2009-06-15_GENERAL DOCUMENTS - C1982056 (2)

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• calcium-magnesium-sulfate water type with TDS values about 4,000 mg/1. Increases in calcium, magnesium, and sulfate ions has been seen in certain wells down-dip of the spoil piles and in inflow water into the Foidel Creek up to 2,500 feet down-dip from the spoil piles. Beyond this distance. natural water quality values for the Wadge overburden aquifer are seen in the mine inflow water. Natural water in the Wadge overburden aquifer is generally a sodium bicarbonate type with relatively low calcium. magnesium, and sulfate ion concentrations and TDS values ranging from 400-600 mg/1. The Twentymile Sandstone aquifer occurs in a massive, fine-grained sandstone, ranging from 100 to 200 feet thick in this area. It is laterally continuous throughout the basin and. like the Trout Creek, outcrops as a white cliff along the rim of the basin. It is under confined hydraulic pressure from shale with interbedded siltstone. sandstone, and coal above and approximately 500 to 700 feet of predominantly marine shale below. The water within the Twentymile Sandstone aquifer is also of a sodium bicarbonate type with TDS values about 300 mg/1. The alluvial aquifers exist under unconfined conditions in the shallow unconsolidated stream deposits within the floodplains of the Middle Creek. Foidel Creek, and Fish Creek drainages of Twentymile Park. The only,alluvial aquifer potentially affected by this proposed action is in Fish Creek that runs from west to east just north of Tracts A and B. Recharge to the Fish Creek alluvial aquifer is from spring snowmelt. rainfall, and a significant portion is from discharge from confined bedrock aquifers, particularly the Twentymile Sandstone and, to a lesser degree. the Wadge overburden aquifer through faults and fractures. Surface Water Fish Creek lies just north of Tracts A and B and is the only stream likely to be impacted from the proposed action. Fish Creek is a perennial stream that flows easterly into Trout Creek and then into the Yampa River to the north. Utilization of water from Fish Creek is limited to flood irrigation of crops and minor amounts of stock watering. As stated above, Fish Creek's perennial flow is thought to be a function of not only spring runoff, but also discharge to the stream from the Twentymile and Wadge overburden aquifers. According to Map 15 of the Twentymile Coal Company's mine permit application package, the Fish Creek floodplain is a designated Alluvial Valley Floor in sections 19 and 20 of T. 5N.. R. 86W.. however, the floodplain lies north of Tracts A & B. Water in Fish Creek is characterized as a calcium-sulfate-bicarbonate type with relatively high concentrations of magnesium. Upstream of . the mine disturbance. TDS values have been measured around 250 mg/l during high runoff periods and 500 mg/l during base flow periods. Near the mouth of Fish Creek. TDS values range from 200 mg/l to over