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<br />1 <br />mean due to problems with the field measurements in late 1983 and early <br />' 1984 which elevated the mean. The laboratory measurements did not show the <br />same high levels during that period. <br />' SURFACE WATER MGNITORIN'G <br /> There are two rivers in the vicinity of the Empire Energy mine site. The <br /> major river, the Yampa, flows in a southeasterly direction across the mine <br />' site. The Yampa River drains most of the northeast corner of Colorado and <br /> part of south-central Wyoming. The second river is the Williams Fork <br />~I ' which is a major tributary of the Yampa River. The Williams Fork River <br />joins the Yampa River on the mine property. In addition, data is <br /> collected from three springs: 1) the No. 1 Strip Pit (NPDES site), <br /> 2) North Spring, and 3) Haxton Spring. <br /> <br /> kIVERS <br />' <br /> River Flow <br /> Flow data,is collected by the US Geologic Survey at two continuous gaging <br /> stations and two staff gages. The Williams Fork River continuous gaging <br /> station is near the confluence with the Yampa River. The Yampa River <br /> continuous gaging station is upstream of the confluence with the Williams <br /> Fork River. <br />' A summary of the staff gage readings are presented on Table 21. A plat of <br />daily mean flow verses time for the Yampa and Williams Fork Rivers for <br />1985 are presented on Figures 25 and 26. The plot for the Yampa River <br />includes the mean monthly discharge near Hayden and the plot for the <br />' Williams Fork River includes the mean monthly flows for the Williams Fork <br />at Hamilton (a discontinued USGS gaging station) for the Yampa River. The <br />maximum mean daily flow was 9830 cfs and the minimum mean daily flow was <br />' 158 cfs. For the Williams Fork River the maximum mean daily flow was 2630 <br />cfs and the minimum mean daily flow was 56 cfs. While the flows in the <br />Williams Fork River were on the average lower in 1985 than in 1984, the <br />minimum mean daily flow is approximately the same in both years. <br />' The flows in the Williams Fork and Yampa Rivers measured to date by Empire <br />Energy do not show any significant variation from expected values. <br />' River Water Quality <br />' Summaries of the water quality data are presented on Table 2"c to Table 29. <br />Plots of upstream and downstream field electrical conductivity <br />measurements for each river are presented on Figure 27 and Figure 28. The <br />' data indicates that the surface water quality does not show any <br />significant variation from expected values. The data from the upstream <br />and downstream station on the Williams Fork River indicate that there is <br />no detectable effect of mining on river water quality. As expected, <br />conductivity decreases with increasing flow raie in the rivers. This is <br />-4- <br />