In a recent decision, Hawai’i Wildlife Fund v. County of Maui, the Ninth Circuit Court of Appeals held that a Clean Water Act (“CWA”) permit is required when pollution found in navigable waters is fairly traceable from point source discharges to groundwater.

The case involved Maui County’s discharges of treated sewage into four groundwater wells. That sewage seeps into the groundwater and, based on a tracer dye study, flows into the Pacific Ocean 84 days later and a half mile away from the wells. The Ninth Circuit held that the discharges require a CWA permit because (1) the wells were each a point source, (2) pollutants are fairly traceable from a point source to a navigable water, and (3) the pollutants reaching the navigable water are not de minimis.

The County primarily argued that indirect discharges do not require a CWA permit. The Court disagreed, relying on the plain language of the statute, which does not mention direct discharges, and Justice Scalia’s plurality opinion in Rapanos v. United States, 547 U.S. 715, 743 (2006), which favorably cites decisions requiring permits for other indirect discharges.

While the Ninth Circuit explains that its decision only imposes the same permit requirement the County would have faced had it constructed an outfall, future cases likely will be less clear. For now, operations discharging to groundwater should consider the likelihood of tracing non de minimis pollution to navigable waters when evaluating permit compliance.