Most environmental law practitioners are familiar with the federal Clean Water Act’s (CWA) National Pollutant Discharge Elimination System’s (NPDES) permitting program and the types of discharges subject to the program. Put simply, the NPDES permit is required for the discharge of pollutants (broadly defined to even include “cellar dirt”) from a point source (again, broadly defined) into a “navigable water,” which is often referred to as a water of the United States, including the territorial seas. Most of the navigable waters regulated under the CWA, including lakes, rivers, streams and wetlands, have one important feature in common—they are all considered to be a surface water, as opposed to a groundwater (which is the water beneath the surface of the earth that flows slowly through geologic formations called aquifers, and which is often a source of recharge for many surface water bodies, including lakes and streams).

Historically, NPDES permits under the CWA have generally been issued for discharges of pollutants directly to surface water. However, a recent line of federal cases has reignited a debate as to whether discharges requiring a CWA NPDES permit should also include those discharges of pollutants to groundwater, where the pollutants ultimately come to be located in a navigable water (e.g., surface water) because the groundwater is hydrologically connected to the surface water. This scenario has often been referred to as the “groundwater conduit theory.”