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SEC ® R <br /> . Mr Mice Infurna <br /> March 8, 2005 <br /> Page 4 <br /> Attachment A) were installed to further define the lateral extent of dissolved petroleum hydrocarbon <br /> plume within the deeper water bearing zone <br /> MONITORING AND SAMPLING <br /> TRC's Quarterly Monitonng Report, October Through December 2004 dated November 18, 2004 is <br /> included as Attachment B The report includes groundwater elevation and analytical data for the <br /> fourth quarter 2004 (Table 1), cumulative historical data through fourth quarter 2004 (Tables 2 and <br /> 3), TRC's field and laboratory procedures, field data sheets, and groundwater analytical reports The <br /> site has been monitored and sampled since the first quarter 2000 Currently, a total of 14 wells are <br /> monitored and sampled quarterly Samples are analyzed for total petroleum hydrocarbons as <br /> gasoline (TPHg), benzene, toluene, ethylbenzene, total xylenes (BTEX), and fuel oxygenates by <br /> EPA Method 8260B Well construction details summarized by SECOR are included as Table 1 of <br /> the current report <br /> Each of the 14 groundwater monitoring wells at the site was gauged and sampled on October 26, <br /> 2004 Water levels within groundwater monitoring wells that are part of the monitoring and sampling <br /> program at the ARCO Service Station (16 East Harding Way) were cooperatively measured by <br /> SECOR on October 26, 2004, and sampled on October 26 and 27, 2004 Regional groundwater <br /> flow direction within the shallow zone was to the northeast at 0 005ft/ft, with a local radially inward <br /> gradient toward well EW-7 (an active extraction well in the ARCO plume) Regional groundwater flow <br /> direction within the deep zone was to the northeast at a gradient of 0 004 ft/ft Shallow and deep <br /> groundwater contour maps are included as Figures 1 and 2 <br /> Based on the fourth quarter 2004 monitoring and sampling event (October 26, 2004, Attachment B) <br /> the maximum TPHg, methyl tertiary butyl ether (MtBE), and 1,2-dichloroethane (1,2-DCA) <br /> concentrations were 4,200 parts per billion (ppb) (MW-5), 2,700 ppb (MW-10), and 28 ppb (MW-11), <br /> respectively <br /> TPHg and MtBE concentrations in shallow groundwater have exhibited an increasing trend in wells <br /> MW-1 and MW-4, likely due to upgradient gasoline service stations such as the ARCO site <br /> TPHg, benzene, MtBE, and 1,2-DCA generally show a stable or decreasing trend in deep wells, with <br /> the exception of TPHg and MtBE in wells MW-5 and MW-10, and 1,2-DCA in well MW-8 <br /> Based upon data collected during ongoing quarterly groundwater monitoring and sampling, TPHg, <br /> benzene, and MtBE are effectively delineated laterally in the vicinity of the site 1,2-DCA is not <br /> currently delineated <br /> Review of shallow isoconcentration maps indicates that ConocoPhdlips has performed adequate <br /> delineation within the shallow zone, except for 1,2-DCA and MtBE to the southeast Deep <br /> isoconcentration maps indicate the following TPHg is delineated to 100 ppb or below, MtBE and <br /> benzene are delineated to below their respective maximum contaminant levels (MCL's), and 1,2- <br /> DCA is not currently delineated Shallow and deep isoconcentration maps are included as Figures 3 <br /> through 10 <br /> 11ConocoPhdlipslRetad Sdes144091Qssrs000414Q2004_QSR doc SECOR International Incorporated <br />