BRING YOUR TOWEL, AND DON’T PANIC: THERE COULD BE LONG, DEEP FLOW PATHS BENEATH APPALACHIAN BRINES

Historical work on the Manhattan Project at the U.S. Department of Energy Oak Ridge Reservation has resulted in a legacy of initially buried, now capped and regulated waste. Downgradient domestic wells that could be connected via groundwater pathways to waste disposal areas on the Oak Ridge Reservation are being sampled in an effort to ensure public safety and protection of the environment. Additional data are being collected upgradient of the reservation to establish background parameters. Our methods include groundwater fingerprinting (Ca, Mg, Na, K, Cl, SO4, HCO3, CO3), using the calcite saturation index, uranium-series isotopes, stable isotopes (2H, 18O in water; 15N, 18O in nitrate), as well as an appropriate suite of contaminants. From the data we have constructed a conceptual model based on the fingerprint and persistence of meteoric groundwater revealing a system where there is rapid recharge and deep flow of meteoric waters, as was shown by Nativ et al. (1997) in deep wells on the reservation. This is also consistent with work in carbonates and often in clastic rocks (Worthington et al., 2016). The Lower Paleozoic (Cambrian – Mississippian) carbonate and clastic rocks were pathways for deep migration of brines > 380 Ma, but subaerial exposure and weathering have advanced meteoric water recharge to considerable depths. Karst and paleokarst persist to great depth in the Knox Group, perpetuating this influx and circulation of meteoric water. Several kilometers downgradient from the Oak Ridge Reservation is a borehole with a Chickamauga Group Witten Limestone interval continuously discharging contaminated groundwater below an Appalachian-type brine from a carbonate interval >165 m below the water table. Potential depth of circulation below the water table is hundreds of meters suggesting that contaminants can migrate beneath the present day (late Cenozoic exhumed) 7 – 5 m.y. old landscape profile and the superposed Clinch and other rivers.