Monitoring Underground Water Contaminants using EIT

The extraction and processing of ores generally require the use of harmful chemicals. In 2008, the UN reported that the entire population, around two thousand, of a rural village named “Khongor Soum”, located north of the capital city Ulaanbaatar, had excessive mercury levels due to pollution, and that animals and livestock in the area were also affected. The costly operation of neutralizing polluted soil and revivifying the environment of this area is ongoing. The desire to prevent these costs is driving a demand for monitoring systems suitable for use in Mongolia. Because of the country’s extensive size and the sparse population in areas of suspected contamination, a low-cost remote monitoring system is required. In addition, detecting and monitoring underground contamination pose the challenge of locating contaminants only by observing the surface (without excavation), and by the fact that the situation is already serious by the time contaminants reach the surface. We developed a remote near-real-time method for monitoring underground contamination that uses electrical impedance tomography(EIT), which is non-destructive, non-invasive, cheap to maintain, and requires little manpower. EIT uses the relation between electrical current and voltage to compile tomographic images, by determining the electrical impedance inside an electrically conducting object from knowledge of the injected current and the measured voltage data. The generally static nature of the ground allows the continuous monitoring of changes in underground conductivity distribution to reveal any emerging variations in underground contamination. Typically, a target area with a high conductivity contrast is advantageous for monitoring by EIT. Moreover, monitoring geoelectrical properties by EIT can provide results in near-real-time, or on demand. The recorded data can then be transmitted via several communication methods to a distant location. Common mining contaminants are highly conductive, as are heavy industrial contaminants such as benzene, toluene, xylenes, tetrachloroethene, andtrichloroethene. We developed a new electrode configuration to monitor the conductivity distribution of a target region, using conventional EIT and the local projective image method, which each have advantages for use in different sub-surface areas. For details, see the paper, Remote Real Time Monitoring for Underground Contamination in Mongolia Using Electrical Impedance Tomography.

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