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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 an area of natural metals enrichment. The <br />mineral deposits that host the Sunday Mines Group are located in areas containing <br />the largest natural accumulations of uranium, vanadium and other associated <br />elements. These deposits are located within the upper portion of the Salt Wash <br />Member of the Morrison Formation, which in some places are saturated with <br />groundwater. The estimated flow rate of groundwater within these units is relatively <br />slow (3.3-6.2 feet per year), and therefore groundwater flow through these naturally <br />metalliferous zones takes thousands of years. Therefore, it is likely that groundwater <br />has equilibrated with the naturally enriched zones of uranium, vanadium and other <br />metals. Therefore, anomalous concentrations these elements in groundwater are <br />expected. <br />Mining processes such as tunneling, excavating rock, and ventilating the <br />underground workings may affect the concentration of metals in groundwater. These <br />activities are inherent parts of the mining process, and although they have the <br />potential to affect equilibrium conditions, these affects are unavoidable in close <br />vicinity of the underground workings. <br />• <br />8-1 <br />T:\64986-Denison Mines\Task Order 4- EPP Sunday Mines GroupTINAL EPPTINAL - Environmental Protection Plan Sunday Mines.doc