Comments on Geologic Parameters
10 Fluid Residence Time:
Few data are available to determine fluid residence times in the Tuscaloosa Group in the Mobile area. Miller (1990) generally described ground-water flow through the Black Warrior River aquifer (Tuscaloosa Group). He determined that water infiltrates from the surface outcrop belt into the Tuscaloosa Group. The ground water generally flows downdip toward the coast. Miller (1990) determined that the increase in dissolved solid concentration (DSC) in the subsurface water with depth (that is, distance downdip from the outcrop area) is a direct function of fluid residence time. In addition, Miller (1990) concluded that as the ground water encounters the marine water beneath the coastal zone, stagnant conditions prevail. Because the ground water in the Tuscaloosa Group is highly saline (Alverson, 1970; Tucker and Kidd, 1973; Miller, 1990), we determined that the ground water in the Mobile area has protracted residence times. Tuscaloosa ground water in the Mobile area is perhaps as old as 18,000 yr. At that time sea level was about 120 m lower than the present level, the shoreline was near the present shelf edge, and ground-water flow in the Tuscaloosa Formation (in the Mobile area) was more active and not influenced by the marine saltwater wedge. We used a modified version of the Black Warrior River ground-water-flow map of Miller (1990) to describe fluid residence times in the GIS.
Alverson, R. M., 1970, Deep well disposal study for Baldwin, Escambia and Mobile Counties, Alabama: Alabama Geological Survey, Circular 58, 49 p
Miller, J. A., 1990, Ground water atlas of the United States-segment 6, Alabama, Florida, Georgia, and South Carolina: U.S. Geological Survey, Hydrologic Investigations Atlas No. HA-730-G, 28 p.
Tucker, W. E., and Kidd, R. E., 1973, Deep-well disposal in Alabama: Alabama Geological Survey, Bulletin 104, 229 p., 4 plates.