Geochemical characteristics of groundwater for domestic and drinking purposes in the Republic of Khakassia

The territory of the Republic of Khakassia can be divided in terms of geomorphology: about a third of the most inhabited area is located on the plain of the Minusinsk Basin and two-thirds of the territory in the mountain areas of the Kuznets Alatau and the Western Sayan. The middle-mountain relief with mountain-taiga landscapes dominates in the mountain areas, and the high-mounted one in the most elevated parts of the mountain ranges. The Minusinsk Basin (including the South-Minusinsk, Sydo-Erbinskaya and North Minusinsk basins) is characterized by steppe and forest-steppe landscapes. When estimating the water resources provision of the population of the Republic, it is necessary to note that the average-annual specific provision by local resources formed in its own territory is 38000 m and reaches 193000 m per capita, taking into account the flow of transit rivers. These values are significantly higher than the corresponding all-Russian parameters. However, resources are unevenly distributed, and the problem of reliable water supply of individual settlements remains quite acute in the region. At the same time, the main source of water supply in the Republic is groundwater, whose share is 96.7 % in total water consumption. Within the mountain structures of the Kuznetsk Alatau and the West Sayan, groundwater is localized in the Paleozoic deposits and is confined mainly to areas of exogenous fractures having regional distribution. Within the Minusinsk depression stratum-crack and crack waters in mid-Upper Paleozoic (Middle Devonian - Permian) sediments are common. At the same time, the main sources of the water supply for the cities of Abakan, Chernogorsk, Sa-yanogorsk and a number of other, smaller, settlements are the aquifers of alluvial deposits of large rivers. A variety of natural landscape-climatic, geological-structural and hydrogeological conditions determines the characteristics of the composition and quality of water in the region. It is noted that the variability of ion-salt composition, the amount of total salinity, water quality is defined by the altitudinal zonation. Mainly bicarbonate fresh water is formed within hypsometrically raised and drained hydrogeological massifs, in conditions of excess moisture and, accordingly, it is used for the water supply. Waters of the steppe part area are much more mineralized (on average, 2.1 times more than the taigawaters) and complex by their ion-salt composition, and, of course, are more enriched with both macro- and microcomponents. There are no particular problems with the quality of drinking water in the mountainous part of the region, and substandard water, appropriately treated, can relatively easily meet the requirements of SanPiN (Sanitary Regulations and Standards). The steppe part of the region does not have good drinking water. Here, the waters of almost all water-bearing rocks, with the exception of granitoids and Quaternary alluvial deposits, often have indices above regulations on the total hardness and salinity, bromine, lithium, and sometimes on the content of sulfate, chloride, boron, strontium and barium. Bringing these waters up to a standard quality requires quite complex and expensive water treatment technologies. Calculation of equilibrium of groundwa-ter with rocks showed that they are not in equilibrium with the primary alumosilicate minerals, but are in equilibrium with secondary alumosilicate and some carbonate and sulfate minerals. Groundwater of mountain-taiga and sub-taiga zones is generally in equilibrium with kaolinite and quartz, in addition, a significant portion of them with Ca- and Mg-montmorillonite, illite, carbonate minerals, and sometimes barite. Groundwater of forest-steppe and steppe zones is often in equilibrium with barite, celestite, along with the mentioned minerals and, in rare cases, even with fluorite and gypsum. All these minerals limit the level of accumulation of corresponding elements in groundwaters.

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