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ERI 205513 QSR15 Tosco Service Stapon 5885 StocMn,Cahfomia Janum 25 2001 sample after the silica clean-up was performed Groundwater samples collected from the groundwater monitoring wells were analyzed for diesel past the Environmental Protection Agency (EPA) recommended holding time • MTBE was not detected at or above laboratory method detection limits in groundwater samples collected from wells MWSD, MWSS, MW7D/MW7S, MWBS, MWBD, MW9S/MW9I/MW9D, MW 10S, and MW IOD MTBE was detected in the remaining wells ranging from 2 1 ppb to 19,000 ppb using EPA Method 8260, (ranging from 5 1 ppb to 15,000 ppb using EPA Method 8020) MTBE was not detected in wells MW81 and MW 10I using EPA Method 8020 The groundwater sample collected from well MWBS was analyzed past the EPA recommended holding time for 8260 analysts • Oxygenated compounds ethanol, tertiary butyl alcohol (TBA), di-isopropyl ether (DIPE), ethyl tertiary butyl ether (ETBE), and tertiary amyl methyl ether (TAME) were not detected at or above laboratory method detection limits in the groundwater monitoring well samples with the exception of wells MW1 and MW2 TBA was detected at 1,200 ppb in the groundwater sample collected from well MW2 TAME was detected up to 54 ppb in groundwater samples collected from wells MW 1 and MW2 FIRST QUARTER 2001 ACTIVITIES The following activities are proposed to be completed during first quarter 2001 • During January 2001, Tosco will re-mitiate weekly purging activities at the site utilizing the UST cavity well and groundwater monitoring well MW3 as extraction wells The extracted groundwater will be transported to Tosco's refinery in Rodeo, California for disposal In response to a letter from the County dated December 4, 2000 (Attachment B), Tosco will collect pre-purging and post-purging water samples from the UST cavity well and groundwater monitoring well MW3 and a water sample from the vacuum (VAC) truck following purging The water samples will be submitted to a California-certified laboratory for analysis for total extractable petroleum hydrocarbons as diesel (TEPHd), TPPHg, benzene, toluene, ethylbenzene and total xylenes (BTEX), MTBE, ethanol, TBA, DIPE, ETBE, and TAME The laboratory analysis results from the water samples will be used to calculate the dissolved hydrocarbon mass removal from groundwater beneath the site and the effectiveness of interim remedial activities The calculated mass of dissolved hydrocarbons removed and the volume of groundwater purged from beneath the site will be reported in ERI's Quarterly Summary Report for Environmental Investigation (Report) submitted during the month following each reporting period • Tosco will continue to perform quarterly groundwater monitoring and sampling at the subject site • Tosco and ERI will continue to conduct a comprehensive review of the data acquired during previous work The results will be presented to the County in quarterly reports, which describe the status of the proposed work by the dates established by the County t 4