APPLICATION OF ELECTRICAL RESISTIVITY IMAGING TECHNIQUE AND COLLOIDAL BOROSCOPE ON GROUNDWATER STUDY

AT BLOCK 33, MALAYSIAN NUCLEAR AGENCY

Mohd Muzamil Mohd Hashim, Mohd Abdul Wahab Yusof, Kamarudin Samuding, Nazran Harun, Nurul Fairuz Diyana Baharudin

Waste Technology and Environmental Division Malaysian Nuclear Agency

Bangi, 43000 Kajang, Selangor Email: muzamil@nm.gov.my

Abstract

Electrical resistivity imaging is a geophysical surveying technique that used to obtain two

dimensional (2D) subsurface profile. Base on resistivity value, the potential zone that contained

groundwater has been identified. A borehole with 100m depth has been constructed on the

groundwater potential zone. Then, a Colloidal Boroscope is being used to get the groundwater

velocity and direction. From the resistivity profile, a groundwater zone identified at the north

and south area of the study site but the actual direction of groundwater system at that area

cannot be recognized so that, the colloidal boroscope data being used to clarify the actual flow

and direction. Combination from this two type of data produced a good result of groundwater

direction in this study area.

Keywords; Electrical resistivity imaging, Colloidal boroscope, groundwater

INTRODUCTION

The electrical resistivity imaging technique is a geophysical technique that often used for

determine the earth subsurface condition such as the subsurface thickness, rock structure,

groundwater flow and aquifer, groundwater salinity and mineral exploration (Reynolds 1997).

This technique can produce a 2D profile of subsurface condition base on the resistivity value of

subsurface materials. In this study, the focus is on the groundwater potential zone. The

groundwater existing in the earth was determined by the default value of freshwater resistivity

value (Table 1).

The resistivity profile only cannot give a factual data of groundwater flow because the profile is

in two dimensional only. To get the groundwater flow and velocity, a borehole must construct

at the potential zone of groundwater. Then, colloidal boroscope will measure the groundwater

flow and velocity. Colloidal boroscope is a equipment that can measure the direction and

velocity base on the movement of particles in the groundwater itself.

Data of groundwater potential zone, groundwater direction and velocity is very important data

that must have if there have any idea to build a radioactive waste repository facility. Before a

repository facility built in that area, the groundwater contamination study have to do in order

to get the groundwater contamination plumes direction and to indentify the groundwater

monitoring area.

LOCATION AND GEOLOGICAL BACKGROUND

Block 33 is a Nuclear Malaysia’s facility which is a Radioactive waste storage facility. It is located

on a hilly area named as Bukit Rupa. Bukit Rupa stands at about 110 metres above sea level. It

is a conical hill with four main spurs radiating towards the north, southsoutheast, south-

southwest and the west. Several streams drain northwards into Sungai Langat and several

others drain southwards and southwestwards into Sungai Semenyih.

Base on the geological report that produced by Mineral & Geoscience department, this site is

located on rocks of the Kajang Formation of Carboniferous to Permian age. The rocks consist

originally of thick shale, siltstones, sandstones and interbedded shale and sandstones that have

been metamorphosed into schists, phyllites and quartzites. There is no natural rock exposure

within this area.

Figure 1: Location of resistivity survey at Block 33

MATERIALS AND METHODS

Electrical Resistivity Imaging Technique

Electrical imaging is a surveying technique for an area of complex geology where the use of

resistivity sounding and other techniques are unsuitable for providing detailed subsurface

information in a limited area (Barker, 1999). Electrical resistivity surveys are normally carried

out with multi-electrode system. Such surveys use a number of electrodes (25 to 100)

deployed in a straight line with constant spacing, connected to a multicore cable. (Ibrahim et al

2003).

In this survey, field data were obtained using ABEM Terrameter SAS4000 that connected to the

electrode selector Lund ES464 with Schlumberger configuration (Figure 2). This equipment was

linked to the 400m multicore cables. 41 electrodes were connected to the cables with a fixed

distance of 10m spacing for each electrode (Figure 3).

One survey line have been carried out in this survey. The survey line was located on

101°46'26.671"E 2°54'26.742"N to 101°46'29.29"E 2°54'38.816"N (Figure 1). The centres of

these survey line was located at the center of open space area at Block 33 to get the maximum

depth of the subsurface profile. The field data obtained from the survey were processed using

RES2DINV software in order to get the resistivity profile of the survey line.

C = Current electrode P = Potential electrode

Resistant , R = ΔV/I

Figure 2: Schlumberger configuration on resistivity survey

Figure 3: Configuration of equipment on site

Colloidal Borescope System

Colloidal Borescope System consist Charged Couple Device (CCD) camera, a flux gate compass,

an optical magnification lens, an illumination source and a stainless steel housing (Figure 4).

Basically, this colloidal boroscope was used in the borehole or monitoring well that contained

groundwater. The measurement of velocity and direction are base on the particles movement

in the groundwater system. Upon the measurement in the well, an electronic image magnified

140x is transmitted to the surface, where it is viewed and analyze. The flux gate compass will

align the direction of boroscope in the well while the source of illumination is a source of

lighting for the lens to capture the movement of particles in the groundwater. All the particles

flow and direction that has been captured will transmitted to the video digitizer and analyzed

using a software.

The groundwater flow direction in this study area most possibly influence by geological

structures. So that, the measurement of groundwater direction must apply to shallow depth

until the deeper depth of the borehole to get the overall direction of groundwater in that area.

The initial groundwater measured at 22m below ground level. This first depth of measurement

is 30m and will continue at 10m interval until the deepest level 70m.

