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have three bedrooms, which would result in a flow value of 200 gpd. The maximum <br /> daily flow for each parcel is thus estimated to be 500 gpd. <br /> A typical residential concentration of 35 mg/L of nitrate as N was selected for the <br /> 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 clay soils <br /> present at the percolation test locations. <br /> Nitrate Loading Estimate <br /> Two nitrate loading scenarios were employed for each proposed parcel to <br /> determine the impact from the project to ground water: one scenario assuming <br /> no future development, and one scenario assuming the hypothetical future <br /> homes discussed above. The scenarios utilize the variables discussed previously, <br /> which represent the estimated conditions and uses associated with this project. The <br /> nitrate loading calculations are presented in Plates 15 through 22. <br /> The following table summarizes the results of the nitrate loading calculations for each <br /> proposed parcel of the Site, where Nc represents the long-term average concentration <br /> of percolating effluent: <br /> LOGE 20-54 Page 12 <br />