Stable carbon isotope ratios and the existence of a gas phase in the evolution of carbonate ground waters |
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Authors: | Peter Deines Donald Langmuir Russell S Harmon |
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Institution: | Department of Geosciences, The Pennsylvania State University, University Park, Pennsylvania, 16802, U.S.A.;Department of Geology, McMaster University, Hamilton, Ontario, Canada |
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Abstract: | The chemical and stable isotope compositions of unpolluted ground waters in carbonate terranes are a function of the pH, , 13C content of the ground water recharge, the 13C content of the carbonate rock, and the manner in which the rock is dissolved or precipitated. Physico-chemical models show that significantly different relationships exist between Ca2+ plus Mg2+, HCO3?, pH and 13C content of unpolluted ground waters when carbonate solution occurs in the presence or absence of a gas phase. A study was made of these relationships in waters from 21 springs and 13 wells in Nittany Valley, Pennsylvania. Assuming that CO2 in the recharge zone has a 13C contents below ?21%. vs PDB, the data indicate that ground water flow to wells and springs, and carbonate rock solution probably occurs chiefly in the absence of a gas phase. This is in spite of the fact that most of such flow is under water table conditions. 13C contents averaged ?12·3%. for the spring waters and ?13·3%. for the well waters. Five well waters polluted by septic tank or sewage effluents had carbon isotopic compositions from ?13·5 to ?16·4%.,vs ?11·3 to?12·7 %. for the eight well waters relatively free of organic wastes. |
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