Multidisciplinary Investigation of a Landfill and Its Host Sediments

8/19/2019 Multidisciplinary Investigation of a Landfill and Its Host Sediments

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Diss. ETH No. 14082

Multidisciplinary investigation of a landfilland its host sediments

A dissertation submitted to the

SWISS FEDERAL INSTITUTE OF TECHNOLOGY ZURICH

for the degree ofDoctor of Natural Sciences

presented byREMO DEIACO

Dipl. Phys. ETHborn April 16, 1967

citizen of Liechtenstein and Italy

accepted on the recommendation ofProf. Dr. Alan G. Green, examiner

Dr. Hansrnedi Maurer, co-examtnerDr. Peter Jordan, co-examiner

2001


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"here is iA,otkiiA,g noblerthan to put up with a few inoom/eniei^ôesLike snakes and dust

or the sake of absolute -freedom

lack Kerouac

%ommt £eit, Aommt (Rat

(fcanAßäAe*

Vv/jr flauer ja Zeit"

Remo De Taeo (an Jer Doktorprüfung


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1 Contents

Contents

Zusammenfassung 1

Abstract 3

Chapter 1: Introduction 5

1.1 Waste management in Switzerland 5

1.2 Non-destructive site assessments using geophysical techniques 7

1.3 Considered methods of investigation 8

Diffusive electromagnetic

(EM) methods 8

Magnetic methods 10

Seismic methods 12

Ground-penetrating radar 15

1.4 The study object 17

Landfill 18

Geology 18

1.5 Outline of the thesis 20

Chapter 2: An integrated geophysical study of a landfill and its host

sediments 41

2.1 Abstract 42

2.2 Introduction 42

2.3 The Härkingen test site: Geological setting 43

2.4 Data acquisition ...44

Electromagnetic and magnetic data 44Georadar data 44

2.5 Data processing 45

Electromagnetic and magnetic data .....45Georadar data ......46

2.6 Principal features of the data .........49

Electromagnetic and magnetic data 49

Georadar data volume ...50

2.7 Discussion .........51

Characterizing the waste material ......51

Delineating the landfill boundaries .......52

Mapping a buried water pipe .........53

Characterizing the host sediments and mapping the

groundwater table ..53


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Contents ii

The R reflector and groundwater table 54Gravel sheets and scour pool 54

Minor faulting 55

Flow direction of the ancient river system 55

Determining the effects of contamination 56

2.8 Conclusions 56

Chapter 3: A combined seismic reflection and refraction study of a landfill

and its host sediments 81

3.1 Abstract 82

3.2 Introduction 82

3.3 Local geology and Härkingen landfill 83

3.4 Seismic data acquisition 843.5 Identifying reflections in highly complex data 85

3.6 Seismic reflection data processing 86

3.7 Picking, inverting and ray tracing 88

Picking first-breaks 88

Tomographic inversion (refracted arrivals) 88

Ray tracing refracted and reflected arrivals 88

3.8 Gradient input model 89

Tomographic inversion results 89

Contradictions between Model 1 and other data 893.9 Trial-and-error Model 2 90

Ray trace modelling refracted and reflected arrivals 903.10 Refined Model 3 91

Tomographic inversion results 91

Combining the results of the refraction and reflection

analyses 92

3.11 Conclusions 92

Chapter 4: Achievements and outlook 117

4.1 Achievements 117

4.2 Outlook 118

4.2.1 Efficiency in data acquisition for waste disposal studies 119

Simultaneous recording coordinate and geophysical data 119

Increasing speed of seismic receiver deployment 119

Recording less data by careful planning 1194.2.2 Lateral and vertical localization of waste material 120

Magnetic methods for routine estimation of

depths-to-sources 120

Diffusive electromagnetic method and georadar 120


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iii Contents

Seismic methods 121

4.2.3 Characterization of waste material 123

Electromagnetic methods 123

Magnetic methods 1244.2.4 Characterization of host sediments 125

Georadar method 125

Seismic method 126

4.2.5 Concluding remark 126

References 133

Acknowledgements 169

Curriculum vitae 171

Appendix A: Differences between a 50 - 50 MHz and a 50 -100 MHz

georadar antenna configuration (Chapter 2) 173

Appendix B: Accuracy of the georadar velocity analysis (Chapter 2) 175

Appendix C: Effects of a seismic velocity inversion in the shallow

subsurface (Chapter 3) 179

Appendix D: Effects of near-surface waveguides on shallow

high-resolution seismic refraction and reflection data 181

Appendix E: International deep reflection survey along the

Hungarian Geotraverse 193

Appendix F: Georadar and electromagnetic studies of a landfill (1) 197

Appendix G: High-resolution, high-fold seismic reflection profileacross a landfill 203

Appendix H: Georadar and electromagnetic studies of a landfill (2) 209

Appendix I: Georadar, electromagnetic, and magnetic studies of alandfill and its host sediments 215


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Contents i\


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1 Zusammenfassung

Zusammenfassung

Die Schweiz verabschiedete 1998 eine Verordnung, welche alle Kantone verpflichtet,belastete Standorte (z.B. Deponien) auf ihr Gefahrenpotential und die Art eventuellschon aufgetretener Umweltbelastung hin zu untersuchen. Selbst wenn jeden Tag einerder geschätzten 50 000 in Frage kommenden Standorte abgeklärt werden könnte, würdees über 100 Jahre dauern, dieser Verordnung nachzukommen. Die unglaubliche Anzahldieser Standorte und die Notwendigkeit, schnell zu handeln, wenn eine Verschmutzungder Umgebung entdeckt wird, verdeutlichen die Wichtigkeit, zuverlässliche, schnelleund billige Untersuchungsstrategien zu entwickeln. Viele Studien in den letzten zehnJahren haben das Potential von geophysikalischen Methoden zur Untersuchung von

Deponien aufgezeigt. Allerdings hat kaum eine der vorgestellten Techniken alleerforderlichen Eigenschaften (Zuverlässigkeit, Schnelligkeit und tiefe Kosten) erfüllt.Meine Doktorarbeit hat gezeigt, dass die Zuverlässigkeit durch Kombination derResultate von


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Zusammenfassung i

Grundwasserspiegel in 9 - 16 m Tiefe zu durchdringen. Südöstlich der Deponie bildetenGeoradar-Reflexionen von vier Schichtgrenzen die räumliche Lage von ausgedehntenKiesschichten ab. Südlich und nördlich der Deponie erzeugten der Grundwasserspiegel

zusammen mit der Grenzschicht zwischen stark permeablen Kies und Sand (oberhalb)und schwach permeablen Lehm und Silt (unterhalb) die stärkste Rcflektion der 3-DGeoradar-Untersuchung. Andere wichtige Entdeckungen waren ein oval-geformtesObjekt, das möglicherweise das Abbild eines ehemaligen Auswaschbecken ist, unddeutliche, längliche Gebilde, die wahrscheinlich ehemalige mäandrierende Flusskanäledarstellen. Diese lithologischen Details lieferten wichtige Informationen zum generellenFliessregime unterhalb und ausserhalb studieren.


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3 Abstract

Abstract

In 1998, Switzerland passed a law that obliges each of its cantons to assess potentiallyharmful locations (e.g., landfills) for their risk or degree of pollution. Even if on eachday, one of the estimated 50 000 locations could be fully investigated, it would takemore than 100 years to obey this law. The incredible number of such sites and the needto react quickly when contamination is discovered, highlight the importance ofdeveloping reliable, fast and inexpensive investigation strategies. Many studies over thepast ten years have demonstrated the utility of geophysical methods for analysinglandfills. However, the presented techniques rarely satisfied all three requirements:dependability, speedy results and low cost. My thesis work has demonstrated that

reliability may be improved by combining the results of different geophysical methods.Speed was not a critical issue during my investigations, but ongoing parallel studieshave shown the feasibility of decreasing acquisition time and, as a consequence,reducing the costs.

I chose the "Fritschi" landfill in Härkingen (in the following, this landfill will be referee!to as the Härkingen landfill) as an appropriate test object for application of severalgeophysicaltechniques.Extensiveelectromagnetic,magnetic,georadarandseismicdatawererecordedacrossthelandfillanditshostsediments.Objectiveswereto:(i)delineatethelateralanddepthextentofthelandfill,(ii)characterisethewastematerial(e.g.,tolocatesteeldramsthatcouldcontaindangerouschemicals),(iii)mapthedepthtothegroundwatertable,and(iv)imagegeologicalunitswithintheadjacentsediments,whichcouldactaspathwaysorbarrierstoanyleakingcontaminants.Independently,three-dimensionalgeoradardataandanovelcombinationofarealapparentelectricalconductivityandreduced-to-the-polemagneticdataallowedthelandfillborderstobedefinedwithanaccuracyof-2.5m.Thiswasasignificantimprovementonthe10-15maccuracyobtainedbyusingstandardapparentelectricalconductivityandmagneticmapsattheHärkingenlandfill.Varioustypesofconductive-resistiveand/ormagnetic-non-magneticmaterialwereidentifiedthroughoutthelandfill.Verylargeamountsofironandsteel(i.e.,exceedingthevolumeand/ormagnetizationofseveral50000-litresteelstoragetanks)weredetectedwithinarelativelynarrowzoneextendingalongthesouthernandwesternedgesofthelandfill.Lowapparentelectricalconductivitiesof


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Abstract 4

meandering stream channels. These lithological details provided critical information onthe general flow regime beneath and around the landfill.

