Evaluation of long-term leaching of a full-scale carriageway using treated incineration bottom ash as subbase material

Leaching of hazardous substances, particularly heavy metals, from incineration bottom ash (IBA) presents a significant challenge for its utilization in construction. Laboratory leaching tests are commonly used to assess the environmental compliance of IBA; however, they are conducted under controlled conditions that do not directly simulate real field situations, which lead to discrepancies between laboratory results and field monitoring due to the lack of robust linking with material- and site-specific parameters. This can lead to misjudgment of risks or unnecessary precautions. This study evaluates the long-term leaching behavior of a full-scale carriageway using IBA as a subbase material through a release model based on laboratory leaching tests. Column leaching and compacted granular leaching tests were conducted to simulate percolation- and diffusion-controlled scenarios. Additionally, the interaction between the underlying reclaimed sand (hereafter referred to as “engineered soil”) and IBA leachate was studied, considering the buffering capacity of the vadose zone to prevent the transport of elements to groundwater. A one-dimensional advection–dispersion transport model, incorporating site-specific parameters, was applied to assess the potential threat to groundwater over time. The release and transport models were combined to reflect progressive changes in source terms and arrival at the groundwater table. Various geochemical and hydrogeological parameters were determined through laboratory testing, field monitoring, and data collection to strengthen the model. The simulation spans from 100 to over 10,000 years, depending on soil retardation, and fully covers the typical lifespan of a road. Results indicated that metal elements may be influenced by different leaching scenarios, suggesting that appropriate measures can reduce leaching potential. Additionally, enhancing soil attenuation is crucial in slowing the transport of elements to groundwater.