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Initiated: October 2001
Team: Cliff Ho, Bob Hughes
Traditional methods for monitoring sites that may be contaminated with toxic chemicals can be expensive, time consuming, and misrepresentative of in-situ conditions. A few in-situ chemical monitoring systems exist, but they do not attempt to quantify or characterize the contaminant (e.g., location, composition, etc.). This sensor website ( presents the development of a microsensor monitoring system that can be used to monitor and characterize VOCs in the subsurface. A microchemical sensor that employs an array of chemiresistors is packaged in a unique, waterproof housing (early version made of PEEK and later version made of stainless steel) that is designed to protect the sensor from harsh subsurface environments, including completely water-saturated conditions. The array of sensors is calibrated to provide "training sets" for pattern recognition of various chemicals and chemical mixtures. The sensors and packaging has been tested in the laboratory and field, and unique characterization methods are being developed that utilize contaminant transport models and time-dependent, in-situ sensor data. Additional characterization methods that can be employed during soil remediation methods such as soil venting and air sparging are also being tested.

The sensor system consists of an array of miniature sensors, called chemiresistors, that can detect volatile organic compounds (VOCs). Each chemiresistor is fabricated by mixing a commercial polymer dissolved in a solvent with conductive carbon particles. The ink-like fluid is deposited and dried on wire-like electrodes on a specially designed integrated circuit. When VOCs are present, the chemicals absorb into the polymers, causing them to swell. The swelling changes the electrical resistance that can then be measured and recorded. The amount of swelling corresponds to the concentration of the chemical vapor in contact with the polymers. The process is reversible, and the polymers will shrink once the chemical is removed, reverting the resistance to its original state.

This printable Fact Sheet (12 KB) provides information on the problem, objectives, and collaborative opportunities for this project.

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