THE FORMATION MECHANISMS OF COMPOSITION OF DRINKING GROUNDWATER OF THE Kyiv DEPOSIT (ON THE EXAMPLE OF THE OBOLON WATER INTAKE STRUCTURE)

Abstract

This paper presents the results of the assessment of interactions in the water-rock system using an integrated approach including the balance method and the method of geochemical (thermodynamic) modelling. Assessment is carried out for conditions of Cenomanian-Callovian and Bajocian aquifers within the Obolon groundwater intake structure in Kyiv. The results obtained demonstrate that groundwater of the Cenomanian-Callovian and Bajocian aquifers within the Obolon groundwater intake structure differ in chemical composition, physicochemical conditions, and especially in the formation of water composition due to the interactions in the water-rock system. This paper proposes division of water into groups, taking into account both the features of chemical composition and its formation process. The water group characterized by anomalous ratio of chlorine and sodium is distinguished, as well as the possible formation mechanism of this water composition is proposed. The chemical composition of the waters of both aquifers meets the requirements of Ukrainian legislation for drinking water quality (GSanPiN 2.2.4-171-10). Groundwater quality of the Cenomanian-Callovian complex is shown to be higher than that of the Bajocian aquifer. For both aquifers, the water of higher quality is the one with cationic composition determined largely by ion exchange. The ion exchange processes can be controlled to a certain extent by regulating the water withdrawal from the wells, and hence the water quality can be regulated in this way as well. Another way to regulate water quality could be the mixing of water from two aquifers during water treatment, which would, on the one hand, compensate the insufficient water quality of individual aquifers and, on the other hand, provide for continuous well operation contributing to the maintenance of more or less stable physicochemical processes. However, these hypotheses require further detailed consideration and, if confirmed, a detailed justification of their feasibility.