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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, 2018 Edition.

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Wastewater Treatment Units

Facilities sometimes find that more than one environmental program applies to a single waste stream. An example of this situation is a characteristic or listed wastewater, which is subject to RCRA regulation from its point of generation on, but whose management and discharge is subject to the CWA as well. This is a common occurrence as a significant percentage of the hazardous waste produced in the United States is aqueous waste or otherwise amenable to wastewater treatment. It would appear that equipment (e.g., tanks and other units) used to treat hazardous wastewater or hazardous wastewater treatment sludge would have to be permitted under both RCRA and the CWA and meet design and operating standards under both of these regulatory programs.

EPA recognized the above situation during the early stages of RCRA implementation and promulgated the so-called wastewater treatment unit (WWTU) exemption from RCRA requirements on November 17, 1980. [45 FR 76074] Designed specifically to avoid duplicative control standards under both RCRA and the CWA, the WWTU provision exempts equipment used to treat hazardous wastewater and wastewater treatment sludge from the 1) RCRA permitting requirements of Part 270, 2) general facility standards in Parts 264 and 265, and 3) specific tank design and operating standards in Subpart J of Parts 264 and 265. [RO 11066, 11379, 11408, 13526, 13727, 14122]

In our discussions below, we first summarize the specific applicability requirements of the three-part definition of a WWTU. A review of the scope of this exemption is then presented, illustrated by a number of WWTU examples.

The key definition

To qualify for the WWTU exemption, a piece of equipment must meet the three-part definition in §260.10, which reads as follows:

Wastewater treatment unit means a device which:

“(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; and

“(2) Receives and treats or stores an 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 tank or tank system in §260.10 of this chapter.”

In the sections below, we examine each of the three parts of this definition.

Part 1—The CWA must apply to the wastewater treatment system

In order to qualify for the WWTU exemption, treatment units must be subject to regulation under one of two CWA programs: 1) the National Pollutant Discharge Elimination System (NPDES) permitting program, which is outlined in Section 402 of the CWA; or 2) the national pretreatment program, mandated by Section 307(b) of the CWA for facilities that discharge to POTWs. (Note that EPA added a third option of being subject to an effluent guideline issued under Sections 301 and 402 of the CWA in RO 11408.) The agency’s logic is as follows: “The underlying assumption used in justifying the wastewater treatment unit exemption was that tanks used to handle hazardous wastewaters at these facilities would be provided with EPA oversight under the Clean Water Act, thereby ensuring no significant decrease in environmental control afforded at these facilities.” [RO 11519; see also RO 14122]

Although the NPDES program is based on source discharge permits and most POTWs issue permits to upstream facilities, EPA notes that WWTUs are not required to have CWA permits to qualify for the RCRA exemption:

“The agency also intends that the phrase ‘subject to regulation under either Section 402 or 307(b) of the Clean Water Act’ should be given a broad interpretation. This phrase includes all facilities that are subject to NPDES permits and encompasses facilities subject to either categorical pretreatment standards or general pretreatment standards. It is not necessary that the permits actually be issued or that pretreatment standards actually be in force. It is sufficient that the facility be subject to the requirements of the Clean Water Act.” [Emphasis in original.] [RO 11020] See also RO 13526.

Can zero-discharge facilities qualify for the WWTU exemption?

The WWTU exemption’s applicability to zero-discharge facilities is based on whether a connection exists between CWA requirements and the facility’s lack of a discharge. In other words, a facility that produces no effluent as a direct result of the CWA is eligible for the WWTU exemption. [RO 11036, 11374] This includes facilities that achieve zero discharge by onsite wastewater storage or disposal [RO 11139], or where applicable effluent guidelines or pretreatment standards specify zero discharge. [RO 14608] Stated another way, the WWTU exemption would be available to a facility that eliminated its discharge of treated effluent in order to meet an NPDES or pretreatment requirement, but the exemption would not be available to a facility that never had a discharge regulated under the CWA. [September 2, 1988; 53 FR 34080, RO 13526, 14608] In fact, EPA expects that some facility owners/operators may attempt to apply for a zero-discharge NPDES permit at an otherwise unregulated facility in order to qualify for the WWTU exemption from RCRA. [RO 13112]

