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Work Plan for UGT Investigations -6- 7 November 1991 <br />DDRW, Sharpe Site <br />provided the justification for analyzing soil samples for lead in the <br />area of Building S-119. <br />Page 4-3. Figure 4-1 is a construction diagram of the proposed monitor wells. <br />These diagrams depict that a minimum of five feet of bentonite is to be <br />used in the annulus between the cement and the filter pack and is to be <br />placed a minimum of five feet above the screened interval. In general, <br />only two to three feet of filter pack are needed above the screened <br />interval. Additional filter pack increases the effective screen length <br />of the well. In addition, only two to three feet of bentonite are needed <br />in the annulus to prevent the cement slurry from penetrating the filter <br />pack. When the screen interval is across the water table, such that the <br />bentonite seal is above the water table, Sharpe should consider the use <br />of a finer mesh sand between the filter pack and the cement in order to <br />avoid potential shrink -swell that may occur when bentonite is placed <br />above the water table. <br />Page 4-4. The Plan states that a the new monitor wells will be developed by pumping <br />a minimum of five well volumes. More than five well volumes may be <br />needed to evacuate the borehole of excessive fines. In addition, it is <br />unclear why a development method, such as a surge block, is not used for <br />well development. With the surge block method, the evacuated water is <br />kept to a minimum thereby reducing a potential disposal problem. It is <br />unclear why pumping is favored over other development methods. In <br />addition, the Plan does not specify where the development (and purge) <br />water is disposed. <br />CKW:cw <br />