The estimated risk presented in the figure above, and the assumptions used to determine these risks, are not based on a specific source of diesel PM. Instead, general assumptions bracketing a fairly broad range of possible operating scenarios were used. The estimated risks are based on the diesel PM concentration at the point of maximum impact as determined using air dispersion modeling. The estimated risk ranges are used to provide a "qualitative" assessment of potential risk levels near sources of diesel PM. These estimates are based on the risk assessment methodology and assumptions identified in Appendix 7 of the Proposed Diesel Risk Reduction Plan, September 13, 2000. Actual risk levels from these types of sources at any individual site will vary due to site specific parameters, including equipment technologies and emission rates, fuel properties, operating schedules, meteorology, and the actual location of off-site receptors.

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Slide 12 of 39