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Ge0[0gkA(Techda14c. Page 5 ' Groundwater Monitoring Report Project No.989.2 July 24,2003 ' • TPH-G fluctuates with groundwater and has decreased exponentially over time as seen in Chart: MW-I TPH-G vs. Groundwater Elevation. ' • MTBE plume has moved downgradient from the source, the former USTs. However, MTBE concentrations are low and potential risks are negligible. ' • Chart: MW-6 MTBE vs. Groundwater Elevation shows that MTBE fluctuates with groundwater elevation. It clearly shows a decreasing MTBE plume over time and is likely attenuating from natural causes. ' • Dissolved oxygen measurements recorded in the water table wells during the May 2003 monitoring event range from 0.27 to 1.14 ppm. The background dissolved oxygen range is conducive to promoting aerobic biodegradation activity. ' • pH measurements recorded in the water table wells range between 7.4 and 7.8. This range is conducive to aerobic biodegradation activity. ' • Groundwater analyses of MW-101 suggest there are no gasoline range petroleum hydrocarbons impacting deep groundwater at this site. The thick clay found during the installation of the deep monitoring well should form a barrier to contaminant migration. ' • 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. • We believe the petroleum contamination plume has been adequately defined vertically and laterally at this site. Recommendations ' 1. Four quarters of groundwater monitoring have been conducted at the site since the installation of the new monitoring wells. GTI recommends that a site conceptual model and an Appendix B for site closure be prepared and submitted for review. ' 2. The data shows the hydrocarbon concentrations at this site have remained stable or have decreased. GTI recommends the site be considered for closure. 3. Quarterly groundwater monitoring should not be interrupted during site closure preparation. GTI recommends that sampling for fuel oxygenates, other than MTBE, be discontinued since none have ever been recorded at the site. 4. If the site receives closure, GTI recommends the proper abandonment of all monitoring wells associated with this site. ' 4.0 LIMITATIONS This report was prepared in accordance with the generally accepted standard of care and ' practice in effect at the time Services were rendered. It should be recognized that definition and evaluation of environmental conditions is an inexact science and that the state or practice of environmental geology/hydrology is changing and evolving and that i