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Court of Appeal Confirms Correct Causation Test in Environmental Contamination Case

5 minute read

The Court of Appeal for Ontario has recently confirmed that the “but for” test remains the correct test to establish causation in environmental cases involving contamination arising from the negligence of multiple parties.

In the case, Donleavy v. Ultramar Ltd.[1], the plaintiff homeowners commenced a negligence action against the fuel supplier, Ultramar Ltd., and the oil tank inspection subcontractor, Kilpatrick Fuels Ltd. and its employee following an oil spill from a fuel oil tank on the plaintiffs’ property.

The trial judge found Ultramar and Kilpatrick liable in negligence as the standard of care required compliance with the regulatory regime set out in the Technical Standards and Safety Act, 2000 S.O. 2000, C.16, its fuel oil regulations and fuel oil codes adopted by reference in the regulations, which had not been done.  The tank was clearly marked to be for indoor use, yet was installed outdoors. The trial judge also found the plaintiffs contributorily negligent for failing to discharge their obligations as owners to maintain the tank.

Regarding causation, the trial judge relied on the material contribution test.[2] She appeared to hold that Kilpatrick’s negligent inspections and Ultramar’s failure to fulfill its obligations under the regulatory regime materially and contributed to the plaintiffs’ losses.

On appeal, the parties agreed that the trial judge articulated the wrong test for causation. The Court of Appeal confirmed that the trial judge misinterpreted the leading causation case, Clements v. Clements[3] as it appeared that she felt Clements meant that she had to apply the material contribution test because there were multiple actors whose conduct was at issue and contributed to the failure of the tank resulting in the oil spill.

In its decision, the Court of Appeal helpfully summarized the governing principles of the alternative approaches to causation:

  • The “but for” test is almost always applied in establishing causation in negligence and requires a plaintiff to prove that without the negligence of a defendants, the injury would not have occurred.[4]
  • The “material contribution” test is an alternative and exceptional approach.[5]
  • The fact that there are multiple defendants or more than one potential case of injury, is not a reason to depart from the “but for” test.[6]
  • “But for” causation applies as the default test in cases where there are multiple defendants unless “something more” warrants application of the “material contribution to risk” approach.[7]
  • The critical threshold for the application of the material contribution approach is the impossibility of proving which of two or more possible tortious causes is, in fact, a cause of the injury.[8]

The Court of Appeal also attempted to clarify some continuing confusion regarding use of the term “contribution” in the “but for” analysis as follows:

Causation is made out under the “but for” test if the negligence of the defendant caused the whole of the plaintiff’s injury, or contributed, in some not insubstantial or immaterial way, to the injury the plaintiff sustained.[9]

Used in this way, the Court concluded, stating a defendant “materially contributed” to a plaintiff’s injury or loss simply recognizes that the defendant’s negligence was not the only cause.[10] The Court of Appeal went on to say that although the trial judge stated she was applying the “material contribution” test, she actually applied the correct “but for” analysis.

It remains to be seen whether this Court of Appeal decision will become or at least endeavoured to be used as a gateway toward a more liberal and flexible application of the “but for” test, which might ultimately blur the analytical lines between these two approaches to causation.  For now, the Court of Appeal has confirmed that in multi-tortfeasor environmental contamination cases the default causation test is the “but for” approach.


[1] Donleavy v. Ultramar Ltd., 2019 ONCA 687

[2] Donleavy v. Ultramar Ltd., 2017 ONSC 7438, at para 155.

[3] Clements v. Clements, 2012 SCC 32.

[4] Donleavy v. Ultramar Ltd., 2019 ONCA 687, at para 62.

[5] Donleavy v. Ultramar Ltd., 2019 ONCA 687, at para 64.

[6] Donleavy v. Ultramar Ltd., 2019 ONCA 687, at para 68.

[7] Donleavy v. Ultramar Ltd., 2019 ONCA 687, at para 68.

[8] Donleavy v. Ultramar Ltd., 2019 ONCA 687, at para 69.

[9] Donleavy v. Ultramar Ltd., 2019 ONCA 687, at para 72.

[10] Donleavy v. Ultramar Ltd., 2019 ONCA 687, at para 73.

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