In Situ Remediation within Bedrock

Video Transcription

Jack: My name is Jack Shore. I’m the District Manager for the U.K. and Scandinavia. Thank you for tuning in. Today I’ll be talking about in-situ remediation of fractured bedrock, really, emphasizing that this is something that can absolutely be done. And the motivation for putting this webinar together was when I’m talking to people about different sites that they’re looking at, maybe they’re undertaking remediation options appraisal for one site and they’ll also say, “Oh, we have another one where we have totally [inaudible 00:00:28] impact or PCE impact. But it’s in a fractured bedrock, so I guess maybe that’s not something you can help us with. Really, it’s something that we absolutely can, but fractured bedrock sites do have their challenges. So, we’re gonna look at those challenges, the solutions to those challenges, and then I’m gonna draw on four separate case studies where we’ve used injectable substrates to remediate fractured bedrock sites to illustrate the success and the different ways in which you can remediate those sites.

So, yeah. We’re gonna look at, first of all, how we work as Regenesis, why this is important for bedrock sites. Many of you have logged on today. I had to look through the attendee list. And some of you may not have interacted with Regenesis directly before. And I’ll just walk you through how we evaluate sites, why this kind of consultation is important broadly for most remediation, but particularly for bedrock sites. We’re then gonna look at the challenges that come with fractured bedrock, delineation of contamination, and coming up with an appropriate remediation strategy. And then I’m gonna point you to different resources that are out there for site investigation planning. Now, I will say I’m not an expert in this area. It’s been a while since I’ve had to plan a site investigation on my own. But there are a wealth of resources out there that can really help you come up with different tools and techniques that perhaps aren’t part of your standard site investigation suite. Finally, then we’ll end on a series of case studies, looking at sites where we have remediated dissolved phase, chlorinated solvents in the fractured bedrock system where we have remediated sites where you have three-phase petroleum hydrocarbon contamination. A third way we’re looking at DNAPL concentrations of chlorinated solvents. This is a fairly early ongoing site that we’re working with with Ramboll where the results are looking excellent. The injections were actually completed in January of this year. And then finally, we’ll look at a site where we remediated metals. We remediated hexavalent chromium plume with BRD Environmental where we have over two years of validation monitoring, showing the success of that particular site. And then finally, we’ll end with a summary of remediation options and the strategies that you can draw on to treat bedrock sites in-situ.

As Regenesis, as a company, we’ve been around for a while, and over 25 years, completed some 28,000 projects worldwide. Within the U.K., Scandinavia, we certainly look at something between 20 and 35 sites a month. And I would expect two to five of those to be bedrock sites. So, this is something that has absolutely been done many times before across the world in many different geological settings. And in order to make these solutions successful, this upfront consultation approach that we do is critically important. So, first of all, we will review the site to see if it is appropriate for our remediation technologies. Now, at Regenesis, we have a lot of different technologies, a lot of different techniques that we can deploy on a site, but that doesn’t mean we’re the panacea, we’re the absolute solution for everything. It’s important for us and for you guys that we identify if the site is appropriate for these technologies or if there’s just some gap analysis. So, maybe if there’s a little bit more investigation done, we can give you a more certain answer. We’ll then help you with the technology selection. That selection of technology will not only be dependent on the conceptual site model of the site, but it’s also going to be dependent upon the commercial landscape that surrounds that project. So, are you looking to clean this site up very quickly because it’s a development so you don’t have time to do a protracted enhanced natural attenuation program? Or are we looking… Or actually, do we have the time? It’s an active manufacturing facility. It is going to be an active manufacturing facility for many years. These sorts of things are gonna influence what kind of technology we’re gonna recommend for that site. We provide you with the remediation design that will outline the cost and that will outline the injection configuration and the dosing and broadly a program for the application and the remediation. Something that we do fairly routinely now, I’d say about 70% of the larger projects that we do are ones where we’re offering a turnkey service. So, we come onto site and do those application works for you, do those injection works for you. Very more often than not, we are subcontracted in by a remediation contractor or we’re contracted by a design and build consultancy.

And then finally, post evaluation. Now, we in Regenesis, we don’t do this. We don’t do the sampling, we wouldn’t do the report writing. That’s always done by a third party. But we do like to be involved just to see the data that’s coming through after these injection works have been completed. Really, it gives us the opportunity to see if sites are going well, if they could make a good case study. But equally, if something isn’t going to plan, it gives us the opportunity to rectify that if you have a particular recalcitrant area on the site. So, we’re all about from cradle to grave support. And that consultation period for these bedrock sites is really important and I’m gonna illustrate this in a second. So, the key thing when it comes to bedrock sites and broadly all in-situ groundwater remediation is that there are always gonna be known unknowns. And no matter how much site investigation you do, the over tens of years, there’s going to be parts of that site where perhaps there is a pool of DNAPL and it hasn’t been picked up as part of the site investigation. Now, as long as this is acknowledged and there are appropriate contingencies put into place and everyone’s expectations are managed accordingly, then this can make for a good and robust remediation strategy.

