On Thursday, the Ninth Circuit ruled that wastewater injections whose pollutions reach navigable U.S. waters via groundwater are subject to the Clean Water Act (“CWA”). Experts say this decision could drastically expand the scope of CWA liability and includes activities ranging from coal ash and pipeline spills to agricultural runoff.

In coming to this decision, the Ninth Circuit upheld a lower court ruling that Maui County of Hawaii violated the CWA. The Court found that the use of four state-permitted wastewater disposal wells at a municipal waste water treatment plant required National Pollutant Discharge Elimination System (“NPDES”). The Ninth Circuit explained that because of the indirect discharge of pollutants into the Pacific Ocean through groundwater, the NPDES provisions of the CWA were triggered. The Court rejected the County’s argument that the wastewater injections were well disposals exempt from NPDES requirements and found the level of pollution was more than “minimal”. Furthermore, the Court ignored warnings from the industry and municipal water regulator groups who argued that this holding would expand the NPDES permitting program to unfeasible levels and undermine state authority over water resources.

The environmental groups who brought the original suit against the County say the Court’s decision is simply the latest in a long line of rulings and regulatory determinations that the CWA regulates indirect discharges of pollutants. The groups point to the Ninth Circuit’s citation of the Rapanos case, as well as holdings from the Second and Fifth circuits, which all state that indirect discharges from point sources into navigable waters are enough to establish CWA liability.

While the Court found the County was liable under the CWA, it is important to note this does not necessarily translate similar results in other cases. The County had conceded that its injection wells were point sources under the CQA. Additionally, the record showed that the County discharged pollutants in the form of treated effluent into groundwater, through which the pollutants entered a navigable water in the Pacific Ocean. Finally, the discharged pollutants from the wells were then clearly traced to the Ocean by an EPA study.

Some have questioned whether other courts will adopt the Ninth Circuit’s “fairly traceable connection” rule establishing CWA liability for indirect discharges. Experts do note that the Court overrode the EPA’s suggestion that liability be determined by a “direct hydrological connection” between the point source and navigable water. However, they also say they would be surprised if other courts embrace this type of standard. While they conclude that permitting programs are not likely to change immediately, individuals and entities should consider the potential for pollutants to leave their sites by way of groundwater.

The case is Hawaii Wildlife Fund et al. v. County of Maui, case number 15-17447, in the U.S. Court of Appeals for the Ninth Circuit.