Canadian Consulting Engineer

Brownfield risks

LETTERSThe article entitled "Brownfields and Health" by Don Fugler, P.Eng. and Michael Rankin (CCE June-July 1999) caught my attention because I was involved in the health risk assessment done for the...

October 1, 1999   Canadian Consulting Engineer


The article entitled “Brownfields and Health” by Don Fugler, P.Eng. and Michael Rankin (CCE June-July 1999) caught my attention because I was involved in the health risk assessment done for the Vancouver Expo lands pictured on the first page. The stated intent of the research [on the hypothetical site] was to evaluate variability in screening risk assessments conducted by different consultants. The authors concluded, “screening level risk assessments should be conducted cautiously and by experienced practitioners.”

Although I don’t disagree, the information presented in the article did not support this conclusion. In fact, the article stated, “There was no apparent trend … between [the consultants’] capability … and the degree of conservatism they employed.” The authors also stated that, “Some consultants applied a conservative bias to all aspects of the risk assessment … resulting in an unrealistic estimate.” The clear implication was that consultants who overestimated the risks because they used too many conservative assumptions were in error.

Screening level risk assessments are, by definition, not realistic and should always overestimate risks to some extent. The purpose of a screening risk assessment is to eliminate innocuous sites from the requirement for a detailed risk evaluation by demonstrating that risks are within an “acceptable” range even when using conservative assumptions. The authors’ suggestion that conservative bias be used for key parameters only, implies a level of effort beyond a screening level assessment, as one would have to establish realistically defensible values for all the non-key parameters to calculate the risk. The most serious error that can be made in a screening level risk assessment is to underestimate the risk, not overestimate it.

The conclusion that should be drawn from this research is that not enough guidance or consensus exists for conducting screening level risk assessments, resulting in widely varied findings among even experienced practitioners. Since the actual risk levels posed by this hypothetical site were not determined, it is impossible to say whether risks were under- or over-estimated for any given contaminant.

In the real world, all participants would have to conclude the same thing: this site should be subject to a detailed risk assessment and/or risk management measures because everyone ranked at least one contaminant in the unacceptable risk range.

David E. Roberson

SCS Engineers, Bellevue, WA

We agree that screening level risk assessments need to be conservative. However, it is not clear that detailed risk assessments would produce significantly different results as the predicted indoor concentrations varied largely due to modeling differences. It is likely that the models used for detailed assessments would have remained the same (although some assumptions might change) and that most of the wide variation shown would also remain.

Don Fugler, P.Eng., CMHC and Michael Rankin, Golder Associates.

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