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Exploring new alternatives for treating and reusing soil

When Theresa Phillips began her career as an environmental consultant some 15 years ago there was a lot of excitement over bio-remediation techniques for contaminated soil.


When Theresa Phillips began her career as an environmental consultant some 15 years ago there was a lot of excitement over bio-remediation techniques for contaminated soil.

Stakeholders foresaw a time when genetically modified bacteria would “chew up” contaminants like Pac-man on steroids. But when concerns arose over releasing genetically engineered organisms into the environment, interest cooled. And so did talk of alternatives to simply digging up contaminated soil and dumping it in landfill.

“People aren’t really using risk assessment and remediation to its full advantage,” reflects Phillips, a senior toxicologist and risk assessment specialist with exp Services Inc. in Markham, Ont. “Dig-and-dump isn’t really remediation at all,” she says.

Though governments tend to pay lip service to the need for innovative soil management, they also default to overly conservative approaches, she adds.

“We find when we do an ecological risk assessment, the MOE (Ontario Ministry of the Environment) requires us to build in all kinds of levels of conservativeness,” she explains. “We make all these assumptions on the ultra-conservative side, because it’s an assumption so you can’t know for sure.”

The risk assessment might indicate chemicals on the site that are harmful to plants and the best alternative is to dig the soil up and get rid of the contaminants. “Then you go to the site and it’s covered with plants,” says Phillips. “They’re surviving. Is the solution to kill them all by digging them up?”

While she feels Ontario’s MOE is beginning to loosen up a little, at least in the case described, there’s plenty of room for improvement.

Jim Skeoch echoes the idea. As head of business development for AIM Environmental Group (with offices in Stoney Creek, Ont. and Calgary), Skeoch says soil remediation will have to change as regulations grow tighter and landfill becomes scarcer and more expensive.

“In Europe, it’s very expensive to get rid of contaminated soil, so they’ve come up with alternative solutions and methodologies,” he says. “As things tighten up here, they’re going to increase the cost of landfill, particularly for soil.”

It’s a trend he welcomes, given the environmental damage wrought by dig-and-dump. Not only does it drastically disturb the environment and potentially release harmful gasses and chemicals into the air when contaminants are dug up, there’s the increased carbon footprint and the dangers associated with trucking contaminated soil to landfill over public highways.

Most important of all, by treating contaminated soil as waste and digging it up only to chuck it in landfill, we’re really just moving the problem from one place to another, adds John Willms, managing partner with Willms & Shier Environmental Lawyers of Toronto.

Because landfill space is scarce and expensive, private land-owners often accept clean fill for a fee and dumpers take advantage of the offer because “it’s cheaper than sending it to landfill—hugely cheaper.”

The problem, says Willms, is the Ministry isn’t policing those so-called clean fill sites to ensure the soil has been treated because they fall into a grey area in its mandate. And that leaves a void in the protection of human and ecological health.

Other options

The good news, says Skeoch, is there are good alternatives for treating and reusing soil, and they can be a lot less expensive than dig-and-dump.

The technique chosen depends on a number of factors, including the soil’s level of contamination; the types of contaminants and the acceptable level of contamination. Each province has its own regulations regarding acceptable levels of contamination, he points out, and that’s going to vary according to whether the future use of the site will be residential or industrial. Some of the available techniques outlined by the experts include:

1). Soil vapour extraction (SVP) and air sparging (in situ): Both techniques remove contaminant vapours below ground for treatment above ground. SPV requires drilling one or more extraction wells, then using a vacuum to suck vapours up for treatment.

During air sparging, oxygen is pumped underground into wet soil and ground water in order to make chemicals evaporate faster. Then, they can be extracted using a technique such as SPV. Target contaminants include VOCs and some fuels; and the time frame is several years.

2). Phytoremediation (in situ): This approach uses plants to clean up contaminants in soil and groundwater by either absorbing them (plants must then be removed), stabilizing or detoxifying them. Cleanup is limited to the depth of roots. Target contaminants are metals and organic compounds and the time frame is two to five years.

