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Quarterly Monitoring July 2001 and Sensitive Receptor Survey Report Canepa's Car Wash(Pacific Avenue) Page 6 shut down Condor is currently evaluating operation of the SVE system with carbon treatment as a ' replacement for the thermal oxidation system 5 0 DISCUSSION OF RESULTS 5 1 DISCUSSION OF GROUNDWATER ELEVATIONS The average depth to groundwater measured during the .July 2001 groundwater-monitoring event was approximately 34 0 feet below the monitor well measuring points, which is approximately 12 to 16 feet above the top of all monitoring well screens The groundwater elevation ranged from 20 53 to 21 50 feet bmsl Since November 1993, the depth to groundwater at the site has ranged from approximately 54 5 feet to 31 2 feet bgs The groundwater elevation contour map (Figure 2, Appendix A) indicates groundwater mounding in the center of the site in the vicinity of MW-1 and MW-2 with a primary groundwater gradient to the west, but with a northeast groundwater gradient reversal on the east side of the mound The groundwater mounding effect identified during the July 2001 quarterly groundwater- monitoring event is generally consistent with previous monitoring results 5.2 DISCUSSION OF ANALYTICAL RESULTS The second quarter laboratory analytical results (see Figures 4 through 10, Appendix A) are generally consistent with recent historical laboratory analytical results The laboratory analytical results indicate that none of the analytes of interest were detected at or above the laboratory reporting limits in the groundwater samples collected from MW-4, MW-5, MW-6, MW-7, and MW-8 BTEX, TPH-G, and MTBE were detected in the groundwater samples collected from MW-1 and MW-2 MTBE was detected in the groundwater sample from MW-3 ' • 5.21 DISCUSSION OF BENZENE CONCENTRATIONS Concentrations of benzene have decreased over time in MW-1, but appear to have generally increased in MW-2 (Figures 6 and 7, Appendix A) It appears that as the groundwater elevation increased there was an increase in the concentration of benzene in MW-2 The highest peaks in benzene concentration in Figure 7 generally occur at the sampling event coinciding with and/or following the peak in groundwater elevation The most recent groundwater samples collected from selected soil vapor extraction wells have contained significantly lower concentrations of benzene relative to groundwater samples collected from selected soil vapor extraction wells during previous monitoring events, particularly since startup of the SVE system (Figure 8, Appendix A) 5.2 2 DISCUSSION OF MTBE CONCENTRATIONS ' MTBE concentrations have generally increased in both MWA and MW-2 over time, with the greatest increase observed in MW-1 (Figures 9 and 10, Appendix A) The highest concentrations of MTBE have been present in groundwater samples collected from the soil vapor extraction wells, the only wells to have screens not completely submerged in groundwater (see Table 3, next page, and Figure 8, Appendix A) �� CONDOR