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water aquifer, it is possible that any remaining surface contaminants may be transported <br /> to the first saturated zone of the aquifer. <br /> Sources of Nitrate <br /> Dairies, orchards that require fertilization in sandy soils, and septic systems have been <br /> found to be the most significant sources of nitrate in ground water. <br /> Percolating Recharge Waters <br /> One of the most determinant factors in the Hantzsche and Finnemore equation is the <br /> rate of recharge from percolating waters, which mix with the downward-percolating <br /> effluent generated by on-site septic systems. In the original Hantzsche and Finnemore <br /> paper, only "average recharge rate of rainfall" was considered. For the Chico area, <br /> Hantzsche and Finnemore present an average rainfall of 22.5 inches per year and an <br /> estimated recharge of 16.8 inches per year. <br /> Based on San Joaquin County Environmental Health Department policy (personal <br /> communication, March 18, 2019), the recharge input for the Hantzsche and Finnemore <br /> equation should be derived from average monthly precipitation of rainfall and <br /> evapotranspiration rates for the area; the data should be obtained from the California <br /> Irrigation Management Information System (CIMIS), preferably from stations located <br /> within San Joaquin County. Recharge is calculated by first determining whether the <br /> average monthly precipitation exceeds average monthly potential evapotranspiration. If <br /> so, then the difference is the percolating recharge water into the aquifer. Runoff and <br /> stream infiltration drainage are not factored into the calculation. This approach likely <br /> under-estimates recharge to the aquifer and, consequently, over-estimates nitrate <br /> loading. <br /> The project Site is located relatively far from any CIMIS stations (10.1 miles to the <br /> closest station) but somewhat closer (7.8 miles) to a station monitored by the Western <br /> Regional Climate Center (WRCC). In addition, the CIMIS station is located east of the <br /> Site, while the WRCC station is located west of the Site; as a result, data from the two <br /> stations have been averaged to present a reasonable representation of rainfall levels <br /> near the Site. <br /> CIMIS Ripon Station <br /> For the CIMIS station, the local precipitation and evapotranspiration rates obtained <br /> through CIMIS are presented in Plate 12. The closest CIMIS station to the Site is Ripon <br /> (249), located approximately 10.1 miles east of the Site. Data for the Ripon station <br /> were available for 2017 and 2018; based on the calculation shown, the estimated rate of <br /> recharge from percolating waters for the Ripon station is determined to be 3.12 inches. <br /> An error of 46 percent is associated with this value. <br /> LOGE 1910 Page 8 <br />