Specifications for survey methodology with combined techniquesinfoterre.brgm.fr/rapports/RP-51731-FR.pdf · Specifications for survey methodology with combined techniques BRGM/RP-51731-FR

0

Specifications for survey methodologywith combined techniques

Deliverable D4.1 realized in the framework of WP4 of the HYGIEA CEE project

june 2002BRGM/RP-51731-FR

Specifications for survey methodologywith combined techniques

Deliverable D4.1 realized in the framework of WP4 of the HYGIEA CEE project

G. Grandjean

june 2002BRGM/RP-51731-FR

Specifications for survey methodology with combined techniques

2 BRGM/RP-51731-FR

Keywords: Brownfields, Geophysics, Bibliography.

In bibliography, this report should be cited as follows:

Grandjean G., (2002) – Specifications for survey methodology with combinedtechniques. Deliverable D4.1 realized in the framework of WP4 of the HYGEIACEE project. BRGM/RP-51731-FR, 89 p., 3 tables, 1 app.

© BRGM, 2002, all rights reserved. No part of this publication may be reproduced, stored in a retrieval system, ortransmitted in any means, electronic, mechanical, photocopying, recording or otherwise, without the priorpermission of BRGM.


BRGM/RP-51731-FR 3

Synthesis

he work presented here has been realized in the framework of workpackage 4 ofthe HYGEIA project. We present the state of the art concerning geophysical

techniques for brownfields characterisation from a bibliographic review.

After analysis, the results are presented and discussed in order to identify a technicalsolution that will constitute the starting point of the project.

The methodology includes: i) GPR for characterizing polluted areas in a fine, fast and3D manner; ii) the resistivity methods, use both in [x,z] electrical tomography and [x,y]electromagnetic maps of apparent resistivity to roughly detect buried metallic objects,polluted areas and localize the water table in the geological context; iii) seismicmethods to characterize wastes geometry (basement, lateral extensions), thecomposition of filling material and the geological contexts.

T


4 BRGM/RP-51731-FR

Contents

1. Introduction.................................................................................................................5

2. Analyzed documents ...................................................................................................7

2.1. The sources used ........................................................................................................7

2.2. Results........................................................................................................................7

3. Exploitation of the scientific review ..........................................................................9

3.1. Relation between site typologies and geophysical methods ......................................9

3.2. Geophysical Method limitations ..............................................................................10

3.3. Technical proposition...............................................................................................10

4. Conclusion .................................................................................................................13

List of tables

Table 1 - Inventory of the different site typologies described in the analyseddocuments..........................................................................................................7

Table 2 - Inventory of the different geophysical methods carried out in theanalyzed documents...........................................................................................8

Table 3 - Comparison between geophysical methods and main groups ofproblematic encountered in the studied site typologies.....................................9

Appendix

Appendix 1 - List of documents analyzed. ....................................................................15


BRGM/RP-51731-FR 5

1. Introduction

he main objective of the HYGEIA project is to propose new geophysicaltechnologies dedicated to help improve rehabilitation of brownfields, contaminated

sites and waste disposal. The project is designed to address this problem by thedevelopment of a combination of geophysical techniques (seismics, GPR, resistivity)capable of mapping heterogeneities in the 0-50 m space without disturbing the mediumby means of highly cost-effective and rapid acquisition, processing andinversion/interpretation of data.

The specific objective of the workpackage 4 is to define a methodological design and toidentify the specifications of geophysical acquisition and processing systems. This workis the following of workpackage 3, describing site typologies and requirements fromend users about costs and time constraints.

We present here the first part of workpackage 4 constituting the deliverable D4.1 of theproject. This task aims to specify, from a bibliographic review, a survey methodologycombining several geophysical techniques. The most important point of this workconsisted in reviewing a sufficient large number of scientific publications, reports andstudies, in order to establish the state of the art of geophysical methodologies applied tocontaminated sites and other brownfields. But to restrict the quantity of references onthe subject to the most representative ones, we constrained our work with specificationsgiven by the main objectives of HYGEIA, and by the site typologies given by end usersin the deliverable D3.1. This constituted the first part of this work.

The section 2 gives a summary of all analyzed documents.

Information related to the site description, the methodology used, the efficiency of themethod, etc. was afterwards extracted and analyzed. In order to have the same criterionsduring the review, we proposed to use a form that reviewers could fill for each of theanalyzed documents. All forms can be found in the appendix of this report.

Finally, the documents analyzes was organized according to the following sequence:

1. the relation between site typologies and geophysical methods was analyzed to knowmore about the efficiency of these techniques;

2. geophysical method limitations indicated in the references was also extracted;

3. the technical proposition was then derived.

Each of these steps is detailed in section 3.

T


6 BRGM/RP-51731-FR


BRGM/RP-51731-FR 7

2. Analyzed documents

2.1. THE SOURCES USED

The documents analyzed here comes from different sources:

- reports realized for commercial or public purposes by partners of the HYGEIAconsortium. POLIMI and BRGM were concerned by this activity and produced a totalof 10 reviews;

- reports from governmental institutions realized in the framework of EuropeanResearch Programs or the U.S. Environmental Protection Agency, etc. BRGM led thispart of the review:. EPA action on field analytical and site characterization technologies,. RESCOPP CEE project on the detection of hydrocarbon pollution,. AFNOR (French Normalization Agency) recommendations for geophysical polluted

site characterization;

- scientific publications from conference proceedings and geophysical journals. EOSTand UNICRE analyzed a total of 20 papers.

2.2. RESULTS

We present here a synthesis of site typologies and geophysical methodologies that arepresented in the analysed studies (Tables 1 and 2).

Site typologies Ocurence PercentageWaste disposal 9 30Contaminated area 8 27Gas/Petrochemical station 7 24Sand pit 3 10Industrial brownfields 1 3Coking plant 1 3Nuclear waste 1 3

Table 1 - Inventory of the different site typologies described in the analyseddocuments.


8 BRGM/RP-51731-FR

Geophysical methods Occurrence PercentageGPR 16 40Resistivity tomography 12 30Seismics 6 14Electromagnetics 5 12Magnetics 2 4

Table 2 - Inventory of the different geophysical methods carried out in the analyzeddocuments.

Referring to Table 1, wastes disposal are the most studied sites with contaminated areasand gas/petrochemical stations. Consequently, the problematics related to these sites canbe restricted to two families:

- characterization of waste disposal in order to estimate its geometry and thecharacteristics of the different filling material;

- detection of hydrocarbon pollutions in contaminated areas in order to estimate theextension and the level of saturation of plums.

Among the different geophysical methods, Table 2 indicates that GPR and resistivitymethods are the most used, but seismics and electromagnetics can also be proposed.

A more detailed study we will be presented in the next section concerned with thetechnical exploitation of this review.


BRGM/RP-51731-FR 9

3. Exploitation of the scientific review

In this section we first analyze the relation between the problematic related to a sitetypology and the geophysical method used. Then, the limitations of these techniques arepresented prior to describe the technical proposition. This last one should describe thefirst prototype that HYGEIA is supposed to test during the first field works.

3.1. RELATION BETWEEN SITE TYPOLOGIES AND GEOPHYSICALMETHODS

The relation between site typologies and geophysical methods is summarized in thetable 3. For more convenience, we tried to merge the different problems related to eachsite into more general ones, as described here below:

- buried object detection (buried object): concerns the detection of pipes, tanks, or otherburied constructions;

- waste structure and geometry (waste): includes basement detection and mapping,waste extensions determination, characterization of different filling materials;

- pollution detection (pollution): concerns hydrocarbons (DNAPL, LNAPL), but alsosaline contaminations;

- water table detection (water): for studying interactions between sub-surface pollutedareas and ground water.

Buriedobject Waste Pollution Water Total

GPR 2 (5 %) 3 (10 %) 11 (25 %) 16 (40 %)Resistivity 2 (5 %) 8 (20 %) 2 (5 %) 12 (40 %)Seismics 6 (15 %) 6 (15 %)Electromagnetics 2 (5 %) 3 (10 %) 5 (15 %)Magnetics 2 (5 %) 2 (5 %)Total 4 (10 %) 13 (30 %) 22 (55 %) 2 (5 %) 41 (100 %)

Table 3 - Comparison between geophysical methods and main groups of problematicencountered in the studied site typologies.

Table 3 indicates, for both methods and problematics, the context for which thescientific community has been recently involved to work on. The most frequentlygeophysical tools are GPR, resistivity and seismic method when applied respectively onpollution detection, and waste structure or geometry characterization.


10 BRGM/RP-51731-FR

3.2. GEOPHYSICAL METHOD LIMITATIONS

The limitation of selected geophysical methods is also an important criterion to take intoaccount prior to select what kind of technique has to be used to resolve a particularproblem. The factors that limit efficiency of the different methods are:

- GPR: the main limitations come from i) the weak radar wave penetration induced byground high conductivity, i.e., clays or shales, and ii) the surface conditions, i.e., highsurface roughness, that decrease the coupling of antenna;

- resistivity methods: they can be perturbed by the presence of conductive buriedobjects, i.e., pipes, that deform locally the electric field. By the way, these methodssuffer generally of a lack of resolution compared to wave propagation methods;

- seismics: most of the time the signal to noise ratio depends on the level of thevibrations caused by human activity. Ground properties generating wave attenuation,especially for high frequencies, can also be invoked;

- electromagnetics: limitation is caused by the presence of electromagnetic noise due toindustrial activity;

- magnetics: particularly devoted to metallic object detection, the efficiency of thismethod decrease when the object depth increase.

With a more general view, the efficiency of all geophysical methods depends on thesurface conditions, soil heterogeneity and on the contrast of petrophysical propertiesthat exists between the host material and the targets.

3.3. TECHNICAL PROPOSITION

The technical proposition that we are going to describe here is a set of geophysicaltechniques that we could applied to brownfields characterization. According to the endusers remarks (WP3), we need to respect some economic constraints:

1. mobility and ease to use for competitive costs with respect to current techniques;

2. a high resolution/penetration;

3. applicable to a wide range of use.

These remarks lead us to orient the methodology to :

1. a restricted multi-method geophysical approach, to be sure that a maximum ofproblematics will be considered without increasing the costs. Three methods will beconsidered;

2. techniques offering a large potentiality for improving signal to noise ratio,penetration, resolution and acquisition times;

3. methods that can be integrated into a 2D/3D interpretation tool for a faster and moreefficient diagnosis.


BRGM/RP-51731-FR 11

Finally, the proposed methodology is based on the following basic techniques:

1. GPR: use to characterize polluted areas in a fine, fast and 3D manner;

2. resistivity methods: use both in [x,z] electrical tomography and [x,y] electromagneticmaps of apparent resistivity to roughly detect buried metallic objects, polluted areasand localize the water table in the geological context;

3. seismics: use to characterize wastes geometry (basement, lateral extensions), thecomposition of filling material and geological contexts.


12 BRGM/RP-51731-FR


BRGM/RP-51731-FR 13

4. Conclusion

he main objective of the HYGEIA project is to propose new geophysicaltechnologies dedicated to help improve rehabilitation of brownfields, contaminated

sites and waste disposal. The specific objective of the workpackage 4 is to define, froma bibliographic review, a methodological design and to identify the specifications ofgeophysical acquisition and processing systems.

From a representative list of documents, information related to the site description, themethodology used, etc. was extracted and analyzed. The relation between sitetypologies and geophysical methods was also studied to know more about theapplicability of these techniques. Geophysical Method limitations indicated in thereferences was also considered in order to derive the following technical proposition:

1. GPR: use to characterize polluted areas in a fine, fast and 3D manner;

2. resistivity methods: use both in [x,z] electrical tomography and [x,y] electromagneticmaps of apparent resistivity to roughly detect buried metallic objects, polluted areasand localize the water table in the geological context;

3. seismics: use to characterize wastes geometry (basement, lateral extensions), thecomposition of filling material and the geological contexts.

Although these techniques can be considered as the most appropriate to tackle theproblem of polluted soils characterization, we must keep in mind that physicalphenomena are always complex and merit to be studied using numerical simulations orlaboratory measurements.

T


14 BRGM/RP-51731-FR


BRGM/RP-51731-FR 15

Appendix 1 - List of documents analyzed.

APPENDIX 1

List of documents analyzed

This appendix gives the list of the documents analyzed in this report. The first letter ofthe review form name indicate the origin of the source (R for report, A for Article). Thefollowing word indicates the name of the partner who examines the document, and thelast number is an incremental index.


