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G�t�gicatTuluticslxc. - Additional Site Characterization Page 11 And 151 Quarter 2004 Groundwater Monitoring Project No.425.2 March 22,2004 during late spring and summer. Upward vertical gradients dominate over downward i gradients by a 4:1 ratio. ❑ Vertical groundwater gradients between the intermediate and deep wells have historically been found to be flowing upward. ❑ The dominance of upward vertical flow of groundwater may be the primary reason ! the contaminants has not impacted the drinking water aquifer. 3. Contaminant Plume 3 ❑ The shallow water table groundwater plume is laterally defined except to the west. Increases in TPH-G concentration in the western monitoring wells indicate that the plume may be spreading laterally toward the west. ; ❑ Petroleum hydrocarbon concentrations in the groundwater at the site fluctuate with each monitoring event. The residual contamination in soil, up gradient of MW-2, remains a significant source of impact to the groundwater plume. ❑ The deeper groundwater plume may be undefined vertically since MW-106 and MW-201 were found to contain BTEX and TPH-G constituents. ❑I The three domestic wells sampled for the event remain non-detect, indicating that the drinking water aquifer has not been impacted_ - i Recommendations The following recommendations are made: ' 1. Prepare and submit a feasibility study reviewing the best remediation alternatives available and corrective action plan selecting the best remediation alternative. 2. Test for fuel oxygenates by EPA method 8260 annually during the second quarter of each year. 3. Continue quarterly groundwater-monitoring events. 5.0 LIMITATIONS This report was prepared in accordance with the generally accepted standard of care and practice in effect at the time Services were rendered. It should be recognized that definition and evaluation of environmental conditions is an inexact science and that the state or practice of environmental geology/hydrology is changing and evolving and that standards existing at the present time may change as knowledge increases and the state of the practice continues to improve. Further, that differing subsurface soil characteristics can be experienced within a small distance and therefore cannot be known in an absolute sense. 6 All conclusions and recommendations are based on the available data and information. f 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 made. 'F k