Engineering Geology of Landfill Gas Migration.

The migration or threat of migration of landfill gas has become of central importance to a large number of people during the period of this research, it is widely considered to be a 'black art' by many, and in some sense this has been true, because there have been relatively few research projects which previously attempted to examine how ground gases move within the ground. Consequently, given the level of ignorance on the subject, it was not surprising that gas migration was considered to be ill-defined. The present thesis was undertaken in order to bring together the various parts of a very multidisciplinary subject, and present a state of art review of these strands. Having achieved that, the next objective was to develop and describe techniques which have practical application for measuring and predicting landfill gas migration, in order that legal controls over the waste disposal industry could be given greater meaning and definition. These are necessary if the industry is to maintain viable and safe landfilling, and clearly demonstrate this to the public. The thesis is divided into five chapters dealing with the subject in an increasingly practical manner, so that: Part one is an introduction to landfill gas, and why it is considered to be a problem. Some definition of terms is introduced along with the state of art of the waste disposal industry in dealing with the subject. The subject of the migration of the gas is taken further with an examination of the state of art with respect to theories of gas transport mechanisms, starting with a review of the gas laws, academic principles of gas thermodynamics as it influences fluid mechanics, and ending with a description of work which has previously been carried out upon real soils and landfill sites. In part two the technique developed in this research to enable a laboratory examination of real soils is discussed. It is concluded that despite the difficulties of obtaining, and testing rocks simply, cheaply and realistically the method described gives a good order of magnitude method for the examination and prediction of rock and soil characteristics with respect to their 'permeability' to gas. Field experiments are then described which form part of the landfill gas monitoring programme in the field. The whole group of data, collected at a variety of sites, included measurements of meteorological conditions, ground pressures on and off the landfill, and ground gas concentrations. The observations were used to construct a model of ground gas interchange between the landfill and surrounding land. Field pumping trials have been used to confirm these findings. The third part of the thesis is an examination of case histories, presented in order of detail available for each; results of a survey carried out between other county councils in England , and then the results of a survey in the county of Kent. Finally there is a presentation of the detailed histories of the waste disposal sites which have been examined for the purposes of this research. There follows a conclusion and discussion on the results of the research , and implications for further work. A series of appendices give essential supplementary information which will not be available from references elsewhere