NUCLEAR FACILITIES IN THE OAK RIDGE RESERVATION: INFLUENCES OF BEDROCK GEOLOGY AND STRUCTURE ON SITING AND 50+ YEARS OF PERFORMANCE

The Oak Ridge Reservation (ORR), located in the Appalachian Valley and Ridge (V & R) is most geologically complex of the Department of the Energy (DOE) sites. Three nuclear facilities were built during World War II, two (K–25 and Y–12) for isotope separation and weapons production, and a third (X–10, Oak Ridge National Laboratory, ORNL) primarily for research. Each was located in a separate valley for safety reasons. V & R topography played a role in siting facilities. Geology consists of SE-dipping Cambrian and Ordovician clastic and carbonate rocks repeated by several major NW-vergent thrusts. Sandstone and cherty carbonate rocks form ridges, and shale and limestone underlie valleys. The first waste disposal was in Ordovician limestone at ORNL. It was also recognized that shale would absorb and immobilize many dissolved radionuclides, so additional low-level waste disposal was in the Cambrian Consasauga Shale. Highly contaminated liquid nuclear waste has been disposed of in Conasauga Shale by several methods, including seepage pits and trenches (1950’s) and deep-well injection (1960’s-1980’s). Organic compound, heavy metal, and radionuclide contamination exists in parts of the ORR. Some contaminants migrated off site into the Tennessee River, and have been detected at Chattanooga, TN. Ground water systems do not form classic aquifers, inhibiting use of computer-based transport models, but hydrostratigraphic units have been defined that correspond to major clastic and carbonate units. The Knox Group was designated an aquifer because of its widespread karst development and subsurface dissolution enhancement of fracture aperture. Attempts to employ the diverse contaminants, whose sources and times of introduction into the environment are often known, for research directed toward increased ability to model ground water pathways and movement rates in this complex geologic setting have mostly not occurred. Perhaps justifiably, greater funding priority has emphasized contaminated area remediation. The new Spallation Neutron Source was located on a ridge top underlain by pinnacled Knox Group karst creating problems in foundation excavation and stabilization. Overall, the original location and disposal concept have performed reasonably throughout the history of the ORR, and the large contamination problems are gradually being remediated.