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distribution that has a uniformity coefficient of 2.5 or less shall be the Contractor's <br /> responsibility subject to the supervising geologist's approval. <br /> 2.3.9 Filter Pack Placement <br /> When the assembled casing and screen are centered in the borehole, <br /> tubing or drill pipe with one close-fitting swab located near the bottom of the <br /> screen will be inserted. Clear water shall be circulated while installing the sand <br /> pack. The fluid properties of the well bore fluids will be approved by the <br /> supervising geologist before the introduction of filter pack. The filter pack will be <br /> placed by pumping through a tremmie pipe extending to the bottom of the casing- <br /> hole annulus. The tremmie pipe will gradually be withdrawn as the filter pack is <br /> placed. <br /> After the filter pack has been placed, circulating and swabbing will continue <br /> in stages across the entire screen section until the filter pack is consolidated and <br /> cleaned. As the filter pack settles, more shall be added. <br /> A careful record will be kept of the amount of filter pack added during <br /> placement and consolidation. <br /> A transition zone consisting of four feet of clean fine grained sand shall be <br /> placed above the filter pack or as directed by the supervising geologist. A <br /> bentonite seal shall be placed immediately above the transition zone material. <br /> 2.3.10 Bentonite Seal <br /> A bentonite seal consisting of three-eighths (3/8) inch diameter bentonite <br /> pellets such as Volclay (or equivalent) will be emplaced on top of the filter pack <br /> material within the well annulus. This seal will be at least five (5) feet thick and will <br /> 12 <br />