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4.4 Conclusions <br /> Since May 1992, the groundwater surface has risen an average of approxunately 20 feet This <br /> extreme rise in the groundwater table has resulted in groundwater elevations above the screened <br /> ' interval of the groundwater monitoring wells This condition has probably resulted in <br /> inconsistent groundwater flow direction and gradient interpretations and unrepresentative <br /> groundwater sample collection and analytical results To obtain data that better represents <br /> ' groundwater conditions, groundwater samples were collected from two vapor extraction wells, <br /> which are screened across the current groundwater table <br /> Groundwater samples collected this quarter from vapor extraction wells VW-1 and VW-2 <br /> indicate an increase in gasoline hydrocarbon concentration since the last sampling event on <br /> September 20, 1995 <br /> The historical and current groundwater analytical data indicate that the hydrocarbon plume <br /> ' persists and is not degrading Because high concentrations of chemicals of concern(CDCs) are <br /> encountered in site groundwater (12,000 yg/L TPH-gasoline and 1,000,ug/L benzene), to achieve <br /> site closure, IT recommends active remedial action at the site to reduce the CDCs to acceptable <br /> regulatory levels Alternatives including soil vapor extraction or groundwater pumping should <br /> be considered in conjunction with continued groundwater monitoring <br /> r <br /> 3 <br />