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_ AdiscussionoftheprobablehydrologicconsecjuencesandreGamationplanarecontainedinSection 1J 2.05.6(3) and Section 2.05.6(3)(b)(v) of the pemtit application document. The follov~ing discussion • is intended to supplement the description of potential impacts of mining and mitigation of these potential effects. The determination of significance has been made considering the impact on the quality of the human environment, existing water uses, and the intended post mining land use of the area. Irderruption of grourxMater flaw and drawdov~n. In order to develop the impact assessment for groundwater quantity, two different analyses techniques were utilized. First, pit inflowvolumes were determined on an annual basis using an analytical approach developed by McWhorter, 1982. The second analysis involved the determination of annual pit inflow rates and annual dravvdowns in the adjacent overburden and coal aquifers as a result of the pit inflows. This analysis utilized the USGS 3-dimensional finite~fifference groundwater flow model MODFLOW. Transient simulations were perfom~ed for afive-year period, using the maximum drawdown estimates for the overburden and coal. These drawdown results are expressed as a maximum at the pit and are expressed as a conical depression which results in decreased drawdown at further distance from "~ the mine. For the overburden, the pit drawdown was 5 feet for years 1 and 2, 8 feet during year 3, • 15 feet during year 4, and 30 feet during year 5. The drawdown for the coal simulation was 8 feet during year 1, 5.8 feet during year 2, 6 feet during year 3, 7.3 feet during year 4, and 8 feet during year 5. The zero impact contour for the overburden and coal after five years of mining is approximately 4,000 feet. The overburden and coal drawdown contours do not intersect any of the boundaries, therefore, no impact of the San Miguel River from drawdown in the deeper part of the overburden or coal is predicted. Shallow aquifer Flow into Tuttle and Calamity Draws in the vicinity of the pit vall be decreased, but vnll be offset by pumpage from the pit. Simulated average daily pit inflow for the coal and overburden aquifers vaned from 1,255 cubic feet per day in year 1 to 5,604 cubic feet per day in year 5. WFC's approach to these potential impacts is to monitor the aquifers and discharge from the pit to determine the extent of drawdown. The hydrological monitoring program should provide reasonably accurate measurements of effects of mining. Should the monitoring show that impacts to the groundwater aquifers are precluding its use, WFC vlrill provide alternate water sources of comparable quantity and quality. As described in the water augmentation plan, WFC has a 114 acre foot consumptive use right on the Highline Canal which would be used to mitigate the potential 26 acre foot impact on surface water right users from pit inflow drawrlown. 4r (Revised4S96) 2,p4.7.g3 lJ ~:.