Portable Acoustic Wave Sensor

Sandia National Laboratories

Description

The Portable Acoustic Wave Sensor (PAWS) is a downhole sensor being developed to characterize contamination and monitor contaminant levels of volatile organic compounds (VOCs) at sites in real-time. These sensors will be used with on-site monitoring wells or placed in the ground using a technology such as a cone penetrometer.

The sensor module contains (1) a coated sensor, (2) gas handling equipment, and (3) electronics to operate the device. The PAWS system monitors changes in the speed and power of the wave as it travels across the sensor. These changes occur because a film coating the sensor softens and becomes heavier when it absorbs the contaminant. Coatings have been developed that respond to VOCs. Using one coating material, polyisobutylene, the PAWS system can discriminate carbon tetrachloride from many other contaminants based on a comparison of the two sensor responses. This and other coatings will be tested and used with the probe.

Technical Performance Data

PAWS can perform continuous in situ monitoring, with rapid and reversible response. In comparison to off-site grab sample analysis, PAWS will perform real-time monitoring of carbon tetrachloride (CCl₄). This technology can identify molecular species and concentrations in dilute gas streams greater than 50 ppm, which can be beneficial during remediation activities. The sensor can be placed down a hole for in situ monitoring and can be automated to provide chemical information to site remediation workers on the distribution and concentration of contaminants. PAWS has capabilities for determining both molecular species and concentration of isolated chemicals. It is faster, cheaper, and as safe as a gas chromatograph (GC) infrared (IR) analyzer.

For analysis of chemical mixtures, PAWS will not provide all of the information that can currently be acquired with a GC or IR analyzer. When used for real-time analysis, the sensitivity is not as high as in some of the alternative techniques. Like most of the alternatives, calibration of PAWS is compound specific. Field demonstrations of above ground and in situ systems have demonstrated an accuracy of better than 10%.

Cost. Vadose zone monitoring unit cost is $10K; operation of the unit requires about 1 h/wk and low maintenance; and life-cycle costs will depend upon use, frequency, and volume of data required.

Projected Performance

Future developments include hardware miniaturization for use with the cone penetrometer; development of coatings and pattern recognition for simultaneous characterization of multiple chemical species; decrease in the detection limits based upon improved coatings and environmental sampling techniques; and the development and evaluation of semipermeable membranes for groundwater analysis.

Waste Applicability

This field monitoring system is applicable to the quantitative detection of volatile organic compounds in soil, vapor and water. Targeted contaminants are CCl₄ (at Hanford) and trichloroethylene (at Savannah River Site).

Status

The PAWS for above ground and in situ vadose zone for a single contaminant is currently available. In situ vadose zone mixture analysis and in situ groundwater analysis with the cone penetrometer will be available in 2 to 3 years.

Regulatory Considerations

In some situations the sensor may not be sensitive enough. For example the Occupational Safety and Health Administration (OSHA) Permissible Exposure Limit (PEL) for CCl₄ may be lowered to 2 ppm.

Potential Commercial Applications

This technology has the potential for many industrial applications for real-time, on-line monitoring of exhaust stacks, or work place environments. Sensors can be integrated into on-line process control systems to optimize process operations.

Baseline Technology

Grab samples and subsequent laboratory or field analysis with a GC or IR analyzer are the baseline technologies.

Intellectual Property Rights

Patent Ownership: DOE and Sandia National Laboratories
Patent No: 5,076,094

For more information, please contact:

DOE/OTD Environmental Technology

Information Service

(800) 845-2096

DOE Program Manager

David Biancosino

EM-551, Trevion II

U.S. Department of Energy

Washington, DC 20585

(301) 903-7961

Principal Investigator

Greg Frye

Sandia National Laboratories

P.O. Box 5800, Org. 1315

Albuquerque, NM 87185-5800

(505) 844-0787

Participating DOE Laboratory

Pacific Northwest Laboratory

Richland, WA

References

1. Frye, G.C., S.J. Martin, R.W. Cernosek, and K.B. Pfeifer, ``Portable Acoustic Wave Sensor Systems for On-Line Monitoring of Volatile Organics'', International Journal of Environmentally Conscious Manufacturing, Vol. 1 37/1992.

2. Frye, G.C., S.J. Martin, R.W. Cernosek, K.B. Pfeifer, and J.S. Anderson, ``Portable Acoustic Wave Sensor Systems,'' Proceedings 1991 Ultrasonic Symposium, IEEE, Piscataway, New Jersey, p. 566.

3. Frye, G.C. and S.J. Martin, ``On-Line Monitoring of Volatile Organic Species,''Proceedings First Annual International Workshop on Solvent Substitution, Weapons Complex Monitor Forums, Chicago, IL, 1991, p. 215.

4. Frye, G.C., R.W. Cernosek, and S.J. Martin, ``Portable Acoustic Wave Sensors for Volatile Organic Compounds'', Proceedings of the Information Exchange Meetings on Characterization, Sensors and Monitoring Technologies, Dallas, TX, 1992.

5. DOE-AL, ``Technology Information Profile (Rev. 3), Technical Name: Portable Acoustic Wave Sensor,'' DOE ProTech Database, TTP Reference Number: AL-2211-04, March 29, 1993.

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