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r. Members of the Roseville City Council November 23, 2010 Page 5 —. c�<<< Moss & Barnett Figure 13 of the EAW depicts the Maximum Acute Risk Value associated with the levels of hydrogen sulfide concentration determined from the odor modeling completed for the EAW. That analysis concerns health risk standards. It does not respond directly to the performance standard. However, the concentration levels reported to consider the health risk can also be used to determine whether the odor associated with hydrogen sulfide can be detected. When the concentration of hydrogen sulfide is at a threshold level developed by the U.S. Department of Health and Human Services, fifry percent (50%) of the population can detect its distinctive rotten egg smell. When the concentration is higher than the threshold level, the percentage of people who can smell the odor increases. Mulloy analyzed the concentration levels reported in the EAW with respect to the odor detec[ion threshold. He concluded as follows: During my review of the EAW and the related MPCA file, I reviewed the odor modeling completed with respect to the proposed asphalt plant. The modeling shows that when using the air quality control measures in the proposed air permit, odors from the plant (hydrogen sulfide (H75)) will be readily detectible beyond the property limits of the proposed site. The extent of the area in which the odors will be perceptible may depend on each individual. We do not know that the mitigation technology will be effective to the extent assumed by the model, and therefore may be perceptible in a larger area than shown by the EAW. I have specifically reviewed the odor discussion in the EAW. The EAW shows maximum concentrations of hydrogen sulfide (H25) of 21.54. It also shows maximum concentrations of hydrogen sulfide (H2S) of 21.54 (Ng/m3) at the properry line, 3.63 (Ng/m3) at the Gross National Golf Club, and 2.95 (Ng/m3) at the nearest residence. The Agency for Toxic Substances and Disease Registry {ATSDR), a federal public health agency of the U.S. Department of Health and Human Services, states that HZS has "...a characteristic rotten-egg odor that is detectable at concentrations as low as 0.5 parts per billion (ppb). At 25� C, 1 ppb H25 = 1.4 ug/m3 and 0.5 ppb under the same conditions equal 0.7 Ng/m3. This concentration is accepted as the concentration level at which 50% of the population will detect the rotten egg odor associated with HzS. The EAW provides a diagrem of Atute Risk Impacts (Fgure 13). The diagram shows Maximum Acute Risk values ranging from 0.46 to 0.02 plotted on a map of the area. Assuming that the risks at different locations are mathematical ratios of the concentrations in the modeled exhaust stream, converting the Max Acute Risk values to H75 concentrations (Vg/m3) shows that at least 50% of the population will detect a rotten egg odor from HZS in an area from roughly County Road C West on the north; Long Lake Road on the east; County Road 8 West on the south; and the second and tenth fairways of the Gross National Goif Club to the west. The table below converts Max Acute Risk values to approximate HZS concentrations: