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Mont Terri Project Geochemistry of Water in the OpalinusClay Formation at the Mont Terri Rock LaboratoryF. J. Pearson, D. Arcos, A. Bath, J. -Y. Boisson, A. M. Fernndez, H.-E. Gbler, E. Gaucher, A. Gautschi, L. Griffault, P. Hernn and H. N. Waber

Berichte des BWG, Serie Geologie Rapports de lOFEG, Srie Gologie Rapporti dellUFAEG, Serie Geologia Reports of the FOWG, Geology Series

No. 5 Bern 2003

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Umschlag 30.10.2003 12:05 Uhr Seite 1

ISSN 1660-0754ISBN 3-906723-59-3

Umschlag 30.10.2003 12:05 Uhr Seite 2

Eidgenssisches Departement fr Umwelt, Verkehr, Energie und KommunikationDpartement fdral de lenvironnement, des transports, de lnergie et de la communicationDipartimento federale dellambiente, dei trasporti,dellenergia e delle comunicazioniFederal Department of Environment, Transport,Energy and Communications

Mont Terri Project Geochemistry of Water in the OpalinusClay Formation at the Mont Terri Rock Laboratory

F. J. Pearson, D. Arcos, A. Bath, J. -Y. Boisson, A. M. Fernndez, H.-E. Gbler, E. Gaucher, A. Gautschi, L. Griffault, P. Hernn and H. N. Waber

Berichte des BWG, Serie Geologie Rapports de lOFEG, Srie Gologie Rapporti dellUFAEG, Serie Geologia Reports of the FOWG, Geology Series

No. 5 Bern 2003

Chapter 30.10.2003 10:37 Uhr Seite 1

2

Impressum

Editor Federal Office for Water and Geology,FOWG

ISSN / ISBN ISSN 16600754/ ISBN 3906723593

Recommended Pearson, F.J. et al. (2003): Mont Terri Projectquotation Geochemistry of Water in the Opalinus

Clay Formation at the Mont Terri Rock Labo-ratory. Reports of the Federal Office forWater and Geology (FOWG), Geology SeriesNo. 5.

For individual chapters: Authors of chapter X (2003): Titel of chapterX. In: Pearson, F.J. et al. (2003): Mont TerriProject Geochemistry of Water in theOpalinus Clay Formation at the Mont TerriRock Laboratory. Reports of the FederalOffice for Water and Geology (FOWG), Geo-logy Series No. 5.

Cover photos Nagra, Comet

Internet This report is available in PDF format atwww.bwg.admin.ch

Impression 1200 copies

Distribution BBL, Vertrieb Publikationen, CH-3003 Bernwww.bbl.admin.ch/bundespublikationen

Order Number 804.605e

Copyright FOWG, Bern-Ittigen, 2003


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Responsible for the Mont Terri motorway tunnel system and authorizations

RCJURpublique et Canton du JuraDpartement de lEnvironnement et de lEquipement

Project Partners

ANDRAAgence nationale pour la gestion des dchets radioac-tifs, France

BGRBundesanstalt fr Geowissenschaften und Rohstoffe,Germany

CRIEPICentral Research Institute of Electric Power Industry,Japan

ENRESAEmpresa Nacional de Residuos Radiactivos, S.A., Spain

FOWG/SGSFederal Office for Water and Geology, Swiss Geologi-cal Survey

GRSGesellschaft fr Anlagen- und Reaktorsicherheit mbH,Germany

HSKSwiss Federal Nuclear Safety Inspectorate

IRSNInstitut de radioprotection et de sret nuclaire,France

JNCJapan Nuclear Cycle Development Institute, Japan

NAGRANational Cooperative for the Disposal of RadioactiveWaste, Switzerland

OBAYASHIObayashi Corporation, Japan

SCKCENStudiecentrum voor Kernenergie, Centre d'tude del'nergie nuclaire, Belgium

Direction of the Project

FOWGFederal Office for Water and Geology, Switzerland

Project Management

GIGeotechnical Institute Ltd., St-Ursanne, Switzerland

Organizations involved in the Mont Terri Project


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F.J. Pearson Jr., Ground Water Chemistry, New Bern,NC 28560, [email protected]

David Arcos, ENVIROS (Quantisci S.L.), Parc Tecnolgicdel Valls, E-08290 Cerdanyola del Valls, [email protected]

Adrian Bath, Intellisci Ltd., Willoughby-on-the-Wolds,Loughborough LE12 6SZ, United [email protected]

Jean-Yves Boisson, I.R.S.N. / D.E.S. / S.E.S.I.D., F-92 262 Fontenay aux Roses, [email protected]

Ana Mara Fernndez Daz, Dept. Impacto Ambientalde la Energia (DIAE), CIEMAT, E-28040 Madrid, [email protected]

Hans-Eike Gbler, Bundesanstalt fr Geowissen-schaften und Rohstoffe (BGR), D-30655 Hannover,[email protected]

Eric Gaucher, BRGM, F-45060 Orlans, [email protected]

Andreas Gautschi, Nagra, CH-5430 Wettingen,[email protected]

Lise Griffault, ANDRA , F-92298 Chatenay-MalabryCedex, [email protected]

Pedro Hernn, ENRESA, Coordinacin y Soporte Tec-nolgico, E-28043 Madrid, [email protected]

Niklaus Waber, Institut fr Geologie, Universitt Bern,CH-3012 Bern, [email protected]

List of authors


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The first experiments of the international researchproject Mont Terri (St-Ursanne, Canton Jura) started inJanuary 1996. Research is carried out in a gallery andin niches excavated from the security gallery of theMont Terri road tunnel. The Swiss Geological Survey, adivision of the Federal Office for Water and Geology(FOWG), supports hydrogeological research projects inlow-permeability formations and is one of the MontTerri partners since the beginning of the project. Theaim of the project is the geological, hydrogeological,geochemical and geotechnical characterisation of aclay formation, specifically of the Opalinus Clay. Twelvepartners from six different countries participate todayin the project. The FOWG is in charge of the projectdirection since July 2001 and is also responsible for thepublication of the reports. For geological reasons, arepository for radioactive waste in the Mont Terri re-gion has been ruled out.After the completion of different experiments in thefield of geochemistry, their results were compiled in anextensive synthesis. Following the publication of ageneral synthesis related to the initial part of the MontTerri Project (SNHGS, Geological Report No. 23, 1999)and the geological description of the Mont Terri region(Reports of the FOWG, Geology Series No. 4, 2003),we are pleased to present now the geochemical syn-thesis to a broader scientific audience. The editorwould like to express his best thanks to the authorsand all others contributing to this volume for their spe-cial effort. We would also like to thank the Mont TerriPartners for their excellent collaboration and the feder-al and cantonal authorities for their support in theproject. Dr. R. Burkhalter and Dr. P. Heitzmann (FOWG)are gratefully acknowledged for thorough review andthe edition of the report.The authors alone are responsible for the content ofthe text and the illustrations.Further information can be found on the Internet sitewww.mont-terri.ch.

Les premires expriences ralises dans le cadre duprojet de recherche international du Mont Terri (St-Ur-sanne, Canton du Jura) ont t entreprises en 1996.Les recherches sont ralises dans une galerie et desniches excaves partir de la galerie de scurit dutunnel autoroutier du Mont Terri. Le Service golo-gique national (Office fdral des eaux et de la golo-gie, OFEG) soutient ltude des formations golo-giques faible permabilit et collabore ds le dbutcomme partenaire au Projet Mont Terri. Lobjectif prin-cipal du projet est la caractrisation gologique, hydro-gologique, gochimique et gotechnique dune for-mation argileuse, les Argiles Opalinus. Douze parte-naires de six diffrents pays collaborent aujourdhui auprojet. La direction du projet est depuis juillet 2001place sous la responsabilit de lOFEG, auquel incom-be galement la publication des rapports. Pour des rai-sons gologiques, il nest pas question dentreposerdes matriaux radioactifs dans la rgion du Mont Terri.Aprs avoir termin diffrentes expriences gochi-miques, les rsultats obtenus ont pu tre mis en valeursous la forme dune synthse tendue. Cest avec plai-sir que nous prsentons ici, aprs une premire syn-thse gnrale relative la partie initiale du ProjetMont Terri (SHGN, Rapport gologique No 23, 1999)et la description gologique de la rgion du Mont Terri(Rapports de lOFEG, Srie gologie No 4, 2003), lasynthse gochimique un large public de spcialistes.Lditeur tient remercier les auteurs ainsi que les per-sonnes qui, par leur comptence et leur engagement,ont permis la ralisation de cette synthse. Nos remer-ciements sadressent aussi nos partenaires du ProjetMont Terri pour leur prcieuse collaboration et auxautorits fdrales et cantonales pour leur soutiendans le projet. R. Burkhalter, dr.sc., et P. Heitzmann,dr.sc.nat. (OFEG) sont remercis de leur lecture atten-tive du manuscrit et du suivi de ldition du rapport.Les auteurs sont seuls responsables du contenu dutexte et des illustrations.Pour toute information supplmentaire veuillez consul-ter le site Internet www.mont-terri.ch.