Based on the above discussion, a hazardous wastewater treatment tank at a zero-discharge facility that does not meet the first part of the §260.10 definition would generally have to be RCRA-permitted (and would have to meet Part 264, Subpart J tank standards). Explaining this approach, EPA stated: “while it is true that a zero-discharge system does not require a NPDES permit, the absence of this permit (or an applicable effluent guideline or pretreatment standard specifying zero discharge) necessitates a RCRA Part B permit. Otherwise, a wastewater unit treating hazardous wastes could escape regulations developed to ensure protection of human health and the environment. Although this approach may, at first, be viewed as a disincentive to developing zero-discharge systems, a NPDES permit that specifies ‘zero discharge’ may be the most appropriate alternative to a RCRA Part B permit in industries without zero-discharge effluent guidelines, encouraging zero-discharge systems while being consistent with the agency’s mandate to protect human health and the environment.” [RO 11408]

Part 2—The unit must be managing hazardous wastewater or hazardous wastewater treatment sludge

The second part of the WWTU definition is pretty wordy, but the bottom line is that a WWTU must be receiving and treating or storing hazardous wastewater or hazardous wastewater treatment sludge. Guidance on how EPA defines those two materials is summarized below.


For the purposes of the WWTU definition, EPA has not promulgated a definition of “wastewater,” although it notes that states can define it if they want. [RO 11582] The agency has, however, provided guidance on what wastewater is (and isn’t). Wastewater is generally assumed to be wastes that “are substantially water with contaminants amounting to a few percent at most.” [RO 11020, 14472]

The following examples apply the above logic in determining if a given stream is wastewater:

  • A mixture of 50% alcohol/50% water is not wastewater, but a D002 corrosive waste containing 95% water and 5% total dissolved solids is. [RO 11173]
  • Wastewater is not concentrated chemicals or nonaqueous wastes. [RO 11020, 11561, 11749] For example, free-phase tetrachloroethylene from a dry cleaner is not wastewater. [RO 11749]
  • Petroleum tank bottoms are neither wastewater nor wastewater treatment sludge. [RO 11561]
  • Spent solvents and D001 ignitable liquids are also not wastewater. [RO 12182]
  • Hazardous landfill leachate may meet the definition of wastewater. [February 11, 1999; 64 FR 6807]

Note that the LDR definition of wastewater at §268.2(f) cannot be used to determine applicability of the WWTU exemption. [RO 11551]

Wastewater treatment sludge

Although not defined in the regulations, EPA has described the term “wastewater treatment sludge” in guidance, stating that “wastewater treatment sludge is any material that precipitates or otherwise is separated from wastewater during treatment.” [RO 11551] For example, petroleum tank bottoms are not generated from the treatment of wastewater and so would not meet this definition. [RO 11561]

Part 3—Tanks and tank systems only

The third portion of the WWTU definition requires that a WWTU be either a tank or a tank system, both of which are defined in §260.10 as follows:

Tank means a stationary device, designed to contain an accumulation of hazardous waste which is constructed primarily of non-earthen materials (e.g., wood, concrete, steel, plastic) which provide structural support.”

Tank system means a hazardous waste storage or treatment tank and its associated ancillary equipment and containment system.”

Normally when we think of a tank, we think of an aboveground, cylindrical structure. But many other types of units may qualify for the WWTU exemption under the above definition of “tank.”

What is the RCRA status of an air stripping unit used to treat RCRA-hazardous contaminated ground water?

The air stripper may fit the definition of a tank in §260.10 and, assuming it meets the other two criteria in the WWTU definition, may qualify for the WWTU exemption. [RO 12783, 12880]

What about benzene strippers operating in a refinery’s wastewater treatment system?

