ARCHIVED REPORTS_XR0008332 - Laserfiche WebLink

Home Browse Search

' 20 BACKGROUND • In May 1991, three underground storage tanks (USTs) were removed from the common tank pit shown ' on 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 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-1 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-dichloroethane (1,2-DCA), and 1,2-dibromoethane (EDB) In September 2000, Secor International Incorporated (Secor) began remedial activities and oversaw the installation of six soil vapor extraction (SVE) wells (V1 through V6) and one air sparge (AS) well (ASI) in or adjacent to the former tank pit at the Site (Figure 3) Soil samples collected from V 1, V2, V3, and ASI contained elevated concentrations of TPHg, BTEX, and MTBE 21 Soil Vapor Extraction & Air Sparge Feasibility Testing In October 2000, Secor conducted a two-day SVE and AS feasibility test using wells VI through V6 10 and ASI Based on the test results, the amounts of TPHg and benzene removed during the SVE/AS feasibility test were 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 While 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 indicated a radius of influence of approximately 30 feet Details related to the feasibility test are presented in Secor's Problem Assessment Report dated November 8, 2000 22 Final Remediation Plan ' Secor submitted a Final Remedialion 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 Secor estimated the contaminant mass in soil to be approximately 25,000 pounds of gasoline, as detailed in the FRP Due to an expansion of the remedial objectives, Secor submitted a Work Plan far Remedial Approach and Well Installation dated May 2, 2002 The final remediation plan included 10 soil vapor extraction (SVE) wells (VI through V 10 each approximately 30 feet deep) and 20 ozone-sparge wells (Sl through S20, each approximately 45 feet deep) The RWQCB approved the work plan in a letter dated May 13, 2002 The RWQCB indicated that Secor had not established Site cleanup levels in the FRP Project No S8643-06-01 -2- September 28 2005