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island. The tanks and dispensers were removed in March 1998, and the facility ceased selling gasoline. The former Chevron station is located to the west of the site, on the northwest corner of the intersQction of Country Club Boulevard and Franklin Avenue. Both sites are roughly the same size, although the Chevron site was demolished prior to 1994, when investigation of the Kwikee site began. The Chevron site is now vacant, except for the soil and groundwater remediation system that was constructed in 2000. The fuel tanks at the Chevron site were located in the eastern portion of that site, and were removed in 1987. 2.0 SITE CONCEPTUAL MODEL This section compiles a variety of geological and chemical data that have been collected at the Kwikee and Chevron sites to develop a conceptual model of the origin and subsequent evolution of the plume of gasoline-contaminated groundwater that underlies the sites. Lithologic data collected from borings indicates that three principal stratigraphic units have been drilled, and that the middle unit is the principal water-bearing deposit beneath both sites. Groundwater-elevation data indicate that the depth to groundwater has changed rather gradually over time, declining during the late 1980's through the early 1990's and then rising again through the end of the decade. Regionally, groundwater flow has been in a general east to northeast direction during this time, but flow has been more variable on a local scale. Laboratory analyses of many soil samples that have been collected demonstrate that soil beneath the Chevron site has been widely impacted by a gasoline release, whereas soil beneath the Kwikee site has not. Gasoline has been detected in groundwater samples from both sites, but concentrations in several wells at the Chevron site have consistently been several times greater than any of the wells at the Kwikee site, and whereas all of the wells at the Chevron site have been impacted in the past few years, no contaminants have been detected in some of the wells at the Kwikee site. As will be shown in the following sections, the data lead to the conclusion that fuel releases at the Chevron site have migrated eastward in groundwater and subsequently impacted the Kwikee site. 2.1 Hydrogeologic Units 2.1.1 Lithology Three distinct stratigraphic units are present within the upper 40 feet of the Kwikee Foods site. Cross sections oriented east-west and north-south illustrate the lithology and geometry of these units (Figure 3). A clay layer is present at the surface. This layer extends to a depth of at least 5 feet in all borings, and to more than 10 feet in some borings (e.g. KF-5, cross section C-C'). Below 10 feet, this unit becomes slightly coarser grained, with up to 50% silt. Near the surface, the color is black, blue, or brownish gray, but in the lower part it is generally brown or grayish to reddish brown. This upper unit is between 17 and 21 feet thick. A relatively thin bed of sandy silt has been reported locally • 5