16 BRGM/RP-51731-FR


BRGM/RP-51731-FR 17

Review form R-POLIMI-001

References

Bibliographic source: Georadar 2D and 3D to map the sub-surface utilities in a gasstation for safe drilling of contaminant inspection boreholes.

Financial support: Private (Tamoil oilfield).

End users: Environmental Engineering society.

Problematic

Main objectives: Mapping the sub-surface utility in a gas station for safe drilling ofcontaminant inspection boreholes.

Scientific and economic constraints: GPR is the most appropriate geophysical methodfor the type of problem.

Description of the methodology : We executed a number of GPR 2D surveys to map theutilities of the gas station; it is on a public area crossed by a street and in the subsoilthere are all types of sub-surface utilities: aqueduct, telecom pipes, optic cables, gaspipe, sewage, tanks and utilities of the gas station. ARPA (Regional Agency for theProtection of the Environment) asked to Tamoil oilfield to drill the area in some givenpoints to explore the soil for suspected contamination (an oil contamination eventoccurred some months before during the tank filling operation).

The Environmental Engineering society asked for preliminary GPR investigations toprevent accidents during the drilling operations because the available maps of theunderground utilities were not sufficiently updated and reliable. The reconstructed mapof the utilities obtained by the radar 2D profiles indicated that the gas station subsoil isfull of pipes, including also some unexpected electrical power lines and old dismissedutilities. As a result, drilling the area in the points indicated by ARPA was really veryrisky although the GPR 2D profiles were quite close to each other (50 cm). For a moreaccurate reconstruction of the complex distribution of utilities in the proximity of themost critical drilling points, we decided to perform GPR 3D surveys. The 3Dacquisitions were executed on a regular grid (with an interdistance between parallellines of 9 cm) and the Georadar data were pre-processed and then migrated with a 3Dalgorithm. On the basis of the 3D volume reconstructions, we were able to define thesafest areas close to the points proposed by ARPA. The size of these clean areas wasvery small (no larger than 1 square meter) because of the high density of the sub-surfaceutilities.

The 2D methodology is standard. The 3D investigations were performed by executingaccurate 3D acquisitions and the data were processed with a non commercial softwaredeveloped by Polimi.


18 BRGM/RP-51731-FR

Technical work

Site description: Gravel soil, pollution by oil for gas station.

Geophysical technique used: Shielded Antenna (500 MHz), GPR processing softwaredeveloped by POLIMI.

Validation protocol: No accidents occurred, i.e., all the drilling operations (for a totalnumber of 11 boreholes) were performed successfully on the points selected after the3D radar inspections.

Results

List of technical results: 3D reconstructions are absolutely needed to solve situationswith a so dense population of subsurface utilities; for a successful reconstruction of 3Dfocused images by migration algorithms the acquisitions must be executed with a veryaccurate geometry.

Synthetic illustration with caption: See below.

List of technical difficulties: The GPR surveys were executed on an area where thevehicle traffic was not restricted; the experience indicates the need of easy and low-costsystems to monitor the exact geometry of the 3D surveys.

Appreciation:


BRGM/RP-51731-FR 19

Front view and top view of the focused 3D radar data at one drilling point of the gasstation area. Two pipes are clearly detected at a depth of about 120 cm.


20 BRGM/RP-51731-FR

Review form R-USEPA-001

References

Bibliographic source: Field Analytical and Site Characterization Technologies,Summary of Applications, EPA-542-R-97-011, November 1997.

Financial support: U.S. Environmental Protection Agency, Office of Solid Waste andEmergency Response.

End users: U.S. authority.

Problematics

Main objectives: They are to provide information about experiences in the use of fieldanalytical and site characterization technologies at contaminated sites drawn from 204applications of the technologies listed below. For each technology, information ispresented on the reported uses of the technology; including the types of pollutants andmedia for which the technology was used; reported advantages and limitations of thetechnology; and cost data for the technology, when available.

Scientific and economic constraints: Systematic tests.

Geophysical technique used: Tests included geophysical, chemical, and radionucleidetechnologies. Only geophysical (electrical resistivity, electromagnetic sounding, GPRand seismic profiling) ones are analyzed in this review.

Technical work

Site description: EPA has collected information about the uses of field analytical andsite characterization technologies at 204 sites and has summarized the experiences ofthose involved in applying the technologies at contaminated sites.

Description of the methodology: Different geophysical methods were tested:

- Electrical conductivity: This technology was used for site characterization andmapping to support placement of monitoring wells, and to define subsurface geologicand hydrogeologic conditions.reported advantages:- potentially cost-effective,- easy to use,- portable,- quick turnaround time,- capability to identify 1 thin stratigraphic

layers that conventional methods miss,

reported limitations:- large metal objects can cause interference,- susceptible to operator error,- experienced operator needed to calibrate

and interpret logs.


BRGM/RP-51731-FR 21

- no soil cuttings.

- Electromagnetic Induction : This technology was used during site characterization tolocate disposal trenches at a landfill.reported advantages:- easy to use,- portable,- quick results.

reported limitations:- large metal objects such as fences can

cause interference.

- Ground Penetrating Radar: This technology was used during site characterization toidentify abandoned waste pits and other subsurface disturbances, bedrock stratigraphy,and the depth to water table. The technology was also used to develop profiles of ariver bottom.reported advantages:- data useful in identifying subsurface

disturbances without soil borings,- data allowed the selection of optimal soil

boring locations,- focused mapping of sample location,- information compared favorably with that

obtained through other methods.

reported limitations:- surface vegetation can inhibit

transmission of signals,- soils with high electrical conductivity can

inhibit transmission of signals,- interpretation of data is complex;

experienced data analyst required.

- Magnetometry: Hand-held and vehicle-towed magnetometry units were used duringcharacterization and mapping to identify buried ferrous metals.reported advantages:- ability to detect large ferrous metal objects

12 to 20 feet below ground surface,- ability to discriminate among subsurface

anomalies.

reported limitations:- vehicle-based magnetometers limited by

terrain and field conditions,- vehicle-based magnetometers tend to

underestimate the number of targets,compared with hand-held devices,

- signals from extraneous metals must befiltered out.

- Seismic Profiling: Two- and three-dimensional seismic profiling technologies wereused during site screening and characterization to determine bedrock stratigraphy, soiltype, and depth to water table.reported advantages:- potentially cost-effective,- very detailed image of soil stratigraphy,- bedrock fractures defined to within one

foot,- easy to use,- drilling costs minimized.

reported limitations:- large surface objects cause interference,- data return is very specific,- trained technician required to interpret

data,- vegetation must be removed,- equipment requires direct contact with the

ground, presenting a problem for use inbuildings.

Validation protocol:


22 BRGM/RP-51731-FR

Results

List of technical results: A table indicating the context of use for the geophysicalmethod:direct-push electrical conductivity, site screening,electromagnetic induction, site characterization,ground penetrating radar, site screening and site characterization,magnetometry, site characterization,seismic profiling, site screening and site characterization.

List of technical difficulties: Listed above by methods.

Appreciation: Good review derived from more than 200 studied sites.


BRGM/RP-51731-FR 23

Review form R-BRGM-001

References

Bibliographic source: Gourry J.C., Jeannot R., Proust E. (2001) - Couplage de mesuresgéophysiques et d'analyses de gaz pour la détection de polluants organiques sur uneancienne cokerie. Report BRGM/RP-50856-FR, 27 p.

Financial support : French National Project Criterre, BRGM.

End users : Charbonnages de France.

Problematics

Main objectives: Detection of organic pollution with geophysics and gas analyses.

Scientific and economic constraints: The destructive auscultation by bore-holes of largeareas is economically unrealistic. Geophysical methods are proposed to spatially extendbore-holes information.

Description of the methodology: Coupling of electrical sounding with surface gasmeasurements.

Technical work

Site description: The site is located on a old coking plant belonging to Charbonnages deFrance, North of France. The soil consists of filling material down to 3 m, claysbetween 3 and 6 m, and finally rough sands until 14 m. Two water tables are locatedrespectively in the first and third layers. Polluted areas were identified in some placefrom bore-holes measurements; there, organic elements exceed 300 mg for 1 kg of soil.

Geophysical technique used:

2D electric tomography (dipole-dipole) was conducted along a profile of 235 m using aspacing of 5 m and a order comprised between 1 and 8. Apparent resistivities andchargeabilities were measured.

Surface gas measurements consisted to analyze 6 organic elements from soil samplespicked up every 5m on the polluted zone and every 20 m outside.

Validation protocole: Qualitative using bore-hole information; quantitative from soilsamples measurements.


24 BRGM/RP-51731-FR

Results

List of technical results:

The water table is well detected on geoelectric sections. It lies from 6 to 3 m along theprofile.

Some local anomalies in resistivities and chargeabilities observed on the last part of theprofile are rather related to the presence of pollution.

Organic analyses confirm this interpretation.

List of technical difficulties:

A lack of resolution in geoelectric sections.

The relationship between electrical properties of soils and the type/concentration ofpollution remains difficult to appreciate.

Organic elements analyses don't give the depth of pollutions.

Appreciations:

This methodology seems is interesting to locate anomalies related to pollutions, but itneed to be coupled with quantitative bore-hole information to retrieve more accurateparameters related to the type of pollution, its concentration, etc.

Organic elements measured from gas analyses along the geophysical profile: a) G1 andG2 indicate anomalies; b) organic elements measured from soil samples; c) apparentchargeability from induced polarization measurements; d) inverted resistivities andchargeabilities.


BRGM/RP-51731-FR 25


26 BRGM/RP-51731-FR


References

Bibliographic source: Baltassat J.M., Richalet G., Dupont F. (1993) – Reconnaissancede décharge par géoradar, à Feyzin (69). Rapport BRGM N 0952, 17 p., 4 fig.

Financial support: DRIRE.

End users: Local authority.

Problematics

Main objectives: Determination of the extension of an ancient waste.

Scientific and economic constraints: Commercial action.

Geophysical technique used: Geological radar with antennas of 500, 300, 120 MHz.

Technical work

Site description: In Feyzin, near Lyon city, local authority aim to reuse land which wasused as waste. This waste is covered and land is partially used for agriculture (corn).The exact localisation of the waste is lost. The basement of the waste is gravel and sandrocks, with clayey silts on the top. Objects in the waste may be metallic (drums or pipesother things), rests of buildings destruction (bricks, concrete elements, pipes and so on).Five bore holes, was used as piezometer before the beginning of the study.

Description of the methodology: Three radar antennas with different frequencies (500,300, 120 MHz) were tried to choose the most efficient one for this specific field. Thenthe whole work (3410 m of profile) is performed with this antenna (120 MHz).

Validation protocol: The conclusion of the study was given to the client who shouldverify with bore holes or trenches.

Results

List of technical results: Radar film interpretation gave indication of the groundstructure (layers, objects). Depth penetration varies between 2 and 3 meters. This allowsdrawing maps of waste limitation and of specific areas (metallic objects concentration,ancient trenches and so on).


BRGM/RP-51731-FR 27

List of technical difficulties: A part of the field to prospect was covered with groundheap, big concrete blocks and tree stump. Another part was under water because of bigrains. So only 3 410 m of profile was performed instead of 5 000 m aimed in theproject.

Appreciation: Practical use of geophysical method.


28 BRGM/RP-51731-FR


References

Bibliographic source: Mathieu F., Miéhé J.M., Richalet G. (1994) – Reconnaissance parsismique réfraction de la décharge municipale de Villefranche-de-Rouergue (Aveyron).Rapport BRGM N 1597, 10 p., 1 fig., 3 pl.

Financial support: commercial action for ANTEA.

End users: Lefevre-Broussos (road project planning).

Problematics

Main objectives: Description of the topographic surface of the basement undermunicipal waste. Data are required for the work management of a new road project.


Geophysical technique used: Refraction seismic.

Technical work

Site description: The waste lied in a small valley across marls and limestone formations.

Description of the methodology: 24 geophones seismic array (2.5 m betweengeophones), five shots per array (1 on the middle, 1 on each extremity, 1 far from eachextremity). Gun is used for shooting, and a 24 channels digital seismic recorder is usefor recording. Interpretation used intercept method for calculus and took care of thetopography.

Validation protocol: Client should verify interpretation.

Results

List of technical results: P waves velocity varies from 350 to 760 m/s in the waste; itvaries from 1 370 to 1 500 m/s in part of the basement (marls and marly limestone), andraise 3 000 m/s in limestone. Width of waste is about 10 to 11 m. Topography level ofthe basement seems to be under the level as it was known before the waste installation.This means that the field was dug to improve waste capacity.

