Remediation Myth Debunker Edition – Part 2

It’s Myth Debunking time again!

We hope you enjoyed Part 1 of our remediation Myth Debunker edition newsletter last month. If you missed it, you can read it here. In it we debunked myths related “risking away” contamination concerns, whether in-situ remediation is long, slow and uncertain, and the low-bid process for tendering.

But these aren’t the only myths circulating out there like conspiracy theories. So, in this month’s newsletter we are bringing you a few more myths that are ripe for debunking. Once again, we hope you find this interesting and informative – enjoy!

Also, be sure to also read Kevin French’s blog here that debunks The Biggest Myth of All!

MYTH #4: MIXING DIFFERENT REMEDIAL AMENDMENTS IS THE SAME AS USING AN INTEGRATED REMEDIAL AMENDMENT

One classic example of this we hear is that applying zero-valent iron (ZVI) together with activated carbon (AC) is just as good as applying an engineered remedial amendment like Trap & Treat® BOS 100®. This has definitively been proven false. The elemental iron in BOS 100® is physically integrated into the AC structure – the two not just mixed together as separate particles.

A simple laboratory test was completed (you can read about in more detail here) demonstrating the difference between ZVI alone, ZVI mixed with AC (ZVI + AC), and BOS 100® in treatment effectiveness. In the first figure below, BOS 100® outperformed ZVI alone and ZVI + AC in terms of reducing concentrations of trichloroethylene (TCE).

Figure 1 TCE Concentrations Over Time When Exposed to BOS 100®, ZVI and ZVI+AC

But it’s not just about adsorption. Destruction is essential to permanent remediation. Proof of TCE degradation is chloride generation. In the next figure, BOS 100 is clearly superior in chloride generation. In contrast, ZVI generates 8.5x less chloride than BOS 100 but still outperforms the ZVI + AC mixture – by far the least effective of the three.

Figure 2 Chloride Generation Over Time When Exposed to BOS 100®, ZVI and ZVI+AC

In the first figure, the ZVI + AC mixture absorbs the TCE, lowering its concentration in the solution, but the same absorption isolates the TCE from the ZVI, so less chloride is produced than by ZVI alone. BOS 100® is different. It generates 16x more chloride than the ZVI + AC mixture because the iron is integrated within the AC.

AC in the subsurface “locks away” the contaminants from separately co-applied remedial amendments, rendering the combination less effective.

Obviously, the same mechanisms apply to other mixtures of AC plus whatever other remedial amendment is being co-applied. You might see short-term treatment related to parallel adsorption and destruction mechanisms, but the combination will be less effective than with an integrated remedy. Over the longer term, the AC will become saturated and will stop adsorbing contaminants – allowing “breakthrough” and possibly even creating a secondary, more concentrated source of contamination that will need to be addressed in the future.

Which leads directly into Myth #5…

MYTH#5: ALL AC-BASED REMEDIAL AMENDMENTS ARE CREATED EQUAL

There are many AC-based remedial amendments on the market today – ranging from simple colloidal, powdered or granular activated carbons (CAC, PAC or GAC) to proprietary blends specifically engineered to combine carbon adsorption with various forms of permanent contaminant destruction mechanisms. As discussed in Myth #4, remedial amendments that contain only AC can offer only a finite adsorption capacity for contaminants and will cease to offer any treatment once the AC becomes saturated.

As a rule of thumb, dry, solid, AC-based amendments contain much more AC than liquid-based amendments (you are also paying for the water they’re mixed with).

But even more so, different AC-based remedial amendments contain vastly different concentrations of actual AC, affecting their performance. Dry, solid PAC and GAC contain 100% AC by weight, Trap & Treat® products contain approximately 80% to 93% AC, whereas some common CAC products contain less than 10% AC as purchased, never mind once diluted for injection!

Does a smaller the AC particle size (like CAC) provide better performance? Unlike for ZVI, adsorption of organic contaminants using AC takes place within the pore structure as opposed to on the surface. While grinding AC into smaller particle sizes does increase its external surface area, the internal micropore space does not appreciably change.

Particle size matters – not!
Smaller AC particle size ≠ more contaminant adsorption capacity

The overall adsorption capacity of CAC is essentially the same as it is for PAC and GAC on a percent weight of AC basis. Adsorption capacity is a function of the compound, its concentration, and the carbon used. However, the rule of thumb is that plain AC can only adsorb approximately 20% to 25% of its weight in organic contaminants. So, the takeaway here is that it is not how small the AC particles are that you are applying, it’s the mass of AC that you are introducing into the subsurface and concentration of contaminants of concern that drives overall in-situ adsorption capacity.

