Understanding Risk Assessment as a form of Sustainable and Green Remediation

One of my New Year’s resolutions is to write more posts that explain, in plain language, how our environmental regime in BC protects the public with respect to contaminated sites and to help clear up common misconceptions about contaminated sites.

My area of professional expertise is the investigation and remediation of former industrial and commercial sites. My specialization is risk assessment, specifically the assessment of petroleum hydrocarbon contamination and its effects on human and ecological health. For those of you not familiar with the terminology, I have included a background section at the bottom that can help you understand the topic of risk assessment in this context as well as links to previous blog posts where I address issues surrounding contaminated sites.

There is a common fallacy in the environmental and regulatory community that risk assessment is a cop-out. A way to avoid doing “real” remediation and is thus inherently unsustainable. Nothing could be further from the truth. Often risk assessment is the most green and sustainable choice for remediating contaminated sites in BC.

A typical example of the negative regulatory viewpoint was presented in the BC Ministry of Environment & Climate Change Strategy (BC ENV) discussion paper Making Contaminated Sites Climate Ready put out in the fall of 2022. The document repeatedly suggests that risk-based instruments should be subject to additional scrutiny without acknowledging that risk assessment often represents a preferred green/sustainable form of remediation.

Historically, the standard approach for a “real” and “permanent” remediation at a hydrocarbon-impacted site was the “dig and dump” excavation. In a dig and dump excavation, contaminated soils are dug out of the ground, along with significant volumes of less contaminated, or even uncontaminated soils, using diesel powered excavators which deposit the soil into diesel trucks to be transported to a landfill.

Given the presence of the hydrocarbons in these soils they typically cannot be shipped to just any landfill. Instead, they need to go to specially permitted facilities designed to receive and treat this type of waste soil. Most of these facilities are located in the lower mainland (in Richmond or Abbotsford). If your impacted site is in the interior this might require a 1000+ km round trip for soil disposal.

The trips are carried out by diesel trucks and each trip presents a real risk on the roads. The trucks will travel along community roads to the highway then often hundreds of kilometers on the highways before driving through more residential and busy urban communities to reach their goal. Each trip can generate hundreds of kilograms of carbon emissions and well as harmful diesel exhaust and multiple trips are typically required to achieve numerical closure.

Once the waste soils arrive at a permitted facility for treatment they will generates dangerous vapours while more diesel and greenhouse gas emissions are given off during their treatment. Once treated, the soils then get sent to the main landfill, taking up limited landfill space, for final disposal. But remember, you are only halfway done at this point. Having dug out the hole, you still need to fill it in.

To fill in the hole you need to excavate clean fill from somewhere else and transport that clean fill to your site which entails further transportation emissions, transportation risk and ecological consequences because that fill soil has to come from somewhere.

To summarize, a typical remedial excavation generates massive GHG and diesel emissions; poses transportation risks through busy communities; while using up non-renewable landfill space; and requiring the excavation and transportation of clean fill which entails further transportation emissions, transportation risk and ecological consequences. None of this is recognized in the BC ENV document.

So what is the alternative? The Environmental Management Act (EMA) provides the legislative framework for addressing contamination in British Columbia. The Contaminated Sites Regulation  provides the specific regulatory regime for managing contaminated sites under the EMA. Both identify risk assessment as a viable mechanism to remediate a site because it is a safe, environmentally friendly mechanism of addressing contamination. The decision to remediate via risk assessment has been a standard remedial approach in British Columbia for decades and BC ENV has repeatedly supported the use of risk assessment in their protocols and guidance documents. If a risk assessment demonstrates that there are no unacceptable risks to human health and the environment at a site, that site is considered remediated to risk-based standards.

Under risk assessment a qualified professional can develop a risk management plan to ensure that a contaminated site does not pose unacceptable risks to human or ecological health. Sometimes a risk assessment can’t make that assessment and other remedial options may be necessary, but often a series of relatively simple precautions can be undertaken that eliminate any real risk to the community posed by a contaminated site.

This is often the case in parts of Vancouver where the deep subsurface is dominated by dense glacial tills (sand and gravel that has been compacted by glaciers until it is as hard as concrete). Glacial tills are not only as hard as concrete they are virtually impenetrable by contamination and contain no extractable groundwater. Contamination confined by a glacial till poses no short or long-term risk to human or ecological health and will eventually biodegrade (naturally attenuate) until it no longer exists. Building a properly designed parking structure (as part of a high-rise building for example) over top of this type of contamination can ensure the contamination poses zero risk to the community as it attenuates over time.

Ultimately, the choice will often be to either leave contaminated soil where it poses no current or reasonable future human or ecological harm or conduct a remedial excavation which would generate massive greenhouse gas and diesel emissions, create additional traffic on the highways and in busy urban and residential corridors while taking up limited landfill space and requiring the importation of clean fill soil to replace the removed material.

