D published a Notice of Intent to Develop Rulemaking and an Advance Notice of Proposed Rulemaking, which set forth detailed questions on each of the subsections of Subtitle C of the Resource Conservation and Recovery Act (RCRA). D wanted to establish nine characteristics typical of hazardous wastes and to provide a list of wastes deemed to be per se hazardous. Non-listed wastes would be non-hazardous, and listed wastes would be subject to regulation. Ps could elect to perform tests demonstrating that a per se hazardous waste should be exempt. D circulated for comment several drafts of regulations, met with experts and representatives of interested groups, and held public hearings. D then published proposed regulations covering most of the statutorily required standards. After several deadline misses, D finally published the final rules. D ended up with a mixture rule wherein any mixture including a listed hazardous waste was presumptively hazardous. The derived-from rule stated that any residue derived from the treatment of hazardous wastes was deemed hazardous. Ps opposed the rules asserting that the regulations proposed on December 18, 1978, did not foreshadow the inclusion of the mixture and derived-from rules in the final rule's definition of 'hazardous waste.' Ps assert, they were deprived of adequate notice and opportunity for comment. They also claim that the EPA exceeded its statutory authority by including the two rules in the final definition of hazardous waste. Ps contend the proposed regulations did not address the possibility of imposing such a requirement, thus depriving them of adequate notice and opportunity for comment. Ps assert that the issuance of the permit-shield rule, which first appeared in the May 1980 rulemaking, was arbitrary and capricious and that the rule is outside the scope of the statute.