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DISCUSSION - IpResults of this groundwater monitoring event indicate that levels of dissolved gasoline hydrocarbons remained generally consistent from the previous sampling events TPHG was below the method reporting limit and BTEX concentrations decreased to 3 36 ppb, 0 616 ppb, 0 565 ppb, and 2 04 ppb, respectively, in well MW -5 TPHG and BTEX concentrations also decreased in wells MW -6 and MW -7 MTBE was detected in wells MW -1, MW -3, and MW -4 at concentrations of 34 4 ppb, 5 82 ppb, and 58 6 ppb, respectively, using USEPA Method 8260 The groundwater flow direction (southeast to northeast) and gradient are consistent with previous sampling events Groundwater elevation increased 0 05 foot in well MW -1 and decreased 0 86 foot in wells MW -2 through MW -7 from the previous sampling event (August 1999) Access issues have delayed implementation of the additional site assessment proposed in the approved September 29, 1999 Workplan The investigation was scheduled to begin on December 22, 1999 and was rescheduled to begin on January 18, 2000 At present the investigation is postponed pending resolution Details of the access -related issues were outlined in ARCO's letter dated January 18, 2000 ATTACHMENTS • Table 1 • Table 2 • Table 3 • Figure 1 • Figure 2 • Figure 3 • Appendix A • Appendix B W• Appendix C Groundwater Monitoring Data Groundwater Analytical Results for Oxygenates Groundwater Flow Direction and Gradient Site Location Map Groundwater Analytical Summary (Fourth Quarter 1999) Groundwater Elevation Contours (Fourth Quarter 1999) Field Procedures Laboratory Analysis Reports for Groundwater Samples and Chain -of -Custody Records Groundwater Monitoring Field Data Sheets CP 1N 1CamPklData\Aichive\Arco121681Qtr1y12168Q499 DOC-9811sg 1 IT Corporation 03110M