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for calculating residential flow, developed in consultation with Norman Hantzsche <br />(author of the 1992 paper discussed previously). 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, the four-bedroom house would contribute 250 gpd, and the two- <br />bedroom ADU would contribute 150 gpd, for a total wastewater flow rate of 400 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 <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 denitrification factor of 35 percent was selected for the Site because of the clayey soil <br />present at the percolation test location. <br />Nitrate Loading Estimate <br />A nitrate loading scenario was employed to determine the impact from the existing and <br />proposed homes to ground water. The scenario utilizes the variables discussed <br />previously, which represent the estimated conditions and uses associated with this <br />project. The following table presents a summary of the assumptions for the nitrate <br />loading calculation for the Site, as presented in Plate 14. <br />LOGE 2213 Page 11 <br />