Preface of the Editor Prface de lditeur


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Die ersten Experimente, die im Rahmen des internatio-nalen Forschungsprojektes Mont Terri (St-Ursanne,Kanton Jura) realisiert worden sind, haben im Januar1996 begonnen. Die Untersuchungen werden in ei-nem erweiterten Teil des Sicherheitsstollens des Mont-Terri-Autobahntunnels durchgefhrt. Die Landesgeolo-gie im Bundesamt fr Wasser und Geologie (BWG)untersttzt die hydrogeologischen Untersuchungengeringdurchlssiger geologischer Formationen und ar-beitet deshalb seit Beginn als Partnerin im Mont-Terri-Projekt mit. Das Hauptziel dieses Projektes ist die geo-logische, hydrogeologische, geochemische und geo-technische Charakterisierung von Tongesteinen, imSpeziellen des Opalinus-Tons. Heute sind zwlf Partneraus sechs Lndern am Projekt beteiligt. Die Leitung desProjektes liegt seit Mitte 2001 beim BWG. Dieses istauch fr die Verffentlichung der Berichte verantwort-lich. Aus geologischen Grnden ist im Mont-Terri-Ge-biet jegliche Planung eines Endlagers fr radioaktiveAbflle ausgeschlossen.Nach Abschluss verschiedener geochemischer Experi-mente sind deren Ergebnisse zu einer umfassendenSynthese verarbeitet worden. Es freut uns, im Rahmender Mont-Terri-Publikationen nach der einfhrendenZusammenfassung (LHG, Geologische Berichte Nr. 23,1999) und der geologischen Beschreibung des Mont-Terri-Gebietes (Berichte des BWG, Serie Geologie Nr. 4,2003) jetzt auch die geochemische Synthese einembreiten Fachpublikum vorlegen zu knnen. Der Her-ausgeber mchte den Autoren und allen andern, diean diesem Band beteiligt waren, fr ihren grossen Einsatz bestens danken. Ebenfalls danken mchten wir unseren Mont-Terri-Partnern fr die wertvolle Zu-sammenarbeit sowie den eidgenssischen und kan-tonalen Behrden fr ihre Untersttzung im Projekt.Dr. R. Burkhalter und Dr. P. Heitzmann (BWG) sei frdie aufmerksame Durchsicht des Manuskripts und dieBegleitung der Herausgabe gedankt.Fr den Inhalt des Textes und die Illustrationen sind dieAutoren allein verantwortlich.Weitere Informationen zum Mont-Terri-Projekt findenSie unter www.mont-terri.ch.

I primi studi effettuati nellambito del progetto di ricer-ca internazionale Mont Terri (St-Ursanne, Canton Giu-ra) sono iniziati nel gennaio 1996. Le ricerche sonorealizzate in un cunicolo e nelle nicchie scavate a parti-re dalla galleria di soccorso del tunnel autostradale delMont Terri. Il Servizio geologico nazionale dellUfficiofederale delle acque e della geologia (UFAEG) promuo-ve gli studi di formazioni geologiche a bassa permeabi-lit, collaborando fin dallinizio come partner del pro-getto Mont Terri. Lobiettivo principale del progetto la caratterizzazione geologica, idrogeologica, geochi-mica e geotecnica di una particolare formazione argil-losa: lArgilla ad Opalinus. A tuttoggi collaborano alprogetto dodici partner di sei diverse nazioni. Dal luglio2001, il progetto sotto la direzione dellUFAEG, alquale compete anche la pubblicazione dei rapporti. Lapianificazione di un deposito finale per le scorie ra-dioattive sotto il Mont Terri da escludere per ragionigeologiche.Dopo aver concluso diverse ricerche geochimiche, i ri-sultati sono stati presentati in unampia sintesi. La sin-tesi, destinata a un largo pubblico di specialisti, fa se-guito alla parte introduttiva edita nellambito del pro-getto Mont Terri (SIGN, Rapporti geologici, n. 23,1999) e alla descrizione geologica della regione pubbli-cata nei Rapporti dellUFAEG, Serie geologia n. 4,2003. Ringrazio tutti gli autori e le persone che, con leloro conoscenze e il loro impegno, hanno contribuitoalla riuscita dellopera. I ringraziamenti vanno estesianche ai partner del Mont Terri e alle autorit cantona-li e federali per la preziosa collaborazione e il sostegnoal progetto. Un ringraziamento particolare va al Dr. R.Burkhalter e al Dr. P. Heitzmann (UFAEG) per lattentarilettura del manoscritto e ledizione del rapporto.Gli autori sono gli unici responsabili del contenuto deitesti e delle illustrazioni.Ulteriori informazioni sono pubblicate allindirizzowww.mont-terri.ch.

Federal Office for Water and GeologyThe Head of the Swiss Geological Survey

Dr. Christoph Beer

Vorwort des Herausgebers Prefazione delleditore


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This report describes the methods, results and inter-pretations of a series of integrated geochemical stud-ies carried out at the Mont Terri Rock Laboratory inSwitzerland. Scientists from partners in the interna-tional Mont Terri project consortium carried out the in-vestigations, under the patronage of the Swiss Geo-logical Survey (Federal Office for Water and Geology FOWG) with logistical support by Nationale Genossen-schaft fr die Lagerung radioaktiver Abflle (Nagra,Switzerland). The aims of the studies were to developtechniques for establishing in situ chemical conditionsfor pore water in a claystone rock. At Mont Terri, theformation of interest is the Middle Jurassic OpalinusClay which occurs with thickness of about 150 metres.The Rock Laboratory, in which the Opalinus Clay oc-curs with a maximum present-day overburden ofabout 300 metres, has enabled various methods forsampling and testing water and its constituent solutes,stable isotopes and gases in the claystone to be evalu-ated. These methods include sampling in sealed bore-holes drilled from the tunnel, squeezing water frompreserved drillcores, and carrying out leaching experi-ments on core samples. A large number of data forwater compositions has resulted. The reliability andsignificance of these data have been considered bygraphical and geochemical modelling methods to pro-duce an interpretation of the most probable descrip-tion of in situ geochemical conditions in the OpalinusClay at Mont Terri. Further interpretation and model-ling of key data have improved the understanding ofthe chemical and transport processes that control thegeochemical environment in both natural and per-turbed states, and that have contributed to the naturalevolution of the claystone pore water system over along timescale. The significance and uncertainties inthe results are discussed and recommendations aremade for strategy and supporting research in futuresimilar investigations.

Ce rapport dcrit les mthodes, les rsultats et linter-prtation dune srie dtudes gochimiques intgresexcutes au laboratoire souterrain du Mont Terri enSuisse. Des scientifiques des organisations partenairesdu projet international du Mont Terri ont ralis lesexpriences sous le patronage du Service gologiquenational (Office fdral des eaux et de la gologie OFEG) et avec le support logistique de la Socit co-oprative nationale pour lentreposage de dchets ra-dioactifs (Nagra). Le but des tudes tait le dveloppe-ment de techniques pour interprter les conditions insitu des eaux dans les pores dune roche argileuse. AuMont Terri, la formation intresse est reprsente parles Argiles Opalinus du Jurassique moyen, qui ontune paisseur denviron 150 mtres. Dans le labora-toire souterrain, o les Argiles Opalinus sont sur-montes actuellement dune couverture de rochesdenviron 300 mtres au maximum, il a t possibledvaluer diffrentes mthodes pour prendre deschantillons et tester les eaux, les principales sub-stances dissoutes, les isotopes stables et les gaz danslargilite. Ces mthodes comprennent lchantillonna-ge dans des trous de forages scells par un obturateurexcuts dans le tunnel, lextraction sous pression deleau de carottes de forages, et des expriences de les-sivage sur des carottes. Il en a rsult de nombreusesdonnes sur la composition des eaux. La fiabilit et lasignification de ces donnes ont t prises en consid-ration au moyen de mthodes de modlisation gra-phique et gochimique pour interprter de la manirela plus probable les conditions gochimiques in situdans les Argiles Opalinus du Mont Terri.Une interprtation et une modlisation supplmen-taires de donnes clefs ont amlior les connaissancessur les processus de transport et les processus gochi-miques qui contrlent lenvironnement gochimiquedans ltat naturel et dans ltat perturb, et qui ontparticip lvolution naturelle du systme des eauxdes pores des argilites pendant une longue priode. Lasignification et les incertitudes des rsultats sont discu-tes et des recommandations pour une stratgie et unprogramme de recherche pour des expriences futuressont prsentes.

Abstract Rsum


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Dieser Bericht beschreibt die Methoden, Resultate undInterpretationen einer Serie von integralen geochemi-schen Studien, die im Mont-Terri-Felslabor in derSchweiz durchgefhrt wurden. Wissenschafter derPartnerorganisationen im Mont-Terri-Projekt haben dieExperimente unter dem Patronat der Landesgeologie(Bundesamt fr Wasser und Geologie BWG) und mitder logistischen Untersttzung der Nationalen Genos-senschaft fr die Lagerung radioaktiver Anflle (Nagra)durchgefhrt. Das Ziel der Studien war es, Technikenzu entwickeln, um die chemischen In-situ-Bedingun-gen von Porenwasser in Tongesteinen feststellen zuknnen. Die untersuchte geologische Formation amMont Terri ist der mitteljurassische Opalinus-Ton, dereine Mchtigkeit von ca. 150 m besitzt. Im Felslabor,in dem der Opalinus-Ton heute eine berlagerung vonca. 300 m aufweist, war es mglich, verschiedene Me-thoden fr Probennahmen und Tests von Wasser, dendarin gelsten Komponenten, den stabilen Isotopenund von Gasen im Tongestein zu entwickeln. Unterdiesen Methoden figurieren Probennahmen in abge-dichteten Bohrlchern, die vom Tunnel aus gebohrtwurden, das Auspressen von Wasser aus Bohrkernenund die Durchfhrung von Auslaugungs-Experimentenan Bohrproben. Eine Vielzahl von Daten ber die Was-ser-Chemie wurde gewonnen. Die Zuverlssigkeit undBedeutung dieser Daten wurden mittels graphischerMethoden und geochemischer Modellierungen ber-prft, um eine Interpretation ber die wahrscheinlich-ste Beschreibung der geochemischen In-situ-Bedingun-gen im Opalinus-Ton zu erhalten. Eine weitere Interpretation und Modellierung derSchlsseldaten haben wesentlich zur Verbesserung derKenntnisse ber die Transport- und die chemischenProzesse beigetragen, welche die geochemische Um-gebung sowohl bei natrlichen als auch bei gestrtenVerhltnissen kontrollieren und die Entwicklung desPorenwasser-Systems in Tongesteinen ber einen ln-geren Zeitraum beeinflusst haben. Die Bedeutung unddie Unsicherheiten der Resultate werden laufend dis-kutiert. Zudem werden Empfehlungen fr eine Strate-gie und mgliche Experimente fr hnliche zuknftigeProjekte abgegeben.

