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t <br /> Geological Technics!/. Page 5 <br /> Groundwater Monitoring Report <br /> Project No.750.2 <br /> August 16,2002 <br /> • For the °fifth consecutive event, the discretely screened deep well MW-101',did not <br /> contain contaminant concentrations above the laboratory reporting limits. This suggests <br /> that the previously recorded contamination was a drilling artifact. <br /> • Vertical groundwater gradient was calculated for the event of June 28, 2002, and was <br /> determined to be downward with a magnitude equal to the horizontal gradient of the <br /> water table. The magnitude of the vertical gradient has been getting progressively <br /> smaller during the last several monitoring events. This may be a result of influence <br /> from the vacuum of the vapor extraction system. <br /> • Oxidation-Reduction Potential measurements (Table 4) are positive for all the wells <br /> suggesting that the volume of contaminants leaching into groundwater is minimal and <br /> that biodegradation of the contaminants is at a rate sufficient to keep the BTEX/TPH-G <br /> plume in a small area around the source without depleting the oxygen to a level,.which <br /> would slow the reaction process. <br /> Recommendations: <br /> • Continue Quarterly groundwater monitoring at the site. The next event will occur by the <br /> end of September 2002. <br /> j • 'The vapor extraction system has operated for approximately 3 months: It is <br /> recommended that it continue operation for a total of six months to remove the high <br /> concentration ofcontaminants in the vadose and provide protection of the groundwater. <br /> 3.0. LIMITATIONS <br /> CThis report was prepared in accordance with 'the accepted standards and practices of the <br /> field of environmental geology, groundwater-hydrology and good business practices. It <br /> r should be recognized that definition and evaluation of environmental conditions is a <br /> Ldifficult and an inexact science. Judgments leading to conclusions and recommendations <br /> are,generally made with an incomplete knowledge of the site-specific conditions present. <br /> The tasks proposed and completed during this project were reviewed and approved by the <br /> local regulatory agency for compliance with the law. No warranty, expressed or implied, is <br /> made. <br /> i <br />