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Christy Woodward <br />September 17, 2008 <br />Page 13 <br />¦ Estimate hydraulic conductivity of the Top Rim sandstone, which is a geologic unit within <br />the Salt Wash Member of the Morrison Formation; <br />¦ Develop a conceptual hydrogeological model based on data collected in this work plan and <br />existing published data to evaluate potential migration of groundwater including <br />"estimation of the direction and rate of groundwater flow. <br />¦ Report Preparation <br />Evaluation of Ambient Water Quality <br />The evaluation of ambient water quality will be based on samples collected from the <br />upgradient monitoring wells. The purpose of collecting ambient growid water quality data is <br />to understand naturally occurring geological and geochemical conditions, and the affect that <br />these conditions cause to groundwater quality. <br />These monitoring wells are designed to provide a sample of groundwater from a distance of <br />approximately 100 feet upgradient from the mine workings: These'wells will be sampled for <br />the analyte list shown in Table 2, which includes analytes that are necessary from a regulatory <br />perspective as well as tritium, which is an isotope of hydrogen. The purpose of the <br />regulatory-based analytes is to evaluate ambient groundwater quality in relation to <br />potentially applicable standards. <br />The purpose of the tritium analysis is to age d?ite the water, which will provide information <br />regarding the degree of connection between the surface water and groundwater systems, and <br />the extent to which underground mining has affected groundwater. Tritium is the heavy <br />isotope of hydrogen (3H). It occurs naturally in the atmosphere; however atmospheric <br />thermonuclear weapons testing that occurred between 1952 and 1963 overwhelmed the <br />naturally occurring concentration of this isotope. Water that has equilibrated with the <br />atmosphere since 1952 contains elevated levels of tritium. Water that has not equilibrated <br />with the atmosphere during the period since 1952 contains very low levels of tritium <br />(Domenico and Schwartz, 1990). <br />The Sunday Mines Group was first developed in the 1950s, and mine ventilation as well as <br />natural barometric. pumping of air into the mines resulted in exposure of mine water to <br />atmospheric concentrations of tritium. Therefore, if tritium concentrations in upgradient <br />groundwater are very low, it supports an interpretation that this water has not interacted <br />with the underground mine workings. If tritium is present in the upgradient wells, it does not <br />necessarily prove that the water is not ambient because surface water may have infiltrated <br />into the aquifer since 1952. But the local hydrogeological framework of the Brushy Basin <br />Member of the Morrison Formation (shale) overlying the Top Rim Sandstone unit suggests <br />that the water currently encountered in the underground workings may be very old. <br />Therefore isotopic age dating of the water using tritium may be an effective tool to support <br />evaluation of ambient water quality using the sub-surface monitoring wells.