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Monitoring waste in groundwater (without all the waste)

Mon, 03/07/2011 - 4:42am
EurekAlert

The U.S. spends around 2 billion dollars a year on remediation at hazardous waste sites, with a large portion of this used for groundwater monitoring. Yet according to Rolf Halden, a researcher at Arizona State University's Biodesign Institute, the information gathered is often of limited value.

Under a new three-year, $1.15 million grant from the U.S. Department of Defense, Halden, assistant director at the Institute's Swette Center for Environmental Biotechnology, is pursuing a novel method to conduct these vital tests. His team's efforts are part of a quest to provide more accurate results at lower cost and produce fewer harmful byproducts during the monitoring process.

When considering techniques suitable for groundwater monitoring, three components are key: the quality of data provided, the cost of the procedure and the environmental impact. Conventional monitoring typically accounts for at least 20 percent of the total cleanup costs incurred during site remediation. From a project management standpoint, however, the analyses and acquired data can often be misleading and unsatisfactory, as well as environmentally damaging.

Normally, groundwater is extracted from the earth for testing and then sent to a lab for detailed analysis. The method is financially and environmentally costly, because the water must be transported and the process can generate significant amounts of hazardous waste at the surface.

Halden's technique involves monitoring groundwater while it is still in place in the subsurface, using a device known as the in situ sampler or IS2, which may be custom fit into groundwater monitoring wells. The IS2 is deployed downhole, where its integrated pumps draw up ambient groundwater at milliliter per day rates. Analytes of interest are concentrated onto solid adsorption media for analysis. One of the advantages of this in situ approach is that effluent from the device remains in the subsurface. Only the device itself with the extracted analytes is removed from the well. In this way, monitoring can be conducted without the use of purge water or the liberation of wastewater at the surface.

Once the device has completed its work and is removed from the well, the contaminant-charged media are shipped to the laboratory, where they undergo automated analysis assisted by robotics, as well as standard methods including mass spectrometry and ion chromatography. The new technology boasts extremely low detection limits?in the ng/L to pg/L range. Further, it produces no wastewater and may be carried out at a low cost per sample, thanks to the use of automation.

The IS2 sentinel will be applied on a pilot basis at DoD sites and used in multiple deployments to examine a range of groundwater contaminants, including volatile organic compounds like tetrachloroethene, trichloroethene, and vinyl chloride, water-soluble fuel components (benzene and toluene), explosives (RDX and TNT), semi-volatile compounds (phenol), polycyclic aromatic hydrocarbons (naphthalene and phenanthrene), inorganic water contaminants (perchlorate), and heavy metals (arsenic and lead). Each of these analytes will be captured in situ, using a pair of customized IS2 devices. Results will be compared to those obtained with conventional water monitoring approaches.

The project seeks to demonstrate improved detection limits, 10 to 100-times lower than those achieved through current EPA methods. The accuracy, reproducibility and precision of results should also exceed EPA methods, providing detailed analyses of a broad spectrum of compounds at considerably lower costs. While initial efforts focus on monitoring at DoD hazardous waste sites, ultimately, the technology should find broad applicability for groundwater oversight.

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