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method to determine flow from residential sources. He indicated that wastewater flow <br />from a single-family residence should be calculated as 100 gallons per day (gpd) for the <br />first bedroom and 50 gpd for each additional bedroom; additional residences should be <br />calculated in the same manner (personal communication, March 4, 2020). <br />Using this method, each two-bedroom house will contribute 150 gallons per day, for a <br />total maximum daily flow for the Site of 300 gpd. <br />A typical residential concentration of 35 mg/L of nitrate as N was selected for the <br />proposed residence (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 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 (NO 3) 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 <br />soils present at the percolation test location. <br />Nitrate Loading Estimate <br />A nitrate loading scenario was employed to determine the impact from the proposed <br />project to ground water. The scenario utilizes the variables discussed previously, which <br />represent the estimated conditions and uses associated with this project. The following <br />table presents a summary of the assumptions for the nitrate loading calculation for the <br />Site, as presented in Plate 13. <br />LOGE 20-59 Page 12