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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 (13.7 miles to the <br />closest station within San Joaquin County) but relatively close (4.5 miles) to a station <br />monitored by the Western Regional Climate Center (WRCC). As a result, two scenarios <br />have been run for the Site, the first using strictly CIMIS data, and the second using a <br />combination of CIMIS and WRCC data. <br />Recharge Scenario 1 — CIMIS Holt Station <br />For the CIMIS-only scenario, the local percolation and evapotranspiration rates obtained <br />through CIMIS are presented in Plate 12. The closest CIMIS station to the Site is Holt <br />(248). Data for the Holt station were available for 2017 and 2018; based on the <br />calculation shown, the estimated rate of recharge from percolating waters for the Holt <br />station is determined to be 3.72 inches. <br />LOGE 1909 Page 9