Environmental aspects of a field-scale underground coal gasification trial in a shallow coal seam at the Experimental Mine Barbara in Poland

A study on the environmental impacts of underground coal gasification (UCG) was conducted during a field-scale, in situ coal gasification experiment at the Experimental Mine “Barbara” in Poland. This two-week experiment was a part of a technological effort aiming to produce hydrogen-rich product gas using the UCG technology. As groundwater pollution is recognised to be the most serious environmental risk related to UCG, extensive investigations on the formation, release, and migration of contaminants were conducted. The study revealed a wide range of organic and inorganic contaminants that were characteristic for the UCG. The main organic contaminants were phenolic compounds and aromatic hydrocarbons (mono- and polycyclic). Among the inorganic species, heavy metals, ammonia and cyanides were the most serious group of contaminants. These compounds were identified in the post-processing effluents and in groundwater near the test site. The impact of the gasification process on the groundwater, however, was small and tended to effectively decrease over the time and distance from the cavity zone. A possible negative environmental impact of the gasification by-products, including ash and char left underground, was also evaluated. This study revealed that these post-gasification residuals are the main source of toxic trace elements, but the most volatile species, such as Hg, As and Se, tended to escape the cavity zone with the product gas during gasification phase. Monitoring activities detected no chemical hazards on the surface during the course of the experiment and after its termination; however, UCG-induced thermal effects on surface were observed.