2009-03-27_REPORT - C1981044 (5)

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• 3.0 2008 HYDROLOGIC MONITORING PROGRAM The BTU EC hydrologic monitoring program includes data collected specifically to meet requirements of the DMG, as well as data collected to meet the requirements of the Colorado Wastewater Discharge Permit System (CDPS). Note that "CDPS" parameters were formerly referred to as National Pollutant Discharge Elimination System (NPDES) parameters in prior AHRs. Specific monitoring locations are illustrated on Figure 2. In June 2001, Technical Revision TRO1-32 was approved, allowing suspension of many DMG hydrologic monitoring requirements while the mine was in temporary cessation (TC). In 2005 BTU EC began to examine options for future re-activation of the mine site. In view of this considerations, BTU EC reverted back to the active monitoring plan (pages 1- 14 of Exhibit 29), during the second quarter of 2006. Table 1 presents a summary of hydrologic monitoring requirements. Field parameters are outlined in Table 2. Water quality monitoring includes field parameters (Table 2), surface water quality parameters (Table 3), and CDPS parameters (Table 4). 3.1 Groundwater Monitoring 0 3.1.1 Bedrock Wells Three sandstone aquifers are found beneath the subject site. In ascending order, they are: Trout Creek Sandstone, Middle Sandstone, and Twentymile Sandstone. The Eagle No. 5 and Eagle No. 6 Mines are located between the Trout Creek Sandstone and the Middle Sandstone. Water Levels The potentiometric surface represented by water level measurements in the Trout Creek Sandstone 5 Mine well (Fig. 3), has remained very consistent with that of 2006 and 2007, although these levels are lower than levels measured prior to Temporary Cessation. This drop is apparently from consistent subsurface dewatering with the No. 5 mine pump. The well was historically used as a water supply, as well as for monitoring. Historical annual water level fluctuations of 20 to 200 feet have been observed at this well but no seasonal pattern is evident. The former Okie Plaza Trout Creek well was abandoned in June 1994 as mining advanced through its location. The water levels in the Middle Sandstone formation as measured in wells TR-4, TR-7a, 81-01, 83-01, 83-02, and 83-03 show fluctuations which are apparently related to dewatering and subsidence associated with Mines 5 and 6. Wells TR-4, TR-7A, and 81-01 levels in 2008 are very consistent with that seen in 2006 and 2007. The water levels in well 83-02 (Figure 8) also show some historic fluctuations. The water level decline of about 150 feet from 1987 to mid 1990 in well 83-02 was determined to be related to mine dewatering as 0 Page 3 G:\Environmental\EMPIRE\AHR\2008\Empire2008 AHR. doe