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OF particular importance, piezometers installed at [he Big Bottom area of <br />the Yampa River indicate that [he alluvium is hydraulically isolated from <br />• the Williams Fork Formation aquifer. This proves that even if [here is <br />cross bed flow in [he Williams Fork Formation, [he impact on the alluvium <br />would be negligible. <br />4.5 Stream Aquifer Relationships <br />Besides the piezometer studies referred to above, Machin (1979) undertook <br />a study to determine contributions to the base flow of the Yampa River <br />iaunediately downdip from [he Trapper Mine. To accomplish this, flow <br />measurements were taken above and below the mine site. A copy of the <br />~_ report is attached as Appendix C. The study found [hat the existence of <br />• ~ groundwater discharge could no[ be conclusively established because the <br />potential ground water discharge vas at or less than the accuracy of the <br />field technique. <br />As a result of these studies, we think that there are no significant <br />hydraulic connections between [he Trapper Mine area and [he Yampa River <br />system. <br />4.6 Cround-Water Quality and Use <br />The U.S. Geological Survey describes ground water from [he Mesa Verde <br />Group as predominantly calcium and sodium bicarbonate types. Coal- <br />.~ <br />-37- <br />