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A Unique Approach to Evaluating Natural Attenuation is Applied Worldwide

The popularity of using natural processes to clean up contaminated sites (natural attenuation) is increasing dramatically; however, reliable methods have not been available for determining if natural attenuation is effective. As a result, regulators are trying to identify the facts needed for cleanup professionals to demonstrate that natural attenuation is successfully remediating a contaminated site. Toxics Program scientists and their partners have combined hydrological, chemical, and microbiological field methods to developed a unique approach for determining when subsurface microorganisms are effectively and efficiently degrading contaminants in the subsurface. This approach to evaluating natural attenuation involves the detailed mapping of overlapping biogeochemical zones in contamination plumes. The biogeochemical zones identify areas where microorganisms are flourishing and actively degrading contaminants. Such zone mapping is not possible when either microbiological or geochemical methods are used in isolation. Identification of these biogeochemical zones is key to evaluating the efficacy of natural attenuation because organic contaminants can degrade at different rates and to different extents within contaminant plumes.

This unique approach to evaluating the effectiveness of natural attenuation is starting to be used throughout the world; examples include:

  1. Wurtsmith Air Force Base, Michigan, where a former fire-training pit resulted in contamination of the subsurface with petroleum hydrocarbons and chlorinated solvents that are now naturally degrading;
  2. Six Mile Village near Fairbanks, Alaska, where a subarctic aquifer contaminated with chlorinated solvents had such low rates of biodegradation that dilution was determined to be the primary mechanism behind the observed natural attenuation;
  3. A shallow sandy aquifer in Denmark where the approach was applied to document the fate of herbicides in ground water; and
  4. A jet fuel spill in Norway where the approach was used to document the natural biodegradation of the contamination.

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Page Last Modified: Thursday, 04-Dec-2014 10:16:58 EST