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' RGI # 04518198 <br />Holnam, Inc <br />' January 27,1999 <br />Page S <br />' downgradient from the CKD /sludge landfill areas (i.e., Cut 6 and Cut 8) and one (1) well upgradient from <br />the CKD/sludge landfill areas. <br />The fvst monitoring well, MW-5, was installed in a location suspected as being downgradient from the <br />1 CKD/sludge landfills. Upon completion of the well, the water levels in this well and the four (4) wells <br />installed in 1991 were used to conduct a preliminary evaluation of the ground water flow direction to aid <br />' in the placement of the two (2) subsequent ground water monitoring wells (i.e., MW-6 and MW-7). <br />Based on the final ground water elevation in well MW-5 and the elevation of the Codell Sandstone in the <br />vicinity of well MW-7, it appears that well MW-5 was completed in the Codell Sandstone. In addition, <br />samples of cuttings collected during drilling indicated that the interval screened in this well also included <br />a portion of the Blue Hill Shale which underlies the Codell Sandstone in the area. As indicated on the <br />Hydrogeologic Map, Figure 4, ground water in the mined area flows through the Codell Sandstone. In <br />addition, any leachate from the CKD landfills in Cuts 6 and 8 would also flow through the Codell <br />' Sandstone. <br />' Prior to drilling the monitoring wetls, the relative productivity (i. e., hydraulic conductivity) of the aquifer <br />at the site was unknown. During the drilling of MW-5, it became apparent that the aquifer had a very low <br />' hydraulic conductivity. Due to the drilling method employed (i.e., air-rotary) and the low hydraulic <br />conductivity of the aquifer, it was dieicult to identify the depth at which Bound water was encountered. <br />In low-yield aquifers, air-rotary drilling methods tend to force some of the Bound water back out into the <br />formation and dry out the remaining moisture in the borehole. On several occasions, drilling was halted <br />' for up to an hour to observe whether or not any Bound water Bowed into the borehole. No Bound water <br />was observed until the maximum depth of the boreholes in MW-5 and MW-6 was reached (i.e., 120 and <br />1 100 feet, respectively). As a result, significant overdrilling and lengthy screen intervals were necessary <br />to help assure the successful completion of the monitoring wells. In addition, due to the low hydraulic <br />' conductivity of the aquifer, development of the wells required more time than originally estimated. The <br />1 <br />1 <br />