A recent cover story in Environmental Science and Technology (ES&T), an internationally renowned scientific journal, highlighted SERDP research and ESTCP demonstrations of in situ remediation of contaminated sediments. The article, In-Situ Sorbent Amendments: A New Direction in Contaminated Sediment Management, describes recently concluded laboratory studies and provides a summary of ongoing pilot-scale trials, field challenges, regulatory issues, and future research needs. It describes how the addition of sorbent amendments can be used to alter sediment geochemistry and increase contaminant binding to sediment, thereby reducing contaminant exposure risks to humans and the environment (i.e., bioavailability).
Aquatic sediments are often the ultimate receptors of contaminants in effluent from military activities on installations. Sediments contaminated with hydrophobic organic compounds (HOCs)—polychlorinated biphenyls (PCBs) and polycyclic aromatic hydrocarbons (PAHs)—in addition to metals and metalloids can be found in marine and estuarine bays, harbors, lakes, wetlands, and rivers. HOCs tend to bind to the sediment particles and persist in the environment for long periods of time, representing a long-term source of contaminants. Hundreds of Department of Defense sites with contaminated sediments already have been identified. And, as estuarine and coastal areas fall under increasing scrutiny, the number of sites requiring action is expected to increase.
The more widely used remediation approaches, dredging and capping, are costly, energy-intensive, and disruptive to the environment. The application of in situ amendments provides a less invasive approach to remediate and monitor contaminated sites in addition to avoiding concerns of contaminant resuspension.
Activated carbon (AC), which is a clean manufactured carbonaceous material, is the amendment used in the majority of the research and demonstrations highlighted in the article. AC provides a binding platform for HOCs that decreases their bioavailability to organisms. When AC is mixed with existing sediment as an amended layer, this layer provides a platform where “clean” sediment can settle and a “barrier” for the surface sediment and aquatic environment. In the laboratory, amended sediment showed a decrease in the bioavailability of HOCs. The movement of the organisms living in the sediment through the amended layer also allowed for a natural mixing of these amendments with the new and old sediment layers.
Demonstrations have been conducted at field sites in the United States and Norway to evaluate different methods of applying AC to sediments in a variety of contaminated aquatic environments. The ESTCP pilot study at Hunter’s Point Naval Shipyard in San Francisco, California, found that an AC-amended sediment layer could be placed in a “real world” setting and be stable for several years. There was no significant impact on the organisms present at the site, and the technology was proven to be a less-expensive alternative to dredging and other remediation approaches.
Although amended sediments are showing promising results, regulators remain cautious because the contaminant is not removed. Rather, exposure risks are decreased by contaminant binding to sediment. With further research, the scientific community is laying the groundwork to support a balanced and scientifically defensible evaluation of all potentially applicable remedial methods.
: Ghosh, U., R.G. Luthy, G. Cornelissen, D. Werner, and C. Menzie. 2011. In-situ Sorbent Amendments: A New Direction in Contaminated Sediment Management. Environ. Sci. Technol. 45:1163-1168.