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 74078todd.halihan@okstate.edu

Stuart W. McDonald, P.E.Aestus, LLC2605 Dotsero CourtLoveland, CO 805381.888.Geo.Trax or(970) 278-4090swm@aestusllc.com

www.aestusllc.com