Field testing of poplar tree systems as evapotranspiration barriers on decommissioned MSW landfills in southern Ontario

A young poplar tree system (PTS) was field tested as an evapotranspiration barrier on a decommissioned municipal solid waste (MSW) landfill cover in southern Ontario, Canada. One direct method---field monitoring and measurement of deep drainage using Gee Passive Capillary Lysimeters (water flux meters or drain gauges), and two indirect methods---SHAW model simulations of soil water flow and heat transfer and horizontal borehole GPR surveys to explore soil water preferential flow pathways in the field, were used in this research.; For deep drainage field measurement, due to the drain gauges' frequent flooding (i.e. measurement reservoirs and sampling reservoirs were submerged in water, causing the siphon systems not to work properly to record deep drainage), no discernible effect to reduce deep drainage with and without PTS was obtained. Based on the soil water content measurement analysis, some possible reasons for the flooding are presented and explained.; The SHAW model was successfully used in this research to simulate soil water flow and heat transfer in this MSW landfill cover. The simulation results show that a young PTS can act as an excellent evapotranspiration barrier by noticeably increasing yearly evapotranspiration and significantly reducing yearly deep drainage.; Horizontal borehole GPR surveys using zero offset profile (ZOP) and multiple offset gather (MOG) modes verified that preferential flow pathways existed in this structured clay-rich landfill cover soil profile. However, these pathways seemed to be more prominent and noticeable in the areas with PTS due to the broader and deeper penetration of the poplar tree rooting systems.