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1 � 4 <br /> A S S Q C i A T E S I N C <br /> 1_2 Background <br /> On October 6, 1987, Al Williamson, General Contractor, removed two 1,000-gallon leaded <br /> gasoline tanks and one 550-gallon waste oil tank from the Iocations shown on Figure 2 Soil <br />' samples collected after the tank removals contained elevated concentrations of petroleum <br /> hydrocarbons and volatile organic compounds (VOCs) <br />' On January 21, 1988, Falcon Energy, attempted to remove all VOC contaminated soil by <br /> overexcavating the former tank locations The former tank locations were excavated to a depth <br /> of approximately 22 feet below ground surface (bgs) The excavation was limited to the north by <br /> 1 the on-site building The confirmation samples collected from the base of the overexcavat>on <br /> still contained elevated concentrations of volatile organics The overexcavated soil was disposed <br /> of at Forward Landfill <br /> 1 On June 30 and July 1, 1997, Smith Technology personnel supervised advancement of seven soil <br /> borings, SB 1 through SB7, at the site to depths ranging from approximately 40 to 45 feet bgs at <br />' the s>te o investigate t e horizontal and vertical extent of petroleum hydrocar on soil and <br /> groundwater contamination Three of the soil borings were completed as groundwater <br /> 3 monitoring wells and two of the soil borings were completed as vapor extraction wells The soil <br /> boring, groundwater monitoring well, and vapor extraction well locations are shown on Figure 2 <br /> Field activities and analytical results were detailed in Smith Technology's Summary Report <br />' dated September 17, 1997 The report contained recommendations for the installation of <br /> additional soil borings and groundwater monitoring wells to fully delineate the vertical and <br /> 1 horizontal soil and groundwater contamination PHS/EHD agreed with these recommendations <br /> with minor modifications in correspondence dated November 13, 1997 <br /> Smith Technology, whose assets were purchased by ATC Associates Inc on August 20, 1997, <br /> prepared a workplan for the additional soil and groundwater investigation and submitted the <br /> workplan and permits to PHS/EHD for review and approval on December 2, 1997 San Joaquin <br />' County Public Health Services Environmental Health Division (PHS/EHD) approved the ATC <br /> workplan, with minor modifications, in correspondence dated March 9, 1998 <br /> On March 24 and 25, 1998, ATC personnel supervised the advancement of seven soil borin s at <br /> the site Drilling was performed by V&W Drilling using hollow stem auger and direct push <br /> technology In accordance with the approved workplan, four of the soil borings were completed <br />' as groundwater m for wells-MW4,MW5 MW , an MW7 One soil boring was advanced <br /> to approximat ly 68 feet t d terms e e vertical xtent of contamination and one soil boring <br />' was advanced t_an anile .unnder the 65---site buildin ATC conducted a well survey of any <br /> groundwater wells located with t 2;000 eet of the site The results of the site investigation and <br /> well survey were detailed in ATC's Summary Report Subsurface Investigation, at 610 North <br />' Hunter Street, Stockton, California, dated August 14, 1998 <br /> W 162SWreportslptlotcap doc 2 <br />