USGS Washington Water Science Center
|U.S. Department of the Interior
U.S. Geological Survey
Release: December 20, 2002
253-428-3600, ext. 2623
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[Note: The report can be viewed on the Web at http://pubs.water.usgs.gov/wri024274/.]
An innovative ground-water sampling method for detecting contamination provides results similar to more expensive traditional methods while avoiding the problem of generating potentially hazardous waste water, according to a report published today by the USGS, in cooperation with the U.S. Air Force.
Two detection methods--tree-tissue analysis and passive diffusion sampling--were evaluated in a USGS study of ground water at a site on McChord Air Force Base. Because of past activities on the base, ground water at the site had been contaminated with trichloroethene (TCE), a degreaser. The passive diffusion sampling method proved to be an accurate, reliable way to detect and monitor TCE in ground water. However, the tree-tissue analysis method was not effective at this site, possibly because tree roots didn't reach ground water.
"We compared concentrations from passive diffusion and traditional pumping methods," said Stephen Cox, USGS scientist and author of the report. "The passive-diffusion method gave us concentrations similar to those from pumping. The pumping method produces waste purge water, which is treated as a hazardous waste, but the passive diffusion method doesn't generate any waste."
The passive-diffusion sampler is a low-density polyethylene bag, filled with pure water, that is lowered into a well. Because volatile compounds like TCE can permeate the bag, it is left in the well for 10 days or more so that the amount of TCE in the bag is the same as in the ground water. The bag is then taken out of the well for analysis.
The report, "Preliminary Assessment of Using Tree-Tissue Analysis and Passive-Diffusion Samplers to Evaluate Trichloroethene Contamination of Ground Water at Site SS-34N, McChord Air Force Base, Washington, 2001," by S.E. Cox, is published as U.S. Geological Survey Water-Resources Investigations Report 02-4274. The report can be viewed on the Web at http://pubs.water.usgs.gov/wri024274/. Copies can be purchased from the U.S. Geological Survey, Information Services, Box 25286, Federal Center, Denver, CO 80225-0286, telephone 303-202-4200.
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