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Soil Suitability/Nitrate Loading Study <br /> Soares Property ■ Escalon, CA Irerracon <br /> December 13, 2019 ■ Terracon Project No. NA197095 <br /> 2.3 Sources and Impact of Nitrate to Groundwater <br /> 2.3.1 Current Off-Site Sources of Nitrate <br /> Agriculture and septic systems in the area may be the most significant sources of nitrate in <br /> 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 data were obtained from the California <br /> Irrigation Management Information System (CIMIS) from the Manteca (070), Oakdale (194) and <br /> Ripon (249) stations. The estimate of deep percolation of rain is based on the average monthly <br /> precipitation of rain fall and evapotranspiration for San Joaquin County, California. The estimate <br /> first determines whether the average monthly precipitation exceeds average monthly potential <br /> evapotranspiration. If so, then the difference is potential deep percolation. This method does not <br /> consider runoff, although due relatively flat nature of the site runoff should be minimal. <br /> Table 9. <br /> Estimate of Deep Percolation of Rain <br /> Location Average Deep Percolation of Rain <br /> Manteca Area 2.89 inches per year <br /> Based on this method, the average deep percolation of rain for San Joaquin County is estimated <br /> to be 2.89 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 system 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 the sizing of septic systems include a peak use <br /> factor, whereas the numbers discussed here are based on long-term averages. <br /> Responsive ■ Resourceful ■ Reliable 14 <br />