To delineate the base of the landfill and further map geological interfaces within theadjacent undisturbed ground, a high-resolution (CMP spacing = 0.125 m), high-fold(>120 in the central part of the study area) seismic survey was conducted. Unfortunately,the recorded data suffered from severe source-generated noise and large lateral andvertical velocity variations, making it extremely difficult to identify reflections onprocessed shot and CMP gathers. Standard stacking and time-to-depth conversion of aquasi-continuous sequence of events interpreted as reflections led to no meaningfulcorrelation with boundaries intersected in nearby boreholes. In an attempt to address thisissue, improved velocity estimates were determined via tomographic inversions of~ 183 000 first-arrival times. Disappointingly, the velocity model that resulted from thefirst suite of tomographic inversions did not correspond with the borehole informationand the seismic reflection section. By including the traveltimes of the assumedreflections and the known depths to the corresponding reflectors as constraints on theinversion process, a second suite of tomographic inversions yielded a satisfactorymodel. This model included a thin layer of humus and sandy clay (velocities of 400 -1000 m/s) overlying (i) low-velocity waste material (200 - 600 m/s) within the landfill

boundaries and (ii) a southwards-thickening sequence of fluvial deposits (600 - 900 m/s)south of the landfill. Extending across the entire profile at greater depth was asouthward-thinning layer of lacustrine sediments (2000 - 3800 m/s) and


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5 Introduction

Chapter 1

Introduction

With the nearly exponential growth of the Earth's population, the pressure on such vitalresources as water, air. and land has risen considerably over the past few decades.Whereas the need for protection of water and air is increasingly recognised in theindustrialised world, the land is still mostly considered unlimited, especially in the largecountries. This results mainly from the view that built-up or contaminated land does notthreaten our lifes directly. Yet, erosion, excavation, farming, construction, pollution, andnatural and man-made hazards may lead to significant destruction of valuable land.

In Switzerland, about 20 % of all reserves of water arc in the ground, residing in highlypermeable layers (e.g., gravel deposits). Nearly 80 c/c of consumed water originates fromthese sources (BFS/BUWAL, 1997). Although the Swiss environmental protection lawwas passed in 1983 (USG, 1983), it was not until 1995 that an article regarding landprotection was added to the revised environmental protection law (USG, 1995). Threeyears later, additional regulations concerning the impact on the land were enacted to

"preserve the

reproductiveness of the

ground in the

long term''

(VBBo, 1998).

1.1 Waste management in Switzerland

By September 1996, 35 000 potentially "contaminated" areas were identified,57%ofwhichwerelandfills,38c/cindustrialsites,and5c/cwerethelocationsofaccidentalspills.Anestimated,butmorerealisticnumberof'"contaminated"areasis-50000(BFS/BUWAL.1997).Some3000-4000sitesarebelievedtorequireremediation.ThetotalcostsarcestimatedtobefivebillionSwissfrancs(SFr)overthenext25-30years.Over80%ofthesesiteswillconsumelessthanSFr1meach,whereas10seriouscaseswillcost>SFr50meach(BFS/BUWAL,1997).Thissituationisaconsequenceofthelackofrigorouswastedisposalguidelinesuntilthemiddle1980's.Then,foratransitionalperiod,wastemanagementwasbasedontheairprotectionregulations(LRV,1985)andonrecommendationspublishedin1986(BUWAL,1986).Technicalregulationsconcerningwastematerial(TVA,1990)werethefirstlawsconcerningexplicitelythehandlingofrefuse.Theirscopewasto"protecthumans,animals,plants,water,air.andgroundagainstpollutionbyreducingandtreatingwasteinanappropriateway".Themostrecentregulationsconcerningheavilyusedlocationswereenactedin1998:(i)Cantonsmustlistalllandfillandindustrial s i t e s


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Introduction 6

as well as all locations of accidental contamination, (ii) By means of reconnaissance

investigations, the innocuous cases should be identified and eliminated from furtherconsideration, (iii) Detailed surveys must clarify the risk or degree of pollution, (iv)

Appropriate remediation measures must be employed to minimise or stop, in the longterm, the release of dangerous substances (AltlV, 1998).

The present and future policy is to: (i) avoid waste (through high fees), (ii) reduce

pollutants (through prohibition by law), (iii) recycle, and (iv) treat waste in a non-polluting way using state-of-the-art and clean combustion plants. Already in 1990, adecision was made to stop the dumping of untreated and burnable household waste bythe beginning of 2000 (TVA, 1990). In view of the urgency to defuse the waste problem,additional measures, such as fees for waste disposal (in 2001) and liability insurancesfor dump sites (in 2002), have been scheduled for the near future (BUWAL, 1999).Table 1.1

provides a

chronological overview of the

important guidelines, laws, and

regulations concerning waste disposal and protection of land.

Every new waste disposal site must be one of three types (TVA, 1990):• landfill containing inert substances, such as construction waste with

little or no harmful material; no sealing of landfill is necessary;• landfill containing heavy metal-rich waste, such as slag from

combustion plants; special treatment of waste, sealing of the landfill and

collecting of leachates are necessary;• reactor landfill, in which


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7 Introduction

1.2 Non-destructive site assessments using geophysicaltechniques

The estimated 50 000 "contaminated" areas and the legal requirements to classify and, ifnecessary, remediate them, call for reliable, fast and inexpensive methods ofinvestigation. Important points of concern are:

• location of the landfills and their lateral and depth extent;• pollutant plumes emanating from the waste;• possible leakage pathways of pollutants into the surrounding host

sediments;• position of the sites within the groundwater flow regime;• amount of contaminated soil and pollutant types in cases where

remediation is required.

The typically large contrasts of such physical properties as electric conductivity a,magnetic susceptibility ll, and acoustic and electromagnetic wave progagationvelocity v between natural and disturbed ground makes non-intrusive geophysicalmethods suitable for landfill investigations. Mapping changes of these properties allows,for example, the lateral and depth extent of waste material and contaminated soil to bedetermined, metal objects to be located, and structures within the natural ground (e.g.,Quaternary sediment - bedrock interface, groundwater table, aquifers and aquitards) tobe imaged.

Geophysical methods offer opportunities for either reconnaissance surveys prior toextensive drilling programs or comprehensive detailed studies in which sets


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Introduction 8

(electromagnetic, magnetic, georadar, and seismic refraction and reflection surveys) toyield a detailed image of a typical composite landfill and its host sediments.

Table 1.2

at the end of thischapter gives

a

representative overview of

landfill studiesconducted in the past ten years. The investigation tools include the well-known DC-

resistivity, self-potential (SP), induced polarization (IP), frequency-domainelectromagnetic (FDEM), transient electromagnetic (TEM), radio magnetotelluric(RMT), very low frequency resistivity (VLF-R). magnetic, georadar (GPR), seismicreflection, and seismic refraction techniques. Less used are the very early transient

electromagnetic (VETEM), controlled source audio-frequency magnetotelluric(CSAMT), thermal infra-red, surface wave attenuation, and gamma radiation methods.The frequency of use of the DC-resistivity (employed in 36 % of all listed landfillinvestigations), frequency-domain electromagnetic (in 32 %), and magnetic (in 25 %)methods is due their easy handling, relatively low cost and amount of experience gainedwith them over the past years. Becauseofthehighcostsofdrilling,non-intrusivemeasurementshavebeenrarelyconstrainedwithextensiveboreholeinformation(Lanzetal,1994,1997a,1997b,1998a,1998b;Tezkanctal„1996,2000;Zacheretal,1996;DeIacoetal.,1996;1997a,1997b,1998;Fontetal,1998;Greenetal.,1999).Inthepastthreeyears,thenumberoflandfillinvestigationshasconsiderablygrown.Nevertheless,inmostcasesonlyoneortwotechniqueshavebeenused,whereasmulti-disciplinarystudieshavebeenexceptions(Lanzetal.,1998b;Baileyetal.,1999;Greenetal,1999;Tezkanetal.,2000).1.3ConsideredmethodsofinvestigationAppliedgeophysicalmethodswerefirstemployedfortheexplorationandexploitationofhydrocarbonsandmetallicores(Nettleton,1949;Beatty,1953;Lundberg,1955;Salt,1959;Breene,1964;Steenland,1965;HoodandKellogg,1968).Inotherwordstheywereusedintheserviceofdebitingtheground.Duringthepasttwodecades,theusefulnessofgeophysicsfornon-intrusiveimagingoftheshallowsubsurfacewasdiscoveredanddeveloped(Ward,1990;Nabighian,1991).Applicationshaverangedfromnumerousgroundwaterandsedimentarystudiestoarchaeologicalandenvironmentalsurveys(e.g.,McNeill,1990;Zacheretal,1996;Bükeretal.,1998a.1998b,2000;Lanzetal,1998b;Ogilvyetal..1998;BachrachandNur,1999;Flerwangeretal.,2000).Inthefollowing,IdescribethosetechniquesIbatwereconsideredintheframeworkofthisproject:diffusiveelectromagnetic,magnetic,seismicandground-penetratingradar.Diffusiveelectromagnetic(EM)methodsMethodsandtoolsAvarietyofelectromagnetictools,suchasfrequency-domainelectromagnetic(e.g.,groundconductivitymeterEM31),transientelectromagnetic,radiomagnetotelluric, a n d


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9 Introduction

very low frequency resistivity have been developed for the investigation of thesubsurface (Frischknecht et al., 1991; Nabtghian and Macnae, 1991; McNeill andLabson, 1991; Vozoff, 1991 ; Zonge and Hughes, 1991 : Pellerin and Alumbaugh. 1997).The

very early time

electromagnetic (VETEM) method is a new technology especiallydesigned for shallow applications (Smith et al., 2000; Wright et al., 1999, 2000a.2000b). The electromagnetic methods are currently amongst the most popular andmultifaceted type of geophysical techniques. This is mainly a result of their highacquisition speed. Inductive coupling allows data to be collected without the need tohave physical contact between the electromagnetic equipment and the ground.

