Innovative multi-criteria risk assessment framework for unsanitary, closed landfills: Integrating the fuzzy analytic hierarchy process with a weighted geometric mean approach

In the past, unsanitary landfills were a common method for municipal solid waste disposal in developing countries. Although many nations have closed these landfills, the environmental pollution risks and impacts persist. This study introduces a new multi-criteria risk assessment framework specifically designed for closed, unsanitary landfills. The framework focuses on 18 key indicators categorized into three groups: landfill characteristics, waste composition, and properties of leachate and landfill gas. The Analytic Hierarchy Process (AHP) was employed to determine the weighting of these criteria, providing a more accurate way to account for uncertainties and subjective judgments. The study conducted a sensitivity analysis comparing the weighted arithmetic and geometric mean aggregation methods, finding that the geometric mean is superior for synthesizing the sub-indices in land risk assessment. The framework not only assesses risk but also provides specific action recommendations tailored to different risk levels, enabling local authorities to prioritize and implement risk reduction measures effectively, even in resource-constrained settings. The application of the framework on the Trung Son landfill indicated that the majority of waste at the landfill was ordinary waste, with high moisture content, varying over time and at different depths. The leachate was rich in organic matter, and the site was in the acidification phase of biodegradation, resulting in limited methane emissions. The landfill presented a very high environmental risk, and required immediate remediation. In the absence of allocated funding and resources, it is recommended to construct a temporary final cover and runoff collection system to minimize rainwater infiltration and odor dispersion in the surrounding areas. © 2024 Elsevier B.V.