· POSIVA OY Olkiluoto FI-27160 EURAJOKI, FINLAND Phone (02) 8372 31 (nat.), (+358-2-) 8372 31 (int.) Fax (02) 8372 3809 (nat.), (+358-2-) 8372 3809 (int.) December 2019

POSIVA OY

Olki luoto

FI-27160 EURAJOKI, FINLAND

Phone (02) 8372 31 (nat. ) , (+358-2-) 8372 31 ( int . )

Fax (02) 8372 3809 (nat. ) , (+358-2-) 8372 3809 ( int . )

December 2019

Working Report 2019-44

Marja Vuorio,Ti ina Lamminmäki, Petteri Pitkänen, Reetta Ylöstalo ,

Teea Penttinen, Anneli Wichmann, Kyösti Ripatti , Jorma Nummela,

Elina Yli-Rantala, Laura Wendling, Sami Partamies

Results of Monitoring at Olkiluoto in 2018 Hydrogeochemistry

ONKALO is a registered trademark of Posiva Oy

Working Reports contain information on work in progress

or pending completion.

Working Report 2019-44

Results of Monitoring at Olkiluoto in 2018 Hydrogeochemistry

Marja Vuorio,Ti ina Lamminmäki, Petteri Pitkänen, Reetta Ylöstalo ,

Posiva Oy

Teea Penttinen, Anneli Wichmann, Kyösti Ripatti , Jorma Nummela ,

Pöyry F in land Oy

Elina Yli-Rantala, Laura Wendling, Sami Partamies

VTT Oy

December 2019

RESULTS OF MONITORING AT OLKILUOTO IN 2018 HYDROGEOCHEMISTRY

ABSTRACT

Possible changes in the chemical environment in shallow and deep groundwaters caused

by construction of the final disposal facility are monitored on a regular basis. This report

presents the annual hydrogeochemical monitoring results and observations for 2018.

The effect of works on ground surface was seen in analysis results of many groundwater

pipes. Elevated sulfate concentrations were detected in OL-PP56 and OL-PVP17, which

are located between the site of the Encapsulation plant and and the previously built

parking area, in OL-PVP42A and OL-PVP42B located on the construction site of the

encapsulation plant. Increasing sulfate concentrations were also seen in the upper part of

ONKALO (ONK-KR1, ONK-KR2, ONK-KR3). In the shallowest sampling section of

OL-PP56 and in OL-PVP42A pH decreased clearly from the values of the previous year.

In the points between Olkiluoto main road (Olkiluodontie) and Natura nature reserve, OL-

PVP4A and OL-PP2, the long increased salinity (TDS) values had remained stable since

2016. Infiltration from Korvensuo water reserve affected the composition δ18O ja δ2H

isotopes in the water of OL-PVP12 and OL-PVP30.

Changes that in most cases are related to the hydraulic gradient caused by open

underground spaces were observed in deep groundwaters. Downward movement

of sulfate rich groundwater along either hydrological zones (BFZ045, HZ056) or

open drillhole (OL-KR45, open from 2007–2015) was seen in elevated sulfide

concentrations. Dilution of the water in HZ20 structure was still detected. In an

intersecting sampling section of OL-KR4 an increase in sulfate was seen, respectively.

Elevated sulphate concentrations were observed also in the underground monitoring

points at the final disposal depth. Dilution of ONK-PVA2 continued and changes in

ONK-KR4 and ONK-PVA1 were stabilised. Gas samples collected with PAVE and PFL

devices corresponded to previus gas sampling results from Olkiluoto. Instead, samples

collected with SWA technique indicated lower gas contents.

Sampo electromagnetic soundings were not carried out in 2018 because the broken device

could not be fixed during the year.

Keywords: Hydrogeochemistry, final disposal facility, ONKALO, monitoring,

groundwater, gas sampling, analysis results

HYDROGEOKEMIAN MONITOROINTITULOKSET OLKILUODOSSA VUODELTA 2018

TIIVISTELMÄ

Posivan maanalaisen loppusijoituslaitoksen rakentamisen aiheuttamia mahdollisia

muutoksia matalien ja syvien pohjavesien kemialliseen ympäristöön on seurattu

säännöllisesti. Tässä raportissa esitetään hydrogeokemiallisen monitoroinnin vuoden

2018 mittaukset ja havainnot.

Maanpintatöiden vaikutus näkyi monesta matalien pohjavesien monitorointipisteestä

saaduissa tuloksissa. Kohonneita sulfaattipitoisuuksia havaittiin kapselointilaitostyömaan

ja aiemmin rakennetun parkkipaikan välissä sijaitsevista pisteistä OL-PP56 ja OL-PVP17

ja kapselointilaitostyömaalla olevista pohjavesiputkista OL-PVP42A ja OL-PVP42B.

Myös ONKALOn yläosan näytepisteissä (ONK-KR1, ONK-KR2, ONK-KR3) havaittiin

sulfaattipitoisuuden kasvua. OL-PP56 L3:ssa (ylin tulppaväli) ja OL-PVP42A:ssa nähtiin

selvä pH:n lasku vuoteen 2017 verrattuna. Olkiluodontien ja Natura-alueen lähellä

sijaitsevissa pisteissä OL-PVP4A ja OL-PP2 pitkään jatkunut suolaisuuden (TDS) kasvu

on tasaantunut 2016–2018. Korvensuon altaasta tuleva suotauma nähtiin OL-PVP12 ja

OL-PVP30 vesien δ18O ja δ2H isotooppikoostumuksessa.

Syvissä pohjavesissä havaittiin edelleen muutoksia, jotka ovat useimmissa tapauksissa

loppusijoituslaitoksen avoimista maanalaisista tiloista johtuvan hydraulisen gradientin

aiheuttamia. Sulfaattipitoisen kalliopohjaveden painuminen alaspäin joko vettä johtavia

rakenteita (BFZ045, HZ056) tai avointa reikää (OL-KR45, avoinna 2007–2015) pitkin

havaittiin paikoin myös kohonneina sulfidipitoisuuksina. HZ20-rakenteen pohjaveden

laimentumista havaittiin edelleen. Rakennetta leikkaavassa OL-KR4:n tulppavälissä

havaittiin vastaavasti sulfaattipitoisuuden kasvua. Kohonneita sulfaattipitoisuuksia

havaittiin myös ONKALOn mittapisteissä loppusijoitussyvyydellä. ONK-PVA2:n

laimeneminen jatkui ja ONK-KR4:ssä ja ONK-PVA1:ssa edellisvuonna havaitut

muutokset tasoittuivat. PAVE- ja PFL-laitteistoilla kerättyjen kaasunäytteiden tulokset

vastasivat aiemmin Olkiluodosta kerättyä dataa. SWA-tekniikalla kerätyistä näytteistä

kuitenkin mitattiin matalampia kaasupitoisuuksia.

Sampo-elektromagneettisia luotauksia ei tehty vuonna 2018, koska rikkoutunutta

mittauslaitteistoa ei saatu vuoden aikana korjattua.

Avainsanat: Hydrogeokemia, loppusijoituslaitos, ONKALO, monitorointi, pohjavesi,

kaasunäytteenotto, analyysitulokset

1

TABLE OF CONTENTS

ABSTRACT TIIVISTELMÄ

APPENDICES............................................................................................................... 3

PREFACE ..................................................................................................................... 5

1 INTRODUCTION................................................................................................... 7

2 OLKILUOTO SITE ................................................................................................. 9

2.1 Surface environment ..................................................................................... 9 2.2 Groundwater recharge and discharge conditions ........................................... 9 2.3 Host rock and ground water types ............................................................... 11 2.4 Main field activities in 2018 .......................................................................... 12 2.5 Cases where the monitoring action limits were exceeded during 2018 ........ 13

3 RESULTS OF MONITORING AT OLKILUOTO IN 2018 HYDROGEOCHEMISTRY – SHALLOW GROUNDWATERS ............................................................................... 15

3.1 Sampling points ........................................................................................... 15 3.2 Sampling in 2018 ......................................................................................... 18 3.3 Field measurements, sampling and laboratory analysis ............................... 24 3.4 Quality evaluation ........................................................................................ 25 3.5 Salinity, water types and main trends .......................................................... 36 3.6 Comparison and evaluation of the results by different groundwater groups in 2001–2018 .............................................................................................................. 39

3.6.1 The Northern coastline group .................................................................. 39 3.6.2 The Outcrop group .................................................................................. 43 3.6.3 The Peatland group ................................................................................. 46 3.6.4 The Southern central area group ............................................................. 52 3.6.5 The Central area and Korvensuo groups ................................................. 58 3.6.6 The Extraordinary points .......................................................................... 67

3.7 Isotopes – 2018 results ............................................................................... 72 3.7.1 Oxygen δ18O and deuterium δ2H ............................................................. 72 3.7.2 Tritium 3H ................................................................................................ 76 3.7.3 Other isotope results ............................................................................... 77

4 RESULTS OF MONITORING AT OLKILUOTO 2018 HYDROGEOCHEMISTRY – DEEP GROUNDWATERS .......................................................................................... 85

4.1 Sampling and field measurements at ground surface .................................. 86 4.2 Laboratory analysis ..................................................................................... 87 4.3 Quality evaluation of deep groundwater samples ........................................ 88 4.4 Comparison of deep groundwater compositions to baseline hydrogeochemical conditions................................................................................................................ 93

4.4.1 Salinity ..................................................................................................... 93 4.4.2 pH............................................................................................................ 98 4.4.3 Redox .................................................................................................... 101 4.4.4 Groundwater compositions .................................................................... 104 4.4.5 Stable isotopes of water (δ2H and δ18O) ................................................ 105

4.5 Temporal changes in monitoring data ........................................................ 109 5 OBSERVATIONS FROM THE MONITORING OF GROUNDWATER CHEMISTRY FROM UNDERGROUND TUNNELS AND FACILITIES IN 2018 ............................... 117

2

5.1 Sampling points and monitoring ................................................................ 117 5.2 Quality evaluation of samples from underground tunnels and facilities ...... 120 5.3 Observations from monitoring of groundwater chemistry from underground tunnels and facilities .............................................................................................. 123 5.4 Temporal changes in the underground tunnel drillholes ............................. 129

5.4.1 Isotopes ................................................................................................. 141 5.4.2 Leaking fractures and wall channel monitoring in the underground tunnels 144

5.5 Dissolved gases in groundwater samples .................................................. 152 6 SUMMARY AND CONCLUSIONS .................................................................... 157

6.1 Deep groundwater ..................................................................................... 157 6.2 Dissolved gases ........................................................................................ 158 6.3 Shallow groundwaters ............................................................................... 159

7 REFERENCES ................................................................................................. 161

3

APPENDICES

Appendix 1. Modifications on monitoring programme of hydrogeochemistry

Appendix 2. Observations during monitoring of hydrogeochemistry in Olkiluoto

Appendix 3. Information on shallow groundwater sampling points

Appendix 4. Information on groups of shallow groundwater sampling points

Appendix 5. Information on pre-pumping of shallow groundwaters

Appendix 6. Parameters and analytical methods

Appendix 7. Analysis results and saturation indices for shallow groundwaters

Appendix 8. TDS values and water types for shallow groundwaters during monitoring

period

Appendix 9. Main observations and suggested actions for the shallow groundwater

sampling points

Appendix 10. Basic analysis results of shallow groundwater samples as a function of the

time in the different groups

Appendix 11. Isotope results of shallow groundwaters as a function of the time in the

different groups

Appendix 12. Basic information of monitored deep drillholes.

Appendix 13. The quality evaluation results of 2018 deep groundwater samples

Appendix 14. Analysis results of deep groundwater samples

Appendix 15. Main cations, anions and trace components as a function of Cl- content in

deep groundwater

Appendix 16. The quality evaluation results of samples from the underground tunnels

and facilities taken in 2018

Appendix 17. Analysis results of samples from the underground tunnels and facilities

taken in 2018

Appendix 18. Information on the pilot holes sampled in 2018

Appendix 19. Information on groundwater stations (ONK-PVA) and drillholes (ONK-

KR) sampled in 2018

4

Appendix 20. pH, main cations and trace components as a function of Cl- content in

drillhole water in underground tunnels and facilities

Appendix 21. Transmissivity calculations for fractures

Appendix 22. Gas analysis results

Appendix 23. RSD values for samples from deep drillholes (OL-KR) and from the

underground tunnels and facilities (ONK-)

Appendix 24. Revised action limits for the monitoring programme of hydrogeochemistry

Appendix 25. In situ EC in open drillholes

5

PREFACE

This working report has been supervised by Marja Vuorio and Reetta Ylöstalo (Posiva Oy). Several experts have participated in the writing of this report:

The Introduction has been written by Teea Penttinen (Pöyry Finland Oy) and Tiina Lamminmäki (Posiva Oy).

The sections ‘Olkiluoto site’ and ‘Results of Monitoring at Olkiluoto in 2018 Hydrogeochemistry – Shallow groundwaters’ have been prepared by Teea Penttinen and Anneli Wichmann (Pöyry Finland Oy).

‘Results of Monitoring at Olkiluoto in 2018 Hydrogeochemistry – Deep groundwaters’ and ‘Monitoring of Underground Influences caused by Construction of ONKALO’ sections have been prepared by Elina Yli-Rantala, Laura Wendling and Sami Partamies (VTT), Tiina Lamminmäki and Petteri Pitkänen (Posiva Oy).

In situ EC section is prepared by Kyösti Ripatti (Pöyry Finland Oy).

Section ‘Field measurements, sampling and laboratory analysis’ has been written by Tiina Lamminmäki (Posiva Oy) and Teea Penttinen (Pöyry Finland Oy).

We would like to thank Jorma Nummela (Pöyry Finland Oy) for compiling the maps in Figure 2-2 and Figure 3-1.

There is a list of the abbreviations used in this report along with explanations at the end

of the preface.

6

Abbreviation Explanation CB Charge balance

Class B1 or 2– T1 or 2 – E Class Baseline – Time series – Erroneous (see text for details)

DIC Dissolved inorganic carbon

DOC/NPOC Dissolved organic carbon/non purgeable organic carbon

EC Electrical conductivity

GWML Global Meteoric Water Line

HZ Hydrogeological zone

INEX Infiltration experiment

K Hydraulic conductivity (unit m/s)

LMWL Local Meteoric Water Line

masl Metres Above Sea Level

OL-BFZ Brittle Fault Zone in Olkiluoto

OL-EP Permanent multi-level piezometer

OL-HP Seepage water tube

OL-KK Soil test pit

OL-KR Core drilled drillhole

OL-L Percussion drilled seismic source hole

OL-PP Shallow core drilled hole in bedrock

OL-PR Shallow percussion drilled hole in bedrock

OL-PVP Groundwater observation tube with perforated section in the

overburden

OL-RS1 Korvensuo Reservoir

OL-RWS04 River monitoring point Eurajoki

OL-TK Investigation trench

ONK-KER Water collector on the ceiling in ONKALO

ONK-KOU Local collector in ONKALO

ONK-KPE Shaft drift in ONKALO

ONK-KR Drillhole in ONKALO

ONK-KU Shaft in ONKALO

ONK-MPL Measuring weir in ONKALO

ONK-PH Pilot hole in ONKALO

ONK-PP Shallow core drilled hole in bedrock in ONKALO

ONK-PVA Groundwater monitoring station in ONKALO

ONK-RV Water leakage from fractures or structures in ONKALO

PAVE Down-hole sampling equipment (in situ –pressurised gas and

microbe sampling)

PFL Posiva Flow Log method

RSD Relative Standard deviation

SI Saturation index

SRB Sulfate Reducing Bacteria

T Transmissivity (unit m2/s)

TDS Total dissolved solids

TOC Top of casing

TU Tritium Unit

VPDB Vienna Pee Dee Belemnite (‰)

VSMOW Vienna Standard Mean Ocean Water (‰)

7

1 INTRODUCTION

In November 2015, the Finnish Government granted Posiva a construction license for a

final disposal facility (later in this report also: ONKALO) for spent nuclear fuel at

Olkiluoto, Finland. Disposal will take place in a geological repository implemented

according to the KBS-3 method. One of the key requirements for the construction license,

and later the operational license is a safety case that, according to the internationally

adopted definition, is a compilation of the evidence, analyses and arguments that quantify

and substantiate the safety and the level of expert confidence in the safety of the planned

repository (Posiva 2012). The safety case bases on several reports (Posiva 2012).

Hydrogeochemistry of the site plays a major role in Posiva’s safety case, as understanding

of the groundwater chemistry, its evolution over time and changes caused by construction

of the disposal facility, is needed as input for the design of the engineering barriers,

assessment of their performance and as an input to radionuclide release and transport

calculations.

The objective of this report is to give an overview of the progress of the monitoring of

the hydrogeochemistry in Olkiluoto. This report presents the hydrogeochemical

measurements and observations made in 2018. The basis for the hydrogeochemical

monitoring programme is described in Posiva (2003b). Modifications have been made in

the programme on the basis of the experience obtained from monitoring and they are

presented in Appendix 1. The current hydrogeochemical monitoring programme is

presented in Table 1-1 (in 2018 modified version, see also Appendix 15 for the

modifications). The monitoring programme for the period before repository operation

2012–2018, is presented in Posiva (2012). Observations made during monitoring of

hydrogeochemistry in Olkiluoto since 2004 are presented in Appendix 2.

Local collectors (ONK-KOU) and water collectors on the ceiling in ONKALO (ONK-

KER) representing HZ20 structure, as well as ONK-RV4385 were sampled three times

in 2018, which was more often than earlier.

In 2018, process water completely or partly without sodium fluorescein as tracer mark

was used for a week 3/2018 at ONKALO. Process water was incompletely dyed until

week 5/2018 (low sodium fluorescein concentration). If a groundwater sample contained

a residue of flushing water used in the ONKALO during this period, it would not have

been detected by the sodium fluorescein analysis. However, due to the hydrostatic

pressure, process water used in the ONKALO cannot easily spread out in the bedrock and

to the groundwater system. Therefore, it is likely to be of minor importance to the

obtained chemical results.

The monitoring of hydrogeochemistry is connected to the monitoring of foreign materials

and surface environment what comes to ONKALO process waters and leaching from rock

spoil (Posiva 2012). The monitoring of hydrogeochemistry during the operational phase

will be planned in 2019 to support construction and long-term safety.

8

Table 1-1. Hydrogeochemical monitoring programme for the years 2012–2018 (Posiva

2012, in 2018 modified version). 1, 2, 3, or 4 = number of sampling campaigns per year,

C = continuous, w = weekly, x = according to a yearly plan. Modifications to the

programme are presented in Appendix 15.

Process Target / method Location started 2012 -13 -14 -15 -16 -17 -18 NOTES

Evolution of groundwater properties and salinity distribution in shallow groundwater

Groundwater sampling: chemistry

OL-PVP, OL-PP, OL-PR

2001

2 2 2 2 2 2 2

Evolution of groundwater properties and salinity distribution in deep groundwater

Groundwater sampling: chemistry

OL-KR, ONK-PVA, ONK-KR, ONK-PP

2001

x x x x x* x* x* * no sampling from ONK-PP in 2016–2018

On-line measurements (pH, EC, O2, Eh, T)

OL-KR, ONK-PVA, ONK-KR

OL-KR 2003, ONK-PVA and

ONK-KR

2005

x x x x x x x

Microbe and gas samplings

OL-KR, ONK-PVA, ONK-KR

2005 x x x x x x x

In situ EC Deep drillholes ONKALO

2014

X X X X X

Parameter "salinity (in situ EC)" was removed from hydrogeology to hydrogeochemistry

Influence of Korvensuo reservoir

Stable isotope samples (δ 2H and δ 18O)

Shallow drillholes 2001 x x x x x x x

Deep drillholes 2003 x x x x x x x

ONKALO drillholes

2005 x x x x x x x

Influence of foreign material

Sampling of defined parameters

ONK-PVA, ONK-KR, ONK-PP

2005

x x x x x* x* X* *no sampling from ONK-PP in 2016–2018

ONK-RV and ONK-KOU

2005

1 1 1* 1* 1* 1* 1**

*HZ20 structures and ONK-RV4385 twice a year ** HZ20 structures and ONK-RV4385 three times

Inflow into ONKALO tunnel

Automatic observation system

ONK-MPL (EC and pH)

2006 C C C C C C C

Chemical analysis

ONK-MPL 2012 1 1 1 1 1 1 1

ONK-RV and ONK-KOU

2005 1 1 1 1 1 1 1

ONK-KOU, ONK-KER (HZ20 fractures)

2014 2 2 2 2 2

9

2 OLKILUOTO SITE

2.1 Surface environment

Olkiluoto is a regionally large island (currently approximately 12 km2) off the coast of

Bothnian Sea, separated from the mainland by a narrow strait. The Olkiluoto Nuclear

Power Plant, with two operational reactors, and a repository for low- and intermediate-

level waste is located in the western part of the island. The construction of a new reactor

unit is underway at the site. The repository for spent fuel will be constructed in the central

and eastern parts of the island. The construction of an underground rock characterisation

facility, called ONKALO, was started at the repository site in June 2004. The construction

licence for the spent fuel repository was obtained in November 2015.

The average overburden thickness in Olkiluoto Island is 2.2 m, varying usually between

1.5–3 m and being thicker in the western part of the Island (Mönkkönen et al. 2017). In

Olkiluoto there are several landfill sites and excavated rock crushing areas (Posiva 2011).

The Korvensuo Reservoir and sedimentation pools are located in the central parts of the

Island. The harbour lies in the northern coastline. Some locally important ecological areas

have been identified on the Olkiluoto Island. The most valuable nature area is the old-

growth forest of Liiklansuo, which is a Natura 2000 site.

2.2 Groundwater recharge and discharge conditions

On the basis of the topography and flow directions in ditches, Olkiluoto Island is divided

into several local catchment areas (Figure 2-1). Groundwaters near the overburden have

shorter residence time and thus contain less dissolved elements and react quicker for the

percolating water and to a large extent to seasonal changes than deeper groundwaters.

Also the constructed areas have altered the runoff and infiltration patterns. More detailed

description of surface hydrology is presented in the Olkiluoto surface hydrology model

by Karvonen (2013). Figure 2-2 shows the locations for the hydrogeological zones (HZ)

at the ground level (Vaittinen et al. 2019b), together with the network of shallow

groundwater sampling sites 1995–2018 (also presented in Figure 3-1) on aerial image of

Olkiluoto in 2017 (Blom Kartta Oy/Posiva Oy 15.7.2017). Hydrological monitoring

results at Olkiluoto in 2018 is presented in Vaittinen et al. (2019). In 2018, precipitation

was clearly lower than on average. The total leakage of ONKALO varied between 24 and

35 L/min, but the exact range was difficult to determine due to the construction activities

carried out in ONKALO and interrupted leakage measurements in the lowest shaft

sections of ONK-KU1 and -KU3 (-290…-455 m) (Vaittinen et al. 2019).

Measurements of hydraulic conductivity by the slug method in 2002 and 2004–2017 are

presented in Hellä & Heikkinen (2004), Tammisto et al. (2005), Tammisto & Lehtinen

(2006), Keskitalo & Lindgren (2007), Keskitalo (2008, 2009), Isola (2010), Hinkkanen

(2011, 2012), Tammisto (2014), Pentti (2014, 2016, 2017, 2018), Vaittinen et al. (2019)

and Pentti & Hinkkanen (2016).

10

Figure 2-1. Drainage basins and ditches at Olkiluoto (Karvonen 2008, the fields

marked with yellow). Background map: topographic database by the National Land

Survey of Finland. Map layout by Jani Helin.

Figure 2-2. Locations of the hydrogeological zones at the ground level (Vaittinen et al.

2019b) and the network of shallow groundwater sampling sites 1995–2018 on aerial

image of Olkiluoto in 2017 (Blom Kartta Oy/Posiva Oy 15.7.2017).

11

2.3 Host rock and ground water types

The bedrock at Olkiluoto consists of variably migmatised, supracrustal, high-grade

metamorphic rocks, which consist of migmatised metapelites, meta-arenites and

intermediate, pyroclastic metavolcanites. The supracrustals are intruded by

Palaeoproterozoic felsic, granitic–tonalitic plutonic rocks and granitic pegmatoids, and

diabase dykes, probably of Mesoproterozoic age. The rocks were metamorphosed under

different metamorphic conditions simultaneously with the different phases of ductile

deformation. The peak metamorphic mineral assemblages of all rock types found at

Olkiluoto, with the exception of the diabase dykes, belong to the upper amphibolite facies

(Tuisku & Kärki 2010).

The salinity of the groundwaters changes according to the depth and forms a layered

system (Posiva 2011). In the depth range 0–1000 m, the salinity varies widely: fresh

groundwaters (TDS < 1 g/L) are found in the uppermost tens of meters, brackish

groundwaters (1 < TDS < 10 g/L) dominate at depths from 30 m to 400 m, and saline (10

< TDS < 100 g/L) waters below 400 m (Posiva 2011). Fresh and brackish groundwaters

are divided into three groups on the basis of characteristic anion contents: Fresh/Brackish

HCO3-type, Brackish SO4-type (at depths 100–300 m) and Brackish Cl-type (the deepest

layer) (Posiva 2011). On the basis of Posiva (2011), there are water types from at least

six different sources: modern (meteoric water, sea water from the Gulf of Bothnia,

Korvensuo Reservoir water) and relic sources (Littorina sea water, glacial meltwater,

brine).

The four extreme reference groundwaters, which govern the current groundwater

compositions by mixing, have been recognised according to age: brine reference, glacial

reference, Littorina reference and meteoric water and in addition, Baltic seawater

(basically diluted Littorina seawater) (Posiva 2011).

The main processes affecting the hydrogeochemical conditions are the mixing of groundwater types, water-rock interaction, microbial processes at interfaces between different groundwater types and in overburden as well as weathering. In shallow groundwaters, weathering during infiltration plays a major role in increasing the amount of solutes. Prevailing redox conditions at Olkiluoto are anoxic, except in shallow infiltrating groundwater at a few locations. Pyrite and other iron sulfides are common in fractures. Two natural metastable interfaces occur. The upper interface occurs in the overburden (from oxic to anoxic) and the lower interface at depth of approximately 250–350 m, where brackish SO4-rich groundwater is mixed with saline methane rich water with the result of dissolved sulfide (Pastina & Hellä 2010).

Surface environment, groundwater recharge and discharge conditions and host rock, which are only briefly introduced here, are described in more detail in earlier reports together with additional information on soil processes e.g. in Penttinen et al. (2014).

12

2.4 Main field activities in 2018

Excavations of vehicle connections (AJYH 5, 15, 15.1, 17, 17.1, 17.2, 17.3, 19 and 21) continued in 2018 (Vaittinen et al. 2019). The central tunnel for cooperation tests and the tunnel for starting of deposition tunnel for integrated system test were excavated. A pilot hole ONK-CTPH5.1 for central tunnel 5, and new groundwater monitoring stations ONK-PVA12 and ONK-PVA13 were drilled in 2018 (Vaittinen et al. 2019).

The pre-groutings of canister shaft ONK-KU5 continued in 2017–2018. In 2018, ONK-KU5 was raise bored from the level of -281 m up to the surface. Concerning the lowest part of -288 m to -429 m, also the depth of ca. -387 m to -429 m was raise bored (Vaittinen et al. 2019).

In OL-KR28, a double packer pumping test was carried out during January–March and multi-packer system was installed into drillhole in May (head monitoring started in June). On November 1, packer pressure was lost due to a technical problems and packers were removed in November–December 2018 (Vaittinen et al. 2019). The sulfide project (subproject MetWeb) continued in the drillholes OL-KR11 (L3 411–430 m), OL-KR13 (L3 405.5–414.5 m) and OL-KR46 (570–573 m) in 2018. Multi-packer system installations/removals and the further information on the open hole phases is presented in Table 2-1.

Table 2-1. Multi-packer installations in 2018 and the further information on the open phase period.

Drillhole Installation Open phase Comments

OL-KR10 31.10.2018– Packers removed.

OL-KR12 May 2018 2.3.2017–

29.5.2018

Packer combination 2 installed.

OL-KR14 Sep 2018 28.7.–9.9.2018 Packer combination 2 removed on July

2018 and packer combination 3 installed on

Sep.

OL-KR28 June 2018 19.10.2017–

28.6.2018,

13.11.2018–

Packer combination 3 installed and

removed during 2018.

OL-KR46 25.10.2018– Double packers for sulfide project removed

in October. Packer comb. 1 installed on Jan

2019.

ONK-PH17 March 2018 19.10.2010–

25.3.2018

Packer combination 1 installed.

13

2.5 Cases where the monitoring action limits were exceeded during 2018

The monitoring action limits for selected parameters have been defined based on the depth

of the groundwater sampling location. The limits were revised in 2017 and have thus been

applied to the results of 2018. The revised action limits are presented in Appendix 24.

Five different sets of action limits have been defined for the following sampling depths:

0–50 m, 50–200 m, 200–350 m, 350–500 m and 500–800 m. A total of 31 analyses

exceeded the action limit in 12 different drillholes (six deep drillholes and six ONKALO

drillholes) in 2018. All of the cases where limits were exceeded were due either to high

sulfide concentration or low salinity (TDS, Cl-). The samples with parameters exceeding

action limits and a reference to the chapter where the sampling sections are discussed are

presented in Table 2-2.

Table 2-2. Cases where monitoring action limits were exceeded during 2018.

Sample Exceeded Parameter values Reference

code parameter(s) (respectively) (Chapter)

Deep drillholes

OL-KR4_T296_0418 TDS

Cl-

1146 mg/L

310 mg/L 4.4.1

OL-KR4_T351_0618

TDS

Cl-

HS-

2782 mg/L

1440 mg/L

1.6 mg/L

4.4.1

OL-KR11_T411_0318 Cl- 2390 mg/L 4.5

OL-KR11_T411_0718 Cl- 2340 mg/L 4.5

OL-KR11_T411_0818 Cl- 2250 mg/L 4.5

OL-KR13_T405_0318 HS- 11 mg/L 4.5

OL-KR13_T405_0718 HS- 12 mg/L 4.5

OL-KR13_T405_0818 HS- 13 mg/L 4.5

OL-KR40_T600_0218 TDS

Cl-

8614 mg/L

5140 mg/L 4.4.1

OL-KR45_T606_0818 HS- 33 mg/L 0

OL-KR46_570_0318 HS- 35 mg/L 0

OL-KR46_570_0718 HS- 25 mg/L 0

OL-KR46_570_0818 HS- 22 mg/L 0

ONKALO samples

ONK-PVA3__0118 Cl- 140 mg/L 5.4

ONK-PVA5__0118 TDS

HS-

3548 mg/L

1.1 mg/L 5.4

ONK-PVA5__1118 TDS

HS-

3623 mg/L

1.2 mg/L 5.4

ONK-PVA8__0118 HS- 5.3 mg/L 5.4

ONK-PVA8__1018 HS- 4.8 mg/L 5.4

ONK-PVA12_11_1218 TDS 755 mg/L 5.3

14

Sample Exceeded Parameter values Reference

code parameter(s) (respectively) (Chapter)

Cl- 100 mg/L

ONK-PVA13_14_1218 TDS

Cl-

1278 mg/L

330 mg/L 5.3

ONK-PH22_34_0218 HS- 3.3 mg/L 5.3

ONK-PH22_34_1218 HS- 7.5 mg/L 5.3

ONK-PH22_60_0218 HS- 4.0 mg/L 5.3

15

3 RESULTS OF MONITORING AT OLKILUOTO IN 2018 HYDROGEOCHEMISTRY – SHALLOW GROUNDWATERS

3.1 Sampling points

The groundwater samples have been taken from the groundwater observation tubes (OL-

PVP) in overburden as well as from the shallow core drilled holes (OL-PP) and

percussion-drilled holes (OL-PR) in bedrock to establish hydrogeochemical properties,

to study natural variations in groundwater close to the surface and observe the effects of

the construction works of ONKALO but also construction on ground level. The

monitoring of shallow groundwaters started on a regular basis in 2001 (regular

samplings). In 2003, the monitoring programme for the ONKALO construction and

operation work was launched (Posiva 2003b), the monitoring programme for the period

before repository operation 2012–2018, is presented in Posiva (2012). The current

monitoring programme consists of two sampling campaigns per year, in spring and in

autumn. Each campaign consists of 15 yearly selected sampling points.