The work reported here and the data on which it isbased could not have been achieved without vitalcontributions from a number of individuals who donot appear as authors. Thomas Fierz (Solexperts) designed and constructedthe boreholes for water sampling. Lorenz Eichinger(Hydroisotop) and Claude Degueldre (PSI) developedsampling and field and laboratory analytical tech-niques. Without their efforts, collection and analysesof the borehole water and gas samples would nothave been possible. David Entwisle, Shaun Reeder andMark Cave (BGS) performed much of the core squeez-ing and chemical analyses on the small water samplesthat resulted from it.Administration of the WS experiments at various timeswas handled by Andreas Scholtis (then with NAGRA)and Corinne Bauer (ANDRA). We also gratefully ac-knowledge the administrative support of Paul Bossart(Geotechnical Institute), the Project Manager of theoverall Mont Terri project.The opportunities for a geochemical project at MontTerri were first identified by Andreas Gautschi (NAGRA)and were promoted by Marc Thury, then Chairman of the Programme Committee for the Rock Laboratory.The report was brought to final completion and pu-blication under the leadership of Scott Altmann (ANDRA), the final Principle Investigator of the Geo-chemical Modelling Task, and with the support ofAndreas Gautschi (NAGRA).This report has greatly benefited from a thoughtfuland complete review by Professor Gil Michard.

Acknowledgments Zusammenfassung


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Background

The principal objective of the Mont Terri project is todevelop techniques to determine the hydrogeological,rock mechanical, geochemical and transport propertiesof clay rock. Work towards this objective is being car-ried out in the Mont Terri Rock Laboratory, locatedabout 1000 metres from the south-eastern portal of a3900 metre-long motorway tunnel in the Jura moun-tains of north-western Switzerland. The formation ofinterest in the Rock Laboratory is the Opalinus Claywhich is a claystone of Aalenian (Middle Jurassic) age.The Mont Terri Project is carried out under the patron-age of the Swiss Geological Survey (Federal Office forWater and Geology FOWG, formerly the NationalHydrological and Geological Survey, SNHGS), which al-so has an operational monitoring role on behalf of theCanton du Jura. It is run jointly as a consortium ofnine partners. In addition to the Swiss Geological Sur-vey and NAGRA, the original partners were ANDRA(France), PNC (now JNC, Japan) and SCKCEN (Bel-gium). Since then, BGR (Germany), IPSN (France), EN-RESA (Spain) and Obayashi (Japan) have joined theconsortium.This report describes the methods, results and inter-pretations of the WS (water sampling) and GM (geo-chemical modelling) experiments in the Mont TerriRock Laboratory, which were supported by NAGRA,ANDRA, JNC, BGR, IPSN and ENRESA. These were con-cerned with (a) developing and evaluating methodolo-gy for measuring compositions of pore waters in low-permeability clay rocks with low water contents, and(b) describing and modelling in situ compositions andprocesses that control the geochemical environment inthese rocks and their responses to perturbations.The Opalinus Clay formation is subdivided into fivelithological sub-units with silty-shaly, sandy and car-bonate-rich sandy facies. It is underlain by more than100 metres of Liassic marls, shales and limestones. Be-low the Liassic units is the Rhaetian and the Keuper,which is dominantly marl and anhydrite/gypsum. TheOpalinus Clay is overlain by the rest of the Dogger, c.250 m thick and comprising mostly sandy limestonesand limestones, and by the Malm limestone which isthe top of the sequence at Mont Terri. Between theunderlying Muschelkalk aquifer and the overlyingMalm aquifer, the shale succession from Keuper/Lias toDogger forms a 300450 metre-thick sequence of lowto very low permeability rocks.The Opalinus Clay was deposited about 180 millionyears ago in the Jurassic sea, and is presently foundthroughout northern Switzerland. Middle Jurassic clay-stones and limestones, of which the Opalinus Clay ispart, were covered by more than 1000 metres of lime-

Executive Summary

stones and marls/clays through to the mid- to late-Cre-taceous period. Compaction and consolidation result-ed in a vertical thickness for the Opalinus Clay ofabout 80160 metres in northern Switzerland. Some-time between mid- to late-Cretaceous and the mid-Tertiary Oligocene period (i.e. between about 100 and25 million years ago), there was a period of marine re-gression such that the top of the Malm limestone wassubaerially exposed for at least 30 million years. Re-newed subsidence during the early- to mid-Tertiary pe-riod submerged the sequence again under the sea.Late Alpine folding during the late Miocene toPliocene stages of the upper Tertiary period (about 10to 2 million years ago) formed the Folded Jura. Upliftand erosion during the Tertiary and Quaternary periodsinitiated the influx of meteoric water to the sequence.Fresh water infiltration to the Dogger limestoneswould have commenced towards the end of thePliocene period (about 2.5 million years ago) whenerosion exposed the core of the Mont Terri anticline.Similarly, infiltration to the Liassic limestones wouldhave started in the Quaternary, around 350 thousandyears ago.The reconnaissance tunnel at Mont Terri passesthrough a 239 metre long section of Opalinus Clay,corresponding to a true thickness of about 160 me-tres. The maximum overburden above the Rock Labo-ratory is about 300 metres. Mont Terri is the northern-most of a series of anticlines of the Folded Jura, andhas been overthrust at least 1 km north-westwardsover the Tabular Jura. The south-eastwards dips of NE-SW trending strata in and around the Rock Laboratoryvary from 22 at the Opalinus Clay Lias contact to55 at the Lower Dogger Opalinus Clay contact. Asingle thrust zone with increased fracturing is locatednear to the centre of the Opalinus Clay section and iscalled the main fault. The absence of any hydro-chemical anomalies in the zone of the main fault isconsistent with the fact that the hydraulic conductivityof the fault is comparable with that of undisturbedrock matrix.The Opalinus Clay is a well consolidated, dark greyclaystone that has a uniaxial compressive strength of48 MPa. Calcite is quantitatively dominant, as expect-ed, in the carbonate-rich sandy facies, and is also amajor component in at least parts of the sandy andshaly facies. Dolomite/ankerite and siderite are minoror trace phases in all facies, in proportion to the calcitecontents. Pyrite is present mostly at

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have remained poorly crystalline due to the low tem-perature history (maximum burial temperature 80C). Hydraulic testing gives hydraulic conductivities between2 x 10-13 and 9 x 10-13 m/s. Permeabilities are up to twoorders of magnitude higher in the bulk of the excava-tion disturbed zone (EDZ) around the tunnel wall, in-creasing in localised zones to around 10-8 m/s. Inflowrates in boreholes correspond to hydraulic conductivi-ties between 3 x 10-15 and 3 x 10-12 m/s.A time series of the combined data from seepages thatare located in Liassic claystones/limestones adjacent tothe Opalinus Clay shows that the salinity declinedsharply from the initial flow in 1989 when first sampledsoon after tunnelling. This freshening was accompa-nied by rising tritium (3H) levels. These changes indicatethat the seepages in the Liassic are sufficiently connect-ed to the surface that meteoric water has been drawn-down towards the tunnel. Seepages in the Lower Dog-ger have not responded to the tunnel in this way.

Sampling Methodology

Because of the very low permeability of the OpalinusClay, samples of pore water cannot be collected by themethods conventionally used for sampling groundwa-ter. The initial hydrochemical experiments at Mont Ter-ri, therefore, focused on unconventional methods forcharacterising pore water.There are three sources of data on water chemistry atMont Terri: analyses of water samples collected in situfrom sealed sections of boreholes drilled from the un-derground laboratory, analyses of water samples ob-tained by high-pressure squeezing of core samples,and aqueous extraction (leaching) from core samples.When combined with knowledge of the free water(geochemical) porosity, and with cation exchange data,mineralogical information and geochemical modelling,leaching data have been used in an integrated methodfor characterising pore water and the artefacts thatperturb its composition.The WS-A experiment has tested the feasibility of sam-pling water directly by allowing it to seep into sealedsections of boreholes drilled from the undergroundlaboratory. Initially, three boreholes were drilled for thepurpose of installing water sampling packer systems inthe Opalinus Clay. Borehole BWS-A1 was in the shalyfacies and was oriented so that it intersected the so-called main fault. BWS-A2 was drilled from the sandyfacies into the shaly facies of undisturbed OpalinusClay with no identified fractures. BWS-A3 was drilledentirely in the shaly facies. They were core-drilled to2028 metres length, upwards at about 60 from thegallery and approximately normal to bedding. To max-imise the quality of core recovered for pore water ex-

traction and other tests, double or triple core barrelswere used with external diameter of 86 mm.Water was successfully collected by gravity flow intoboreholes BWS-A1, A2, and A3. Fluxes of water intothe boreholes increased to maxima of 2065 ml/day at1824 months after drilling. Flow rates can be approx-imated by Darcys Law, i.e. they are consistent with thehydraulic conductivity of the clay rock and the hy-draulic gradient towards the tunnel. BWS-A1 yieldedthe most saline water of any of the Mont Terri bore-holes, with mean Cl- and SO4

2- contents of 288 and13.6 mmol respectively.The WS-E experiment has provided drillcores from nineboreholes spanning the full thickness of the OpalinusClay and adjacent claystones. They were core-drilledhorizontally to about 5 metres length. Boreholes BWS-E1 to E5 were located in the sandy facies of the Opali-nus Clay, close to the contact with the Lower Doggerformation. BWS-E6 to E8 were in the Liassic and BWSE9 was right at the top of the Keuper marl formation.Water samples have been obtained from drillcoresfrom the BWS-A and BWS-E boreholes by mechanicallysqueezing sections of drillcore under high loads inpurpose-built rigs and collecting the expelled waters.Water could be recovered at pressures of 70 MPa orless from all samples with water contents greater than6 wt%.Two types of leaching studies on core material havebeen made. One, using pure water as the leaching so-lution, was intended to measure the quantity of readilysoluble salts present in the pore water in situ. The oth-er was made using solutions intended to extract ex-changeable cations while minimising mineral dissolu-tion.Aqueous leaching of drillcore removes pore watersolutes by diluting them into the leaching solution.However, the aqueous leaching process also stimulatessome reaction between water and rock. Thus, in gen-eral, aqueous leaching does not give a reliable esti-mate of pore water solutes except for solutes such aschloride and bromide (and sulphate if there are no sul-phate minerals present), that are conservative becausethey are present only in pore water. Comparison ofporosity implied from chloride dilution on leachingwith the physical porosity has led to the concept ofchloride (or geochemical) porosity. Values for chlorideporosity are lower than water loss porosities becauseanionic solutes such as chloride are excluded from thebound layer of water that is adjacent to the negative-ly-charged mineral surface. The range of reduction fac-tors in these samples is between 0.25 and 0.92 with amean of 0.570.06. This is consistent with the ratiobetween free and bound water estimated from specif-ic surface area.


