January 20, 2021
No bright-line test provided to determine whether a discharge is functionally equivalent to a direct discharge
On December 4, 2020, the U.S. Environmental Protection Agency (EPA) released a draft guidance memorandum discussing how to determine whether a pollutant discharge to groundwater is the functional equivalent of a direct discharge to surface waters. This memorandum was developed in response to the U.S. Supreme Court's 2020 ruling in the Maui case, which held that if a discharge of a pollutant to groundwater migrates to navigable surface waters, it may constitute the functional equivalent of a direct discharge to surface waters. Discharges found to be functionally equivalent to a direct discharge may require a National Pollutant Discharge Elimination System (NPDES) permit under the Clean Water Act (CWA).
EPA's draft guidance memorandum affirms that two threshold conditions must be met for a discharge to be regulated under the CWA: (1) there must be a discharge from a point source, and (2) the discharge must migrate to a navigable water of the U.S. Additionally, further analysis is required to determine whether the discharge is the functional equivalent of a direct discharge, which can be difficult to ascertain. For example, the Supreme Court cited time and distance as "the most important factors in most cases" that will determine whether a discharge to groundwater constitutes a direct discharge.
However, the Court also stated there are "too many potentially relevant factors applicable to factually different cases … [prohibiting the use of] more specific language." The Court listed additional factors, including the nature of the material through which the pollutant travels, the extent to which the pollutant is diluted or chemically changed as it travels, and the degree to which the pollution has maintained its specific identity. Determining whether a discharge constitutes the functional equivalent of a direct discharge should be determined on a case-by-case basis.
Rather than provide a definitive (a.k.a., bright-line) test for determining whether a discharge to groundwater is functionally equivalent to a direct discharge, EPA's draft guidance memorandum provides examples of situations where scientific analyses will help determine whether an NPDES permit is needed — e.g., for the discharge of highly mobile pollutants from a point source directly to sandy soils or in an area with shallow groundwater in close proximity to navigable waters. However, if environmental conditions favor attenuation mechanisms, and there is sufficient time for them to occur, then EPA suggests the original discharge to the subsurface may have changed such that it no longer constitutes the functional equivalent of a direct discharge and does not require a permit. Mechanisms of pollutant attenuation specified in the draft guidance memorandum include but are not limited to "chemical or biological interaction with soils, microbes, plants and their root zone, groundwater, or other pollutants, or physical attenuation or dilution."
EPA's draft guidance memorandum may affect discharges similar to those at issue in legal cases involving the discharge of petroleum products from pipelines, acid mine drainage and mining-related discharges to groundwater, seepage of coal ash constituents to groundwater, and the discharge of septic system effluent. EPA's draft guidance memorandum does not resolve the issues but instead highlights the need for scientific and technical analyses to support the determination of whether an NPDES permit is needed, indicating that continuing and future litigation on the topic is likely.
How Exponent Can Help
Exponent's scientists and engineers have extensive experience evaluating the factors that EPA and the Supreme Court suggested should be considered in determining whether a discharge meets a "functional equivalence" test. Exponent's expertise includes understanding and predicting the transport, reaction, and fate of pollutants in groundwater systems, modeling geochemical reactions and groundwater movement, evaluating groundwater-surface water interactions, analyzing the fate of discharges to surface waters, and applying environmental forensics and pollutant source identification and allocation. Exponent also has deep knowledge of and expertise with the Clean Water Act, state water quality regulations, and the interplay between the two.