Sources of Salinization of the Baton Rouge Aquifer System, Southeastern Louisiana

摘要

A major environmental and economic problem confronting the Baton Rouge area, southeastern Louisiana, is the progressive salinization of the Baton Rouge aquifer system, an important source of municipal and industrial groundwater. Identifying the sources of the saline waters is essential in developing plans for managing this resource. It has been proposed that the saline fluids have migrated vertically up the Baton Rouge fault from depth. However, spatial variations in formation water salinity calculated from a large number of spontaneous potential-resistivity logs support the alternative hypothesis that there has been lateral, density-driven migration of shallow saline waters northward from above the St. Gabriel salt dome toward the Baton Rouge fault. Plumes of saline water, perhaps from the expulsion of over-pressured fluids, extend vertically upward above the top of salt all the way to the water table. Highly saline water has migrated to the northwest from St. Gabriel in the lower part of the Mississippi River alluvial aquifer, and there is a more diffuse brackish zone below this to a depth of 3000 ft (914 m) where there has been mixing of saline waters from St. Gabriel to the south with topographically-driven fresh meteoric waters from Baton Rouge aquifer sands to the north. We thus conclude that the sources of salinization are to the south and not below the Baton Rouge aquifer system. Although the presumed anisotropy in permeability of the Baton Rouge fault zone should have favored flow vertically up the fault over flow perpendicular to the fault, the large density contrast between the fresh and brackish waters above a depth of 3000 ft (914 m) with the more highly saline waters below may have inhibited this.