Migration of Organic Contaminants from Landfill: Minimum Thickness of Barriers

ABSTRACT

Point sources such as landfills, can release high concentrations of contaminants into the groundwater because of migration of leachate from its bottom, which is generated primarily as a result of precipitation falling on an active landfill surface, leaching out the potential organic and inorganic contaminants from landfilled waste and discharging the same to groundwater in underlying aquifer. Leachate from young landfills has high dissolved solids content as well as a high concentration of organic matter. Landfill leachate has the potential to contaminate the surrounding environment and impair groundwater use. Organic contaminants in landfill leachate originate from incoming wastes or are produced as a result of biochemical reactions taking place in landfills. To protect the groundwater from contamination by landfill leachate, it is quite essential to provide the bottom barrier of suitable thickness, and to minimize the amount of water that could enter the landfill to create leachate. The present study was undertaken to determine the rate of movement of potential contaminants from its bottom to the aquifer media, so as to evolve a rational method for the determination of thickness of bottom barrier on sound engineering practice, in place of adopting a prescriptive standard, which is very common in most of the Asian countries. The study was undertaken for non conservative contaminant Dissolved Organic Carbon (DOC). The governing equation of contaminant transport was solved using finite difference method, and finite mass boundary condition to ape the finite mass of contaminants in a landfill. The solution of the model was run in MatLab 7.0 for a range of Darcy velocities and retardation factors for a representative equivalent height of leachate. Design curves were drawn which can be used for determination of suitable barrier thickness on the basis of expected maximum concentration of DOC in landfill leachate and maximum permissible concentration of the same.

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