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Soil Suitability/ Nitrate Loading Study Irerracon <br />Munsch Property ■ Lodi, California <br />January 7, 2022 ■ Terracon Project No. NA217092 <br />2.3 Sources and Impact of Nitrate to Groundwater <br />2.3.1 Current Off -Site Sources of Nitrate <br />Septic systems and agricultural land use in the area may be the most significant sources of nitrate <br />in groundwater. Septic tank use in the vicinity is discussed in Section 1.3.5, <br />2.3.2 Contribution of Rainfall <br />An estimate of the quantity and quality of rainfall was required for the nitrate loading analysis. <br />Average precipitation and potential evapotranspiration (ETo) data was obtained from the <br />California Irrigation Management Information System (CIMIS) from the Lodi Station (042) and <br />Lodi West (166). The estimate first determines whetherthe average monthly precipitation exceeds <br />average monthly evapotranspiration (ET). If so, then the difference is potential rainfall recharge. <br />Due to the relatively flat nature of the site and proposed stormwater retention basins, runoff should <br />be minimal. In February 2020, the EHD approved an adjustment to the evapotranspiration (ET) <br />rate based on net rainfall recharge calculation utilizing University of California (UC) plant factors <br />(PF) for established landscape plants. Terracon calculated the ET adjustment factor (actual ET) <br />based on the proposed development. Refer to Appendix F Water Balance Recharge Analysis for <br />monthly precipitation and ET averages. <br />Table 8. <br />Net Rainfall Recharge <br />Based on this method, the average net rainfall recharge for Lodi area is estimated to be 8.90 <br />inches/year. <br />The nitrate concentration of rainfall is estimated to be 1 mg/L-N (Hantzsche and Finnemore, <br />1992). <br />2.3.3 Current On -Site Sources of Nitrate <br />The current on-site sources of nitrate include natural processes. <br />2.3.4 Future On -Site Sources of Nitrate <br />Future on-site sources of nitrate include the proposed septic systems and natural processes. <br />Responsive ■ Resourceful ■ Reliable 14 <br />ET <br />Net Rainfall <br />CIMIS Station <br />Average Precipitation <br />Potential ETO <br />Actual ET <br />Adjustment <br />Recharge <br />Number/ Location <br />(in/year) <br />(in/year) <br />(in/month) <br />Factor <br />(in/year) <br />042/Lodi <br />15.46 <br />50.50 <br />0.37 <br />18.69 <br />8.90 <br />166/Lodi West <br />Based on this method, the average net rainfall recharge for Lodi area is estimated to be 8.90 <br />inches/year. <br />The nitrate concentration of rainfall is estimated to be 1 mg/L-N (Hantzsche and Finnemore, <br />1992). <br />2.3.3 Current On -Site Sources of Nitrate <br />The current on-site sources of nitrate include natural processes. <br />2.3.4 Future On -Site Sources of Nitrate <br />Future on-site sources of nitrate include the proposed septic systems and natural processes. <br />Responsive ■ Resourceful ■ Reliable 14 <br />