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Responses to Environmental Checklist For CEQA Compliance lift station and appurtenances. Because odors associated with construction would be brief and transitory, impacts are determined to be less than significant. Odors from sewage systems are primarily due to inorganic or organic molecules. The #wo most common inorganic molecules are hydrogen sulfide {H2S} and ammonia (NH3). Hydrogen sulfide is the end product of decay processes of materials containing sulfur that occur during oxygen-deficient (anaerobic} decomposition. Ammonia evolves from reduction of high nitrogen content liquids such as urea. H2S is created when sewage becomes stagnant, while NH3 formation usually occurs when pH is high. Fresh sewage within the wastewater system from its disposal in a toilet or sink until it reaches the nearby pump station is still aerobic and has a neutral pH. H2S or NH3 formation is low. Some H2S can be generated within the pump chamber from organic scum or debris adhering to the wet well walls, but not in any appreciable concentration. Odor strength is described in terms of the number of dilutions with clean air that is required to reduce odor levels to where half the amount of people can no longer detect the odor. The factor is called the number of "odor units" (OU) or "dilutions-to-threshold" (D/T) in the sample. An odor of 1- 5 D/T is considered marginally detectable, 5-10 D/T is considered clearly detectable, but not yet highly offensive. When levels exceed 10 D/T and the odor is normally considered offensive, such as from sewage, a significant impact is presumed to exist. Odors may be released from the vents on a lift station and carried downwind. During the daytime, winds across the project site are mainly from west to east and during nighttime, winds are east to west. Thus, any odor-sensitive development directly east or west of the lift station would be possibly affected by odors. The distance extent of any odor "envelope" was estimated based upon normal and worst-case odor conditions. To estimate the odor level (in units of D/T} for a vent release of fresh versus stale sewage gas, an odor concentration of 30 D/T was assumed for fresh sewage, and 2000 D/T for stagnan# material. Under normal operational conditions ("fresh sewage"), the limits of marginal detestability (1 D/T) is 25 feet. The clearly offensive odor limit (10 D/T) is around 6 feet from the vent. No odor sensitive uses are located within 25 feet of the proposed lift station, thus, impacts under normal operating conditions would be less than significant. During upset conditions with stagnant sewage in the system, the zone 'of clearly offensive odor would be around 75 feet from the source. Maintaining a distance buffer of at least 75 feet from the lift station to the nearest odor-sensitive property is anticipated to maintain potential worst-case odor conditions at less-than-significant levels. The nearest residential property is located approximately 85 feet northeast of the site. Additionally, effluent would be continuously moving through the wet well with a minimum retention time. As such, it is unlikely that any significan# odors detectable above ground will be generated. However, due to the complexities in evaluating the sensitivity of nearby receptors to pa#ential odor impacts associated with the proposed facility, and given the relative close proximity (i.e., 85 feet} of Page 40 of 64 75E-44