Efficiency of Stepwise Magnetic-Chemical Site Assessment for Fly Ash Derived Heavy Metal Pollution

frederick w. daily, bethany k. laurence;

Previous works revealed a close relationship between magnetic susceptibility (MS) and heavy metal (HM) contents originating from industrial sources. However, despite general statements on the usefulness of magnetic mapping, the benefit of this procedure for geochemistry was not quantified yet.We present a study on fly ash pollution in soil around a coal-burning power plant complex and simulate a stepwise approach of magnetic pre-screening and subsequent targeted sampling for chemical analysis. The aim of this study is not to discuss correlations between MS and HM, but to show that a combined stepwise magnetic-chemical approach is the most efficient way for outlining HM contamination. In order to provide quantitative evidence,
we explored map similarities of spatial HM distributions based on magnetochemical data and chemical data only. We determined 3-D triangular planes defined by categorized HM values at the sampling coordinates and calculated the average dihedral angle of the normal vectors as a similarity result. The study shows that the ‘Targeted’ HM map (selection of 30 sites based magnetic pre-screening) has a higher similarity with the ‘True’ Pollution HM map (85 sites) than HM maps resulting from site selections (30 sites) without using magnetic pre-screening information.