The selection of the sampling points is based on the earlier results for the years 2001–

2017 (Hatanpää 2002, Backman et al. 2002, Posiva 2003b, Kröger 2004, Hirvonen &

Mäntynen 2005, Hirvonen et al. 2006, and Pitkänen et al. 2007b, Pitkänen et al. 2008a,

Pitkänen et al. 2009, Penttinen et al. 2011, 2013, 2014, 2017, Lamminmäki et al. 2017a-

c, Vuorio et al. 2018, 2019). In addition to these, the results of the other monitoring

sectors, especially the hydrology, environment and foreign materials (Safety Classified

Materials), are taken into account when sampling points are selected and also in result

evaluation.

The network of monitoring points covers most of the island and monitoring samplings

are performed almost all around the island. Around thirty sampling points (OL-PVP, OL-

PP, OL-PR) have been regularly in the monitoring programme. The longest time series

of the results are since 1995 (Honkasalo 1995) or 1997 (Tuominen 1998) and the longest

regular time series are since 2001. There have been four OL-PVP tubes (OL-PVP2, OL-

PVP3B, OL-PVP5A, OL-PVP9A) and three OL-PP holes (OL-PP7, OL-PP37, OL-PP38)

and one OL-PR sampling point (OL-PR4), which have been sampled for monitoring

purposes earlier, but have been later destroyed/gone broken and left outside the

programme. The locations of all the sampling points (1995–2018) are shown in Figure

3-1, the points sampled in 2018 are marked with circles. A−D tubes, which have the same

serial number, are located less than 5 m from each other. The perforated sections in

A/B/C/D tubes locate at different depths and they represent different parts of the

overburden. More detailed description of tubes and drillholes is presented in Appendix 3.

Figure 3-2 shows the total lengths, the thickness of the overburden, the depth of the

perforated section for OL-PVP and the elevation of the ground level (masl), for all the

sampling points.

16

Fig

ure

3-1

. L

oca

tions

of

all

the

sam

ple

d g

roundw

ate

r obse

rvati

on t

ubes

(O

L-P

VP

), s

hall

ow

dri

llhole

s (O

L-P

P a

nd O

L-P

R)

and O

L-

KR

14 d

uri

ng 1

995

– 2

018. C

lass

ifie

d g

roups

are

mark

ed w

ith d

iffe

rent co

lours

(and O

L-P

R3, n

ot cl

ass

ifie

d).

In 2

018 s

am

ple

d s

am

pli

ng

poin

ts a

re m

ark

ed w

ith

cir

cles

.

17

Fig

ure

3-2

. T

he

tota

l le

ngth

s, t

he

thic

knes

s of

the

ove

rburd

en,

the

dep

th o

f per

fora

ted s

ecti

on i

n O

L-P

VP

and t

he

elev

ati

on o

f th

e

gro

und l

evel

pre

sente

d f

or

the

gro

undw

ate

r obse

rvati

on t

ubes

(O

L-P

VP

), s

hall

ow

dri

llhole

s (O

L-P

P a

nd O

L-P

R)

and

OL

-KR

14. T

he

tota

l le

ngth

of

OL

-KR

14 5

14.1

m i

s out

of

the

scale

; als

o n

oti

ce t

he

scale

change

bel

ow

15 m

asl

The

OL

-PP

56 d

rill

hole

incl

inati

on i

s

45.1

o, th

e dri

llhole

rea

ches

the

dep

th -

29.5

masl

(th

e le

ngth

>50 m

) (d

=des

troye

d, c.

u.=

clogged

up,

c.i.

=ca

ved i

n).

18

3.2 Sampling in 2018

This report presents the shallow groundwater results obtained in 2018 (Chapter 3.5 ), and

compares and evaluates them by groundwater groups, together with the monitoring results

from the years 2001–2017 (Chapter 3.6 ). A total of 30 shallow groundwater samples

were taken in 2018 (Table 3-1). The monitoring sampling campaigns were performed

during 15 May–5 June and 1–18 October.

The group classification of shallows is presented in Appendix 4. The samplings in 2018

did not include samples of the group Infiltration experiment, and thus, the group is

excluded from Chapter 3.6 (Comparison and evaluation by groups). The monitoring

periods, groups and information on environmental features of the locations of sampling

points 2018 are presented in Table 3-2. The perforated sections of OL-PVP tubes are

presented in Figure 3-2 and Appendix 3. In the shallow drillholes, the whole drillhole has

been pumped with an exception in OL-PP56 (packed-off since January 2015). In 2018,

the samples of OL-PP56 were taken from packed-off sections L1 (38–55.9 m), L2 (28–

37 m) and L3 (2.3–27 m). The packed-off sections of shallow drillholes are presented in

Appendix 3.

The groundwater table levels (Heads, masl) for the observation tubes in 2018 are

presented in Figure 3-3 and for the shallow drillholes in Figure 3-4. In OL-PVP42A and

-PVP42B, the hydrological monitoring was suspended during December 2017 and the

beginning of October 2018, because of construction work of encapsulation plant base, but

continued later in October 2018 (Vaittinen et al. 2019). The automatic monitoring of

groundwater level was started in OL-PVP42A and -PVP42B holes in November 2018

and the results of automatic monitoring (marked with A) are also shown in Figure 3-3.

For OL-PP56, the head levels of packed of L1–L3 are presented in Figure 3-4, whereas

the other head data of shallows represents open hole conditions. The sampling periods are

marked with blue lines. A more detailed description of hydrology of the shallow holes is

presented in Vaittinen et al. (2019).

19

Table 3-1. Groundwater observation tube (OL-PVP) and shallow drillhole (OL-PP) samples taken during 2018. Different sampling campaigns tabled separately. The samplings were done according to the plan 2018.

Spring 2018 Autumn 2018

OL-PVP3A OL-PVP14

OL-PVP4A OL-PVP17

OL-PVP11 OL-PVP18A

OL-PVP12 OL-PVP30

OL-PVP13 OL-PVP39

OL-PVP17 OL-PVP40A

OL-PVP18A OL-PVP41A

OL-PVP20 OL-PVP42A

OL-PVP36 OL-PVP42B

OL-PVP40A OL-PP36

OL-PVP40B OL-PP39

OL-PP2 OL-PP56 L2

OL-PP56 L1 OL-PP56 L3

OL-PP56 L2 OL-PP70

OL-PP56 L3 OL-PP71

20

Table 3-2. The monitoring period, the group classification and the main characteristics

of the locations for the groundwater observation tubes and the shallow drillholes in the

samples of 2018.

Observation

tube/

drillhole

Length

(m)

Monitoring

period

Group Environmental and other

comments

OL-PVP3A 7.80 2001–2018 Peatland Situated near the main road at a moist

site, which continues until the road to the

visitor centre.

OL-PVP4A 9.55 2001–2018 Southern

central

area

Situated near the natural conservation

area and very near to a small road, also

in the vicinity of the main road. Rather

near the ONKALO construction site.

OL-PVP11 5.20 2003–2018 Central area

West

Near a small road in the central part of

the island.

OL-PVP12 6.30 2003–2018 Korvensuo Situated near the Korvensuo reservoir,

on the northern side.


East

Situates east from the road to the

harbour.


East

Situated close to OL-PVP13, near a

small road.

OL-PVP17 6.30 2005–2018 Extraordinary

points

(previously

Peatland)

Situated close to a peat-covered area,

which for heavily modified during 2016

so that the peatlands were removed.

Near the ONKALO construction site.

OL-PVP18A 9.00 2005–2018 Peatland Situated very close to the ONKALO

(above the tunnels) in a small peaty area,

next to the ONKALO quarry road.

OL-PVP20 14.10 2004–2018 Southern

central

area

Situated in the nature conservation area.

Thick overburden, woody site.

OL-PVP30 3.80 2009–2018 Korvensuo Situated near the Korvensuo reservoir,

on the northern side. Perforated section

only 1 m.

OL-PVP36 5.50 2012–2018 Peatland Situated north from the Korvensuo

reservoir, near the outlet ditch of

ONKALO.

OL-PVP39 10.25 2014–2018 Northern

coastline

Situated in the northern part of the

island, near OL-KR6.

OL-PVP40A 10.20 2014–2018 Northern

coastline



OL-PVP40B 8.80 2014–2018 Northern

coastline



OL-PVP41A 11.90 2016–2018 Peatland Situated near parking area next to Power

Plant Main Gate. Near shoreline –

ground level near zero.

OL-PVP42A 7.98

9.466*

2016–2018 Central area

West

Near the ONKALO area and the

encapsulation plant excavation area. On

7.12.2017, PVC-pipe was extended (*

1.726 m). Fence line rock filling

changed ground level surface (1.486 m),

land filling with crushed rock from

ONKALO excavation.

21

Observation

tube/

drillhole

Length

(m)

Monitoring

period

Group Environmental and other

comments

OL-PVP42B 5.80

7.24*

2016–2018 Central area

West

Near the ONKALO area and the

encapsulation plant excavation area. On

7.12.2017, PVC-pipe was extended (*

1.8 m). Fence line rock filling changed

ground level surface (1.43 m), land

filling with crushed rock from

ONKALO excavation.

OL-PP2 23.80

2001–2018 Southern

central

area

Situated very close to the main road.

Thick overburden. Rather near the

ONKALO construction site.

OL-PP36 12.05 2003–2018 Outcrop Situated in the western part of the

switch-yard, in the northern part of the

island and very near the coast.

OL-PP39 13.71

2003–2018 Peatland Situated very close to the main road, at a

swampy area; also near OL-PP56 and

construction works.

OL-PP56

L1, L2, L3

55.87 2007–2018 Extra-

ordinary

points

Situated very close to the main road and

to the ONKALO construction site.

During 2014, a parking area was

constructed around the drillhole (hole is

on the parking line). Inclination 45.1°.

Packed during June–October 2014 and

January 21 2015 onwards.

OL-PP70 20.05 2012–2018 Central area

East

Situated very far from ONKALO area,

in the north-east corner of the island.

OL-PP71 21.02 2012–2018 Outcrop Situated in the eastern part of the island,

at an outcrop.

22

Fig

ure

3-3

. G

roundw

ate

r ta

ble

in t

he

gro

undw

ate

r obse

rvati

on t

ubes

in 2

018.

Sam

pli

ng t

imes

are

mark

ed w

ith v

erti

cal

lines

.

23

Fig

ure

3-4

. Gro

undw

ate

r ta

ble

lev

el in the

shall

ow

dri

llhole

s in

2018 (

manual m

easu

rem

ents

, auto

ma

tic

for

OL

-PP

56 L

1–3).

Sam

pli

ng

tim

es a

re m

ark

ed w

ith v

erti

cal

lines

.

24

3.3 Field measurements, sampling and laboratory analysis

Pre-pumping was performed in case of both shallow drillholes and groundwater

observation tubes. During the pre-pumping phase, the pH and the electrical conductivity

(EC) of the groundwater were monitored. The yield was also measured and sensory

impressions (odour, colour) noted. Pre-pumping was carried out for a period long enough

to flush out the standing water and replace it with representative water of the surroundings

and as well as get as clear sample as possible. The groundwater observation tubes and

shallow drillholes were typically pumped for three to four hours prior to the sampling.

The exceptions were the samples from OL-PP56. In the spring, OL-PP56 L1–L3 were

pumped for 18–24 h prior to the sampling and all these sections had low yield <0.2 L/min.

In the autumn, OL-PP56 L2 was pumped 3 h and L3 for 18 h prior to the sampling and

the yield was slightly higher (0.3–0.4 L/min).

The measured yield values were between 0.1 L/min (OL-PP56 L3 spring) and 2.4 L/min

(OL-PVP39) in 2018. In the tubes OL-PVP42A and –PVP42B, the yield was low (0.2

L/min) in the sampling in October 2018. Total amount of pumped water prior to the

sampling varied from a few liters to >500 L, in 2018.

The field and laboratory values of pH and EC are presented in (Table 3-3). The last value

prior to the sampling is marked as field value. The laboratory pH values were between

6.0 and 7.6 and the field pH values from 6.0 to 7.7. The conductivity of the samples

(laboratory values) was between 21 mS/m and 309 mS/m and the range of field EC values

was consistent (22–326 mS/m). Thus, the laboratory and field values of pH and EC were

consistent in the samples 2018.

Posiva was responsible for the pre-pumping and groundwater sampling. A more detailed

description of the field measurements is presented e.g. in Kröger (2004). The results of

the field measurements and information on pre-pumping periods are presented in

Appendix 5.

Groundwater samples were collected according to Posiva's water sampling guide (Alho

et al. 2017). Groundwater samples for a sulfide analysis were filtered already in the field

and collected into Winkler bottles (100 mL), which contained preserving chemicals.

The water samples were delivered directly from the investigation site to TVO's laboratory

as quickly as possible. The water samples were filtered with a membrane filter (0.45 μm),

where necessary, and bottled in the laboratory. The exact sample preparation is described

in Posiva’s water sampling guide (Alho et al. 2017).

The TVO laboratory at Olkiluoto performed the main chemical analyses according to

TVO's instructions. Isotope analyses were made in several subcontractor laboratories. All

the laboratory analyses were performed using standard methods or other generally

accepted methods to the appropriate extent. All analysis methods, detection limits and the

uncertainty of measurements are shown in Appendix 6.

25

Table 3-3. pH and electric conductivity (EC) in 2018, measured in the field before the

sampling, compared with the laboratory measurements of samples from the groundwater

observation tubes and shallow drillholes. Notable differences were not observed in 2018.

3.4 Quality evaluation

Sodium fluorescein

Sodium fluorescein is used as a trace compound in drilling and process waters (250 µg/L,

Sacklén 2017). In all shallow samples 2018, the sodium fluorescein concentration was

below the detection limit (< 1.0 µg/L).

Charge balance

The charge balances (CB %) can be evaluated by Hounslow's (1995) criteria (good results

are within ±5 %). The calculated charge balance is an important parameter to indicate the

potential analytical uncertainties within a sample. The charge balances of the groundwater

samples are expressed as a percentage, calculated by the following equation:

Sampling

point

Date

(ddmmyy)

pH

Field

pH

Lab

EC Field

(mS/m)

EC Lab

(mS/m)

Comments

OL-PVP3A 150518 6.9 6.8 45 45

OL-PVP4A 220518 7.3 7.1 111 111

OL-PVP11 040618 7.2 7.0 52 52

OL-PVP12 150518 6.7 6.6 28 27

OL-PVP13 210518 7.2 7.3 56 55 The first pH and EC lower.

OL-PVP14 031018 7.2 7.3 89 87

OL-PVP17 210518 6.6 6.6 103 105 The first EC higher.

011018 6.8 6.9 160 157 The first EC higher and pH lower.

OL-PVP18A 280518 7.7 7.5 99 100 The first EC notably higher.

011018 7.5 7.5 141 138

OL-PVP20 220518 7.3 7.2 50 50

OL-PVP30 031018 6.9 6.9 39 38

OL-PVP36 240518 6.8 6.7 75 74

OL-PVP39 091018 6.9 6.7 84 82 The first EC notably lower.

OL-PVP40A 290518 6.8 6.7 71 70 The first EC notably lower.

081018 6.7 6.6 31 30

OL-PVP40B 310518 7.1 6.9 51 49

OL-PVP41A 111018 7.5 7.4 191 189 The first pH and EC higher.

OL-PVP42A 091018 6.5 6.5 85 82 The first EC notably higher (188 mS/m) and

pH low (5.3), increasing trend in pH and decreasing in EC prior to the sampling.

OL-PVP42B 081018 7.1 7.2 61 59

OL-PP2 240518 7.3 7.2 120 120 The first pH higher and EC lower.

OL-PP36 181018 6.0 6.0 22 21 The first pH and EC notably higher.

Decreasing trend in pH and EC prior to the sampling.

OL-PP39 111018 6.6 6.6 111 108 The first EC value significantly lower.

OL-PP56 L1 38–55.9 m

310518 7.7 7.5 326 309

OL-PP56 L2

28–37 m

300518 7.6 7.5 200 186

181018 7.6 7.5 200 195

OL-PP56 L3

2.3–27 m

050618 * 7.6 * 139 *Field values were not measured.

161018 6.4 6.1 119 119

OL-PP70 041018 7.2 7.3 80 79 pH 6.2 and EC 16 mS/m in the beginning of the pumping. Strong increasing trend in EC.

OL-PP71 041018 6.7 6.6 29 28

26

%.100AnionsCations

AnionsCationsCB

(Eq. 2-1)

For this formula, the amounts of cations and anions are expressed in terms of equivalent concentrations, converted from the corresponding mass concentrations by:

,M

Qcc

M

E (Eq. 2-2)

where cM is the mass concentration of the ion (mg/L), Q its charge number (formally

mEq/mmol) and M the molar mass of the ion (g/mol). The total concentrations cE (mEq/L)

of the anions and cations are summarized and calculated using Equations 2-1 and 2-2.

The comparison of the charge balance with the previous data may indicate anomalies in

the individual parameters, account for the deviation in CB value and provide important

additional information for the geochemical calculations, e.g. Pitkänen et al. (2004) and

Pitkänen et al. (2007a). On the other hand, CB values may vary a lot in dilute waters with

low pH. Straightforward calculations of CB for a sample do not take carbonic acid

dissociation into account, and alkalinity titration, if only used to detect DIC, is itself

uncertain in low pH waters. Acidity is also determined for waters with low pH and these

values can be used in checking carbonate concentration and CB calculations.

Organic substances that are generally notable in shallow, low salinity and low pH

groundwaters, (e.g. humic or fulvic acids with anionic functional groups such as carboxyl

groups) may also increase the cation content in the solution and the CB-value can lead to

misinterpretations, because cations are included in cation results but these anionic

functional groups are not included in anion results. In fresh waters, CB is very sensitive

to measured ion concentrations and even an inaccuracy of a few mg/L in analysis of a

single anion or cation may change the CB-value by several percent, whereas several

hundreds or even more than a thousand mg/L in saline groundwaters do not greatly affect

the CB-value (Pitkänen et al. 2007a). A converging CB value with increasing chloride

concentration is used in the evaluation of Olkiluoto groundwater samples. Acceptable CB

is from ±10 % to ±5 %, when the chloride concentration is 0–355 mg/L, and from ±5 %

to ±3 % when 355–3550 mg/L, and ± 2 % when chloride concentration is >35500 mg/L.

For the majority of shallow groundwater samples, CB % up to ±10 % is acceptable.

In Figure 3-5 and Table 3-4, the charge balances are presented for all the shallow

groundwater samples during 2018. Blue lines border the range of acceptable CB % in

Figure 3-5. All charge balances were within the acceptable limit in 2018.

27

Figure 3-5. Charge balances in the shallow groundwater samples in 2018. The blue

lines border the acceptable CB value.

28

Table 3-4. Charge balances of the shallow groundwater samples in 2018.

Hole ID Sample

ID

Date

(ddmmyy)

Charge

Balance

%

Hole ID Sample

ID

Date

(ddmmyy)

Charge

Balance

%

OL-PVP3A 4388 150518 +4.70 OL-PVP14 4482 021018 +0.54

OL-PVP4A 4393 220518 +0.33 OL-PVP17 4479 011018 -0.28

OL-PVP11 4395 040618 +2.90 OL-PVP18A 4480 011018 -0.61

OL-PVP12 4389 150518 +4.43 OL-PVP30 4481 031018 +2.37

OL-PVP13 4391 210518 -2.71 OL-PVP39 4488 091018 +0.75

OL-PVP17 4390 210518 -1.73 OL-PVP40A 4485 081018 +4.64

OL-PVP18A 4387 280518 +0.23 OL-PVP41A 4489 111018 -0.16

OL-PVP20 4392 220518 +1.54 OL-PVP42A 4487 091018 +1.75

OL-PVP36 4397 240518 -2.53 OL-PVP42B 4486 081018 +4.28

OL-PVP40A 4394 290518 +5.21 OL-PP36 4493 181018 +2.41

OL-PVP40B 4396 310518 +5.50 OL-PP39 4490 111018 +1.96

OL-PP2 4386 240518 -2.52 OL-PP56 L2 4491 181018 -0.76

OL-PP56 L1 4398 310518 -4.22 OL-PP56 L3 4492 161018 +0.25

OL-PP56 L2 4399 300518 +3.26 OL-PP70 4483 041018 +1.28

OL-PP56 L3 4400 050618 -0.09 OL-PP71 4484 041018 +2.92

29

RSD

The quality of the analysis is controlled through laboratory quality control (QC) samples

and reference solutions. The assigned relative standard deviations (RSD) were calculated

for at least three parallel groundwater subsamples. The RSD is calculated by dividing the

standard deviation by the mean value.

The RSD values were exceeded by 5 % in 13 analyses for the shallow groundwater

samples in 2018 (Table 3-5).

The RSD value is higher near the detection limit, when even a small difference between

parallel results increases the RSD value at low concentrations. Four of six sulfide analyses

with high RSD, were near the detection limit 0.02 mg/L (0.02–0.04 mg/L), the other two

with high RSD were 0.06–0.07 mg/L.

Ferrous iron and acidity are sensitive to interference from oxygen or carbon dioxide in

the air. For shallow samples, there is preserving chemicals added already during

sampling, so air cannot affect to sulphide analyses. Dissolving or degassing of gases, such

as carbon dioxide or oxygen from air, may occur before titration as a result of filtration

or temperature changes of samples. Higher RSD in total acidity analysis could be caused

from the interference of carbon dioxide. However, the analyses with higher RSD did not

show significant difference in measured dissolved inorganic carbon (DIC) vs. inorganic

carbon results calculated from the alkalinity titration. Also two Fe2+ analyses, one fluoride

analysis and nitrogen analysis had higher RSD.

Overall, analyses succeeded well, as the other RSD values were <5 %. The main source

of errors for the water analyses is presented in Tuominen (1994).

30

Table 3-5. The groundwater analysis having RSD values > 5 % in 2018.

Sample

Date

(ddmmyy) Analysis Result Unit RSD% Reason

OL-PVP3A 150518 Sulfide, S2− 0.04 mg/L 7.5 at the DL

OL-PVP3A 150518

Total acidity,

NaOH uptake 0.25 mmol/L 11

Air

sensitive

method

OL-PVP4A 220518

Nitrogen, N

(total) 0.24 mg/L 5.5

Closeness

of DL of

raw data

OL-PVP18A 280518

Total acidity,

NaOH uptake 0.13 mmol/L 6

Air

sensitive

method

OL-PVP40A 290518 Sulfide, S2- 0.06

mg/L 8 Closeness

of DL

OL-PVP40B 310518 Sulfide, S2- 0.04 mg/L 7 Closeness

of DL

OL-PP2 240518 Sulfide, S2- 0.02 mg/L 6 at the DL

OL-PP56 L1 310518 Fluoride, F 0.3 mg/L 8

OL-PP56 L1 310518 Iron, Fe2+ 0.03 mg/L 12

Closeness

of DL and

air sensitive

method

OL-PP56 L3 050618

Total acidity,

NaOH uptake 0.08 mmol/L 5.5

OL-PVP18A 011018 Sulfide, S2- 0.02 mg/L 7 at the DL

OL-PVP39 091018 Sulfide, S2- 0.07 mg/L 7 Closeness

of DL

OL-PVP41A 111018 Iron, Fe2+ 2.0 mg/L 10

Closeness

of DL and

air sensitive

method

CO2= interference of carbon dioxide, DL= detection limit

31

Dissolved inorganic carbon (DIC) and Sulphur (S)

Figure 3-6 presents dissolved inorganic carbon concentrations (DIC) as a function of the

inorganic carbon concentration calculated from the alkalinity results for the groundwater

tube and shallow drillhole samples. The samples with >6 mg/L difference and the samples

with 20–25 % difference are marked in the figure.

In the sample of OL-PP39, the carbon calculated from the alkalinity titration was 12 mg/L

lower than DIC mg/L. In two samples, OL-PP36 and OL-PP39, the carbon calculated

from the alkalinity titration was 20–25 % lower than DIC mg/L.

Carbonic acid is a dominant species at acidic pH values (<6.3), and at the intermediate

pH values (7–10) bicarbonate HCO3- is the dominant species, while CO3

2- is the dominant,

when pH is alkaline (> 10.3) (Appelo & Postma 2005). Low pH (<7) can be the main

reason for the difference between the measured DIC and the amount of carbon calculated

from alkalinity titration. This is because a significant fraction of DIC is dissociated to

dissolved CO2, which is not detected in alkalinity titration. Both samples OL-PP36 and

OL-PP39 had pH <7.

Figure 3-6. Measured dissolved inorganic carbon (DIC) as a function of inorganic

carbon results calculated from the alkalinity titration for the shallow groundwater

samples in 2018 (the line is 1:1). The sample of OL-PP39 with >6 mg/L difference and

pHf < 7 is marked with the red circle, also the samples OL-PP36 and OL-PP39 with

20 % – 25 % difference and pHf < 7 are marked with the red square.

32

Figure 3-7 presents measured sulphur (S) concentrations as a function of sulphur

concentrations calculated from sulfide and sulfate results for the shallow groundwater

samples. They are generally in good accordance.

Figure 3-7. Measured sulphur (S) concentrations as a function of sulphur

concentrations calculated from sulfide (when analysed) and sulfate results for the

shallow groundwater samples in 2018 (the line is 1:1).

33

Saturation index (SI)

The saturation index (SI) is used to interpret the potential behaviour of minerals in

groundwaters and SI of calcite is used to evaluate measured pH values due to the

sensitivity of calcite to react to pH changes. The SI of a particular mineral that may be

reacting in the system is defined as

K

IAPlogSI 10

, (Eq. 2-3)

where IAP is the ion activity product of the mineral (product of Ca2+ and CO32- activities

in case of calcite) and K is the solubility product. Mineral is in equilibrium with solution if SI is zero. SI is greater than zero for supersaturation, and less than zero for subsaturation, indicating precipitation and dissolution for a particular mineral, respectively. Thermodynamic solubilities were calculated with PHREEQC code (version 3) (Appelo & Postma 2005).

Calcite saturation index SIcalcite and logPCO2, were calculated for the shallow groundwater samples taken in 2018 and are presented in Figure 3-8 and Appendix 7. The saturation state indicates in which direction the process may go; dissolution is expected for subsaturation and precipitation for supersaturation (Appelo & Postma 2005). Higher PCO2,

and the associated increase of dissolved carbonic acid enable more calcite to dissolve (Appelo & Postma 2005).

Over half of the shallow groundwater samples 2018 were subsaturated (SIcalcite < -0.2, dissolution expected) and a minority of the samples was saturated (SIcalcite ±0.2) or supersaturated (SIcalcite > +0.2, precipitation expected) (Figure 3-8). Saturation indices here were calculated in standard temperature (6 °C).

OL-PVP12 samples have earlier plotted mostly among the Eurajoki River water samples, but in 2018, the sample of OL-PVP12 plotted close to the main group of shallow samples.

In 2018, also the October sample of OL-PP56 L3 was close OL-PVP12 indices due to lowish PCO2. In OL-PVP12, logPCO2 has plotted earlier mostly close surface water samples due to surface water effect from close Korvensuo reservoir. The October sample of OL-PP56 L3 might be slightly shifted to the direction of surface waters, at least it differed a lot from the May sample.

When the partial pressure of CO2 increase, increases also the amount of dissolved carbonic acid and pH of water decreases. In all shallow groundwater samples (Figure 3-8), the partial pressure of CO2 was higher than the atmospheric value of -3.5.

34

Figure 3-8. The plots of a) pH and calculated calcite saturation index SIcalcite, b) pH and

calculated logPCO2 and c) calculated calcite saturation indices SIcalcite and logPCO2 for

the shallow groundwater samples 2018. Oversaturated samples marked with red triangle,

samples within the uncertainty limit of SI ±0.2 (saturated) marked with black triangle; other

samples are subsaturated. As reference, shallows 1995–2017, Sea water, Korvensuo

reservoir and Eurajoki River points are added to the figure. In 2018 taken samples of OL-

RS1 and OL-RWS04 are marked separately. In 2018, the indices of OL-PVP12 (15.5.2018)

and OL-PP56 L3 (16.10.2018) were close. In OL-PP56 L3, the indices differed a lot

between the May and the October sample.

35

Classes for the samples 2018

Shallow groundwater samples were classified until 2013 according to the guidelines for the classification given in Pitkänen et al. (2007a, classes B1−2, T1−2, E). The classification of shallow samples will be modified and launched later within the ongoing data evaluation project. The temporary classification, used in 2014–2018, consists the classes T1, T2 and E. Classes B1–2 for the baseline samples, are removed, because the definition of the baseline for the shallow samples cannot be defined as clearly as for the deep groundwater samples.

- Class T1 (Time-series), includes chemically valid samples with no significant sampling or analytical problems.

- Class T2, includes samples with a poor analytical programme or anomalous charge balance (CB-value).

- Class E, (Erroneous) includes samples with severe quality problems e.g. high sodium fluorescein and/or a very poor analytical programme or disturbed chemistry.

On the basis of the quality evaluation, class T1 was given for all 30 samples in 2018 (Table 3-6).

Table 3-6. Classes for the shallow groundwater samples 2018 on the basis of the quality

evaluation.

Drillhole ID / Sampling

point

Date

(ddmmyy)

Class Drillhole ID / Sampling

point

Date

(ddmmyy)

Class

OL-PVP3A 150518 T1 OL-PP2 240518 T1

OL-PVP11 040618 T1 OL-PP36 181018 T1

OL-PVP12 150518 T1 OL-PP39 111018 T1

OL-PVP13 210518 T1 OL-PP56 L1 38–55.9 m 310518 T1

OL-PVP14 031018 T1 OL-PP56 L2 28–37 m 300518 T1

OL-PVP17 210518 T1

T1

181018 T1

011018 OL-PP56 L3 2.3–27 m 050618 T1

OL-PVP18A 280518 T1

T1

161018 T1

011018 OL-PP70 041018 T1

OL-PVP20 220518 T1 OL-PP71 041018 T1

OL-PVP30 031018 T1

OL-PVP36 240518 T1

OL-PVP39 091018 T1

OL-PVP40A 290518 T1

T1

081018

OL-PVP40B 310518 T1

OL-PVP41A 111018 T1

OL-PVP42A 091018 T1

OL-PVP42B 081018 T1

36

3.5 Salinity, water types and main trends

TDS, water type, the main anion and cation

According to the Davis’s TDS-classification system (1964), 23 of the groundwater

samples taken in 2018, were classified as fresh (TDS < 1000 mg/L) and seven samples

were brackish waters (1000 mg/L < TDS < 10000 mg/L). TDS values in 2018 are

presented in Appendix 8.

Waters were classified according to the main cation and anion concentrations (Davis and

De Wiest 1967). The water types and total dissolved values (TDS, mg/L) since 2001 until

2018 are presented in Appendix 8. The observed trends are presented in Appendix 9. The

main cation has been mainly calcium or sodium and the main anion bicarbonate

(Appendix 8).