List of technical difficulties: Working waste are difficult areas for geophysicist: a partof the waste retains water where scraps bags were floating; in other part, scraps were not


BRGM/RP-51731-FR 29

covered with soil, so it was impossible to fix geophones; in other part , scraps were notsqueezed enough, so it did not transmit seismic waves. This is why seismic arrays can’tbe performed exactly on the road project but 30 to 100 m away from the project axe.

Appreciation: The work team did not appreciate the work and still remind it. But theycan transmit a lot of experience to anybody who wants to perform this kind of job.


30 BRGM/RP-51731-FR


References

Bibliographic source: Gourry J.C., Lebert F. (1996) - Prospection radar à la raffineriePetro-Midia de Constanta (Roumanie). Détection de conduites enterrées. Détection depollution par hydrocarbure. Rapport BRGM N 2233, 26 p., 10 fig., 4 tabl.

Financial support: Commercial operation.

End users: Petrochemical plant (Petro-Midia, Constanta – Romania).

Problematics

Main objectives: Detection of oil pollution in a petrochemical plant.

Scientific and economic constraints: Work localisation was imposed by plantrepartition.

Geophysical technique used: Geological radar, with 500 MHz antenna.

Technical work

Site description: The petrochemical plant of Petro-Midia was working, so there was alot of pipes and buildings every where. The plant is built on sand, near the sea. So,water level is very near from the ground level. Work was done in spring, when snowthaws

Description of the methodology: In a “street”, inside the plant, 3thre 45 m long profileswere recorded, with 2 m between each. Computation was performed on numericalrecord: band pass filter (200 to 800 MHz), selective amplification, deconvolution,Hilbert transform. Mapping of ringing an amplitude anomalies.

Validation protocol: Client should verify with trenches or bore holes.

Results

List of technical results: The study shows the underground repartition oil repartition:very long lenses, few meters large, with 0.5 to 1 meters separation. Depth pollution isabout 0.75 m.

List of technical difficulties: It seems that oil lies on normal water level an is coveredwith water coming from snow thaw. So it is between two water body like bacon


BRGM/RP-51731-FR 31

between bread in a sandwich. This fact explains the high reflective power and theringing of the polluted areas, which characteristics was not expected.

Appreciation: The author shows conclusion with tortuous arguments.


32 BRGM/RP-51731-FR


References

Bibliographic source: Baltassat J.M., Benot R. (1995) – Essai de caractérisationgéophysique d’une pollution par hydrocarbure sur le site d’une ancienne usine à gaz deVilleneuve-la-Garenne (Hauts-de-Seine). Rapport BRGM N 1892, 29 p., 12 fig., 1 ann.

Financial support: RESCOPP CEE project, through BRGM Research.

End users:

Problematics

Main objectives: Characterisation of pollution with hydrocarbon in area of ancient gasplant.

Scientific and economic constraints: Methodological work.

Geophysical technique used: Electrical and electromagnetic methods.

Technical work

Site description: The plant was built on gravel-sand layer, with clay cover. It wasdestroyed and part of the plant scraps staid lying on the polluted ground. Main pollutionwas shown on or near the water level (5 m deep) in bore holes. Pipes and cables stillremained underground.

Description of the methodology: BRGM choose electrical an Electromagnetic methodsbecause hydrocarbon pollution changes soil electrical properties: conductivity mappingwith EM31 and EM34 (10 m spacing), IP and resistivity pole-pole profiles, radarprofiles (500, 300 and 100 MHz antenna).

Validation protocol: Ground proprietary should verify interpretation with trenches orbore holes.

Results

List of technical results: EM maps and radar profiles seemed to show ancient structures(cables, pies and buildings). IP and resistivity pole-pole sections did not show anythingwhich can be surely interpreted.

List of technical difficulties: Underground anthropisation masked eventual pollution.

Appreciation: No result.


BRGM/RP-51731-FR 33


References

Bibliographic source: Baltassat J.M., Benot R., Le Jeune F. (1995) – Essai decaractérisation géophysique d’une pollution par hydrocarbures sur un ancien site destockage d’hydrocarbures à Saint-Herblain (Loire-Atlantique). Rapport BRGM N 2055,25 p., 9 fig., 1 ann.

Financial support: RESCOPP project through BRGM Research.

End users: Field owners (ELF).

Problematics

Main objectives: Detection of pollution with hydrocarbons.

Scientific and economic constraints:

Geophysical technique used: Electrical, electromagnetic and radar methods.

Technical work

Site description: Petroleum company ELF stopped use of petroleum tank plant in Saint-Herblain near Saint-Nazaire. Plant was on the Loire river bank, where tire movementare still important. Plant is destroyed, and it remained only scraps on clayey sand.Nature and location of the pollution with hydrocarbons is known (trenches, bore holes,chemical analysis…). Pollution is observed on the water table (2 to 3 m deep).

Description of the methodology: BRGM choose electrical an Electromagnetic methodsbecause hydrocarbon pollution changes soil electrical properties: conductivity mappingwith EM31 and EM34 (10 m spacing), IP and resistivity pole-pole profiles, radarprofiles (500, 300 and 100 MHz antenna).

Validation protocol: Ground proprietary should verify interpretation with trenches orbore holes.

Results

List of technical results: EM measurements clearly showed ancient underground pipes;resistivity pole-pole profile showed the emplacement of a removed underground tankand IP measurements were not significant. Radar showed a zone where amplitudes were


34 BRGM/RP-51731-FR

attenuated, in the vicinity of the known location of the pollution. As true limits of thepollution were unknown conclusion were not sure.

List of technical difficulties: Underground anthropisation masked eventual pollution.Complete results of analysis were not known when data were interpreted.

Appreciation: May be radar.


BRGM/RP-51731-FR 35


References

Bibliographic source: Lebert F. (1996) – Rescopp – Saint-Herblain (44) – Révision desconclusions géophysiques compte tenu des sondages et analyses. Rapport BRGM N38896, 27 p., 5 fig., 3 tab., 1 pl., 1 ann.

Financial support: RESCOPP project through BRGM research.

End users:

Problematics

Main objectives: Control of radar data interpretation (cf. review form 6) with completeanalysis data.


Geophysical technique used: Radar 500 and 120 MHz.

Technical work

Site description: cf. review form 6.

Description of the methodology: Complete study and comparison of analysis data withradar data.

Validation protocol: Ask for new analysis.

Results

List of technical results: Zone of radar amplitude attenuation seems really to becorrelated with hydrocarbons pollution, even if analysis data were not precise enough.

List of technical difficulties: Analysis data were done without any precise localisationon field by two different societies. There was no analysis profile that could showpollution repartition in a section. So analysis data and radar data are difficult tocompare.

Appreciation: Non-methodical work.


36 BRGM/RP-51731-FR


References

Bibliographic source: Barrès M., Caulier P., Valentin J., Van den Hoeck A. (1981) –Mise en évidence de panaches de pollution des eaux souterraines à l’aval des déchargesurbaines ou industrielles par prospection électrique. Rapport BRGM 81 SGN 222 ENV,10 p., 9 fig.

Financial support: Ministry of Industry (1980’s research program).

End users: Not identified.

Problematics

Main objectives: Detection of contaminant plume.


Geophysical technique used: Resistivity (depth sounding and linear profiles).

Technical work

Site description: Two sites are prospected:

- wild deposit of acidic tars in old sandpit, in Noyelles-sous-Bellone (62). Sands are onclay layer and contain water. There are level variations which induce variations inthickness of both dry and wet sands. Water of wet sand is contaminated with Ca, Mg,SO4, NH4, H2S, HnCn, Sulfonates…

- urban waste of Frétin (59) is in old chalkpit. Water level is 15 meters deep. Water iscontaminated with CO2, SiO2, Cl, SO4, NO3, NH3… artificial clay and graves depositslay on the vicinity.

Both sites are controlled with piezometers.

Description of the methodology: First resistivity soundings are performed nearpiezometers. Interpretation is done using depth of geological logs of bore holes; thisallows to evaluate the true resistivity of the different layers and to check theirhomogeneity. This phase also allows to design the length of the quadripole which willbe used to perform resistivity profiles. Plume appears as conductive anomalies inresistivity profiles. Succession of profiles allows to show plume axes.

Validation protocol: New bore holes are asked on plume axes.


BRGM/RP-51731-FR 37

Results

List of technical results: Results are different in each site.

In Noyelles, electric methods show plume extension and allows to evaluate pollutionintensity with water resistivity determination (under Archie’s law).

In Frétin, only one bordure of the plume is showed by resistivty profiles.


In Noyelles, results are obtained despite variations of water charge and aquiferthickness.

In Frétin, local clayey deposits hide one part of the plume.

Appreciation: It’s so far. Is it truly post diluvian geophysic?


38 BRGM/RP-51731-FR


References

Bibliographic source: Lebert F., Richalet G. (1999) – Centre technique Mont-Saint-Sebastien (Soignolles-en-Brie – 77). Prospection sismique réfraction. Rap. BRGM N2826, 15 p., 2 fig., 5 pl.

Financial support: Commercial action.

End users: Waste office.

Problematics

Main objectives: Determination of bedrock depth under the waste.


Geophysical technique used: Refraction seismic.

Technical work

Site description: The waste fill a small valley across a cliff. Original ground level iscurrently unknown, but it is required to plan hydraulic work.

Description of the methodology: We performed seismic profiles across and along theplaned path: 24 geophones, 3 or 5 meters between each, 5 shots per profiles. Interceptmethod interpretation.

Validation protocol: Bore holes along planed path.

Results

List of technical results: Interpretation show 3 layers with very low P waves velocity(150 to 220 m/s, 200 to 400 m/s and 500 to 900 m/s). The deepest one cannot beidentified to bedrock because of its low velocity. Firsts boreholes show clayey gravesfilling at this depth.

List of technical difficulties: Urban waste is heterogeneous deposit (nature andcompaction); there was important ground level variations. Gas recovery system impliesno explosive source using, but AWD. Waste activity (truck and compressors) generatehigh level noise.

Appreciation: Practical use of a geophysical method.


BRGM/RP-51731-FR 39


References

AFNOR, Méthodes de détection et de caractérisation des pollutions. NormalisationFrançaise X 31-611-2.

Financial support: AFNOR.

End users:

Problematics

Main objectives : General guide for detection and characterization of pollution withgeophysical methods.

Scientific and economic constraints: Feasibility.

Description of the methodology: Standard.

Technical work

Site description :General application (the document contents no case history):- conductive objects,- non conductive objects,- conductive networks,- non conductive networks,- old waste disposal (geometry),- contaminated soils,- contaminated water,- floated pollution,- dense pollution.

Geophysical technique used:- micro-gravimetry,- magnetic methods,- electromagnetic methods,- ground penetrating radar,- infrared thermography,- electric methods,- seismic refraction.

Validation protocole: Not indicated.


40 BRGM/RP-51731-FR

Results

List of technical results: See table.

List of technical difficulties: The performances and limits of geophysical methods aredescribed for each kind of investigated site:

- Conductive objects and networks detection (up to 10 m depth):Magnetic method is the more convenient method if the target are ferromagneticobjects. It is cheap, simple and fast to acquire data. It provides map or curves with iso-values for qualitative interpretation. In case of non-ferromagnetic objects,electromagnetic methods are well adapted. Measurements are also cheap and quick tocarry. A geostatistical study is recommended for interpretation of results. However,these methods can not be used on a working site because of perturbations due toelectric current.GPR can be used but the depth investigation is limited by the conductivity (limit at50 �.m). Microgravimetry can be carried in the case of dense targets but it isexpensive.In the case of networks instead isolated targets, all these methods work well but theyare limited by the depth and the size of the network.

- Non conductive objects and networks: GPR is well adapted for the shallow targets andresistant media. In special cases, micro-gravimetry, electromagnetic or electricmethods can be convenient. EM methods are less perturbed by working electric linesbut are more difficult to provide data profiles For networks detection andcharacterization, the methods are limited by their size and depth like in the case ofconductive target.

- Geometry/extension of old waste disposal: Seismic refraction method is the bestmethod for this kind of investigation. However, it is perturbed by noise generated bynatural source or working industry. Measurements and interpretation need an expertgeophysicist. It is quite more expensive than electric or EM methods but it is in thesame order than GPR method. Resistivity measurements can be used because wasteare generally more conductive than natural soil. Microgravimetry method can also beused if density contrast between waste and soil is high enough.

