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i 20 BACKGROUND May 1991, three underground storage tanks(USTs) were removed from a common tank pit as shown in the Detailed Site Plan, Figure 3 Strong petroleum hydrocarbon odors and discolored soil were noted in the tank pit Confirmation soil samples were collected and laboratory analysis of those samples confirmed the presence of total petroleum hydrocarbons as gasoline (TPHg) Several ' subsurface investigations partially defined the extent of impacts in soil and groundwater resulting in the installation of nine groundwater monitoring wells (MW-I through MW-9) The contaminants of concern include TPHg, benzene, toluene, ethylbenzene and xylenes (BTEX), methyl tert-butyl ether ' (MTBE), tert-butanol (TBA), di-isopropyl ether(DIPE), ethyl tert-butyl ether (ETBE) and tert-amyl methyl ether (TAME) otherwise known as fuel oxygenate compounds (FOCs), 1,2-dichloroetlnane ' (1,2-DCA), and 1,2-dibromoetliane(EDB) In September 2000, Secor International Incorporated (Secor) began the remedial investigation and ' oversaw the installation of six soil vapor extraction (SVE) and one air sparge (AS) wells on or adjacent to the former tank pit at the Site (Figure 3) Soil samples collected from V-1, V-2, V-3, and AS-I contained elevated concentrations of BTEX, TPHg, and MTBE Soil Vapor Extraction &Air Sparge Feasibility Testing In October 2000, Secor conducted a two-day SVE and AS feasibility test using six SVE wells and one AS well Based on the test results, the total mass of TPHg and benzene removed during the SVE/AS feasibility test was 102 pounds and 1 9 pounds, respectively Based on the induced vacuum response (0 2 inches of water at 40 feet) and the slight rise in groundwater levels in offsetting monitoring wells, the SVE radius of influence was estimated to be 40 feet Although the air sparging did not result in an immediate increase in TPHg vapor concentrations, the increase in dissolved oxygen concentration and slight rise in the water table in offsetting wells indicate a radius of influence of approximately 30 feet Details related to the feasibility test are presented in Secor's Problem Assessment Report dated November S, 2000 Final Remediation Plan SECOR submitted a Final Remediation Plan (FRP) on March 2, 2001, that was approved by the California Regional Water Quality Control Board, Central Valley Region, (RWQCB) in a letter dated March 26, 2001 Due to an expansion of the remedial objectives, Secor submitted a Work Plan for Remedial Approach and Well Installation dated May 2, 2002 The RWQCB approved the work plan in a letter dated May 13, 2002 The final remediation plan includes 10 soil vapor extraction (SVE) wells (V I through V 10 each approximately 30 feet deep) and 20 ozone-sparge wells (SI through S20, each 43 . to 45 feet deep) S8643-06-01 -2- July 25 2003 1