Push-Pull Tests to Evaluate Natural Attenuation at a ... · Slide 3 Study Objectives • Evaluate...

Push-Pull Tests to Evaluate Natural

Attenuation at a Uranium ISR Site

Paul Reimus1, Mike Rearick1, George Perkins1

Oana Marina1, Jesse Punsal1, Kevin Chamberlain2

and James Clay3

1Los Alamos National Laboratory, 2University of Wyoming

3Cameco Resources

2015 Uranium Recovery Workshop

Denver, CO

June 9, 2015

LA-UR-24178

Outline

• Objectives

• Overview of Push-Pull Test Method

• Test Location

• Push-Pull Test Results and Interpretations

• Implications of Test Results

Study Objectives

• Evaluate the ability of the aquifer downgradient of an ISR

ore zone to geochemically attenuate the transport of

uranium and other contaminants

– Accomplished by conducting single-well, push-pull tests

– Focus on uranium transport, although other contaminant species

considered (Se, As)

• Translate test results into predictions of downgradient

transport of Uranium

Smith Ranch-Highland Operation, Wyoming

Push-Pull Test Method

Ore Body

Shale

Overlying

Aquifer

Shale

Underlying Aquifer

Shale

Ore

Bearing

Aquifer

Injection Well Injection Well Production Well Production Well

Plan View

Inject Residual Ore Zone Water and Tracers

Ore Body

Shale

Overlying

Aquifer

Shale

Underlying Aquifer

Shale

Ore

Bearing

Aquifer

Injection Well Injection Well Production Well

Inject Residual Ore Zone Water with Tracers

U U

U

Production Well

Plan View

Inject Unmined Ore Zone Water (Chase)

Ore Body

Shale

Overlying

Aquifer

Shale

Underlying Aquifer

Shale

Ore

Bearing

Aquifer


Inject Unmined Ore Zone Water (Chase) Production Well

Plan View

U U U U

Ore Body

Shale

Overlying

Aquifer

Shale

Underlying Aquifer

Shale

Ore

Bearing

Aquifer

Rest or Drift Period


U U U U

Production Well

Plan View

Pump Back the Well

Ore Body

Shale

Overlying

Aquifer

Shale

Underlying Aquifer

Shale

Ore

Bearing

Aquifer


Pump Back the Well

U U U U

Production Well

Plan View

Pump Until Tracers Recovered and Then Some

Ore Body

Shale

Overlying

Aquifer

Shale

Underlying Aquifer

Shale

Ore

Bearing

Aquifer


Recover Injection Solution with Tracers

U U U U

U

Production Well

Plan View

Single-Well Push-Pull Tests

Conducted in 3 production wells in MU-

7 in an area that had not been mined

(proxy for downgradient conditions)

Procedure:

