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.

Well System for Field-scale Test for in situ Bioremediation of Uranium Contaminated site, FRC Area 3

Injection of Electron Donor (ethanol) for Bioremediation

(day 137-710)

Accumulated ethanol injected

0

2000

4000

6000

8000

10000

100 200 300 400 500 600 700 800

Time, day

Accumulated ethanol (g as COD)

Started ethanol injection on day 137

Nitrate Concentration Changes during Remediation

0.010

0.100

1.000

10.000

100.000

1000.000

0 100 200 300 400 500 600 700

Time, day

Nitrate, mM

FW101-2 Nitrate

FW101-3 Nitrate

FW102-2 Nitrate

FW102-3 Nitrate

0.010

0.100

1.000

10.000

100.000

1000.000

0 100 200 300 400 500 600 700

Time, day

Nitrate, mM

FW104 Nitrate

FW026 Nitrate

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

U(VI) Concentrations in inner loop wells and MLS wells

The maximum concentration of uranium in drinking water is 0.03 mg/l (US EPA).

0.001

0.010

0.100

1.000

10.000

160 210 260 310 360 410 460 510 560 610 660 710

Time, day

U(VI) mg/l

FW101-2 U(VI)FW101-3 U(VI)FW102-2 U(VI)FW102-3 U(VI)

U(VI) Concentrations in injection and extraction wells

0.01

0.10

1.00

10.00

160 210 260 310 360 410 460 510 560 610 660 710

Time, day

U(VI) mg/l

FW104 U(VI)

FW026 U(VI) Injection and extraction wells

Monitoring wells

0.00

1.00

2.00

3.00

4.00

5.00

1 2 3 4 5

Uranium (g/kg)

FW104

FW101-2

FW026

Before bioremediation the uranium content in core samples from FW104 ranged from 0.03 to 0.8 g/kg Day 247 Day 409 Day 535 Day 622 Day 670

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.

injection well

monitoring well

extraction well

Uranium Content in Sediments from Injection, Monitoring and Extraction Wells during Bioremediation

Energy (eV)

17140 17150 17160 17170 17180 17190 17200

Normalized Flourescence

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1.6

1.8

Uraninite [U(IV)]Injection Well - 51% U(IV)MLS Well - 35% U(IV)Extraction Well - 28% U(IV)Uranyl Nitrate [U(VI)]

Uranium Redox State – Day 535

The sediment changes color as microbial reduction progresses

injection wellmonitoring well

Day 333

Day 670

extraction well

monitoring well

injection well

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

Now black

brown