Hydrogeologic and Hydrochemical Properties of Salt-Dissolution Zones, Palo Duro Basin, Texas Panhandle: Preliminary Assessment

Ground water that moves downward from aquifers in clastic rocks of the Triassic Dockum Group and Neogene Ogallala Formation dissolves bedded halite and anhydrite in the Upper Permian evaporite section along the perimeter of the Southern High Plains in the Texas Panhandle. Ground-water velocity in salt-dissolution zones beneath the Canadian River valley and Rolling Plains may be greater than ground-water velocity in salt-dissolution zones beneath the Southern High Plains because of greater hydraulic conductivity and greater hydraulic-head gradient. Hydraulic conductivities measured at two test wells in salt-dissolution zones beneath the Canadian River valley and Rolling Plains are 0.7 and 1.6 ft/d (0.2 to 0.5 m/d), much larger than hydraulic conductivities of 2 × l0-4 to 0.03 ft/d (6 × 10-5 to 0.007 m/d) measured at another test well in salt-dissolution zones beneath the Southern High Plains. Inferred differences in flow rate correspond to differences in salinity and probably account for some variation in halite dissolution rate. The Na-Cl ground waters in salt-dissolution zones beneath the Rolling Plains and Canadian River valley are probably no older than 16,200 and 23,500 yr, respectively. Salinity of this ground water 33 to 46 ft (10.1 to 14.0 m) above the uppermost halite beds ranges from 68,000 to 95,000 mg/ L; the water is undersaturated with respect to halite but saturated with respect to gypsum. Age of ground water in salt-dissolution zones beneath the northern part of the Southern High Plains has not been determined. Salinity of ground water there is 288,000 mg/ L because of dissolution of evaporite minerals; organic-acid anions, not dissolved bicarbonate, account for alkalinity. Additional wells in the salt-dissolution zones and further hydrologic testing and geochemical sampling are needed to completely evaluate the timing and rate of salt dissolution in the northern part of the Southern High Plains.