The bottom and the side of a waste disposal facility (landfill) area must be designed with two distinguished and complementary barriers: active barrier and passive barrier. Passive barriers have to be designed with a very strict regulation in order to avoid the contamination of subsoils and groundwater with waste. The bottom of the area must present, from top to bottom, a soil layer with a low-permeability level equal to 10-9 m/s or less for least one meter thick then a soil layer presenting a permeability equal to 10-6 m/s or less for at least 5 meter thick. Sides of the area must present a permeability equal to 10-9 m/s or less for their entire height. However with the luck of sites responding to regulatory standards and with technicoeconomical considerations, designers used to perform equivalency on a landfill geographical site by considering the potential environmental impact of wastes on water resources and aquifers. In that regards, this article presents a real case of study on how a landfill barrier can been designed on a lime stone deposit and how to reinforce it for better performances and less contamination effect on aquifers. The equivalency check must be based on the knowledge of the geological and hydrogeological context allowing a reliable site model establishment.
This equivalency study is based on analytical and numerical studies of advective and diffusive analysis about relative concentration evolution of the contaminant through the barrier and the soil liner and their comparison with conventional passive barrier behavior in the same contamination configuration. SEEP/W and Ctran from Geostudio (2012) have been coupled in numerical modeling in order to reproduce leakage and contaminant transfers into the whole barrier to the aquifer. Results from this study show that the reinforcement of the passive barrier by a GCL and the reduction of the low permeable layer thickness used to increase the performance of the whole barrier by limiting the evolution of the contaminant migration into the ground water and sub soils compared to regulatory one. In conclusion, equivalency is possible for passive barrier however each case of study must be studied separately with a careful attention to contaminant transfers and its amount with time.