In OL-PVP39, both main anion (HCO3 to Cl) and cation (Ca to Na) changed, as well as

in OL-PP70 (SO4 to HCO3 and Ca to Na).

The main anion changed in OL-PVP3A, OL-PVP40B and OL-PVP41A (SO4 to HCO3)

and in OL-PVP12 (HCO3 to SO4). The main cation changed in the spring sample of OL-

PVP18A from Na to Ca, but changed back to Na in the autumn sample. In both OL-PP56

L2 samples, Ca changed to Na as main cation. In OL-PVP40A and OL-PVP42A Mg

became as second cation and to third in OL-PP39. In OL-PP56 L1 sample SO4 was not

anymore included in the water type, as in all earlier samples has been.

Trends in sulfate concentration

In the samples of OL-PP56 L1–L3 (375 mg/L–700 mg/L), the sulfate concentration was

lower than in 2017. Sulfate concentration showed decreasing trend also in L1–L2, in

addition to L3 samples, but SO4 was still at high level.

On the basis of 2018 results, rising sulfate trend levelled off in OL-PVP17 (440–625

mg/L) and OL-PVP18A (267–378 mg/L), being still at high level. In both tubes, sulfate

concentration has been at higher level during 2016–2018 and peaked at autumns.

In 2018, a notable increase of sulfate was observed in OL-PVP42A tube from 37 mg/L in

2017 to 287 mg/L in 2018. Also in B-tube, the minor increasing trend in sulfate continued

to 68 mg/L in 2018.

In OL-PVP40B tube, SO4 concentration increased notably in 2017 (146 mg/L) being

higher than in A-tube. Sulfate concentration in OL-PVP40B was clearly lower in the

spring 2018 (84 mg/L) compared to the 2017 results. In 2018, strong annual fluctuation

in sulfate continued (peaks in springs) in OL-PVP40A. Sulfate concentration fluctuation

range (from spring 115 mg/L to autumn 38 mg/L) was higher than in 2017 and A-tube

had higher sulfate concentration than B-tube in spring.

In OL-PP39, sulfate concentration peaked in autumn 2018 to 153 mg/L. In OL-PVP36

(125 mg/L, spring) and in OL-PP70 (165 mg/L, autumn) sulfate remained at high level in

2018 as it was in 2017.

37

Trends in the chemistry near the Olkiluoto Natura area and the old forests preservation

area

In OL-PVP4A, Na has increased from 2007 till 2017. In 2017–2018, TDS or Na has not

shown increase anymore. Also Cl concentration has been the same in all samples during

2015–2018. TDS has earlier increased in stepwise manner mainly due to increase of Na

and Cl since the autumn 2007.

In the shallow drillhole OL-PP2, close the Olkiluodontie road and near OL-PVP4A, TDS

has increased earlier due to rising Na and Cl. In OL-PP2, Cl or Na has not shown increase

anymore in 2017–2018. Sodium concentration has shown minor decreasing trend since

the maximum value in the spring 2016 (79 mg/L) to the spring 2018 (68 mg/L).

OL-PVP20 locates also near these and at the Nature area. In OL-PVP20, TDS has not

shown increase, the decreasing trend in TDS ended in 2012. Br/Cl in OL-PVP20 has not

shown decrease to anomaly low values like observed in OL-PVP4A and OL-PP2.

Seasonal fluctuation

In the following sampling points seasonal fluctuation of concentrations has been

observed:

- OL-PVP3A, earlier in 2004–2009, seen in TDS and due to the changes in SO4,

Ca and Mg, but not anymore in 2015–2018

- OL-PVP13, fluctuation observed earlier when sampled twice a year, not

detected anymore when sampled once a year

- OL-PVP14, not as regular as in OL-PVP13, not detected anymore when

sampled once a year

- OL-PVP17, with higher TDS in autumns (due to SO4)

- OL-PVP18A, with the higher TDS in autumns (due to SO4)

- OL-PVP20, with the higher TDS in autumns earlier, but not anymore when

sampled once a year. Fluctuation in TDS was due to the changes in HCO3, Na

and Cl concentrations.

- OL-PVP36, with the higher TDS in autumns (due to Cl, Na, HCO3, SO4)

- OL-PVP40A, with the higher TDS in springs (due to HCO3, SO4, Ca)

- OL-PP36, some kind of irregular fluctuation, peaks time to time

- OL-PP70, some kind of irregular fluctuation, peaks time to time

- OL-PP39, very regular strong variation with the higher TDS values in

autumns. Reason has been the fluctuation of all main ions (Na, Ca, HCO3, Cl,

38

K and Mg), except of SO4 concentration which has not shown a seasonal

fluctuation.

The seasonal behaviour of concentrations has been related to high naturally fluctuating

concentrations in these sampling points, where ion concentrations tend to vary a lot

between spring and autumn samplings, and often also between the years.

39

3.6 Comparison and evaluation of the results by different groundwater groups in 2001–2018

3.6.1 The Northern coastline group

The Northern coastline group includes:

- groundwater observation tubes OL-PVP8A, OL-PVP9A, OL-

PVP9B, OL-PVP39, OL-PVP40A and OL-PVP40B

- shallow drillholes OL-PP8 and OL-PP90

The tubes OL-PVP39 and OL-PVP40A–B were sampled in

2018 from this group.

The ground level at these points is 1.5–4 m.a.s.l. The

observation tubes have a perforated section from the depth of

the sea level to 6 m below the sea level, thus, all the perforated

sections locate below the sea level. The shallow drillholes reach

the depth of -12…-22 m.a.s.l (Figure 3-9).

The analysis results of 2001–2018 from selected analyses are

presented in Figure 3-10, more analysis results 2001–2018 are

presented in Appendix 10. All the analysis results of 2018 for

the shallow groundwater samples are presented in Appendix 7.

Typical features for the groundwaters in this group has been low

concentrations in most of the analysed parameters e.g. typically

in Na and Cl, and there has not been earlier evident signs of the

sea water infiltration (Figure 3-10). However, the points OL-

PVP39–OL-PVP40A/B (sampled in 2014–2018) and OL-PP90

(sampled in 2014–2017), have showed much higher

concentrations and fluctuation range of Na and Cl, as well as in

SO4, Ca, K and Mg, than the other points of group.

Concentrations of iron and DOC (Dissolved organic

carbon)/NPOC (Non purgeable organic carbon) results have

been among the highest when compared to the results of all

monitored shallow groundwaters.

Figure 3-9. The Northern coastline group.

40

OL-PVP39

Chemistry

TDS (517 mg/L) increased significantly and seems to be rising steadily from 2014.

Both Na and Cl have been untypically high for the points of this group, and both

concentrations increased still. Na was 72 mg/L and Cl 150 mg/L. SO4 was at the same

level as in 2017 at 52 mg/L.

The ratio of Br/Cl in 2018 was 0.0040 and remained close to the sea water ratio (0.0035)

as in 2016–17. The isotope composition δ34S(SO4) and δ18O(SO4) changed in 2015–

2016 towards more marine composition and the results 2018 were close the results in

2017.

Other notes

The yield was good 2.4 L/min. During the sampling pumping, the groundwater level

lowered almost 1 m, being then below sea level. The groundwater level was also below

sea level in September prior to sampling and only rose above sea level two weeks

before sampling. The lowering of groundwater level below sea level was steeper than

in 2016–2017. This may have affected high Na and Cl results.

OL-PVP40A and B

Chemistry

In OL-PVP40A, TDS has fluctuated strongly in 2014–2017 and this tendency

continued also in 2018. Two samples were taken during 2018 and there was wide

variation in TDS from 571 mg/L in the spring to 249 mg/L in the autumn sample. Total

variation in this tube has been 245–571 mg/L. Fluctuation seems to be mainly due to

SO4, Ca and HCO3. SO4 and Ca concentrations peaked in the spring sampling, being

115 mg/L and 110 mg/L, respectively. The isotope composition of δ34S(SO4) was

around 8 ‰ during these SO4 peaks, which did not differ from the other δ34S(SO4)

results of OL-PVP40A.

More narrow fluctuation was observed in Mg and Cl concentrations. Na concentration

was stable in both samplings in 2018 (16 mg/L). During 2014–2017, pH has decreased

from 7.2 to 6.7. In 2018, pH was 6.8 in the spring and 6.7 in the autumn sampling.

In spring sample of A-tube, Fe2+ concentration increased to 11 mg/L, being the

dominant iron form, Mn 1.5 mg/L was higher than typically, and NPOC 16 mg/L was

lowish. The water type changed to Ca-Mg-Na-HCO3. The ratio of Br/Cl of the spring

sample (0.0256) was close to the summer 2017 sample. Iron concentration tend to peak

at spring samples.

TDS of shorter B-tube has been stable, close 430 mg/L in all samples, but in 2018

sampling, TDS was lower, 397 mg/L. This was mainly due to decrease in SO4

concentration, which was 84 mg/L compared to 146 mg/L in 2017. pH increased to 7.1,

41

also HCO3 increased to 171 mg/L. Total iron concentration was 8 mg/L, both forms

Fe2+ and Fe3+ were present, but Fe2+ was the dominating species.

In B-tube, δ34S(SO4) 3.66 ‰ in spring 2018 was close A-tube result 3.79 ‰ in autumn

2018, while earlier it has clearly lower δ34S(SO4) -3.41 ‰ in 2017.

Other notes

In A-tube, the yield of both samples was good (ca. 1.6 L/min). In the spring sampling

EC was at first at lower level, but increased strongly after the beginning of the pumping.

In B-tube, the yield was low 0.2 L/min. The yield has been 0.3–0.7 L/min earlier.

42

Figure 3-10. a) TDS, b) pH (field), c) sulfate, d) chloride, e) bicarbonate and f) calcium

concentrations as a function of the time in the Northern coastline group.

a) b)

c) d)

e) f)

43

3.6.2 The Outcrop group

The Outcrop group includes shallow drillholes OL-PP36, OL-PP37 (caved in, the last results from April 2007), OL-PP71, OL-PR1, OL-PR2 and OL-PR4 (clogged up, the last results from June 2003).

In the monitoring programme 2018, OL-PP36 and OL-PP71were

sampled.

The drillholes are located in the northern, eastern and central parts of the island and are drilled on the outcrops (or only thin layer of overburden at site). The ground level at these points is approx. +5…+10 m.a.s.l and the bottom of the drillholes is at the depths of -3…-20 m.a.s.l (Figure 3-11).

The analysis results of 1995–1997 (OL-PR1–OL-PR4) and 2001–2018 from selected analyses are presented in Figure 3-12, more analysis results 2001–2018 are presented in Appendix 10.

In these outcrop drillholes, the most ion concentration and pH

values have been typically low, which indicates that there has

been no interaction or only limited interaction with water and thin

soil layers. The surface runoff is dominant. TDS values have been

relatively low and ranged mainly between 50–300 mg/L, with

some peaks of 500 mg/L.

Figure 3-11. The Outcrop group.

44

OL-PP36

Chemistry

The sample of 2018 represented the mid-level TDS (142 mg/L). Compared to the 2016–

2017 samples, the 2018 sample was more concentrated (mainly due to higher Na, Cl,

SO4 and HCO3 concentrations). Overall, the sample of 2018 was close the

concentration levels of earlier sample in 2015. pH was 6.0 and shows a constant decline

since 2013. Total iron was low 0.69 mg/L, and almost the half of it was in form Fe3+.

Low nitrate concentrations have been measured in OL-PP36 occasionally, also in 2018.

The amount of NPOC (12 mg/L) was lower than in 2017. The difference between DIC

and calculated carbon from alkalinity titration was ca. 25 % (2.7 mg/L). Low pH

explained the difference (CO2).

Other notes

The yield 0.8 L/min in 2018 was slightly higher than in 2017 (0.5 L/min), but yield has

varied much during the years (<0.1–9 L/min), as well as the analysis results. This

sampling point has suffered occasionally from notably low yield due to hydrological

conditions (dry summer effect in 2013–2014). The groundwater level in OL-PP36 has

fluctuated just above the sea water level within 1.5 masl head level and after the dry

summer in 2018, the head level was just above the sea level being within 1 m during

the timing of sampling in October.

OL-PP71

Chemistry

The previous sample was taken in the autumn 2016. TDS and HCO3 were lower than

in 2016, being 233 mg/L and 116 mg/L, respectively. Concentrations of major cations

were slightly lower than in 2016. Sulfate seems to show a slow increasing trend since

the start of monitoring in 2012, but the concentration (34 mg/L) is still low compared

to many shallow sampling points in Olkiluoto.

Other notes

Annual fluctuation in the groundwater table level has been typical strong, ca. 2.5–3 m

during 2016–2018. The yield, 0.92 L/min in October 2018, was slightly higher than in

2016 (0.68 L/min).

45

Figure 3-12. a) TDS and b) pH (field), c) sulfate, d) chloride f) bicarbonate and f)

sodium concentrations as a function of the time in the Outcrop group.

a) b)

c) d)

e) f)

46

3.6.3 The Peatland group

The Peatland group includes:

- the groundwater observation tubes OL-PVP3A, OL-PVP3B, OL-PVP10A, OL-PVP10B, OL-PVP18A, OL-PVP34A, OL-PVP34B, OL-PVP36, OL-PVP41A and OL-PVP41B

- the groundwater observation tube OL-PVP17 was removed in 2016 from the peatland group and added to the group of extraordinary points (the geochemical and hydrological environment was changed, soils were removed)

- the shallow drillhole OL-PP39

From these points the tubes OL-PVP3A, OL-PVP18A, OL-PVP36, OL-PVP41A and shallow drillhole OL-PP39 were sampled in 2018.

The sampling points are situated from the southern part to the eastern central parts of the island in peaty and swampy areas. At the studied peatland sites on Olkiluoto Island, the organic layer is typically 10–30 cm (Tamminen et al. 2007). The maximum 50 cm peat layers are found at the young Olkiluodonjärvi mire (Leino 2001, Ikonen 2002).

The ground level of the tubes at these points varies between 0.2 m.a.s.l. and 7.5 m.a.s.l and the tubes have perforated sections at depth of +4…-9.5 m.a.s.l. Only the drillhole OL-PP39 reaches the depth of -7 m.a.s.l (Figure 3-13).

The analysis results of 2001–2018 from selected analysis are presented in Figure 3-14, more analysis results 2001–2018 are presented in Appendix 10. OL-PVP41A−B have ground level near sea level and the perforated sections few meters below sea level. A-tube has the perforated section at the deep most position of all the groundwater tubes -6.5…-9.5 m.a.s.l.

Chloride has been often abundant (50–200 mg/L, and up to 350 mg/L) in the samples of this group as a

group specific feature. Typical features for this group have been high TDS and pH values, as well

as high Fe, Cl, SO4, HCO3, Mg, Na and K concentrations. Other typical features have been seasonal variation and the large concentration ranges with occasional high peaks.

Figure 3-13. The Peatland group.

47

Sulfate sources may be very young or even currently forming. There may be

modern/currently on-going sulphur accumulation in peatlands – and also seasonal or

periodical release of sulphur. Sulfates are transported in groundwater. While reaching the

reducing conditions in the catothelm, where there is a lot of decomposing organic matter

and little oxygen, sulphur accumulates as metal sulfides to the basal peat or possibly even

to mineral subsoil. Sulphur mobilises again as sulfates seasonally (in the end of summer

period) or periodically (dry year). Source of the groundwater sulfates may be in bedrock,

mineral soil or seawater infiltrating to groundwater. The peatland redox state controls the

amount of sulphur released and also the isotope composition of released sulphur.

SO4 concentrations in Finnish shallow groundwaters are typically <15 mg/L (Lahermo et

al. 2002). Near coastal areas, also remnants of ancient sea water and sulfide-rich clay soils

increase sulfate concentrations in groundwaters and due this the highest sulfate

concentrations in groundwaters have been found in western and south-western Finland,

especially where the Littorina clay and silt sediments exists (Palko 1994). Decomposition

of organic matter may also increase SO4 content and isotopic results of SO4 have indicated

this for the significant additional source (Posiva 2011). Breitner (2011) has reported on

sulfide-rich minerals on till layers at Olkiluoto.

The water colour has been typically yellowish in most of the samples of this group. Organic matter, typically fulvic and humic acids, can give water the observed yellowish colour. Within this group, NPOC concentrations have been typically rather high.

Seasonal variation has been observed in OL-PVP3A (2004–2009), OL-PVP18A, OL-PVP36 and OL-PP39 (very strong).

OL-PVP3A

Chemistry

TDS continued to decrease and the measured value of 289 mg/L resembles the values

of early 2000s in the beginning of the monitoring. During 2004–2016, TDS fluctuated

at higher level of 400–600 mg/L. Decreased TDS was mainly due to lower SO4 and Na

concentrations (57 and 39 mg/L, respectively). All other major ions also had lower

concentrations than in 2017. The fluctuation of pH has been modest, and has been 6.9

in 2013–2018.

Other notes

The yield 0.7 L/min was good, but lower than in 2017. The groundwater level

fluctuated within 1 m above the sea water level. The prepumping lowered the

groundwater level ca. 1.5 m. The sampling was carried out in May, but later after the

dry summer 2018, the groundwater level decreased temporarily below the sea level in

August–September.

The tube was probably frozen in the beginning of the year, which has prevented the

groundwater level measurement.

48

OL-PVP18A

Chemistry

TDS fluctuated strongly in 2018 samples, in the same range as in 2005 samples in the

beginning of the monitoring. Only the autumn sample can be regarded as slightly

brackish (TDS 1076 mg/L) whilst in the spring sample TDS was only 776 mg/L, which

is a new minimum value.

Sulfate concentration was lower than in 2017, but the variation between spring and

autumn samples was greater (267 mg/L and 378 mg/L compared to 323 mg/L and 403

mg/L in 2017). Sulfate concentration has been high since 2010 (200–400 mg/L).

Magnesium and calcium concentrations varied between spring and autumn samples

(Mg 27 mg/L and 41 mg/L, Ca 84 mg/L and 96 mg/L, respectively). SO4, Ca and Mg

concentration have been typically higher than in the other points of this group, as in the

autumn 2018 sample.

2018 samples were saturated (SIcalcite 0.06–0.11). The pH was between 7.5–7.7. The pH

value 7.5 was measured during the autumn campaign and is the new minimum value.

Br/Cl ratio (0.0032–0.0056) in 2018 was closer seawater ratio (0.0035) in the autumn

sample. In spring, the most of iron was in the form Fe3+ and none in autumn sample.

High sulfate levels in 2010–2018 can relate to natural peatland properties and to the natural changes in groundwater level (oxic conditions and oxidation), which can be enhanced by the drawdown caused by the ONKALO construction work. Activities (blasting, drilling, grouting) at ONKALO were accelerated again in 2016–2018.

Other notes

The yield (ca. 0.6 L/min) was close the earlier measurements. During 2018, the groundwater table level fluctuated ca. 1.5 m reaching its lowest value in September. The decrease in groundwater level during the dry summer months was similar as in 2013 (dry summer). The groundwater level reacted quickly in July to heavy rainfall peak, but continued typical decrease after this until the end of September.

The ONKALO construction has been reported to have caused drawdown in the groundwater level of OL-PVP18A according to Vaittinen et al. (2019). The drawdown (0.3 m) developed during 2004–2008 (Vaittinen et al. 2019). The drawdown might be a consequence of the penetration in the HZ19 system due to the ONKALO access tunnel in autumn 2005.

For OL-PVP18A, no analysis data before the ONKALO construction work exists, so it suffers from the lack of true comparison data before the construction.

OL-PVP36

Chemistry

TDS has fluctuated a lot (520–940 mg/L). In 2018, TDS of 537 mg/L was close to 2013

sample. TDS has decreased slowly since peak value in 2015. The decrease in TDS is

49

mainly due to decrease in Na, Cl, and SO4 concentrations (43, 130, and 125 mg/L,

respectively). SO4 concentration was still >100 mg/L like in 2017. Strong seasonal

fluctuation was seen and Na and Cl have controlled the great fluctuation. Ca (74 mg/L)

and Mg (16 mg/L) concentrations were at the same level in 2018 as in 2017. Br/Cl

0.0037 was close the seawater ratio (0.0035). pH (6.8) was close to the previous value.

In tubes OL-PVP3A and OL-PVP36, the development of TDS and trend lines in SO4

concentration during 2013–2018 are alike. The tubes locate far from each other

referring to common unite hydrological factor behind the concentration changes in

both.

Other notes

The yield was 0.4 L/min; the earlier variation has been 0.2–0.9 L/min. The groundwater

level dropped within the perforated section during the prepumping.

OL-PVP41A

Chemistry

Compared to the earlier sample, the changes were modest. TDS was slightly higher

than in 2017 with value of 1285 mg/L. pH (7.5) was the same as in summer sample of

2017. SO4 (264 mg/L) concentration was slightly lower compared to 2017. Slightly

brackish TDS of OL-PVP41A/B-tubes has been the highest of this group in 2016–2018.

In addition to SO4, high TDS is due to high Na (300 mg/L) and Cl concentration (260

mg/L), which differed from the other points of this group. Br/Cl (0.0042) was just

above the seawater ratio (0.0035).

Compared to the point OL-PVP18A in this same group, but rather far from this point,

sulfate concentration in OL-PVP41A (far from ONKALO area, near seashore) has been

close the spring sample SO4 concentrations in OL-PVP18A. The isotope composition

δ34S(SO4) 7.39 ‰ and δ18O(SO4) -0.56 ‰ did not refer to untypical isotope composition

like in OL-PP56 L3 samples (δ34S(SO4) -0.93…0.17 ‰ and δ18O(SO4) -10.6…-9.1 ‰),

but more to typical values observed in the other near sea located OL-PP36 δ34S(SO4)

6.83 ‰ and δ18O(SO4) 3.7 ‰.

Other notes

The yield was 0.6 L/min. The tube is located near seashore and the groundwater level

has shown only minor fluctuation annually just above the sea level. The perforated

section is at deep position at depth -6.5…-9.5 m.a.s.l.

OL-PP39

Chemistry

OL-PP39 was sampled in October. TDS (775 mg/L) was higher than in recent years,

resembling more the autumn 2014 sample. TDS has typically been higher in autumn

50

samples. Both Cl and Na were lower than in 2017, 120 mg/L and 95 mg/L, respectively.

Br/Cl of the sample (0.005) was above sea level ratio (0.0035).

SO4 concentration (153 mg/L) increased by a factor of three from autumn 2017 to

autumn 2018. δ34S(SO4) decreased to 2.23 ‰ (after strong enrichment 2016–2017) and

δ18O(SO4) to 3.07 ‰ in 2018.

Also calcium and magnesium peaked with sulfate concentration. At the same time,

HCO3 decreased from 317 mg/L in autumn 2017 to 244 mg/L. pH also dropped 0.5 pH

units to 6.6. Iron was mainly present as Fe2+; total iron concentration was 17 mg/L,

which is at the same level as in 2014. Difference of DIC vs. calculated carbon from

alkalinity titration was 12 mg/L (20 %), when pH was 6.6.

However, the peak of SO4, Mg and Ca in 2018 was significantly lower than in spring

2014, when all these peaked even strongly, but turned to decrease after the peak values.

Strong seasonal variation in TDS has been typical for the whole monitoring period.

Seasonal fluctuation contributes to the regularly higher TDS (HCO3, Ca, Mg, K, Na,

Cl) in the autumn.

Higher HCO3 in the autumn samples emphasises the significance of summer conditions

on the hydrogeochemical and microbial activity in the shallow depths (Pedersen 2007).

Other notes

The yield was ca. 0.6 L/min, typical to this point. Groundwater level fluctuation is

annually minor, <1 m in 2018. The groundwater level has dropped the most during the

dry summers 2013 and 2018 thus, the hydrological changes can be the reason to

temporary high peak values (SO4, Ca, Mg) in spring 2014 and in autumn 2018. OL-

PP39 locates near the parking area, where the land area was under heavy modifications

in 2014–2016, which may also have effected the hydrological conditions.

51

Figure 3-14. a) TDS, b) pH (field), c) sulfate, d) chloride, e) sodium and f) magnesium concentrations as a function of the time in the Peatland group.

a) b)

c) d)

e)

e)

52

3.6.4 The Southern central area group

The Southern central area group includes:

- the groundwater observation tubes of OL-PVP4A, OL-PVP4B, OL-PVP20

- the shallow drillhole OL-PP2

From these, all but OL-PVP4B were sampled in 2018.

All these points are located either near or within the Natura area.

Also the conservation area of old-growth forests is also nearby.

These sampling points situate south of the Olkiluoto main road.

The ground level at these points is app. 3–6 m.a.s.l and the tubes

have perforated sections at the depths of +3…-8 m.a.s.l. OL-

PVP20 and OL-PP2 locate at the bedrock depressions, where

there is the thickest overburden of the shallow groundwater

sampling points, observed so far at Olkiluoto (see Figure 3-15).

The drillhole OL-PP2 reaches over the depth of -15 m.a.s.l

(Figure 3-15). The analysis results of 2001–2018 from selected

analysis are presented in Figure 3-16, more analysis results

2001–2018 are presented in Appendix 10.

Typical features for this group are medium-level TDS values and

sodium concentrations, but high chloride and calcium

concentrations. Also bicarbonate concentrations and DIC values

are rather high, which is due to the significant geochemical

water-soil interaction during infiltration. pH in this group has

typically varied from 7.0 to 7.5.

Figure 3-15. The Southern central area group

53

OL-PVP4A

Chemistry

OL-PVP4A was sampled during the spring campaign. TDS showed a long-term upward

trend during 2001–2016 but has levelled since that and no notable changes have been

observed anymore. Br/Cl ratio was low (0.0013), being significantly lower than

seawater ratio (0.0035). The sample was saturated (SIcalcite 0.05).

Other notes

The yield 1.5–1.6 L/min was good.

OL-PVP20

Chemistry

Changes in groundwater chemistry has been minor since 2013. Earlier observed

decreasing overall trend in TDS (until 2013) has ended and turned to minor annual

fluctuation around 400 mg/L. The Br/Cl ratio was 0.0071 and clearly above the

seawater ratio and the anomalously low ratios of OL-PVP4A and OL-PP2.

Other notes

The yield 0.7–1 L/min was good. The groundwater level dropped >2 m during sampling

pumping, when groundwater level was just above the sea level.

OL-PP2

Chemistry

OL-PP2 has followed somewhat the element concentration development of OL-

PVP4A. TDS (Na, Cl) has been higher than in OL-PVP4A since the beginning, because

the hole is deeper than observation tubes. TDS in 2018 was slightly lower than in 2017

at 826 mg/L. There seems to be a decreasing trend in Na concentration starting in 2016.

The Br/Cl ratio was 0.0011 and significantly lower than in seawater. The sample was

saturated (SIcalcite 0.05).

In the basis of 2018 results, there was not anymore increasing trend in TDS or Na in

2016–2018, Na has started to decrease in 2016.

Other notes

The yield was good 2.3 L/min.

54

Figure 3-16. a) TDS, b) pH (field), c) sulfate, d) chloride, e) sodium and f) calcium

concentrations as a function of the time in the Southern central area group.

a) b)

c) d)

e) f)

55

Concentration developments in OL-PVP4A and OL-PP2 remind each other. Road salting

(NaCl) is reported as a source of increased sodium and chloride concentrations in some

of the shallow groundwaters in the southern parts of the island along the main roads. OL-

PP2 is located near (a few meters from) the main road. OL-PVP4A is located closer to a

smaller road, 140 m from the main road.

Meri (2010) refers to road salt with the ratio of 0.65 for Na/Cl. However, sodium takes

easily part into cation exchange processes in soil and is highly dependent on local

geology, e.g. clays work actively in these exchange processes. Increased amount of

sodium in the soil from the road salting can enhance the amount of calcium released into

the groundwater, as well the rainfalls can release sodium from soil and so Na/Cl ratio can

decrease (Meri 2010). Thus, Cl concentration increase from road salting can lead to Na/Cl

ratio decrease when Cl concentration increases. The ratio of Br/Cl is useful in detecting

the origin of chloride. Br- and Cl- are conservative, easily mobile anions. Br/Cl ratio

should be more reliable method than Na/Cl ratio in the study of the origin (road salting,

relictic sea water) of chloride. The sea water ratio is near 0.0035 (Pitkänen et al. 1996),

and the major of the Olkiluoto groundwater shallow groundwater samples have Br/Cl

around 0.0035 or > 0.0035 and only a few Olkiluoto shallow groundwater samples have

Br/Cl < 0.001.

The first samples in 2001 include uncertainty in Br results and the uncertainty may have

resulted in low Br/Cl ratios. The notable change in Br/Cl ratio has been seen in both OL-

PVP4A and OL-PP2 after the autumn 2006, when the ratio dropped from 0.005 to 0.001

(Figure 3-17). Since the spring 2007, Br/Cl ratio in both OL-PVP4A and OL-PP2 has

mainly been below the sea water ratio (0.0035), which is untypically low for the Olkiluoto

shallow groundwater samples (Figure 3-18). In the other sampling points near the

Olkiluodontie road or south side the road (OL-PVP3A, OL-PVP41A-B, OL-PP39, OL-

PP56 L1–L2) the ratios has been close or only slightly below the sea water ratio. In 2018

samples Br/Cl of these other road side points were from 0.0027 to 0.0051, in the similar

range as in 2017. The timing of the change in Br/Cl ratio suites with the information, that

TVO has expanded the area of road salting and started to use NaCl road salting at

Olkiluodontie in December 2006.

In rather near located OL-L14 (percussion drilled seismic source hole) has been observed

drawdown in the groundwater levels (Vaittinen et al. 2014, 2015, 2016, 2017, 2018,

2019).

56

Figure 3-17. Br/Cl ratios in OL-PVP4A and OL-PP2 in a function of the sampling time.

57

Figure 3-18. Cl concentration vs. Br/Cl ratio in shallow groundwater samples in 2018.

58

3.6.5 The Central area and Korvensuo groups

Figure 3-19. The Central area and Korvensuo groups.

59

The Central area and Korvensuo groups include

- the groundwater observation tubes OL-PVP1, OL-PVP2, OL-PVP5A, OL-

PVP11, OL-PVP12, OL-PVP13, OL-PVP14, OL-PVP30, OL-PVP31A, OL-

PVP31B, OL-PVP32, OL-PVP33, OL-PVP35, OL-PVP37A, OL-PVP37B, OL-

PVP37C, OL-PVP42A and OL-PVP42B

- the shallow drillholes OL-PP3, OL-PP5, OL-PP9, OL-PP38 and OL-PP70.

The points OL-PVP12, OL-PVP30 and OL-PP3 are separated into the Korvensuo subgroup based on the isotope results, which confirm the influence of the Korvensuo reservoir on the groundwaters. Influence has been observed only in the northern side, rather near the reservoir (Pitkänen et al. 2007b, 2008a, 2009, Penttinen et al. 2011, 2013, 2014, 2017, Lamminmäki et al. 2017a-c, Vuorio et al. 2018, 2019).

Because the central area group includes 23 sampling points, the group figures (Figure 3-20, Figure 3-21) are divided into two technical sub groups west and east on the basis of the point location in a relation to the ONKALO area and Korvensuo reservoir and the Harbour road was used as a separator. In the figures west, presented are the results of OL-PVP1, OL-PVP2, OL-PVP5A, OL-PVP11, OL-PVP42A, OL-PVP42B, OL-PP5, OL-PP9, OL-PP38 and Korvensuo points OL-PVP12, OL-PVP30 and OL-PP3. In the figures east, presented are the results of OL-PVP13, OL-PVP14, OL-PVP31A-B, OL-PVP32, OL-PVP33, OL-PVP35, OL-PVP37A-C and OL-PP70.

