Evaluating and Treating DNAPL in Fractured RockCharles Schaefer, Ph.D.

David Lippincott – APTIMRachael Rezez – APTIMGraig Lavorgna - APTIMDr. Michael Annable – UFLErin White – UFL

DNAPL Architecture, Dissolution, and Treatment

2

The DNAPL challenge

Complicating Factors in Bedrock

• Most of the contaminant mass may be in the non-aqueous phase

• Dissolution rate may limit remedial effectiveness and mass discharge

• Locating and contacting DNAPL sources can be challenging

• Many of the technologies for locating and quantifying DNAPL sources are notappropriate, or have not been demonstrated, for bedrock

• DNAPL may be even more difficult to contact in fractured bedrock

• Costs

Investigating DNAPL within a Single Fracture Plane(SERDP Project ER-1554)

3

Construction of Discrete Fracture SystemsInfluent manifold connectedto HPLC pump. Typical flow

of 0.1 mL/min.

Effluent collection

29 cm x 29cm x 5cm

Key Findings – DNAPL Architecture

4

Rock ResidualSaturation(cm3/cm3)

Interfacial Area

(cm2/cm3)

Colorado 1 0.24 21Colorado 2 0.21 48Arizona 1 0.39 56Arizona 2 0.43 20

Area:PCE ratio ~3-times less than in sands

Mass transfer coefficient ~10-times less than in sands

0.0000

0.0006

0.0012

0.0018

0.0024

0 0.01 0.02 0.03 0.04 0.05 0.06

Intri

nsic

Mas

s Tr

ansf

er

Coef

ficie

nt (

cm/m

in)

Re

A1

C1

A2

C2

DNAPL in Fractured Rock Is Difficult to RemoveCompared to Unconsolidated Materials

ISCO for TCE DNAPL in a Rock Fracture(SERDP Project ER-1554)

5

~4% of residual DNAPL removedusing activated

persulfate

Diminished Treatment due to Blockage of DNAPL-Water Interfaces

6

0.0

0.2

0.4

0.6

0.8

1.0

1.2

0 100 200 300 400 500 600

C/C 0

Total Minutes

SDBS

Bromide

0

0.2

0.4

0.6

0.8

1

1.2

0 200 400 600 800 1000 1200

C/Co

Total Minutes

SDBS

Br

Post Persulfate Oxidation- Rate of PCE removal had decreased by approximately 7-fold

- Precipitates likely forming at DNAPL-water interfaces

Prior to Persulfate OxidationRetardation (sorption) of the

interfacial tracer SDBS

No measurable retardation

Illustrative Field Example – Key Insights

7

Demonstration Location - Edwards AFB(ESTCP 201210)Site 37 Characteristics

Ø Large plume (390 acres)Ø Deep (>200 ft)Ø Granite bedrock (quartz/feldspar)Ø Low transmissivityØ Fracture flowØ PCE at >10% solubilityØ No direct evidence of DNAPL

8

Site Characteristics

~100 mL/min recirculation flow

Initial Source Investigation

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• Borehole geophysics

• Rock core analysis

• Discrete interval groundwater sampling & drawdown testing

• Short term pump tests

• Push-pull tracer tests

14

60

65

70

75

80

85

90

B06 B07ft bgs

B11 B12 B13

Pump at ~130 ft bgs

Extraction Wells

Low T

18

21

4.1 5.6

19

25

PCE (mg/L)

Two Phases of Testing Using the Recirculation System

10

• Partitioning Tracer Test (PTT) to assess flow field and DNAPL architecture

• Bioaugmentation

Partitioning Tracer Testing

11

Annable et al., JEE, 1998

14

60

65

70

75

80

85

90

B06 B07ft bgs

B11 B12 B13

Pump at ~130 ft bgs

Extraction Wells

Low T

PTT Limitations

12

• Must contact DNAPL

• Not appropriate for mobile DNAPL

• High TOC solids may limit sensitivity

• Matrix diffusion

Based on conceptual model by Parker et al., 1994

Partitioning Tracer Test

13

Groundwater recirculation (~120 mL/min

Inject 50 gal tracer slug (no PCE)- bromide - alcohols

Collect extracted water & treat with GAC during tracer injection

Continue GW recirculation

Monitor tracers and VOCs at monitoring and extraction wells over a 6 week period

Tracer injection

- No impacts at extraction wells- Primary response at B11(S,D)

Tracer Results – Deep Zone

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• 1% of flow• 0.7% DNAPL

Initial Peak(low T fracture)

• 9% of flow• No DNAPL

Middle Peak

• 40% of flow• 0.04% DNAPL

Late Peak0.0

0.1

0.2

0.3

0 10 20 30

Rela

tive

Conc

entr

atio

n (C

/C0)

Time Elapsed (days)

24DMP

Bromide

0.00

0.01

0.02

0.03

0.04

0.0 0.5 1.0 1.5 2.0 2.5Re

lativ

e Co

ncen

trat

ion

(C/C

0)Time Elapsed (days)

24DMP

Bromide

Mass transfer controlled tailing

Bromide mass eluting through each zone proportional to transmissivity

What Else Did We Learn from the PTT?

