This paper reviews general approaches for applying activated carbon (AC) amendments as an in situ sediment treatment remedy. In situ sediment treatment involves targeted placement of amendments using installation options that fall into two general approaches: 1) directly applying a thin layer of amendments (which potentially incorporates weighting or binding materials) to surface sediment, with or without initial mixing; and 2) incorporating amendments into a premixed, blended cover material of clean sand or sediment, which is also applied to the sediment surface. Over the past decade, pilot- or full-scale field sediment treatment projects using AC—globally recognized as one of the most effective sorbents for organic contaminants—were completed or were underway at more than 25 field sites in the United States, Norway, and the Netherlands. Collectively, these field projects (along with numerous laboratory experiments) have demonstrated the efficacy of AC for in situ treatment in a range of contaminated sediment conditions. Results from experimental studies and field applications indicate that in situ sequestration and immobilization treatment of hydrophobic organic compounds using either installation approach can reduce porewater concentrations and biouptake significantly, often becoming more effective over time due to progressive mass transfer. Certain conditions, such as use in unstable sediment environments, should be taken into account to maximize AC effectiveness over long time periods. In situ treatment is generally less disruptive and less expensive than traditional sediment cleanup technologies such as dredging or isolation capping. Proper site-specific balancing of the potential benefits, risks, ecological effects, and costs of in situ treatment technologies (in this case, AC) relative to other sediment cleanup technologies is important to successful full-scale field application. Extensive experimental studies and field trials have shown that when applied correctly, in situ treatment via contaminant sequestration and immobilization using a sorbent material such as AC has progressed from an innovative sediment remediation approach to a proven, reliable technology. Integr Environ Assess Manag 2015; 11:195–207. © 2014 The Authors. Published 2014 SETAC.

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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).

Four geotechnical stratigraphic units, with different strength characteristics, are identified from four Jumbo Piston Cores taken in stable plateau regions on the Continental Slope in the Northwest Gulf of Mexico where normally consolidated conditions exist. A comparison of data from the plateau regions and the basin slope regions shows clear evidence of past slope failures. From the stress state determined on a slope of a basin, it is estimated that 8 to 12 meters was removed from the site prior to deposition of the existing five meters of overburden.

The full range of stress states; normal consolidation, "true" or mechanical overconsolidation, underconsolidation, and apparent overconsolidation; are reported for typical locations on the slope/rise of the northwestern Gulf of Mexico. On the flatter plateau regions, the upper 2-3 meters exhibits apparent overconsolidation (AOC), and the deeper sections are either normally consolidated or underconsolidated within the cored depths of 20 meters. The underconsolidated zones, with OCR/SSR values of about 0.5, seem to correlate with thick deposits of finely laminated sediments. The possible high rates of sedimentation of the laminates and presence of the AOC zone may be the cause of underconsolidation, but other hypotheses are considered. The in situ effective stresses would be reduced due to the excess pore water pressures that have implications for slope stability analyses and other geotechnical applications. Deep tow, bathymetric data, and core data from most of the slope regions within the deeper basins indicate the full range of mass wasting processes including translatory/slab slides, deep seated rotational slumps and debris flows. Consolidation test results from overconsolidated zones can be used to estimate the amount of sediment removed by mass wasting processes. The analysis of three basin slopes where cores were obtained indicates that 5, 14, and 15 meters have been removed from these sites. Introduction During the 1990's there was increased interest by engineers and scientists in the seabed of the deepwater areas of the northwestern Gulf of Mexico. In order to better understand the seabed processes in this region, a five-year joint project by the University of Rhode Island and Texas A&M University was initiated in 1996. This project is sponsored principally by the National Science Foundation, with supplemental funding from industrial sponsors that now include Chevron, Conoco, Marathon, Phillips, and Texaco (Amoco was a sponsor for one year). The general study area, which includes most of the typical seabed features on the slope and rise, is shown in Fig. 1. Several OTC papers resulting from the first few years of research have been published in proceedings of OTC 1999 and OTC 2000. This paper summarizes the results of laboratory experimental studies relating to the state of stress (stress history) of the sediments in the study area and the relation to slope processes of specific areas. In this paper we are interested in the sediment stress profile, i.e. the vertical variation of effective stress and pore water stress, of the upper 20 meters of the seabed in typical geological settings. If excess pore water pressures (often termed overpressures) exist in the sediment column, there are obvious implications for engineering applications and for analyses of seabed processes such as stability of slopes. Knowledge of the stress state, especially overconsolidation, can also be very useful in determining where and how past slope failures have occurred and assist in interpretation of similar features.