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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 incorporates peak and surge flow factors. The estimates <br />used in the On -Site Wastewater Treatment Systems Standards may be greater than <br />those 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 standard denitrification factor of 25 percent was selected for the Site because of the <br />mixed silt and sand soil type observed at the percolation test location. This is a <br />conservative selection because it is likely that more restrictive soils exist deeper <br />beneath the Site. <br />Nitrate Loading Estimate <br />A nitrate loading scenario was employed to determine the impact from the existing and <br />potential future development to ground water. The scenario utilizes the variables <br />discussed previously, which represent the estimated conditions and uses associated <br />with this project. <br />The following table presents a summary of the assumptions for the nitrate loading <br />calculation for the Site, as presented in Plate 14. <br />LOGE 2236 Page 12 <br />