Compliance Corner.

De Minimis Wastewater Exemptions

Under §261.3(a)(2)(iv)(A–G), mixtures of very small quantities of certain listed hazardous wastes and wastewater managed in a wastewater treatment system subject to the CWA are exempt from regulation as hazardous wastes. These so-called “de minimis” wastewater exemptions prevent the mixture rule from applying to large-volume, nonhazardous wastewaters that 1) get mixed with small quantities of listed hazardous wastes that are not principal waste streams, and 2) are managed in a facility’s onsite wastewater treatment system. Accordingly, if wastewater mixtures meet EPA’s criteria (described below), they are not hazardous wastes once they reach the headworks of the wastewater treatment system, and they will not produce wastewater treatment sludges that are listed hazardous waste. This is the primary reason the de minimis wastewater exemptions were promulgated: to protect wastewater treatment sludge from carrying listed waste codes.

The §261.3(a)(2)(iv) de minimis wastewater exemptions are sometimes referred to as the “headworks exemptions” because they exempt eligible wastewater mixtures from the mixture rule when they reach the headworks of the facility’s wastewater treatment system. [RO 11116, 11614] For instance, if a facility’s wastewater treatment system leaks waste that meets a listing description before it reaches the headworks, the leaked material is classified as listed hazardous waste. [RO 14095] So where is the headworks of a specific wastewater treatment system? EPA says it is where “final combination of raw or pretreated process wastewater streams typically takes place.” [October 4, 2005; 70 FR 57775] “[H]eadworks can include a central catch basin for industrial wastewaters, a pump station outfall, equalization tank, or some other main wastewater collection area that exists in which transport of process wastewaters stops and chemical or biological treatment begins.” [April 8, 2003; 68 FR 17242]

The de minimis wastewater exemptions cover seven different types of listed wastes, but only if they are mixed with wastewater subject to regulation under Section 307(b) or 402 of the CWA. (Section 307(b) deals with discharges to POTWs; Section 402 deals with NPDES-permitted discharges.) Facilities that have eliminated their wastewater discharge as a result of NPDES or pretreatment program requirements (i.e., zero dischargers) may also take advantage of these exemptions. The agency noted facilities that have eliminated the discharge of wastewaters using permitted Class I injection wells can claim the de minimis exemptions: “EPA continues to believe that underground injection wells can meet the headworks’ definition of zero discharge if the injection well is being used for the purposes of complying with a NPDES permit, other applicable effluent guideline, or pretreatment program requirements.” [October 4, 2005; 70 FR 57777]

The seven specific exemptions are discussed in the following sections.

Listed spent solvents

Two exemptions are provided for spent solvents discharged to a plant’s wastewater system:

1. Listed spent solvents that are carcinogens—Four F001/F002/F005 spent solvents (benzene, carbon tetrachloride, tetrachloroethylene, and/or trichloroethylene) in wastewater mixtures at a concentration of no more than 1 ppm are not hazardous. [§261.3(a)(2)(iv)(A)]
2. Listed spent solvents that are toxic—Fourteen F001–F005 spent solvents (methylene chloride, 1,1,1-trichloroethane, chlorobenzene, o-dichlorobenzene, cresols, cresylic acid, nitrobenzene, toluene, methyl ethyl ketone, carbon disulfide, isobutanol, pyridine, chlorofluorocarbon solvents, and/or 2-ethoxyethanol) in wastewater mixtures at a concentration of no more than 25 ppm are not hazardous. [§261.3(a)(2)(iv)(B)]

These two regulatory sections exempt wastewater containing certain spent solvents listed in §261.31 if the specified concentration limit is not exceeded. What EPA has in mind here are spills or incidental losses from degreasing, maintenance, or manufacturing operations in which small amounts (not principal waste streams) of spent solvents are washed or otherwise released into a sump or drain and are subsequently managed in the onsite wastewater treatment system. [RO 11845] The agency believes these small releases of organic solvents can be reasonably and efficiently managed by the chemical or biological wastewater treatment system associated with most affected facilities.

