The former industrial site of the Angarsk Metallurgical Plant (Svirsk, Russia) 10 years later: current geochemical state and interannual change analysis based on Earth remote sensing data

As part of proactive geoecological research, the purpose of which was to assess the impact of waste from the industrial site of the Vostsibelement plant on the ecosystem of the town of Svirsk (Irkutsk region), the authors discovered anomalies with strong arsenic and polymetallic contamination located 200 m north-west from the boundary of the industrial site of the “Vostsibelement” plant. Part of the contaminated site is the former industrial site of the Angarsk Metallurgical Plant, which was successfully remediated in 2009–2013. This raised the questions of a detailed study of the current environmental and geochemical situation at the site and identification of the processes causing the presence of significant contamination on the previously successively reclaimed site. To estimate the current geochemical state of the site, an environmental-geochemical survey, which was four times more detailed than the requirements of the state standard, was carried out, accompanied by rapid X-ray fluorescence analysis of samples. As a result, it was found out that on the area of more than 30 hectares,13 hectares of which belong to the former industrial site of the Angarsk Metallurgical Plant, the present pollution exceeded the standards for arsenic, lead, copper and zinc by tens and hundreds of times. At the same time, it was determined that the nature of pollution and the spatial localization of the main anomalies had changed relative to the initial situation in 2009: currently, pollution is concentrated in the peripheral areas of the industrial site and beyond and is chaotic in nature (pollutant concentrations in neighboring samples, even taken over a mesh of 50×50 m, may differ by hundreds of times). The sites reclaimed with soil removal feature no significant contamination. For a retrospective analysis of changes in the situation at the site during reclamation works in 2009–2013 and after their completion, until the summer of 2022, the analysis of Landsat and Sentinel satellite multispectral sensing data was applied. With a time resolution of no worse than one image per month, the materials in the visible and near-infrared range were analyzed. The normalized differential vegetation biomass index (NDVI) was chosen to be the main informative indicator as it clearly reflects the facts of changes in the surface type of the industrial site and allows to assess the vegetation development on the site, which is an important indirect indicator of the environmental and geochemical situation. As a result, a good convergence of geochemical and remote sensing data was established and it was shown that reclamation measures had been carried out to the required extent and gave a noticeable result: the measures taken to remove the polluted soil and deliver conditionally clean and conditionally fertile soil are clearly recorded. A positive geobotanical effect from these measures is noticeable since there is the change in the vegetation type and biomass increase in the reclaimed areas compared to peripheral areas left for self-overgrowth by native vegetation. It is shown that with the time this effect disappears and a single type of vegetation is formed on the area. However, no obvious facts of significant technogenic impact on the industrial site after the end of monitoring activities in 2016 according to multispectral satellite data were revealed. There was not any soil removal or delivery of large volumes of waste on the site. The vegetation developed synchronously with the background areas. Thus, the study reliably confirmed the fact of pollution and described it in detail, tracked the progress of reclamation measures and proved the presence of positive environmental effects. It also refuted the hypothesis about the possibility of secondary pollution as a result of obvious anthropogenic influence. At the same time, it is shown that geochemical studies of such objects conducted in accordance with current state standards can distort understanding about their condition, while greater methodological freedom of scientific research compared to the work within the framework of government assignments allows to reveal the chaotic nature of pollution in the peripheral areas of the area and beyond. But even the achieved detailed description definitely does not allow us to consider the ecological and geochemical characteristics of the object presented in the article as final as it seems necessary to thicken the sampling mesh at least by four times. The degree of probable “soft” gradual pollution of the industrial site due to the transfer and migration of pollutants from nearbyт objects (up to II hazard class), which can be sources of additional secondary pollution with all detected elements, also remains unexplored. Thus, the data obtained indicate the need for an additional set of engineering and environmentalт work that goes far beyond the scope of the proactive scientific research. The methodological conclusion from the work is the proof of the applied approach effectiveness and applicability to geoecological research, which can make it possible to assess the current situation quickly, reliably and at low cost as well as to analyze, confirm or refute the hypotheses about the development of the situation and therefore can be successfully used in other similar cases.