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LIVE OAK GEO ENVIRONMENTAL, INC. <br /> 407 W. Oak St., Lodi, CA 95240 t• (209) 369-0375 :• logelodi.com <br /> March 20, 2019 <br /> Project Number: 1902 <br /> Linda Turkatte, Director <br /> San Joaquin County Environmental Health Department <br /> 1868 E. Hazelton Ave. <br /> Stockton, CA 95205 <br /> Regarding: Addendum to Nitrate Loading Study <br /> Medina Property <br /> 5850 E. Ashley Ln., Stockton, CA <br /> Original report dated January 17, 2019 <br /> Ms. Turkatte: <br /> Based on our meeting at your office on Monday, we have prepared this addendum to <br /> the above Nitrate Loading Study. You indicated that the nitrate loading calculation for <br /> the Site should be re-evaluated using precipitation and evapotranspiration data <br /> obtained from the California Irrigation Management Information System for the past <br /> 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 /> Plates 1 and 2. The Site is located between the CIMIS Stations at Holt (station 248) <br /> and Staten Island (station 242), taking both stations into account will yield a value more <br /> representative of the Morada area. During the past five-year period, data from the Holt <br /> station were only available for 2017 and 2018; based on the calculation shown, the <br /> estimated rate of recharge from percolating waters for the Holt station is determined to <br /> be 3.72 inches. A statistical error of 25% is associated with this value, as calculated on <br /> Environmental Engineering Geology Geophysics <br />