Remediation: In-Situ Technologies vs. Dig & Dump

Society as a whole is continuously demanding new, better, and more advanced methods to complete tasks in faster, easier, more convenient, and of course, cheaper ways. The environmental industry is no exception to this rule. The environmental remediation market is rapidly evolving with new methods and technologies to address the unique challenges of contaminated sites. This is especially true in cases where conventional excavation approaches historically would have been far too challenging or costly to truly address the problem. The big question is, “does in-situ remediation work for all sites?” The short answer is no – conditions must always be ideal for an in-situ approach, or it simply won’t work.

So, how does one decide if an in-situ remediation approach, rather than a straight dig and dump approach is best? Well, first off, we have to understand more about the site itself. A lot of factors impact the decision on how to remediate or mitigate environmental contaminant risk. One of the most common misconceptions with in-situ remediation is that after the initial round of treatments, significant improvements will be seen in the site’s overall contaminant reduction. However, this is inaccurate; it takes time – sometimes numerous rounds of injections, and very frequently often necessary for a change in approach and treatment methodologies to reach generic site condition standards. To satisfy the contractors ECA (Environmental Compliance Approval), follow up sampling programs need to be completed, which also takes time to complete.

Physical conditions on-site relating to both subsurface conditions and access need to be considered prior to establishing an in-situ remedial action plan. When looking at access, in a lot of instances, the contractor has to be able to easily access or drill in areas where environmental impacts are present. In some cases, it’s challenging to install the piping or well infrastructure necessary to deliver the amendment into the ground. Clients and/or site owners need to be aware that, in some cases, this means drilling indoors or around active worksites, all of which can be disruptive to other operations or tenants on the site. Other considerations, such as subsurface ground conditions, need to be thoroughly reviewed in order to design a successful remedial approach. In-situ remediation relies heavily on the injected amendment coming in direct contact with the contaminated soil or groundwater. If the soil porosity is low, it will be a lot more challenging to deliver amendment directly into the impacted area. Common examples of this would be denser tills, bedrock or silty clays. In situations like these, sometimes more intensive drilling or fracturing into bedrock is required. In a lot of cases where soils are impermeable, simple excavation or combined remedy of both
approaches is the best way to go.

Soil and groundwater chemistry also need to be carefully evaluated in order to select the right delivery method, as well as amendment. Some chemicals react faster or instantly in comparison to other amendments, which may endure and react over a longer period of time. It is important to identify the source area and relative concentrations. It’s not effective to deliver amendments into intensely contaminated areas simply because the amendment will be exhausted or spent too quickly. Removal of contaminant mass or source area can be achieved through conventional excavation methods, and/or pumping and treating of impacted groundwater. In-situ remediation is an excellent tool for addressing residual contamination, which can’t be excavated economically or that is difficult to access due to site constraints.

When selecting any remedial approach, whether it’s an excavation or in-situ remediation technology, the most useful tool in your toolbox is hard data. Effective vertical and horizontal delineation of a site is essential for identifying the limits of the contamination, as well as where it resides below the ground’s surface. With limited data and lack of detail of the contaminated site, it’s challenging to select an effective approach, as well as to establish an accurate cost estimate and the timeline for completing the project. This, more often than not, leads to huge cost over-runs, uncertainty in the schedule, and ultimately a lack of confidence in the remedial approach.

In closing, in-situ remediation and new technologies to deliver amendments into impacted site conditions absolutely do work, however, there are numerous important steps and considerations in selecting this approach. It’s important to understand the client’s objectives of remediating their site. In almost all cases, we are mitigating or removing environmental and financial risk to the client and their project. In cases where in-situ remediation is a similar cost to the conventional excavation of the impacted material, the obvious choice would be to excavate and remove the contamination. Removal takes care of a far larger fraction of all environmental risks and provides greater certainty in achieving the remedial objective. Clients should select a contractor that is unbiased and can offer both technology-based remediation services, as well as excavation. There is no off-the-shelf technology that will ‘fix’ all contaminant issues. If it sounds too good to be true – it likely is. The environmental remediation and construction market are ever-evolving, and we should embrace these new technologies, however; approach them with questions and a desire for proof-of-concept and approach.

Devin Rosnak, Hon. B.Sc. is a Project Manager at Ground Force Environmental.  He manages construction projects relating to brownfield development and contaminated site remediation. Devin can be contacted at drosnak@gfei.ca