2010-12-17_REVISION - C1981019 (153)

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• Groundwater 5.3.7 Aqueous geochemistry The geochemistry of groundwater is a function of numerous factors, including the chemistry of the infiltrating water, the geologic units that the groundwater has interacted with, the contact time between the groundwater and the geologic materials, and the degree of mixing between chemically distinct waters due to hydrostratigraphic heterogeneities and /or vertical hydraulic gradients. Anthropomorphic contamination can also affect groundwater quality, but the Collom study area has had minimal historic activities that might impact groundwater quality. Analysis of major ion chemistry of all waters within the Collom Mine study area (groundwater, stream water, seeps and springs) is a powerful tool for analyzing the movement of water through a water - bearing unit as well as the interaction between surface and groundwater. As discussed in previous sections, each type of water has a distinct inorganic signature that provides information on its source. Comparison of the alluvial, surface, and spring waters provides evidence of their relationship and origin. The following discussion is based on Figures 4.3, 4.4, and 5.15 through 5.17, which show the inorganic chemistries of the surface water, springs /seeps, bedrock groundwater, and valley fill groundwater, respectively. Jubb Creek In the East Fork of Jubb Creek, the inorganic chemistry from valley fill well MJ -95 -02 is similar to other samples collected from the valley fill. The chemical signature of spring sample SPRJ -01 (Figure 4.4) indicates that the valley fill groundwater and spring water are the same. Samples from the valley fill at the confluence of East and West Jubb Creeks (MJ- 95 -03), the stream (CJC) and spring (SPRJ -02) are all magnesium - sulfate type waters indicative of an interconnected hydrologic system. Both the surface water and spring have a slightly higher percentage of sodium, possibly indicative of discharge from bedrock. Little Collom Gulch Spring sample SPRLC -01 is a magnesium- carbonate type water that appears to originate from the F sandstone. Spring sample SPRLC -02 does not resemble any of the valley fill groundwaters or surface water samples. It appears to be a surface discharge from the F/G sequence or a unit with similar chemistry. SPRLC -03, located on the lower reach of Little Collom Gulch, is a sodium - bicarbonate water similar to groundwater from the F/G sequence. Due to lack of information on how the groundwater chemistries evolve downdip of the existing bedrock wells, the source of the water is difficult to state with certainty, but the spring appears to originate from the bedrock. 73 2572 -R2 Water Management Consultants Colowyo Coal Company