Section 264.259 - Special requirements for hazardous wastes FO20, FO21, FO22, FO23, FO26, and FO27(a) Hazardous Wastes FO20, FO21, FO22, FO23, FO26, and FO27 must not be placed in waste piles that are not enclosed (as defined in § 264.250(c) ) unless the owner or operator operates the waste pile in accordance with a management plan for these wastes that is approved by the Regional Administrator pursuant to the standards set out in this paragraph, and in accord with all other applicable requirements of this part. The factors to be considered are: (1) The volume, physical, and chemical characteristics of the wastes, including their potential to migrate through soil or to volatilize or escape into the atmosphere;(2) The attenuative properties of underlying and surrounding soils or other materials;(3) The mobilizing properties of other materials co-disposed with these wastes; and(4) The effectiveness of additional treatment, design, or monitoring techniques.(b) The Regional Administrator may determine that additional design, operating, and monitoring requirements are necessary for piles managing hazardous wastes FO20, FO21, FO22, FO23, FO26, and FO27 in order to reduce the possibility of migration of these wastes to ground water, surface water, or air so as to protect human health and the environment.50 FR 2004, Jan. 14, 1985, as amended at 71 FR 40273 , July 14, 2006