Abstract
Underground coal gasification (UCG) generates potential groundwater pollution because it changes local hydrogeological parameters. Groundwater pollution is caused by diffusion and penetration of contaminants generated by UCG processes towards surrounding strata and possible leaching of residue by natural groundwater flow after gasification. A large number of hazardous water-borne contaminants were identified during different UCG operations conducted so far, and in some locations long-term groundwater contaminations were observed. Organic pollutants were detected after UCG process are phenols, benzene with its derivatives, polycyclic aromatic hydrocarbons (PAHs), heterocycles etc. and inorganic pollutants includes ammonia, mercury, zinc, sulphates, cyanides, heavy metals etc. Adsorption function of coal and surrounding strata makes a significant contribution to decrease the contaminants over time and distance from the burn cavity. Possible pollution control measures regarding UCG include identifying unsuitable zone, sitting a hydraulic barrier and pumping contaminated water out for surface disposal. The paper enumerates major pollutants identified in different UCG sites and its mitigation measures during gasification processes, and groundwater remediation after gasification. Key words: Underground coal gasification, groundwater contamination, water influx.
Highlights
Underground coal gasification (UCG) is a procedure for extracting the synthesis gas from in-situ underground coal seams that could not be economically extracted by conventional mining methods
UCG process, involves air/oxygen and steam pumped into the underground coal seam through an injection well
Before starting UCG operation ensures that wells and boreholes used in the process are adequately sealed and maintain a ‘cone of depression’ in the groundwater around the reactor (Sury et al, 2004)
Summary
Underground coal gasification (UCG) is a procedure for extracting the synthesis gas (syngas) from in-situ underground coal seams that could not be economically extracted by conventional mining methods. In UCG process, physico-chemical interaction changes natural stress in the surrounding rock mass, which influences contaminants formation in the UCG reactor as well as inducing potential subsidence, and pollution of groundwater, surface water and atmospheric quality. The paper identifies possibility of underground water pollution due to UCG and analyzes the fate of contaminants (organic and inorganic) as well as formulates strategies for groundwater pollution control.
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