Ninth Circuit Decision Extends Clean Water Act Reach to Groundwater Discharges to Surface Waters and Expands Requirements for NPDES Permits
February 7, 2018
The Ninth Circuit Court of Appeals issued an opinion on February 1, 2018, that vastly expands the reach of the Clean Water Act (CWA). The Ninth Circuit’s finding in Hawai’i Wildlife Fund v. Co of Maui has potentially broad implications for anyone responsible for managing impacts in groundwaters that discharge to surface water. Extended CWA jurisdiction could lead to requirements for discharge permits for groundwater plumes and open businesses, regulators, and municipalities to CWA citizen suits.

Currently, federal jurisdiction extends to “navigable waters of the United States.” Because groundwater is not navigable, CWA has generally been assumed to not cover discharges to groundwater. This assumption has been challenged in recent cases related to permitted waste injection wells (Maui) and coal ash storage ponds (Yadkin Riverkeeper, Inc. v. Duke Energy Carolinas, Sierra Club v. Virginia Elec. & Power Co, and Tennessee Clean Water Network v. TVA). The district courts in these cases have found that CWA may cover situations where impacted groundwater discharges to surface water.

The Ninth Circuit Court of Appeals opinion in the Maui case supports this interpretation. The Ninth Circuit found that discharges of highly treated wastewater into groundwater that subsequently flows to the ocean (a navigable water) violated CWA, even though these discharges were permitted under Safe Drinking Water Act (SDWA) programs. The Ninth Circuit largely upheld the district court’s findings that the groundwater acted as a “conduit” that conveyed treated effluent from the underground injection control (UIC) wells (a point source) to navigable waters.

The Ninth Circuit’s broad opinion deviates from decades of regulatory practice and has the potential to expand the CWA regulatory program, and the likelihood of third party citizens’ suits, to surface impoundments, ash ponds, underground storage tanks, contaminant plumes, septic tanks, injection wells, restoration projects, and other sources that have not previously required National Pollutant Discharge Elimination System (NPDES) permits.


The County of Maui discharges tertiary-treated, disinfected wastewater that is either sold for irrigation or injected into four Class V UIC wells located approximately half a mile from the Pacific Ocean. Effluent injected via the County’s wells enters groundwater at a depth of 180 to 255 feet, where it mixes both vertically and horizontally with ambient groundwater. The groundwater flows to and enters the ocean primarily through small, distributed seeps in the ocean floor.

A tracer study conducted in 2013 confirmed that treated wastewater from the wells reached the Pacific Ocean over approximately two miles of shoreline, with an average travel time of more than a year. The tracer study found that treated wastewater experiences further chemical reactions, including loss of dissolved oxygen, nitrate, and organic matter and increases in temperature and phosphorus levels, as it travels from the wells to the ocean, and that the diffuse discharge into the ocean mixes rapidly with ambient ocean water in the nearshore zone (Glenn et al. 2013).

The County has discharged treated wastewater to its injection wells since the 1980s under UIC permits issued pursuant to federal and state SDWA programs. Historically, the Hawaii Department of Health (DOH) found that discharges into groundwater did not require a NPDES permit, and neither DOH nor the U.S. Environmental Protection Agency required an NPDES permit for the County’s discharges to the UIC wells.

In 2012, several environmental organizations filed citizen suits under CWA, alleging the County’s discharges of treated effluent to the UIC wells require NPDES permit coverage. The district court entered two separate rulings finding that a “party is liable if, without an NPDES permit, it indirectly discharges a pollutant into the ocean through a groundwater conduit,” concluding that “the discharge is functionally one into navigable water.” The County appealed this decision to the Ninth Circuit Court of Appeals.

The Ninth Circuit’s Opinion

On February 1, 2018, the Ninth Circuit Court of Appeals issued an opinion that found the County “liable under the CWA because (1) the County discharged pollutants from a point source, (2) the pollutants are fairly traceable from the point source to a navigable water such that the discharge is the functional equivalent of a discharge into the navigable water, and (3) the pollutant levels reaching navigable water are more than de minimis.” The Ninth Circuit found that “well disposals do not always constitute nonpoint source pollution. If pollutants from those wells are discharged into a navigable water from a discrete source, that is point source pollution, and the polluter must obtain an NPDES permit if it wants to avoid liability under the CWA.” The Ninth Circuit also found that the County had “fair notice” that its discharges to UIC wells were prohibited absent an NPDES permit.

Of note, the Ninth Circuit stated, “we leave for another day the task of determining when, if ever, the connection between a point source and a navigable water is too tenuous to support liability under the CWA.”

Maui is the first of these cases to have a circuit court reach an opinion. The Fourth Circuit has been asked to review the district court’s finding in Sierra Club v. Virginia Elec. & Power Co, and the Sixth Circuit has been asked to review findings in Tennessee Clean Water Network v. TVA. As of now, the legal issues are still in flux and potentially subject to a circuit split.

How Can Exponent Help?

Exponent is currently working with clients whose permits and operations are expected to be affected by this ruling. Experts in our Environmental & Earth Sciences Practice and our Ecological & Biological Sciences Practice can assist with understanding its potential technical implications; evaluating interactions between groundwater and surface water; regulatory and compliance evaluations; reviewing and evaluating data characterizing water quality, sediment, and ecological health; planning of monitoring and implementation strategies; evaluating treatment options; and negotiating permit limits.


Glenn, C.R., R.B. Whittier, M.L. Dailer, H. Dulaiova, A.I. El-Kadi, J. Fackrell, J.L. Kelly, C.A. Waters, and J. Sevadjian. 2013. Lahaina Groundwater Tracer Study – Lahaina, Maui, Hawaii, Final Report. Prepared for the State of Hawaii Department of Health, the U.S. Environmental Protection Agency, and the U.S. Army Engineer Research and Development Center.