The aim of this paper was to determine the capability for metal elution that may constitute potential contamination to the water environment from post-process cavern residue after underground coal gasification (UCG). Samples of raw coals that had been subjected to gasification (three samples of hard coal, the coal mine ``Bobrek'', the experimental mine ``Barbara'' and the coal mine ``Piast'', and a sample of brown coal from the coal mine ``Belchatow'') were analysed for their physicochemical properties. Similar tests were performed with samples of ash and char that remained in the cavern after experiments associated with underground coal gasification. For comparison, samples of raw coals were also burned under controlled conditions in air, in a specially designed furnace, until their complete incineration. Each of these materials was subjected to an elution test using deionised water. An analysis of the physicochemical composition of the water extracts for the selected parameters was carried out. The qualitative-quantitative composition of the water extracts was related to the hydro-geochemical background characteristics of groundwater. The effect of the degree of coal conversion on the ability of metals to elute into the water environment was discussed. (C) 2015 Elsevier Ltd. All rights reserved.