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t� <br /> 6.2 Discussion <br /> Soil chemical analytical data collected to date suggest that the lateral extent of residual <br /> hydrocarbons in the unsaturated zone remains uncharacterized to the east The measured impacts <br /> to soil are sporadic and low and, coupled with the historically high groundwater elevations <br /> beneath the site (6 to 10 feet bgs), this suggests that the bulk of the subsurface impact beneath the <br /> site is primarily in the dissolved phase Vertically, soil impact does not appear to be adequately -� <br /> characterized Additional characterization of impacted soil is not warranted <br /> The lateral and vertical extents of dissolved hydrocarbons beneath the site have not been <br /> adequately characterized The dissolved hydrocarbon plume remains uncharactenzed to the east <br /> and west The vertical extent of the dissolved hydrocarbons has not been completely assessed <br /> The lateral and vertical extent of the dissolved hydrocarbon impact requires additional <br /> characterization <br /> The apparent hydrologic connection between the sandy units above and below the hard clay <br /> layer, as shown by close groundwater elevation and dissolved MTBE values measured in wells <br /> MW-2 and MWO-1X, needs further assessment Based on the geological data collected to date, <br /> it is not possible to determine if the hard clay layer is discontinuous in the vicinity of the former <br /> northern USTs or if the sand hack installed around well_M_W_O-1X_is_connecting_the_two_sand <br /> units hydrologically The lateral and vertical extent of the lower sand unit and the clay stratum <br /> that underlies it also require additional characterization <br /> 63 Recommendations <br /> Additional soil bonngs should be advanced in the vicinity of the former northern USTs in order <br /> to assess the lateral extent of the hard clay layer <br /> Additional soil borings should be advanced across the site to evaluate the vertical and lateral <br /> extent of the hard clay layer and the sand and clay strata that underlie the hard clay layer <br /> Petroleum hydrocarbon impact to soil and groundwater should be assessed within the underlying <br /> sandy unit <br /> Further evaluation of the dissolved hydrocarbon plume east of monitoring well MW-3 should be <br /> performed to constrain the lateral hydrocarbon impact to groundwater downgradient of the site <br /> Aquifer pump and dual phase extraction tests should be performed to establish aquifer <br /> characteristics beneath the site <br /> P voe's Truck Plaza\Reports\SCM_09-20031Joes truck plaza SCM doe Page 15 STRATUS <br />