OL-PVP5A and OL-PP38 have been destroyed and are excluded from the monitoring programme. OL-PP38 was sampled only in the autumn 2003. The sampling point OL-PVP18A, drilled in 2005 (belongs to the Peatland group), has replaced the OL-PVP5A.

In OL-PVP42A and OL-PVP42B, PVC-pipe was extended in December 2017, because the fence line rock filling increased ground surface 1.4–1.5 m. Land filling was crushed rock from ONKALO excavation. Modified lengths/ground surface of these tubes is presented in Figure 3-19.

In 2018, the sampling programme included OL-PVP11, OL-PVP12, OL-PVP13, OL-PVP14, OL-PVP30, OL-PVP42A, OL-PVP42B and OL-PP70.

The ground level at the Central area and Korvensuo groups is app. 2.5–10.5 m.a.s.l and the tubes have a perforated section at the depths of +6.5…-7.5 m.a.s.l. The drillholes reach the depths of -4.5…-11.5 m.a.s.l (Figure 3-2). Typical feature for the central area groundwaters is great variability in concentrations between the different sampling points. Analysis results of years 1997 (only for OL-PVP1 and OL-PVP2) and 2001–2018 from the selected analysis are presented in Figure 3-20 and Figure 3-21, more analysis results 1997–2018 are presented in Appendix 10.

60

OL-PVP11

Chemistry

Previous sample was collected in the autumn 2013 and tube has been only occasionally

monitored since 2003. TDS has been typically rather high (>400 mg/L) mainly due to

high bicarbonate concentration.

In 2018, the main observed variation was a small increase in TDS to 447 mg/L (2013

392 mg/L). This is mainly accounted by increased sulfate and HCO3 concentrations

(2018 50 mg/L and 256 mg/L, 2013 30 mg/L and 238 mg/L, respectively). pH was 7.2.

Other notes

The yield was good, 0.5 L/min. Yearly groundwater fluctuation was ca. 1 m, which is

typical for this site.

OL-PVP12

Chemistry

The sample 2018 was taken during spring sampling campaign as in 2017, which departs

from the typical timing of the sampling in this tube. OL-PVP12 is sampled regularly

for the closeness of Korvensuo reservoir and detected Korvensuo effect (seen in isotope

results).

In 2018, the TDS was closer 2017 results, compared to low level TDS samples before

2017. TDS decreased to 185 mg/L, and resembled the level of early 2000’s. The

decrease of TDS was mainly due to lower HCO3, 2018 result (53 mg/L) was within the

lowest HCO3 concentrations in this tube. pH decreased to 6.7.

SO4 increased to a new maximum value of 59 mg/L. Concentrations of Ca, Mg and K

were lower than in 2017, but the higher Ca, Mg and K concentrations 2017–2018 have

departed from the low level TDS samples before 2017. TDS, Ca, Mg and K were close

the concentrations in the beginning of the monitoring (2003).

Sulfate has fluctuated between 1 and 59 mg/L, and increased to a maximum value of

59 mg/L in 2018. Also the notable changes in sulfur isotope δ34S values have been

observed – to the opposite direction than SO4 concentrations. δ34S(SO4) 1.38 ‰ was

almost as low as in 2003. The amount of 14C 100.88 pMC was the highest of shallows

in 2018.

Sulfate concentration has increased above the concentration of Korvensuo reservoir

(OL-RS1 SO4 value from the year 2018 44 mg/L, TDS 103 mg/L). Both OL-PVP12

samples 2017–2018 have had clearly higher TDS than in Korvensuo Reservoir.

In 2018, SIcalcite -2.09 and logPCO2(g) -2.19 of OL-PVP12 plotted better among the other

shallow groundwaters (Figure 3-8). Earlier – in the autumn samples– logPCO2(g) has

been low and the composition has plotted closer Eurajoki river water.

61

Other notes

The yield was good, 0.36 L/min (averagely only 0.3 L/min) and NPOC was low 8.5

mg/L. The yearly groundwater level fluctuation has been typically minor since 2010,

but during 2016–2017 hydrological changes were observed. The changes in

groundwater level were minor in 2018.

Hydrological changes in 2016–2018 and the effect on isotope compositions of δ18O vs.

δ2H

The groundwater level started to drop in 2016 and dropping continued until October

2017, when groundwater level increased 0.8 m within one month. During 2018, the

groundwater table was more stable and recovered to the long term average level

(Vaittinen et al. 2019). In 2017, Korvensuo water balance analyses (Vaittinen at al.

2018) showed sharp increase in the amount of infiltration through the embankments

and bottom (more in Chapter 3.7.1 ). The results of Korvensuo water balance analyses

in 2018 are not available yet.

In 2018, the isotope composition of δ18O (-8.92 ‰ VSMOW) and δ2H (-67.9 ‰

VSMOW) in OL-PVP12 was the lightest during 2003–2018. In Korvensuo reservoir

OL-RS1, δ18O (-8.3 ‰ VSMOW) and δ2H (-64.6 ‰ VSMOW) composition changed

also to lighter compared to the results 2017.

OL-PVP13

Chemistry

OL-PVP13 was sampled during the spring campaign; the previous sample is from

autumn 2016. Compared to the earlier sample, the changes were minor. TDS 464 mg/L

in the spring 2018 was lower than the earlier (503 mg/L). SO4, Ca, Mg, K, and Na

concentration were lower than in 2016; Ca, Na, and SO4 contributing the most part of

the TDS decrease.

Fluoride 0.8 mg/L was close to 1.0 mg/L measured in nearby OL-PVP14. Compared

to the beginning of the monitoring, when TDS was close the same in both these tubes

OL-PVP13 and OL-PVP14, the development has been different in TDS, especially in

parameters SO4 and Ca. In OL-PVP13, SO4 and Ca have stayed at the same level as in

the beginning of the monitoring.

Other notes

The yield was 1.2 L/min. The groundwater table level fluctuated ca. 2.5 m; the annual

fluctuation in this tube has been typically wide. The lowering of groundwater level

during dry summer months was similar as in dry summer 2013.

62

OL-PVP14

Chemistry

Changes in 2018 were modest. Increasing trend (2010–2015) in TDS has levelled out;

like also the increasing trend of SO4 concentration. SO4 increased in 2010–2015 from

70 mg/L to 170 mg/L, but the result 128 mg/L in 2018 was clearly lower than in 2017.

In 2010 started increase in Mg and Ca has also stopped. Na and Cl were slightly lower

than in 2017. Seasonal variation has been observed earlier, when sampled twice a year.

The water is rich in HCO3, 348 mg/L in 2018 with a slight increase compared to 2017.

Fluoride 1.0 mg/L was among the highest of Olkiluoto shallow groundwaters in 2018.

SIcalcite was saturated.

Other notes

The yield 2.4 L/min was good. The annual groundwater table level fluctuation has been

typically wide, being ca. 3 m in 2018.

Higher pH, HCO3 and Ca, seem to be typical features for the sampling sites in the

eastern central parts. Carbonate-rich stones, found in till, could be an extra source for

Ca in Olkiluoto shallow groundwater (see studies of Breitner 2011).

OL-PVP30

Chemistry

The groundwater chemistry remained stable compared to the earlier sample in 2016.

The largest changes were in pH (6.9 in 2018 and 7.1 in 2016), which was the lowest

measured pH from this tube.

Other notes

The yield was 1.3 L/min was typical for this point. The pumping level 3.0 m was below

the perforated section (the section is only 1 m long; typically the perforated sections

are 2 m). The groundwater table fluctuated ca. 1.5 m in 2018.

OL-PVP42A

Chemistry

The monitoring began in 2016, and the site has been sampled three times previously.

Compared to the earlier samples of 2017, the changes were significant. TDS 614 mg/L

and SO4 287 mg/L were maximum values. The change was also seen in isotopes as

δ34S(SO4) decreased to -2.25 ‰ and δ18O(SO4) was notably low -10.22 ‰ (like in OL-

PP56 L3 and deviating from the shallow groundwaters).

Despite the peaked SO4, the increase of TDS remained relatively low, because HCO3

decreased substantially from 299 mg/L in the 2017 autumn sample to 92 mg/L in 2018.

pH also decreased by 1 pH-unit to 6.5 suggesting a decline in buffer capacity. Ca

63

concentration remained at its previous level (92 mg/L), Mg more than doubled to 29

mg/L. Also Na concentration increased heavily, from 10 mg/L in the autumn 2017 to

36 mg/L in 2018. Cl concentration was slightly lower than in 2017, but Cl results were

low in this group overall.

There was also a significant increase in NO3 concentration to 42.8 mg/L while previous

results have been at the detection limit (0.2 mg/L). Nitrite NO2 was below the detection

limit (<0.1 mg/L). The water type changed to Ca-Mg-SO4 from previous Ca-HCO3.

Fluoride 0.9 mg/L was among the highest of shallow samples in 2018. SIcalcite was

subsaturated in 2018.

Other notes

The yield was low, 0.19 L/min. The PVC-tube was extended in December 2017,

because the fence line rock filling increased ground surface. The groundwater

monitoring was continued in October 2018 after being temporarily suspended in

November 2017.

The effect of the crushed rock storage area was seen clearly from the monitoring data

of both A- and B-tubes. The high sulfate concentrations were most probably caused by

sulfide bearing minerals in the crushed rock from the ONKALO excavation. Crushing

expands the surface area available for oxidation of the sulfides, hence the high SO4

concentrations. The source of NO3 was most likely explosive residues from the crushed

rock storage pile.

OL-PVP42B

Chemistry

The changes in the water quality observed in the A-tube were in some extent present in

the shallower B-tube sample. TDS increased strongly from 395 mg/L in autumn 2017

to 514 mg/L in 2018. The change was caused by increase in all major ions: HCO3, SO4,

Ca, and Mg. SO4 concentration was 68 mg/L, while it was 29 mg/L in 2017. The

increase of sulfate was much less than in A-tube. Also pH was slightly higher, 7.1.

Compared to A-tube, the concentration of HCO3, Ca, K, Cl, F, Fe2+/Fe3+, Mn, NPOC

and pH were higher than in A-tube in 2018.

Nitrate could be detected in trace amount in the B-tube, 0.9 mg/L, where it previously

had been under detection limit. The water type remained Ca-HCO3. SIcalcite was

subsaturated in in 2018.

Other notes

The yield was low 0.2 L/min like in A-tube. The groundwater monitoring was

continued in October 2018 after being temporarily suspended in Nov. 2017.

64

OL-PP70

Chemistry

The 2018 sampled resembled the first sample in 2012. TDS has fluctuated strongly in

the samples 2012–2018, from 650 mg/L to 190 mg/L. In 2018, TDS was 610 mg/L,

which was higher than in 2017. Also pH has fluctuated between 6.0 and 7.2, the 2018

sample being 7.2.

HCO3 increased significantly from 5.5 mg/L in 2017 to new maximum of 244 mg/L.

Ca concentration doubled from 2017 to 57 mg/L, in Mg there was a slight increase to

15 mg/L. Na concentration increased significantly, from 20 mg/L to 89 mg/L.

SIcalcite -0.53 vs logPCO3(g) -2.0 is plotted into the main group of shallow samples better

than the sample 2017 mainly due to increase in SIcalcite.

Other notes

The yield was 0.5 L/min. The groundwater table level has fluctuated a lot annually, ca.

2.5 m in 2018.

The sampling point is located far from the other points (inc. deep drillholes) and areas

with activities (far from ONKALO), near the sea. This is also the deepest shallow

drillhole in this Central area group and reaches the depth of -11.5 m.a.s.l. Any specific

reason for major fluctuation in results cannot be defined. The groundwater level has

fluctuated a lot at point, but the yield has stayed at range 0.2–0.8 L/min. Only the

sample 2014 has represented low yield sample. It is probable, that the fluctuation is

caused from hydrological factors and represents occasional seasonal fluctuation.

65

Figure 3-20. a) TDS (west), b) TDS (east), c) pHfield (west), d) pHfield (east), e) sulfate (west) and f) sulfate (east) concentrations as a function of the time in the groups Central area and Korvensuo. Notice different scales in the figures from the west/east located points of the Central area and Korvensuo group.

a) b)

c) d)

e) f)

66

Figure 3-21. a) Bicarbonate (west), b) bicarbonate (east), c) calcium (west), d) calcium (east), e) magnesium (west) and f) magnesium (east) concentrations as a function of the time in the groups Central area and Korvensuo. Notice different scales in the figures from the west/east located points of the Central area and Korvensuo group.

a) b)

c) d)

e) f)

67

3.6.6 The Extraordinary points

The Extraordinary points include:

- the tubes OL-PVP17 and OL-PVP38A-D

- the shallow drillholes OL-PP7 and OL-PP56

The sampling programme of 2018 included samplings from

OL-PVP17 and OL-PP56 packed-off section samples from

L1–L3.

These sampling points are put in their own group due to their

special features. Analysis results of 2001–2018 from the

selected analysis are presented in Figure 3-23, more analysis

results 2001–2018 are presented in Appendix 10.

The ground level at the points of this group is app. 3.5–8.5

m.a.s.l and the tubes have a perforated section at the depths

of +5.5…-6 m.a.s.l The drillholes reach to the depths of -

12.5…-29.5 m.a.s.l (Figure 3-22). The OL-PP56 is the

deepest of the monitored shallow drillholes (56 m) (Figure

3-22). Drillhole inclination is 45.1° and it reaches to the

depth of -29.5 m.a.s.l The point has been packed during

June–October 2014, and since January 2015. The drillhole

locates near ONKALO.

In 2014, the parking area construction works done in the

surroundings of OL-PP56 and thereafter the encapsulation

plant construction works started in 2017, changed totally the

nearby areas. In 2015–2016, the land area near OL-PVP17

(and also OL-PP56) was strongly modified and for this, OL-

PVP17 was removed from the group Peatland to the group

Extraordinary points.

Figure 3-22. The Extraordinary points

68

OL-PVP17

Chemistry

The major seasonal fluctuation first observed in 2016 continued also in 2018. TDS was

slightly brackish in the autumn sample. The spring sample was more dilute than in

2016–17. The spring sample pH was the same as in autumn 2017, 6.6, but rose to 6.8

in the autumn sample. pH has been the lowest in this tube in spring 2015 and 2017–

2018 during the monitoring.

The fluctuation range in SO4 started to increase in 2015 and increased majorly during

2016–2017 compared to the earlier results. During 2017–2018, there was no increase,

but the range 440–625 mg/L stayed at high level and near the range in 2017.

Also in both Mg and Ca, the fluctuation range increased strongly in 2016–2017, but

stayed in 2018 closer the range in 2017. The autumn values were higher. Also K

concentration was higher in autumn sample.

Sodium and chloride has been at the lowest in in this tube in samples 2017–2018. Both

have decreased clearly compared to the level in the beginning of the monitoring.

However, Na increased in the autumn sample (94 mg/L), also Cl was higher in the

autumn sample.

HCO3 concentration was low (79 mg/L) in the spring sample, but more than doubled

to 183 mg/L in the autumn sample. No difference between measured and calculated

DIC was observed in either of the samples.

Iron concentration was high in the spring sample, 14 mg/L, but decreased to more

typical level (4.5 mg/L) in the autumn sample.

Sulfate has been the main anion since the autumn 2014 and an upward trend has been

seen since the year 2009. The latest changes are related to land area modifications

around the point (peatlands removed) and related hydrological changes. Regular

seasonal variation has typically affected the ion concentration.

Other notes

The yearly groundwater level fluctuation has been minor, ca. 50 cm in 2018. The

deepest lowering in groundwater level has been seen during dry summers 2013 and

2018. The yield was 0.3–0.4 L/min. The yield was lower in the spring.

OL-PP56 L1 (38–55.9 m)

Chemistry

TDS continued to increase. The measured TDS was brackish 1865 mg/L and it was the highest measured value in 2018 for shallows. The increase was mainly due to increased

69

Na and Cl concentrations, 360 mg/L and 660 mg/L respectively. SO4 concentration 375 mg/L was lower than in 2017, even still high. HCO3, Ca, and Mg concentrations remained at the same level as in 2017. pH (field value) 7.7 was lower than in 2017, being among the highest of shallows. SIcalcite 0.26 was the only slightly supersaturated sample of shallows.

Increasing trend of Na and Cl in this most deep section L1 is expected development as the drillhole was open until 2015, when a multi-packer system was installed. The section is recovering from the fresh water contamination during the open hole period since the drilling in 2007. This sampling section represents also deeper drillhole conditions than the other shallow samples, and this is seen in e.g. Na, Cl, Br and pH. Br/Cl 0.0032 was near the sea water ratio (0.0035) and the sample differed from the other shallow samples in high Cl (660 mg/L) concentration, also with high TDS.

The isotope results did not deviate compared to the results of 2017. δ18O (SO4) result, -0.09 ‰ in 2018, has stayed higher than in sections L2–L3. Tritium result 3.4 TU was the lowest of shallow groundwater samples.

Other notes

The yield was low, 0.12 L/min, as typical. The prepumping was started the day before the sampling and lasted 17.5 h. The pressure head levels of sections L1 and L2 fluctuated congruently between +2.9 m.a.s.l and +4.5 m.a.s.l. In both sections has observed drawdown, especially during 2018.

OL-PP56 L2 (28–37 m)

Chemistry

Two samples were taken from L2 section. Brackish TDS 1414–1426 mg/L was lower

than in 2017. SO4 concentration was lower than in 2017, ca. 700 mg/L in both samples.

So, there was not seen increasing trend in SO4 in 2017–2018, but the level was still

high. HCO3, Na, and Cl concentrations were at the same level as in the 2017 samples.

There was a minor decrease in Ca and Mg concentrations, for Ca in the autumn sample

and for Mg in both samples. Ca and Mg concentration increased earlier together with

SO4.

pH was 7.6 and slightly lower than in 2017. SIcalcite values were saturated. Br/Cl

(0.0027–0.0038) in both samples was near sea water ratio (0.0035), the spring sample

ratio was slightly below the sea water ratio.

δ34S(SO4) results were almost similar in section L2 and L3 samples in the 2018. In L2,

δ18O (SO4) was still low -7.62…-6.77 ‰ in 2018, but slightly higher than in section

L3.

Other notes

The yield was 0.19–0.30 L/min and prepumpings lasted from 24 h in the spring and only 3 h in autumn. In spring, the yield decreased during the prepumping being only 0.01 L/min, when sampling started. In autumn, the pumping time was much shorter and the yield value was measured twice (0.3 L/min) prior to the sampling. The amount of

70

pumped water before the sampling was much lower in the autumn. The pumping level and groundwater level was not measured due to a broken level gauge in autumn.

OL-PP56 L3 (2.3–27 m)

Chemistry

Two samplings were carried out. Compared to the first sample 2014, TDS values 964–1120 mg/L were clearly lower and similar to TDS values in 2017. SO4 concentration remained at the level of autumn 2017, 655 mg/L and 630 mg/L in the spring and autumn 2018 samples, being significantly lower than exceptionally high 1720 mg/L in 2014. Low nitrate concentration was observed in both samples.

pH decreased in the autumn 2018 over 1 pH unit from 7.6 in spring to 6.4. This is the largest difference in pH values observed since the beginning of the monitoring. HCO3 also reached its lowest value in the autumn, dropping from 128 mg/L to only 34 mg/L. In autumn, carbon from alkalinity titration was 6.7 mg/L and measured DIC 8.1 mg/L, both were low (difference of 17 %). Ca and Mg concentrations were unaltered. Acidity in the autumn sample was 0.43 mmol/L, which is a maximum value. Fe and NPOC were also low, and the dominant iron species was Fe2+. Br/Cl ratios of L3 samples differed the most from the other OL-PP56 samples. The spring sample SIcalcite was saturated, in autumn subsaturated.

δ34S(SO4) results were similar in section L2 and L3 samples. Section L3 samples have had anomaly low δ18O (SO4) around -10 ‰ since 2014. The isotope value of δ18O (SO4) was -10.58 ‰ in spring and -9.09 ‰ in autumn in L3 section samples in 2018. This low δ18O (SO4) values are not characteristics for shallow groundwaters.

The area of OL-PP56 was totally modified during 2014 due to the parking area construction works and the reason for these elevated levels of sulfate is suspected the crushed rock from ONKALO used in the road and parking area construction. The crushed rock may have contained also the lefts from the explosives used in ONKALO, which increased the nitrate concentrations (studied were made of crushed rock as a possible sulphur source).

Other notes

The yield was low 0.1 in spring and 0.4 L/min in autumn. The both prepumpings lasted almost 18 h. In spring, field pH or EC was not measured. In 2018, the groundwater head data showed several ca. 3 m drops in March and from the end of May to early September. These are related to the construction work of the encapsulation plant. The groundwater level was relatively stable outside these incidents, fluctuation was ca. 0.5 m. The typical annual shallow groundwater level fluctuation was not seen in head level of OL-PP56 L3 anymore, the parking are is asphalted.

71

Figure 3-23. a) TDS and b) pH (field), c) sulfate, d) chloride, e) calcium and f)

magnesium concentrations as a function of the time in the group Extraordinary points.

a) b)

c) d)

e)

72

3.7 Isotopes – 2018 results

The analysed isotope results for the groundwater observation tubes and the shallow

drillholes, sampled in 2018, are presented in Appendix 7. All δ18O and δ2H results from

2002–2018 for the shallow groundwaters are included in Figure 3-24, where in 2018 taken

samples, including also the reference samples from the Korvensuo Reservoir (OL-RS1),

are marked with red.

3.7.1 Oxygen δ18O and deuterium δ2H

The contents of stable isotopes generally point to a meteoric origin for the Olkiluoto

groundwater samples that are on, or in the immediate vicinity, of the Global Meteoric

Water Line (GMWL) (Craig 1961). The equation Eq. 3-1 of this line is presented by Craig

(1961):

δ2H = 8 × δ18O + 10 (Eq. 3-1)

Local meteoric water lines also exist, and have slightly different slopes and intercepts

than the GMWL, as a result of differences in altitude, local climate and distance from

moisture source. If isotope results of the water sample do not plot along this line, water

has been impacted by some physical or chemical process prior to recharge, or during the

groundwater’s route through the aquifer. In Hendriksson et al. (2014) is presented Local

Meteoric Water Line (LMWL) for the Olkiluoto area on the basis of precipitation data

collected during January 2005 – December 2012. The equation of the line is presented by

equation:

δ2H = 7.45 × δ18O + 3.82 (Eq. 3-2)

The long-term weighted annual mean isotope values of the shallow groundwater are:

-11.27 ‰ VSMOW (oxygen) and -80.3 ‰ VSMOW (deuterium),

both these mean values are temperature dependent (Hendriksson et al. 2014).

Figure 3-24 presents a plot of δ18O ‰ VSMOW versus δ2H ‰ VSMOW for all the

shallow groundwaters during the monitoring period 2002–2018. In the 2018 samples

(Figure 3-24) δ18O ‰ VSMOW and δ2H ‰ VSMOW were:

from -7.7 ‰ VSMOW to -13.6 ‰ VSMOW (oxygen) and

from -61.0 ‰ VSMOW to -98.3 ‰ VSMOW (deuterium).

The results of OL-PVP12, OL-PVP30 and OL-PP3 are exceptional (Figure 3-24)

compared to other shallow groundwater samples. From the samplings 2018, only the

results of OL-PVP12 and OL-PVP30 did not plot to the LMWL (discussed more in next

chapter).

73

Effect of Korvensuo reservoir: OL-PVP12, OL-PVP30, OL-PP3

In OL-PVP12, the oxygen has fluctuated between -4.5 ‰ VSMOW (10/2009) and -8.9

‰ VSMOW (05/2018) and the deuterium values between -49.7 ‰ VSMOW (10/2009)

and -67.9 ‰ VSMOW (05/2018), which have been partly similar to the values of the

nearby Korvensuo reservoir water (distance about 20 m from the reservoir). In Korvensuo

reservoir, the oxygen was -8.3 ‰ VSMOW and the deuterium -64.6 ‰ VSMOW in 2018.

In 2006–2009, OL-PVP12 autumn samples have had heavy isotope compositions. The

raise of Korvensuo reservoir surface in 2007 effected on OL-PVP12 (in 2006–2010,

Vaittinen et al. 2015). At the previous maximum infiltration year 2010, δ18O changed

strongly (to lighter) and became like in the reservoir. Also the seasonal groundwater table

level fluctuation ended then.

In 2016 – October 2017, the groundwater table level dropped 1 m in OL-PVP12, but

increased 0.8 m within one month in late 2017. Reasons for the drop/sudden increase of

groundwater table in OL-PVP12 and the notable changes in the Korvensuo water

balance/infiltration were reported in Vaittinen et al. (2018). In 2015–2016, infiltration

through the embankments and bottom of Korvensuo reservoir increased, but during the

year 2017, the sharp increase was remarkable compared to earlier results (double increase

compared to the earlier year). Water level of Korvensuo reservoir was clearly lower (0.4

m) in the end of the year 2017 compared to the beginning of the year and the infiltration

was at the new maximum level during the monitoring since 2003. The sample 2017 was

taken in May before the change in groundwater level in OL-PVP12 and the water level

change in Korvensuo reservoir.

During 2018, the groundwater table of OL-PVP12 was more stable and recovered to the

long term average level (Vaittinen et al. 2019). The results of Korvensuo water balance

analyses in 2018 are not available yet.

In May 2018 sample of OL-PVP12, δ18O was -8.92 ‰ VSMOW and δ2H -67.9 ‰

VSMOW.

The results differed from the earlier in 2017 (δ18O -7.16 ‰ VSMOW and δ2H -59.2 ‰

VSMOW) and from the range of all earlier samples of OL-PVP12. The 2018 sample had

the lightest composition of OL-PVP12 samples during 2003–2018. The isotope

composition of OL-PVP12 moved to the direction of Eurajoki river water isotope

composition and also along the evaporation line towards LMWL. The change 2017–2018

was also seen in δ18O and δ2H composition in Korvensuo reservoir, which had also clearly

lighter composition in 2018 sample (δ18O -8.3 ‰ VSMOW and δ2H -64.6 ‰ VSMOW)

than in 2017. In Korvensuo reservoir, δ18O and δ2H composition has showed variation

between the spring and autumns samples and the autumn samples has had typically the

heavier composition. Both samples 2017–2018 of OL-PVP12 were spring samples, while

the earlier samples have been taken mostly at autumns.

Calculated SIcalcite and logPCO2 values have shown that logPCO2 in OL-PVP12 samples

has been mainly lower than in the other shallow groundwater samples. The earlier sample

2017 (2017 SIcalcite -1.34 and logPCO3(g) -2.19) plotted closer to the shallow groundwaters

group. The sample 2018 (SIcalcite -2.09 and logPCO3(g) -2.26) plotted also close shallow

74

groundwaters, but closer older Eurajoki River water samples than the sample 2017. The

calculated SIcalcite -2.4 and logPCO3(g) -3.2 for Korvensuo reservoir sample in 2018 differed

clearly from OL-PVP12 sample.

In OL-PVP30, the oxygen and deuterium has changed less than in OL-PVP12: oxygen

has ranged from -7.7 ‰ VSMOW to -8.64 ‰ VSMOW and deuterium from -61 ‰

VSMOW to -66.7 ‰ VSMOW during 2003–2018.

In 2018, the results were δ18O -7.73 ‰ VSMOW and δ2H -61.0 ‰ VSMOW.

The sample 2018 of OL-PVP30 was the heaviest composition of all OL-PVP30 samples

during 2009–2018.

OL-PP3 was not sampled in 2018, but the effect of the Korvensuo reservoir has been seen

in isotope composition (δ18O and δ2H) of earlier samples (Figure 3-24).

OL-PP56 L3

In 2018, the results of δ18O -9.47 ‰...-13.63 ‰ VSMOW and δ2H -64.2 ‰...-98.3 ‰

VSMOW (Figure 3-24) fluctuated a lot between the spring and autumn sample and the

lowest values were the maximum values of shallow samples during the monitoring.

The spring sample represented cold winter conditions during the infiltration, like

shallow samples have not observed earlier. As well as the autumn sample represented

the warm and arid summer conditions at the opposite end of the local meteoric water

line.

75

Figure 3-24. A plot of δ18O versus δ2H in all shallow groundwater samples in 2002–

2018. During 2018 taken samples are marked with red open circles. The samples plot

mainly on the LMWL line. The exceptions are OL-PVP12, OL-PVP30 and OL-PP3

(marked separately in the figure), which are most likely caused by the effect of the

closeness of the Korvensuo reservoir, OL-RS1 (about 20 m away), where the water from

the River Eurajoki, OL-RWS04, is pumped. The Korvensuo reservoir (dark green square,

2018 samples bordered with red), sea water (turquoise diamond) and the River Eurajoki

(purple triangle, 2018 samples bordered with red) results are marked in the Figure.

76

3.7.2 Tritium 3H

Tritium concentrations in the atmosphere have decreased due to decay of the minor

concentrations of 3H from nuclear bomb tests, and concentrations are, therefore, closer to

the natural level (before nuclear bomb tests the concentration was 2–8 TU).

According to Hendriksson et al. (2014), the eight-year (2005–2012) mean value for the

tritium concentration in the shallow groundwater was 9.1 TU. Tritium also showed

seasonal variation being higher in the summer months and lower in the winter.

For major of the shallow groundwaters, the general natural decreasing tritium

concentration trend has been observed from 11–17 TU to 3–10 TU during 1995–2018,

reflecting tritium concentration decline in precipitation. The tritium results for the shallow

groundwaters during 2012–2018 have not shown common decrease anymore. In

Appendix 11, tritium concentrations are presented for every group as a function of time.

Tritium result

3.4 TU of OL-PP56 L1was the lowest and

9.9 TU in OL-PP36 was the highest in 2018.

The fluctuation in tritium values in 2018 was similar as in 2017, only the result 9.9 TU in

OL-PP36 was slightly higher than typically.

There are no tritium results from the timespan June 26, 2006 – February 22, 2007, because

of contamination of samples.

OL-PP56 L1

The lowest tritium value 3.4 TU of shallow groundwater samples in 2018 was measured

in OL-PP56 L1. The result was similar to samples in 2016–2017 (3.6 TU). The section

is the deepest from this packed-off shallow drillhole.

77

3.7.3 Other isotope results

In 2018, the isotope results of 14C pMC, δ13C ‰ VPDB, δ34S(SO4) and δ18O(SO4), were

analysed for all the monitoring samples. All results are shown in Appendix 7. From the

Olkiluoto samples the radiocarbon values can be used to evaluate relative mean residence

times between groundwaters (Pitkänen et al. 2004). High 14C values indicate minor

interaction with the dead carbon (calcite and/or old organic carbon) sources.

14C

In the shallow groundwaters, 14C values have ranged from 34.3 pMC (OL-PP56 L3, in

June 2017) to 114.4 pMC (OL-PVP1, in 2008) during the monitoring. The range in 2018

samples was from 45.2 pMC (in OL-PP56 L3) up to 100.88 pMC (in OL-PVP12). In

Appendix 11 14C (pMC) values are presented for every group as a function of time.

OL-PVP18A and OL-PVP41A

In group Peatland sampling points lower amounts of 14C have been typical, which

referes to source of old carbon. In 2018, the lowest 14C of this group was 63.3 pMC in

OL-PVP18A in May 2018 and in the autumn 14C was 68.8 pMC. The 14C result of OL-

PVP41A (69.8 pMC) was similar as observed in OL-PVP18A.

OL-PVP40A–B

In both tubes, the amount of modern carbon has fluctuated a lot. In tube OL-PVP40A,

the spring result 90.2 pMC was close the spring 2017 result (91.5 pMC), like autumn

2018 result 84.7 pMC was close July 2017 result (83.3 pMC).

