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Soil Investigations for Data Collection in the Delta Initial Study/Proposed Mitigated Negative Declaration 33 3.3.2.1 Air Basins San Francisco Bay Area Air Basin. The SFBAAB consists of Alameda, Contra Costa, Marin, Napa, Santa Clara, San Francisco, and San Mateo Counties, the southern portion of Sonoma County, and the western portion of Solano County. While the topography of the SFBAAB is characterized by complex terrain, consisting of coastal mountain ranges and inland valleys and bays, the Study Area within this air basin is located in the Sacramento-San Joaquin Delta, with flat terrain and lower elevations. The area is characterized by moderately wet winters and dry summers; winter rains account for about 75 percent of the average annual rainfall. Annual precipitation can vary greatly from one part of the air basin to another even within short distances, from 40 inches in the mountains to less than 16 inches in sheltered valleys. Temperatures can also vary greatly across the air basin; in the Study Area, high temperatures in summers often exceed 100 ºF, and the average high temperature is in the low 90s. The average low temperature in winter is in the high 30s. The SFBAAB is classified as non-attainment for the State and Federal Ozone standards, the State PM10 and PM2.5 standards and the Federal PM2.5 standards. Sacramento Valley Air Basin. The SVAB covers all of Butte, Colusa, Glenn, Sacramento, Shasta, Sutter, Tehama, Yolo, and Yuba Counties, the westernmost portion of Placer County and the northeastern half of Solano County. The SVAB is bound by the North Coast Ranges to the west and the Northern Sierra Nevada Mountains to the east. The intervening terrain is relatively flat. It has a Mediterranean climate characterized by hot dry summers and mild rainy winters. During the year the temperature may range from 20 to 115 ºF, with summer highs usually in the 90s and winter lows occasionally below freezing. Average annual rainfall is approximately 20 inches, with about 75 percent of the rain occurring during the rainy season generally from November through March. Ozone is the primary criteria pollutant of concern in the SVAB. Portions of Study Area are within in the Sacramento Federal Ozone Nonattainment Area (SFNA), designated by the EPA as a “severe” ozone nonattainment area with an attainment date of 2005 for the federal one-hour ozone standard. Another criteria pollutant that exceeds NAAQS or CAAQS is particulate matter. The SMAQMD was designated as “nonattainment” for PM10 and PM2.5 based on both NAAQS and CAAQS, and the classification is moderate for 24-hour PM10 by the national standard. Yolo County was also designated as a nonattainment area for the state PM10 standard. San Joaquin Valley Air Basin. The SJVAB consists of Fresno, Kings, Madera, Merced, San Joaquin, Stanislaus, and Tulare counties, and the western portion of Kern County. The SJVAB is bound by the Coast Ranges to the west, the Sierra Nevada Mountains to the east and the Tehachapi Mountains to the south. The intervening terrain is relatively flat with a slight downward gradient to the northwest. The SJVAB has an “inland Mediterranean” climate averaging over 260 sunny days per year. Summers are dry and warm, high temperatures often exceed 100ºF, and the average high temperature in the