11

Two other methods of obtaining samples directly fromdrillcore have been used in determining the stable iso-topic composition of water (18O/16O and 2H/1H) and thecontents and isotopic compositions of noble gases dis-solved in pore waters (He, Ne, Ar, Kr, Xe, 3He/4He and40Ar/36Ar). A new method for extracting pore watersfrom clay rocks for stable isotope analysis has been de-veloped. This replaces vacuum distillation for which itis shown that resulting stable isotopic data have amuch higher degree of uncertainty due to incompleteextraction of water. The new method involves the ex-change to isotopic equilibrium between pore water inthe clay rock and a small amount of water with known(and similar) isotopic composition in a sealed containerat room temperature. Noble gases in pore waters wereanalysed after vacuum extraction of gases directlyfrom drillcores, followed by purification, separationand analysis by mass spectrometer.

Analysis and Interpretation of Unstable ChemicalParameters

Unstable chemical parameters were measured directlyon water that had accumulated in boreholes BWS-A1,A2 and A3. Water samples were periodically bled offthrough the sampling lines and were passed directlyinto a series of flow-through cells in which Pt-elec-trode potential (i.e. measuring redox conditions as Eh),pH, electrical conductivity (EC), temperature (T), anddissolved oxygen could be monitored. Monitoring re-sults suggest that oxygen contamination has prevailedin most if not all redox measurements, even in thosewhere relatively large volumes are available to flushthe cells. pH of borehole waters was generally measured in-lineusing a combined glass electrode in a flow-throughcell. The importance of using the closed conditions ofthe flow-through cell is demonstrated by the pHchanges that occur when samples are exposed to airand allowed to exchange CO2. The pH of less salinesamples drifted to values about 0.5 pH units lower,whereas more saline samples drifted to higher values,as much as 1 pH unit higher.More saline waters have lower alkalinities (0.2 to 2.5mmol) and hence lower pH-buffer capacities than lesssaline waters (3.6 to 5.1 mmol). Thus end points inpotentiometric titrations of the former are less well de-fined than those of the latter. Consequently alkalinitydata for the former waters have greater variability anduncertainty than those for the latter.pCO2 is an important parameter for describing thepore water geochemistry. The pCO2 values calculatedfrom field pH and alkalinity or total inorganic carbon(TIC) data range from 10-3.0 to 10-4.7 bar. For less saline

samples, values calculated from measured alkalinity orTIC values and pH are internally consistent. A tendencyfor calcite saturation indices calculated from these wa-ters to be positive, along with a tendency for the pHof the samples to increase on exposure to the atmos-phere, both indicate CO2 outgassing during samplingor analysis. Evidence about the pCO2 of more salinewater samples is less consistent. The alkalinity and TICvalues of these samples are very low and there is widevariation in the analytical results. The average of pCO2values calculated from two internally consistent sets ofanalyses is 10-3.7, i.e. below that of the atmosphere.An additional approach to understanding the pH-TICsystem in these pore waters has been developed, us-ing laboratory experiments to estimate in situ pCO2.The pCO2 in a sample of core was measured in asealed cell within a few hours of its extraction fromthe borehole. Reasonable values of pCO2 were givenby these tests for lower salinity pore waters, i.e. pCO2in the range 10-2.4 to 10-2.2 bar. The only measurementin core with high-salinity pore water gave a muchhigher pCO2, attributed to the long storage time ofthe core before the measurement was made.Pt-electrode potentials are mostly consistent with thepresence of dissolved oxygen. They approach those ex-pected from the redox couple for free oxygen. Com-positions of gases in the sealed boreholes show thatO2 was present, in spite of precautions to avoid suchcontamination. Thus the Pt-electrode measurementsrepresent contamination. A few lower values for Pt-electrode potentials could originate from corrosion ofiron in borehole construction materials.Concentrations of electrochemically-active soluteswere measured in both filtered and unfiltered boreholesamples. The range of total analysed Fe in filteredsamples is from

12

redox potentials corresponding to the N2/NH4+, C0/CH4

or H2O/H2 couples even though all three gases werepresent, as well as higher hydrocarbons. The stablecarbon and hydrogen isotopic compositions of thegases provide information on bacterial processes in theboreholes. The carbon isotopic composition of theethane and propane are consistent with the vitrinitereflectance of the Opalinus Clay, suggesting the originfor these gases is the formation itself. The carbon andhydrogen isotopic composition of the methane is notconsistent with such an origin, suggesting that bothacetate fermentation and oxidation to CO2 may affectmethane.

Perturbations of Samples and Measurements

Perturbations are processes that lead to differences be-tween reported values of water chemical parametersand their values for water in situ. The main perturba-tions are disturbances to the formation during under-ground laboratory construction and borehole drilling,effects on core and water samples during collection,storage and preparation, and artefacts due to theprocess of collecting water samples by squeezing. Themost pervasive perturbation is oxidation following ex-posure to the atmosphere.The extent of the excavation disturbed zone (EDZ) as itaffects the in situ compositions of pore water hasbeen investigated by analyses of the dissolved He con-tents of core samples from a borehole drilled perpen-dicular to the tunnel wall. Losses of dissolved heliumshow evidence of disturbance in the rock at distancesup to 3 metres from the tunnel wall, although excava-tion-induced fracturing can be detected visually onlyto about 2 metres. Core samples for measurements ofin situ dissolved gas and for pore water extractionswere therefore taken at distances of at least 5 metresfrom the tunnel wall.Increased rates of water flow were detected in bore-holes, corresponding to a period of blasting for exca-vation of the new gallery. The coincidence betweenblasting and increased flow rates suggests that therock close to the boreholes has responded, though themechanism for this is not clear. There is not a corre-sponding detectable anomaly in water compositions.There is no evident systematic variation over time inthe concentration of any constituent of borehole wa-ter samples.When Opalinus Clay core samples are exposed to airduring drilling, storage, squeezing or leaching, sul-phate is produced by oxidation of pyrite. The variabilityof both SO4

2- and SO4/Cl ratios among water samplessuggests that oxidation may affect almost any sample.For interpreting in situ water chemistry, greater re-

liance is therefore placed on the samples with the low-est SO4/Cl ratios. There are higher SO4/Cl ratios inmany squeezed water samples than in water samplestaken from corresponding boreholes, indicating thatmore oxidation is associated with squeezing.The potential impacts of pyrite oxidation have been in-vestigated in greater detail in the course of aqueousleaching tests, because the potential for oxidation isgreater. In some tests, leaching was carried out in anoxygen-free glovebox. The extent of sulphide oxidationincreases with core exposure to air during drilling andcollection, storage time between collection and labora-tory investigation (even if the core is stored in air-tightcontainers), core drying (even in inert atmospheres)and core exposure to air during laboratory preparationand the leaching itself. To avoid, or at least to min-imise pyrite oxidation, air contact with the sampleshould be avoided entirely at all stages.In those samples that had suffered greatest degrees ofoxidation, the precipitation of gypsum is thought tohave had a significant effect on the concentrations ofCa2+ and SO4

2- in squeezed waters. It is also possiblethat jarosite [KFe3(SO4)2(OH)6] could form, in whichcase K+ concentrations in squeezed waters would alsobe affected. Some potential perturbations may be more marked insqueezed water samples because of the artificialprocess of squeezing and the amount of rock samplepreparation that is required. Squeezing could lead todifferences between in situ and sampled water by pro-moting ultrafiltration of solutes. The effect should bemost evident in the squeezing done at the highestpressures. It has been investigated by analysing se-quential fractions of expelled pore water as the com-paction load increased. Ultrafiltration was not a con-cern until squeezing pressures were above 200 MPawhen Cl-, as well as SO4

2-, Na+, K+, Br - and TOC, con-centrations decrease systematically until, at 512 MPa,Cl- has only 75% of its concentration in the initialwater.

Geochemical Patterns and Comparisons ofSampling Methods

The overall pattern of pore water chemistry at MontTerri is evident from the compositions of borehole andsqueezed water samples. At the base of the OpalinusClay, and in the adjacent Liassic claystones, the porewater is of the Na-Cl type with maximum Cl concen-trations about 340 mmol. The salinity decreases up-wards through the Opalinus Clay and downwardsthrough the Liassic units. Near its boundary with theLower Dogger units, the Opalinus Clay contains wa-ter with about 60 mmol Cl.


