Recently, in a 6-3 decision in County of Maui v. Hawaii Wildlife Fund (Maui), the United States Supreme Court held that a discharge of pollution to groundwater may be regulated under the Clean Water Act (CWA).  The Supreme Court’s review arose from a case involving a wastewater treatment and reclamation facility in Hawaii that injects through disposal wells 4 million gallons per day of partially-treated waste water hundreds of feet deep into groundwater. The wells are located roughly half a mile from the Pacific Ocean, and dye tracer studies revealed the injected wastewater reached the ocean within 84 days. The facility had not obtained a National Pollution Discharge Elimination System (NPDES) permit under the CWA for its operation of the injection wells

The Court’s Opinion in Maui does not provide CWA protection for groundwater itself.  Surface waters, including territorial seas, navigable rivers, and lakes and their tributaries, and some wetlands remain the only waters generally subject to CWA jurisdiction.  However, the Court recognized that where a point source discharges to groundwater that has a hydrologic connection to a jurisdictional surface water, the groundwater can serve as a conduit between an identifiable point source discharge and the surface water.  Thus, the question presented to the Court was whether a NPDES permit is required “when pollutants originate from a point source but are conveyed in navigable waters through a nonpoint source,” here “groundwater.”  The Court held that a point source discharge of pollutants that travels through groundwater to surface water may require a NPDES permit “when there is the functional equivalent of a direct discharge” to a navigable surface water.  In the same vein, it reasoned that “[w]hether pollutants that arrive at navigable waters after traveling through groundwater are ‘from’ a point source depends upon how similar to (or different from) the particular discharge is to a direct discharge.”

In making its decision, the Court vacated and remanded a Ninth Circuit ruling that a NPDES permit is required when “pollutants are fairly traceable from the point source to a navigable water” because using a “fairly traceable” standard was too broad and could lead to permitting for discharges of pollutants that reach a surface water through groundwater, but only after traveling hundreds of miles over a century or more.  In contrast, the Court also determined that US EPA’s 2019 Interpretive Statement, which categorically excluded any discharges to groundwater from NPDES permitting, was too narrow.  The Court favored a middle ground, multi-factor approach requiring lower courts to take into consideration the particular factual nuances of a discharge. In doing so, the Court freely admitted its approach does not “clearly explain how to deal with middle instances.” However, it reasoned “there are too many potentially relevant factors applicable to factually different cases” for it to use more specific language than “functional equivalent” in its Opinion.  Under this standard, many site-specific factors will have to be taken into account by the lower courts in determining in a particular case whether a discharge to groundwater was the “functional equivalent” of a direct discharge to surface water.

The Court noted, “[t]ime and distance will be the most important factors in most cases, but not necessarily every case.”  It also provided a non-exhaustive list of additional factors that could be considered, including, (1) the nature of the material through which the pollutant travels, (2) the extent to which the pollutant is diluted or chemically changed as it travels, (3) the amount of pollutant entering the navigable waters relative to the amount of the pollutant that leaves the point source, (4) the manner by or area in which the pollutant enters the navigable waters, and (5) the degree to which the pollution (at that point) has maintained its specific identity.

It is no surprise that the Court did not develop a bright line rule for this highly fact intensive issue.  The Maui multi-factor approach will require a large number of lower court opinions before the application of the Maui “functionally equivalent” standard can be predicted with any certainty. This issue has the potential to affect a wide variety of sectors, and future attention should be paid to the lower court rulings as well as efforts by the States to regulate groundwater in the context of direct hydrologic connection with surface water.