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` Draft Environmental Impact Report Page IV.D-24 1 Forward Landfill Expansion Together with hydrocarbons, the second group is probably responsible for the background smell associated with a landfill. The sensory perception of odorants has four major dimensions: detectability, intensity, character, and hedonic tone. Odor detectability consists of a detection threshold and a recognition threshold. The detection threshold is the lowest concentration of an odorant that will elicit a sensory response in 50 percent of the population. There is an awareness of the presence of an added substance,but not L necessarily an odor sensation. The detection thresholds are determined using human subjects and sophisticated dilution equipment. Detection thresholds are published for more than 900 chemicals. The recognition threshold is the minimum concentration that is recognized as having a characteristic odor quality by a segment of the population. Odor intensity refers to the perceived strength of the odor sensation, and odorant character is what the substance smells like (e.g., fishy, rancid,hay, sewer, turpentine, ammonia,etc.). Garbage has been demonstrated to possess an odor with an unpleasant tone. Because offensive odors rarely cause any physical harm and no requirements for their control are included in state or federal air quality regulations, the SJVAPCD does not currently impose any rules or regulations that place quantifiable limitations on emissions of odorous substances,other than its Nuisance Rule 4102. Any actions related to odors are based on citizen complaints to local governments and the District. i The SJVAPCD identifies a sanitary landfill as a type of facility that is a potential odor 1 source. Because there are one or more sensitive receptors with the screening trigger distance of one mile from the landfill property, potential odor impacts from the Project must be considered. The District has established the following significance threshold for odor problems: • More than one confirmed complaint per year averaged over a three-year period, or .; • Three unconfirmed complaints per year averaged over a three-year period. Based on information obtained from the SJVAPCD and the number of verifiable odor t complaints at the site, the odor impact would be less than significant, and no additional measures to reduce odor impacts are recommended. Mitigation Measure IV.D.4: None required. F Impact IV.D.S. Emissions of diesel particulate matter and other air toxics could pose a risk to human health. F, As with the criteria pollutants, the project would increase toxic air contaminant (TACs) emissions from LFG-derived and vehicle-derived sources with two options: additional F4 LFG is controlled either by additional flare capacity (flare option)or LFG engines at a new LFG to energy facility(LFG engine option). The two Baseline scenarios were evaluated: Current Actual emissions, determined using 2006 and 2007 operational data; �;' and Current Permitted emissions,based on emissions of landfill sources at maximum F" permitted levels. Air toxics within LFG typically consist of benzene, chloroform, methylene chloride, perchloroethylene,trichloroethylene, vinyl chloride, as well as other air toxics. Mobile sources emit diesel particulate matter(DPM).17 Haul truck emission factors are based on F,11 17 In August of 1998,the CARE identified particulate emissions from diesel-fueled engines as an air toxic.