13

The Br/Cl ratios of all samples are virtually the same asthat of seawater and indicate that the origin of thenon-reactive solutes was seawater. The SO4/Cl ratios ofmost of the borehole samples are also close to that ofseawater. Higher SO4/Cl ratios are attributed to oxida-tion of pyrite during core collection, storage andpreparation for analysis.Na+ is the dominant cation in all waters and varies sys-tematically with Cl-. Decreasing Na+ with decreasingCl- leads to decreasing Ca2+ and Mg2+ concentrations,with Mg2+ concentrations decreasing relatively morethan those of Ca2+. To maintain carbonate mineralequilibria with decreasing Ca2+ and Mg2+ requires anincrease in the CO3

2- activity. This is associated withthe increase of alkalinity with decreasing Cl-. K+ does not vary simply with Na+ and there is consider-able spread in the K+ concentrations in these waters.The K+ concentrations appear to be constrained bycation exchange but the range of data shows that thisexchange is complex and difficult to quantify.Overall consistency within the data sets is less goodamong the squeezed samples than among the watersamples from boreholes, except for Cl- and Na+ whichare the dominating anion and cation respectively in allpore waters. There are particularly wide scatters forSO4

2- and alkalinity, with the SO42- values in squeezed

waters being higher than those of corresponding bore-hole samples due to sample oxidation. Alkalinity valuesare low like those of the borehole samples and are sub-ject to the same analytical difficulties and instabilities.There is considerable scatter among the compositionsof the aqueous extract samples. Both their SO4

2- andalkalinity values are higher than those of any boreholeor squeezed sample. High SO4

2- is a result of oxidationwhile the high alkalinity is attributed to carbonatemineral dissolution in the relatively dilute aqueousleachate solutions. Aqueous extracts have lower Ca2+

and Mg2+ concentrations than either squeezed orborehole waters in spite of carbonate mineral dissolu-tion. Both the Na+ and K+ contents of the aqueous ex-tracts are higher than those of either the borehole orsqueezed samples. This suggests that Ca2+ and Mg2+

have displaced Na+ and K+ on cation exchange sites.Essentially, the effect of these perturbations duringleaching is that only Cl- and Br- in the leachate can bereliably assumed to come from dilution of pore watersolutes alone.

Geochemical Modelling of Pore Water Compositions

Equilibrium modelling of aqueous speciation and solu-tion-mineral reactions in the Opalinus Clay rests ontwo assumptions. The first is that, with the exceptionof certain free or non-reacting constituents, the pore

water chemistry is controlled by chemical equilibriawith its host rock. This seems reasonable, given thefine-grained nature of the Opalinus Clay and the resi-dence time of pore water. The free constituents areanions such as Cl-, Br-, and probably SO4

2-, the concen-trations of which are determined by the evolutionaryhistory of the pore water rather than by local water-rock reactions. Concentrations of free constituents arefixed in model input either explicitly or implicitly byspecifying mixing ratios of end-member waters.The second assumption is that the water-rock equilib-ria controlling the major cation concentrations in theOpalinus Clay can be modelled adequately using car-bonate minerals and cation exchange reactions. Thevalidity of this assumption is supported by the fact thatthe water analytical data and the results of laboratorywater-rock equilibria can be successfully reproducedusing equilibrium modelling. Gypsum is not includedas a controlling phase except in models specifically ex-ploring oxidation processes. Gypsum has been foundin Opalinus Clay samples, but only on surfaces whereit could have been formed by pyrite oxidation. All wa-ter samples, except those with high SO4/Cl ratios dueto oxidation, are undersaturated with respect to gyp-sum. pH values used in modelling are obtained by formallyassociating pH with solution electroneutrality. That is,the modelling program iterates on pH to minimise thealgebraic sum of anion and cation charges.The modelling uses a defined initial water compositionand allows it to react to equilibrium with specifiedphases. The initial waters chosen have the compositionof normal seawater diluted with pure water to the Cl-

content of the water being modelled. The diluted sea-water has higher K+ and Mg2+ and lower Ca2+, Sr2+, al-kalinity, total Fe and total Mn values than the boreholesamples. SO4

2- is fixed at its seawater ratio to Cl- formost runs except that in which it was calculated fromcelestite (SrSO4) saturation.A disadvantage of this approach is that there may beinsufficient equations in the model to fix all importantparameter values so that an additional parameter val-ue must be specified. For these waters, this is the totalinorganic carbon content (TIC) or the partial pressureof CO2 (pCO2). pCO2 values used for this modellingvary with salinity, from 10-2.2 bar to 10-3.7 bar.With known values for pCO2 and pH, the concentra-tions of the other major dissolved carbonate speciesHCO3

- and CO32- are also fixed. Both calcite and

dolomite are present in the formation and are suffi-ciently reactive that the pore water should be in equi-librium with them, thereby fixing Ca2+ and Mg2+ con-centrations. Na-Mg exchange, rather than dolomitesolubility, could be chosen as the control on Mg2+ con-


14

mineral assemblage. In the Opalinus Clay the principalexchanging minerals are clays. The selectivity coeffi-cients depend on the identity and properties of thespecific clay minerals present. In the Opalinus Clay,those with the dominant exchange capacity are illiteand illite/smectite.Exchangeable cation populations have been measuredusing displacement with nickel ethylenediamine (Ni-en)and cobaltihexamine (Co-ihex) at high solid:liquid ra-tios and analysis of the leach solutions. Data for ex-changeable cation (Na+, K+, Ca2+, Mg2+) populationswere adjusted for the components that are attributa-ble to pore water and to dissolution of gypsum by cor-recting them with the aqueous leachate data obtainedfrom a sample aliquot. Selectivity coefficients have been estimated usingaqueous leaching of bulk samples. There is uncertaintyin the results because there are significant perturba-tions in the leaching of whole rocks for which ade-quate corrections are hardly possible. Exchangeisotherms were also measured on clay mineral frac-tions of Opalinus Clay samples. Two types of sites, anillite type and a smectite type, can be distinguishedin Na/H and Na/K exchange isotherms in solutions ofcircum-neutral pH. Only one type can be distinguishedin Na/Ca and Na/Mg exchange isotherms. Selectivitycoefficients derived from these isotherms are consis-tent with literature values. Similar modelling results areobtained using either isotherm or literature values.Na+ is the dominant exchangeable cation (about 50equ % of the total exchange capacity). The Ca2+ con-centration found from calcite saturation is used withthe specified selectivity coefficients and exchangeableion populations to calculate Na+. K+ is then calculatedfrom the Na+ concentration. K+ contents modelled us-ing laboratory-determined exchangeable K contents (6to 8 equ %) are higher than those of the borehole wa-ters and of diluted seawater. Measured K+ contents ofthe borehole waters are lower than those of dilutedseawater. These differences may indicate systematic er-rors in the laboratory techniques for extracting ex-changeable K, or may be due to core oxidation duringsampling, storage or laboratory manipulation, or tothe lack of consideration of NH4

+ exchange. Mg2+ contents of the borehole waters and all modelresults are lower than the Mg2+ concentrations of sea-water diluted according to their Cl- contents, whilethose of the measured and modelled Ca2+ and Sr2+

contents are higher. The Mg/Ca ratios in model runs inwhich Mg2+ is controlled by dolomite saturation areless than one, whereas the ratios in runs in whichMg2+ is controlled by Mg exchange are greater thanone. This indicates that Mg and Ca exchange data anddolomite solubility data are inconsistent.

centrations. Using Na-Mg exchange to fix Mg2+ anddolomite saturation to fix pCO2 gives pH values from0.3 to 0.8 units higher than those calculated withfixed pCO2 values.The redox buffer capacity of the Opalinus Clay de-pends principally on the SO4

2- content of the system tobuffer reducing tendencies and the reduced S, Fe(II)and reduced C contents to buffer oxidising tendencies.Several hypotheses about redox-controlling reactionswere tested by modelling. These include SO4

2 pyrite,goethite siderite, and microcrystalline Fe(OH)3 siderite. The preferred model involves a fixed SO4

2-

concentration, and control of solution redox potentialby the FeS2 SO4

2- reaction. The goethite sideritereaction would lead to conditions so reducing thatSO4

2- would be reduced while the microcrystallineFe(OH)3 siderite reaction would produce conditionsso oxidising that U concentrations orders of magnitudehigher than measured would be expected. Modellingwith siderite saturation gives Fe concentrations a fac-tor of ten higher than concentrations measured oncarefully collected borehole water samples. This differ-ence could be the result of oxidation during samplecollection or storage causing Fe(OH)3 to precipitate.Modelling with goethite leads to calculated Fe concen-trations a factor of ten lower than those measured,and modelling with microcrystalline Fe(OH)3 leads tomuch higher Fe concentrations. Neither goethite norany other simple ferric mineral has been reported fromthe Opalinus Clay, except when associated with theartefact of pyrite oxidation.Uranium concentrations are a useful additional checkon redox controls. U is modelled assuming saturationwith respect to solid UO2 although this phase has notbeen observed in the Opalinus Clay. The resulting Uconcentrations, calculated at p values correspondingto the SO4

2- pyrite couple, vary less than one orderof magnitude from concentrations measured in bore-hole water samples.Manganese is included in the modelling usingrhodochrosite as the controlling mineral although thisis not observed as a discrete phase. The modelled Mnconcentrations are higher than the measured valuesand the real controlling solid is probably the Mn com-ponent of a carbonate mineral solid solution whichcannot be modelled without the solid solution proper-ties. The water is greatly undersaturated with respectto oxidised Mn minerals such as pyrolusite or mangan-ite even under conditions so oxidising that the mod-elled uranium is orders of magnitude above the meas-ured values. Thus, manganese concentrations are onlya very general indicator of the oxidation state.Modelling of ion exchange requires the exchangeableion populations and the selectivity coefficients of the


15

There are two possible controls on the dissolved Sr2+

concentrations. One is saturation with respect to ce-lestite which is found in traces in the rock matrix andin veins throughout the Opalinus Clay. The other isNaSr exchange which is the control generally used ingeochemical modelling here.In spite of these small inconsistencies between ob-served and modelled compositions, the overall agree-ment between the major ion chemistry of the bore-hole waters and the results of modelling based oncation exchange and carbonate mineral equilibria indi-cates that the borehole water samples are reasonablyrepresentative of in situ pore water.

