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April 17, 2019 <br /> BGG Job No. G001.05 <br /> Table 2—Weighted Avera a Concentration Calculation <br /> Use Average Daily Flow Estimated Waste Weighted Average <br /> Water Quality Product <br /> Employees 18.6 gpd 85 mg/L-N 1,581 gpd-mg/L-N <br /> full-time <br /> Employees 14.3 gpd 85 mg/L-N 1,216 gpd-mg/L-N <br /> art-time <br /> Totals 32.9 d 2,797 d-m /L-N <br /> Weighted Average 2,797 gpd-mg/L-N/32.9 gpd= 85 mg/L-N <br /> Concentration: <br /> Denitrification Reductions <br /> Denitrification is a process that occurs in the septic system drain field whereby certain bacteria <br /> oxidize the nitrate(NO3)in the wastewater and release nitrogen gas(N2)to the atmosphere. Due to <br /> the biologic processes in the shallow soils, nitrogen in the drain field may undergo a reduction <br /> between 10 percent to 35 percent. Soils with higher clay content,moist soil conditions,high pH,and <br /> organic material denitrify by about 35 percent,and soils with high sand content and fast percolation <br /> rates tend to denitrify at a lower rate of about 10 percent. A typical denitrification factor of 25 <br /> percent was estimated for the site due to the moist soil conditions from irrigation, the organic <br /> material from vineyard farming,and the presence of cemented hardpan lenses below 3 feet deep at <br /> the site. <br /> Nitrate Loading Estimate <br /> A nitrate loading scenario was employed to determine the impact from the proposed project to <br /> ground water. The scenario utilizes the variables discussed previously, which represent the <br /> estimated conditions and uses associated with this project. The following table presents a summary <br /> of the assumptions for the nitrate loading calculation for the Site, as presented in Plate 11. <br /> Table 5—Assumptions for Nitrate Loading Calculation <br /> Variable Value Units Description <br /> 32.9 gpd Effluent flow rate <br /> Nw 85 mg/L-N Effluent stream <br /> concentration <br /> A 19.92 acres Site area <br /> Nb 1.00 m /L-N Concentration of rain <br /> D 0.25 constant Denitrification factor <br /> R 11.7 inches per year Deep percolation of <br /> rain water <br /> W 0.9 inches per year Uniform waste water <br /> loading <br /> The details of the nitrate loading calculation are included in Plate 3.The results of the calculation are <br /> presented in the following table. <br /> VS vl° w 5 <br /> e,4 0 <br /> BAEZ GEOTECHNICAL GROUP Soil Suitability Study and Nitrate Loading Study-DFV Guard Station Page 9 <br />