- Pollution research: There was not a lot of case histories when the document waspublished, except for saline pollution. In this case, electric and EM methods are thebest. The manual only recommends coupling methods (density and resistivitycontrasts) and adding chemical punctual analysis. However, geophysics method couldbe interesting for monitoring surveys of pollution on a site without needing initialstate.

Appreciation: The document has no example of result. It although points out thedifferent kind of scientific problem encountered in waste disposal problem and thedifferent methods adapted for each case.


BRGM/RP-51731-FR 41


42 BRGM/RP-51731-FR

Review form A-EOST-001

References

Bibliographic source: Orlando L., Marchesi E. (2001) - Georadar as a tool to identifyand characterise solid waste dump deposits. J. Appl. Geophys., 48, 163-174.

Financial support:

End users:

Problematic

Main objectives: Reporting the ability of a GPR survey to detect and characteriseuncontrolled waste dumps.

Scientific and economic constraints: Outside of Rome, many abandoned quarries wereused as waste dumps during the 1960’s. No account was taken to the geological featuresor to the refuses.

Description of the methodology: Surveys were carried out with 3 antennas, verticalelectrical soundings (VES), multielectrode profiles and boreholes bring moreinformation over the sites.

Technical work

Site description: 2 waste dumps were surveyed. Ponte Malnome is a hill with a flat topoverlying Quaternary alluvial sediments. The dump thickness is estimated at 3-4 m. Thewaste is mainly building rubble. Regione Lazio is located in a quarry in Plio-Quaternarysediment. The quarry layer was below a silt and clay layer. Waste was dumped into thetopographic ditches. Household inorganic refuse could mainly be present (with quarrydeposit).

Geophysical technique used: A Sensor and Software PulseEKKO100 equipped with 50,100 and 200 MHz antennas was used to carry out the survey. Data were acquired incontinuous mode. Dewow, low-pass frequency filters and AGC were applied to therecords. Topographic corrections were applied if necessary.

The VES were carried out using the Schlumberger array, the 2D multielectrode surveywas acquired using dipole-dipole arrangement with 28 electrodes spaced 1 m apart.

Validation protocole: Boreholes give stratigraphy of different points in the dump, VESpermits to know the resistivity at different depths and multielectrode profile showlateral variations of the resistivity.


BRGM/RP-51731-FR 43

Results


Ponte Malnome: The 3 antennas showed little differences in depth investigation. Theresolution is lower for the 50 MHz antenna than for the other. Stratified parts of thesections correspond to the in situ sediments. High reflective zones are interpreted aswaste deposits, more resistive than the sediments. VES, Boreholes and multielectrodedata confirm the preliminary results of georadar data. The bottom of the dump isreached with the 50 MHz antenna.

Regione Lazio: Some profiles show reflections until 200 ns whereas other have a verylow penetration (around 50 ns). Many profiles show a heterogeneous surficial unit (50-80 ns) overlying a unit characterized by a complete absence of reflections. Bycomparison with earlier seismic measurements, the surficial layer can be interpreted ashousehold refuse. The underlying non-stratified layer may be silt and clay discardedduring the quarrying. On some profiles, there is a stratified unit corresponding to in situsand and gravel sediments. The radar does not reach the bottom of the dump.

List of technical difficulties: Limitation to shallow depth in presence of conductivewaste.

Synthetic illustration:


44 BRGM/RP-51731-FR


References

Bibliographic source: Atekwana E.A., Sauck W.A., Werkema Jr. D.D. (2000) -Investigations of geoelectrical signatures at a hydrocarbon contaminated site. J. Appl.Geophys., 44, 167-180.

Financial support: American Society Petroleum Research Fund Grant and NSF ILIGrant.

End users:

Problematic

Main objectives: Evaluation of the utility and response of different geoelectricalmethods in mapping contaminant distribution in the subsurface.

Scientific and economic constraints: The geoelectrical signature of hydrocarbon plumesare varying from one site to the other. Resistivities on hydrocarbon plumes can beinterpreted as high or low.

Description of the methodology: Data acquisition with GPR, electrical resistivitymeasurements and electromagnetic induction, constraint with soil borings and thencomparison between the different results.

Technical work

Site description: The site is situated near a refinery located in Carson City (Michigan),constructed in the 1930’s. 2 hydrocarbon plumes are observed since 1945 in a river nearthe refinery. The southern one is the focus of this study and has a extension ofapproximately 229 m long by 82 m wide. Dissolved phase hydrocarbons are found atthe fringes of the free product plume. The geology is composed of 4.6 to 6.1 m of fineto medium sands, coarsening to gravel under the water table (at a depth from 0.6 m nearthe river to 5.8 m in the eastern part of the site). Below the sands, there is a clay aquitardunit with a thickness varying from 0.6 to 3.1 m.

Geophysical techniques used: Vertical resistivity probes, with 2.5 cm spacing, wereinstalled at 3 locations, 20 m south of the refinery. Apparent resistivity measurementswere obtained using a 5 cm Wenner array. 2D electrical measurements were carried outwith a dipole-dipole array, with an a spacing of 5 m. The software RES2DINV was usedto invert the data. A finite difference forward modeling sub-routine was used tocalculate the modelled resistivities.


BRGM/RP-51731-FR 45

GPR data were acquired with a GSSI SIR10A equipment with a 300 MHz bistaticantennae recording for 160 ns.

An electromagnetic survey was conducted using a Geonics EM31 unit in the verticaldipole mode.

Validation protocol: Hand augered borings were accomplished along one of the GPRlines, 15 m south of the refinery.

Results

List of technical results: The vertical resistivity shows an anomalous conductivity zonecorresponding to the lower part of the residual/free product hydrocarbon and the upperpart of the saturated zone. Where significant alteration of the hydrocarbon contaminantsand host media has occurred, there is a change in the geoelectrical signature fromresistive to conductive (due to biodegradation of the contaminants?).

The 2D resistivity pseudosection shows a vadose zone with high resistivities reducing tolower resistivities corresponding to the saturated zone. To the west and to the east, azone of lower resistivity rises to surface and is coincident with the GPR shadow zones.It can be due to a shallow water table or to more conductive ground waters.

On GPR data, the reflector due to the water table is well seen. A second reflector is seentens of nanosecond above the water table. By correlation with soils borings, it isinterpreted as the reflection of the top of an oil-stained, grey sand layer. At the west andeast ends of the profiles, the reflections are attenuated below the water table. This canbe related to enhanced conductivities.

The EM data show high conductivity values in the eastern and southern part of thesurveyed area. This is due to the increasing of soil moisture and to the shallower depthof the water table. The highest conductivities can be correlated with a drainage ditch.No anomaly due to hydrocarbon contamination is observed.

List of technical difficulties: The conductive may not be easily monitored, because it isthin, relative to its depth of burial.



46 BRGM/RP-51731-FR


BRGM/RP-51731-FR 47


References

Bibliographic source: Carcione J., Marcak H., Seriani G., Padoan G. (2000) - GPRmodeling study in a contaminated area of Krzywa Air Base (Poland): Geophysics, 65,521-525.

Financial support: In part by the European Union under the INCO-Copernicus projectDetection of Hydrocarbon Contaminated Soils by Electromagnetic Techniques.

End users:

Problematic

Main objectives: Simulation and evaluation of the expected ground-penetrating radarresponses for uncontaminated and contaminated layers, in prelude to acquisition of fielddata.

Scientific and economic constraints: High soil pollution of a former Soviet Air Base inPoland.

Description of the methodology: The simulation is based on a modelling codedeveloped by Carcione (1996) and the model of permittivities and conductivities isgiven in Carcione and Seriani (2000). The simulation may be field tested by acquisitionof real data in the future.

Technical work

Site description: Area located on the pre-Sudetic block, where Tertiary and Quaternarydeposits (sands of different sizes, gravels, clays and interbedded silts) of a totalthickness from 80 to 100 m lie on Mesozoic crystalline basement.

Geophysical technique used: Radar simulation based on a forward-modeling codedeveloped by Carcione (1996) and the model for computing the effective permittivitiesand conductivities is given in Carcione and Seriani (2000). A Cole-Cole model is usedto describe the dielectrical properties of clay and water. The radar source is a Ricker-type wavelet.

Validation protocole: Field-data acquisition is foreseen to test the simulation.


48 BRGM/RP-51731-FR

Results

List of technical results: The top of the contaminated area can be seen with a 200 MHzantenna and a contamination rate of 0.1 %, a conductivity of 0.5 mS/m in the upperlayers and a radar performance of 140 dB. If the conductivity is higher (5 mS/m), thesaturation needs to be greater than 30 % to be detected by a 200 MHz antenna. With a50 MHz antenna, the penetration is higher, but the resolution limit is close to thicknessaround 1 m.

List of technical difficulties: Field surveys are needed to test the prediction of thesimulations.

Synthetic illustration: See next page.


BRGM/RP-51731-FR 49


References

Bibliographic source: Doll W.E., Nyquist J.E., Beard L.P., Gamey T.J. (2000) - Casehistory: Airborne geophysical surveying for hazardous waste site characterization on theOak Ridge Reservation, Tennessee: Geophysics, 65, 1372-1387.

Financial support:

End users:

Problematic

Main objectives: Showing that methods used for mineral and petroleum exploration canbe applied to environmental problems.

Scientific and economic constraints: Trying to characterize the geological andhydrogeological setting of hazardous waste sites by airborne geophysical methods.

Description of the methodology: Magnetic, electromagnetic and radiometricmeasurements were acquired after some tests measurements over 4 tests sites.

Technical work

Site description: The Oak Ridge Reservation is a US Department of Energy facility,used for 50 years as hazardous waste disposal (nuclear materials, solvents, contaminatedmetallic debris). Geology: interbedded shale and carbonate units with dip about 45°south, ranging from near horizontal to near vertical.

Geophysical technique used: An Aerodat 6 frequencies helicopter EM system withhorizontal and vertical coplanar coils at different frequencies, a vertical magneticgradiometer (2 cesium magnetometers suspended 30 m below the helicopter, totemVLF-EM sensors, an Exploranium gamma-ray spectrometer and a GPS antenna weremounted on and below a helicopter).

Validation protocole: Measurements were carried out over test sites, where the mainfeatures were known (type of waste stored, man-made target…). Sediment cores werecollected to a depth of 60 cm to see if contamination giving gamma-ray anomalies lieson surface or is buried under clean sediments.


50 BRGM/RP-51731-FR

Results

List of technical results: Magnetic data are effective for confirming the boundaries ofwastes sites and discriminating between areas containing differing quantities ofmagnetized waste. Some anomalies can be correlated with geological contacts.

EM data show a strong correlation with geologic features. Some anomalies could berelated to known karst features and then discover other possible karsts.

Radiometric data can be used to locate surface contamination (gamma radiation areseverely attenuate by presence of vegetation or uncontaminated soil cover). The map ofK40 reflects the local geology.

List of technical difficulties: Loss of sensitivity due to distance from the target,influences of the position between the towed systems and the helicopter, variations inhelicopter altitude, topography, wind conditions and vegetation affect noise. A spacingof acquisition lines closer than 10 m is difficult to maintain. The measuring bird wascommonly at an altitude between 20-40 m. Anomalies from cultural (man made) objectsmust be identified (data base, aerial photographs, in-flight videos). It is not a substitutefor ground-based surveys.



BRGM/RP-51731-FR 51


52 BRGM/RP-51731-FR


References

Bibliographic source: Holt J., Daniels J., Vendl M., Baumgartner F., Radziviscius S.(1998) - Brownfield site investigation using geophysics: a case history from EastChicago. Proceedings of the Symposium on the Application of Geophysics toEnvironmental and Engineering Problems (SAGEEP’98), 389-398.

Financial support:

End users:

Problematic

Main objectives: Demonstrating the effectiveness of utilizing geophysics anddeveloping strategies for applying geophysics to brownfields.


Description of the methodology: Data acquisition of several methods, data processingfor GPR data, and comparison between the different results.

Technical work

Site description: The site is located in Chicago, Illinois, in what was a small industrialarea, occupied by a disinfectant factory, a sheet metal shop and a steel plating works.Now the site is vacant, covered on the western site with grass and on the eastern sidewith remains of foundations and concrete floor.

Geophysical techniques used: Magnetic measurements, with a Geometric’s G-858Cesium gradiometer magnetometer: vertical and horizontal gradient data.

Electromagnetic measurements: EM-31, with a Geonics EM31-MK2, EM-61 and aGEM system by Geophex with 2 frequencies (2430 and 9510 Hz).

