SU0014502 - Laserfiche WebLink

Home Browse Search

Administrative Draft Environmental Impact Report Gill Medical Center Project 4.5 AIR QUALITY This section evaluates the Project-related effects to air quality.This section is based on the Air Quality and Greenhouse Gas Emissions Assessment prepared by ECORP Consulting, Inc. (2020) (see Draft EIR Appendix D).The information provided below is an abridged version of this report.This analysis was prepared using methodologies and assumptions recommended by the San Joaquin Valley Air Pollution Control District (SJVAPCD) and California Air Resources Board (CARB). Regional and local existing conditions are presented, along with pertinent standards and regulations.The purpose of this assessment is to estimate Project-generated criteria air pollutant emissions attributable to the Project and to determine the level of impact the Project would have on the environment. 4.5.1 Environmental Setting 4.5.1.1 San Joaquin Valley Air Basin The California Air Resources Board (CARB) divides the state into air basins that share similar meteorological and topographical features.The San Joaquin Valley Air Basin (SJVAB) occupies the southern two-thirds of the Central Valley and includes the Project site. The SJVAB is mostly flat, less than 1,000 feet in elevation, and is surrounded on three sides by the Sierra Nevada, Tehachapi, and Coast Range mountains.This bowl-shaped feature forms a natural barrier to the dispersion (spreading over an area) of air pollutants. As a result, the SJVAB is highly susceptible to pollutant accumulation over time. Climate and Meteorology The climate in the SJVAB is strongly influenced by the presence of mountain ranges.The mountains create a partial rain shadow over the valley and block the free circulation of air, trapping stable air in the valley for extended periods.The climate is semi-arid and is characterized by long, hot, dry summers and cool, wet, and foggy winters. Based on historical data obtained from the meteorological station located in Bakersfield, ambient temperatures range from an average minimum of 39'F in January to an average maximum of 98°F in July.The average monthly precipitation is approximately 6.24 inches per year, with January and February averaging 1.35 inches. The average daily wind speed is 5.9 miles per hour (mph). The air flow patterns are characterized by one of four directions depending on the season. For example, during the summer, winds are predominantly northwestern (up valley), while winters typically feature a prevailing stagnant condition that leads to high incidence of valley fog. Atmospheric Stability and Inversions Stability describes the relative resistance of the atmosphere to vertical motion,which in turn mixes the air. The stability of the atmosphere is dependent on the vertical distribution of temperature with height. Unstable conditions often occur during daytime hours when solar heating warms the lower atmospheric layers while the upper layers remain cold. In contrast, an inversion is a layer of warmer air over a layer of cooler air. Inversions influence the mixing depth of the atmosphere, which is the vertical depth available for diluting air pollution near the ground.The SJVAB experiences both surface-based and elevated inversions.The shallow surface-based inversions can be present in the morning but are often broken by daytime heating of the air layers near the ground. The deep, elevated inversions occur less frequently than Air Quality 4.5-1 October 2021