The exemption also applies to scrubber water generated during combustion of these spent solvents if it is discharged to the combustion facility’s wastewater treatment system. Extending the de minimis exemption to such scrubber waters is a departure (see October 4, 2005; 70 FR 57777) from the agency’s previous position (see RO 11116, 11845). EPA justified adding scrubber waters derived from such combustion, noting that “these scrubber waters would be comparable in expected constituents and concentration levels with the already exempted F-listed solvents.” [70 FR 57777]

However, the de minimis exemption does not apply to spent solvent-contaminated sludges that are mixed or otherwise commingled with wastewater or to such sludges that generate a wastewater through dewatering. [RO 12283]

Refinery wastes

Mixtures of one or more of the following K-wastes and wastewater are not hazardous if the wastes are discharged to the refinery’s oil recovery sewer upstream of primary oil/water/solids separation: K050 heat-exchanger bundle cleaning sludge, K169 crude oil storage tank sediment, K170 clarified slurry oil tank sediment, K171 spent hydrotreating catalyst, and K172 spent hydrorefining catalyst. [§261.3(a)(2)(iv)(C)]

This provision exempts wastewaters from refinery cleaning operations in certain situations. The exemption is not designed to allow the discharge of the entire waste stream (e.g., tank sediments or spent catalysts) into the wastewater collection and treatment system; rather, dilute wastewaters generated during tank or unit cleanout and dewatering operations are covered. [August 6, 1998; 63 FR 42120] The listed wastes excluded under this exemption are discussed below:

• K050 heat-exchanger bundle cleaning sludge—This hazardous waste is generated during periodic backflushing and/or hydroblasting of heat-exchanger bundles. The sludges from these routine maintenance operations (listed as hazardous due to the presence of hexavalent chromium) are usually discharged to the refinery’s sewer system. EPA believes that mixtures of K050 sludges and nonhazardous wastewater do not pose a threat to human health and the environment because the hexavalent chromium from the sludge is almost completely reduced to the trivalent state by reducing agents, such as sulfides, in the raw wastewater. Furthermore, the chromium is present in very low concentrations.
• K169 crude oil storage tank sediment and K170 clarified slurry oil tank sediment—Wastewater containing these wastes is typically generated by dewatering (e.g., centrifuging) the sediment removed from tanks and by final rinsing of the tanks themselves. However, these residues are dilute and contain low levels of the listed wastes.
• K171 spent hydrotreating catalyst and K172 spent hydrorefining catalyst—Application of the headworks exemption to these catalysts allows refiners to continue to use water to cool and wash out spent catalysts from process units prior to further management. Wastewater recovered from “drilling out” the catalyst, steam stripping or washing, or pad drainage are all covered by the de minimis exemptions.

De minimis losses of commercial chemical products and F- and K-wastes

EPA recognizes that small amounts of products produced by, or used as raw materials in, a manufacturing process are often unavoidably lost during normal material handling operations. Many of these materials are P- and U-listed hazardous wastes in §261.33 when discarded. Additionally, small amounts of F- and K-wastes are also inadvertently lost during normal material handling activities. All of these materials are typically managed by draining or washing them into floor drains leading to the wastewater treatment system, a “reasonable and practical means of disposing of these lost materials.” [November 17, 1981; 46 FR 56586]

Since these small quantities of listed wastes can be managed and treated in the facility’s wastewater treatment system without posing a substantial hazard to human health and the environment, the regulations allow mixtures of wastewater (which will be discharged under the CWA) and de minimis losses of §261.31 F-wastes, §261.32 K-wastes, and §261.33 P- and U-chemicals to be exempt from hazardous waste management. [§261.3(a)(2)(iv)(D)]

Laboratory wastes

Laboratory wastewaters containing listed wastes that were listed due to their toxicity are eligible for the de minimis exemption if: 1) the annualized average flow of laboratory wastewater does not exceed 1% of total wastewater volumetric flow into the headworks of the facility’s wastewater treatment system, or 2) the combined annualized average concentration of toxic §§261.31, 261.32, and 261.33 wastes resulting from laboratory operations does not exceed 1 ppm at the headworks. Toxic laboratory wastes demonstrated not to have been discharged to wastewater do not have to be included in this calculation. [§261.3(a)(2)(iv)(E)]

