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LOGE 20-22: Affonso SSNLS Addendum Page 2 <br /> July 6, 2020 <br /> Nitrate Logftq Estimate (page 11-12 of report) <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 <br /> summary of the assumptions for the nitrate loading calculation for the Site, as presented in the <br /> attached plate. <br /> Assumptions for Nitrate Loading Calculation <br /> Variable Value Units Description <br /> Q 400 gpd Effluent flow rate <br /> Nw 35 mg/L-N Effluent stream concentration <br /> A 2.83 acres Site area <br /> Nb 0.30 mg/L-N Concentration of rain <br /> d 0.35 constant Denitrification factor <br /> R 3.86 inches per year Recharge rate of rainfall <br /> W 1.9 inches per year Uniform waste water loading (calculated) <br /> The details of the nitrate loading calculation are included in the attached plate. The results of the <br /> calculation are presented in the following table. <br /> Result of Nitrate Loading Calculation <br /> Variable Value Units Description <br /> Long-term average concentration of percolating <br /> Nc 7.7 mg/L-N effluent <br /> The US EPA recommended MCL for nitrate in drinking water is 10 mg/L-N. Ina worst-case <br /> situation, the maximum buildup of nitrates in the aquifer from the use of septic systems on the <br /> Site is predicted to be 7.7 mg/L-N. <br /> Conclusions and Recommendations (page 13 of report, 5th paragraph) <br /> Based on the methods and assumptions described, the nitrate loading calculation indicates that <br /> the use of on-site septic tanks and drain field systems on the Site has the potential to cause a <br /> buildup of nitrate in the aquifer up to 7.7 mg/L, below the MCL of 10 mg/L-N. <br />