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4�ealogicalTeckaics1 <br /> ac. Page 5 <br /> l Groundwater Monitoring Report <br /> 16 <br /> Project No. 989.2 <br /> November 14,2003 <br /> Conclusions <br /> • Concentrations of TPH-G and BTEX have progressively decreased since 1996, <br /> suggesting that the plume is attenuating from natural causes. <br /> ' • TPH-G fluctuates with groundwater and has decreased exponentially over time as seen <br /> in Chart: MW-1 TPH-G vs. Groundwater Elevation. <br /> MTBE plume has moved downgradient from the source, the former USTs. However, <br /> MTBE concentrations are low and potential risks are negligible. <br /> + Chart: MW-6 MTBE vs. Groundwater Elevation shows that MTBE fluctuates with <br /> groundwater elevation. It clearly shows a decreasing MTBE plume over time and is <br /> likely attenuating from natural causes. <br /> + Dissolved oxygen measurements recorded in the water table wells during the May 2003 <br /> 1 monitoring event range from 0.38 to 3.85 ppm. The background dissolved oxygen <br /> range is conducive to promoting aerobic biodegradation activity. <br /> 4 pH measurements recorded in the water table wells range between 7.6 and 8.2. This <br /> range is conducive to aerobic biodegradation activity. <br /> • Groundwater analyses of MW-101 suggest there are no gasoline range petroleuin <br /> hydrocarbons impacting deep groundwater at this site, The thick clay found during the <br /> installation of the deep monitoring well should form a barrier to contaminant migration. <br /> • The plume is defined to the south by MW-3, to the east by MW-2 and to the west by <br /> MW-7. The plume is defined vertically by MW-101. <br /> • The MTBE plume is essentially defined to the north by MW-8 and to the northeast by <br /> MW-9. <br /> • We believe the petroleum contamination plume has been adequately defined vertically <br /> and laterally at this site. <br /> ' Recommendations <br /> 1. Five quarters of groundwater monitoring have been conducted at the site since the <br /> installation of the new monitoring wells. GTI is preparing a site conceptual model and <br /> will submit the model for review within 30 days. <br /> 2. The data shows the hydrocarbon concentrations at this site have remained stable or have <br /> decreased. GTI recommends the site be considered for closure. <br /> 3. Quarterly groundwater monitoring should not be interrupted during site closure <br /> preparation. <br /> 4. If the site receives closure, GTI recommends the proper abandonment of all monitoring <br /> wells associated with this site. <br /> M <br />