HEAVYMETALAND AS TRANSPORT UNDER LOW AND HIGH FLOWS IN THE RIVER GUADIAMAR THREE YEARS AFTER THE AZNALCÓLLAR TAILINGS DAM FAILURE: IMPLICATIONS FOR RIVER RECOVERY AND MANAGEMENT

This paper presents work from an ongoing research programme examining the recovery of the Guadiamar River following the April 1998 Aznalcóllar tailings dam failure. Analysis of heavy metals (Cd, Cu, Pb and Zn) and As in surface waters, valley floor alluvium, overbank, and suspended sediments are compared between six study reaches downstream of the dam, over five sampling periods. The principal aims of the paper are to examine the distribution of contaminants in sediments and river waters and their delivery downstream under low and high flows, and the implications for river channel recovery and management three years after the tailings dam failure. Results from a survey of Guadiamar alluvium carried out in January 1999 showed that, although clean-up operations were largely successful in restoring the affected area to pre-spill conditions, sediments continued to exceed intervention thresholds for the region. Residual contaminant levels were highest near the spill source, with isolated hotspots of elevated contamination throughout the affected area, superimposed on a general downstream decline in concentrations. In terms of contaminant mobility, surface water samples taken in May 1999, under very low flows, had dissolved Cd, Cu, and Zn concentrations that failed EC directive thresholds for surface water abstraction.