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ENSR AECOM <br /> appropriate location to delineate the downgradient extent of the commingled plume is the intersection of <br /> Lindsay Avenue and Grant Street. <br /> Although concentrations are declining in Zone C relative to the shallower subsurface, concentrations at several <br /> locations are well above MCLs and there is a downward component to the hydraulic gradient at the site. <br /> Therefore, the depth of impacts should be further assessed by installing a deeper monitoring well adjacent to <br /> existing monitoring well couplet U-20/U-21, where Zone C groundwater concentrations are the greatest. <br /> Permeability would be assessed by a series of slug tests at wells across the site. ENSR recommends that <br /> slug testing be performed at monitoring wells U-1, U-8, U-12, U-13, U-15 and U-21 to evaluate the permeability <br /> of the more permeable strata at the site over a representative area, range of depths and geological conditions. <br /> These data would be used in assessment of plume fate and transport and natural attenuation and for <br /> ' optimizing remedial system design. <br /> 1 <br /> JARem_EngTroject Files1P60(6000 <br /> 6999)16940-UNOCAL Portfolio Closure16940 3-5 January2006 <br /> UNOCAL Portfolio Closure\Site 0187-Stockton { <br /> East Mlnor\CSM ReportlCSM Report_Final.doc <br />