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GENERAL52614
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Last modified
8/24/2016 8:38:26 PM
Creation date
11/23/2007 7:54:23 PM
Metadata
Fields
Template:
DRMS Permit Index
Permit No
C1981044
IBM Index Class Name
General Documents
Doc Date
4/24/1987
Doc Name
Proposed Decision & Findings of Compliance for PR1
Permit Index Doc Type
Findings
Media Type
D
Archive
No
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The alluvial deposits associated with the Williams Fork and Yampa Rivers, <br />within the permit area of the Eagle Mines are broad, but relatively thin. The <br />Wiitiams Fork alluvium is between 800 and 1,000 feet wide and 10 to 15 feet " <br />thick. The Yampa River alluvium in Big Bottom averages about 5,000 feet in <br />width but may range up to a maximum of 9,000 feet, and is between 10 and 35 <br />feet thick. <br />The Yampa River alluvium in the Big Bottom consists of sandy silts overlying <br />poorly sorted silts, sand, and cobble size stream deposits with occasional <br />layers of clean sand and gravel. The alluvium coarsens toward its contact - <br />with the underlying bedrock. Parts of both the Iles and Williams Fork <br />Formation subcrop beneath the Yampa alluvium in the general area. <br />The Williams Fork alluvium ranges from poorly sorted clay to cobble size <br />material, It too coarsens toward its contact with the underlying bedrock, <br />The surficial soils consist of two to four feet of fine sands and sandy <br />loams. Strata of the upper Iles Formation and lower Williams Fork Formation <br />subcrop beneath the Williams Fork alluvium in the permit area. <br />Ground Water <br />Ground water occurs in both rock and alluvial bodies within the permit and <br />adjacent areas. Bedrock aquifers include the Tow Creek and Trout Creek <br />sandstones of the Iles Formation and the Middle sandstone, Twentymile <br />sandstone, and White sandstone of the Williams Fork Formation. Less prominent <br />lenticular and interbedded sandstone as well as coal seams of both the Iles <br />and Williams Fork Formations are also water bearing, however, they either <br />yield insufficient amounts of water to wells or are of such limited areal <br />extent that they are not considered regional aquifers. The alluvial bodies <br />associated with the Yampa River and Williams Fork River also contain ground <br />water, but these too are not regarded as significant aquifers in the immediate <br />area. <br />Ground water flow in the general area is controlled by geologic structure, <br />stratigraphy, and geomorphology. The flows of ground water in the rock <br />aquifers are functions of structure and stratigraphy while water movement in <br />the alluvium is controlled by the geomorphology of the stream valleys. <br />The sandstone aquifers are under atmospheric pressure {water table conditions) <br />near their recharge areas and under hydrostatic pressure (artesian conditions) <br />within the structural basins or at discharge points. Artesian conditions are <br />common in local rock aquifers and develop as a result of the confinement of <br />the sandstones over large areas by overlying and underlying strata with low <br />permeabilities. Several flowing artesian we)15 have resulted from drilling <br />into rock aquifers within the study area. <br />The sandstone aquifers involved in the Big Bottom synclinal fold are recharged <br />at their outcrops found at higher elevations in the valley wa1}s of the Yampa <br />and Williams Fork Rivers as well as in the southern portions of the Williams <br />Fork Mountains. Some bedrock aquifers may a7 so be recharged at their subcrops <br />beneath the Yampa and Williams Fork Yalleys. There are too few local wells <br />completed in the Trout Creek sandstone to be certain of the direction of <br />-23- <br />
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