Structure and thermal history of the Wełnowiec dump, Poland : a municipal dump rehabilitated with coal waste

Abstract

The Wełnowiec municipal dump, Katowice, Poland, rehabilitated with coal waste, is self-heating and igniting. This paper presents a novel application of the use of electrical- and resistivity geophysical methods in the investigation of burning coal waste to help explain why the heating occurred. Geoelectrical methods allowed the internal structure of the dump to be revealed, and the municipal wastes and their rehabilitation cover containing coal waste to be differentiated. Instead of a planned 2.2-m-thick multi-barrier system, the cover consists of irregularly distributed material of varying thickness (< 1 to 8 m) and organic carbon content (> 5%). This caused the fire to arise 3–4 years after the coal waste deposition. In areas where the rehabilitation layer is<3m thick, a landslide enabled oxygen access, initiating self-heating. Changes in conductivity clearly identify sites of active burning where measured conductivity values are more than twice those for parts of the dump with no thermal activity. Field observations in particular, complemented to a degree by petrographic, mineralogical and geochemical data, enabled four types of heating zones to be distinguished, namely, (1) initial zones of fire overtaking new volumes of coal waste, (2) active zones with temperatures < 400–500 °C in exhalation vents, (3) overburned zones characterized by long-lasting high temperatures (800-900 °C) and (4) short-lived zones, ephemeral (< 1–2 months) with temperatures between 70 and 100 °C. The geophysical methods applied could not distinguish between these zones. The combined results strongly suggest that the use of coal waste as a remediation layer covering waste dumps should be prohibited. Coal waste which, by its nature, is too prone to unpredictable self-heating and self-ignition with the potential environmental consequences that follow.