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Adequacy Items SFIH AGRA Project E92-7075 ~~~ Page 13 i' Bi formations stratigraphically below the Fort Hays Limestone. With one exception, all the wells were completed in the Morrison, Lykins, or Lyons Formation. The one exception was completed in a black shale member of the Benton Formation. Though all these wells yield quantities of water suitable for domestic use, locally only the Lyons Formation is considered a significant aquifer (Jertldns, E., 1961). The average production rate for these local wells (wells completed in the Lyons Formation excluded) was 9 gallons per minute (gpm). The average production rate for the wells completed in the Lyons Formation was approximately 40 gpm. Geologic formations which exist between the bottom of the Fort Hays Limestone and the Lyons Formation are depicted on the generalized cross-sections on Figure 1 and 2 (see Attachment 15). The units aze the Benton Formation (alternating laminated clays, shales, and limestones), Dakota Formation (shales and sandstones), Morrison Formation (claystones, siltstones and limestones), Entrada/Jelm Formation (sandstone), and the Lykins Formation (siltstone, shale, and limestone). This constitutes approximately 1,500 feet of geologic strata (Master, C.D. 195'n which are typically effective barriers to the movement of ground water in the area of the mine site. The low well yields from the formations lying above the Lyons Formation (9 gpm) support the probability that the formations which support local domestic ground water wells are completed have low transmissivities and resultant small radius of influences within each unit. • The mine dewatering will occur in the lower portion of the Fort Hayes Formation which is stratigraphically above the local domestic wells. Since the mine dewatering well will be completed in the lower portion of the Fort Hays Formation which is stratigraphically above and separated by aquitards from the existing wells, it was not deemed necessary to conduct computer modeling in a series of poor producing units with known minimal historic use in this azea. This fact is substantiated by the fact that the nearest well is approximately 1,000 feet from a northern terminus of the mine property. For the past 25 years or so, the mining operation has dewatered the limestone by pumping the Fort Hays Formation locally with no discernable impact on any of the significant bedrock aquifers in the azea. In addition, here has been no reported impact on any wells completed in the low transmissivity units between the lower Fort Hays Formation and the significant aquifers around the plant site. The pit will be dewatered as is currently being done at the Lyons Quarry by pumping from open sumps. Since the existing and proposed mine sites aze relatively close together and in similaz geologic settings, the decision not to conduct extensive computer modeling was based on a dewatering performance with a 25-year history. ~^ A G R A Eerth & Environments/Group