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TABLE 17-29 Summary of Probable Hydrologic Consequences of the Life-of-Mine Mining Plans for the Seneca II-W Mine Probable Hydrologic Consequences Analysis Results Significance Ground Water 1, Removal of wells and ponds by mining. One well and two ponds will be removed by mining. Impacts have been mitigated per legal agreements (Tab 16, Appendix 16-1). Replacement sources will consist of water of at least similar or better quality and quantity. 2. Pit pumpage drawdown effects on adjacent water users. 3. Production well impacts on adjacent water users. Computer simulation of maximum pit pumpage drawdown in the Overburden and the Wadge Coal for the duration of the open mine pit (13 years) was performed. Radial distances at 1,554 feet and 204 feet were computed for the one-foot and five-foot drawdown levels, respectively, in the Overburden. Radial distances of 249 feet and 31 feet were computed for the one-foot and five-foot drawdown levels, respectively, in the Wadge Coal. Pit pumpage drawdown effects are directed to the west and south- west areas of the Seneca II-W leasehold. Computer simulation of production well pumping over a 15 year period followed by a 25 year recovery period yielded maximum drawdowns of 172 ft. and 12.5 ft., respectively (see Attachment 16-B). A maximum drawdown of 1.0 ft is estimated to occur in the Trout Creek Sandstone aquifer at a radial distance of 2.5 miles. Drawdown is directed toward west and southwest area of aquifer unit along Hubberson Culch. Estimated total stream depletions for the region from the production r+ell operation is less than 1.5 percent. The No impact to adjacent r+a ter users because the drawdown is limited to areas within the Seneca II-W leasehold. Potentially affected water sources, Frank Temple Stock Pond, Temple Pond No. 2, and Temple Well No. 1 ti will be removed by mining and replaced by Peabody per legal agreements (Tab 16, Appendix 16-1). Temple Pond No. 1 will not be impacted by mining or by drawdorm in the Overburden since it is a surface water catchment. Peabody has negotiated to replace Temple Pond No. 1 if necessary. Peabody Well No. 1 will not be impacted by pit pumpage draw- down because it produces from a hydraulically separate aquifer below base elevation of the pit. The losses in flow from Dry Creek and Sage Creek from induced infiltration via draw- downs in the Trout Creek Sandstone where it crops in both stream beds will be minimal. Because both drainages are over appropriated, a water augmentation program, including alternative water sources, has been developed by Peabody and approved by the Colorado State Engineer's Office. Any minor impacts from Peabody pumpage of the Trout Creek Sandstone to Dry and Sage Creek streamf lows has been mitigated by the augmentation plan (Tab 16,