SR0084165_SSNL - Laserfiche WebLink

Home Browse Search

Nitrate Loading Analysis BSK Job E21-002-01B 2482 Carpenter Road July 13, 2021 Stockton, California P a g e | 7 Table 1: Input Values and Source of Average Nitrate-Nitrogen Concentration in Recharge Water Input Values Input Value Explanation and Derivation I = 6.17 inches/year This volume is derived based on the adult care facility producing 2,145 gpd (286.7 ft3) into the property (203,426 ft2). nw = 40 mg/L 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 = 0.25 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). A value of 25% was chosen as discussed with a San Joaquin County employee due to the clay content of the soil. R = 3.37 inches/year Based on NOAA Precipitation data from 1991 to 2021 and evapotranspiration data from California Irrigation Management Information System and a discussion with and employee of San Joaquin County. nb = 1 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 San Joaquin County that contractors had tested rainfall in the Stockton area and found concentrations of nitrate-nitrogen was around 1 mg/L. 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 entire 4.76-acre site – 203,426 ft2 • Faults do not interfere with recharge. • Uniform soil composition composed of Jacktone Clay with the following characteristics: o Somewhat Poorly Drained, o High Runoff o Low water capacity o 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 19.76 mg-N/L.