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Ge0kgica1 Tech4ics Inc. <br /> Page 5 <br /> Groundwater Monitoring Report <br /> Project No. 989.2 <br /> March 12,2004 <br /> 3.0 CONCLUSIONS AND RECOMMENDATIONS <br /> ' The following conclusions have been drawn from the data generated from this site <br /> investigation work: <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 1: MW-I TPH-G vs. Groundwater Elevation. <br /> ' • MTBE plume has moved downgradient from the source, the former USTs. However, <br /> MTBE concentrations are low, potential risks are negligible, and the concentrations <br /> continue to decrease with each monitoring event. <br /> • Chart 2: MW-6 MTBE vs. Groundwater Elevation shows a linear decrease in MTBE <br /> concentrations and suggests that their is a correlation between decreasing MtBE <br /> concentrations and lower groundwater elevation. <br /> ' • Dissolved oxygen measurements recorded in the water table wells during the November <br /> 2003 monitoring event range from 0.79 to 1.92 ppm. The background dissolved oxygen <br /> range is conducive to promoting aerobic biodegradation activity. <br /> • pH measurements recorded in the water table wells range between 7.7 and 8.1. This <br /> range is conducive to aerobic biodegradation activity. <br /> ' • Groundwater analyses of MW-101 suggest there are no gasoline range petroleum <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 TPH-G plume is defined to the south by MW-3, to the east by MW-2 and to the <br /> west by MW-7. The plume is defined vertically by MW-101. <br /> • The MtBE plume is defined to the north by MW-8, to the northeast by MW-9, to the <br /> southeast by MW-2, to the northwest by MW-7 and vertically by MW-101. <br /> • We believe the petroleum contamination plume has been adequately defined vertically <br /> and laterally at this site. � <br /> "V 1!5Recommendations d <br /> ' 1. The data shows the hydrocarbon concentrations at this site have decreased significantly <br /> over time. GTI recommends the site be considered for closure. <br /> 2. Five quarters of groundwater monitoring have been conducted at the site since the <br /> ' installation of the new monitoring wells. VWDC prepared and submitted a site <br /> conceptual model in December 2003 and awaits response comments and <br /> recommendations from SJC/EHD. <br /> 3. We recommend that VWDC receive a response from SJC Environmental Health <br /> Department regarding the recommendations in the 2003 quarterly groundwater <br />