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used in the On-Site Wastewater Treatment Systems Standards may be greater than <br />those discussed here. <br />The maximum average daily flow for the Site was estimated to be 55.7 gallons per day <br />(gpd), as calculated in the following table. <br />Table 4. Average Daily Flow Calculation <br />Use Units Rate Subtotal Reduction Average Daily <br />Flow <br />Employees 5 13 gal/employee 65 gpd 6/7 55.7 gpd <br />Reduction factors convert calculated flow into average daily flow over a year: 6/7 converts for days of operation per <br />week. <br />The nitrate as nitrogen (N) concentration of the employee use is estimated to be 85 <br />mg/L (US EPA, 1980). <br />Denitrification Reductions <br />Denitrification is a process that occurs in the septic system drain field whereby certain <br />bacteria oxidize the nitrate (NO 3) 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 standard denitrification factor of 25 percent was selected for the Site because of the <br />mixed silty and sandy soil type present at the percolation test location. <br />Nitrate Loading Estimate <br />A nitrate loading scenario was employed to determine the impact from the proposed <br />project to ground water. The scenario utilizes the variables discussed previously, which <br />represent the estimated conditions and uses associated with this project. The following <br />table presents a summary of the assumptions for the nitrate loading calculation for the <br />Site, as presented in Plate 13. <br />LOGE 2130 Page 1 1