Studies of Quaternary Deposits of Investigation Trench OL-TK13 at the Olkiluoto Study Site, Eurajoki, SW Finland

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1 Working Report Studies of Quaternary Deposits of Investigation Trench OL-TK13 at the Olkiluoto Study Site, Eurajoki, SW Finland Pekka Huhta May 2007 POSIVA OY FI OLKILUOTO, FINLAND Tel Fax

2 Working Report Studies of Quaternary Deposits of Investigation Trench OL-TK13 at the Olkiluoto Study Site, Eurajoki, SW Finland Pekka Huhta Geological Survey of Finland May 2007 Base maps: National Land Survey, permission 41/MYY/07 Working Reports contain information on work in progress or pending completion. The conclusions and viewpoints presented in the report are those of author(s) and do not necessarily coincide with those of Posiva.

3 ABSTRACT The Quaternary deposits in investigation trench OL-TK13 were studied by the Geological Survey of Finland in autumn The investigations were carried out in three phases as the excavation progressed. Samples for grain size determinations were taken from vertical profiles, placed 25 m apart along the trench. The profiles extended from the soil surface down to bedrock or, if the bedrock was covered with water, to the water table. Between 6 and 7 kg of sediment was taken in a bucket with a shovel and placed in plastic bags for transport to the laboratory. The samples were first dried in the laboratory after which they were sieved. In addition, grain size distribution of the < 63 µm fraction was analyzed with the Sedigraph 5100 instrument. Sedimentological observations of the sampling profiles were documented in field by drawing on a field observation form and the profiles were photographed using a digital camera except profiles 7 and 8. In addition, the excavated section was photographed along their whole length. The length of OL-TK13 is approximately 250 m and 11 profiles were studied. The height of the profiles varied from 7.3 m to 2.3 m, with an average of 4.6 m. The till cover in OL-TK13 consist of two parts. The upper till has three layers. Surface layer is oxidized, brown sandy till, which is underlain by grayish brown intermediate layer of sandy till. This layer represents the grounwater table, which is moving up and down. The lower layer is unoxidized, grey sandy till. The thickness of the upper till varies from 2.3 to 5.5 meters. The upper till in OL-TK13 is classified as having a normal amount of cobbles and boulders with the size of the larger clasts varying from 6 to 60 cm. The edges of clasts have been eroded and rounded. The upper till has normal compactness. The lower till has been spared in bedrock depressions. Part of it s material has ascended the upper till. The lower till is compact, dark grey silty till with over 15 % of fine material (under mm). The lower till is classified as having a normal amount of cobbles and boulders with the size of the larger clasts varying from 6 to 60 cm. The edges of clasts have been eroded and rounded. Part of the clast material is weathered. The upper till in OL-TK13 was deposited in the last flow phase of the continental ice. Bedrock striations indicate that the ice moved in a WNW-ESW direction. The lower till bed has been deposited in flow phase from N to S according to one till fabric analysis. The till beds level out the bedrock topography. No signs of postglacial faults were detected either in the tills or in the exposed bedrock. The tills showed no signs of disturbance related to bedrock movements. Key words: overburden, glacial geology, till, stratigraphy, trench, grain size, Quaternary, Finland; Western Finland Province; Satakunta; Eurajoki; Olkiluoto