In B-tube, the result in May 2018 (83.5 pMC) was higher than in July 2017 (74.2 pMC),

but similar to June 2016 (74.1 pMC). The fluctuation has been wide in B-tube

(74.1…83.5 pMC) between the years.

OL-PP56 L1, L2 and L3

Low 14C results have been measured in all sections L1–L3 with wide fluctuation. In

section L1, 14C was 46.7 pMC in 2018, being close the earlier results.

In the samples of section L2, the spring result 75.7 pMC differed from the autumn

sample result 49.8 pMC, similar larger fluctuation was observed also in 2015.

In the samples of section L3, also notable difference was seen between the spring (45.2

pMC) and autumn (70.5 pMC) sample, but the opposite way. Also in this L3, a wide

fluctuation has been seen earlier.

78

δ13C

δ13C values of the shallow groundwater samples have variated during the monitoring from

-27.5 ‰ VPDB (OL-PR1, in 1995) to -1.38 ‰ VPDB (OL-PP56 L3, in 2018) (Appendix

11). The range in 2018 was

from -20.39 ‰ (OL-PP36 18.10.2018)

to -1.38 ‰ (OL-PP56 L3 16.10.2018).

The range of -20 ‰…0 ‰ VPDB fits to the DIC range in groundwaters (Clark & Fritz

1997). The atmospheric CO2 is near -7 ‰ VPDB and photosynthetic uptake of CO2(atm)

is accompanied by significant depletion in 13C and the amount of fractionation depends

on photosynthetic cycles. Values -30 ...-10 ‰ VPDB are related to plants or soil CO2. As

comparison, δ13C of the latest sea water samples was from -0.6 ‰ VPDB to -0.99 ‰

VPDB in 2017.

The composition near the atmospheric CO2 has been found in near-surface conditions, in

immature groundwater in Olkiluoto shallow groundwaters.

OL-PVP12

In OL-PVP12 that is affected with Korvensuo water, δ13C values have changed a lot

during the years (from -18.9 ‰ VPDB to -2.82 ‰ VPDB). δ13C value has been higher

than the atmospheric CO2 (-7 ‰ VPDB) in three samples: 4.10.2007 (-4.51 ‰ VPDB),

26.8.2014 (-2.82 ‰ VPDB) and 15.5.2018 (-4.39 ‰ VPDB).

OL-PP56 L3

In 2018 measured δ13C values were from -7.19 to -1.38 ‰ VPDB. The autumn 2018

value was the highest of δ13C values of the shallow samples during the monitoring (like

δ13C in sea water samples).

79

δ34S(SO4) and δ18O(SO4)

In Figure 3-25 and Figure 3-26 is presented δ34S(SO4) (‰ VCDT) and δ18O(SO4) (‰

VSMOW) values for the groups Northern coastline, Peatland, Central area West and

Extraordinary points as a function of time (see sampling point specific descriptions in

table below). For all the groups, the results as a function of the time are presented in

Appendix 11. The dissolved sulfate isotope values of modern seawater are 21 ‰ VCDT

for δ34S(SO4) and 9.5 ‰ VSMOW for δ18O(SO4), the “terrestrial” sulfates are categorised

to compositions lower than δ34S(SO4) 10 ‰ VCDT and δ18O(SO4) 4 ‰ VSMOW, when

distinguished from marine sources (Clark & Fritz 1997).

Overall the range in the samples 2018 was similar as in 2017,

δ34S(SO4) from -2.3 ‰ to 13.9 ‰ and

δ18O(SO4) from -10.6 ‰ to 10.7 ‰.

In peatland environment 34S-depleted H2S is formed (in catothelm, due to decomposition

processes). H2S can be trapped in the groundwater or sulphur from it via different routes

react and form SO4. Drainage or other factors oxidizing peatlands decrease the probability

of samples poor in 34S.

OL-PVP12 and OL-PVP30

The earlier results 2017 in OL-PVP12, δ34S(SO4) 9.62 ‰ and δ18O(SO4) 12.96 ‰,

showed that enrichment of 34S had stopped. The results 2018, δ34S(SO4) 1.38 ‰ and

δ18O(SO4) 10.68 ‰ reminded the isotope results in the beginning of the monitoring in

2003 with low δ34S(SO4) 1.38 ‰. SO4 concentration was even slightly higher than in

2003. The change during 2016–2018 has been notable.

In all the Korvensuo influenced points (OL-PVP12, OL-PVP30, OL-PP3), δ34S(SO4)

has been typically deviating strongly and fluctuating.

In OL-PVP30, the differences between the samples has been minor that in OL-PVP12

and OL-PP3. In 2018, the isotope composition δ34S(SO4) 8.41 ‰ and δ18O(SO4) 3.98

‰, did not differ much from the results of the same Central West group points or earlier

results.

OL-PVP18A

δ34S(SO4) has been almost the same, 4–5 ‰, in most of the samples, and only slightly

lower 3.62 ‰ in 2018. δ18O(SO4) has decreased during the monitoring, being at -6.71

‰ in the autumn 2018, similarly as in autumn 2016–2017. The higher sulfate

concentration peaks in autumns 2016–2018 co-occur with these lowest δ18O(SO4)

values.

80

OL-PVP36

The isotope composition enriched strongly in 2014–2016 up to δ34S(SO4) 19.4 ‰ and

δ18O(SO4) 11.2 ‰ in 2016. The results showed abrupt change to clearly lower

composition in 2017, which continued in 2018. δ34S(SO4) was 4.62 ‰ and δ18O(SO4)

-3.98 ‰ in 2018, both were close the results in 2017. Also SO4 concentration has been

higher in 2017–2018, like in the first sample in 2012. The isotope composition was

similar as in OL-PVP18A in spring 2017 and 2018.

OL-PVP40A-B

In the spring 2018, the isotope composition of δ34S(SO4) 3.66 ‰ and δ18O(SO4) 4.48

‰ of B-tube was close the composition measured later in A-tube in the autumn. Earlier

in 2017, B-tube had notably high SO4 and low δ34S(SO4) -3.41 ‰. Both results SO4

and δ34S(SO4) were closer A-tube results in 2018. In both A- and B-tube, δ34S(SO4)

was 10–14 ‰ in the first samples in 2014, and clearly lower in 2017–2018.

In OL-PVP40A, sulfate concentration has peaked in spring 2017 and 2018. The isotope

composition of δ34S(SO4) ‰ has been close 8 ‰ during both peaks. In A-tube,

δ34S(SO4) ‰ was 7.89 ‰ in spring and 3.79 ‰ in autumn 2018. The isotope

composition of δ18O(SO4) has been always lower in spring samples than in autumn

samples; 0.69 ‰ in spring 2017 peak and -3.17 ‰ in spring 2018 peak.

OL-PVP42A-B

High SO4 concentration was observed in autumn 2018. The change 2017–2018 was also seen in the isotope composition as δ34S(SO4) decreased to -2.25 ‰ and as notable decrease in δ18O(SO4) to -10.22 ‰. δ18O(SO4) value was notably low for shallow groundwater sample and similar as observed in OL-PP56 L3 samples. This low δ18O (SO4) values are not characteristics for shallow groundwaters.

Also in B-tube SO4 concentration was higher than in 2017 and δ34S(SO4) 0.82 ‰ and

δ18O(SO4) -2.8 ‰ were clearly lower than in 2017, but not as low as in A-tube.

OL-PP39

The composition enriched strongly during 2016–2017 up to δ34S(SO4) 18.4–19.1 ‰

and δ18O(SO4) 10.54–10.92 ‰ and decreased from this clearly in autumn 2018.

δ34S(SO4) 2.2 ‰ and δ18O(SO4) 3.07 ‰ was close the composition in June 2016. The

deepest drop in these isotope results was observed in May 2014, when SO4

concentration peaked strongly. In June 2016 and October 2018 minor sulfate peaks

were observed.

OL-PP56 L1, L2 and L3

In section L1 sample the results were close the 2017 results.

In sections L2 and L3, δ34S(SO4) results were similar, as they have been since 2016.

δ34S(SO4) was near 0 ‰ or slightly below in both sections.

81

δ18O (SO4) results, especially in L3 (-9.09 ‰…-10.58 ‰ in 2018) were notably low

and not characteristics for shallow groundwaters. The lowest values below -10 ‰ have

been in all spring samples since 2015. The autumn samples of L3 have been closer L2

results, which were -7.62 ‰ and -6.77 ‰ in 2018.

In all sections, SO4 concentration has been high, especially in sections L2 and L3, but

lower than the peak in section L3 in 2014.

82

Figure 3-25. δ34SSO4 (‰ VCDT) and δ18OSO4 (‰ VSMOW) values as a function of the

time in the groups a-b) Northern coastline and c-d) Peatland group.

a) b)

c) d)

83

Figure 3-26. δ34SSO4 (‰ VCDT) and δ18OSO4 (‰ VSMOW) values as a function of the

time in the groups a-b) Central area West and c-d) Extraordinary points.

a) b)

c) d)

84

85

4 RESULTS OF MONITORING AT OLKILUOTO 2018 HYDROGEOCHEMISTRY – DEEP GROUNDWATERS

The construction of the final disposal facility has the potential to change the groundwater

flow regime, resulting in the mixing of water types and increased hydrochemical

reactivity compared to the natural state hydrogeochemical system due to higher hydraulic

gradients. This may become evident as increased infiltration of surficial waters,

drawdown of shallower groundwater types, or upconing of deep saline groundwaters in

the connective fracture system within the bedrock. Mixing of different waters in

potentially different thermodynamic states activates chemical reactions, especially

microbially mediated redox processes, which drive the hydrogeochemical system towards

thermodynamic equilibrium. The hydraulic connection between the underground tunnels

and/or between an underground tunnel and an open drillhole creates a pathway for

interaction between groundwaters originally at different depths.

This issue of pathway creation for groundwater flow was observed in open drillholes,

where hydrologically active fractures exhibited a different hydraulic head, prior to the

ONKALO construction (Pitkänen et al. 2007, Posiva 2013, Section 7.3.6). Head

differences in drillholes cause groundwater flow along open holes from a higher pressure

section to a lower pressure section. This has been notably problematic in drillholes which

intersect both higher head feature HZ19 and lower head feature HZ20 in the middle of

the island around the ONKALO site. Less saline groundwater from HZ19 flowing

through the open pathway towards a zone of lower pressure has diluted groundwater

particularly in the HZ20A intersections – incidents that have been observed in several

drillholes. In addition, the high transmissivity of hydrogeological zones enables a

significant volume of water flow between pressure zones within a short time period.

Similar hydraulic conditions in OL-KR13 resulted in elevated dissolved sulfide

concentrations (12 mg/L) in the low head intersection of feature HZ001 in 2001. Sulfate-

rich groundwater drawdown and mixing with hydrocarbon-rich brackish Cl type

groundwater in this fracture zone activated sulfate reducing bacteria (SRB), as these

groundwater types possess a different oxidative-reductive potential, or redox state, prior

to mixing. Elevated sulfide concentrations have frequently been observed in analogous

hydraulic situations. The electron donor (energy source) that enables the SO4 reduction

process in brackish Cl and saline type groundwaters remains unclear, with only minor

indications of anaerobic CH4 or other hydrocarbon oxidation (Posiva 2013; Section 7.4).

Hydrogen in hydrocarbon-rich groundwaters has been considered a possible electron

donor, which is easily usable by SRB. Recently, this subject of sulfide formation has been

studied in more detail (e.g. MetWeb-project) and new information can be expected in the

following sulfide project reports.

The high hydraulic gradient created by the underground spaces and excavations in the

final disposal facility may intensify chemical effects in open drillholes compared with

natural head distribution at the site where these drillholes are in hydraulic connection with

open tunnels. The majority of drillholes have now been plugged with multi-packer

systems, particularly near the underground tunnels and facilities, in order to avoid open

drillhole issues. Occasional malfunctions in multipacker systems (e.g., pressure loss from

plugs) result in open drillhole situations and, generally, in the drawdown of upper-level

groundwater types to deep fractures.

86

4.1 Sampling and field measurements at ground surface

Twenty-six (26) deep groundwater samples were collected during 2018 from ten different

drillholes (samples from OL-KR6 excluded). The locations of the drillholes are presented

in Figure 4-1. Detailed information regarding the samples can be found in Appendix 14.

Eighteen (18) of the samples were collected using a multipacker system. Eight samples

were collected from open drillholes, three with PAVE-equipment (Öhberg, 2006) and five

with PFL WS2 equipment (Ripatti et al. 2019). The PAVE unit and PFL WS2 equipment

contain pressure vessels, which also enable sampling of dissolved gases at in situ pressure.

Sampling sections were selected in order to monitor hydrogeochemical changes caused

by ONKALO. No new drillholes were added to the monitoring program in 2018 but two

new sampling intervals were used, OL-KR40/1005–1030 and OL-KR45/606–610 m. The

monitoring of underground tunnels and facilities was emphasised at the planned

repository depth (-420 masl).

Detailed information regarding the pumping depths in drillholes, the sample codes used,

hydrogeological properties and pumped water volumes for each sampling section are

presented in Appendix 9.

Figure 4-1. Locations of deep drillholes sampled at Olkiluoto in 2018.

87

The chemical characteristics of the groundwater pumped to the surface were monitored

throughout the pumping period according to Alho et al. 2017. All data collected online in

the monitoring system were logged using a computer-aided data acquisition system and

are shown in Appendix 10. Field personnel typically recorded measurements manually

once each day. In addition, pH and EC were measured weekly, and occasionally more

often, using WTW Multi 340i or Multi 3620 IDS field instruments.

The manual measurements and the values recorded from the flow-through cells deviated

slightly. In particular, pH values measured manually and recorded from flow-through

cells generally showed a difference of a few tenths of a pH unit. The Eh values measured

with Pt-electrodes mainly showed consistent results and generally indicated anaerobic

conditions (Appendix 14).

4.2 Laboratory analysis

Groundwater samples were collected in the field using the Posiva water sampling guide

(Alho et al. 2017). PAVE and multipacker samples were collected with a groundwater

sampler (with 0.45 μm membrane filter for most analyses) under a nitrogen gas

atmosphere. Alkalinity and acidity were titrated in ambient atmosphere. Acidity was

titrated in a closed container. Sample collection and treatment of PFL WS2 samples is

described in more detail elsewhere (Ripatti et al. 2019).

Water samples were delivered directly to TVO’s laboratory from the sampling sites. The

samples were filtered with a membrane filter (0.45 μm) as necessary and bottled in the

laboratory. Some of the water samples required chemical preservation following

filtration. Details of the sample preparation procedure are provided in the Posiva water

sampling guide (Alho et al. 2017).

Most water analyses were carried out in TVO's laboratory in Olkiluoto according to

TVO's instructions. All the laboratory methods used are based on standard methods or

other generally accepted methods (Appendix 6). The hydrogeochemical data gathered in

2018 are presented in Appendices 12, 14, and 19. All analytical results have been

uploaded into Posiva's POTTI database. Some metal analyses and isotope analyses were

performed by subcontractor laboratories.

The quality of the analytical results was confirmed using laboratory quality control (QC)

samples and reference solutions. Assigned relative standard deviations (RSD) were

calculated from at least three parallel groundwater samples. Relative standard deviation

values exceeded 5% for 46 analyses during 2018 (Appendix 23). The most common

explanation for RSD values greater than 5% was that result was near the analytical limit

of detection, where the uncertainty is greatest and even a small difference results in higher

RSD.

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4.3 Quality evaluation of deep groundwater samples

Pitkänen et al. (2007a) developed a quality evaluation methodology for groundwaters

sampled before construction of the underground tunnels and facilities started at Olkiluoto,

i.e., groundwater samples representing baseline conditions at the site as of late May 2004.

The evaluation of these data is based on analysing observations of the influence of

drillhole internal hydrological conditions together with observations during field work,

and on the consistency of the results of chemical analyses of potential

disturbed/undisturbed areas of the sampling section. Comparison with the hydrologic

measurements has been possible only for water samples from deep drillholes.

Uncertainties in overall chemical results of a groundwater sample (charge balance,

drilling fluid contamination) also affect quality evaluation of groundwater samples. A

transparent evaluation method suitable for groundwater samples has been developed to

classify samples according to their representivity and reliability. Samples are graded in

four classes: quantitatively (class B1) and qualitatively (class B2) reliable samples

representing Baseline conditions; samples representing Temporary changes (class T);

and, samples Excluded (class E) from the grading process either due to evident

uncertainties in samples or because they represent a reference analysis. Class T samples

are either from sections sampled previously (from the monitoring network) or have been

contaminated by waters from near-surface portions of drillholes, due to the potential for

considerable water flow along open drillholes. In addition, the quality of single chemical

measurements in each water sample is also evaluated on a four-step scale describing the

technical reliability of the individual measured values. Basic information about the

samples, the analytical results, classification of the samples and single data values with

comments related to the quality of the results are included in Posiva’s hydrogeochemical

database of Olkiluoto.

A similar quality grading system was applied by Pitkänen et al. (2007b, 2008, 2009),

Penttinen et al. (2011, 2013, 2014, 2017), Lamminmäki et al. (2017a, 2017b, 2017c) and

Vuorio et al. (2018, 2019) to groundwater samples collected since June 2004. Chemical

indicators cannot be applied when interpreting artificial mixing in a similar manner to

those used for baseline data because the construction of the underground tunnels, as well

as final disposal facilities, and the presence of open drillholes may have resulted in

mixing, which is dominant only in specific parts of the bedrock (e.g., in the main

hydrogeological zones; see Posiva 2013). Groundwater chemistry in these particular

zones is likely to exhibit the greatest degree of deviation from hydrogeochemical baseline

conditions. Therefore, the hydrogeological background to the sampling and the analytical

factors of the chemical measurements such as their charge balance (CB) and the

percentage of tracer in the drilling water, are most significant for quality grading the data

to classes of quantitatively (T1) and qualitatively (T2) reliable.

For certain samples collected since June 2004, there are reasons to apply the same grading

procedure as that used for baseline data, which may increase the number of groundwater

samples that describe undisturbed baseline groundwater conditions in Olkiluoto. Water

leakage in the underground tunnels has remained fairly lows with the exception of short

time periods when tunnel construction passed through hydrogeological zones HZ19 and

HZ20. The quality evaluation procedure applied to the baseline data is therefore

considered applicable to samples collected since 2004 if sampling was performed in

89

drillhole sections either spatially distant from the underground tunnels, particularly the

eastern and northern part of the site, or at considerably greater depths than the existing

tunnels. The results of hydrogeological monitoring at Olkiluoto (Klockars et al. 2007,

Vaittinen et al. 2008, 2009, 2010, 2011, 2013a, 2013b, 2014, 2015 and 2016) have been

useful for evaluation of samples potentially representing baseline conditions, i.e.,

identifying potential observations of hydrological disturbances in sampling sections

and/or sampling sections in an area characterised by interference with major zones.

Approximately 415 deep groundwater samples have been reported to the end of 2018

during the ONKALO monitoring phase. Twenty-six (26) of the 2018 samples are

discussed in the present report.

Four samples in 2018 contained a substantial quantity (>1%) of drilling or process water.

The greatest quantity of remnant drilling water (3.2%), based on sodium fluorescein used

as a tracer, was detected in OL-KR58_547_0818.

The calculated charge balance (CB; Eq. 4-1) is an important parameter to evaluate

potential analytical uncertainties within a sample. The comparison of CB value with

previous data may, for example, help to identify anomalies in individual parameters that

account for the observed deviation in CB and provide important additional information

for geochemical calculations.

𝐂𝐁 =𝐂𝐚𝐭𝐢𝐨𝐧𝐬 − 𝐀𝐧𝐢𝐨𝐧𝐬

𝐂𝐚𝐭𝐢𝐨𝐧𝐬 + 𝐀𝐧𝐢𝐨𝐧𝐬× 𝟏𝟎𝟎%

Eq. 4-1

Cations and anions are expressed in terms of charge equivalents (CE) in the preceding

equation, converted from the corresponding mass concentrations by Eq. 4-2:

𝑪𝑬 =𝑪𝑴 × ⌈𝑸⌉

𝑴

Eq. 4-2

where CM is the mass concentration of the ion (mg/L), Q is the charge number of the ion

(mEq/mmol), and M is the molar mass of the ion (mg/mmol). The total charge equivalent

concentrations (CE, in mEq/L) of cations and anions in solution, respectively, are summed

and used in Eq. 4-1 to calculate charge balance.

Mass balance models are easily disturbed due to anomalies in element concentrations

(e.g., Pitkänen et al. 2004, 2007a) and both mass balance and thermodynamic reaction

calculations may terminate within generally acceptable CB values in a laboratory

analysis, i.e., 5%, particularly at increased solution salinities with high mass transfer.

Alternately, CB values may vary greatly in dilute waters with low pH. Straightforward

calculations of CB for groundwater samples do not account for carbonic acid dissociation

whilst alkalinity titration, if only used to detect dissolved inorganic carbon (DIC), is itself

uncertain in low-pH waters. Acidity is also determined for low-pH waters and these

values can be used in CB calculations. Organic substances which are notable in shallow,

low-salinity and low-pH groundwaters, (e.g., humic or fulvic acids with anionic

functional groups such as carboxyl groups) may also increase the overall cation content

of the solution and the resultant CB value can lead to misinterpretations because all

cations are included in cation results, but these anionic organic functional groups are not

90

included in anion results. In fresh waters, CB is highly sensitive to measured ion

concentrations and even an inaccuracy of a few mg/L in analyses of a single ion may

change the CB value by several percent, whereas anything from several hundred to more

than one thousand mg/L in saline groundwaters does not substantially affect the CB value.

A fixed, constant limit to determine recommended CB values for modelling purposes was

not considered viable to evaluate the quality of groundwater samples (Pitkänen et al.

2007a). Therefore, a converging CB value limit with increasing Cl- content (Figure 4-2)

was suggested as an uncertainty indicator in the evaluation of Olkiluoto data. The

converging CB value limit decreases from 10 to 5% as Cl- concentration increases from

0 to 10 mmol/L (355 mg/L), then further decreases from 5 to 3% and finally to 2% as

Cl- concentration further increases from 10 to 100 mmol/L (3 550 mg/L) then to >1 000

mmol/L (35 500 mg/L), respectively.

The majority of the 2018 groundwater samples exhibited negative CB values yet

remained within the uncertainty limits. Negative CB values in the majority of

groundwater samples (consistent with previous years’ observations) may be due to

slightly elevated chloride concentration. Despite the adjustments to Cl- measurement

methodology and improved awareness of the quality control protocol in the analysing

laboratory enacted in 2017, a negative shift in CB values remains observable in 2018

groundwater samples. However, the shift is substantially smaller than that observed in

previous years. All groundwater samples collected in 2018 exhibited CB values within

defined uncertainty limits.

Negative charge balances may occur as a result of elevated anion or depressed cation

values, respectively. In solutions with Cl- concentration greater than 50 mg/L the

uncertainty of the measurement for chloride titration is 6.7%, in addition to unspecified

measurement uncertainty due to sample dilution during analyses. Such variation in Cl-

concentration is sufficient to shift the charge balance from acceptable to unacceptable.

91

Figure 4-2. Calculated charge balance (CB) versus Cl- content of deep groundwater

samples collected from surface drillholes at Olkiluoto during 2018. Due to scaling, the

most saline sample is shown in the inset. All values were within acceptable limits.

Carbonate concentration used in CB was calculated from the measured alkalinity.

Sodium fluorescein has been used as a trace compound in drilling water and process water

(e.g., in freshwater head measurements in multipackered drillholes) in Olkiluoto and

ONKALO. Sodium fluorescein presence in samples indicates that the samples contain

drilling or process water in addition to sampled groundwater. Detectable quantities of

tracer were found in eight deep groundwater samples in 2018. The greatest quantities

(1.8–3.2%) of sodium fluorescein dyed water were detected at different depths in OL-

KR58. The drillhole OL-KR58 was drilled in 2016 and the drilling water remained

detectable in 2018 groundwater samples due to the low transmissivity of the water

conducting fractures in this drillhole. In addition, sodium fluorescin content indicated

1.2% drilling water content in the water sample collected from OL-KR40_600. This

section is in hydraulic connection to ONKALO, which may draw process water to this

section. The detected drilling water quantities in other drillholes were less than 1.0%.

Samples containing detectable quantities of sodium fluorescein and the corresponding per

cent (%) quantity of drilling or process water are presented in Table 4-1.

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Table 4-1. The 2018 deep groundwater samples containing drilling or process water.

Sample Sodium fluorescein, µg/L Amount of drilling or

process water in sample, %

OL-KR1_T606_1018 1.7 0.3

OL-KR4_T351_0618 2.3 0.5

OL-KR40_T600_0218 2.9 1.2

OL-KR40_T785_0418 2.0 0.8

OL-KR45_T606_0818 1.5 0.6

OL-KR58_547_0818 7.9 3.2

OL-KR58_742_0818 4.5 1.8

OL-KR58_1076_0918 5.8 2.3

Figure 4-3 shows the measured dissolved inorganic carbon (DIC) concentration of

groundwater samples as a function of inorganic carbon as calculated from the results of

alkalinity titration. Samples with DIC values less than the analytical limit of detection

were excluded from the figure (OL-KR1_T606_1018, OL-KR40_T785_0418, OL-

KR40_T1005_0618, OL-KR44_T644_1118, OL-KR45_T606_0818). In addition, all

PFL samples were excluded because the total alkalinity was not analysed.

Alkalinity represents the quantity of carbonates in water in general, but silicates,

phosphates, borates, arsenates, aluminates, and acetates, as well as sulfide and conjugate

bases of weak humic acids associated with humic substances, also contribute to alkalinity.

Whilst acetate increases the alkalinity, rather than increasing the inorganic fraction of

carbon, acetate increases organic fraction of carbon in water and is thus not considered in

DIC analysis.

In the majority of the samples included in the comparison, measured and calculated

inorganic carbon concentrations were in good accordance. Those samples exhibiting

>15% deviation between the two analyses included three saline samples taken from OL-

KR46_570 in 03/18 (measured DIC 3.4 mg/L vs. calculated inorganic carbon 30.1 mg/L),

07/18 (1.5 mg/L measured vs. 24.0 mg/L calculated) and 08/18 (2.3 mg/L measured vs.

24.0 mg/L calculated). The results of DIC and calculated inorganic carbon also differed

from one another in the three samples taken from OL-KR13_T405. These six samples are

highlighted by a red circle around the respective data point in Figure 4-3. The most

significant exceptions were the three saline samples taken from OL-KR46_570. The

differences occurred due to high acetate and sulfide concentrations (110‒120 mg/L and

22‒35 mg/L, respectively) measured in these samples. These parameters increase

alkalinity but are not measured by DIC analyses. The sulfide concentration was also

elevated in samples taken from OL-KR13_T405, at 11‒13 mg/L.

93

Figure 4-3. Dissolved inorganic carbon (DIC) as a function of calculated inorganic

carbon from the alkalinity titration for deep groundwaters sampled during 2018.

The quality evaluation for 2018 deep groundwater samples is presented in Appendix 13.

Two samples were classified as class B1, one as B2, nineteen (19) as T1 and four as T2.

4.4 Comparison of deep groundwater compositions to baseline hydrogeochemical conditions

4.4.1 Salinity

Groundwater chemistry over the depth range 0−1000 m under baseline conditions at

Olkiluoto is characterised by a wide range in both salinity and chemical composition.

Fresh groundwater with low total dissolved solids (TDS <1 g/L; Davis 1964) is observed

only at shallow depths in the uppermost tens of metres (Figure 4-4). Brackish

groundwater with TDS up to 10 g/L dominates at depths from 30 to 450 m. Fresh and

brackish groundwaters are classified into three groups on the basis of characteristic anions

(Figure 4-4), which also reflect the origin of salinity in each groundwater type (Posiva

2013). Chloride is normally the dominant anion in all bedrock groundwaters, but near-

surface groundwaters are also rich in dissolved carbonate (high DIC in fresh/brackish

HCO3 type). The intermediate layer (100−300 m) is characterised by high SO42-

94

concentrations (brackish SO4 type) and the deepest groundwater layer where SO42- is

virtually absent is characterised solely by Cl- (brackish/saline Cl type). In crystalline

rocks, a high DIC content is typical for meteoric groundwaters that have infiltrated

through organic soil layers, whereas a high SO42- content is a strong indication of a marine

origin in rocks without any SO42- mineral phases (as in Olkiluoto). Saline groundwater

(TDS >10 g/L) dominates below 400 m depth. Sodium in general, and calcium to an

increasing extent with increasing salinity, are the dominant cations in all groundwaters.

Mg is notably enriched in SO4-rich groundwaters, supporting their marine origin.

The saline groundwater component is considered to be of ancient origin, representing

geological time scales, whereas marine and meteoric components have been derived

recently during the post-glacial period in the Littorina Sea stage and current

hydrogeological conditions (Posiva 2013). The contents of HCO3- and SO4

2-, as well as

salinity, vary between groundwater samples, which reflects variable mixing of these

water components with groundwater flow in bedrock.

The highest salinity observed in groundwater samples collected thus far is 130 g/L

measured in OL-KR1_980 in 2015 (Lamminmäki et al. 2017c), which exceeds the limit

generally used to indicate a brine (TDS >100 g/L). In 2018, the highest salinity was

observed in OL-KR58_1076, 117 g/L.

Twenty-six (26) deep groundwater samples (OL-KR6 samples excluded) were collected

during 2018. Three of the samples represented typical fresh/brackish HCO3 type water.

Four samples had typical brackish SO4 type groundwater characteristics, which are

mainly derived from Littorina Sea water (Pitkänen et al. 1996, 1999a, 2004). These four

samples exhibited the high SO42- and relatively low DIC content typical of brackish SO4

type samples not mixed with later meteoric water infiltration. Five of the samples

represented typical brackish Cl type water and thirteen (13) had saline type groundwater

characteristics. The majority of the 2018 deep groundwater samples corresponded well

with baseline data (Figure 4-4 and Figure 4-5) with respect to the depth dependency of

the main parameters TDS, Cl-, SO42-, DIC, Ca2+, Na+, K+ and Mg2+. However, a few

anomalies are further discussed in this chapter.

The strong dilution of hydraulic zone HZ20 (marked with blue background in

corresponding samples in Figure 4-4 and Figure 4-5) due to its low hydraulic head caused

by the underground tunnels has been observed in previous years (Lamminmäki et al.

2017c). In 2018, the HZ20 dilution was observed in two fresh/brackish HCO3 type

groundwater samples: OL-KR4_T296_0418 (-279 masl) and OL-KR4_T351_0618

(-332 masl) (denoted by dark grey diamonds in Figure 4-4 and Figure 4-5). In the baseline

data, the groundwaters with low TDS and high DIC content occur only in the top 100 m,

yet these samples were collected from depths between -275 and -350 masl (Figure 4-4).

To a lesser degree, the HZ20 dilution was also observed in the brackish SO4 type sample

OL-KR40_T600_0218. The underground tunnel intersection with HZ20 appears to be

drawing HCO3 rich groundwater from above into the drillhole section and causing the

observed anomaly.

95

The salinity of the three brackish SO4 type samples from OL-KR11_T411 (-367 masl),

indicated by yellow triangles, was slightly lower (Figure 4-4a), whereas the SO42- and

DIC contents were clearly elevated (Figure 4-4c and d, respectively) compared to the

baseline data at similar depths. The deviations, which were also observed in 2017,

resulted at least partly from the accidental mixing of more diluted water into the system

via a leakage in the tube. The leakage, located between sections L3 (411-430 m) and L7

(124.4-135 m) in 2019, is thus confirmed, but the extent of its effect on water chemistry

remains unclear.

