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. pH The pH for all wells changed from slightly basic during the end of water year 1996 to slightly acidic at the beginning of water yeaz 1997. This change was also noted in the springs on-site. During water year 2001, the pH of the three groundwater wells rose slightly, with the lazgest change in well 17-B (6.9-7.5). This water year, pH at well 17-B decreased slightly in value from last water year, though remaining within the historic range. pH at well 94-1 rebounded from a slightly acidic value (6.9) during the last quarter of the 2002 water year to alkaline in water yeaz 2003 (7.8}. The pH of well 95-1 increased significantly in alkalinity over the course of water year 2004 (7.7-9.2), and decreased slightly this water year. These changes in value may reflect larger anion concentrations in the wells during seasonal periods. Electrical Conductivity (EC) Over the last ten yeazs, electrical conductivity (EC) values were highest for well 94-1 (mid-mine), median for well 95-1 (downgradient), and lowest for well 17-B (upgradient). EC levels this water year increased slightly for Well 17-B, though remaining within the recorded historic range. Levels for well 95-1 remained low this year continuing a general downward trend beginning in 1997. ' Total Dissolved Solids (TDS} Total dissolved solids (TDS) levels in well 17-B remained within historic values during this water year. Well 17-B shows the least overall variability for TDS values of the wells, ranging from 235 to 470 mglL over the past ten years. Well 94-1 showed the widest range in TDS values from 720 mg/L (W.Y. 1999) to 1490 mg/L (W.Y. 1995). Since water yeaz 1998 the TDS concentrations for well 94-1 have been 720-970 mg/L, a significantly narrower range than prior to that time. TDS values for well 95-1 decreased between water yeaz 1997 and 2004, this yeaz values increased slightly to 300 mg/L in Apri12005. Ionic Constituents The monitoring wells showed some fluctuation in ionic concentrations this water yeaz. The fluctuations were not consistent as far as the wnstituents that fluctuated or the wells that showed fluctuations. The majority of the fluctuations were within historic ranges observed for the wells over the last nine water years. Notable changes are further described below. Ammonia Ammonia concentrations for wells 17-B and 95-1 remained very low and within historic ranges during the 2005 water year. Well 95-1 exhibited a significant rise in ammonia • concentrations during the 2000 water yeaz from 1.50 mg/L in the second calendar quarter Carbon Junction Mine Page 8 Mnual Hydrologic Report for Water Year 2005