Some of the things that are unique to fractured bedrock sites is how this contamination is gonna be distributed in the subsurface. Contaminant distribution and transport is gonna be largely governed by fracture flow. The extent of that contaminant transport is gonna be dependent on fracture interconnectivity. And when you’re designing your site investigation, I’d stress that this should be one of the major objectives for your SI, is to understand the interconnectivity of the fracture network on your particular site. And chances are if you’re looking for that, if you’re looking to delineate that, to understand how the structure network is behaving on your site, then what will follow is a plume delineation because you’ll find all of these preferential pathways, you’ll find all of these flex zones that are gonna be responsible for 99% of your contaminant transport and you’ll end up delineating your plume.

With sedimentary bedrock, there’s an added complication, in that, you are gonna have contamination. The primary flux of contamination is gonna be in your fractures, but you’re also gonna have a pool of secondary contamination in your primary porosity. So, as that contaminant moves through the fracture, through advection, and diffusion, you’re gonna get contamination diffusing into your primary porosity into your rock matrix. And this is something that is gonna be crucial to, one, understand, but also to communicate to all stakeholders, be that remediation practitioners or the liability holder for the site because while in the initial phases of remediation you may see a significant drop in contaminant levels from remediating contaminant mass in the fractures, you’ve got the secondary source of contamination in the rock matrix. And within those fractures, you’ll have reduced contaminant mass efficiently, so you’ll likely create a concentration gradient. Fick’s law then says you’ll get diffusion. So, you’ll get back diffusion of contamination from that primary porosity that will lead to, in some cases, a protracted lead-in time for cleaning up sites to particularly stringent criteria. So, this is something to be thought about, to be communicated about both at a regulatory level, so to establish expectations as to when the site is likely to be cleaned up, and also to the liability holder as to time frames and maybe why you’ll see a lot of action early on in those remediation phases and then why maybe there’ll be this protracted period of back diffusion. But back diffusion is not necessarily an obstacle that we can’t overcome. There are many different engineered injectable substrates that can overcome this and I’m gonna talk about that as part of this presentation.

The direction and flow of the contamination is gonna depend significantly on fractured geometry. Sometimes the contaminants will be behaving in ways that you wouldn’t expect them to. I reviewed a site a couple of years ago in a bronze gray sandstone where we were dealing with three-phase petroleum hydrocarbons. These three…the three-phase, however, appeared to be diving. And that was down to the fracture configuration dipping on the site. So, this is, again, something that’s super important. With these hardrock sites, your site investigation and drilling is going to be costly. So, when it comes to planning this, you want to try and make sure that every well on your site is working as hard as possible for you so you can better…not only delineate and understand the conceptual site model, but also try and take the opportunity to use this infrastructure as part of your remediation strategy.

So, as I said before, sort of how we work in REGENESIS, it’s not always the case that somebody comes to us with a completed site investigation and says, “There’s not gonna be any more investigation. This is what you’ve got. Work out a solution for that site.” For complicated fractured bedrock sites, what often happens is the first and maybe second phase of site investigation has been completed, and that we’re now into another phase of remediation design characterization. So, there’s gonna be a third phase of site investigation focusing on better understanding the site in terms of remediation. This works very well if you can get a remediation practitioner on board sort of ahead of finalizing a remediation strategy. And often we will be looking for things that may not…that a consultant who is focused on risk and delineation may not be looking at. And we can help you with how to construct monitoring wells or delineation wells that may not be used as part of the validation strategy. These wells could then be utilized for extraction using a pump and treat system or they certainly could be used as injection points as well. So, it’s all about capturing and generating those much value from those costly monitoring wells so that they can be used as part of the remediation phase as well. So, engaging with remediation practitioners early on, as this sort of cost-time graph shows you, can save you both time and money in terms of the total project cost.

Something I will stress is that for these fractured bedrock sites, you do need an experienced geologist to be there logging those cores. It’s fairly standard in our industry that you see that brand new graduates the first thing that they do when sent out to site, it’s important that they are 100% billable, that they may not have the experience of working in fractured bedrock settings. So I would always stress if you can, if the budget allows, do have somebody more experienced on site. If you can, get them both on site so there’s gonna be some cross-training so they can understand what they’re looking at and what they’re logging. But these kind of complex fractured sites, the best ones that I’ve worked on is where there is a multidisciplinary approach where you have people not only from the land quality group, but people that we’ve drawn…that have drawn on from geotechnical that perhaps have a slightly different understanding to this than I’ve seen the contaminated land profession do, as well as water resource hydrogeologists that will bring another angle to the discussion to then better delineate and understand what’s going on on the site0. So, they’re very much one of these where you need to draw on as many people as possible. And we in Regenesis we’re here to help as well. It’s fairly routine for me to be involved in these sorts of discussions, so don’t ever hesitate to give us a call even if it’s just to bounce around an idea.

