Environmental Project No. 2118, 2019

Methodology for risk assessment of stream water contamination by landfills

Mixing of landfill leachate plumes in streams

18-12-2019

The Danish Environmental Protection Agency has in collaboration with the Danish Waste Association and DepoNet, completed a project with the purpose of developing a methodology for visualizing the site-specific contamination of ground water, surface waters and nature surrounding Danish landfills. The methodology includes description of the contaminant source, transport of contaminants in and above the saturated zone as well as evaluation of the environmental impact.

This report describes the processes in play when a leachate plume originating from a landfill disperses and dilutes in streams. Furthermore, a general methodology is proposed for appointing point of compliance (POC) in the stream for comparison with relevant environmental quality standards (EQS). The estimation of contaminant concentration in stream waters originating from a landfill leachate plume can be handled using an analytical mixing/dilution model. The model Dimicon was developed for this purpose by The Technical University of Denmark. The data input for the model is the output from a transport model of the contaminant in the aquifer (e.g. GrundRisk Landfill). Limitations and assumptions of the Dimicon model are described in this report. The model gives the concentration of contaminants in each grid between plume discharge into the stream and fully mixed conditions.

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