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feet of alluvium. The alluvium consists of sandy silts overlying poorly sorted, silty sand to cobble size material with <br />occasional thin layers of clean sands and gravels. The material generally coarsens with depth and is sometimes mantled with <br />two to four feet of fine sandy to loamy soil. Underlying bedrock consists of sandstones, siltstones, and shales of the <br />Williams Fork Formation and Lewis Shale. As the No. 5 and No. 6 Mines will not conduct full extraction mining or pull <br />pillars under the Yampa River Alluvium, it will not be impacted. For additional information on the Yampa River Alluvium, <br />refer to EC Energy (1983a). <br />Ground Water Uses in Vicinity of Mine Site <br />Ground water uses in [he vicinity of EC's mine are limited. Most of the ground water uses in the area are permitted for <br />domestic and stock purposes. Except for the EC wells completed in the Twentytnile and Trout Creek Sandstones, there are <br />no wells in the immediate area that deliver water for municipal, industrial, or commercial uses. Shown on Table 12, Wells <br />Registered with the State Engineer (Colorado) near the EC Site, and the Water Rights Map (Map 18), are wells registered <br />with the state Engineer's Office. Any unregistered wells are probably used for domestic and stock purposes because there <br />are no reported irrigation or other high capacity wells on or adjacent to the mine site. <br />Ground water use is therefore limited because of the low demand for water supplies near the mine. The Twentymile, <br />Middle, and Trout Creek Sandstones contain sufficient water for ground water development; however, they occur at great <br />depth, and to date, have been developed little for water supplies in the mine area. The potential exists to locally obtain high <br />yields from these sandstones; however, yields vary from location to location. <br />GROUND WATER QUALITY <br />General Ground Water Oualit <br />Ground water occurs in three-(3) distinct environments within the EC pemvt area. These are: 1) bedrock aquifers, 2) <br />alluvial sediments, 3) discharges from abandoned surface and underground mines. The quality of ground water is the best <br />in the bedrock aquifers. The total dissolved solids within the bedrock aquifers is generally within maximum recommended <br />and maximum permissible limits specified by Environmental Protection Agency (EPA) drinking water standards. EPA <br />primary and secondary drinking water standards are presented on Table 13, Applicable Water Quality Standards. Ground <br />water from the bedrock aquifers is generally suitable for most uses including potable water supply. <br />Ground water in the alluvial sediments is relatively poor in quality. Average dissolved solids concentrations typically <br />exceed drinking water standards. In addition, maximum primary and secondary standards are exceeded for several <br />dissolved metals. Ground water from the alluvial sediments may be suitable, with limitations, for some uses including <br />irrigation. <br />Discharges from the underground mines are relatively poor in water quality. Average values for dissolved solids of these <br />discharges exceed the drinking water standards. Drinking water standards for the dissolved metals and fluoride are <br />exceeded in several instances. However, water discharged to the Williams Fork River, adjacent to the thine, meets CDPS <br />water quality standards. <br />There is no evidence of significant variations in ground water chemistry versus time within the permit area. Analysis of <br />dissolved solids concentrations over time suggests a relatively constant water chemistry for the period of record. There is <br />no indication of a deterioration of water quality with time for the period (since approximately 1981). Water quality of the <br />bedrock aquifers, alluvial sediments, and abandoned mine discharges are discussed in more detail in the following section. <br />A comparison of the water quality for the ground water sources is presented in Figure 23, Typical Stiff Diagram. Typical <br />Stiff diagrams and mean dissolved solids values are shown graphically on this figure. <br />There are many different water types on the EC mining site. Water types can vary considerably within a single <br />Permit Revision 04-34 2.04-16 Revised 7/2/04 <br />