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A typical residential concentration of 35 mg/L of nitrate as N was selected for the <br /> proposed residences (Crites and Tchobanoglous, 1998). <br /> The estimated flow values discussed here should not be used for the design and sizing <br /> of the septic system. The design and sizing of the septic system should utilize the San <br /> Joaquin County Environmental Health Department On-Site Wastewater Treatment <br /> Systems Standards which incorporate peak and surge flow factors. The estimates used <br /> in the On-Site Wastewater Treatment Systems Standards may be greater than those <br /> discussed here. <br /> Denitrification Reductions <br /> Denitrification is a process that occurs in the septic system drain field whereby certain <br /> bacteria oxidize the nitrate (NO3) in the wastewater and release nitrogen gas (N2) to the <br /> atmosphere. Due to the biologic processes in the shallow soils, nitrogen in the drain <br /> field may undergo a reduction between 10 percent to 35 percent. Soils with higher clay <br /> content, moist soil conditions, high pH, and organic material denitrify by about 35 <br /> percent, and soils with high sand content tend to denitrify at a lower rate of about 10 <br /> percent. <br /> A denitrification factor of 35 percent was selected for the Site because of the clayey soil <br /> present at the percolation test location. <br /> Nitrate Loading Estimate <br /> Two nitrate loading scenarios were employed to determine the impact from the <br /> proposed project to ground water: the first scenario includes two three-bedroom houses, <br /> and the second scenario includes a three-bedroom house and a four-bedroom house. <br /> The scenarios utilize the variables discussed previously, which represent the estimated <br /> conditions and uses associated with this project. The following table presents a <br /> summary of the assumptions for the nitrate loading calculations for the Site, as <br /> presented in Plates 13 and 14. <br /> LOGE 2106 Page 11 <br />