Most sites, whether consisting of natural soils or made ground, have heterogeneities. These are a major concern in the understanding of contaminant transport mechanisms and in the selection and success of remedial measures.
In the UK, 25 million car tyres and 3 million truck tyres are discarded each year. Of this 18% is used for retreading, 6% for regeneration (eg granulation, carbon/oil extraction and steel recovery) and 9% is incinerated. This leaves 67% which is stockpiled, landfilled or illegally dumped, although the problem is far worse in the US. The best way to reduce the environmental and health hazards associated with scrap tyres is to minimise, and ultimately eliminate, stockpiling.