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' Quarterly Monitoring Report January 2001 Canepa s Car Wash(Pacific Avenue) Page-0 ' bmsl Since November 1993, the depth to groundwater at the site has ranged from approximately 54 5 feet to 31 8 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 cast side of the mound The groundwater mounding effect identified during the Januaty 2001 quarterly groundwater- monitoring event is generally consistent with previous monitoring iesults ' 5 2 DISCUSSION OF ANALYTICAL RESULTS The first quarter laboratory analytical results (see Figures 3-4 and 6-10, 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 labotatory reporting limits in the groundwater samples collected frorn MW-5, MW-6, and MW-8 BTEX, TPH-G, and MTBE were ' detected iii the gror.Indwatcr samples collected from MW-1 and MW-2 MTBE was detected in the groundwater sample from MW-3 Benzene and TPH-G were detected in MW-4 BTEX constituents 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, except for a decrease in January 2001 (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 this monitoring event The highest peaks in benzene concentration 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 lower concentiatrons of benzene relative to groundwater samples collected fiom 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 increased in both MW-1 and MW-2 over time, with the greatest increase obscived in MW-i (Figures 9 and 10, Appendix A) There is a recent sharp increase in Concentration of MTBE in MW-1 The highest concentrations of MTBE have been present in grouridwatet samples collected from the soil vapor extraction wells, the only wells to have screens not submerged in groundwater (see Table 3, next page) • �� CONDOR