Risk assessments involving contaminated sediments sometimes neglect the influence that geomorphological processes may have on the spatial distribution of contamination. In the arid southwest of the United States, sediment particles in ephemeral stream systems are sorted by water flow into a mosaic of distinct geomorphological features, often with different characteristic particle size fractions. Contaminant concentrations, as well as intake via a variety of exposure pathways, may be correlated with particle size. In a recent investigation of a stream system impacted by mining operations, a sampling design based on fluvial geomorphology was used to collect data for risk assessment purposes. Chemical concentration data for different particle size fractions were obtained within geomorphological features over several miles of an ephemeral stream. Several exposure pathways were employed to evaluate the potential significance of particle size and geomorphological sorting on risk estimates.
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