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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), dl-Isopropyl ether (DIPE), ethyl tert-butyl ether (ETBE) and tert-amyl <br />' methyl ether (TAME) otherwise known as fuel oxygenate compounds (FOCs), 1,2-dichloroethane <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(V 1 through V6)and one air sparge (AS) well <br /> (AS-1) in or adjacent to the former tank pit at the Site (Figure 3) Soil samples collected from V-1, V- <br /> 2, V-3, and AS-1 contained elevated concentrations of TPHg, BTEX, 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 l 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 1 9 pounds, respectively Based on the Induced vacuum response <br />' (0 2 Inches of water at 40 feet) and the slight rise in groundwater Ievels in offsetting monitoring <br /> wells, the SVE radius of influence was estimated to be 40 feet While the air sparging did not result in <br />' an immediate increase in TPHg vapor concentrations, the increase in dissolved oxygen concentration <br /> and slight rise in the water table in offsetting wells indicated a radius of influence of approximately <br /> 30 feet Details related to the feasibility test are presented in Secor's Problem Assessment Report <br /> 1 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 dated <br /> March 26, 2001 Secor estimated the contaminant mass in soil to be approximately 25,000 pounds of <br />' gasoline, as detailed in the FRP <br /> 1 <br /> Project No S8643-06-01 -2- May 5 2005 <br />