1
Innovative High ResolutionElectrical Resistivity Imaging (ERI)
(Aestus’ GeoTrax Survey™)
Used to Detect Soil/Groundwater ContaminationFrom Leaking USTs and Other Sources
The 11th National Israeli NDT conference Tuesday, April 27, 2010; Tel Aviv, Israel
Presented by
Stuart W. McDonald, P.E.President, Aestus, LLC
PROBLEM
Conventional environmental site characterization techniques are and are not producing satisfactory results; Site cleanup too costly
Other historically available technology such as conventional geophysical tools (GPR, EM, Seismic, etc.) not helping enough
Need new approach/tools – look at other industries faced with similar problems (oil/gas; medical)
SOLUTION
Environmental consulting and non-traditional geophysics experts from Aestus/Oklahoma State University teamed to develop a subsurface scanning tool that works at virtually any site
This tool has changed paradigms of contamination behavior/distribution in subsurface
Yields lower project costs and faster cleanup
Topics Covered Today
PROOF THAT IT WORKS ● EXAMPLES ● COSTS
Review Case Studies
Validation by EPA’s Ada, Oklahoma laboratory
Validation by State Regulators
Validation by Environmental Consultants
Backed up by University Research and Peer Reviewed Publications
QUESTIONS & ANSWER SESSION
Topics Covered Today (continued)
Typical Site Characterization
Monitoring Well (Typ.)
Previously Unknown LNAPL
?
Monitoring Well (Typ.)
Confirmed Contact
Interpreted Contact
??Soil Core
GW LevelLNAPL
Recovery/monitoring Well (Typ.)
Previously Unknown LNAPL
Defined Contact LocationActual image from a refinery LNAPL recovery system
…and thus allows reality-based decisions
WOULD YOU HAVE SURGERY WITHOUT A CAT-SCAN/MRI/X-RAY?
Why do this with your environmentally impacted sites?
Medical X-ray MRI Sonogram
Petroleum Seismic Gravity Magnetics
Environmental Drill Probe Excavate
Sampling array at the Cape Cod Site; over 10,000 subsurface sampling ports. –USGS-
Medical X-ray MRI Sonogram
Petroleum Seismic Gravity Magnetics
Environmental Drill Probe Excavate
And you thoughtmedical surgery
is expensive!
Based on
DC resistivity techniques (>100 yrs old) Computing/electronics power (<10 yrs old)
Instead of 10’s of data, collect thousands (high data density)
Analogous to “Geological Digital Photography” Provides map of electrical properties of the
subsurface
What is Electrical Resistivity Imaging (ERI)?
Standard Electrical ResistivityTechniques
ProprietaryOSU/Aestus
DataAcquisitionAlgorithms
AestusProprietary
SupplementalField
Equipment
High Resolution Subsurface Image
That is “Drillable”
ProprietaryOSU/Aestus
DataReduction/Processing
56 Electrode Stakes (3/8-inch diameter) Hammered Into GroundGeophysical Cables Attached to Electrode StakesData Collection Starts (~1-2 Hours; Site Dependent)
How ERI Works – “Setting Up The Camera”
“Take Only Pictures…Leave Only Footprints”!
One Data Point or “Pixel”
Four Electrodes Yield One Measurement Data Point (“pixel”)
How ERI Works – “Taking the Picture”
How ERI Works – “Focusing the Camera”
(1.5 m Survey) 271 feet long 54 feet deep
(2.5 m Survey) 451 feet long 92 feet deep (* Optimal Choice)
(3.0 m Survey) 541 feet long 108 feet deep
(2.0 m Survey) 361 feet long 72 feet deep
Target
Imaging
Depth
How ERI Works – “Developing the Film”
Iterative Measurements Yield Matrix of Data Points or “Pixels”D
ep
th (
fee
t)
Proprietary Software Generates Subsurface 2-D Image from Data Set
A “Kilo-pixel” Digital Camera Taking Electrical Picture of Subsurface
Suspected
LNAPL “Blob”
Below LUST
How ERI Works – Viewing Multiple “Pictures” Together3-D Perspective View - GeoTrax SurveysTM
(From Above and Looking North at All On-Site Surveys)LEGEND:
Current UST Tank Basin
Former UST Basins
ERI Output – 2-D Data “Fences” in 3-D Space
NAPL “Blobs”NAPL “Blobs”
Below LUST’sBelow LUST’s
Existing Remediation Wells
How ERI Works – Viewing the Data in 3-D & 4-D
Pre-Remediation36 ohm-m ~ 20,000 mg/kg TPH
Pre-Remediation46 ohm-m ~ Free Product (LNAPL)
7 mos. into Remediation46 ohm-m ~ Free Product (LNAPL)
2-D Data Fences
How ERI Works – Viewing the Data using 3-D Model
3-D ERI Model Output from GeoTrax SurveyTM Data
NAPL “Blobs”
Shown in 3-D
Technological Progression
• Data acquisition now 100x faster than 1990
• Data processing now 350x faster than 1990
• Images were not “drillable”
– OSU/Aestus created dramatically improved images– Images can “see” resistive subsurface targets others
can’t
X Standard ERI methods barely able to detect “blob” with the highest concentration of LNAPL detected on this site
X Second LNAPL “blob” does not show up using standard ERI
OSU’s/Aestus’ ERI Methods detect both LNAPL “blobs” present
Image shows concentrations in a semi-quantitative manner
Images are “Drillable”
* Confirmation Drilling Data Collected by EPA;
Images from Golden, OK Site Case Study
45 mg/kg TPHLNAPL21,283 mg/kg TPH
LNAPL21,283 mg/kg TPH 45 mg/kg TPH
“Simple” LNAPL plume:• Undergone pump-and-treat and a surfactant flush• At least 92 wells on the site• Is the site “clean” now?
