Salt domes in the East Texas Basin are being studied as potential sites for deep burial of nuclear wastes. Site selection and risk assessment must address the possible fate of radionuclides should they escape from such a repository. Waste escaping from a dome would, at worst, move into either the Wilcox-Carrizo (Wx-Cz), a thick (~2,000 ft, 600 m), semi-confined, fresh to brackish ground-water system, or the Woodbine Formation, a deeper, saline aquifer. Contaminant transport and destinations would be controlled by: (1) pathways determined by ground-water circulation (i.e., recharge, discharge, and general velocity field), and (2) dilution along pathways, determined by advective dispersion and geochemical attenuation. Because of very large head declines in the Woodbine resulting from hydrocarbon production, potential for upward discharge from the Woodbine to the Wx-Cz appears nonexistent presently. Owing to apparently slow rates of recharge to the Woodbine, its heads may not completely recover for thousands or millions of years after pumping ends. The predominant control on regional ground-water circulation in the Wx-Cz aquifer is topography, which induces downward and upward leakage across the overlying Reklaw aquitard in topographically high and low areas, respectively. Major discharge areas are the Sabine and Trinity Rivers and their tributaries. Fluid pressure versus depth relationships indicate that upward flow components can extend as deep as 1,200 ft (365 m) beneath the Trinity River. Potential impacts of a nuclide escape from Oakwood or Keechi domes into the Wx-Cz would depend in large part on: (1) how deeply recharge occurring over each dome would move contaminants downward, and (2) whether the contaminants would then migrate upward toward discharge areas in the basin due to topographic effects. Orientation of a moderately brackish-water plume extending away from Oakwood dome infers local topographic control on flow but does not appear to. discharge upward. The plume suggests that contaminants escaping from the dome would become significantly diluted within a distance of 5 to 6 mi (9 to 11 km). Details of ground-water circulation around the domes are being analyzed through construction of numerical flow models. Processes of advective dispersion and geochemical attenuation are being investigated by preliminary mapping of aquifer heterogeneities and characterization of aquifer geochemistry by analysis of fluids and core samples. Ground-water chemistry indicates a trend toward greater capacity for attenuation of radionuclides as fluids move from recharge areas into more alkaline, reducing environments in the artesian sections of the Wx-Cz.

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