2.2.3 Large-Scale Spatial Heterogeneity
The highest level of matrix heterogeneity is large-scale heterogeneity. Its spatial scale is usually on the order of tens of meters and larger, and it is the type of heterogeneity that practitioners expect. This is the heterogeneity caused by common release and transport mechanisms, such as spills, dumping of contaminated soil or sediment, atmospheric deposition downwind of a source, or contamination carried downstream via overland flow or a stream. Large-scale heterogeneity is reflected in the difference between soil areas that are, for example, highly contaminated, moderately contaminated, lightly contaminated, and not contaminated. This is the spatial scale often assumed for discrete samples in traditional sampling designs looking for contamination, estimating the volume of contaminated media, and delineating areas for cleanup.