The extent of the Aznalcollar pyritic sludge spill and its effects on soils

This paper presents some initial results from the Institute Tecnologico Geo minero de Espana's (ITGE) study of the Aznalcollar mine spill. The spatial distribution of the pyritic sludge released was surveyed by using remote se nsing data, aerial photography, and more than 700 field measurements on the sludge thickness. Initial estimation of the extent of the sludge was provi ded by radar data. Maps at 1:10 000 scale, drawn on the basis of field data and interpretation of aerial photos, show the distribution of the sludge, divided into 168 subsections on the basis of average thickness. GIS analysi s provided estimates of the area and volume of the sludge. Three approaches were followed in order to survey the effects of the spill on the Guadiamar river alluvial soils: (1) Mineralogical and chemical characterization of t he sludge and its evolution until its removal. Alteration products of the p yritic sludge were also analyzed. (2) Determination of geochemical backgrou nd of soils in the Guadiamar river basin, in order to establish the content of heavy metals and other elements in the soil before the spill. (3) Asses sment of the sludge effect on soils caused by the acid water and the deposi ted sludge, by comparison of the heavy metal content of soil under the slud ge layer with that of background soil. Finally, an airborne multispectral s urvey was carried out over the Aznalcollar-Donana area to evaluate its effi ciency for monitoring soil condition during and after sludge removal. (C) 1 999 Elsevier Science B.V. All rights reserved.