Information Last Revised: 3/29/93
TTP Reference Number: AL-2211-04
1. Technical Name of Technology: Portable Acoustic Wave Sensor
2. Common Name of Technology: PAWS
3. PI and Telephone No: Greg Frye, (505) 844-0787
4. Affiliation: Sandia National Laboratories
5. Technology Category: Characterization and Monitoring Technologies - DT&E
6. Developers: VOC Arid ID/Sandia National Laboratories
7. Application:
7.1. Where (in-situ/ex-situ): in-situ
7.2. Media: soil, vapor, water
7.3. Targeted Contaminants: carbon tetrachloride (Hanford); TCE (Savannah River Site)
8. Scope of project (feasibility study, treatability, bench, pilot, field):
Development, bench and field test
9. Integrated Demonstration (ID) Need/Requirements:
Many DOE sites have been contaminated with volatile organic compounds, such as the carbon tetrachloride and trichloroethylene that are found at the Hanford site. To characterize this contamination (that is, to determine the physical extent of the contamination and contaminant concentrations), sensors are being developed that can be put down into monitoring wells or holes drilled for characterizing a site. One example of these sensors is a portable acoustic wave sensor (PAWS) being developed by Sandia National Laboratories. Using a down-hole sensor allows for characterization of a site in real time, instead of waiting for a laboratory to analyze every sample. This is beneficial when conducting remediation activities. It will allow a sensor to be placed into a hole for in-situ monitoring and will provide chemical information to site remediation workers on the distribution and concentration of contaminants. PAWS can identify both the contaminant and its concentration and will be used to characterize both liquid and vapor contamination.
10. Objective
10.1. Objective of technology (i.e., This technology will destroy VOCs in groundwater.):
The objective of this project is to develop, test, and demonstrate field monitoring systems capable of quantitative detection of volatile organic contaminants found in vadose zone soils and in groundwater. These systems need to provide long term, continuous, and in situ monitoring of contaminant concentrations using existing monitoring wells or based on permanent placement of probes at key locations on the site. The information is needed so effective remediation strategies can be selected and accurate monitoring of the contaminant occurs during remediation. These systems should be automated for continuous operation and operate in a relatively passive manner, with the exception of mild local heating due to power dissipation and possibly some purging of the sensor using in situ adsorbents or purging with air from the surface.
10.2. Baseline (baseline technology to which it is compared):
Gas Chromatography with Purge and Trap (GC with P&T)
11. Process Description:
PAWS Down-Hole Liquid/Vapor Phase will involve monitoring down-hole contaminant levels for volatile organic compounds using acoustic wave sensors. These sensors will be used with on-site monitoring wells or placed in the ground using a technology such as a cone penetrometer (see the fact sheet on the cone penetrometer).
The sensor module contains 1) a coated sensor 2) gas handling equipment and 3) electronics to operate the device. The Portable Acoustic Wave Sensor (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 volatile organic compounds. Using one coating material, polyisobutylene, the PAWS system is able to 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.
11.1. Input:
For vadose zone monitoring, the only input to the monitoring system will be a small recirculating flow of gas from the formation under test. For groundwater monitoring, the only input will be sampling of contaminant removed from the groundwater using a semi-permeable membrane.
11.2. Output:
The only physical outputs of the system will be gas pulled from the formation to purge the borehole prior to analysis (for vadose zone monitoring), a small amount of heat (<10 Watts) due to power dissipation, and a small volume (<1 lb/year) of contaminant adsorbent. The data output will be contaminant concentration as a function of time.
12. Summary of Technology Advantages (relative to the baseline: faster, better, cheaper, safer):
PAWS can perform continuous in situ monitoring, with rapid and reversible response. In comparison to offsite grab sample analysis, PAWS will perform real-time monitoring of CCl4. This can be beneficial when conducting 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 GC or IR analyzer.
13. Limitations of Technology (relative to the baseline: faster, better, cheaper, safer):
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 some of the alternative techniques. Like most of the alternatives, calibration of PAWS is compound specific.
14. Major Technical Challenges:
Hardware miniaturization is especially important if used with the cone penetrometer. Development of coatings and pattern recognition for characterizing multiple chemical species simultaneously is another challenge. Another challenge is to decrease the detection limits based upon improved coatings and environmental sampling techniques. The development and evaluation of semi-permeable membranes for groundwater analysis is another challenge.
15. Technical Effectiveness:
15.1. Performance
15.1.1. Remaining Contamination: (contamination mobility reduction, volume reduction, toxicity reduction)
Summary (20 words or less): Not relevant for a monitoring technology.
Further Description (unlimited length):
15.1.2. Process Waste
15.1.2.1. Status of waste (mobility, volume, hazard, recyclability)
Summary (20 words or less): A small amount (<1 lb/year) of contaminated carbon based adsorbent material may be generated.
