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Proposal 2106c: Ruvalcaba SS/NLS Addendum Page 3 <br /> February 11, 2021 <br /> Assumptions for Nitrate Loading Calculation <br /> Variable Value Units Description <br /> Q 150 gpd Effluent flow rate, 2-bedroom house <br /> Q 200 gpd Effluent flow rate, 3-bedroom house <br /> Nw 35 mg/L-N Effluent stream concentration <br /> A 1.50 acres Site area <br /> Nb 0.20 mg/L-N Concentration of rain <br /> d 0.35 constant Denitrification factor <br /> R 2.25 inches per year Recharge rate of rainfall <br /> W 1.3 inches per year Uniform waste water loading (calculated), <br /> 2-bedroom house <br /> W 1.8 inches per year Uniform waste water loading (calculated), <br /> 3-bedroom house <br /> Nc 8.6 mg/L-N Long-term average concentration of percolating <br /> effluent, 2-bedroom house <br /> Nc 10.2 mg/L-N Long-term average concentration of percolating <br /> effluent, 3-bedroom house <br /> The US EPA recommended Maximum Contaminant Level (MCL) for nitrate in drinking <br /> water is 10 mg/L-N. <br /> For a single two-bedroom house on the Site, the worst-case maximum buildup of <br /> nitrates in the aquifer from the use of a septic system is predicted to be 8.6 mg/L-N. <br /> This result is below the drinking water standard, and no nitrate mitigation would be <br /> recommended. <br /> For a single three-bedroom house on the Site, the maximum buildup of nitrates in the <br /> aquifer from the use of a septic system is predicted to be 10.2 mg/L-N. The result of <br /> the nitrate loading estimate is roughly equivalent to the maximum drinking water <br /> standard; the difference between the predicted result and the drinking water standard is <br /> well within the margin of error of the method, which is highly dependent on off-site <br /> rainfall monitoring. As discussed in the original report, due to the conservative nature <br /> of the calculation, clayey soil present, and lack of existing nitrate exceedances in the <br /> area, the actual nitrate loading experienced on the Site over time may be less than <br /> predicted. Additionally, because the Site is located in an agricultural area with sparse <br /> development, it is the opinion of Live Oak that the project is unlikely to lead to nitrate <br />