Quantitative assessment of dust propagation at a hazardous waste landfill: directional monitoring with elemental analysis

The proportion of air pollution control (APC) residue in fugitive dust from the active cell of a hazardous waste landfill has been quantified using multi-element analytical data in combination with directional information about the dust samples collected. Passive sampling gauges (DustScan) were deployed at the periphery of the cell, and samples were collected at fortnightly intervals. They were scanned for dust coverage and direction, and sub-samples were digested using HF and HNO(3) prior to analysis for a range of metals using ICPAES. Dust samples were initially categorised on the basis of direction and distance with respect to the active cell, and overall colour. Independent graphical manipulation of the elemental data revealed separate dust populations with several demonstrably different inter-element ratios. These populations accord well with the initial dust characterisation, and consequent designation as "APC" and "background" has been confirmed by chemical comparison with grab samples from the active cell, the landfill clay and the topsoil cap. As well as allowing confident graphical discrimination between APC and background dusts, the technique provides datasets amenable to multivariate statistics. Principal component analysis followed by partial least-squares regression provides a rigorous way of investigating correlations within the data and predicting the explicable variance resulting from chosen end members. Element loadings on the first two components essentially confirm the results of the intuitive graphical approach. APC and clay/soil grab samples are successful signatures for PLS, for complementary sample groups. On the basis of both the intuitive and the statistical data handling, distinctive elemental ratios characteristic of APC and background dusts can be paired in order to define binary mixing trajectories, and thus quantify APC proportion in any individual sample. In one of the sampling intervals under consideration, some 65% APC was recorded close to the active cell margin, decreasing rapidly with dust fall out to 30% within a few hundred metres. This trial study indicates the potential of combining directional sampling with sensitive multi-element analysis to quantify fugitive dust from landfill and other facilities in the waste and industrial sectors.