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1 <br /> 20 BACKGROUND <br /> In May 1991, three underground storage tanks (USTs) were removed from the common tank pit <br />' shown on the Detailed Site Plan, Figure 3 Strong petroleum hydrocarbon odors and discolored soil <br /> were noted in the tank pit Confirmation soil samples were collected and laboratory analysis <br /> confirmed the presence of total petroleum hydrocarbons as gasoline (TPHg) Several subsurface <br /> investigations partially defined the extent of impacts in soil and groundwater, resulting in the <br /> installation of nine groundwater monitoring wells (MW-1 through MW-9) The contaminants of <br /> concern include TPHg, benzene, toluene, ethylbenzene and xylenes (BTEX), methyl tert-butyl ether <br /> (MTBE), tert-butanol (TBA), di-isopropyl ether (DIPS), ethyl tert-butyl ether (ETBE) and tert-amyl <br /> methyl ether (TAME) otherwise known as fuel oxygenate compounds (FOCs), 1,2-d1chloroethane <br />' (1,2-DCA), and 1,2-dibromoethane (EDB) <br /> In September 2000, Secor International Incorporated (Secor) began remedial activities and oversaw <br /> the installation of six soil vapor extraction (SVE) wells (VI through V6) and one air sparge (AS) <br /> well (AS-1) in or adjacent to the former tank pit at the Site (Figure 3) Soil samples collected from <br /> rV-1, V-2, V-3, and AS-1 contained elevated concentrations of BTEX, TPHg, and MTBE <br /> 21 Soil Vapor Extraction & Air Sparge Feasibility Testing <br />' In October 2000, Secor conducted a two-day SVE and AS feasibility test using wells V 1 through V6 <br /> and AS-1 Based on the test results, the amounts of TPHg and benzene removed during the SVE/AS <br /> feasibility test were 102 pounds and 19 pounds, respectively Based on the induced vacuum <br /> response (0 2 inches of water at 40 feet) and the slight rise in groundwater levels in offsetting <br /> monitoring wells, the SVE radius of influence was estimated to be 40 feet While the air sparging did <br /> not result in an immediate increase in TPHg vapor concentrations, the increase in dissolved oxygen <br /> concentration and slight rise in the water table in offsetting wells indicated a radius of influence of <br /> approximately 30 feet Details related to the feasibility test are presented in Secor's Problem <br /> Assessment Report dated November 8, 2000 <br /> 22 Final Remediation Plan <br />' Secor submitted a Final Remediation Plan (FRP) on March 2, 2001, that was approved by the <br /> California Regional Water Quality Control Board, Central Valley Region, (RWQCB) in a letter <br /> dated March 26, 2001 <br /> Due to an expansion of the remedial objectives, Secor submitted a Work Plan for Remedial <br /> Approach and Well Installation dated May 2, 2002 The RWQCB approved the work plan in a letter <br /> dated May 13, 2002 The final remediation plan included 10 soil vapor extraction (SVE) wells (VI <br />' through V I O each approximately 30 feet deep) and 20 ozone-sparge wells (SI through 520, each <br /> approximately 45 feet deep) <br /> 1 <br /> Project No 58643-06-01 -2- February 14 2005 <br /> r <br />