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t <br /> i <br /> BUILDING _ t_EGENo <br /> o IJcn�l.ru:g YhnEttti:n. <br /> 92.02 U•.unAiale�Eb•01 (11) <br /> AI'fnOlit.A1L - —— --� AI'(:lu.in..l.DMpe•IY p.vna.tY <br /> SCAIE'YI iLFT <br /> IAW4 Lot / 1 <br /> --_ O <br /> 92.72 <br /> 'a'' <br /> ;9z-85 <br /> s BUILDING <br /> 1 <br /> L <br /> on a•.n... <br /> ' Arca <br /> 9A <br /> 1 <br /> • RBY-I t 1 <br /> /92.02 91.07 <br /> -TAIL STf� 1 CENTS 13UII-DI qG <br /> FICURE 1. Groundwater Gradient Map. <br /> In the contaminant source area located directly beneath the dry cleaner's building, <br /> the COCs had affected subsurface soils in excess of site target concentrations below the <br /> building foundation to a depth of approximately 9 feet (fl) [2.4 meters (m)] bgs. This <br /> source area was excavated [excavation size approximately 10 ft(3.0 m) by 10 tt(3A in)by <br /> 10 0(3.0 m)deep] in 1998,and all soils exceeding site target concentrations were removed. <br /> Removal of this highly contaminated soil, which was located in close proximity to and in <br /> contact with the shallow aquitcr, was crucial to the overall success of this project, as a <br /> continuing source of contaminants to the shallow aquitcr was permanently removed by <br /> excavation. <br /> Site investigations revealed that the perched groundwater with COC concentrations <br /> above site target concentrations occupied an area of approximately 3,500 f12(330.5 nt2 ) <br /> directly beneath and downgradienl of the source area. GI'OUndwalet-modeling performed in <br /> 1998 indicated that unassisted natural attenuation would require approximately 20 to 25 <br /> years to reduce contaminant concentrations at the site to target concentrations. <br /> Geology and Hydrogeology. Topography in the site vicinity slopes very gently toward <br /> the north; however, the surface relief is probably not stiMeiently pronounced to <br /> definitively affect shallow groundwater gradient. The site is located on the outcrop of the <br /> F.agleford Group (Bureau of Economic Geology, 1972). This formation is generally <br />