The laboratory de minimis wastewater exemption applies only to incidental losses of listed hazardous waste from laboratory operations. This would include small amounts of listed spent solvents, listed wastes brought in for analysis, and §261.33 chemicals used during analysis added unavoidably to large volumes of water. Also included are laboratory spills and residues from cleaning glassware washed into sink drains and carried into the sewer. Deliberate bulk discharges of chemicals not part of laboratory operations are not covered. “The introduction of other listed wastes into the plant wastewater system [outside the conditions set forth in §261.3(a)(2)(iv)(E)] may void the exclusion for the facility.” [RO 11727; see also RO 12257]

Both analytical and research and development laboratories may qualify for this exemption. However, EPA does not consider a pilot plant to be a laboratory operation, and wastes generated from such a unit are not exempt. [November 17, 1981; 46 FR 56587]

Facilities may prove compliance with the 1% wastewater flow limit by measuring (EPA’s preferred approach) or conservatively calculating the annual average wastewater discharge from the laboratory and the annual average wastewater flow entering the wastewater treatment system.

EPA recognizes that, even though some laboratories may exceed the 1% limit, they still may not discharge enough listed hazardous wastes into their drains to warrant regulation under the mixture rule. As a result, the agency allows the 1-ppm compliance test to be used in lieu of the 1% wastewater flow limit. If a facility chooses this option, compliance may be demonstrated using an audit of laboratory chemical purchases, an estimate of the aggregate amounts of toxic §§261.31, 261.32, and 261.33 materials disposed of, and estimates of wastewater flow into the headworks of the treatment or pretreatment facility. “Facilities must make the worst-case assumption that all listed hazardous wastes used in the laboratories will be discarded to wastewater, unless they can demonstrate through appropriate records that these materials were disposed of elsewhere.” [November 17, 1981; 46 FR 56587]

Carbamate production wastes

De minimis losses of certain wastes (K156 and K157) from the production of carbamates and carbamoyl oximes are also exempt when mixed with wastewater and pass through the headworks of a facility’s wastewater treatment system. [§261.3(a)(2)(iv)(F–G)] These exemptions operate similarly to those for losses of listed spent solvents discussed above; that is, the exemptions are predicated on meeting certain chemical concentration limits at the headworks of the wastewater treatment system.

Miscellaneous issues

The de minimis wastewater exemptions apply only to mixtures sent to a facility’s onsite wastewater treatment system discharging under Section 402 or 307(b) of the CWA. Any mixtures of listed wastes and wastewater sent offsite must be managed as hazardous waste, including using a manifest. [RO 14181]

The exemptions in §261.3(a)(2)(iv) do not limit the manner in which the listed wastes are transported to the wastewater treatment plant. Therefore, the wastes can be transported via truck, for example, in addition to direct discharge to a sewer and still qualify for the exemption. [RO 13488, 14181]

The de minimis wastewater exemptions do not apply to facilities which discharge into privately owned treatment works. However, the privately owned treatment works may qualify for a de minimis exemption if its own discharge is subject to regulation under an NPDES permit or pretreatment program and any listed wastes that it generates meet the §261.3(a)(2)(iv) exemption criteria. [November 17, 1981; 46 FR 56584]

If a facility meets the criteria for one of the §261.3(a)(2)(iv) de minimis wastewater exemptions, does the exemption also apply to sludge produced by the wastewater treatment plant that treats the wastewater? Sludge generated from a wastewater that meets all of the criteria for a de minimis exemption would also be exempted from the hazardous waste listing. Since the wastewater is not listed at the headworks of the treatment facility (by virtue of the exemption from the mixture rule), the derived-from rule would not apply the listing to the resulting sludge. However, if the sludge exhibits a hazardous waste characteristic, it would be considered a hazardous waste for that reason. Additionally, if the influent wastewater meets a listing description not addressed by the de minimis exemptions, the sludge would be hazardous via the derived-from rule. [RO 13419, 13784]