Background/Objectives. Bench-scale treatability studies are commonly used to evaluate remedial options for contaminated sites prior to field implementation. The studies provide the ability to compare different treatment technologies in a relatively short time frame, test multiple conditions concurrently and the flexibility to allow changes to a remediation strategy that would be impractical at field-scale.
Natural or stimulated biodegradation processes in sediment caps can significantly improve the protection provided by caps installed over contaminated sediments. Treatability studies can demonstrate the potential benefits of amendments including electron acceptors and/or donors, pH neutralization agents, nutrients and bioaugmentation cultures and activated carbon addition. These amendments can promote sequestration or degradation of common sediment contaminants including chlorinated solvents, petroleum hydrocarbons, benzene, toluene, ethyl benzene and xylenes (BTEX), metals (e.g., mercury) and polychlorinated biphenyls (PCBs). Approach/Activities. Treatability studies are frequently performed to evaluate amendments for engineered sediment caps. These studies are conducted using site sediment samples to evaluate the potential for biodegradation or sequestration of contaminants under a variety of geochemical conditions that may develop in the different intervals typically observed within an engineered sediment cap. Microcosms are constructed from intact sediment cores to preserve in situ redox conditions and are retrieved from different locations to represent conditions across the site. Study design includes sterile controls, baseline conditions (i.e., no amendments) plus site specific amendment regimes. Case Study Results/Lessons Learned. In one study, treatments included electron donor amendment, electron acceptor amendment (sulfate, nitrate and oxygen) and pH adjustment. The results demonstrated intrinsic dechlorination of dichlorobenzene (DCB) to chlorobenzene (CB) and degradation of phenol and toluene under anaerobic conditions. Furthermore, the addition of electron donor appeared to reduce the lag time associated with intrinsic DCB dechlorination. Under anaerobic conditions no further dechlorination of CB was observed, however degradation of naphthalene, BTEX and CB was observed under induced aerobic conditions through addition of oxygen added to microcosms. Degradation was also observed in some microcosms where nitrate and sulfate were added as electron acceptors. The study results are currently contributing to the design of the engineered cap. The benefits and limitations of performing laboratory treatability studies for engineered sediment caps will be discussed, and additional case studies will be presented to illustrate the practical uses of bench scale sediment treatability studies