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20 BACKGROUND <br /> May 1991, three underground storage tanks (USTs) were removed from a common tank pit as shown <br /> in the Detailed Site Plan, Figure 3 Strong petroleum hydrocarbon odors and discolored soil were <br />' noted in the tank pit Confirmation soil samples were collected and laboratory analysis of those <br /> samples confirmed the presence of total petroleum hydrocarbons as gasoline (TPHg) Several <br /> subsurface investigations partially defined the extent of impacts in soil and groundwater resulting in <br /> the 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 (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 /> i <br /> In September 2000, Secor International Incorporated (Secor) began the remedial investigation and <br />' oversaw the installation of six soil vapor extraction (SVE) wells (V l through V6) and one air sparge <br /> (AS) well (AS-1) in or adjacent to the former tank pit at the Site (Figure 3) Soil samples collected <br /> from V-1, V-2, V-3, and AS-1 contained elevated concentrations of BTEX, TPHg, and MTBE <br /> Soil Vapor Extraction & Air Sparse Feasibility Testing <br /> tIn October 2000, Secor conducted a two-day SVE and AS feasibility test using wells VI through V6 <br /> and AS-1 Based on the test results, the total mass of TPHg and benzene removed during the <br /> SVE/AS feasibility test was 102 pounds and 1 9 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 Although the air spaigmg <br /> did not result in an immediate increase in TPHg vapor concentrations, the increase in dissolved <br /> oxygen concentration and slight rise in the water table in offsetting wells indicate a radius of <br />' influence of approximately 30 feet Details related to the feasibility test are presented in Secor's <br /> Problem Assessment Report dated November 8, 2000 <br /> 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 or Remedial <br /> p J � f <br />' Appi oach and Well Installation dated May 2, 2002 The RWQCB approved the work plan m a letter <br /> dated May 13, 2002 The final remediation plan includes 10 soil vapor extraction (SVE) wells (VI <br /> thi ough V I 0 each approximately 30 feet deep) and 20 ozone-sparge wells (SI through S20, each 43 <br /> Ito 45 feet deep) <br /> • <br /> i'miec,t No 58643-06-01 -2- November 3,2003 <br />