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water aquifer, it is possible that any remaining surface contaminants may be transported to the first saturated zone of the aquifer. 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. The project Site is located relatively far from any CIMIS stations (10.1 miles to the closest station) but somewhat closer (7.8 miles) to a station monitored by the Western Regional Climate Center (WRCC). In addition, the CIMIS station is located east of the Site, while the WRCC station is located west of the Site; as a result, data from the two stations have been averaged to present a reasonable representation of rainfall levels near the Site. CIMIS Ripon Station For the CIMIS station, the local precipitation and evapotranspiration rates obtained through CIMIS are presented in Plate 12. The closest CIMIS station to the Site is Ripon (249), located approximately 10.1 miles east of the Site. 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. An error of 46 percent is associated with this value. LOGE 1910 Page 8