Puget Sound sediment cleanup remedy effectiveness retrospective.

The monitoring of completed large-scale sediment remediation projects has revealed mixed effectiveness at reducing risks, thus highlighting uncertainties regarding whether and which remedial measures are necessary to achieve protective goals. To support valid statements about changes over time and the overall effectiveness of sediment remedial action, robust pre- and postremediation monitoring is required with sufficient time points, reference sites, and biological metrics. The five completed Puget Sound sediment remediation case studies reviewed here (Bellingham Bay, St. Paul Waterway, Eagle Harbor, Hylebos Waterway, and Sinclair Inlet) employed particularly robust remedy effectiveness monitoring programs that spanned decades, revealing common lessons for improving remediation outcomes. First, although sediment remediation can play an important role in reducing contaminant exposure in areas with higher sediment concentrations, at lower levels, sediment links with fish tissue concentrations diminish. As water column exposure from diverse sources becomes predominant, remediating sediments with lower concentrations yields proportionately less risk reduction. Second, timely monitoring of effective source controls achieving substantial (i.e., >80%) contaminant source load reductions as well as large-scale capping projects have revealed rapid changes in Puget Sound surface sediment concentrations and biological recovery metrics with an average recovery half-time of 1.6 ± 0.8 years. The weight of evidence suggests that natural recovery of Puget Sound surface sediments is significantly accelerated by exchange across the sediment-water interface from benthic organism feeding behaviors, porewater flux, and tide-generated currents. As a result, effective source controls in Puget Sound have rapidly improved surface sediment quality and achieved more significant risk reductions than broadscale sediment remediation. Going forward, comprehensive Puget Sound source control efforts that incorporate robust monitoring in an adaptive management framework are the best way to achieve protective remediation objectives. These lessons may apply more broadly across similar complex urban aquatic ecosystems. Integr Environ Assess Manag 2024;00:1-11. © 2024 The Authors. Integrated Environmental Assessment and Management published by Wiley Periodicals LLC on behalf of Society of Environmental Toxicology & Chemistry (SETAC).

Environmental dredging residual generation and management.

The presence and magnitude of sediment contamination remaining in a completed dredge area can often dictate the success of an environmental dredging project. The need to better understand and manage this remaining contamination, referred to as "postdredging residuals," has increasingly been recognized by practitioners and investigators. Based on recent dredging projects with robust characterization programs, it is now understood that the residual contamination layer in the postdredging sediment comprises a mixture of contaminated sediments that originate from throughout the dredge cut. This mixture of contaminated sediments initially exhibits fluid mud properties that can contribute to sediment transport and contamination risk outside of the dredge area. This article reviews robust dredging residual evaluations recently performed in the United States and Canada, including the Hudson River, Lower Fox River, Ashtabula River, and Esquimalt Harbour, along with other projects. These data better inform the understanding of residuals generation, leading to improved models of dredging residual formation to inform remedy evaluation, selection, design, and implementation. Data from these projects confirm that the magnitude of dredging residuals is largely determined by site conditions, primarily in situ sediment fluidity or liquidity as measured by dry bulk density. While the generation of dredging residuals cannot be avoided, residuals can be successfully and efficiently managed through careful development and implementation of site-specific management plans. Integr Environ Assess Manag 2018;14:335-343. © 2018 The Authors. Integrated Environmental Assessment and Management Published by Wiley Periodicals, Inc. on behalf of Society of Environmental Toxicology & Chemistry (SETAC).

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.