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k Geological Tec vda lac. Page 5 • Groundwater Monitoring Report Project No. 750.2 December 20,2001 $ • The remaining wells were found to be free of contaminants, which is consistent with other events. ` • Vertical groundwater gradient was calculated and determined to be downward and r greater than the horizontal gradient of the water table, suggesting that the contaminants in the water table may be transported to deeper depths in the subsurface. • Oxidation-Reduction Potential measurements (Table 4) are positive for all the wells, suggesting that the volume of contaminants leaching into groundwater is minimal and that biodegradation of the contaminants is at a rate sufficient enough to beep the BTEX/TPH-G plume in a small area around the source without depleting the oxygen to a level to slow the reaction process. Recommendations: • Quarterly groundwater monitoring will continue at the site. The next event will occur by February 28, 2002. • A Vadose Zone Remediation - Corrective Action Plan has been approved by San Joaquin County PHS/EHD and the USTCFP. The soil vapor extraction system is in the process of being installed and should be completed by early January 2002. 3.0 LIMITATIONS +' This report was prepared in accordance with the accepted standards and practices of the field of environmental geology, groundwater hydrology and good business practices. it should be recognized that definition and evaluation of environmental conditions is a a difficult and an inexact science. Judgments leading to conclusions and recommendations are generally made with an incomplete knowledge of the site-specific conditions present. The tasks proposed and completed during this project were reviewed and approved by the local regulatory agency for compliance with the law. No warranty, expressed or implied, is I made, i I t k 1