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' AMILA; HORIZON ENVIRONMENTAL INC. Specialists in Site Assessment,Remedial Testing,Design and Operation r� August 26, 1997 IP211YX Mr. Kenneth Earnest SEP 0 5 1997 Ultramar Inc. 525 West Third Street ENVIRONMENTAL HEALTH Hanford, California 93230 PERMIT/SERVICES Subject: Results of Remedial Testing Beacon Station No. 474 3440 East Main Street, Stockton, California Mr. Earnest: At the request of Ultramar Inc. (Ultramar), Horizon Environmental Inc. (Horizon) has prepared this letter report which presents the results of aquifer pumping tests at the above- referenced site (Figure 1). The purpose of the aquifer pumping tests was to evaluate aquifer characteristics of the shallow water-bearing zone beneath the site, and to evaluate the potential of groundwater pumping as a remedial option for the recovery of petroleum hydrocarbon-impacted groundwater from beneath the site. The purpose of the vapor extraction test was to evaluate the potential of soil vapor extraction.as a remedial option for the petroleum hydrocarbon-impacted soils beneath the site. The work was performed as outlined in the January 23, 1995, Work Plan fior Hdro eolo is Testing and Additional Subsurface Assessment at Beacon Station No. 474 prepared by Acton, Mickelson, van Dam, Inc. (AMV). The site is an operating gasoline service station located on the southwestern corner of the intersection of East Main Street and Broadway Avenue in Stockton, California. Site facilities include a station building, two gasoline product dispenser islands located toward the northern property boundary, and three underground gasoline storage tanks (USTs) located toward the northeastern property boundary. There are currently five groundwater monitoring wells, MW-1 through MW-5, at the site. Locations of these and other pertinent site features are shown on the Site Plan (Figure 2). Previous environmental work at the site was performed by Horizon and others. This previous work included drilling three onsite soil borings (SB-1 through SB-3) prior to removing the UST's, the removal and replacement of the UST's in September 1993, drilling three soil borings and the installation of three onsite 4-inch inside diameter (ID) groundwater monitoring wells (MW-1 through MW-3) in December.1993, and drilling six additional soil borings and the installation of two offsite 2-inch ID groundwater monitoring wells (MW-4 and MW-5) in May 1996. Detectable concentrations of gasoline hydrocarbons were found to be present in the soil and groundwater during theses previous site investigations. During drilling, groundwater was found to be present at a depth of approximately 80 feet below ground surface (bgs). The subsurface water-bearing zone previously encountered beneath 5011 Golden Foothill Parkway,Suite 7 - EI Dorado Hills,CA 95762 - (916)939-2170 - FAX(916)939-2172 P.O.Box 5283 - Bakersfield,CA 93388 9 (805) 589-8389 - FAX(805)589-1456