Utilization of coal wastes in municipal waste landfill reclamation – a Katowice-Wełnowiec case study, Poland

Coal mining produces a huge amount of waste which is stored in dumps located in close vicinity of coal mines and settlements. As organic matter is still present in deposited claystones, mudstones, sandstones, carbonates, and conglomerates, they are susceptible to self-heating, causing environmental problems. However, these wastes can also be utilized to reduce the amount of waste and the number of dumps.

The municipal waste landfill, operating from 1991 to 1996 for the Katowice town in Wełnowiec district, in Upper Silesia Coal Basin, Poland, was reclaimed with coal wastes. In total, a rubbish dump collected about 1.6 million tonnes of urban waste, composed of ca. 22.5% of coal waste, ca. 21.5% of municipal waste, ca. 40% of building waste and the remainder of composting plant waste. The residents living next to the dump complained about unpleasant odours. This is why it was decided to reclaim the municipal waste landfill and form a multi-barrier system composed of 0.3 m of compacted coal mine wastes, 0.5 m of clays, 0.1 m of sand, 0.3 m of gravel, 0.6 m of uncompacted coal mine waste mixed with soil, and 0.4 m of humus on the top. In 2001, it was decided to exploit biogas (methane) from the dump, and a total of 39 boreholes were drilled. Unfortunately, the rehabilitation caused self-heating and self-ignition to occur, and the first intense fire broke out in the eastern part of the northern slope in November/December 2008, emanating harmful components to the soil, air, and groundwater.

We proved geophysically, that properly planned reclamation has never been performed. Much more coal wastes with much higher organic matter content were deposited on the dump without any packing and fire-preventing measures. The most intensive fire expanded at the northern slope and appeared as hot spots in the eastern and southern parts. The temperature was elevated exceeding 80^oC in these places preventing plants from growing. The highest measured temperature reached 770^oC at 0.3 m subsurface. Vents and fissures which emit hot exhalations containing water vapour, carbon mono- and dioxide, methane, and other light hydrocarbons were encrusted by exhalating minerals. There the dump surface was permeated with water and bitumen formed in pyrolytical conditions in a self-heating zone located deeper within the dump.

Geophysical methods revealed up to 26 m of municipal waste covered by the irregularly distributed material of varying thickness and composition instead of a designed 2.2-m-thick multi-barrier system. The real thickness of coal wastes used for reclamation of the municipal Wełnowiec dump was documented and amounts from 1 to 8 m. The consequence is intensive burning and the necessity of prevention. Where the volume of coal waste is not adequate for thermal activity, no thermal activity was noticed. Where the volume is only just sufficient, small hot spots (< ~20m in diameter) appear and wane. Where the volume of coal waste used in rehabilitation was much greater than planned, as on the northern slope of the dump, burning could spread for many years and require professional firefighting to stop it.