Like various other air and steam strippers, benzene strippers may qualify as tanks and be eligible for the WWTU exemption. [RO 13558]

As described below, a variety of different types of equipment can be considered to be a tank or part of a tank system and, therefore, eligible for the WWTU exemption.

Evaporators, filter presses, dryers, etc.

Based on its belief that they fit the definition of tank or tank system (and assuming that the other two parts of the WWTU definition are met), EPA has determined that the following types of equipment qualify for the WWTU exemption: aeration tanks, blenders, clarifiers, dehydrators, dryers, evaporators, filters, grit chambers, presses, sludge digesters, thickeners, and many other types of processing equipment. [November 17, 1980; 45 FR 76078, RO 11020, 11118, 11379, 11561, 11749, 11752, 11840, 12527, 13003, 14472] Case Study 1 presents an example of determining whether a sludge dryer in a wastewater treatment system qualifies as a WWTU. Bear in mind, however, that EPA encourages facilities to check with their state RCRA authority for final decisions on the WWTU exemption for a given piece of equipment.

Case Study 1


Sumps that meet the definition of “tank” are WWTUs if they are managing hazardous wastewater or wastewater treatment sludge and are associated with a wastewater treatment system that is subject to regulation under the CWA. [RO 11134, 14028]

A sump meeting the definition of a tank that is used to collect and then convey hazardous wastewater to a separate WWTU could be considered ancillary equipment to the WWTU and would still be excluded from RCRA tank standards. [53 FR 34080, RO 11561]

If the sump does not meet the definition of a tank (i.e., its walls are not self-supporting), then it is a surface impoundment and, if managing hazardous waste, a hazardous waste surface impoundment subject to RCRA permitting and Part 264, Subpart K standards.

Sinks and sewers

Although the types of equipment listed above that may qualify for the WWTU exemption are broad, several miscellaneous items merit additional clarification.

A facility dips small parts in a 50/50 mixture of alcohol and water. Is the dilution of spent alcohol/water dip solution in a sink to render the D001 ignitable waste nonhazardous considered wastewater treatment, and, if so, is the process eligible for the WWTU exemption?

Since the dilution is intentional, rather than incidental to conveyance to the treatment plant, hazardous waste treatment is occurring. Although the sink is part of a CWA-permitted wastewater collection and treatment system and would probably meet the definition of a tank, the spent dip solution is not wastewater since it contains 50% alcohol. Thus, the sink does not qualify as a WWTU and the exemption would not apply. [RO 11173]

If D002 corrosive hazardous waste from deionization units travels from a building to an onsite, industrial wastewater treatment plant via a sewer and the waste is neutralized in the sewer (so as to not exhibit the characteristic of corrosivity), could that sewer be a WWTU?

First, the wastewater treatment plant is subject to CWA requirements. Second, the corrosive hazardous waste is wastewater since it contains 95% water and only 5% total dissolved solids. Third, EPA considers that: “devices such as flumes, gutters, troughs, and pipes…are not commonly considered to be tanks, but…nevertheless meet the expansive definition of tank in §260.10.” [November 17, 1980; 45 FR 76078] Thus, the sewer may qualify for the WWTU exemption (if state RCRA authorities concur). [RO 11173]

Ancillary equipment

On September 2, 1988 [53 FR 34080], EPA modified the WWTU exemption to ensure that it applies not just to tanks, but also to tank systems. The agency’s intent was to extend the scope of the WWTU exemption to include ancillary equipment that is associated with an exempt hazardous waste storage or treatment tank. (Recall that the definition of “tank system” includes “associated ancillary equipment.”)

The agency defines “ancillary equipment” in §260.10 as follows:

“[A]ny device including, but not limited to, such devices as piping, fittings, flanges, valves, and pumps, that is used to distribute, meter, or control the flow of hazardous waste from its point of generation to a storage or treatment tank(s), between hazardous waste storage and treatment tanks to a point of disposal onsite, or to a point of shipment for disposal offsite.”

