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on data from USGS Gauging Station 09247600, Yampa River below Craig, CO) results in an estimated <br />TDS baseline concentration of 280.2 mg/I in the Yampa River below Johnson Gulch. <br />TDS Yampa River = 1000 mg/1(20gpm) + 200 cfs (448.8 qpm/cfs)(280 mg/l) = 280.2 mg/I <br />Below Johnson Gulch (20 gpm + (200 cfs) (448.8 gpm/cfs)) <br />This represents a baseline addition of 0.2 mg/I TDS in the Yampa. This potential variation will be <br />undetectable in the Yampa River due to the much larger natural variations in TDS concentrations that <br />occur. Trapper might develop additional drainages that will contain increased TDS concentrations in spoil <br />spring-derived base flows. However, some of the backfill aquifers at Trapper contain water that is <br />essentially the same quality as the baseline surface water quality (see backfill well GF-5 as compared to <br />the No Name drainage surface water data). Trapper projects that under a worst case scenario where <br />multiple drainages contribute TDS-affected base flows to the Yampa River, TDS concentrations in the <br />Yampa might be increased by approximately one tenth of one percent. The actual increase will probably <br />be significantly less than this due to the likelihood that such small flows from the mine will never reach the <br />Yampa River. <br />The Annual Hydrologic Reports (Appendix W) present summaries and discussions of surface water <br />quality for selected water quality constituents at monitoring locations throughout the project site. <br />4.8.3.2 Groundwater Impacts <br />The following sections present discussions of the probable hydrologic consequences due to mining on <br />groundwater quantity and groundwater quality. These sections are followed by a discussion of the <br />expected impacts to adjudicated wells in the vicinity of the project area. <br />Post-mine Groundwater Quantity <br />The following discussions address the post-mine recharge characteristics of affected aquifers, aquifer <br />restoration, and impacts to flows from springs. <br />Post-mine Recharge: <br />Radian (1981) conducted an infiltration investigation of the spoils at Trapper and predicted that on <br />balance no percolation or resaturation of the spoil aquifers would occur under normal precipitation <br />4-236 <br />PRc <br />I(ze (?i