Under Sections 311 and 312, when extremely hazardous substances are contained within a mixture, does a facility still have the option to report the mixture as a whole or by its hazardous components?

Yes, the mixture may be reported as a whole or by its hazardous components.   To determine whether a reporting threshold for an EHS has been met or exceeded, the owner or operator of a facility shall aggregate the quantity of the EHS present as a component in all mixtures at the facility and all other quantities of the EHS present at the facility, including the quantity of the EHS present in mixtures that the facility is reporting as a mixture.