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Regulatory Updates

Final Guidance from EPA on Applying the U.S. Supreme Court’s Decision on County of Maui vs. Hawaii Wildlife Fund to NPDES Permits

January 4, 2021

On October  19, 2020, the EPA issued a Draft Guidance Memorandum on how permitting authorities and permit writers should apply the U.S. Supreme Court’s recent decision on the case of the County of Maui vs. the Hawaii Wildlife Fund.  A 30-day public comment period was initiated on December 10, 2020.

This case involved whether discharge from a point source to groundwater that discharged to a “navigable” water would require a National Pollutant Discharge Elimination System (NPDES) permit.  The Supreme Court’s decision stated that a point source discharge to groundwater could be the “functional equivalent” of a discharge to a navigable water and could require a NPDES permit. The Court identified seven factors to be evaluated in this determination. The factors include:

  • travel time to reach the navigable water;
  • distance between the initial discharge to groundwater and navigable water;
  • the nature of the subsurface geology through which the pollutant travels;
  • the extent to which the pollutant is diluted or chemically changed as it travels;
  • the amount of pollutant entering the navigable water relative to the amount of the pollutant that leaves the point source;
  • the manner by or area in which the pollutant enters the navigable water; and
  • the degree to which the pollution has maintained its specific composition when it enters the navigable water.

Until recently, federal courts were divided on the question of whether a “discharge of a pollutant” subject to the Clean Water Act (CWA) occurs when a pollutant is released from a point source and subsequently moves through groundwater before reaching a “water of the United States (WOTUS).” The US Supreme Court’s decision has not modified the two threshold conditions for triggering NPDES permit applicability from the CWA—(1) an actual discharge of a pollutant to a WOTUS; and (2) the source of the pollution is a point source.  If these two conditions are not met, a NPDES permit would not be required.  The CWA defines a “point source” as “any discernible, confined and discrete conveyance, including but not limited to any pipe, ditch, channel, tunnel, conduit, well, discrete fissure, container, rolling stock, concentrated animal feeding operation, or vessel or other floating craft, from which pollutants are or may be discharged.”

In situations where discharge may enter groundwater and eventually enter a navigable water, it may be important for the potentially regulated facility to evaluate hydraulic conductivity based on the soil type or porosity; hydraulic gradient through which the pollutant travels; the depth to groundwater; groundwater flow path (including distance and travel time over which the pollutant reaches the receiving WOTUS); and/or pollutant-specific dynamics along the groundwater flow path (e.g., sorption, biological uptake, microbial processing). This evaluation would be necessary to understand not only whether an actual discharge of a pollutant is occurring to a WOTUS via groundwater, but also whether the discharge is the functional equivalent of a direct discharge to a WOTUS. In a typical NPDES permitting process (whether or not groundwater is involved), the facility owner or operator may provide to the permitting agency engineering, modeling or other technical information to support a permit application. These analyses often evaluate the likely fate and transport of pollutants that travel from the point source and into the environment and are often included in the record of decision for a final NPDES permit.

Historically, few NPDES permits have been issued for point source discharges of pollutants that reach WOTUS via groundwater. EPA anticipates that the issuance of such permits will continue to be a small percentage of the overall number of NPDES permits issued once the application of the Supreme Court’s “functional equivalent” analysis to a potential discharge is conducted.

After the end of public comment, EPA finalized the guidance on January 13, 2021.  The guidance and additional information can be found at:

This guidance memorandum will provide EPA administrative guidance to assist the regulated community and permit writers with incorporating the Maui decision into existing EPA-administered NPDES permit programs and authorized state programs.

Catriona Smith

Catriona (Cat) Smith has over 30 years of professional experience in the interpretation and application of regulations for industrial facilities relating to compliance, remediation and negotiations with regulatory agencies. Her clients include upstream and downstream oil and gas, chem-pharma, petrochem, manufacturing and federal, state, and local governments. Ms. Smith is a Vice President and Environmental Sector Market Director for TRC, with nationwide responsibilities to manage our clients’ PFAS challenges, support and grow our Oil and Gas clients and bring multi-disciplinary solutions to their complex projects. Contact Cat at

Jean Decker

Jean Decker is a Senior Project Manager located in Fort Collins, Colorado. She has more than 49 years of experience in environmental consulting, process engineering and operations management. She had 18 years in industry, working for the largest steel mill in the U.S. and then the largest water treatment company in the country at the time. Ms. Decker joined an environmental consulting company 31 years ago and has specialized in compliance programs across a wide variety of industries and clients. Ms. Decker has managed projects for companies such as bp, Encana, GE Healthcare, Cessna, Terex, Koch Industries, Georgia Pacific, Halliburton and BNSF. She has also managed projects for municipalities and military installations. Contact Jean at

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