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Mr Ronald Rowe <br /> August 17, 1999 <br /> CAMBRIA j <br /> well screen, well MW-10 defines the down-gradient extent of hydrocarbons in groundwater The <br /> up-gradient extent is defined by wells MW-1 and MW-6 If hydrocarbon concentrations in wells <br /> MW-5, MW-8 and MW-9 arc representative of subsurface conditions, then these wells define the <br /> cross-gradient extent of hydrocarbons in groundwater <br /> Water samples from all wells were analyzed for methyl-tertiary-butyl-ether (MTBE) using EPA <br /> Method 8250 in November 1997 The highest concentration detected was 94 ppb in well MW-2, <br /> located in the former gasoline tank excavation However, no MTBE was detected in a duplicate <br /> sample collected from well MW-2 Therefore, the 94 ppb detection is suspect No MTBE was <br /> detected in wells MWA, MW-5, MW-b, MW-7 and MW-9 during the November 1997 sampling <br /> event Therefore, it appears that there is no significant MTBE mass in groundwater <br /> Estimated Hydrocarbon Source Area <br /> There appear to be two source areas at the site, the former gasoline tank area and the current <br /> gasoline tank area The area with the largest apparent hydrocarbon mass is the former tank area <br /> This area is within the former free product plume area and is evidently the source of the free <br /> product <br /> Proposed Scope of Work <br /> The primary objective of our investigation is to determine the vertical extent of hydrocarbons in <br /> soil and groundwater at the site If the extent of hydrocarbons is accurately represented by the <br /> concentrations detected in the wells despite the submerged well screens, then installing <br /> additional wells would be unnecessary Therefore, we recommend using a dual-tube direct push <br /> drilling rig to drill borings for vertical profiling of hydrocarbons in soil and groundwater instead <br /> of installing wells If the results of the investigation indicate that additional wells are needed, <br /> then we will have better information on how to properly screen the wells to monitor the plume <br /> core However, if the investigation indicates that there is no significant hydrocarbon mass <br /> remaining in soil and groundwater, then we will pursue site closure without installing any <br /> additional wells Specific steps that we will take for this investigation are described below <br /> Proposed Scope of Work <br /> I <br /> Permits <br /> Appropriate permits for drilling permits will be obtained from SJCPHS <br /> i <br /> 5 <br />