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�CoEpS CESK.'f/C..tpMy/TµTq � Table 3-2 Organic Analytical Results San Joaquin County Human Services Agency 10 and 11 May 2000 Groundwater Ethyl- Total ' Well Elevation Benzene Toluene benzene Xylene TPH-G MTBE feet) /L) ( /L) ( a/L) ( IL) ( IL) IL MW-2 NM 11,000 90 2,100 850 25,000 NA ' MW-2A -14 26 250 ND 5 0 160 60 2,900 ND 2 0 MW-2A da -14 26 260 16 160 48 2,400 NA MW-3A -14 45 ND 0 5) 0 71 0 75 ND 0 5) 200 ND 2 0 MW-4 -13 56 ND 0 5 ND 0 5 ND 0 5 ND 0 5 ND 50 NA MW-6 -12 86 6 7 ND (0 5) ND 0 5) ND 0 5 88 NA MW-7 -14 62 12 ND 0 5) ND 0 5) ND 0 5) 53 NA MW-9 -14 28 ND (0 5) ND (0 5) ND (0 5) ND LILL ND 50) ND 2 0) Notes ND (0 5) = Analyte not detected, detection limit indicated in parentheses NM = Not measured NA = Sample was not analyzed for this constituent 4.0 CONCLUSIONS ' Concentrations of petroleum hydrocarbons decreased In source area wells MW-2 and MW-2A The decreasing concentrations are most likely due to natural degradation Petroleum hydrocarbons ' and benzene were detected in MW-6 and MW-7 at concentrations slightly above the concentrations detected in MW-6 and slightly below the concentrations detected in MW-7 in the fourth quarter ' 1999, law concentrations of total xylenes were also detected in the samples from these wells These detections are likely due to the seasonal rise in the water table that occurred during this ' quarter Groundwater flows into a trough and then to the northeast with a horizontal gradient of 0 0018 ft/ft MTBE was not detected In samples from wells MW-2A, MW-3A and MW-9 this quarter Based on the 16 May letter from Margaret Lagono, Supervising REHS of Unit IV, this constitutes the first quarterly sampling for MTBE MTBE sampling will be conducted next quarter in wells MW- 2, MW-2A and MW-9, and then discontinued if not detected f NCASha ai PµOIEGTSZAN10QlliSA4000RPT WPO 5