2012-09-28_REVISION - M1977307 (23)

Home Browse Search

increasing amounts of uraninite in deeper deposits began to raise a valence problem. The possibility began to develop that uraninite is an early uranium mineral and that carnotite is an oxidation product - the result of weathering (Garrels and Christ, 1965). Hostetler and Garrels (1962) used Eh -pH diagram to illustrate the conditions under which uranium might be transported in underground waters in the presence of vanadium. The diagrams show for conditions of groundwater with a pH greater than 2 and oxidizing conditions, carnotite is stable and the dominant mineral. Several other studies suggest that uranium minerals, especially minerals that contain vanadium, are relatively insoluble including carnotite. 8.6 Mobilization of Uranium Related Constituents With an understanding of the site geology, hydrology, and geochemistry, a scenario of possible mobilization and transport of uranium and related constituents needs to be developed to design an effective monitoring strategy. Mining would disturb the uranium deposits by introducing oxygen into reduced mineralized zones. It is possible that changes in redox conditions could mobilize uranium related constituents but the geochemistry indicates that only limited amounts could be mobilized due to the low solubility of these uranium minerals. The lack of groundwater in the area further prevents a viable pathway for the transport of these constituents. If groundwater was encountered in sufficient quantities to transport the uranium and related constituents (all hydrologic data suggests this is not the case), then groundwater in the upper Salt Wash sandstone would migrate down dip toward the syncline between the Paradox and Uncompahgre uplifts and toward the San Miguel River. Kearl (2005) conducted transport modeling studies to estimate the transport of mineral constituents associated with uranium ore deposits at the SM -18 Mine, approximately 2 miles to the north. These studies assumed that the Entrada Sandstone was the upper most aquifer in the area. A conservative approach consistent with the Nuclear Regulatory Commission requirements for high -level nuclear waste sites was used to develop a worst - case scenario - not necessarily the most likely scenario. Even under the worst case conditions, the modeling predicted that after 1000 years, uranium related constituents migrated approximately 200 feet vertically at a concentration of 10 -6 (1 /1,000,000 of the source concentration) of the initial concentration in the pore water of the waste rock. The uranium plume is contained in the Salt Wash Member of the Morrison Formation. The plume does not enter the Entrada Sandstone. The Summerville Formation provides an additional buffer zone restricting potential contamination from entering the groundwater. The limited well data for the area suggests that the Entrada Sandstone is dry and the Wingate Sandstone is the upper most aquifer. With the low permeability values measured in the Peel Engineering study for the Kayenta Formation that overlies the Wingate Sandstone, there is even less likelihood of uranium mining impacting valuable local groundwater resources. The results of this analysis indicate that conditions are not conducive to the transport of uranium related constituents to the environment. Geochemistry suggests that O'Connor Design Group Inc. T - 15