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Mayo and Assotlaies, LC <br />• Ca`', Mg", and SO; . As with most stream waters, the elevated Na' contents in the springs <br />are attributed to ion exchange reactions. <br />Spring water issuing from [he landslide on the Rollins Sandstone is of the Mg`'-SO; type <br />with lesser amounts of Ca", Na', and HCO;. I[ is unlikely that this chemically unusual water <br />actually issues from Rollins Sandstone bedrock that has been involved in the landslide <br />because the Rollins Sandstone is a very competent rock. <br />4.2.2.3 Grouudwater in Mesaverde Group Bedrock <br />The TDS and solute compositions of bedrock groundwater in the Mesaverde Formation <br />belong to four statistically distinct general clusters. The clusters, which include Barren <br />• Member springs, Barren Member wells, and Upper and Lower Coal Member wells and <br />springs (including F-, E-, and B-Seam wells), and in-mine Rollins Sandstone groundwater <br />discharges, have solute concentrations that tend to become greater with what may be thought <br />of as increasing stratigraphic depth. <br />The cluster of springs issuing from the Barren Member, which constitute approximately 20% <br />of the monitored sites, has a mean TDS of only 329 mg 1-' (Table 3) and a small variability in <br />the range of TDS values (Figure 6). These groundwaters are of the Ca"-Na'-HCO; type with <br />lesser amounts of Mg'-' and SO;". <br />Groundwater encountered in Barren Member monitoring wells, which constitute <br />• approximately 15% of the monitored sites, have a mean TDS about twice as great as <br />Charactzrization of Groundwater Systems in the Vicinity of the West Elk Mine, Somerset, Colorado <br />29 January 1999 <br />Page 42 <br />