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rR A ERI 205513 05822 Tosco Facility 5886,_Stockton,Cahfon= October 29,2002 • Gettler-Ryan, Inc (GRI) of Dublin, California, under direct contract to Tosco, performed quarterly groundwater monitoring and sampling at the site on August 1 and 2, 2002 The GRI Third Quarter Event of August I and 2, 2002, Groundwater Monitoring and Sampling Report (GRI, September 13, 2002) is provided as Attachment A The results of the third quarter monitoring and sampling event indicate the following • Groundwater was measured at approximately 6 3 to 9 4 feet below ground surface (bgs) in the groundwater monitoring wells During August 2002, groundwater flow direction remained towards the southwest with a calculated hydraulic gradient ranging from approximately 0 003 to 0 004 Historical groundwater flow directions are shown on the Groundwater Flow Direction Rose Diagram(Plate 4) • Total petroleum hydrocarbons as gasoline (TPHg), and benzene were not detected at concentrations at or above laboratory method reporting limits in groundwater samples collected from the groundwater monitoring wells, however, laboratory reporting limits were elevated for samples collected from wells MW1, MW2, and MW3_ • MTBE was not detected at concentrations at or above laboratory method reporting limits in groundwater samples collected from wells MW5D/MW5S through MW7D/MW7S and MW8S/I through MW l OS/MW IOI1MW IOD using Environmental Protection Agency (EPA) Method 8260B MTBE was detected in wells MW1 through MW4S/D and MW8D at concentrations ranging from 3 5 parts per billion(ppb) to 3,400 ppb using EPA Method 8260B Oxygenated compounds including ethanol, tertiary butyl alcohol (TBA), di-isopropyl ether • (DIPE), ethyl tertiary butyl ether (ETRE), and tertiary amyl methyl ether (TAME), and lead scavengers including 1,2-dichloroethane (1,2-DCA) and ethylene dibromide (EDB) were not detected at concentrations at or above laboratory method reporting limits in the groundwater samples collected from the wells, however, laboratory reporting limits were elevated for samples collected from wells MW1, MW2, and MW3 FOURTH QUARTER 2002 ACTIVITIES The following activities are proposed to be completed during fourth quarter 2002 • ERT will continue to perform monthly O&M at the site and collect monthly groundwater samples from wells MW1 through MW3 to evaluate the effectiveness of the microsparge remediation system and the extent of dissolved TPHg, benzene, toluene, ethyl benzene, total xylenes (BTEX), and MTBE concentrations in groundwater beneath the site • Tosco will continue to perform quarterly groundwater monitoring and sampling at the subject site The water samples will be submitted to a California state-certified Iaboratory for analysis • 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 4