Playa Basin Fills Near the Pantex Plant- Stratigraphic and Geomorphic Analysis

Playa basins on the Southern High Plains pond water and focus recharge to the Ogallala aquifer. Cores of the sedimentary fills of six of these basins near the Pantex Plant, northeast of Amarillo, have been examined to identify (1) the types of sediments beneath the floors of playa lakes, (2) the relative permeabilities of these sediments, (3) the geometries of playa lake clays and interbedded and interfingering facies, and (4) potential flow paths through the clays. This report focuses on core data rather than exposures because (1) core recovery was excellent, whereas most exposures have been degraded, (2) cores penetrate to greater depths than most exposures, (3) playas cored are close to the Pantex Plant, and (4) core data can be integrated with hydrologic and geochemical test results.

Basin sediments have been examined by drilling 30-m-deep hollow-stem auger cores in a suite of playas and corresponding interplaya areas in a variety of geomorphic settings adjacent to the Pantex Plant (Fig. 1). To date, 41 cores totaling 766 m (2513 ft) of section from six playa basins adjacent to the Pantex Plant have been collected (Table 1). Playa basins were selected to examine a spectrum of geomorphologic characteristics and flooding histories. Playas examined are: (1) Seven Mile Basin located south of US 60 south of the Pantex Plant; (2) Wink playa basin located outside the west gate of the Pantex Plant; (3) TDCJ playa north of Pantex Lake; (4) Koesjan playa west of Pantex playa 5, (5) E. Vance playa, east of the east gate of the Pantex Plant, and (6) Finley playa in Armstrong County (Fig. 1). Seven Mile Basin is a large basin with a playa that has not been flooded during the past year. Wink, Koesjan, and TDCJ playas are average size playa basins with lakes that were flooded above the rim during the late summer of 1992, but playa lake levels dropped during the winter of 1993 and permitted coring of playa sediments. The E. Vance playa is in a composite of two basins and the Finley playa is in a shallow basin; both have been mostly dry during 1992-1993.