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I ` <br /> AL HORIZON ENVIRONMENTAL INC. <br /> Specialists in Site Assessment,Remedial Testing,Design and Operation <br /> i <br /> September 28, 1998 <br /> Mr Joe A Aldridge <br /> Ultramar Inc <br /> 525 West Third Street <br /> Hanford, California 93230 <br /> Subject Results of Remedial Testing <br /> Beacon Station No 641 <br /> 1210 East Hammer Lane, Stockton, California <br /> Mr Aldridge <br /> At the request of Ultramar Inc (Ultramar), Horizon Environmental Inc (Horizon) has <br /> prepared this letter report which presents the results of vapor extraction, air sparging, and <br /> aquifer pumping tests at the above-referenced site (Figure 1) The purpose of these tests was <br /> to evaluate remedial alternatives and remediation design criteria for the site <br /> Beacon Station No 641 is an operating service station located on the southwest corner of the <br /> intersection of East Hammer Lane and Kathleen Drive in Stockton, California (Figure 1) <br /> The site is located within a primarily commercial area of Stockton Site facilities include a <br /> service station/ convenience store, two canopy-covered product dispenser islands situated in <br /> the central portion of the property, and three newly installed double-walled underground <br /> storage tanks (USTs) located in the western portion of the property There are currently four <br /> groundwater monitoring wells (MW-1, MW-3, MW-4, and MW-5), eight vapor extraction <br /> wells (VW-1 through VW-8) and one air sparge well (S W-1) located within the site <br /> boundaries, and one offsite groundwater monitoring well (MW-2) located to the west of the <br /> site The locations of these facilities and other pertinent site features are depicted on the Site <br /> Plan (Figure 2) <br /> Previous environmental work at the site was performed by Horizon Detectable <br /> concentrations of gasoline hydrocarbons were found to be present in the soil and <br /> groundwater during these previous site investigations In June 1996, Horizon personnel <br /> were onsite to perform soil sampling subsequent to removal and prior to replacement of the <br /> USTs at the site Four 10,000-gallon capacity single-walled, steel gasoline USTs and <br /> associated product lines were removed at that time Also in June 1996, three new (two <br /> 10,000-gallon and one 12,000-gallon capacity), double-walled, fiberglass-clad, steel USTs <br /> were installed in the overexcavated cavity as reported in the Tank Closure Letter_Report <br /> (Horizon, August 2, 1996) At the time of the station upgrade, conductor casings were <br /> installed at selected locations to allow for assessment and installation of wells around the <br /> USTs and dispensers <br /> t <br /> 5011 Golden Foothill Parkway,Suite 7 . EI Dorado HMIs,CA 95762 • (916)939-2170 • FAX(916)939-2172 <br /> PO Box 5283 • Bakersfield CA 93388 • (805)589-8389 FAX(805)589-1456 <br />