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conditions. This analysis indicated that recharge to the spoil aquifers will occur only with above normal <br />precipitation conditions. This conclusion was based upon an idealized representation of average monthly <br />precipitation amounts as compared to average potential monthly evapotranspiration. Experience at <br />Trapper has shown that some surface water infiltration and resaturation of the spoil aquifers does in fact <br />occur as evidenced by the documented increasing water levels in the backfill monitoring wells established <br />at Trapper. A discussion of Radian's (1981) water balance calculations is presented in Section 2.7.6. <br />The entire Radian Report (1981), evaluating hydrologic impacts associated with the management of coal <br />combustion byproducts from Craig Station, is available at the Trapper Mine offices. Relevant findings <br />from the report are further discussed in Section 4.3.4.6. <br />Pre-mine recharge of the groundwater aquifers at Trapper occurs mainly in the outcrop areas of the <br />aquifer units, while recharge to the spoil aquifers is believed to occur over most of the backfilled areas of <br />the various pits. Radian (1981) expected permeabilities in the range of 1 x 10-3 to 1 x 10' cm/sec for the <br />overburden spoils at Trapper. The permeabilities of the backfill aquifers from the four spoil wells <br />established at Trapper to date (wells GD-3, GF-5, GF-7, and GF-11) vary from 1.7 x 103 to 1.6 x 10' <br />cm/sec. Table 2.7-21 b presents the calculated backfill permeabilities. These permeability values are <br />similar to values derived from the Upper Williams Fork aquifers in this area. Based upon these findings, <br />the capacity of the spoil aquifers to recharge from infiltration at the surface should at least equal the <br />combined recharge capacities of the aquifers disturbed by mining. <br />The geologic structures of Johnson, No-Name, and Flume drainages are similar to the Pyeatt structures <br />with beds dipping generally to the north at approximately 9 degrees (see Map M34). Groundwater flow in <br />the Upper Williams Fork aquifers has been shown in Section 2.7 to be controlled by geologic structure. <br />The aquifer units contributing water to the shallow alluvial fill systems north of the Trapper project area do <br />not extend very far south of the shallow alluvial fills before they crop out. Recharge to the Upper Williams <br />fork aquifers is mainly in their outcrop areas. The outcrop areas occur throughout the Trapper permit <br />area with shallower units tending to outcrop along the northern portions of the permit area and deeper <br />units surfacing as one moves to the south. The northern edge of the mined area in eachdrainage is <br />typically several thousand feet south of the shallow alluvial aquifer systems identified to the north of the <br />mine permit area. Geologic structure generally controls the groundwater movement in the other <br />drainages as it does in Pyeatt Gulch (see Map M32). Upper Williams Fork units that discharge to the <br />shallow aquifer systems typically do not extend south into the mine areas with the exception of the Third <br />White Sandstone in three areas. <br />The Third White Sandstone extends into the northern pit limits of Trapper's B pit on the west side of the <br />4-237 <br />`? lu (off