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� <br />� <br />Memorandum to: Kcnt Peterson <br />Bimminous Roadways <br />October 2q 2010 <br />Page 2 <br />� <br />The modeling results summarized in Table ] were compiled on a one-hour basis. AERMOD can <br />estimate concentra�ions for a minimum time period of one-hour. However, peopk can detect the <br />presence of hydrogen sulfide at time intervals less than 1-hour. Notwithstanding the l-hour odor <br />results previously tabulated by Wenck for the Environmental Assessment Worksheet, we <br />attempted to locate an odor nuisance level for time periods less than one houc A 7'ask Force of <br />the International Programme on Chemical Safety (IPCS)Z recommended that a 30-minute <br />average time period with hydrogen sul£de concentrations less than 7 pg/m3 is unlikely to <br />produce odor nuisances in most situatiuns. <br />The 1-hour concentrations fisted in Table ] can be scaled down to 30-minute concen[rations <br />using a conversioh technique outlined by the "Air Dispersion Modelling Guideline for Ontario"3. <br />The conversion from I-hour concentrations to 30-minu[e concentrations is: <br />C30.min ° CI-lu #(60 min/30 min) o zn <br />C30-min = C�.M � 1.2 <br />Using this conversion factor and the predicted concentrations listed in Table l, the 30-nilnute <br />average concentrations are calculared as summarized in Table 2. <br />Table 2. 30-Minute Hydrogen Sulfide Predicted Concentrations <br />As you can see in Table 2, the HMA plant alone is ]ess than the IPCS 30-nunu[e odor nuisance <br />threshold at the property boundary. 'C'he attached isopleth of 1-hour concentration 5�om the <br />HMA plant alone shows the area of maximum concenVations is located a[ the west side of the <br />property. Concentrations dissipate from 4.4 Ng/mi [o less than 1 µg/m3 with distance from the <br />HMA planl. This suggests that people are unlil:ely to experience odor nuisance levels of <br />hydrogen sulfide odors from the HMA plant operating alone. <br />°Imerrw�ionel liogrsmme on Chcmical SaMy. 19A I. 6nvimnmrmal Henl�h Criiuia 19. Hydrogen Sulfida Genevx wmW Heallh lhgani a�ion. <br />p.ni. <br />�Omuno Minigry o! i�e F;nviromnen�. 3009. Av Disp�+sion Modclling Guitlebne tor Oniono Version 4.0. Tqonw, Omano. Ma�ch 2W 9 <br />N\Tm�ne��W L].P+uni.ous Rf I 1 ifD3 Pa.en1M [ VwMei..ng�mnno`!2� nemr.:U]U W Ea� <br />