after Halihan et al, 2005
.
268
SB-2
2
5,8344,321
2
14,732 21,283
Total Petroleum Hydrocarbons (TPH in mg/kg) vs. Depth
SB-1
SB-1
SB-2
50 ft wide x25 ft depth
22
SB-4
2.5
SB-3
SB-4
Total Petroleum Hydrocarbons (TPH in mg/kg) vs. Depth
SB-3
0.4
SB-5
45
SB-6
SB-5
SB-6
Total Petroleum Hydrocarbons (TPH in mg/kg) vs. Depth
Separate “Blobs”
(met
ers)
(meters)Distance (ft)0 180
Dep
th (
ft)
30
0
180Distance (ft)0
Dep
th (
ft)
30
0
Data Density Comparison – NAPL Site
Sampling data indicate that these monitoring wells are clean….
Aestus’ GeoTrax Survey™ shows that monitoring welldata was not representative of site conditions
Actual Research Site - Anomaly soil sampling data provided by EPA Ada, OK Laboratory
LNAPL21,283 mg/Kg LNAPL
45 mg/Kg
To approach the data density of an Aestus GeoTrax Survey™,
approximately 35 monitoring wells/soil borings would be required
every ~5 feet along a 185 ft transect
At ~US$3,500 per monitoring well, cost would be ~US$122,500 and takes weeks
At ~US$2,500 per GeoTrax Survey™, cost would be US$2,500 and take only 2-3 hours
* Above budgetary costs do not include mobilization/demobilization; survey costs vary depending on site constraints
Distance (ft)0 180
Dep
th (
ft)
30
0
This is a “magic bullet”
2
5,8344,321
2
14,732 21,283
SB-2
This is not
Complex sites are still complex, you just have a better tool to obtain sufficient data.
Every site is different- there are infinitesimal combinations of lithology, pore fluids, pore structure, contamination, and previous remediation attempts.
We don’t have a “magic” resistivity scale that categorizes every site.
Images MUST be calibrated in order to provide the best interpretation.
Other Potential Applications in Israel
o Sinkhole Detectiono Clandestine Tunnel Detection
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For Finding Tunnels/VoidsIn Subsurface
Computer Modeling Predicts:
Success Using GeoTrax Survey™ Failure Using Standard ERI
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(GeoTrax Survey™)
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(GeoTrax Survey™)
(Not enough resolution to detect small tunnels;
confirmed by Israel MOD testing)
(Data indicates probable success; untested to date)
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TunnelTrax Survey™(Conceptual Approach)
Scale-Up to Provide Continuous Subsurface Scanning
at Country Border
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Located Caves in Anhydrite Gypsum
Located Coal Mines Below Former Gas Station
X Suspected LNAPL
X “Blobs”
X SuspectedX Locations
of Flooded Coal Mines
• Sink hole detection
• Homeland Security – Terrorist Tunnels; Illegal Immigration Tunnels
• Brownfields Site Characterization for Property/Liability Transfer
• Point of Compliance Site Boundary Monitoring (Dedicated System)
• Groundwater/Surface Water Interaction
• Optimize Locations for Water Wells
• Salt Water Intrusion into Drinking Water Wells
• Geotechnical Engineering
• Landfill Leakage
• Others
Stop Drilling Blind!
Thank You
AdditionalQuestions?
Dr. Todd HalihanOklahoma State UniversitySchool of Geology105 Noble Research CenterStillwater, OK [email protected]
Stuart W. McDonald, P.E.Aestus, LLC2605 Dotsero CourtLoveland, CO 805381.888.Geo.Trax or(970) [email protected]
www.aestusllc.com