In April 2020, the United States Supreme Court issued its final ruling Cty. of Maui v. Hawaii Wildlife Fund, 590 U.S. – (2020), concluding that the discharge of pollutants into groundwater was a violation of the Clean Water Act (“CWA”). This landmark decision represents the first time that the Supreme Court has found a discharge of pollutants into groundwater to be a violation of the CWA as the statute has historically been interpreted to apply only to surface water. However, instead of establishing a bright line test to help determine when a discharge into groundwater would violate the CWA, the Court put forth a series of factors that courts and federal regulators could use when analyzing individual groundwater discharges. Now, almost four years later, courts and federal agencies continue to wrestle with how best to apply the Cty. of Maui ruling. In November 2023, the Environmental Protection Agency (“EPA”) released a new draft guidance document detailing how regulators should approach the Supreme Court’s decision. Between the new guidance, and some federal court decisions interpreting the Cty. of Maui ruling, it is becoming clearer when a groundwater discharge may be regulated under the CWA.


The CWA is the primary federal statute regulating water pollution in the United States. Broadly, the CWA prohibits “the discharge of any pollutant by any person” unless permitted by the Act. 33 U.S.C. § 1311(a). The CWA goes on to define the “discharge of a pollutant” as “any addition of any pollutant to navigable waters from any point source[.]” 33 U.S.C. § 1362(12). In turn, a “point source” is defined as “any discernible, confined and discrete conveyance” such as a pipe, ditch, well, concentrated animal feeding operation, or other conduit. 33 U.S.C. § 1362(12). “Navigable waters” is defined as “waters of the United States,” and refers to the waters that fall under the jurisdiction of the CWA. 33 U.S.C. § 1362(7). Put simply, the CWA prohibits the introduction of pollutants into protected waters from a discernible source without a permit.

Crucially, while there has been persistent debate as to which waters should be included in the term “waters of the United States,” at no point in the CWA’s history have groundwaters been included in the Act’s jurisdiction. This means that an action that would otherwise violate the CWA if it occurred in surface waters would be unlikely to violate the CWA if it occurred in groundwater. For example, if an industrial facility discharged pollutants from a pipe directly into a nearby river without an appropriate permit, that action would likely be a CWA violation. However, if the facility instead made unpermitted discharges into a pipe that fed directly into groundwater, that action would not be a CWA violation. While the relationship between groundwater and surface water was not well understood when the CWA was adopted in 1972, fifty years later it is commonly accepted that surface water and groundwater regularly interact as part of the same hydrologic system. The increased understanding of how surface water and groundwater interrelate has prompted questions as to whether any groundwater discharges should be regulated under the CWA.

In a landmark ruling, the Supreme Court indicated that at least some discharges of pollutants into groundwater should be subject to CWA regulation. The dispute in Cty. of Maui centered around discharges of wastewater from a facility operated by the County of Maui. The wastewater was discharged through four injection wells directly into groundwater. From there, the wastewater traveled roughly half a mile through the groundwater system before entering the Pacific Ocean. The environmental groups that filed a lawsuit against the County of Maui argued that the discharges violated the CWA because they resulted in pollutants reaching a navigable water, the Pacific Ocean. Ultimately, the Supreme Court agreed, concluding that the County of Maui’s groundwater discharges were the “functional equivalent of a direct discharge.” For more information on that decision, click here.

While the Supreme Court in Cty. of Maui was clear that the discharges at issue in the case were in violation of the CWA, it declined to provide a specific test to determine when other discharges would be considered the “functional equivalent of a direct discharge.” Instead, the Court provided a list of seven factors that lower courts and regulating agencies should consider when determining whether a particular discharge met the “functional equivalent” standard. Those factors include transit time, distance traveled, nature of the nonpoint source material, extent to which the pollutant becomes diluted, and the amount of pollutant to reach a navigable water. Of those factors, the Court clarified that time and distance would usually be the most important. However, other than that clarification, the Court declined to provide further guidance on how to interpret and apply those factors. Instead, the Court noted that further guidance could be provided by EPA.

