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-13- <br />fill. We anticipate The only significant source of moisture will be <br />precipitation on the fill surface. The average precipitation in this part of <br />Colorado is approximately 10 inches (Linsley, Kohler, Pablhos; McGraw <br />Hill). Most of The precipitation occurs in the form of snow in the winter <br />months or rain during summer thunderstorms. This moisture is normally lost <br />through evaporation and evapotranspiration. The ThornThwaite Moisture <br />Index is negative for This area (PTI, 1980) indicating a moisture deficit <br />exists. Infiltration may occur into the fill during spring runoff. We believe <br />The permeability of the fill will be very high. The amount of moisture <br />required to saturate the fill would be considerable, considering the probable <br />volume of voids within The fill. `Ne do not believe a water surface will <br />develop in the fill. If it does develop, we believe iT is likely to be near the <br />interface between the fill with the underlying natural soil and rock. <br />Recommended drains at the base of the valley should control This wafer and <br />limit further rise of free water levels into the spoil. However, our stability <br />analyses considered rise of water into The spoil. <br />An existing landslide was observed on the slope west of the spoil <br />disposal site, adjacent to Taylor Creek. We believe precautions should be <br />taken during backfill of the pit upslope of Taylor Creek to limit risk of water <br />from the pit "charging" the existing slope. 'Ne recommend placing a layer of <br />claystone/shale fill on each bench where coal is exposed to "seal" the coal <br />layer and direct free water to the south. Alternatively, the benches can be <br />sloped by cutting to provide flow away from the "sealed" coal lenses. <br /> <br />