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Nitrate Loading Study Irerracon Roque Property e Victor, California July 6, 2018 e Terracon Project No. NA187032 potential sewage flow rate for both the existing and proposed future site use is 560-gallons per day. The average total nitrogen concentration of domestic wastewater is normally considered to be 20 to 85 mg/L-N with 35 to 45 mg/L-N being typical (Crites and Tchobanoglous, 1998). It is estimated that commercial use will have higher concentrations of total nitrogen when compared to residential use. For the purposes of the nitrate loading estimate, it is estimated that the average concentration for total nitrogen in wastewater for the project is approximately 35 mg/L-N over the long term. 3.5.1 Denitrification Estimate Denitrification is an important process which occurs within the leach field whereby certain bacteria utilize the oxygen in the nitrate (NO3) and release nitrogen gas (N2) to the atmosphere. Denitrification is expressed as a percentage, and the normally accepted range is 10 percent to 35 percent. Soils with higher clay content, moist soil conditions, high pH, and organic material denitrify by about 35 percent, and soils with high sand content and fast percolation rates are estimated to denitrify at a lower rate, about 10 to 15 percent. Based on the USDA soil survey (Section 1.1), Tokay fine sandy loam soils are anticipated at the site, depth to groundwater of 80 to 120 feet bgs, and the potential for interstratified finer grained soils to exist between the upper sandy loam and groundwater that are anticipated at the site with some layers of hardpan; a denitrification factor of 25 percent was selected. 3.5.2 Nitrate Loading Scenario The following table presents a summary of the nitrate loading calculation for the proposed site use. A copy of the nitrate loading calculation is included in Appendix B. Table 3. Summary of Nitrate Mass Balance Equation. Result Effluent Deep Average Leachfield Land Use (Nc)* Acres (A) Daily Flow Concentration Denitrification Percolation (mg/L- (a)(gpd) (Nw) (d) of Rainfall N) (mg/L-N) (R) (in) Proposed 24.0 0.13 560 35 25% 5.76 residential use * Maximum contaminant level (MCL)for nitrate in drinking water is 10 mg/L-N. Based on the nitrate loading balance calculation (Table 3), nitrate levels for the proposed future use is anticipated to be 24.0 mg/L-N which is above the MCL of 10.0 mg/L-N. Responsive■ Resourceful ■ Reliable 7