Quantifying the settlement of an aerated landfill using remote sensing methods

Abstract

As part of the Dutch sustainable landfill project iDS, two compartments of the Dutch landfill Wieringermeer have been treated by in-situ aeration since 2017. The chosen method of aeration is over-extraction, where suction pressure is created causing ambient air to intrude into the landfill. Aeration induces enhanced settlement due to the acceleration of aerobic degradation of the waste. The aeration infrastructure comprises 110 wells, separated by around 10 to 15 m, covering an area of approximately 5 ha. This study analysed the spatial and temporal variability of settlement of the landfill, and aimed to correlate this with the carbon extracted by the wells. In order to quantify the settlement of the landfill various remote sensing methods have been utilised and compared. The methods include an Aerial Laser Scanner (ALS), Terrestrial Laser Scanner (TLS) and Global Navigation Satellite System (GNSS) measurements from a rover. In total 11 GNSS surveys, 4 TLS point clouds, and 2 ALS point clouds were available to this study.

Ground settlement plates have been measured using the GNSS rover since the start of aeration, showing a maximum settlement of ∼1.17 m on the western slope from August 2017 to June 2022. The slopes of the landfill experience more settlement than the top of the landfill, as a plate installed on the top only
experienced ∼ 0.09 m over this same time period. This is due to the increased surface area of the landfill exposed to the outside air at the slopes. The UAV-based ALS and TLS point clouds were able to measure spatial and temporal variations in settlement. Whereas the trends in settlement are consistent between the methods, the absolute values show notable variance. The ALS and TLS data contain significant uncertainty due to the effect of vegetation on the landfill, to which this variance can almost entirely be attributed. At its peak the vegetation contributed to a difference of 0.95 m in settlement, compared to the GNSS measured settlement. Several processing steps were taken to help negate the effect, but these were not able to fully filter vegetation out. ALS data was impacted to a lesser extent due to the high angle of incidence of its laser
signals as it flies overhead, because of this the signals generally penetrated the vegetation to a deeper depth than the TLS.

The aeration wells extracted 2583 tonnes of carbon from August 2017 to March 2022. Both visually and through the Pearson Correlation Coefficient clear correlations were observed between the variability of settlement and carbon extraction by the wells. The highest correlation coefficient reached was 0.503 using GNSS and gas data from August 2021 to March 2022, signifying a strong correlation.