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New NPDES Guidance on Discharges to Groundwater

Posted on 11/27/2023 by Roger Marks

US EPA recently released a draft copy of new guidance intended to help the regulated community comply with NPDES permitting requirements for discharges of pollutants to groundwater.

The newly drafted guidance is meant to clarify when a NPDES permit is required to discharge pollutants to a water of the United States (WOTUS)—including some discharges that travel through groundwater before reaching a WOTUS.

New NPDES Guidance on Discharges to Groundwater

Why NPDES Guidance? Why Now?

The new NPDES draft guidance stems from a 2020 Supreme Court decision in the case County of Maui v. Hawaii Wildlife Fund. That legal fight centered on whether a wastewater treatment plant needed a NPDES permit to discharge pollutants into underground injection wells.

The wells led the plant’s discharges to groundwater, which carried the pollutants to the Pacific Ocean. Because the Pacific is a WOTUS, citizen groups argued that the treatment plant should have obtained a NPDES permit before discharging pollution.

The Court agreed with those groups, partly, deciding that discharging pollution to groundwater sometimes requires a NPDES permit. Sometimes, the Court reasoned, discharging pollution to groundwater is “functionally equivalent to discharging pollution directly to a WOTUS.

The purpose of EPA’s draft guidance is to help facilities determine when a discharge to groundwater meets this “functional equivalent” standard (and therefore requires a NPDES permit). 

EPA will accept public comments on the new Maui/NPDES draft guidance until December 27, 2023. 

When is a NPDES Permit Required?

The Clean Water Act NPDES permitting program requires any person to obtain a permit before discharging "any pollutant to navigable waters from any point source." To determine when a NPDES permit is required to discharge pollutants to groundwater, the facility first must determine if the discharge will eventually reach a water of the United States. 

If the pollutants will reach a WOTUS, the facility must determine whether that discharge is “functionally equivalent” to a direct discharge to the navigable water. This determination must be based on a variety of factors which EPA gives details about in the draft guidance. 

In addition to outlining general principles for an “overall approach” to NPDES permitting decisions with respect to groundwater pollution, EPA’s draft guidance provides a list of considerations included in the Supreme Court’s Maui decision. 

Factors for determining NPDES applicability (i.e., "functional equivalence") for a discharge to groundwater that reaches a WOTUS include: 

  • Transit time and distance traveled to reach the WOTUS (The draft guidance calls this the “most important factor in most cases, an in many cases the only factor that need be considered…”).
  • The manner or area in which the pollutants enter the water of the US. 
  • The nature of material through which the pollutant travels. 
  • The amount and concentration of pollution. 

From EPA's draft guidance:

“If the operator does not seek permit coverage for a functionally equivalent discharge, the operator may be subject to administrative or judicial enforcement proceedings and associated liability under the CWA (including civil and criminal penalties.”

US EPA, Applying the Supreme Court's Maui Decision... ("Maui Draft Guidance")

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