Darcy's Law and the Supreme Court.

Abstract

In a historic 6–3 decision, the U.S. Supreme Court (SCOTUS) ruled in April 2020 that some groundwater is now regulated under the Clean Water Act (CWA) and a National Pollutant Discharge and Elimination System (NPDES) permit is required when it can be demonstrated there is a “functional equivalent” of a direct discharge of a pollutant from a point source into navigable waters via groundwater. This is the first time in the CWA's nearly 50-year history that groundwater is regulated under the act. Prior to this ruling, the CWA only regulated point source discharges of pollutants directly into navigable waters and regulation of groundwater was left to the purview of individual states. This ruling has important implications for the groundwater profession because the legal language used to describe a functionally equivalent NPDES discharge maps directly to technical concepts embodied in Darcy's Law for groundwater flow. In this case, titled County of Maui v. Hawaii Wildlife Fund (2020), the county operates a wastewater reclamation facility on the island of Maui, Hawaii. The facility collects sewage from surrounding areas, partially treats it, and pumps the effluent into four underground injection wells at depths of 180 to 255 feet below ground at a combined rate of about four million gallons per day. The receiving hydrogeologic formations consist of weathered, vesicular, and massive fractured basalt bedrock layers. Hydrogeologic studies performed by researchers at the University of Hawaii demonstrated a direct hydrogeologic connection between the injection wells and nearby coastal waters of West Maui, which are navigable waters under the CWA (Glenn et al. 2013). Through underwater mapping, sampling using scuba divers, high-resolution airborne thermal infrared mapping, geochemical analyses, tracer studies, and mathematical modeling, Glenn et al. (2013) determined that effluent from the County of Maui wastewater reclamation facility discharges from the seafloor primarily as diffuse flow but also through hundreds of submarine springs. Groundwater tracer velocities were found to vary between approximately 5 and 30 feet per day. The pertinent question is, when is a discharge of groundwater containing pollutants from a point source “functionally equivalent” to a NPDES direct discharge into navigable waters? On this point SCOTUS provided the following guidance: “Time and distance will be the most important factors in most cases, but other relevant factors may include, e.g., the nature of the material through which the pollutant travels and the extent to which the pollutant is diluted or chemically changed as it travels.” Groundwater scientists and engineers should recognize in SCOTUS' language that time and distance point directly to Darcy's Law of groundwater flow because Darcy's specific discharge is defined in units of time and distance. Moreover, “the nature of the material through which the pollutant travels and the extent to which the pollutant is diluted or chemically changed” point directly to contaminant transport principles including dispersion, sorption, retardation, and chemical transformations. Here it appears SCOTUS is speaking directly to the groundwater profession in legal terms that are equivalent to scientific terms in the advection dispersion equation (ADE) for contaminant transport. This is important because groundwater scientists and engineers are uniquely qualified to understand, explain, and evaluate proper use of Darcy's Law and the ADE. Groundwater professionals should therefore be the ones to assess, analyze, and provide guidance, advice, and opinions regarding whether a groundwater discharge is a functionally equivalent NPDES discharge. SCOTUS apparently has left it to the groundwater community to provide a scientific basis for evaluating functionally equivalent NPDES discharges. Groundwater professionals should not sit idly by and allow this opportunity to pass because if we do not fill this gap, people with different or the wrong expertise will make these determinations and that could result in bad decisions. The National Ground Water Association (NGWA) is fully qualified, ready, willing, and able to provide technical guidance for determining when groundwater discharges are functionally equivalent NPDES discharges due to its strong emphasis on groundwater science and engineering, the breadth and depth of expertise among members, and NGWA's good working relationships with USEPA. Any technical guidance would need to be practical, useful, and cost-effective. We applaud SCOTUS' decision because it leaves the fact-finding to hydrogeologic experts who can and should assist in determining the legal status of underground injection wells and other CWA-defined point sources such as contaminated sinkholes and recharge ponds. Please read the SCOTUS ruling and oral argument transcript. It is compelling reading and it is encouraging to see SCOTUS devote so much time to considering responsible management and regulation of groundwater resources. The author(s) does not have any conflicts of interest.