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The rennaining four oxygenants, TBA DIPS ETBE, and TAME, were not found above <br /> laboratory detection innnits in any of the five monitor wells despite the large increase in <br /> groundwater elevation since the previous analyses for those compounds in Deceinber 1997 <br /> Figure 5 shows the distribution of TPH-G, BTEX and MTBE in groundwater and the lateral limits <br /> of the TPH-G in groundwater as determined from groundwater samples collected on June 2, 1998 <br /> The decrease in groundwater elevations since the previous quarterly monitoring sound in March <br /> 1998 has been accompanied by an increase in TPH-G and BTEX concentrations at MW1 and the <br /> presence of TPH-G and BTEX at MW3, currently hydraulically downgradient from the former <br /> UST aiea <br /> RECOMMENDATIONS <br /> 1) Implement Wm J Hunter & Associates "Workplan for Removing Contaminated Soil" dated <br /> October 1997 Remove contaminated soil to a depth of 26 feet bgs <br /> 2) Install two additional monitor wells to measure FPH-G, BTEX, and MTBE concentrations at <br /> depths below the current monitor well slotted intervals Install one monitor well at the center of the <br /> groundwater contarnniination plume following removal of contaminated soil to 26 feet bgs and one <br /> well downgradient of shallow groundwater plunne Collect hydropunch water samples during the <br /> drilling of the boreholes for each monitoi well at 5 foot intervals below 40 feet bgs and screen <br /> water samples on-site with a portable chromatograph to establish the tequiied total depth of the <br /> nnonitoi wells foi measuring historical groundwater contamination Complete the two nnonitoi <br /> wells with slotted casing fiom 30 feet bgs to the total depth of the wells <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 California <br /> Changes in groundwater conditions can occur due to variations in rainfall, temperature, local and <br /> regional water use, and local construction practices In addition, variations in the soil and <br /> groundwater conditions could exist beyond the points explored in this investigation State Certified <br /> Laboratory analytical results are included in this report This laboratory follows EPA and State of <br /> Califotnia approved procedures, howevet, WEGE is not responsible for errors in these laboratory <br /> results <br /> 3 Sanchez QM 6-98 <br />