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Title: Numerical modelling of organic contaminant reaction and transport in bed-sediments
Author: Go, Jason
ISNI:       0000 0004 2668 1393
Awarding Body: University of London
Current Institution: University College London (University of London)
Date of Award: 2008
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Reactive transport modelling of contaminants in the environment is being increasingly relied upon for a wide range of tasks associated with risk-based decision making, such as interpretation of historical contamination data, optimisation of attenuation and remediation methods, and monitoring of changes resulting from an implemented remediation scheme. However, in the area of contaminant fate and behaviour in bed-sediments, reactive transport modelling has until now stopped short of integration of various mechanistic models to a single modelling environment that would allow a cohesive understanding and prediction of contaminant profiles. This study has developed CoReTranS, a predictive modelling environment that simulates one-dimensional organic contaminant reaction and transport in bed- sediments, using an object-oriented modelling approach. The CoReTranS model has been verified and benchmarked by comparing numerical results of simplified problems with their analytical solutions. The following simulations were undertaken to validate the CoReTranS model: 1. Simulation of the dataset from a diffusion-controlled laboratory experiment for the transport and distribution of selected trace level organic contaminants in a riverine environment gave new numerical results to improve on predicted modelling approach. 2. Simulation of the dataset from a study of marsh sediments contaminated with petroleum-derived hydrocarbons from Wild Harbour, West Falmouth, MA and Kitimat Arm, Douglas Channel, British Columbia resulted in an excellent agreement between the numerical results of the transport model in CoReTranS and the numerical results and data of the original study. The CoReTranS model was also used to interpret results from the following field studies in order to explain key processes that controlled the fate and transport of PAHs and PCBs in bed-sediments: 1. Simulation of the dataset from Kitimat fjord system near Kitimat, British Columbia, wherein PAHs in sediments were purported to be derived from atmospheric particle emissions, wastewater discharges and accidental spillages from a nearby duminium smelter provided a better understanding of the post-depositional reactive transport of PAHs in the fjord system. 2. Simulation of the dataset from a study on the natural recovery of PCB-contaminated sediments at the Sangamo-Weston/Twelvemile Creek/Lake Hartwell Superfund Site in the US showed that it would take nearly 30 years to achieve the 1 mg/kg clean-up goal for total PCB in the chosen transect sites, and 20 years more than the predicted time in the original study. The CoReTrans model was also used to predict the effect of capping contaminated sediments as a remedial strategy. Results from the various simulation scenarios using the CoReTranS model showed that sediment capping as a remedial strategy in managing contaminated sediments can effectively reduce contaminant flux to the overlying water through interaction with the sediment cap matrix and by increasing the dissolved contaminants' transport lengths (i.e., cap thickness). Comparing the results obtained from laboratory experiments or field monitoring studies of bed-sediment systems with different accumulation, degradation and release mechanisms, with the results from the CoReTranS model was critical in identifying the key processes that drive the fate and transport of organic contaminants in bed-sediments. The information derived from the use of the CoReTranS model highlighted recommendations to guide future experiments, field monitoring and model extension which include other relevant transport mechanisms such as colloid- enhanced transport, rate-limited reaction processes and the effect of sediment consolidation to contaminant fate and transport. This information will further enable practical application of such information by engineers to site-specific risk assessment and remediation, as well as continued research and technology development.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available