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Soil Suitability /Nitrate Loading Study Irerracon <br />JPM ® Lathrop, California <br />May 24, 2022 o Terracon Project No. NA227026 <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 Manteca (70), Tracy (167), <br />and Ripon (249) stations. The estimate first determines whether the average monthly precipitation <br />exceeds average monthly evapotranspiration (ET). If so, then the difference is potential rainfall <br />recharge. Due to the relatively flat nature of the site runoff should be minimal. In February 2020, <br />the EHD approved an adjustment to the evapotranspiration (ET) rate based on net rainfall <br />recharge calculation utilizing University of California (UC) plant factors (PF) for established <br />landscape plants. Terracon calculated the ET adjustment factor (actual ET) based on the <br />proposed commercial landscape. Refer to Appendix F Water Balance Recharge Analysis for <br />monthly precipitation and ET averages. <br />Table 9. <br />Net Rainfall Recharge <br />Based on this method, the average net rainfall recharge for the site is estimated to be 5.58 <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 the existing septic systems and natural processes. <br />2.3.4 Future On -Site Sources of Nitrate <br />Future on-site sources of nitrate include the existing septic systems, proposed septic systems, <br />and natural processes. <br />2.3.4.1 Quantity and Quality of Wastewater from Project <br />The following discussion is for determining the long-term wastewater flow generated from the <br />proposed development for the nitrate loading analysis and should not be used for septic system <br />design purposes. Typically, use estimates for septic system sizing include a peak use factor. <br />Responsive ■ Resourceful ■ Ez --, " r„l 16 <br />ET <br />Net Rainfall <br />CIMIS Station <br />Average Precipitation <br />Potential ETO <br />Adjustment <br />Actual ET <br />Recharge <br />Number/ Location <br />(in/year) <br />(in/year) <br />Factor <br />(in/month) <br />(inlyear) <br />70/Manteca, <br />167/Tracy, <br />11.14 <br />55.14 <br />0.335 <br />18.47 <br />5.58 <br />249/Ripon <br />Based on this method, the average net rainfall recharge for the site is estimated to be 5.58 <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 the existing septic systems and natural processes. <br />2.3.4 Future On -Site Sources of Nitrate <br />Future on-site sources of nitrate include the existing septic systems, proposed septic systems, <br />and natural processes. <br />2.3.4.1 Quantity and Quality of Wastewater from Project <br />The following discussion is for determining the long-term wastewater flow generated from the <br />proposed development for the nitrate loading analysis and should not be used for septic system <br />design purposes. Typically, use estimates for septic system sizing include a peak use factor. <br />Responsive ■ Resourceful ■ Ez --, " r„l 16 <br />