The Genesis of Selected Hydrochemical Facies in Baton Rouge, Louisiana, Ground Waters

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Abstract
Bicarbonate‐rich ground waters are present beneath Baton Rouge, Louisiana. They may be subdivided into two subtypes based on the dominant cation. Many ground waters are Na‐rich, the others are Ca and Mg‐dominant bicarbonate waters. Na/Ca and Na/Mg epm ratios in the Na‐rich subfacies are 126‐394 and 347‐1649, respectively. The corresponding ratios in the Ca + Mg‐dominant subfacies are 0.14‐0.58 and 0.17‐0.58. The HCO3 concentration varies from 77 to, 412 ppm and the total dissolved solids content is usually lower than 500 ppm.The chloride ion is dominant in some chemical analyses of Baton Rouge ground waters. These waters form a separate hydrochemical facies whose origin is not discussed in this report.Multiple regression analyses of the ion distributions and calculated correlation coefficients for ion associations help quantify the distribution of the dissolved species and help to define the proposed mechanisms for genesis of the ground waters. Ion exchange, selective filtration of dissolved constituents, and mixing of surface waters in the aquifers are the primary mechanisms controlling the chemical composition of the ground waters. The occurrence of the Na‐HCO3 facies at shallow levels in the area of maximum offtake is especially interesting. This is attributed to the accelerated ion filtration accompanying the high rate of ground‐water production.