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Nitrate Loading Study Irerracon Guillermo Ramirez Property ■ Ripon, California April 29, 2019 ■ Terracon Project No. NA197019 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 sandy soils and relatively low clay content anticipated on the site (Section 1.1), a denitrification factor of 10 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 4. Summary of Nitrate Mass Balance Equation. Result Effluent Deep (Nc)'` Average Concentration Leachfield percolation Land Use _ Acres (A) Daily Flow Denitrification ( Ng/L- (Q) (gpd) (mg/L)N) (d) o(R) (nRain)II Proposed 20.0 1.80 560 35 10% 2.54 residential use * EPA maximum contaminant level (MCL)for nitrate as N in drinking water is 10 mg/L-N. Based on the nitrate loading balance calculation (Table 4), nitrate levels for the proposed future use is anticipated to be 20.0 mg/L-N which is above the MCL of 10.0 mg/L-N. 3.5.3 Impact of Nitrate Loading to Nearby Water Sources Based on a review of the USGS Avena (1994) California Quadrangle topographic map (Appendix A), the site is located at approximately 80 feet above mean sea level with a topographic gradient toward the west. The nearest surface water source to the site is an unidentified irrigation canal located approximately 1,000 feet southwest of the site. As the subject property is relatively flat, we do not foresee percolating effluent affecting the surface water resources. Responsive ■ Resourceful ■ Reliable 8