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1 ' Quarterly Monitoring Report April 2001 Canepa s Car Wash(Pacstoe Avenue) bmsl Since November 1993, the depth to groundwater at the site has fanged fiom approximately 54 5 ' feet to 31 2 feet bgs The gioundwater 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 April 2001 quarterly gioundwater- monitoring event is generally consistent with previous monitoring iesults 5 2 DISCUSSION OF ANALYTICAL RESULTS The second quartei 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-6, and MW-8 BTEX and TPH-G were detected in the groundwater samples collected from MW-1 and MW-2 MTBE was detected to the groundwater samples ' from MW-I and MW-3 Benzene was detected in MW-5 Benzene and total xylenes were detected in MW-7 ' 5.2 1 DISCUSSION OF BENZENE CONCENTRATIONS Concentrations of benzene have decreased over time in MW-1, but appear to be increasing in MW-2 (Figures 6 and 7, Appendix A) It appears that with an increase in groundwater elevation there is an increase in the concentration of benzene in MW-2, except with the January 2001 monitoring event The highest peaks in benzene concentiation in Figure 6 generally occur at the sampling event following the . peak in groundwater elevation Relatively recent groundwater samples collected from selected soil vapor ' extraction wells have contained significantly lowei concentrations of benzene relative to groundwater samples collected from selected soil vapor extraction wells during previous monitoring events, particularly since startup of the soil vapor system 5 2 2 DISCUSSION OF MTBE CONCENTRATIONS MTBE concentrations have generally increased in both MW-1 and MW-2 over time, with the greatest iincrease observed in MW-1 (Figures 9 and 10, Appendix A) There is a recent decrease in concentration of MTBE in MW-1, while MTBE was not detected in MW-2 at the raised laboratory reported detection limit of 200 µg/L The highest concentrations of MTBE have been present in groundwater samples collected fiom the soil vapor extraction wells, the only wells to have screens not submerged in groundwater(see Table 3, next page) I ' �� CONDOR