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3.0 DISCUSSION OF DISPUTED ISSUES Item 2.Vertical Extent of Impacted Groundwater EHD noted in its November 17, 2002 letter that it did not find information regarding the vertical extent of the groundwater impact. EHD had raised this same issue in September 1998 and directed Gillies Trucking to install two additional monitor wells to complete the vertical delineation of the contamination. As noted in our chronological summary of the site investigation, which was presented to EHD at the November 13 meeting in the EHD offices, Upgradient Environmental contacted the State UST Cleanup Fund in November 1998 on the behalf of Gillies Trucking to discuss this request for additional wells, and was informed by the technical staff at the UST Fund in January 1999 that the State Fund concurred with the written conclusion issued by EHD in January 1997 that the extent of contamination had been adequately assessed both laterally and vertically. The UST Fund therefore refused to pre-approve any additional deep monitor wells to further investigate groundwater contamination, but agreed to pay for an additional shallow well within the contaminated channel deposit and an additional deep boring through the UST excavation to assess the vertical extent of soil contamination. EHD accepted this determination and the shallow well and deep boring were drilled in March 1999. At the time, Gillies Trucking and Upgradient Environmental were under the impression that the issue (vertical extent of contamination) had been settled. In light of EHD's continuing concern regarding this issue, it appears that further clarification is required. As described in previous reports, two geologic formations have been penetrated by drilling at this site. An ancient soil horizon at a depth of 60-70 feet separates these formations. Both units contain sand beds that are potential aquifers, but in some years groundwater is not present in the upper formation, which is mapped as the Modesto Formation by the U.S. Geological Survey. Groundwater has been present in the lower unit (Riverbank Formation) throughout the eight years of this investigation. Diesel was detected in water samples from the Riverbank Formation on two or three occasions between late 1990 and late 1997, when the static water level was near the top of the screened interval of monitor wells GT-1, GT-2, and GT-3 (75-100 feet below grade). Maximum concentrations of approximately 1,000 ppb were detected in GT-2 in September 1994 and in GT-1 in January 1995. Concentrations of 100 ppb or less were detected in all three wells on other occasions. After the water level rose above the screened interval in those wells in 1995, concentrations remained stable at about 100 ppb. At that time,the water level was near the contact between the Modesto and Riverbank formations, below the contaminated soil that is present within the Modesto Formation channel deposit. The water level was not at this depth again until the middle of 2002, and samples collected from GT-1, 2, and 3 in May 2002 and early January 2003 were either below the diesel detection limit of 50 ppb or slightly above it (57- 89 ppb).