Hydrogeochemistry and sulphate contamination of water environment around the coal stock pile in Tamabil, Sylhet

The study area Tamabil, Sylhet, is an important area in importing coal and its storing for supplying to different industrial uses in Bangladesh. This area is located in the north-eastern part of Bangladesh. Currently, the water environment in the study area is threatened by the processing of high sulphur coal, agricultural activities, and other anthropogenic effects. Hence, the protection of water resources in terms of quality and quantity from such contamination should be considered a serious issue. From this view point, this study intends to evaluate the hydrogeochemical characteristics and sulphate contamination of water bodies in the area. The hydrochemical evaluation of water for all samples has been carried out under standard laboratory methods with various diagrams, charts, and statistical methods. From the results of the laboratory testing, it has been observed that the water in the wells close to the coal stock pile is highly acidic (pH = 3.41), whereas the water shows the standard pH values as its distance increases from the stock area. The hydrogeochemical evaluation of water under the Piper chart implied that mixed type of water facies such as (i) Ca–Mg–Cl (38.7%), (ii) CaHCO3 (38.7%), (iii) NaCl (16.12%), and (iv) CaCl (6.4%) are dominant in the area. The Gibbs diagram showed the rock- and evaporation-dominant mixed environment, while the Durov Diagram reflected mixing–dissolution state with few in reverse ion-exchange condition. These results suggest that the major geochemical facies and evolution of water are prevailed by the carbonate rock dissolution and the weathering process. In the case of sulphate contamination, the overall concentration of sulphate falls within the standard limit of WHO and EQS, but this study observed that the intensity of SO4 is high in the samples adjacent to the coal stock pile. These scenarios entailed that the stored coal is primarily responsible for it while the sulphur content ranges from 1.42 to 7.26 Wt% (average 3.73 Wt%) of this coal. In addition, the leaching experiment of this coal shows that the pH values of the water reduce from 7 to 1.2, consequently increasing the acidity of the water environment around the area. In conclusion, this study recommends that (i) more cautious and watchful activity has to be taken to import, store, and use this coal; (ii) more precautions have to be considered to protect the water from such contamination to save the green environment as a whole for the present and future.