Water-resources appraisal of the Camp Swift lignite area, central Texas

The Camp Swift lignite area was studied to describe the hydrogeology and to provide baseline data of the ground-water and surface-water resources that could be affected by the strip mining of lignite. The investigation was centered on the 18-square mile Camp Swift Military Reservation where a reported 80 to 100 million short tons of commercially mineable lignite occurs within 200 feet of the land surface.

Monthly ground-water levels from a network of 22 wells showed that water levels in wells in the Hooper, Simsboro, and Calvert Bluff Formations of the Wilcox Group had slight and generally insignificant waterlevel changes from May 1980 to May 1981. The water quality in the Calvert Bluff Formation, which contains the lignite, and in the Simsboro Formation, which is the major aquifer beneath the Calvert Bluff, generally is satisfactory for most uses. Hydraulic pressures in the Calvert Bluff are greater than in the Simsboro, and this pressure differential results in the potential for downward movement of water from the Calvert Bluff to the Simsboro. However, confining beds of lignite, clay, silt, and other fine-grained material at and near the base of the Calvert Bluff greatly retard this interformational movement of water but do not totally prevent downward leakage.

Data were collected from four streamflow stations and five automated rain gages to appraise the quantity and quality of the surface-water resources. Big Sandy Creek, which crosses Camp Swift, generally has a base flow of less than 0.5 cubic feet per second and infrequently is dry. Dogwood Creek, which originates on Camp Swift, normally is dry. The flow of both streams changes rapidly in response to rainfall in the watersheds. The quality of the water in both streams generally is suitable for most uses, but varies significantly in response to variations in discharge and related factors.

Alithologic examination of 255 feet of cored section that represents the overburden and the included lignite showed cyclic layering of fine sand, silt, clay, and lignite. Chemical analyses of the core were performed to determine the contents of major inorganic and trace constituents. These analyses indicate that the content of pyritic sulfur generally is small but variable.