The use of 2D Resistivity Imaging Technique to investigate subsurface contamination at Sungai Besar landfill site, Selangor ,Malaysia Tan Chin Lee, Abdul Rahim Samsudin & Umar Hamzah School of Environment & Natural Resources Science Faculty of Science & Technology National University of Malaysia UKM 43600 Bangi

INTRODUCTION Geophysical surveys using electrical imaging methods have been used in many application ever since the interpretation techniques have been developed by Loke and Barker (1996a). A laboratory measurement was carried out for estimating the resistivity of clay and leachate.

3. A waste disposal site at Sungai Besar, Sabak Bernam Selangor was selected for this study 4. Four resistivity lines were arranged in the NE-SW directions and three lines were in NW-SE directions. The length of each survey lines were between 200 to 400 metres. 5. Maximum depth of soil resistivity information are approximately about 30 to 60 metres.

EXPERIMENTAL STUDY Field measurement -Geoelectrical imaging surveys are normally carried out with multielectrode resistivity system -In this survey 61 electrodes are deployed in a straight line with constant spacing and connected to a multicore cable.

A computer-controlled system (Griffith, Turnbull and Olayinka 1990) is then used to select the active electrodes for each measurement. The data gathered in this survey is interpreted using an inexpensive microcomputer to provide an inverse resistivity section.

Terrameter SAS 1000 system was used for the data collection -Wenner array electrode confuguration was used to provide a good vertical resolution - The data collected in the field is interpreted using the computer programme RES2DINV (Loke and Barker 1996b)

cable battery Terrameter SAS 1000 Lund system electrode Connection clip Battery for Lund system

2. Tank modeling - Marine clay samples at the landfil site was taken to the laboratory for measurement of resistivity in a tank model of 100 X 100 X 75 cm in size. - A small scale resistivity measurement were carried out in the tank -This is followed by subsequent several measurements after one day, One week and one month introduction of leachate into the clay layer.

Tank modeling

Small scale electrode

RESULTS AND DISCUSSION Field measurement Solid waste Clay layer contaminated clay leachate Line 1

Line 2 Line 3 Solid waste leachate contaminated clay Clay layer

Line 4 Line 5 leachate Clay layer contaminated clay contaminated clay

contaminated clay leachate Line 6 contaminated clay leachate Line 7

Tank modeling Fresh clay without leachate A day after putting leachate Clay layer Fresh clay without leachate Clay layer leachate A day after putting leachate

A week after putting leachate Clay layer A week after putting leachate leachate Clay layer A month after putting leachate

migration in clay at the waste disposal sites. CONCLUSION - This study has been very succesful in determining the extend of leachate migration in clay at the waste disposal sites. - Major direction of leachate flow based on plumes concentration was found to be towards the sea.

ACKNOWLEDGEMENT We would like to thank the Ministry of Science and Environment for the IRPA 03-02-02-0003 grant and to all staff for their help in the field data collection and processing.

Thank you