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• 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 waste water and release nitrogen gas (Nz) 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 and fast percolation rates tend to denitrify at a <br /> lower rate of about 10 percent. <br /> As discussed earlier, the soil on the Site was found to be silty clay. A denitrification <br /> factor of 35 percent was selected for the Site because of the clayey nature of the <br /> shallow soil near the proposed new residences. <br /> Nitrate Loading Estimate <br /> A nitrate loading scenario was employed to determine the impact from the project to <br /> ground water. The scenario utilizes the variables discussed previously, which represent <br /> the estimated conditions and uses associated with this project. The following table <br /> presents a summary of the assumptions for the nitrate loading calculation for the Site, <br /> as presented in Plate 8. <br /> • Table 3. Assumptions for Nitrate Loading Calculation <br /> Variable Value Units Description <br /> Q 1,960 gpd Effluent flow rate <br /> Nw 35 mg/L-N Effluent stream concentration <br /> A 2.13 acres Site area <br /> Nb 1.00 mg/L-N Concentration of rain <br /> d 0.35 constant Denitrification factor <br /> inches per <br /> R 7.4 year Deep percolation of rain water <br /> inches per <br /> W 12.4 year Uniform waste water loading for calculation <br /> The details of the nitrate loading calculation are included in Plate 8. The results of the <br /> calculation are presented in the following table. <br /> • LOGE 1833 Page 7 <br />