Ground penetrating radar: with a GSSI Sir10 system and a 500 MHz frequency antenna.The data were processed (lines normalization, 1D-filtering and gain improvement).

Validation protocol:

Results

List of technical results: The magnetic measurements show a probable filled pit.


BRGM/RP-51731-FR 53

The electromagnetic measurements show again the probable filled pit and a void to thesouth and east of the pit. A linear anomaly is interpreted as a trench. Other linearanomalies may be pipes.

The GPR shows some anomalies corresponding to pipes. The pit, pipes and aninterpreted tank can be easily seen. Another object is interpreted as a rebar.

The comparison between all the results gives the following conclusions: an anomaly canbe interpreted as a pipe in a void. Another one is probably a tank. A pit that has beenfilled can be seen too. Another anomaly may be a rebar. A void and several pipes werediscovered. A trench may be present too.

Only the combination of several geophysical methods permits to detect many differenttypes of objects buried in the subsurface. GPR, EM31 and EM61 are the 3 best choicesat this site. Magnetic data added the least information.

List of technical difficulties: Resolution could be improved by reducing the spacingbetween the lines and the measurements points. Instruments should be run in orthogonaldirections. The magnetic method is difficult to interpret. In electromagneticmeasurements, the orientation of the instruments makes a difference. Using one method,some small anomalies could be interpreted as background noise.


54 BRGM/RP-51731-FR


References

Bibliographic source: Lanz E., Maurer H., Green A.G. (1998) - Refraction tomographyover a buried waste disposal site. Geophysics, 63, 1414-1433.

Financial support: ETH Research Commission Grant and Swiss National ScienceFoundation Grants.

End users:

Problematic

Main objectives: Determining precisely depth and geometry of the waste dump’s lateraland lower boundaries.

Scientific and economic constraints: Remediation of dangerous landfills requires preciseknowledge of boundaries and depth, of nature and location of the types of waste, of thepresence from a groundwater table within or below the landfill…

Description of the methodology: Field survey during night, data analysis, newtomography scheme, data inversion, discussion of the tomograms.

Technical work

Site description: 2 adjacent landfills in the Alpine foreland of Switzerland. Complexstratified till and outwash (including channels and lenses of clean or silty gravel)overlies lacustrine deposit. Groundwater flows northwesterly and the groundwater tablelies at a depth of 3 to 5 m. Industrial refuse (chemical and oil waste, paper, plastics,textile fibres) and domestic waste were dumped in the landfills.

Geophysical technique used: Seismic profiles were selected on the other geophysicaldata. 100 g dynamite was used as seismic source, the receiver were 30 Hz geophones,with a record length of 0.5 s, a sampling interval at 0.25 ms and a receiver spacing of 2or 4 m, on 120 or 210 channels. The profiles had lengths from 240 to 450 m. Atomographic algorithm using a fast finite difference eikonal solver for propagatingwavefronts through 2D heterogeneous media and an inversion method incorporatingappropriate damping and smoothing constraints were developed.

Validation protocol: Ground magnetic gradient, inductive electromagnetic and georadardata helped to define the boundaries of the landfills. Matching between synthetic(obtained from the tomography) and observed traveltime data. Traveltime residualdiagrams show residuals limited to � 5 ms (with a majority less than � 3 ms).


BRGM/RP-51731-FR 55

Comparison of coincident velocity/depth profiles extracted from crossover points of theprofiles. The sensitivity to input 1D model for the 2D inversion was tested on the mostheterogeneous dataset and show that the results are very similar.

Results

List of technical results: On the basis of the velocity information, the maximum depthsof the landfills are around 11 m for the western and 9 m for the other one (mostlybetween 2 and 6 m). The most pronounced velocity decreases and the largest deepeningof 1000 m/s isovelocity are associated with landfills, but can also appear in undisturbedarea. Then, they are due to presence of gravel lenses and channels.

List of technical difficulties: Noisy environment (acquisition during night), largenumber of closely spaced geophones, multiple sources of sufficient energy, robust 1st-break picking. Other geophysical methods were necessary to define the lateralboundaries of the landfills. Resolution lower than that obtained by high resolutionseismic reflection, but these rarely provide information on the shallow parts of theunconsolidated sedimentary section.

Limitations of the method: Choosing appropriate values for regularization parameterduring inversion, lateral resolution is controlled by source-receiver spacing and by thesize of the inversion cells, difficulties to delineate horizontal to shallow dipping lowvelocity zones which are laterally extensive and sandwiched between higher velocityregions.



56 BRGM/RP-51731-FR


BRGM/RP-51731-FR 57


References

Bibliographic source: Benson A.K., Payne K.L., Stubben M.A. (1997) - Mappinggroundwater contamination using DC resistivity and VLF geophysical methods. A casestudy: Geophysics, 62, 80-86.

Financial support:

End users:

Problematic

Main objectives: Mapping an area of contaminated soil and groundwater with electricalresistivity and VLF.

Scientific and economic constraints: Many studies used apparent resistivities to modelplumes of hydrocarbon contamination. Here, interpreted resistivities, obtained bycomputer modelling of apparent resistivities, will be used.

Description of the methodology: 32 electrical resistivity soundings and VLF data on 9profiles were acquired, and then modelled using numerical programs.

Technical work

Site description: It’s a parking lot, ones paved with asphalt that was removed afterweathering deterioration, in the alluvial basin in central Utah Valley. The subsurfacegeology is composed of alluvial deposit more or less consolidated (gravel, sand, silt,clay). A service station located in the north of the area reported a leak from anunderground gasoline tank.

Geophysical technique used: 32 dc-electrical soundings were collected with a BisonOffset Sounding System, with a-spacing from 0.5 to 16 m each. Some of the soundingswere repeated 2 months later to assure reproductibility and accuracy of the data. Theresistivities were modelled using the BOSSIX program (Interpex).

The VLF data were acquired using a Wadi system manufactured by ABEM. They werefiltered with a Karous-Hjelt filter, processed and plotted at a selected depth near watertable.

Validation protocole: 4 monitoring wells are installed on the site and permitted wateranalyses, groundflow direction.


58 BRGM/RP-51731-FR

Results

List of technical results: 1 cross section of interpreted resistivities shows a highresistivity layer whereas this layer doesn’t exist in another cross-section. It is interpretedas HC contamination wetting the soil in the unsaturated vadose zone. At a depth nearbythe top of the water table, the resistivities high appear to decrease from the north to thesouth like the contaminant levels.

The VLF values show a resistivity high correlating with the resistivities above Thesedata show that the plume is narrowing towards south.

List of technical difficulties: The resistivity values depend on the presence of TotalDissolved Solids (TDS): the higher the TDS, the lower the resistivity. So, atcontaminated but already biodegraded sites, the resistivities of the contaminant plumemay be lower.



BRGM/RP-51731-FR 59


References

Bibliographic source: Cardarelli E., Bernabini M. (1997) - Two case studies of thedetermination of parameters of urban waste dumps. J. Appl. Geophys., 36, 167-174.

Financial support:

End users:

Problematic

Main objectives: Verifying whether some of the most applied geophysical methods innear surface investigations may be used to determine geometrical parameterscharacterizing waste dumps.

Scientific and economic constraints: Determining the characteristics of buried wastedumps for urban planning.

Description of the methodology: Data acquisition on 2 urban waste sites, with diversecharacteristics and on different geological formations.

Technical work

Site description: Site 1 (Caprarola): dump in an old quarry of volcano formations(phonolitic tefritic tuffs). Permanent water table deep exists 50 m below topographicsurface.

Site 2 (Pisana): the dump is covered with loam soil, is situated on a former quarry ofaggregate material, in a heterogeneous fluvial lacustrine formation presenting variationsfrom sand and gravel to clay. Area and thickness of the dump are unknown.

Geophysical technique used: Site 1: 10 vertical electric soundings using theSchlumberger array with an electrodic distance AB of maximum 100 m. One seismicrefraction line from 55 m length was carried out.

Site 2: 20 vertical electric soundings were carried out (13 of which were placed on 2profiles). A seismic line was placed on one of the profiles and another was carried outperpendicularly to it.

Validation protocol: Comparison of the thickness computed and direct investigations.Soundings in and outside of the presumed waste dumps.


60 BRGM/RP-51731-FR

Results

List of technical results: Site 1: the seismic results show a zone of low velocities and athickness from 5 to 12 m corresponding to the dump. Laterally and deeper, thevelocities correspond to normal values for a weathered tuff and a litoid tuff.

The soundings show a very low resistivity zone corresponding to the dump. Thethickness is the same as found with the seismic method. Below, there is a zone of lowerand heterogeneous resistivities (due to organic liquids soaking through the bottom of thedump). Deeper, the values are near the normal values for tuff.

Site 2: the seismic results show a low velocity zone with a thickness of 13-14 m, notcompatible with a fluvial lacustrine formation. This velocity must be due to the waste.A lateral velocity increasing in an intermediate layer may indicate the dump limit.

Soundings carried out away the dump show a superficial layer with variableresistivities, then an intermediate one with resistivities around 40 �.m and below a lowresistiviy zone. In the dump, the characteristics are the same, with higher resistivities forthe intermediate layer.

The materials constituting a waste dump show lower velocities with respect to the air.They increase in depth but with values lower than normal values for weathered layers.The resistivities can be higher or lower in the materials composing the dump.




BRGM/RP-51731-FR 61


References

Bibliographic source: De Lima O.A.L., Sato H.K., Porsani M.J. (1995) - Imagingindustrial contaminant plumes with resistivity techniques. J. Appl. Geophys., 34, 93-108.

Financial support: Financiadora de Estudos e Projectos (FINEP) and the ConselhoNacional de Desenvolvimento Cientifico e Tecnologico (CNPq).

End users:

Problematic

Main objectives: The purposes are to delineate the structural configuration, to inferpetrophysical characteristics and water quality of the upper layers and demonstrate theefficiency of an electrical resistivity procedure in distinguishing between conductiveand resistive contaminant plumes.

Scientific and economic constraints: An aquifer in the Bahia region (Brazil) furnisheswater for domestic use in many cities and villages and for industrial use. Thegeohydrological conditions must be well known to prevent irreparable damages to thewater supply. Contaminations can be due to the raw materials, the intermediate productsand the residual liquid wastes used by a petrochemical complex.

Description of the methodology: The procedure used combines electrical soundingswith multiple profiling at several electrode spacing. Complete and partial soundings areinverted and correlated assuming horizontally layered resistivity models.

Technical work

Site description: Copec industries are located on a thick sedimentary sequence in apaleorift structure developed in the early Cretaceous. The upper formation is anassociation of alluvial fans and river deposits (poorly consolidated kaolinic sandstones,massive or stratified conglomeratic bodies, locally thin beds of shale) that overlies asandstone formation, a thick fluvial sequence (thick stratified sandstones interlayeredwith shales, siltstones and limestones).

Geophysical technique used: 45 Schlumberger electrical soundings were made, usingelectrode separations up to 300 m. 15 multiple resistivity profiles were obtained troughmore than 170 partial soundings at 6 depths levels corresponding to AB/2 spacings from5 to 50 m. Electrical logs from 12 water production were obtained. An ABEM


62 BRGM/RP-51731-FR

Terrameter system was used for the resistivity soundings. A software program wasdeveloped.

Validation protocol: The interpreted results of adjacent soundings are compared andlogs of existing wells are compared to soundings centered on them. The fit of aninterpreted structure to a given pseudo-section is estimated using a finite-differencealgorithm to compute the electric potential distribution due to point sources of currenton a heterogeneous medium having 2 dimensional symmetry. At a given step, the errorbetween the computed section and the observed one is computed and if too large, thestructure is changed until the error drops below 10 %.

Results

List of technical results: Some conductive anomalies were identified within the upperaquifer. These anomalies can’t be explained by the natural compositional changes in thegeologic formation. They result from an increase in the salinity of the groundwater,associated with the heated and acidified waters used in the industrial processes.

A deeper aquifer may be partially protected at intermediate depths by shales or by thebasal conglomerate of the upper formation.

List of technical difficulties: In an industrial site, there are many anomalies that can bedue to ditches and buried pipes.



BRGM/RP-51731-FR 63


References

Bibliographic source: Kalantzis F., Stevens K.M., Kanasewich E.R., Lodha G.S. (1994)- Ground penetrating radar imaging of nuclear waste repositories. 56th Meet. Eur. Assoc.Explor. Geophys. Extended abstracts, session: P050.

