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Re-visiting Acceptance Criteria Calculations for Monolithic Waste Landfill with Reactive Transport Modeling: Application to Total Dissolved Salts (TDS)

Abstract : Stabilization and solidification of hazardous waste before storage in an engineered landfill has been used at an industrial scale for more than 10 years in several European countries. The European decision 2003/33 specifies a waste acceptance criteria (WAC) for granular waste but there is still no common rules for monolithic waste. One alternative is to define WAC from reverse environmental impact calculations based on compliance of the storage site release with drinkable water criteria at the local water table. However - and contrarily to reactive transport modeling - most published studies do not take into account the physical-chemical processes taking place in the waste and the liners, as well as their long-term evolution with time. Such a simplification can lead to very low acceptance criteria, especially for salts. Chloride and sulfates salts are the major species in air pollution control (APC) residues, which represent the majority of treated waste in France and the Netherlands. A model of the stabilized waste material was set on total element content, mineralogy and physical parameters (diffusion, porosity, density). In a first stage, the model was validated on dynamic leaching tests by modeling element release and mineralogical evolution of leached monoliths. The model was also used to simulate a French compliance leaching test. Modeling is in good agreement with experiment in both cases. These results show that limit values defined by European decision on chloride and total dissolved solid (TDS) are not equivalent. For the studied sample, chloride release is very close to the European limit (25 000 mg/kg) while TDS release is well below the European limit (10%). In a second stage, the model was extended to assess the impact of landfilling stabilized waste on groundwater resources. Modeling hypotheses were similar to the scenario of the European Technical Application Committee (TAC) prescribed for defining acceptance criteria on granular waste, i.e. assuming a complete failure of the geomembranes, a defective drainage system and no effect of the cover slope. The evolution of the waste chemistry and the migration of the pollutant plume were modeled for undamaged monoliths in agreement with recent studies based on the examination of aged site samples. Chloride content in the water table at the point of compliance infinite source term, which is physically impossible as the waste cannot release more chloride than it contains. Chlorides were then assumed to be present in very mobile phases or partly trapped as less soluble Friedel's salts (a chloroaluminate cement phase). Chloride concentrations at POC are below the drinkable water thresholds in both cases, and systematically lower when chlorides are trapped as Friedel's salts. This reactive transport modeling study shows that landfill of monoliths as presently managed should have a negligible impact on the water table. This coupled model is also important for bridging the gap between compliance tests and field conditions. Field modeling is consistent with WAC based on a short monolithic leaching test and the existing TDS limit. Therefore, it is likely that no stricter WAC will need to be defined on salt release for monolithic waste.
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https://hal-mines-paristech.archives-ouvertes.fr/hal-00568748
Contributeur : Pascale Nalon <>
Soumis le : mercredi 23 février 2011 - 14:17:37
Dernière modification le : jeudi 24 septembre 2020 - 16:34:09

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  • HAL Id : hal-00568748, version 1

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Laurent de Windt, Rob Bleijerveld, Nicolas Humez, Arno Keulen, Marie-Claire Magnié, et al.. Re-visiting Acceptance Criteria Calculations for Monolithic Waste Landfill with Reactive Transport Modeling: Application to Total Dissolved Salts (TDS). International Solid Waste Conference, Oct 2009, Lisbonne, Portugal. 8p. ⟨hal-00568748⟩

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