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' C7utgXat rahfiWS laic <br /> Page 5 <br /> Groundwater Monitoring Report <br /> Project No 989 2 <br /> March 29,2004 <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-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 2 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 February <br /> 2004 monitoring event range from 0 51 to 126 ppm The background dissolved oxygen <br /> range (defined by upgradient well MW-2) is conducive to promoting aerobic <br /> biodegradation activity <br /> • pH measurements recorded in the water table wells range between 7 68 and 7 98 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 downward moving <br /> contaminant migration <br /> ' Recommendations <br /> 1 As per the SJCEHD request, dated March 12, 2004, GTI is preparing a work plan to <br /> ' further define the lateral extent of the plume <br /> 2 Quarterly groundwater monitoring should continue uninterrupted during additional site <br /> investigation <br /> 4.0 LIMITATIONS <br /> ' <br /> This report was prepared in accordance with the generally accepted standard of care and <br /> ' practice in effect at the time Services were rendered It should be recognized that <br /> definition and evaluation of environmental conditions is an inexact science and that the state <br /> or practice of environmental geology/hydrology is changing and evolving and that <br /> ' standards existing at the present time may change as knowledge increases and the state of <br /> the practice continues to improve Further, that differing subsurface soil characteristics <br /> can be experienced within a small distance and therefore cannot be known in an absolute <br /> ' sense All conclusions and recommendations are based on the available data and <br /> information. <br /> 1 <br />