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IIi <br /> !i <br /> KEI-P86-084A-1 <br /> April 15 , 1987 <br /> Page 4 <br /> 2 . The low level of contamination detected in soil <br /> samples from wells MW-6 and MW-8 during drilling <br /> indicates potential off-site sources of <br /> hydrocarbons . <br /> 3 . It is our understanding that another service <br /> station located within few hundred feet of the <br /> Mobil property had a leak recently , resulting in <br /> groundwater pollution . This leak may also have <br /> contributed to presence of dissolved hydrocarbons <br /> in the area under investigation . <br /> 4 . As there are 3 service stations proximal to one <br /> another , any one of which may have contributed to <br /> the impact of the shallow groundwater , the lateral <br /> extent of hydrocarbon contamination may be <br /> substantially greater than our studies indicate . <br /> 5 . The shallow groundwater is non-usable and the <br /> usable groundwater is well protected by thick <br /> impervious clay deposit . <br /> 6 . Natural migration of the dissolved plume is <br /> anticipated to be very slow due to the clayey <br /> nature of subsurface formation and fairly flat <br /> gradient of the water table . Dilution , adsorption <br /> and natural bio--degradation would reduce the <br /> contamination over -time thus , reducing the impact . <br /> RECOMMENDATION <br /> The next stage of the investigation should focus primarily on <br /> I <br /> obtaining a better definition of the extent of dissolved i <br /> product plume and to develop an effective cleanup if <br /> necessary . We recommend the following : <br /> a . A pump test should be conducted in one of <br /> the existing wells to assess the effect <br /> of water table draw down on the dissolved <br /> plume and to provide additional data on <br /> the physical characteristics of the <br /> shallow aquifer . <br /> I <br /> i <br /> 1 <br /> 1 <br />