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Man- Mine - 2006 Annual Hydrology Repoli March 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 Stations. <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 and 2006 water years). The water levels measured in <br />2006 were consistent with the previous water levels (1995.2001, 2005). In this water year, the <br />spoil well SP-01 was monitored on a "quarterly" basis beginning in October 2005 and then for <br />three quarters in 2006. Note that the water levels in the spoil fluctuate almost 50 feet throughout <br />each year monitored. It is usually at its highest level during the spring and lowest during the late <br />fall. <br />Table 1, 2006 Groundwater Quality Statistics, includes a summary of the water quality data for all <br />wells monitored in the 2006 water year. The individual analyses of samples collected are <br />presented in Appendix B, 2006 Mine Spoil and Bedrock Water Quality Analyses. Figures 1 and <br />1A, Mine Area Water Levels, shows 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 and 79-3) and the coal water quality well (79-61) were <br />monitored in 2005 - 2006 ending the deferment period. Well 79-3 has only been monitored for <br />water levels historically. The other wells were last monitored in October 1998. The annual mean <br />field measurements and laboratory results for spoil monitoring to date are presented in Table 2, <br />Site SP-01 Historic Mine Area Spoil Water Quality Data. The data indicates that sulfates and <br />nitrates (as nitrogen) are generally decreasing in concentration while iron is increasing. Tables 3, <br />4, 5 and 6 presents historic mean concentrations for the overburden wells for the 1997, 1998, <br />1999, 2005 and 2006 water years. The most significant changes in water quality are listed below. <br />• Well 79-1 -Decreasing sulfate and increasing chloride <br />• Well 79-2 -Decreasing sulfate and increasing carbonate <br />• Well 79-3 -There is no historical data for this well <br />• Well 79-61 - No obvious consistent changes in quality <br />• Well SP-01 -Decreasing sulfate <br />Note that the decreasing conductivity observed in the data was due to malfunction of field <br />equipment. It was replaced this year and the data is more consistent with previous readings. The <br />field recorded measurements are contained on the field data logs in Appendix A. Tables <br />presenting all historic monitoring data for the spoil and overburden wells are provided in Appendix <br />B. <br />File: 6371/2(g6/1D06 hydcolo~ cpt Page 3 <br />