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.
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
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.
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.
Chromatography and Spectrometry Sensors
Chromatography is a method for the separation and analysis of complex mixtures of volatile organic and inorganic compounds. A chromatograph is essentially a highly efficient apparatus for separating a complex mixture into individual components. As the mixture is separated by the column, a detector positioned at the end of the column quantifies the concentrations of the individual components.
Spectrometry can be considered a sub-class of chromatography. A gaseous sample is injected into the spectrometer and ionized by a radioactive source, resulting in positive and negative charged species. These species are accelerated over a short distance and the time-of-flight is determined.
- Agilent Technologies offers a full line of laboratory and field Gas Chromatographs.
- Femtoscan has developed a hand portable Gas Chromatograph/Ion Mobility Spectrometer (GC/IMS) instrument.
- HAPSITE is a field-portable Gas Chromatograph/Mass Spectrometer (GC/MS) for on-site analysis of VOCs.
- Bruker-Daltronics, Inc. has developed a lightweight, rugged GC/MS system for analysis of air, water, and soil.
- Process Analyzers produces a field portable instrument which is able to analyze liquids, soilds, and gasses.
- Sandia National Laboratories has developed the Micro-Chem-Lab on a chip (uChemLab) that is a miniaturized GC-type device.
- Bruker-Daltronics, Inc. has developed a hand-held chemical agent detector based on IMS.
- DLK Spectro has produced an IMS with a gas-chromatic cell for gas analysis.
Electrochemical sensors can be categorized into three groups: (1) potentiometric (measurement of voltage); (2) amperometric (measurement of current); and (3) conductometric (measurement of conductivity). In general, electrochemical sensors interact with the contaminant of interest. This produces changes in its electrical properties that are measured and related to concentration.
Surface Acoustic Wave Sensors (SAWS) are small miniature sensors used to detect VOCs. A SAW device consists of an input transducer, a chemical adsorbant film, and an output transducer on a piezoelectric substrate. The input transducer launches an acoustic wave which travels through the chemical film and is detected by the output transducer. The velocity and attenuation of the signal are sensitive to the viscoelasticity as well as the mass of the thin film which can allow for the identification of the contaminant. A signal pattern recognition system that uses a clustering technique is needed to identify various chemicals.
- Sandia National Laboratories has developed and tested a six-array Surface Acoustic Wave (SAW) device able to identify 14 different individual organic compounds over a wide range of concentrations with 98 percent accuracy. An integrated GaAs SAW sensor device has been integrated with a microprocessor on a single 5mm x 5mm chip. A hand-held Portable Acoustic Wave Sensor (PAWS) system using the SAW sensor that can be used down-hold for monitoring. High temperature SAW devices are also being developed for monitoring in temperatures as high as 525 degrees C.
has developed a portable sensor to detect real-time Chemical Wepons dispersal in the field using a portable SAW sensor.
Fiber optic sensors are a class of sensors that use optical fibers to detect chemical contaminants. Light is generated by a light source and is sent through an optical fiber. The light then returns through the optical fiber and is captured by a photo detector. Three general classes of fiber optic sensors include: (1) passive spectroscopic; (2) chemically interacting thin film attached to the tip of the fiber; and (3) injection of a reagent near the sensor.
S&E - Remote Chemical Vapor Characterization using infrared spectroscopy technology.
- The Laser Lab in Germany has developed an optical sensor for analyzing polycyclic aromatic hydrocarbons (PAHs) and monoaromatics like benzene, tolouene, xylene, and ethylbenzene. Scroll down page to abstract
- Ion Optics, Inc. offers a MEMS
infrared gas sensor.
- Georgia Institute of Technology has developed an environmental monitoring system based on integrated optic sensors.
- Burge Environmental offers the Optrode Detection System for TCE.
Biological sensors rely on biologically produced enzymes or biocatalysts to detect the presence of a contaminant of interest.
- INEEL lead research to use molecular engineering and genomics for the development of environmental biosensors using robust biocatalysts
- Sandia National Laboratories Visual Empirical Region of Influence (VERI) Algorithm. Presents a new, nonparametric pattern recognition (PR) method based on the visual empirical region of influence (VERI) clustering technique.
- Innovative Technology Summary Report (April, 1996) describes the use of a cone penetrometer to provide cost-effective, real-time data for the use in characterization of the subsurface. The cone penetrometer uses sensors to measure cone tip pressure and sleeve friction. Other sensors available include two-axis inclinometers, acoustic cone (for identificaiton of soil type), temperature, pH, radioactivity (gamma), and geophones for measurement of pressure (P) and shear (S) waves (surface to borehole seismic measurements).
- EIC Laboratories, Inc. has developed two optical sensors for the cone
penetrometer used for the detection of DNAPLs.
- The U.S. Army Environmental Center has developed the Site Characterization and Analysis Penetrometer System (SCAPS) which uses an in situ HydroSparge Volatile Organic Compound (VOC) Sensor incorporated into a cone penetrometer truck.
Data Collection and Telemetry
- NetAcquire (tm) products combine three key technologies: intelligent real-time data acquisition, signal processing, and high-speed networking.
Scientific offers a PC-Based Telemetry Server Suite that utilizes satellite technology to transfer data.
Telemetry offers systems for permanent data collection, reliable data transfer, and user-friendly data visualization on the PC.
- INEEL Grand Challenge for Subsurface Characterization. Describes need for remote sensing of more parameters, localized sensing of more parameters, comprehensive point measurements, and measurement integration.
- Eksigent combines micropumping, microfluidics, and microfabrication for use in creating new devices for use in the life sciences, MEMS, and microelectronics industries.
Technology, Inc. offers gas and chemical vapor sensors.
- EnviroEquip offer a variety of instruments for environmental monitoring.
- Patent information for a hydrocarbon vapor sensing unit (US6102085). Many reference links to other sensors on this page.
has a Portable Soil Vapor Monitor for hydrocarbons available.
Engineering Company manufactures industrial process instrumentation
such as annunciators, temperature transmitters, alarm monitors, leak detection
monitors, non-contact level/flow/density, IS barriers, I/P transducers,
graphic displays, vibration monitors, and calibrators.
- PetroVend offers liquid and vapor hydrocarbon sensors for monitoring wells.
Corporation offers gas monitoring and vapor leak detection systems.
Gas & Chemical Co Ltd offers gas monitoring and vapor leak detection systems.
Systems offers various gas detection capabilities.
- Savannah River website offering ER technology descriptions.
- VaporTec offers state-of-the-art passive soil gas sampling services.
Technology News Chemical Sensor Offers Sensitive Real-Time
Systems, Inc. offers solutions for on-line, on-site VOC monitoring in air, water, and soil.
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For more information:
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.
updated: July 13, 2001
Created and maintained by:
Michael J. Kelley and Cliff K. Ho