Electrical resistivity tomography and distributed temperature sensing monitoring to assess the efficiency of horizontal recirculation drains on retrofit bioreactor landfills

In bioreactor landfills, the recirculation of water can accelerate biodegradation and increase gas production. The dedicated infrastructure aims at increasing wastewater content over a wide area, with a long-lasting effect. To assess the efficiency of horizontal drains in bioreactor landfills, we use electrical resistivity tomography (ERT) and distributed temperature sensing (DTS) to monitor two injection experiments. The first monitoring experiment focuses on image resolution and takes advantage of a pseudo 3D ERT data set. This technique successfully highlights the waste horizontal anisotropy and the crucial role of existing gas wells, acting as vertical preferential flow paths. The observations are supported by borehole temperature logging. The second monitoring experiment focuses on temporal resolution and requires repeated 2D ERT measurements. The hourly acquisition frequency offers better insight on the water-flow dynamics, such as the flow direction and velocity and the water retention trough time. Temperature logging along the horizontal drain indicates that the injected water is distributed over the entire drain length. Altogether, the two recirculation experiments inform us on the suitability of large horizontal drains for water recirculation on bioreactor landfills. In conclusion, the two geophysical tools provide essential information to determine the most appropriate water-injection protocol in terms of frequency, volume, and flow rate. © 2018 Society of Exploration Geophysicists.