Vargas Serrano, Kateleen

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    A hydrogeochemical analysis to evaluate the water-rock interaction in the North Coast Limestone Aquifer System of Puerto Rico
    (2022-05-20) Vargas Serrano, Kateleen; Ramírez-Martínez, Wilson R.; College of Arts and Sciences - Sciences; Padilla-Cestero, Ingrid Y.; Santos-Mercado, Hernán; Department of Geology; Román-Paoli, Elvin
    Analyzing the mineralogical composition, and saturation indices in springwaters helps to understand the internal structure of karst aquifers since they affect the porosity, the permeability and the rock alterations (including karstification). This project evaluated the variations in the water chemistry relative to the geologic formations the water moves through to assess whether the composition is related to calcite or dolomite; determined the variations of the saturation indices of calcite, and dolomite during the sampling period (2013 to 2019), specifically during the dry and wet seasons; and assessed the possible geochemical rock-water interactions producing the chemical parameters observed in the springwaters. Seven spring waters of the North Coast Limestone Aquifer System of Puerto Rico were analyzed: Maguayo, Mackovic, Tallonal, Ojo de Agua, Ojo de Guillo, San Pedro, and Zanja Fría springs. Physical and chemical parameters of the spring waters were analyzed for temperature, pH, TDS, specific conductivity, alkalinity, major ion concentrations (calcium, magnesium, sodium, potassium, chloride, bicarbonate, and carbonate) during the sampling period from 2013 to 2019. Ions concentrations of the spring waters were measured by Ion Chromatography. Piper Diagrams were used to classify the springwaters. The PHREEQC code was used for the calculations of the calcite and dolomite saturation indices. The difference between both average concentrations of calcium and magnesium in the seven springs suggested that the spring waters moving through the Aguada Limestone Formation, Aymamón Limestone Formation, and the Montebello Limestone Member of the Cibao Formation were mostly composed of calcite suggesting the waters from the studied springs does not move to the depth where the dolomites are found. The calcite saturation indices did not show statistically significant difference between the wet and dry seasons during the sampling period, therefore the changes in rainfall patterns from 2013 to 2019 do not influenced the interaction of the water with the carbonate rocks. Variations in the saturation indices with respect to dolomite were significantly different between the wet and dry seasons in all the seven studied springs. Supersaturated dolomite values in certain intervals during the sampling period does not indicate the dolomite precipitation since high temperatures and/or high ratios of Mg/Ca are needed for the precipitation to occur and those conditions are not present in these spring environments. Calcite saturation indices for most of the sampling period of the seven springs presented indices greater than zero, indicating that the waters of the springs were supersaturated, suggesting that calcite precipitation in the springs. Dolomite saturation indices are lower than zero for most locations and most of the sampling period, indicating the waters of the springs were undersaturated, and suggesting dolomite dissolution.