So, in terms of the solutions, what do we in Regenesis need to know in order for us to provide you with an in-situ remediation design? So, this can broadly be broken down into four categories. These are the importance of which, you know, we’re going from top to bottom, we need to understand the geology because this will define flow regimes, and we need to understand hydrogeology because this is going to influence flow and transport. And together, with these, we can understand the contaminant flux. Now, one of the methods that I favor and if it’s technically feasible, but when it comes to fractured bedrock sites is the installation of permeable reactive barriers or a series of permeable reactive barriers or PRBs across the site utilizing what can sometimes be quite a high-flow regime, so, it’s something with a significantly high seepage velocity across the site, to provide sequential treatment. As that plume moves across the site, you get comparatively cleaner water and migrating off site. So, you’re managing risk that way. And it’s not always possible, but it’s a method that I favor because you’re ultimately installing less wells. And if you’re looking to treat a depth, it’s gonna be the drilling that’s gonna be the major cost rather than the reagent and the application. So, a series of PRBs can often mitigate against that high-drilling cost.

Similarly, geochemistry and microbiology is very important in fractured bedrock sites, particularly if the contamination is at depth. The reasons why natural attenuation may not be occurring at depth can be quite complex. It’s something that we see quite often in fractured, say, crystalline granite, for example. You may have a PCE spill from a former dry cleaner. That spill happened some 30, 40 years ago, but there’s very little evidence of natural attenuation occurring. You have to ask yourself, “Well, why is that?” And it could be that you have very high flow of groundwater moving through the system, so you’re getting lots of aerobic water that is inhibiting that reductive dechlorination process. It could well be that you’re dealing with quite a barren system, so there isn’t much micronutrients down there. So, that could be in the form of if we’re sticking with the chlorinated solvent theme, electron donors, it may be that they are lacking in micronutrients such as B12 and other dissolved metals. So, these things need to be established in order for us to know, “Do we just need to inject an electron donor into the subsurface or is there something else that needs to be added to kickstart that natural attenuation process?”

Similarly, microbiology is important, particularly, like I say, if we’re looking to treat at depth. When I say at depth…I mean, every site is different, but, I would say, if you’re looking at 10 meters and below, then these things really start to come into play. I’ve recently…well, not so recently. A couple of months ago I looked at a site where they had completed some qPCR analysis of the microbial consortia across the site. I think it was something like 1,500 square meters. So, it wasn’t a particularly large area. But what I did notice was 10 meters apart you had one well where the cell count of the dehalococcoides and dehalobacter bacteria was really quite high, so high that I would assume some kind of bioaugmentation may have happened ahead of these guys getting to site, but then you go 10 meters the other way and you’re dealing with really low populations of these microbes in the subsurface, but similar levels of contamination. And it could well be that we’re dealing with two different fracture networks, one may be drawing on deeper water with less electron donors and other micronutrients, whereas the other is part of a different fracture network where these nutrients are abundant for whatever reason. So, these are the sorts of things that you need to look at. And they will inform what you would inject where.

In terms of tools that are out there, as I said, I’m not an expert in different site investigation techniques, but what I will say there’s an abundance of free information out there that is available from the ITRC and other regulatory websites that can help you come up with additional ideas to better characterize the site. And this one is a site investigation matrix. You can input a series of parameters. So, here I’ve done hydrogeology bedrock that’s saturated. I’m looking for semi-quantitative data. You hit Search. What appears to be quite a lot of macros were in the background because it’s taking my computer a while to come up with the answer. So, if you just zoom in there, you see that it tells you where it’s applicable for, so geology, hydrogeology, chemistry. And then in each of those techniques, you have a hyperlink that then tells you more about that particular investigation methodology. Now, take a screenshot there if you need that web page. Another way of doing it… I think if you Google ITRC investigation matrix one, probably put DNAPL in there as well, you’ll likely get to the page where you can download this. But it’s a tool that I was quite impressed with. And CLU-IN is another website, I would say, packed with full of really useful resources. Maybe if you’re listening to this and you’re just starting off in your career, there’s lots of webinars out there that can really kind of open your eyes to how to do different things on these sorts of sites.

