Management of PCB-contaminated Sediments Through Sediment Characterization and Evaluation of Active Capping Techniques PDF Download

Author: Michael Christopher Scullion
Publisher:
ISBN:
Category : Sediment capping
Languages : en
Pages : 164

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Book Description
Abstract: Polychlorinated biphenyls (PCBs) were heavily used for over fifty years in industrial applications, primarily inside capacitors and transformers. Over twenty years after their phase-out in the United States PCBs are still one of the most widespread contaminants in the environment. PCBs are stable compounds with low aqueous solubility and vapor pressure. These unique properties led to the extensive use of PCBs and are also responsible for their continued presence in the environment today. Due to their hydrophobic nature PCBs tend to accumulate in soils and sediments, and also bioaccumulate in the fatty tissues of aquatic organisms. At higher levels of the food chain, biomagnification produces elevated PCB concentrations in tissue due to the transfer of PCBs from smaller organisms consumed by the larger organisms. Several locations across the United States have fish consumption advisories in place due to PCB contamination. Currently used management techniques include monitored natural recovery, in- situ capping, and dredging and dewatering. All of these methods have major drawbacks preventing their wide-scale use. Monitored natural recovery is subject to a large degree of uncertainty and is also viewed negatively by the public. In-situ capping is prone to disruption and caps are difficult to install at a controlled thickness. Dredging and dewatering is the most commonly used process because it physically removes contaminants from the site. However, it is also a very time consuming and costly process. An emerging technology in contaminated sediment management is active capping involving the use of a sorbent material instead of inert sand to control the release of contaminants from sediment. The application of the sorbent has been shown to be a problem, however a new product from CETCO (reactive core mat, RCM) has shown the potential to alleviate this problem. This study examines sediment management technologies in two parts. First, sediments from three geographically diverse locations across the Great Lakes were characterized to examine trends in the distribution of PCBs throughout the sediment based on physical and chemical characteristics. The second part of the work evaluates the performance of CETCO's organoclay, activated carbon, and sand in sediment capping applications. Sediment characterization involved measuring a variety of physical and chemical properties of bulk sediment from the Ashtabula River, the Lower Fox River, and the Grand Calumet River. Sediment fractions were isolated in order to evaluate variations in the carbon and nitrogen content, and the PCB content as a function of sediment grain size and specific gravity. Results from the characterization suggest that PCBs tend to accumulate in the large-sized, less-dense organic fraction in sediments with low levels of PCB contamination and low bulk sediment carbon concentration. The distribution of PCBs is more uniform in sediments with larger levels of contamination, and higher bulk carbon content. Evaluation of the sorbents in ten day equilibrium batch tests showed for the two PCB congeners examined that activated carbon has a greater affinity for PCBs than organoclay. Both sorbents were found to have a greater affinity for the more highly chlorinated PCB congener, which is consistent with the literature. Consolidation tests used to simulate rapid dewatering revealed that the majority of PCBs released from the sediment are associated with suspended particles. The organoclay and activated carbon both proved to be more effective at reducing PCB release than sand; however, the organoclay was better able to control release for all PCB congeners examined, reducing the total amount of release by 94 percent. Loose organoclay and an organoclay filled RCM were found to be equally effective at removing PCBs during dewatering. The results of this study suggest that sediment characterization at a given site may be beneficial when choosing an appropriate management strategy. CETCO's organoclay proved to be more effective during rapid dewatering than activated carbon, and the use of an RCM to retain the capping material was equally effective in removing PCBs from the pore water.