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7-Eleven/Stockton 9 <br /> February 1990 <br /> Since June, 1988, RW-1 has failed to capture dissolved hydro- <br /> carbons that exist in MW-1. This can be explained by the <br /> discontinuity and limited aerial extent of permeable sand lenses <br /> within the lower sequence. The geologic cross-section (Figure 3) <br /> shows that RW-1 penetrates permeable sands within the lower <br /> sequence, whereas MW-1 does not. Therefore, since June, 1988, <br /> groundwater pumped from RW-1 has been derived from discontinuous <br /> permeable sands in the lower sequence that have not been impacted <br /> by dissolved hydrocarbons. <br /> This subsurface geologic model also suggests that the <br /> highest concentrations of hydrocarbons in the adsorbed phase may <br /> be primarily restricted to the unsaturated upper stratigraphic <br /> sequence, particularly the basal gravelly coarse sand unit. This <br /> is supported by the sharp permeability contrast which exists at <br /> the base of the gravelly coarse sand and the marked attenuation <br /> of the lateral extent of the dissolved-hydrocarbon plume <br /> coincident with the decline of the groundwater elevation below <br /> the base of the gravelly coarse sand. <br /> SCOPE OF WORK <br /> Services performed by Groundwater Technology during this <br /> reporting period consisted primarily of regularly scheduled <br /> operation and maintenance of the groundwater treatment system, <br /> and monitoring and sampling of the groundwater monitoring wells. <br /> specifically, the following services have been conducted since <br /> - the previous update report was submitted in November, 1989: <br /> . o Monitored on-site and off-site wells for depth-to- <br /> water and depth-to-product on six separate occasions. <br /> ~ o Sampled groundwater from twelve monitoring wells and <br /> ` from ten nearby domestic wells for laboratory analyses. <br /> GRaUxoiiiiii eR <br /> TECH VIOGY.INC. <br />