Processing and interpretationGeneral basic research over the past few decades has led to an improved understandingof the interactions of electromagnetic fields with matter (Wait, 1955 and 1960; Grantand

West, 1965; Hohmann, 1971; McNeill et al..

1984; Tabbagh, 1985; Ward andHohmann, 1987; West and Macnae. 1991). As a consequence, numerous 2-D and 3-D1999).


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Introduction 10

Environmental (landfill) studiesClosely associated with groundwater studies are investigations of landfills, industrialregions, and the sites of accidential spills of pollutants. The use of frequency-domain

electromagnetic systems for mapping the lateral extent of anomalous conductive zonesis widespread because of their rapid recording, processing and interpretationcharacteristics (Jansen et al, 1992; Lanz et al., 1994; De laco et al., 1997b; Black andCarpenter, 1998; Nobes and McCahon, 1999; Wisén et al., 1999). On the other hand, thedepth sounding capability of the transient electromagnetic technique can be used to mapboth the lateral and vertical extent of waste material and groundwater pollution (Buselliet al., 1990; Senos et al., 1994). Zacher et al. (1995) combined 2-D inversion results ofmore than 500 radio magnetotclluric soundings recorded on a closely spaced grid toyield a detailed pseudo 3-D image of an investigated landfill. So far. characterizing thecontentsand


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11 Introduction

"straight-slope" methods, and Smith's rale (Nettleton, 1954, Smith, 1961). Over the pastdecade, various modifications of Euler deconvolution and numerous 2-D and 3-Dinversion and modelling strategies have been designed to determine the shape and

location of magnetic bodies (Reid et al.. 1990; Mnshayandebvu et al., 1999; Fedi andRapoUa, 1999:^ Furness, 1999; Hcrwanger et al.. 2000). Salem et al. (2000) havepresented a fast and accurate method for locating buried steel drums using neuralnetworks. Many of the recent processing and interpretation advances are based onBhattacharya's pioneering theoretical work. Among other things, he presented a methodfor computing the total magneti7ation vector of a rectangular block-shaped body (e.g.,Bhattacharyya, 1965. 1966,^1972, 1980).

Exploration and deep crustal applicationsSweden was reported to undertake commercial iron-ore prospecting as early as in the17th

century by looking for local anomalies of the

Earth's magnetic field are


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Introduction 12

potential-field methods, such that they suffer from similar non-uniqueness limitations aselectromagnetic techniques.

Seismic methods

Methods and tools

Commercial use of seismic reflection and refraction methods began in the 192()'s. Sincethen, the main purpose of seismic techniques has been oil prospecting with target depthsof several thousand meters (Sheriff and Geldart, 1995). A little more than a decade ago,introduction of the "optimum window"' and limited fold techniques marked thebeginning of the wide use of seismic reflection imaging in shallow engineering andenvironmental studies (Steeples and Knapp, 1982; Hunter et al., 1984; Steeples, 1984;Knapp and Steeples, 1986; Miller et al., 1989; Pullan and Hunter, 1990; Steeples and

Miller, 1990). Promising results have been obtained in recent studies to close the gapbetween the resolution provided by georadar data and that provided by very high-resolution seismic reflection data (Steeples et al., 1999; Baker et al., 1999, 2000).Various approaches for optimizing the shallow seismic reflection technique haveincludeddecreasingthetimefordeploymentofgeophonesandcablesbymeansofalandstreamer(VanderVeenandGreen,1998;VanderVeenetal.,2001),optimizingthenumberofgeophonepositionsbycarefulanalysisandmodelling(Spitzeretal.,2000),andincreasingresolutionpowerbyemployingahigh-frequencyportablevibrator(Ghoseetal.,1998b)andrecordinglowervelocityshear-waves(Ghoseetal.,1998a).Inhydrocarbonexploration,theseismicrefractionmethodwassoondisplacedbythehighimagingpoweroftheseismicreflectiontechniquebutremainedthereinanimportanttoolfordeterminingrefractionstaticcorrections(Yilmaz,1987;MacridesandDennis,1994;SheriffandGeldart,1995;Cox,1999).Forsimplestructureshowever,theseismicrefractiontechniqueoffersarelativelyinexpensiveandrobustalternativetothetime-consumingacquisitionandprocessingofseismicreflectiondata.Overthepastdecades,itsfieldofapplicationhasshiftedtostudiesoftheshallowsubsurface(Musgrave,1967:Green,1974:Lankston,1990).Recently,methodshavebeendevelopedtodetermineparametersotherthantheP-wavevelocity.Invertingphasevelocity-frequencydispersioncurvesofRayleighwaves(i.e.groundrollinreflectionseismics)hasyieldedestimatesofS-wavevelocitystructure(Xiaetal.,1999a,1999b;Parketal.,2000).RothandHoUigcr(1999)havedeterminedsuccessfullyS-andP-wavevelocitiesbyincludingguidedwavesintheinversion.WithknowledgeofS-andP-wavevelocities.Poisson'sratio,akeyparameterinvariousgeotcchnicalinvestigations,canbecalculated(Ivanovetal.,2000).ProcessingandinterpretationEnormeousefforthasbeendevotedtofurtherdevelopingandperfectingtheacquisition,processingandinterpretationofconventionalseismicreflectiondata(Geophysics,1936-2000;Yilmaz,1987).Ontheotherhand,the.semethodsoftenfailorcauseproblemswhenacquiring,processing,andinterpretingshallowseismicreflectiondata


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13 Introduction

(Knapp and Steeples, 1986; Steeples et al., 1995, 1997; Miller et al., 1998; Steeples andMiller, 1990, 1998).

The importance of ray tracing and full waveform modelling to ensure correctinterpretation of recorded data has been long recognised and a variety of appropriatealgorithms derived (Zelt and Smith. 1992; Robertsson et al., 1994; Robertsson, 1996;Jurado et al, 1996; Biondi et al., 1998; Sava and Fomcl, 1998; Hayashi, 2000).

In the case of a simple layered subsurface, inversion of seismic refraction data isstraightforward. Tt can be achieved by solving relatively simple equations (Musgrave,1967). For analysing first-arrival times of large data sets recorded over layeredstructures characterised by undulating boundaries, more advanced algorithms have beendeveloped (e.g., ABC, Hales", plus-minus, generalised reciprocal, and common refractorelement methods; Heiland. 1940; Hales, 1958; Hagedoorn, 1959; Palmer, 1980; Seisa,1996). Inthecaseofcomplexstructureshowever,sophisticatedforwardmodellingandtomographicinversiontechniquesarcrequired(WhittalandClowes,1979;Spenceetal.,1984;Vidale,1988,1990;PodvinandLecomte,1991;Schneideretal,1992;ZeltandSmith.1992;Zhangctal..1998;Lanzetal,1998a).ExplorationanddeepcrustalapplicationsThedetectionofsaltdomesintheGulfCoastareaoftheUSAinthe1920'sinitiatedcommercialapplicationsofreflectionandrefractiontechniquesforoilexploration(SheriffandGeklärt,1995).Currently,high-resolutionimagingofstructuresforhydrocarbonexplorationandexploitationisconductedalmostexclusivelywiththeseismicreflectiontechnique(e.g.,TheLeadingEdge,1993-2000;CalvertandLi.1999;Hunteretal.,1999;Rigattietal.,1999;Willacy,1999;Brewetal.,2000).Numerousseismicreflection(e.g..Greenetal.,1987;CalvertandLudden,1999;Onckenetal.,1999)andseismicrefractionapplicationshavedealtwithnon-commercialtectonicstudiesofcrustalanduppermantlefeaturessuchassedimentarybasinsandsubductionzones(Mooneyetal.,1985;HolbrookandMooney,1987;Ansorgeetal.,1992;Mayeretal.,1997;Zeltetal.,1999).SedimentaryandhydrologicalinvestigationsTherearenumerousexamplesinwhichshallowseismicreflectiondatahaveyieldeddetailsonthestructuresofQuaternarysedimentsandthegeometriesoftheuppermostbasement(Hunteretal.,1984;PullanandHunter,1985̂1990;Milleretal,1989;SteeplesandMiller,1990;Keiswetteretal.,1994:Harrisetal.,1996;BachrachandNur,1998b;Shtivelmanetal,1998;Bükeretal,2000).Surfaceanddownholehigh-resolutionseismicimagingofshallowsedimentarylayers(e.g.,aquifersandaquitards)hasprovidedanimportanttoolforhydrologicalstudies(Hunteretal.,1987;Hajnaletal,1995;Hackworthetal..1998;Pullanetal.,2000).Underfavourableconditions,ithasbeenpossibletomapdirectlythegroundwatertable(BachrachandNur,1998a,1999).Shallowseismicreflectionstudieshavenotbeenconfinedtosolidground:Water-borneseismicsurveyshaveimagedfinesedimentarystructureswithinriverdeltasandlakes,andseismicreflectionprofilingoverglaciershavemappedicethicknesses(e.g..Levatoetal.,1999;Benjumeaetal,1998:Tacchimctal.,1999).


