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Crites and Tchobanoglous (1998) list a typical flow rate of 50 to 70 gallons per person per day for an individual residence. In the past, San Joaquin County Environmental Health Department has requested that the flow rate be calculated as 140 gallons per bedroom per day to reflect maximum usage. On March 4, 2020, however, 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). The new procedure required that wastewater flow from a single-family residence 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 house would contribute 250 gpd, and the proposed two-bedroom ADU would contribute 150 gpd, for a total wastewater flow of 400 gpd for the Site. 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's On-Site Wastewater Treatment Systems Standards, which incorporate peak and surge flow factors. The estimates used in the On-Site Wastewater Treatment Systems Standards may be greater than those discussed here. A typical residential concentration of 35 mg/L of nitrate as N was selected for the residences (Crites and Tchobanoglous, 1998). 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 denitrification factor of 25 percent was selected for the Site because of the clay soil observed at the percolation test location. Nitrate Loading Estimate A nitrate loading scenario was employed to determine the impact from the existing and proposed development to ground water. The scenario utilizes the variables discussed previously, which represent the estimated conditions and uses associated with this LOGE 2637 Page 12