Bench-Scale Testing to Support Engineered Sediment Cap Design

摘要

Background/Objectives. Bench-scale treatability studies are commonly used to evaluateremedial options for contaminated sites prior to field implementation. The studies providethe ability to compare different treatment technologies in a relatively short time frame,test multiple conditions concurrently, and the flexibility to allow changes to a remediationstrategy that would be impractical at field-scale.Natural or stimulated biodegradation processes in sediment caps can significantly improvethe protection provided by caps installed over contaminated sediments. Treatabilitystudies can demonstrate the potential benefits of amendments including electron acceptorsand/or donors, pH neutralization agents, nutrients and bioaugmentation cultures andactivated carbon addition. These amendments can promote sequestration or degradationof common sediment contaminants including chlorinated solvents, petroleum hydrocarbons,benzene, toluene, ethyl benzene and xylenes (BTEX), metals (e.g., mercury) andpolychlorinated biphenyls (PCBs).Approach/Activities. Treatability studies are frequently performed to evaluate amendmentsfor engineered sediment caps. These studies are conducted using site sedimentsamples to evaluate the potential for biodegradation or sequestration of contaminants undera variety of geochemical conditions that may develop in the different intervalstypically observed within an engineered sediment cap. Microcosms are constructed fromintact sediment cores to preserve in situ redox conditions and are retrieved from differentlocations 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 donoramendment, electron acceptor amendment (sulfate, nitrate and oxygen) and pH adjustment.The results demonstrated intrinsic dechlorination of dichlorobenzene (DCB) tochlorobenzene (CB) and degradation of phenol and toluene under anaerobic conditions.Furthermore, the addition of electron donor appeared to reduce the lag time associatedwith intrinsic DCB dechlorination. Under anaerobic conditions no further dechlorinationof CB was observed, however degradation of naphthalene, BTEX and CB was observedunder induced aerobic conditions through addition of oxygen added to microcosms. Degradationwas also observed in some microcosms where nitrate and sulfate were added aselectron acceptors. The study results are currently contributing to the design of the engineeredcap.The benefits and limitations of performing laboratory treatability studies for engineeredsediment caps will be discussed, and additional case studies will be presented toillustrate the practical uses of bench scale sediment treatability studies.