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Table 3: Estimated Average Rainfall at Site <br />Station, dates monitored Average annual <br />rainfall (inches) <br />Elliott (040010), 7/1/1926-5/8/2016 18.27 <br />Lodi (045032), 1/1/1893-1/30/2015 17.24 <br />Average 17.75 <br />Based on this approach, the rate of recharge from percolating waters is <br />calculated to be an average of 17.75 inches per year. <br />Evapotranspiration Reduction: This method involves using average monthly <br />precipitation of rainfall and evapotranspiration rates for the area. The calculation <br />first determines whether the average monthly precipitation exceeds average <br />monthly potential evapotranspiration. If so, then the difference is the percolating <br />recharge water into the aquifer. Runoff and stream infiltration drainage are not <br />factored into the calculation. This approach likely under-estimates recharge to <br />the aquifer. <br />The San Joaquin County Environmental Health Department is in the process of <br />developing a modified version of the evapotranspiration reduction method which <br />may be recommended for use in future nitrate loading calculations. For this <br />method, it is our understanding that the source for both the precipitation and <br />evapotranspiration data will be the California Irrigation Management Information <br />System (CIMIS); data from the most recent five years will be utilized. Because a <br />final determination on the recommended method has not yet been made, for this <br />project a straight subtraction of monthly evapotranspiration from precipitation per <br />year will be used to derive a recharge value. <br />For the project Site, the local percolation and evapotranspiration rates are <br />presented in Plate 12. The closest station to the Site, Staten Island (station 242) <br />has been utilized; within the past five years, complete annual data were only <br />available for 2016 through 2018. Based on the calculation shown (Plate 12), the <br />estimated rate of recharge from percolating waters for the Acampo, California <br />area would be 12.6 inches per year by this method. <br />Reduced Rainfall: For this method, rainfall levels from the closest rain station <br />are multiplied by a percentage based on a reasonable assumption from the <br />literature. Because the Hantzsche and Finnemore model utilized a value of <br />approximately 75 percent rainfall as the rate of recharge from percolating waters <br />in the Chico area (which is more geologically similar to San Joaquin County than <br />LOGE 1906 Page 10