Spatio-temporal changes in the chemical composition of groundwater in the central part of the Lviv

Abstract

The article characterizes the hydrogeological conditions of the central part of Lviv (Western Ukraine), the nature and intensity of anthropogenic load, assesses the degree of protection of aquifers from pollution, spatial and temporal analysis of changes in groundwater chemical composition. Groundwater in urban areas undergo significant changes in chemical composition, hydrodynamic properties, which excludes this resource from economic use, causes their aggressiveness to building structures, provokes the development of a number of dangerous geological processes. The main factor of hydrochemical and hydrodynamic changes in the state of groundwater in urban areas is mainly anthropogenic activity. The research area is located in the Lviv Basin, formed by the valley of the Poltva River and its tributaries. The groundwater of the study area is represented by a diverse complex of Quaternary deposits and accumulations of the Upper Cretaceous. The Quaternary aquifer is distributed locally and can be traced only within the bottom of the Lviv Basin. This horizon is unprotected from anthropogenic pollution. The Upper Cretaceous aquifer is confined to fractured marls and belongs to the category of insufficiently protected. Due to the presence of filtration windows, there is a hydraulic connection between the Quaternary and Upper Cretaceous aquifers. Components of groundwater chemical composition such as total mineralization, hydrocarbons, sulfates, ammonium nitrogen and chlorides were used to identify the relationship between spatiotemporal changes in groundwater chemical composition and the nature and intensity of anthropogenic pressures. It is established that the largest anthropogenic changes in chemical composition were experienced by virtually unprotected waters of the Quaternary aquifer. Its maximum changes are recorded in the sphere of influence of the Poltva sewer. The waters of the Upper Cretaceous aquifer are most changed in the north-eastern part of the site, in the area close to the surface by the occurrence of marls covered only by man-made accumulations. Significant seasonal changes in the chlorine content in the waters of the Quaternary aquifer have been identified.