2025-07-30_PERMIT FILE - C1981019A (2)

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RULE 2 PERMITS South Taylor – Rule 2, Page 18 Revision Date: 7/21/25 Revision No.: MR-267 other major ions. The concentration of total dissolved solids (TDS) is low to moderate, ranging from 440 milligrams per liter (mg/L) to 640 mg/L (CDM, 1985a). The CDM investigation revealed that the water type of the Trout Creek Sandstone is more variable than that of the Williams Fork Formation. TDS concentrations ranged from 600 mg/L to 710 mg/L, and the water type ranged from a sodium-sulfate, sodium-bicarbonate type, to a predominantly mixed cation-bicarbonate type water with equal percentages of calcium, magnesium, and sodium (CDM, 1985a). The water quality of the bedrock during the 1985 investigation did not exhibit significant seasonal variability. The water quality of the alluvium in the general area was also investigated by CDM in 1985. These investigations revealed two distinct trends in water quality: a temporal uniformity in water type, in the relative percentages of major cations and anions, and general variability in the water quality from well to well. The water type is predominantly a magnesium-sulfate type, with moderate to high concentrations of TDS, ranging from 645 mg/L to 3,780 mg/L (CDM, 1985a). In contrast to the water quality of the bedrock, the alluvial water quality showed significant seasonal variation in the majority of the wells sampled, with TDS concentrations increasing in the spring. General Groundwater Use – Groundwater withdrawals in the Lower Yampa River basin totaled nearly one million gallons per day (mgd) in 1995 (USGS 1995). Groundwater consumption in the basin is predominantly associated with irrigation use. About 52 percent of the groundwater withdrawals (0.5 mgd) are used for irrigation. Livestock and mining use account for the remaining groundwater withdrawals. A search of the Colorado Office of the State Engineer's files revealed 71 permitted wells located within the permit revision area and extending at least one mile beyond the perimeter of the expansion area. Of these, five permitted wells have reported well yields of 20 gallons per minute (gpm) or greater. The maximum reported yield of these wells is 50 gpm. The remaining wells have reported yields of less than 16 gpm; with most of the wells having reported yields of less then 5 gpm. There are 49 wells with reported flows of 0 gpm. Most of the permitted wells are used for monitoring purposes, however, a few of the permitted wells support domestic and livestock uses. The permitted wells are illustrated on Map 11B. Detailed Groundwater Information Groundwater Characteristics – The principle structural features in the permit revision area that influence groundwater flow are an unnamed syncline, located southeast of the South Taylor mining area, and an unnamed anticline, located beneath the southern part of the South Taylor permit revision area. The synclinal axis generally corresponds to the drainage valleys of the West Fork of Good Spring Creek. The unnamed anticline parallels the topographic divide between Wilson and Good Spring Creek. The result is a stratigraphic dip-slope towards Good Spring Creek. Both the anticline and syncline axes plunge in a northeasterly direction. These structural features result in the area at the top of the anticline being the recharge area for groundwater, and the area near Good Spring Creek being the discharge area. The area for recharge of groundwater is limited to the eastern half of the anticline and does not result in the formation of a continuous aquifer in the South Taylor permit revision area. Groundwater in the South Taylor permit revision area occurs under perched conditions in areas that are not laterally extensive, and in the alluvial of the stream valleys. The perched areas are generally within the interbedded and lenticular sandstones and on the contacts between different lithologic units of the Williams Fork Formation. Beneath the South Taylor mining area, the top of the Trout Creek Sandstone underlies the lowest seam to be mined by approximately 590 feet. The coal seams to be mined in the South Taylor mining area is lower in the coal seam sequence than found at the adjacent West and East Pits. For South Taylor, the lowest seam currently considered to be mined is the G8/9 seam. .