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LOGE 2126 Page 8 Using this method, each three-bedroom house would contribute 200 gpd, for a total wastewater flow of 400 gpd for the Site. The estimated flow values discussed here should not be used for the design and sizing of the septic system. The design and sizing of the septic system should utilize the San Joaquin County Environmental Health Department’s On-Site Wastewater Treatment Systems Standards (2017), which incorporate peak and surge flow factors. The estimates used in the On-Site Wastewater Treatment Systems Standards may be greater than those discussed here. A typical residential concentration of 35 mg/L of nitrate as N was selected (Crites and Tchobanoglous, 1998). Denitrification Reductions Denitrification is a process that occurs in the septic system drain field whereby certain bacteria oxidize the nitrate (NO3) in the wastewater and release nitrogen gas (N2) to the atmosphere. Due to the biologic processes in the shallow soils, nitrogen in the drain field may undergo a reduction between 10 percent to 35 percent. Soils with higher clay content, moist soil conditions, high pH, and organic material denitrify by about 35 percent, and soils with high sand content and fast percolation rates tend to denitrify at a lower rate of about 10 percent. The soil on the Site was found to be silty sand. A standard denitrification factor of 25 percent was selected for the Site because of the mixed silt and sand content of the soil encountered. Nitrate Loading Estimate A nitrate loading scenario was employed to determine the impact from the existing development to ground water. The scenario utilizes the variables discussed previously, which represent the estimated conditions and uses associated with this project. The following table presents a summary of the assumptions for the nitrate loading calculation for the Site, as presented in Plate 11.