With regards to the reagents that we’re injecting them, how is it different on fractured bedrock sites, and then crucially how are we, Regenesis, slightly different when it comes to the reagents that we offer? So, the reagent flow will be faster on fractured bedrock sites than in superficial deposits, so soils, silt, sands, clays, things like this. This has an advantage, though. It means that you will have a higher radius of influence you may be injecting across the fracture aperture that isn’t particularly wide. So, you’ll be injecting under fairly high pressure. So, you will be able to get better advective distribution from your injection well. So, that’s a positive thing. But the reagent will be more diluted. This is something we would need to keep into account. This is something that we would need to take into account when it comes to the design of that solution. So, this is why understanding the fractures, the size of those fractures, the frequency of them is really important. There’s also gonna be less matrix interaction. And this kind of goes both ways. So, there’s less matrix interaction. So, it could be more susceptible to changes in pH. This will need to be managed. You’re gonna have less sorbed contamination. This is particularly true for crystalline bedrock where you don’t have issues of fusion into primary porosity. You’re gonna have reduction in matrix retention of both the reagent and also the contaminant. Again, it could be a positive, though. If most of that contamination is in the dissolved phases in the water, then using chemical reduction or oxidation technologies may yield quite a rapid reduction as you’re not dealing with that excessive amounts sorbed phase contamination.

And then finally, you have a reduced surface area interactions between the reagent and the contaminant. However, this can all be ameliorated by the fact that the product will have been in place across a wider distance. So, the contact may be greater as you have this wider radius of influence or distance in the direction of the groundwater and the contaminant transport. So, it can work both ways. But what I would say is, the choice of substrate is gonna be really important. If you are a remediation contractor or if you are an environmental consultant and you’re auditing, if you like, the different options you have out there, I would argue that these are the four key things you need to look at. So, the first is distribution. And it’s obvious why that’s important. If you’re injecting something into the subsurface, you want it to distribute far, but not too far because that will reduce the number of injection wells you’re gonna need to install into this hardrock. Second is persistence. So, because the reagent flow will be faster in fractured bedrock than in superficial deposits, you’d want something that is appropriately soluble. You don’t want something that is going to wash away and require multiple injections. You want something that’s going to hang around, but also be appropriately reactive. So, an example would be vegetable oil. If you were to inject vegetable oil into these settings, it might be persistent, but it will take a while to start fermenting, so you haven’t got something that is appropriately reactive. And then finally, and I’d argue that this is probably the most important thing, is ease of use, because if you’ve nailed the other three, but it’s a nightmare to use on site, it’s not being injected as it should be, it has high issues when it comes to health and safety, and I’ve seen that with some zero-valent iron technologies, then it’s a non-starter from the beginning. So, making sure all of those four things are balanced is gonna be really important.

In terms of application techniques, something I’m often asked is, “Okay. How do you stop all of your reagents just disappearing down one fracture, one large fracture rather than get it…disappearing down one large fracture and ensuring that you get an even distribution of that reagent within your treatment zone?” So, there’s a number of ways you can do this. We probably more often than not, rather than the picture that you can see here, we would favor nested well installations, if that’s possible, where you have maybe three wells with 3 meters of slots installed at different levels to sort of mitigate against this concern of all the reagents flying down the single fracture. It may well be that that’s what you want it to do. It could be that you’re dealing with a site where you have a single fracture system. If you can just intercept that, you can address 90% of your contaminant mass, but that’s gonna be fairly unusual. So, another option would be to install an injection well similar to this where you have these 3-meter lifts. You drop a double packer down those wells. You inflate them. So, you’re isolating those 3-meter horizons and then you’re injecting under pressure to ensure that you aren’t just, as I say, injecting all of that reagent down a single fracture.

With regards to application configurations, there’s a number of different ways that you can do this. I’ve just illustrated four of them. As I said, I personally favor through multiple in-situ PRBs across a site sort of barrier configuration. I think it’s a nice compromise between the cost of drilling and then the speed and efficacy of treatments. And not always applicable, though, particularly if you have quite a slow-moving groundwater regime, but that’s seldom the case in fractured bedrock sites. Another option would be recirculation. So, the drilling cost there would be relatively low, but I would say it is probably your higher risk of it not working. You’d certainly have to do a pilot trial maybe with a reagent, maybe with a tracer to ensure that there is conductivity between your injection and your obstruction well. While you may save on drilling, you’ve got operational costs in there. Someone’s gotta manage and maintain that recirculation system so that something has to be thought about. But it’s certainly something that could be considered, particularly, if you’re on a site where you have buildings and it’s not possible to drill inside using some kind of recirculation system to drag a reagent beneath that building to ensure even treatment could be an option.

