Tim Johnson, Mike Truex, Jason Greenwood, Chris Strickland, Dawn Wellman: Pacific Northwest National Laboratory

Transcription

1 3D Site Characterization and Autonomous Remedial Process Monitoring Using High Performance Electrical Resistivity and Induced Polarization Tomographic Imaging Tim Johnson, Mike Truex, Jason Greenwood, Chris Strickland, Dawn Wellman: Pacific Northwest National Laboratory Roelof Versteeg: Sky Research Fred Day-Lewis and John Lane: U.S. Geological Survey William Major: NAVFAC 1

2 Acknowledgements ESTCP Environmental Resotoration Optimized Enhanced Bioremediation Through Four- Dimensional Geophysical Monitoring and Autonomous Data Collection, Processing, and Analysis, ER Andrews AFB CH2MHILL Plateau Remediation Company 2

3 Outline Autonomous Electrical Resistivity Tomography (ERT) characterization and monitoring systms. What and how we measure How we monitor spatial and temporal changes in electrical properties (time-lapse inversion) What does it mean in terms of properties we re re interested in Examples Brandywine MD DRMO Superfund Bioremediation Monitoring Soil desiccation characterization and monitoring at the Hanford BC Cribs Concluding comments 3

4 ELECTRIC GEOPHYSICAL MONITORING COMPONENTS Server: Data QA/QC, Management Automated & on demand results Data Electrical geophysical Hydrologic Geochemical Time-lapse Inversion Time-lapse Amendment Maps 4

5 Field scale electrical geophysical measurements Measurement 1 Current Electrodes: 55,77 Potential Electrodes: 46,49 Current: 150 ma Voltage: 112 mv Surface electrodes Borehole electrodes 112 mv Current Sink 150 ma Current Source 5

6 3D characterization and monitoring flowchart Baseline Characterization Inversion Starting M 0 Reference model model M 1 ΔM 1 Time-laps se data Electrical M 2 ΔM 2 Resistivity / Induced d M 3 - = ΔM 3 Polarization Tomography... Inversion M N ΔM 4 D 1 D 2 D 3 D N 6

7 Pore-scale current conduction mechanisms Ionic Conduction is sensitive to: Pore fluid conductivity Saturation Temperature + Electric Field - Electronic Conduction is sensitive to: Mineral conductivity Temperature Interfacial Conduction is sensitive to: Interfacial electrochemistry Temperature Total Conductivity = ionic + electronic + interfacial 7

8 Brandywine MD DRMO Superfind Site Andrews AFB Site location Brandywine DRMO (green box) Brandywine - Primary groundwater contaminant is TCE - Primary soil contaminants PCB - Plume has spread from Air force property to residential property - Contamination resides in upper 30 feet, sandy gravel, aquitard at 30 ft bgs 8

9 DRMO Enhanced Bioremediation Site location Remedial Action - Amendment injections at ~1000 injection points - Injection point spacing ~ 20 ft - Dem/Val effort monitored two of the injections at edge of March/April 2008 treatment area Dem/Val study area (injections B6 & B7) Brandywine DRMO (green box) 9

10 ERT/IP Monitoring Systems Details 8 Chem sample wells 7 ERT/Chem wells - ERT wells: 15 2 feet spacing. 2 inch Sampling ports at 11,19 and 26 feet -Sampling wells: sampling ports at 11 and 19 feet. Well screen at bottom (26 feet) -45 total sampling ports -ERT data acquisition: repeat 3D survey with measurements ERT/IP Well Electrodes Sample Well Injection Well (3/10/08) Sample Ports Groundwater Flow to West ~60 ft/year 10

11 Time-lapse ERT imaging results Baseline Characterization Sodium dominated 3/18/08 6/18/08 12/17/08 Aquifer 3/23/09 6/16/09 3/18/09 Confining Unit 1/22/10 4/09/10 Biological processes effect 11 Simplified description: initially conservative tracer (first year) (signal results from changes in fluid conductivity) followed by changes in solid phase conductivity resulting from precipitation

12 Relating changes in bulk conductivity to changes in geochemistry ~3.5 m bgs ~6.0 m bgs ~8.5 m bgs Note: Dots are ERT inversion results at sample ports. Triangles are fluid conductivity measurements taken at sample ports 12 March 2008 to Jan summary: Little microbial activity Rise and fall in bulk conductivity due primarily to sodium transport and subsequent dilution.

13 Relating changes in bulk conductivity to changes in geochemistry ~3.5 m bgs ~6.0 m bgs ~8.5 m bgs Note: Dots are ERT inversion results at sample ports. Triangles are fluid conductivity measurements taken at sample ports Jan 2009 to April 2010 summary Geochemical data suggest vigorous microbial activity Fluid conductivity decreases, bulk conductivity increases suggesting increase in interfacial conductivity (iron-sulfide precipitation) 13

14 Hanford BC Cribs Desiccation Treatability Test Plan View ERT Array Historical liquid waste crib. Primary vadose zone contaminants Nitrate, Tc 99, Uranium Liquid nitrogen system Instrument panels Extraction Blower 14

15 Background ERT Characterization Section View Oblique View High electrical conductivity contaminated zones high sat. and/or ionic strength low permeability (fine) 15

16 16 4D desiccation induced changes in bulk conductivity

17 Other example applications Vadose zone infiltration monitoring 0.22 t=0 Hyporheic exchange monitoring at Hanford along the Columbia River Depth (m) 1 day 2days 4 days 1 week 2 weeks 6 weeks 9 weeks River Stage / Conductivity Correlation Paleochannel Distance (m) 17

18 Conclusions Changes in subsurface electrical conductivity obtained from ERT inversions coupled with sparse supporting data from sampling can be interpreted with high confidence in terms of spatiotemporal information on remedial processes. Capability to see in 4D Petrophysics are important Automation for long term monitoring is feasible 18