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Mayo and Assocla/es, LC Model runs were perfornred using the mean solute and isotopic compositions of WEM fault waters as the initial water and the solute and isotopic compositions of Edwards portal spring waters as the final water. Based on our experience in modeling chemical reactions in non- acid producing coal mine we selected a range of possible chemical reactions. Modeled reactions included: 1) the dissolution and precipitation of calcite, dolomite, gypsum, pyrite, geothite, 2) CaZ'-Na` and MgZ'-Na' ion exchange on clay minerals and the mineral analcime, 3) the introduction and loss of CO, gas, and 4) S"C fractionation. It was no[ possible to model any chemical reaction pathways that would evolve WEM fault water to Edwards portal spring water while maintaining S"C compositions. The S'BC tracks the carbon history of a water. Mass balance calculations in [he reactions required appreciable reverse ion exchange (i.e. up to 11 mmole L-') and appreciable calcite precipitation (i.e. up to 33 mmole L-'). Model runs predicted the S"C of Edwards portal spring water to be about - 2°~.o whereas the actual value is about -13%0. This difference is significant and means that the modeled reactions are no[ possible. S2H and 5180 Compositions Figure 5 is a plot of the stable isotopic compositions of surface and groundwaters in the vicinity of West Elk Mine relative to the meteoric water line (MWL). All of the waters plot near the MWL indicating that they are of meteoric origin and have not been elevated above 100°C. The plotting locations of BEM vs. 14 SEHG faults waters suggest that these waters are not part of a hydrodynamically continuous aquifer. Rather, they are discrete bodies of groundwater, which have limited hydraulic communication with each other. What is significant to this investigation is that the water from the Edwards portal spring is isotopically different than both 14 SEHG and BEM fault waters. Because the S'H and 5180 compositions are independent of solute content, the stable isotopic compositions of these water indicate that water discharging from the Edwards portal spring did not originate as either 14 SEHG or BEM fault water. Conclusions We conclude that the water dischazging from the Edwards portal spring does not originate as WEM fault water. The two groups of water have fundamentally different chemical and isotopic signatures. To evolve from WEM fault water to Edwards portal spring water would require appreciable amounts of reverse ion exchange, which is very unlikely. Chemical reaction pa[h~vay modeling indicates that carbon in Edwards portal spring water does not evolve from WEM fault water as indicated by the S"C compositions. Additionally the S'H and 5180 compositions of these two groups of water are fundamentally different indicating a different source. edwspr.doc 6 20 January 1998