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 ) .

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    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

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    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

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    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

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    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

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    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;

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    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.

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    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.

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    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¬

    ing household andindustrial waste;

    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.

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    Introduction 24

    Waste site;

    location Objectives Methods Reference

    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

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    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¬

    ing household andindustrial waste;

    Stetten, Switzer¬land

    Determining depthextent of landfill

    Seismic refraction

    tomographic anddrilling

    Lanzetal., 1997b

    Landfill contain¬

    ing mainly house¬hold and

    construction waste;

    Härkingen, Swit¬zerland

    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.

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    Introduction 26

    Waste site:

    location Objectives Methods Reference

    Landfill contain¬ing mainly house¬hold and

    construction waste;

    Härkingen, Swit¬zerland

    Locating buriedwaste

    FDEM, GPR anddrilling

    De Iaco et al..1997b

    Landfill contain¬

    ing household andindustrial waste;

    Stetten, Switzer¬land

    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¬

    ing household andindustrial waste;

    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.

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    27 Introduction

    Waste site;location Objectives

    Methods Reference

    Landfill;Oak Ridge Reser¬vation, Tennessee,USA

    Mapping faults andfracture zones near

    landfill

    Seismic reflection Doll, 1998

    Landfill contain¬

    ing household andindustrial waste;

    Arnstadt, Germany

    Locating buildingburied in landfill

    Seismic reflection Pasasaetal, 1998

    Landfill;

    not specified

    Locating buriedwaste

    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;

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    Introduction 28

    Waste site;location Objectives

    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;

    Härkingen, Swit¬zerland

    Locating buriedwaste

    FDEM, magnetic,GPR and drilling

    DcTacoctaL, 1998

    Landfill;

    Pennsylvania,USA

    Locating buriedwaste

    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,

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    29 Introduction

    Waste site;location Objectives

    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

    Locating buriedwaste

    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

    Locating buriedwaste

    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

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    Introduction 30

    Waste site;

    location Objectives Methods Reference

    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

    DC-resistivity andIP

    Carlson et al, 1999

    Landfill contain¬

    ing municipalwaste;

    Venice province,Ttaly

    Mapping high per¬meability layersand detecting

    potential leakage

    DC-resistivity andIP

    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.

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    31 Introduction

    Waste site;

    location Objectives Methods Reference

    Landfill contain¬

    ing household andindustrial waste;

    Stetten, Switzer¬land

    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¬

    ing household andindustrial waste;

    Stetten, Switzer¬land

    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.

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    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

    .

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    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