3). Bioremediation (in situ or ex situ): This is a form of composting. Micro-organisms, (bacteria, fungi, green plants or enzymes) are used to attack soil contaminants, rendering them less toxic or turning them to water and harmless gas.

“The methodology that we use takes advantage of indigenous bacteria that already exists in the soil. We just optimize their growing opportunities to enhance the degradation of the contamination,” Skeoch says. Target contaminants are petroleum constituents and chlorinated hydrocarbons and time frame is six months to two years.

4). Soil washing (in situ or ex situ): Uses chemical and/or mechanical processes to scrub soil clean. Target contaminants are SVOCs, petroleum and fuel residuals, PCBs, PAHs, pesticides, metals. The time frame is one to six months.

5). Solidification and stabilization. Chemical/physical treatments convert contaminants into a more solid form that is less likely to migrate, such as a block, clay-like material or granular particulate. The technique doesn’t actually get rid of the contaminants, but rather contains them. Target contaminants are radioactive, hazardous, and mixed wastes and the time frame is weeks or months.

6). Chemical oxidation. This approach converts hazardous contaminants to less toxic ones through a chemical reaction with oxidants. Target contaminants are fuels, solvents and pesticides and the time frame is a few months to a few years.

Assessing the alternatives

The first step in considering whether to remediate and which techniques to use is a site specific risk assessment (SSRA). The SSRA is designed to identify the potential hazards posed by various contaminants on a specific site, including migration of the substance off-site and the danger to plants and animals on-site.

Having identified areas of concern, consultants might choose to remediate or implement a formal soil management plan (SMP) to ensure that “everyone working on the site is aware of what might be in the soil and appropriate handling procedures,” adds Phillips.

“For example, if you know there are contaminants below one meter, and the risk assessment says they’re okay so long as they stay there, the SMP might stipulate that if any excavations are made at that depth, the soil needs to be handled such that (contaminated) dust doesn’t blow off-site,” she explains.

“It must be sampled to determine if it is, in fact, contaminated, and it needs to be segregated from other soil until it is known what the extent of contamination is, and then disposed of properly, or placed back at the same depth.”

The downside of many remediation techniques, adds Skeoch, is the time they take to work. “If someone wants to sell a property quickly, dig-and-dump might be the first choice,” he says. “If they have a bit of time, they can use an in-situ program. It might take two or three years depending on what type of contamination they’re dealing with, the soil type, the
water level and other factors.”

The most recent 2012 MOE draft document, ‘Soil Management—A Guide for Best Management Practices’ could be a step in the right direction, says Willms. But it presents guidelines, not laws, and “it’s very expensive to do all the testing required to meet all these best management practices.”

He wonders if municipalities doing public works, for example, are likely to add to their project costs by complying with them, rather than simply hiring contractors who will dump contaminated soil elsewhere.

“What I’m saying and I think basically what the Ontario Environment Industry Association and the Ontario Waste Management Association are saying is that, until MOE rationalizes the regulatory framework, makes sense out of that; and then enforces it properly, you’re never going to get a handle on the movement of dirty soil,” says Willms.

That’s a shame, contends Skeoch because “soil is a non-renewable resource…You want to keep as much of it useful as you can.”

In the absence of clear expectations for innovative soil remediation, the industry will continue to be shaped by voluntary approaches aimed at boosting projects’ environmental performance and client satisfaction.

Camilla Cornell is a Toronto-based freelance writer.


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2 Comments » for Exploring new alternatives for treating and reusing soil
  1. Ken Lyon says:

    Except for the use of risk assessment, it doesn’t seem like much has changed in the last 20 years!

  2. George Duncan says:

    Great article but can someone explain how phytoremediation removes contaminants. Surely, all it does is transfer them from soil to plant? What happens to the toxic plants?

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