Development of geoelectrical techniques for investigation and monitoring of landfills

A review of geophysical applications to investigation and monitoring of landfills identified that the geoelectrical methods, such as ERT, SP and EM, are ideally suited because much information can be inferred from the electrical characteristics of landfill waste. The review identified scope for further development due to constraints of geophysical surveying along the ground surface. In particular, the ERT method suffers a loss of data accuracy and resolution with increasing depth of investigation. These constraints have provided the main focus for interest during this research project. A field test site was examined on a reconnaissance basis using a multi- method geophysical approach to obtain the best possible sub-surface characterisation and interpretation in the absence of intrusive calibration data. On the basis of results obtained a model was produced showing combined geoelectrical response, which may be used to plan further detailed investigations including conventional intrusive site examination. It is further demonstrated that the effectiveness of ERT in a landfill setting lies with the arrangement of measurement electrodes and application of specialised electrode address configurations. In an active landfill setting, basal electrodes installed within the cell drainage medium prior to waste emplacement were used in conjunction with ground surface electrodes and the address configuration applied across the array pair. Delineation of basal leachate accumulation and differentiation from perched tables within the waste profile was possible. In a closed landfill setting, where restorative capping and leachate extraction was scheduled, a system for ERT monitoring was established by installing vertical electrode arrays during routine drilling and emplacement of gas wells. In this setting, baseline sub surface geoelectrical characteristics were identified against which the effects of landfill capping and leachate extraction were assessed through variance in model resistivities and percentage resistivity change. This research has provided recommendations for geophysical monitoring best practice, which may help site stakeholders to achieve a more effective management of leachate control systems, to assess the effectiveness of restorative strategies, and to demonstrate legislative compliance with a greater degree of certainty