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• 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 /> The soil on the Site was found to be sandy silt. A typical denitrification factor of 25 <br /> percent was selected for the Site because of the moderately fine-grained nature of the <br /> shallow soil near the proposed new residence. <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 2. Assumptions for Nitrate Loading Calculation <br /> Variable Value Units Description <br /> • Q 420 gpd Effluent flow rate <br /> Nw 35 mg/L-N Effluent stream concentration <br /> A 0.30 acres Site area <br /> Nb 1.00 mg/L-N Concentration of rain <br /> d 0.25 constant Denitrification factor <br /> inches per <br /> R 10.32 year Deep percolation of rain water <br /> inches per <br /> W 18.82 year Uniform waste water loading for calculation <br /> • LOGE 1802 Page 7 <br />