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Soil Suitability / Nitrate Loading Study <br /> 11065 North Alpine Road I Stockton, California r rerracon <br /> June 30, 2026 1 Terracon Project No. NA267068 <br /> 2.3.4.2. Denitrification Estimate <br /> Denitrification is an important process which occurs within the leach field whereby <br /> certain bacteria utilize the oxygen in the nitrate (NO3) and release nitrogen gas (1\12) to <br /> the atmosphere. Denitrification is expressed as a percentage, and the normally accepted <br /> range is 10 percent to 35 percent. Soils with higher clay content, moist soil conditions, <br /> high pH, and organic material denitrify by about 35 percent, and soils with high sand <br /> content and fast percolation rates are estimated to denitrify at a lower rate, about 10 to <br /> 15 percent. <br /> Based on the results of the shallow and deep soil borings, the estimated depth to <br /> groundwater at greater than 70 feet bgs, and the proposed leach field expected to be <br /> located within a silty sand; a denitrification estimate of 35 percent was selected. <br /> 2.3.5. Nitrate Loading Scenario <br /> A nitrate loading scenario was performed to determine the impact from the proposed <br /> ADU. The scenario utilizes the variables discussed previously which represent the <br /> estimated conditions and uses associated with this project. The following table presents <br /> a summary of the nitrate loading calculation for the site. A copy of the nitrate loading <br /> calculation is included in Appendix F. <br /> Table 10 <br /> Summary of Nitrate Mass Balance Equation <br /> Effluent <br /> Net Rainfall <br /> Result (Nc) Average Concentration Leachfield <br /> Proposed Acres Recharge <br /> Development (A) Daily Flow (Nw) Denitrification (in/year) <br /> (mg/L-N) (Q) (gpd) (d) (R) <br /> (mg/L-N) <br /> Proposed ADU 7.7 1.50 200 45 35% 5.74 <br /> Proposed ADU and <br /> 12.7 1.50 450 45 35% 5.74 <br /> Existing Residence <br /> Note: Maximum contaminant level (MCL) for nitrate in drinking water is 10 mg/L-N <br /> Based on the nitrate loading balance, nitrate levels for the proposed ADU is anticipated <br /> to increase nitrate levels to 12.7 mg/L-N for the project area which is above the MCL of <br /> 10 mg/L-N. <br /> Facilities I Environmental I Geotechnical I Materials 18 <br />