| A sediment cap can prevent and/or reduce the transport of pollutants from legacy contaminated sediments to levels acceptable through sequestration, degradation, and/or hydraulic containment; particularly in the case of active caps which have specific amendments to improve some or all of these functions. This thesis was focus on characterization of contaminated sediments in terms of contamination type, hydraulic condition and topography, active capping transport simulations, isotherm studies to provide better parameter data, and comparisons between column transport experiments and model.;The Collateral Channel sediment characteristics indicate heavy PAHs pollution, low bioturbation and large amounts of gas ebullition. Therefore gas ebullition control is considered in the cap design. Transport simulations were employed to model cap performance for 12 organic compounds under five cap amendments with model parameters obtained from a comprehensive literature review. Granular activated carbon and organoclay demonstrated the best treatment due to their large sorption capacity and low hydraulic conductivity. However, less hydrophobic organics such as benzene, toluene and ethylbenzene were not retarded in the thin caps used in the simulations and thus may require thicker caps. The sensitivity of model output to variation in the literature-obtained input parameters may result in wide variations in field performance. Therefore laboratory-scale isotherm and column studies were conducted to validate the model simulations. Overall agreement between the literature-derived and experimentally obtained parameter values was achieved. Less variation in partitioning coefficient values were generated from the isotherm data than from the breakthrough data generated in the column studies. With the three phases of study, a basic model has been set up to provide a database of values for long-term simulation of active capping technology effectiveness for in situ implementation. |