4 Maaperätutkimukset tutkimuskaivannossa OL-TK13 Olkiluodon alueella Eurajoella Lounais-Suomessa TIIVISTELMÄ Olkiluodon tutkimuskaivanto OL-TK13 tutkittiin syksyllä 2006 kolmessa eri vaiheessa kaivuutyön edistymisen mukaisesti. Kaivannoista otettiin lapiolla raesuuruusnäytteet 25 metrin välein vertikaalisesti läpi koko moreenipeitteen kallioon tai vesipintaan asti, jos alla oleva kallio oli veden peitossa. Näytettä otettiin ämpäriin noin 6-7 kg. Tämän jälkeen näytteet suljettiin muovisäkkeihin, joissa ne kuljetettiin laboratorioon. Laboratoriossa näytteet kuivattiin, jonka jälkeen ne seulottiin. Seulottu alle 63 mikronin osanäyte analysoitiin Sedigraph 5100-laitteella. Jokainen näytteenottoprofiili kuvattiin piirtämällä lomakkeelle ja digitaalikameralla paitsi profiilit 7 ja 8, joita ei ehditty kuvata kameralla ennen kaivannon täyttämistä näiltä kohdin. Lisäksi tutkimuskaivanto kuvattiin kameralla päästä päähän. Tutkimuskaivanto OL-TK13 pituus on noin 250 metriä ja tälle matkalle tuli 11 näytteenottoprofiilia. Näyteprofiilien syvyys vaihteli 7.3:sta metristä 2.3:een metriin ollen keskimäärin 4.6 metriä. TK 13:sta löydettiin kahden eri jäätiköitymisvaiheen moreenipatjat. Ylempi moreeni koostuu kolmesta kerroksesta. Pintaosassa on hapettunut, ruskea hiekkamoreeni, jonka alla on ruskean harmaa välikerros. Tämä kerros edustaa pohjaveden korkeusvaihtelua maaperässä. Alin kerros on hapettumaton, harmaa hiekkamoreeni. Ylemmän moreenipatjan paksuus vaihtelee 2.3:sta 5.5:een metriin. Moreeni on tiiviydeltään ja kivisyydeltään normaalia hiekkamoreenia, jossa keskimääräinen kivikoko vaihtelee 6-60 senttimetriin ja kiviaines on kulmistaan pyöristynyttä. Alempi moreenipatja on säilynyt kallion painanteissa. Kappaleita sen pinnasta on kulkeutunut ylempään moreeniin. Alempi moreeni on tiivistä, tummanharmaata silttimoreenia, jossa savespitoisuus (<0.002 mm:n ainesta) on yli 15%, kun sitä ylemmässä moreenissa on normaalisti alle 10%. Alemman moreenin kivisyys on normaalia ja kivikoko vaihtelee 6-60 senttimetriin. Kiviaines on kulmistaan pyöristynyttä. Kiviaines on myös osittain rapautunutta. Ylemmän moreenin kerrostanut jäätikkö on uurresuuntien perusteella virrannut länsiluoteesta itäkaakkoon ja alemman moreenin kerrostumisen aikana yhden suuntauslaskun perusteella pohjoisesta etelään. Maastossa moreenipeite tasoittaa kalliopinnan epätasaisuudet. Mitään merkkejä postglasiaalisista siirroksista ei moreenipeitteestä tai paljastetusta kallion pinnasta löydetty, eikä moreenissa havaittu kallioperän liikuntoihin viittaavia häiriörakenteita. Avainsanat: maapeite, glasiaaligeologia, moreeni, stratigrafia, kaivannot, raekoko, kvartääri, Suomi; Länsi-Suomen lääni; Satakunta; Eurajoki; Olkiluoto

5 1 TABLE OF CONTENTS ABSTRACT TIIVISTELMÄ 1 INTRODUCTION SAMPLING AND GRAIN SIZE DETERMINATIONS RESULTS OF INVESTIGATION SUMMARY... 9 REFERENCES APPENDICES... 13

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7 3 1 INTRODUCTION The Quaternary deposits in investigation trench OL-TK13 were studied by the Geological Survey of Finland in autumn The investigations were carried out in three phases as the excavation progressed. Samples for grain size determinations were taken from vertical profiles, placed 25 m apart along the trench. Sedimentological observations of the sampling profiles were documented in field by drawing on a field observation form and the profiles were photographed using a digital camera, except profiles 7 and 8 because the trench was filled in these places before photographing. In addition, the excavated section was photographed along the whole length. Sampling profiles are numbered as TK13/ The coordinates of sampling profiles are in Appendix 1 and the locations in charts 1-2. The location of each sampling profile was determined with the help of pre-determined starting and end points of sections for bedrock mapping. Observation forms and grain size analyses of each profile are in Appendices of this report.

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9 5 2 SAMPLING AND GRAIN SIZE DETERMINATIONS Samples for grain size determinations were taken from vertical profiles extending from the soil surface down to bedrock or, if the bedrock was covered with water, to the water table. Between 6 and 7 kg of sediment was taken in a bucket with a shovel and placed in plastic bags for transport to the laboratory. The samples were first dried in the laboratory. Grains over 6 mm were extracted before analysis. The samples were first sieved and then the grain size distribution of the < 63 µm fraction was analyzed with the Sedigraph 5100 instrument. Table 1 shows the soil sampling depths and soil type classification in OL- TK13. Table 1. Soil sampling depths and soil type classification in OL-TK13. Profile depth in Soil type classification metres d50 (GEO) geotechnical classification (RT) TK13/ sandy till fine sandy till TK13/ sandy till fine sandy till TK13/ sandy till fine sandy till TK13/04U sandy till fine sandy till TK13/04L silty till fine sandy till TK13/ sandy till fine sandy till TK13/06U sandy till fine sandy till TK13/06M sandy till fine sandy till TK13/06L silty till fine sandy till TK13/ sandy till fine sandy till TK13/ sandy till fine sandy till TK13/ sandy till fine sandy till TK13/ sandy till fine sandy till TK13/11U sandy till fine sandy till TK13/11L silty till fine sandy till Soil type classification after Aaltonen et al (RT) and Korhonen et al (GEO).

