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JJJIVIJ,) 1:1 <br /> 7-Eleven/Stockton 7 <br /> May 1990 <br /> potential upgradient source possibly emanating from the former <br /> underground-storage tank pit at the Thornton Automotive Repair <br /> Shop, located approximately 300-feet north of the site. <br /> In November 1989, Vapor Extraction Technology (VET) was <br /> retained by Southland to expand the soil-vent system. Groundwater <br /> Technology continues to oversee operation of the groundwater <br /> treatment system. <br /> In February 1990, an on-site, monitoring-well cluster <br /> (MW-17) was installed in the vicinity of the inactive <br /> underground-storage tanks to further define the lateral and <br /> vertical extent of groundwater impacted by gasoline hydrocarbons. <br /> Soil samples were analyzed to monitor the progress of the <br /> expanded soil-vent system. During the same month, all wellheads <br /> were upgraded with water-tight expansion caps and new locks, and <br /> were professionally surveyed. <br /> SITE SUBSURFACE CONDITIONS <br /> The application of continuous coring during the drilling of <br /> - MW-15, MW-16, and MW-17, provided for a more-accurate character- <br /> ization of the subsurface soil profile at the site. These <br /> .�, additional details have enhanced the interpretation of the <br /> subsurface geology and hydrogeology and have allowed us to <br /> formulate a conceptual model for the geology underlying the site. <br /> Subsurface materials encountered during the recent drilling <br /> suggest that the subsurface stratigraphy is composed of two <br /> distinct sequences. The upper sequence is marked by a basal <br /> gravelly coarse sand, overlain by fine sands and silts, and <br /> capped by a silty clay. The lower sequence consists of laterally <br /> discontinuous lenticular sand bodies encased within silts and <br /> silty clays. A generalized geologic cross-section (Figure 3) <br /> illustrates the site subsurface geology. <br /> �• �� GR0UxnWATER <br /> TECHNOLOGY.INC. <br />