(a) Except as provided in §437.1(b), (c), or (d) or in paragraph (b) of this section, facilities that treat wastes subject to more than one of the previous subparts must comply with either provisions of this subpart or the applicable provisions of subpart A, B, or C. The provisions of this subpart are applicable to that portion of wastewater discharges from a centralized waste treatment facility that results from mixing any combination of treated or untreated waste otherwise subject to subpart A, subpart B, or subpart C of this part only if a facility requests the permit writer or control authority to develop subpart D limitations (or standards) and establishes that it provides equivalent treatment as defined in §437.2(h).

(b) In order to ensure appropriate treatment rather than dilution of dissimilar wastes, an NPDES permit writer or control authority may require a new or existing facility subject to paragraph (a) of this section to achieve alternative effluent limitations or standards as defined in §437.2 (b) in the following circumstances:

(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) The process wastewater flows received for treatment at the facility have relatively consistent pollutant profiles.