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Section 7 <br />Groundwater Information <br />The Burro Canyon Formation is underlain by the Brushy Basin member of the <br />Morrison Formation, which is a confining layer. The bentonitic shale of the Brushy <br />Basin Member restricts downward percolation of groundwater from the overlying <br />Burro Canyon Formation. The Brushy Basin Shale is underlain by the Salt Wash <br />Member of the Morrison Formation. <br />The Van 4 Mine underground workings are located within the upper portion of the <br />Salt Wash Member. Where saturated, this unit forms the Salt Wash aquifer. As <br />described previously, the Van 4 Mine underground workings are not currently <br />accessible. However, the underground workings are reported to be dry (J. Showalter, <br />Denison project geologist, personal communication 2008), which suggests that <br />saturated conditions are not present in the mine area. <br />Several features shown on the geologic cross-section (Figure 7-2) are important to <br />understanding the presence of local groundwater at the base of Burro Canyon <br />Formation, with underlying unsaturated conditions within the Salt Wash Member. <br />The Brushy Basin Member is a confining unit that occurs between the Burro Canyon <br />Formation and the Salt Wash Member. Therefore, water percolating from the surface <br />in the vicinity of the mine would be expected to migrate downward through the <br />overlying strata, encounter the Brushy Basin member, and move laterally down-dip <br />towards Bull Canyon. Recharge of the Salt Wash aquifer is therefore limited by the <br />presence of the Brushy Basin Member confining layer. <br />The Summerville Formation is a confining unit that underlies the Salt Wash Member. <br />This confining unit restricts downward migration of groundwater from the Salt Wash <br />Member into stratigraphically lower strata. Therefore, mine workings within the Salt <br />Wash Member are hydraulically isolated from the underlying Navajo aquifer. Any <br />groundwater present in the Salt Wash Member would be expected to move laterally <br />and discharge at springs near the contact between the Salt Wash Member and the <br />underlying Summerville Formation. <br />Fawn Springs is located approximately 8,000 ft southwest of the Van 4 Mine affected <br />area at the approximate contact between the Salt Wash aquifer and the underlying <br />Summerville Formation. The stream below the springs is shown as intermittent, <br />suggesting that groundwater discharges only seasonally from the Salt Wash Member. <br />This suggests that the Salt Wash Member is saturated in this area on only a seasonal <br />basis. Although groundwater is not reported within the Van 4 Mine, the Salt Wash <br />Member may be saturated in areas either beneath or adjacent to the Van 4 Mine. <br />It is unknown whether the Navajo aquifer is saturated in the area of the Van 4 Mine. <br />Sandstones hosting the Navajo aquifer are exposed in Bull Canyon within <br />approximately three miles of Fawn Springs and within five miles of the Mine (Cater <br />1954). The entire Bull Canyon drainage, extending to the junction with the Dolores <br />River, is mapped as an intermittent stream suggesting that groundwater does not <br />discharge from strata exposed in Bull Canyon in quantities sufficient to maintain <br />stream flow throughout the year. <br />7-2 <br />7164986-Denison Mines\Task Order 4 - EPP Sunday Mines Group?Van4\Van4\FINAL Report\FINAL - Environmental Protection Plan Van4.doc