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• The nitrate as nitrogen (N) concentration of the employee and customer use is estimated to be 85 mg/L (US EPA, 1980). 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 incorporate peak and surge flow factors. The estimates used in the On-Site Wastewater Treatment Systems Standards may be greater than those discussed here. The maximum average daily flow for the Site was estimated to be 158 gallons per day (gpd). Please see the following table: Table 3. Average Daily Flow Calculation Use Units Rate Subtotal Reduction* Average Daily Flow Employees 6 13 gal/employee 78 gpd 6/7 66.8 gpd Customers 20 5 gal/customer 100 gpd 6/7 85.7 gpd Total 152.5 gpd *Reduction factors convert calculated flow into average daily flow over a year: 6/7 converts for days of operation per week. 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 will 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 and fast percolation rates tend to denitrify at a lower rate of about 10 percent. A denitrification factor of 30 percent was selected for the Site because of the fine- grained nature of the shallow soil at the percolation test location. Nitrate Loading Estimate A nitrate loading scenario was employed to determine the impact from the proposed project to ground water. The scenario utilizes the variables discussed previously, which represent the estimated conditions and uses associated with this project. The following • LOGE 1806 Page 9