A controlled landfill is a potential source of environmental contamination of water, soil and air. One of the main problems regarding environmental pollution is the leachate spilling, which contains random chemical compositions that can disperse in the soil and in the groundwater, due to the inefficiency of the retaining systems. For this reason, a constant monitoring through all the stages of the landfill lifecycle, from the design to the closure, is needed to reduce the contamination risk.
In this framework, geophysical investigations and, most of all, geoelectrical measurements, are suitable for landfill monitoring. Geoelectrical methods with DC current injection are the most used in this field, since the geoelectrical response of the percolate, with a much lower resistivity compared to the surrounding soil, is easily detectable.
In the past, several geoeletrical techniques have been proposed and used to localize seepage zones in landfill geomembrane lining, among them the standardised and widely used Dipole method (ASTM D7007, 2004), with a direct current injection trough two electrodes, one inside and one outside the landfill. A leakage in the lining causes an anomaly in the measured voltage. The methodology gives good results but only if the laid material is homogenous and with a maximum depth of 1-2m, otherwise the measured anomaly can be misleading or too low to be detected.
The G.Re.T.A. system (Geoelectrical Resistivimeter for Time lapse Analysis), the autonomous geo-resistivimeter for fixed installations by LSI Lastem, using the Electrical Resistivity Tomography (ERT), is an innovative solution that solves the problem.
The electrical resistivity tomography, thanks to the non-invasive technology, is widely used in the landfill field to map the structure, to identify possible percolate leakages beyond the theoretically impervious boundaries and to track the subsurface infiltration paths.
This technology has been applied as a one-shot or time-lapse measurement so far, on the contrary G.Re.T.A. allows a continuous monitoring of the landfill to underline possible percolate leakages beyond the confined area. The system can be used to assess the good success of a melioration work and to manage the landfill after the closure. The remote data management, through a cloud platform with configurable alarms, allows to use the device as an early-warning system to detect leachate spilling before the damage becomes irreversible.