Long-term Evolution of Pore Waters

Having obtained a comprehensive data set for watercompositions, including various environmental isotopesand noble gases, and an understanding of geochemicalreactions in the system, it is possible to interpret howthe pore waters have evolved to their present stateover the long geological history of the Opalinus Clay atMont Terri. Two particular aspects of how the systemhas evolved are the origins of water and solutes andthe transport and mixing of solutes.Mixing and reaction of pore waters during post-deposi-tional burial, compaction, expulsion and diffusive ex-change with waters in adjacent formations are themain processes that influenced the alteration of theoriginal seawater. Solutes that are controlled by water-rock reactions originated from both seawater and wa-ter-rock reaction (i.e. diagenesis of the claystone). Thesignificance of water-rock reaction to the mass budgetsof solutes depends on the particular reaction (i.e. ionexchange on clays or mineral dissolution) and the massratio of the solute between pore water and minerals.The solid phases have been the dominant reservoir formost or all of the controlled solutes, in other words theclaystone-pore water system is rock buffered.Spatial variation of pore water compositions throughthe Opalinus Clay is the key to understanding geo-chemical evolution and transport processes for naturalsolutes. Hydrochemical and isotopic profiles along thegallery section, which cuts obliquely across the strati-graphic section of the Opalinus Clay, contain evidenceof the physical and chemical processes that have oc-curred since deposition of the sediments.Some of the chemical and isotopic parameters varysystematically through the claystone sequence. Theseare the free ions Cl-, Br-, and possibly also SO4

2-, theratios of stable oxygen and hydrogen isotopes (18O/16Oand 2H/1H), and the stable isotope ratio of chloride(37Cl/35Cl). Noble gases that are produced radiogenical-ly: dissolved helium (4He) and the isotope ratio of ar-

gon (40Ar/36Ar) also show systematic variations. The Cl- profile shows a regular and well defined varia-tion through the Opalinus Clay, reaching a maximumconcentration of about 340 mmol close to the contactof the Opalinus Clay with Liassic claystones. The fewdata for pore waters in the Lias suggest that Cl- con-centrations decline sharply, giving the profile an asym-metric shape. The overall pattern of salinity indicatesthat the Opalinus Clay and Liassic claystones and silt-stones can be regarded as a single low permeabilityclaystone unit with respect to solute movement andgeochemical evolution. Concentrations of Cl- in theprofile decrease towards the low values found in seep-ages in the Dogger limestone and near to the Lias-Ke-uper boundary in the tunnel.The maximum Cl- concentration is about two-thirdsthat in seawater and the ratios of Br/Cl and SO4/Cl arevery close to the values for seawater. It is thereforeconcluded that these free solutes have a marinesource. The most likely provenance for this seawater isformation water that was in the sediments since depo-sition and was subsequently altered as it underwentburial and compaction. The retention of marine salinitywith an ancient origin within the Opalinus Clay, andthe regular patterns of solute concentrations and iso-topic compositions towards the boundaries of theOpalinus Clay indicate that the dilution process hasbeen very slow. Diffusion is the most likely processthat would control the movements of solutes and wa-ter molecules at such a slow rate and with such unifor-mity across the claystone formation. The asymmetry ofthe Cl- profile may be due to water in the Doggerlimestones having freshened earlier than water in theKeuper, although it could also be due to the Liassicclaystones having a lower apparent diffusion coeffi-cient for Cl- than the Opalinus Clay though there is noadditional evidence of this.Diagenetic reactions would have modified manysolutes during burial of the sediments. Variations ofsome reactive solutes with respect to Cl- show a netloss to the rock relative to simple dilution of seawater,e.g. K+ and Mg2+. Other solutes show net gains rela-tive to seawater dilution e.g. Li+ and I-. The inverse cor-relation of Li+ with Cl- indicates greater enrichment ofLi+ in the more dilute pore waters. The equilibriumcontrolling this has not been identified but it may in-volve a mineral that became undersaturated as porewater was diluted. Unlike Cl- and Br-, I- has beenstrongly affected by diagenesis. This is consistent withevidence elsewhere for enrichment of I due to releasefrom organic matter at an early stage of diagenesis.The strong correlation with Cl- indicates that I- was en-riched in marine pore water before dilution, support-ing an early diagenetic source.


Fluoride, F-, concentrations measured in borehole sam-ples are from 10-1.5 to 10-2.0 mmol, similar to the con-centration of 10-1.8 mmol that corresponds to the sea-water F/Cl ratio. Equilibrium modelling of the boreholewaters shows that they are strongly undersaturatedwith respect to fluorite. Thus F- could be considered afree solute in these pore waters.Evidence of the origin of water, i.e. of molecular H2O,in the Opalinus Clay is given by the 18O/16O and 2H/1Hratios which vary spatially in a similar way to Cl-,though there is considerably more analytical uncertain-ty. 18O and 2H values are most positive at the base ofthe Opalinus Clay and most negative in the fresh wa-ter seepages. 18O and 2H correlate along a trend thatscatters around the local Meteoric Water Line. Theprevalence of isotopic compositions heavier than localmeteoric water is generally consistent with the modelof seawater dilution. However the saline end memberhas been depleted in 18O and 2H relative to seawaterat some stage in its history. This means that the iso-topic composition has been modified in situ or thatthe original saline pore water was mixed with an iso-topically-light, non-meteoric water before the dilutionprocess. Diffusional fractionation most likely accountsfor the apparent shift in the isotopic composition ofthe saline pore water end-member.The profile of 37Cl/35Cl through the Opalinus Clay israther different to those for Cl- and 18O. The peak val-ue for 37Cl seems to occur in pore water near to theDogger limestones boundary, whereas the peaks forCl- and 18O are close to the Liassic boundary. Howev-er there are large uncertainties in the 37Cl values, so itis not certain whether the apparent peak is significant.Diffusion and ultrafiltration are the only processes thatfractionate Cl isotopes under these conditions.The profile for concentrations of dissolved 4He has asimilar shape to that for Cl-. The development of theprofile has involved the in situ production and dissipa-tion of radiogenic 4He, which is diagnostic of whetherdiffusion is the controlling transport process. Diffusiveloss is expected to have resulted in a parabolic distri-bution of 4He at steady state, which is very close towhat is observed in the pattern of measured concen-trations. The measured maximum helium content isabout 1 x 10-4 cm3 STP 4He/g. The fit of measurementsto model curves suggests that the in situ diffusioncoefficient value, Da, for He in these pore waters isaround 2-5 x 10-11 m2/s.The evolution of 4He content, which is close to steadystate with the present boundaries, contrasts with thedilution/mixing of Cl- and 18O/16O, which are clearly notat equilibrium with respect to the fresh water bound-aries. These geochemical systems have different charac-teristics: 4He is a trace component that is internally-pro-

16

duced and remains close to steady state, whereas Cl-

and 18O/16O originate from the depositional environ-ment and geological evolution of the claystone andhave responded only very slowly to external changes atthe hydrogeological boundaries of the claystone unit.Diffusion modelling is being used in ongoing work tointerpret dilution of Cl- and other mobile solutes andthe mixing of water sources as indicated by 18O/16Oand 2H/1H. Amongst the aspects of the profiles acrossthe clay rocks that have yet to be considered are: theasymmetry of the chloride profile with the peak con-centrations close to the stratigraphic base of the Opali-nus Clay, the possible magnitudes of differences in theprofiles that might reflect different diffusion coeffi-cients for different species, and also the effects of dif-ferent patterns and timescales for evolution of thecompositions of water at the boundaries of the diffus-ing system. The last issue is one that is potentially sig-nificant, because of the difference in the timing of me-teoric water ingress to the Dogger limestones ataround 2.5 million years ago and to the Liassic ataround 350 thousand years, so that there was proba-bly a time lag of about 2 million years between freshwater reaching the Dogger and the Liassic.An initial step towards integrating hydrogeological andgeochemical interpretative modelling has been takenby constructing a one-dimensional reactive transportmodel. This uses the PHREEQC geochemical code tocouple modelling of reactions and diffusive transport.The coupled model is simplified because it has bound-ary conditions that do not represent the current under-standing for the Opalinus Clay at Mont Terri and it usesa single diffusion coefficient for all solute species.The model simulates evolution of pore water in theOpalinus Clay by dilution of seawater, which is as-sumed to have been present in the system prior to itsopening to exchange, with fresh groundwaters in adja-cent formations. It models diffusive dilution and theconcomitant geochemical reactions between pore wa-ters and the claystone formation. The approach hasbeen simplified by assuming that the physical andchemical boundary conditions were fixed over themodelled time period. Reactions that have been mod-elled are: dissolution-precipitation of quartz, calcite,dolomite, pyrite and celestite, plus ion exchange ofNa+, K+, Ca2+, Mg2+ and Sr2+. Measured data and mod-elling results are in reasonable agreement for thecations Na+, K+ and Ca2+. Only Mg2+ shows some dis-crepancy between modelling results and measure-ments. However there is a systematic disagreement be-tween the modelled results and measurements for car-bonate and pH. The coupled model is preliminary andconsiderably more work would be required to make asubstantial comparison between data and model.


17

In conclusion, the remaining uncertainties in defining insitu geochemical conditions in the Opalinus Clay andthe lessons learned from the geochemical investigationsin the Mont Terri Rock Laboratory are summarised.

The remaining questions and suggested approaches tominimising their impacts fall in three areas: Perturbations in sampling techniques which cannot

be easily or completely overcome. The dominant ef-fects here are oxidation and alteration of pCO2 val-ues. The emphasis should be on eliminating expo-sure to air at every stage of drilling, sample storageand processing.

Incomplete understanding of geochemical process-es that affect pore waters in claystone rocks. Themajor areas of uncertainty are the range of cationsthat are controlled by ion exchange, control ofcations by equilibrium with solid phases in whichthey occur in solid solution, and equilibria for re-dox-sensitive solutes. Further work is required onmore fully characterising the compositions of ionsin exchange sites and in mineral solid solutions.

Effects of tunnelling itself on the hydrogeologicaland geochemical properties of the claystone. The re-lation between diffusion-controlled movement ofwater and solutes at a large scale and local respons-es due to heterogeneities at a small scale is not fullydescribed for the transient system initiated by exca-vation. Very careful monitoring needs to be built in-to the early stages of future tunnelling projects.

