ARCHIVED REPORTS_DRAFT ENVIRONMENTAL IMPACT REPORT

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Unlike the other TACs,no ambient monitoring data are available for diesel PM because no routine measurement method currently exists. However,ARB has made preliminary concentration estimates based on a PM exposure method. This method uses the ARB emissions inventory's PMIo database, ambient PMIo monitoring data, and the results from several studies to estimate concentrations of diesel PM. In addition to diesel PM,the TACs for which data are available that pose the greatest existing ambient risk in California are benzene, 1,3-butadiene, acetaldehyde, carbon tetrachloride,hexavalent chromium,para-dichlorobenzene, formaldehyde,methylene chloride, and perchloroethylene. Diesel PM poses the greatest health risk among these 10 TACs. Based on receptor modeling techniques,ARB estimated the diesel PM health risk in the SJVAB in 2000 to be 390 excess cancer cases per million people. Since 1990,the health risk of diesel PM in the SJVAB has been reduced by 50%. Overall, levels of most TACs, except for para-dichlorobenzene and formaldehyde,have gone down since 1990(ARB 2006a). EXISTING AIR QUALITY CONDITIONS—ODORS Odors are generally regarded as an annoyance rather than a health hazed. However,manifestations of a person's reaction to foul odors can range from psychological(e.g., irritation, anger, or anxiety)to physiological(e.g., circulatory and respiratory effects,nausea,vomiting,and headache). The ability to detect odors varies considerably among the population and overall is quite subjective. Some individuals have the ability to smell very minute quantities of specific substances; others may not have the same sensitivity but may have sensitivities to odors of other substances. In addition,people may have different reactions to the same odor; an odor that is offensive to one person may be perfectly acceptable to another(e.g., fast food restaurant). It is important to also note that an unfamiliar odor is more easily detected and is more likely to cause complaints than a familiar one. This is because of the phenomenon known as odor fatigue, in which a person can become desensitized to almost any odor and recognition only occurs with an alteration in the intensity. Quality and intensity are two properties present in any odor. The quality of an odor indicates the nature of the smell experience. For instance, if a person describes an odor as flowery or sweet,then the person is describing the quality of the odor. Intensity refers to the strength of the odor. For example, a person may use the word strong to describe the intensity of an odor. Odor intensity depends on the odorant concentration in the air. When an odorous sample is progressively diluted,the odorant concentration decreases.As this occurs,the odor intensity weakens and eventually becomes so low that the detection or recognition of the odor is quite difficult. At some point during dilution,the concentration of the odorant reaches a detection threshold.An odorant concentration below the detection threshold means that the concentration in the air is not detectable by the average human. The existing WQCF is a source of odors as a result of the biological processes that occur within the treatment process. Persons who have been bothered by the odors from the WQCF, as well as from many other sources in the wastewater collection(sewer) system,have telephoned complaints to the WQCF staff.A history of complaints from the WQCF logs from May 04,2001 through July 08,2005 shows a total of 44 calls. The years and nature of these calls are summarized in Table 4.3-4. Of the three calls in 2005, one was related to composting in a park not near the WQCF, one was related to the sludge drying beds, and one to the equalization ponds. Persons with odor complaints may also contact the SJVAPCD. The SJVAPCD reported one call received in recent years. The call was in June 2003, during same the period of 8 complaints received at the WQCF (SJVAPCD 2006c). EDAW Manteca WQCF and Collection System Master Plans EIR Air Quality 4.3-10 City of Manteca