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Colowyo Coa[ Company L.P. Neilson Pit • Neilson Pit, into the underlying bedrock. Any water that recharges the bedrock units tends to accumulate along unit contacts since these tend to be areas of least flow resistance. Any groundwater that has been discharged from the mine highwall has been found to evaporate from the pit floor or be consumed by pit highwall. Past hydrological studies also reveal the mined units tend to have low permeabilities (even the sandstones) and do not allow for large water movement, even if the groundwater is present. This is also the case where the groundwater is under confined or unconfined conditions (i.e. below the elevation of the valley bottoms). If any groundwater does percolate vertically through the discordant geologic units, it encounters a tonstein bed near the base of the Williams Fork Formation. This bed is approximately 150 feet above the top of the Trout Creek Sandstone and is approximately 400 feet below the bottom of the active pit. The tonstein bed has an approximate thickness of 2.5 feet. Permeability tests of this material show it has penneabilities greater than 1x10'10 centimeters per second. Thus, this bed is an effective aquiclude and prevents downward movement of any groundwater to the underlying Trout Creek Sandstone. All surface water runoff is contained at the base of the Neilson Pit by a ditch and small containment area. The ditch runs north to south below the entire Neilson Pit and directs all surface runoff to a small containment area at the north end of the disturbance area. • This ditch will be maintained to catch all surface water runoff from exiting the disturbance area. Furthermore, any runoff that flows down the access road to the Neilson Pit is contained in a ditch on the north side of the road to contain and transfer runoff to Colowyo's existing ditches and containment sumps Water Quality The quality of the water in the azea of the Neilson Pit has been rated as poor by the USGS and designated for limited agricultural use. Since USGS testing in 1978, no water quality analysis performed at monitoring points at the adjacent Colowyo Coal Mine have shown any significant difference in water quality compared with what the initial USGS work. The water is slightly saline, alkaline and definitely classified as `hard' water. This can be seen in the water quality measurements for total dissolved solids (TDS) and electrical conductivity (eC). Both TDS and eC exceed the EPA secondary drinking water standards. Since the water is alkaline, the pH is above 7, but rarely exceeding 8.4. Concentrations of heavy metals rarely exceed health limits, as stated in the USGS report. This has also been confirmed by the shallow groundwater monitoring performed since the Neilson Pit began operation. Conclusions The Neilson Pit has no single or multiple continuous geologic units in the mine that contains groundwater under unconfined or confined conditions. The only groundwater encountered is the discontinuous perched pockets of groundwater. This lack of 5