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Hydrogeological Evaluation of Sunday Mines Group <br />Geologic and Hydrologic Conditions <br />2.4.5.2 Local Groundwater Quality <br />The Sunday Mines Group is located in an area of natural metals enrichment as <br />discussed previously in Section 2.4.4. The mineral deposits that host the Sunday <br />Group mines are located in areas containing the largest natural accumulations of <br />uranium, vanadium and other associated elements. These deposits are located within <br />the upper portion of the Salt Wash Member of the Morrison Formation, which in <br />some places is saturated with groundwater. The estimated flow rate of groundwater <br />within these units is relatively slow (3.3-6.2 feet per year), and therefore groundwater <br />flow through these naturally metalliferous zones takes hundreds of years. Therefore, <br />it is likely that groundwater has equilibrated with the naturally enriched zones of <br />uranium, vanadium and other metals. Therefore, anomalous concentrations of these <br />elements in groundwater are 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 in the mining process, and although they have the potential to <br />affect equilibrium conditions, these affects are unavoidable in close vicinity of the <br />underground workings. <br />Investigation of Groundwater Quality Near the Underground Workings <br />This investigation evaluated groundwater quality in close proximity to the <br />• underground mine workings. Additional data will be collected from wells installed in <br />this investigation, and only preliminary data analyses are presented here. The , <br />primary purpose of this investigation is evaluation of ambient groundwater quality. <br />The investigation also attempted to evaluate the persistence of any mining-related <br />affects to groundwater downgradient from the underground mine workings. <br />However, this information was not obtained in the investigation as a result of the <br />proximity of the underground monitoring wells in relation to the mine dewatering <br />system, which causes groundwater to flow into the mine from all directions (i.e. no <br />downgradient groundwater is present in the area). <br />Ambient groundwater quality is defined in HRMMR 1.1(5) as follows: <br />"Ambient Groundwater Quality" for mining operations permitted prior <br />to January 31,1994, Ambient Groundwater quality shall mean the quality <br />of the groundwater at the mine site as of 1994. For mining operations <br />permitted on or after January 31, 1994, ambient groundwater shall mean <br />the quality of groundwater at the time of submittal of the permit <br />operation. In establishing ambient groundwater quality, an Operator or <br />Applicant shall use available or collected groundwater data sufficient to <br />characterize the site's ambient groundwater quality and submit such <br />information in a form suitable to the Office. <br />The Sunday Mines Group has been in existence since the mid 1950s, and the vast <br />majority of underground mine development occurred prior to 1994. It is unlikely that <br />cm 2-21 <br />T:\64986-Denison Mines\Task Order 3 - DMO Sampling and Analysis Plan\Task 3.14 - Hydrogeology Repor final sunday hydro report\texl\FINAL Sunday Hydrageology Report.doc