Thus, the piping, fittings, flanges, valves, pumps, etc. associated with a WWTU also qualify for the exemption from RCRA permitting and Subpart J standards. [RO 13126]

Responding to questions from regulated facilities, EPA notes that the following items do not qualify as ancillary equipment:

  • A container used to store wastewater prior to introduction to a tank used for treating wastewater is not considered ancillary equipment to that tank and cannot qualify for the WWTU exemption. Such containers would be 90- or 180-day containers subject to §262.17 or 262.16, respectively. [RO 11551]
  • An unlined earthen ditch used to direct hazardous wastewater to a treatment tank (and any other device that is not designed to prevent leakage or discharge) cannot be considered ancillary equipment and cannot qualify for the WWTU exemption. EPA bases this conclusion on its opinion that any device that allows leakage or discharge of hazardous waste is actually disposing hazardous waste. Thus, tank systems (including associated ancillary equipment) must provide containment in order to qualify for the WWTU exemption. [RO 11631, 13653, 13669]

Incinerators, lagoons, and surface impoundments

While certain circumstances may sometimes render tanks, tank systems, and associated ancillary equipment ineligible for the WWTU exemption (see the section below for such examples), incinerators and lagoons/surface impoundments never qualify for the WWTU exemption, even if they are part of a wastewater treatment system subject to regulation under the CWA. [July 18, 1990; 55 FR 29230, RO 11020, 11134, 12605, 13147]

Scope of the WWTU exemption

This subsection addresses a number of questions that come up regarding the scope and reach of the WWTU exemption.

WWTU exemption applies to equipment, not to wastes

The regulatory exemption provided to a WWTU applies only to the unit (i.e., to the equipment that makes up the WWTU)—not to the waste within or discharging from the unit. Thus, if hazardous waste enters a WWTU, it remains a hazardous waste while in the unit (unless a characteristic waste is decharacterized), and the residues, including treated wastewater effluent and any sludge, may still be hazardous based on the derived-from rule. [RO 11066, 11551, 12527, 12605]

Because their WWTUs are exempt from RCRA standards, some owners/operators mistakenly believe that the hazardous waste managed in those units is also exempt from regulation. For example, if the hazardous waste being managed in a WWTU is listed, some people would argue that the effluent from the unit or sludge generated in the unit is no longer hazardous (as it would otherwise be under the derived-from rule). This is not true. Only the equipment itself is exempt from RCRA regulation—not the waste managed within it. EPA has noted:

“Only the wastewater treatment unit (i.e., the tank) is exempt; the exemption does not ‘follow’ or attach to the waste. Consequently, all applicable hazardous waste management standards apply to the waste prior to treatment in the WWTU, and to any residue generated by the treatment of that waste. In other words, solid waste resulting from the treatment of a listed hazardous waste in an exempt WWTU will remain a listed hazardous waste, and solid waste resulting from the treatment of a characteristic hazardous waste in an exempt unit will remain hazardous as long as the solid waste continues to exhibit a characteristic.” [RO 13541]

For example, sludge removed from a WWTU that exhibits a characteristic is subject to all RCRA requirements if stored in a container and/or manifested offsite. [RO 14718] Any leaks from the WWTU could still be hazardous waste depending on the derived-from rule.

What are WWTUs exempt from?

Three specific provisions within the RCRA regulations implement the WWTU exemption:

  • §264.1(g)(6) exempts WWTUs located at permitted TSD facilities from the requirements of Part 264, including the tank standards of Subpart J and the air emission standards of Subparts AA–CC. [December 6, 1994; 59 FR 62913]
  • §265.1(c)(10) exempts WWTUs located at interim status TSD facilities and generator facilities from the requirements of Part 265, including the tank standards of Subpart J and the air emission standards of Subparts AA–CC.
  • §270.1(c)(2)(v) exempts owners/operators from the requirement to obtain a RCRA permit for their WWTUs.