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Introduction 14

Already decades ago. the seismic refraction method was applied successfully forgroundwater exploration. It was found to be a powerful tool for solving the equivalence

problem of methods such as electrical resistivity and gravity (Van Overmecren, 1981).Saturation of sedimentary units with water is generally accompanied by increases ofseismic velocity, whereas decreases of seismic velocity in solid rock may indicateincreased occurences of fissures, possibly bearing water (Hasselström, 1969; VanOvcrmeeren, 1980). Musil et al. (1999) determined the thickness of a rock glacier byinterpreting different velocities for ice and rock obtained from tomographic inversionsof first-arrival times.

Multichannel Analysis of Surface Waves (MASW) has been found to be an alternativemethod for mapping bedrock topography (Miller et al., 1999). Successful detection offluid-induced

changes in S-velocity has

provided a means for

monitoring transient

groundwater flow (West and Menke, 2000). Initial tests have been conducted to locateunderground voids using the MASW method (Phillips et al., 2000).

Environmental (landfill) studiesSeismic


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15 Introduction

arrivals and the onset of the ground roll (Robertsson, 1996; Robertsson et al., 1996a,1996b; Roth et al, 1998a, 1998b). Extreme vertical velocity gradients, which are

present at interfaces between sediments and bedrock or at junctions of the vadose and

saturated zone, may prevent the standard stacking of seismic reflection data (Miller andXia, 1998).

Severe obstacles to obtaining correct subsurface models through seismic refractiontechniques are the hidden layer problem and traveltime offsets and skips due to velocityinversions (Domzalski, 1955; Soske, 1959; Hawkins and Maggs, 1961). Somelimitations of tomographic inversion techniques depend on the algorithms used forcalculating traveltimes. For example, finite-difference eikonal solvers are restricted tothe computation of first-arrival times (no reflections), whereas ray tracing using"shooting" and "bending"' methods can only handle relatively simple models and mayyield local minimum traveltime paths, missing the global minima (Vidale, 1988; Moser,1991; Sethi an and Popovici, 1999). Full-waveform viscoclastic finite-differenceforward modelling based on the wave equationyieldssyntheticdatathatcomeveryclosetorecordeddata,butrequireslongcomputingtimescompletelyinappropriateforinversiontechniques.Ground-penetratingradarMethodsandtoolsGeoradartechniquesarebasedonsimilarprinciplesastheseismicmethods,exceptthatelectromagneticwavesoffrequenciesrangingfrom10MHzto2000MHztravelthroughthemedia.Theysupplementtheseismicmethodsbyprovidingdetailedinformationontheveryshallowsubsurface(BachrachandNur,1998c;Powersetal.,1999).Thefirstapplicationsofthegeoradarmethodinvolveddeterminingicethicknesses(Steenson.1951;Evans,1963;Lalumièreetal.,1994).Aboutadecadeago,thefirsteffecientgeoradarsystemdesignedformappingsmall-scalestructureswithintheupper10-50mofthesubsurfacewereintroduced(seereviewsbyDavisandAnnan,1989andAnnan,1992).Sincethen,severalnewapproachestorecordinggeoradardatahavebeenproposedandimplemented.Amulti-channelacquisitionsystemthatallowstheefficientuseofthecommonmidpointstackingmethodstobeemployedingeoradarsurveyingwasdescribedbyPeacock(1997).LehmannandGreen(1999)increasedtheacquisitionandprocessingspeedofconventionalsingle-fold3-1)GPRdataconsiderably.Theyaddedthecoordinatesofantennaepositionsdeterminedbyaself-trackingtheodolithetothetraceofgeoradardataheadersinrealtime.Tiltinggeoradarantennaebyanangleofupto45°fromthehorizontalprovidedawaytoobtaininformationonthedepthextentofburiedobjects(DanielsandBrower,1998).Awidelyacceptedapproachistolowertheantennaedownboreholeswiththeintentionofproducingtomographicimagesofthevolumebeweentheboreholes(Satoetal,,1995;Liuetal.,1998;ZhouandSato,1999).Recently,anunderwatersystemforincreaseddepthpenetrationoverlakeswaspresented(VanderRijstetal.. 1 9 9 9 ) .


22/227

Introduction 16

Processing and interpretationThe similarities between the georadar and seismic techniques have inspired manyresearchers to apply seismic reflection recording, processing, and imaging techniques to

georadar data. Examples have included multi-fold data acquisition, spatial filtering,stacking, and migration. (Maijala, 1992; Malagodi et al., 1994; Beres et al. 1995, 1999,2000; Pipan et al, 1996; Verstecg et al, 1996:"orrey et al.. 1999; Rousseau et al., 1999;Zhou and Sato, 1999, Berkovitch et al, 2000; Grasmueck, 1994a, 1994b, 1996).However. Lehmann and Green (2000) have pointed out that conventional seismicmigration algorithms are not suitable for regions characterised by moderate to hightopographic relief. They presented a new migration method suitable for processing datasets from such regions. As for the seismic methods, full wave-form finite-differencemodellingofelectromagneticwavepropagationinattenuatinganddispersivemediaisanimportantinterpretationtool(RobertsandDaniels,1994;Bergmannetal..1996,1997,1998,1999).Acriticalaspectforunderstandinggeoradardataistheinfluenceofcouplingtothegroundorboreholewallontheantennaradiationpattern(Turner,1994;Carcione,1996;HolligerandBergmann,1998.1999).Tomographicinversionshavebeenpredominantly,butnotexclusively,performedoncrossholegeoradardata(Jessopetal.,1991;Stevensetal.1995;CaiandMcMechan.1999;ClementandKnoll,2000).ExplorationandengineeringapplicationsInGermany,georadarsurveyshavebeenusedforover20yearstodetectsaltdeposits(Thierbach,1994).Othermineralsandconstructionmaterialssuitableforexplorationwithgeoradarincludedcoal,sulphide,potash,bauxite,limestoneandornamentalstone(Annanetal.,1988;BakerandCull.1992;BensonandYuhr,1992;GrandjeanandGourry,1996;Grasmueck,M.,1996;Momayczetal.1996;Hensonetal,1997;SigurdssonandOvergaard,1998).Engineeringapplicationshaveinvolvedmonitoringroaddeteriorationandpotentialweaknessofanicerunway,slopestabilityanalysis,detectingkarsticvoidsinatunnelconstructionarea,andcharacterizingburiedtanksandpipes(Scullionetal.,1994;Beaubicnetal..1995;Corinetal.,1995;Arconc,1996;ZengandMcMechan,1997).ValleandZangi(1997)testedgeoradarforstudyingconcretestructuresofwallsandpillars.SedimentaryandhydrologicalinvestigationsGeoradarmethodshavebeenusefulfornon-intrusive2-Dand3-DstudiesofQuaternarysedimentsthatarecriticalcomponentsofthegroundwaterregime(BeresandHaeni,1991;Huggenberger,1993;DuandRummel,1994;Young.1995;Beresetal.,1995,1999,2000;Martinezetal.1999;Perettietal.,1999).Thegroundwatertable,astronggeoradarwavereflector,canoftenbeimageddirectly(VanOvermeeren,1994;Arconeetal.,1998;BachrachandNur.1998c:TrenholmandBentley,1998).Initialstudiesrelatedtopaleoseismologicalinvestigationshavebeenconducted(Grossetal.,1999).Georadarisalsogainingincreasedacceptanceasanarchaeologicalinvestigationtool(Bevan,1991;Seren,1998;LeckebuschandGreen.2000).Environmental(landfill)studiesVariousreportshavedemonstratedthesuitabilityofgeoradarmethodsforlandfillstudies.Reduceddepthpenetrationduetohighelectricalconductivityhasusually


23/227

17 Introduction

prevented their use for determining waste pit thicknesses, but they have provided ameans for locating lateral boundaries (Lan/ et al., 1994; De laco et al., 1997b).Nevertheless, large metallic objects, such as drums, may be detected (Kutrubes et al,

1992). Daniels and Brower (1998) have tested a new technique for determining thedepth extent of waste by tilting the georadar antennae. Knowledge about aquifers,subsurface barriers, and possible pathways in the sediments surrounding waste materialis critical for estimating potential risks of groundwater contamination (Busby, 1997; Delaco et al.. 1998; Pellerin et al.. 1998; Green et al. 1999; Guy et al., 2000). Georadartechniques have not only been used for imaging pathways, but they have also beenemployed for the direct detection of pollutants, such as DNAPL's and LNAPL's(Bowders et al., 1983; Brewster and Annan, 1994: Nobes ct al., 1994; Redman ct al.,1994; Ulrych et al, 1994; Daniels et al, 1995).

