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Hydrogeological Evaluation of Sunday Mines Group <br />Geologic and Hydrologic Conditions <br />salt originally present in the rock unit has dissolved and been dispersed in the <br />environment. Enrichments of sodium, potassium, and sulfate are expected in this area <br />as a result of dissolution and geochemical dispersion of rock salt and gypsum. This <br />area is host to several plant species that inhabit this uncommon salt-rich ecosystem <br />(BLM 2008). It is likely that the high natural salinity also contributes to increased <br />salinity in the Dolores River in a similar manner to the documented effects of salt <br />dissolution on surface water quality in the Paradox Valley area (Chafin 2002). Natural <br />enrichments of other elements such as selenium, which is geochemically associated <br />with sulfate enrichment, are also likely in the area. Natural evaporative concentration <br />of sulfate and selenate salts would also be expected in the and environment of Big <br />Gypsum Valley. <br />The Sunday Group Mines are located within the larger Uravan Mineral District, and <br />natural enrichments of uranium, vanadium and other metals are present in the area. <br />Although the Sunday Group deposits are largely sub-surface, outcropping uranium- <br />vanadium mineralization is present in numerous locations within the Big Gypsum <br />Creek watershed (e.g. Cater 1955). Other elements that are associated with naturally <br />occurring uranium-vanadium enrichment include arsenic, molybdenum, selenium, <br />lead, and copper (Rose et al, 1979). <br />2.4.5 Groundwater Quality <br />• 2.4.5.1 Regional Groundwater Quality <br />Groundwater quality data for hydrogeological units within the Alluvial, Dakota, Salt <br />Wash and Navajo aquifers is summarized in Table 2-5 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 total <br />dissolved solids, chloride and sulfate with neutral pH; <br />¦ Groundwater from the Dakota aquifer has high concentrations of total dissolved <br />solids, chloride and sulfate with neutral pH; <br />¦ Groundwater from the Salt Wash aquifer has moderate concentrations of total <br />dissolved solids, chloride and sulfate with neutral pH; <br />¦ Groundwater from the Navajo Aquifer varies with depth and hydrogeological unit. <br />Groundwater from depths of less than 500 ft. has moderate to high concentrations <br />of total dissolved solids, chloride and sulfate, with moderate to slightly alkaline <br />pH. Groundwater from depths of greater than 500 ft. have very high concentrations <br />of total dissolved solids, sulfate and chloride, and slightly alkaline pH. <br />0 <br />cm 2-20 <br />7:\84986-Denison Mines\Task Omer 3 - DMO Sampling and Analysis Plan\Task 3.14 - Hydrogeology ReponUnal sunday hydro reponVextTINAL Sunday Hydrogeology Report.doc