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gg <br /> Eli <br /> aquifer or known high water level. Properly graded, clean filter sand will be used in the <br /> annulus of the well and prevent the migration of fine particles into the well.The filter sand <br /> will extend at three to five feet above the perforated interval in the well. A seal of at <br /> least three to five feet of bentonite shall be placed above the filter. Sack or neat cement <br /> will be used to seal the annulus from the bentonite pellets to the ground surface where a <br /> well box will be installed. All sand, bentonite, and cement will be placed with a tremie <br /> pipe. <br /> Double cased wells may be specified where the wells are screen below an upper aquifer. <br /> In this situation, a minimum 10 inch diameter bore hole is drilled to the base of the first I <br /> . . I <br /> aquifer and at least two feet into the aquitard. A conductor casing is then grouted in place j <br /> and allowed to set for at least 72 hours. Drilling shall then continue within the conductor <br /> casing, with a drill bit smaller than the inside diameter of the conductor casing to the <br /> desired completion depth. <br /> All wellheads shall be completed with a watertight structure and furnished with a watertight <br /> cap which shall be enclosed in a locked well covering device. <br />