Assessing Post-MACT Risks for Air Toxics. M. G. Dusetzina and K. A. Rimer, US EPA/OAQPS (MD-15) Research TrianglePark, NC 27711; and D. A. Amaral, EC/R Inc., Chapel Hill, NC 27514
Residual risk assessments are usually conducted for an entire source category, thus the number of sources addressed can range from a few, to thousands. Also, EPA is to assess the public health protection provided by each MACT standard. Approximately 174 assessments will be conducted over a 10-year period. In these risk assessments, several of which are underway, the Agency applies an iterative, tiered approach, which progresses from using simple models and limited data to more sophisticated models and more site-specific data. Multiple routes of exposure will be assessed when needed. In developing this approach to risk assessment, we consider the limited resources available for conducting such a large number of risk assessments, while developing a methodology that is robust. This presentation will describe the current approach to estimating human exposures, based on lessons learned from conducting screening level and more site-specific assessments for sources emitting air toxics. Subjects addressed will include data gathering, effectiveness of various screening-level models, use of assumptions, data generally needed, and how uncertainty and variability will be quantified.
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