Further Description (unlimited length):
15.1.2.2. Treatment (needed, available)
Summary (20 words or less): The carbon based absorbent could be treated in the same manner as GACs used to treat the vapor extraction system off-gas.
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15.1.2.3. Decontamination / Decommissioning
Summary (20 words or less): Probe decontamination may be necessary only when exposed to radioactive contamination during field operations.
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15.1.2.4. Disposal (needed, available)
Summary (20 words or less): The carbon based absorbent will be disposed of in a manner similar to the GACs used with the vapor extraction system.
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15.1.3. Practicality
15.1.3.1. Foreclose Future Options
Summary (20 words or less): No effects on future options.
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15.1.3.2. Reliability
Summary (20 words or less): It is anticipated that PAWS can operate unattended with little maintenance for long periods of time (months to years).
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15.1.3.3. Failure Control
Summary (20 words or less): For the currently anticipated uses, there are no immediate consequences due to probe failure.
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15.1.3.4. Ease of Use
Summary (20 words or less): The system is designed for automated and continuous operation.
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15.1.3.5. Infrastructure
Summary (20 words or less): No significant infrastructure is required.
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15.1.3.6. Versatility
Summary (20 words or less): It is capable of use with most VOC; based on recalibration for the chemical of interest. Repackages for several applications have been demonstrated.
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15.1.3.7. System Compatibility
Summary (20 words or less): Electronic output is compatible with most existing systems.
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15.1.3.8. Off-the-Shelf (procurement ease)
Summary (20 words or less): Although there are currently some specifically fabricated components, the technology lends itself to full commercialization.
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15.1.3.9. Maintainability
Summary (20 words or less): For systems using the carbon absorbent, periodic (every few months) maintenance is required.
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15.1.3.10. Safety Measures
Summary (20 words or less): Isolated electronics and self contained gas system for fire safety.
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15.1.4. "Works" (functions as intended)
Summary (20 words or less): Field demonstrations of above ground and in situ systems have demonstrated an ability to function with an accuracy of better than 10%.
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15.2. Cost
15.2.1. Start-Up Cost
Summary (20 words or less): For vadose zone monitoring, a present unit cost is approximately $10K (excluding labor), and 2 hours is required for probe placement.
Further Description (unlimited length): To be developed and field tested in FY' 93 the cost is estimated at $450K, FY' 94 - $550K, FY' 95 - $625K, and FY' 96 - $600K.
15.2.2. Operations and Maintenance Cost
Summary (20 words or less): Operation should require about one hour/week and low maintenance is anticipated (<2 hours/month).
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15.2.3. Life-cycle cost
Summary (20 words or less): It is difficult to estimate the life cycle cost at this stage of development. However, it will depend on several factors, i.e., use, frequency, etc.
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15.3. Time
15.3.1. Years Until Available
Summary (20 words or less): Above ground and in situ vadose zone for single contaminant is currently available.
Further Description (unlimited length): In situ vadose zone mixture analysis and in situ ground water analysis with cone penetrometer probe available will be available in 2 years.
FY '92 - carbon tetrachloride in above-ground streams (i.e., pull out of well)
FY '93 - vadose zone monitoring for carbon tetrachloride in 4 inch or larger boreholes.
FY '95 - miniaturization of instrument for down-hole cone penetrometer placement into groundwater.
FY '96 - above ground or vadose zone monitoring for mixtures in 4 inch or larger boreholes.
15.3.2. Speed/Rate
Summary (20 words or less): Less than 2 hours is needed for probe placement. Upon placement, rapid (a few seconds) and continuous analysis is possible.
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15.3.3. Years to Finish
Summary (20 words or less): Three years for full capabilities including mixture analysis in vadose zone boreholes and groundwater analysis with cone penetrometer probe.
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16. Environmental Safety and Health
16.1. Worker Safety
16.1.1. Exposure to Hazardous Materials/Hazards
Summary (20 words or less): Potential exists for exposure to contaminant venting from the well head during probe placement.
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16.1.2. Physical Requirements
Summary (20 words or less): Handling of a 50 lb. (maximum) and 6 foot long (maximum) probe is required during the placement.
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16.1.3. Number of People Required
Summary (20 words or less): At least 2 people are required to place the probe into the well.
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16.2. Public Health and Safety
16.2.1. Accidents
Summary (20 words or less): Not applicable
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16.2.2. Routine Releases
Summary (20 words or less): Not applicable
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16.2.3. Transportation
Summary (20 words or less): Not applicable
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16.3. Environmental Impacts
16.3.1. Ecological Impacts
Summary (20 words or less): No ecological impacts are anticipated.
