HR: 13:45h
AN: H13C-02    [Abstracts]
TI: Saltwater Sources for Saltwater Intrusion in Shallow Aquifers in South Louisiana
AU: * Stoessell, R K
EM: ronlondi@charter.net
AF: University of New Orleans, Department of Geology and Geophysics, New Orleans, LA 70148 United States
AU: Prochaska, L
EM:
AF: University of New Orleans, Department of Geology and Geophysics, New Orleans, LA 70148 United States
AB: Shallow southward-dipping Quaternary and Upper Neogene aquifers across South Louisiana are used as sources of freshwater. Local accumulations of brackish waters occur within these aquifers on the north shore of Lake Pontchartrain, in the Baton Rouge area, in Southwest and South-central Louisiana, and in the New Orleans area. The low Br/Cl ratios, high Na/Cl ratios, low K/Cl ratios and low ⁸⁷Sr/⁸⁶Sr ratios in these brackish waters form linear mixing trends which are inconsistent with the saline-water sources being in situ marine formation fluids of similar age. Extrapolation of these ratios to fluids of high salinity suggests the saline-water sources are Lower Neogene or Paleogene marine formation fluids that dissolved halite. South Louisiana overlies the deep Jurassic Louan salt, which is the source of salt diapirs. The region is cut by a series of east-west trending gravity faults with southward-dipping fault planes. Deeper migrating formation fluids are hypothesized to be dissolving halite through contact with salt diapirs and moving up fault planes to enter shallow aquifers and mix with the in situ groundwaters. High freshwater withdrawal rates are accelerating this process, causing updip movement of the shallow saltwater fronts, e.g., within the Pliocene and Upper Miocene Baton Rouge aquifers and in the Pleistocene Lake Charles "500-foot" sand. Conversely, the absence of significant freshwater withdrawal has apparently caused a static saltwater front, e.g., in the Pliocene Big Branch Aquifer on the north shore of Lake Pontchartrain.
DE: 1040 Isotopic composition/chemistry
DE: 1045 Low-temperature geochemistry
DE: 1829 Groundwater hydrology
DE: 1831 Groundwater quality
DE: 1832 Groundwater transport
SC: Hydrology [H]
MN: 2005 Joint Assembly