Myth-busting Monday: Guidelines are not indicators of environmental impact
I read reports that apply guidelines to contaminated sites every day and I often see them being used as an indicator of environmental impact. In my mind this is irresponsible from both a financial and environmental perspective. The role of guidelines is to identify levels of contamination that may represent an impact. It is the job of environmental professionals to determine if the mass and concentrations of contamination present actually represent an impact based on site-specific conditions.
Here is something to think about: In order for guidelines to be protective of most sites, they have to be over-protective of the average site. In fact, most guidelines are designed to be protective of 95% of sites. In statistical terms (you knew we’d go there eventually right?) this accounts for all of the data that exists within two standard deviations of the mean. Consequently, guidelines are protective of sites that are significantly more sensitive than the average site as shown in the line drawing below.
If we blindly apply the guidelines to a site that falls to the left of the 95th percentile in terms of sensitivity we will be remediating material that does not pose a risk of harm to humans or the environment. So what are guidelines good for? They should be used as a screening tool to tell us when it’s time to turn on our brain. For concentrations below the guideline we don’t need to think at all. For concentrations above the guideline we need to apply good science to determine if the contamination at our site poses a risk of harm to humans or the environment.
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