75B - PH - AMEND DEVELOPMENT AGMT 2005-02

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MacArthur Project Modification - Santa Ana - Air Quality Assessment KPC Environmental, Inc. The emissions estimates represent a "worst-case," because they incorporate the assumption that construction activities occur at the peak daily levels throughout the entire construction period. Data utilized to forecast emissions was obtained from available project data, development plans, and resource material where indicated. The information for the modeling programs used to forecast emissions is based on the project data, resource material, or default values where no data was available. 3.0 Regional Setting 3.1 South Coast Air Basin (SCAB) Santa Ana, Orange County is located in the South Coast Air Basin (SCAB). The SCAB's severe air pollution problem is a consequence of the combination of emissions and meteorological conditions which are adverse to the dispersion of those emissions. The summertime maximum mixing height (an index of how well pollutants can be dispersed vertically in the atmosphere) in Southern California averages the lowest in the U.S. The Southern California area is also an area with abundant sunshine, which drives the photochemical reactions, which form pollutants such as ozone. In the SCAB, high concentrations of ozone are normally recorded during the spring and summer months, while high concentrations of carbon monoxide are generally recorded in late fall and winter. High PM 10 and PM2.5 concentrations can occur throughout the year, but occur most frequently in the fall and winter. Although there are changes in emissions by season, the observed variations in the pollutant concentrations are largely a result of seasonal differences in weather conditions. 3.2 Description of Regional Climate and Its Effect on Air Quality Section 15125 of the State CEQA Guidelines requires that environmental studies include a description of the environment in the vicinity of the project, as it exists before initiation of the project. The information describing the Environment Setting of the project site includes information on the climate, the existing quality of ambient air at the proposed project site, significant air pollutant sources, both stationary and mobile. 3.2.1 Climate The climate of the South Coast Air Basin (SCAB) is determined by its terrain and geographical location. The Basin is a coastal plain with connecting broad valleys and low hills, bounded by the Pacific Ocean and high mountains forming the remainder to the perimeter. The general region lies in the semi-permanent high-pressure zone of the eastern Pacific. As a result, the climate is mild, tempered by cool sea breezes. This usually mild climatological pattern is interrupted infrequently by periods of extremely hot weather, winter storms, or Santa Ana winds. The climate of Southern California found in the Santa Ana area of the SCAB is described as a Mediterranean-type climate characterized by long warm summers and moderate winters with moderate precipitation and a maritime influence giving a marine layer and a temperature inversion layer. 02/02/11 75B-110