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Julie Morelli
Julie Morelli
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From Ground to Ocean: Impacts of the Maui Decision on NPDES Permitting

The U.S. Supreme Court (SCOTUS) decision in County of Maui, Hawaii v. Hawaii Wildlife Fund (Maui Decision) marked a significant moment in environmental regulation, specifically impacting the Clean Water Act’s (CWA) National Pollutant Discharge Elimination System (NPDES) permitting program.

The 2020 case centered on a wastewater treatment plant operated by the County of Maui, Hawaii, which legally discharged treated pollutants into permitted underground injection wells. The wastewater was found to have traveled through groundwater and eventually reached the Pacific Ocean—a “Waters of the United States” (WOTUS) as defined by the CWA. The question before SCOTUS was whether these discharges through groundwater required an NPDES permit, despite not directly entering surface waters. This ruling clarifies how discharges through groundwater could be subject to NPDES permitting requirements.

NPDES Background

The NPDES program—established under Section 402 of the CWA—regulates the discharge of pollutants into WOTUS by issuing permits. Although the WOTUS definition has been frequently litigated and modified, the primary goal of NPDES is to prevent pollutants from entering surface water. As a result, NPDES permit applications focus on surface water quality (stream-specific) and technology-based (clean-up based) effluent limits (TBELs) that protect the designated beneficial uses of surface water, like recreation, fishing, agricultural or industrial uses.

State regulatory agencies monitor surface water quality, comparing actual conditions to the standards that support designated beneficial uses. If a surface water fails to meet these standards, it is classified as “impaired.” The state must then implement additional measures to protect, restore and maintain water quality.

The manufacturing and industrial sectors are familiar with NPDES permit limits, as they are required to apply for general permits that typically include TBELs based on achievable industry median values. Similarly, individual permits feature both TBELs and site-specific water quality-based effluent limits tailored to a receiving water. As a result, water quality professionals evaluate the necessary limits for each discharge location, map the discharge route and apply treatments to mitigate pollutants, and ensure receiving waters are protected.

Functional Equivalent Standard

What happens when pollutants from regulated stormwater or wastewater infiltrate the subsurface? Existing permitting frameworks rarely

address the fate and transport of these pollutants, which can move through a subsurface and reappear in a WOTUS.

In its decision, SCOTUS established the “functional equivalent” standard to determine when a groundwater discharge requires an NPDES permit. Under this standard, a permit is required if pollutants flow through groundwater and re-appear in surface water mostly unaltered (functionally equivalent of a direct discharge). For example, if a facility discharges chemicals into the ground and those same chemicals appear in a surface water, the groundwater discharge would be subject to NPDES permit limits to protect the surface water.

SCOTUS outlined the following factors to consider when deciding if a discharge is functionally equivalent to a direct discharge.

  1. Transit time (how long it takes for a pollutant to travel from insertion to discharge)
  2. Distance traveled
  3. Nature of the material through which the pollutant travels
  4. Extend of dilution or chemical change of the pollutant as it travels
  5. Volume of pollutant entering navigable waters relative to what leaves the source
  6. Manner by which pollutant enters navigable waters (i.e., spring flow, surface water, etc.)
  7. Degree to which pollution maintains its specific identity.

SCOTUS further clarified that intent does not matter. A permitted and compliant injection well does not limit the need to protect surface water quality from unintentional discharges. Compliance with groundwater protection standards is not a defense against a functionally equivalent determination. Whether a discharge to groundwater is permitted or not, and whether it was intended to transmit pollutants to surface water via groundwater or not, the NPDES rules still apply.

Underground Challenges

The pathways of underground water flow are largely unknown and more challenging to quantify than surface water routes. To understand these pathways, we need to ask: How fast is the water moving? Is the speed constant? What twists and turns does it encounter? How does the subsurface alter the effluent? What sources might dilute the flow? What other effluents might commingle underground? Where does the underground flow return to the surface? Can we identify the pollutant load from others in the drainage area? These and many other technical challenges lie ahead in making a functionally equivalent determination.

Chevron Doctrine

In June, SCOTUS overturned the longstanding precedent established in 1984 by the Chevron U.S.A., Inc. v. Natural Resources Defense Council, Inc. case, which required federal courts to defer to government agencies’ interpretations of laws or statutes. This change presents a significant challenge in determining water quality protection measures, especially given the many variables of making a functionally equivalent determination and the lack of quantifiable data on subsurface conditions. When contested in a legal setting, permittees will rely on the courts to interpret the law and the applicability of regulations.

Future Implications on NPDES Permitting

Because the Maui decision expands the regulatory guidelines for NPDES permitting, several significant implications include:

  • Broadened scope of NPDES permitting: The concept of functional equivalence may now include more facilities discharging pollutants through groundwater, which were previously not considered under the NPDES program
  • Site-specific analysis requirement: The Maui Decision emphasizes the need for detailed, site-specific analyses to determine functional equivalence, requiring assessments of each facility’s unique conditions
  • Increased compliance and enforcement: Operators who fail to seek NPDES permit coverage for functionally equivalent discharges may face administrative or judicial enforcement actions and associated liabilities under the CWA
  • State and federal authority collaboration: Operators must consider both federal and state requirements, as states may have different definitions and regulations concerning “state waters”
  • Detailed permit applications: Permit applications will likely require more specific details and comprehensive data for discharges through groundwater, complicating the permitting process

Moving forward, there will likely be a greater emphasis on site-specific analyses, detailed permit applications and compliance efforts to ensure the new guidelines established by the decision are met. Water scientists and permittees alike will expand their understanding of groundwater pathways with greater awareness and use alternate discharge and treatment practices to avoid impacts to surface waters.

Article originally published in the Fall 2024 issue of Currents. Subscribe today to stay current on environmental insights and regulatory updates that impact your projects.