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16.3.2. Aesthetics
Summary (20 words or less): No impacts are anticipated.
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16.3.3. Natural Resources
Summary (20 words or less): Interconnection with the aquifer could occur during well installation or probe placement.
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16.3.4. Energy Demands
Summary (20 words or less): Energy usage is minimal (<50 Watts continuous).
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17. Socio-Political Interests
17.1. Public Perception
17.1.1. Proponent Reputation
Summary (20 words or less): There may be concern with how this sensor operates in environments with multiple contaminants.
Further Description (unlimited length): There may be a question regarding the polymer coatings. These are plastic-like coatings that are no more dangerous than plastics.
17.1.2. Familiarity / Understandability
Summary (20 words or less): Interested non-technical parties and individuals are unlikely to be familiar with this technology.
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17.2. Tribal Rights / Future Land Use
17.2.1. Capacity for Unrestricted Use (terrestrial, aquatic)
Summary (20 words or less): No impacts are anticipated and unrestricted land use will not be impaired.
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17.3. Socio-Economic Interests
17.3.1. Economic Impacts
Summary (20 words or less): No significant economic impacts are anticipated.
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17.3.2. Labor Force Demands
Summary (20 words or less): No significant labor force demands are anticipated.
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18. Regulatory Objectives
18.1. Compatibility with Cleanup Milestones
Summary (20 words or less): The level of detection of the prototype is approximately 50 ppm. This current level of detection appears to be low enough for field testing.
Further Description (unlimited length): For example, the concentration of the vapor extraction system off-gas is in the 100's of ppm at the Hanford site. In some situations the current level of accuracy may need to more sensitive. For example, the OSHA Permissible Exposure Limit (PEL) for carbon tetrachloride may be lowered to 2 ppm. Also, for groundwater measurements, the sensor may need to operate in the ppb range. There appear to be no major technical issues associated with dropping the order of magnitude of the sensors, i.e., making the sensor more sensitive. The sensor is more sensitive to contaminants in water than in gas.
18.2. Regulatory Infrastructure / Track Record
Summary (20 words or less): Currently EPA has no system for certifying sensors technology for site characterization.
Further Description (unlimited length): There is an on-going effort to establish a federal center for site characterization technologies.
18.3. Regulatory Compliance
Summary (20 words or less): Not available
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19. Industrial Partnerships
19.1. Company Names:
None at this time.
19.2. Rationale:
A press release in 1991 resulted in 40 companies interested in cooperating in the development or use of the technology. The PI is currently working to transfer the technology to industry to miniaturize the technology and develop microprocessor circuits.
19.3. Contract Mechanism:
19.4. Other Potential Companies:
Over 40 companies have expressed an interest in this technology.
19.5. International:
20. Intellectual Property
20.1. Patent Ownership:
DOE or Sandia
20.2. Other Owners:
20.3. Patent Number:
Patent #5,076,094
21. Cost Sharing:
Similar work is being done by universities and private industry but no sensors have dual output. This technology could have applications in industry for real-time, on-line monitoring of exhaust stacks, or work place environments. Sensors could be integrated into on-line process control systems to optimize process operations.
Current work is also being performed under the Environmentally Conscious Manufacturing-Integrated Demonstration.
22. Background on this technology (Where did the idea come from? Who else is doing similar work? What have the results been to date? What is the most significant competitor to this technology?):
Technologies using acoustic wave sensors have been in existence for 15 years. Currently, about 10 research companies and universities are involved in some aspect of acoustic wave sensing. PAWS is a unique technology because it has dual output capabilities. This technology can identify molecular species and concentrations in dilute gas steams greater than 50 ppm.
23. Reference Documents:
Frye, G.C. Martin, S.J., Cernosek, R.W., and Pfeifer, K.B., "Portable Acoustic Wave Sensor Systems for On-Line Monitoring of Volatile Organics", International Journal of Environmentally Conscious Manufacturing, Vol. 1 37/1992.
Frye, G.C. Martin, S.J., Cernosek, R.W., Pfeifer, K.B. and Anderson, J.S., "Portable Acoustic Wave Sensor Systems," Proceedings 1991 Ultrasonic Symposium, IEEE, Piscataway, New Jersey, p. 566.
Frye, G.C. and Martin, S.J., "On-Line Monitoring of Volatile Organic Species," Proceedings First Annual International Workshop on Solvent Substitution, Weapons Complex Monitor Forums, Chicago, IL, 1991, p. 215.
Frye, G.C., Cernosek, R.W., and Martin, S.J., "Portable Acoustic Wave Sensors for Volatile Organic Compounds", Proceedings of the Information Exchange Meetings on Characterization, Sensors and Monitoring Technologies, Dallas, TX, 1992.