EPA Guidance

EPA issued its first guidance for how to apply the Cty. of Maui factors in 2021. However, that guidance was rescinded shortly afterwards. More information on that initial guidance is available here. In late 2023, EPA issued a draft of its latest guidance document for Cty. of Maui. The draft focuses on the seven factors identified by the Supreme Court, and how federal regulators and permit applicants should treat those factors when applying for CWA permits.

The guidance document breaks down what EPA has termed the “overall approach” to determining whether a discharge into groundwater is the functional equivalent of a direct discharge. EPA’s overall approach consists of four principles that the agency recommends for helping to inform a functional equivalent analysis. The first principle holds that a functional equivalent analysis is “highly dependent on site-specific features.” EPA notes that the Supreme Court identified seven different factors for determining whether a groundwater discharge is functionally equivalent to a direct discharge, and while time and distance are the most important factors, all seven may be considered. The second principle finds that other factors beyond those identified in Cty. of Maui, may be relevant. While the seven factors identified by the Supreme Court are illustrative of what the Court would find informative when making a functional discharge analysis, the Cty. of Maui opinion stated that other factors may prove relevant. The third principle states that a functional equivalent analysis does not need to be complex. EPA notes that in some circumstances, a functional equivalent may be so clear that further consideration is not required. The final principle provides that if a groundwater discharge consists of more than one recognized pollutant, one indicator pollutant from the discharge may be used to help determine how the pollutant combination travels through groundwater.

After setting out those four principles, the guidance document moves on to discuss the factors that may be considered during a functional discharge analysis. EPA notes that while the Cty. of Maui decision did not establish any “bright lines” for evaluating when time and distance is sufficient to make a functional equivalent finding, the Supreme Court did provide some limits to help inform analysis. In Cty. of Maui, the Court found that the groundwater discharges were functional equivalents of direct discharges because the pollutants traveled only half a mile and reached the Pacific Ocean in a matter of days. However, in speculating on what discharges would not pass the functional equivalent analysis, the Court expressed doubt that Congress intended the CWA to regulate “a 100-year migration of pollutants through 250 miles of groundwater to a river.” EPA finds that these limitations should be kept in mind when making a functional equivalent analysis.

With regard to other factors that may be relevant, EPA highlights “the nature of the material through which the pollutant travels,” “the amount of pollutant entering the navigable water relative to the amount of the pollutant that leaves the point source,” and “the extent to which the pollutant is diluted or chemically changed as it travels” for consideration. EPA notes some circumstances when each of these factors may carry greater weight. For example, a discharge made through a highly porous material that allows pollutants to travel further or faster may weigh in favor of a functional discharge finding. Similarly, a functional discharge finding may be supported by the finding that a relatively high concentration of pollutants have reached a water of the United States, even if the discharge traveled several miles through groundwater.

A thirty-day period of public comment on the draft guidance closed December 27, 2023. EPA has not indicated when a final guidance document will be released.

What Courts Have Said

While EPA works on finalizing its Cty. of Maui guidance, federal courts have also been tasked with applying and interpreting the opinion. In the nearly four years since Cty. of Maui was issued, a handful of federal courts have considered the issue. So far, courts appear hesitant to make a functional equivalent finding without ample evidence showing that the Cty. of Maui factors had been met.

