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• 3.0 2006 HYDROLOGIC MONITORING PROGRAM <br />The BTU EC hydrologic monitoring program includes data collected specifically to meet requirements of the <br />DMG, as well as data collected to meet the requirements of the Colorado Wastewater Discharge Permit <br />System (CDPS). Note that "CDPS" parameters were formerly referred to as National Pollutant Discharge <br />Elimination System (NPDES) parameters in prior AHRs. Specific monitoring locations are illustrated on <br />Figure 2. <br />In June 2001, Technical Revision TROT-32 was approved, allowing suspension of many DMG hydrologic <br />monitoring requirements while the mine was in temporary cessation (TC). In 2005 BTU EC began to exam <br />options for future re-activation of the mine site. In view of this considerations, BTU EC revered back to the <br />active monitoring plan (pages 1-14 of Exhibit 29), during the second quarter of 2006. <br />Table 1 presents a summary of hydrologic monitoring requirements. Field parameters are outlined in Table 2. <br />Water quality monitoring includes field parameters (Table 2), surface water quality parameters (Table 3), and <br />CDPS parameters (Table 4). <br />3.1 Groundwater Monitoring <br />• <br />3.1.1 Bedrock Wells <br />Three sandstone aquifers are found beneath the subject site. In ascending order, they are: Trout Creek <br />Sandstone, Middle Sandstone, and Twentymile Sandstone. The Eagle No. 5 and Eagle No. 6 Mines are <br />located between the Trout Creek Sandstone and the Middle Sandstone. <br />Water Levels <br />The potentiometric surface represented by water level measurements in the Trout Creek Sandstone 5 Mine <br />well (Fig. 3), has dropped from levels measured prior to Temporary Cessation. This drop is apparently from a <br />consistent subsurface dewatering pumping. The well was historically is used for water supply as well as <br />monitoring. Historical annual water level fluctuations of 20 to 200 feet have been observed at this well but no <br />seasonal pattern is evident. The former Okie Plaza Trout Creek well was abandoned in June 1994 as mining <br />advanced through its location. <br />The water levels in the Middle Sandstone formation as measured in wells TR-4, TR-7a, 81-O1, 83-O1, 83-02, <br />and 83-03 show fluctuations which are apparently related to dewatering and subsidence associated with <br />Mines 5 and 6. Wells TR-4, TR-7A, and 81-O1 displayed unusually large fluctuations during 2006. BTU EC <br />will continue to monitor this trend toward large fluctuations in water level. The water levels in well 83-02 <br />Page 3 <br />. I:\Env\Empire\AHR\2006\Tesr\Empire2006AHR.doc <br />