Karrar Azez Hassen Arab
Characterising the nature and extent of contamination at a restored coal mining area in Staffordshire and assessment of remediation options
Arab, Karrar Azez Hassen
Mine site management, monitoring and restoration are important, long term environmental activities that are needed in many regions of the UK and around the world. This project characterised the nature and level of contamination at a former coal mining site in Staffordshire, UK, that was partially restored and is currently used for agriculture and recreation but which was understood to still have problems of mine-affected soils, sediment and water. The characterisation included analysing elemental contents, the mobility and fractionation of meta(loid)s in soils using single (CaCl2) and sequential (BCR) extraction methods, metal content in soil solution, the total and dissolved fraction of meta(loid)s (0.45µm filtered) in water, and testing ecotoxicology of mining impacted water using the crustacean Daphnia magna. The characterisation results revealed probable Al toxicity and Ca, K and Mg deficiency in the mine-affected soils as well as potential Co, Fe, Mn, Ni and Zn toxicity risks in soils and water. The aquatic sediment was found to have elevated concentrations of elements associated with mining pollution, such as Fe. The aquatic toxicity tests revealed the stream waters to be hostile to crustaceans (100% mortality was observed in many samples), while measurements of turbidity, elemental concentrations and other water quality parameters indicated that the stream was now uninhabitable by fish. The characterisation work identified likely points of mine drainage input to the stream and thus established a basis to build further hydrological investigations upon. The soils of the most severely impacted positions in the area, which were apparent mining drainage upwelling or seep points, were shown to be in need of remediation if they were to be rendered useful for agricultural or other purposes. A soil remediation trial was thus embarked upon.
Iron and Aluminium water treatment residuals (Fe-WTR and Al-WTR), by-products of drinking water clarification, are generated in vast quantities around the world and have potential beneficial uses in environmental applications (e.g. soil remediation). This study first successfully demonstrated metal (Pb and Zn) sorption and retention capacity of WTRs in batch experiments (single metal and in combination), from the point of view of verifying their capacity for immobilising potentially toxic elements in treated soils, and then investigated directly WTR-based remediation potential for the soils at the site through conducting a series of laboratory trials on field collected soils. Remediation trial treatments comprised non-amended controls, Al-WTR, Fe-WTR and lime amendments (10% w/w), with subsequent outcomes for soil properties (e.g. pH), plant yield, earthworm survival, tissue element concentrations and soil solution chemistry all assessed. Effects of a wetting-drying cycle on subsequent plant yield, earthworm survival, and element uptake were also examined to investigate longer term aspects. The remediation trials revealed that WTRs generated significant improvements in pH, plant yield and element content, earthworm survival, and soil solution properties that were comparable to, and in some cases better than, those achieved by liming. These positive effects generally persisted after a wetting-drying cycle. Importantly, the WTRs applied to less impacted reference soils also showed quality indicator improvements or maintenance of good conditions. The remediation trials were therefore highly successful and provide strong evidence that field trials, which are the next logical step, should be conducted to examine the remediation benefits of adding WTRs to mining impacted soils at the field scale.
|Publicly Available Date||May 30, 2023|