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Denitrification Reductions Denitrification is a process that occurs in the septic system drain field whereby certain bacteria oxidize the nitrate (NO 3) 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 percent, and soils with high sand content tend to denitrify at a lower rate of about 10 percent. A denitrification factor of 35 percent was selected for the Site because of the clayey soil soil present at the percolation test location. Nitrate Loading Estimate A nitrate loading scenario was employed to determine the impact from the proposed project to ground water. The scenario utilizes the variables discussed previously, which represent the estimated conditions and uses associated with this project. The following table presents a summary of the assumptions for the nitrate loading calculations for the Site, as presented in Plates 14 through 16. Table 3. Assumptions for Nitrate Loading Calculation Variable Value Units Description Q 280 gpd Effluent flow rate, 2-bedroom 420 gpd Effluent flow rate, 3-bedroom 560 gpd Effluent flow rate, 4-bedroom Nw 35 mg/L-N Effluent stream concentration A 0.94 acres Site area Nb 1.00 mg/L-N Concentration of rain 0.35 constant Denitrification factor 6.17 inches per year Recharge rate of rainfall, scenario 2 4.0 inches per year Uniform waste water loading (calculated), 2-bedroom 6.0 Uniform waste water loading (calculated), 3-bedroom 8.0 Uniform waste water loading (calculated), 4-bedroom The details of the nitrate loading calculations are included in Plates 14 through 16. The results of the calculations are presented in the following table. LOGE 1909 Page 11