EVALUATING THE STABILITY OF CONTAMINATED SEDIMENTS

The common situation at contaminated sediment sites is one in which the chemical concentration is highest in buried sediments. If the sediments are stable, these high concentrations will remain isolated from biota and will not pose a risk. If the sediments are unstable when the water body is subjected to a high-energy event, it is possible that the high concentrations would cause an increase in the impacts to human health and the environment. In the former case, the most prudent decision could be to allow natural recovery to continue. In the latter case, the most prudent decision could be to remediate the sediments by removal or capping.The methods to evaluate sediment stability are broadly separated into two categories: empirical analysis and modeling. Empirical analyses use site-specific data to evaluate whether sediments have been stable through high-energy events that occurred in the past. Examples include: bathymetric, geochronologic, and geomorphologic evaluations; assessments of temporal and spatial trends in contaminant concentrations; and development of sediment and chemical mass balances during storms.Models developed from sediment transport theory and site-specific data provide a means to predict whether sediments will be stable when subjected to an event that has not yet occurred. They predict the location and depth of bed scour and changes in surficial chemical bed concentrations.