The Influence of Karst Aquifer Mineralogy and Geochemistry on Groundwater Characteristics: West Bank, Palestine
O 19.14 in Forum Junge Hydrogeologen
21.03.2018, 16:00-16:15, 3
This work reports, for the first time, the mineralogical and geochemical characteristics of karst aquifers in the Central West Bank (CWB) catchment in Palestine. It provides an integrated study approach by correlating geochemistry and hydrochemical data of groundwater samples. Groundwater and aquifer rock samples were collected from 20 different spring water sites at CWB. The crushed rock geochemistry and mineralogy of the samples was investigated using INAA, ICP-MS, ICP-OES and XRD, while hydrochemical analyses included on-site physico-chemical parameters, HPLC and ICP-MS. Further aliquots of the samples were analyzed for carbon (Corg/Cinorg) and sulfur (Stotal/Spyrite) contents in a combustion analyzer. The mineralogical analysis showed that all samples are dominantly composed of either calcite CaCO3 (5-100 wt.-%) or dolomite CaMg(CO3)2 (4 -100 wt%), with minor amounts of quartz and feldspar, which is supported by inorganic carbon content (9–13 wt.-%) and hydrochemical composition of spring water samples. Ionic ratios were used to delineate mineral-solution reactions and weathering processes. All of the investigated groundwaters are categorized into one hydrochemical type: slightly mineralized and neutral to slightly basic waters of Ca-Mg-HCO3 type with EC and pH values ranging from 132 to 590 μS/cm and 7.1 to 8.0, respectively. Interpretation of the chemical data suggests that the evolution of groundwater composition is primarily controlled by (1) water-rock interaction processes, involving dissolution of carbonate minerals (calcite and dolomite), and (2) cation exchange. The whole-rock geochemical data indicate that the samples have low contents of trace elements and transition metals. In contrast, the concentrations of alkaline earth elements (Mg, Ca, Sr, Ba) and Mn are high in rock and groundwater samples. Generally, the trace elements of rock samples with concentrations >10 ppm include Sr (17–330 ppm), Mn (17-367 ppm), Ba (2-32 ppm), W (5–37 ppm), Cr (3-23 ppm), Zn (1.7–28 ppm), V (4-23 ppm), and Zr (1-22 ppm), while the concentration of all the other trace elements is below 10 ppm. Geochemical compositions results were also subjected to the Hierarchical Cluster Analysis (HCA), results hint at two distinct groups of samples that correspond to the dolomite and calcite dissolution. This separation is clear in alkaline earth elements (Mg, Ca, Sr, Ba), especially Sr values. The calcite rock samples have higher Sr (mean 170 ppm, n=11) than those of the dolomite rocks (mean 76 ppm, n=9).
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