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of the San Joaquin County Environmental Health Department dictated a new procedure for calculating residential flow, developed in consultation with Norman Hantzsche (author of the 1992 paper discussed previously). He indicated that wastewater flow from a single-family residence should be calculated as 100 gallons per day (gpd) for the first bedroom and 50 gpd for each additional bedroom; additional residences should be calculated in the same manner (personal communication, March 4, 2020). Using this method, the existing four-bedroom home contributes a flow of 250 gpd, and the proposed three-bedroom home contributes 200 gpd, for a total estimated flow of 450 gpd. A typical residential concentration of 35 mg/L of nitrate as N was selected for the existing modular home and theoretical residences (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 (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 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 mixed silty and sandy soil present at the percolation test location. Nitrate Loading Estimate A nitrate loading scenario was employed to determine the impact from the existing and proposed homes 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 2210 Page 11