Dredging processes and remedy effectiveness: Relationship to the 4 Rs of environmental dredging

Timely and effective remediation of contaminated sediments is essential for protecting human health and the environment and restoring beneficial uses to waterways. A number of site operational conditions influence the effect of environmental dredging of contaminated sediment on aquatic systems. Site experience shows that resuspension of contaminated sediment and release of contaminants occur during dredging and that contaminated sediment residuals will remain after operations. It is also understood that these processes affect the magnitude, distribution, and bioavailability of the contaminants, and hence the exposure and risk to receptors of concern. However, even after decades of sediment remediation project experience, substantial uncertainties still exist in our understanding of the cause-effect relationships relating dredging processes to risk. During the past few years, contaminated sediment site managers, researchers, and practitioners have recognized the need to better define and understand dredging-related processes. In this article, we present information and research needs on these processes as synthesized from recent symposia, reports, and remediation efforts. Although predictions about the effect of environmental dredging continue to improve, a clear need remains to better understand the effect that sediment remediation processes have on contaminant exposures and receptors of concern. Collecting, learning from, and incorporating new information into practice is the only avenue to improving the effectiveness of remedial operations.