Section 279.21 - Hazardous waste mixing(a) Mixtures of used oil and hazardous waste must be managed in accordance with § 279.10(b) .(b) The rebuttable presumption for used oil of § 279.10(b)(1)(ii) applies to used oil managed by generators. Under the rebuttable presumption for used oil of § 279.10(b)(1)(ii) , used oil containing greater than 1,000 ppm total halogens is presumed to be a hazardous waste and thus must be managed as hazardous waste and not as used oil unless the presumption is rebutted. However, the rebuttable presumption does not apply to certain metalworking oils/fluids and certain used oils removed from refrigeration units.57 FR 41612, Sept. 10, 1992, as amended at 58 FR 26425, May 3, 1993