Concept/HypothesesConcept/Hypotheses

ORIGINAL HYPOTHESIS: “Radionuclides in low-permeability porous matrix regions of fractured saprolite can be effectively isolated and immobilized by stimulating localized in-situ

biological activity in highly-permeable fractured and microfractured zones within the saprolite.” (Roden and Scheibe, 2005)

Field Site DevelopmentField Site Development

• Geophysical wells GP-1, GP-2, GP-3, GP-4 and GP-5 were recently completed.

• Additional monitoring wells (blue in figure to the left) will be multi-level sampling (MLS) wells. Materials have been delivered and construction will begin soon.

• Site infrastructure will then be complete. Wells FW212, FW213, and FW214 will serve as electron donor injection wells; flush experiment (tracer and water injection) will be conducted using FW215.

In Situ Immobilization of Uranium in Structured Porous Media via Biomineralization at the Fracture/Matrix

Interface (FRC Area 2 Field Project)

The original hypothesis focused on the intact fractured saprolite zone

INTACT SAPROLITE HAS ISSUES:• Low U(VI) concentrations• High nitrate concentrations• Low permeability

REVISED HYPOTHESIS: “In heterogeneous porous media, microbial activity can be stimulated at interfaces between zones of high and low groundwater flow rates in such a

manner as to create a local, distributed redox barrier. Such a barrier will inhibit the transfer of contaminants from the low-flow zones that serve as long-term contaminant sources into the

high-flow zones that transport contaminants to receptors.”

BROMIDE MISSING AT GOVERNMENT NUCLEAR RESERVATION

Area 2 Tracer Test 10 Aug 04IC data through 22 Sep 04

0

20

40

60

80

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120

140

0 10 20 30 40 50 60 70 80 90 100

Elapsed Time (h)

[Br]

-mg/

L - I

C

FW212

FW213FW214

FW216-1FW216-2

TPB16GW835

FW202-2

DP13

Seep1Seep2

Events

FW215 - Injection Well

0

100

200

300

400

500

0 200 400 600 800

Bromide breakthrough curves from the Area 2 tracer test conducted August 2004.

GRAVEL CAPTURES RESEARCHERS’ ATTENTION

Vertical profiles of total sediment-associated uranium at two boreholes in

Area 2. Gravel layer is at approximately 18 feet below ground surface.

Saprolitic Fill Material

Intact Saprolite Material

GravelZone

0.01.02.03.04.05.06.07.08.09.0

10.0

0 10 20 30 40 50 60

Time (d)

(mM

)

CH3CH2OHCH3COO-CH3CH2OHCH3COO

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

0 10 20 30 40 50 60

Time (d)

NO

3-, S

O42

- (m

M) NO3-

SO42-NO3SO4

0.02.04.06.08.0

10.012.014.016.018.020.0

0 10 20 30 40 50 60

Time (d)

Fe(II

) (m

mol

/L)

TotalDissolvedFe2TotFe2aq

0.0

2.0

4.0

6.0

8.0

10.0

12.0

14.0

16.0

0 10 20 30 40 50 60

Time (d)

CH4,

DIC

(mM

)

CH4CH4DICDIC

Terminal Electron Accepting Processes (TEAPs) –Experimental and Model Results

0.000.010.020.030.040.050.060.070.080.090.10

0 10 20 30 40 50 60

Time (d)

U(VI

) (m

mol

/L)

TotalUVITot

0.00

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1.00

1.50

2.00

2.50

3.00

0 10 20 30 40 50 60

Time (d)

U(VI

)aq

(uM

)

TotalUVIaq

U(VI) Partitioning and Reduction –Experimental and Model Results

cDNA clone library (Total clones 41)

Geobacter

Oxalobacter

Clostridium

Dechloromonas

Desulphosporinus

Ferribacter

Uncultured

DNA clone library (total clones 30)

Geobacter

Oxalobacter

Clostridium

Dechloromonas

Desulphosporinus

Ferribacter

Uncultured

y = 0.4788x + 7.4456R2 = 0.3234

0.0

5.0

10.0

15.0

20.0

25.0

30.0

35.0

40.0

0.0 5.0 10.0 15.0 20.0 25.0 30.0 35.0 40.0 45.0

% Total Clones cDNA

% T

otal

Clo

nes

DNA

FWB215Slurry ExperimentsSlurry Experiments

Tracer Test / Flush ExperimentTracer Test / Flush Experiment

Timothy D. Scheibe Pacific Northwest National Laboratory, Richland, Washington, USA

Eric E. Roden The University of Alabama, Tuscaloosa, Alabama, USA

Scott C. Brooks Oak Ridge National Laboratory, Oak Ridge, Tennessee, USA

John M. Zachara Pacific Northwest National Laboratory, Richland, Washington, USA

CRITICAL ISSUE: How to test hypothesis at the field scale?

We added electron donor and saw U(VI)

decrease…

OK… But WHY?

Hmmm.. .Did they account for the U(VI) coming in from up-gradient sources?

EXPERIMENTAL CONCEPT: Flush Experiment for Mass Transfer Rate Determination

Schematic diagram showing streamlines of injected water (with tracer) in dark blue and diverted streamlines under injection conditions of contaminated water flowing into the study zone from upgradient (red lines with arrows). The light blue circle represents the injection well (i.e., FW215) and dark green circles represent nearby monitoring points (FW212, FW213, FW214). Contours of hydraulic head are indicated by the grey lines.

Accessible porosity within the zone of the aquifer encompassed by the blue streamlines is “flushed” of ambient contamination during the injection event. Any remaining solutes must then be provided from a local source (e.g., desorption and/or mass transfer from

secondary porosity or an non-advective zone)

Simulated (two cases)

Observed

Effect of Desorption KineticsObserved

Simulated

Core/Well DataCore/Well DataPrevious Cores GP01 – Geophysical Well

Installed Feb. 2005

0.00

0.50

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2.00

2.50

3.00

0 200 400 600

Total Fe (umol/g)

Dep

th B

elow

Top

Bou

ndar

y (f

t)

> 4000

2000-4000

1000-2000

106-1000

53-106

< 53

0.00

0.50

1.00

1.50

2.00

2.50

3.00

0 50 100 150 200 250Total U (umol/g)

Dep

th B

elow

Top

Bou

ndar

y (f

t)

> 4000

2000-4000

1000-2000

106-1000

53-106

< 53

Above: Borehole flowmeter data from well GP-01. Total pumping rate = 2 L/min.

Right: Map of experimental cell showing those wells with bromide breakthrough