ARCHIVED REPORTS LEC APPLICATION FOR CERTIFICATION

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5.1 AIR QUALITY is representative of conditions in the northern portion of San Joaquin County.13 This area includes the project site. The SJVAB consists of a continuous intermountain valley approximately 250 miles long and averaging 80 miles wide. On the western edge of the Valley is the Coast Mountain range,with peaks reaching over 5,000 feet, and on the east side is the Sierra Nevada range with some peaks exceeding 14,000 feet. The Tehachapi Mountains form the southern boundary of the Valley. Terrain is open only at the northern end of the valley. Both the project site and the monitoring site are located near the northern end of the San Joaquin Valley, in the broad,flat center of the valley. There are no nearby large terrain features, such as hills or mountain ranges,to affect local wind flow patterns. Prevailing winds in the northern end of the valley are from the west through northwest on an annual basis,although there is a strong southeasterly component during the fall and winter months (see Appendix B for wind roses). Both the project site and the monitoring site are affected by the marine air that generally flows into the basin from the San Joaquin River Delta to the north. Based on these factors,we concur with SJVAPCD's conclusion that the wind direction and wind speed data collected at the Stockton meteorological monitoring stations are similar to the dispersion conditions at the project site and to the regional area. Thus,the Stockton meteorological data set satisfies the definition of representative data. Representativeness has also been defined in the"Workshop on the Representativeness of Meteorological Observations" (Nappo et. al., 1982) as"the extent to which a set of measurements taken in a space-time domain reflects the actual conditions in the same or different space-time domain taken on a scale appropriate for a specific application." Representativeness is best evaluated when sites are climatologically similar,as are the project site and the Stockton meteorological monitoring station. Representativeness has additionally been defined in the PSD Monitoring Guideline (EPA, 1987a) as data that characterize the air quality for the general area in which the proposed project would be constructed and operated. As discussed above,because of the relative proximity of the Stockton meteorological data site to the proposed project site,the same large-scale topographic features that influence the meteorological data monitoring station also influence the proposed project site in the same manner. 5.1.5.6 Screening Modeling Analysis To ensure the impacts analyzed were for maximum emission levels and worst-case dispersion conditions, a screening procedure was used to determine the inputs to the impact modeling for the new gas turbine. The screening procedure is used to identify the CTG/ HRSG operating conditions that would result in the maximum impacts on a pollutant-specific basis. The operating conditions examined in this screening analysis, along with their exhaust and emission characteristics, are shown in Appendix 5.1B,Table 5.1B-2. These operating conditions represent CTG operation at maximum, average, and minimum ambient operating temperatures (107.7°F,61.2°F and 23.7°F), and at full load,peak load (with duct firing), and minimum load (50 percent). Ambient impacts for each of the 9 operating cases were modeled using EPA's AERMOD model and 5 years of Stockton meteorological data, as described above. The results of the unit impact analysis are presented in Appendix 5.1B,Table 5.1B-3 and summarized in Table 5.1-26. The analysis showed that for short-term averaging periods,modeled impacts 13 SJVAPCD,"Guidance for Dispersion Modeling,"Working Draft,Rev 2.0,January 2007,p.49.Available at http://www.valleyair.org/busind/pto/Tox_Resources/Modeling%20Guidance%20W_O%20 Pic.pdf. SAC/371322/082410013(LEC_5.1_AIR_QUALITY.DOC) 5.1-37