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 The DNAPL challenge • 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 Complicating Factors in Bedrock • 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 2

Investigating DNAPL within a Single Fracture Plane (SERDP Project ER-1554) Influent manifold connected to HPLC pump. Typical flow Construction of Discrete Fracture Systems of 0.1 mL/min. Effluent collection 29 cm x 29cm x 5cm 3

Key Findings – DNAPL Architecture Rock Residual Interfacial Area Saturation (cm 2 /cm 3 ) (cm 3 /cm 3 ) Area:PCE ratio ~ 3-times Colorado 1 0.24 21 less than in sands Colorado 2 0.21 48 Arizona 1 0.39 56 Arizona 2 0.43 20 0.0024 Intrinsic Mass Transfer Coefficient (cm/min) 0.0018 Mass transfer coefficient A1 C1 0.0012 ~ 10-times less than in sands A2 C2 0.0006 0.0000 0 0.01 0.02 0.03 0.04 0.05 0.06 Re DNAPL in Fractured Rock Is Difficult to Remove 4 Compared to Unconsolidated Materials

ISCO for TCE DNAPL in a Rock Fracture (SERDP Project ER-1554) ~ 4% of residual DNAPL removed using activated persulfate 5

Diminished Treatment due to Blockage of DNAPL-Water Interfaces 1.2 Prior to Persulfate Oxidation 1.0 0.8 Retardation (sorption) of the SDBS C/C 0 interfacial tracer SDBS 0.6 Bromide 0.4 0.2 0.0 0 100 200 300 400 500 600 Total Minutes No measurable retardation 1.2 Post Persulfate Oxidation 1 0.8 SDBS C/Co - Rate of PCE removal had decreased by approximately 7-fold 0.6 Br 0.4 - Precipitates likely forming at DNAPL-water interfaces 0.2 0 0 200 400 600 800 1000 1200 6 Total Minutes

Illustrative Field Example – Key Insights Demonstration Location - Edwards AFB Site 37 Characteristics (ESTCP 201210) 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 Ø 7

Si Site Ch Characterist stics ~ 100 mL/min recirculation flow 8

Initial Source Investigation B06 B11 B07 ft bgs 60 • Borehole geophysics 65 19 • Rock core analysis 70 • Discrete interval 75 groundwater sampling & PCE (mg/L) Low T drawdown testing 4.1 80 5.6 18 • Short term pump tests 85 • Push-pull tracer tests Pu 25 21 90 ~13 9

Two Phases of Testing Using the Recirculation System • Partitioning Tracer Test (PTT) to assess flow field and DNAPL architecture • Bioaugmentation 10

Partitioning Tracer Testing B11 B07 B06 ft bgs Annable et al., JEE, 1998 60 65 70 75 Low T 80 85 Pu 90 ~13 11

PTT Limitations • 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 12

Partitioning Tracer Test Tracer injection 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 - No impacts at extraction wells - Primary response at B11(S,D) 13

Tracer Results – Deep Zone Bromide mass eluting through each zone Initial Peak proportional to transmissivity (low T fracture) 0.04 0.3 24DMP Relative Concentration (C/C 0 ) 24DMP • 1% of flow Relative Concentration 0.03 Bromide • 0.7% DNAPL 0.02 Bromide 0.2 0.01 (C/C 0 ) Middle Peak 0.00 0.0 0.5 1.0 1.5 2.0 2.5 0.1 • 9% of flow Time Elapsed (days) • No DNAPL 0.0 0 10 20 30 Late Peak Time Elapsed (days) • 40% of flow Mass transfer controlled tailing • 0.04% DNAPL 14

What Else Did We Learn from the PTT? 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 15

PCE Distribution Rock Matrix vs Fractures 10 Distance Inward from Fracture 8 Based on PTT DNAPL estimate 6 76 ft bgs (cm) 4 98 ft bgs 2 0 0 50 100 150 200 PCE Concentration ( µ g/kg) 149 g PCE in rock matrix 2,400 g PCE as DNAPL in fractures PCE concentration profile suggests back-diffusion not occurring 16 So treating to remove DNAPL might make sense

Bioaugmentation (August 29, 2014) • 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) • 5x10 11 cells DHC • 9 months of active treatment (gw recirc.) • 10 months rebound (no recirc.) 17

Geochemical Changes During Treatment Bioaugment Bioaugment c c r i r c i c e End e r End r W W G G 500 500 B11S B11D 400 400 Sulfate (mg/L) Sulfate (mg/L) 300 300 200 200 100 100 0 0 0 200 400 600 800 0 200 400 600 800 Days Days 12 12 B11S B11D Dissolved Fe (mg/L) Dissolved Fe (mg/L) 9 9 6 6 3 3 0 0 0 200 400 600 800 0 200 400 600 800 Days Days 18

Dehalococcoides sp. (DHC) Dehalococcoides sp. Bioaugment c c r i r c i c e e r End r End W W G G 1.E+07 1.E+07 B11S B11D 1.E+06 1.E+06 DHC (cell/mL) 1.E+05 1.E+05 DHC (cell/mL) 1.E+04 1.E+04 1.E+03 1.E+03 1.E+02 1.E+02 1.E+01 1.E+01 1.E+00 1.E+00 0 200 400 600 800 0 200 400 600 800 Elapsed Time (days) Date 19

Electron Donor Bioaugment Bioaugment c c r r i i c c e e r r End End W W G G 3000 B11D 3000 B11S Propionic Acid (mg/L) Propionic Acid (mg/L) 2000 2000 1000 1000 0 0 0 200 400 600 800 0 200 400 600 800 Days Days 20 20

VOC and Ethene Results - Shallow Bioaugment c r i c e End r W 1.E+01 G PCE Concentration (mM) 1.E+00 Ethene primary product at end of • TCE rebound, and only trace CVOCs 1.E-01 DCE 1.E-02 VC Total molar concentrations decrease • 1.E-03 ~ 20x during rebound Ethene 1.E-04 Data suggest minimal on-going • 1.E-05 impacts from PCE sources 0 200 400 600 800 Days

VOC and Ethene Results - Deep Bioaugment c r i c e r End W 1.E+00 G PCE Concentration (mM) 1.E-01 Ethene primary product at end of • TCE rebound, and only trace CVOCs 1.E-02 DCE Total molar concentrations decrease • VC 1.E-03 ~ 3x during rebound Ethene 1.E-04 Data suggest on-going reducing • 1.E-05 conditions are masking VOC rebound, 0 200 400 600 800 and DNAPL source is still present Days 22

Chloride Generation Bioaugment End 200 Generated Chloride (mg/L) 150 Shallow 100 Deep 50 0 -50 0 100 200 300 400 500 Days DNAPL mass removal based on chloride generation 23

Impact of DNAPL Architecture n Treatment 1.000 1.000 Relative Concentration B11S B11D 24DMP 24DMP Relative Concentration 0.100 Bromide 0.100 Bromide (C/C 0 ) (C/C 0 ) 0.010 0.010 0.001 0.001 0 10 20 30 0 10 20 30 Time Elapsed (days) Time Elapsed (days) ~ 100% DNAPL removal Only 45% DNAPL removal Large molar decrease post treatment Limited molar decrease post treatment DNAPL Architecture Matters! (a tool to manage treatment) 24

Summary – DNAPL Architecture, Dissolution, and Treatment ● 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 25