Expert Testimony in Environmental Claims: Participant vs Litigation Experts

May 7, 2015 | Tamara Farber

The Ontario Court of Appeal has recently discussed the drafting of expert reports and the nature of expert testimony (respectively in Moore v Getahun, 2015 ONCA 55 (CanLII) and Westerhof v Gee, 2015 ONCA 206 (CanLII)).  Neither of these cases related to environmental claims, but both have implications relating to the rules under which experts might testify in environmental cases.  This article will discuss the Westerhof case in that vein.  The question at issue addressed the very core of what constitutes an “expert” witness: to whom do the expert witness provisions in the Ontario Rules of Civil Procedure apply?  Do they apply to anyone offering an expert opinion?

Often in environmental claims more than one expert will testify at trial.   For example, in a contaminated land case, the expert who carried out the remediation might testify, while an opposing expert might be called to give an opinion as to whether that remediation was carried out appropriately.  Both involve expert opinions that might include the following:

  • the first witness, a “participant” expert (a term used by the Court of Appeal in Westerhof), might provide trial testimony including opinions as to groundwater flow direction, the extent of contamination, hydraulic conductivity or the ability of contamination to move within subsurface conduits or fractures.  Specific remedial method analysis may have been done to assess which method should have been used. 
  • the second witness, a litigation expert, might provide trial testimony offering different opinions from the first expert concerning groundwater flow, hydraulic conductivity, contaminant migration, whether the first expert’s analysis of the remedial options was flawed, or whether the implementation of those options was flawed.

The question is: are both experts subject to the same requirements under the Rules?  The Ontario Court of Appeal says no. 

In Westerhof, the plaintiff was injured in a car accident.  He was treated by a number of experts, including his family doctor, a psychiatrist, a chiropractor, a neurologist, an orthopaedic surgeon, and others. Many of these witnesses were not considered to be “expert witnesses” by Westerhof’s lawyer for the purposes of trial and their evidence did not comply with Rule 53.03 (which sets out specific requirements for the content of an expert report). The trial judge excluded much of this evidence as being expert evidence that was non-compliant with the Rules and dismissed the action.

Westerhof appealed to the Divisional Court. In dismissing the appeal, that Court noted that the “important distinction is not in the role or involvement of the witness, but in the type of evidence sought to be admitted. If it is opinion evidence, compliance with Rule 53.03 is required; if it is factual evidence, it is not.”[1]  The Divisional Court concluded that “evidence of diagnosis and prognosis were opinions because they involve inferences from observed facts and may turn out to be either right or wrong. Thus, although a treating physician may give evidence of his or her diagnosis to explain the treatment provided, such evidence is not admissible for the truth of its contents. Rather, it is admissible only to understand the basis of the treatment provided.”[2]

The decision was then appealed to the Ontario Court of Appeal. The appeal raised the question whether Rule 53.03 applied only to experts described in Rule 4.1.01 and Form 53 – being those “engaged by or on behalf of a party to provide opinion evidence in relation to a proceeding” – or whether it applied more broadly to all witnesses with special expertise who give opinion evidence. As the Court of Appeal stated, “this broader group of witnesses would include, for example, treating physicians who form opinions based on their participation in the underlying events [referred to in these reasons as “participant experts”] rather than because they were engaged by a party to the litigation to form an opinion.”[3]

The Court of Appeal granted the appeal and ordered a new trial.  Writing for a unanimous panel, Madam Justice Simmons disagreed with the Divisional Court’s conclusion that the type of evidence (fact or opinion) is the key factor in determining whether Rule 53.03 applies. Instead, she held that a witness with special skill, knowledge, training, or experience, who has not been engaged by or on behalf of a party to the litigation may give opinion evidence for the truth of its contents without complying with Rule 53.03 if:

  • the opinion to be given is based on the witness’s observation of or participation in the events at issue; and
  • the witness formed the opinion to be given as part of the ordinary exercise of his or her skill, knowledge, training and expertise while observing or participating in such events.

Simmons J. A. termed these witnesses “participant experts”.  The Court of Appeal was particularly influenced by the wording of Rule 4.1.01 which relates to “experts engaged by or on behalf of a party to provide [opinion] evidence in relation to a proceeding” in concluding that the rule was not intended to cover participant experts.  A party does not “engage” an expert to provide opinion evidence in relation to a proceeding simply by calling the expert to testify about an opinion the expert has already formed[4].  Similarly, the Court noted that the requirement in Rule 53.03(2.1)3 that an expert’s report set out “the instructions provided to the expert in relation to the proceeding” makes it clear that Rule 53.03 only applies to litigation experts.  A party does not provide instructions to a participant expert in relation to the proceeding because the expert has already formed their opinions[5].  The Court was mindful of the potential for a participant expert to stray into opinion evidence falling outside of the opinions formed from their observations or participation; those opinions would have to comply with Rule 53.03.

The analysis of the expert evidence in the Westerhof case is equally applicable in contaminated land cases.  The nature of the expert evidence in contaminated land litigation is not distinctive, per se.   Whether medical, engineering, geotechnical or hydrogeological opinions are offered, the issue is when the opinion was formed.    The “participant expert” formed the opinion at the time of the undertaking.  The participant expert could testify, therefore, without a report, without a certification in advance attesting to the expert’s impartiality or duty to the court, but presumably with some documents demonstrating their opinions were formed during their participation in, for example, remediation.

Consider, however, if litigation had been contemplated when the participant expert was engaged in a contaminated land case.  Counsel might consider, if litigation is contemplated and counsel is engaged at this early stage, retaining a separate expert – a peer review or advisory expert – at the time of the retainer of the participant expert to consider whether the opinions formed by the participating expert might be called into question by a future opposing litigation expert.  There are obviously practical limiting factors to such an approach.  The cost of retaining a peer reviewing expert at the time of the event might be prohibitive, the likelihood of litigation might be small, the relationship between the client and the participant expert might be strained by the involvement of a peer reviewer, and the timing of decisions made by the participant expert might be constrained by the peer reviewer.  This could lead to delays and possible effects on migrating contamination.

Practically, a participant expert might never have to comply with the Rules.  It makes sense to favour a decision to allow those experts to do what they were retained to do – participate in the process.  If they ever have to testify, their evidence will be admissible for the truth of the events and for the truth of the opinions that formed the basis for their actions and decisions.  There may still be room for nuances when litigation is contemplated early in the process.  For now, however, the Court of Appeal has spoken.  Apparently, timing is everything.


[1] 2013 ONSC 2093 (CanLII) at para 21.

[2] 2015 ONCA 206 (CanLII) at para 58.

[3] supra, at para 6.

[4] supra, at para 82.

[5] supra, at para 83.


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