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MINING PLAN <br />of the material. Based on the cross-sectioning done in the planning of this gravel <br />operation, it is suspected that considerable variation may be found in the extent and <br />quality of the gravel over such a large site. <br />Underneath the gravel deposit is shale, probably of the Pierre Formation. This <br />formation commonly occurs in this area, but another formation found under these gravel <br />deposits is the Carlisle Shale. These two formations are very similar and for the purposes <br />of this planning need not be distinguished. The groundwater in the alluvium above the <br />shale is confined with a very strong horizontal flow component and very little flow <br />downward into the shale. This shale does not present any difficulties with respect to its <br />chemistry or physical properties. It does tend to fragment into thin, flat pieces when <br />exposed to the air for some time, but this does not appreciably alter its properties. <br />General Groundwater Considerations <br />The groundwater conditions at this site, based on work done within the existing <br />permit, presents some challenges. First, the amount of fine material mixed with the <br />gravel in the initial excavations seems to retain an unusually large amount of water <br />making the dewatering process appear to be rather slow. Furthermore, it is possible that <br />the groundwater flow through the gravels may be at a fairly high rate. <br />Because mining gravel in alluvial deposits can impact the groundwater, it is <br />important to have a reasonably good understanding of the groundwater system. For this <br />reason, as described in Exhibit G -Water Information, a study is being conducted of the <br />groundwater system. This will involve pump tests to determine the rate of flow as well as <br />monitoring wells to more fully describe the dynamics of the system. <br />Because a slurry wall is expected to ultimately surround much of the operation so <br />a reservoir basin can be created, the effects of the slurry wall on groundwater levels <br />needs to be considered. To some extent this has been predicted as the basic parameters of <br />the groundwater system are known. The monitoring program will further refine the <br />dynamics of the groundwater system and the effects of mining and dewatering. <br />Permit Area and Affected Land Area <br />Permit Area: The permit area, shown on Exhibit C-1, encompasses a much larger area <br />than the area where the operation is designed to occur. In fact, most of the mining and <br />Puehlo East Pit Amendment Exhibit D Page 3 <br />