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lierracon Soil Suitability / Nitrate Loading Study <br />Morada Produce — Ag Processing Building a Stockton, California <br />May 14, 2021 t Terracon Project No. NA217014 <br />2.2.2 Potential Ground Water Contamination Issues <br />A discussion of issues related to potential groundwater contamination is included in Section 1.4.2. <br />2.2.3 Current and Future On-Site Ground Water Uses <br />The proposed agricultural processing building will be connected to the existing onsite domestic <br />well. <br />2.3 Sources and Impact of Nitrate to Groundwater <br />2.3.1 Current Off-Site Sources of Nitrate <br />Agriculture land use in the area may be the most significant sources of nitrate in groundwater. <br />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 Holt Station (248), Lodi <br />Station (042) and Manteca Station (070). The estimate first determines whether the average <br />monthly precipitation exceeds average monthly evapotranspiration (ET). If so, then the difference <br />is potential rainfall recharge. This method does not consider runoff, although due to the relatively <br />flat nature of the site, runoff should be minimal. In February 2020, the EHD approved an <br />adjustment to the evapotranspiration (ET) rate based on net rainfall recharge calculation utilizing <br />University of California (UC) plant factors (PF) for established landscape plants. Terracon <br />calculated the ET adjustment factor (actual ET) based on the anticipated commercial landscape. <br />Refer to Appendix F Water Balance Recharge Analysis for monthly precipitation and ET averages. <br />Table 9. <br />Net Rainfall Recharge <br />CIMIS Station <br />Number! Location <br />Average Precipitation <br />(in/year) <br />Potential ETO <br />(in/year) <br />ET <br />Adjustment <br />Factor <br />Actual ET <br />(in/month) <br />Net Rainfall <br />Recharge <br />(in/year) <br />248 Holt, 042/Lodi, <br />070 Manteca 13.88 52.28 0.355 18.56 7.79 <br />Based on this method, the average net rainfall recharge for Stockton area is estimated to be 7.79 <br />inches/year. <br />The nitrate concentration of rainfall is estimated to be 1 mg/L-N (Hantzsche and Finnemore, <br />1992). <br />Responsive • Resourceful • Reliable 15