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CARB investigated the ability of H2S to cause annoyance to the general population. This study63 concluded that"an unpleasant odor is at or above the threshold of annoyance for half the people, when its concentration reaches 5 times the average threshold of detection." Recent work using reliable test methods indicates that the detectable threshold for H2S ranges from 0.4 µg/m3 (in studies in the Netherlands using a dynamic flow method) to 0.7 gg/m3 (in studies in Japan using a static test method in an odor-free test room).64 Thus, the concentration of H2S ` that would annoy half the people would range from 2 µg/m3 to 3.5 pg/m3. 6- This is consistent with conclusions reached by the World Health Organization ("WHO"),which"considered that a level of 0.008 mg/m3 (0.005 ppm) averaged over 30 min should not produce odour nuisance in most situations. 65 Extrapolating this B-56 to a 1-hour averaging time, this is equivalent to 3.5 µg/m3 for a 1-hour exposure. cont. These values are consistent with the annoyance range of 2 to 3.5 gg/m3 estimated using CARB guidance. Thus, the threshold that the Draft EIR used to evaluate t- nuisance and annoyance is too high. The maximum modeled H2S concentration significantly exceeds the H2S nuisance odor threshold. Thus, odor impacts are significant and must be mitigated. The Draft EIR should be revised to disclose this significant impact and to impose mitigation. ` Third, the Draft EIR appears to evaluate odor impacts using only the increase in H2S concentrations. Individuals experience the total concentration, consisting of the increment due to the Project plus the background, not just the increment. Thus, L total H2S concentrations should be evaluated to determine if H2S odors would cause r significant nuisance and annoyance impacts. Thus, the increase in ambient concentrations of H2S during both Project operation is high enough to cause annoyance to nearby residents. This is also a L violation of Health&Safety Code Section 41700 and is a significant impact under CEQA. Therefore, H2S emissions from Project operation must be mitigated. C L LL63 John E. Amoore,The Perception of Hydrogen Sulfide Odor in Relation to Setting an Ambient Standard,Prepared for California Air Resources Board,ARB Contract A4-046-33,April 10,1985. 64 Y.Hoshika and others,International Comparison of Odor Threshold Values of Several Odorants in LJapan and in The Netherlands,Environmental Research,v.61,1993,pp.78-83. 65 World Health Organization,Hydrogen Sulfide, Environmental Health Criteria No.19,1981,p.13; L National Research Council,Hydrogen Sulfide,University Park Press,Baltimore,1979;T. Lindvall,On Sensory Evaluation of Odors Air Pollutant Intensities,Nord.Hyg.Tidskr.,Supplement v.2,1970,pp. E 1-181. L 45 L