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June 27,2005 NOA Project Number: E05087A 1 1 concentration level of the aquifer from which the well is drawing. It i -- q g s Neil O. Anderson and Associate's opinion that,in general,near surface aquifers are more likely to have elevated concentrations of Nitrate and DBCP than the deeper aquifers. However the contaminant concentration of one aquifer cannot give any indication as to the concentrations of any other aquifer regardless of proximity. The presence of nitrates is not uncommon in shallow ground water Joaquin County n i aquifers ifu a San J q and other parts of the Central Valley. Nitrate in ground water occurs as a result of die application of fertilizers, livestock waste, and untreated septic tank waste. Nitrate is mobile and often accumulates _4 in the shallow ground water zones. In the early 1900s, natural levels of nitrate in ground water were measured in forty-three (43) wells throughout the Sacramento Valley by Bryan (1923). It was thought that ground water at that time was close to "natural" conditions. Based on the work by Bryan,it is estimated that under"natural" conditions, ground water concentration containing nitrate is no more then about 13.5 mg/L-NO3 (3 mg/L-N). Areas having 24.75 mg/L-NO3 (5.5 mg/L-N) or more are those in which nitrate concentrations may be increasing (Hull, 1984). DBCP was not found in the water sample. DBCP is a nematocide and soil fumigant for vegetables and grapes. It is thought to cause health problems consisting of kidney damage,liver damage, and cancer. The use of DBCP was discontinued in 1979. The Environmental Protection Agency (EPA) set the maximum contaminant limit (MCL) at 0.2 parts per billion (ppb) because the EPA believes that given present technology and resources, this is the lowest level to which water systems can reasonably be required to remove this contaminant should it occur in drinking water. 4.5 Well Water Sample Collection, Handling, and Transportation The sample for nitrate was collected in a clean plastic container, the sample for DBCP was collected in two clean glass vials. The samples were then transported on ice and remanded under chain of custody to Precision Enviro-Tech, Stockton., 4.6 Chain of Custody The Chain of Custody document has been included in the appendix of this report. 5.0 SOIL PROFILE AND GEOLOGIC INFORMATION The Site is depicted on the Geologic Maps of the Sacramento-San Joaquin.Delta as within the Quaternary Modesto Formation and Quaternary Riverbank Formation (Plate 7). The Quaternary Modesto Formation (undifferentiated) is unit of undifferentiated alluvial deposits, mainly arkosic, forming toe of the Mokelumne alluvial fan,generally covered by 0.3 to 1.0 in of Holocene intertidal deposits. 6