2009-05-19_REVISION - M1981021 (36)

Home Browse Search

7.0 Groundwater Information The local hydrogeologic framework is relatively complex as a result of structural displacements associated with the Gypsum Valley anticline, the Disappointment Valley syncline and associated faulting and folding. The Mesozoic aquifer and the lower portion of the Tertiary to Upper Cretaceous aquifer are present in the general vicinity of the Sunday Mines Group. The following sections provide additional detail regarding the local hydrogeologic framework. The groundwater investigation, Groundzaater Cliaracterization Data Collection Work Plan, to Address Designated Mining Operations (DMO) Status, Sunday Mines Group (CDM 2008e), is presented in Attachment N. Additional information regarding regional and geology is discussed in the Hydrogeological Evaluation of Sunday Mines Group, included as Attachment O. 7.1 Local Geologic Framework This section focuses on aspects of the local geologic framework that are pertinent to understanding the hydrogeologic framework of the mine areas. This discussion includes descriptions of rock units underlying affected areas of the mines, and the location of faults that could influence movement of water in the subsurface. Details regarding the hydrogeologic framework of the areas are included in a subsequent section of this document, Section 7.2. The geologic framework in the affected areas of the Sunday Group mines is depicted on the geologic map included as Figure 7-1 and on geologic cross-sections included as figures 7-2 through 7-5. 7.1.1 Sunday and Carnation Mines The affected area of the Sunday and Carnation Mines are shown on Figure 7-2. The affected area of the mine lies on the Brushy Basin Member of the Morrison Formation, which is composed primarily of bentonitic shale. Several faults are present in the mine area. One of the faults is present near the northern edge of the affected area, which displaces Brushy Basin Member downward towards Big Gypsum Valley. A marked variation in the orientation of the rock units is apparent between the fault blocks, with steep northerly dipping rock units present in the eastern portion of the section. This structural orientation exhibits the collapse of clastic sedimentary units into the central portion of Big Gypsum Valley. 7.1.2 St. Jude Mine The local geology in the area of the St. Jude mine affected area is shown in Figure 7-3. The affected area of the mine also overlies the Brushy Basin Member of the Morrison Formation. Three faults are present on the section with downward displacement of rocks towards Big Gypsum Valley. These faults form several fault bound blocks of sedimentary rocks in the general vicinity of the mine affected area. Folding, faulting and collapse of rock units into the central portion of the valley is evident, which is also associated with collapse of clastic sedimentary rocks into the central portion of Big Gypsum Valley. 7-1 T:\84986-Denison Mines\Task Order 4 - EPP Sunday Mines Group\FINAL EPP\FINAL - Environmental Protection Plan Sunday Mines.doc