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In the United States, hazardous wastes are subject to regulations mandated by the Resource Conservation and Recovery Act (RCRA). Every month, we provide clear, in-depth guidance on a different aspect of the RCRA regulations. The information presented here is an excerpt from McCoy’s RCRA Unraveled, 2024 Edition.

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NPDES Discharge Exclusion

Wastewater discharged from an industrial facility to surface water of the United States ceases to be a solid or hazardous waste at the outfall point where the waste enters surface water. This exclusion works similarly to the domestic sewage exclusion and is extremely beneficial to facilities located near lakes, rivers, streams, or the ocean.


The RCRA statutory definition of solid waste excludes “industrial discharges which are point sources subject to permits under Section 402 of [the CWA].” [RCRA Section 1004(27)] Section 402 of the CWA outlines the National Pollutant Discharge Elimination System (NPDES) permitting program; such a permit is required whenever an industrial facility discharges wastewater into waters of the United States. This exclusion was created to avoid duplicative regulation of point-source wastewater discharges under both the CWA and RCRA. Without the provision, discharging wastewater into surface water would be disposal of solid (and potentially hazardous) waste and would potentially be regulated under both statutes. [May 19, 1980; 45 FR 33098]

The NPDES discharge exclusion is codified in §261.4(a)(2). Based on this regulatory language, point-source discharges subject to regulation under Section 402 of the CWA are excluded from the definition of “solid waste.” As illustrated in Figure 1, this means that once wastewater from an NPDES-permitted discharge or outfall point enters waters of the United States, it is excluded from RCRA regulation. According to EPA, this is true even if the discharge is not regulated under a Section 402 permit. The agency believes a point-source discharge without an NPDES permit would be a violation of the CWA, not RCRA. [RO 11125, 11408, 11895, 12604]

Figure 1

Where does the exclusion apply?

EPA notes in §261.4(a)(2) that the exclusion “applies only to the actual point-source discharge. It does not exclude industrial wastewaters while they are being collected, stored, or treated before discharge, nor does it exclude sludges that are generated by industrial wastewater treatment.” In other guidance [RO 11139], EPA states:

“Since the Clean Water Act applies to discharges to navigable surface waters, point-source discharges cannot apply to some internal midway point in the wastewater treatment train on the grounds of a facility or another facility (unless it is a POTW) which treats, stores, or collects these wastewaters. Even if the wastewaters themselves were exempt from regulation while they were being treated, collected, or stored prior to discharge, the sludges are not exempt as the result of any exemption of the wastewater.”

In other words, the exclusion does not apply to hazardous wastewater prior to its discharge point, because most of the potential environmental hazards (e.g., ground water contamination) are posed during upstream treatment and storage activities, which are not controlled under the CWA. [45 FR 33098, RO 11309, 12604] Thus, treatment, storage, and disposal of hazardous wastewater and sludge occurring upstream of the discharge point remain subject to RCRA regulation, unless another exemption applies. In Figure 1, the sludge generated in a wastewater treatment tank upstream of the NPDES-permitted discharge point is not eligible for the NPDES discharge exclusion. If sent for disposal, it is a solid waste that must be evaluated for listings and characteristics. [RO 11628]

A “point source” is defined in §122.2 of the CWA regulations: it is “any discernible, confined, and discrete conveyance, including but not limited to, any pipe, ditch, channel, tunnel, conduit…from which pollutants are or may be discharged.” (EPA has codified this same definition in the RCRA regs at §260.10.) Typically, this would be a pipe discharging wastewater into a river, etc., and would be referred to as the “outfall point” by industry. Those CWA regulations also define “discharge” as the “addition of any pollutant or combination of pollutants to waters of the United States from any point source.” Finally, “waters of the United States” are defined as “The territorial seas, and waters…in interstate or foreign commerce, including waters which are subject to the ebb and flow of the tide; tributaries; lakes and ponds, and impoundments of jurisdictional waters; and adjacent wetlands…. The following are not ‘waters of the United States’: …wastewater recycling structures, including detention, retention, and infiltration basins and ponds, constructed or excavated in upland or in non-jurisdictional waters; and waste treatment systems.” [40 CFR 120.2]

An NPDES permit will occasionally specify intermediate, upgradient points at which certain conditions must be met in addition to the limits and conditions at the outfall. Facilities will sometimes argue that their wastewater ceases to be regulated under RCRA (i.e., it ceases to be a solid or hazardous waste) at the intermediate point. “As the comment following §261.4(a)(2) and the CWA definitions make clear, however, only the wastewater discharge itself is excluded. It is thus critical to find the NPDES discharge point, which depends on where the waste stream enters the waters of the United States.” [RO 12604] Furthermore, based on the specific definitions of “point source” and “discharge” noted above, the exclusion does not take effect until the wastewater actually mixes with waters of the United States.

