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[? <br />CNAPTERTHREE Affected Environment <br />average of 1.56 inches, while January is the driest month with an average of only 0.74 inches. <br />On average, there aze 51 days a yeaz with measwable (? 0.1 inches) precipitation. In the past, the <br />number of days with measurable precipitation has varied from as many as 84 days to as few as 30 <br />days. The maximum daily precipitation was 2.3 inches, which occurred on August 6, 1986. <br />Snowfall has been measured in al] months except July and August. An average of 73 inches of <br />snow falls each year. Historically, snowfall has ranged from as much as 124 inches (1979) to as <br />little as 38 inches (1982). <br />Table 3.5-1 illustrates some of the climatic conditions in the vicinity of the Project Area. The <br />temperature differences are largely due to the location of the meteorological stations (valley vs. <br />plateau) as well as their elevations. <br />The mean monthly temperature is 43°F. July is the hottest month with an average temperature of <br />65°F, and January is the coldest month with an average temperature of 20°F. Temperature <br />extremes vary from as low as -48°F (1963) to 101°F (1989). On average, there are 12 days a <br />year with temperatures greater than 90°F and 24 days a yeaz remain below freezing all day. <br />Grand Junction wind data measured at approximately 10,000 feet are believed to closely <br />represent the upper level winds over the Project Area. The data show that the predominant wind <br />direction varies from the west to southwest. Near the surface, these winds blow from a more <br />southerly direction due to effects related to friction with the surface. The Piceance Creek valley <br />is oriented along the northeast (down-valley) and southwest (up-valley) axis in the vicinity of the <br />Piceance Site. Thus, the prevailing synoptic-level wind direction is from the southwest, with <br />locally driven up-valley and down-valley flows also influencing observed wind directions. Wind <br />data taken at the neazby Occidental Oil Shale Tract Cb oil shale tract Site 023 aze presented as <br />wind roses in Figure 3.5-1. These data show that the greatest frequency of wind 100 feet from <br />the surface on top of a plateau is from the south-southwest. <br />Meteorological data collected in 1984 at the Occidental Oil Shale Tract Cb tract aze considered to <br />be representative of the Project Area. This meteorological data and mixing height data from <br />Grand Junction, Colorado, for the same time period would be used for dispersion modeling. <br />Deviation in wind direction, referred to as sigma-theta measurements, from the same Cb tract <br />data set would be used to determine Pasquill-Gifford stability classes. <br />3.5.3 Regulatory Setting <br />The Clean Air Act (CAA) Amendments of 1977, Part D, Prevention of Significant Deterioration <br />(PSD), require that certain new, major stationary sources and major modifications be subject to a <br />pre-construction review, which includes an ambient air quality analysis based on dispersion <br />modeling. <br />Emissions that would result from the product dryer at the Parachute site are anticipated to exceed <br />the threshold amount (250 tons per year), thus triggering PSD review for this site. PSD review <br />would also be required at the Piceance site because the fossil-fuel-fired boilers exceed the hourly <br />heat input threshold of 250 million British Thermal Units (BTU). Because each site is subject to <br />PSD review, the significant sources of pollutants at each site would be required to apply "best <br />available control technology." The project would also be required to demonstrate compliance <br />~ with ambient air quality standards, document that the PSD increments aze not exceeded, and <br />Meteorology and Air Qualify 3-23 <br />