In this paper, thed3C values and concentrations of carbon pools (DOC, DIC, CH4 and acetate) were used to recognize leachate impact on the surrounding groundwater and to evaluate carbon biogeochemistry within the Ottawa landfill plume. The enriched 13CDIC for groundwater (-6.4 ‰ to - 1.0 ‰) confirm that the leachate (+8.8‰ to +10.7‰) has had an impact on aquifers. In addition, in proximal ground water, methane concentrations are high (~10 mg l-1) and the d3CCH4 values demonstrate reactive loss of acetate in the leachate plume by methanogenic fermentation, and methane oxidation in the plume fringe. Continued reaction of DOC in groundwater is confirmed by deviation from the mixing lines on diagrams of DIC vs. d3CDIC and DOC vs. d3CDOC, and by the absence of acetate.

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