Spatial and temporal analysis of nitrate content in the groundwater of the Zadonsk-Optukhovian aquifer carbonate complex of the right bank of the Lipetsk industrial district between 2001 and 2019

Abstract

Introduction: The purpose of the study is a spatial and temporal analysis of the nitrate content in the groundwater of the Zadonsk-Optukhovian aquifer carbonate complex of the right bank of the Lipetsk industrial district between 2001 and 2019. The study is important due to significant levels and area of pollution caused by a powerful technogenic impact. The ecological and hydrogeochemical anomaly led to the shut-down of a number of water intakes in Lipetsk. Methodology: Spatial and temporal analysis of the nitrate content in the groundwater of the ZadonskOptukhovian aquifer carbonate complex of the right bank of the Lipetsk industrial district between 2001 and 2019 was carried out for 23 observation points (water intakes). The time interval during which the quality of the groundwater was monitored is associated with the period when the main field of the ecological and hydrogeochemical anomaly was formed: 2001 – 2019 The data used for comparison were for 2001, 2005, 2015, and 2016-2019. Time intervals with the maximum amount of data were used. Nitrate content was analysed both by the area and time. To analyse the area of pollution, schemes were built describing the nitrate content in the groundwater of the Zadonsk-Optukhovian aquifer carbonate complex. Time regularities were shown in the diagrams for minimum and maximum nitrate concentrations for each time interval. Diagrams for the average level of groundwater pollution were also built and the percentage of wells with excess nitrate concentrations was calculated. Pollution focuses were identified by processing statistically the chemical analysis data for the groundwater in all of the wells. The statistical analysis included: calculating average nitrate concentrations for the observation period and for each well, calculating a standard deviation, identifying the highest concentrations of pollutants for each time interval, and identifying nitrate concentrations in wells exceeding the standard deviation. Results and discussion: The study allowed obtaining environmental characteristics of the groundwater nitrate contamination of the Zadonsk-Optukhovian aquifer carbonate complex between 2001 and 2019. The estimated area was about 500 km2. The groundwater conditions in the Zadonsk-Optukhovian aquifer carbonate complex was determined as moderately hazardous. Its area was 255.37–402.73 km2. The direction of nitrate groundwater contamination was south-western. Over the studied period, nitrate concentrations varied between 16.4 mg/dm3 (0.36 MPC) and 186.10 mg/dm3 (4.14 MPC). Annual average nitrate concentrations in the groundwater varied between 52.66 mg/dm3 (1.17 MPC) and 72.15 mg/dm3 (1.60 MPC). The locations of the main groundwater nitrate contamination focuses included: Tuzhilovka village, Novaya Derevnya, Severnaya Shakhta (Rudnik) district, and Koptsevy Khutora village. The main sources of groundwater nitrate contamination of the right bank of the Lipetsk industrial district included: a poultry farm, a manure storehouse, cattle farming complexes, agricultural irrigation fields, and a chemical industry enterprise. Conclusion: The results of the studies were used to conduct a spatial and temporal analysis of the nitrate content in the groundwater of the Zadonsk-Optukhovian aquifer carbonate complex of the right bank of the Lipetsk industrial district between 2001 and 2019. The main characteristics of groundwater pollution within the studied area were identified. A following set of environmental protection measures was proposed: elimination or modification of the existing sources of negative impact, including elimination of accumulated environmental damage; consideration of the need to enable groundwater protection when placing potentially hazardous facilities; shielding the territory within the areas of groundwater nitrate contamination; modernisation of water purification systems and waste disposal systems.