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October 13, 2004 ` NOA Project Number: E040109A drilling of two percolation test holes to a depth of 25 feet on September 17,2004. ✓4.2 Potential Ground Water Contamination Issues Identifying potential ground-water contamination sources was not part of the scope of work for the soil suitability study. Potential ground-water contamination can occur from a number of sources which often include leaky underground storage tanks,agricultural activities, dairies, septic systems, 60 and storm water infiltration. Any past agricultural activities and the present use of septic systems in the area should be considered potential ground-water contamination sources. 4.3 Water Sample Location One domestic well exists on the Site. No records of these wells were found during file review at EHD on October 4, 2004,presumably because the well was recently developed. Three water samples were collected at the well head of the on-site domestic water well on October 1, 2004 by Mr.Angel Chavez of our office. The locations of the well and water sample are indicated in Plate 1. /4.4 Water Sample Constituents The water sample was analyzed for nitrate and DBCP. Nitrate was found at m /L-N3iOell belo_ a maximum contaminant level (MCL) set by the US EPA of 45 mg/L-NO3. DBCP was of detectedn the water sample. The analytical reports prepared by Precision Enviro-Tech can be found in the appendix of this report. 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. i 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' ion 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