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Nitrate Loading Analysis BSK Job E21-002-01B 2482 Carpenter Road June 23, 2021 Stockton, California Page 1 7 Table 1: Input Values and Source of Average Nitrate-Nitrogen Concentration in Recharge Water Input Values Input Value Explanation and Derivation I = 143 inches/year This volume is derived based on the adult care facility producing 4,100 gpd (548 ft3 ) into half the property area (16,800 ft2 ). n v,= 40 mg/L I The acceptable range is between 30 to 50 mg/L (Hantzsche and Finnemore, 1992). Additional sources support a value of 40 mg/L such as U.S. EPA, 1980; Canter and Knox, 1985; Burks and Minnis, 1994 d = 0.05 The acceptable range was between 0 to 0.25. A low, but non-zero, denitrification rate was chosen because the soil has slightly favorable conditions for denitrification based on high soil moisture content (13.0.%-25.3%) (Hantzsche and Finnemore, 1992). R = 17.7 inches/year Based on NOAA Precipitation data from 1991 to 2021. nb= 5 mg/L Background levels of nitrate-nitrogen in the Stockton area are generally negligible in areas not affected by septic, wastewater, livestock, or fertilizer so it is assumed nitrate from rainfall would be low. The acceptable range was between 0.5 to 1.0 mg/L (Hantzsche and Finnemore, 1992). However, BSK has been informed by Kern County that a value of 5 mg/L must be used in California. Each modeled scenario used the same assumed input values and assumptions, including: Assumed input values, as provided in Table 1 Recharge basin size is comprised of the 70 ft x 240 ft septic area or 16,800 ft 2 Faults do not interfere with recharge. Uniform soil composition composed of Jacktone Clay with the following characteristics: Somewhat Poorly Drained, High Runoff Low water capacity Rare flooding and no frequency of ponding Using the equation from Hantzsche and Finnemore, 1992, and the inputs based on information found in Table 1, including the size of the septic field and estimated yearly output of wastewater, the estimated average concentration of nitrate-nitrogen in recharge water will be 35 mg-N/L. Using the upper limit of 50 mg/L for total nitrogen concentration of wastewater (nw) results in an estimated average concentration of nitrate-nitrogen in recharge water to be 43 mg/L. 4.6 Impact of Nitrogen Loading from Site Project to Downgradient Wells, Rivers, etc.: The impact of nitrogen loading from the site should not change to down gradient wells, river, lakes, etc., due to the fact the amount nitrate-nitrogen containing recharge from the adult care facility should not be changing. The site project is replacing the current septic/leech line system with a commercial septic system. 13-4=-PC