EPA is promulgating revisions to previously existing Toxicity Characteristics which are used to identify those wastes defined as hazardous and which are subject to regulation under subtitle C of the Resource Conservation and Recovery Act (RCRA) due to their potential to leach significant concentrations of specific toxic constituents. This final rule replaces the Extraction Procedure (EP) leach test with the Toxicity Characteristic Leaching Procedure (TCLP); it adds 25 organic chemicals to the list of toxic constituents of concern; and it establishes regulatory levels for these chemicals based on health-based concentration thresholds and a dilution/attenuation factor that was developed using a subsurface fate and transport model. The rule incorporates modifications in the leaching procedure, a list of toxicants, chronic toxicity reference levels, and the fate and transport model. Overall effect of the rule will be to subject additional wastes to regulatory control. Effective date is 9/25/90. CONTACT: Superfund Hotline (800)424-9346, or for specific aspects of the rule, Steve Cochran, (202)475-8551.