ground magnetic survey at olkiluoto 2007 · suomen malmi oy conducted magnetic ground survey at...

POSIVA OY

Olki luoto

FI-27160 EURAJOKI, F INLAND

Tel +358-2-8372 31

Fax +358-2-8372 3709

Anna-Maria Tarvainen

Mari Lahti

January 2008

Working Report 2008-02

Ground Magnetic Survey at Olkiluoto 2007

January 2008

Base maps: ©National Land Survey, permission 41/MYY/08

Working Reports contain information on work in progress

or pending completion.

Anna-Maria Tarvainen

Suomen Malmi Oy

Mari Lahti

Posiva Oy

Working Report 2008-02

Ground Magnetic Survey at Olkiluoto 2007

ABSTRACT Ground Magnetic Survey at Olkiluoto 2007 17.01.2008 Anna-Maria Tarvainen, Suomen Malmi Oy Mari Lahti, Posiva Oy

Suomen Malmi Oy conducted magnetic ground survey at Olkiluoto site in Eurajoki

during December 2007. The survey is a part of Posiva Oy’s detailed investigation

program for the final disposal of spent nuclear fuel. The assignment included field

work and processing of the data. The report describes field operation, equipment

as well as processing procedures and shows the obtained results and an analysis

of their quality in the appendices. The results were also compared with earlier

magnetic surveys. The raw and processed data files delivered digitally in Geosoft

xyz file format.

Key words: Geophysics, magnetic, field survey, structural geology, nuclear waste disposal

TIIVISTELMÄ Magneettiset maastomittaukset Olkiluodossa vuonna 2007 17.01.2008 Anna-Maria Tarvainen, Suomen Malmi Oy Mari Lahti, Posiva Oy

Suomen Malmi Oy suoritti magneettisia maastomittauksia Olkiluodon

tutkimusalueella joulukuussa 2007. Työ tehtiin Posiva Oy:n tilauksesta, ja se on

osa yksityiskohtaisia kallioperätutkimuksia käytetyn ydinpolttoaineen

loppusijoitusta varten. Työ sisälsi kenttätyön ja aineiston käsittelyn. Raportissa on

kuvattu kenttätöiden kulku, käytetty kalusto ja tehdyt korjaukset sekä esitetty

analyysi tulosten laadusta liitteissä. Tuloksia verrattiin myös aiemmin tehtyihin

magneettisiin tutkimuksiin. Tulokset on toimitettu tilaajalle digitaalisesti Geosoft

xyz -tiedostoina.

Avainsanat: Geofysiikka, magneettinen, maanpintamittaus, rakennegeologia, ydinjätteen loppusijoitus

Contents

Abstract

Tiivistelmä

1 Introduction ..............................................................................................................1

2 Field work.................................................................................................................2

3 Data Processing and Results.....................................................................................5

4 Comparison with 1989 and 2004 data ......................................................................7

4.1 Levelling.............................................................................................................8

4.2 Overview of the detail areas.............................................................................14

4.2.1 Area 1...................................................................................................... 14

4.2.2 Area 2...................................................................................................... 15

4.2.3 Area 3...................................................................................................... 16

5 Conclusions ............................................................................................................17

References ................................................................................................................................... 18

Appendices.................................................................................................................................. 19

Appendix 1

1.1 Magnetic map: Area 1 ...................................................................................... 19



Appendix 2

2.1 Magnetic base station readings ......................................................................... 22

Appendix 3: Tool technical information

3.1 Scintrex ENVI-MAG Magnetometer................................................................ 24

3.2 Scintrex MP-2 Magnetometer........................................................................... 25

Appendix: CD

Raw Data, Corrected Data and Maps in digital form

1

1 INTRODUCTION

In 1999, Posiva Oy filed an application for a policy decision from the council of state

for a construction permit to build a final disposal facility for spent fuel at the Olkiluoto

area in the Eurajoki municipality. In December 2000, the Council of State made a

positive policy decision and in May 2001, the Parliament ratified the decision. The

policy makes it possible to concentrate the research activities at Olkiluoto.

Suomen Malmi Oy (Smoy) carried out magnetic ground survey in December 2007 and

January 2008 according to the purchase order 9536-07. The survey was carried out at

three investigation areas. The idea of the survey was to test if detailed magnetic ground

survey method would be applicable at the Olkiluoto site. The goal was to enhance the

magnetic image of these three test areas and make possible to characterise anomalies

and their origin with other sources of geological and geophysical information.

