Micro-Chemical Sensors for In-Situ Monitoring and Characterization of Volatile Contaminants

This website provides information about Sandia's Laboratory Directed Research and Development (LDRD) project that investigates and develops micro-chemical sensors for in-situ monitoring of subsurface contaminants.

The contents and intellectual property described in this website are protected by SNL Technical Advance SD-6894/S-97,517


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 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 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.

This printable Fact Sheet (233kb) provides information on the problem, objectives, and collaborative opportunities for this project.

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Background and Objectives

Tens of thousands of sites containing toxic chemical spills, leaking underground storage tanks, and chemical waste dumps require accurate characterization and long-term monitoring to reduce health and environmental risks and ensure public safety (Superfund Program). In addition, over two million underground storage tanks containing hazardous (and often volatile) contaminants are being regulated by the EPA (U.S. EPA, 1992), and the tanks require some form of monitoring to detect leaks from the tanks and pipe network. However, current methods are costly and time-intensive, and limitations in sampling and analytical techniques exist. Looney and Falta (2000, Ch. 4) report that the Department of Energy (DOE) Savannah River Site requires manual collection of nearly 40,000 groundwater samples per year, which can cost between $100 to $1,000 per sample for off-site analysis. Wilson et al. (1995, Ch. 36) report that as much as 80% of the costs associated with site characterization and cleanup of a Superfund site can be attributed to laboratory analyses. In addition, the integrity of off-site analyses can be compromised during sample collection, transport, and storage. Clearly, a need exists for accurate, inexpensive, real-time, in-situ analyses using robust sensors that can be remotely operated.

Although a number of chemical sensors are commercially available for field measurements of chemical species (e.g., portable gas chromatographs, surface-wave acoustic sensors, optical instruments, etc.), few have been adapted for use in geologic environments for long-term monitoring or remediation applications. The purpose of this LDRD project is to identify and develop sensor technologies that can be used in these long-term geologic applications. As a result, technologies such as electrical-resistivity monitoring and ground-penetrating radar are not considered here because they require significant amounts of manual labor and supervision to operate. Instead, we seek low-cost sensors that can be emplaced and operated with minimal supervision, which yield continuous real-time monitoring capabilities.

The particular focus of this project is limited to the detection and monitoring of volatile organic compounds (VOCs). These include compounds such as aromatic hydrocarbons (e.g., benzene, toluene, xylene), halogenated hydrocarbons (e.g., trichloroethylene (TCE), carbon tetrachloride (CT)), and aliphatic hydrocarbons (e.g., hexane, octane). As a result, sensors and technologies that detect gas-phase constituents in the vadose zone are emphasized because VOCs are most conveniently and economically monitored in the gas phase. However, the ability to detect VOCs in groundwater and saturated environments is also an important objective of the LDRD project.

This website presents the development of microchemical sensors that can be used to provide real-time monitoring and characterization of volatile organic compounds (VOCs) in situ, which can provide cheaper and more reliable information.

Specific objectives for this LDRD project include the following:

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Below is a list of reports and presentations:

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Partnering and Collaborative Opportunities

We are interested in teaming with various agencies, institutions, and companies to further develop, deploy, and refine our chemiresistor technology. The table below lists contacts that have expressed interest in evaluating, testing, and deploying the in-situ chemiresistor sensor technology. We would appreciate hearing from you if you would also like to team with us.

Note: These links will open a new web browser.




About Us

The micro-chemical sensor development team is led by Cliff Ho (6115) and Bob Hughes (1744).

Cliff Ho has over 10 years of experience in experimental and numerical studies involving multiphase flow and transport processes in porous media. He has performed work for Yucca Mountain, WIPP, and Hanford, and he has performed numerical simulations of environmental remediation problems involving soil vapor extraction, steam injection, and capillary barriers. Cliff Ho will be leading the experimental testing of the sensors and the subsurface modeling studies. Cliff is being assisted by Paul Reynolds, Mark Jenkins, Dan Lucero, Angela McLain, Michael Kelley, and Michael Itamura.

Bob Hughes has over 35 years of experience in physical chemistry and micro-sensor technology. He was a principal investigator in the development of the chemiresistors proposed in this LDRD and has extensive experience in the design and implementation of sensors for various applications. His silicon chip hydrogen sensor is now a commercial product yielding royalties to Sandia. Bob Hughes will be leading the development of the chemiresistors and associated technologies for the integrated sensor development. Bob is being assisted by Chad Davis, Michael Thomas, and Graham Yelton.

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We have found the following links to be interesting and useful in our research developing microsensors for in-situ chemical detection and characterization. If you have a site that you would like to have included on this page, please send the URL and brief description to Cliff Ho.

Contact Us

For more information:

Cliff Ho
Sandia National Laboratories
(505) 844-2384

Contact: Cliff Ho


Ho, C.K., M.W. Jenkins, R.C. Hughes, and P.G. Reynolds, "Microchemical Sensor Package and Characterization Methods for Real-Time In-Situ Sensing of Volatile Contaminants," Sandia National Laboratories Technical Advance SD-6894/S-97,517, 4/2001.

Looney, B.B. and R.W. Falts (editors), 2000, Vadose Zone Science and Technology Solutions, Battelle Press, Columbus, OH, 1540 pp.

U.S. Environmental Protection Agency (EPA), 1992, Measurement and Analysis of Adsistor and Figaro Gas Sensors Used for Underground Storage Tank Leak Detection, Report #EPA/600/R-92/219.

Wilson, L.G., L.G. Everett, and S.J. Cullen (editors), 1995, Handbook of Vadose Zone Characterization & Monitoring, CRC Press, Boca Raton, FL.

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Page updated: July 13, 2001

Created and maintained by: Michael J. Kelley and Cliff K. Ho