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Mam7tAine - 2005 Annual Hydrology Report February 2006 <br />3.0 MINE AREA GROUNDWATER (WATER TABLE) <br />Deep groundwater occurs under water-table conditions in two primary water-bearing zones in the <br />mine area; the Sudduth Coal Seam, and the undifferentiated overlying overburden materials. The <br />Sudduth Coal Seam is monitored at well 79-61. This well is located just north of the historic Pit 1, <br />along Bush Draw in the undisturbed coal seam. The mine area overburden wells are designated <br />79-1, 79-2, and 79-3. These wells are located at the south, middle and north sections of the <br />historic 720 Pit, respectively, adjacent to what was formerly the east crest of the pit. Spoil <br />monitoring well SP-01 was installed in the north end of the 720 Pit area in 2001 and monitoring <br />was initiated in 2002. The general locations of the monitoring points are presented on Map 1, <br />Mine Area Monitoring Stafions. <br />Historical groundwater monitoring data for the coal seam and overburden wells have shown that <br />the characteristics of the water-table groundwater system, in terms of quality and quantity, have <br />been consistent and stable, such that monitoring at these locations was deferred until the last two <br />years preceding final bond release (2005 water year). The water levels measured in 2005 were <br />consistent with the previous water levels (1995-2001). The spoil well SP-01 was monitored on a <br />quarterly basis in October 2003 and for three quarters in 2004 and 2005. Note that the water <br />level in the spoil fluctuates almost 50 feet during this monitoring period. It is usually highest <br />during the spring and lowest during the late fall. <br />Table 1, 2005 Groundwater Quality Statistics, includes a summary of the water quality data for all <br />wells monitored in the 2005 water year. The individual analyses of samples collected are <br />presented in Appendix B, 2005 Mine Spoil and Bedrock Water Quality Analyses. Figures 1 and <br />1A, Mine Area Water Levels, show the relative groundwater levels for the coal, overburden and <br />spoil since 1996. Note that spoil monitoring was initiated during the 2002 water year and that the <br />overburden wells at the mine (79-1, 79-2, 79-3) and the coal water quality well (79-61) were again <br />monitored in 2005 ending the deferment period. Well 79-3 has only been monitored for water <br />levels historically. The other wells were last monitored for water quality in October 1998. The <br />annual mean field measurements and laboratory results for spoil monitoring to date are presented <br />in Table 2, Site SP-01 Historic Mine An'a Spoil Water Quality Data. The data indicates that <br />sulfates, electrical conductance and nitrates (as nitrogen) are generally decreasing in <br />concentration while iron is increasing. Tables 3, 4, 5 and 6 presents historic mean concentrations <br />for the overburden and coal water quality wells for the 1997, 1998, 1999 and 2005 water years. <br />The most significant changes in water quality are noted below. <br />• Well 79-1 -Decreasing electrical conductivity (EC), calcium and sulfate; Increasing <br />chloride <br />• Well 79-2 -Decreasing EC and sulfate; Increasing carbonate <br />• Well 79-3 -There is no historical analytical data for this well other than baseline. <br />• Well 79-61 -Decreasing EC; Increasing sulfate <br />• Wetl SP-01 -Decreasing EC and sulfate <br />Note that the decreasing conductivity observed in the data may be due to malfunction of field <br />equipment. It will be replaced prior to the next monitoring season. The field recorded <br />measurements are contained on the field data logs in Appendix A. Tables presenting all historic <br />monitoring data for the spoil and overburden wells are provided in Appendix B. <br />File: 6371/2005/2005 hydrology cpt Page 3 <br />