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November 23,2004 <br /> NOA Project Number: E04140A <br /> The presence of nitrates is not uncommon in shallow ground water aquifers in San Joaquin County <br /> and other parts of the Central Valley. Nitrate in ground water occurs as a result of the application <br /> of fertilizers,livestock waste,and untreated septic tank waste. Nitrate is mobile and often <br /> accumulates in the shallow ground water zones. <br /> In the early 1900s,natural levels of nitrate in ground water were measured in forty-three (43) wells <br /> throughout the Sacramento Valley by Bryan (1923). It was thought that ground water at that time <br /> was close to "natural' conditions. Based on the work by Bryan,it is estimated that under"natural' <br /> conditions,ground water nitrate concentration is no more then about 13.5 mg/L-NO3 (3 mg/L-N). <br /> Areas having 24.75 mg/L-NO3 (5.5 mg/L-N) or more are those in which nitrate concentrations may <br /> ` be increasing (Hull, 1984). <br /> DBCP is a nematocide and soil fumigant for vegetables and grapes. It is thought to cause health <br /> ` problems consisting of kidney damage,liver damage,and cancer. The use of DBCP was <br /> discontinued in 1979. The Environmental Protection Agency (EPA) set the maximum contaminant <br /> limit (MCL) at 0.2 parts per billion (ppb) because the EPA believes that given present technology <br /> and resources, this is the lowest level to which water systems can reasonably be required to remove <br /> this contaminant should it occur in drinking water. <br /> ` 4.6 Well Water Sample Collection, Handling, and Transportation <br /> The samples were collected in a clean plastic container,then decanted into clean,glass vials. The <br /> ` samples were then transported on ice and remanded under chain of custody to Precision Enviro- <br /> Tech, Stockton. <br /> ` 4.7 Chain of Custody <br /> The Chain of Custody document has been included in the appendix of this report. <br /> 5.0 SOIL PROFILE AND GEOLOGIC INFORMATION <br /> The Site is in an area of the Modesto Formation. According to the Geologic Map of the Sacramento <br /> Quadrangle, California, this unit consists of Pleistocene alluvium from distinct alluvial terraces and <br /> some alluvial fans and abandoned channel ridges (Plate 8). It is comprised of tan and light-gray <br /> gravely sand, silt and clay except where derived from volcanic rocks of the Tuscan Formation;then <br /> it is distinctly red and black with minor brown clasts. <br /> 6 01 <br />