December 16, 2022

Wastewater Treatment Unit Exemption Applicability

In recent guidance, EPA addressed a question on the applicability of the wastewater treatment unit (WWTU) exemption to a tank storing hazardous wastewater prior to offsite trucking to a publicly owned treatment works (POTW). [RO 14950] If the storage tank is eligible for the WWTU exemption, it would be exempt from RCRA tank requirements.

To determine applicability, EPA refers to the regulatory definition of a WWTU in §260.10:

  1. Is part of a wastewater treatment facility that is subject to regulation under either section 402 or 307(b) of the Clean Water Act (CWA); and
  2. Receives and treats or stores influent wastewater that is a hazardous waste as defined in §261.3 of this chapter, or that generates and accumulates a wastewater treatment sludge that is a hazardous waste as defined in §261.3 of this chapter, or treats or stores a wastewater treatment sludge which is a hazardous waste as defined in §261.3 of this chapter; and
  3. Meets the definition of a tank or tank system in §260.10 of this chapter.

EPA also refers to the preamble of a final rule that clarified the scope of the WWTU exemption:

“However, any tank system that is employed in managing wastewater at a facility prior to its off-site transfer to another location, whether or not the off-site location is an NPDES-permitted wastewater treatment facility (or one that discharges to a POTW), is not covered by this exemption. EPA intends that this exemption apply to any tank system that manages hazardous wastewater and is dedicated for use with an on-site wastewater treatment facility. However, if a tank system, in addition to being used in conjunction with an on-site wastewater treatment facility, is used on a routine or occasional basis to store or treat hazardous wastewater prior to shipment off-site for treatment, storage, or disposal, it is not covered by this exemption. Unless the tank system qualifies for another exemption, it would be subject to the revised hazardous waste tank systems standards.” [53 FR 34080]

Based on the definition of a WWTU in §260.10 and the explanation in 53 FR 34080, the storage tank in question is not eligible for the WWTU exemption because the stored hazardous wastewater is being trucked offsite to the POTW. In fact, even if this happens just occasionally, and the wastewater is usually treated and discharged to the sewer, the occasional offsite trucking voids the exemption.

Regarding the status of the tank, the facility is a large quantity generator (LQG) of hazardous waste, and the tank is holding hazardous wastewater. The tank is not exempt, so it must either be RCRA-permitted or a 90-day tank, both subject to the RCRA tank standards in Part 265, Subpart J. As an LQG, the facility may manage the tank as a 90-day tank in compliance with §262.17 without the need for a RCRA permit

EPA also clarified and expanded on other guidance brought to its attention by the facility regarding the WWTU exemption:


©2022-2023 McCoy and Associates, Inc. All rights reserved.

McCoy and Associates has provided in-depth information to assist environmental professionals with complex compliance issues since 1982. Our seminars and publications are widely trusted by environmental professionals for their consistent quality, clarity, and comprehensiveness.



Considerable care has been exercised in preparing this document; however, McCoy and Associates, Inc. makes no representation, warranty, or guarantee in connection with the publication of this information. McCoy and Associates, Inc. expressly disclaims any liability or responsibility for loss or damage resulting from its use or for the violation of any federal, state, or municipal law or regulation with which this information may conflict. McCoy and Associates, Inc. does not undertake any duty to ensure the continued accuracy of this information.

This document addresses issues of a general nature related to the federal RCRA regulations. Persons evaluating specific circumstances dealing with the RCRA regulations should review state and local laws and regulations, which may be more stringent than federal requirements. In addition, the assistance of a qualified professional should be enlisted to address any site-specific circumstances.