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In a 6-3 decision penned by Justice Breyer, the United States Supreme Court held on April 23 that discharges of pollutants to groundwater that reach surface water may require a Section 402 permit under the Clean Water Act. The decision in County of Maui v. Hawaii Wildlife Fund (No. 18-260) resolved a split of the circuit courts and established  a new “functional equivalent” test to determine when a permit is required. However, the Court explicitly left defining “functional equivalent” to the lower courts on a case-by-case basis, and to EPA through administrative guidance.

Clean Water Act Permitting Scheme

Section 402 of the Clean Water Act permits are required for the discharge of any pollutant into navigable waters from a point source. “Point source” is defined as “any discernible, confined and discrete conveyance… from which pollutants are or may be discharged.”  The most common point sources are pipes and drainage ditches. “Discharge of a pollutant” is defined as “any additional of any pollutant to navigable waters [including navigable streams, rivers, the ocean, or coastal waters] from any point source.” (Emphasis added). The question before the Supreme Court was:  is a Section 402 permit required if a pollutant that is discharged from a point source travels to navigable waters through groundwater?

Summary of the Case

County of Maui involved a wastewater reclamation facility that discharged treated wastewater into groundwater injection wells. The pollutants travelled about half a mile from the injection wells (a point source) through groundwater to the ocean. The Ninth Circuit held that a Section 402 permit was required here because the pollutants were “fairly traceable” to the facility even though they were not directly discharged into the ocean. Other circuits had reached different conclusions about the reach of Section 402, and the Supreme Court agreed to resolve the split between circuits when it granted cert on February 19, 2019.

On April 23, 2020, the Supreme Court vacated the Ninth Circuit’s opinion and remanded the case for further proceedings based on the new functional equivalent test. The Supreme Court explained that the Ninth Circuit’s fairly traceable test would lead to broad and undefined permitting authority, including an example where it could take 100 years for pollutants to migrate through 250 miles of groundwater to get to a river. The Supreme Court also rejected the County of Maui’s, EPA’s and the Solicitor General’s argument that no permit was required if a pollutant had to travel through any amount of groundwater before reaching navigable waters. Rejecting this bright-line position, the Supreme Court held that Congress did not intend to allow dischargers to evade permitting under the Clean Water Act if they simply moved a pipe back a few feet from the navigable water so that it could travel through groundwater first. The Supreme Court gave no Chevron deference to the EPA’s interpretation, which it characterized as a “massive,” “serious” and “unreasonable” loophole in the statutory scheme.

Functional Equivalent Test

The focus of the majority’s analysis was on the plain meaning of the words “from” and “to” in the Clean Water Act and held that the origin and the destination are the most important factors, not what happens in between. In one of many illustrative analogies, the majority opinion explained “[i]f Timmy is told to ‘add water to the bath from the well’ he will know just what it means – even though he will have to use a bucket to complete the task.”  A Section 402 (or NPDES) permit is now required “when there is a direct discharge from a point source into navigable waters or when there is the functional equivalent of a direct discharge.” (Emphasis in original). The Supreme Court found what it called a middle ground in the functional equivalent test but recognized that their decision does not “clearly explain how to deal with middle instances.”  Instead, the majority opinion describes “functional equivalent” as meaning “roughly similar to” and stresses that transit time and distance travelled are the most important factors to determine what is functionally equivalent. Other factors that could be considered are:

  • Nature of the material through which the pollutant travels;
  • Extent to which the pollutant is diluted or chemically changed as it travels;
  • Amount of pollutant entering the navigable waters relative to the amount of the pollutant that leaves the point source;
  • Manner by or area in which the pollutant enters the navigable waters;
  • Degree to which the pollution (at that point) has maintained its specific identity.

The Supreme Court noted permits are likely not required “if the pipe ends 50 miles from navigable waters and the pipe emits pollutants that travel with groundwater, mix with several other materials, and end up in navigable waters only many years later.”  By contrast, permits are likely required if the pipe ends a few yards from the beach. But it will be up to EPA and the lower courts, relying on hydrogeological expert reports, to make factual determinations in middle ground cases.


In California, the Supreme Court’s decision does little to alleviate the concerns expressed by water and sanitation agencies, cities and counties in an amicus brief they filed about broad categories of discharges of pollutants to groundwater (such as unintentional leaks from conveyance systems and intentional groundwater recharge pumping) that could be subject to Clean Water Act liability under the “fairly traceable” test. The functional equivalent test may cover fewer discharges, but the fact-intensive inquiry the new functional equivalent test will require creates considerable uncertainty. While many of these discharges would have already been otherwise regulated under state law, the application of Section 402 of the Clean Water Act imposes not only a greater regulatory burden, but also opens the door to federal lawsuits under the Clean Water Act’s citizen suit provisions.

Stakeholders must now look to EPA and to California’s State Water Resources Control Board (SWRCB) to clarify this extension of the reach of Section 402. For example, SWRCB may adopt a statewide approach for discharges to groundwater requiring NPDES permits under the Court’s ruling. This would be similar to how SWRCB has addressed other broad categorical discharges. SWRCB has previously issued Statewide General NPDES Permits for Natural Gas Utility Construction Operations and Maintenance Activities (for activities including hydrostatic pressure testing of pipelines and site dewatering) and for Drinking Water System Discharges (for intentional and unintentional discharges of drinking water to surface waters). A similar approach would streamline future permitting for discharges that could fall under this ruling. But in the meantime, dischargers to groundwater in California face the risk that their ongoing operations could subject them to Clean Water Act liability.