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• 4.6.1.3.4 <br />The instream impact on North Thompson Creek is an increase of total dissolved solids <br />(TDS) which is indicated by the water quality data. The TDS of the downstream <br />measurement is consistently higher than the upstream measurement. <br />The main reason for the increase in TDS is from changes in the geologic strata which the <br />creek flows across. As North Thompson Creek flows to the Crystal River, it flows across <br />several different geologic unit outcrops. The headwaters and the upstream site of North <br />Thompson Creek originate in the Wasatch and Ohio Creek formation. This formation has <br />a volcanic origin and traditionally has high water quality and low TDS. <br />North Thompson Creek then flows across the Mesa Verde formation, below the upstream <br />gaging station. The Mesa Verde contains the coal bearing formations which have lower <br />water quality and higher TDS. This formation increases the TDS. <br />The downstream site is located in the Mancos Shale. The Mancos Shale was deposited <br />under marine conditions. Marine deposition is normally high in salt and TDS; both of <br />• which increase the TDS in North Thompson Creek. <br />The entire mine site has been reclaimed and seeded. Good plant growth occurred during <br />1988 through 1993. During 1992 a study was performed at the mine site that <br />demonstrates that untreated drainage from the reclaimed area contributes fewer <br />suspended solids than untreated drainage from the natural surrounding area, (permit <br />pages 4-19i though 4-19iii). <br />Mine Discharye <br />For a discussion of the projected effect the mine discharge has on North Thompson Creek, <br />please refer to the discussion beginning on page 120. <br />. 4-111 b Revised June 1998 <br />kN -v ~ <br />T~-moo <br />