Geophysical foreman Antero Saukko coordinated field surveys. Jalle Tammenmaa and

Anna-Maria Tarvainen conducted data processing. Anna-Maria Tarvainen conducted

reporting. This report describes the field operation and the data processing. The quality

of the results was analysed and the data is presented in Appendices. Mari Lahti (Posiva

Oy) added chapter 4 to compare the detail survey with earlier results.

2

2 FIELD WORK

The survey consisted on 63 North-South profiles, which were located at three different

survey areas in Olkiluoto investigation site. Each area is approximately 200 m x 200 m.

The survey areas are presented in Figure 1. Area 1 is uppermost in Figure 1. Area 2 and

Area 3 are below area 1, Area 2 is on the left side and Area 3 is on the right side.

The magnetic survey was carried out using Smoy’s Scintrex Envimag magnetometer.

Scintrex MP-2 magnetometer with KTP data logger was used as a magnetic base

station. Both tools are portable proton-precession magnetometers. The positions of the

profiles were located with a standard handheld GPS before the actual survey. The

magnetometers’ technical information is found in Appendices in 2.1 and 2.2.

Profile interval was 10 meters and station interval 5 meters. The coordinates and lengths

of the surveyed profiles are listed in Table 1. The total survey amount was

approximately 11540 meters. The fieldwork was carried out within 4 working days, in

December 2007 and January 2008.

Figure 1. The magnetic survey areas in Olkiluoto investigation site (Ismo Aaltonen,

2007).

3

Table 1. Profile coordinates and length.

Easting Northing

/Line Number Starting point Ending point Length [m]

Area 1 1526800 6791790 6792000 210

1526810 6791805 6792005 200

1526820 6791795 6792000 205

1526830 6791800 6792005 205

1526840 6791800 6792000 200

1526850 6791800 6792005 205

1526860 6791800 6792000 200

1526870 6791800 6792000 200

1526880 6791805 6792000 195

1526890 6791800 6792005 205

1526900 6791800 6792000 200

1526910 6791800 6792000 200

1526920 6791800 6792000 200

1526930 6791800 6792000 200

1526940 6791800 6792000 200

1526950 6791800 6792000 200

1526960 6791800 6792000 200

1526970 6791800 6792000 200

1526980 6791800 6792000 200

1526990 6791800 6792000 200

1527000 6791800 6792000 200

1526360 6791360 6791560 200 Area 2

1526370 6791360 6791560 200

1526380 6791360 6791560 200

1526390 6791360 6791560 200

1526400 6791360 6791560 200

1526410 6791360 6791560 200

1526420 6791360 6791560 200

1526430 6791360 6791560 200

1526440 6791360 6791560 200

1526450 6791360 6791560 200

1526460 6791360 6791560 200

4

Easting Northing

/Line Number Starting point Ending point Length

Area 2 1526470 6791360 6791560 200

1526480 6791360 6791560 200

1526490 6791360 6791560 200

1526500 6791360 6791560 200

1526510 6791360 6791560 200

1526520 6791360 6791500 140

1526530 6791360 6791485 125

1526540 6791360 6791465 105

1526550 6791360 6791460 100

1526560 6791360 6791455 95

Area 3 1527160 6791320 6791520 200

1527150 6791320 6791520 200

1527140 6791320 6791520 200

1527130 6791320 6791520 200

1527120 6791320 6791520 200

1527110 6791320 6791520 200

1527100 6791320 6791520 200

1527090 6791320 6791520 200

1527080 6791320 6791520 200

1527070 6791320 6791520 200

1527060 6791320 6791520 200

1527050 6791320 6791520 200

1527040 6791325 6791520 195

1527030 6791320 6791520 200

1527020 6791320 6791520 200

1527010 6791335 6791520 185

1527000 6791330 6791520 190

1526990 6791470 6791520 50

1526980 6791470 6791520 50

1526970 6791490 6791520 30

1526960 6791470 6791520 50

Total length [m] 11540

5

3 DATA PROCESSING AND RESULTS

The data processing followed the standard procedure. The base magnetic field intensity

of the investigation site was 51 580 nT. The readings from the magnetic base station

were used to remove the short-term temporal variation of magnetic field. The location

of the magnetic base station was 152 7307 (E), 679 0946 (N) (Figure 3). The corrected

data were stored in Geosoft xyz file format. The corrected data are presented in the

maps in Appendices 1.1–1.3. The magnetic base station readings are presented in

Appendix 2.1. The raw and corrected data are presented on a CD. Figure 2 gives an

overview of the results.

