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' Quarterly Monitoring Report October 2400 Canepa's Car Wash(Pacific Avenue) Page-6 ' 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 MWA 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 October 2000 quarterly groundwater- monitoring event is generally consistent with previous monitoring results I 5 2 DISCUSSION OF ANALYTICAL RESULTS The fourth quarter 2000 laboratory analytical results (see Figures 3-4 and 6-8, 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- 7 and MW-8 BTEY, TPH-G, and MTBE were detected in the groundwater sample collected from MW-1 BTEX and TPH-G were detected in the groundwater sample from MW-2 Benzene, toluene, and MTBE were detected in the groundwater sample from MW-3 Benzene, toluene, and TPH-G were detected in MW-4 Benzene, toluene, total xylenes, and TPH-G were detected in MW-5 Benzene, toluene, and total xylenes were detected in MW-6 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 (Figure 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 The highest peaks in benzene concentration in Figure 6 generally occur at the sampling event following the peak in groundwater elevation Benzene concentrations in the soil vapor extraction wells (SV-1 through SV-9) have been decreasing as of late (Figure 8, Appendix A) 5.2 2 DISCUSSION OF MTBE CONCENTRATIONS MTBE concentrations have risen in both MW-1 and MW-2 over time, with the greatest increase observed I in MW-1 (Figure 9 and 10, Appendix A) There is a recent sharp increase in concentration of MTBE in MW-1 MTBE was not detected at a raised laboratory reporting limit of 200 micrograms per liter (µg/L) in MW-2 The highest concentrations of MTBE have been found in the soil vapor wells, the only ' undrowned sampling points (see Table 3, next page) I CONDOR