Evaluating and Treating DNAPL in Fractured Rock Charles Schaefer, - - PowerPoint PPT Presentation

Evaluating and Treating DNAPL in Fractured Rock

Charles Schaefer, Ph.D.

David Lippincott – APTIM Rachael Rezez – APTIM Graig Lavorgna - APTIM

• Dr. Michael Annable – UFL

Erin White – UFL

DNAPL Architecture, Dissolution, and Treatment

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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 not

appropriate, 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)

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Construction of Discrete Fracture Systems

Influent manifold connected to HPLC pump. Typical flow

• f 0.1 mL/min.

Effluent collection

29 cm x 29cm x 5cm

Key Findings – DNAPL Architecture

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Rock Residual Saturation (cm3/cm3) Interfacial Area (cm2/cm3) Colorado 1 0.24 21 Colorado 2 0.21 48 Arizona 1 0.39 56 Arizona 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 0.01 0.02 0.03 0.04 0.05 0.06

Intrinsic Mass Transfer Coefficient (cm/min) Re

A1 C1 A2 C2

DNAPL in Fractured Rock Is Difficult to Remove Compared to Unconsolidated Materials

ISCO for TCE DNAPL in a Rock Fracture

(SERDP Project ER-1554)

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~4% of residual DNAPL removed using activated persulfate

Diminished Treatment due to Blockage of DNAPL-Water Interfaces

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0.0 0.2 0.4 0.6 0.8 1.0 1.2 100 200 300 400 500 600 C/C0 Total Minutes SDBS Bromide 0.2 0.4 0.6 0.8 1 1.2 200 400 600 800 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 Oxidation

Retardation (sorption) of the interfacial tracer SDBS No measurable retardation

Illustrative Field Example – Key Insights

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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 transmissivity

Ø

Fracture flow

Ø

PCE at >10% solubility

Ø

No direct evidence of DNAPL

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Si Site Ch Characterist stics

~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

60 65 70 75 80 85 90

B06 B07

ft bgs

B11

Pu ~13

Low T

18 21 4.1 5.6 19 25

PCE (mg/L)

Two Phases of Testing Using the Recirculation System

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

Partitioning Tracer Testing

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Annable et al., JEE, 1998

60 65 70 75 80 85 90

B06 B07

ft bgs

B11

Pu ~13

Low T

PTT Limitations

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• 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 Peak

0.0 0.1 0.2 0.3 10 20 30

Relative Concentration (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 2.5

Relative Concentration (C/C0) 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 distribution DNAPL present in high transmissivity fractures, but also in low transmissivity zones Average fracture porosity 0.004 DNAPL mass 2.4 kg in 15 ft radius around injection well interval DNAPL persistence under ambient conditions (dissolution only) DNAPL in moderate to high T zones – 65 years DNAPL in low T zone – 194 years

PCE Distribution

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Rock Matrix vs Fractures

2 4 6 8 10 50 100 150 200

Distance Inward from Fracture (cm) 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 fractures PCE 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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100 200 300 400 500 200 400 600 800

Sulfate (mg/L) Days

100 200 300 400 500 200 400 600 800

Sulfate (mg/L) Days

3 6 9 12 200 400 600 800

Dissolved Fe (mg/L) Days

3 6 9 12 200 400 600 800

Dissolved Fe (mg/L) Days

B11S B11S B11D B11D

G W r e c i r c Bioaugment End G W r e c i r c Bioaugment 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+07 200 400 600 800

DHC (cell/mL) 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+07 200 400 600 800

DHC (cell/mL) Date

B11S B11D

G W r e c i r c End G W r e c i r c Bioaugment End

Dehalococcoides sp.

Electron Donor

20 20

1000 2000 3000 200 400 600 800

Propionic Acid (mg/L) Days

1000 2000 3000 200 400 600 800

Propionic Acid (mg/L) Days

B11S B11D

G W r e c i r c Bioaugment End G W r e c i r c Bioaugment 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+01 200 400 600 800

Concentration (mM) Days

PCE TCE DCE VC Ethene

G W r e c i r c End Bioaugment

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+00 200 400 600 800

Concentration (mM) 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

G W r e c i r c Bioaugment End

Chloride Generation

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• 50

50 100 150 200 100 200 300 400 500

Generated Chloride (mg/L) Days

Shallow Deep

Bioaugment 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 10 20 30

Relative Concentration (C/C0) Time Elapsed (days)

24DMP Bromide

0.001 0.010 0.100 1.000 10 20 30

Relative Concentration (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