LimitationsThe performance of georadar over landfills is often impaired by the high electricalconductivity of the waste material. This may result in considerably reduced depthpenetration(Delacoetal..1998).Aseriouslimitationofgeoradar.ingeneral,isitssensitivitytosurfaceconductors(e.g.,wirefences)andothersurfaceobjects(e.g.,trees,buildings).Althoughnewdevelopmentsareontheway,theacquisitionspeedisstillunsatisfactory,especiallyinnoisyenvironmentswherehighstackingisrequired.Lehmannetal.(2000)havedemonstratedthatrecordinggeoradardatawithonlyoneantennaorientation,whichisthestandardprocedure,yieldsonlypartofthesubsurfaceinformationandcouldbeproblematicwhenapplyingseismicprocessingsoftware(e.g.,migrationroutines).1.4ThestudyobjectChoiceofanappropriatestudysitedependedonseveralfactors:(i)Availablefieldequipment,(ii)challengingobjectives(seealsoparagraph1.2),(iii)qualityofresultsofpreliminarytestmeasurements,(iv)existenceofcomplementarynon-geophysicalinformation,and(v)supportfromlocalofficialsandfarmers.Atthetimeoftheinvestigation,ourequipmentconsistedoftwoBISON120-channelseismicrecorders,twoCesiummagnetometerunits,aPULSE-EKKO100georadarsystem,afrequency-domainelectromagneticEM3Linstrument,anAEMDC-resistivityrecordingsystem,andatransientelectromagneticEM47system.Allexceptthelatterhadbeentestedextensivelyandfoundreliabletoolsforsedimentary,archaeological,andlandfillstudies.TogetherwiththetransientelectromagneticIexcludedtheDC-resistivitymethodfrommyinvestigationsbecausethistechniquedidnotsatisfymyrequirementsforahigh-resolutionstudyofthelandfill.ThemagnetometerandtheEM31systemscanbeusedtodeterminethelateralboundariesandtocharacterisethewastematerialofalmostanylandfillinatime-andcost-effectivemanner.Georadarisgenerallyoflimiteduseoverhighlyconductivewastematerial,butisapowerfultoolforimagingfinestructures,includingpossiblepollutantpathwayswithinhostsedimentsoflowelectricalconductivity(i.e.,thosewithlowclaycontent).Abasicrequirementforthesuccessful


24/227

Introduction 18

application of seismic methods for mapping the base of a landfill is that its verticalextent is not too shallow.

On the basis of measurements at several landfill sites in Switzerland, the "Fritschi"landfill in Härkingen (Fig. 1.1) was chosen for detailed investigation. All testedgeophysical methods yielded promising results at this landfill, especially the high-resolution georadar and the seismic reflection techniques. In addition, a Ph.D. projectconducted simultaneously at the same landfill provided important supplementaryinformation, including critical borehole logs (Kissling, 1998). There was also strongsupport from the Cantonal geologist and from local officials at Härkingen, whereas atother sites farmers impeded our activities. Throughout the rest of this thesis, the"Fritschi" landfill will be re fere d to as the Härkingen landfill.

Landfill Although the Härkingen landfill is a reactor-type landfill, there is no appropriate sealingand there is no collection of ieachates and gases as specified in the technical regulations(TVA. 1990). Originally, the government of Canton Solothurn


25/227

19 Introduction

basement of northern Switzerland comprises migmatitic gneisses that originate from theCentral European Variscan orogeny of Precambrian and Early Palaeozoic age. They areexposed in the Black Forest (marked red in Figs. 1.1a and b). These gneisses deepensouthwards

(Trumpi. 1980).

The overlying -1.5 km thick Triassic and Jurassic formations crop out in the TabularJura (marked light green in Figs. 1.1a and b) and Folded Jura (marked dark green inFigs, l.la-c). The complete absence of Cretaceous rocks in northern Switzerlandsuggests that there was no sedimentation in the Late Mesozoic, rather than thatCretaceous sedimentary layers were eroded completely (Diebold, 1990). In the Tertiary,the deepening Molasse basin was filled with Oligocène and Miocene sediments (markedyellow in Fig. l.la-c). The thickness of the Tertiary Lower Freshwater Molassesedimentary sequence increases from the


26/227

Introduction 20

Molasse basin form the Aaregäu and Dünnerngäu groundwater regimes, which areseparated by the Born anticline.

The very local geology of the Härkingen region is defined by several boreholes in thevicinity of the landfill (Figs. 1.5 and 1.7; Kissling, 1998). A 0.2 - 0.3 m thick surfacelayer of humus overlies 10 - 16 m of heterogeneous outwash. comprising channels ofsandy and silty gravel that reflect the general east-west to northeast-southwest flowdirection of Quartcnary rivers and streams. These highly permeable gravel deposits areunderlain by 3 - 5 m of lacustrine sediments composed mainly of sandy clay and silt.Beneath this aquitard are 0.5 - 6.3 m of till, a typical component of basal moraines.Boreholes B1 and B2 encountered bedrock at -20 m depth. Reddish-brown marlysiltstone in B I likely presents Lower Freshwater Molasse sediments, whereas greylimestone found in B2 is believed to be part of the Upper Jurassic sequence of the Bornanticline (Jäckli and Kempf, 1972; Kissling, 1998).

Hydrological settings

My study site is located within the important 21 km" Aaregäu groundwater reservoir(Fig. 1.1c). During the time period 10. 10. 95 to 31. 10. 97, the depth to material;


27/227

21 Introduction

• volumetric georadar data provided two-dimensional (i.e., timeslices)and three-dimensional (i.e., picked horizons) images of geologicstructures within the sediments encompassing the landfill.

In Chapter 3, the results of conventional seismic data acquisition (Fig. 1.10) andprocessing as well as more sophisticated approaches, such as tomographic inversion andforward ray-trace modelling, were presented. My seismic study has demonstrated thatcombining several methods (i.e., seismic refraction and reflection analysis and boreholelogging) may not only be helpful, but critical for obtaining meaningful results. Incontrast to Lanz et al.'s (1998a) tomographic investigation of the Stetten landfill inCanton Aargau. the lower boundary of the Härkingen landfill could only be mapped viajoint analyses of refracted and reflected traveltimes appropriately constraint by boreholedata.

Chapter 4 summarises the achievements of this study and provides an outlook forfuture geophysical investigations of landfills. I have presented several methods forimproving the processing and integration of geophysical data. The next important stepwould be to speed up data acquisition over landfills.

Additional information on special topics and copies of published articles are provided inthe Appendices as follows:

• During the 3-D georadar survey (see Chapter 2). one of the 50 MHzantennae malfunctioned.


28/227

Introduction 22

Waste site;

location Objectives Methods Reference

Landfills and liq¬uid waste disposalsites;Perth, Australia

Mapping ground¬water contamina¬

tion

DC-resistivity andTEM

Buselli et al.. 1990

Thomas Farm

landfill;

TippecanoeCounty, Indiana,U.S.A.

Quantitative multi-

technique investi¬

gation of solid-waste landfills

Magnetic and

gravity

Hinze et ah. 1990

Thomas Farm

landfill;

Tippecanoecounty, Indiana,USA

Quantitative multi-

technique investi¬gation of solid-waste landfills

Magnetic andgravity

Roberts et al., 1990

Mallard North

landfill containingmunicipal waste;

Hanover Park, Illi¬

nois, USA

Identifying and

characterizingfractures in the

cover of a landfill

DC-resistivity Carpenter et al.,1991

Landfill contain¬

ing municipalwaste includingindustrial solvents

and sludge;Illinois, USA

Determining depthof landfill and

locating drums and

heavy metal sludge

FDEM Jansen et al., 1992

Landfill;Vermont. New

Hampshire

Determining lat¬eral extent of land¬

fill, characterizingsubsurface mate¬

rial, and locatingburied drums

Magnetic and GPR Kutrubes ct al.,1992

Fable 1.2:

Representative o\er\ie\\ of landfill papers published between1990and2000.


29/227

2j Introduction

Waste site;location Objectives

Methods Reference

Mallard Northlandfill containingmunicipal waste;Hanover Park, Illi¬

nois, USA

IdentiJying andcharacterizingfractures in the

cover of a landfill

DC-resistivity Carpenter et al,.1994

Two landfills;Illinois, USA

Identifying and

classifying depres¬sions in landfills

Airborne thermal

infra-red

Stohr et al., 1994

Landfill contain¬

ing household andindustrial waste;

Ovar, Portugal

Studying aquifercontamination

DC-resistivity,

FDEM and hydro-geological

Senosetal., 1994

Landfill contain¬


Stetten, Switzer¬land

Landfill contain¬ing household andconstruction waste;

Huttcnried, Ger¬

many

Determining opti¬mum strategy for

investigation of

typical Swiss land¬fills in non-inva¬

sive manner

DC-resistivity,magnetic and GPRand drilling

Lanzetal., 1994

Locating2000.