• Inject traced waters from a previous-

ly mined unit (MU-4A) into ore zones

• ‘Chase’ with low-U ore zone water

• Allow injected water to ‘rest/drift’ in

ore zone

• Pump back waters

• Compare uranium and other

constituent recoveries with tracers

• Model results to allow downgradient

predictions

Photos of Push-Pull Tests

Push-Pull Test Specifics

7P-129 7P-30 7P-29 Injection water MP-423 MP-423 4P-61

Injection volume, gallons 1100 1520 1550

Chase (7P-38) volume, gallons 4680 5060 5900

Rest Period 17 days 3 months 3 months

Pumped volume, gallons 24,500 90,000 61,000

Wellscreen length, ft 16 19 24

Penetration distance, ft 8.8 8.5 8.2

Unrestored Waters Partially-

Restored Water

Same Water, Different Rest Times









Restored Water









Restored Water

Different Waters, Same Rest Times

Water Chemistries in Push-Pull Tests

Unrestored

Ore Zone

Partially-Restored

Ore Zone

Unmined

Background

Constituent MP-423 4P-61 7P-38 Ca2+ (mg/L) 461 162 102

Na+ (mg/L) 46 28 26

Mg2+ (mg/L) 108 42 26

K+ (mg/L) 20 12 8

Fe (total, mg/L) 2.5 2.0 0.3

Uranium (mg/L) 40.7 4.7 0.17

Si (mg/L) 7.5 6.5 7.5

SO42- (mg/L) 895 300 290

Cl- (mg/L) 131 41 2.2

Alkalinity (mg/L as CaCO3) 550 275 160

HCO3- (mg/L calculated) 670 335 195

pH ~6.3 ~6.3 ~7.4

Water Chemistries in Push-Pull Tests

Constituent MP-423 4P-61 7P-38 Ca2+ (mg/L) 461 162 102

Na+ (mg/L) 46 28 26

Mg2+ (mg/L) 108 42 26

K+ (mg/L) 20 12 8

Fe (total, mg/L) 2.5 2.0 0.3

Uranium (mg/L) 40.7 4.7 0.17

Si (mg/L) 7.5 6.5 7.5

SO42- (mg/L) 895 300 290

Cl- (mg/L) 131 41 2.2

Alkalinity (mg/L as CaCO3) 550 275 160

HCO3- (mg/L calculated) 670 335 195

pH ~6.3 ~6.3 ~7.4

Unrestored

Ore Zone

Partially-Restored

Ore Zone

Unmined

Background

Push Pull Test Results – Unrestored Waters

17-Day Concentrations 17-Day Recoveries

3-Month Recoveries 3-Month Concentrations

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

0 5000 10000 15000 20000 25000

C/C

o

Gallons pumped

2,6 DFBA

U (total)

U Injected

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

0 20000 40000 60000 80000 100000

C/C

o

Gallons pumped

2.6DFBA

U (total)

U Injected

Flow rate raised from 9.5 gpm to 27.8 gpm

0.000

0.005

0.010

0.015

0.020

0.025

0 20000 40000 60000 80000 100000

C/C

o

Gallons pumped

2.6DFBA

U (total)

U Injected


Fra

ctional R

ecovery

F

ractional R

ecovery

0.00

0.02

0.04

0.06

0.08

0.10

0.12

0.14

0.16

0 5000 10000 15000 20000 25000

C/C

o

Gallons pumped

2,6 DFBA

U (total)

U Injected

Push Pull Test Results – Restored vs. Partly Restored

Unrestored Recoveries Unrestored Concentrations

Partially Restored Recoveries Partially Restored Concentrations

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

0 20000 40000 60000 80000 100000

C/C

o

Gallons pumped

2.6DFBA

U (total)

U Injected


0.000

0.005

0.010

0.015

0.020

0.025

0 20000 40000 60000 80000 100000

C/C

o

Gallons pumped

2.6DFBA

U (total)

U Injected


0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

0 10000 20000 30000 40000 50000 60000

C/C

o

Gallons pumped

2.6 DFBA

U (total)

U Injected

Flow rate raised from 9 gpm to 28 gpm

Fra

ctional R

ecovery

F

ractional R

ecovery

0.00

0.02

0.04

0.06

0.08

0.10

0.12

0.14

0 10000 20000 30000 40000 50000 60000

C/C

o

Gallons pumped

2.6 DFBA

U (total)

U Injected

Flow rate raised from 9 gpm to 28 gpm

234U/238U Activity Ratio Corrections for Uranium

7P-129

Unrestored, Short

7P-30

Unrestored, Long

7P-29

Partly Restored, Long

Injection Ratio: 1.12

Chase Ratio: 1.025

‘Background’ Ratio: 1.375


Chase Ratio: 1.025



Chase Ratio: 1.025


Push-Pull Tests: Evidence of Inadvertent Mining

7P-129

Unrestored, Short

7P-30

Unrestored, Long

7P-29

Partially Restored, Long Unrestored Inj. Se = 0.051

As = 0.002

V = 0.012

Partly Restored Inj. Se = 0.066

As = 0.015

V = 0.005

Chase Water Se = 0.1

As = <0.002

V = 0.014

238U/235U Ratios to Look for Evidence of Reduction

7P-129 Unrestored, Short 7P-30 Unrestored, Long

7P-29 Partially Restored, Long

ORP and pH in Push-Pull Tests



3-Site Adsorption/Desorption Model


7P-29 Partially Restored, Long Non-Mechanistic Model,

Based Loosely on 3-Site

Model of Davis and Curtis

(2003) (NUREG/CR-6820):

