Some geotechnical studies of waste landfills in Portugal were used in order to address several questions concerning the best geological formation for their foundation. The geotechnical features which were adopted in the selection and classification of the chosen sites are discussed. As it is difficult to find thick clayey layers, a region where the geological structure is composed of medium thick layers, alternately clayey and sandy, was proposed. The results of some tests on migration of contaminants which were performed at the foundation of a waste landfill are presented. Monitoring programmes are recommended in order to obtain more quantitative information for further studies and for a more suitable design of waste landfills.


For many years, in Portugal, urban waste was collected by the municipalities and was deposited on fields without previous analysis of the site suitability or of the pollution effect on the environment. In general, the selection of those waste deposit sites was merely based upon the commercial value of the site or availability from the owner. Thus, many unsuitable sites were used and the waste deposits polluted the soils and the groundwater as no geotechnical or environmental studies were performed and no engineering designs or practices were used or adopted. In small municipalities the waste was deposited directly over the surface. Thus, during rainy seasons the water swamped the whole area creating a big amount of leachates which were drained in open air conditions along the fields and directly to the water courses. The rivers and streams existing nearby were submitted to an intensive contamination and become hardly polluted. According to most of the environmental criteria, that water become unsuitable to be used for human, animal, agricultural and farming or industrial purposes without a previous treatment.

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