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manner. Hydrologic methods available to achieve contaminant <br /> containment include pumped wells to develop local cones of <br /> depression near contaminant hot spots and picket fence deployment <br /> of pumped wells to achieve coalesced cones of depression <br /> resulting in a barrier to subsurface flow. Modifications to soil <br /> structure, including grout slurry walls can also be employed to <br /> achieve containment , though such methods may not prove cost <br /> effective at this site. <br /> Once the contaminant plumes are contained ultimate mitigation <br /> will entail pumped withdrawal of ground water from the <br /> 1 contaminated aquifer, followed by treatment of the contaminated <br /> water for contaminant removal prior to ultimate disposal . One <br /> I disposal alternative to evaluate will be the treatment of these <br /> f waters with the contaminated surface water discussed previously <br /> and combined discharge to surface waters under NPDES permit. <br /> A potential extension of the ground water withdrawal treatment <br /> system would consist of the withdrawal of contaminated ground <br /> water through a series of wells located downgradient of the <br /> contaminant plume, treatment of the contaminated water through a <br /> surface treatment facility as described above, and the subsequent <br /> reinjection of the treated ground water back into the same <br /> I aquifer at a point upgradient of the contamination source. In <br /> f this way , the ground water gradient is modified such as to allow <br /> "sweeping" of the contaminated fluid from the existing plume area <br /> Linto the collection wells in a more rapid manner. Such a <br /> 23 <br />