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5.1E:CONSTRUCTION EMISSIONS AND IMPACT ANALYSIS TABLE 5.1 E-4 Modeled Maximum Onsite Construction Impacts Maximum Onsite Total State Federal Averaging Construction Background Impact Standard Standard Pollutant Time Impact(fag/m3) (pg/m3) (Ng/m3) (pg/m3) (pg/m3) Notes: a. Ozone limiting method applied for 1-hour average, using concurrent 03 data.ARM applied for annual average, using national default 0.75 ratio. b. PM10 and PM2.5 impacts shown are from fugitive dust as well as combustion sources.Annual average PM2.5/PM10 impact from combustion sources only is 0.45 Ng/m3. As shown on these isopleth diagrams,maximum impacts occur on the project site fenceline, and concentrations decrease rapidly within a couple of hundred meters of the project site. For example,maximum modeled 24-hour average PM10 impacts along the fenceline are approximately 36 µg/m3. However,impacts are reduced by half within tens of meters from the facility fenceline. Maximum impacts are reduced to 10µg/m3 or less at the freeway. It is also important to note that emissions in an exhaust plume are dispersed through the entrainment of ambient air,which dilutes the concentration of the emissions as they are carried away from the source by winds. The process of mixing the pollutants with greater and greater volumes of cleaner air is controlled primarily by the turbulence in the atmosphere. This dispersion occurs both horizontally, as the exhaust plume rises above the emission point, and vertically,as winds carry the plume horizontally away from its source. The rise of a plume above its initial point of release is a significant contributing factor to the reductions in ground-level concentrations,both because a rising plume entrains more ambient air as it travels downwind,and because it travels farther downwind (and thus also undergoes more horizontal dispersion)before it impacts the ground.Vertical plume rise occurs as a result of buoyancy (plume is hotter than ambient air, and hot air,being less dense,tends to rise) and/or momentum(plume has an initial vertical velocity). In AERMOD, area sources are not considered to have either buoyant or momentum plume rise, and therefore the model assumes that there is no vertical dispersion taking place. Thus a significant source of plume dilution is ignored when sources are modeled as area sources. The project construction site impacts are not unusual in comparison to most construction project analyses. Construction sites that use good dust suppression techniques and low- emitting vehicles typically do not cause exceedances of air quality standards. The input and output modeling files are being provided electronically. 5.1 E.4.4 Health Risk of Diesel Exhaust The combustion portion of annual PM10 emissions from Table 5.1E-5 above was modeled separately to determine the annual average Diesel PM10 exhaust concentration. This was SAC/371322/082330017(LEC_5.1 E_APPENDIX.DOC) 5.1 E-7