THE IMPACT OF OPEN DUMPING METHOD IN NGIPIK LANDFILL INVESTIGATED WITH ELECTRICAL RESISTIVITY TOMOGRAPHY (ERT) AND VERY LOW-FREQUENCY ELECTROMAGNETIC (VLF-EM)

The open dumping is a dangerous yet common landfilling method in the developing countries. In Indonesia, 90% of landfills across the country still apply the open dumping method. A minimum construction cost and time, by disposing the waste directly to the ground pit, make the open dumping method as the easiest waste disposing option. However, this method potentially causes uncontrolled leachate deployment which result in groundwater contamination. To assess the risk of this method, this research employed geophysical measurements in Ngipik landfill, Gresik - East Java, which has been operated since 2002 with open dumping method. The geophysical measurement is the quickest method to investigate contamination mapping in a large area without drilling many wells to investigate water contamination. Very low-frequency electromagnetic (VLF-EM) method is one of the most used methods to investigate groundwater contamination, because of the easy operating and flexible equipment, while the electrical resistivity tomography (ERT) investigation is a quick and excellent method to map the contamination in the landfill area. In this study, 10 profiles of VLF-EM and 7 profiles of ERT investigation are employed to evaluate the leachate deployment in Ngipik landfill area. A 3D image of both methods is presented in the dry and rainy season to map the leachate plume in the landfill area. A laboratory-scale investigation is conducted to interpret the leachate resistivity on the field. The result shows that the leachate has been deployed up to 25 meters in some profiles nearby the waste mound. The water quality of surrounded wells has also affected by the leachate agreed to the geophysical method. Finally, this research proves that, VLF-EM and ER methods are effective to analyze the leachate plume in the landfill area.