Figure 2. The results of the magnetic survey.

6

Figure 3. Base station location on a field southeast from the survey areas. Distance

from the SE corner of Area 3 is 400 meters.

7

4 COMPARISON WITH 1989 AND 2004 DATA

Earlier ground magnetic data from Olkiluoto comprise surveys from 1989 and 2004.

The North-South directional 50 m line spacing survey carried out in 2004 (Lahti 2004)

covers mostly the site of 2007 surveys. This data has been combined with survey data

from 1989 (Laurila 1989) also with 50 m line spacing to produce a ground magnetic

grid that covers extensive part of Olkiluoto island (Figure 4). This combined magnetic

map has been used as a basis for assessing the benefits of increased survey resolution.

Figure 4. Ground magnetic grid presenting combined 1989 and 2004 data. The three

detail survey areas are outlined and numbered.

8

4.1 Levelling

The level of the new detail survey is not directly comparable with earlier data. The

results are tied into a local base station level, which differs from the base level of the

1989 and 2004 surveys. New survey lines overlap with the old survey lines and that

allows comparison and levelling (Figure 7). Based on brief inspection the 2007 data was

shifted 490 nT down to level better with the 1989-2004 grid. After this level shift some

of the overlapping profiles show comfortable match. On the other hand major

differences occur where human influence is causing cultural noise. Minor differences

can be spotted on all overlapping profiles. These can be explained by survey accuracy

(positioning, sensor attitude), changes in the environment (development) and possibly in

some cases increased resolution (from 10m to 5m station spacing). The level shift

performed is by no means final levelling and the result should be considered as

preliminary. When data is actually integrated the levelling problem should be

considered more thoroughly.

Measuring profile L1526490 from Area 2 altogether three times tested the survey

accuracy and repeatability. This test shows a surprisingly high noise level. Table 2

shows the statistics for the three repetitions. The difference in mean values is up to 7.4

nT and the maximum amplitude difference over a distinct though narrow anomaly is 80

nT (Figure 5 and Figure 6). Major features are reproducible but low amplitude details

(below 10 nT) can be missed in noise.

Table 2. Statistics for three repetitions over line L1526490.

Rep 1 Rep 2 Rep 3

41 41 41 number of items

51404.7 51481.8 51504.1 min

52200.6 52166.8 52173.0 max

51820.6 51821.0 51828.0 mean

143.5 136.6 138.7 standard deviation

9

Figure 5. Three measurements over profile L1526490. The amplitude range is 800 nT

which hides small deviations. Still amplitude differences over distinct anomalies are

visible.

Figure 6. Detail from profile L1526490 showing the one-point anomaly with an

amplitude difference of up to 80 nT on three repetitions. Two of the repetitions fit fairly

well and differ only 10 nT.

Results how profile data from 2004 and 2007 surveys match together are demonstrated

in Figure 8-12. Table 3 shows the same thing in numbers although this time as area

based statistics to compare old and new data after the level shift but before any cultural

cleaning for 2007 data. The mean and standard deviation values for Areas 1 and 3 are

distorted by low magnetic values from cultural sources. The deep negative peaks are

obvious in Figure 10 and Figure 11. Area 2 has better match between 2004 and 2007

data mainly due to lack of major man-made interference. Please note that only

overlapping data has been used to calculate the statistics.

10

Table 3. Statistical comparison of old and new data for the three detail areas.

profiles) Area1 (5 profiles) Area2 (3.5 profiles) Area3 (4

2007 2004 (1989) 2007 2004 2007 2004

number of items 208 154 105 144 74 83

min * 50973.6 50861.2 51003.9 50890.4 45327.8 49873.9*

max 51213.4 51214.4 51596.2 51575.2 51431,9 51431.1

mean 51047.5 51261.7 51259.0 51087.2 51020.2* 51057,3*

standard dev. 437.0* 41.6 160.3 156.2 92.1 173.3*

*clearly cultural influence

Figure 7.

New survey lines overlapping with the 2004 and 1989 surveys.

