DEEP CIRCULATION OF METEORIC WATER IN CARBONATES IN EAST TENNESSEE: IS THIS A 50 M.Y. OLD GROUNDWATER SYSTEM THAT IS STILL ACTIVE?

Oak Ridge, TN, hydrogeology is characterized by complicated settings and some of the most exotic mixed contaminants anywhere. The geology is that of the Valley and Ridge and early Paleozoic carbonates and clastic sediments form both valleys and ridges. Although much has been done to investigate ground-water, until relatively recently most work has been within the confines of the ORR and in most cases only at moderate depths (100 - 200 m bls) with the deeper wells being characterized by more saline waters or brines. At the boundaries of the Department of Energy Reservation (ORR) the Clinch River has been considered to be a barrier to ground-water flow. However, data from some of the deeper ORR wells show contamination and meteoric water is mixing with saline water and there are signs of flow. Offsite wells also show ORR-related signatures, but a problem both on and off the reservation is that there are few deeper wells available for sampling. In contrast, deep drilling mostly in carbonates elsewhere in the Valley and Ridge in East Tennessee and in the flanks of the Nashville dome has penetrated fresh water at more extreme depths (600 m - 1500 m bls). Conduit tier spacing in Valley and Ridge carbonates is calculated to be in the range of ~ 90 m. Tracing between wells at the ORR northeast boundary, geomorphological and contamination data support the 90 m value. However, there are conflicting concepts: (1) that discharge of all ground water is shallow and to the Clinch River, and (2) that long-established ground water flow paths underflow the Clinch River. We believe the latter. At the Gray Fossil Site, to the northeast, Paleocene – Miocene sediments are preserved in deep pockets in a karst landscape. The landscape must be older, and is possibly 90–65 m.y. old. An areally extensive sediment cover would have preserved the underlying karst. During the Miocene and Pliocene, significant erosion is evident from increased sedimentation in the Atlantic and Gulf of Mexico with several km of sediment being removed. Also, 20 ka BP sea level was 130 m lower than present and presumably causied accelerated downcutting and deepening of the flow system.