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Gealagkol redmics Inc. Page 8 Additional Site Characterization and 3'd Quarter Groundwater Monitoring Project No.989.2 October 31,2002 ' ranged from 1.45 feet above MSL to 1.28 feet below MSL. Groundwater elevation calculated from the three new shallow monitoring wells indicates an average of 2.22 below MSL. Calculations from the new wells are outside of historical figures and future- monitoring events will contribute to a more accurate hydrologic picture. Site-specific groundwater bearing and slope were calculated and found to be N22°W @ ' 0.0054 ft/ft. These results are consistent with historical groundwater bearing and slope for this site. ' Groundwater elevation, bearing and slope were calculated from data gathered during the August 22 and September 26, 2002, monitoring events and the results are summarized in Table 1 of Appendix A. 4.0 CONCLUSIONS AND RECOMMENDATIONS This investigation was an effort to define the lateral and vertical extent of the gasoline range petroleum hydrocarbons plume in the groundwater under the site. The following conclusions have been drawn from the data generated from this site investigation work: Conclusions • Groundwater analyses of MW-101 suggest there are no gasoline range petroleum hydrocarbons impacting deep groundwater at this site. The thick clay found should form a barrier to contaminant migration. • BTEX and TPH-G concentrations are insignificant and are found only near the source_ ' Potential hazards are negligible. MTBE concentrations are low and potential risks are negligible. • MTBE plume has moved downgradient from the source, the former USTs. 0 The plume is defined to the south by MW-3, to the east by MW-2 and to the west by MW-7. • The MTBE plume is essentially defined to the north by MW-8 and to the northeast by MW-9. • The clay layer at 31 feet bgs provides a significant barrier to vertical plume migration. * We believe the petroleum contamination plume has been adequately defined vertically ' and laterally at this site. RECOMMENDATIONS t • We recommend that two more quarters of monitoring be performed. if the data shows the site conditions are remaining stable, we recommend that the site should be ' considered for closure. 0 If the site receives, closure GTI recommends the proper abandonment of all monitoring wells associated with this site.