GEO-ELECTRIC INVESTIGATION OF UNDERGROUND LEACHATE DISTRIBUTION AT A CLOSED LANDFILL IN SOUTHWESTERN ONTARIO, CANADA

Contamination due to landfill leachate can cause disastrous effects to aquifers used for groundwater supply. In this study, two geo-electric techniques were employed to investigate the underground leachate distribution and the subsurface geology at a closed site in southwestern Ontario, Canada. Conductivity mapping was first conducted over the study site using a frequency-domain EM terrain conductivity meter, which reveals an anomalous zone with the apparent conductivity values ranging between 130-500mS/m, concentrated in the 200m (S-N) by 80m (W-E) rectangle area at western half of the site. The DC resistivity survey was then carried out in the same area with 8 S-N profiles and 3 W-E profiles measuring 200m in length using a Wenner-α configuration. This arrangement of electrodes has an approximate exploration depth of 30m, which aids in outlining the waste and upper sand aquifer, the underlying silt/sand aquitard, and the lower sand aquifer. Our resistivity survey results exhibit an inconsistency in the clay cap thickness on almost all the profiles conducted. The results also indicate that the contamination plume is mainly travelling southwards at the base of the upper aquifer just below the waste, with a minor vertical component into the upper weathered portion of the silt/sand aquitard at some locations. No contamination plumes seem to exist in the lower sand aquifer. These findings are critical in assessing the current leachate conditions and in evaluating the existing compliance monitoring plan for potential implementation at the site or other sites in elsewhere.