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Figure 8 illustrates the isohyetal precipitation map for San Joaquin County showing lines of equal precipitation on a countywide basis (San Joaquin County Department of Public Works, 1991). The isohyetal precipitation map divides the whole of San Joaquin County into three rainfall intensity zones. The project site is located in Zone 2 of the three rainfall zones, as illustrated in Figure 8. Mean annual precipitation for Zone 2 on the San Joaquin County isohyetal precipitation map is approximately 13.5 inches. Specific precipitation intensities used for project site development and designs were based on precipitation data from the Stockton WBAP Station number B00-8560 located approximately 8 miles northwest of the site at latitude 38000', longitude 121 °316', and an elevation of 12 feet NGVD (California Department of Water Resources, 1981). This precipitation station was selected due to its long and reliable period of record and its proximity to the project site. The precipitation depth-duration-frequency data used for the project site development and design are: • 100-year, 24-hour storm intensity of 3.25 inches • 1,000-year, 24-hour storm intensity of 4.11 inches • 100-year annual precipitation of 25.42 inches • Annual mean precipitation of 14.27 inches The current WDR Order No. 94-014 lists the 24-hour maximum precipitation for the 100- year event and the 1,000-year event as 3.25 and 4.11 inches, respectively. From the late 1980s to the early 1990s, California experienced a severe drought. Although the precipitation data available during this period may not represent the statistical minimum precipitation that could occur at the project site, the likely minimum precipitation range anticipated during the service life and post-closure period of the landfill can be estimated. Table 3.5 presents monthly precipitation totals recorded at the Western Regional Climate Center, Stockton Weather Station Office (WSO), approximately 7.5 miles northwest of the project site, for a period of 59 years, between 1948 and 2007. During this period, the minimum annual precipitation recorded at the airport was approximately 13.96 inches. Considering the drought conditions experienced during that period, a minimum annual precipitation of 13.96 inches during the service life and post-closure period of the landfill site was estimated. Forward Composting Facility RCSI 7/20/09;Page 40 SWT Engineering