Using Trees to Determine How Fast Contaminated Groundwater is Moving

In the early 1990’s some hydrogeologists needed to know how fast a plume of contaminated groundwater was moving toward Chesapeake Bay.   A large area of land near the Bay had been a dumpsite for unexploded munitions from World War II following the war.   Apparently these munitions had been buried and forgotten until some rusted through from infiltrating rainfall and exploded, bringing attention to their existence.  Fear that the toxic chemicals in the burial site would reach the Chesapeake Bay caused the site owners to investigate.   However, because they were aware that drilling sampling wells might cause additional explosions, they had to find another way to determine if the plume was really moving toward the Bay and how fast.  The project chief noticed that there was a line of mature trees between the dump site and Chesapeake Bay.   Knowing that the plume contained very high concentrations of iron, he took cores from the trees and by analyzing the specific rings representing specific years, was able to determine that the source of water for one tree had a significant rise in iron concentration in 1960.   He took additional samples from another tree about 500 feet closer to the Bay from the first tree.   This tree had a peaked concentration of high iron in about 1965.   The findings indicated that the plume was moving at a rate of about 100 feet per year (500 feet/ 5 years).  

Several studies using this tree ring dating method have been conducted in recent years with similar success and many companies are now conducting analyses of tree rings to determine the extent plumes of specific toxic organic chemicals.   See publication: “Phytoforensics, Dendrochemistry and Phytoscreening: New Green Tools for Delineating Contaminants from Past and Present” in Environmental Science and Technology dated June 14, 2011 pp. 6218-6226.  Also check web site: http://pubs.water.usgs.gov/sir2008-5088, which contains a user guide for this technology.

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