Detection of Oil Release in Unsaturated Soil and Estimation of Oil Infiltration Rate Using Hydraulic Control System and Water Content Sensor

Rapid detection of oil released from underground storage tanks and estimation of its flow rate allows for the prevention of further contamination or the limitation of the spread of contaminants. In this research, we developed a method for oil release detection by sensing volumetric water contents (VWC) in a hydraulic control system. Oil release detection tests were conducted at bench and pilot scales. In the bench-scale test, oil and water were released directly on top of the oil release detection system. In the pilot-scale test, the release detection system was installed in the soil and the oil was spilled on the soil surface. The new oil release monitoring system was capable of detecting the oil release using the VWC decrease (0.42 → 0.11 m³/m³). The infiltration of water did not affect the value of VWC. Sequential injection or mixture of oil and water also showed a decrease in VWC (0.42 → 0.12 m³/m³). The rate of VWC decrease was directly proportional (− 0.003 ml/min) to the rate of oil infiltration. A conceptual model was suggested to delineate the mechanism of oil release detection and to estimate the rate of oil infiltration. The detectability of the oil release in soil was also verified in the pilot-scale test (0.45 → 0.12 m³/m³). The rate of oil infiltration could be estimated using the slope of the measured VWC. The amount of time for oil infiltration through the soil and dispersion during the migration should be considered to analyze the VWC curve properly. These results showed that the oil release detection system can be used to monitor oil release and to determine the rate of oil infiltration by installation in the soil near an underground storage tank.