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EFCI Southfield Mine -Year 2006 Annual Hydrology Report Apri125, 2007 <br />dewatering well in 1994. In 2003, it was converted to a monitoring well and will be referred to as <br />the well MW-NW. <br />In Technical Revision 35 (TR-35), the groundwater monitoring schedule was reduced from <br />quarterly to semi-annually and is conducted in June and December. Field measurements and <br />laboratory data for active monitoring wells are summarized in the following discussions. Raw field <br />and laboratory data for the 2006 water yeaz are provided in Appendices A and B respectively. <br />Measured water levels for all Mine Area monitoring wells aze summarized in Table 4, Monitor Well <br />Water Levels, for the yeazs 2000-2006. Table 4 Historical, in Appendix A, presents ground water <br />levels from 1980-1999. The historic water level data aze presented graphically for the five <br />monitoring wells (including historical information for Wells MW-8 and MW-10) on Figures 3, 4, 5, <br />6, and 7. <br />Water levels for well MW-16 have shown some cyclic/seasonal fluctuations. It was essentially dry <br />from December 2001 until June 2004, possibly associated with drought conditions. The well has <br />silted up to approximately 110 feet below ground surface, which leaves 4 feet of perforated casing <br />above the current depth. Water levels for 2004 and 2005 were between 97 and 106 feet but the well <br />was dry throughout 2006. Well MW-23 has demonstrated steadily declining water levels since July <br />of 1984. Water levels for Well MW-65 have generally remained stable with minor fluctuations of t <br />10 feet. MW-NW has been dry since monitoring was initiated in eazly 2003. <br />Water quality data for monitoring wells MW-10, MW-16, MW-23, MW-65 and MW-NW are <br />provided on Tables 5, 6, 7, 8, and 8A, respectively. Only wells MW-23 and MW-65 have new data <br />to report. These tables provide any analytical results for 2006 and the minimum, maximum and <br />average values calculated using all historical monitoring data. Consistent with the historic <br />monitoring schedule, water quality samples were not obtained for Well MW-8. Review of 2006 <br />data and historic water quality monitoring data compared to the Colorado Groundwater Standards <br />provided in Regulation no. 41 -Basic Standazds for Ground Water indicated the following <br />exceedances. <br />• The historic averages for iron, dissolved and sulfate in MW-16 exceed the Secondary <br />Drinking Water Standrsd but not the Agricultural Standrsd; <br />• Manganese, dissolved in MW-65 exceeded the Secondary Drinking Water Standard in both <br />samples in 2006 and the historical average also exceeds; and <br />• Iron, dissolved in MW-23 exceeded the Secondary Drinking Water Standard once during <br />2006 and the average also exceeds the standard <br />3.1.2 Loadout Area <br />In the Loadout Area, ground water occurs primarily in alluviaUcolluvial deposits in and adjacent to <br />the Oak Creek floodplain. Due to limited surface and ground water flows and recharge and the <br />character of the alluviaUcolluvial deposits, these deposits do not appeaz to store or transmit <br />significant quantities of water, as indicated by the lack of sub-imgation (refer to Section 2.04.7 of <br />the Southfield Mining and Reclamation Plan document for more details). Because the <br />alluviaUcolluvial deposits associated with Oak Creek do not represent a significant ground water <br />source or aquifer, there is not ongoing ground water monitoring in the Loadout Area or immediate <br />6417/2006annuaihydrpt.doc NWCC INC. Page $ <br />