Water flow dynamics in bottom ash landfills.

Area of Science:

• Environmental Engineering
• Hydrogeology
• Geochemistry

Background:

• Understanding material reactivity and transport properties of bottom ash landfill leachate is critical for effective waste management.
• Hydrological processes in landfills, particularly bottom ash landfills, are complex and influenced by factors like age and precipitation.
• Existing models often need refinement to fully capture the dynamics of leachate flow, especially concerning preferential pathways.

Purpose of the Study:

• To achieve a mechanistic understanding of material reactivity and transport properties in bottom ash landfill leachate.
• To investigate hydrological processes, focusing on competitive solution supply from matrix flow and preferential transport paths.
• To analyze the impact of varying landfill ages and heavy precipitation events on leachate transport.

Main Methods:

• Field monitoring of hydrological processes across seven Swiss bottom ash landfills of varying ages.
• Comparison of monitoring data with conceptual fluid flow models based on Richards Equation for a selected landfill.
• Conducting multiple simulations to assess the effects of material properties and rainfall intensity on hydrogeochemical behavior.

Main Results:

• Preferential flow paths significantly influence leachate discharge during precipitation events.
• Matrix flow controls water flux during drier periods, indicating a dual-flow system.
• A high flow-through drainage system is necessary to accurately model peak arrival times observed after heavy precipitation.

Conclusions:

• Water transport in landfills is governed by three main pathways: matrix flow, preferential flow within the landfill body, and preferential flow along edge zones and drainage layers.
• Surface ponding and low-permeability layers promote funnelled flow towards edge zones and drainage, allowing precipitation to bypass bottom ash.
• Backflow processes after peak flow mobilize highly interacted porewater from the matrix zone, highlighting the importance of considering dynamic flow regimes.