Geochemical studies in the Mont Terri Rock Laboratoryhave largely achieved the objectives of testing and im-proving investigation methods for pore water chem-istry in such lithologies and of determining the geo-chemical properties of the claystone formation. Anumber of features of the experiment design and im-plementation have had important influences on thedegree to which the objectives have been achieved.These include: Collaboration between a multidisciplinary group of

geoscientists with support by the rock laboratoryengineers in making the formation accessible tovarious sampling and testing methods.

Hydraulic and geomechanical properties of the hostformations, the Opalinus Clay and adjacent units,that make it possible to use a number of comple-mentary methods for sampling water and obtainingdata for pore water compositions.

Innovative construction and operation of sealedboreholes for sampling that eliminated most, butnot all, of the potential artefacts and made it possi-ble to monitor the perturbations that could not beeliminated.

Considerable progress towards anaerobic handlingand other special experimental facilities for labora-tory work on drillcores.

Useful results from all sampling approaches thatcould be compared and contrasted to evaluate theirstrengths and weaknesses and to suggest how eachcould be refined and improved.

For future investigations requiring geochemical charac-terisation of claystone formations including in situ porewater compositions, it is recommended that the multi-plicity of methodologies that have been developedand demonstrated here should be used. Should allmethods succeed, the reliability of each method andthe uncertainty in the formation properties will be bet-ter assessed. If exploratory conditions limit the rangeof methods, then this study shows that each of the in-dividual investigation methods can give valuable datawithin the constraints that have been exemplified inthe Mont Terri study.


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Organizations involved in the Mont Terri Project ................................... 3List of authors.................................................... 4Preface / Prface................................................ 5Vorwort / Prefazione......................................... 6Abstract / Rsum ............................................. 7Zusammenfassung / Acknowledgements ....... 8Executive Summary........................................... 9Table of Contents .............................................. 18

Chapter 1: Introduction..................................... 231.1 The Mont Terri Rock Laboratory ............. 231.2 The Mont Terri Project ............................ 231.3 Scientific Background for Clay Rocks...... 241.3.1 Physiochemical Properties....................... 241.3.2 Studies of Pore Water Compositions ...... 241.3.3 Previous Studies of the Opalinus Clay..... 251.4 Geochemical Studies at Mont Terri ......... 271.5 Implementation of WS and

GS Experiments...................................... 281.6 Terminology for Water Samples and

Pore Water............................................. 281.7 Contents of Report ................................ 28

Chapter 2: Geological Setting and Sample Locations............................................... 302.1 Geological Setting.................................. 302.1.1 Regional Lithostratigraphy...................... 302.1.2 Structural Location of the

Mont Terri Tunnel................................... 302.1.3 Geological History and Palaeohydro-

geology.................................................. 322.2 Geological Section Through the

Rock Laboratory ..................................... 332.2.1 Facies and Lithologies in

Opalinus Clay......................................... 332.2.2 Formations Above and Below the

Opalinus Clay......................................... 342.2.3 Petrography and Mineralogy of the

Opalinus Clay......................................... 342.2.4 Structural and Artificial Features in the

Tunnel Section ....................................... 342.3 Hydrogeological Characteristics.............. 352.4 Geomechanical Characteristics ............... 35

Chapter 3: Geochemical Investigations ........... 363.1 Design of Investigations ......................... 363.1.1 General Approach.................................. 363.1.2 Timing of Geochemical Work................. 363.2 Sample Locations ................................... 373.3 Sampling Procedures.............................. 393.3.1 Water from Boreholes and Seepages...... 393.3.2 Water Squeezed from Drillcores ............. 403.3.3 Aqueous Leachates ................................ 41

3.3.4 Vacuum Distillation of Water from Drillcore ................................................. 42

3.3.5 Diffusive Equilibration for Stable Isotopic Analysis..................................... 43

3.3.6 Vacuum Extraction of Dissolved Noble Gases........................................... 43

3.3.7 Free Gases in Borehole Headspaces and Dissolved Gases ..................................... 43

3.4 Analytical Methods for Water Samples ... 443.4.1 Unstable Parameters: Redox, pH and

Alkalinity................................................ 443.4.2 Other Chemical Parameters.................... 453.4.3 Dissolved Organics and Colloids ............. 453.4.4 Environmental Isotopes in Water

Samples ................................................. 463.5 Analyses of Gases .................................. 473.5.1 Headspace Gases from Packered

Borehole Intervals................................... 473.5.2 Gases Dissolved in Borehole Waters ....... 473.5.3 Noble Gases in Drillcore Samples............ 473.6 Analyses of Rocks and Minerals.............. 473.6.1 Petrographic and Mineralogical Charac-

terisation................................................ 473.6.2 Vein Mineralogy and Geochemistry ........ 493.6.3 Chemical Composition of Whole Rock ... 493.6.4 Organic Geochemistry............................ 503.6.5 Cation Occupancies of Exchange Sites

on Clays................................................. 503.7 Measurements of Water Contents and

Porosities ............................................... 513.8 Characterisation of Mineral Surfaces ...... 53

Chapter 4: Perturbing Effects ........................... 544.1 Introduction ........................................... 544.2 Perturbations from Tunnel Excavation

and Borehole Construction..................... 544.2.1 Geochemical Effects of the Excavation

Disturbed Zone (EDZ) ............................. 544.2.2 Contamination and Other Effects

Related to Blasting ................................. 554.2.3 Contamination in Boreholes ................... 554.3 Perturbations of Water Samples from

Boreholes............................................... 564.3.1 Oxidation of Pyrite ................................. 564.3.2 Oxidation of Redox-Sensitive Solutes...... 574.3.3 Outgassing or Ingassing of Dissolved

CO2........................................................ 574.3.4 Chemical Reactions with Solid Particles .. 584.3.5 Fractionation of Solutes in Water

Entering the Borehole ............................ 594.4 Perturbations of Squeezed Waters.......... 594.4.1 Detection and Causes of Squeezing

Artefacts ................................................ 594.4.2 Sulphide Oxidation and Lowering of pH. 59

Table of contents


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4.4.3 Outgassing of CO2 and Raising of pH ..................................................... 60

4.4.4 Other Sources of Hydrochemical Contamination....................................... 60

4.4.5 Solute Fractionation During Squeezing... 614.4.6 Evaporation and Outgassing During

Core Storage.......................................... 614.5 Perturbations in Core Leachates ............. 624.5.1 Aqueous Leachates ................................ 624.5.2 Cation Exchange Leachates.................... 624.6 Effects on Field and Laboratory

Analyses................................................. 634.6.1 Field Measurements of Unstable

Parameters............................................. 634.6.2 Laboratory Analyses ............................... 644.7 Perturbations in Free Gas Samples from

Borehole Headspaces ............................. 654.8 Perturbations in Measurements of

Water Contents and Porosities ............... 654.9 Recommendations for Obtaining

Reliable Samples .................................... 65

Chapter 5: Pore Water Chemistry and Geo-chemical Modelling ........................................... 675.1 Introduction ........................................... 675.2 Water Sample Chemistry........................ 675.2.1 Comparison of Sample Types ................. 675.2.2 Patterns of Borehole Sample

Chemistry .............................................. 685.2.3 Redox State of Borehole Samples and

Opalinus Clay......................................... 695.2.3.1 Redox Nomenclature and Controls on

Electrode Potentials................................ 705.2.3.2 Results of Electrode Measurements ........ 705.2.3.3 Redox Potentials from Concentrations

of Redox-active Solutes .......................... 725.2.3.4 Redox-active Substances in the

Opalinus Clay......................................... 755.2.4 Cation Exchange Reactions and

Constants .............................................. 765.3 Geochemical Modelling Approach.......... 795.3.1 Overview................................................ 795.3.2 Input Parameters and Constraints .......... 825.3.2.1 Temperature and Pressure ...................... 825.3.2.2 Constituents with Fixed

Concentrations ...................................... 825.3.2.3 Constituents Fixed by Water-Rock

Reactions ............................................... 855.4 Modelled Results: Pore Water

Chemistry .............................................. 885.4.1 BWS-A3 Modelling Results..................... 885.4.2 BWS-A1 Modelling Results..................... 915.5 Conclusions ........................................... 94

Chapter 6: Geochemical Evolution ................... 1056.1 Introduction ........................................... 1056.2 Spatial Variations of Pore Water

Compositions......................................... 1056.3 Conceptual Model for Long Term

Evolution: Processes and Boundaries ...... 1096.3.1 Origins and Reactions of Solutes ............ 1096.3.2 Origins of Water .................................... 1116.3.3 Processes of Dilution and Mixing............ 1126.3.3.1 Helium Production and Diffusion............ 1136.3.3.2 Argon Production and Diffusion ............. 1146.3.3.3 Diffusion of Chloride, 18O/16O and

2H/1H ..................................................... 1146.3.3.4 Fractionation of 37Cl/35Cl ........................ 1156.3.4 Groundwater Boundaries and Palaeo-

hydrogeology......................................... 1166.4 Modelling of Geochemical Evolution

Coupled with Diffusion .......................... 116

Chapter 7: Summary and Conclusions ............. 1197.1 Introduction ........................................... 1197.2 Geochemical Principles........................... 1197.3 Perturbations of In Situ Conditions......... 1207.4 Sampling for Geochemical Analyses ....... 1227.5 Analysing Water Samples ....................... 1247.6 Characterising the Geochemistry of

Rocks and Minerals ................................ 1267.7 Understanding the Geochemical

System................................................... 1287.8 Remaining Questions and

Uncertainties.......................................... 1337.9 Overview: Lessons Learned in the

Rock Laboratory ..................................... 134

Chapter 8: References ....................................... 136

ANNEXESAnnex 1: Water Sampling and Analyses for Boreholes and Seepages............................. 142A1.1 Locations and Construction of Bore-

holes...................................................... 142A1.2 Locations of Seepages............................ 143A1.3 Water Fluxes and Hydraulic Interpre-

tation..................................................... 144A1.4 Borehole Sampling Programme .............. 145A1.5 Sampling of Free Gases in Borehole

