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d <br /> } <br /> -� the proposed screened interval using a 15 1/2-inch diameter drag bit and <br /> conventional fluid rotary methods. A 10 3/4 diameter steel casing will <br /> then be set from the surface to the bottom of the borehole and pressure- <br /> ;I <br /> cemented in place. After allowing the cement to cure, the borehole will be <br /> drilled to its total depth and 4-inch flush-threaded PVC casing will be <br /> installed from the surface to the bottom of the borehole, with slotted <br /> casing over the appropriate interval. Since volatile organics are not the <br /> contaminants of concern and groundwater samples will only be analyzed for <br /> total chromium and hexavalent chromium, PVC casings will be suitable for <br /> the proposed wells . and will not interfere with the analyses of the <br /> groundwater samples.,.-' 7be casing will be sand-packed from the total depth <br /> . to approxi.matelxx"2 #eet above the top of the slotted casing. A bentonite <br /> seal will be pla6ed�on toy Qf the sand pack and the remaining annular space <br /> will be filled with pea eyel to within 20 feet of the land surface. The <br /> annulus will be sealed with cement over the remaining distance to the Lx4 <br /> eurface. A subgrade utility vault will be set around the conductor c;asitig <br /> and cemented in place. A locking steel well housing will also be installed <br /> within the utility vault. Each well will be equipped with a dedicated <br /> submersible pump to facilitate sampling. <br /> Following well development and water level drawdown and recovery <br /> m ur+wienta, sash of thc, new wells will bed sampled. Existing monitor" <br /> wells will also be sampled, if the location and the depth of the screened <br /> interval in specific existing wells are such that sampling these wells will <br /> help to define the contaminant Plume. In addition, tl-ie one operational <br /> private groundwater well downgradient of the MCTC facility identified in <br /> the Off-site Residential Well Summary will be sampled. <br /> r Wells will be purged until temperature, conductivity, anti ph hx4e <br /> stabilized, as indicated by variation of less than 10 percent for 3 <br /> successive measurements of 2 of the 3 parameters, before samples are <br /> collected. Samples will be collected at the wellhead and placed in 1/2 <br /> _ liter wide-mouth plastic bottles. Tree samples will be filtered and <br /> preserved with acid for total chromium at the laboratory within 24 hours. <br /> Duplicate samples will be collected for a minimum of 10 percent cf ttie <br /> 4-9 <br /> A <br />