1999-03-15_PERMIT FILE - C1981010 (3)

Home Browse Search

�u 999iii»�u_ S/ Doc D3te:1211112001 SECTION 2.0 Annual Hydrology Report for Trapper Mine (1998) 2.1 Climatological Data The 1998 National Weather Service Cooperative monthly summaries and the historical precipitation sum- mary (1978-1998) are included in Section 2.5. 1998 precipitation totaling 15.71", provided 116 percent of the established historical pre-mining (44-YR) annual precipitation mean (Figure 2-1). The highest monthly precipitation amount was recorded in June (2.81 ) with the second highest total occurring in October (2.49'). An abrupt warming occurred in late March triggering a rapid melting of the residual snowpack. As a result, extensive flooding occurred at Trapper and in the surrounding area as well. News reports following the event indicated the 500-year flood plain in nearby Craig, CO, was inundated by snowmelt runoff stemming from this event causing flooding in the Fortification Creek drainage. This proved to be the most significant climatological event occurring at Trapper in 1998. 2.2 Pit Dewatering and Consumptive Water Use for 1998 During 1998, Trapper dewatered approximately 78 acre-feet of water from three active pits and an addf tional 34 acre-feet from dewatering wells in Derringer and Flintlock pits (Table 1-1 of Section 2.5 shows the pumping volumes for each pit. The Derringer pit dewatering well produced 26 acre-feet of water during the first fire months of the year. The well was deactivated during the shutdown period for the Molly Brown dragline (May 98). Two dewatering wells in Flintlock pit produced 8 acre-feet of water during the first four months of the year. No further well dewatering occurred during 19W. All pit water and well water was routed into the NPDES drainage system with resulting discharges monitored accordingly. Pit • dewatering volumes were slightly higher in 1998 than the 1997 totals and would have been significantly lower but for the March snowmell/runoff event discussed previously. Well dewatering overall in 1998 was lower than in 1997 due in general to the shorter duration of pumping from both the Flintlock and Derringer pit wells. Both the Derringer and Flintlock pit well dewatering operations were discontinued due to pit advancement. Approximately 76 acre-feet of water were used for dust suppression on haul roads and topsoil handling operations in 1998. This higher use of water for dust suppression is generally attributed to the extension of haulroads into the Flintlock pit area and further movement of the mine to the east in Ashmore pit. In addition,the months of April, May,August and September 1998 were notable drier than in 1997 and likely contributed to higher water usage during these months. Total water volume used by Trapper Mine in 1998 was approximately 188 acre-feet,slightly higher than the 1997 total. 2.3 Mining Advancement and Ash Disposal Sites The 1998 Annual Hydrology Report maps depict the following mining activities through year end: a) Project to date utility waste disposal sites. b) Project to date pit advancement (Toe of pit). c) Project to date monitoring and dewatering wells; and natural and spoil springs and seeps. In the 1998 report, all spring and seep sites within the permit area are depicted to provide location information for future reference. Sites that exhibited flows exceeding 5 gpm during the reporting year are distinguished from sites exhibiting flows less than 5 gpm. . Three maps (Annual Hydrologic Report Map 2, Sheets 1, 2, & 3) are provided to present this information. These maps include the locations of monitoring wells that are proximal to active mining and that could be affected in this permit tens.