Drift and inject could be useful for some colloidal technologies that we will talk about. However, it’s not always a good idea to do this. We in Regenesis have mechanisms to control the spread of our colloidal technologies, but it’s certainly an option that is out there. And then finally, grid pattern injection. So, that’s the most expensive, but it’s the most expensive and it gives you the greatest certainty of results. If you’re injecting many more wells, you’re doing it as a grid across your whole plume, you would expect to see pretty rapid cleanup quite quickly, but that is something that you pay for. Indeed, with these sites, often, I find that it’s a combination of barriers. There’s a standalone technology or it’s barriers with grid applications where there is good delineation of that contamination in that fracture network. Indeed, the case studies that I’m going to present to you, the first two are two case studies where we’ve used in-situ PRBs, and then the second two is a combination of in-situ PRB, so in-situ permeable reactive barriers with great applications across known hotspots and source areas.

So, the first two case studies then of these in-situ PRBs, the first one I’m gonna talk about is actually one that we recently had a webinar on. And Emma from Golder kindly agreed to co-present this. I think this was sort of just back before the summer. So, if you are interested in this particular case study, on our website we’ve got this recorded. Emma does a much better job than I will of explaining the site and the history rather than the 10 minutes that I’ll take you through this one. But the site itself is an active design and engineering site. It has been since the 1960s. It did have a series of previous uses, though. So, it was greenfield. It was a farm before that. But it was also an airport/aerospace facility where they developed light aircraft and bombers. The site is located on the edge of the city with two rivers running close to the site sort of acting as site boundaries, really. And there was a known use of historic solvents, some of which were reported, some of which it would appear not due to the age. And as such a fairly extensive site investigation phase was completed from 1998, really, in various stages up to about 2016. There was clear evidence of TCE found and this spurred on these further phases of site investigation, which amalgamated into 150 boreholes drilled and installed across the site. This included your standard 50-mil wells as well as dual installations, CMT-3s and CMT-7s. The culmination of this work showed that we had some superficial deposits, though I believe they weren’t that heavily impacted. They varied in thickness across the site. We are looking at quite a large area that had been investigated here between 1 meters and 4.5 meters. The bedrock was interbedded sandstone and mudstone, so pretty complicated. It was fractured. Those sandstones dominated at the higher elevations. And what was found was that it was the fractures in the bedrock that was the primary flow mechanism for the DNAPL through the aquifer.

So, as part of our… I’ll step back one. As part of our remediation strategy, we were suggesting that, let me get my laser pointer, that source and then treatment using appropriately soluble electron donor should have occurred here. And then a in-situ PRB comprising PlumeStop and another electron donor called HRC was to be installed along the downgradient edge of the site to protect the stream. So, the results I’m gonna show you is from a very early pilot trial from 2016. The pilot trial comprised about a 10-meter barrier where we injected PlumeStop in combination with HRC. Here you have two additional wells that were installed, GA16/01 and GA16/02. 01 was our upgradient well, so our control, if you like, and then 16/02 was our target well. GA16/15, this was a pre-existing well that gave us some historical data. The technologies that were installed, so the first one was PlumeStop. PlumeStop has been around since 2014 now. What it is, it’s a finely milled granular activated carbon that’s been milled down to 1 micron to 2 microns. So, that’s the size of the bacterium. That’s the size of a pore-throat. And what we’ve done is we’ve coated this granular activated carbon in a dispersive polymer so that these carbon particles flow and behave in such a way that they don’t stick together when they’re injected into the subsurface. They repel each other, but they stick to the aquifer matrix so they can paint the subsurface with carbon. This dispersive polymer means that they behave and act as a colloid. So, blood is a colloid, wine is a colloid. They move very freely in the subsurface. So, distribution, really important here.

Fractured bedrock sites, you don’t want to be indexing hundreds of wells to get interconnectivity of radius of influence. But sometimes that is necessary with these sorts of…with these PlumeStop jobs where you are dealing with very high contaminant loads, but here we had lower dissolved phase concentrations. We could get away with wider spacing.

Just to illustrate how well it moves in the subsurface, here you have PlumeStop on the left and then you have powdered activated carbon on the right. This is just an experiment done at our R&D facility in California. And you can see here that the PlumeStop migrates right the way through which is flush 14 pore volumes through that column, whereas the powdered activated carbon doesn’t move very far at all. In terms of distribution of the reagent, here you can see a before shot, so these are sand grains, very flat and a lot of sorption sites. In these fractured bedrocks, it’s important to remember that you will have maybe cemented sand or even weathered sand particles that are in the fractures. So, there is gonna be some matrix for this to dissolve onto. Afterwards…after applying the PlumeStop, that coats that sand grain greatly increasing its surface area and greatly increasing its sorption capacity. We then would pair it with an electron donor to create an environment conducive to reductive dechlorination. The microbes that are responsible for reductive dechlorination, they’re not planktonic. They’re sessile. They sit on the aquifer matrix and they secrete a biofilm to capture and metabolize that contamination. But by using the PlumeStop, we’ve sorbed those organic contaminants onto the PlumeStop matrix. We have then added an electron donor. The electron donor in this case is a technology called HRC. It comes in a series of strengths, I guess, if you like. The primer is used to prime an aquifer to create anaerobic conditions very quickly. You then work your way up to HRCX which provides a controlled release of hydrogen for up to 48 months.

