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L9 LEWSMIU-MERKEN"OFF. WC. . IHTROQUCTIOH 1 . 1 HISTORICAL REVIEW The following report describes LEEDSHILL-HERKENHOFF, INC'S (LH) Preliminary Site Assessment (PSA) of the former underground fuel tank site located at 141 North E1 Dorado Street, Stockton, California (see Figure 1) . �n 1955, the Shell Oil Company constructed a gasoline and service station at 141 North El Dorado Street in Stockton, California. This construction included the installation of four 4,000-gallon underground storage tanks (UST) used to store ---� leaded gasoline which was dispensed at two pump islands and one 500-gallon UST use orarily store waste oil prior to disposal . In 1963, one of the 4,000-gallon USTs was removed and two 7,500-gallon USTs were installed to store and dispense unleaded gasoline. The station discontinued selling gasoline in - 1981 and all five of t e gasoline USTs were removed. The UST excavation was ��- backfilled and paved to grade. The waste oil UST remained on the site and was still used to temporarily store waste oil until June of 1990. In September of 1989, ERM West of Sacramento, California conducted a Phase I Environmental Site Assessment of the property. This site assessment concluded that soil testing within the former gasoline UST excavation and a tank test of the existing waste oil UST be conducted. On May 30, 1990, Kleinfelder, Inc. conducted a soil vapor survey of that portion of the site which overlays land, and found detectable levels of gasoline constituents in and around the former UST excavation. This soil vapor data was used to tentatively identify potential areas of petroleum hydrocarbon soil contamination. Kleinfelder, Inc. also performed a precision tank test on the _ waste oil UST on June 1 , 1990. The tank failed the test and on June 5 1990, the contents of the waste oil tank were pumped out and properly disposed of off-site. The tank inlets were capped and the tank is no longer being used to store waste oil . Kleinfelder, Inc. ' s investigation implied that petroleum hydrocarbons from the former gasoline USTs may have impacted the soil in the vicinity of the former excavation and that further investigation of the soil was necessary to properly assess actual concentration levels . Kleinfelder also recommended that the soil be further investigated to determine the lateral and vertical extent of contamination to assess if the groundwater resources in the area of the site have been impacted. In July 1990, C.M. Weber Enterprises, Inc. contracted with LH to conduct a Phase IA Preliminary Site Assessment to analytically verify the presence or absence of suspected soil contamination of gasoline and waste oil , and to develop an approximation of the lateral and vertical extent, if any, of the soil contamination at this site. If significant levels of soil contamination were found at depths that could possibly impact the groundwater, a Phase IS PSA would be performed to analytically verify the presence or absence of petroleum ,J 1 1 E .A