Tritium, oxygen-18, and deuterium diffusion at the Confederation Road landfill site, Sarnia, Ontario, Canada

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Abstract
The isotopes 3H (tritium), 18O (oxygen-18), and 2H (deuterium), which appear to have been concentrated in the leachate at the Confederation Road landfill site, Sarnia, Ontario, Canada, are shown to have migrated into the underlying natural clay barrier by molecular diffusion. The theoretical best-fits to the observed concentration profiles, using the error function solution to the transient diffusion equation (analogous to Fick's second law), give diffusion coefficients of 13 × 10−6, 13 × 10−6, and 8.5 × 10−6 cm2/s for 18O, 2H, and 3H, respectively. Field concentration profiles for Cl− and Na+ are also presented for comparison. Diffusion coefficients obtained for Cl− and Na+ were 6.4 × 10−6 and 3.3 × 10−6 cm2/s, respectively. Tritium and chloride appear to have migrated a similar distance of ~2.0 m from the clay–waste interface, compared with only 1.2 m for Na+, which has probably been retarded by adsorption onto clay exchange sites. Oxygen-18 and deuterium appear to have migrated the furthest at ~2.3 m.The 3H profile indicates that post-1953 rainwater entered the landfill site, probably mostly in 1967 when the landfill trench was excavated. High δ18O and δ2H values, especially near the clay–waste interface, suggest mixing of 1967 rainwater with an isotopically enriched water, probably produced in the landfill either directly from enriched organic wastes such as leaves or by biodegradation processes. Key words: diffusion, landfill leachate, oxygen-18, tritium, clay barrier, chloride.

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