This study quantifies the field hydraulic performance of a dual-functionality landfill cover, combining microbial methane oxidation with water diversion using a capillary barrier. The investigated 500 m2 test field, constructed on a landfill in the Netherlands, consisted of a cover soil optimised for methane oxidation, underlain by a sandy capillary layer and a gravelly capillary block. Outflows from these layers were measured between 2009 and 2023. Average precipitation was 848 mm/a, evapotranspiration, diverted infiltration and breakthrough amounted to 504 (59.4 %), 282 (33.3 %) and 62 (7.3 %) mm/a, respectively. On average, the capillary barrier diverted 82 % of the inflow into the capillary layer. Breakthrough occurred mainly from October to March when evapotranspiration was low and the maximum water storage capacity of the cover soil was reached. During this period, inflow into the capillary barrier exceeded its diversion capacity, caused by the relatively high hydraulic conductivity of the cover soil due to its optimisation for gas transport. The diversion capacity declined drastically in the year after construction and increased again afterwards. This was attributed to suffusion of sand from the capillary layer into the capillary block and subsequent washout to greater depths or the influence of iron precipitates at the bottom of the capillary layer. The effect of a more finely grained methane oxidation layer on the hydraulic and methane oxidation performance should be investigated further. These measures could further improve the combined performance of the dual functionality landfill cover system under the given conditions of a temperate climate.

In order to reduce the environmental and financial burden for future generations, approaches are needed to shorten aftercare of landfills. Aeration of the waste-body is a promising approach, however, the poor understanding of transport of gas and water through a waste-body makes it difficult to design an effective aeration strategy. The aim of this study is to develop a tool to determine the optimal aeration strategy for landfills. This study presents a comparison of aeration strategies based on the air distribution they generate with a 3-D multiphase model. The implemented theory is based on parameter values obtained from (laboratory) experiments performed under conditions which are similar to those in a full scale landfill. Calibration with field scale gas extraction data from the Dutch pilot site Wieringermeer shows that the model gives a good description of the average gas flow under extraction. Scenario analyses for the case study landfill indicate that injection strategies reach a larger volume fraction of waste with a higher air flow compared with extraction strategies, especially at the bottom of the landfill. Extraction, however, supplies oxygen more homogeneously through-out the waste. An import design criterion is also the distance between the wells. Too large distances lead to ineffective treatment because too large volumes of waste/leachate remain untreated. In addition to the comparison of aeration strategies, an optimal aeration strategy for the pilot site is presented. A combination of (alternating) injection and extraction wells which are maximum 20m apart seems to be the optimal strategy.