Additionally, EPA guidance notes that WWTUs are exempt from the generator accumulation standards in §§262.16–17. Therefore, for example, no “Hazardous Waste” marking or 90- or 180-day accumulation start dates would be necessary for these units. [RO 13727]

As is evident from this list, the WWTU exemption provides owners/operators a significant advantage for treating hazardous wastes in qualifying units. As noted at the beginning of this section, however, the exemption applies only where the treatment unit is subject to certain provisions of the CWA.

WWTUs must be dedicated to onsite wastewater treatment systems

Having been asked repeatedly about this issue, EPA has stated that the WWTU exemption applies to “any tank system that manages hazardous wastewater and is dedicated for use with an onsite wastewater treatment facility.” [Emphasis added.] [53 FR 34080] See also RO 11066, 11551, 13112, 13226.

For the purpose of the WWTU exemption, EPA allows a broad interpretation of the term “onsite.” There need be no direct mechanical connection between tanks or sumps holding hazardous wastewater and other components of the wastewater treatment system. [RO 12354] The means of conveyance of the waste between storage and treatment units does not affect the applicability of the WWTU exemption. [RO 13112] “The applicability of the [WWTU] exemption does not depend on whether the wastewater is piped or trucked, or conveyed in any other manner to the wastewater treatment facility within the boundaries of the facility generating the wastewater.” [53 FR 34080]

Hazardous wastewater is stored in a tank or sump that is emptied by a vacuum truck. The vac truck then drives across the facility and discharges the wastewater into the onsite wastewater treatment plant. Can the tank or sump be considered a WWTU?

Yes. No requirement exists for WWTUs to be hard-piped together. Wastewater may be piped, trucked, or otherwise conveyed from one unit to the next and still be eligible for the exemption. [53 FR 34080, RO 12354]

Hazardous waste is treated in a RCRA-permitted tank subject to Part 264, Subpart J requirements. Can another tank that receives a residue from this treatment qualify for the WWTU exemption?

Yes. “The [WWTU] exemption is not altered by the regulatory status of other storage tanks located at the same facility.…[I]f the storage of a waste results in the generation of a wastewater or wastewater treatment sludge, and a ‘downstream’ tank receives this wastewater or sludge, that downstream tank may be eligible for the exemption provided that it…meets the…criteria in §260.10.” [RO 11561]

Based on the above guidance, EPA notes [in RO 11519] and we strongly recommend that any tanks or sumps that are considered WWTUs at a facility should be identified in the facility’s CWA (NPDES or pretreatment program) permit—specifically in the process flow diagram associated with the permit.

Onsite handling with subsequent shipment for offsite treatment/disposal

As noted above, EPA clearly intends that the WWTU exemption apply only to units dedicated for use with an onsite wastewater treatment system that discharges under the CWA. “However, if a tank system, in addition to being used in conjunction with an onsite wastewater treatment facility, is used on a routine or occasional basis to store or treat a hazardous wastewater prior to shipment offsite for treatment, storage, or disposal, it is not covered by this exemption.” [Emphasis added.] [53 FR 34080] Thus, facilities that generate hazardous wastewater, store it in tanks, and then ship it to offsite facilities for treatment or disposal cannot claim the WWTU exemption for those tanks. This limitation on the scope of the WWTU exemption holds 1) regardless of whether onsite treatment of the wastewater occurs at the generating facility prior to offsite shipment, and 2) even if the wastewater is shipped offsite to a POTW or another facility with an NPDES permit. [53 FR 34080, RO 13112, 13226, 13318]

As such, tanks that are used, even on a part-time basis, for the treatment and/or storage of hazardous wastewater prior to shipment offsite for treatment and/or disposal are not eligible for the WWTU exemption. Rather, these tanks would be RCRA units subject to Subpart J hazardous waste tank standards. [RO 11066, 11551, 13126, 13203, 14262] The agency explains its reasoning as follows:

