDES permitting agencies and federal courts begin to grapple with applying the “functional equivalency” test. In the meantime, facilities that discharge pollutants onto or into the ground such that the pollutants might reach waters of the United States through groundwater or otherwise will need to evaluate the circumstances of their discharge in light of the factors identified by the Court to determine whether a permit is needed. Moreover, because of the possibility of citizen suit enforcement of the permit requirement, it is important to keep in mind that a determination by EPA or a delegated state NPDES permitting agency that a permit is not required, although certainly helpful, will not necessarily provide a safe harbor for dischargers.


1 County of Maui, Hawaii v. Hawaii Wildlife Fund, Docket No. 18-260 (Apr. 23, 2020).
2 85 Fed. Reg. 22,250 (Apr. 21, 2020).

Related Professionals

Related Practices & Industries


Media Contact

Jamie Moss (newsPRos)
Media Relations
w. 201.493.1027 c. 201.788.0142

Mac Borkgren
Senior Manager, Marketing Communications & Operations

Jump to Page
Stay Informed Arrow

Subscribe to Our Updates