Washington State University and
Pacific Northwest Laboratory
Description
The Unsaturated Flow Apparatus (UFA) Centrifuge is a laboratory instrument that simulates the migration of volatile organic compounds (VOCs), microbial nutrients, and water in the subsurface environment of arid sites, as well as the migration of other contaminants. UFA is based on open-flow centrifugation and provides a technique in which a hydraulic steady-state can be achieved in a matter of hours in most geologic materials at very low water content.
The advantage of using centripetal acceleration as the fluid driving force is that it is a body force similar to gravity and acts simultaneously over the entire system and independently of other driving forces (e.g., gravity or matric suction). The system is a more rapid method for obtaining transport data. The UFA can address any flow transport problem involving any fluid in any porous medium under almost any condition. UFA improves the predictive capabilities of VOC migration and increases the probability of choosing a successful restoration strategy for site-specific conditions. The technology can also be used for quick screening and can provide data to describe field conditions.
Technical Performance Data
The UFA consists of an ultracentrifuge with an ultraflow constant-rate flow pump that provides any liquid to the sample surface through a rotating seal assembly and microdispersal system.
In the UFA, accelerations up to 30,000g are attainable at temperatures from -10° C to 150°C and flow rates as low as 0.001 ml/h. The effluent is collected in a transparent, volumetrically calibrated container at the bottom of the sample assembly that can be observed during centrifugation using a strobe light assembly. The UFA measures transport parameters at water contents as low as a few percent and hyrolic conductivities down to 10^[-10] cm/s in a few days.
Cost. The present cost of the UFA and support equipment is $100K. An alternate UFA system that can be used only for soil has no temperature capability and does not have a strobe light can be purchased for $50K. The annual operating and maintenance cost is $10K, including the maintenance contract and sample holders. The centrifuge is guaranteed for 5 to 10 yrs.
Projected Performance
A new generation UFA is being developed for the VOC Arid Integrated Demonstration. Soil samples will be collected from the Hanford Site using cable tool drilling/split spoon sampler technology. The soil or bedrock samples are transferred to a specially designed titanium canister and subjected to as much as 20,000 g in an open-flow centrifugation device. A rotating seal assembly fitted to the canister allows an ultra-low flow pump to deliver liquid (carbon tetrachloride in this case) or gas to the sample surface during centripetal acceleration. When steady-state conditions are reached (within a matter of hours), three transport parameters will be evaluated; (1) hydraulic conductivity to measure permeability, (2) diffusion coefficient, and (3) breakthrough retardation. Transport data and a compilation of data for Hanford sediments will also be the final output elements.
Modification may need to be made for application of this technology in radioactive environments.
Waste Applicability
The UFA can address all flow transport problems involving fluid in any porous media under almost every condition. This technology is applicable VOCs, microbial nutrients, and water in the subsurface.
Status
The UFA is available off-the-shelf. UFA was developed and has been deployed in a number of Pacific Northwest Laboratory programs since 1991. Improvements to the UFA are continuing.
Regulatory Considerations
Environmental regulations are not expected to impact this technology. Proper laboratory procedures will be followed to minimize workers' exposure to contaminants.
Potential Commercial Applications
UFA supports the development of restoration technologies such as vapor extraction (e.g., estimate vapor migration rates) or bioremediation (e.g., estimate nutrient delivery rates) for unsaturated soils. In addition, the UFA technology is a predictive tool, that is, a ``time machine'', that can be used (1) to validate the predictive models of subsurface contaminant migration, and (2) to screen the performance of various remediation technologies in the field.
The concrete industry has expressed interest in this technology to test reactivity of concrete aggregate to alkaline solutions. In addition, the movement of pore water through bentonite barriers for waste repository programs is being studied with the Japanese.
Baseline Technology
The baseline technology is traditional column experiments or in situ analysis such as lysimeter measurements that require months to years to achieve results. UFA data have been shown to be in complete agreement with data generated using traditional column experiments.
Intellectual Property Rights
Beckman has the intellectual property rights.
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References
Go to the Characterization and Monitoring Technology Profiles Index