Alluvial aquifer contamination : exchangeable heavy metals and factors affecting their spatial distribution

The distributions of ammonium acetate - extracted ('exchangeable') Co, Ni, Cu, Zn, Cd and Pb were determined in alluvial sediments of the Sava River at Novi Beograd (Belgrade aquifer, Yugoslavia). Samples were taken from the river bottom and from three drill-holes in the alluvial formation (in increasing distance from the river-bed). The alluvial samples included the quaternary formation - humified surface layers, sands and clays, as well as some samples from the impervious tertiary layer at about 25 m depth. A combined method for the interpretation of results was introduced in order to obtain a clear insight into the factors of heavy metal distribution within the examined aquifer sequence, including elementary statistical methods, as well as factor analysis. There are no significant correlations between metal concentrations and burial depth, river distance, or lithologic type. The application of factor analysis on the exchangeable metal phase, however, reveals the existence of two sample populations and two dominant ecochemical factors, governing the distribution of heavy metals within the aquifer. One factor represents surface contamination, and the other represents river water influence, accumulating exchangeable heavy metals within a sharply outlined zone. This zone spreads over most layers in the immediate vicinity of the river, as well as over a few, more distant layers which are at roughly the same level as the river-bed.