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' Nitrate Loading Study Irerracon <br /> Arriaga Property _°. Stockton, California <br /> April 26, 2019 _•,; Terracon Project No. NA187059 <br /> On February 26, 2019 two groundwater samples (GW -1 and GW-2) were collected from an <br /> exterior faucet connected to the onsite groundwater well and submitted on ice to McCampbell <br /> Analytical Inc. for analysis. Sample GW-1 was collected into a clean unpreserved plastic 125 <br /> milliliter(ml) bottle and analyzed for nitrate as N by EPA Extraction Method E300.1. Sample GW <br /> -2 was collected into two clean glass 40 ml amber VOA preserved with ascorbic and meleic acid <br /> and analyzed for DBCP (1,2-Dibromo-3-chloropropane) by EPA Extraction Method E524.3. <br /> Nitrate as N was reported at 5.9 mg/L in groundwater sample GW-1 which is below the MCL of <br /> 10 mg/L N. Groundwater sample GW-2 reported below laboratory reporting limits of 0.020 <br /> micrograms per liter(ug/L)for DBCP. <br /> 3.0 SOURCES AND IMPACT OF NITRATE TO GROUNDWATER <br /> 3.1 Current Off-Site Sources of Nitrate <br /> The adjoining northern property consists of Mariposa Road followed by agricultural land used for <br /> row crops. The adjoining eastern property consists of a residence and equipment yard. The <br /> adjoining western property consists of a residence. The adjoining southern property appears <br /> vacant and/or agricultural land. Terracon assumes the adjoining properties are connected to <br /> individual septic systems based on the absence of municipal sewer systems in the area as <br /> reported on the San Joaquin County District Viewer. Therefore, off-site sources of nitrate include <br /> septic systems, agricultural land use, and natural processes. <br /> Based on information obtained from the DWR Water Data Library, dissolved nitrate (<41.7 mg/L) <br /> was reported in a groundwater well located approximately 930 feet southwest of the site below <br /> the MCL of 45 mg/L for nitrate. The State Water Resources Control Board Website did not identify <br /> nitrate impacted groundwater wells within 2,000 feet of the site. <br /> A groundwater study titled Addressing Nitrate In California's Drinking Water Technical Report 2 <br /> Nitrogen Sources and Loading to Groundwater dated 2012 prepared by the University of <br /> California Davis for the Tulare Lake Basin and Salinas Valley, indicated crop land contributed <br /> 96% of the human-generated nitrate sources to groundwater. The study indicated other minor <br /> contributors to nitrate in groundwater included waste water treatment plants, septic systems, <br /> corrals, lagoons and urban runoff. Based on the groundwater study, agricultural land use in the <br /> site vicinity is anticipated to be the highest contributor to nitrates in groundwater. <br /> 3.2 Contribution of Rainfall <br /> An estimate of the quantity and quality of rainfall was required for the nitrate loading analysis. <br /> Average precipitation and potential evapotranspiration data was obtained from the California <br /> Irrigation Management Information System(CIMIS). Data from the Manteca (070)and Holt(248) <br /> stations was used to estimate a rainwater recharge rate. The estimate is based on the average <br /> monthly precipitation of rain fall and evapotranspiration (ETo) for Stockton. The estimate first <br /> Responsive m Resourceful m Reliable 6 <br />