So, combine these two, what do you get? You get wide distribution of PlumeStop, really important in these fractured sites. You get contaminant absorption, which then promotes the growth of the biofilm. That then promotes biological degradation. When you pair it with an electron donor that is accelerated more, in this case, electron donor is in the subsurface so you get enhanced reductive dechlorination. And the key thing is that as those sorption sites get freed up, more contamination can then resorb on to the PlumeStop, which then deals with further influx or back diffusion of contamination. As I’m talking about this, maybe there’ll be time if I can scramble and find it, we did a really interesting experiment looking at…we did a sand tank and it was filled with permeable sand and then fairly impermeable clay and PlumeStop was sent through it. And you could see that the PlumeStop actually diffused into those impermeable clay layers, and to a degree you could expect that to happen, depending on the geology into the bedrock. And then around and around you go. So, you can engineer a self-cleaning Brita filter in the subsurface.

In terms of our results, so, these are the downgradient wells. You can see here that there was some pretty dramatic drop-offs after the PlumeStop had been injected. It works very well with the chlorinated solvents, not only things like TCE which do have a pretty high affinity to carbon, but also vinyl chloride as well, sort of just above the detection limit. Something else that we had in this plume was benzene and MTBE. That wasn’t the target of… These weren’t, you know, the target of our treatment, MTBE, in particular. We were kind of managing expectations really. MTBE is a fuel oxygenate. It’s not particularly toxic, but at pretty low levels, it can taint…it can make drinking water taste bad. So, there wasn’t a particular risk driver for this one. But it also doesn’t have a particularly high affinity to carbon, but we were able to reduce MTBE levels down to non-detect as well. So, that was a bit of a result.

In terms of the other case study, so this is one that we did with Jacobs. This was an active factory. So, unlike the site that we did with Golder where most of our work really was done sort of off-site, though, within the redline boundary, if you like, here we were very much on an active site. There was a series of spillages of honing oil. So, this is a heavy oil. It’s a lubricant that is infiltrated through the vadose zone into the groundwater via fractures impacting the underlying chalk. Here we have very high levels of dissolved phase contamination that would suggest an excessive solubility, and we did have some NAPL as well. So, pretty heavily contaminated site. Here, we utilized existing wells on site to apply the reagents into the subsurface.

There was already quite a dense array of delineation wells. And based on the validation strategy that Jacobs came up with, we could sacrifice some of those wells for injection wells. So, that goes back to us, you know, trying to utilize the infrastructure that’s already there to keep remediation costs down.

So, what we initially did, we injected a product called PetroCleanze into the subsurface. We did this across the wells where there was the most heavy impact, where there was measurable three-phase. We were lucky here we were able to utilize a vacuum tanker to remove the desorbed contamination as we have pretty good recovery rates from each of those wells. Just to illustrate how PetroCleanze… So, we have far too many products that start with Petro. PetroCleanze that works… Typically, we would pair it with some kind of physical obstruction system. So, in this example, we’re looking at a pump and treat system. In the case study, we did this with vacuum tankers. So, you have a site, you have three-phase sat on the groundwater. The first thing that you do, if you have measurable three-phase, the most efficient and appropriate thing for you to do is to pump it off. So, at this point we can’t really help you. But the thing is as that pumping regime goes on, you get progressive desorption. And that desorption can lead to asymptotic recovery of contamination. Something I will say is that to use PetroFix, you need a total fluids recovery system. Skimming alone won’t help…won’t be compatible.

So, to overcome this, essentially, you’re dealing with a system once that asymptotic recovery occurs where you have most of your contamination now bound to the soil and diffusing into the aquifer. You then add PetroCleanze, and what it does is it raises the pH of the groundwater to pH 11 and it partially chemically oxidizes the petroleum hydrocarbon molecules in-situ. Now, because we’ve raised the pH, we’ve reduced the charge, which means that these polar molecules, so one half wants to be in the soil, the other half wants to be in the groundwater, can’t resorb to the soil, so they bunch together to form a surfactant. And that surfactant can then be recovered using a pump and treat system. So, once you inject, typically targeting the smear zone to the upper element of the aquifer, you leave it two weeks, allow that desorption process to happen. It’s after two weeks that the pH will start to buffer out fairly quickly and, actually, you can end up with resorption of contamination. So, that two-week window is important to keep an eye on. And with PetroCleanze your recovery rate will tend to look a bit like this. So, you’d have three desorption events each progressively less dramatic and followed by three obstruction events. You find all desorption event likely below your cleanup target, and then you continue to pump, turn the system off, and crucially, what you’re not seeing there is rebound from the sorbed phase contamination. So, it’s a way of ensuring that, you know, you turn that system off, you demobilize it, go back and monitor things, maybe not quite as you left them as a way of mitigating against that risk.

