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Soil Suitability/ Nitrate Loading Study 1rerracon <br /> Manteca Farm Improvement r Manteca, California <br /> October 29, 2019 Terracon Project No. NA197073 <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 was obtained from the California <br /> Irrigation Management Information System (CIMIS) Manteca (070) CIMIS station located nearest <br /> to the site. The estimate of deep percolation of rain is based on the average monthly precipitation <br /> of rain fall and evapotranspiration for San Joaquin County, California. The estimate first <br /> 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 to the 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 2.70 <br /> Based on this method, the average deep percolation of rain for Manteca is estimated to be 2.70 <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 and current septic system. <br /> 2.3.4 Future On-Site Sources of Nitrate <br /> Future on-site sources of nitrate include the proposed septic system, current septic system, and <br /> 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 /> The estimated sewage flow rates for use categories are available from a number of references. <br /> The uses presented below were guided by the San Joaquin County On-Site Wastewater <br /> Treatment Standards (OWTS) dated 2017, Crites and Tchobanoglous(1998), and EPA (1980). <br /> Responsive■ Resourceful ■ Reliable 15 <br />