Detection of landfill cover damage using geophysical methods

In closed hazardous waste (i.e. industrial) landfills, impermeable covers are used to seal in the waste so as to minimise water infiltration and the accumulation of leachate inside the waste. In this paper, we present a geophysical study performed on a French landfill where the cover was designed using impermeable (clay) and drainage (sand) layers along with a Geosynthetic Clay Liner (GCL) in between. As observed, the quantity of leachate increases after rain events making the leachate treatment more expensive. This could be due to areas of weakness in the cover that have developed over time or which date back to its installation. Three different geophysical methods were employed and confronted to detect and assess such damage, and, if necessary, to help choose the most suitable remediation of the cover: Automatic Resistivity Profiling (ARP) which enables a rapid mapping of the entire landfill; the self‐potential method (SP) as one of its sources is water drainage; and electrical resistivity tomography (ERT) to obtain 2D resistivity models. Based on the ARP results revealing high lateral heterogeneities of the superficial cover materials, the SP and ERT measurements were conducted on a limited area. A negative SP anomaly was observed at the top of the landfill, where the cover is the thinnest and the GCL the most damaged, suggesting preferential infiltration under the GCL. The 2D ERT profile showed both vertical and horizontal variations. Comparison with manual auger holes showed that the alternating clayey and sandy layers did not conform to plans for the original cover when it was installed at this site about twenty years ago. Variations in electrical resistivity noticed at the depth of the GCL were attributed to possible damage to the GCL and a greater than expected permeability since the GCL is normally very resistive. The results obtained in this study were important to understand the damage to the cover due to the use of different types and thicknesses of cover materials compared to what was originally planned, and deterioration of the GCL.