Heavy metals adsorbed by sediments are of particular concern due to their mobility and toxicity in the aquatic ecosystem. Harbour areas, particularly on the banks of large rivers, have been facing deposition of polluted sediment. Considering a technique for remediation of contaminated sediment needs a comprehensive understanding of the geochemical and physical characteristics of sediment. In this study, a set of surface sediment samples was taken from a harbour on the bank of the St. Lawrence River, Quebec, Canada. The harbour area was polluted by heavy metals and there was an urgent need to dredge the sediments. However, prior to managing the sediments, the toxicity and availability of metals in sediment should be evaluated. Determination of the particle size distribution was performed in addition to pH, loss on ignition (LOI) and oxidation-reduction potential (ORP). To examine the mobility and dynamics of heavy metals in sediments, a sequential extraction technique was used. Cr, Ni, Cu, Zn, As, Cd and Pb were the elements investigated in this study. Results showed that the sediment samples were highly organic and the textures were pretty fine. The results also indicated that the copper, zinc and chromium were the main elements that exceeded the occasional effect level based on the Environment Canada sediment quality guidelines. However, the risk of mobility due to the availability of cadmium and lead was significantly more than the other elements. For example, the concentration of cadmium in a location was around 60% in exchangeable and carbonate fractions of the total. The most contaminated location was near the dock area, where usually receive the runoffs from the boat maintenance area. To conclude, the concentration and potential mobility of heavy metals in sediments near the dock area must be considered when determining the most appropriate management strategy.

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A convection-diffusion transport model of soluble contaminant suitable for one-dimensional homogeneous unsaturated three-layered soils is established. The transport processes of soluble contaminant are analyzed by a semi-analytical method, which takes into account the boundary conditions of pond infiltration. Various combined soil layers and various absorption models (e.g. linear or nonlinear adsorption) are discussed. Studies show that, under pond infiltration, the immigration velocity in coarse grained soil will be greater than that in fine grained soil; furthermore the diffusion ratio of the former will also be higher than the latter. Besides, the influence of initial pressure head on immigration velocity can be neglected; however the concentration peaks of contaminant will increase with the decrease of initial pressure head.

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With considering the distance-dependent diffusion coefficient, a one-dimensional contaminant diffusion model was developed. An analytical solution was obtained by using the orthogonal expansion method. The corresponding program was compiled on the basis of the proposed solution, and the effect of the relevant parameters on contaminant transport was analyzed. The results indicate that the diffusion coefficient has complex effects on the transport of contaminants. On one hand, the initial diffusion coefficient and heterogeneity parameter will affect the time of contaminant concentration reaches steady state, and on the other hand, the heterogeneity parameter affects the concentration of steady state. In addition, the influence of related parameters on the bottom flux of contaminant was discussed. The proposed analytical solution can be used for verification of complicated numerical models and experimental data fitting.

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The groundwater always rich in corrosive ions such as sulfate and chloride in coastal or industry developed regions. Exposing to the corrosive groundwater environment could cause the secondary contamination of the cement solidified/stabilized heavy metal contaminated soils. Corrosive ions may change the deformation behaviors of the solidified soils by binding into the cement binders. To investigate the stress-strain properties of the cement stabilized/solidified chromium contaminated soils that had been soaked in the sodium chloride solution, a series of triaxial stress-strain tests were performed. The results showed that the stress-strain curve of the specimens included three phases: ①Elastic deformation;② Plastic yield deformation ;③ failure-deformation. Both the failure stress and failure strain increased with the confining pressure increased. The presence of corrosive caused the failure stress decrease and the slope of the stress-strain curve in failure-deformation stage decline. Compared with the short-time soaking specimens, the failure stress increased and the failure strain decreased of the long-time soaking specimens. Generally, the stress-strain curves of the specimens presented strain softening, and belonged to brittle failure.

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In this study, a microbial fuel cell has been designed for the marine sediment to generate bio-electricity and to improve the geo-environmental condition simultaneously. Four different kinds of sediments were used in the laboratory tests to generate the bio-electricity. The acid volatile sulfide (AVS) was measured to verify the improvement of the geo-environment of the marine sediment. The effects of temperature, number of anode and the different conditions of the circuit were evaluated to observe the bio-electricity generation . The amount of voltage value showed almost twice when two anodes were used compared with single anode. Higher temperature showed the higher voltage due to enhanced activity of the bacteria in the higher temperature. Acid volatile sulfide values reduced quickly when the circuit was completed. All the samples showed the decreasing trend of AVS value with time and reached at the 0.2 mg/g dry mud indicating the geo-environmental improvement of the marine sediments.

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The objective of this paper is to provide results of a study on verifying the remediation of sand contaminated by LNAPL. The remediation mechanism used was air injection and a micro x-ray computed tomography (CT) scanner was used to show the effectiveness of the mechanism. First, air at 20oC and 60oC was injected into dry sandy soil. Then, the specimen was observed for effluent change. In this paper, the following three items will be shown: 1) development of the test apparatus for fluid injection into the sandy soil, 2) establishing a scan method using a micro-focused x-ray CT scanner and 3) development of a new image processing technique that can evaluate residual fluids in the pore structure of sandy soil.

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