More moderate deviation from the baseline data was observed in saline type (blue square)

sample OL-KR40_T785_0418 (-704 masl), which is connected to feature HZ056 (grey

background). This sample had an elevated SO42- content in comparison to the baseline

data, but other measured parameters followed the baseline well. The drillhole has been

open for several years, and SO4-rich water from above has been able to flow along the

drillhole to the fracture that has flow from drillhole to bedrock due to lower head of

HZ056 caused by ONKALO intersection.

OL-KR58, the so-called Sea drillhole, was sampled for the first time in 2016. The hole

has been drilled below the Bothnian Sea from a small island west of Olkiluoto. In 2018,

it was sampled from four depths using the PFL method (Appendix 14). The collected

groundwater samples were saline at all sampling depths (-517 masl, -529 masl, -696 masl,

and -981 masl) and all correlated well with baseline data.

Sample salinity, among other chemical compositions and pH, is more thoroughly

addressed in Chapter 4.5 Temporal changes in monitoring data.

96

Figure 4-4. Depth distributions of a) TDS (mg/L, logarithmic), b) Cl- (mg/L, logarithmic),

c) SO42- (mg/L) and d) DIC (mg/L) contents of groundwater samples collected in 2018.

The TDS of the deepest sample (OL-KR58_1075, 117700 mg/L) is beyond the scale of

chart a). Results below the respective limit of detection are presented as zeros in charts

c) and d). Baseline samples (Posiva 2013) are shown in grey and classified according to

groundwater type. Samples associated with major hydrogeological features HZ19, HZ20,

HZ21, HZ056 and HZ099, as well as brittle fault zone sample BFZ045, are indicated by

blurred discs.

97

Figure 4-5. Depth distributions of a) Ca2+ (mg/L, logarithmic), b) Na+ (mg/L,

logarithmic), c) K+ (mg/L), and d) Mg2+ (mg/L) contents of groundwaters collected in

2018. Baseline data (Posiva 2013) are shown in grey and classified according to

groundwater type. Samples associated with major hydrogeological features HZ19, HZ20,

HZ21, HZ056 and HZ099, as well as brittle fault zone sample BFZ045, are indicated by

blurred discs.

98

4.4.2 pH

The pH of groundwater samples collected in 2018 were generally consistent with baseline

data (Figure 4-6a). In the figure, field pH values are used if available, otherwise laboratory

pH values are used (Appendix 14). Measured pH values ranged from 6.9 (OL-

KR13_T405_0818) to 9.2 (OL-KR45_T606_0818), a slightly wider pH range relative to

the measured pH values reported in the 2016 monitoring report (Lamminmäki et al.

2017c) but consistent with the pH range reported for 2017 monitoring data (Vuorio et al.

2019). The measured pH of four samples exceeded the equilibrium pH of 8.3 observed in

calcite (CaCO3)-water systems open to the atmosphere (air-water-calcium carbonate

systems).

The mineral saturation index (SI) of calcite, CaCO3, was calculated and is reported herein

to assess the measured pH values with respect to calcite mineral behaviour as a function

of pH changes. The mineral SI is defined as (Eq. 4-3):

𝑺𝑰 = 𝐥𝐨𝐠𝑰𝑨𝑷

𝑲𝑻

Eq. 4-3

where IAP is the ion activity product of a given mineral (in the case of calcite, IAP =

product of Ca2+ and CO32- activities) and KT is the temperature-adjusted thermodynamic

equilibrium constant. A mineral solid phase is considered to be in thermodynamic

equilibrium with the solution where SI is equal to zero. Where the SI is greater than zero,

the solution is oversaturated with respect to the given mineral solid phase and mineral

precipitation is likely. Conversely, where the SI is less than zero, the solution is

undersaturated with respect to the given mineral phase, indicating mineral instability and

the likelihood of mineral solid phase dissolution. Thermodynamic solubility indices were

calculated using the PHREEQC code (version 2) (Parkhurst and Appelo 1999).

As the principal carbonate phase in hydrothermally altered bedrock at the Olkiluoto site,

calcite is one of the most common fracture minerals (Posiva 2013). The estimated

thickness of carbonate mineral-bearing zones across the Olkiluoto site range from a few

meters to tens of meters. In addition, calcite occurs in individual fractures, outside

hydrothermally altered zones, as an alteration product of retrogressive metamorphism of

minerals in gneisses. Previous studies have demonstrated the importance of calcite in

buffering changes to groundwater pH at Olkiluoto. Herein, calcite mineral saturation

indices were calculated using dissolved inorganic carbon values for carbonate (or

alkalinity where DIC was not measured) in the 2018 Olkiluoto groundwater samples.

These calculations showed that Olkiluoto groundwaters were mainly at equilibrium or

oversaturated with respect to calcite (Figure 4-6b). Calcite saturation differed the most

from saturation equilibrium (SI=0) in the saline type groundwater samples; note that ±0.2

is employed as an uncertainty limit in the saturation index. Where the CaCO3 mineral

phase is in an approximate equilibrium with the aqueous phase, calcite formation largely

controls Ca2+ and CO32- concentrations in the groundwater and, hence, pH buffering.

99

Calcite saturation in 2018 fresh/brackish HCO3 rich groundwaters is consistent with

measured CO2 partial pressure in the typical range for surface waters, between PCO2=10-3.5

(calcite-water equilibrium in a system open to the atmosphere) and PCO2=10-2.0 (Figure

4-6c). This PCO2 range corresponds to pH values between 7.3 and 8.4 in waters that are in

thermodynamic equilibrium with calcite. Saline and brackish groundwaters generally

exhibit lower PCO2 as the Ca content gradually increases with depth. The saline type

groundwater sample OL-KR45_T606_0818 (-501 masl) represents an exception to this

generalisation with analyses showing unusually high pH and SIcalcite, and low logPCO2, for

water of this type. The three saline samples from OL-KR46_570 with elevated pH also

behave rather similarly with respect to SIcalcite, but their PCO2 is closer to the baseline

range.

The interpretation of carbonate mineral-groundwater interactions requires concomitant

consideration of solution pH, bicarbonate and carbonate ion activities, and CO2

concentration in aqueous samples.

Deep groundwater samples are highly sensitive to disturbances in measured DIC and CO2

content, which are low and in many cases are approaching or less than analytical detection

limits in saline groundwaters. The extremely low DIC and CO2 contents of Olkiluoto deep

groundwaters (e.g. PCO2 10-4 to 10-6) may enable external CO2 diffusion through

polyamide tubes, thereby contaminating groundwater during sampling and artificially

increasing the measured PCO2 in these samples. This relative increase in PCO2 will result

in a lower measured pH and a decrease in calcite mineral saturation.

All measured DIC values for the 2018 deep groundwater samples, including those below

detection limit, were used in calcite saturation index calculations. Geochemical modelling

yielded SIcalcite values indicative of undersaturation for all deep groundwater samples with

measured DIC less than the limit of detection; however, the degree of calcite

undersaturation may be understated for those samples with measured DIC below

detection limit. The use of DIC values equivalent to 50% of the limit of detection for the

purposes of geochemical modelling may have resulted in artificially elevated SIcalcite

values for the samples in question.

100

Figure 4-6. The variation of a) measured pH, b) calculated calcite saturation indices and

c) calculated logarithmic partial pressures of CO2 with depth (m) in Olkiluoto

groundwater samples. Calcite equilibrium tolerance (0.2) and partial pressure for

atmospheric CO2 are specified in b and c with blue lines, respectively.

101

4.4.3 Redox

Hydrogen ion (H+) activity, expressed as pH, and the availability of electrons (e-),

expressed as Eh, are the master variables in geochemical reactions. The oxidation-

reduction potential, or redox status, of a system can be broadly classified based on the

chemical species acting as a terminal electron acceptor in microbial respiration. Dissolved

oxygen, O2, yields the greatest energy per mole of reduced species (typically organic

carbon) oxidised, and thus is preferentially used by subsurface microorganisms. The

relatively low solubility of O2 from the atmosphere in water (ca. 8 µg/mL freshwater at

25°C and 100 kPa; Benson and Krause, 1980) and its consumption by biological activity

means that O2 can rapidly become depleted in subsurface systems that are isolated from

the atmosphere.

Figure 4-7 a shows the results of Eh measurements for 2018 Olkiluoto groundwater

samples. The Eh values presented herein are averages calculated using five days of online

measurements prior to initiation of groundwater sampling. The Eh results, apart from a

few exceptions, generally fall along the SO42-/HS- thermodynamic equilibrium as

indicated in Figure 4-7. Although 2018 redox data are not completely consistent with

baseline measurements, some improvement in groundwater sampling and analysis

techniques with time may be inferred when comparing the distribution of 2018 Eh results

to baseline data. Alternately, the significance of the SO42-/HS- redox couple may have

increased in groundwaters over time (i.e., bacterial reduction of SO4) due to mixing

between sulfate- and methane-rich groundwaters caused by the different activities at the

site according to the classification of Berner 1970 (see Posiva 2013).

Three Eh values greater than zero were recorded in 2018: +26 mV for OL-

KR40_T600_0218; +31 mV for OL-KR40_T785_0418; and, +36 mV for OL-

KR44_T644_1118. In addition, Eh values near 0 mV were recorded in OL-

KR1_T606_1018 (-15 mV) and OL-KR40_T1005_0618 (-29 mV). The redox potential

of OL-KR_T600_0218 is likely to be a sampling issue: redox potential has decreased to

less than –100 mV after sampling. The positive or near-zero redox potentials ofthe other

samples mentioned are possibly due to low yields and the effect of atmospheric oxygen.

The saline samples, OL-KR45_606_0818 and all three samples from OL-KR46_570,

differ greatly from the saline baseline samples, but fall well along the SO42-/HS-

thermodynamic equilibrium line. The primary difference between these 2018 saline

groundwater samples and saline baseline samples is less due to differences in absolute Eh

value and more to differences in pH. OL-KR45_606_0818 and all three samples from

OL-KR46_570 exhibit higher pH values relative to baseline saline groundwater samples,

skewing their relative location on the Eh versus pH plot.

Dissolved sulfide in Olkiluoto groundwaters has relevance to repository safety as this ion

causes corrosion of metals in anaerobic environments. Sulfide occurs in a range of

Olkiluoto samples from shallow groundwaters to deep saline groundwaters, but the

concentrations are low and generally well below 1 mg/L. However, eight of the deep

groundwater samples in 2018 contained dissolved sulfide at concentrations greater than

1 mg/L (Figure 4-7b). The most significant values have been observed in OL-KR46_570

samples and in OL-KR45_606, where sulfide concentrations were over 20 mg/L.

102

Elevated sulfide content has occasionally been observed at depths around 300 m, where

SO4-rich brackish groundwaters comes into contact with CH4-rich brackish Cl-type or

saline-type groundwaters. It was previously believed that endemic microbial populations

within the region of this groundwater interface may activate SO42- reduction by CH4

oxidation (Andersson et al. 2007, Pitkänen et al. 2004, Posiva 2009). Recent

interpretations, however, indicate that CH4 is not the primary microbial energy source

and other short chain hydrocarbons and DOC or hydrogen are considered more probable

energy sources (see Posiva 2013 Chapter 7).

103

Figure 4-7. a) Measured Eh (mV) values determined with Pt electrodes as a function of

pH in deep groundwaters at Olkiluoto and b) dissolved sulfide contents with depth at

Olkiluoto during 2018. pH values are field pH values in cases where these were

measured. If field pH was not available, pH (lab) was used. Lines describing theoretical

SO42-/HS- equilibrium (25 °C) are calculated for total dissolved sulfur contents: upper 1

mmol/L and lower 0.1 mmol/L. The detection limit of HS- is 0.02 mg/L. The results below

the detection limit are presented as zero.

104

The 2018 groundwater monitoring samples with the most significant sulfide content were

OL-KR45_T606_0818 (33 mg/L) and the three MetWeb samples from OL-KR46_570

(22‒35 mg/L), all saline water type. Likewise, the three MetWeb samples of brackish Cl

water from OL-KR13_T405 also exhibited high sulfide contents, ranging from 11 mg/L

to 13 mg/L. One additional groundwater sample with measured sulfide concentration

greater than 1 mg/L in 2018 was fresh/brackish HCO3 water sample OL-

KR4_T351_0618 (1.6 mg/L). Apart from OL-KR45_T606, all of these sampling sections

belong to hydrogeological zones, where recent mixing of groundwater types has occurred

due to hydrological transients. OL-KR45_T606, on the other hand, was open from 2007,

when it was drilled, to 2015, when packers were installed. During this open drillhole stage

of several years, sulfate rich water was able to flow into the fracture.

4.4.4 Groundwater compositions

Chloride is considered a conservative ion for the interpretation of hydrogeochemistry and,

therefore, generally used in the interpretation of other parameters. In Appendix 15, the

main cations, anions and sometrace components are presented as a function of Cl- content

in order to visualise potential changes in groundwater compositions compared with

baseline conditions.

All cations (Na+, Ca2+, Mg2+, K+, Sr2+, Fe2+ and NH4+) behaved similarly with respect to

Cl- across much of the groundwater data, regardless of whether samples were collected

during 2018 or during the baseline monitoring period. Anions (SO42-, DIC, Br-, and F-)

also generally corresponded well with baseline data. Some deviations from the baseline

data were however observed, as discussed below.

OL-KR40_785_0418 exhibited high SO42- concentration (85 mg/L) compared with

baseline samples with similar Cl- content. It also had a rather high ammonium content of

0.27 mg/L. This behaviour can be associated with the open drillhole stage. OL-KR40 was

drilled 2005 but not packered until 2013, providing waters from the upper portion with

access to the deeper fracture system during the open drillhole phase. The depth of OL-

KR40_785_0418 is favourable for H2 and SO42- reduction, whilst hydrogeological

conditions are likely favourable for H2 diffusion in the system due to low transmissivity.

Further investigation is required to clearly identify the processes responsible for elevated

SO42- and NH4

+ concentration in this sample. Clearly elevated ammonium concentration

compared to other fresh/brackish HCO3 samples was also observed in sample OL-

KR4_T76_0918, in which NH4+ concentration of 0.94 mg/L was measured. Fluorine

contents ranging from below detection limit to 0.3 mg/L were observed in samples from

OL-KR46_570, which are low compared to baseline data at similar chloride

concentrations.

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4.4.5 Stable isotopes of water (δ2H and δ18O)

The stable isotopic composition of water can be used to identify or trace source waters of

groundwater samples, e.g. sea water, meteoric recharge, glacial water, or old brine due to

unique isotopic composition as a result of predictable temporal and spatial partitioning of

stable isotopes. Climatic changes and the land mass altitude also reflect on the stable

isotopic composition (see Posiva 2013, Chapter 7). Stable isotopic data for Olkiluoto

groundwater samples collected in 2018 were relatively consistent with stable isotope

baseline data as shown in plots of δ2H versus δ18O and δ18O versus Cl (Figure 4-8 a and

b). These data indicated some mixing between groundwater types since the establishment

of δ2H and δ18O stable isotope baseline measures, and/or that δ2H and δ18O stable isotope

baseline data include the major hydrogeochemical features at the Olkiluoto site.

As noted in previous years’ monitoring reports, fresh groundwaters generally exhibit δ18O

values between -10‰ and -12‰ VSMOW (Vienna Standard Mean Ocean Water, an

international measurement standard for stable isotope analyses). As the groundwater

salinity increases, the stable isotope signature of samples shifts towards brackish SO4 type

groundwaters, with heavier isotopic composition (derived from Littorina seawater signal;

see Posiva 2013, Chapter 7).

In 2018, the three fresh/brackish HCO3 type groundwater samples shown in Figure 4-8

were all taken from the same drillhole, OL-KR4, and had stable isotopes values

approximately fitting in the typical range for fresh/brackish HCO3 samples. However, the

samples from the uppermost sections of the drillhole (OL-KR4_76_0918 and OL-

KR4_296_0418) showed slightly heavier isotopic compositions, δ18O ranging from -9.87

‰ to -10.11 ‰ and δ2H from -73.5‰ to -74.5‰, compared with the deepest sample, OL-

KR4_351_0618.

The brackish SO4 type groundwaters are characterised by a heavy isotope signature as

well as increased Cl content relative to fresh/brackish HCO3 type waters. This suggests

the possible influence of Baltic Sea water in brackish SO4 type groundwater samples with

Cl content trending more towards old Littorina Sea water.

106

Figure 4-8 presents the isotopic composition of four brackish SO4 type samples from

2018 and one from 2017 (OL-KR11_T411_1217), the latter distinguished by a red outline

in the marker. The isotopic data of this 2017 sample is presented in this report due to a

delay in the delivery of isotope results. Four of the samples were taken from OL-

KR11_T411 and one from OL-KR40_T600. The brackish SO4 type samples had stable

isotope values exhibiting only little variance with one another, with δ18O ranging

from -9.84‰ to -10.07‰ and δ2H ranging from -72.6‰ to -73.4‰.

107

In brackish Cl type groundwaters the stable isotope ratios usually shift to lighter

composition indicating an increase in the colder climate meteoric water fraction, which

is likely due to glacial meltwater influence. The four brackish Cl type samples in 2018

showed a moderate shift to lighter compositions, especially OL-KR13_T405. The results

from the isotopic assay of one brackish Cl type sample, OL-KR20_410_1218, were not

available during the time this report was being finalised and are therefore discussed in the

next year’s report.

The saline groundwater samples all fell above the global meteoric water line (GMWL) in

2018. The baseline and 2018 saline groundwater samples clearly positioned above the

GMWL are strongly indicative of a water component (brine) with primary silicate mineral

hydration under a low water/rock ratio. The sample with the heaviest isotopic signature

(-8.37‰ δ18O / -33.0‰ δ2H) was taken from the Sea drillhole OL-KR58 at a depth of

981 m, closely following the interpreted dilution trends (Figure 4-9). In addition, the 2018

δ18O and δ2H values of OL-KR46 groundwater samples seem to exhibit a slight shift

towards brackish SO4 type water, with -10.19 to -10.66‰ δ18O and -66.0 to -67.3‰ δ2H

measured in 2018. This shift towards brackish SO4 type water characteristics indicates

potential mixing of saline and sulfate water types at OL-KR46.

108

Figure 4-9. Relationship between (a) δ18O and δ2H and (b) Cl (in mg/L) and δ18O in

Olkiluoto water samples in 2018. GMWL shown in (a) according to Craig (1961). Arrows

in (b) depict ancient dilution of brine to brackish Cl-type water and postglacial mixing

by groundwater derived from the Littorina Sea (Posiva 2013).

Brine ref.

Meteoric ref.

Littorina ref.

Glacial ref.

109

4.5 Temporal changes in monitoring data

The groundwater samples taken in 2018 are grouped into different timeline figures

according to the categorisation method used for Olkiluoto groundwaters: fresh/brackish

HCO3 type (Figure 4-10); brackish SO4 and brackish Cl types (Figure 4-11); and saline

groundwaters (Figure 4-13). Only series with two or more samples in total (and the latest

in 2017) are presented in the figures. The given pH values are the results of laboratory

measurements, which were used for consistency due to the lack of available field pH data

for samples analysed in previous years. Hydraulic zones influencing the sampling

sections are indicated in the legends.

The sample series in the figures are labelled with the drillhole number followed by the

upper packer depth of the sampling section. Samples taken from multipackered drillholes

are coded with a letter T. When referring to a specific sample (in the text), the month and

year (in mmyy format) of the sampling date are indicated at the end of the sampling

section code. In some cases, a specific sampling section may have changed over the years

due to the packers being in slightly different positions in previous samplings. In the

figures, these samples are presented in the same continuum with current sampling

sections and indicated by circles around the current marker design.

The start of the construction of the underground tunnels and facilities in autumn 2004 is

also shown in the figures. The tunnel penetrated HZ19 at approximately 100 m depth in

late 2005 and HZ20 at about 300 m depth in summer 2008. It is worth noting that both

monitoring and characterisation samples, as well as the samples taken from multipackered

drillholes (coded with T) or open drillholes with PAVE technique, are illustrated in the

same figures.

In 2018, samples categorised as fresh/brackish HCO3 type groundwaters were collected

from the same drillhole, OL-KR4 from three sampling intervals in connection to three

hydrogeological zones: HZ19A, HZ20A and HZ20B. Figure 4-10 presents the time series

for these samples.

The uppermost section OL-KR4_T76 (HZ19A), marked with red diamonds, was

previously sampled in 2017. The pH, K+ and DIC levels (Figure 4-10a, g and h,

respectively) approached the respective level they each were before the sampling in 2017,

when the changes in groundwater composition of this section were associated with the

possible influence of activities near OL-KR4. However, the sulfate concentration has

continued to increase, even more steeply during the latest measurement interval, reaching

151 mg/L in 2018. The heavy isotopic signature observed in 2007 (Figure 4-10 k and l)

was assumed to result from a fractional input from Korvensuo. The effect mostly

disappeared in the next sampling in 2009, but after the slow increase during the following

years 2H and 18O increased substantially in the latest measurement and reached

approximately the same level as observed in 2007.

110

HZ20 dilution was evident in the following two sampling sections. The middle section

OL-KR4_T296 (HZ20A), marked with blue diamonds, was analysed for the second time

in 2018 and is thus showed in the time series for the first time. Compared to the results

measured in the previous sampling in 2015, the section showed a slight decrease in

salinity and an increase in DIC. The most notable change was seen in tritium content,

which increased to 6.7 TU.

The deepest section OL-KR4_T351 (HZ20B), marked with yellow diamonds, continues

to show dilution in most of the parameters (Cl-, Ca2+, Na+, Mg2+, and K+) with time, very

similarly to the upper section OL-KR4_T296. The sulfate concentration continued to rise

steeply, whereas sulfide concentration decreased back to the level observed in the first

measurement in 2012.

During the time of sampling of the middle and the deepest sections of OL-KR4, the

drillhole OL-KR28 was open and due to head difference between the main

hydrogeological systems, water from the HZ19 system was able to penetrate into the

HZ20 system, which could also have affected the dilution.

111

Figure 4-10. a) pH, b) Cl-, c) Ca2+, d) Na+, e) Mg2+, f) SO4

2-, g) DIC, h) K+, i) HS-

(detection limit 0.02 mg/L), j) 3H, k) 2H and l) 18O results from time series sampling of

fresh/brackish HCO3 type waters at Olkiluoto in 2018. Results less than the limit of

detection are shown as zero in i). The number at the end of the sample label in the key

denotes the drillhole length of the upper packer. T indicates sampling from a

multipackered drillhole, whereas the others are sampled with the double packer PAVE

system from an open drillhole. The start of the construction of the ONKALO is marked in

each plot by a vertical red line.

112

The drillhole sections OL-KR11_T411 and OL-KR13_T405 are part of the Sulfide

project (a microbiological subproject MetWeb). In addition to these two sections, OL-

KR46_570 is also part of the project. The MetWeb-project concentrates on understanding

the mechanisms for sulfide formation in drillhole sections with differing groundwater

chemistries. The sections were intensively sampled in 2016, and the sampling was

continued by two samples taken from two sections in 2017, followed by three samples

from each section in 2018. Continuous pumping was performed in the drillhole sections,

which may have affected the groundwater chemistry. Only the first samples taken from

each section in 2018 are included in Figure 4-11 and discussed with respect to other

brackish SO4 and brackish Cl type samples. The complete time series of the three sections

included in the MetWeb project are shown in Figure 4-12; all results will be reported and

discussed in greater detail in the forthcoming MetWeb report.

Section OL-KR11_T411, marked with blue triangles, has been decreasing in total

dissolved solids (salinity) since 2003, with the exception of magnesium. The results

observed in 2018 were very similar to the previous sampling. The earlier changes

indicated a carbonate rich groundwater addition from above the sampling section, but in

2017 there was also a suspicion of a leakage in the tube, which was confirmed in 2019.

Section OL-KR40_T600 (HZ20B), marked with yellow triangles, was sampled for the

second time in 2018. Earlier sampling was performed by PAVE from a slightly shorter

interval in 2008. Strong HZ20 dilution can be observed in this section. Sulfates, sulfides

and isotopes have remained stable after the time period of ten years since the previous

sampling.

Sampling in section OL-KR13_T405 (BFZ045), marked with green rounds, started in

2013. Following the trend seen in recent years, the section shows recovery towards saline

conditions. However, the sulfate input, likely through BFZ045 connection, that was seen

until 2017 was diminished in 2018 and the sulfate concentration started to slowly

decrease, as seen more clearly in Figure 4-12. On the other hand, sulfide concentration

has been elevated, ranging from 8.8 to 16 mg/L, during the entire monitoring period,

including MetWeb samples. Activation of microbial SO4 reduction has been a source for

the observed sulfide.

The two sampling intervals in OL-KR20 are marked with red (OL-KR20_T410) and

purple (OL-KR20_T460) rounds. Both sections belong to HZ099. Compared to the

previous sampling in 2013, salinity has slightly increased in both sections. SO4 and DIC

concentrations have systematically decreased from initial samplings, which indicate a

recovery of groundwater composition from an open drillhole stage during the years with

multipackers. The higher salinity in the first sample of OL-KR20_T460 is probably a

result from a fraction of more saline groundwater flown from the deep bottom part of the

drillhole during the open drillhole stage. The stable isotopic values for OL-KR20_T460

have slightly decreased compared to the previous sampling. Other isotopic data for

samples from OL-KR20 was not available during the finalisation of this report.

113


2- (detection limit ≥0.1 mg/L,

depending on sample salinity), g) DIC, h) K+, i) HS- (detection limit 0.02 mg/L), j) 3H

(detection limit 0.2 TU), k) 2H and l) 18O results of time series samplings of brackish SO4

and Cl type waters at Olkiluoto sampled in 2018. Results less than the respective limit of

detection are shown as zero in f), i) and j). The number at the end of sample label in the

key denotes the drillhole length of upper packer. T marks sampling from a multipackered

drillhole, whereas the others are sampled with the double packer PAVE system from an

open drillhole. The start of the construction of the ONKALO is marked by a vertical red

line in each plot.

114



depending on sample salinity), g) DIC, h) K+, i) HS- (detection limit 0.02 mg/L), j) 3H

(detection limit 0.2 TU), k) 2H and l) 18O results of time series samplings for subproject

MetWeb sampled in 2018. Results below the respective limit of detection are shown as

zero in i) and j). The number at the end of sample label in the key denotes the drillhole

length of upper packer. T marks sampling from a multipackered drillhole, whereas the

others are sampled with the double packer PAVE system from an open drillhole.

115

Time series for saline samples are presented in Figure 4-13. The sections included are

- OL-KR1_T606 (HZ21),

- OL-KR40_T785 (HZ056),

- OL-KR44_T644 (HZ20B),

- OL-KR44_T766 (HZ20B), and

- OL-KR46_570 (HZ056).

Section OL-KR1_T606 (HZ21), marked with blue squares, was previously sampled in

2013 from a slightly different interval, as all the previous samplings taken by PAVE.

Most parameters have been stable throughout the monitoring except for pH, which

decreased significantly in the latest measurement to 6.8. The field pH of 8.0, however,

was consistent with the previously measured laboratory pH values. Tritium result was not

available for OL-KR1_T606 by the time this report was being finalised.

OL-KR44_T644 (HZ20B), marked with yellow squares, was previously sampled in 2015.

This section has been stable compared with previous samplings, except for tritium and

DIC, which each decreased to less than their respective limit of detection. Section

KR44_T766 (HZ20B), marked with purple squares, has also been rather stable

throughout its monitoring period, which started in 2012. In 2018, the section showed a

slight increase in salinity (Cl-, Ca2+, Na+) and sulfide concentration, whereas Mg2+, K+

and DIC decreased. Tritium fell below the detection limit as it did with all saline samples

in the time series in 2018.

Section OL-KR40_T785 (HZ056), marked with green squares, was sampled for the first

time from this exact interval. It has been previously sampled by PAVE from slightly

shorter intervals, with the latest sampling done in 2011. In 2018, the section showed a

slight increase in salinity (Cl-, Ca2+, Mg2+, K+). Although the SO4 concentration in OL-

KR40_T785 slightly decreased, the concentration is still significant. However, sulfide is

under the detection limit indicating that microbial SO4 reduction has not started.

In contrast to other sections, OL-KR46_570 (HZ056), marked with orange squares, has

exhibited large deviations during its monitoring period. The section is part of the MetWeb

project. Samples from this section have been mixtures of two groundwater types from the

beginning of this section’s monitoring. During the open drillhole phase, the brackish SO4

water from an upper part of bedrock flowed via drillhole to deeper and penetrated to a

fracture at drillhole depth 570 m. The fracture is part of hydraulic zone HZ056 that

withdraws water towards ONKALO and causes the SO4 rich groundwater to mix with the

saline groundwater originally present in the fracture. Salinity in the sampling section has

increased (Figure 4-13b) and sulfate content decreased (Figure 4-13f) since 2014,

indicating an increase in the original saline groundwater fraction and a decrease in the

SO4 rich groundwater fraction. The section has been under nearly constant pumping due

to several samplings, especially in 2016 within MetWeb monitoring, and this has

enhanced recovery. Remarkably high sulfide concentrations have been measured since

the monitoring started, but the HS- concentration has also started to decline, reaching

35 mg/L in the first sampling in 2018, and further decreasing to 22 mg/L in the last

measurement in 2018, as shown in Figure 4-12i.

116



depending on sample salinity), g) K+, h) HS- (detection limit 0.02 mg/L), i) HS- (different

scale), j) 3H (detection limit 0.2 TU), k) 2H, l) 18O and m) DIC (detection limit 0.4 mg/L)

results of time series samplings of saline type waters at Olkiluoto sampled in 2018.

Results less than the respective limit of detection are shown as zero in f), h), i) and j). The

number at the end of sample label in the key denotes the drillhole length of upper packer.

T denotes sampling from a multipackered drillhole, whereas the others are sampled with

the double packer PAVE system from an open drillhole. In the figures a square marker

surrounded by a circle also denotes PAVE sampling technique from open drillhole.

117

5 OBSERVATIONS FROM THE MONITORING OF GROUNDWATER CHEMISTRY FROM UNDERGROUND TUNNELS AND FACILITIES IN 2018

5.1 Sampling points and monitoring

The hydrogeochemistry from the underground tunnels and facilities has thus far been

based on the groundwater sampling from:

1. The nineteen (19) pilot holes ONK-PH2–ONK-PH6, ONK-PH8–ONK-PH11,

ONK-PH14, ONK-PH16–ONK-PH18, ONK-PH19, ONK-PH21–ONK-PH23,

ONK-PH28 and ONK-PH29 drilled along the tunnel profiles prior to their

excavation, and the one central tunnel pilot hole ONK-CTPH5.1. Only ONK-

PH21–ONK-PH23 could have been monitored as their profiles were not

excavated before 2017. ONK-PH29 is part of the integrated systems test.

2. The four drillholes (ONK-KR1–ONK-KR4) and the groundwater station ONK-

PVA7 drilled for monitoring the influence of cement grout on the groundwater

and shallow/short drillholes ONK-PP73 (sampled only once in 2006), ONK-

PP262 and ONK-PP274 in the HYDCO niche (Toropainen 2011), ONK-PP319

and ONK-PP321 in the REPRO niche (Toropainen 2012b) and the

characterisation drillholes ONK-KR13, ONK-KR14, ONK-KR15, ONK-KR16

and ONK-KR17 (2016).

3. The twelve (12) groundwater stations (ONK-PVA1–ONK-PVA13), except for

ONK-PVA7, which has turned into a cement grout monitoring hole.

