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Sources of Nitrate Dairies, orchards that require fertilization in sandy soils, and septic systems have been found to be the most significant sources of nitrate in ground water. Percolating Recharge Waters One of the most determinant factors in the Hantzsche and Finnemore equation is the rate of recharge from percolating waters, which mix with the downward-percolating effluent generated by on-site septic systems. In the original Hantzsche and Finnemore paper, only "average recharge rate of rainfall" was considered. For the Chico area, Hantzsche and Finnemore present an average rainfall of 22.5 inches per year and an estimated recharge of 16.8 inches per year. Based on San Joaquin County Environmental Health Department policy (personal communication, March 18, 2019), the recharge input for the Hantzsche and Finnemore equation should be derived from average monthly precipitation of rainfall and evapotranspiration rates for the area; the data should be obtained from the California Irrigation Management Information System (CIMIS), preferably from stations located within San Joaquin County. Recharge is calculated by first determining 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. This approach likely under-estimates recharge to the aquifer and, consequently, over-estimates nitrate loading. For the project Site, the local percolation and evapotranspiration rates are presented in Plates 12 and 13. The Site is located closest to the CIMIS Ripon (249) station, and slightly farther from the Manteca station (70). As a result, the average recharge values from the two stations have been averaged. Data for the Ripon station were available for 2017 and 2018; based on the calculation shown, the estimated rate of recharge from percolating waters for the Ripon station is determined to be 3.12 inches (Plate 12). A statistical error of 46% is associated with this value. Data for the Manteca station were available for 2014 through 2018, based on the calculation shown, the estimated rate of recharge from percolating waters for the Manteca station is determined to be 3.64 inches (Plate 13). A statistical error of 48% is associated with this value. The average recharge rates from the above two stations were then averaged, for a regional recharge rate of 3.38 in. The nitrate concentration of the recharge waters was estimated to be 1 mg/L-N (Hantzsche and Finnemore). LOGE 1911 Page 9