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Soil Suitability/ Nitrate Loading Study <br />Eagle's Nest Motorcycle School Stockton, California <br />July 27, 2021 Terracon Project No. NA217040 <br />2.2 Groundwater Analysis <br />2.2.1 Regional Groundwater <br />Irerracon, <br />A discussion of regional groundwater, including depth to groundwater is included in Section 1.4.1. <br />No significant seasonal trends were evident from the sources consulted. <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 building will be connected to Cal Water supply wells. <br />2.3 Sources and Impact of Nitrate to Groundwater <br />2.3.1 Current Off -Site Sources of Nitrate <br />Septic system 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 8. <br />Net Rainfall Recharge <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 />248 Holt, 042/Lodi, <br />13.88 <br />52.28 <br />0.21 <br />10.98 <br />9.17 <br />070 Manteca <br />Responsive ■ Resourceful ■ Reliable 14 <br />