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DNAPL distributionDNAPL present in high transmissivity fractures, but also in low transmissivity zones

Average fracture porosity0.004

DNAPL mass2.4 kg in 15 ft radius around injection well interval

DNAPL persistence under ambient conditions (dissolution only)DNAPL in moderate to high T zones – 65 yearsDNAPL in low T zone – 194 years

PCE Distribution

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Rock Matrix vs Fractures

0

2

4

6

8

10

0 50 100 150 200

Dist

ance

Inw

ard

from

Fra

ctur

e (c

m)

PCE Concentration (µg/kg)

76 ft bgs

98 ft bgs

149 g PCE in rock matrix

Based on PTT DNAPL estimate

2,400 g PCE as DNAPL in fracturesPCE concentration profile suggests

back-diffusion not occurring

So treating to remove DNAPL might make sense

Bioaugmentation(August 29, 2014)

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• Initial electron donor delivery- 59L lactate (2,000 mg/L) in injection interval- GW recirculation overnight

• 19 L SDC-9 culture + 38 L lactate chaser (500 mL/min)

• 5x1011cells DHC

• 9 months of active treatment (gw recirc.)

• 10 months rebound (no recirc.)

Geochemical Changes During Treatment

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0

100

200

300

400

500

0 200 400 600 800

Sulfa

te (

mg/

L)

Days

0

100

200

300

400

500

0 200 400 600 800

Sulfa

te (

mg/

L)

Days

0

3

6

9

12

0 200 400 600 800

Diss

olve

d Fe

(m

g/L)

Days

0

3

6

9

12

0 200 400 600 800

Diss

olve

d Fe

(m

g/L)

Days

B11S

B11S B11D

B11DGW re

circ

Bioaugmen

t

EndGW re

circ

Bioaugmen

t

End

Dehalococcoides sp. (DHC)

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1.E+00

1.E+01

1.E+02

1.E+03

1.E+04

1.E+05

1.E+06

1.E+07

0 200 400 600 800

DHC

(cel

l/m

L)

Elapsed Time (days)

1.E+00

1.E+01

1.E+02

1.E+03

1.E+04

1.E+05

1.E+06

1.E+07

0 200 400 600 800

DHC

(cel

l/m

L)

Date

B11S B11DGW re

circ

EndGW re

circ

Bioaugmen

t

End

Dehalococcoides sp.

Electron Donor

2020

0

1000

2000

3000

0 200 400 600 800

Prop

ioni

c Ac

id (

mg/

L)

Days

0

1000

2000

3000

0 200 400 600 800

Prop

ioni

c Ac

id (

mg/

L)

Days

B11S B11DGW re

circ

Bioaugmen

t

EndGW re

circ

Bioaugmen

t

End

• Ethene primary product at end of rebound, and only trace CVOCs

• Total molar concentrations decrease ~20x during rebound

• Data suggest minimal on-going impacts from PCE sources

VOC and Ethene Results - Shallow

1.E-05

1.E-04

1.E-03

1.E-02

1.E-01

1.E+00

1.E+01

0 200 400 600 800

Conc

entr

atio

n (m

M)

Days

PCE

TCE

DCE

VC

Ethene

GW recir

c

End

Bioaugmen

t

VOC and Ethene Results - Deep

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1.E-05

1.E-04

1.E-03

1.E-02

1.E-01

1.E+00

0 200 400 600 800

Conc

entr

atio

n (m

M)

Days

PCE

TCE

DCE

VC

Ethene

• Ethene primary product at end of rebound, and only trace CVOCs

• Total molar concentrations decrease ~3x during rebound

• Data suggest on-going reducing conditions are masking VOC rebound, and DNAPL source is still present

GW recir

c

Bioaugmen

t

End

Chloride Generation

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-50

0

50

100

150

200

0 100 200 300 400 500Gen

erat

ed C

hlor

ide

(mg/

L)

Days

Shallow

Deep

Bioaugmen

t

End

DNAPL mass removal based on chloride generation

Impact of DNAPL Architecture n Treatment

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0.001

0.010

0.100

1.000

0 10 20 30

Rela

tive

Conc

entr

atio

n (C

/C0)

Time Elapsed (days)

24DMP

Bromide

0.001

0.010

0.100

1.000

0 10 20 30

Rela

tive

Conc

entr

atio

n (C

/C0)

Time Elapsed (days)

24DMP

Bromide

B11S B11D

~100% DNAPL removal

Large molar decrease post treatment

Only 45% DNAPL removal

Limited molar decrease post treatment

DNAPL Architecture Matters!(a tool to manage treatment)

Summary – DNAPL Architecture, Dissolution, and Treatment

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● DNAPL in fractures more problematic than in unconsolidated media

● ISCO may be ineffective for relatively high levels of residual DNAPL

● DNAPL can be identified and quantified in fractured rock

● DNAPL in low transmissivity fractures can sustain plumes (not just matrix back diffusion)

● DNAPL architecture and flow field can determine the efficacy of DNAPL source treatment

● Bioaugmentation can be effective for treating DNAPL sources and reducing mass discharge