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Soil Suitability/Nitrate Loading Study Irerracon <br /> Vacant Commercial Property■ Stockton, California <br /> December 7, 2018 ■ Terracon Project No. NA187056 <br /> not in use, Terracon recommends the well be abandoned in accordance with applicable laws and <br /> regulations. Refer to Section 1.4.2. <br /> 2.3 Sources and Impact of Nitrate to Groundwater <br /> 2.3.1 Current Off-Site Sources of Nitrate <br /> Agriculture land use and residential septic systems in the area may be contributing sources of <br /> nitrate to groundwater. A groundwater study titled Addressing Nitrate In California's Drinking <br /> Water Technical Report 2 Nitrogen Sources and Loading to Groundwater dated 2012 prepared <br /> by the University of California Davis for the Tulare Lake Basin and Salinas Valley, indicated crop <br /> land contributed 96% of the human-generated nitrate sources to groundwater. The study <br /> indicated other minor contributors to nitrate in groundwater included waste water treatment plants, <br /> septic systems, corrals, lagoons and urban runoff. Based on the groundwater study, agricultural <br /> land use in the vicinity is anticipated to be the highest contributor to nitrates in groundwater. <br /> 2.3.2 Contribution of Rainfall <br /> An estimate of the quantity and quality of rainfall was required for the nitrate loading analysis. <br /> The estimate of deep percolation of rain is based on the average monthly precipitation of rain fall <br /> and evapotranspiration for the Stockton California area. The estimate first determines whether <br /> the average monthly precipitation exceeds average monthly potential evapotranspiration. If so, <br /> then the difference is potential deep percolation. This method does not consider runoff, although <br /> due relatively flat nature of the site runoff should be minimal. Average potential <br /> evapotranspiration and precipitation data was obtained from the California Irrigation Management <br /> Information System (CIMIS). The below table was compiled from multiple stations located near <br /> Stockton including Lodi, Lodi West, Holt, Staten Island, Manteca, Ripon, and Tracy and the <br /> estimated deep percolation data was averaged over a 35 year period (the number of years the <br /> data was available). <br /> Table 8. <br /> Estimate of Deep Percolation of Rain for the Site <br /> Location Deep Percolation of Rain <br /> Stockton Area 12.78 inches per year <br /> Based on this method, the average deep percolation of rain for the Stockton area is estimated to <br /> be 12.78 inches/year. The nitrate concentration of rainfall is estimated to be 1 mg/L-N (Hantzsche <br /> and Finnemore, 1992). <br /> Responsive ■ Resourceful ■ Reliable 17 <br />