1

2 3

11

Figure 8. Profile data from line 1526400 (Area 2). New 2007 data is presented with

continuous line, 2004 data by dots. The difference of mean values for this line is 7 nT.

A small new anomaly has been detected in the southern part of the line.


continuous line, 2004 data with dots. The difference of mean values for this line is about

5 nT.

12


continuous line, 2004 data with dots. The magnetic low in 2007 data is cultural noise

(drilling site). The difference of mean values for this line is about 5 nT if 7 data points

inside the blue arrow are excluded (209 nT with all data included).



4.4 nT. The difference of mean values for this line is 18 nT when 6 data points inside

the blue arrow are excluded (130 nT with all data included).

13



4.4 nT. This is an example that 5 m station spacing can bring out more detail. The

anomaly pointed with red arrow has one peak in 2004 data but is divided into three in

2007 data.

14

4.2 Overview of the detail areas

This chapter gives a short geophysical overview of the three detail survey areas and

compare the new enhanced magnetic grids with earlier surveys. The magnetic data has

not been connected to geological data yet. All data is presented as total magnetic

intensity maps that are produced using minimum curvature gridding and illuminated

from northeast. As no actual levelling has been applied the new grids are independent

and no colour scale bars are presented.

4.2.1 Area 1

The 1989-2004 ground magnetic data in Figure 13 indicates a nearly E-W directional

structure crossing the study area. Also a NW-SE trending feature is cutting the northeast

corner of the detail area. The 10 m line spacing survey carried out in 2007 brings out a

lot of detail that partially fade out the major alignments. Generally most detail scale

features have NW-SE tendency, which is enhanced by illumination from northeast. As

the area has been developed after earlier surveys man-made influence is unavoidable.

Major cultural interference comes out in the northern side of the area on lines 1526870-

1526900. This is the drilling site of OL-KR45 and OL-KR40. Figure 13 show the 2007

data cleaned of this evident cultural noise. The deep blue hues are partly residual of this

man-made anomaly but blending in with the magnetic low mapped in 1989 and 2004

surveys.

Figure 13. Ground magnetic data of 1989 and 2004 surveys (left) improved with 2007

detail survey (right) on Area 1.

15

4.2.2 Area 2

Area 2 presented in Figure 14 is characterised by a single peak anomaly in the northern

part and a smaller feature composed of three peaks in the south. These are divided by a

faint line with roughly SW-NE heading. Detail survey defines the northern anomaly and

shows the pinnacle in slightly different location. The division of the north and south

becomes more distinct. A sharp mainly SE-NW directional ridge emerges in the

southern part. Also two negative bull’s-eye anomalies are detected, one in the northwest

corner of the area and another in the middle part. Maps and aerial images fail to indicate

that these would have cultural sources. Some man-made interference is visible in the

northeast corner near the new accommodation village. Figure 14 shows 2007 data subtly

cleaned at the edge of accommodation village in northeast.

Figure 14. Ground magnetic data of the 2004 survey (left) improved with the 2007


16

4.2.3 Area 3

On the 2004 ground magnetic map in Figure 15 Area 3 is featured by a N-S or NW-SE

trending low. At the same time the grid seems to be slightly distorted in E-W direction.

Detail survey defines the positive anomaly in the northeast corner and brings out some

detail scale E-W directional features. A NW-SE tendency comes out as well. The

western side of the area extends to the new accommodation village and is not partly

surveyed due to barracks. The positive anomaly in the southwest corner is mapped

having overlaying NW-SE details. Some but not all of them correlate with made ground

and roads in the perimeter of the accommodation village.

Figure 15. Ground magnetic data of the 2004 survey (left) improved with the 2007


17

5 CONCLUSIONS

The magnetic survey of Olkiluoto investigation site was carried out within 5 working

days in December 2007 and January 2008. The survey consisted of 63 profiles at three

different investigation areas. The total survey amount was approximately 11540 meters.

The quality of the data widely achieved the required level. The processed and

interpreted data is delivered to the Client in digitally in Geosoft xyz file format. The

draft report was compiled in January 2008.

A brief comparison with earlier survey data enhances the amount of detail that 10 m line

spacing will bring out. On the other hand the 2007 survey reveals the effect that

increasing site development has on geophysical data. Cultural noise will be inevitable

and extra attention has to be paid when interpreting detail scale features.

