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• All TDS values obtained for Trout Creek and the CDPS discharge points <br />were analytically derived by an independent laboratory. The data was then <br />incorporated into the flow balance equation to estimate the short term TDS <br />loading on Trout Creek as a result of all mining activity. <br />Premining TDS Concentrations <br />The TDS concentrations used to determine premining conditions were <br />taken during 1979-1980. This data set is most appropriate because 1980 was <br />the year immediately prior to the beginning of mining activity on West <br />Ridge, and West Ridge was the first mining performed under the permanent <br />program rules and regulations. <br />TDS values at TR-A (upstream) between April and October of 1979-1980 <br />averaged 148 mg/1 and had a range from 62 mg/1 (June 1960) to 261 mg/1 <br />(September 1960). TDS values at TR-D (downstream) during the same time <br />period averaged 320 mg/1 and had a range from 126 mg/1 (June 1980) to 565 <br />mg/1 (April 1980). The average increase in TDS concentration from TR-A to <br />TR-D during 1979-1980 was 172 mg/1 with a maximum difference of 965 mg/1 <br />(April 1960) and a minimum difference of 69 mg/1 (June 1980). <br />• TDS Concentrations 1981-1996 <br />TDS values at TR-A between April and October for the years 1981 <br />through 1996 averaged 122 mg/1 and had a range from 19 mg/1 (May 13, 1996) <br />to 250 mg/1 (August 19, 1992). TDS values at TR-D during the same time <br />period averaged 992 mg/1 and had a range of 100 mg/1 (July 19, 1988) to <br />1990 mg/1 (April 16, 1996). The average increase in TDS concentration from <br />TR-A to TR-D during this period was 319 mg/1 with a maximum difference of <br />1,332 mg/1 (April 16, 1996) and a minimum difference of -52 mg/1 (July 19, <br />1986; TDS at TR-D was less than TDS at TR-A). <br />The mine's production of TDS encountered in Trout Creek is believed <br />to come from two primary sources. The first source is ground water passing <br />through the spoil of mined areas (i.e., West Ridge, Center Ridge and East <br />Ridge). These TDS laden waters pass through the Trout Creek alluvium and <br />eventually into Trout Creek (evidenced by the increasing TDS levels in the <br />alluvial wells in a downstream fashion - see 1996 Annual Hydrology Report). <br />The second source is the CDPS discharge points. These discharges occur at <br />various locations along Trout Creek between TR-A and TR-D. CDPS points <br />• 002, 003 and 009 are sedimentation ponds while CDPS point 006 is a spring. <br />In June 1996, flows from points 002, 003 and 006 were combined and <br />Renewal 3 2.SA-3 June 13,1997 <br />