P Investigation of sulphide in core drilled boreholes KLX06, KAS03 and KAS09 at Laxemar and Äspö - PDF

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P Investigation of sulphide in core drilled boreholes KLX06, KAS03 and KAS09 at Laxemar and Äspö Chemical-, microbiological- and dissolved gas data from groundwater in four borehole sections Anette

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P Investigation of sulphide in core drilled boreholes KLX06, KAS03 and KAS09 at Laxemar and Äspö Chemical-, microbiological- and dissolved gas data from groundwater in four borehole sections Anette Rosdahl, Geosigma AB Karsten Pedersen, Lotta Hallbeck Microbial Analytics Sweden AB Bill Wallin, Geokema AB January 2011 Svensk Kärnbränslehantering AB Swedish Nuclear Fuel and Waste Management Co Box 250, SE Stockholm Phone ISSN Tänd ett lager: SKB P P, R eller TR. Investigation of sulphide in core drilled boreholes KLX06, KAS03 and KAS09 at Laxemar and Äspö Chemical-, microbiological- and dissolved gas data from groundwater in four borehole sections Anette Rosdahl, Geosigma AB Karsten Pedersen, Lotta Hallbeck Microbial Analytics Sweden AB Bill Wallin, Geokema AB January 2011 Keywords: groundwater, sulphide, acetate, microbiological analyses, stable isotopes, dissolved gaseous compounds, stable isotopes in gaseous compounds. This report concerns a study which was conducted for SKB. The conclusions and viewpoints presented in the report are those of the authors. SKB may draw modified conclusions, based on additional literature sources and/or expert opinions. Data in SKB s database can be changed for different reasons. Minor changes in SKB s database will not necessarily result in a revised report. Data revisions may also be presented as supplements, available at A pdf version of this document can be downloaded from Abstract This report describes a study performed during 2009 which focused on the production of sulphide (microbial sulphate reduction) in deep groundwater that was implemented in the core drilled boreholes KLX06, 475 to 482 meter above sea level, m a s l, KAS03, 97 to 241 and 613 to 984 m a s l, and KAS09, 96 to 125 m a s l, at Laxemar and Äspö. The study aimed to increase knowledge of background groundwater levels of sulphide and its variations in time and space through the analysis of sulphide and parameters related to sulphide production. Sampling of groundwater was conducted in three core drilled boreholes of varying age as time series with continuous pumping and as single samples. The analysis program covered chemical parameters (ph, chloride, sulphate, iron, and organic carbon), dissolved gas composition, stable isotopes in groundwater (δ 2 H, δ 18 O, δ 34 S, δ 13 C), stable isotopes of gaseous compounds (δ 2 H, δ 13 C, δ 18 O), microbiological parameters (sulphate- and iron reducing bacteria, SRB and IRB), phthalates and low molecular mass organic acids (LMMOA). The sampling in KLX06 was carried out as time series with a 9 week pause in pumping. When the water volume discharged was about 150 times that of the packer-isolated borehole section, sulphides decreased from 7 mg L 1 to 0.05 mg L 1 and the salinity increased from 740 to 1,480 mg L 1. After a 9 weeks pause in pumping, the sulphide concentration and salinity again approached the original values, i.e. 7 mg L 1 of sulphide and 450 mg L 1 of chloride. The SRB and IRB showed high concentrations that were reduced during pumping in the borehole. The water in the standpipe which has a different water composition than the groundwater, also showed similar high concentrations of sulphide and SRB. The standpipe is a plastic pipe in the wider upper part of the borehole; connected with the tube from the packer of the borehole section and used to accommodate a filter and a groundwater pump when collecting samples. Analyses of δ 34 S in dissolved sulphide and sulphate showed a fractionation corresponding to about +20, which is expected for open systems where microbial sulphate reduction occurs. Analyses of dissolved gases showed that those gases that are biochemically active (carbon dioxide, hydrogen and methane) decreased in concentration during pumping, while the concentrations of gaseous compounds such as nitrogen and argon were unchanged. In KAS03 and KAS09, drilled and equipped at the end of the 1980s, the installed equipment was lifted up and inspected visually following completion of sampling. Water standpipes were partially filled with black sludge; connection pipes and tubing were covered with deposits that seemed to be of salt and rust. Analyses of the water in the standpipes reflected the conditions in which water was not exposed to the impact of pumping for a couple of years back. The concentrations of SRB were high ( 10 4 cells ml 1 ), especially in KAS09, where sulphides were sometimes also very high between 92 and 102 mg L 1. A comparison of the ionic product of iron (II) and sulphide with the saturation indices of amorphous and crystalline (mackinawite) monosulphides shows that the measured sulphide