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11 7 3 RESULTS OF INVESTIGATION The length of OL-TK13 is approximately 250 m and 11 profiles were sampled from it. The height of the profiles varied from 7.3 m to 2.3 m with an average of 4.6 m. Summary of the sampling profiles is presented in Fig. 1. The figure shows, how the till cover very effectively levels out the bedrock topography. Figure 1. Summary of the sampling profiles OL-TK 13/ The till cover in OL-TK13 consist of two till beds. The upper bed has three layers. Surface layer consists of oxidized, brown sandy till, which is underlain by grayish brown intermediate layer of sandy till. This layer represents the groundwater table, which is moving up and down. The lower layer is unoxidized, grey sandy till. The thickness of the upper till varyes from 2.3 to 5.5 meters. The upper till is classified as having a normal amount of cobbles and boulders with the size of the larger clasts varying from 6 to 60 cm. The edges of clasts have been eroded and rounded. The upper till has normal compactness. The lower till bed has been preserved in bedrock depressions. Part of it s lower till material has ascended the upper till as seen in profile drawings. The lower till is compact, dark grey silty till with over 15 % of fine material (under mm). The

12 8 lower till is classified as having a normal amount of cobbles and boulders with the size of the larger clasts varying from 6 to 60 cm. The edges of clasts have been eroded and rounded. Part of the clast material is weathered. This dark grey silty till was earlier found in investigation trench OL-TK7 ca. 250 m west of OL-TK13 (Paulamäki 2005), and it is widely known in Eurajoki area as patasavi by the local well diggers. The contact between grey sandy till and dark grey silty till is sharp as can be seen in Fig. 2. The upper till bed in OL-TK13 was deposited in the last flow phase of the continental ice. Bedrock striations indicate that the ice moved in a WNW-ESW direction. The lower till bed has been deposited during an earlier flow phase from N to S according to one till fabric analysis. No signs of postglacial faults were detected either in the tills or in the exposed bedrock. The tills showed no signs of disturbance related to bedrock movements. Figure 2. The contact between grey sandy till and dark grey silty till

13 9 4 SUMMARY Two till beds were found in trench OL-TK13 in Olkiluoto. The upper till bed has three layers. Surface layer is oxidized, brown sandy till, which is underlain by grayish brown intermediate layer of sandy till. This layer represents the grounwater table, which is moving up and down. The lower layer is unoxidized, grey sandy till. The lower till bed has been preserved in bedrock depressions. It is compact, dark grey silty till with over 15 % of fine material (under mm). The upper till bed in OL-TK13 was deposited in the last flow phase of the continental ice. Bedrock striations indicate that the ice moved in a WNW-ESW direction. The lower till bed has been deposited in an earlier flow phase from N to S according to one till fabric analysis. No signs of postglacial faults were detected either in the tills or in the exposed bedrock. The tills showed no signs of disturbance related to bedrock movements.

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15 11 REFERENCES Aaltonen, V.T., Aarnio, B., Hyyppä, E., Kaitera, P., Keso, L., Kivinen, E., Kokkonen, P., Kotilainen, M.J., Sauramo, M., Tuovila, P. & Vuorinen, J., Maaperäsanaston ja maalajien luokituksen tarkastus v Summary: A critical review of soil terminology and soil classification in Finland in the year Maataloustieteellinen Aikakauskirja: 21, Korhonen, K.-H., Gardemeister, R. & Tammirinne, M., Geotekninen maalajiluokitus. Geotekniikan laboratorio, tiedonanto 14, 20 s. 2 liitettä. Paulamäki, S., Geological mapping of investigation trench OL-TK7 at the Olkiluoto study site, Eurajoki, SW Finland. Working Report Posiva Oy, Eurajoki. 63 p.

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17 13 APPENDICES Appendix 1. Coordinates of the soil sampling profiles in trench OL-TK13. Appendix 2. Location of investigation trench OL-TK13. Appendix 3. Location of sampling profiles OL-TK13/ Appendix 4. Field observation forms OL-TK13/ Appendix 5. Till fabric analysis OL-TK13/11. Appendix 6. Grain size analyses from samples OL-TK13/01 11.

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19 15 Appendix 1. Coordinates of the soil sampling profiles in trench OL-TK13. Profile x y TK13/ TK13/ TK13/ TK13/ TK13/ TK13/ TK13/ TK13/ TK13/ TK13/ TK13/ Notes for field observation forms: TF = till fabric analysis GS = sample for grain size analysis CO = compactness ST = stone content SSZ = stone size RO = roundness of clasts

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