Supreme Court Decision Includes Groundwater Under Clean Water Act

On April 23, 2020, the Supreme Court decided in a 6-to-3 ruling that, in some circumstances, the Clean Water Act applies to pollutants that reach the sea or other navigable waterways via groundwater. The Supreme Court decision came after a recent case, County of Maui vs Hawaii Wildlife Fund, where it was decided that a wastewater treatment plant’s groundwater discharge - which migrated approximately half of a mile to the ocean - should be considered the equivalent of a “direct discharge” and require National Pollution Discharge Elimination System (NPDES) permitting. Whether a discharge to land potentially requires permitting depends on several factors addressed in the ruling:

  • Does the discharge originate from a point source, such as an underground injection control well or other conveyance?
  • Does the discharge contain contaminants that are “fairly traceable” from the point source to a navigable water?
  • Is the groundwater connection to surface water the “functional equivalent” of a direct discharge to surface water, such as a pipe?
  • Do the contaminant levels reaching navigable waters exceed de minimis levels?

Based on this revised interpretation of the applicability of the Clean Water Act to groundwater, it is not the intention of the Supreme Court to expand the Clean Water Act to apply to non-point source discharges, or to spills that travel years through groundwater and eventually reach surface water. 

Some background on the Clean Water Act

The Clean Water Act of 1972 established a basic structure for regulating pollutants, gave the EPA authority to implement pollution control programs, set water quality standards, made discharge from a point source pollutant into navigable waters unlawful, funded sewage treatment plants, and more. Point sources have been defined under the Clean Water Act as “any discernible, confined and discrete conveyance…from which pollutants are or may be discharged.”  Examples of point sources that may now fall under the Clean Water Act may include injection wells, dry wells, pipelines, ditches, tunnels, and concentrated animal feeding operations (CAFOs). The Clean Water Act has not generally been used to regulate groundwater quality, which is directly regulated under the Safe Drinking Water Act. Therefore, this ruling has a profound impact on the future of groundwater quality protection.

What does the decision mean for the regulated community?

The decision to include groundwater under the Clean Water Act is important for several reasons. First, industrial discharges into groundwater that ultimately flow into nearby lakes, streams, and bays may now fall under the Clean Water Act when they previously did not. This means that while dischargers may have already met point source pollution compliance, they may now have to determine whether a discharge of a pollutant that travels through groundwater is subject to NPDES permitting requirements.  Hydrogeologists would make this determination based on a number of factors, including groundwater transit time and distance traveled.

Second, the ruling could also expand the need for groundwater modeling and tracking. Because pollutants can take days to decades to appear in groundwater sources, tracing groundwater movement in the subsurface can be a difficult task. However, groundwater modeling tools can help predict concentrations of constituents in space and time. Models can be used to determine whether groundwater discharges to surface water; estimate the resulting concentrations of constituents in surface water; and predict whether discharges may violate the Clean Water Act. 

Lastly, Underground Injection Control (UIC) permits over a broad range of market sectors could be affected. Municipal sanitary re-injection sites, similar to the County of Maui facility, will be especially subject to this ruling.  In addition, industrial sites such as utility companies, manufacturers, and refineries that depend on injection as a disposal mechanism for management of wastewater using UIC permits may need to evaluate whether a previously issued permit may violate the Clean Water Act, particularly if the injection point is proximal to navigable waters as defined under the Clean Water Act.  States that have administrative authority to issue UIC permits could experience an increase in administrative costs for regulating proposed injection wells, and could turn to establishing large default surface water setbacks for injection activities to become compliant with the new ruling. NPDES permitting of remediation injection activities could also potentially be required, potentially affecting in situ bioremediation sites and oxidant injection sites.


The recent ruling brings surface water quality and groundwater quality regulation more in alignment, though forthcoming guidance on this ruling from the EPA will provide further clarity. Contact Trihydro’s specialists in hydrogeology, NPDES permitting, and Clean Water Act interpretation with questions.

Allison Riffel, P.E.
Engineering Specialist
[email protected]

Allison Riffel
Allison Riffel, PE
Engineering Specialist, Golden, CO

Allison is a professional engineer with over 20 years of experience in site assessment, remediation, regulatory compliance and permitting. She specializes in remediation of chlorinated solvents, petroleum, and PCBs under RCRA, TSCA, CERCLA, and state voluntary cleanup programs with regulatory expertise in 11 states.

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