Measurement of soil water content below a wastewater trench using ground-penetrating radar

Ground-penetrating radar (GPR) was used to measure the distribution of soil water content below a wastewater trench. Two household septic system trenches were installed in a sandy soil. Vertical time domain reflectometry (TDR) probes were installed through the bottom of one of the trenches. The TDR probes were used to measure soil water content for comparison to the GPR data. The GPR measurements were performed in zero-offset gather (ZOG) and multiple-offset gather (MOG) survey modes with the antennas in horizontal boreholes located on opposite sides and below the wastewater trench. The ZOG survey mode gave an estimate of the average water content in the horizontal plane below the trench at a prescribed interval along the trench. The MOG survey mode produced a tomographic image of the distribution of soil water content in the same horizontal plane below the trench. A similar range of values of water contents was measured by TDR and GPR methods.