- Weak (~95%)

- Strong (~5%)

- Very Strong (<1%)

Using Model Parameters to Predict Downgradient Transport

7P-129 Partly Restored, Short 7P-30 Partly Restored, Long


Blue: Nonreactive

Red: Uranium

Solid: Pe = 8

Dashed: Pe = 100

Assumes downgradient

distance is distance to

monitoring well ring

Abundance of strongest

site controls transport

Effect of Doubling the Downgradient Distance

1X Distance 2X Distance

v

v

1X

2X

Doubling the distance improves

‘performance’ by factor of 5 or more

- A consequence of large

influence of small number of

very strong sites

In Lieu of Modeling

• ‘Immobilization’ Capacities based on Uranium

Recoveries and Aquifer Volumes Interrogated:

– 7P-129 (unrestored, short): 2.85 g U/m3 aquifer

– 7P-30 (unrestored, long): 4.06 g U/m3 aquifer

– 7P-29 (partially restored, long): 0.38 g U/m3 aquifer

• Aquifer volume is quite uncertain

• Unrecovered uranium may not be irreversibly

immobilized

Conclusions

• Results suggest significant downgradient attenuation of

Uranium

– The test methodology appears useful for refining restoration

targets and perhaps helping establish ACLs in ore zone

– It also may prove useful for refining long-term monitoring

requirements

– Linkage of test results to robust models will be important

• Uncertainties and questions remain

– Single-well push-pull method has limitations

– Why did we see lowest apparent attenuation of restored water?

– ‘Geochemistry’ model is nonmechanistic and nonunique

– Questions of scale and representativeness

– Se and As results inconclusive

Conclusions

• Cross-well attenuation test might be more definitive

– Would offer some advantages over single-well methods

– Low concentrations expected based on push-pull test results

• Perhaps downgradient wells could be designed into ISR

wellfields to evaluate attenuation in the downgradient

aquifer either before or after mining (or both)

– Would have to expand monitoring well ring

– Could draw restored/unrestored waters toward wells while

avoiding ‘excursions’:

Thank You

• University of Wyoming School of Energy Resources

and US EPA for financial support

• Many helpful staff at Smith Ranch-Highland

– Dennis Zimbelman

– Mike Beshore

– Field Operations and Analytical Lab staff

– Larry Reimann

– Brent Berg

Thank You for Your Attention!

BACKUP SLIDES

Hydrologic Dispersion from Pattern Tracer Tests

4I-217(PFBA)

4I-218 (2,5 DFBA)

4I-214(2,6 DFBA)

4I-213 (2,4 DFBA)

4P-121

Corehole

67.2’3.9o

68.9’, 259.9o 76.0’, 84.9o

69.3’180.4o

30’ interval

24’ interval

22’ interval

27’ interval

16’ interval

4I-206(2,4 DFBA)

4I-207 (PFBA)

4I-202(2,5 DFBA)

4I-201 (2,6 DFBA)

4P-113

78.6’348.0o

84.1’, 246.7o 67.9’, 78.4o

68.6’173.8o

17’ interval

18’ interval

41’ interval

27’ interval

16’ interval

0

100

200

300

400

500

600

0 1000 2000 3000 4000 5000 6000

No

rmal

ized

Co

nce

ntr

atio

n

Volume since Injection, m3

Observed

Ideal

0

100

200

300

400

500

600

0 1000 2000 3000 4000 5000

No

rmal

ized

Co

nce

ntr

atio

n

Volume since Injection, m3

Observed

Ideal

4P-121 Pattern 4P-113 Pattern

Translating Sweep Efficiency to a Peclet Number

Peclet Number = Length Scale/Dispersivity

Green and red are ‘difference curves’ –

difference between observed and ideal curves

Conceptual Model of Flow in Push-Pull Tests

Tracers During Injection Tracers During Pumping

Gas-locked orotherwise impededsectionsduring injection

Sections impeded during injection flowedmuch better duringpumping, resulting inslower recovery andgreater dilution oftracers that were injectedprimarily into non-impeded sections

