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r L November 3,2004 NOA Project Number: E040118A 6 appendix of this report. The presence of nitrates is not uncommon in shallow ground water aquifers in San Joaquin County 61 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. U it 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 Lwas 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 u concentrations may be increasing (Hull, 1984). L DBCP is a nematocide and soil fumigant for vegetables and grapes. It is thought to cause health Lproblems 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 Land resources, this is the lowest level to which water systems can reasonably be required to remove this contaminant should it occur in drinking water. L4.5 Well Water Sample Collection, Handling, and Transportation The water sample was obtained at the well head at both locations. The samples were collected in a clean plastic container, then decanted into clean,glass vials. The samples were then transported on ice and remanded under chain of custody to Precision Enviro-Tech, Stockton. David Welch of NOA collected the water samples. L 4.6 Chain of Custody ' L 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 USGS Geologic Map of the Sacramento-San Joaquin Delta, California, L1982. The map show the Site as Holocene peat and mud as part of tidal wetlands and waterways (Plate 4). L it 5 v ..