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74 Groundwater <br />Lower Little Collom Gulch valley fill groundwater samples from MLC -04 -01 resemble <br />surface water sample LCG, indicating that they both originate from the surficial /valley fill <br />water system. <br />Collom Gulch <br />The uppermost spring in Collom Gulch (SPRC -01) is a magnesium - sulfate type water <br />that is unlike any other water sample collected at the site. With 70 percent sulfate in the <br />anions, this water is unlikely to originate from the valley fill. <br />Groundwater from valley fill well MC -04 -01 is a magnesium /calcium - bicarbonate type <br />water, similar to most of the valley fill groundwater samples. Between December 2004 <br />and March 2005, the chemistry at this location displayed a visible shift in anion <br />chemistry, with a 10 percent relative increase in sulfate, and concomitant loss in <br />bicarbonate. Surface water samples (UCG) were calcium- bicarbonate, indicating that <br />upstream source areas produce a water that has relatively higher proportion of <br />bicarbonate. <br />The spring sample at SPRC -02 has the high magnesium percentage (55 percent) <br />characteristic of the valley fill groundwater and high bicarbonate (67 percent) <br />characteristic of groundwater from the F/G sequence. <br />Water samples collected in Lower Collom Gulch, (MC- 04 -02, LCG and spring samples <br />SPRC -03 and SPRC -04) are very similar. The differences all originate from minor <br />variations in the percentages of bicarbonate and sulfate. They all appear to originate <br />from water flowing in or below the stream channel. The surface water sample collected <br />in April showed the effects of seasonality, in that it had a much lower TDS and lower <br />percentage of bicarbonate. <br />The surface water at Upper Straight Gulch (USG) and valley fill groundwater (MS- 04 -01) <br />are very similar, indicating that they are a single flow system. <br />Water in Lower Straight Gulch from the valley fill well (MS- 04 -02), surface water (LSG) <br />and nearby spring (SPRS -01) are very similar, indicating that they are a single flow <br />system. <br />Based on the analysis of the trilinear diagrams, there appear to be three interrelated <br />water systems — bedrock, valley fill, and surface water. The inorganic chemistry <br />supports the theory that the surface water and valley fill groundwater are a single <br />integrated flow system. Contrasts between the surface water and valley fill groundwater <br />at a given location appear to be caused by seasonal effects (snowmelt has a different <br />chemistry than alluvial groundwater), and distance downgradient, which tends to <br />homogenize the water chemistries. The valley fill groundwaters have unique chemistries <br />that appear to be a function of the drainage and location within a given drainage. These <br />variations are attributed to spatial variations in the surface water chemistry, residence <br />time in the valley fill water - bearing unit, and discharge from the bedrock units into the <br />valley fill. The inorganic signatures of the seeps and springs indicate that most are <br />( simply local diversions of surface water or surface expressions of valley fill groundwater, <br />while several clearly originate from units of the Williams Fork Formation. <br />2572 -R2 Colowyo Coal Company <br />Water Management Consultants <br />