Ground water geochemistry in the Baton Rouge area is intimately related with the hydrology of the region. Chemical character of the ground water is a function of several physico chemical processes, principal among them are ion exchange, f i l t r a tion due to clay compaction, mineral s o lu b ility and mixing of the w aters. Two genetic types among the ground water have been recog nized, (i) Chloride water, contains usually high to ta l dissolved so lid s, (ii) Bicarbonate water, which is a

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... ge complex group of fresh waters. Hydrochemical facies defined on the basis of ionic abundances are especially useful in interpreting the geochemical hydrology of the area. Sixteen different cation and anion com binations were used in defining the hydrochemical fac ies. Chloride water is considered a mixture of diagenetically altered sea or estuarine water with fresh water. The chloride waters have originated from the d ilu tio n of orig in al trapped salty water by fresh waters. Sodium dominant bicarbonate water is the resu lt of ion exchange and membrane f il tr a ti o n . Membrane f iltr a tio n is the most active in the area of maximum land surface subsidence. The Ca and Mg dominant bicarbonate waters a t shallower depths are principally due to solution of carbonate minerals. The principal mechanisms responsible for the generation of each major water type may be augmented or modified by the other agents. ix Reproduced with perm ission of the copyright owner. Further reproduction prohibited without perm ission. Regression analyses of the hydrologic parameters in this area upon hydrochemistry suggests that ionic character of the ground water is not related with the area of supposed recharge. The depth of occurrence, the M ississippi River and the extensive production of water in the industrial area are related to the chemical facies of the water. Sodium is inversely related to Ca and Mg abundance, and Ca and Mg are d ire c tly related to one another. Hydrochemical facies indicate that Baton Rouge fau lt acts as a hydrologic b a rrier. x Reproduced with perm ission of the copyright owner. Further reproduction prohibited without permission.