Decision analysis for leachate control at a fractured rock landfill

The municipal landfill at the Complexe Environnemental de Saint-Michel (CES M) in Montreal, which is:the third largest in North America, is located in a former quarry in fractured limestone. Impressive measures are-taken to mo nitor and control biogas and leachate: generated at the site. Leachate cont ainment is presently performed with a pumping well completed within the was te. The efficiency of the well in controlling off-site leachate migration i s questioned because field observations strongly suggest that:the nearby fo rmer Francon quarry is diverting local: ground water flow. To address this issue, four additional hydraulic control options are considered: (1) increa sed pumping at the existing waste well; (2) new pumping Wells;in The rock o n 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 loca tion and new water:supply wells upgradient of the landfill. We evaluated:th e four hydraulic control options at the CESM using two,coupled models: (1)a decision model based on an objective function weighting the risk, costs, a nd benefits-of each option translated into dollar units; and (2) a numerica l ground water flow model-to represent the effect of operational conditions and ascertain success. Decision analysis offers a quantitative unbiased to ol to evaluate the potential and relative: cost of each option, but qualita tive considerations and judgement:still must-be used for a complete evaluat ion. Our analysis confirms that scenario 4, which was the intuitively favor ed option, represents the best containment strategy.