Assessment of the groundwater for household and drinking purposes in central Kazakhstan

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Water resources, including potable water availability, are complicated issues in many Kazakhstan regions. Central Kazakhstan region is one such region, which requires the proper support in the water supply. Most of the Kazakhstan regions had been using mostly surface water, however, with the limitation of the surface water, the groundwater resources have been used more intensively during the last decades. At the same time, the groundwater chemical composition plays a decisive role for categorization as the potable water. Within this research work the chemical composition of groundwater formation features in the arid conditions of Kazakhstan are presented. The regional hydrogeochemical field works were carried out to establish the patterns of fresh and brackish groundwater formation. In the arid conditions of Kazakhstan, the two main factors influencing the chemical compositions were investigated, including: a) the water-rock interaction for mountain-folded areas, and b) water-soil-gas interaction and evaporative concentration (water evaporation and salts accumulation) for flat areas. The physical and chemical modeling by the Gibbs free energy minimization method, which is based on the thermodynamics laws, were provided to analyze processes of these two main factors influencing the chemical compositions. The results of these analyses, for the a) mountain-folded areas, we found that with the growth of gypsum (1.2%) in the rock, the content of sulfate compounds in water increases tenfold. In the fractured rocks of mountain-folded areas with free access to atmospheric air (open system), waters are enriched with oxygen and carbon dioxide. At the same time, the cationic composition of waters is determined by the lithological composition of the rocks. The sodium cations predominate in granite massifs. Calcium is predominant in enriched calcium minerals. Bicarbonate anions predominate in the anionic component with weak mineralization. For the b) flat areas, as mineralization increases due to the interaction of water-soil-gas and evaporative concentration, the chemical composition changes. The changes occur from sulfate to chloride in anions and from calcium to sodium in cations. These two main factors pattern a-b influencing the chemical compositions were also observed in the bigger regional hydrogeochemical studies, mountain-folded with connected flat areas. Waters are predominantly fresh bicarbonate calcium-sodium in the feeding zones of the mountain-folded areas originally. With water movement down to the flat areas, the mineralization increases. The water's mineralization increases and becomes more sulfate to chloride. The hydrogeochemical zonings are traced. This study is applicable for forecasting, searching the fresh and slightly brackish waters, which could be suitable for domestic water supply.