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• is a principal local aquifer for areas in southeastern Colorado where alluvial groundwater is not readily available (Aiken et al. eds. 2000). This aquifer unit consists of an upper sand member, the Dakota Sandstone, and a lower sand member, the Cheyenne Sandstone, sepazated by an intervening shale layer (Aiken et al. eds. 2000). The Dakota-Cheyenne Group is a confined aquifer. Cretaceous shales (impermeable confining layers) occurring above the Dakota Sandstone are shown in the Generalized Geologic Section. Limited information is available regarding the artesian conditions associated with the Dakota- Cheyenne aquifer. The static water level in a well located within T.22S. R.64W., Section 19, an estimated one mile east of the mine site, was reported to be 231 feet below the land surface, with a total depth (TD) of the well being 580 feet (Vinckier 1982). The static water level in a well located within T.22S, R.65W, Section 21, an estimated three miles west of the mine site, was reported to be 35 feet below the land surface with the well TD being 495 feet (Vinckier 1982). Local Characterization Groundwater wells permitted with the Office of the State Engineer (OSE) that are located within five miles of the proposed mine permit boundary are shown on Figure H-1. Existing surface water adjudication rights within the area are summarized in the table attached at the end of this Appendix, based on a CDWR water rights database (CDWR 2001). The mine and plant site is isolated from the Southern High Plains aquifer system and the alluvial aquifer associated with the Arkansas River and its tributaries due to the lack of continuous alluvial deposits. The alluvial aquifer is not continuous along the reach of the Saint Charles River • upstream from its confluence with the Arkansas River to the vicinity of the mine and plant site. The areal extent of the continuous valley-fill aquifer in the Arkansas River valley is an estimated 2.5 miles up the Saint Charles River from its confluence with the Arkansas River (Nelson et al. 1989). This is approximately 125 miles from the mine and plant site. The nearest alluvial and terrace deposits are exposed an estimated 1.5 miles north of the mine property. The deposits occurring along the Saint Charles River consist of poorly sorted, unconsolidated cobbles, pebbles, sand, silt and clay, 0 to 25 feet thick and up to 25 feet above the present level of the river (Scott 1969). Alluvial deposits occurring along the river, near the proposed bridge location, are very thin. The depth of alluvium in the river channel was found to range from 1.5 to 5.0 feet (West and Associates 1999). This alluvial aquifer is in hydraulic connection with the Saint Charles River. Groundwater quality near Lime, an estimated 1.5 miles northwest of the project area, was reported from one well as 681 mg/L TDS (Repplier 1981). The inferred hydraulic gradient within the mine and plant site area likely slopes downward to the north, toward the Saint Charles River, and follows the dip of the sedimentary rocks. The predominant path of meteoric waters would be lateral downslope movement to the north, toward the Saint Charles River, rather than vertically downward, into underlying strata. The Fort Hays Limestone, the mineable unit, is recognized as part of the Great Plains Confining System overlying the Dakota-Cheyenne aquifer (Aiken et al. eds. 2000). No groundwater wells completed in the Fort Hays Limestone have been identified within five miles of the proposed mine permit boundary (CDWR 2001). This fractured limestone can yield small amounts (not quantified) of poor quality water (661-6, 110 mg/L TDS) to stock wells and springs (Repplier et . al. 1981). However, test holes in the mine area drilled to depths of more than 60 feet in the limestone were dry.