Performance Evaluation of 5TM Sensor for Real-Time Monitoring of Volumetric Water Content in Landfill Cover System

Accurate measurement of volumetric water content (theta) is essential for studying soil-water interaction efficiently. The accuracy of various types of theta measuring sensors needs to be ascertained before deploying in specific projects. The objective of this study is to evaluate the performance of electromagnetic 5TM sensor for real-time monitoring of theta in a cover system (CS). This CS is provided on top of the hazardous waste containment to isolate it from the surrounding environment and minimize interaction with rain water. The CS consists of different layers of soil and geosynthetics that interact with the atmosphere and undergo changes in theta with changing local weather conditions. Because theta governs the hydraulic and mechanical characteristics of geomaterials, its variation is monitored as a function of space and time for evaluating the performance of CS. Performance assessment of 5TM sensor was carried out under controlled conditions for ten different soil materials that may find application in CS. This study indicates the importance of material specific calibration of a 5TM sensor for improving its measurement accuracy before deploying it for field monitoring. The accuracy of 5TM measurement was marginally better when the polynomial calibration equation was adopted as compared to linear calibration. In the absence of soil-specific calibration, the new set of calibration parameters proposed in this study can be used for the generic soils used in CS. With improved accuracy of 5TM, it was shown that the error in the determination of soil water storage for different layers of a trial CS reduced from 15 to 0.4 %.