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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
1.2 Magnetic map: Area 2 ...................................................................................... 20
1.3 Magnetic map: Area 3 ...................................................................................... 21
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.
Figure 9. Profile data from line 1527000 (Area 1). New 2007 data is presented with
continuous line, 2004 data with dots. The difference of mean values for this line is about
5 nT.
12
Figure 10. Profile data from line 1526900 (Area 1). New 2007 data is presented with
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).
Figure 11. Profile data from line 1527000 (Area 3). New 2007 data is presented with
continuous line, 2004 data with dots. The difference of mean values for this line is about
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
Figure 12. Profile data from line 1527150 (Area 3). New 2007 data is presented with
continuous line, 2004 data with dots. The difference of mean values for this line is about
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
detail survey (right) on Area 2.
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
detail survey (right) on Area 3.
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
Magnetic Field SurveyArea 2
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
Magnetic Field SurveyArea 3
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
Magnetic base station, Date: 19.12.2007
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
Magnetic base station, Date: 20.12.2007
51525
51530
51535
51540
51545
51550
8:30 9:00 9:30 10:00 10:30 11:00 11:30
Time
nT
Magnetic base station, Date: 3.1.2008
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
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