AC feedstock matters.

Unlike particle size, the feedstock used to make the AC does contribute to how much and what type of contaminants it can adsorb. AC can be made from a wide range of organic matter, the most common being wood, coconut husks and coal.

Coal or bituminous AC is best for adsorbing most organic contaminants and industrial pollutants, like petroleum hydrocarbons (PHCs) and chlorinated solvents (CVOCs), while coconut AC with its smaller pore size is more limited to targeting only the smaller organic molecules like some VOCs. A great example here is that the bituminous AC used to make Trap & Treat® BOS 200® can adsorb approximately 58% of its weight in PHCs – more than 2x the amount of regular AC!

So, your remedial design should consider the type of AC, how much AC mass is being applied, and whether it is merely AC or an integrated AC-based remedial amendment, to ensure the desired remedial outcome and lifespan of treatment.

MYTH #6: There’s no way to know where something goes when you are injecting it into the subsurface

This myth stems from the fact that you can’t “see” what’s going on in the subsurface. You’re limited to interpretations made using indirect measurements or widely spaced, discrete monitoring points. Obviously, the last thing you want to do is to start injecting a remedial amendment into a well or temporary point and just keep on pumping with the hope that it goes where you want it to go.

When completing large volume liquid injections, the risk of the injectant encountering a preferential pathway, like a utility bedding or a permeable sand seam, and heading off to who-knows-where is just too high!

This was a real concern in the past when chemical oxidant injections were the norm and incidents of “purple creeks” sometimes occurred. Fortunately, those days are long behind us!

Advances in remedial amendments and injection techniques have overcome these uncertainties and alleviated the associated risks.  Solid, particulate remedial amendments like ZVI and the Trap & Treat® products don’t migrate in the subsurface once injected unlike aqueous solutions and some CAC products.

On the injection side of the equation, by using a series of closely spaced injection points with overlapping radii of influence, and vertically off-setting injection intervals with small injection volumes, remedial amendments can be emplaced in the subsurface in a precise and controlled manner that vastly reduces the risk of “fluid flight”.

VEI also now exclusively employs custom-built Environmental Site Model (ESM) software for our injection programs. This powerful tool can be used to visualize site details like geological and hydrogeological data, environmental sampling data, and infrastructure, as well as remedial injection design details.

Once the model is set up for a site, the status of the injection is available in real time. This is an incredibly useful tool to aid our Project Managers and is also a powerful communication platform that can be shared with clients and other stakeholders to keep them informed of the overall progress of the project and convey abstract concepts in a more digestible manner.

Of course, when all of this is combined with monitoring for injectant and hydraulic influence in nearby monitoring wells during injection, and interim and post-injection QA/QC testing to validate the in-situ distribution and loading rate of remedial amendments in the subsurface, injection programs are highly certain and predictable and able to overcome subsurface heterogeneity to a higher degree than ever before.

QUICKY MYTHS

Sadly, there are an abundance of remediation myths that we encounter and try to debunk as they arise. We hope that this newsletter (and the prior one) has gone a long way towards that goal! But, to close out. we thought we’d highlight a few more “quicky” myths that also need debunking.

QM#4: YOU SHOULD BE ABLE TO GUARANTEE REMEDIATION

This all comes down to limited data, heterogeneities and uncertainty. If we were to know exactly what mass of contamination was present in the subsurface, and where and how it was distributed, we could design a remediation program that we would be willing to guarantee! But as you know, with limited up-front investigation budgets, it is nearly impossible to know everything about the subsurface at a site, and thus educated and professional assumptions are made with regards to remediation approach and design. And when assumptions are made, one should never guarantee remediation.

QM#5: MONITORED NATURAL ATTENUATION (MNA) IS SUFFICIENT FOR MOST SITES

MNA can be part of a remediation strategy, but it requires favorable conditions and may take years or even decades to achieve desired results. You also need to be aware of the potential risk of contaminant migration in the interim that might affect other areas of the site or result in third party liability. While MNA might be sufficient for sites, it is more likely that a combination of some of Risk Assessment, Risk Management Measures, Remediation, and MNA is required.

QM#6: THERE IS AN IN-SITU REMEDIAL APPROACH FOR EVERYTHING

Any reputable remediation contractor will tell you that some environmental contaminants simply can’t be remediated via in-situ means. Think bulk heavy metals (however, we can readily make metals non-leachable), chloride and non-volatile organics above the water table. In these cases, some form of extraction or risk management measure (RMM) are usually needed.

As always, we’re happy to answer any questions you may have about in-situ environmental remediation – myth or otherwise!

Contact us at (519) 653-8444 or info@vei.ca