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November 3, 2005 NOA Project Number: E05123A be considered potential ground-water contamination sources. 4.3 Water Sample Location According to Jeff Colombini,no wells exist on the site. No well permits were found during file review at EHD on September 29, 2005. A water sample was taken from the well head of the agricultural well to the immediate west of the Site by Ms. Nancy Rosulek on September 13, 2005. The well was directly to the east of the Bear Creek levee on the northwest corner of the proposed parcel one,indicated in the Appendix on the Site Map (Plate 1). 4.4 Water Sample Constituents l The water sample wa trate and DBCP. DBCP was not detected in the water sample. lyl Nitrate wasa 3.9 3,below the maximum contaminant level (MCL) of 45 mg/L- NO se yke United States EPA. The analytical reports prepared by Precision Enviro-Tech ca Te found in the appendix of this report. Well construction, seals, p age and depth of the well screens may play significant part in assessing the ` levels of Nitrate and DBCP in various aquifers. Without knowing specific details regarding well construction and condition,it would be difficult to accurately comment of the condition of the aquifer. Essentially, the water sample concentration approximately indicates the contaminant concentration level of the aquifer from which the well is drawing. It is 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 aquifers in San Joaquin County and other parts of the Central Valley. Nitrate in ground water occurs as a result of the application of fertilizers,livestock waste, and untreated septic tank waste. Nitrate is mobile and often accumulates in the shallow ground water zones. ' = In the early 1900s, natural levels of nitrate in ground water were measured in forty-three (43) wells i throughout the Sacramento Valley by Bryan (1923). It was thought that ground water at that time I4 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). 5 F1