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Work Plan for UGT Investigations -6- 7 Nove ber 1991 <br /> DDRW, Sharpe Site <br /> provided the justification for analyzing soil samples for le d 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 scr�en 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 `riner 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 ( nd purge) <br /> water is disposed. <br /> CKW:cw <br />