IN-SITU MICROCHEMICAL SENSORS FOR LONG-TERM MONITORING OF SUBSURFACE CONTAMINANTS

An in-situ chemiresistor sensor has been developed that can continuously monitor volatile organic compounds in a variety of media including air, soil, and water. The chemiresistor consists of a conductive polymer deposited onto a microfabricated circuit that changes its electrical resistance in the presence of volatile organic compounds. The change in resistance can be calibrated to known concentrations of analytes, and arrays of chemiresistors can be used on a single chip to aid in discrimination. A rugged, waterproof housing was constructed to allow the chemiresistor to be emplaced in monitoring wells or immersed in water, and a cable connects the sensor to a surface-based solar-powered data logger employing wireless telemetry. This system has been deployed at Sandia’s Chemical Waste Landfill, where in-situ sensor data are posted continuously to a web site (www.sandia.gov/sensor/cwl). The monitoring system at the Chemical Waste Landfill includes two chemiresistors to detect trichloroethylene (TCE) and other sensors to monitor environmental changes at the site. This system has been operating continuously since March of 2003.