Assessment of Temporal and Space-Time Changes of Groundwater Chemical Composition at the “Рridniproivsky Chemical Plant” Uranium Production Legacy Site

Abstract

This study provides an analysis of data from long-term (2005-2021) observations of the chemical composition of groundwater in the impact zone of the former uranium ore processing enterprise (Production Union Prydniprovskyi Chemical Plant (PU “PChP”) in the city of Kamianske, in particular, areas of near-surface tailings of uranium ore processed residues (“Zapadnoe”, “Central Yar” and others). All tailings on the site of the former PU “PChP” were built without installation of anti-permeable barriers, and therefore under the influence of atmospheric precipitation, the water, formed in the tailings body, highly contaminated of uranium series radionuclides and residues of chemical reagents, can penetrate to the groundwater aquifers, with which they spread beyond the limits of their technological localization in tailings. In addition, the entire territory of the former industrial site of mining and chemical production “PChP” is a complex of former enterprises, septic tanks, production waste holding sites, warehouses of chemical reagents and residues of former production, which are also sources of man-made pollution of the territory and influence on chronic pollution of groundwater. Therefore, environmental monitoring programs in the impact zone of tailings impoundments included not only monitoring of indicators of the content of uranium series radionuclides in elements of the natural environment, but also studying of the chemical composition of waters. The analysis of observation data during the period from 2005 to 2021 was carried out in order to assess the extent of the spread of polluted waters beyond the limits of the location of the tailings ponds, to identify major macroions in the composition of groundwater as indicators for assessing the spread of the contamination plume beyond the boundaries of the tailings ponds, as well as to identify patterns of formation the groundwater quality within the site under the influence of man-made and natural factors. It is shown that the mineralization of groundwater, as well as its chemical composition, significantly changed as the sampling site moved away from the tailings. Changes in the chemical composition of water and the dominant content of the major macroions at different distances from the tailing’s ponds made it possible to determine the difference in the characteristics of the influence of infiltration waters from the source of the tailing’s ponds and scattered sources of pollution within the boundaries of the PChP site along the groundwater flow line. The main factors of uncertainty in the estimations of the formation of groundwater chemistry in the zone of the industrial complex are shown, which must be taken into account for the development of the network of monitoring observations.