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LIVE OAK GEO ENVIRONMENTAL, INC. <br /> 407 W. Oak St., Lodi, CA 95240 fi (209) 369-0375 •: logelodi.com <br /> March 19, 2019 <br /> Project Number: 1901 <br /> Linda Turkatte, Director <br /> San Joaquin County Environmental Health Department <br /> 1868 E. Hazelton Ave. <br /> Stockton, CA 95205 <br /> Regarding: Addendum to Soil Suitability/Nitrate Loading Study <br /> Armosino Property <br /> 16724 S. Lawrence Rd., Escalon, CA <br /> Ms. Turkatte: <br /> Based on our meeting yesterday, we have prepared this addendum to the above <br /> Nitrate Loading Study. You indicated that the nitrate loading calculation for the Site <br /> should be re-evaluated using precipitation and evapotranspiration data obtained from <br /> the California Irrigation Management Information System for the past five years. <br /> As in the previous report prepared by our office, the method utilized for the nitrate <br /> loading analysis is based on a mass balance formula discussed in a published paper by <br /> Hantzsche and Finnemore (1992). The Hantzsche and Finnemore equation is a <br /> conservative approximation of ground-water nitrate-nitrogen concentration resulting <br /> from the combined effect of on-site sewage disposal systems and percolating recharge <br /> 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 />