In Black Warrior River-Keeper, Inc. v. Drummond Co., 579 F.Supp.3d 1310 (N.D. Ala. Jan. 12, 2022), the evidence was sufficient for the court to find that groundwater discharges made by the defendant were functionally equivalent to direct discharges. In this case, the discharges in question originated from “an enormous waste pile” located on an abandoned mine site owned and operated by the defendant. According to the plaintiffs, the pollutants discharged from the waste pile seeped into groundwater and eventually entered the Locust Fork of the Black Warrior River, a body of water protected by the CWA. The plaintiffs claimed that these groundwater discharges were the functional equivalent of direct discharges because the polluted groundwater flowed 10 to 100 feet to reach the Locust Fork, took approximately 1.5 to 14 days to make the journey, passed through porous material, and testing showed that the pollutants transported by the groundwater maintained their identity after reaching the Locust Fork. In response, the defendants argued that the groundwater system beneath the mine site was relatively small in volume and weak in flow compared to the surface water in the Locust Fork. Ultimately, the court sided with the plaintiffs, finding that the time and distance factors, along with porous sediment and evidence showing that pollutant levels were just as high at the discharge site as they were in the Locust Fork weighed in favor of a functional equivalent finding. Additionally, the court noted that the volume and flow of the groundwater system was not relevant to reaching its conclusion.

While the court in Black Warrior River-Keeper, Inc. v. Drummond Co. reached a functional equivalent finding, the court in Conservation Law Found., Inc. v. Town of Barnstable, 615 F.Supp.3d 14 (D. Mass. July 20, 2022) reached the opposite conclusion. In that case, the plaintiffs alleged that the defendant’s discharges of nitrogen-laden wastewater into groundwater were the functional equivalent of a direct discharge. According to the plaintiffs, the wastewater traveled at a rate of one foot per day, taking roughly 21 years to reach surface waters in the Lewis Bay Watershed System approximately 1.5 miles away. Here, the court determined that the time and distance factors weighed against a functional equivalent finding. In reaching this conclusion, the court noted that the Cty. of Maui decision stressed that groundwater traveling many miles over a period of years would weigh against a functional equivalent finding. In Conservation Law Found., Inc. v. Town of Barnstable, the court determined that the discharges at issue in this case which took 21 years to travel 1.5 miles were “precisely the kind of discharge that the Supreme Court sought to exclude from being considered the ‘functional equivalent’ of a direct discharge.” Therefore, the court declined to find that the defendant had violated the CWA.

Finally, in a ruling from this year, the Tenth Circuit Court of Appeals became one of the first federal appellate courts to apply the Cty. of Maui factors. In Stone v. High Mountain Mining Co., LLC, No. 22-1340 (10th Cir. 2024), the court was asked to review discharges of wastewater made from four unlined settling ponds located on a gold mine owned and operated by the defendant. The plaintiffs argued that the discharges of contaminated wastewater from the settling ponds into groundwater were the functional equivalent of direct discharges because the settling ponds were located less than 100 feet away from Middle Fork of the South Platte River and wastewater discharged from the settling ponds took approximately two days to reach the river. While the Tenth Circuit agreed with the plaintiffs that the time and distance at issue would typically weigh in favor of a functional equivalent finding, it found that evaluation of the other Cty. of Maui factors weighed against such a finding. The court noted that water sampling showed that levels of river pollutants taken from locations both above and below the discharge point were essentially the same. Additionally, the court found that no evidence was presented showing how diluted the contaminated groundwater became as it traveled from the discharge site to the South Platte River. Without more evidence showing that significant amounts of wastewater were actually reaching the South Platte River, the court declined to find that the defendant’s groundwater discharges were the functional equivalent of direct discharges.

Going Forward

In the time since the Supreme Court issued Cty. of Maui, both regulators and the regulated have grappled with how to appropriately apply the functional equivalent analysis. While the upcoming guidance from EPA will hopefully offer some clarity, recent court decisions have also helped shed light on how the judiciary is approaching the issue. So far, it appears that functional equivalent rulings are highly fact specific. What may weigh heavily in making a functional equivalent finding in one case could weigh against making such a finding in another. While time and distance will generally be the most important factors, those factors alone may not be enough to reach a functional equivalent finding in every scenario. Increased guidance from EPA and the courts will likely be needed to help individuals regulated by the CWA determine whether their groundwater discharges are impact by the Cty. Of Maui decision.


To view EPA’s new draft guidance, click here.

To read the decision in Cty. of Maui, click here.

To read the text of the CWA, click here.

For more National Agricultural Law Center resources on the CWA, click here.