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Geological Tecwcs Inc. Page 4 Groundwater Monitoring Report lie Project No. 989.2 April 30,2003 2.2 Groundwater Analytical Results ' • Low concentrations of BTEX constituents were present in MW-1, MW-3 and MW-4. • No constituent of BTEX was found in the remaining monitoring wells. ' • Low concentrations of TPH-G were detected in MW-1, MW-3 and MW-4. TPH-G was not present in any other monitoring wells. • Low concentrations of MTBE were present in MW-1, MW-4, MW-5, MW-6, MW-8 and ' MW-9. The levels are consistent with previous monitoring events. • Concentrations of MTBE in MW-1 and MW-6 decreased since the November 2002 monitoring event. t • A plot of TPH-G versus groundwater elevation for MW-1 shows that generally the concentrations of TPH-gasoline fluctuate with groundwater elevation and that the ' overall concentrations are decreasing over time. • Historically, the fuel oxygenates DIPS, ETBE, TAME and TBA as well as 1,2 DCA and EDB have not been detected in any of the site's monitoring wells. This holds true for ' the new monitoring wells. Laboratory Data Sheets are included in Appendix C. The data are summarized in Table 2 of Appendix A. Chart 1 is a plot of TPH-G versus groundwater elevation for MW-1. During purging of the monitoring wells, field measurements of the oxidation-reduction ' potential (ORP) of the water were taken using an YSI 3560 Flowcell meter. During this groundwater-monitoring event, dissolved oxygen was measured in all the wells using an YSI dissolved oxygen meter. These measurements are summarized in Table 3 of Appendix ' A and in the field logs of Appendix B. ' 3.0 CONCLUSIONS AND RECOMMENDATIONS The following conclusions have been drawn from the data generated from this site investigation work: Conclusions • Concentrations of TPH-G and BTEX have progressively decreased since 1996, suggesting that the plume either is migrating or is attenuating from natural causes. ' • TPH-G fluctuates with groundwater and has decreased exponentially over time as seen in Chart: MW-1 TPH-Gvs. Groundwater Elevation. • MTBE plume has moved downgradient from the source, the former USTs. However, MTBE concentrations are low and potential risks are negligible. • MW-6 has consistently had the highest MTBE concentrations. Figure 5 contours the MTBE plume based on analytical results from the February 2003 monitoring event.