From diagnosis to real-time monitoring

with geophysical techniques: Case studies and on-going questions at BRGM for pollution

detection and remediation

Jean-Christophe GOURRY

Geophysical parameters

> Electrical Resistivity • Conduction of electric current in soils

• Mainly due to ionic species in pore water

> Electrical chargeability • Capacitive effect of soils

• Polarization effects

Coal tar – cokery plant

primary source and plume

0 1000 m

Regional

Water flow

Monitoring wells

N

Drinking water well

3 km

Former coal refinery Plant Coal waste heap

Test Site

Preliminary geophysical works: 2006

4 ERT profiles (1 km long)

A

B

0 50 100 150 200 250 300 350 400 450 500 550 600 650 700 750 800 850 900 950

-80

-60

-40

-20

0

water flow

Water tableBackfill silt

Chalk 1

Chalk 2

NS

E-W ProfilePzW PzN Pz1

Marl

Tar pond

43 m

A B

0 50 100 150 200 250 300 350 400 450 500 550 600 650 700 750 800 850 900 950

-80

-60

-40

-20

0

water flow (?)

Water table

PzW PzC

Tar pond

Backfill silt

Chalk 1

Marl

EW

Chalk 2Plume

N-S ProfilePzS

43 m

C D

D

C

Resistivity (ohm.m)

0.6

0.8

1 1.2

1.4

1.6

1.8

2 2.24 6.3 10 16 25 40 63 100 160

Pollution is conductive

3D interpolation of the 12 ERT profiles

Map at 20-30 m depth

3D ERT under the allotment

Map at 20-30 m depth

Contaminant

plume migration

Contamination

through fractures ?

30 Ohm.m

100 m

Oil spill in Genoa harbour

OhmMapper

Transmitter

Receiver

5m

5m

5m

Electrostatic injection and reception

0 à 20 cm

crude oil

2 m investigation depth

Gravels

Gravels

Brakich water

OhmMapper results

1120 1140 1160 1180 1200 1220 1240 1260 1280 1300 1320 1340 1360 1380 1400 1420 1440 1460 1480 1500

320

340

360

380

400

420

440

460

480

500

520

SIGEMI3 4

5 6

7

10

13

12

17

18

8

9

1

IPLOM

CHIMICO

LABORATORIO

AREA POMPE

INGRESSO

PRODOTTI FINITI

SERBATOIO

DI CONTROLLO

CENTRALE

AREA COMPRESSORI E POMPE

VASCA

SLOP

SPOGLIATOI

INGRESSO

EX AREA AGIP

SMW2

SMW8

SMW7

SMW3

SMW1

SMW6

SMW4SMW5

NMW3

NMW13

NMW4

NMW2

NMW1

NMW6

NMW5

NMW7

NMW14 NMW15

P1

P5

P4

P3

P2

P7

P6

11.522.533.544.555.566.577.588.599.51010.51111.51212.51313.51414.515

Resistivity (Ohm.m)

Bridge

> 20 cm oil over brakish water level (1 m deep)

Pollution

Pollution is resistive

Oxysol : In situ chemical

Oxidation of PAH (coal

refinery wastes)

Experiment description

> Lysimeter • Platform at Homecourt (GISFI)

• Cylinder of 2 m3 (Height = 2m ; Diameter : 1.12 m)

• Filled with tar-contaminated soils from a former cokery plant

• USEPA16 PAH : ~ 1500 mg/kg

• Organic matter : ~ 120 g/kg

16 Non polarizable

potential electrode

16 Metallic current electrode

0.45 m

0.65 m

0.90 m

1.05 m

1.20 m

1.35 m

1.50 m

0.75 m

Resistivimeter

PC

Monitoring Equipments and Fenton’s reagent H2O2 FeSO4

Time Day 5 Day 2 Day 3 Day 4 Day 1

3D Resistivity Tomography / 30 minutes

Injection periods

1.12 m

2 m3 tar contaminated soils

(1500 mg/kg PAH16)

Oxidation

Resistivity variations : (Rho(t) – Rho (t0))/Rho(t0)

Relative variations (%)

Top

-0.5 m

-1 m

-1.5 m

Start Injection #1

0

h

8

h

Stop Injection #1 Start Injection #2

20h

-2 m

Results : variation of resistivity and chargeability

0.45 m

0.90 m

1.35 m

FeSO4 + H2O2

Level 2

- resistivity decrease 100%

- Norm. Charg increase 50%

Level 1

- resistivity decrease 200%

- Norm. Charg increase 200%

No PAH degradation

[PAH] / 4

Oxidation reactions are characterized by

Normalized Chargeability increase

Chlorinated solvent

pumping tests

Chlorinated Solvents Pumping monitoring with electrical

Resistivity Tomography

18

> Site pilote :

• Bassin

• 4 casiers étanchéifiés

• Piézomètres et pompage

> Géophysique :

• Mesures de résistivité

électriques

• Domaine temporel et spatial

• Traverse tout le bassin

• 96 électrodes

Concrete Barriers

(10 m deep)

Pumping wells

Clay layer

Time zero (reference) Electrical Resistivity Tomography

20

Résistivité (Ω.m)

> Chlorinated solvents (DNAPL) = Resistive

pollutant

Injection wells Pumping well

Distance (m)

Altitu

de

(m

)

Distance (m)

Altitu

de

(m

)

012345678

176.5

177

177.5

178

178.5

179

179.5

20/07/2015 12:00 27/07/2015 12:00 03/08/2015 12:00 10/08/2015 11:00 17/08/2015 11:00 24/08/2015 11:00

pumping activity

Water/DNAPL interface (C4D)

Resistivity variation (%)

Altitu

de

(m

)

Distance (m) Distance (m)

Altitu

de

(m

)

Electrical Resistivity Tomography Monitoring

Conclusions

>Diagnosis • No direct detection of pollution with geophysics

• Resistivity contrasts are representative of pollution or

degradation by-products concentration

–Necessary to know site history

–A few boreholes and soil/water analyses to calibrate

resistivity/chargeability

>Monitoring during remediation • Resistivity and chargeability are very sensitive to

–pollution concentration variations during a pure phase Pumping

–Oxidation / reduction reactions plume during Chemical Oxidation

/ Reduction

– Biodegradation reactions due to bacteria activity

On-going works at BRGM

> Calibration of resistivity and chargeability

models at laboratory scale • Relation between resistivity or chargeability and residual

solvents during pumping stages

• Effect of temperature on resistivity and chargeability during tar

viscosity decrease by heating

• Physical modeling of chargeability during chemical oxido-

reduction process

Thanks for your attention