FRC Area 3 Site Bioremediation (August 24, 2003

1
FRC Area 3 Site Bioremediation (August 24, 2003
August 7, 2005)

• Tests were performed in two phases
• (1) a clean water flush to remove bulk nitrate,
  Al, and Ca (days 9-137).
• (2) biostimulation by repeated ethanol injection
  (days 138-present).
• Uranium is immobilized in the sediments at
  700-2000 mg/kg
• Uranium concentration in the groundwater has
  dropped below US EPA drinking water maximum limit
  (0.03 mg/l) in the monitoring wells.
• An active remediation zone has been established
  with high microbial activity for denitrification,
  Fe(III) reduction, sulfate reduction and U(VI)
  reduction.

2
Well System for Field-scale Test for in situ
Bioremediation of Uranium Contaminated site, FRC
Area 3
3
Injection of Electron Donor (ethanol) for
Bioremediation (day 137-710)
Started ethanol injection on day 137
4
Nitrate Concentration Changes during Remediation
Clean water flush (day 9-137)
Bioremediation (day 138-670)
To avoid production of nitrogen gas bubbles in
subsurface and inhibition, nitrate should be
reduced below 1 mM
5
U(VI) Concentrations in inner loop wells and MLS
wells
Injection and extraction wells
Monitoring wells
The maximum concentration of uranium in drinking
water is 0.03 mg/l (US EPA).
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Uranium Content in Sediments from Injection,
Monitoring and Extraction Wells during
Bioremediation
injection well
monitoring well
extraction well
Variability in the content of U in the injection
well sediment is likely due to variability in the
removal of U during the surging operation.
Before bioremediation the uranium content in core
samples from FW104 ranged from 0.03 to 0.8 g/kg
Day 409
Day 247
Day 535
Day 622
Day 670
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Uranium Redox State Day 535
8
The sediment changes color as microbial reduction
progresses
Day 333
injection well
monitoring well
brown
Day 670
extraction well sample from day 670 incubated 3
days with no added ethanol
extraction well sample from day 670 incubated 3
days after adding 100 mg/L ethanol
injection well
extraction well
monitoring well
Now black