4. Samples from leaking fractures collected directly from the tunnel walls (ONK-

RV), with metal plates from tunnel walls (ONK-KOU), or with plastic collectors

on the ceiling with plastic piping for sampling (ONK-KER).

5. Water from nine measuring weir lines (ONK-MPL208, ONK-MPL580, ONK-

MPL1255, ONK-MPL1970, ONK-MPL3003, ONK-MPL3125, ONK-MPL3209,

ONK-MPL3356 and ONK-MPL3941).

Altogether, 67 groundwater samples from different locations (19 from ONK-PVA

groundwater stations, nine from ONK-KR drillholes, 13 samples from pilot holes, seven

from ONK-RV leaking fractures, and 19 from ONK-KOU and ONK-KER water

collectors) have been collected from the underground tunnels and facilities during the

2018 calendar year (Appendix 17). Most of the sampling points in the underground

tunnels represent relatively low transmissivity compared to groundwater sampling from

deep drillholes at ground surface (cf. Appendix 14 and 16). The locations of the tunnel

drillholes and main hydrogeological zones are presented in Figure 5-1. A close-up of the

demonstration tunnel section at -420 m is presented in Figure 5-2.

118

Figure 5-1. Locations of the hydrogeochemical samplings in the underground tunnels

and facilities. Main hydrogeological zones are shown as coloured planes.

Figure 5-2. Drillholes in the demonstration tunnel section at -420 m and nearby

hydrogeological zones.

119

The groundwater samples from pilot holes represent the best initial hydrochemical

conditions in the underground tunnel volume. Information about the pilot holes (location,

sample date, drillhole length, intersecting hydraulic zones, transmissivity, water type,

TDS) is presented in Appendix 18. Groundwater stations, which have been drilled in

native ungrouted rock, most likely describe long-term hydrogeochemical evolution

without interaction with cementitious materials caused by the construction of tunnels.

Long characterisation drillholes ONK-KR13, ONK-KR14 and ONK-KR15 were drilled

in 2010−2011 and ONK-KR16 was drilled in 2013 for characterisation and monitoring

of repository-type bedrock. ONK-KR17 was drilled in 2015 to investigate gas inventory

in rock matrix and pore water. Similar information to that from pilot holes is presented

for groundwater stations (ONK-PVA) and drillholes (ONK-KR) in Appendix 19.

Transmissivities in the groundwater sampling locations in the underground tunnels are

generally low (<10-8 m2/s) except at shallow depths or intersections with major

hydrogeological zones (HZ19 and HZ20 systems).

Sampling was not carried out from OL-PH1. Transmissivity (water inflow) was

insufficient in pilot holes ONK-PH7, ONK-PH12, ONK-PH13, ONK-PH15 and ONK-

PH20 (2012) to support water sampling. Sampling in the pilot hole ONK-PH19 started in

2016, although it had been drilled already in 2012. Pilot holes ONK-PH21−23, across

from the demonstration area, were drilled in 2013 and have been available for

investigation purposes since.

The drillholes for monitoring the influence of cement were drilled in August 2005 (ONK-

KR1 through ONK-KR4) and October–November 2009 (ONK-PVA7). These drillholes

represent grouted areas of slightly different ages, different grout amounts and different

cement mixes, e.g., Ahokas et al. (2006). However, cement-filled fractures were observed

only in the drill cores from the drillholes ONK-KR3 and ONK-KR4 (Rautio 2005).

Cement from tunnel grouting was also found in fractures from ONK-PVA7 (Toropainen

2009).

The continuous (manual) monitoring of the drillholes ONK-KR1 through ONK-KR4 for

water inflow rate, pH, temperature and electrical conductivity (EC) started within tens of

days to up to nine months after grouting. Monitoring indicates that the inflow rate has

been relatively stable. The observations on the continuous manual monitoring results are

discussed in more detail in the report by Arenius et al. (2008). The groundwater samplings

continued after 2008 at a frequency of one sampling campaign per annum.

Monitoring of groundwater stations with groundwater samples started from ONK-PVA1

in 2005. ONK-PVA4 (drilled to ca. 150 m depth in April−May 2007) represents very low

transmissivity bedrock with T value 1.1x10−10 m2/s. Similar or lower transmissivity

monitoring points have later been included in the programme at deeper levels of the

underground tunnels (<300 m depth). Especially REPRO experiment drillhole ONK-

PP319 and ONK-PP321 have extremely low transmissivities of approximately

1x10−12 m2/s and 2x10−13 m2/s, respectively. More details of ONK-PVA and ONK-PP

drillholes are shown in Appendix 19.

120

Four metal channels (ONK-KOU) for monitoring leaking fractures in the tunnel wall were

installed in 2006 and three in 2011. Two water collectors (ONK-KER) monitoring

leakage from the ceiling were installed in 2011.

The representivity of groundwater samples from leaking fractures varies. Some of the

samples have interacted with grout cement whilst some have contained high

concentrations of sodium fluorescein, used as a tracer in water from the tunnel drillings

and other work actions. However, samples of groundwater from leaking fractures may

yield important information regarding salinity and its changes along the tunnel.

Water measuring weir lines have been built in the underground tunnels to facilitate total

water inflow measurements. The results of the measuring weir lines are not examined in

this report because they are not considered to represent any natural conditions or changes

of groundwater characteristics in the underground tunnels due to the mixing with the

process water used in different work actions, as well as interaction on the tunnel walls

and floor.

5.2 Quality evaluation of samples from underground tunnels and facilities

Charge balance as a function of chloride concentration is presented in Figure 5-3 for the

2018 data from the underground tunnels and facilities. Blue lines represent acceptable

charge balance limits for the groundwater samples (see Chapter 0). According to the

criteria, one sample (ONK-PH22_60_0218) had a CB value outside the acceptance limits,

indicated by a red circle in the figure. The anions and cations were re-analysed, but the

reason for the excessively negative charge balance remains unknown. In this sample,

sulfate concentration in particular differed substantially from earlier samplings.

A negative charge balance may occur as a result of over-enrichment of anions or

excessive depletion of cations. At chloride concentrations greater than 50 mg/L,

uncertainty of the measurement for chloride titration is 6.5% and even 1% variation in

chloride concentration may shift the charge balance from non-acceptable to the

acceptable level in the sample mentioned above. The dilution of samples for laboratory

analysis further complicates charge balance uncertainty, as the measurement uncertainty

for the diluted sample may increase by the factor of dilution for the raw (undiluted)

sample. For the purposes of data reporting herein, the uncertainty of measurement for

chloride titration is assumed to be at least 6.5% for samples with chloride concentration

greater than 50 mg/L.

121

Figure 5-3. Calculated charge balances versus Cl- content in samples collected from the

underground tunnels and facilities during 2018. Carbonate concentration used in CB was

calculated from measured DIC value.

Measured DIC concentrations and carbon concentrations calculated from total alkalinity

were in rather good accordance, as seen in Figure 5-4. Alkalinity represents the quantity

of carbonates in water in general, but silicates, phosphates, borates, arsenates, aluminates,

humic substances and acetate all contribute to alkalinity. Eight samples with DIC content

less than the limit of detection were excluded from the figure. In four samples – ONK-

PH22_34_0218, ONK-PH22_60_0218, ONK-PVA8__0118, and ONK-KR16_14_0918

– the difference between DIC and calculated dissolved carbon was more than 15%, as

denoted by red circles in Figure 5-4. The differences were, however, so minor that there

is no clearly identifiable reason for the observed disparity.

122

Figure 5-4. Dissolved inorganic carbon (DIC) as a function of calculated dissolved

carbon from the alkalinity-titration for groundwaters sampled from the underground

tunnels and facilities in 2018. Samples where the difference between DIC and calculated

dissolved carbon was greater than 15% are marked with a red circle.

The quality evaluation results of samples from the underground tunnels and facilities

taken in 2018 are presented in Appendix 16. Fifty-nine (59) samples were classified as

T1, three as T2 and none as class E. Five of the samples collected in 2018 were classified

as B1 or B2 baseline samples.

123

5.3 Observations from monitoring of groundwater chemistry from underground tunnels and facilities

The figures in this chapter present the main chemical parameters measured in

groundwater samples from the underground tunnels and facilities as a function of depth,

along with the baseline samples. The interpreted water types are indicated by the shape

of the markers used commonly in reports for different water types of Olkiluoto ground

waters (i.e., fresh/brackish HCO3 = diamond; brackish SO4 = triangle; brackish

Cl = circle; and, saline = square).

Figure 5-5 shows the TDS variation of all the samples collected from the underground

tunnels and facilities throughout the end of 2018. The concentrations of TDS have mainly

correlated well with the baseline samples at corresponding depths. The highest salinity

(TDS = 21 010 mg/L) in the underground tunnel drillholes during the monitoring period

was measured in 2017 from ONK-PVA11_11 (z = -427 masl). Worth noting is the wide

salinity range at the repository level at approximate depth of 420−430 m; the variation in

the TDS data above and at -300 m is lesser than the variation of baseline data, whereas

the variation in data below -300 m is greater than that of the baseline samples.

Brackish SO4 type groundwater (rich in SO42-, Mg2+ and K+), is mostly infiltrated from

the former Littorina Sea and therefore higher salinities are mostly missing from the

underground tunnel data above -300 m. The reason is that the underground tunnels and

facilities do not intersect with any highly transmissive fractures between the fracture

zones HZ19 and HZ20, i.e., between the depths of 100 m to 300 m, where brackish SO4

type groundwater typically occurs in baseline conditions (Posiva 2013).

The measured TDS concentration varies widely between the different sampling sections

and sampling occasions even in single drillholes, such as in ONK-KR15 (Figure 5-5,

z = -399 masl, round with violet stripes) and ONK-PVA6 (Figure 5-5, z = -327 m, green

triangle). Salinity variation in ONK-PVA6 results from a diluting influence of brackish

SO4 type groundwater, which increasingly discharges into the groundwater station from

the nearby HZ20B along the intersecting OL-BFZ045 (see Chapter 5.4 ).

The salinity (cation and chloride results, no mixing of upper groundwaters) was lower

than the baseline data at corresponding depths in some low transmissivity fractures. These

conditions are represented in the underground tunnels, e.g., by sampling points ONK-

PP262 and ONK-PP274 (Figure 5-5, z = -375 masl), most recently sampled in 2015.

These short drillholes are located in the HYDCO experiment-niche (Appendix 19).

Bicarbonate-rich groundwater has been found at a depth of 300 m (ONK-PH8 in Figure

5-5). The pilot hole intersected HZ20A, which is known to be contaminated by open

drillhole flow of HCO3-rich groundwater from the upper reaches (Pitkänen et al. 2007a,

Posiva 2013) prior to the construction of the underground tunnels and facilities. Also the

samples taken from leaking fractures (ONK-RV, -KOU and -KER) in the area of HZ20

have clearly been diluted (see further discussion in Chapter 5.4.2 ).

124

Figure 5-5. Depth distribution of TDS (mg/L) in samples from the underground tunnels

and facilities through the end of 2018. The shape of the marker indicates the interpreted

water type of the sample (fresh/brackish HCO3 = diamond, brackish SO4 = triangle,

brackish Cl = circle and saline = square). The samples are categorised by the water type

that was observed in the latest sampling.

125

The following three figures present the main chemical parameters measured in

groundwater samples taken from the underground tunnels and facilities in 2018 vs. depth:

Figure 5-6: Cl-, SO42-, DIC, 18O; Figure 5-7: the main cations Ca2+, Na+, K+ and Mg2+;

Figure 5-8: HS- and DOC. The baseline samples are included in each figure.

Two new groundwater stations were added to the monitoring program in 2018: ONK-

PVA12_11 (HZ19C) and ONK-PVA13_14 (HZ20A). Some of the most notable

deviations from baseline samples of corresponding depths occurred in sample ONK-

PVA13_14_1218 (-307 masl). Its chloride, sodium and calcium concentrations were low

(Figure 5-6a and Figure 5-7a and b, respectively), whereas its DIC and DOC

concentrations were clearly elevated (Figure 5-6c) compared to baseline samples at

similar depths. The section is in connection with HZ20A. ONK-PVA12_11_1218

(HZ19C) exhibited somewhat similar behaviour. Results of isotopic assay for these two

samples were not available by the time this report was being finalise and therefore are not

seen in Figure 5-6d.

The central tunnel pilot hole ONK-CTPH5.1 was drilled and sampled in 2018. One

sample was taken on the whole length of drillhole, and four other samples were taken at

different sections (Appendix 17). All parameters versus depth corresponded well with the

baseline data (Figure 5-6, Figure 5-7, Figure 5-8).

Pilot hole ONK-PH21 was sampled at three individual sections and ONK-PH22 at four

sections in 2018 (Appendix 17). These pilot holes were open during the excavation of the

nearby Integrated System Test -central tunnel. Samples from ONK-PH21_38, ONK-

PH21_65, ONK-PH22_27, ONK-PH22_34, and ONK-PH22_60 represented brackish Cl

type water and were characterised by slightly low salinity (Cl-, Na+). In addition, calcium

concentration was low in ONK-PH21_38 and ONK-PH21_65. Dissolved inorganic

carbon (DIC) was observed to be elevated in three sampling intervals in ONK-PH22.

Sulfate and sulfide contents were somewhat elevated in all samplings in ONK-PH22.

Values of DIC and SO42- were notably lower in ONK-PH22_37, which was defined as

saline water, compared to other sampling sections in the same pilot hole.

ONK-PVA7 (z = -344 masl) was classified as brackish SO4 type water due to its high

sulfate content of 302 mg/L (Figure 5-6b, red triangle). Brackish SO4 waters of the

baseline data do not appear at corresponding depths (below -300 masl). The main

parameters rather correlate with the brackish Cl baseline data, with the exception of

sulfate. The drillhole ONK-PVA7 has likely been influenced by SO4-rich groundwater

flow along hydraulic zone HZ056 towards the underground tunnels (Figure 5-1). Sulfide

was included in the analysis programme of this groundwater station for the first time in

2018 (Appendix 17).

The groundwater station ONK-PVA10 (z = -379 masl) retained a brackish Cl type

groundwater composition with relatively low salinity in 2018 (orange round in Figure

5-6a, Figure 5-7). The 18O result, approximately -13‰, indicated a minor glacial water

fraction in the sample (Figure 5-6d). ONK-PVA10 is in hydraulic connection with the

drillholes OL-KR39 and OL-KR3 (Vaittinen et al. 2015) and the results resemble those

obtained from similar depths.

126

The highest sulfate concentration (458 mg/L) was measured from near the surface in

ONK-KR1 (Figure 5-6b, diamond with red stripes). The sulfate concentration is

postulated to have increased due to the use of biotite-rich crushed rock from the

underground tunnels in the civil engineering works on the surface. The rock potentially

releases sulfate in the presence of oxygen and water.

Figure 5-6. Depth distribution of a) Cl-, b) SO4

2- (detection limit 0.1 mg/L), c) DIC

(detection limit 0.4 mg/L) and d) 18O. The shape of the marker indicates the interpreted

water type of the sample (fresh/brackish HCO3 = diamond, brackish SO4 = triangle,

brackish Cl = circle and saline = square). Results less than the respective limit of

detection are shown as zero in b) and c).

127

Elevated sulfate and sulfide concentrations were observed in ONK-KR16_14 (Figure

5-6b, Figure 5-8a, z = -421 masl), which was sampled four times in 2018. The first two

samples were classified as saline type waters, and the two latter samples as brackish SO42-

type waters as a result of their slightly lower salinity. These four samples are denoted by

markers with a shape corresponding to their actual water type (i.e., triangle or square),

but their colouring is the same, blue tilted stripes. The intersection with OL-BFZ045 is

the reason for the increased sulfate content in this drillhole section: SO4-rich water is

drawn down from the upper part of bedrock along the subvertical fracture zone OL-

BFZ045.

Figure 5-7. Depth distribution of a) Ca2+, b) Na+, c) K+ and d) Mg2+ (all in mg/L). The

shape of the marker indicates the interpreted water type of the sample (fresh/brackish

HCO3 = diamond, brackish SO4 = triangle, brackish Cl = circle and saline = square).

128

The samples from ONK-PVA8 (z = -279 masl) were also classified as brackish SO4 type

water. Thus far, the highest sulfide concentration in the underground tunnels has been

measured in this groundwater station. In 2018, ONK-PVA8 was sampled two times and

the measured sulfide concentrations were 5.3 and 4.8 mg/L, respectively (Figure 5-8a).

The composition of the samples represented a mixture of brackish Cl and brackish SO4

type groundwaters. Elevated sulfide concentrations have been observed occasionally in

zones characterised by the mixing of these types of groundwaters. This groundwater

station is in a hydrogeological connection to the vertical OL-BFZ100 and may also be

influenced by HZ20A, although not intersecting it.

Organic carbon contents were primarily low in the underground tunnels in 2018, as seen

in Figure 5-8b.

Figure 5-8. Depth distribution of a) sulfide (HS-, detection limit 0.02 mg/L) and b) DOC.

The shape of the marker indicates the interpreted water type of the sample (fresh/brackish

HCO3 = diamond, brackish SO4 = triangle, brackish Cl = circle and saline = square).

Results less than the respective limit of detection are shown as zero in both a) and b).

129

The figures showing pH, main cations and anions, as well as inorganic and organic carbon

contents and silica as a function of Cl- content are presented in Appendix 20. Most of the

parameters exhibited trends as a function of Cl- content similarly to groundwater types

representing the baseline data (Posiva 2013). This indicates that no extraordinary

mixtures have formed in the vicinity of the underground tunnels to date. The notable

deviations from the baseline data were detected in relation to NH4+, SO4

2- and SiO2 vs.

Cl-.

The NH4+ concentration of fresh/brackish HCO3 sample ONK-KR4 was elevated

compared with baseline data, in addition to that of saline sample ONK-PVA11_11. The

fresh/brackish HCO3 sample ONK-KR1 had clearly elevated sulfate concentration in

relation to chloride content. ONK-PVA1 and ONK-PVA12_11 had notably high

concentrations of silica. Two pH values less than 7.0 were measured: 6.9 in both ONK-

PH21_20 and ONK-PH21_38. The distribution of magnesium, potassium and sulfate

show that the extreme brackish SO4-type groundwaters were missing in the samples

collected from the underground tunnels in 2018.

5.4 Temporal changes in the underground tunnel drillholes

Monitoring results for sampling points in the underground tunnels at depths

above -100 masl (Figure 5-1), typically dominated by HCO3-rich groundwaters, are

presented in Figure 5-11 and Figure 5-12. The monitored drillholes in the upper part

(0−100 m) of the tunnels are ONK-KR1–4 and ONK-PVA1–3, of which all were

monitored in 2018. These holes were drilled either for monitoring the influence of cement

grouting or for monitoring the influence of construction on groundwater where no

grouting was done (Appendix 19).

A trend of decreasing pH with time (Figure 5-11a) has been observed in the monitoring

results of grouting cement drillholes, slightly in ONK-KR2 (green stripes), and more

clearly in ONK-KR3 (light blue stripes) and ONK-KR4 (purple stripes). The pH has been

stable in all groundwater stations (ONK-PVAs). The high pH values, >10 pH units,

measured in ONK-KR3 and ONK-KR4 in the beginning of the monitoring period, were

evidently caused by cement-water interaction. Different grouting cement was used in the

area of these drillholes during construction (Ahokas et al. 2006). ONK-KR3 is impacted

by low pH injection grout (Ultrafin 16 + GroutAid + Mighty 150), which has a weaker

pH effect than the normal pH injection grout used in the area of ONK-KR4 (Ultrafin 16

+ GroutAid + SP40). Aside from differences in the pH of contacting water, the influence

of cement can also be seen in the NH4+, DIC, alkalinity, K+ and Ca2+ results of several

samples.

The influence of both grouting cements have disappeared, as seen in pH values less than

8.2 in ONK-KR3 since 2013, and pH values below 8.0 reached in ONK-KR4 in 2017 and

in 2018. The trends of K+, Ca2+ and NH4+ concentrations (Figure 5-11c, d and f) have

been consistent with the measured pH in drillholes showing cement-water interaction as

evidenced by high pH, which indicates that relatively high proportions of these cations

have been dissolved from cement grouting. The opposite behaviour of Mg2+ content

suggests some initial fixation of Mg2+ within the cement, or the possible formation of Mg-

hydroxide (brucite) surface precipitate.

130

The clear diluting trend of Mg2+ (Figure 5-9e) and Cl- (Figure 5-10a) in ONK-PVA2

(yellow diamond) has been ongoing during the whole monitoring period, and also Na+

and Ca2+ concentrations (Figure 5-9b and d) have started to again decline during the two

last years, after a few years more stable phase.

Apart from ONK-PVA2, the chloride results (Figure 5-10a) in general have shown a

slightly decreasing or stable long-term behaviour. However, the slow increase in Cl-

concentration in ONK-KR4 occurring since 2013 exhibited a slightly more noticeable

increase in 2018.

131

Figure 5-9. a) pH, b) Na+, c) K+, d) Ca2+, e) Mg2+ and f) NH4

+ as a function of the

sampling date in the upper part (0-100 m) of ONKALO.

Sulfate concentrations have been increasing in ONK-KR1‒3 and ONK-PVA1 since 2013

(Figure 5-10b, similar observations at surface level, see Chapter 3.6.3). The increase in

SO42- content has been most notable in ONK-KR1, although the increase was not as

marked in 2018 as seen in previous years. However since 2014, the sulfate concentration

has more than doubled in ONK-KR1. In ONK-PVA3, the SO42- concentration has been

rather variable. In 2018, the sulfate concentration was again in decline after a couple of

years’ increase. The SO42- concentration has recently been stable in ONK-KR4 and ONK-

PVA2. The SO4-Cl relation above the seawater dilution line of the brackish/HCO3 type

132

samples (Appendix 20, Figure A20-1 a) suggests a source of SO42- other than the marine

water origin, typical in brackish HCO3 and SO4 type groundwaters. One possible source

has been considered to be crushed rocks from the underground tunnels used at the

construction sites on ground level. Sulfide minerals in rocks can be oxidised and form

sulfate in the infiltrated water.

The DIC results (Figure 5-10c) were slightly increasing as a function of time in all

sampling points until 2013. Since 2013, the gradual increase has been ongoing in ONK-

PVA2 and in ONK-KR4, whereas in ONK-KR1 the concentration has decreased. In

ONK-PVA1, ONK-KR2 and ONK-KR3 the observed DIC concentrations have been

rather stable, whereas DIC in ONK-PVA3 returned to the level observed in 2016 after a

noticeable increase seen in 2017. Increased dissolved carbonate had earlier been observed

in similar conditions in the Äspö Hard Rock Laboratory (Pitkänen et al. 1999b) and was

considered to be the result of microbial activation in the near surface groundwater system

with increased infiltration, when organic carbon is oxidised to CO2 which dissociates to

HCO3- and CO3

2- depending on pH conditions. The stable DIC as well as the low DOC

content (Figure 5-10d) in ONK-PVA2 most likely result from the low transmissivity of

groundwater station and weak connection to the near surface aquifer. In general, the DIC

concentrations, pH and calcium concentrations have been relatively stable in all of these

sampling points during recent years, thus indicating an equilibrium in calcite dissolution

and precipitation.

The DOC results (Figure 5-10d) have generally exhibited stable behaviour. Some high

DOC contents have been measured over the years from ONK-KR1, ONK-KR2 (and

ONK-PVA1), but they have been regarded as unreliable and omitted from the data. In

2018, the DOC in ONK-KR1‒ONK-KR4 were in a slight decline, whereas the DOC in

ONK-PVA3 showed an opposite behaviour compared to the DIC content, and increased

to a value of 7.6, which is the level most recently observed in 2014.

Sulfide concentrations (Figure 5-10e) have remained low (≤0.6 mg/L) throughout the

monitoring period in all sampling points in the upper part of ONKALO.

In ONK-KR4, the alkalinity has decreased with time, consistent with the decrease in pH

and decreasing OH- concentration. Stable, low DIC content (Figure 5-10c) in ONK-KR4

may be due to calcite mineral precipitation on or near cement grout (Posiva 2013).

However, the DIC content in ONK-KR4 has been slowly increasing since 2007 along

with a steady decrease in Ca2+ content and solution pH. The observed increase in DIC

could be an artefact of declining CO2 loss to diffusion during sampling, due, e.g. to

increasing yield and/or improved sampling protocols. Continued monitoring, including

field testing of sample pH, should be undertaken to elucidate the process(es) causing these

changes to ONK-KR4 water chemical composition.

133

Figure 5-10. a) Cl-, b) SO4

2-, c) DIC, d) DOC e) HS- (detection limit 0.02 mg/L) and f)

Alktot as a function of the sampling date in the upper part (0−100 m) of ONKALO. The

results less than the limit of detection are shown as zero in e). Sulfide was analysed for

ONK-KR1–KR4 only in 2005.

134

ONK-PVA4–ONK-PVA11 monitor chemical changes below -100 m depth (Figure 5-1).

ONK-PVA4, ONK-PVA5 and ONK-PVA8 are situated between HZ19 and HZ20 zones.

This area is characterised by brackish SO4-type groundwater in highly transmissive

fractures, and by brackish Cl-type groundwater in poorly transmissive bedrock, i.e.,

where these groundwater stations have been drilled. The rest of the groundwater stations

are below HZ20, where brackish Cl- and saline-type groundwaters are typical. ONK-

PVA9 (-426 masl), ONK-PVA11 (-437 masl) and ONK-KR16 (-422 masl) are situated

at repository level. The samples collected from groundwater stations ONK-PVA4–ONK-

PVA10 and samples from ONK-KR15_75 are shown as a function of time in Figure 5-11

and Figure 5-12.

The salinity (Na+, Ca2+, Cl-) of groundwaters from ONK-PVA4 (light green diamond),

ONK-PVA5 (blue triangle) and ONK-PVA8 (light blue triangle) has been stable

throughout the monitoring period (Figure 5-11b, d and Figure 5-12a). However, the

sulfate concentrations had earlier an increasing trend in ONK-PVA5 and ONK-PVA8

(Figure 5-12b) due to the hydrological connection to OL-BFZ100, which drew SO4-rich

groundwater from above into these groundwater stations. Recently, the increase in

sulfates in these groundwater stations has stabilised. The sulfate level in ONK-PVA4 has

remained stable throughout the monitoring period. The sulfate input in ONK-PVA5 and

ONK-PVA8 has launched sulfide production (Figure 5-12e). ONK-PVA5 has had a

relatively stable low sulfide content since the initiation of monitoring, but exceeded the

monitoring action limit for sulfide concentration (1.0 mg/L at this depth) in 2018 with

values of 1.1 and 1.2 mg/L. Much higher sulfide concentrations have been measured in

ONK-PVA8: the HS- concentration was 2.0–2.5 mg/L during 2010–2014, and has since

increased to the current level of approximately 5 mg/L (the highest concentration,

5.3 mg/L, was measured in January 2018).

The groundwater composition in ONK-PVA6 (green triangle) had been changing during

2009–2013, which can be seen as a decrease in Na+, Ca2+ and Cl- concentrations and as

an increase in SO42- and in DIC concentration. These changes were caused by the flow of

SO4-rich groundwater from the upper part via a connection of OL-BFZ045, which is

connected to HZ20B locating above ONK-PVA6. However, the change in composition

ceased in 2014 and the composition has remained stable, or even started reversing since.

The sulfide concentration was less than or near the detection limit in ONK-PVA6 at the

beginning of the monitoring period, but after sufficient mixing with sulfate-rich water,

low sulfide concentrations have been measured (since 2014). In 2018, the measured

sulfide concentrations were 0.30 and 0.59 mg/L in January and November, respectively.

ONK-PVA7 (red triangle) is one of the drillholes monitoring the effect of cement grouting

on groundwater composition. The majority of the ion concentrations (Na+, K+, Ca2+ and

Cl-) have shown no change, but the sulfate concentration has increased notably since the

monitoring started (Figure 5-12b), reaching a peak value of 307 mg/L in 2017. In 2018,

the sulfate concentration was slightly lower, at 302 mg/L. Magnesium concentration has

also shown an increasing trend during the monitoring period (Figure 5-11e). The

hydrological connection to HZ056 is causing the drawdown of SO4-rich groundwater

from the upper part into the groundwater station. The sulfate and magnesium

concentrations have been stabilising during recent years.

135

The monitoring of ONK-PVA9 (purple square) started in 2011. The sampling point

showed a slow dilution with SO4-rich groundwater from OL-BFZ045 (and/or HZ056)

until the end of 2013. Then the nearby drillhole ONK-KR16, which also intersects OL-

BFZ045, was drilled in November 2013 and salinity started to strongly increase in ONK-

PVA9 (Figure 5-12a) while at the same time sulfate concentration decreased (Figure

5-12b). The rapid increase of salinity and decrease of sulfate concentration stopped in

June 2014 and started to return to the earlier level. In August 2015, the pilot hole ONK-

PH28 was drilled intersecting OL-BFZ045 after which the salinity in ONK-PVA9 started

increasing again and sulfate concentration respectively started decreasing, reaching a

quite stable situation until the first measurement of 2018 (in January). The second sample

taken in 2018 (in November) showed again a clear dilution with SO4-rich groundwater,

which also resulted in an increase in the sulfide concentration (Figure 5-12e), which

reached 1.1 mg/L. BFZ045 was penetrated by tunnel AJYH17 between these samplings,

which again demonstrates the sensitivity of ONK-PVA9 to react to new intersections of

the fracture zone.

The monitoring of ONK-PVA10 (orange round) started in 2012. The groundwater station

is intersecting a local hydraulic zone and leakages from this zone in the underground

tunnels have been seen as a reason for the strong decrease in hydraulic head observed in

monitoring sections OL-KR3 L1–L5 and OL-KR39 L1–L3 (Vaittinen et al. 2014, 2015).

The brittle fault zone OL-BFZ130b has been interpreted to the underground tunnels

intersection. Despite the evident hydraulic transient, chemical results in ONK-PVA10

have been stable with minor variation. However, a notable decrease in pH, from 8.0 to

7.3 (Figure 5-11a), was observed between the first and second values measured in 2018.

The sulfate and sulfide levels have been below or near the detection limit (Figure 5-12b

and e) as typical for groundwaters at similar depths in baseline conditions.

The decrease in salinity in ONK-KR15_75 (round with purple stripes) has stabilised

(Figure 5-11b, d and Figure 5-12a), having TDS of 8.5 g/L for the past two years. Similar

to ONK-PVA10, the sulfate and sulfide concentrations were less than or approaching the

limit of detection, as was typical for groundwaters at similar depths (Figure 5-12b and e).

136


+ (detection limit

0.02 mg/L) as a function of sampling date in the deeper part (>100 m) of ONKALO. The

results less than the limit of detection are shown as zero in f).

137

Figure 5-12. a) Cl-, b) SO4

2- (detection limit 0.1 mg/L), c) DIC (detection limit 0.4 mg/L),

d) DOC (detection limit 0.3 mg/L), e) HS- (detection limit 0.02 mg/L) and f) Fe2+

(detection limit 0.01 mg/L) as a function of sampling date in the deeper portion (>100 m)

of ONKALO. HS- and Fe2+ were determined for ONK-PVA7 for the first time in 2018.

Results less than the respective limit of detection are shown as zero in b), c), d), e) and

f).

