Geohydrology of the Keechi, Mount Sylvan, Oakwood, and Palestine salt domes in the northeast Texas salt-dome basin

Abstract

The U.S. Department of Energy is considering the feasibility of using salt domes in the northeast Texas salt-dome basin as repositories for radioactive wastes that may require complete confinement for as much as 250,000 years. Four of fourteen known shallow piercement salt domes within the basin--Keechi, Mount Sylvan, Oakwood, and Palestine Salt Domes—have been selected as candidate domes for further study and possible selection as storage sites. The salt within these domes has penetrated as much as 20,000 feet of Mesozoic and Cenozoic strata, and presently .extends to within 120 to 800 feet of the land surface. The salt penetrates or closely underlies major freshwater and salinewater aquifers within the basin. To provide a safe repository for radioactive wastes within one or more of these domes, a thorough understanding of the geohydrology needs to be obtained, and the hydrologic stability of the domes needs to be established for the expected life of the storage facility. Dissolution may exist at all four candidate salt domes, possibly through contact with Cretaceous or Tertiary aquifers, or through fault systems in the vicinity of the domes. Strata overlying and surrounding Palestine and Keechi Salt Domes have been arched into steeply-dipping folds that are complexly faulted. Similar conditions exist at Oakwood and Mount Sylvan Domes, except that the Tertiary strata have been only moderately disturbed. Cap rock, which is generally accepted to be an indication of salt dissolution, is present in varying amounts over all four domes. Salinewater has been reported at the surface at all candidate domes except Oakwood, but only two water wells near the domes yield water containing possible anomalous concentrations of dissolved chloride--one at Keechi and one at Oakwood. Possible subsurface plumes of salinewater, which are indications of instability, exist at all four domes. Additional problems concerning the hydrologic stability of Oakwood and Palestine Salt Domes have resulted from the disposal of oil-field salinewater in the cap rock at the Oakwood Dome and previous solution mining of salt at the Palestine Dome Additional investigations are needed to determine if a selected dome is hydrologically stable. Needed investigations include: (1) A more complete comparative analysis of the regional and local geohydrologic system; (2) a site-specific drilling and sampling program to analyze the cap rock-aquifer boundary, sediment distribution, hydraulic-parameter variations, hydraulic-head relationships, and hydrochemical patterns; and (3) mass-transport computer modeling of ground-water flow at the domes.