The Idaho National Engineering and Environmental Laboratory (INEEL), a facility operated by the United States Department of Energy, is located near the northern edge of the Eastern Snake River Plain in southeast Idaho. The Snake River Plain Aquifer is composed of a complex layering of fractured basalt flows intercalated with sedimentary interbeds deposited during prolonged periods of volcanic quiescence. Depth to water in the vicinity of Test Area North (TAN) is approximately 64 m (210 ft). The average thickness of basalt flows deposited during individual events is about 6 m near TAN. Ground water flow is controlled primarily by the distribution of interflow zones consisting of highly vesicular, fractured basalt formed when the base of a new lava flow cooled rapidly as it was deposited on an existing, weathered basalt surface. On a small scale this can result in highly preferential ground water flow, but beyond the scale of a single basalt flow (i.e., a few hundred to thousands of meters), ground water flow can generally be predicted adequately with equivalent porous medium models. This is because fractures within basalt flows and intersections with other basalt flows provide significant vertical hydraulic communication among the interflow zones.

• Fractured Bedrock

The TSF-05 injection well was identified as the source of ground water contamination. Liquid waste was disposed in the well directly to the SRPA between the mid-1950s and 1972. The wastes included organic, inorganic, and low-level radioactive wastes added to industrial wastewater and sanitary sewage. Characterization of sludge that remained in the well in 1990 revealed that the sludge was comprised of as much as 3% TCE and contained high levels of radionuclides (Kaminsky et al., 1994). Ground water monitoring determined that the TCE plume emanating from the injection well extends approximately 2740 m (9000 ft) to the southeast. At its widest point the plume measures approximately 1000 m across. Vertically, the contamination appears to be isolated between the water table at 64 m (210 ft) below ground surface and a continuous, areally extensive sedimentary interbed located about 125 m (410 ft) below ground surface at Well TSF-05.

• Trichloroethene (var)
• Tetrachloroethene (var)
• 1,1-Dichloroethene (var)
• Tritium (var)
• Strontium 90 (var)
• Cesium 137 (var)
• Uranium (var)

• Borehole Geophysics
  • Natural Gamma
  • Caliper
  • Acoustic Televiewer
  • Video Camera Televiewer
  • Other
• Fluid Loggings
  • Temperature
• Flow
  • Heat Pulse Flowmeter
  • Electromagnetic Flowmeter
• Vertical Chemical Profiling
  • Packer Isolation
  • Cluster Wells
  • Multi-sampling port
• Downhole Seismic Surveys
• Coring
• Tracer (dye) Test

Comments:
The seismic surveys were performed in collaboration with Lawrence Berkeley National Lab to generated tomograms. The tomograms were very useful for identifying the locations of interflow zones (high permeability zones) between wells. The data correlated very well with that from other methods.

• Pump and Treat
• Bioremediation (In Situ)
  • Reductive Dechlorination (In Situ Bioremediation)

This is a study site.

Additions of sodium lactate to the trichloroethene (TCE) source zone have resulted in the complete dechlorination of nearly all aqueous-phase TCE to ethane and the continued depletion of the residual source since 1999.

The sodium lactate additions have also enriched the indigenous microbial community. The bacterial and archaeal consortia in groundwater obtained from the residual source were assessed using PCR-amplified 16S rRNA genes. The HAAP-1 species was the most abundant bacteria in the culture. The remaining bacteria consisted of Sphingobacteria, Bacteroides, Spirochaetes, Mollicutes, Proteobacteria, and candidate divisions of OP11 and OP3. A Dehalococcoides-like phylotype was also identified using genus-specific primers. Four distinct archaeal phylotypes were identified, including the predominant Methanosaeta concilii.

The results of this study provide evidence for the electron donor utilization pathways and suggest implications for reductive dechlorination. Anaerobic reductive dechlorination has proceeded efficiently within the residual source for more than 5 years in the presence of substantial methanogenesis. At the same time, there has been no evidence of the spiral-to-failure paradigm of hydrogenotrophic methanogens outcompeting dechlorinators, despite high concentrations of electron donors and hydrogen. The majority of methane production at this site apparently occurs via the acetoclastic pathway using acetate generated by lactate fermentation and acetogenesis. Therefore, competition for hydrogen between methanogens and dechlorinators does not appear to be a significant concern under field conditions at this site. Given that methanogenesis is not necessarily detrimental to bioremediation, other benefits of using this strategy of injecting high-concentration electron donors in the field, such as residual source dissolution, can be realized. Ongoing characterization of this microbial community may provide additional insight into interspecies relationships, helping to guide future bioremediation efforts.

Reference:
Macbeth, Tamzen W.; Kent S. Sorenson. 2005. Molecular characterization of a TCE-dechlorinating field community and implications for bioremediation performance. The Eighth International In Situ and On-Site Bioremediation Symposium, Baltimore, Maryland. June 6-9.

Mecham, Gary, Joe Rothermel, Kevin Harris, Ryan Wymore, and Kent Sorenson. Full-Scale Aqueous and Solid Phase Electron Donor Injection System. Remediation of Chlorinated and Recalcitrant Compounds: The 4th International Conference. Monterey 24-27 May, 2004.