Impact Analysis and Sampling Design in the Pollution Monitoring Process of the Aznalcollar Accident Using Geostatistical Methods

On the morning of the 25 of April 1998, an accidental spill of the waste damp basin of the Aznalcóllar mine (Seville, SW Spain) occurred. The basin, containing mud and acid waters, suffered a rupture spilling 4 hm of acid waters and 2 hm of acid mud directly into the Agrio and Guadiamar rivers. This accidental spill spread to an area of about 49 km and they had very important ecological consequences due to those rivers are the basic water resource of the Doñana National Park aquifer (located 60km downstream the mine) that was declared as Biosphere Reserve by UNESCO in 1994. Remediation actions were taken immediately in order to protect the population health and agriculture and minimize the ecological impact in the Park. Once the primary remediation actions were applied, it was very important to characterize the residual contamination distribution patterns and to obtain environmental hazards maps in which areas with high heavy metals concentration (Cu, Pb, Zn, Cd and As) can be identified. This paper presents the most important results of the geostatistical treatment of this data. The basic objectives of this treatment were to establish the impact analysis of the contaminant (environmental hazards maps) using the direct cosimulation technique and remediation levels that defines if a certain zone can be considered as contaminated or clean and the design of a new sampling schema that would be applied in future sampling campaigns and planning the optimum sampling for the next campaigns. * Corresponding author.