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RECEPTOR LOCATIONS Receptors were placed at locations within residential areas surrounding the Proposed Project. Receptor base elevations were determined based on USGS mapping programs. Receptors were also positioned as flagpole receptors at a height of 1.8 meters above the ground(breathing height). METEOROLOGICAL DATA The rate at which emissions are dispersed in the atmosphere depends upon the intensity of the ambient turbulence,the velocity of the wind,the position relative to obstacles in the flow field, and any dilutions attributable to the source itself. The most important factor leading to plume spread in the atmosphere is the amount of ambient turbulence. In a stable atmosphere,the horizontal and vertical turbulence is very limited. The plume remains near its emission height and undergoes minimal mixing. This situation is common during the nighttime and early morning hours. If the layer below the plume height becomes neutral to unstable, the plume mixes rapidly to the surface. This is known as a fumigation condition and can cause high concentrations. This occurs for short duration during the early morning. As heating of the surface persists, a fully unstable mixing layer develops,and the plume loops up and down in _ response to large-scale convective eddies. A neutral stability atmosphere yields moderate amounts of turbulence and results in a cone-shaped plume. Finally, if an inversion is present below the emission height,a lofting condition exists and the plume is cut off from ground level impacts. Stability class frequencies were calculated from the deviation of the horizontal wind direction (sigma theta). The Sigma Theta method was used to categorize stability class as a function of ' wind speed and time of day. Stability classes range from extremely unstable(A)to moderately stable(F). These classes are used in dispersion models to estimate how much a plume will spread _ over time and space. In general,the more stable the atmosphere is, the less potential for plume spread,creating higher plume concentrations. Surface meteorological data and upper air meteorological(mixing height)data from Fresno and Sacramento, California, respectively, were used for the modeling analysis (http://www.valleyair.orwbusind/pto/Tox Resources/toxics resources.htm). Meteorological data were obtained from SJVUAPCD and used for modeling impacts of the Proposed Project. Data from 1986 through 1990 was used and the worst case year of analysis was reported. SOURCE RELEASE CHARACTERISTICS Onsite equipment was treated as area sources located within the phases of operations. The area source was modeled with a release height of 3 meters.