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• The nitrate concentration of rainfall was estimated to be 1 mg/L-N (Hantzsche and Finnemore, 1992). Quantity and Quality of Domestic Wastewater The proposed project is an expansion to an existing warehouse operation, bringing the total number of employees to 17. The business operates Monday through Friday. No customers are anticipated. The estimated sewage flow rates for various uses are available from a number of references, including the San Joaquin County On-Site Wastewater Disposal Standards (2003), Crites and Tchobanoglous (1998), and US EPA (1980). Crites and Tchobanoglous indicate that 13 gallons per day is typical for an industrial building employee; this rate was used for the warehouse employees. The nitrate as nitrogen (N) concentration of the employee 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 Disposal Standards which incorporate peak and surge flow factors. The estimates used in the On-Site Wastewater Disposal 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 4. Average Daily Flow Calculation Use Units Rate Subtotal Reduction* Average Daily Flow Employees 17 13 gal/employee 221 gpd 5/7 158 gpd *Reduction factors convert calculated flow into average daily flow over a year: 5/7 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 • LOGE 1628 Page 10