Determining Water Content in an Active Landfill with the Aid of GPR
Landfill gas (LFG) continues to receive a great deal of attention due its potential for negative environmental impacts while also representing a green energy source. However, predicting the quantity of LFG generated at a given landfill is difficult due to the heterogeneities present in waste, and the lack of accurate in-situ waste parameters like water content. Measuring water content in-situ is challenging within an active landfill, so ground penetrating radar (GPR) is evaluated as a tool for measuring in-situ water content. Due to the large degree of subsurface heterogeneity and the electrically conductive clay cap covering landfills, both of which affect the transmission of the electromagnetic pulses, there is much scepticism concerning the use of GPR to quantify in-situ water content within a municipal landfill. The utility of GPR was evaluated at two municipal landfills. The first landfill was used to develop the measurement protocols, while the second landfill provided a means of confirming these protocols. GPR measurements were initially completed using the surface GPR approach, but the lack of success led to the use of borehole GPR. Both zero offset profiling (ZOP) and multiple offset gathers (MOG) modes were tried, with the results indicating that borehole GPR using the ZOP mode is the most simple and efficient method to measure in-situ water content. Effectiveness decreased with an increase in separation distance between boreholes, with a higher water content further decreasing the effective separation distance. However, the increased water content did appear to increase in accuracy of the GPR measurements. For a separation distance of 2 m at the two landfills, the difference in GPR and lab measured water contents were reasonable.