Financial support: Canadian Nuclear Fuel Waste Management Program.

End users:

Problematic

Main objectives: Showing that GPR data processed with seismic algorithms are capableof imaging near surface reflectors and fracture zones in the granite.

Scientific and economic constraints: Determining structure of granitic rock for disposalof nuclear waste.

Description of the methodology: Data acquisition, data processing using seismicprocessing algorithms.

Technical work

Site description: The measurements were carried out over the granitic Lac du BonnetBatholith, in Manitoba (Canada).

Geophysical methods used: Ground penetrating radar with an antenna frequency of25 MHz, with an offset between transmitter and receiver of 3 m. Spacing between tracesof 1 m, each trace consisting of a stacked radar signal (128 stacks). Seismic processingwas applied to the data.

Validation protocol: Drill cores.

Results

List of technical results: The seismic processing applied on radar data improved them.Signal to noise ratio is enhanced. Steeply dipping reflectors due to a vertical rock faceare suppressed after migration. The resolution of reflectors is better after processing.



64 BRGM/RP-51731-FR



BRGM/RP-51731-FR 65


References

Bibliographic source: Seren S.S., Blaumoser N.H. (1994) - Combined implementationof geophysical methods for the investigation of old waste deposits in alpine area. 56th

Meet. Eur. Assoc. Explor. Geophys. Extended abstracts, session: P037.

Financial support: Austrian Geophysical Service of the Central Institute forMeteorology and Geodynamics.

End users:

Problematic

Main objectives: Delineation of the 3D extent of the deposit and evaluation of thestratigraphy to provide the basic knowledge for a cost effective redevelopment andpossible extension of the deposit.


Description of the methodology: Data acquisition, data processing and then comparisonof the different results in conjunction with borehole data.

Technical work

Site description: The waste deposit is embedded in layered fluvial deposits betweenoutcropping rock (quartzitic shales) to the South and a river to the North.

Geophysical techniques used: P-wave refraction seismic, Schlumberger geoelectricalsoundings and magnetometry were used.

Validation protocol: Borehole data.

Results

List of technical results: Refraction seismic: the thickness of the deposit could bedetermined easily, but didn’t help to know about silt layers. A part of the rock basementcould be detected.

Electrical soundings: the surroundings of the waste deposit could be determined in alarge extent. At some places, a second silt layer could be determined.


66 BRGM/RP-51731-FR

The magnetic data helped to delineate the lateral extend of the deposit, metallic areaswere detected and a wall built to prevent flooding from the river appeared clearly.




BRGM/RP-51731-FR 67


References

Bibliographic source: Ross H.P., Mackelprang C.E., Wright P.M. (1990) - Dipole-dipole electrical resistivity surveys at waste disposal study sites in Northern Utah. InWard, H. (Ed), Geotechnical and Environmental Geophysics. Soc. Explor. Geophys., 2,145-152.

Financial support: U.S. Air Force Occupation and Environmental Health Laboratory,Brooks AFB, Texas.

End users:

Problematic

Main objectives: Determining the lateral extent and thickness of clay lenses and locatingcontaminant plumes on waste disposal sites at Hill Air Force Base near Ogden.

Scientific and economic constraints: Industrial and military development have resultedin waste disposals at landfills in Utah. Migration of contaminants is presenting problemsto surface water used for irrigation.

Description of the methodology: Determination of all grounded electrical structuresfrom field inspection and maps, then location of the survey lines to avoid as many noiseas possible from these cultural structures, and finally data acquisition.

Technical work

Site description: The zone is in a highly faulted overthrust belt. Alluvial deposits layover the bedrock units and are composed from 300 m to more than 1000 m thickunconsolidated silts, clays, gravels and sands. Beach, near-shore and off-shore depositswere formed at every stable level of the ancient lake Bonneville. Deltaic sediments arealternate fine and coarse erosional debris from the Wasatch Mountains. Several siteswere studied:

Berman pond: 1st an unlined evaporation pond for industrial waste waters was used as adumping site for wheel rims, barrels, concrete with steel reinforcement.

Chemical disposal pit 3: disposal of large quantities of trichloroethylene bottoms from asolvent recovery unit and vapor degreasers.

Chemical disposal pits 1 and 2: liquid petroleum wastes, periodically burned, but muchseeped into soil.


68 BRGM/RP-51731-FR

Golf course area: located immediately south of chemical disposal pits 1 and 2 andlandfill 3 (waste solvents, bottoms from solvents cleaning operations, barrels, trash,concrete, petroleum waste).

Geophysical technique used: Dipole-dipole array with a dipole separation of 9.1 m, withthe Bison Instruments 2390 resistivity system (which stacks and averages 10 cycles).When this system was not available, a Fluke 8050 Digital Multimeter was used asreceiver in conjunction with an Elliot model 15A time-domain IP transmitter with1500 W. Numerical resistivities models were then computed.

Validation protocol: In some areas, boreholes helped to understand the geology. Othergeophysical methods (ground magnetics, self-potential) were carried out to define thelimits of the dumps.

Results

List of technical results: In the landfill at the Berman Pond, the resistivities aremoderate to low in an area of high resistivity sands. The survey at Chemical disposal pit3 revealed a complex geology, with disruption of clay layers. High resistivity values aredue in part to hydrocarbon residues visible at the surface and monitor wells. At the Golfcourse, the measurements confirm the presence of a low resistive clay layer, dippingtowards north, that can provide a hydrologic lead for contaminant migration. Groundmagnetic profiles helped to delineate landfill and dump areas. Metallic debris causedstrong magnetic field variations in a short distance, whereas on places containing nometallic debris, the field variations are low.

List of technical difficulties: Several computed models can explain the observed data.



BRGM/RP-51731-FR 69


70 BRGM/RP-51731-FR

Review form A-UNICRE-001

References

Benson A.K. (1995) - Applications of ground penetrating radar in assessing somegeological hazards: examples of groundwater contamination, faults, cavities: J. Appl.Geophys., 33, 177-193.

Financial support: ?

End users:

Problematic

Main objectives: Delineating the contaminant plume boundaries in the subsurface andlocating positions of monitoring wells with GPR surveys.


Description of the methodology: Data acquisition with GPR in order to outlinecontaminated areas and determine locations for monitoring wells, chemical analysis ofsoil and groundwater samples obtained from these wells, integration and correlation ofthe GPR data with the chemical analyses.

Technical work

Site description: Two sites of groundwater and soil contamination produced by leakingliquid hydrocarbon underground fuel tanks located in north-central Arizona and centralUtah:

- north-central Arizona: the geology was found to consist of sand 1-2 m thick and sandcontaining gravels and some clay 1.5-3.5 m thick. The bedrock is the KayentaFormation of the Glen Canyon Group consisted of interbedded sands, silts and clay;

- central Utah: the geology was determined to consist of an asphalt/sand layer (1.1-1.4 m thick), a layer of silty sand containing gravel (1.7-2.4 m thick) and a water-bearing gravel layer.

Geophysical techniques used: The surveys were carried out using a SIR SYSTEM-3consisting of a Model PR-8304 profiling recorder with automatic gain ranging andgraphic and/or magnetic tape analog data recording and a copper-foil dipole antennahaving a center operating frequency of 100 MHz.

Relative dielectric constants in the observable depth zones estimated using an Adeckdielectric constant meter on soil samples taken from test borings at the sites. The depthsto reflectors were determined using estimated dielectric constants for each layer.


BRGM/RP-51731-FR 71

Validation protocol: Chemical analyses of groundwater samples, taken fromstrategically installed monitoring wells, were carried out by an independent laboratoryfor hydrocarbon content in order to better understand the extent and severity ofcontamination at the sites.

Results

List of technical results: The qualitative interpretation of the GPR data is in reasonableagreement with the differences expressed by borehole well data. The depths to reflectorsand all values by well groundwater sample data typically correlated well with the GPRdata.

- north-central Arizona: the water table is interpreted to be the reflector at about 4.5 m.Apparent hydrocarbon contamination is noted near the bottom of the GPR profilebetween the surface locations of 50-80 m and in the time interval of 50-85 ns.Contaminated fluids having higher resistivity than ordinary groundwater, indicative ofleaking hydrocarbons, could cause these increased reflections in this part of thesection. The resulting contaminated groundwater and soil would have a lowerelectrical conductivity than the unaffected groundwater and soil, which would reducethe attenuation of the radar signals.

- central Utah: the water table is interpreted to be the reflector at about 3.6-3.8 m.Between the surface locations of 40 and 90 m, the water table is “smeared out” byreflections interpreted to come from hydrocarbon contamination. These dispersedhydrocarbons are less conductive than water and, therefore, enhance the radarreflectivity in this part of the GPR profile.

Synthetic illustration: See next pages.

List of technical difficulties: -


72 BRGM/RP-51731-FR


BRGM/RP-51731-FR 73


References

Sauck W.A, Atekwana E.A., Nash M.S. (1998) - High electrical conductivitiesassociated with an LNAPL plume imaged by integrated geophysical techniques. J.Environmental and Engineering Geophysics, 2, 203-212.


Problematic

Main objectives: Application and integration of different geophysical methods in orderto evaluate the cause of the attenuation of GPR signals leading to the “fuzzy/shadow”character coincident with areas of hydrocarbon contamination (LNAPLS) and explorethe cause for the discrepancy in characterizations of LNAPL contaminated sitesbetween the controlled spill experiments and field experiments at uncontrolled spillsites.

Scientific and economic constraints: LNAPL plumes in the natural environmentpresumptively cause changes in bulk electrical properties with time, from electricallyresistive to conductive behaviour, due to biodegradation.

Description of the methodology: An integrated geophysical investigation wasundertaken at a study site using GPR, electrical resistivity (dipole-dipole profiling andSchlumberger vertical electrical sounding) and self potential (SP) methods. A surveygrid of 15.24 x 15.24 m (50 x 50 ft) already established at the site was utilized.

Technical work

Site description: The study site is the former fire training cell (FT-02) located on thedecommissioned Wurtsmith Air Force Base (AFB), in Oscoda Michigan, where aquantity of fuel had infiltrated into the subsurface in 1982 and recent reports indicateelevated amounts of benzene, toluene, ethyl benzene and xylene compounds in thesubsurface along with elevated conductivities of the groundwater.

The shallow subsurface stratigraphy is uniform and consists of well sorted fine tomedium sands coarsening with depth. Underlying the sandy deposits at approximately65 ft is a lacustrine silty clay unit ranging in thickness from 20 to 100 ft. The silty clayunit is underlain by a thin glacial till deposit, resting upon the Paleozoic bedrockconsisting of the Mississippian Marshall Sandstone and the Coldwater Shale. The depthto groundwater ranges from 12 to 17.4 ft.


74 BRGM/RP-51731-FR

Geophysical techniques used:

GPR: Measurements were made with 100 MHz bistatic antennae recording for a total of400 ns. The 100 MHz Transmit-Receiver pair was set at a fixed separation of 1.4 meters(between centers). Slight horizontal smoothing was done by applying a 3-scan movingaverage filter. Two-dimensional (x,z) profile sections were produced for interpretation.

Electrical Resistivity: Two types of resistivity survey arrays were utilized, dipole-dipoleprofiling and vertical electrical soundings (Schlumberger array). The data were acquiredusing the Iris Syscal R2 resistivity system. Both data sets have been inverted to providegeoelectric sections and I-D models.

A dipole-dipole resistivity (DDR) profile was collected using an “a” spacing of 10meters and “n” varying from 1 to 4. The DDR data were inverted using RES2DINV toproduce the inverted or model resistivity section. A finite-difference forward modelingsubroutine is then used to calculate the apparent resistivity values of the model, whichcan be compared with the field data.

Three vertical electrical soundings (VES) were taken and VES data were plotted andinverted using SCHLINV that creates a 1-D model from the sounding data.

Self Potential (SP): Measurements were taken using two non-polarizing electrodes and ahigh-input impedance voltmeter. The field system measured the potential differencebetween a fixed reference electrode and a roving electrode placed at each grid node. Theraw SP data were plotted and contoured using the Geosoft® mapping system.

Validation protocol: Several borings completed by the United States Geological Survey(USGS) give stratigraphy of the subsurface and previous field investigations bring moreinformation over the study site.

