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Report Draft Environmental Impact R epo Page IV.D-2 Forward Landfill Expansion 4. The project area lies within the San Joaquin Valley Air Basin(SJVAB),a relatively topographically broad, flat area (250 miles long and 35 miles wide)bordered on the east by _ the Sierra Nevada Mountains;on the west by the Coast Ranges;and to the south by the Tehachapi Mountains. Airflow in the SJVAB is primarily influenced by marine air that enters through the Carquinez Straits where the San Joaquin-Sacramento Delta empties into the Sari Francisco Bay. The region's topographic features restrict air movement through and out of the basin. As a result,the SJVAB is highly susceptible to pollutant accumulation over time. Frequent transport of pollutants into the SJVAB from upwind sources also negatively contributes to air quality. Wind speed and direction play an important role in dispersion and transport of air pollutants. During summer periods, winds usually originate from the north end of the San Joaquin Valley and flow in a south-southeasterly direction through the valley,through the Tehachapi pass and into the neighboring Southeast Desert Air Basin. During winter months, winds occasionally originate from the south end of the valley and flow in a north- northwesterly direction. Also, during winter months, the valley experiences light, variable winds, less than 10 miles per hour(mph). Low wind speeds, combined with low inversion t-J layers in the winter, create a climate conducive to high concentrations of certain air pollutants. t The SJVAB has an inland Mediterranean climate that is characterized by warm, dry summers and cooler winters. Summer high temperatures often exceed 100 degrees Fahrenheit(°F), averaging from the low 90s in the northern part of the valley to the high 90s in the south. The daily summer temperature variation can be as high as 30 degrees °F. Winters are for the most part mild and humid. Average high temperatures during the winter are in the 50s,while the average daily low temperature is approximately 45 degrees °F: Precipitation in the Stockton area falls almost exclusively from mid-November to mid- t.} April from the fringes of mid-latitude storms. The Stockton area averages 13.5 inches of rain annually. The vertical dispersion of air pollutants in the valley is limited by the presence of persistent temperature inversions. Air temperatures usually decrease with an increase in altitude. A reversal of this atmospheric state, where the air temperature increases with height, is termed j an inversion.Air above and below an inversion does not mix because differences in air density thereby restrict air pollutant dispersal. Regulatory Framework Air quality issues are under the jurisdiction of the United States Environmental Protection Agency(EPA), the California Air Resources Board (CARB), and the SJVAPCD. Regulation E, of air pollution is achieved through both Federal and State ambient air quality standards and emission limits for individual sources of air pollutants. An"ambient air quality standard" represents a level of an air pollutant in the outdoor (ambient) air that is necessary Fk to protect public health. The ambient standards do not apply to indoor environments. Again, as required by the federal Clean Air Act(CAA),the EPA identified criteria pollutants and established National Ambient Air Quality Standards (NAAQS,or national standards)to F. protect the public health and welfare. There are NAAQS for ozone (03), carbon monoxide (CO), nitrogen dioxide (NOA sulfur dioxide (SO2), respirable particulate matter equal to or less than 10 microns in diameter (PM,o), fine particulate matter equal to or less than 2.5 F microns in diameter (PM2.5), and lead (Pb). These pollutants are known as "criteria" air pollutants because standards have been established to meet specific public health and welfare criteria. t �