18

References

Lahti, M 2004. Horizontal loop electromagnetic (HLEM) and magnetic ground surveys

at Olkiluoto 2004. Posiva Oy. Working report 2004-29.

Laurila, T 1989. Geofysikaaliset maanpintamittaukset Olkiluodon tutkimusalueella.

Teollisuuden Voima Oy. Työraportti 89-35.

Scintrex: ENVI-MAG Manual. 1993.

Scintrex: Instruction Manual, MP-2 Portable Proton Precession Magnetometer. 1982.

10 0 10 20 30 40 50

(meters)

Scale 1:1000

Magnetic Field SurveyArea 1

51327515025151151515515185152151523515255152851530515335153651539515435154751552515575156251569515755158251592516075162451648

6791

7806

7918

0067

9182

067

9184

067

9186

067

9188

067

9190

067

9192

067

9194

067

9196

067

9198

067

9200

0

67917806791800

67918206791840

67918606791880

67919006791920

67919406791960

67919806792000

1526800 1526820 1526840 1526860 1526880 1526900 1526920 1526940 1526960 1526980 1527000

1526800 1526820 1526840 1526860 1526880 1526900 1526920 1526940 1526960 1526980 1527000

Appendix 1.1 19

10 0 10 20 30 40 50

(meters)

Scale 1:1000


51398514815152651555515835160751628516485166651684516995171551732517485176551782517975181551834518555187751903519295196752024

6791

360

6791

400

6791

440

6791

480

6791

520

6791

560

67913606791400

67914406791480

67915206791560

1526360 1526400 1526440 1526480 1526520 1526560

1526360 1526400 1526440 1526480 1526520 1526560

Appendix 1.2 20

10 0 10 20 30 40 50

(meters)

Scale 1:1000


50348512055140251442514585146651475514825149151499515055151151518515265153751551515635157551586516035161951635516575168151727

6791

320

6791

360

6791

400

6791

440

6791

480

6791

520

67913206791360

67914006791440

67914806791520

1526960 1527000 1527040 1527080 1527120 1527160

1526960 1527000 1527040 1527080 1527120 1527160

Appendix 1.3 21

22

Appendix 2.1 Magnetic base station readings during the survey

Magnetic base station, Date: 18.12.2007

51525

51530

51535

51540

51545

51550

51555

51560

51565

51570

51575

51580

9:00 9:30 10:00 10:30 11:00 11:30 12:00 12:30 13:00 13:30 14:00 14:30 15:00 15:30 16:00

Time

nT


51525

51530

51535

51540

51545

51550

8:00 8:30 9:00 9:30 10:00 10:30 11:00 11:30 12:00 12:30 13:00 13:30 14:00 14:30 15:00 15:30

Time

nT

23


51525

51530

51535

51540

51545

51550

8:30 9:00 9:30 10:00 10:30 11:00 11:30

Time

nT


51525

51530

51535

51540

51545

51550

9:00 9:30 10:00 10:30 11:00 11:30 12:00 12:30 13:00 13:30 14:00 14:30 15:00 15:30 16:00

Time

nT

24

Appendix 3.1 SCINTREX ENVI-MAG MAGNETOMETER Total field range 20 000 - 100 000 nT Total field absolute accuracy +/- 1 nT

Sensitivity 0.1 nT at 2 second reading time, reduced at other reading times

Reading period 0.5, 1 or 2 s

Data output format

Data dump of all acquired data in memory or on a mode by mode and line by line basis in XYZ or printer listing format. Separate dump for Notes.

Data presentation Present and three previous readings in numerical form. Up to 178 readings in graphic form.

Environmental range Temperature: – 40 to +60 C Humidity 0 – 100 %

25

Appendix 3.2 SCINTREX MP-2 MAGNETOMETER Resolution 1 nT Total field accuracy +/- 1 nT Range 20 000 - 100 000 nT Gradient Tolerance Up to 5000 nT/meter

External Trigger Sampling intervals longer than 3.7 seconds

Display Total magnetic field in nT or normalized battery voltage

Data Output Multiplied precession frequency and gate time outputs for base station recording

Sensor Omnidirectional, shielded, noise-cancelling dual coil, optimized for high gradient tolerance

Operating Temperature range - 35 to +60 C

ground magnetic survey at olkiluoto 2007 · suomen malmi oy conducted magnetic ground survey at...

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