Results


GPR: The GPR profiles show a very strong reflector seen in the records atapproximately 80 ns which is equivalent to a depth of 4.35 m, which is the depth to thewater table at the site. The most interesting component in the radar record is a region of“muted” (attenuated) reflections or “shadow” zone 60-70 m wide which can be spatiallycorrelated with the area of known hydrocarbon contamination, as determined from soilborings and hydrochemical studies. The signal strength begins to decrease not above theinterpreted water table reflection, but right below it and remains low to the end of therecord.

Electrical Resistivity: The electrical resistivity results complement the GPR results andassist in the interpretation of the GPR data by providing important insights into thevertical resistivity distribution causing the attenuation of the GPR signals over theplume.

The inversion results (soundings VES01-VES02) show a region of low resistivity (highconductivity) extending from 288 m to 358 m. The conductive body at depth most likelyrepresents conductive groundwater and an impacted vadose zone. Further, the area of


BRGM/RP-51731-FR 75

elevated conductivities is also coincident with the area of “muted” GPR reflections andthe area of known hydrocarbon contamination of groundwater.

The result from the third sounding (VES 04), outside the contaminated zone, shows thatthe apparent resistivity of the vadose zone is considerably higher (complements theDDR results) and the low resistivity layer seen in sounding curves VES 01 and 02below the saturated zone is absent.

Self Potential (SP): The SP data show values of +8 mV to +25 mV observed over areascoincident with known groundwater hydrocarbon contamination, GPR shadow zones,and elevated conductivities on the DDR pseudo-section. Thus, this method providesfurther evidence that a conductive groundwater plume is located below the LNAPL freeand residual product contamination zone and coincident with the dissolved hydrocarbonplume further downgradient.

Synthetic illustration: See next pages.

Conclusions: The shadowing effect prompts to an indication of radio wave attenuationdue to elevated conductivity associated with the biodegradation of the LNAPL plume inthe subsurface. This explanation is supported by DDR, VES, and SP results, which allshowed a conductive body in areas coincident with the known hydrocarboncontaminant.

The absence of vadose zone contaminant effects within the GPR records suggests thatthe resistivity method is a more sensitive method for detection of the shallow vadosezone conductivity enhancement than the GPR method, while the attenuation of the GPRreflections is an excellent mapping tool for enhanced conductivity below water table.

List of technical difficulties: Interpreting exact depths to changes in physical propertieshas led to considerable uncertainty in the vertical location of critical boundaries.


76 BRGM/RP-51731-FR


References

Buselli G., Kanglin Lu (2001) - Groundwater contamination monitoring withmultichannel electrical and electromagnetic methods. J. Appl. Geophys., 48, 11-23.

Financial support: Cooperative Research Centre for Australian Mineral ExplorationTechnologies (CRC AMET), Northern Territory Department of Lands, Planning andEnvironment (NT DPLE), ERA.

Problematic

Main objectives: Electrical and electromagnetic methods in the detection ofgroundwater contamination and seepage of the tailings dam, where wastewater withhigh concentrations of Mg2+ and SO4

2_ ions from the processing plant is stored.

Scientific and economic constraints: at the Ranger uranium minesite seepage is detectedfrom structures used to store ore processing tailings.

Description of the methodology: A combination of self potential (SP), direct current(DC) resistivity, induced polarisation (IP), and transient electromagnetic (TEM)methods with the results being interpreted in conjunction with hydrogeological data.

Technical work

Site description: Surveys have been carried out at the Ranger minesite in the NorthernTerritory, Australia. The area covered by the geophysical surveys north of the tailingsdam, consists of 2–5 m of relatively conductive sediments overlying resistive crystallinebasement. The northern wall of the tailings dam is about 1 km. The basement rocksconsist of equigranular granitic and augen gneiss (AG) with subordinate interlayeredquartz mica feldspar schist (MS) and migmatitic gneiss (MG). Augen gneiss occupiesthe majority of the survey area.

Geophysical technique used: The TEM survey (at 25-m station spacings with a 50-msingle loop geometry) was carried out with SIROTEM (Buselli and O’Neill, 1977) andby using the series inversion method (Spies and Raiche, 1980).

All other data were collected with a 64-channel system assembled at the CRC AMETusing a 16-bit ADC to sample all the channels simultaneously at a rate of 200 kilo-samples per second for each channel. From these multichannel measurements wereextracted several types of apparent resistivity and chargeability sections, such as aconventionalpole–dipole pseudosection and a Schlumberger array sounding section.Schlumberger soundings centred at 30 separate stations and were made inapproximately half a day.


BRGM/RP-51731-FR 77

SP data were obtained several times each day over a period of several days with the 2Darray of electrodes, before switching on the transmitter for DC resistivity and IPmeasurements.

In-line array DC resistivity and IP measurements were made efficiently at 10-m stationintervals with multichannel system. The data were collected simultaneously from 31receiver electrodes.

Validation protocole: Measurements using a time-domain airborne electromagnetic(AEM) method, a ground-based time-domain EM (TEM) system (Mayes, 1994), andground-based frequency domain were at first carried out (1990-1994). Without the useof IP and SP methods.

Monitored boreholes were carried out to indicate major chemical properties of thegroundwater and surface water of the area.

Results

List of technical results: In the IP survey the chargeability pseudosections, obtainedfrom Schlumberger array, show a correlation between the increasing chargeability andthe increasing ion concentration in the groundwater. There is especially one large near-surface chargeability (8650E), which is not caused by geological anomalies, but islocated in the Fault 2a and is furthermore characterized by increased ion concentrations.Thus, the IP method detects the presence of seepage in the surface aquifer and thechargeability pseudosection agrees well with the geological section and the knownseepage pattern.

In the DC resistivity survey there is little evidence of low near-surface resistivity in theapparent resistivity section, even though contaminated groundwater should be moreconductive than fresh groundwater. The apparent resistivity section does not show thenear-surface layer as clearly as the IP section.

The results of SP measurements show a high degree of reproducibility and slightdifferences between the maps can be attributed to spatial variations in telluric noise. Theinterpretation of SP data is not straight forward because the source of SP is not certain.

The TEM section plotted to a latest delay time of approximately 0.113 ms showsstructure similar to the apparent resistivity section from the DC resistivity method overthe common range of measurement stations from 8150E to 8650E. Low-resistivityvalues are measured approximately between stations 8200E and 8350E, in the same areawhere the DC resistivity method obtained a low-resistivity anomaly possibly caused bythe effects of irrigation or by a groundwater channel. In time window 35-µs delay time abroad conductive area is observed in the western area of the survey, and this areabecomes progressively more resistive in later time windows, i.e. at greater depths wherethe response of the highly resistive basement is detected.

List of technical difficulties: The region of possible near-surface seepage indicated bythe IP and SP methods is not detected by either the resistivity or TEM methods, eitherbecause the contamination does not significantly change the near-surface bulk


78 BRGM/RP-51731-FR

conductivity, or possibly because the survey configurations used do not have sufficientresolution at shallow depths. Measurements at earlier delay times (in the case of TEM)and with electrode spacings smaller than 10 m (in the case of DC resistivity) arerequired before the origin of the SP anomalies can be fully understood.

Conclusions: DC resistivity and EM methods are sensitive to the resistivity of thesubsurface, while the results of IP and SP methods are affected by the electrochemicalproperties of the ground as well as its resistivity. Of the geophysical survey methodsused to date, the IP method is the most effective for use in the detection of seepage inthe experiment area. The region of possible near-surface seepage indicated by the IP andSP methods is not detected by either the resistivity or TEM methods, either because thecontamination does not significantly change the near surface bulk conductivity, orpossibly because the survey configurations used do not have sufficient resolution atshallow depths.

However, the DC resistivity and TEM methods both produce apparent resistivitypseuodsections that are compatible with basement geology.



BRGM/RP-51731-FR 79


References

Garambois S., Senechal P., Perroud H. (2001) - On the use of combined geophysicalmethods to assess water content and water conductivity of near-surface formation. J.Hydrology, 259, 32-48.

Financial support: Elf Exploration Production.

Problematic

Main objectives: Estimating quantitatively the soil moisture content and porosity fromGPR and seismic methods. Also solving the problem of trade-off between bulkresistivity, water salinity and water content in Archie law.

Scientific and economic constraints: Geophysical methods in heterogeneous media isproblematic because the physical parameters that explain the observations are notunique, leading to an ambiguity in the interpretation.

Description of the methodology: 2 experiments were carried out with seismic studies(P-wave refraction, P and S-wave refection), multioffset GPR and dipole-dipoleelectrical profiles.

Technical work

Site description: The studied formation is located at the Anglade test site, near Pau inthe alluvial valley of the Gave de Pau river in France. It belongs to the Würm glaciationperiod and is mainly composed of coarse deposits of pebbles and sands. The water tablevaries from 1-5 m in depth, depending on the weather and season.

Geophysical technique used: The GPR measurements were conducted using aRAMAC/GPR unit system connected to 100 MHz antennas. In experiment A radar datawere collected with a set of 8 transmitters to receiver offsets, ranging from 1-8 m, 401CMPs of 8 traces spaced every 0.1 m on 40 m profile.

In experiment B CMP radar data were recorded every 4 m on a 60 m profile withtransmitter to receiver offsets ranging from 0.6 to 10 m, every 0.2 m.

Seismic surveys used 48, 50-Hz vertical geophones located every 1 m along a profilecentred around the 100MHz GPR profile. Many shots were recorded for every 12 m.

The 2D electrical profiles were carried out with 64 electrodes (experiment A) and 80electrodes (experiment B) spaced every 1m using the dipole-dipole configuration. Theprogram RES2DINV was used.


80 BRGM/RP-51731-FR

Validation protocole: Nearby wells give information of the water table. Soil analysisenlighten us about the conductivity, pH, clay composition.

Results

List of technical results: GPR estimates directly the water content of near surface rocks,using the Archie law. Also from GPR data 3-4 quasi horizontal layers can berecognized. 3 similar layers are observed in seismic refraction methods. A combinedanalysis of GPR and seismic results identifies the water table around 4 m depth and itslateral fluctuations.

2D electrical models show a higher water salinity intrusion near the surface and possiblesalinity transfers along preferential zones at depths.

List of technical difficulties: Semblance in GPR data is determined as a function of bothstacking velocity and arrival time. In order to reduce the noise a 15-250 MHz zero-phase band pass filter was applied to the GPR data. Experiment A was conducted afterstrong precipitation and the soil in this zone was almost saturated, contrary toexperiment B which was conducted on dry soil.

Conclusions: GPR data can provide reliable quantitative information of the soil watercontent from the surface, avoiding drilling. Seismic reflections and refraction’s areinfluenced by partial saturation and do not follow the phreatic surface. Also wavevelocity can de directly inverted into water saturation.

This illustrates the advantage of combining different methods, which are based ondifferent physical parameters. However, this report is useful only for the way thegeophysical methods were carried out, as it is specifically focused on Archie law andthe way the water content is determined.


BRGM/RP-51731-FR 81


References

Orlando L. (2002) - Detection and analysis of LNAPL using the instantaneousamplitude and frequency of ground-penetrating radar data: Geophysical Prospecting,50, 27-41.


Problematic

Main objectives: Reporting the ability of a GPR survey to detect LNAPL floating on thewater table in an area where the thickness of the hydrocarbon layer can also bedetermined.

Scientific and economic constraints: In northern Italy an area was contaminated withgasoline and diesel after a break in a hydrocarbon pipeline. Restoration of the areastarted later.

Description of the methodology: 2 surveys (1996-1997) were carried out at the finalphase of restoration using ground-penetrating radar. Comparison of the GPR data,acquired at different times along the same profile and for different LNAPL thicknesses,was made. Theoretical radar responses were also calculated for models constructed onthe basis of hydrogeological characteristics of the investigated site.

Technical work

Site description: The study area is characterized by alluvial sediments of the Holocene-Pleistocene age with alternating sandy-gravel permeable and impermeable deposits ofvariable thickness.

Geophysical technique used: A Sensor and Software EKKO Pulse 100 equipped with200 MHz antenna was used to carry out the survey.

Validation protocole: Several piezometers and wells are spread all over the area.

Results

List of technical results: In the northern zone of the area there is slight contamination.On the contrary in the southern zone contamination was found during the first as well asthe second survey. In the contaminated area the velocities of the electromagnetic wavesare higher in the layer above the water table, in comparison to the uncontaminated area.


82 BRGM/RP-51731-FR

It can also be seen that the reflection from the water table has greater amplitude in thecontaminated zone, which cannot be attributed to the geology.

The theoretical model depends on the type of contaminant and the time of measurement.The instantaneous phase gives good lateral continuinity to the reflectors, but it does notproduce any significant laterel difference in the water table reflection.

