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1' ERI 205513 OSR24 76.Facility 5886,Stockton, California April 29,2003 • (GRI, March 26, 2003) is provided as Attachment A The results of the first quarter monitoring and sampling event indicate the following • Groundwater was measured at approximately 6 02 to 9 12 feet below ground surface(bgs) in the groundwater monitoring wells During February 2003, groundwater flow direction remained towards the southwest with a calculated hydraulic gradient ranging from approximately 0 004 to 0 008 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 MW I,MW2,MW4S/D through MW7S/D and MW8S/I/D through MW I0S/1/D, however, laboratory reporting limits were elevated for samples collected from well NMI TPHg was detected in groundwater samples collected from well MW3 at 140 parts per billion(ppb) • MTBE was not detected at concentrations at or above laboratory method reporting limits in groundwater samples collected from wells MW4S/D through MW7S/D and MW8S/1/D through MW10S/1/D MTBE was detected in wells MWI through MW3 at concentrations ranging from 2 8 parts per billion(ppb)to 5,500 ppb using EPA Method 8260B • Oxygenated compounds including ethanol, tertiary butyl alcohol (TBA), di-isopropyl ether (DYPE), ethyl tertiary butyl ether(ETBE), 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 NIW 1, MW2, MW4S/D through MW7S/D and MW8S/I/D through MW10S/1/D, however, laboratory reporting limits were elevated for samples collected from well MW I TBA was detected in samples collected from well MW3 at 180 ppb SECOND QUARTER 2003 ACTMTWS The following activities are proposed to be completed during second quarter 2003 • ERY will continue to perform monthly O&M at the site and collect monthly groundwater samples from wells MW 1 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 • ConocoPhillips will continue to perform quarterly groundwater monitoring and sampling at the subject site The water samples will be submitted to a California state-certified laboratory for analysis • ConocoPhillips 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 i4