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Uncertainty on Maui: How Will Functional Equivalence Work in the Real World?

Uncertainty on Maui: How Will Functional Equivalence Work in the Real World?

Key Points

  • A discharge of pollutants to groundwater may require a permit under the Clean Water Act.
  • The new “functional equivalent of a direct discharge” test will be difficult to apply.
  • It will be a long and arduous process to reach uniformity as agencies, courts, and the regulated community try to figure out how to proceed on a case-by-case basis.

On April 23, 2020, the Supreme Court published its much-awaited opinion in County of Maui v. Hawai’i Wildlife Fund. The Court held that the discharge of pollutants to groundwater may require a permit under the Clean Water Act if the discharge is “the functional equivalent of a direct discharge.” The Court did not define “functional equivalent.” Rather, it offered a list of factors to help regulators, the regulated community, and district courts make that determination.

This means that projects like green infrastructure, recycled water, groundwater recharge, and septic tanks—activities that have not typically required a permit—may now require a Clean Water Act permit. But since the Supreme Court did not provide a bright-line rule to which regulated entities may conform their conduct, the decision also means that regulators, the regulated community, and courts will continue to wrestle with the issue of indirect discharges for years to come.

Many saw County of Maui as an opportunity for the Supreme Court to clarify the Clean Water Act’s scope. Unfortunately, the Supreme Court did not seize the moment.


Almost fifty years ago, Congress enacted the Clean Water Act. At its core, the Act requires a permit when a pollutant is added to a navigable water from a point source. A “point source,” in turn, means a discernible, confined, and discrete conveyance, like a pipe or ditch. The classic example of a regulated point source is a pipe that directly discharges pollutants into a navigable river. In that scenario, the discharges require a National Pollutant Discharge Elimination System, or NPDES, permit.

But what happens when that pipe is upland and several miles from the water? If pollutants from that upland pipe eventually reach the navigable water, does the Clean Water Act require an NPDES permit? These questions were posed to the Supreme Court in the Maui case.

In Maui, the County’s wastewater reclamation facility pumped treated water into the ground through four injection wells. Once discharged, the treated water migrated with groundwater for about a half mile to the Pacific Ocean. Environmental groups filed a citizen suit under the Clean Water Act that claimed the indirect discharges from the County’s injection wells required an NPDES permit.

The “Functional Equivalent” Test

The majority opinion holds that the Clean Water Act “requires a permit when there is a direct discharge from a point source into navigable waters or when there is the functional equivalent of a direct discharge.” Unfortunately, this holding raises more questions than it answers.

What is the “functional equivalent of a direct discharge”? Does it mean an indirect discharge that is equal to or the same as a pipe that directly discharges pollutants to navigable water? Or does it mean something less?

The Supreme Court offered some guidance to determine functional equivalence by identifying seven factors that regulators, the regulated community, and district courts may consider when evaluating an indirect discharge: (1) transit time; (2) distance traveled; (3) the nature of the material through which the pollutant travels; (4) the extent to which the pollutant is diluted or chemically changed as it travels; (5) the amount of pollutant entering the navigable waters relative to the amount of the pollutant that leaves the point source; (6) the manner by or area in which the pollutant enters the navigable waters; and (7) the degree to which the pollution (at that point) has maintained its specific identity.

But this is not an exhaustive list. Instead, the Court announced that it represents “just some of the factors that may prove relevant.” So while the majority considers time and distance the most important of the factors, it acknowledged that other factors may be relevant. With uncertain types of factors, an uncertain number of factors, and uncertainty in how each will be weighed in different contexts, Maui invites multiple approaches to Clean Water Act regulation. Instead of providing clarity and uniformity, Maui prescribes uncertainty.

Uncertainty Abounds

The majority acknowledges that its multi-factor test is not a bright-line rule that easily can be implemented. As a result, the majority concedes that parties must feel their way on a case-by-case basis. This lack of uniformity could prove costly.

For instance, underground septic tanks were once considered generally to fall outside the ambit of the Clean Water Act. But septic tanks are intended to discharge waste to soil, which then migrates downward and may impact groundwater. Septic tank owners—of which there are 26 million in the United States—may now have to face the “functional equivalent” test and determine whether to apply for an NPDES permit.

Indirect discharges also affect myriad other groundwater activities of particular concern in California, including indirect potable reuse projects that typically involve injecting water containing pollutants into groundwater. The “functional equivalent” test may also affect implementation of groundwater storage projects and the Sustainable Groundwater Management Act. And, of course, it affects wastewater treatment facilities—the very facility type at issue in Maui.

Given the reach of the Supreme Court’s opinion, the EPA will likely need to issue general permits and provide guidance for more commonly-affected discharges. But the ongoing Covid-19 pandemic will hinder that effort, and the upcoming presidential election could affect the rulemaking process. Regardless, that guidance will not make up for the hoped-for clarity that the regulated community had placed on the long-awaited Maui decision. Whatever may come, one thing is certain: Maui is not the final word on this issue.

For More Information, Please Contact:

Sean Herman
Sean Herman
San Francisco, CA
Nathan Metcalf
Nathan Metcalf
Walnut Creek, CA
Rosslyn 'Beth' Hummer
Rosslyn "Beth" Hummer
Los Angeles, CA