in KAS09 results in significant supersaturation. Given the fast kinetic processes for precipitation of monosulphides, supersaturation is unlikely. A possible reason for the supersaturation, which was mainly observed in samples with high content of organic matter and particulates, could be that the analysis of sulphide most likely included both dissolved and particulate sulphide. Overall, this study has shown that elevated sulphide concentrations in core drilled boreholes may occur in the periods between pumping. Different chemical and physical conditions prevail in the isolated borehole section, in the tubes and in the standpipe as compared with the surrounding rock fractures. For example, new surfaces and materials are added (drilled borehole walls and installed equipment), chemical gradients may be generated during pumping and by differences in composition between standpipe and section water. Further studies are required in order to understand what parameters are important for the growth of sulphate reducing bacteria in the borehole sections, tubes and standpipe, and to demonstrate the relative importance of the possible reductants, hydrogen, methane, acetate, biogenic carbon, and organic carbon in equipment material, which are involved in the reduction of sulphate. P Sammanfattning En undersökning fokuserad på produktionen av sulfid (mikrobiell sulfatreduktion) i djupa grundvatten har genomförts i kärnborrhålen KLX06, 475 till 482 meter över havsytan, m ö h, KAS03, 97 till 241 och 613 till 984 m ö h, och KAS09, 96 till 125 m ö h, på Laxemar och Äspö. Syftet med undersökningen var att öka kunskapen om bakgrundshalter sulfid och variationer i tid och rum i kärnborrhål genom att analysera sulfid och parametrar relaterade till sulfidproduktion. Provtagning av grundvatten genomfördes i tre kärnborrhål av varierande ålder, dels som tidsserier under kontinuerlig pumpning och dels som enstaka prov. Analysprogrammet omfattade kemiska parametrar (ph, klorid, sulfid, sulfat, järn och organiskt kol), gassammansättning, stabila isotoper i grundvatten (δ 34 S, δ 13 C), stabila isotoper i gaser (δ 2 H, δ 13 C, δ 18 O), mikrobiologiska parametrar (sulfat- och järnreducerande bakterier, SRB och IRB) samt ftalater och lågmolekylära organiska syror. I KLX06 utfördes provtagningen som tidsserier med ett längre uppehåll i pumpningen. När sektionsvattnet omsatts ca 150 gånger hade sulfidhalten sjunkit från 7 mg L 1 till 0,5 mg L 1 och kloridhalten ökat från 740 mg L 1 till mg L 1 Då ett 9 veckor långt uppehåll gjordes i pumpningen steg sulfidhalten återigen till det ursprungliga 7 mg L 1 och kloridhalten sjönk till 450 mg L 1.Även halterna SRB och IRB var höga i sektions vattnet och minskade vid pumpning i borrhålet. Vattnet i vattenståndsröret (plaströr i den bredare övre delen av borrhålet) hade en annan kemisk sammansättning än sektionsvattnet och motsvarande höga halter sulfid och SRB. Analyser av δ 34 S i löst sulfid och sulfat visade att fraktioneringen motsvarade 20, vilket motsvarar det förväntade i öppna system. Analyserna av lösta gaser visade att gaser som är biokemiskt aktiva, koldioxid, väte, metan, minskade i koncentration under det att pumpning pågick medan koncentrationen av gaser som kväve och argon var oförändrade. I KAS03 och KAS09, som borrades och instrumenterades i slutet av 1980-talet, lyftes den installerade utrustningen upp och inspekterades visuellt efter utförd provtagning. Vattenståndsrören var delvis fyllda av en svart slamliknande utfällning, rörstänger och slangar var till synes belagda med utfällningar av salt och rost. Analyserna av vattnet i vattenståndsrör och avgränsade sektionerna avspeglade förhållanden i vatten som inte utsatts för påverkan av pumpning sedan ett par år tillbaka i tiden. Halterna SRB var höga ( 10 4 celler ml 1 ), speciellt i KAS09, där även sulfidhalten var mycket hög mellan 92 och 102 mg L 1. En jämförelse av jonprodukten för järn (II) och sulfid med mättnads index för amorfa och kristallina (mackinawite) monosulfider visar dock att de uppmätta sulfidhalterna i KAS09 resulterar i stor övermättnad. Med tanke på de snabba kinetiska förloppen för utfällning av monosulfider är övermättnad av dessa i grundvatten osannolikt. Jonprodukten översteg mättnadsindex i vattenprover med hög halt organiskt material och partiklar, vilket kan förklaras av att analysen av sulfid sannolikt omfattat både löst och partikulärt sulfid. Sammantaget har undersökningarna visat att förhöjda sulfidhalter i kärnborrhål kan uppstå i perioder mellan pumpningar. Andra kemiska och fysiska förhållanden råder i borrhålet än i det omgivande bergets spricksystem. Dessa förhållanden kan uppstå av flera anledningar; nya ytor och material tillkommer (borrhålsväggar och installerad utrustning), kemiska gradienter kan uppstå vid pumpning och genom olikheter i sammansättning mellan vattenståndsrör och sektionsvatten. Ytterligare studier behövs dock för att förstå vilka parametrar som är viktiga för tillväxt av sulfidproducerande bakterier i borrhål och vilka reduktanter som medverkar vid reduktionen av sulfat (möjliga reduktanter är väte, metan, acetat, biogent kol, organiskt kol från material i utrustningen). 