Wel

l Scr

een

Length of bars proportional to flow rate

Push-Pull Well Observed Theoretical

7P-129 7500 5230

7P-30 58,000 5830

7P-29 22,000 6680

Gallons Pumped at Mean Arrival Time

Push-Pull Test Charge Balance, HCO3-, and Alkalinity

Charge Balance

HCO3- and

Alkalinity

7P-30

Test

Tracer and Uranium Recoveries

Constituent 7P-129 7P-30 7P-29 7P-129 7P-30 7P-29

2,6 DFBA 0.946 0.774 0.919 0.995 0.941 0.95

Iodide 0.925 0.797 0.895 0.974 0.99 0.927

Bromide 1.06 0.773 0.994 1.11 0.994 1.025

Chloride 0.92 0.715 0.988 - - -

Total Uranium 0.483 0.249 0.844 0.498 0.253 0.848

Injected Uranium 0.225 0.130 0.213 0.225 0.130 0.213

At End of Pumping Extrapolated

Uranium Speciation Calculated by PHREEQC

Uranium Species

MP-423, M

MP-423

Fraction

4P-61, M

4P-61

Fraction

Ca2UO2(CO3)30 1.53 x 10-4 0.8900 1.61 x 10-5 0.8140

CaUO2(CO3)3-2 1.78 x 10-5 0.1040 3.38 x 10-6 0.1709

MgUO2(CO3)3-2 6.21 x 10-7 0.0036 1.26 x 10-7 0.0064

UO2(CO3)2-2 1.33 x 10-7 7.77 x 10-4 9.49 x 10-8 0.0048

UO2(CO3)3-4 1.31 x 10-7 7.62 x 10-4 2.90 x 10-8 0.0015

Mg2UO2(CO3)30 1.17 x 10-7 6.83 x 10-4 1.41 x 10-8 7.12 x 10-4

UO2CO3 2.05 x 10-8 1.19 x 10-4 3.05 x 10-8 0.0015

SrUO2(CO3)3-2 8.80 x 10-9 5.14 x 10-5 2.34 x 10-9 1.18 x 10-4

UO2(OH)2 6.76 x 10-10 3.94 x 10-6 1.68 x 10-9 8.50 x 10-5

UO2OH+ 4.70 x 10-11 2.74 x 10-7 1.11 x 10-10 5.60 x 10-6

(UO2)2CO3(OH)3- 1.09 x 10-11 6.37 x 10-8 3.81 x 10-11 1.93 x 10-6

UO2+2 7.17 x 10-12 4.18 x 10-8 1.43 x 10-11 7.25 x 10-7

Includes Ca- and Mg-Uranyl Ternary Complexes from Dong and Brooks (2006)

Push-Pull Test 3-Site Model Parameters

Parameter 7P-129

push

7P-129

pull

7P-30

push

7P-30

pull

7P-29

push

7P-29

pull

kf1, ml/g-hr 5 5 5 5 8 8

kr1, hr-1 7 20 2.0 20 6.4 6.4

Sm1, mmol/g* 1.3 1.3 1.3 1.3 1.3 1.3

kf2, ml/g-hr 2.5 2.5 2.5 2.5 4 4

kr2, hr-1 3.5 1.3 1.0 0.8 3.2 1.08

Sm2, mmol/g 0.067 0.067 0.067 0.067 0.008 0.008

kf3, ml/g-hr 0.1 0.1 0.1 0.1 0.1 0.1

kr3, hr-1 0.05 0.0001 0.05 0.0001 0.0075 0.0001

Sm3, mmol/g 0.020 0.020 0.0111 0.0111 0.0011 0.0011

Iodide and Sum of Fluorinated Benzoates

0

100

200

300

400

500

600

700

800

900

0 5 10 15 20 25 30 35 40 45

No

rmali

zed

Co

ncen

trati

on

Days of Pumping since Start of First Injection

Total FBA

Iodide

0

100

200

300

400

500

600

700

800

0 5 10 15 20 25 30 35 40 45

No

rmali

zed

Co

ncen

trati

on

Days of Pumping since Start of First Injection

Total FBA

Iodide

4P-121 Pattern 4P-113 Pattern

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