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Pursuant to Public Resources Code Section 21081(a)(1), the Board of Supervisors finds that the project's adherence to mitigation measure 4.1-1 and the following mitigation measures will reduce the potential impact of this significant effect to a less than significant level: MM 4.1-2. Heavy-duty diesel engine commercial vehicles will be required to comply with the CARB's 5-minute idling limit Airborne Toxic Control Measure. When available, ultra low sulfur diesel fuel (15ppm) shall be utilized. MM 4.1-6. Unpaved roads shall be watered to reduce fugitive dust emissions. Wet suppression of unpaved road dust, conducted in accordance with procedures recommended in SJVAPCD Regulation — VIII will reduce unpaved roads dust by 50% (URBEMIS recommended control efficiency). Compliance with other requirements in Regulation — VIII will result in additional unquantified reductions in fugitive dust emissions. Potential Significant Effect Without proper mitigation, the project has the potential to expose sensitive receptors to offensive odors affecting a substantial number of people. Description of Specific Impact Biogas odors result from biological and chemical processes, which occur during the decomposition of putrescible wastes. As the volatile solids contained in biosolids are stabilized,trace amounts of odorants may be produced. There will be mitigated fugitive VOC, ammonia and hydrogen sulfide emissions from biosolids that result from the natural evaporation that would occur during the day of receipt,prior to final disposal. These emissions have been included in the odor assessment. Because there was a zero odor emissions baseline at the H. M. Holloway landfill site(due to not receiving biosolids), the increase for the proposed Project from future biosolids disposal represents the entire odor emissions increase. The proposed Project's mitigated increase is 75.09 OU/Sec. Odor concentration is expressed in terms of dilution-to-threshold (D/T) or odor units (OU). A concentration equal to one odor unit is the minimum concentration at which an odor is detectable by 50% of a control group. At an odor concentration of 5 D/T odor may be distinctly noticeable to most people. Odor concentrations ranging between 5 D/T to 10 D/T are reported by agencies to be within the range likely to result in public nuisance complaints. Odorant emissions result in odor concentration (smell). Odor concentration is equal to the number of dilutions that must be made to a volume of gas,to dilute its odor to the detection threshold. Odor concentration is expressed in terms of a dimensionless quantity called an "odor unit" (OU). Although odor units are dimensionless they are often assigned the quasi dimension of OU/m3 and used with volumetric flow rates to calculate odor emission rates. The majority of the odorants emitted during disposal are likely to originate from the application of biosolids used for landfilling in depleted pits. Emissions will be generated when loads are discharged at the designated area of the biosolids disposal area for subsequent processing. Odor emissions will also occur due to the natural evaporation of the volatile compounds contained in the biosolids that occurs during the day of their receipt. Odorant emissions from biogas may be controlled using a gas recovery system and an incineration device (such as a flare or an internal combustion engine) for reducing biogas ._ ------ --- -_--- _ Findings of Fact—Section 15091 March 15,2016 H.M. Holloway Landfill Modification Project Final Board of Supervisors 5