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Memorandum to: Kent Peterson Bituminous Roadways October 20, 2010 Page 2 The modeling results summarized in Table 1 were compiled on a one -hour basis. AERMOD can estimate concentrations for a minimum time period of one -hour. However, people can detect the presence of hydrogen sulfide at time intervals less than 1 -hour. Notwithstanding the 1 -hour odor results previously tabulated by Wenck for the Environmental Assessment Worksheet, we attempted to locate an odor nuisance level for time periods less than one hour. A Task Force of the International Programme on Chemical Safety (IPCS) recommended that a 30- minute average time period with hydrogen sulfide concentrations less than 7 us/m is unlikely to produce odor nuisances in most situations. The 1 -hour concentrations listed in Table 1 can be scaled down to 30- minute concentrations using a conversion technique outlined by the "Air Dispersion Modelling Guideline for Ontario The conversion from 1 -hour concentrations to 30- minute concentrations is: C30 -min CI -kr x (60 min/30 min) 0.28 C30 -min CI -hr 1.2 Using this conversion factor and the predicted concentrations listed in Table 1, the 30- minute average concentrations are calculated as summarized in Table 2. Table 2. 30 Hydrogen Sulfide Predicted Concentrations Impact HMA Tank Railcar All Sources with All Sources with Plant Farm Heating Railcars Controlled Railcars Uncontrolled (Prim) ()iglu 3 )iglm 1 (Wm) Modeled Concentration 5.2 83 23 8.6 22.6 IPCS Odor Nuisance 7 Threshold As you can see in Table 2, the HMA plant alone is less than the IPCS 30- minute odor nuisance threshold at the property boundary. The attached isopleth of I -hour concentration from the HMA plant alone shows the area of maximum concentrations is located at the west side of the property. Concentrations dissipate from 4.4 pg/m to less than 1 pg /m with distance from the HMA plant. This suggests that people are unlikely to experience odor nuisance levels of hydrogen sulfide odors from the HMA plant operating alone. 'International Programme on Chemical Safety. 1981. Environmental Health Criteria 19. Hydrogen Sulfide. Geneva: World Health Organization. p. 41. 'Ontario Ministry of the Environment. 2009. Air Dispersion Modelling Guideline for Ontario Version 2.0. Toronto, Ontario. March 2009 N.mennicom425- nsuminoia R i l l 2039 Roseville C tNnodeli nemoN2s- memo-102010.doc