“[I]n order to satisfy the WWTU exemption, a tank must be dedicated solely for onsite wastewater treatment at all times and for no other purpose…. EPA did not intend the WWTU exemption to apply in situations involving ‘dual use’ of a tank (when a tank is concurrently used for wastewater treatment and for another purpose). Nor did EPA intend for the exemption to apply in situations…involving ‘alternating use’ of a tank. Since the purpose of this exemption is to avoid dual regulation under the [CWA] and [RCRA], EPA believes that a tank must be used only for wastewater treatment purposes at all times in connection with an onsite wastewater treatment facility in order to qualify for the exemption.” [RO 14262]

EPA’s concern behind this restriction is that tanks used to manage hazardous wastewater prior to offsite shipment are probably not subject to CWA regulatory requirements. Allowing the WWTU exemption to apply to such tanks would short-circuit the agency’s belief that the CWA can adequately regulate the units in lieu of RCRA, since such tanks would be subject to neither program. [RO 11519]

This concept often brings up the question of maintenance problems associated with a facility’s wastewater treatment system. If the onsite wastewater treatment plant is shut down due to malfunction or routine maintenance, hazardous wastewater may have to be shipped offsite. Would the hazardous wastewater storage tanks/sumps then lose their WWTU exemption? Although we’ve never seen any guidance on this issue, we suspect the exemption would not be lost for these units, subject to the enforcement discretion of the state agency.

Offsite shipment of sludge for treatment/disposal

If the offsite shipment of hazardous wastewater invalidates the WWTU exemption for a particular tank, what about removing sludge from a WWTU and shipping it offsite for disposal? EPA noted that the removal of wastewater treatment sludge or other residues from tanks for offsite disposal would not disqualify these tanks from the WWTU exemption “provided that this occurs as part of normal wastewater treatment activities. The removal and offsite disposal of treatment sludges and tank bottoms are not necessarily indications that the tanks in question are being used in a manner other than for onsite wastewater treatment; on the contrary, the generation of tank bottoms and filter cakes is a common process in wastewater treatment operations.” [RO 13226; see also RO 14718]

However, we need to be careful about the regulatory status of units that are used to store hazardous wastewater treatment sludge prior to shipping the sludge offsite for treatment and/or disposal. If the sludge is mostly solid (e.g., filter cake), the last unit used to store it before offsite shipment will likely be a roll-off box or some other container. Such a unit cannot be an exempt WWTU because it doesn’t meet the definition of a tank; thus, these containers will likely be 90- or 180-day accumulation containers if they are holding hazardous sludges.

Conversely, if the wastewater treatment sludge is a hazardous liquid (e.g., an oily waste removed from the wastewater), the last unit holding such material before offsite treatment/disposal (e.g., fuel blending) will more likely be a tank. Does this tank qualify as a WWTU? You might be able to make an argument that it does, based on the three-part WWTU definition. However, EPA’s guidance notes that such tanks are not WWTUs:

“While the storage of sludges may in many instances be part of ongoing wastewater treatment, the agency also wishes to emphasize that sludges may be generated and stored as part of activities not related to wastewater treatment under the CWA. In cases where the sludges are to be recycled…sludges might be removed from treatment tanks and placed into tank-like units that mix or slurry and inject the sludges as part of the recycling process, in which case a judgment could be made that the mixing tank is part of the exempt recycling process (§261.6(c)), and is, therefore, not a WWTU…. Also, in instances where the sole purpose of the tank is to accumulate a sufficient volume of waste to facilitate the offsite transport of these sludges for further treatment and/or disposal, the [WWTU] exemption would not apply because that activity is separate and distinct from any wastewater treatment activities covered under the CWA. In this instance, a generator may choose (or be so directed by the implementing agency) to manage the tanks in accordance with the [90/180/270-day] generator accumulation provisions in [§§262.16–17], rather than as an exempt WWTU.” [RO 14465]

Common wastewater treatment facilities

Given that onsite management of hazardous wastewater is key to the WWTU exemption, what about situations where multiple facilities use a common wastewater treatment facility or conveyance system? Figure 1 shows three such situations, which are discussed below.

Figure 1

In the first scenario, the same company operates a chemical plant and a refinery on adjacent sites. Both units generate hazardous process wastewaters that are collected and then piped to an NPDES-permitted wastewater treatment plant located at the refinery. (The treatment plant’s permit limits are based on the waste loads from both facilities.)

Is a tank at the chemical plant that stores hazardous process wastewater eligible for the WWTU exemption, along with the wastewater collection and treatment tanks at the refinery and the common treatment plant?

Yes. Per EPA, “[t]he fact that the NPDES permit is based on the waste loads of both the chemical plant and refinery is not necessarily the determining factor in deciding eligibility for the WWTU exemption…. In order to ensure that the reach of the NPDES permit is sufficient to adequately regulate the wastewater treatment tank at the chemical plant, the chemical plant and/or the tank itself needs to be specifically identified in the permit. This could be accomplished by stating expressly in the permit that it covers the chemical plant, or by making the operator of the chemical plant a co-permittee or a limited co-permittee on the permit with the operator of the refinery. This coverage would ensure adequate day-to-day control over the tank under the CWA to justify an exemption from RCRA requirements.” [RO 11519]

Under the second scenario, Company A and Company B operate separate units within the same RCRA facility boundary. Hazardous process wastewater from each company is piped via a common sewer to an onsite wastewater treatment system operated by Company A. The treatment system has an NPDES permit for its outfall.

Are the wastewater tanks operated by Company B WWTUs?

“The analysis for this scenario essentially is the same as for [the first scenario] above. To be eligible for the exemption, Company B must be a co-signatory to the NPDES permit and/or otherwise identified as a limited co-permittee on the permit issued to Company A, or the permit itself must expressly cover Company B (for example, the description of the facility covers the RCRA boundaries, and ‘upstream’ wastewater treatment processes and equipment are identified) so that CWA authorities can prescribe and enforce tank system requirements at Company B as well as at Company A.” [RO 11519]

In the third scenario, Company A and Company B operate a joint venture at a Company A site that discharges hazardous process wastewater to a POTW.

Are tanks and tank systems within the joint venture facility eligible for the WWTU exemption?

“Both companies must comply with [CWA] Section 307(b) pretreatment requirements, since both are introducing pollutants directly into a POTW. Therefore, both companies are eligible for the WWTU exemption.” [RO 11519]

Treatment of hazardous wastewater/sludge generated offsite

Since one of EPA’s key goals in assessing eligibility for the WWTU exemption is ensuring that RCRA-exempt units are subject to CWA regulations, it follows that the agency would not be overly concerned about where the hazardous wastewater being managed comes from, as long as the unit is subject to CWA control. Thus, EPA has stated that, if a tank receives hazardous wastewater from offsite facilities for treatment and/or storage, it qualifies for the WWTU exemption if it meets all of the eligibility criteria. [53 FR 34080, RO 11020, 11561, 13112, 13318, 14206]

A facility may also receive hazardous wastewater treatment sludge from offsite and still be potentially eligible for the wastewater treatment unit exemption. As long as the sludge received is not a concentrated chemical or nonaqueous waste, the receiving facility may receive it. [RO 11561]

Three related issues are also addressed in guidance. First, such offsite hazardous wastewater or wastewater treatment sludge shipments must (of course) be manifested. [RO 11020, 11039, 11066, 14206] Second, an offsite facility with WWTUs that have qualified for the exemption may be listed as the “designated facility” authorized to receive shipments of hazardous waste on the manifest [per §262.20(b)]. In other words, such WWTUs meet the definition of “designated facility” promulgated at §260.10. [RO 11561, 14206] See Case Study 2. Third, the ownership of the offsite facility and any expense reimbursement for the facility accepting offsite material for treatment are irrelevant to determining the applicability of the WWTU exemption. [RO 11561]

Case Study 2

Portable tanks

Only tanks and tank systems may qualify for the WWTU exemption discussed in this section. What about portable tanks such as frac tanks that are portable when empty but stationary (can’t be moved) when full? Can they qualify as tanks under the WWTU exemption? The answer is “maybe.”

