Scientific basis, development and testing of engineering solutions for the reclamation of mountain territories

The history of the issue. Historically, three main types of structures have developed in the practice of waste storage in the mining and metallurgical industry: dumps (coarse - grained materials), tailings dumps (mainly for fine - grained enrichment waste in the form of pulp) and sludge storage (for sediments, sludge and concentrates). The shape and size of man-made arrays are mainly determined by waste disposal technology. Significant accumulated masses of potentially toxic materials located at mothballed alumina and metallurgical waste disposal facilities can lead to environmental consequences. The remediation measures carried out at these facilities do not always provide the necessary protective measures. Such facilities, having entered the passive phase of their life cycle, transform into difficult - to - control and long - term sources of secondary pollution. Their impact on the environment is carried out mainly through filtration of polluted waters, wind erosion of dry sediments, and diffuse runoff of meltwater and stormwater. At the same time, there remains a gap in the comprehensive analysis of the mechanisms of interaction between the internal properties of accumulated waste and external factors after the termination of operation of these facilities. The objective of this study is to scientifically substantiate and develop a set of engineering solutions for the effective reclamation of mountainous areas disturbed by mining and metallurgical waste disposal (using the sludge storage facility at RUSAL Achinsk and the Unal tailings storage facility as examples). Methods: The study included in - situ observations, soil and natural water sampling and analysis, hydrogeological modeling using the Dupuit and Kusakin formulas, regression analysis of the spatiotemporal dynamics of pollutants (Al, Na, Fe) in groundwater, agrochemical and toxicological studies of soils using test cultures (Triticum aestivum L., Lepidium sativum L.), and the calculation of phytotoxicity indices. For comprehensive monitoring, patented technical means were used: "System for Monitoring Anthropogenic Impact on the Environment" (RU Patent No. 2855884) and "Robotized Soil Sampling System" (RU Patent No. 235054). Results and Discussion. Testing of the developed monitoring system confirmed its effectiveness in detailing the spatial distribution of contamination. Regression models of Al, Na, and Fe migration in groundwater were constructed (determination coefficient >95 %). It was established that engineering protection measures at the mothballed sludge pond No. 1 limit the area of negative impact to a radius of up to 200 m, whereas for active ponds Nos. 2 and 3, the impact zone reaches 400 m or more. A system for intercepting contaminated groundwater (three 500 mm diameter wells) was designed. Hydrodynamic calculations have shown that the total system flow rate (160.4 m³/day) is 3.6 times higher than the capacity of the natural polluted flow (44.2 m³/day), which guarantees the localization of the source of pollution and allows the return of pumped water to the alumina production system, ensuring water intake savings of 12.6 million m³/year. A technology for neutralizing alkaline soils (pH up to 8.9) using ammonium chloride (25-30 g/m²) and urea (14.8 g/m²) has been developed and tested. Agrochemical studies have confirmed a decrease in pH to standard values of 6.8-7.9 units and a significant increase in nitrate nitrogen content (up to 15.9-39.8 mg/kg). An ecotoxicological assessment revealed the absence of phytotoxicity in the reclaimed lands (phytotoxicity indices of 83.2–97.4). A stable grass cover has been established on a 13.8 - hectare site. Conclusions. The developed set of engineering solutions, including an active hydrogeological barrier system and chemical soil reclamation technology, ensures the localization of groundwater contamination, restoration of the agrochemical properties of soils, and the formation of a stable vegetation cover in disturbed mountainous areas. The proposed solutions comply with the principles of best available techniques and can be adapted for other mothballed waste disposal sites.