So, elsewhere on the site, we utilize RegenOx where contaminant levels were pretty bad but wouldn’t warrant the requirement to undertake enhanced extraction. And we also then injected across this area using ORC, so this oxygen-releasing compound. RegenOx is a technology…it’s probably used every working day across the U.K. It’s a two-part product. The first part is a bicarbonate-based chemical oxidant. And then the second part is an iron silicate catalyst. You mix them one to one with water…you mix part A to part B at one to one, then you dilute it at about 5% of water. Here are the illustrations showing direct cross-injection. It can absolutely be injected into wells. It certainly can be applied into excavations. And the key property of RegenOx, and it was why it was chosen on this site, was that Jacobs were very health-safety conscious and the client even more so. And this technology is very safe to handle and very straightforward to apply. It also has a significant longevity. So once injected into the subsurface, RegenOx will continue to be active for up to four weeks. So, unlike commodity oxidants where you could be expecting a week to days of reactivity, once in the subsurface, it will be active for up to four weeks. What this means is you get better treatment. Chemical oxidation as a process depends on contact. The oxidant and the contaminant must make contact with each other in order for that chemical oxidation reaction to occur. So, if you have something persistent in the subsurface, you’re…you have something persistent in the subsurface, you’re more likely to yield better treatment efficacy.

It was important here, even though we were injecting at depth, that it wouldn’t impact any underground services. So, this included plastic pipes, metal pipes, cables and foundations. In terms of the oxidation mechanisms there are three primary ones. This is where the oxidant makes direct contact with the contaminant. That exchange of electrons then breaks apart chemical bonds and destroys your contamination in-situ. Similarly, the propagation of free radicals, so the part A in the presence of ambient salts and metals, will start to degrade and produce these free radicals. These free radicals are essentially molecules with unpaired electrons and will… When they come into contact with the contaminant, they will oxidize it and destroy it.

And then the second…the third, rather, final one is with RegenOx. So, this is the part B. This is the iron silicate catalyst. This is important because the part A is initially activated through base activation, but that pH is very quickly buffered out in the soil. As that pH starts to drop, this catalyst, this iron silicate catalyst will be formed and will act as a sulfate where the oxidant and the…the remaining oxidants and contaminants make contact with each other to yield better treatment efficiency. So, those are your three mechanisms there.

We also polished it off with a bio-polishing step using ORC. That’s our oxygen-releasing compound. It’s been around for a long time now, probably a good 20 years. ORC when you apply it to the subsurface, it’s a calcium oxy-hydroxide where we’ve interpolated phosphate crystals into that structure to give you a controlled release of oxygen. So, you apply it to the subsurface and it starts to dissolve. As it dissolves, it will release oxygen into the dissolved phase where those microbes can utilize it for bioremediation, so as an electron acceptor. Those phosphate crystals regulate the release of oxygen. So, after a single application, you get up to 12 months of oxygen release, so you don’t have to do multiple applications. And they also ensure that you don’t have this impermeable rind forming so that you do get that continual 12-month release of oxygen into the subsurface. That means that single injection, you’re creating a stable environment over a long period of time. That means you grow a large microbial consortia that ensures that you grow a large microbial consortia…consortia, sorry, rather, to break down as much of that contamination as possible all from a single injection. In terms of our results, fairly dramatic. You can see that we were dealing with up to 18,000 micrograms per liter of this honing oil. That was reduced fairly dramatically. You can see here that the ORC is then taking an effect. And you can see that concentrations get low enough for this particular site where it was de-risked and no further action was taken.

So, the final case studies, case studies three and four. Here we’re looking at a slightly different application configuration where you have a grid in the source area and then a PRB to manage off-site or on-site migration. So, this is an ongoing site. This is one that we are doing with Ramboll. We did the injection works in January of this year. Actually, one of the first sites where we’ve used a new technology called S-MicroZVI, and again, another former airfield where they seem to be all about using TCE that had impacted the underlying groundwater. Two principal areas of impact, we had area A, fairly small, about 350 square meter area, and then area B, where we had really quite high levels of TCE and DCE. These are in milligrams, so, you know, pretty high concentrations of these chlorinated solvents. The geology here was very challenging. So, this was a limestone bedrock. It was a cornbrash formation. So, there were some fractures, but in cases, not many. So, it was important to understand where they were and target them appropriately with these reagents. There was also quite a varying groundwater level. Actually, not across that big of a distance. You could have had one injection well 4 meters away and there will be a meter difference in groundwater levels. So, it’s quite a complex regime. Hydraulic conductivity as well varied really between 0.5 to 5 meters per day.