In the preamble to a June 3, 1987 proposed rule [52 FR 20919], EPA stated the following:

“Several members of the regulated community have asked whether a mobile unit could ever qualify as a tank, because §260.10 defines tanks as ‘stationary devices.’ EPA confirms that a mobile tank would qualify as a tank under §260.10 and would be subject to the Subpart J tank standards of Part 264, as long as it was intended to be stationary during operation and it otherwise met the definition of a tank.”

Although the above text addresses portable tanks in terms of TSD facility tank standards, the agency extended its June 1987 logic to apply to the WWTU exemption in several subsequent guidance letters. See RO 12220 (for portable filter presses), 12928 (for mobile sludge dewatering devices), and 13144 (for wheeled tanks). This guidance seems like pretty good evidence that the agency intends for portable tanks to qualify for the WWTU exemption under the right circumstances. However, RO 13144, which has been deleted from EPA’s RCRA Online system, previously had been listed as “SUPERSEDED: NOT CURRENT EPA POLICY.” (No such designation is noted for RO 12220 or 12928.) In addition, §260.10 gives the definition for a container as “any portable device in which a material is stored, transported, treated, disposed of, or otherwise handled.” So, is a portable tank a tank, a container, or both?

The bottom line is that this is probably best left as a “check-with-your-state” issue. For example, we have seen letters written from different states to the manufacturer of a storage device that is portable when empty but stationary when full; some states say the device is a container—others that it is a tank. Bear in mind, however, that a portable tank set up with flexible hoses and quick-connect couplings to manage hazardous waste looks less like a tank than a portable tank with hard piping and permanent connections.

Miscellaneous WWTU exemption issues

EPA has dealt with a number of other issues involving the WWTU exemption, as noted below.

Eligibility decisions are unit-specific

Eligibility decisions for tanks and tank systems in terms of the WWTU exemption should be made on a unit-specific basis. For example, a given facility may have some tanks that handle hazardous wastewater prior to shipment to an offsite treatment plant and other tanks dedicated to an onsite wastewater treatment system. While the first set of tanks would not qualify for the WWTU exemption, this fact has no effect on the eligibility of the latter set of tanks. [RO 11551, 11561]

WWTUs that leak are not WWTUs

Besides contaminating the environment, WWTUs that leak could theoretically lose their designation as WWTUs and, therefore, their eligibility for exemption from Subpart J standards. [RO 11631, 13653, 13669] In short, such units might no longer be considered tanks (Part 3 of the WWTU definition), since a tank must be “designed to contain an accumulation of hazardous waste.” [Emphasis added.] [§260.10] (See also November 17, 1980; 45 FR 76079 for details.)

In addition, leaking WWTUs could be subject to enforcement action based on disposal of hazardous waste without a permit. [RO 14470] We are aware of an enforcement case where a facility was using a leaking tank (sump) that it considered to be an exempt WWTU. Regulators, noting the leaks, determined that the unit was actually a surface impoundment that is not eligible for the WWTU exemption. A significant fine for operating an unpermitted RCRA surface impoundment was imposed.


Even though WWTUs are exempt from most RCRA requirements, they still meet the definition of a solid waste management unit (SWMU). [July 27, 1990; 55 FR 30808] Therefore, they may be subject to RCRA corrective action at facilities that have RCRA permits or operate under interim status.

LDR notices

Despite the WWTU exemption from Parts 264, 265, and 270 RCRA requirements, hazardous wastes managed in WWTUs are still subject to the LDR notification provision of §268.7(a)(7). Thus, when waste treated in a WWTU becomes nonhazardous, the owner/operator must place a one-time notice in the facility files describing 1) the generation of the subject hazardous waste, 2) the subsequent exclusion of the waste from the definition of hazardous or solid waste, and 3) the disposition of the waste. [RO 13547, 14216]


Topic: Universal Waste Handler Requirements

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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.