Figure 4: Conceptual diagram of colloidal borescope

RESULT AND DISCUSSION

The determination of subsurface profile is based on the value of electrical resistivity on the

electrical resistivity profile generated by field data which processed by RES2D Inv software.

Resistivity value of the land surface is influenced by porosity, water content under soil, the

concentration of ions in the pore fluid and the composition of the materials below ground

(Abdul Rahim Samsudin et al., 2007). The interpretation of subsurface profile is based on the

resistivity values of some common rock types by Loke 1997 in Table 1.

Table 1: Resistivities of some common rocks, minerals and chemicals (Loke, 1997).

Material Resistivity (Ωm) Conductivity (Siemen/m)

Igneous and Metamorphic

Rocks

Granite

Basalt

Slate

Marble

Quarzite

Sedimentary Rocks

Sandstone

Shale

Limestone

Soils and Waters

Clay

Alluvium

Groundwater (fresh)

Sea Water

Chemicals

Iron

0.01M Potassium chloride

0.01M Sodium chloride

0.01M Asetic acid

0.02 Xylene

5 x 103 – 10

6

103-10

6

6x102

– 4x107

102 – 2.5 x 10

8

102 – x 10

8

8 – 4 x 103

20 – 2 x 103

50 – 4 x 102

1 – 100

10 – 800

10 – 100

0.15

9.074 x 10-8

0.708

0.843

6.13

6.998 x 106

10-6

– 2 x 10-6

10-6

– 10-3

2.5x10-8

– 1.7x10-3

4 x 10-9

– 10-2

5 x 10-9

– 10-2

2.5 x 10-4

– 0.125

5 x 10-4

– 0.05

2.5 x 10-3

– 0.02

0.01 – 1

1.25 x 10-3

– 0.1

0.01 – 0.1

6.7

1.102 x 107

1.413

1.185

0.163

1.429 x 10-17

On the resistivity profile for line 1 (Figure 5), the 0m was located in South and the 400m located

in North. The maximum depth of subsurface profile is 80m. In this profile, the difference

between high resistivity zone (>500 Ωm), intermediate resistivity zone (75 Ωm - 200 Ωm) and

low resistivity zone (< 5 Ωm) were clearly shown. The occurrence of high resistivity zone

surrounds the intermediate resistivity zone more likely caused by the fractured zone.

Based on the resistivity profile, high resistivity zone (yellow to red colour) was interpreted as

hard rock. The intermediate resistivity zone is in green colour. The occurrence of this zone may

be caused by the fractured zone . In this area, the possible of groundwater zone is high because

the value of resistivity 75 Ωm to 150 Ωm basically will refer as the groundwater resistivity value.

The low resistivity zone is in blue colour. Normally, the low resistivity value can be interpreted

as clay materials.

Figure 5: 2D electrical resistivity profile at Block 33 with a borehole constructed at the center of the survey line

Data from colloidal boroscope has been analyzed base on particle movement in the

groundwater. The average value is taken to interpret the direction and velocity of the

groundwater.

Table: Groundwater direction and velocity for each depth in the borehole

Groundwater Depth Direction (Degree) Particel Velocity (x10-4m/s)

30m 141 2.15

40m 83 2.51

50m 290 3.56

60m 198 5.34

70m 193 4.24

Figure 6: Groundwater direction and velocity at 30m depth

Figure 7: Groundwater direction and velocity at 40m depth

Figure 8: Groundwater direction and velocity at 50m depth

Figure 9: Groundwater direction and velocity at 60m depth

Figure 10: Groundwater direction and velocity at 70m depth

The groundwater direction measured from colloidal boroscope shows that there are different

direction from 30m to 50m depth but almost same direction for 60m and 70m depth. It is

caused by the geological structure below the earth surface that have fractured zone. The

groundwater in that area will flow through the fractured zone from the highest to the lowest

position of the fractured system.

CONCLUSION

Electrical resistivity imaging technique determined a groundwater potential zone at the south

area of study site and a little bit potential at north area. The colloidal boroscope data shows

that the groundwater direction is different for 30m to 50 depth because of geological structure

and almost same for 60m and 70m depth which is flow to south area.

The rely on electrical resistivity imaging technique alone for groundwater flow study is not

enough. It is must supported by colloidal boroscope because it can produce a factual data of

groundwater direction and velocity. Combination of these two types of data will produce a

good result for groundwater study.

REFERENCES

Abdul Rahim Samsudin, Bahaa-Eldin Elwali A.Rahim & Wan Zuhairi Wan Yaacob, 2007. Delineation of leachate plumes at two waste disposal sites, Selangor. Geological Society of Malaysia, Bulletin 53: 47–50

A.N. Ibrahim, Z.Z.T Harith & M.N.M Nawawi (2003). Resistivity Imaging And Borehole

Investigation Of The Banting Area Aquifer, Selangor, Malaysia. Journal of Environmental Hydrology Volume II Paper 10. http://hydroweb.com/jeh/jeh2003/ibrahim.pdf

Barker, R.D.; (1999). Surface and borehole geophysics. In Lloyd J. W. (ed) Water Resources

of Hard Rock Aquifers in Arid and Semi-Arid Zones. Studies and Reports in hydrology, 58, Paris, UNESCO, 287 pp.

C.S Hutchison (2009). Bentong-Raub Suture. Geology of Peninsular Malaysia. Geological Map of Peninsular Malaysia 1985. Department of Mineral and Geoscience Malaysia. Loke M.H., 1999. Electrical Imaging Surveys For Environmental And Engineering Studies.

http://www.georentals.co.uk/Lokenote.pdf