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• A second weighted average is then calculated, which incorporates the metered daily <br /> flow value from the existing facilities, the weighted average nitrate concentration for the <br /> existing facilities (derived above), and the predicted average daily flow and nitrate <br /> concentration of the proposed truck lube. <br /> Table 7. Weighted Average Concentration Calculation <br /> (Including Metered Flow at Existing Facilities) <br /> Use Average Daily Estimated Waste Weighted Average <br /> Flow Water Quality Product <br /> Employees (Proposed Truck 37.1 gpd 85 mg/L-N 3,153.5 gpd-mg/L-N <br /> Lube) ��jj <br /> Customers (Proposed Truck 35.7 gpd 85 mg/L-N 3,034.5 gpd-mg/L-N 0.10 <br /> Lube) <br /> Existing Facilities (Metered) '>491-7-gpd 72.8 mg/L-N 108,595.8 gpd-mg/L-N <br /> Totals 1,584. T14,783. <br /> Weighted Average <br /> Concentration: 114,783.8 gpd-mg/L-N / 1,564.5 gpd =73.4 mg/L <br /> • Once the calculations are completed, the average concentration of all the different <br /> effluent flows and concentrations at the Site is determined to be 73.4 mg/L-N at 1 ,564.5 <br /> gallons per day. <br /> Denitrification Reductions <br /> Denitrification is a process that occurs in the septic system drain field whereby certain <br /> bacteria oxidize the nitrate (NO3) in the wastewater and release nitrogen gas (NO to the <br /> atmosphere. Due to the biologic processes in the shallow soils, nitrogen in the drain <br /> field will may undergo a reduction between 10 percent to 35 percent. Soils with higher <br /> clay content, moist soil conditions, high pH, and organic material denitrify by about 35 <br /> percent, and soils with high sand content and fast percolation rates tend to denitrify at a <br /> lower rate of about 10 percent. <br /> A denitrification fact of 35 percent as selected for the Site because of the clayey <br /> nature of the soil a cation, as well as the slow percolation rates <br /> demonstrated. <br /> • LOGE 1711 Page 14 <br />