Headspaces............................................ 146A1.6 Field Measurements ............................... 146A1.7 Filtration and Preservation of Water

Samples ................................................. 150A1.8 Analyses of Water Compositions ............ 151A1.8.1 Chemical Analyses of Major, Minor

and Trace Solutes ................................... 151A1.8.1.1 Analytical Methods at PSI....................... 151


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A1.8.1.2 Analytical Methods at Hydroistop........... 151A1.8.1.3 Analytical Methods at BGS..................... 151A1.8.1.4 Analytical Methods at Other

Laboratories ........................................... 151A1.8.2 Analyses of Environmental Isotopes........ 152A1.8.2.1 Stable Oxygen and Hydrogen Isotopic

Analyses................................................. 152A1.8.2.2 Stable Carbon and Sulphur Isotopes....... 153A1.8.2.3 Strontium Isotope Ratio............... 153A1.8.2.4 Tritium and Carbon-14........................... 153A1.8.2.5 U- and Th-Series Natural Radionuclides .. 153A1.8.3 Analyses of Dissolved Gases ................... 153A1.9 Analytical Results ................................... 153A1.10 References ............................................. 156

Annex 2: Water Sampling by Squeezing Drillcores ............................................................ 171A2.1 Introduction ........................................... 171A2.2 Principle of Water Extraction by

Squeezing .............................................. 172A2.3 Squeezing Apparatus and Methods........ 173A2.3.1 BGS Laboratory ...................................... 173A2.3.2 CIEMAT Laboratory ................................ 175A2.3.3 CRIEPI Laboratory................................... 176A2.4 Uncertainties in the Analytical

Methods for Squeezed Waters ............... 176A2.5 Locations of Samples ............................. 177A2.6 Results ................................................... 178A2.6.1 Squeezed Water Yields........................... 178A2.6.2 Chemistry of Squeezed Waters............... 181A2.7 Discussion of Chemical Fractionation

by Squeezing ......................................... 183A2.7.1 Squeezing Tests from 25 to 200 MPa

at CIEMAT.............................................. 183A2.7.2 Squeezing Tests from 100 to 500 MPa

at CRIEPI ................................................ 183A2.8 Contamination and Artefacts of

Squeezing .............................................. 188A2.9 Conclusions ........................................... 188A2.10 References ............................................. 189

Annex 3: Aqueous Leachates and Cation Exchange Properties of Mont Terri Claystones .......................................................... 200A3.1 Introduction ........................................... 200A3.2 Conceptual Issues and Definitions .......... 200A3.2.1 Aqueous Leachates ................................ 201A3.2.2 Cation Exchange Properties.................... 201A3.2.2.1 Cation Exchange Capacity...................... 201A3.2.2.2 In Situ Cation Occupancies..................... 202A3.2.2.3 Selectivity Coefficient ............................. 202A3.2.3 Derivation of Pore Water Composition ... 203A3.2.3.1 Chemometric Modelling of Aqueous

Leachates............................................... 203

A3.2.3.2 Geochemical Modelling Using CationExchange Properties ............................... 203

A3.3 Materials and Methods .......................... 203A3.4 Effects of Oxidation during Drilling,

Sampling, Storage and Sample Preparation ............................................ 207

A3.4.1 Oxidation Effects in the Tunnel Excavation Disturbed Zones (EDZ)........... 207

A3.4.2 Oxidation Effects During the Drilling Process................................................... 207

A3.4.3 Oxidation Effects During Sample Handling and Storage ............................ 208

A3.4.4 Oxidation Effect During Laboratory Treatment .............................................. 208

A3.4.4.1 Chloride and Sulphate ........................... 209A3.4.4.2 Sodium and Potassium........................... 209A3.4.4.3 Alkalinity and Alkaline Earth Elements.... 209A3.4.4.4 Relevant Geochemical Processes During

Drying of a Claystone Sample ................ 211A3.4.5 Summary of Oxidation Artefacts

in Aqueous Leachate Experiments of Claystones ......................................... 212

A3.5 Aqueous Leachates ................................ 213A3.5.1 Comparability of Data............................ 213A3.5.1.1 Chloride and Sulphate ........................... 213A3.5.1.2 Sodium and Potassium........................... 214A3.5.1.3 Alkalinity and Alkaline Earth

Elements ................................................ 215A3.5.1.4 Trace Elements ....................................... 217A3.5.1.5 Suitability of Data for Further

Interpretation......................................... 217A3.5.2 Spatial Distribution of Aqueous

Leachate Compositions .......................... 217A3.5.2.1 Chloride................................................. 217A3.5.2.2 Sulphate ................................................ 218A3.5.2.3 Chemical Water Types ............................ 218A3.6 Cation Exchange Properties.................... 219A3.6.1 Cation Exchange Capacity...................... 219A3.6.2 In Situ Cation Occupancy ....................... 220A3.6.2.1 Sodium Occupancy ................................ 220A3.6.2.2 Potassium Occupancy............................. 221A3.6.2.3 Magnesium Occupancy.......................... 222A3.6.2.4 Calcium Occupancy................................ 222A3.6.2.5 Strontium Occupancy............................. 222A3.6.2.6 Ammonium Occupancy.......................... 223A3.6.3 Selectivity Coefficients............................ 223A3.6.3.1 Selectivity Coefficients Derived from

Leaching Data........................................ 223A3.6.3.2 Selectivity Coefficients Derived from

Exchange Isotherms ............................... 225A3.6.4 Spatial Distribution of Cation Exchange

Properties............................................... 228A3.7 Summary and Conclusion ...................... 228A3.8 References ............................................. 230


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Annex 4: Pore Water Extraction by Vacuum Distillation and Diffusive Equili-bration for Oxygen and Hydrogen Stable Isotopic Analyses............................................... 236A4.1 Introduction ........................................... 236A4.2 Extraction of Water by Vacuum

Distillation.............................................. 236A4.3 Diffusive Exchange and

Equilibration of Pore Water .................... 236A4.4 Analysis of Stable Isotope Ratios ............ 237A4.5 18O/16O and 2H/1H Data by Vacuum

Distillation.............................................. 237A4.6 Water Contents from Diffusive Ex-

change................................. 239A4.7 18O/16O and 2H/1H Data by Diffusive

Exchange ............................................... 240A4.8 Discussion of Results .............................. 240A4.9 Implications for Pore Water Analyses...... 241A4.10 References ............................................. 242

Annex 5: Extraction and Analyses of Noble Gases in Pore Waters and Minerals ................. 243A5.1 Introduction ........................................... 243A5.2 Sampling and Preservation of Drillcore ... 244A5.3 Analyses of Concentrations and Iso-

tope Ratios of Dissolved Noble Gases ..... 244A5.4 Results for Tests of Helium Loss in

the EDZ.................................................. 245A5.5 Results of Noble Gas Analyses in

Pore Waters ........................................... 246A5.6 Helium and Argon Isotopes in

Rock Samples......................................... 247A5.7 Discussion of He and Ar in

Pore Waters ........................................... 249A5.8 References ............................................. 250

Annex 6: Dissolved Carbon Dioxide and Hydrocarbon Extraction .................................... 253A6.1 Introduction ........................................... 253A6.2 Theoretical Considerations ..................... 253A6.2.1 Dissolved Gas Composition in the

Laboratory ............................................. 253A6.2.2 In Situ Dissolved Gas Composition ......... 254A6.3 Experimental Details............................... 254A6.3.1 Experimental Device ............................... 254A6.3.2 Samples ................................................. 255A6.4 Hypotheses and Reservations ................. 255A6.5 Experiments and Discussion ................... 256A6.5.1 Cores A6/T1/Min2 and A6/T2/Min2

Under Vacuum....................................... 256A6.5.2 Core BGS-2............................................ 257A6.5.3 Discussion .............................................. 259A6.6 Conclusions ........................................... 260A6.7 References ............................................. 260

Annex 7: Stable Chlorine Isotopic Analysis.... 261A7.1 Background ........................................... 261A7.2 Sample Details ....................................... 261A7.3 Analytical Method for Dissolved

Chloride................................................. 261A7.4 Leaching of Chloride from

Core Samples......................................... 262A7.5 Porosity Measurements .......................... 262A7.6 Analyses of the Chlorine Isotopic

Composition .......................................... 262A7.7 Results ................................................... 263A7.8 Discussion of Results .............................. 263A7.9 References ............................................. 265

Annex 8: Gases in Borehole Headspaces ......... 267A8.1 Introduction ........................................... 267A8.2 Borehole Installation, Gas Sampling

and Analytical Methods ......................... 267A8.2.1 Borehole Installation............................... 267A8.2.2 Sampling Procedure ............................... 267A8.2.3 Analytical Methods ................................ 268A8.3 Headspace Gas Composition.................. 268A8.3.1 Evaluation of Analytical Data.................. 269A8.3.1.1 Borehole BWS-A1 .................................. 269A8.3.1.2 Borehole BWS-A2 .................................. 269A8.3.1.3 Borehole BSW-A3 .................................. 272A8.3.1.4 Borehole BSW-A6 .................................. 272A8.3.2 Compositional Variations with Time ....... 272A8.3.3 Compositional Variations with Space...... 272A8.4 Genesis of Headspace Gas ..................... 273A8.4.1 Potential Source Materials ...................... 273A8.4.1.1 Organic Material in the Rock....... 274A8.4.1.2 Carbon Isotope Composition of

Rock Carbonates.................................... 274A8.4.1.3 Inorganic Carbon Dissolved in the

Borehole Water ...................................... 274A8.4.1.4 Organic Material Dissolved in the

Borehole Water ...................................... 274A8.4.2 Contamination of Headspace Gas

and its Consequences on Gas Composition .......................................... 274

A8.4.3 Origin of Headspace Gases .................... 275A8.4.4 Consequences for Borehole Water

Composition .......................................... 276A8.5 Summary and Conclusions ..................... 277A8.6 References ............................................. 277

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