An NGWA panel examined groundwater conveyance of point source discharges to surface water following the April 2020 Supreme Court decision on this subject during a session of the virtual Groundwater Summit 2021 on December 8.
The session was titled “Perspectives and Challenges in Addressing Functional Equivalency Within the Clean Water Act” and featured comments from several leading groundwater professionals.
Mario Flores, Steve Hock, Dorinda Shipman, and David Henkin (litigator to the Supreme Court) provided collective consistent perspective that the Supreme Court recognized the current state of hydrogeologic science in identifying that groundwater can be a conveyance of point source discharges to surface water (for example, the ocean in the Maui case) under the National Pollutant Discharge Elimination System.
They also recognized the court’s provision of a direction for permit decisions with a set of seven technical factors, most prominently, time and distance of pollutant travel. The court’s decision clearly indicated a need to refine the decision factors and how they might be applied in the permit process.
Peter Mock, Don Rosenfeld, and Ron Green provided perspectives as to how key technical factors might be analyzed in determining functional equivalence. Initial screening could use a hierarchy of steps to evaluate proximity in time and distance of a discharge’s closeness to pollutant-receiving navigable waters.
Middle-ground discharges would receive the most scrutiny. Pollutant transport evaluation will factor in geology and unique settings such as karst, hydrology and key pollutant drivers, variable pollutant velocity in groundwater, and pollutant reaction to subsurface physical-chemical-biological conditions.
Geophysics and multiple groundwater discharge measurement methods can describe pollution potential from groundwater conveyance. Scale and associated potential landscape discharge points point to macro modeling aspects to guide assessment of functional equivalence incorporating hydraulic conductivity in a range of hydrogeologic settings.
Marcus Zobrist provided a perspective of the U.S. Environmental Protection Agency regarding functional equivalence. The EPA views the Supreme Court decision as confirming a particular approach consistent with past court decisions involving groundwater conveyance of pollutants to navigable waters.
While the EPA rescinded its previous guidance that pointed to circumstances not requiring an NPDES permit rather than positive protective steps, senior EPA management is discussing how to proceed with appropriate regulatory paths. The NPDES process will consult with the Underground Injection Control program as situations arise for mutual consideration.
Pollutant discharging facilities seeking input on permit coverage may decide to pursue professional consultation from hydrogeologists and draw on groundwater modeling of potential pollutant transport and impacts. Modeling may be a key tool in evaluating a range of scenarios for discharger and regulator consideration of functional equivalence in permitting.
During an open discussion at the panel session, Mary Musick noted that estimating loadings to surface water for input to permits was an essential step in functional equivalence decisions. Zobrist confirmed that step would require interaction between hydrogeologists and permit writers as well as other consultations.