The hydrogeological and geotechnical properties of household waste in relation to sustainable landfilling
This thesis reports an investigation into the hydrogeological and geotechnical properties of household wastes within the context of sustainable landfilling and, particularly, the development of a high rate flushing bioreactor. The design and construction of a large-scale (2-metre diameter) purpose built compression cell used in the research are described. Tests on a number of different household waste materials (including pulverised and aged wastes) were undertaken at varying applied loads up to 600 kPa, equivalent to a 60 metre depth of landfill. Results of variations in refuse density, stiffness, absorptive capacity, effective porosity and hydraulic conductivity are reported against average effective stress in the waste. It was concluded that the hydrogeological properties of household waste vary considerably with effective stress and, hence, with depth in landfills. For example, the hydraulic conductivity of crude household waste could reduce by over three orders of magnitude from approximately lxi O mis to lxi 4 rn/s between placement (with minimal compaction) and burial to a depth of 60 metres. The principles of sustainable development are considered and applied to landfilling. The view that the polluting potential of landfills should be reduced to acceptable levels within a generation is supported. In most cases this will require that contaminants in the landfill are removed by introducing water into the site and recirculating and flushing leachate from it. The feasibility of achieving this with a variety of different leachate recirculation systems is examined in the light of the findings of the research. A new module has been written for MODFLOW, the USGS's groundwater flow model, to allow hydraulic conductivity to vary throughout simulations with effective stress. The altered code is used to model a grid of leachate abstraction and injection wells to illustrate the potential for flushing. It is concluded that changes are needed to current landfill design and operational practices to enable wastes to be flushed efficiently within landfills. It is argued, in particular, that there are significant benefits of operating landfills with large saturated zones.