Temperature, specific electrical conductivity (E), pH, Eh, concentrations of dissolved gases (O_2 and H_2S), and Na~+ activity were measured in situ by means of hydrogeochemical logging. These data showed that the interaction of fresh groundwater and steel pipes in the well space resulted in water demineralization by 10-60% and the formation of a vertical redox zoning. At the top of the well, meteoric oxygen penetrates to a depth of up to 20 m and produces an oxidizing weakly acidic and neutral environment, which is changed with increasing depth by reducing alkalic one (pH 9.2-11.2). The pH-Eh conditions of water in contact with the casing are controlled by the products of corrosion and encrustation and depend on the duration of the contact. The majorcomponent composition and physicochemical properties of groundwater were strongly modified in the filter zones of 20 observation wells. A method is proposed for the derivation of undisturbed hydrogeochemical information on the basis of the measurement of aqueous environment parameters after in situ controlled short-term pumping.
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