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Quarterly Monitoring Report, Julv 2001 Canepa's Car Wash(Park Street) ' August 27,2001 Page 5 ' indicate that the area of groundwater contamination most impacted by petroleum hydrocarbons is in the northern portion of the site in the vicinity of monitor wells MW-2 and MW-5 5 2.1 DISCUSSION OF BENZENE CONCENTRATIONS The concentration of benzene has decreased with time in monitor well MW-2 as the groundwater ' elevation has increased (Figure 6, Appendix A) Benzene concentrations in MW-5 have generally increased as the groundwater elevation has increased (Figure 8, Appendix A) It is important to note that both wells are drowned, with 16 to 22 feet of water above the well screen Therefore the first ' groundwater, with potentially greater BTEX concentrations, is not being sampled 5 2 2 DISCUSSION OF MTBE CONCENTRATIONS Concentrations of MTBE in monitor well MW-6 have decreased slightly over time, with a recent increase in October 2000 and decrease in April 2001 (Figure 7, Appendix A) There has also been a reappearance of low concentrations of MTBE in monitoring wells MW-3 and MW-4 ' 5 2 3 DISCUSSION OF OTHER ANALYTE CONCENTRATIONS ' Concentrations of toluene, ethyl benzene, total xylenes, and TPH-G have decreased over time in monitor well MW-2, but all have increased in monitor well MW-5 (Table A, Appendix B) In general, concentrations of analytes have decreased as the groundwater elevation has increased, except in MW-5, which has seen an increase in contamination It is important to note that since all of the monitor wells are drowned, the shallowest water with the potentially highest contaminant concentrations is not being sampled Therefore, the actual concentrations of the plumes have not been measured and are not known According to Figures 4 and 5, the plumes probably extend beyond the site, therefore the current monitoring wells cannot measure the northern extent of the contaminant plumes I I ' L� CONDOR