From a sustainable and green remediation perspective the choice could not be any more clear. Risk assessment is often by far the best remedial option both economically and using any sustainability measure anyone can invent. A site remediated by risk assessment typically avoids significant ecological consequences, emissions and human and ecological risks associated with unnecessary dig and dump excavations or gas-fired oxidizers in vapour extraction systems while providing permanent solutions to contamination. This makes risk assessment a legitimate green approach to remediation.


Because I deal with risk all the time in this blog, I have prepared a series of posts to help explain the risk assessment process. The posts start with “Risk Assessment Methodologies Part 1: Understanding de minimis risk” which explains how the science of risk assessment establishes whether a compound is “toxic” and explains the importance of understanding dose/response relationships. It explains the concept of a de minims risk. That is a risk that is negligible and too small to be of societal concern (ref). The series continues with “Risk Assessment Methodologies Part 2: Understanding “Acceptable” Risk” which, as the title suggests, explains how to determine whether a risk is “acceptable”. I then go on to cover how a risk assessment is actually carried out in “Risk Assessment Methodologies Part 3: the Risk Assessment Process. I finish off the series by pointing out the danger of relying on anecdotes in a post titled: Risk Assessment Epilogue: Have a bad case of Anecdotes? Better call an Epidemiologist.

Previous posts on Contaminated Sites topics:

A primer on environmental liability under BC’s Environmental Management Act.

On the Omnibus Changes to the BC Contaminated Sites Regulation

This entry was posted in Chemistry and Toxicology, Risk Assessment Methodologies, Risk Communication, Uncategorized. Bookmark the permalink.

3 Responses to Understanding Risk Assessment as a form of Sustainable and Green Remediation

  1. dcardno says:

    Ha. In a former life I was the senior financial guy at a waste management company in the Vancouver area. At the time (early 90s, or so) there were a number of service stations that weren’t making much money selling gas, and were more valuable as a development site for a condo tower. Unfortunately, virtually every gas station has had tank leaks at some point – so the subsurface is contaminated. A developer would buy the site, and since time is money, they wanted the site remediated as soon as possible. In practice, that meant excavating the contaminated material pronto, and then starting construction (or at least, permitting / approvals, etc).

    But what to do with the excavated material? That’s where we came in – some guy approached us, and he had ‘magic bugs’ – various microbes that were claimed to (and for all I know, did) eat hydrocarbons and excrete CO2 and water. They might’ve been yeast (like I said, I’m a finance guy, not a biologist). Anyway, the developer’s experts measured concentrations of gasoline / MTBE / etc in situ, pronounced it to be the devil’s own soup, and off it went to our facility. We laid it out in windrows, and spread the ‘magic bugs’ then turned it over every week or so (it’s a while ago, so details are hazy) . Three months (or so?) later, we measured the concentration of hydrocarbons (gas / MTBE / etc) in the material – mirabile dictu, the soil was suitable for nearly all uses, and certainly not “hazardous waste” any longer.

    Our little secret was that most of the cleaning happened by aerating the soil when it was excavated – all the contaminants are very volatile, so when the backhoe dumped each load in the dump-truck it was mostly clean just from the agitation and motion through the air; the time spent in the open finished the process (and maybe the bugs helped). We were happy to take a (large) fee for treating the contaminated waste, the developer was happy to get a site he could build on, so we were both good; the (former) gas station owners took a slightly lower price for their property than they should’ve (since it was contaminated), and the upcoming condo owners paid a little more for their box in the sky – but it all came out in the wash, I guess.


  2. Gary Wagner says:

    Very sensible. Unfortunately, there are too many government bureaucrats in the policy realm with time on their hands and no scientific training. To keep their well paid jobs, they produce papers parroting the politically correct mantras that got their ‘woke’ bosses elected.

    Electrification as part of the mythical “energy transition” is another example. Where all of the internal combustion powered equipment, from massive earth movers to gasoline engine weed whackers, will end up is never discussed. Imagine what would happen if suddenly, overnight, by government decree, there are millions of worthless ICE devices parked on huge compounds, abandoned by the side of the road, or dropped off at the landfill. Lawn mowers, ATVs, snowmobiles, chainsaws, snowblowers, motorcycles, RVs, aircraft, generators, outboard motors, etc. would have no market value and might even be illegal to possess. What next?

    GW Sent from my iPad



  3. Cal Lawton says:

    Thanks for the reality check on site reclamation and risk assessment. I have been trying to contact you about getting your views on tanker/freighter/cruise ship exhaust pollution and why there is no global attempt to have some sort of scrubber system made mandatory on the exhaust to reduce emissions. It is my understanding that one of these vessels emissions is equal to 1M cars, is this correct?

    Cal Lawton Calgary, AB 403.804.6203


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