Hazardous waste on waste rock of São Pedro da Cova coal mine (Portugal): site reclamation

Abstract

For 12 years a waste deposit was in direct contact with the underlying ground. The waste, fly ash, was produced by electric arc furnaces of the Portuguese Iron and Steel Company. The subsoil consisted of waste rock spoils from an old coal mine site. The waste was transported to the site as part of a recovery operation. At the time of the recovery operation, the waste was classified as “inert”. Site investigations later performed showed that the waste was hazardous. The waste mainly consisted of high concentrations of lead and petroleum hydrocarbons, and there was no containment structure to confine the waste, which put local public health and the environment at risk. It was therefore recommended that the waste be moved to a hazardous waste landfill. In this paper, after the methodology used to study the waste disposal has been presented, it was followed by the methodology adopted for the reclamation of the site. Firstly, through the excavation of the waste deposited and the remediation of the subsoil by removing contaminated soil areas, whose depth did not exceed 0.75 m; and then, an on-site reuse operation was carried out by backfilling the natural soil that was covering the waste deposit.