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RULE 2 PERMITS <br />other major ions. The concentration of total dissolved solids (TDS) is low to moderate, ranging from 440 <br />milligrams per liter (mg/L) to 640 mg/L (CDM, 1985a). The CDM investigation revealed that the water <br />type of the Trout Creek Sandstone is more variable than that of the Williams Fork Formation. TDS <br />concentrations ranged from 600 mg/L to 710 mg/L, and the water type ranged from a sodium -sulfate, <br />sodium -bicarbonate type, to a predominantly mixed cation -bicarbonate type water with equal percentages <br />of calcium, magnesium, and sodium (CDM, 1985a). The water quality of the bedrock during the 1985 <br />investigation did not exhibit significant seasonal variability. <br />The water quality of the alluvium in the general area was also investigated by CDM in 1985. These <br />investigations revealed two distinct trends in water quality: a temporal uniformity in water type, in the <br />relative percentages of major cations and anions, and general variability in the water quality from well to <br />well. The water type is predominantly a magnesium -sulfate type, with moderate to high concentrations of <br />TDS, ranging from 645 mg/L to 3,780 mg/L (CDM, 1985a). In contrast to the water quality of the <br />bedrock, the alluvial water quality showed significant seasonal variation in the majority of the wells <br />sampled, with TDS concentrations increasing in the spring. <br />General Groundwater Use — Groundwater withdrawals in the Lower Yampa River basin totaled nearly <br />one million gallons per day (mgd) in 1995 (USGS 1995). Groundwater consumption in the basin is <br />predominantly associated with irrigation use. About 52 percent of the groundwater withdrawals (0.5 <br />mgd) are used for irrigation. Livestock and mining use account for the remaining groundwater <br />withdrawals. <br />A search of the Colorado Office of the State Engineer's files revealed 71 permitted wells located within <br />the permit revision area and extending at least one mile beyond the perimeter of the expansion area. Of <br />these, five permitted wells have reported well yields of 20 gallons per minute (gpm) or greater. The <br />maximum reported yield of these wells is 50 gpm. The remaining wells have reported yields of less than <br />16 gpm; with most of the wells having reported yields of less then 5 gpm. There are 49 wells with <br />reported flows of 0 gpm. Most of the permitted wells are used for monitoring purposes, however, a few <br />of the permitted wells support domestic and livestock uses. The permitted wells are illustrated on Map <br />11B. <br />Detailed Groundwater Information <br />Groundwater Characteristics — The principle structural features in the permit revision area that <br />influence groundwater flow are an unnamed syncline, located southeast of the South Taylor mining area, <br />and an unnamed anticline, located beneath the southern part of the South Taylor/Lower Wilson permit <br />revision area. The synclinal axis generally corresponds to the drainage valleys of the West Fork of Good <br />Spring Creek. The unnamed anticline parallels the topographic divide between Wilson and Good Spring <br />Creek. The result is a stratigraphic dip -slope towards Good Spring Creek. Both the anticline and <br />syncline axes plunge in a northeasterly direction. These structural features result in the area at the top of <br />the anticline being the recharge area for groundwater, and the area near Good Spring Creek being the <br />discharge area. The area for recharge of groundwater is limited to the eastern half of the anticline and <br />does not result in the formation of a continuous aquifer in the South Taylor/Lower Wilson permit revision <br />area. <br />Groundwater in the South Taylor/Lower Wilson permit revision area occurs under perched conditions in <br />areas that are not laterally extensive, and in the alluvial of the stream valleys. The perched areas are <br />generally within the interbedded and lenticular sandstones and on the contacts between different <br />lithologic units of the Williams Fork Formation. Beneath the South Taylor mining area, the top of the <br />Trout Creek Sandstone underlies the lowest seam to be mined by approximately 590 feet. The coal seams <br />to be mined in the South Taylor and Lower Wilson mining areas are lower in the coal seam sequence than <br />South Taylor/Lower Wilson — Rule 2, Page 20 Revision Date: 4/7/17 <br />Revision No.: RN -07 <br />