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Nitrate Loading Study Irerracon Valencia Property ■ Ripon, California September 6, 2018 ■ Terracon Project No. NA187044 Based on a review of Table 3,the estimated potential sewage flow rate for the proposed residence is 560-gallons per day. The detached pool house average daily flow is estimated to be 140- gallons per day. The combined average daily flow for both the residence and pool house is approximately 700-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 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 Average Effluent Leachfield Deep (Nc)* Concentration Percolation Land Use (mg/L- Acres (A) Daily Flow (Nw) Denitrification of Rainfall N) (Q) (gPd) (d)(mg/L-N) (R) (in) Proposed 22.7 1.5 700 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 22.7 mg/L-N which is above the MCL of 10.0 mg/L-N. Responsive ■ Resourceful ■ Reliable 8