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ENVIRONMENTAL IMPACT REPORTADDENDUM <br />Bristol Street Widening Phase IIIB — Washington Avenue to 17°i Street <br />Localized Construction Impacts <br />Localized air pollutant emissions are evaluated relative to the exposure of local sensitive uses to air <br />pollutant concentrations generated by the proposed Project. These are pollutant concentrations which can <br />be directly correlated to the health -based ambient air quality standards. This differs from regional <br />emissions which were discussed previously in that regional emissions are used to assess how much air <br />pollution is generated within an air basin and does not have a direct correlation with health effects. <br />Localized Significance Thresholds (LSTs) have been developed by the SCAQMD for nitrogen oxides <br />(NOx), carbon monoxide (CO), PMtc, and PM2.5• The LSTs determine whether project - related emissions <br />would substantially contribute to or exceed the ambient air quality standards and expose sensitive <br />receptors to excessive concentrations of air pollutants. The LSTs differ based on distance such that a <br />greater allowance in air pollutant emissions is allowed for construction activities occurring further from a <br />sensitive use and a lesser allowance in emissions is given for construction activities occurring closer to <br />sensitive uses. <br />Only short -term emissions occurring at the Project site for the Project's construction phase were included <br />to determine if sensitive receptors local to the Project site would be adversely affected. Emissions <br />generated by construction activities disperse rapidly with distance from the construction site. Individual <br />construction phases were compared against the SCAQMD's LST significance criteria. As shown in Table <br />5, Project emissions would not exceed the LST screening level criteria for CO, nitrogen dioxide (NO2), <br />PMto> or PM2.5. Because emissions associated with this alternative would be less than the LST, onsite <br />construction emissions would not be expected to exceed the federal or California AAQS at the nearest <br />sensitive receptors. As such, no significant air quality impacts related to localized air pollutants would <br />occur from the construction phase. <br />TABLE 5 LOCALIZED SIGNIFICANCE THRESHOLDS ANALYSIS FOR CONSTRUCTION <br />ACTIVITIES <br />a ; A CONSTRPCTION PKASE' <br />CRITA <br />,SIDA <br />NOx <br />CO <br />PM10 <br />PMss <br />Demolition <br />66 <br />41 <br />4 <br />3 <br />Grading <br />60 <br />34 <br />6 <br />4 <br />Trenching <br />41 <br />19 <br />2 <br />2 <br />Paving <br />16 <br />11 <br />1 <br />1 <br />SCAQMD Threshold <br />183 <br />1253 <br />13 <br />7 <br />Exceeds Threshold? <br />No <br />No <br />No <br />No <br />Source: Air Quality Assessment Report(URS 2013a). <br />Notes. NOx = nitrogen oxides; CO = carbon monoxide; Mo = particulate matter less than less than or equal to 10 microns in diameter; <br />PM26 = particulate matter less than less than or equal to 2.5 microns in diameter. <br />Intersection Hot-Spots <br />While the proposed Project would not result in any direct sources of localized emissions due to the <br />roadway street lighting being powered by electricity, changes in LOS or traffic volumes due to the Project <br />may cause indirect sources of localized emissions. While emissions of motor vehicles have improved due <br />ANA 111 -334 (PER- 02 -01) CITY OF SANTA ANA (11/25/2013 REV2) 132897 CM PAGE 26 <br />55B -33 <br />