40 CFR §437.20

1. (a)Except as provided in § 437.1(b), (c), or (d) or in paragraph (b) of this section, this subpart applies to that portion of the discharge of wastewater from a CWT facility that results from the treatment or recovery of oil from both oily wastes received from off-site and other CWT wastewater associated with the treatment of, or recovery of oily wastes.
2. (b)In order to ensure appropriate treatment rather than dilution of dissimilar wastes, an NPDES permit writer or control authority may require a new source or an existing source subject to this subpart to achieve alternative effluent limitations and standards, as defined in § 437.2(b), in the following circumstances:
   1. (1)The facility receives, on a continuing basis, flows of process wastewater from five or fewer facilities subject to 40 CFR subchapter N limitations and standards; and
   2. (2)The process wastewater flows received for treatment at the facility have relatively consistent pollutant profiles.