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since the previous quarterly monitoring round on December 7, 1998 The flow direction <br /> is to the north The overall gradient is 0 006 feet/linear foot <br /> RESULTS OF CERTIFIED ANALYSIS OF GROUNDWATER SAMPLES <br /> The results of the certified analyses of groundwater samples collected from the three <br /> monitor wells on March 3, 1999 are shown in Table 1 Copies of the laboratory reports <br /> are included as Appendix D of this report <br /> TPH-G concentrations ranged from a maximum of 4600 ug/l at monitor well MW 1 to <br /> 2100 ug/1 at monitor well MW2 <br /> Benzene concentrations ranged from a maximum of 2500 ug/1 at MW I to 520 ug/I at <br /> MW2 <br /> MTBE concentrations ranged from a maximum of 18 ug/I at MW I to 3 6 ug/l in MW2 <br /> None of the monitor wells showed concentrations of the four remaining oxygenants, <br /> ETBE, TBA, DIPS, or TAME, above the laboratory detection limits <br /> Figure 5 shows the distribution of TPH-G, BTEX, and MTBE in groundwater and the <br /> estimated lateral limits of the TPH-G in groundwater as determined from groundwater <br /> samples collected on March 3, 1999 The increase in overall groundwater elevation and <br /> reversal of flow direction to the north has resulted in decreased concentrations of TPH-G <br /> and BTEX at all three morutor wells <br /> RECOMMENDATIONS <br /> 1) Continue quarterly groundwater monitoring <br /> 2) Construct a workplan to further assess the lateral and vertical extent of soil and <br /> groundwater contamination originating from the former UST at the site The assessment <br /> should address the potential impact on soil and groundwater from possible releases <br /> during periods of reduced groundwater elevation WEGE has determined that the top of <br /> groundwater in site vicinity receded to its lowest recorded elevation (since 1965) in <br /> October 1977 of 60-65 feet below mean sea level (72-77 feet bgs) <br /> LIMITATIONS <br /> The discussion presented in this report is based on the following <br /> 1 The observations and data collected by field personnel <br /> 2 The results of laboratory analyses performed by a state certified analytical laboratory <br /> 3 Our understanding of the regulations of San Joaquin County and the State of <br /> California <br /> 3 Arc Pump QM 1-3 1999 <br />