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LIVE OAK GEO ENVIRONMENTAL, INC. <br /> 407 W. Oak St., Lodi, CA 95240 •:• (209)369-0375 te logelodi.com <br /> March 21, 2019 <br /> Project Number: 1844 <br /> Linda Turkatte, Director <br /> San Joaquin County Environmental Health Department <br /> 1868 E. Hazelton Ave. <br /> Stockton, CA 95205 <br /> Regarding: Second Addendum to Nitrate Loading Study <br /> Farris Property <br /> APN 245-070-89, Allen & Carrolton Rds., Ripon, CA <br /> Original report dated November 14, 2018 <br /> Ms. Turkatte: <br /> Based on our meeting with you Monday, we have prepared this addendum to the <br /> above Nitrate Loading Study. You indicated that the nitrate loading calculation for the <br /> Site should be re-evaluated using precipitation and evapotranspiration data obtained <br /> from the California Irrigation Management Information System for the past five years. <br /> As in the previous report and addendum prepared by our office, the method utilized for <br /> the nitrate loading analysis is based on a mass balance formula discussed in a <br /> published paper by Hantzsche and Finnemore (1992). The Hantzsche and Finnemore <br /> equation is a conservative approximation of ground-water nitrate-nitrogen concentration <br /> resulting from the combined effect of on-site sewage disposal systems and percolating <br /> recharge waters. <br /> For this addendum, the recharge input for the Hantzsche and Finnemore equation is <br /> derived from average monthly precipitation of rainfall and evapotranspiration rates for <br /> the area. The calculation first determines whether the average monthly precipitation <br /> exceeds average monthly potential evapotranspiration. If so, then the difference is the <br /> percolating recharge water into the aquifer. Runoff and stream infiltration drainage are <br /> not factored into the calculation. This approach likely under-estimates recharge to the <br /> aquifer and, consequently, over-estimates nitrate loading. <br /> For the project Site, the local percolation and evapotranspiration rates are presented in <br /> Plate 1. The closest CIMIS station to the Site is Manteca (station 70). Data from the <br /> Manteca station were available for the past five years; based on the calculation shown, <br /> the estimated rate of recharge from percolating waters for the Manteca station is <br /> determined to be 3.64 inches. A statistical error of 48% is associated with this value, as <br /> calculated on Plate 1. <br /> Environmental Engineering Geology Geophysics <br />