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Methods in use in San Joaquin County Within San Joaquin County, four methods have been identified to derive a value for the rate of recharge from percolating waters: • 100 Percent of Rainfall: This method involves identifying rainfall levels from the closest data station to the project site, and assuming that 100 percent of rainfall deep-percolates to the first saturated zone. This method likely over-estimates the rate of recharge from percolating waters. Rainfall data for the Escalon area were obtained from the Western Regional Climate Center. The Site is located virtually equidistant from the Manteca, Oakdale Woodward Dam, and Modesto City County Airport stations. Rainfall data from these stations is presented, and an average is calculated, in the following table: Table 3: Estimated Average Rainfall at Site Station Annual Rainfall (inches) Manteca (045303), 4/1/1965-6/30/1977 11.84 Oakdale Woodward Dam (046305), 3/1/1906- 13.33 12/31/1967 Modesto City County Airport (045738), 3/1/1906- 12.21 6/9/2016 Average 12.46 Based on this approach, the rate of recharge from percolating waters is calculated to be an average of 12.46 inches per year. • Evapotranspiration Reduction: This method involves using average monthly precipitation of rainfall and evapotranspiration rates for the area. The calculation first determines whether the average monthly precipitation exceeds average monthly potential evapotranspiration. If so, then the difference is the percolating recharge water into the aquifer. Runoff and stream infiltration drainage are not factored into the calculation. We believe that this approach under-estimates recharge to the aquifer; indeed, a current assessment of the Chico area by this method yields a value of 11.1 inches per year as compared with the 16.8 inches utilized in the Hantzsche and Finnemore paper. LOGE 1907 Page 11