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Section 8 <br />Groundwater Quality <br />8.0 Groundwater Quality <br />8.1 Regional Groundwater Quality <br />Groundwater quality data for hydrogeological units within the Alluvial, Dakota, Salt <br />Wash and Navajo aquifers is summarized in Table 8 -1 based on regional data <br />provided by Weir et al. (1983). Water quality characteristics vary between the <br />hydrogeological units. General groundwater quality characteristics include the <br />following: <br />• Groundwater from alluvial aquifers has moderate to high concentrations of <br />total dissolved solids (TDS), chloride and sulfate with neutral pH; <br />• Groundwater from the Dakota aquifer has high concentrations of TDS, <br />chloride and sulfate with neutral pH; <br />• Groundwater from the Salt Wash aquifer has moderate concentrations of TDS, <br />chloride and sulfate with neutral pH; and <br />• Groundwater from the Navajo Aquifer varies with depth and hydrogeological <br />unit. Groundwater from depths of less than 500 ft. has moderate to high <br />concentrations of TDS, chloride and sulfate, with moderate to slightly alkaline <br />pH. Groundwater from depths of greater than 500 ft has very high <br />concentrations of TDS, sulfate and chloride, and slightly alkaline pH. <br />8.2 Local Groundwater Quality <br />The Sunday Mines Group is located in the Uravan mineral belt, an area hosting one of <br />the strongest natural concentrations of uranium and vanadium in the United States. <br />The ore deposits that are mined at the Sunday Mines Group are some of the highest <br />grade rocks in the Uravan mineral belt. Other naturally occurring elements such as <br />arsenic, molybdenum and selenium are also elevated in these areas. <br />These ore deposits are located within the upper portion of the Salt Wash Member of <br />the Morrison Formation, which in some places is saturated with groundwater. The <br />estimated flow rate of groundwater within these units is relatively slow (3.3 -6.2 feet <br />per year), and therefore groundwater flow through these naturally metalliferous <br />zones takes thousands of years. Therefore, it is likely that groundwater has <br />equilibrated with the naturally enriched rock, which contains elevated concentrations <br />of uranium, vanadium and other naturally occurring elements. Therefore, anomalous <br />concentrations of these elements in groundwater are expected. Mining processes such <br />as tunneling, excavating rock, and ventilating the underground workings may also <br />affect the concentration of metals in groundwater. These activities are inherent parts <br />of the mining process, and although they have the potential to affect equilibrium <br />conditions in close vicinity to the underground workings, these affects are <br />unavoidable. <br />C \ Users\ cwoodwardiDesl¢op\Sundays\FINAL - Environmental Protection Plan Sunday Mines Revised January 2012 do s <br />8 -1 <br />