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chromatographs of diesel range organics detected upgradient of the plant, relative to hydrocarbons from near the source area are inconclusive because of natural degradation. Groundwater impacts downgradient of the LFC plant probably resulted from migration of hydrocarbons from the initial release area during the following three periods: 1. The time between discovery of the release and the initiation of groundwater remediation. 2. Plant construction in 1999, when the recovery wells (RW-4 and RW-5) were inoperative and replacement wells RW-4A and RW-5A were not yet completed. 3. After plant construction in late 2002, when biofouling significantly reduced recovery from well RW-5A. The downgradient hydrocarbon migration may have resulted in residual impacts to vadose-zone soils, which will leach hydrocarbons to the groundwater during times of elevated water table conditions. In February 2004, three borings were advanced downgradient of the plant to determine the extent of off-site impacts. The results of that study were provided to the RWQCB in the report entitled Downgradient Groundwater Characterization and Monitoring Well Installation, dated April 6, 2004. Field screening was based on odor, which is the basis for the 100 ug/L beneficial use level for diesel in groundwater. At the time the borings were advanced and the wells were installed, diesel odor was not discernable in any soil or groundwater samples from the three locations. The September 2004 sample from well MW-19, which was installed in the middle of the three downgradient borings, showed a diesel detection of 1.1 mg/L, in excess of the diesel beneficial use level. 2.2 Existing Remediation Systems To contain the product and potential dissolved phase impacts, LFC contracted GeoTrans to install a groundwater remediation system. Construction of the new product recovery system at the site was completed on May 17, 1996 and the system was brought on-line on May 22, 1996. The system consists of five recovery wells (RW-1, RW-2, RW-3, RW-4A and RW-5A). Wells RW-4 and RW-5 were abandoned and relocated as RW-4A and RW-5A during the second quarter of 1999 to accommodate plant expansion. The replacement wells are similar in construction to the abandoned wells and are located near the original well locations. Operation of recovery wells RW-1, RW-2 and RW-3 has not been required and could induce movement of impacts closer to the northern site boundary. To supplement recovery and improve capture of impacted groundwater, pumping was initiated at well EW-2 (which had previously been used as a monitoring point) in late October 2002. Free and dissolved phase hydrocarbons in excess of regulatory standards had not been observed in monitoring wells near and downgradient of recovery well RW-4A since before March 2000. GeoTrang 3