Mapping refuse profile in Singapore old dumping ground through electrical resistivity, S-wave velocity and geotechnical monitoring.

The purpose of this study was to track the refuse profile in Lorong Halus Dumping Ground, the largest landfill in Singapore, by electrical resistivity and surface wave velocity after 25 years of closure. Data were analyzed using an orthogonal set of plots by spreading 24 lines in two perpendicular geophone-orientation directions. Both geophysical techniques determined that refuse boundary depth was 13 ± 2 m. The refuse boundary revealed a certain degree of variance, mainly ascribed to the different principle of measurements, as well as the high heterogeneity of the subsurface. Discrepancy was higher in spots with greater heterogeneity. 3D analysis was further conducted detecting refuse pockets, leachate mounding and gas channels. Geotechnical monitoring (borehole) confirmed geophysical outcomes tracing different layers such as soil capping, decomposed refuse materials and inorganic wastes. Combining the geophysical methods with borehole monitoring, a comprehensive layout of the dumping site was presented showing the hot spots of interests.

Evaluation of the leaching behavior of incineration bottom ash using seawater: A comparison with standard leaching tests.

Batch and column tests were conducted on untreated incineration bottom ash (IBA) samples from two incineration plants in Singapore, using seawater as the leachant. The main objective of this study was to investigate the change in the leaching behavior of certain elements (i.e. As, Cd, Cr, Cu, Ni, Pb, Sb, Se and Zn) when IBA comes into contact with seawater. Such an investigation using seawater as leachant was not commonly carried out when investigating leaching behavior in IBA. The leaching tests were then carried out on the same IBA samples using DI water, as a comparison. Lower level of leaching was observed for Pb and Zn when seawater was used as the leachant. Cr and Sb showed significant cumulative release at Liquid-to-Solids (L/S) ratio 5 in the seawater column leaching. The influence of Dissolved Organic Carbon (DOC) on Cu leaching seems to decrease after L/S 2 when using seawater in the column test. Although the leaching behavior of IBA was affected when seawater was used, for the column test, there was no significant difference during the initial release when compared to DI water. The initial L/S fractions collected were important as the low L/S ratios represent the pore water concentration and the maximum output in an actual application. The results from this study would be useful for the future study on using IBA in marine applications.