30/227

Introduction 24

Waste site;


Landfill contain¬ing nonhazardous,hazardous, radio¬active and mixed

wastes;Oak Ridge Reser¬vation, Tennessee,USA

Mapping faul ts andformation contactsfor incorporationinto drilling andgroundwater moni¬toring strategy

Seismic reflection Doll et al.. J 996

Landfill;Brauweiler, Ger¬

many

Delineating bound¬aries of landfill

RMT and drilling Tezkan et al., 1996

Landfill contain¬

ing household,construction and

industrial waste;

Brauweiler, Ger¬

many

Locating lateraland vertical bound¬

aries of landfill and

estimating envi¬ronmental risk of

its content

RMT and drilling Zacher et al., 1996

Landfill contain¬

ing mainly house¬

hold andconstruction waste;

Härkingen, Swit¬zerland

Locating buriedwaste

FDEM and GPR

and drillingDelacoetal., 1996

Landfill contain¬

ing household andconstruction waste;

Huttenricd, Ger¬

many

Delineating bound¬aries of landfill

FDEM,VLF-R,SPand magnetic

Zacher et al., 1996

Central Landfillcontaining mostlysolid waste and

some chemical

waste;Rhode Island,USA

Detecting water¬bearing fractures ingranite under land¬fill

DC-resistivity,aerial photo¬graphic, satelliteand GPR

Fröhlich et al.,1996

Table 1.2:

Representative overview of landfill papers published


31/227

25 Introduction

Waste site;location Objectives Methods Reference

Landfills contain¬ing municipal solidwaste:

Atlanta, Georgia.USA

Determiningdynamic proper¬ties for estimatingseismic stability oflandfill

Surface waveattenuation mea¬

surements

HakeretaL 1997

Landfill contain¬

ing lime-quarryand excavated top-soils, sludge,grease and oil,waste from pro¬

cessing industries;Lernackcn. Swe¬

den

Investigation inconnection with

planned large con¬struction works

DC-resistivity andFDEM

Bernstone and

Dahlin, 1997

Landfill contain¬



Determining depthextent of landfill

Seismic refraction

tomographic anddrilling

Lanzetal., 1997b

Landfill contain¬

ing mainly house¬hold and

construction waste;


Determining depthextent of landfill

Seismic reflectionand drilling

De Iaco et al.,1997a

Landfill;Oak Ridge Reser¬vation, Tennessee,USA

Mapping subsur¬face geolocalstructures within

waste area

Seismic reflection2000.


32/227

Introduction 26

Waste site:


Landfill contain¬ing mainly house¬hold and

construction waste;



FDEM, GPR anddrilling

De Iaco et al..1997b

Landfill contain¬



Determining lat¬eral and depthextent of landfill

FDEM, seismicrefraction tomo¬

graphic and drill¬ing

Lanz et al, 1997a

Cold Test Pit

(CTP);Idaho National

Environmental and

Engineering Labo¬ratory (1NEEL)

Outlining andcharacterizing bur¬ied waste pits

DC-resistivity, IP,FDEM, TEM,VETEM. RMT,

CSAMT, high fre¬

quency ellipticity(HFE) and GPR'

Pellerin and Alum-

baugh, 1997

Landfill contain¬

ing household and

industrial waste;

Coimbra, Spain

Mapping contami¬nant plume

DC-resistivity Figueiredo et al.,1998

Landfill contain¬


Tbadan, Nigeria

Determining sub¬surface structure at

landfill

DC-resistivity Olayinka and Yara-manci, 1998

Idaho National

Laboratory's ColdTest Pit, content

well documented;Idaho, USA

High-resolutionTEM studies

TEM Mauldin-Mayerleet al., 1998

Landfill contain¬

ing industrialwaste;not specified2000.


33/227

27 Introduction


Methods Reference

Landfill;Oak Ridge Reser¬vation, Tennessee,USA

Mapping faults andfracture zones near

landfill

Seismic reflection Doll, 1998

Landfill contain¬


Arnstadt, Germany

Locating buildingburied in landfill

Seismic reflection Pasasaetal, 1998

Landfill;

not specified


Infrared thermo¬

graphic

Sirieix et al., 1998

Laboratory, chemi¬cal and construc¬

tion waste from

Argonne NationalLaboratory;Du Page County,Illinois, USA

Determiningnature of subsur¬

face materials and

hydrological con¬ditions

DC-resistivity andFDEM

Black and Carpen¬ter, 1998

Landfill;

Ohio, USA

Detecting drums FDEM and mag¬

netic

Murray and

Keiswetter. 1998

Landfills contain¬

ing household,industrial and

chemical waste;

Barcelona, Spain

Mapping contami¬nation in a ground¬water aquifer

FDEM and drilling Font et al., 1998

Landfill;


34/227

Introduction 28


Methods Reference

Landfill contain¬

ing household,commercial and

industrial waste;

Cambridge,England

Defining leachateplumes

DC-resistivity and

photogeologicalKlincketal., 1998

Landfill contain¬

ing chemicalwaste;not

specified

Characterizinglandfill

DC-resistivity,VLF-R and TEM

Ogilvy et al, 1998

Landfill contain¬

ing mainly house¬hold and

construction waste;



FDEM, magnetic,GPR and drilling

DcTacoctaL, 1998

Landfill;

Pennsylvania,USA


FDEM, magneticand seismic refrac¬

tion

Murray andKeiswetter, 1998

Aemmässuo land¬

fill containingmunicipal waste;Helsinki, Finland

Mapping landfi 11area and possiblecontaminant

plumes

FDEM, magneticand gamma radia¬

tion

LerssietaL, 1998

Lipeälampi land¬fill containing pulpmill waste effluent;Lievestuore,


35/227

29 Introduction


Methods Reference

Landfill contain¬

ing waste from alu¬minium factory;Mölln, Austria

Mapping extent oflandfill and pol¬luted area

DC-resistivity Seren and Blau-moscr, 1999

Landfill contain¬

ing industrialwaste;

not specified

Mapping spatiallycomplex landfills

3D DC- resistivity Ogilvy et al, 1999

Landfill contain¬

ing mostly con¬struction waste;

Holon. Israel

Mapping base of

landfill

Continuous verti¬

cal electric sound¬

ing (CVES)

Ezerski and Beck,

1999

Landfill contain¬

ing manufacuringresidue;

Canterbury, NewZealand


FDEM Nobes and McCa-

hon, 1999

Cold Test Pit

(CTP);Idaho NationalEnvironmental and

Engineering Labo¬ratory (INEEL)

Outlining and

characterizing bur¬ied waste pits

VETEM Wright et al., 1999

Baker Woodlands

landfills;

Lancaster, Penn¬

sylvania, USA


Magnetic De Wit and Stern¬berg, 1999

Landfill;not specified Locating buried

waste Magnetic Köhler et al, 1999

Landfill;Filborna. Sweden

Mapping hydro-geology and con¬taminant migra¬tion patterns

DC-resistivity


36/227

Introduction 30

Waste site;


Rio Nuevo North

landfill;

Arizona, USA

Detection of not

properly cleaned

up waste

DC-resistivity andIP

Carlson et al., 1999

Cottonwood land¬

fill;

Arizona, USA

Testing accuracyof IP response


Carlson et al, 1999

Landfill contain¬

ing municipalwaste;

Venice province,Ttaly

Mapping high per¬meability layersand detecting

potential leakage


Illiceto and

Morelli. 1999

Landfill contain¬

ing constructionand civil engineer¬ing waste;Belgrade, Jugosla¬via

Mapping subsur¬face structures

DC-resistivity andGPR

Sretcnovic and

Sretenovic, 1999

Landfill contain¬

ing demolition andhousehold waste;

Dalby, Sweden

Studying corre¬

spondencebetween resistivityand shear wave

velocity

DC-resistivity and

spectral analysis ofsurface waves

Svensson el al.,

1999

Landfill;

Cologne, GermanyLocating buriedwaste

IP and RMT Honig et al., 1999

Landfill contain¬

ing industrial

waste;

Mellendorf, Ger¬

many

Mapping verticaland horizontal

resistivity distribu¬tion

TEM and RMT Greinwald et al.,1999Table1.2:Representativeoverviewoflandfillpaperspubhsliedbetween1990and2000.