4 P-10-18 Contents 1 Introduction General Objective and scope Quality Assurance Selection of boreholes Investigations in core drilled boreholes From drilling to monitoring Methods for groundwater sampling Microbiology and gaseous compounds Sulphate reducing bacteria Anaerobic biocorrosion of metals Dissolved gases Isotope geochemistry Biological (microbial) fractionations The Rayleigh destillation equations 16 2 Investigated boreholes Borehole KLX Borehole KAS Borehole KAS Equipment Stationary equipment Sampling equipment Uncertainties associated with the sampling procedure 26 4 Field activities within the project Overview of field work procedure Performance in KLX06, section m Performance in KAS03, sections m and 627 1,002 m Performance in KAS09, section m Water sampling, sample treatment and analyses Nonconformities 33 5 Results Observations during the investigation KLX KAS03 and KAS On-line measurements Water analyses general Chloride and main cations Sulphate and sulphide Concentrations Sulphide concentration as a function of discharged water during pumping in KLX Continuous Stirred-Tank Reactor modelling Ferrous iron monosulphides Sulphur isotopes Carbon Concentration and molecular weight Carbon isotopes Microbiological analyses Numbers Sulphate reducing bacteria (SRB) Iron reducing bacteria (IRB) 58 P 5.8 Gaseous compounds Released gaseous compounds in KAS09 and KLX Dissolved gaseous compounds in KLX Stable isotopes in CO 2 and CH Discussion Dissolved gaseous compounds Composition of gases in KLX06, KAS03 and KAS Stable isotopes in CO 2 and CH Carbon Sulphide Microbial sulphide production processes Sulphur isotopes 69 7 Summary 71 References 73 Appendix 1 Design of cored borehole KLX06 75 Appendix 2 Flow measurements in KLX06 77 Appendix 3 Pressure registrations during measurements and sampling, HMS system 79 Appendix 4 Chemmac measurements in KLX06, section m 81 Appendix 5 Photographs from the field investigations 85 Appendix 6 Sampling and analytical methods water chemistry 89 Appendix 7 Sampling and analytical methods microbiology and gases 95 Appendix 8 Compilation of water analysis data (October 2010) 99 6 P-10-18 1 Introduction 1.1 General Hydrogen sulphide produced by microbial sulphate reduction under anaerobic conditions may corrode the copper canisters used for final disposal of spent nuclear fuel. Important aspects for the safety assessment are therefore information on the conditions that promote microbial sulphate reduction, the reduction rate and the variability of the hydrogen sulphide concentration in space and time. Varying hydrogen sulphide concentrations ( mm) have been observed in groundwater within the same borehole and between boreholes during the pre-investigations ( ) at Äspö as well as during the site investigations and monitoring programmes at Laxemar and Forsmark. In general, low concentrations of hydrogen sulphide were reported from the site investigations at Laxemar and Forsmark using in situ sampling equipment 1, despite that in many cases the number of sulphate reducing bacteria (SRB) was high /Gimeno et al. 2009/. The subsequent monitoring campaigns showed in comparison enhanced sulphide concentrations in several boreholes and in some boreholes the sulphide concentrations were time dependent, i.e. the concentration decreased with pumping, while in others pumping had little or no effect. A number of explanations to the observed variation in sulphide concentration have been discussed, such as pumping method and velocity, sampling method, aging of boreholes and changed physical and chemical conditions due to addition of in situ equipment. The reason could be a single causing factor or a combination of several factors. During the process of reducing sulphate to sulphide a reducing agent must be involved, this could be either dissolved organic carbon or molecular hydrogen. The sources of organic carbon can be leaching of plastic material installed in the drill holes or biological autotrophic activity. The sources for molecular hydrogen can be deep crustal processes or corrosion processes of metal equipment. This project is focused on the concentration of sulphide and sulphide related parameters in core drilled boreholes KLX06, KAS03 and KAS09 at Laxemar and Äspö, see Figure 1-1. The project includes two activities; one concerning sampling and analyses and one regarding the removal and installation of equipment in borehole KAS Objective and scope This project focused on the sulphide production in core drilled boreholes at Laxemar and Äspö. The overall objective was to perform detailed chemical and microbiological characterisation of groundwater in three core drilled boreholes (four delimited sections) with a previous history of elevated sulphide concentrations. The aim was to provide useful information for describing the processes involved in microbiological sulphide production. Single samples (KAS03, KAS09) and time series of samples (KLX06) were collected and analysed. The analytical programme included analyses of basic chemical parameters including sulphide and Fe 2+, dissolved gas composition, stable isotopes (δ 13 C and δ 2 H) in gaseous compounds, δ 34 S in sulphide and sulphate, analyses of iron- and sulphate reducing microbes and in situ measurements of ph and redox (KLX06). 