A facility treats its listed hazardous wastewater and then discharges it to surface water under an NPDES permit. The facility would like to divert a portion of the treated wastewater for spray irrigation and maintenance of an onsite landfill cap. Would the diverted wastewater be excluded under the §261.4(a)(2) exclusion?

No. EPA “determined that wastewater sprayed onto a landfill cap does not qualify for the industrial wastewater discharge exclusion under §261.4(a)(2). Although a portion of the effluent will continue to be discharged from [the NPDES]-permitted outfall to [the creek] (and thus permitted under Section 402), wastewater that is diverted to land application and is not discharged to waters of the United States is not a point-source discharge subject to regulation under the CWA and, therefore, does not qualify for the RCRA exclusion (even if it is part of the [NPDES] permit). Therefore, the wastewater remains a solid and hazardous waste.” [RO 14775]

Sometimes, identifying the discharge point is confusing—especially if there is a surface impoundment as the last unit in an industrial wastewater treatment system. For example, it can be difficult to distinguish where a wastewater treatment lagoon ends and waters of the United States begin. The agency notes that water bodies wholly within the facility’s property boundary and upgradient of the NPDES-permitted discharge point are clearly regulated as surface impoundments under RCRA. Conversely, a surface impoundment created by impounding a portion of a larger body of surface water may or may not be considered a hazardous waste unit; such determinations must be made by states or EPA regions on a case-by-case basis. Ponds located downgradient of an NPDES-permitted discharge point are, by definition, waters of the United States and are not subject to RCRA regulation. [RO 12604, 12826]

Discharges to ground water that have a direct connection to surface water

CWA Section 402 jurisdiction extends to point-source discharges to ground water if there is a direct hydrologic connection between the point source and nearby surface waters of the United States. However, discharges of leachate into ground water from leaking waste management units (e.g., a landfill) are not excluded from RCRA regulation under the §261.4(a)(2) NPDES discharge exclusion. The exclusion applies only to traditional pipe outfall-type point-source discharges and not to discharges that occur upstream of that point. Consequently, the RCRA requirements apply to discharges of leachate to ground water from waste management units, even when the ground water provides a direct hydrologic connection to a nearby surface water of the United States. [RO 11895]

Dredged sediments

In the 1980s and 1990s, EPA’s policy regarding the applicability of RCRA to contaminated dredged sediments was as follows. If the source of the contamination was a point-source discharge regulated under the NPDES program, the §261.4(a)(2) exclusion applied and hazardous wastes were not discharged into the surface water. Consequently, the resulting contaminated sediments were only regulated under RCRA if they 1) were dredged from the surface water, and 2) exhibited one or more hazardous waste characteristics. [RO 11125, 11455, 12604]

On the other hand, if evidence indicated that hazardous wastes had been dumped into surface water in a manner that did not trigger the NPDES regulations (e.g., by illegal dumping), the dumping constituted disposal under RCRA and was subject to the appropriate RCRA regulations. The resulting contaminated sediments were also regulated under RCRA as listed or characteristic hazardous waste under the contained-in policy. [RO 11125]

Dredged sediments now excluded

On November 30, 1998 [63 FR 65874], EPA excluded most dredged sediments from the definition of hazardous waste. Specifically, dredged material subject to the requirements of a permit issued under Section 404 of the CWA or Section 103 of the Marine Protection, Research, and Sanctuaries Act is not a hazardous waste. The permits must be issued by the U.S. Army Corps of Engineers or, in some cases, by the state. This exclusion is for dredged material that will be disposed of in the aquatic environment. It does not apply to dredged material destined for disposal in a landfill. See 63 FR 65921–2. As a result of the exclusion codified in §261.4(g), contaminated sediments will rarely be subject to RCRA regulation.


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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.