Recirculation and infiltration of leachate in landfills are performed to accelerate the process of stabilizing organic matter in waste. At landfill De Kragge (Bergen op Zoom, the Netherlands), leachate recirculation and infiltration measures started in March 2018. This research aims to provide insight related to leachate flow throughout the landfill. Knowledge about the leachate flow is essential for evaluating the success of the stabilization measures. In this research, uniform and point borehole dilution tests were conducted to investigate the horizontal and vertical flow velocities. In addition, measured leachate levels throughout the landfill were analyzed.

The leachate levels indicated perched leachate zones: above the basal drainage system and below the injection drains at the top. Leachate injected through the infiltration drains cannot efficiently infiltrate the waste body, and the effects of the infiltration events were not picked up in the wells and piezometers throughout the landfill, implying little hydraulic connectivity.

The results of the dilution tests indicated horizontal and vertical flow within the landfill. Vertical velocities measured in the wells were estimated to be considerably higher (77 - 225 m/d) than the average horizontal velocities (0.02 - 1.0 m/d). The wells provide a path for vertical flow. Apart from the highest horizontal velocities measured in deeper sections of the landfill (15-18 m below ground level), velocities varied without a clear relation to landfill depth, indicating preferential flow paths. Uniform dilution tests performed with the infiltration drains turned off suggested that leachate infiltration does not increase the horizontal velocities. This research suggests that waste stabilization through recirculation is not optimal at De Kragge.

\noindent Due to an overall lack of understanding about the well and filter pack installation and the high spatial heterogeneity of the waste, the calculated velocities are uncertain. Further research into possible error sources (e.g., the borehole correction factor) is recommended. Additional tracer tests, including tests on the neighboring compartment without stabilization measures, are recommended to further assess the effectiveness of the recirculation system.