Topic Area: 8b. Groundwater/Surface Water Interactions

Formatted Title:

Functional Equivalence: The Increasing Importance of Groundwater-Surface Water Evaluations in Light of the Recent SCOTUS Maui Decision

Background/Objectives:

In 2020, the Supreme Court of the United States (SCOTUS) reached a monumental environmental decision in the County of Maui v. Hawaii Wildlife Fund case, ruling that pollutants discharged to groundwater are subject to the Clean Water Act (CWA) when they are a “functional equivalent” of a surface discharge. In ruling that the discharge of treated wastewater to groundwater (and eventually surface water) via underground injection control (UIC) wells in Lahaina, Hawaii, was a functionally equivalent discharge, SCOTUS outlined seven non-exhaustive criteria for the determination of functional equivalence, focusing on transit time and distance, along with geochemical transformation and dilution along the subsurface travel path. The reverberations from this decision are wide reaching, including recent court rulings and U.S. Environmental Protection Agency (EPA) guidance documents through multiple administrations that signal a still-evolving interpretation of the Maui decision. There is still a great deal of ambiguity regarding 1) the administrative implementation of the functional equivalence analysis, and 2) the quantitative thresholds for the seven criteria to distinguish functional equivalent discharges from non-functional equivalent discharges. While SCOTUS outlined several extreme examples for discharges that do and do not apply to the CWA (a few feet from a surface water body and a few hundred miles from a surface water body, respectively), there is still significant ambiguity in the middle ground, applicable to most situations.

Approach/Activities:

A detailed overview of the seven functional equivalence criteria and the methods available for assessing each criterion will be presented. Site-specific considerations will be discussed, and each criterion will be quantified based on the Maui decision and subsequent rulings thereafter. The focus will be on the state of the science and the state of the regulatory framework, outlining methods such as thermal imaging, modeling, tracer studies, radon mass balance, isotopic fingerprinting, and others, discussing the benefits and drawbacks of each. Several hypothetical scenarios with unique site conditions will be presented, and example approaches for determining functional equivalence will be outlined for each site.

Aly El-Kadi

Affiliation

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Functional Equivalence: The Increasing Importance of Groundwater-Surface Water Evaluations in Light of the Recent SCOTUS Maui Decision