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MEI and Risk Analysis
In the BIF regulations and associated guidance, the concept of an MEI (maximum exposed individual) is established. This MEI is a theoretical person located at the point of maximum annual average plume impingement who lives at that location 24 hours/day for seventy years. Gossman Consulting, Inc.'s (GCI) review of the EPA document, "Comment Summaries and Responses to Comments Submitted on the Proposed Rules for Burning of Hazardous Waste in Boilers and Industrial Furnaces", provides some insight not available in any other EPA guidance. Specifically seven commentors on the proposed regulations noted that use of an MEI overstates risk and that aggregate population-based risk would more realistically represent site-specific health risks. EPA's response to the commentors acknowledged this conservative feature of the screening procedure; but then stated "If the facility does not meet the screening limits, the option of site-specific risk assessment is still available." EPA having previously acknowledged in their response the availability of 1980 census data seems to be suggesting that a theoretical MEI need not be used under Tier III or IA. It is not clear which EPA would accept, a real MEI or an aggregate population-based risk analysis, but either approach might be useful for facilities located in areas of relatively low population density. Use of this type of risk analysis might allow some facilities to operate that would otherwise be forced to stop or significantly reduce waste fuel use. Other facilities might find this strategy useful in shifting selected metals from Tier III to Tier IA, thus significantly reducing compliance costs. Implementation of such an approach is not clear in the regulations since in the response to those commentors the EPA appears to have taken a different approach all together.
Toxicity of Various Metal Species
In the response to another comment EPA acknowledges that the RACs for non-carcinogenic compounds and RSDs for carcinogens are conservatively based by assuming the most toxic/carcinogenic form of the compound is being emitted. Nevertheless, after making this acknowledgement, the EPA states, "In any case, Tier II or Tier III determinations can take into account the actual metal species being emitted." This seems to suggest that actual identification of the metal species being emitted could allow for the use of alternate RACs or RSDs. Except in the case of hexavalent chromium it is not clear how EPA intended this option to be implemented given the existing regulatory language. Clearly, the use of this alternative could allow for more operational flexibility, or as with the previous alternative, the use of Tier IA instead of TIER III for selected metals. Speciation of metal emissions may be possible through a variety of sampling and testing techniques including X-ray diffraction spectroscopy.
Process Sample Testing Frequency
Finally, we note that EPA has repeatedly indicated that process samples must be tested at a frequency sufficient to insure compliance. This rather transparent attempt to avoid providing clear guidance is marginally approved upon by another comment response, "EPA notes, however, that if concentrations of toxic metals in feed materials do not vary significantly over time, the burden of frequent sampling can be minimized by only requiring analysis of those toxic materials whose concentrations are expected to vary." The use of the word "significantly" in this context strongly suggests that testing of a number of samples and subsequent application of statistical analysis techniques could be useful in reducing the frequency and therefore cost of process sample testing in a manner which could be justified to EPA inspectors.
Metal Spiking and Hexavalant Chromium
Next month's issue will examine the issues involved in the form of metal spiking as well as the issue of spiking hexavalant chromium.