37/227

31 Introduction

Waste site;


Landfill contain¬



Mapping locationand geometry ofwaste pits, estimat¬ing nature of con¬tents, and imagingstructure of host

sediments

DC-resistivity.FDEM, magneticand drilling

Lanzclal., 1999

Fort Hunter Lig¬gett landfill;

Monterey county,California, USA

Mapping lateralextent of landfill

FDEM, magneticanclGPR

Smith, 1999

LandfiJl contain¬

ing industrialwaste:

Oscoda, Michi¬

gan, USA

Locating buriedwaste and ground¬water contaminant

plume

DC-resistivity, SRFDEM, magnetic,andGPR

Bailey et al, 1999

Landfill contain¬



Mapping locationand geometry ofwaste pits, estimat¬

ing nature of con¬tents, and imagingstructure of host

sediments

FDEM. magnetic,GPR. seismic

refraction tomo¬

graphic and 3-Dseismic reflection

and drilling

Green et al., 1999

Cold Test Pit

(CTP);Idaho National

Environmental and

Engineering Labo¬ratory (TNEEL)

Characterizingburied objects

VETEM Smith et al,, 2000

Hartland landfill;

Victoria, British

Columbia. Canada

Mapping bedrockfractures

FDEM and GPR Guy et al, 2000

Table 1.2:

Representative overview of landfill papers published between 1990and 2000.


38/227

I n t r o d u c t i o n

3 2

W a s t e s

i t e ;

l o c a t i o n

O b j e c t i v e s

M e t h o d s

R e f e r e n c e

L a n d f i l l

c o n t a i n ¬

i n g

i n

d u s t r

i a

l

w a s t e :

M e

l l e n

d o r

f ,

G e r ¬

m a n y

M a p p i n g

l a t e r a

l

a n d d e p t h

e x t e n t

o f

l a n

d f i l l

R M T a n d

d r

i l l i

n g

T e z k a n e t

a l

.

2 0 0 0

L a n d f i l l

c o n t a i n ¬

i n g

d o m e s t i c

a n d

l i q u

i d

( o

i l y

a n d

n o n -

o i l y

)

w a s t e ;

E a s t

A n g

l i a

,

U K

M a p p i n g s p r e a

d o f

c o n t a m i n a t i o n

a n d

g r o u n

d w a t e r

t a b l e

w i t h i n

l a n

d f i l l

D C

- r e s

i s t i v

i t y

,

I P

a n d d r

i l l i

n g

A r

i s t o d e m o u

a n d

T h o m a s -

B e t t s

,

2 0 0 0

L a n d f i l l c o n t a i n ¬

i n g

i n

d u s t r

i a

l

w a s t e ;

M e

l l e n

d o r

f ,

G e r ¬

m a n y

M a p p i n g

l a t e r a

l

a n d d e p t h

e x t e n t

o f

l a n

d f i l l

R M T a n d

D C -

r e s

i s

t i

v i t y

.

F D E M

a n d

m a g n e t i c

i n

e a r

l i e r

i n v e s t i g a ¬

t i o n s

T e z

k a n e t

a l

,

2 0 0 0

L a n d f i l l

c o n t a i n ¬

i n g m a

i n

l y

h o u s e ¬

h o l d

a n d

c o n s t r u c t i o n w a s t e

;

H ä r

k i n g e n ,

S w i t ¬

z e r l a n d

L o c a t i n g

b u r i e d

w a s t e

F D E M

, m a g n e t i c ,

G P R a n d d r

i l l i

n g

D e l a c o e t a l

. ,

2 0 0 0

T a b i c

1 .

2 :

R e p r e s e n t a

t i v e

o v e r v

i e w

o f

l a n

d f i l l

p a p e r s

p u

b l i s

h e

d

b e t w e e n

1 9 9 0

a n d 2 0 0 0

.


39/227

33 Introduction

Basement locks ot Black Fotcst uplift

Pei mo-Cdi bom lei ous Ti ought s)

Inassit and I owcr luiasMc ol tabulai lui a

Middle and Late fuiassic ot Folded Fui a

Tcitiatv ot Molasse Basin and Rhine Giabcn

Pfatlnau 1 boiehole

C ioss-sections m (b) and (el

Bom and Weissenstem anticlines

Figure 1.1:(a) Simplified tectonic map ot notihwestein Switzerland Haikmgen stud1) aiea lies neai

boundaiy between Molasse basin (maiked \ellow) and Tin a mountains (mostly maiked

gieen) Weissenstem and Bom anticlines aie southeinmost lolds ot Tma Basement)


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Introduction

N

Weisscnstein Bornanticline anticline

b)

Aare

river

S2 km

Pfaffnau 1

borehole

c)

Basement rocks of Black Forest uplift

Pcrmo-Carboniferous Trough

Tnassic and I ower Jurassic of Tabular Jura

Middle and T ate Jurassic of Folded Jura

Tertiary of Molasse Basin and Rhine Graben

Basal moraine and lacustrine sediments

Outuash gra\el with groundwater

Pfafinau 1 borehole


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35 Introduction

Figure 1.2:Before, dumping of waste material, gravel was excavated to ~ 11 m depth. Photograph cour¬tesy of Amt für Wasserwirtschaft. Canton of Solothurn.

Figure 1.3:Waste being buried at Härkingen landfill. Excavation material, construction waste, variousundefined

bulky items, household waste,

cinder, metal objects, tires, and drums withunknown contents were dumped. Photograph courtesy of Amt für Wasserwirtschaft, Can¬ton of Solothurn.


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Intioduction 36

Figure 1.4:Photogtaphs and comments b\ local îesidents suggest that gtavel may have been excavatedto below gioundwatei table Photogiaph comtes} ot Amt lui Wasseiwiitschaft. Canton ofSolothuin

SWITZERLAND

landfill

Figure 1.5:Map ot stud} aiea assumed extent ot landfill is outlined b\ dashed line Black dots niaikpositions ot boieholes Bl B2 B8 and B9 (Kisslmg 1998) Two mounds of soil and alaige gioup ot tiees Gl vveie impediments to sm\e}s Stai with aiiow shows viewingduection ot photogiaph in Fig 1 6


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M Introduction

Figure 1.6:Reactivated landtill ccneied with hunuis Yellow line maiks seismic letlection piotile

NNW

o -

•= 10 -

\s -

20

/ ".

i _ _ .

Bl

B8J— —- -—sj

ss

ö oxi

B2

100 m

humus

s mdy ci i>flmt it depositslacusttmc st-dimeiUs

till (b is il mot une)bedt oc k

\v iste miteti i\

etoundw uet t\M "51 10 97)

Figure 1.7:Ctoss section ot landtill and adjicent natiual giound bised on intoiination tiom boieholesBl B2 B8 and B9 (Fia 1 i Kisslms 1998) Flmial deposits ot 10 16 m thickness o\etlie 3 5 m ot lactistime sediments md 0 5 6 3 ni ot till Bediock is at -20 in depthVppioximatel}

11motwastemiteualhisbeenuneiedb\i~hmthickcapotsand\cla\and~0̂mothumusDepthtogioundwateitablevanedby-1̂mdunngtimepenod101095to111097(Kissing1998)Piotileisvetticall)exaaaeiatedb>atactoiot 1 0


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Introduction 38

O"

•t.

-vi*

Figure 1.8:Geomcs E\H 1 sWem h i ich ible one man opei ittd electiomasnetic system lot îecoidin« appâtent tlettnc conductnit\ and m phase dati (\k\eill 19S0)

Figure 1.9:Iwo tieometnts Ci S~i6 ( esiuni nnuietometets weie mounted on i non im»netit wacontoi ti^t aquiMtion ot tot il titld nid \eitit il srt îditiit m u nttic dm with a const mt onentation ot sensois (Huw hkci et il

2000)


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39 Intioduction

^*H t, mftft»ft.

Figure 1.10:Seismic iellection/iehaction data wclc acqimed usine two 120 channel Bison seismo

giaphs a hammei and shoteun (shown on tight edee ot photoeiaph) souiccs Tlammeiwas only used on path sepaiatine landfill fiom natuial giound A 2^ cm geophone andshot spacing euaianteed hieh fold and dense sampling ot subsuitace

Figure 1.11:Weathet and giound conditions slowed down aquisuion of } D geoiadat data withPU1 SF LKKO 100 s\stem lhe SO \IH? antennae weie sepaiated by 4 m


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Inùoduction 40

t »,

\

i


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41 Integrated study

Chapter 2

AN INTEGRATED GEOPHYSICAL

STUDY OF A LANDFILL AND ITS

HOST SEDIMENTS

R. De Iaco, A.G. Green, and II. Horstmeyer

Published in:

European Journal of Environmental and Engineering Geophysics,

4,223-263(1999/2000)

Institute of Geophysics, Swiss Federal Institute of Technology,ETH-Hoenggerberg, CH-8093, Zurich, Switzerland


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Integrated study 42

2.1 ABSTRACT

Electromagnetic, magnetic and ground-penetrating radar (georadar or GPR) datarecorded on dense grids have been used to

investigate a Swiss landfill and its host

sediments. Specific objectives were to locate clusters of steel drums that may containdangerous chemicals, delineate the landfill borders, map the depth to the groundwatertable, determine the nature of the host sediments with emphasis on outlining potentialpathways and barriers to fluid flow, and detect any leaking contaminants. Large volumesof ferrous material were identified throughout the landfill, with particularly highconcentrations of iron and steel situated below two broad areas and beneath a relativelynarrow zone along its southern and western boundaries. Magnetic anomalies along theseboundaries were consistent with the presence of several discrete centers of ferrousmaterial buried at depths 6 m, each containing material that was either much greater involume or much more magnetic than a 50 000 liter steel storage tank. Landfill borderscould be defined to no better than 10 - 15 m on the basis of standard apparent electrical


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43 Integrated study

may provide a convenient and inexpensive location for the disposal of waste material.Gravel extraction and waste disposal can alter markedly the local groundwater flowpattern. Moreover, discarded waste may be a source of pollutants.