1 Sampling using the Complete chemical characterisation method, CCC. The method is further described in Section P Figure 1-1. Locations of the core drilled boreholes KLX06, KAS03 and KAS09 at Laxemar and Äspö island. 1.3 Quality Assurance This document reports performance and results from the activity Undersökning av sulfidproduktion i grundvatten på Äspö och Laxemar in cored boreholes KLX06, KAS03 and KAS09 at Laxemar and Äspö. The work was carried out in accordance with activity plan AP TD PRAS In Table 1-1 controlling documents for performing this activity are listed. Both activity plan and measurement systems descriptions are SKB s internal controlling documents. This report presents hydrogeochemical and microbiological data from field work carried out during the period of February to May The obtained data from the activity are reported to the SICADA database and are traceable by the activity plan number. The locations of KLX06, KAS03 and KAS09 are shown in Figure P-10-18 Table 1-1. Controlling documents for the performance of the activity. Project plan Number Version Investigation of sulphide production processes in groundwaters at Äspö SKBdoc and Laxemar. Activity plan Undersökning av sulfidproduktion i grundvatten på Äspö och Laxemar. APTDPRAS Measurement system descriptions Number Version Mätsystembeskrivning (MSB) Handhavande del, System för hydrologisk SKB MD och meteorologisk datainsamling. Vattenprovtagning och utspädningsmätning i observationshål. Mätsystembeskrivningar för mobil kemienhet allmän del, slangvagn, borrhålsutrustning, mobil ytchemmac och dataapplikation. SKB MD SKB MD SKB MD SKB MD SKB MD Instructions Instruktion för rengöring av borrhålsutrustning och viss markbaserad utrustning. SKB MD , SKB doc Provtagning och analys-kemilaboratorium. SKB MD Selection of boreholes When selecting suitable boreholes and borehole sections for the investigation several criteria were considered; the physical condition of the borehole and the installed equipment, the presence of a circulation section, which enables water sampling, previously observed enhanced sulphide concentrations, elapsed time since drilling of the borehole. The aim was to investigate boreholes with elevated sulphide concentrations, but at the same time with various characteristics regarding age, location and water composition. KLX06, situated at Laxemar, was drilled during the site investigations in The borehole was however excluded from the monitoring programme at an early stage when the area of interest for a possible repository shifted. KAS03, located at Äspö, was drilled during the pre-investigations in The bore hole had been part of regular monitoring for several years until recently when the installed equipment (packers etc), required repair and exchange. Section m in KLX06 and sections m and 627 1,002 m in KAS03 were circulation sections that enabled water sampling using the equipment for hydrochemical monitoring. KAS09 (section m) was later added to the investigation, since Äspö Laboratory planned to remove and replace the packer system. Descriptions of the investigated boreholes, previous investigations and historic sulphide concentrations are given in Section Investigations in core drilled boreholes The following text describes the drilling and subsequent investigations that were typically performed in core drilled boreholes during the site investigations. The aim is to give an idea of what kind of impact boreholes are subjected to from drilling to the stage of performing different investigations From drilling to monitoring Drilling of a borehole creates new surfaces and the surface to volume ratio is different compared to fractures. Installation of equipment creates new surfaces and adds new materials (metal, plastic, rubber) to a borehole. Intermittent pumping activities can generate new chemical conditions and physical effects (turbulence, high water velocity etc) that are unnatural to bacteria living in the underground. P In connection to different activities, special precautions are taken for boreholes that are intended for chemical and microbiological characterisation. Equipment that is being used in situ in the borehole before and during the investigation is cleaned according to specific routines involving ethanol and other antibacterial substances ( SKB MD ). The sequence below describes a common line of activities in core drilled boreholes, from drilling of the borehole to different kinds of tests and installation of equipment for continuous monitoring of pressure and water chemistry. Drilling of the borehole involves formation of drilling debris
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