Ahead of Brownfield Investigation and Remediation 2019 we've put a few questions to Dr Olivia Hall, Technical Director, Geostream UK and Dr John Haselow, President, Redox Tech, LLC who will be speaking on in-situ remediation and the latest innovations and applications at the conference.
Q. In your opinion, what have been the most important in-situ remediation advances in recent years?
Olivia: Achieving adequate distribution of amendments into low permeability (k) silts and clays remains a challenge in the UK/Ireland, so developments in how we use shear thinning fluids to improve distribution are important.
This is because contaminants residing in low-k portions of an aquifer act as continuing sources of contamination, making remediation difficult.
We recently used shear thinning fluids to target a >1 acre chlorinated solvent plume on a site where we encountered interbedded clay lenses.
This approach allowed us to implement an in-situ solution for our client, enabling both quicker access to the site, and the development to go ahead.
John: In the United States, I think the biggest advances have actually been refinements. There have been improvements in dehalogenating bacteria to tolerate a wider range of field conditions, and modifications to treat chlorinated alkanes. We now have a better understanding of the different forms of zero valent iron and their importance for remediation.
There has also been gradual adoption of rotary blending for treating shallow soils and groundwater, as well as more use of advanced jetting techniques for delivery.
Q. What are the most exciting emerging technologies on either side of the Atlantic?
Olivia: Advances in binder technologies mean stabilisation/solidification is being adopted on many sites, and is also being applied in increasingly innovative ways. We’ve used S/S to target everything from petroleum to chlorinated hydrocarbons (in-situ and ex-situ), and it’s now being applied successfully to target PFAS-impacted soils.
For groundwater treatment, we’ve seen increased use of injectable substrates – eg. ZVI, activated carbon – used alone or in combination with chemical/biological amendments, to target both petroleum and chlorinated hydrocarbons. The driver seems to be the requirement to achieve defined targets on a greater number of sites.
Probably as important as the emerging technologies themselves, are advances in site characterisation. There’s now greater emphasis on remediation design, with specialists defining a plume mass and not just the vertical and lateral extent. For years, we have failed to understand the actual problem we are trying to address. As the saying goes, fail to prepare… prepare to fail.
John: I think injectable activated carbon and sulfidated iron are potentially exciting technologies. There isn’t long-term data available for either technology, so it will be interesting to see if injectable activated carbon is more of an interim measure – similar to pump-and-treat – or if it is a long-term, viable treatment approach.
Q. In your presentation outline, you will mention two technologies in particular: injectable activated carbon and sulfidated zerovalent iron. What are the pros and cons of both technologies?
Olivia: One of the main advantages in the practical application of AC or ZVI as injectable substrates, is the relatively immediate effect observed in contaminant reductions. With AC, it will be interesting to see how quickly it becomes saturated and/or desorption starts to occur. With sulfidated ZVI, it will be interesting to see if the improvement in electron donor efficiency is worth the loss in distribution of hydrogen.
There are challenges relating to the application and distribution of these substrates in the subsurface. It is important to note, however, that these technologies require specialist skills to design and implement them on-site and ensure a successful outcome.
Another concern is long-term performance. As experience of using this technology grows and the number of sites treated increases, assessing this will be important.
Q. Similarly, what are the advantages and disadvantages of current PFAS/PFOA remediation techniques; and, as we learn more about these substances, how do you think best practice will change?
Olivia: The challenges associated with PFAS/PFOA are many, and are certainly not limited to the remediation techniques. We need reliable, quantitative assessment of the levels of these compounds, as well as improved availability of the advanced analytical techniques required for their quantification. The problem is not limited to PFAS/PFOA either, priority and watch list substances present many of the same challenges regarding quantification and remediation.
In terms of remediation, traditional soil remediation solutions, such as ‘dig and dump’, capping and soil washing, are not solving the problem or addressing the liability. However, some success has been reported with stabilisation/solidification, using proprietary binder formulations.
Likewise, with groundwaters, traditional pump-and-treat technologies are not addressing the issue, and leave a residual GAC that requires treatment/disposal. While some success has been reported using chemical oxidation, my concerns would be the extreme conditions needed, as well as overall effectiveness when trying to achieve the low target levels required.
John: In my opinion, treating PFAS/PFOA will be extremely difficult and very expensive. These compounds were designed to be the inert backbone of many products, including fire retardants, which are designed to not be oxidized.
Many practitioners in the US view PFAS/PFOA as potential long-term employment security, but ultimately someone has to finance the treatment. There are many compounds besides PFAS/PFOA that are distributed worldwide (for example, Cesium-137). Unfortunately, the world economy will not support returning the earth to pre-industrialized world conditions. In the end, I think the treatment will focus on targeting source zones and point-of-use treatment.
Q. What are the differences between in-situ remediation practice in the US and the UK (as you see it)?
Olivia: The problems are the same both sides of the Atlantic, and the technologies available to address them are largely the same, too. The difference I see is in regulation. In the UK, improved resources in regulation and enforcement would change our industry for the better.
Also, funding for remediation is managed differently in the US. For example, dry cleaner funds and other such funds available to companies for site remediation have had a huge impact on the US remediation industry.
John: I haven’t been involved in the remediation approval process in the UK, but in the United States, remediation is very fragmented and convoluted. The problem may be regulated at federal, state or local level – depending on the location – and may be classified as Superfund, RCRA hazardous waste, dry-cleaning, petroleum, brownfield or voluntary.
Funding and regulations are different for each classification, even though they are often managing the same problem (for example, chlorinated solvents or benzene). Property transactions and redevelopments are usually the best funded, and also proceed the quickest. At the other end of the spectrum, Superfund sites can remain dormant for years with nothing happening.
While the UK has a concept of ‘betterment’, the US has the similar concept of risk-based corrective action (RBCA).
Q. Would you mind letting me know more about your current projects and telling me what is innovative and exciting about them?
Olivia: We’re working on multiple in-situ remediation projects, including soil and groundwater remediation on a former gasworks site, and NAPL removal/dissolved phase groundwater treatment (using ChemOx) on a commercial site.
One of our most interesting current projects involves the remediation of TCE-contaminated soil and groundwater on the site of a former gas meter factory in Manchester. Here, we’re targeting a >1 acre chlorinated solvent plume using Redox Tech’s ABC+ technology, as well as shear thinning fluids to improve distribution where we’ve encountered interbedded clay lenses.
Instead of using bioremediation for treatment of TCE-contaminated soils, as recommended by the client’s consultant, we saw that stabilisation/solidification would treat contamination, while also improving soils to 130pka to support the piling rig.
Prior to starting onsite remediation works, we carried out additional site investigations to get a better understanding of the contaminant sources and distribution in groundwater, and to assess soils impact in previously inaccessible areas.
As part of the SI, we commissioned degradation studies to be completed by an American laboratory. The objective was to demonstrate the treatability of the contaminants in concern, and establish site-specific degradation half-lives to improve regulatory confidence in the proposed remediation solution.
After presenting new data to regulators, we were able to revise the existing DQRA and set more accurate remediation targets. We could also prove to the EA that half the site did not need remediating, enabling them to agree phased handover of the site and take 20 weeks off the original programme.
Olivia and John will be going into further detail on these topics at the Brownfield Investigation and Remediation conference on 9th October 2019 in London. Find out more here.