Potential impacts of sediment dredging on a contaminated stream in an abandoned sulphide metal mining area in Southern Portugal.

Abstract

Dredging is one of the most efficient techniques for recovering a water body: the only one capable of removing all, or a part of sediments, which are the most common site for accumulation and retention of pollutants. This is an economically viable method and one of the major advantages, compared to chemical or biological methods, is the non-introduction of external substances into the system. To restore contaminated rivers from active or abandoned mining areas, the environmental assessment of the dredging of metal-rich sediments, are important contributions to the design and implementation of sediment remediation since they might have negative impacts, sometimes being a misadjusted methodology in a recovery project. It should be mandatory to assess and predict the five Rs linked to dredging activities: (1) effective removal of sediments, (2) potential effect of sediment resuspension, (3) contaminant release to the water column, (4) residual sediments and (5) associated risks with these processes. This study aims to evaluate the potential environmental risks associated with dredging of sediments from contaminated shallow streams, under the direct influence of large areas of waste accumulation, from an abandoned Cu-Pb-Zn-Ag-Au mine (Caveira mine) included in the Iberian Pyrite Belt, in South Portugal.