EPA530-R-02-005i
RCRA, SUPERFUND & EPCRA CALL CENTER MONTHLY REPORT
September 2002
1. Mixture Rule Exclusion For Wastewater Containing Toxic Wastes
The mixture rule in 40 CFR Section 261.3(a)(2)(iv) regulates mixtures of listed hazardous wastes
and other solid wastes as listed wastes. In some facilities, small amounts of listed laboratory
wastes are discharged into the facility's wastewater treatment system where they mix with
nonhazardous wastewaters from the rest of the facility. Generally, under the mixture rule, these
wastewaters would carry the hazardous waste listing. However, Section 261.3(a)(2)(iv)(E)
provides an exclusion for laboratory wastewaters that contain small amounts of wastes that are
listed as toxic wastes (T). Does this exclusion also include wastes that are listed as toxic wastes
(T) and as characteristic wastes, such as ignitability (I), corrosivity (C), or reactivity (R)?
The Section 261.3(a)(2)(iv)(E) exclusion from the mixture rule applies to wastes listed as toxic
wastes and as characteristic wastes (i.e., I, C, or R). To meet this exclusion, the annualized
average flow of laboratory wastewater into the facility headworks must not exceed one percent
of the total wastewater flow or the estimated combined average concentration of toxic
constituents entering the headworks or pretreatment facility must not exceed one part per million
(ppm) (Section 261.3(a)(2)(iv)(E)). This requirement ensures that only small levels of toxic
constituents are discharged and that the hazardous characteristic is removed by the waste mixing
with the facility's nonhazardous wastewater stream. Facilities may use this mixture rule
exclusion for wastes listed as toxic wastes and as characteristic wastes (i.e., I, C, or R), as long
as their flow of laboratory wastewater does not exceed one percent of the total flow into the
facility's headworks or the flow of toxic constituents does not exceed one ppm into the facility's
headworks or pretreatment system.
Although the wastewaters fall out of Subtitle C regulation through this exclusion, any sludges
that are generated during wastewater treatment are subject to Subtitle C regulation if they exhibit
a characteristic of hazardous waste.
RO 14633

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