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Improving Bioaugmentation Strategies for Remediating Contaminated Fractured Rocks

USGS scientist with equipment used to inject fluids for a bioaugmentation experiment
The set up and equipment used for the bioaugmentation experiment. The bladders contain the solutions that were injected into the subsurface. The injection well is right in front of the blue barrel. Photo credit: Daniel J. Goode, USGS.
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A groundwater bioaugmentation field experiment, conducted by U.S. Geological Survey (USGS) and University of Toronto, Canada, scientists, demonstrates the effectiveness and potential weaknesses of this cleanup technology and provides guidance for improved design of bioaugmentation in fractured-rock aquifers. The experiment also demonstrates the benefits of advanced monitoring of changes in contaminants, microbial communities, isotopes, and tracers for remediation performance evaluation.

The bioaugmentation involved introducing to the subsurface a mixture of (1) microbes designed to degrade trichloroethene (TCE), (2) emulsified oil and lactate substrate which provided energy to the microbes, and (3) deuterated water as a tracer. The liquid mixture was injected into a contaminated portion of the aquifer through an injection well designed to deliver the amendments to a permeable and contaminated fracture zone. Performance of the bioaugmentation was quantified by advanced monitoring of the chemical and biological changes in multi-level monitoring wells for 2 years. Monitored constituents included:

  • concentrations of contaminants and breakdown products,
  • concentrations of substrate breakdown products,
  • stable carbon isotopes of contaminants and breakdown products,
  • the abundance of microbial communities, and
  • changes in tracer concentrations.

Results of the advanced monitoring showed that enhanced biodegradation of contaminants was achieved away from the injection well along fracture flow paths that received the bioaugmentation amendments, and that the bioaugmentation stimulated removal of contamination from within the unfractured rock matrix. The difficulties of removing contamination beyond the injection well and from the small pore spaces within the rock matrix are major challenges to engineered remediation strategies in fractured-rock aquifers, often requiring decades of sustained pump-and-treat remediation. These results highlight the importance of hydrogeologic characterization in delivering the bioaugmentation amendments into fractured rock where they will most effectively enhance biodegradation.

The experiment was conducted at the former Naval Air Warfare Center, West Trenton, New Jersey, where the USGS is carrying out long-term multidisciplinary research on the fate and remediation of contaminants in fractured-rock aquifers. TCE is a widespread groundwater contaminant and a suspected human carcinogen. The research was supported by the USGS Toxic Substances Hydrology Program, the Department of Defense Strategic Environmental Research and Development Program (SERDP), and the U.S. Navy.

References

Révész, K.M., Sherwood Lollar, B., Kirshtein, J.D., Tiedeman, C.R., Imbrigiotta, T.E., Goode, D.J., Shapiro, A.M., Voytek, M.A., Lacombe, P.J., and Busenberg, E., 2014, Integration of stable carbon isotope, microbial community, dissolved hydrogen gas, and 2HH2O tracer data to assess bioaugmentation for chlorinated ethene degradation in fractured rocks: Journal of Contaminant Hydrology, v. 156, p. 62-77, doi:10.1016/j.jconhyd.2013.10.004.

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Created on June 06, 2014