Can Trees Clean Up Ground Water? Phytoremediation of Trichloroethene-Contaminated Ground Water at Air Force Plant 4, Fort Worth, Texas
Type |
- Testing of Remediation Technologies
- Performance Monitoring
- Site Characterization
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Location |
Air Force Plant 4, Fort Worth, Texas, which is adjacent to the
Naval Air Station Fort Worth (formerly Carswell Air Force Base),
Fort Worth, Texas
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Partners |
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Technology |
Phytoremediation
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Contaminants |
Chlorinated Solvents (trichloroethene [TCE]) |
Description |
The U.S. Air Force and its partners conducted a project to test
the concept of phytoremediation.
The test consisted of planting eastern cottonwoods (Populus deltoides)
above shallow ground water contaminated with low levels of trichloroethene
(TCE) near Air Force Plant 4, Fort Worth, Texas. The objective of
the test was to test the hypothesis that:
- Planting trees can hydraulicly contain and remove TCE contaminated
water from an aquifer by transpiration
and volatilization of TCE into the atmosphere, and
- The trees will promote the natural attenuation of dissolved
trichloroethene within the aquifer.
USGS scientists and their partners designed, implemented, and monitored
the performance of the cottonwood trees. The scientists constructed
a ground-water flow model based on monitoring data, and coupled
it to a model of tree transpiration developed by the U.S. Forest
Service. With the assistance of the coupled model the scientists
were able to show that after the third growing season containment
was not achieved, but the volume of ground water moving past the
trees was reduced by 12 percent. A solute transport model also showed
that the mass of TCE moving across the downgradient end of the site
decreased by 11 percent. This demonstrated that after only three
years the trees were removing TCE from the aquifer. Additional monitoring
is being conducted to assess the long-term effectiveness of the
trees as they continue to grow and mature.
The scientists also tracked the plume through the use of tree cores,
and investigated the effect that rain events (recharge events) had
on the concentrations of TCE in the trees. More information on the
tree core study will be available soon.
A major focus of the work was to evaluate if the trees enhanced
the natural attenuation of the TCE plume. USGS scientists and their
partners conducted geochemical and microbiological studies to determine
the geochemical conditions of the ground water in and around the
cottonwood trees and to determine the role that microorganisms associated
with the cottonwoods' roots played in the biodegradation of TCE
at the site. After two years the cottonwood trees were beginning
to affect the microbiology and geochemistry of the ground water
near the trees. Indicators that the system was becoming anaerobic
(without oxygen) were increasing. The increase in the anaerobic
bacteria in general and the appearance of methanogenic
microorganisms in the area suggested that the areas under the cottonwood
plantings were evolving towards an anaerobic ecosystem; however,
the constant concentrations of TCE and the daughter products suggested
that volatilization and transpiration accounted for the majority
of the loss of TCE mass at the time. Continued monitoring and analysis
showed that after six years the system was becoming increasingly
anaerobic, biodegradation rates had increased by two orders of magnitude,
and the extent of the plume had decreased by an order of magnitude.
If the ecosystem continues to evolve towards a mature methanogenic
ecosystem, the natural attenuation (biodegradation) stimulated by
the trees could exceed transpiration and volatilization as the process
most responsible for the loss of TCE from the contaminant plume.
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More Information |
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Contact |
- Project Design and Ground Water Modeling -- Sandra M. Eberts,
USGS, Ohio District, Columbus, OH,
- Microbiology -- Edward M. Godsy, USGS, National Research Program,
Menlo Park, CA,
- Plume Geochemistry -- Sonya A. Jones, USGS, Texas District,
Austin, TX,
- Tree Core Investigation -- Don A. Vroblesky, USGS, South Carolina
District, Columbia, SC,
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Publications |
- Eberts, S.M., Schalk, C.W., Vose, James, and Harvey, G.J., 1999,
- Hydrologic effects of cottonwood trees on a shallow aquifer
containing trichloroethene: Hydrological Science and Technology,
v. 15, no. 1-4, p. 115-121.
- Godsy, E.M., Warren, Ean, and Paganelli, V.V., 2003,
- The role of microbial reductive dechlorination of TCE at the
phytoremediation site at the Naval Air Station, Fort Worth, Texas:
International Journal of Phytoremediation, v. 5, no. 1, p. 73-87.
- Jones, S.A., Lee, R.W., and Kuniansky, E.L., 1999,
- Phytoremediation
of trichloroethene (TCE) using cottonwood trees, in Leeson,
Andrea, and Alleman, B.C., eds., Phytoremediation and innovative
strategies for specialized remedial applications, in The Fifth
International In Situ and On-Site Bioremediation Symposium, San
Diego, Calif., April 19-22, 1999: Battelle Press, v. 6, p. 101-108.
- Lee, R.W., Jones, S.A., and Kuniansky, E.L., 1999,
- Geochemical effects of cottonwood trees on a shallow aquifer
containing trichloroethene, in American Institute of Hydrology,
Fourth USA/CIS Joint Conference on Hydrology and Hydrogeology,
San Francisco, Calif., November 1999, Proceedings: Hydrological
Science and Technology Special Issue.
- Lee, R.W., Jones, S.A., Kuniansky, E.L., Harvey, G.J., and Eberts,
S.M., 1998,
- Phreatophyte
influence on reductive dechlorination in a shallow aquifer containing
TCE, in The First International Conference on Remediation
of Chlorinated and Recalcitrant Compounds, Monterey, Calif., May
18-21, 1998, Bioremediation and phytoremediation: Battelle Press,
p. 263-268.
- Lee, R.W., Jones, S.A., Kuniansky, E.L., Harvey, Gregory, Sherwood
Lollar, B., and Slater, G.F., 2000,
- Phreatophyte
influence on reductive dechlorination in a shallow aquifer contaminated
with trichloroethene (TCE): International Journal of Phytoremediation,
v. 2, no. 3, p. 193-211.
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