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EFU Southfield Mine - 2009 Annual Hydrology Report March 10, 2010 <br />documented in AHR's on file at the Division. All historic water level data are presented <br />graphically for the four monitoring wells on Figures 3, 4, 5, and 6. <br />Water levels for well MW-16, shown on Figure 3, indicate significant cyclic/seasonal fluctuations <br />prior to 2001. It was essentially dry beginning in December 2001 until June 2004, possibly <br />associated with drought conditions. The well has silted-up to approximately 110 feet below ground <br />surface leaving 4 feet of perforated casing above the current depth. Water levels for 2004 and 2005 <br />were between 97 and 106 feet but the well has been dry from 2006 through the reporting period. <br />Well MW-23 has demonstrated steadily declining water levels since July of 1984, shown on Figure <br />4. A slight increase in water level was observed at this well for both measurements taken during <br />2009. Water levels for Well MW-65, shown on Figure 5, have generally remained stable with <br />minor fluctuations of less than 10 feet through the reporting period. MW-NW has been dry since <br />monitoring was initiated in early 2003, shown on Figure 6 (the water level line represents the well <br />depth). <br />Water quality data for monitoring wells MW-16, MW-23, MW-65 and MW-NW are included on <br />Tables 4, 5, 6, and 7, respectively. These tables provide any analytical results obtained during <br />2009, and the minimum, maximum and average values calculated using all historical monitoring <br />data. Only wells MW-23 and MW-65 provided water sample data for the reporting period. <br />A review of the 2009 quality data for MW-65 indicates that sample parameters were close to <br />historic values, suggesting no significant changes to groundwater quality are occurring at this site. <br />Quality data for MW-23, specifically the December sampling, indicates sharply elevated values of <br />dissolved Calcium and Magnesium. This sample date shows a concentration of Calcium <br />approximately 40 percent higher than the historic maximum, and a Magnesium concentration <br />approximately 90 percent higher than any previous sample. All other sample parameters were very <br />close to historic average values. EFCI's field data related to the MW-23 December sample does not <br />document any changed conditions that could affect the sample quality. The unusually high values <br />for the two parameters are likely an anomalous condition. EFCI will verify this assumption by <br />further sampling of the well in accordance with the monitoring plan. <br />For discussion purposes only, EFCI is providing a review of 2009 sampling and historic water <br />quality monitoring data compared to the Colorado Groundwater Standards (Regulation no. 41 - <br />Basic Standards for Groundwater). For each well, quality parameters included in both the <br />monitoring plan and the groundwater standards that exceeded groundwater standards are <br />summarized below. <br />MW-16: The historic averages for dissolved Iron and Sulfate exceed the Secondary Drinking <br />Water Standard (SDWS); no historic sample parameter averages or 2009 samples exceed the <br />Agricultural Standards (AS). <br />MW-23: The historic average for dissolved Iron exceeds the SDWS. The June 2009 sample <br />measurement for pH slightly exceeded SDWS and AG limitations; the December sample was <br />within limitations. <br />MW-65: The historical average, and both samples taken during 2009, of dissolved Manganese <br />exceed the SDWS. Neither the 2009 samples or historic sample parameter averages for dissolved <br />2009 AHR.doc WP Page 5