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16. L May 18, 2005 NOA Project Number. E05059A /4.2 Potential Ground Water Contamination Issues Potential ground-water contamination can occur from a number of sources which often include leaky underground storage tanks, agricultural activities, dairies, septic systems, and storm water infiltration. Agricultural activities and the use of septic systems in the area should be considered potential ground-water contamination sources. 6. Potential contamination sources were discussed in detail in the Surface/Subsurface Contamination Report for the Site (NOA Environmental, 2002). i ✓4.3 Well History and Water Sample Location One agricultural well which will be welded shut, two domestic wells,and one abandoned domestic well exist on the Site. One well permit was found for the Site during file review at EHD on March 3,2005. This 1999 permit for a cross-connection repair has been included in the appendix of this report A water sample was taken from a faucet fed by the domestic well on Parcel 2 by Mr. Conor McGee ` of our office on April 21, 2005. /4.4 Water Sample Constituents � oS The water sample was analyzed for nitrate and DBCP. Nitrate was found at 11.4 m¢/L-NO,,we below the maximum contaminant level (MCL) set by the US EPA of 45 mg/L-NO3. DBCP was not detected in the water sample. The analytical reports prepared by Precision Enviro- eI�"�an 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. 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 6 was close to "natural" conditions. Based on the work by Bryan,it is estimated that under"natural" conditions,ground water concentration containing nitrate has a concentration of no greater then about 13.5 mg/L-NO3 (3 mg/L-N). Areas having 24.75 mg/1,NO3 (5.5 mg/L-N) or more are 6. those in which nitrate concentrations may be increasing (Hull, 1984). �L 5 L "004 L