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Using this method, the four-bedroom home will contribute 250 gpd, and the two- bedroom home will contribute 150 gpd, for an estimated total maximum daily flow for the Site of 400 gpd. A typical residential concentration of 35 mg/L of nitrate as N was selected for the proposed residence (Crites and Tchobanoglous, 1998). 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 On-Site Wastewater Treatment Systems Standards, which incorporates peak and surge flow factors. The estimates used in the On-Site Wastewater Treatment Systems Standards may be greater than those discussed here. Denitrification Reductions Denitrification is a process that occurs in the septic system drain field whereby certain bacteria oxidize the nitrate (NO 3) 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 tend to denitrify at a lower rate of about 10 percent. A standard denitrification factor of 25 percent was selected for the Site because of the sandy silt soil type present at the percolation test location. Nitrate Loading Estimate A nitrate loading scenario was employed to determine the impact from the proposed project 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 13. LOGE 2132 Page 11