A series of tests has been carried out on crude unprocessed household waste in a large purpose-built compression cell, to investigate the variations in density, drainable porosity and hydraulic conductivity with vertical stress. An increase in the particle density of the waste with increasing stress was identified; this may mean that the applicability of some standard soil mechanics theories to household waste may need to be reviewed. The results of the tests are described and discussed, with reference to their implications for the flow and control of leachate in landfills. The hydrogeological limitations on vertical flushing rates in landfills operated as flushing bioreactors are considered and the operation and performance of leachate extraction wells investigated by means of simple analytical models. A series of tests has been carried out on crude unprocessed household waste in a large purpose-built compression cell, to investigate the variations in density, drainable porosity and hydraulic conductivity with vertical stress. An increase in the particle density of the waste with increasing stress was identified; this may mean that the applicability of some standard soil mechanics theories to household waste may need to be reviewed. The results of the tests are described and discussed, with reference to their implications for the flow and control of leachate in landfills. The hydrogeological limitations on vertical flushing rates in landfills operated as flushing bioreactors are considered and the operation and performance of leachate extraction wells investigated by means of simple analytical models.