WM2008 Conference, February 24 -28, 2008, Phoenix, AZ Effectively Managing Risks of Contaminated Sediments – 8309 Danny D. Reible and David Lampert Department of Civil, Architectural and Environmental Engineering The University of Texas at Austin ABSTRACT Various research undertaken over the past decade has improved our ability to assess and effectively manage contaminated sediments. Key to this improvement is a better understanding of the risks, both in time and space. Sediments can pose risks if contaminants are present in the biologically active zone of a water body or if transport processes can move contaminants into that zone. Conversely, effective management of contaminants can be accomplished by physically separating contaminants from the biologically active zone or hindering the transport processes that can result in contaminant migration. Both of these are accomplished by sediment capping, either conventional capping with a passive barrier such as sand, or, when greater control over mobile contaminants is required, by active capping in which amendments are used to retard any applicable transport processes. In this paper, the key transport and exposure processes are assessed and the ability to manage these risks with both passive and active capping evaluated. INTRODUCTION Contaminated sediments pose some of the most difficult problems for site remediation and risk management. Sites typically have large sediment volumes with relatively low contaminant levels. Because of the extent and difficulties of managing these sediments, literally billions of dollars often depend upon the selection and implementation of appropriate remedial decisions. As highlighted by a recent National Research Council study [1], traditional approaches calling for the removal of sediments for subsequent treatment or disposal often leave significant residual contamination and generate large amounts of water that must be treated. Thus invasive removal options are often less protective of the environment in addition to being more costly than other approaches. As a result, efficient and effective management of contaminated sediments has often been a contradiction in terms. Various research undertaken over the past decade has improved our ability to assess and effectively manage contaminated sediments. Key to this improvement is a better understanding of the risks, both in time and space. These risk assessments address three basic requirements. The first is accessibility; strongly sorbed contaminants suggest that only the actively eroded or biologically active zone is relevant. The second is availability and assimilative capacity, which considers whether contaminants can desorb to water or be directly absorbed by benthic organisms. Normally, however, benthic organisms are not the focus of risk assessments and the third requirement is accumulation, which considers whether contaminants can accumulate to toxic levels or be biomagnified as they pass to higher organisms of more relevance to assessing ecological or human health risk.