1. GEO-ELECTRIC INVESTIGATION OF UNDERGROUND LEACHATE DISTRIBUTION AT A CLOSED LANDFILL IN SOUTHWESTERN ONTARIO, CANADA Joshi, Siddharth 1, Yang, Jianwen 1, Sereres, Clayton 2, Tamr, Radwan 2 1 University of Windsor, 2 Genivar Inc. EM Conductivity results Fig.2: Conductive anomalous zones shown in the western half of the site using 2m and 4m coil spacing for both HCP and PRP geometries DC Resistivity results Fig.3: Resistivity inversion results. Left: (N-S) line 2, Right: (N-S) line 3, Bottom: (W-E) line 1 Discussion The conductivity results shows a high anomalous zone occupying an area of 200m (S-N) by 80m (W-E) in the western portion of the landfill site. The conductivity values range between 130-500 mS/m. Leachate and water samples taken from monitoring wells around the site compliment the conductivity results. The DC resistivity method was utilized to get more insight into the contaminant distribution in the area and to investigate the subsurface geology. There are 8 lines measured in the (S-N) direction of which two are shown and 3 lines were measured in the (W-E) direction of which one is shown. All the lines outline the presence of the waste cell in the upper sand aquifer. Line 2 shows a clear plume migration (horizontally) within the aquifer with line 3 showing minor evidence of vertical plume migration. The 1 st (W-E) line shows a man-made divide between the western and eastern portion of the landfill. The resistivity gradually increases as we move eastwards and there was no evidence to prove that leachate was entering the lower aquifer. Conclusions The conductivity and resistivity results were beneficial in assessing the approximate extent of leachate distribution at the closed landfill site. Future work would require running both conductivity and resistivity lines in the eastern and southern portion of the site with a few lines running outside the periphery of the landfill to better understand the potential movement and transport of leachate and/or leachate indicator parameters within the existing subsurface soils and to better assess the general site hydrogeological conditions. Acknowledgments I would like to thank my field assistants Mr. Beiraghdar, Mr. Raveendran, Mr. Hoyle, and Mr. Brzozowski for their support and assistance in collecting the geophysical data. This research was supported by an National Sciences and Engineering Research Council of Canada (NSERC) Engage Grant. Methodology The landfill was mapped for variations in terrain conductivity using a frequency domain (FD) conductivity meter. The instrument has two coil separations (2m and 4m) which allows us to explore depths of 3m and 6m for the horizontal coil winding (HCP) and about 1m and 2m for the perpendicular coil winding (PRP). The conductivity maps were plotted using ArcMap 10.1 GIS based software. Once the area showing the conductive zones were identified, the DC resistivity method was applied to those areas using a Wenner-α array with a 5m electrode separation giving a depth of investigation (DOI) of 30m. Site Description The landfill is situated on a topographic high trending in a northwest to southeast direction and it is a remnant from an ancient beach deposit and consists of a mixture of sand and gravel. The working area of the site has been highlighted below. Fig.1: Site plan map of the landfill Introduction and Objective The leakage of contaminants from landfill sites has been known to cause detrimental impacts to surrounding groundwater/surface water systems and soil. The recent advancement of various near-surface geophysical techniques have enabled scientists to map the extent of such leakages and prevent them from escaping the landfill barrier. This study aims at determining the underground distribution of leachate at a closed municipal solid waste landfill site in southwestern Ontario using geo-electrical investigation.