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:
- 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;
- 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;
- A shallow sandy aquifer in Denmark where the approach was applied
to document the fate of herbicides in ground water; and
- A jet fuel spill in Norway where the approach was used to document
the natural biodegradation of the contamination.
USGS Information on Natural Attenuation
- Cozzarelli, I.M., Suflita, J.M., Ulrich, G.A., Harris, S.H., Scholl,
M.A., Schlottmann, J.L., and Christenson, S., 2000, Geochemical
and microbiological methods for evaluating anaerobic processes in an
aquifer contaminated by landfill leachate: Environmental Science
and Technology, v. 34, no. 18, p. 4025-4033.
- Arildskov, N.P., Pedersen, P.G., and Albrechtsen, H.-J., 2001, Fate
of the herbicides 2,4,5-T, atrazine, and DNOC in a shallow, anaerobic
aquifer investigated by in situ passive diffusive emitters and laboratory
batch experiments: Ground Water, v. 39, no. 6. p. 819-830.
- McGuire, J.T., Long, D.T., Klug, M.J., Haack, S.K., and Hyndman,
D.W., 2002, Evaluating
behavior of oxygen, nitrate, and sulfate during recharge and quantifying
reduction rates in a contaminated aquifer: Environmental Science
and Technology, v. 36, no. 12, p. 2693-2700.
- Richmond, S.A., Lindstrom, J.E., and Braddock, J.F., 2001, Assessment
of natural attenuation of chlorinated aliphatics and BTEX in subarctic
groundwater: Environmental Science and Technology, v. 35, no. 20,
- Zheng, Z., Breedveld, G., and Aagaard, P., 2001 Biodegradation
of soluble aromatic compounds of jet fuel under anaerobic conditions--Laboratory
batch experiments: Applied Microbiology and Biotechnology, v. 57,
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