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• concentrations of 1474 mg/1 represents this equilibrium <br />concentration and also provides an indication of the expected post <br />mining TDS concentrations in rubbelized zone and underground mine <br />workings. <br />ALLUVIUM <br />Sediments in the Williams Fork River Alluvium are monitored. Three <br />wells are in the general area of the loadout facilities and <br />underground discharge sediment ponds. <br />WATER LEVELS <br />Groundwater levels in the alluvium have remained fairly regular, <br />with normal seasonal fluctuations, apparently related to changes in <br />river levels. Groundwater levels in the alluvium are plotted in <br />Figure 22. A piezometric map for the Williams Fork Alluvium <br />(October, 1991) is presented in Figure 23. The data indicates no <br />impact on alluvial water levels related to mining. <br />WATER QUALITY <br />Summaries of the water quality data for the alluvial wells are <br />presented in Tables 23 and 28. A plot of field electric <br />conductivity versus time is presented in Figure 24. <br />• There is no conclusive evidence of seasonal variation of water <br />quality in the alluvium. The field conductivity of Well AVF-5 was <br />above normal in late 1983 and early 1984. The laboratory <br />measurements did not show the same high levels during that period. <br />Only Well AVF-3 is showing an upward trend in dissolved solids. <br />There is also a correlative increase in calcium, magnesium, sulfate <br />and chlorides. The source of this change is not known. However, <br />it is unlikely due to mine discharge because its location and the <br />dissimilar chemical composition of mine discharge. Also, it is <br />unlikely due to the waste water lagoon because the conductivities <br />in the well exceed the levels measured in waste water. <br />SURFACE WATER MONITORING <br />There are two rivers in the vicinity of the mine site. The major <br />river, the Yampa, flows in a southeasterly direction across the <br />mine site. The Yampa River drains most of the northeast corner of <br />Colorado and part of south-central Wyoming. The second river is <br />the Williams Fork, which is a major tributary of the Yampa River. <br />The Williams Fork River joins the Yampa River on the mine property. <br />Monitoring data is collected for the Williams Fork River. <br />Monitoring data is also collected from one spring, the #1 Strip Pit <br />(NPDES site 022). In 1992 there was no discharge from the sediment <br />ponds. <br />• 5 <br />