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July 31, 2023 <br /> BGG No. G130.09D <br /> between 10 percent to 25 percent. Soils with higher clay content,moist soil conditions,high pH,and <br /> organic material denitrify by about 25 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 <br /> 15 percent was estimated for the site due to the silty and sandy soils, in accordance with SJCEHD <br /> OWTS Standards 2017. <br /> Nitrate Loading Estimate <br /> A nitrate loading scenario was employed to determine the impact from the proposed residence to <br /> groundwater. The scenario utilizes the variables discussed previously,which represent the estimated <br /> conditions and uses associated with this project. The following table presents a summary of the <br /> assumptions for the nitrate loading calculation for the site. <br /> Table 3—Assumptions for Nitrate Loading Calculation <br /> Variable Value Units Description <br /> 250 gpd Effluent flow rate <br /> NW 35 mg/L-N Effluent stream <br /> concentration <br /> A 1.87 acres Site area <br /> Nb 1.00 m /L-N Concentration of rain <br /> D 0.15 constant Denitrification factor <br /> R 3.62 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 10.54 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 <br /> 10.54 mg/L-N from the use of the proposed onsite septic system. The result of the nitrate loading <br /> estimate exceeds 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 new residence septic system may cause a buildup of nitrates in the <br /> aquifer slightly above 10 mg/L-N for the site. Based on this result, mitigation measures may be <br /> required. <br /> BAEZ GEOTECHNICAL GROUP Soil Suitability Study&Nitrate Loading Study-Becerra Residence,18163 S.Carrolton Road Page 8 <br />