Site Characterization

Sediment characterization

A sediment's physical and chemical characteristics have considerable impact on the mobility and bioavailability of contaminants--that is, their ability to degrade, transform or affect microorganisms, plants, and animals. Key physical characteristics include:

• texture, a property determined by the distribution of sand, silt, and clay particles in the sediment;
• organic matter content, a property that is important because of the affinity of metals and nonpolar organic contaminants for sediments with high organic (humic) material content; and
• water content in sediments.

Key chemical characteristics include sediment acidity, with strongly acidic sediments slowing down microbial activity and weakly acidic sediments increasing the soluble levels of toxic metals. Another important property is oxidation/reduction status, which strongly influences the retention or release of a number of metals. Other characteristics to be aware of include salinity, sulfide content, amount and type of cations and anions, and the amount of potentially reactive iron and manganese.

Contaminant characterization

Environmental managers not only must catalogue the contaminants in sediments but also map the vertical and horizontal distributions of the pollutants. The ability to model sediment transport as well as the fate and transport of contaminants is an important tool for broadening understanding of a given site. However, no model can have validity without a sound, well executed sampling plan that uses the proper sampling method.

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