Long-term fate of organics in waste deposits and its effect on metal release

The long-term chemical evolution in waste deposits and the release of toxic metals was investigated, The degradation of organic matter and hence the p otential efflux of heavy metals in a long-term perspective was studied by d efining some scenarios for waste deposits containing organic compounds, dif ferent longevity and functions of covers and different water and air intrus ion rates. The scenarios were based on various transport processes as well as different landfill constructions. The rates of influx of oxygen into bot h saturated and partially saturated landfills have been estimated. Each sce nario takes the form of a mathematical model. The starting point for all th e studied cases is the humic phase, i.e. the phase after the methane produc tion has stopped. Based on the different cases studied, it appeared that la ndfills where the waste is below the water table could have advantages over the other cases. Recognizing that this option is not accepted in most coun tries we, nevertheless, suggested it should be reevaluated. The main conclu sion is that the degradation of humic matter and hence the release of toxic metals can be substantially decreased if potential build-up of hydraulic g radients are avoided and if the landfill is located below the water surface . A conceivable alternative construction would be to place it in a depressi on - either natural or artificial - and to construct it so that under norma l conditions it would always be water-saturated, (C) 1999 Elsevier Science B.V. All rights reserved.