During the past decade or so, various geophysical methods have been adapted andapplied to studies of the shallow subsurface. Investigations of landfills have included theuse of electromagnetic (Buselli et al., 1990; Zacher et al., 1996; Pellerin and Alumbaugh, 1997), direct current resistivity (Ross et al., 1990; Ogilvy et al., 1999),induced polarisation (Vogelsang, 1995), self-potential (Hämmann et al.. 1997), magnetic(Roberts et al., 1990), gravity (Hinze et al., 1990), seismic refraction (Lanz ct ak,1998a), seismic reflection (De laco et ak, 1997a), seismic surface wave (Haegeman andVan Impe, 1999), ground-penetrating radar (georadar or GPR; Pelton et ak, 1994) anddiverse logging (Irons, 1989) techniques. Several studies have involved the applicationof multiple methods (Greenhouse et ak, 1987:


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Integrated study 44

borehole information confirm the reports of local residents that gravel was excavated tonear or below the groundwater table. Originally, the abandoned grave] pit was intendedas a landfill for relatively innocuous household and construction refuse. However,

photographs taken of the active

landfill and relatively high concentrations ofcontaminants in groundwater samples extracted from boreholes (Kissling. 1998) suggestthat significant volumes of harmful industrial waste were also dumped in the pit. A primary goal of our study is to determine the locations of buried steel drums that maycontain this hazardous waste. The Härkingen landfill is now covered by -2 m of sandyclay and humus (borehole B9 in Fig. 2.2). Except for some small mounds of soil, thesurvey area is relatively flat and horizontal.

2.4 DATA ACQUISITION

Electromagnetic and Magnetic DataElectromagnetic data were collected across a large part of the study site with a GeonicsEM31 system operating in the vertical mode. The location of the electromagnetic surveywas chosen to include the western part of the landfill and a large region of adjacentundisturbed natural ground (Fig. 2.1a). An irregular area with maximum length


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45 Integrated study

High electrical conductivities measured over the landfill with the EM31 systemsuggested that gcoradar signals might have only limited depth penetration in regionsunderlain by waste material. In contrast, much lower conductivities recorded across

adjacent ground indicated that

penetration should be relatively good in regionscharacterised by undisturbed natural soils and sediments. Considering the time-intensivenature of acquiring three-dimensional (3-D) georadar data, we decided to limit thesurvey area to a -40 m wide corridor that crossed the central region of the landfill.Georadar data were recorded across undisturbed natural ground by extending the survey-75 m northwest and -50 m southeast of the landfill (Fig. 2.1c). Northwest of thelandfill, active farming precluded the georadar survey area extending to the east of asmall road. To avoid a large group of trees (GT in Fig. 2.1), which generated strongsurface reflections, the survey area to the southeast (Fig. 2. Ic) was offset from theintended survey corridor. The total area covered was about 330 m x 40 m.

In the following, unless otherwise specified, undisturbed regions


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Integrated study 46

Although the reduced-to-the-pole magnetic map of Figure 2.4b shows significant lateralmovement and redefinition of anomalies relative to the unprocessed data, areas

distinguished by strong negative anomalies persist. Clearly, rcmanence is an importantcomponent of the landfill's magnetisation. A vertical gradient map (Fig. 2.4c) computedfrom data recorded by the two sensors (Fig. 2.4c) and a maximum horizontal gradientmap (Fig. 2.4d) calculated from lower sensor data (Fig. 2.4d) provide higher resolutiondetails.

Figure 2.5 shows an attempt to combine information contained in the apparentconductivity and reduced-to-the-pole total-field magnetic data. Apparent conductivitiesare represented by varying shades of green (white to dark green), negative magneticvalues by varying shades of blue (white to dark blue), and positive magnetic values byvarying shades of red (white to dark red).

By simply adding together the

appropriatecolours, a composite image of apparent conductivity and total-field magnetic data isobtained. Dark reds and dark blues delineate highly magnetised bodies distinguished byrelativelyaligned.


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47 Integrated study

Scaling Appropriate amplitude scaling is an important processing step for determining thedifferent penetration depths inside and outside of the waste disposal site and for

suppressing the effects of console - antenna interference and system ringing. Figure 2.8outlines the operation of a "smart" AGC that we employ in our processing scheme:

1) On the basis of root-mean-square (RMS) amplitude versus time plots,the user determines the lower limit of useful signal by defining a"noise window" (Fig. 2.8a). The average RMS amplitude A0 withinthe noise window is considerably weaker than that of the useful signaland is fairly constant over large areas. In our application, two values of

A0 are defined, one for data recorded over the landfill and one for datarecorded over undisturbed natural ground. T0 for each trace is definedas the upper limit of the noise window (Fig. 2.8c).

2) Entire traces are then scaled using a conventional AGC. Note theevenly balanced RMS amplitudes in Figure 2.8b after application of aconventional 50 ns AGC.

3) The form of a multiplicative factor F designed to reduce RMS

amplitudes within the noise window is


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Integrated study 48

AGC attenuates successfully the effects of the interpreted noise (compare Fig. 2.9c withFig. 2.9b and Fig. 2.9f with Fig. 2.9e). Advantages of the smart AGC over the standard AGC are also apparent from a comparison of Figure 2.7c with Figure 2.7b; noise eventsM

and surrounding random noise arc notably suppressed in Figure 2.7c.

Velocity analyses and NMO correctionsTo convert times to depths, it is necessary to compensate for the 4 m antenna spacingthrough application of normal move-out (NMO) corrections and to migrate the data withappropriate velocities. Expanding spreads (common-midpoints; CMP's) were recordedat numerous locations throughout the study site. Two typical CMP's acquired acrossnatural land outside of the landfill, together with adjacent profiling data, are displayed inFigure 2.10. Corresponding reflection times, RMS velocities, depths, and intervalvelocities are summarised in Tables 2.1 and 2.2.

In both the NW and SE survey areas, the CMP s show georadar velocities initiallyincreasing and then gradually decreasing (Fig. 2.10; Tables 2.1 and 2.2). ApparentgroundwaveMHz)


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49 Integrated study

helped suppress mono-frequent and random noise in the pre-migrated section ofFigure 2.1 e. Note, for example, the improved continuity of events El and E2.

Migration and time-to-depth conversionThree-dimensional time migration using Stolt's FK-algorithm (Stolt, 1978) improvedfurther the subsurface images (Fig. 2.7f). Most events became more focused and clearer(e.g., El and E2) and, in general, noise was somewhat attenuated. On the basis ofmigration tests performed on the entire 3-D data set, optimum migration velocities werefound to be approximately equal to velocities determined from the CMP analyses. Time-to-depth conversion using average velocities calculated from the RMS velocitiesallowed us to compare directly the georadar images with borehole information.

Visualisation

Interpretation software was used for viewing internal parts of the 3-D georadar data set.Combining information from vertical sections of various orientations enabled u s to tracecertain reflections throughout large


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Integrated study 50

conductivity anomaly A. Simple electrical conductivity models cannot account for therecording of such extensive areas of negative m-phase values by the EM31 system.Comparable phenomena have been reported m the literature (e.g., Ekrcn and

Frischknecht, 1967), but without explanation for their origin. One possibleinterpretation is that these unusual in-phase values are a consequence of the EM31system operating near or beyond its sensitivity limits.

Positive and negative total-field magnetic anomalies with high amplitudes are observedacross the entire surveyed region of the landfill (Fig. 2.4a). The western end of acurvilinear zone of positive magnetic anomalies coincides with conductivity anomaly A (Fig. 2.3a). A rather chaotic pattern of positive and negative magnetic featurescharacterises the B - C zone of high conductivities. Some of the highest amplitudemagnetic values (> 2500 nT with peak values exceeding 4000 nT) are observed across aseries of discrete features (Gl - G4) that lie along the southern border of the landfill.The effects of these anomalies extend >30 m south of the presumed southern landfillboundary. Two zones of high-amplitudeS.


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51 Integrated study

2.7 DISCUSSION

Characterizing the Waste Material

Although many high-amplitude anomalies on the apparent electrical conductivity andin-phase maps (Fig. 2.3) have counterparts on the magnetic maps (Fig. 2.4), there is byno means a one-to-one correlation between the two independent data sets. Thecomposite map of Figure 2.5 and the suite of profiles of Figure 2.6 highlight this point.Generally, anomalies on the apparent conductivity map have longer wavelengths thanthose on the magnetic maps (e.g., note the lack of short-wavelength features inFigs. 2.3a and 2.6a), and several key anomalies on the magnetic maps are either notobserved or only weakly represented on the apparent electrical conductivity and in-phase maps. These general observations

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Multidisciplinary Investigation of a Landfill and Its Host Sediments

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