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<br /> wells TB-7 and TB-8 were advanced to 75 feet bgs Boring TB-5,which was hand-augered, met
<br /> refusal at 10 feet bgs was backfilled with bentonite Groundwater monitoring wells TB-1 and
<br /> TB-10 were installed along the western perimeter of the site to further define the upgradient
<br /> quality of groundwater Wells TB-7 and TB-8 were located within the dissolved groundwater
<br /> plume Nested vapor extraction wells TB-9, TB-11, and TB-12 were installed within the UST
<br /> area Soil sample analyses indicated TPH concentrations ranging from less than the MDL to
<br /> 4,100 mg/Kg(TB-12 at 40'), and benzene concentrations ranged from less than the MDL to 2 1
<br /> ' mglKg(TB-12 at 50') Groundwater sample analyses indicated TPH concentrations ranging
<br /> from 2,200 pg/L (TB-10) to 110,000 gg/L (TB-7) Benzene concentrations ranged from 19 pg/L
<br /> (TB-10) to 11,000 gg/L (TB-7)
<br />' In June 1995, following the completion of well installation activities Thnfty conducted a vapor
<br /> extraction test using wells TB-6, TB-9S, and TB-9D as extraction wells, and wells MW-2, TB4,
<br /> TB-6, TB-7, TB-10, TB-11, and TB-12 as observation wells The report concluded that based on
<br /> the observed flow rates, effective radius of influence values, and calculated mass recovery rates,
<br />' vapor extraction may be a feasible remediation option for hydrocarbon-affected soil in the
<br /> vadose zone The complete results of the vapor extraction test were presented in Vapor
<br /> Extraction Test Report dated August 14, 1995
<br />' In September 1995, Thrifty prepared and submitted a Corrective Action Plan (CAP) dated
<br /> September 26, 1995, to the EHD Based on available data, vapor extraction combined with
<br /> groundwater pump and treat was selected as the most viable remedial alternative for the site
<br /> In September 1997, Pacific Environmental Group, Inc (Pacific) conducted site investigation
<br /> activities in the areas of the USTs and the dispenser islands, which included drilling fifteen soil
<br />' borings (TDD-1 through TDD-15) to depths ranging from approximately 11 to 57 feet bgs
<br /> Results of soil sample analyses indicated up to 46,000 mg/Kg TPHg, 220 mg/Kg benzene, and
<br /> 71 mg/Kg methyl tert butyl ether (MTBE), as found in a soil sample collected from boring TDD-
<br /> 14 at 15 feet bgs MTBE was analyzed for by EPA Method 8020 and was not confirmed using
<br /> EPA Method 8260B
<br /> On July 1, 1999, Thrifty initiated the continuous operation of a vapor extraction treatment system
<br /> at the site The soil vapor extraction system (SVE) consisted of a Baker Furnace Thermal
<br /> Oxidizer Unit connected to wells MW-4, MW-5, TB-3, TB-4, TB-6, TB-7, TB-9, TB-11, and
<br />' TB-12 Vapor samples were collected bi-weekly on the first month of operating and monthly
<br /> thereafter As of August 16, 2004, the system operated a total of 29,975 hours and removed
<br /> 140,299 pounds of hydrocarbon
<br /> In March 2002, Hydrogeo Consultants conducted a 24-hour constant rate aquifer test on well
<br /> MW-5 HGC recommended SVE in conjunction with pump and treat to remediate the site Air
<br />' sparging was not considered technically feasible due to the relatively confined nature of the
<br /> saturated zone (more permeable soil layers at depths ranging from 65 to 70 feet bgs confined by
<br /> fine grained soil above and below) The results of the test were presented in Aquifer Testing
<br /> Report and Remedial Action Plan Report dated July 11, 2002
<br /> In a letter dated August 13, 2002, the SJCDEH requested Thrifty to submit a workplan for
<br /> additional site assessment activities to delineate the vertical and the horizontal extent of the
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