| Abstract: | The municipal landfill at the Complexe Environnemental de Saint-Michel (CESM) in Montreal, which is the third largest in North America, is located in a former quarry in fractured limestone. Impressive measures are taken to monitor and control biogas and leachate generated at the site. Leachate containment is presently performed with a pumping well completed within the waste. The efficiency of the well in controlling off-site leachate migration is questioned because field observations strongly suggest that the nearby former Francon quarry is diverting local ground water flow. To address this issue, four additional hydraulic control options are considered: (1) increased pumping at the existing waste well; (2) new pumping wells in the rock on the eastern limit of the site; (3) new injection wells in the rock on the eastern limit; and (4) combination of new injection wells at the same location and new water supply wells upgradient of the landfill. We evaluated the four hydraulic control options at the CESM using two coupled models: (1) a decision model based on an objective function weighting the risk, costs, and benefits of each option translated into dollar units; and (2) a numerical ground water flow model to represent the effect of operational conditions and ascertain success. Decision analysis offers a quantitative unbiased tool to evaluate the potential and relative cost of each option, but qualitative considerations and judgment still must be used for a complete evaluation. Our analysis confirms that scenario 4, which was the intuitively favored option, represents the best containment strategy. |
