Chemical characteristics of waters in Karst Formations at the Oak Ridge Y-12 Plant

Several waste disposal sites are located adjacent to or on a karst aquifer composed of the Cambrian Maynardville Limestone (Cmn) and the Cambrian Copper Ridge Dolomite (Ccr) at the U.S. Department of Energy Oak Ridge Y-12 Plant in Oak Ridge, TN. Highly variable chemical characteristics (i.e., hardness) can indicate that the portion of the aquifer tapped by a particular well is subject to a significant quick-flow component where recharge to the system is rapid and water levels and water quality change rapidly in response to precipitation events. Water zones in wells at the Y-12 Plant that exhibit quick-flow behavior (i.e., high hydraulic conductivity) are identified based on their geochemical characteristics and variability in geochemical parameters, and observations made during drilling of the wells. The chemical data used in this study consist of between one and 20 chemical analyses for each of 102 wells and multipart monitoring zones. Of these 102 water zones, 10 were consistently undersaturated with respect to calcite suggesting active dissolution. Repeat sampling of water zones shows that both supersaturation and undersaturation with respect to dolomite occurs in 46 water zones. Twelve of the zones had partial pressure of CO2 near atmospheric values suggesting limited interaction between recharge waters and the gases and solids in the vadose zone and aquifer, and hence, relatively short residence times. The preliminary data suggest that the Cmn is composed of a complicated network of interconnected, perhaps anastomosing, cavities. The degree of interconnection between the identified cavities is yet to be determined, although it is expected that there is a significant vertical and lateral interconnection between the cavities located at shallow depths in the Cnm throughout Bear Creek Valley and the Y-12 Plant area