List of technical difficulties: A Butterwoth passband filter (70-180 MHz) and anexponential constant gain were applied to the GPR record. The study was made 2 yearsafter the contaminant spill.

Conclusions: Information concerning contaminant thickness and its lateral variation canbe obtained from the combined analysis of the three attributes (instantaneous amplitude,frequency and phase) and the value of the reflection amplitude. In this case there is goodcorrespondence between theoretical and field data. The study area must include both thecontaminated and uncontaminated zone.


BRGM/RP-51731-FR 83


References

Grumman Jr. D.L., Daniels J.J. (1995) - Experiments on the Detection of OrganicContaminants in the Vadose Zone, J. Environmental and Engineering Geophysics, 31-38.


Problematic

Main objectives: Detecting organic contaminants using GPR and assessing GPRsensitivity to contaminant behavior in the vadose zone.

Scientific and economic constraints: -

Description of the methodology: GPR surveys were conducted to observe the responseof GPR to the presence of free-phase contaminant pools and their associated vaporphase effects. Tank model studies were performed to assess GPR sensitivity to organiccontaminants under more controlled conditions.

Technical work

Site description: Field experiments were performed (1993) at gasoline service stationsthat were closed in response to a documented hydrocarbon spill on sites near Cleveland,Ohio and in northern Indiana. A range of typical glacio-lacustrine soil types werepresent at each site. The soils and stratigraphy at the sites are fairly uniform and semi-homogenous. Free-phase gasoline and strong contaminant vapor were observed at bothsites.

Geophysical technique used: The GPR field surveys consisted of establishing multiplegrids using 0.6 m line spacing. The antennas used included 300 MHz, 100 MHz and80 MHz center frequency antennas. Digital processing of the data included simple timevarying gain adjustment and bandpass filtering to reduce high- and low-frequencynoise. 2-D and 3-D profile sections of each survey grid were produced forinterpretation.

Tank model study: A Plexiglas model tank was used to evaluate in a controlled mannerthe GPR response to various soil, soil moisture, and contaminant saturation conditions.The fluids used were gasoline, diesel fuel and water. The GPR testing was performed bymoving either a 500 MHz or 900 MHz antenna across the top and one side of the tank.The data were collected in a distance-based mode using 17 to 20 survey lines for eachside and displayed 1i 2-D and 3-D cross sections.


84 BRGM/RP-51731-FR

Validation protocole: Additional soil borings and chemical testing were conductedwithin several days of the GPR surveys to provide timely information on thecontaminant distribution.

Results

List of technical results: 3-D data displays from the northwest Indiana site illustrate adistinct region of muted GPR reflections that closely corresponds to the area of theobserved hydrocarbon contamination based on the interpretation of the soil boringobservations.

Data from the Cleveland area site, however, showed no discernible correspondence withthe observed extent of the free-phase contaminants and associated vapor phase.

Increased travel times occur at the top of the experimental tank after gasoline is added.This may indicate some redistribution of soil moisture toward the top of the tank afterthe addition of gasoline to the bottom of the tank. These results illustrate the subtle tonondetectable changes in GPR response which may occur when organic compounds areintroduced in a controlled experimental setting.

List of technical difficulties: Vapor phase contaminants can play significant role inorganic contaminant migration through the vadose zone and the detection of theseeffects using GPR is poorly understood. Additional experimentation (further tank modelexperiments) is required to develop a better understanding of GPR sensitivity tocontaminant processes in the vadose zone.

Conclusions: The results of the field and tank model experiments indicate that subtle,discernible changes do occur in the observed GPR response over spills of volatileorganic contaminants. The field results show that 3-D imaging of these data can assistwith interpreting the subsurface conditions including organic contaminants detectionwhen favourable conditions prevail. In contrast, the initial results of the tank modelexperiments show that organic contaminant vapor effects in the vadose zone may bedifficult to decipher using GPR alone.


BRGM/RP-51731-FR 85


References

Daniels J., Roberts R., Vendl M. (1992) - Site studies of ground penetrating radar formonitoring petroleum product contaminants: Proceedings of the symposium on theapplication of Geophysics to engineering and environmental problems, 597-609.

Financial support: United States Environmental Protection Agency.

Problematic

Main objectives: Reporting the ability of a GPR survey to detect and characterizeLNAPL contamination.

Scientific and economic constraints: At the ElectroScience Laboratory of the Ohio StateUniversity an experiment was conducted in a sand test pit (5 x 5 x 2.9 m deep). Also acontrolled study has been carried out for the past two years at a gasoline storage facilityin Northern Indiana.

Description of the methodology: Surveys were carried out in Ohio University withseveral common commercial antennas over plastic containers filled with kerosene,water and air. Another set of containers was filled with the host sand saturated withkerosene and water, while a third set of containers was filled with a combination ofkerosene and water. All the containers had a capacity of 19 liters with dimensions of0.305 x 0.305 x 0.229 m.

On the other hand in Indiana repeat measurements were made in August-October-December of 1990 and January of 1991.

Technical work

Site description: No geological information is given about the gasoline storage facility.

Geophysical technique used:

Test pit: A detailed grid of lines spaced 15 cm apart were run with each of the 500-300-100 MHz antennas. An unshielded 80 MHz antenna was also tested but interferenceeffects from objects above the surface rendered the data unusable. All the data wereprocessed using a low-frequency cut-off filter and a two-dimensional frequency-wavenumber filter to reduce the ringing on the raw field data.

Field example: Two survey lines were made in order to find out the reason for thedecrease in the received signal amplitude. Line A is removed from the concentration ofthe gasoline, while line C extends into the maximum concentration of the gasolineabove the water table.


86 BRGM/RP-51731-FR

Validation protocol: Four repeat data sets were carried out in Northern Indiana.

Results

List of technical results: The 500 MHz antenna shows distinct anomalies formeasurements across each of the containers. The anomalies are less prominent for thekerosene filled containers than for the water filled containers. There is also a 180-degreephase shift for the response over the kerosene and air filled containers compared to thewater filled container. The amplitude of the response for the 300 MHz antennas over thepartially filled kerosene is more distinct than for the 500 MHz antennas.

In the field example of Northern Indiana results of the study show the depth of the watertable and the affect of seasonal variations and high rainfall on the GPR records. Alsotwo possible explanations for the decrease in the received signal amplitude of GPRrecord are given.

List of technical difficulties: The data sets of the sand test pit were not normalized withrespect to one another for time range-gain, and the zero times were in some casesdifficult to determine exactly.

Conclusions: Results of controlled surveys at the Ohio State University demonstrate thatthere is a clear high amplitude GPR anomaly over plastic containers filled with dieselfuel. On the contrary studies in Northern Indiana show a correlation between thedecrease of the GPR signal amplitude and the presence of gasoline. Explanations for theobserved high amplitude reflections over the confined hydrocarbons in the test pipe andthe low amplitudes in the field include: 1) the hydrocarbon product may be contained insmall-dispersed concentrations in the vadose zone or 2) the hydrocarbon product mayhave a high loss tangent. This reason could help to explain both the observed decreasein amplitude for the electromagnetic wave propagating through the capillary fringe andthe high amplitude reflections from the saturated hydrocarbons.


BRGM/RP-51731-FR 87


References

Brewster M.L., Annan A.P., Kueper B., Sandar K. (1995) - Observed migration of acontrolled DNAPL release by geophysical methods: “Ground Water” Magazine, 33, 6,977-987.

Financial support: Solvents-In-Groundwater.

Problematic

Main objectives: 1) evaluating various geophysical techniques for detecting andmonitoring DNAPL below the water table; 2) describing the migration and finaldistribution of the controlled DNAPL release.

Scientific and economic constraints: 770 liters of a DNAPL tetrachloroethylene (PCE)were released into an isolated volume of a completely natural sandy aquifer. The releasewas monitored over a period of 984 hours with a variety of geophysical methods.

Description of the methodology: At Canadian Forces Base Borden near Toronto,Canada a controlled experiment was conducted within a 9 x 9 x 3.3 m deep volume. Adual wall containment cell was instructed to prevent contamination of the externalaquifer. Both an inner and an outer wall of sealable-joint steel sheet piling were keyed0.6 m into the clay aquitard, which acted as a lower barrier against contaminant leakage.Within the cell the water table was maintained at 15 cm below ground surface.

PCE was injected under a constant head through a 6 inches PVC standpipe at the centerof the cell. The PCE was dyed with a hydrophobic red dye to facilitate visualidentification and spectrophotometer measurements.

Technical work

Site description: The site geology comprises 3.3 m of fine to medium grained sand,underlain by 3 m of medium stiff clay. The clay layer underlain by a 13 m of clayinterbedded with sandy laminations and sand lenses. This clay is composed primarily ofmuscovite and chlorite with trace amounts of smectite and kaolinite. The sand aquiferwas deposited by glacial Lake Algonquin approximately 12,000 years B.P in aprograding foreshore beach environment. The aquifer is considered relativelyhomogeneous.

Geophysical technique used: Several geophysical methods such as ground penetratingradar, time domain reflectometry, in situ resistivity, core analysis and a neutron soilmoisture probe were used. A series of cores (CP-1 to CP-8) was retrieved from the cellapproximately 1000 hours after the start of the injection. Cores CP-1 to CP-4 were cut


88 BRGM/RP-51731-FR

into 5 cm intervals and cores CP-5 to CP-8 into 8 cm intervals. The PCE within eachcore section was extracted into methanol.

Eight access tubes were equally spaced on a circle of 3 m radius about the centralinjection point. These tubes were used for neutron probe measurements, density loggingand borehole radar. Two resistivity probes, two time domain reflectometry probes(TDR) and a ninth access tube were located at a radius of 1m from the injection point.

Data from 16 radar lines, spaced every meter across the cell, were collected during eachmeasurement cycle of the experiment. The radar traces were collected at least every5 cm along each of the lines. Radar data were collected at three different centerfrequencies: 200-500-900 MHz. The 200 MHz data acquired with a Sensors andSoftware Pulse Ekko IV, while the 500 and 900 MHz data with a Geophysical SurveySystems SIR-7.

Validation protocol: A previous release was performed in a 3 x 3 m cell. A smallervolume of PCE (231 liters) was spilled, but the same injection conditions were used. Acomparison between the former and the latter release showed a significantly differentinfiltration rate and PCE migration rates.

A sequence of 200 MHz radar data collected prior to the release so as to show thedielectric stratigraphy and the ground surface conditions.

Results

List of technical results: Once the release began an entire suite of geophysicalmeasurements was collected every eight hours. The PCE formed a pool on a lowpermeability layer at approximately 1 m depth and spread over an area exceeding 32 m2.In its course of downward migration the PCE subsequently formed eight smaller pools.At the end of the experiment an estimated 41 % of the total PCE volume remainedtrapped in the upper pool.

From the radar data we concluded that the depth of investigation decreases and theresolution increases as the frequency increases. The aquitard at the bottom of the cell isvisible in the 200 MHz data, but not in the 500 and 900 MHz. A single horizontalaccumulation of PCE is visible at approximately 1 m depth. In the 500 MHz data thisaccumulation appears segmented and more sharply defined. The 900 MHz data revealthis accumulation is in fact composed of several thin layers. In saturated Borden sand200-500-900 MHz data have a vertical resolution of approximately 10-4-2 cmrespectively.

There is a good correlation between pools in the core and the radar data. Between 48and 100 % of the PCE mass was accounted for by radar measurements. The center ofthe mass moved a total of 0.5 m southeast and 1.3 m downward. The resultsdemonstrate that natural heterogeneities, even in a relatively homogeneous aquifer, cancause DNAPL to spread laterally over large areas in the subsurface.


BRGM/RP-51731-FR 89

List of technical difficulties: The observations made with GPR are limited by thevertical resolution of the technique, approximately 10 cm at 200 MHz. This suggeststhat higher PCE saturations would have been measured with a finer sampling interval.Vertically migrating PCE and narrow vertical zones of residual saturation are notdetected by surface radar.

BRGMSERVICE AMÉNAGEMENT ET RISQUES NATURELS

Unité Mesures, Reconnaissance, Surveillance3, av. Cl. Guillemin – BP 6009 – 45060 Orléans cedex 2 – France –Tél. : 33 (0)2 38 64 34 34

Documents

Specifications for survey methodology with combined techniquesinfoterre.brgm.fr/rapports/RP-51731-FR.pdf · Specifications for survey methodology with combined techniques BRGM/RP-51731-FR