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Investigation of napl migration processes in the unsaturated zone - vadose zone


Research objectives and content
The problem of evaluating the factors controlling the movement of NAPLs in the subsurface has received increasing attention in the last decade after a number of sites in the United States have been found to be contaminated with organic chemicals. Research in this field is just taking off in Europe. With the help of Centrifuge testing, investigating NAPLs migration in the vadose zone would be beneficial to the advancement of knowledge in this field in Europe. Groundwater remediation following a spill of organic contaminants immiscible with water like petroleum product requires knowledge of the subsurface movement and distribution of the contaminant. The primary objective of this research is to evaluate the factors controlling the movement of NAPLs in the vadose zone. This question arises from practical necessity of knowing the distribution and location of NAPLs in order to assess their spreading potential and in particular the time required for NAPLs to reach the groundwater. Many laws and regulations have addressed the need to monitor potential movement of these contaminants. Monitoring coupled with knowledge of transport processes of contaminants in the vadose zone will provide early detection systems to avoid groundwater contamination.
The use of numerical models to predict the migration of
NAPLs has been growing and multiphase flow models have been developed for contaminant hydrology applications. However few of those models have been validated by quantitative laboratory and field data. Recently, centrifuge testing has become a useful tool to model environmental contaminant flow and transport problems. However experimental confirmation for most scaling laws that relate the model to the prototype for flow process has to be accomplished. In this proposed research both column and centrifuge tests allowing instrumented laboratory controlled conditions will be carried out and the effects of the various factors influencing the behaviour of NAPLs migration will be investigated. Those factors include soil type, soil heterogeneity, pressure gradient and amount of NAPL, soil-waterNAPL retention curve and water table fluctuation. Focus will be put on the effect of heterogeneity and water table fluctuation. Use of centrifuge tests able to examine the transport processes in an accelerated time under the correct scaling law of the capillary effect, which is considered to be a major controlling factor of transport mechanisms in the vadose zone. The advantage of the accelerated time in centrifuge tests will allow us to obtain data of relatively impermeable soils which can be time consuming in 1g scale model. In addition the reduced scale model in the centrifuge tests can model the entire length of the vadose zone. Both column and centrifuge experiment will be instrumented and focus will be put on using newly developed sensors and validating new monitoring tools. The research also proposes to examine the available numerical models of vadose zone flow and transport processes which are currently well known and widely used. The centrifuge and the column tests will be used to examine the capability and limitation of those models.
The use of column and centrifuge tests would give estimates of NAPL migration rate in the vadose zone which can be used in practice as well as provide necessary physical data to validate existing numerical models or to develop new models. The comparison with the column tests and the centrifuge tests would provide us with the advantages and the disadvantages of using centrifuge to model multiphase flow and contaminant transport problems.
Training content (objective, benefit and expected impact)
Theoretical and practical training (e.g. Environmental Engineering, Centrifuge Modelling) provided in the form of lectures Academic and research training (research and experimentation, student supervision, laboratory demonstrations, conferences) Participant member of the TMR Network Project NECER and links with the 11 European centrifuge centres The overall impact of the above training will be personal and academic development leading to a PhD.
Links with industry / industrial relevance (22)
Companies and research laboratories like Kajima (Japan), British Petroleum (U.K) and Silsoe Research Institute (U.K) have already shown interest in the project and offered their help and collaboration.

Call for proposal

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University of Cambridge
Trumpington street
CB2 1PZ Cambridge
United Kingdom

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EU contribution
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Participants (1)