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Revised November 4,2020 <br /> BGG Job No. G164.01 <br /> Table 3—Assumptions for Nitrate Loading Calculation <br /> Variable Value Units Description <br /> 535.7 gpd Effluent flow rate <br /> NW 85 mg/L-N Effluent stream <br /> concentration <br /> A 27 acres Site area <br /> Nb 1.00 m /L-N Concentration of rain <br /> D 0.15 constant Denitrification factor <br /> R 10.3 inches per year Deep percolation of <br /> rainwater <br /> W 0.9 inches per year Uniform wastewater <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 /> Table 4—Results of Nitrate Loading Calculation <br /> Variable Value Units Description <br /> Nr 2.8 mg/L-N Estimated long-term <br /> average concentration <br /> of percolating effluent <br /> The US EPA recommended MCL for nitrate in drinking water is 10 mg/L-N. The expected worst- <br /> case scenario would result in a calculated maximum buildup of nitrates in the aquifer of 3.5 mg/L-N <br /> from the use of the proposed onsite septic system. The result of the nitrate loading estimate is below <br /> the maximum drinking water standard. <br /> DISCUSSION OF NITRATE LOADING RESULTS <br /> Based on the method and assumptions described,the result of the nitrate loading estimate indicates <br /> that the proposed use of the nursery septic system would not likely cause a buildup of nitrates in the <br /> aquifer above 10 mg/L-N for the site. As this result is satisfactory, mitigation measures are not <br /> recommended. <br /> SUMMARY AND CONCLUSIONS <br /> The soil conditions encountered near the septic system and leach field appear to be suitable as <br /> designed. A satisfactory soil percolation rate of 18.5 minutes per inch was recorded from a <br /> percolation test conducted in the proposed septic system area. <br /> The depth to groundwater from recent well observations is reported to be more than 40 feet bgs, <br /> fluctuating seasonally. Groundwater flow direction in the general site region is North-Northwest. <br /> Based on the anticipated depth of the leach field to be less than 5 feet deep, modifications from a <br /> standard septic system should not be required. <br /> BAEZ GEOTECHNICAL GROUP Soil Suitability Study and Nitrate Loading Study-I Hsin Orchids Page 8 <br />