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• The Dakota-Cheyenne aquifer is a source of water for domestic, livestock, and industrial supplies <br />in areas where drilling depths and pumping levels are economically feasible and water quality is <br />acceptable (Aiken et al. eds. 2000). Repplier et al. (1981) report TDS concentrations to be 140- <br />1,800 mg/L. Complex stratigraphy is responsible for the non-uniform water chemistry of this <br />aquifer unit (Aiken et al. eds. 2000). <br />Three groundwater supply wells for this project have been permitted by the OSE, Well Pormit <br />Nos. 057033, 057034, and 057035 (OSE 2002). Conditions of Approval for these wells contain <br />the following provisions: the allowed average annual amount of groundwater appropriated by <br />these three wells (in total) is 228.3 acre-feet; the maximum pumping rate on each well will not <br />exceed 180 gpm. . <br />CONCLUSIONS <br />The proposed activities are not expected to have measurable effect on groundwater resources. The <br />discussion below provides salient information to support this conclusion. <br />Within the project area and nearby areas along the Saint Charles River, precipitation evaporates, <br />is transpired by plants, contributes to runoff, or is retained as soil moisture. Recharge potential <br />would be highest when excess soil moisture is maintained during the slow melting of a winter <br />snowpack or during an extended period of winter rainfall. Rare intense storm events would result <br />in more surface runoff than storm events of lower intensity or duration. No alluvial groundwater <br />recharge from surface flows likely occurs outside wetted perennial stream channels. Limited soil <br />moisture supports the sparse vegetation growing in arroyos. These conclusions are consistent with <br />the discussion for this region that is contained in Robson and Banta (1995). <br />Any precipitation falling on the area affected by the project and infiltrating the land surface <br />would not be likely to reach any surface drainage (as groundwater discharge) . It is unlikely that <br />noticeable or measurable quantities of meteoric water would infiltrate the Fort Hays Limestone at <br />the mine site, move downslope toward the Saint Charles River, and discharge to the alluvial <br />deposits occurring along the river. If any shallow groundwater from the mine site did eventually <br />reach the alluvial deposits along Saint Charles River, it likely would be of better quality than the <br />existing quality of the river. For comparison, supplemental information on the existing quality of <br />surface water in the Saint Charles River and the Arkansas River is included in a later section of <br />this appendix. <br />No measurable amount of meteoric water or water used for dust control would infiltrate the <br />limestone or sandstone occurring in the mine area, providing only an extremely small opportunity <br />for contaminants to enter the groundwater. Water for dust control is applied in ]ow quantities only <br />to bind small soil particles, such that runoff rarely, if at all, occurs. <br />The likely path of meteoric waters is not vertically downward into the confined aquifers. <br />Intervening shale layers between the Fort Hays Limestone and the Dakota Sandstone would limit <br />any meteoric water infiltrating the sedimentary rocks, isolating the Dakota-Cheyenne aquifer <br />from meteoric waters. The Dakota-Cheyenne aquifer occurs at depths varying between 525 to 700 <br />feet below the ground surface in the mine permit area (OSE 2002). <br />OSE well construction rules contain the following objectives for protection of groundwater <br />. resources: maintain existing natural protection against pollution of aquifers; prevent the entry of <br />