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SUNDAY MINE COMPLEX-HYDROGEOLOGIC REPORT <br /> Weir and others (1983) also presented a potentiometric surface map for the upper groundwater <br /> system. This map showed high elevations of this surface in the southeast portions of <br /> Disappointment Valley and Big Gypsum Valley and in the high mesas west of the Dolores River <br /> exceeding 6,800 ft amsl. The area of the SMC and associated ridge were shown to be of a <br /> relatively low hydraulic gradient with an elevation of approximately 5,575 ft amsl. Generally, the <br /> hydraulic gradient in the SMC area was mapped as small and flow was implied to be towards <br /> the Dolores River. <br /> 8.0 SMC HYDROGEOLOGY <br /> The hydrogeology of the SMC area has been summarized in previous reports prepared under <br /> Denison and was limited to knowledge of local and regional hydrogeology and underground <br /> observations at the mines. Key reports include: Hydrogeologic Evaluation of the Sunday Mines <br /> Group, San Miguel, Colorado (CDM 2009), and Environmental Protection Plan, Denison Mines <br /> (USA) Corp. Sunday Mines Group (CDM and Denison 2012). Both the 2009 and 2012 reports <br /> were prepared in response to a Designated Mining Operation (DMO) designation by DRMS and <br /> the 2009 report is included in the 2012 report as Attachment O. <br /> 8.1 Physical Description <br /> As partially described in the geology sections of this report and as illustrated in Figure 4-5, Local <br /> Geologic Map, the five individual mines of the SMC are driven into the northeast flank of a <br /> northwest-trending ridge that separates Big Gypsum Valley from Disappointment Valley. With <br /> the exception of the Topaz Mine, which collars in the Salt Wash Member of the Morrison <br /> Formation, the portal collars are in the Brushy Basin Member of the Morrison Formation. The <br /> mine declines have been driven downward at a gradual slope, generally down dip, to the ore- <br /> bearing portion of the Salt Wash Member. <br /> The hydrogeologic units encountered within the mine workings consist of the confining beds of <br /> the Brushy Basin Member, and the underlying Salt Wash Member aquifer, which as will be <br /> discussed later, can more accurately described as an aquitard. The Dakota and Burro Canyon <br /> (D aquifer) units overlie the Brushy Basin and outcrop to the southwest on the northeast flank of <br /> the Disappointment syncline and within Disappointment Valley. With the exception of the deeper <br /> portion of the Sunday Mine, the D aquifer is not present above the underground mine workings. <br /> The Summerville Formation, which is also an aquitard, underlies the Salt Wash and confines the <br /> underlying Entrada Sandstone, Navajo Sandstone, Kayenta Formation, and Wingate Sandstone <br /> Western Water& Land, Inc. 21 <br />