138

The samples collected from ONK-KR16_14 and ONK-PVA11_11 are shown as a

function of time in Figure 5-13 and Figure 5-14. In the vertical OL-BFZ045, groundwater

flow and chemistry seem to be strongly responsive to new drillings intersecting the

fracture, as was seen in changes in ONK-PVA9 in previous figures and can be seen in

ONK-KR16 by Figure 5-13 and Figure 5-14. The drilling of in late 2013 reflected to the

chemistry in ONK-PVA9 as discussed earlier. On the other hand, the drilling of ONK-

PH28 in August – September 2015 reflected on the ONK-KR16_14 (triangle with blue

stripes) chemistry as a decrease in salinity (Figure 5-14a) and increase in sulfate

concentration (Figure 5-14b), the opposite of changes observed in ONK-PVA9. The

salinity increase and sulfate decrease in ONK-KR16_14 stopped in 2016 and remained

stable in the 2018 monitoring. The sulfide concentration, on the other hand, continued to

increase in 2018, reaching a peak value of 2.4 mg/L in 2018.

ONK-PVA11 was drilled in February 2014 and sampled for the first time later in that

year. Since then, the drillhole was separated in two sampling sections, ONK-PVA11_11

and ONK-PVA11_14, of which only the former one was monitored in 2018. Salinity in

ONK-PVA11_11 (light blue square) was mainly stable or in slight decrease in 2018, as

seen in the concentrations of Na+, K+ and Cl- (Figure 5-13b, c and Figure 5-14a).

However, the concentrations of Ca2+ and Mg2+ continued to increase (Figure 5-13d, e).

The groundwater type was saline with a TDS value of approximately 21 g/L (Appendix

17). Sulfate and sulfide concentrations were near or below the limit of detection (Figure

5-14b and e). The ammonium concentration continued to increase rapidly as observed for

the first time in 2017, though still in low concentration, reaching 0.15 mg/L in 2018. It is

possible that the observed increase in ammonium concentration is related to construction

works in the area of ONK-PVA11.

139


+ (detection limit

0.02 mg/L) as a function of sampling date in the deeper part (>100 m) of ONKALO in

sections where sampling started after 2014. The results below the detection limit are

shown as zeros in f).

140

Figure 5-14. a) Cl, b) SO4 (detection limit 0.1 mg/L), c) DIC (detection limit 0.4 mg/L),

d) DOC (detection limit 0.3 mg/L), e) HS- (detection limit 0.02 mg/L) and f) Fe2+

(detection limit 0.01 mg/L) as a function of sampling date in deeper part (>100 m) of

ONKALO in sections where sampling started after 2014. The results below the detection

limit are shown as zeros in b), c), d), e) and f).

141

5.4.1 Isotopes

The δ2H-, δ18O- and 3H -isotopic results of monitoring groundwater samples describe

potential source waters and changes in them due to mixing. The variation in isotopic

compositions (Figure 5-15a) indicates mixing between modern meteoric recharge (data

points on GMWL), seawater and Korvensuo water (shift below GMWL and towards

heavier isotopic composition) and cold climate water (shift to lighter isotopic

composition). A tritium content lower by a few TUs (Figure 5-15b) than in shallow

groundwater data (Section 3.7.2, Figure 3-28) generally suggests a somewhat longer

mean residence time, which in most cases mainly results from the mixing of older

groundwater components in these underground tunnel monitoring points.

The time series of isotope results of the samples from the upper 100 m depth of the

underground tunnels were relatively stable in 2018 (Figure 5-15b-d). Results of isotopic

assay for ONK-PVA12_11_1218 and ONK-PVA13_14_1218 were not available by the

time this report was being finalise and therefore are not seen in Figure 5-15. The δ2H and

δ18O results from ONK-KR2 and ONK-PVA3 have remained approximately at the same

level throughout the monitoring period, which is roughly the mean value of meteoric

recharge at Olkiluoto. ONK-KR1, in turn, has shown a slight upward trend in the

deuterium results (Figure 5-15c, diamond with red stripes). The trend is not so clear in 18O data (Figure 5-15d), but the result in 2018 is clearly higher than that observed in

previous year.

The stable isotopic composition of ONK-PVA1 was roughly representing the current

mean meteoric water composition until it became heavier in 2011 (Figure 5-15c, d, red

diamond). The heavier isotope results during 2011–2013 was interpreted as a result of

minor input of Korvensuo water. In 2018, the stable isotope results for ONK-PVA1

showed again a clear increase.

The stable isotopic composition and tritium in ONK-PVA2 have all the time shown lower

values than the other monitoring points (Figure 5-15a-d, yellow diamond), which

indicates some input of older and colder climate groundwater component in the

groundwater station, i.e., probably a mixture of Littorina sea-water and glacial melt

preserved in low transmissivity fractures and matrix pores.

The increasing trend in deuterium and δ18O in ONK-KR3 and ONK-KR4 since 2006 was

stabilised in 2009. The tendency towards heavier isotopic compositions during this period

was interpreted to be an outcome of water input from Korvensuo reservoir (Pitkänen et

al. 2008a, 2009, Penttinen et al. 2011, 2013). The development froze in 2010 suggesting

that the proportion of water derived from the reservoir became even and the flow field

reached a steady state. The mixing fraction of Korvensuo water seems to be 30–40% to

reach the shift from GMWL observable in ONK-KR4 results and the general level of

stable isotopes in meteoric groundwaters at the site, e.g., ONK-KR1 and ONK-KR2 prior

to 2015. In 2018, δ2H and δ18O results of ONK-KR3 and ONK-KR4 were approaching

each other, i.e. stable isotopes of ONK-KR3 were slightly increasing and those of ONK-

KR4 were in turn decreasing.

142

Figure 5-15. δ2H and δ18O isotopic results of the ONKALO samples as a) δ2H vs. δ18O

plot, b) 3H time series, c) δ2H time series and d) δ18O time series. Global meteoric water

line (GMWL) in a) after Craig (1961).

Contrary to the monitoring points in upper parts of the underground tunnels, the isotopic

results from monitoring points deeper than -100 m indicate mixing of old water

components (negligible tritium) of meteoric water with sea water (shift below GMWL),

saline water (shift above GMWL) and clear cold climate water (shift to light isotopic

composition) (Figure 5-16). The stable isotopic compositions of the monitoring samples

mainly corresponded with the typical brackish Cl-, saline- and brackish SO4-type

groundwaters at Olkiluoto.

The light isotopic composition in samples from ONK-PVA4 and ONK-PVA5 (Figure

5-16a, bright green diamond and blue triangle, respectively) indicated a glacial melt water

fraction in these groundwaters according to the baseline data (Posiva 2013, Chapter 7.3).

The fraction decreased with time in ONK-PVA5, but recent years show stable behaviour

(Figure 5-16c-d).

143

In ONK-PVA6, the general shift towards heavier 18O values (Figure 5-16c-d, green

triangle), with partial seasonal variation, has been ongoing during the whole monitoring

period coinciding with the observed sulfate trend (Figure 5-12b). Similar observations

have been made in ONK-PVA7. Mixing with SO42- rich groundwaters is the reason for

the shift towards less negative 18O values. ONK-PVA6, ONK-PVA7 and ONK-PVA8 as

plotting below the GMWL (Figure 5-16a) have shown a clear signal of some seawater

derived groundwater.

The samples from ONK-PVA9, ONK-KR16_14, ONK-PVA11_11 and ONK-PH21,

ONK-PH22 and ONK-CTPH5.1 plotted slightly above the GMWL as typical for the most

dilute saline groundwaters (Figure 5-16a). Slightly depleted stable isotopes in ONK-

PVA10 and ONK-KR15_75 suggest either minor glacial fraction in groundwater or more

probably typical subglacial signature that dominated before glacial melt water infiltration

mixed with brackish groundwater in Olkiluoto (Posiva 2013, Section 7.3.5).

The 3H results (Figure 5-16b) have mainly been below the detection limit (the detection

limit has varied between 0.3 and 0.9) and in most cases did not indicate young meteoric

water infiltration in the deep groundwater system in the underground tunnels. However,

in recent years tritium has been detected from ONK-PVA7, ONK-KR15_75 and ONK-

KR16_14.

144

Figure 5-16. δ2H and δ18O isotopic results of the ONKALO samples as a) δ2H vs. δ18O

plot, b) 3H time series, c) δ2H time series and d) δ18O time series. Global meteoric water

line (GMWL) in a) after Craig (1961). Values below the detection limit of 3H analysis

(0.2 TU) are shown as zero in b).

5.4.2 Leaking fractures and wall channel monitoring in the underground tunnels

The main part of leaking fractures on the tunnel wall or ceiling are channelled with metal

plates (wall, ONK-KOU) or plastic plates and tubes (ceiling, ONK-KER). Some of the

sampling codes have changed from ONK-RV to ONK-KER and ONK-KOU during the

monitoring period. The number in the local collector sample code in the following figures

refers to the chainage of the installation spot in the tunnel.

145

The results from leaking fractures (water leakage from walls or roof) in the underground

tunnels have shown that bicarbonate-rich groundwaters with relatively low salinity are

observed in the first 3400 m in the underground tunnel (320 m in depth). Groundwaters

with higher salinity, lower DIC and lower sulfate contents have been observed beyond

the chainage 3900 m (z ~ -380 masl). The strong dilution in hydraulic zone HZ20 has

been observed in the leaking water composition between the chainages 3000 and 3500 m.

In 2018, samples were collected from six collectors from walls (ONK-KOU), two roof

water collectors (ONK-KER) and three leaking fractures (ONK-RV). The data for

fresh/brackish HCO3 classified samples (chainages 230–3321 m) collected so far from

most sampling locations is presented in Figure 5-17. ONK-RV605, ONK-RV964 and

ONK-RV3170 are omitted from the figure due to being sampled only two times, of which

latest occurred in 2010. The sample code ONK-KER3155 had changed to ONK-RV3178

in 2015 after the collector was removed due to construction work. Water has been

collected directly from the tunnel wall since then, but samples still represent the same

leaking fracture. The data for more saline samples (beyond chainage 3900 m) is presented

in Figure 5-18. The majority of the leaking water samples represent fresh/brackish HCO3-

type waters. Only ONK-KOU3986 and ONK-RV4385 were classified as brackish Cl-

type waters.

The long term slow dilution in chloride content slowly continued in ONK-RV645 (light

blue), whereas in ONK-KOU230 (dark blue) and ONK-KOU777A (green), the dilution

has stopped (Figure 5-17a). The sulfate content (Figure 5-17b) in ONK-KOU230 slightly

increased after a stable period since 2014, as it did in ONK-RV645, where sulfates

continued the increasing trend observed since 2009. In ONK-KOU777A, the

concentration of sulfate decreased after an increase observed since 2012. Dissolved

inorganic carbon had an increasing trend in these sampling locations at the beginning of

the monitoring period, but the recent results have been stable (Figure 5-17c). pH of ONK-

KOU777A has been decreasing in the last three measurements (Figure 5-13d).

Strong dilution has been observed in the area of the fracture zones HZ20A+B in the

underground tunnels (ONK-KOU3019, ONK-KOU3131, ONK-RV3178 and ONK-

KER3321) (Figure 5-1, Figure 5-5). Chloride concentration has been low since the first

sampling in 2011 when compared to baseline data at corresponding depth. Chloride

concentration in baseline conditions was roughly 4000−5000 mg/L (Figure 5-6a),

whereas observed concentration has been between 500 and 2000 mg/L in ONK-

KOU3019 (yellow), ONK-KOU3131 (grey), ONK-RV3178 (pink) and ONK-KER3321

(purple) as seen in Figure 5-17a. The notable drop in the chloride concentration observed

in ONK-RV3178 in 2017 continued in the first part of 2018, reaching a level as low as

350 mg/L. Probable reason for this behaviour is the dilution of HZ20 salinity with HZ19

groundwater, which occurred due to open drillhole phase of OL-KR28 during Oct 2017‒

Jun 2018. OL-KR28 is again open since October 2018. In the latest sampling of ONK-

RV3178 in November, the chloride content had recovered to 680 mg/L. The chloride

concentration in ONK-KER3321 has also been quite unstable. Since 2016, the chloride

concentration has showed more or less decreasing trend, and this continued in 2018.

146

Monitoring in ONK-KER900 started in 2016, and it the increasing trend in sulfate

concentration turned into a decline in 2018 (lilac, Figure 5-17b). The sampling point is

located in the area of fracture zone HZ19A.

Figure 5-17. Time series of a) Cl, b) SO4, c) DIC and d) pH for leaking water samples

from the underground tunnels (chainages 230–3321 m). ONK-RV605, ONK-RV964 and

ONK-RV3170 not included as latest data from these points are from 2010.

The sulfate content has almost been absent in ONK-KOU3986, showed in orange in

Figure 5-18b, which is typical for groundwaters at similar depths. However, the sulfate

concentration slightly increased during 2015−2017, and stabilised in 2018. The pH in

ONK-KOU3986 decreased in 2012 and the lower level has remained since then, reaching

a new lowest level (7.1) in 2018. The higher value in 2011 was due to grout contamination

and the effect has diminished since.

The deepest leaking fracture ONK-RV4385, showed yellow in Figure 5-18, initially

represented saline groundwaters, but has diluted strongly and been classified as brackish

Cl type water in recent years. Since 2016, the chloride concentration has been rather stable

(Figure 5-18a).

147

The increase in SO4 concentration in ONK-RV4385 stopped in 2013–2014, but continued

again in 2015 and 2016. Similar observations have been made nearby in ONK-PVA9

(Figure 5-12b), which intersects the same vertical hydraulic fracture zone (OL-BFZ045)

as ONK-RV4385. The results suggest that water from above has flown deeper via OL-

BFZ045 during 2013−2015. In 2016, the results differed with ONK-PVA9 having a stable

sulfate content and ONK-RV4385 having an increasing sulfate trend. The high pH result

(9.5) from 2012 had declined to 7.3 in 2014 and since then has stabilised at 7.1‒7.2 in the

measurements of the past two years. This suggests that the grouting contamination is no

longer affecting the pH (Figure 5-18d).

Figure 5-18. Time series of a) Cl, b) SO4, c) DIC and d) pH for leaking water samples

from the underground tunnels (beyond chainage 3900 m).

The flow rates from the fractures were measured intensively in 2006 and since then

approximately once per month along with electrical conductivity (EC) and pH. The flow,

pH and EC data since the fracture monitoring started in 2006 are presented in Figure 5-19,

Figure 5-20 and Figure 5-21, respectively. Transmissivity calculations are presented in

Appendix 21.

The flow rates remained at approximately the same levels as previously observed (Figure

5-19). The flow rate in ONK-KOU230 has been steadily decreasing since 2008. ONK-

148

KOU570B (bright green) has been dry since the end of 2016, thus pH and EC could not

be determined for this sampling point since then.

Figure 5-19. Time series of flow rates a) in a scale of 0–80 L/h, and b) in a scale of 0–10

L/h for ONK-KOU and ONK-KER samples.

Regarding the pH, the results of the year 2018 were mainly unchanged, except for the

decline in pH readings in several sampling points in March (Figure 5-20 a).

149

The majority of the pH values correlated with the values of baseline data. Grouting

cement contamination initially increased the pH in ONK-KOU570A, ONK-KOU570B

and ONK-KOU3986, but the pH in these sampling points have reached the normal level

with time. The pH in ONK-KOU3986 has been somewhat variable, ranging between 7.0

and 8.0 in 2018.

Figure 5-20. Time series of pH results for ONK-KOU and ONK-KER samples a) above

the depth of 100 m and b) below the depth of 100 m.

150

The salinity of baseline samples as estimated from electrical conductivity values were

between 1.5 and 3.0 g/L in the EC region of 0.3–0.6 S/m, and less than 1 g/L in the

sampling points with EC below 0.2 S/m. The high EC (around 1.5 S/m) in ONK-

KOU3986 corresponds with the salinity of around 9 g/L. As seen in Figure 5-21a, the EC

in ONK-KER3321 (blue diamond) has been decreasing the last two years after an increase

observed in 2016. ONK-KOU3019 (brown diamond) has shown a gradual decrease in EC

since 2012, but in 2018 the decrease in EC was more rapid, corresponding to the observed

decrease in Cl- content as seen in Figure 5-17. The EC values of ONK-KOU230

correspond with a salinity value less than 2 g/L representing a typical fresh/brackish

HCO3-type water. The sampling point has had a slightly decreasing trend in EC values

over the monitoring period, but in 2017 and 2018 the values have been again slightly

higher than in previous years. ONK-KOU3986 (pink circle) has mainly had stable EC

values as represented in Figure 5-21a.

151

Figure 5-21. Time series of EC a) in a scale of 0-1.6 S/m, and b) in a scale of 0-0.20 S/m

for ONK-KOU and ONK-KER samples.

The high variation of EC values in ONK-KOU570B were due to extremely low flow and

thus inadequate sample amounts. ONK-KOU430, ONK-KOU570A, ONK-

KOU777A&B and ONK-KER900 have typical fresh/brackish HCO3 type EC values

below 0.2 S/m (Figure 5-21b).

152

5.5 Dissolved gases in groundwater samples

A total of sixteen (16) gas samples were collected and analysed from nine different

drillholes in 2018 (Appendix 22). Thirteen (13) of the samples were from deep drillholes,

and three gas samples were taken from the underground tunnels in 2018. All results are

presented herein as gas volume per litre of water under standard temperature and pressure

(STP). The gas samples were collected either in pressurised vessels at an in situ depth

using the PAVE technique (3 samples, Hatanpää et al. 2005) or PFL WS2 (Posiva Flow

Log Groundwater Sampler, 4 samples) method, or with a simple gas collector (SWA)

from the ground surface (9 samples, Lahdenperä, 2006).

Reference analyses have been performed for most of the samples taken with PAVE. A

significant uncertainty that can decrease the reliability of gas results with PAVE method

is the incomplete filling of sample vessels with groundwater (Gascoyne 2005, Pitkänen

& Partamies 2007, Pedersen 2008). Incomplete filling may cause fractionation of gases

and distortion of both the relative composition and overall content of individual gases,

particularly of the light less soluble gases (H2, He, N2) in CH4-rich samples. A filling

factor of greater than 0.7 is recommended in order for collected gas data to be utilised in

the interpretation of results.

Two of the sampling points presented had two results from different pressure vessels. The

degree of filling presented in Figure 5-22a shows that all PAVE samples taken in 2018

achieved a filling factor greater than 0.7. When results of both duplicate samples collected

using different pressure vessels had an acceptable filling factor, the sample with the

greater filling factor was considered to be more representative.

Another notable uncertainty is the leakage of back-pressure gas in sampling vessels. In

the 2018 sample collection, neon was used as the back-fill gas for all PAVE sampling

vessels. However, no neon contamination was observed in the samples in 2018.

Hydrogeochemical results indicated prevailing anaerobic conditions in bedrock

groundwaters. Regarding the gas analyses, Hatanpää et al. (2005) identified the potential

for air contamination during sampling and, in particular, during the laboratory treatment

of samples. Therefore, the results reported herein have been corrected for air

contamination assuming that all O2 measured from a single sample is due to

contamination during sampling and laboratory measurements. The analysed O2 content

of the groundwater gas samples collected in 2018 (Figure 2-1Figure 5-22) varied from

0.07 mL/L (OL-KR20_410, depth -315 m) to 7.82 mL/L (OL-KR58_559, depth -528 m).

Most of the groundwater samples taken by PAVE or SWA had an O2 content of less than

1.0 mL/L, whereas those taken by PFL all had O2 content higher than 1.0 mL/L.

153

Figure 5-22. Depth distribution of a) filling factor and b) O2 (mL/L) for monitoring

samples in 2018. The acceptance limit of filling factor (0.7) is shown by the vertical blue

line in a).

The hydrogen, helium, nitrogen and methane depth distributions of the accepted and most

valid results for each sampling point are shown in Figure 5-23. The most dominant gases

at Olkiluoto in previous studies were nitrogen at depths above 300 m, and methane with

higher hydrocarbons below 300 masl (Pitkänen & Partamies 2007). Dissolved gas data

from 2018 groundwater samples are consistent with this general trend (although most of

the samples were collected from below -300 masl), exhibiting clear CH4 dominance

below 300 masl (Figure 5-23). Methane is a significant buffer to redox reactions at great

depths.

The hydrogen content of the 2018 samples followed well the baseline trend of increasing

content with depth (Figure 5-23a). The hydrogen content of most SWA samples and all

PAVE samples taken in 2018 was below the detection limit (Appendix 22). The highest

H2 content was recorded for OL-KR58_1075 at a depth of -980 m (2.4 mL/L). The SWA-

sampling method has been considered not suitable for light easily degassing hydrogen,

which most probably is lost during pumping and not gathered into the SWA vessel.

The dissolved helium contents (Figure 5-23b) followed the baseline data in most of the

samples taken in 2018, while most of the SWA samples between -400 masl and -800 masl

had clearly lower He content compared to the baseline data. The greatest He content was

recorded for OL-KR58_742 at a depth of -695 m (29.3 mL/L). In addition, helium can be

partly degassed during pumping, and therefore the SWA method is not able to collect all

helium gas from pumped groundwater.

154

The nitrogen concentrations measured in 2018 generally followed the baseline data

(Figure 5-23c), apart from sample OL-KR40_600 (-541 masl) taken with the SWA

method. In addition, the brackish Cl samples, also taken with the SWA, have slightly

lower nitrogen content than baseline samples at similar depths. The highest nitrogen

content was measured from OL-KR40_1005 (223 mL/L) at -890 masl using SWA

technique.

The methane content of the gas samples analysed in 2018 generally followed the same

trend as baseline gas data (Figure 5-23d). Only OL-KR40_600 (-541 masl) has lower

methane content than expected based upon depth. The highest methane content

(1070 mL/L) was measured from OL-KR40_1005 (-890 masl) by the SWA method.

155

Figure 5-23. Depth distribution of measured a) hydrogen, b) helium, c) nitrogen and d)

methane for baseline and 2018 monitoring samples.

The 2018 monitoring results of dissolved gases from deep drillholes using the PAVE or

PFL WS2 techniques corresponded well with the earlier data from the Olkiluoto site

(samples without a circle in Figure 5-22 and Figure 5-23). Some of the samples collected

using the SWA technique yielded lower dissolved gas values, largely because the method

may not entirely extract the gas content of sample groundwaters. Use of the SWA

technique should be carefully considered in the future monitoring strategies.

156

Changes in the dissolved gas content of groundwater may indicate upconing of saline

groundwater (migration and re-dissolution of N2, He and CH4). The dissolved gas data of

2018 did not indicate such a development; however, it is worth noting that gases measured

from sampling sections with multi-packers are carried out only with the SWA-technique,

which is not totally comparable with baseline PAVE samples.

157

6 SUMMARY AND CONCLUSIONS

6.1 Deep groundwater

Twenty-six deep groundwater samplings from the ground surface were carried out during

the year 2018 in ten different drillholes (Appendix 14). The samples were taken either

from drillholes where permanent multi packer systems had been installed (18 samples),

from open drillholes with PAVE down-hole sampling equipment (three samples) or with

PFL WS2 (five samples). Sixty-seven groundwater samples from several different

locations (19 from groundwater stations, nine from drillholes, 13 samples from pilot

holes, seven from leaking fractures, and 19 from water collectors) were collected from

the underground tunnels during the year 2018 (Appendix 17).

Three of the groundwater samples from deep drillholes collected in 2018 were classified

as baseline samples (Appendix 13). Four deep groundwater samples collected in 2018

had a significant amount (>1%) of drilling/flushing water remaining.

The results from the ground surface based monitoring campaign in 2018 showed some

indications of changes in groundwater composition, which in many cases were most

likely caused by the high hydraulic gradient of the underground tunnels. Elevated sulfide

concentrations were observed in a few sampling locations in 2018, consistent with

observations from previous years.

The highest sulfide concentration in 2018 was measured in OL-KR46_570_0318, which

is also monitored within the Sulfide project (a microbiological sub-project within the

MetWeb project). The concentration remained at the same level as observed in recent

years in this drillhole, and began to decline in the two latter samplings in 2018. Activation

of microbial SO42- reduction has been interpreted as a source for the observed sulfides.

Other samples with elevated sulfide content in 2018 were OL-KR45_T606_0818, the

three samples from OL-KR13_T405 and OL-KR4_T351_0618 (intersects HZ20).

In 2018, a dilution effect was again observed via the hydraulic zone HZ20, especially in

OL-KR4_T351, where the interpreted water type changed from brackish Cl water to

fresh/brackish HCO3 water in 2018. Dilution in the same hydraulic zone, albeit less

marked, was observed in the underground tunnel wall and roof monitoring in 2018.

The pH of groundwater samples collected in 2018 were generally consistent with baseline

data and results from the previous year’s investigation, with 2018 groundwater pH values

ranging from 6.2 to 9.2. The measured pH of four samples exceeded the equilibrium pH

of 8.3 observed in calcite (CaCO3)-water systems open to the atmosphere (air-water-

calcium carbonate systems), and is reflected in the calculated SIcalcite values for the 2018

groundwater samples. pH in ONK-KOU570A, ONK-KOU570B and ONK-KOU3986,

which was initially increased by grouting cement contamination, have reached the normal

level with time.

The results of the monitoring programme in the underground tunnels and facilities during

the year 2018 in general behaved predictably and remained unchanged or were in a state

of slow change. Two new groundwater monitoring stations, ONK-PVA12 and ONK-

158

PVA13 were added to the monitoring programme in 2018. In addition, the results of

central tunnel pilot hole ONK-CTPH5.1 were analysed and presented within the

monitoring programme. The tunnel will however be excavated soon. Five samples

(Appendix 16) were classified as baseline samples, with the results corresponding well to

the previous view of the baseline conditions at repository depth. None of the samples

collected from the underground tunnels were classified as class E (Appendix 16).

The long-term dilution in ONK-PVA2 remained ongoing in 2018. The sulfate

concentration in ONK-KR1 continued an increasing trend, although the increase was

more gradual compared to previous years. A slight increase in SO42- content was also

noticeable in ONK-KR2 and ONK-KR3, while ONK-PVA1‒PVA2 and ONK-KR4 were

stable. In ONK-PVA3 the sulfate concentration decreased back to the level observed two

years earlier. Sulfide concentrations remained low in sampling points located at the upper

part (above -100 masl) of the underground tunnels and facilities.

The salinity in ONK-PVA4, ONK-PVA5 and ONK-PVA8 has remained stable during

recent years. The sulfate concentrations in all sampling points in the deeper part of the

underground tunnels were stabilised approximately to the level of the previous year, or

slightly decreasing. Only ONK-PVA9 showed an increase in the sulfate concentration

during 2018, along with a decrease in salinity, indicating an input of brackish SO4 water.

This resulted in an increase in the sulfide concentration, which reached 1.1 mg/L. The

sampling location is connected to the vertical water conductive zone OL-BFZ045 in

which the groundwater flow and chemistry seem to be strongly responsive to new

drillings (ONK-KR16 in 2013 and ONK-PH28 in 2015) intersecting the fracture, causing

the variation observed in the past.

The slowly increasing trend in the sulfide content of ONK-PVA5 (OL-BFZ100)

continued in 2018, contrary to ONK-PVA8, wherein the sulfide concentration decreased

in 2018 after a few years’ steep increase.

6.2 Dissolved gases

A total of sixteen (16) gas samples were collected and analysed from nine different

drillholes during 2018. Thirteen (13) of the samples were from deep drillholes, and three

gas samples were taken from the underground tunnels. The gas samples were collected

using PAVE technique (three samples), SWA (nine samples) or the PFL WS2 method

(four samples) (Appendix 22).

The 2018 monitoring results of dissolved gases from deep drillholes using the PAVE and

PFL techniques corresponded well with the earlier data from the Olkiluoto site. However,

the samples collected using the SWA technique typically yielded lower dissolved gas

values, largely because the method may not entirely extract the gas contents of sample

groundwaters. Use of the SWA technique should be carefully considered in the future

monitoring strategies.

159

6.3 Shallow groundwaters

In 2018, pH (field) values varied from acidic to slightly alkaline. The common trend was

slightly lower pH values in many 2018 samples, except in OL-PVP42A (pH decreased

from 7.7 to 6.5 in 2017–2018) and in OL-PP56 L3 (from 7.6 to 6.4 during 2018) compared

to earlier results. Slightly brackish waters (TDS > 1000 mg/L) were measured in seven

samples.

High sulfate concentrations (375–700 mg/L) were still measured in OL-PP56 L1–L3, but

SO4 concentrations were slightly lower than in 2017. Also in OL-PVP17 and OL-

PVP18A, sulfate concentration was still high and fluctuated strongly between the spring

and autumn.

The changes in the chemistry of OL-PP56 during 2014–2015, which were still seen in the

2018 results, were related to the parking area construction works and the crushed rock

from ONKALO used in the construction works. OL-PP56 is also near encapsulation plant

excavation area and ONKALO, as well as OL-PVP17 and OL-PVP18A. There has been

increased construction activity in 2016–2018. Land area of OL-PVP17 was modified in

2016 which affected hydrology and groundwater chemistry, too. Also the exceptionally

dry year 2018 has been mobilising sulphur. This so called dry year effect seemed to have

been lower than expected, because precipitation stayed low until late autumn and the

mobilising effect might be stronger until next spring.

SO42- concentration was >300 mg/L in OL-PP56, OL-PVP17 and OL-PVP18A, and

further compared to the earlier results, a notable increase was observed in OL-PVP42A.

In OL-PVP42A, also high NO3 concentration was measured, and Mg as well as Na

increased notably. Increase of TDS remained low as HCO3 decreased strongly and pH

decreased to 6.5. Notable changes were also seen in OL-PVP42B, where all major ions

increased, although SO4 concentration increased only to 68 mg/L and nitrate to 0.9 mg/L.

The point locates near encapsulation plant excavation area. The effect of the crushed rock

storage area was seen clearly. The high sulfate concentrations were most probably caused

by oxidation of sulfide bearing minerals in the crushed rock used in the construction area.

The source of NO3 was most likely explosive residues from the crushed rock storage pile.

In OL-PVP40B, SO4 increased strongly in 2018 being higher than in A-tube and referred

to oxidation of sulphur rich material in shallow depths. In OL-PVP40A sulfate

concentration (together with Ca2+, HCO3- and increased Fe2+) has peaked in spring 2017

and 2018, but low concentrations at autumn samples has referred more to seasonal

fluctuation than increasing trend at sampling point. However, the seasonal fluctuation

typically increases the autumn SO4 results, so the development will be monitored.

On the basis of the isotope results of δ18O and δ2H, the waters of OL-PVP12 and OL-

PVP30 have been affected by the Korvensuo reservoir water. The possible reasons for the

observed changes in the samples 2017–2018, are the different timing of sampling in the

spring and the changes related to the Korvensuo reservoir infiltration amount and the

water level in 2017 (Vaittinen et al. 2018), which have affected the hydrology of OL-

PVP12.

160

The sampling points OL-PVP4A and OL-PP2 locate in the southern side of Olkiluodontie near or within Natura nature reserve. In both sampling points, TDS has shown a long-term increasing trend. In the basis of results 2016–2018, the increase of TDS (main ions Na+, Cl-) has stopped in both points. Br/Cl in both points has been low since the spring 2007. This referred to the effect of road salting and the timing of change in Br/Cl ratio suites with the timing of expanded road salting area. Development of salinity will be followed and the results will be compared to the environmental action limits.

On the basis of 2018 results, the seasonal fluctuation was seen in OL-PVP17, OL-

PVP18A, OL-PVP36, OL-PVP40A (peaks at spring), OL-PP36 (tendency to irregular

fluctuation), OL-PP70 (tendency to irregular fluctuation) and in OL-PP39 (strong

fluctuation). Seasonal fluctuation was mostly seen as higher TDS values in the autumns

in these points. The other observed trends are compiled in Appendix 9.

161

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M. & Vieno, T. 2006. Control of Water Inflow and Use of Cement in ONKALO after

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Documents

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