Unexpected and unusual emissions from a large, mass-burn, waste-to-energy facility caused persistent and elevated opacity readings of the facility’s continuous opacity monitor (COM), and generated a visible pink-purple-tinted plume emanating from the exhaust stack. Non-radioactive iodine associated with medical wastes was determined to be responsible. As iodine is a known respiratory irritant, questions arose regarding potential short-term health risks to nearby residents. The rate of emission of the apparent release was estimated by two different methods, and then compared with facility-specific knowledge of waste composition. First, based on inverse, worst-case air dispersion modeling, the level of iodine emission that would be necessary to cause potential discomfort/mild irritation to people living near the facility was determined. Second, the level of iodine emission that would be necessary to account for elevations of in-stack opacity observed throughout the event was calculated. The level of iodine emissions necessary to cause mild health effects was found to be substantially greater than the actual release level as inferred from the opacity data. Moreover, based on descriptions of visual inspections of the waste stream and potential opacity interferences created by complex in-stack chemistry, it is likely that the opacity-based calculations overestimate the amount of iodine released. Accordingly, actual impacts are likely to have been smaller than those estimated herein. This paper discusses the process and procedures used to assess the health risk from this incident.

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