So, our injection strategy in area one was sort of a grid injection across two hotspots. The pivot you can see on the left there, that was a hotspot quite close to the entrance to the site. And the area two strategy was a series of permeable reactive barriers. Those black rectangles there, that’s just me protecting the street names. This is a confidential site. We can’t identify exactly where in the U.K. it is. Here we injected an electron donor called 3DMe, it stands for 3D…it stands for three donors, three electron donors. This is a molecule that we invented. It’s a polar molecule. So this is the 3DMe molecule. Here you have a glycerol polylactate with an ester bond with fatty acids stuck on the side. So, you end up with a polar molecule. When you mix it with water, you create these micelles. And these micelles are critical. One of the key benefits of 3DMe is that these micelles enable it to be self-distributing. It’s actually a technology I do often reach for, for fractured bedrock sites because how these micelles work, you inject them into the subsurface and about 300 ppm concentration of 3DMe, these micelles will form, they’ll travel down the aquifer, concentration levels drop, they’ll then stick to the aquifer matrix, concentration level is increased, micelles form, travel down, stick, form, stick, form. So, they can distribute very long distances, greatly reducing your drilling cost in fractured bedrock sites. It’s also engineered to be appropriately soluble, so it’s not going to wash out either. And once injected, it will continue to release hydrogen for up to five years. So, you can create a really stable environment with this technology.

We also co-injected it with S-MicroZVI. So, S stands for Sulfidated and ZVI stands for Zero-Valent Iron. At the time, it was the largest S-MicroZVI project we completed in the U.K. What it is, it’s another colloidal product like PlumeStop where we’ve milled sulfidated zero-valent iron particles down to less than 5 microns and we’ve sulfidated the outside of that and suspended it in glycerol. This has resulted in…this can result in when you pair it with an electron donor, abiotic degradation and it’s gonna enhance biological degradation. The reason why we’ve sulfidated it, you may have come across other ZVI products before, we sulfidated it to reduce passivation. So, ZVI in its raw form wants to react with everything. It’s an incredibly reactive reagent, including water which results in hydrogen being produced. If you sulfidate it, however, you can divert that electron exchange. So, if you look at this second image there, sort of kind of like half a pie chart, if you like, on the right, you have non-sulfidated micron-scale ZVI. What you can see there is 92% of those electrons go to react with water with about 8% reacting with the chlorinated solvent. If you flip this, 87% of those electrons go to react with the chlorinated solvent and only about 13% go to react with water. That 13% isn’t necessarily wasted. That can be useful in rapidly acclimating an aquifer, for example.
As a technology, we will feature it on sites where you have high concentrations of chlorinated solvents particularly parent compounds, so PCE and TCE. And I’ll come on to that in a second. The key thing with this is it distributes really well. I’d expect at least a 3-meter radius of influence in superficial geologies. Fractured sites, it might be further if we can inject it under a high enough pressure. Here you can see this is commodity ZVI. It comes in much higher…much bigger particle sizes. I mean, it’s iron, it sinks, and that’s what it’s gonna do in your fractures. It’s not gonna distribute very far. Whereas S-MicroZVI which is at 5 microns and below and it’s a colloidal suspension, you add it to water, you can kind of see it blooming there. You agitate it to create this colloidal suspension and it will migrate much further in the aquifer. Much like in-situ chemical oxidation, in-situ chemical reduction, it relies on contact, so, the better radius of influence that you get from your zero-valent iron amendment, the better treatment you’re going to yield as well.

So, what do you get with ISCR-assisted bioremediation? Well, initially, you’re injecting the 3DMe, that starts to dissolve, and as it dissolves, it releases lactic acid. This lactic acid is then utilized by a different group of microbes, so, fermenters, they break this down and that produces the hydrogen. So, that’s the hydrogen that’s gonna be used as an electron donor by another group of microbes called dehalococcoides. These will utilize the hydrogen, exchange it for a chlorine atom. That exchange releases the energy that they need to live. And as they do that, they’re reducing, here we are, from TCE there to DCE to vinyl chloride, then eventually through to ethene. But the key thing with ISCR-assisted bioremediation is that the PCE and TCE reduction actually goes down a beta pathway where it’s reduced through to unsettling. That means that you mitigate against the amount of daughter products being produced. And that’s a good thing because these daughter products are more toxic, and certainly more mobile, and actually can, to a degree, be recalcitrant in terms of the rate at which they degrade. So, sometimes you can see some DCE stock. It doesn’t take…this isn’t often a problem for us with 3DMe. 3DMe has been engineered to be appropriately soluble. So, you’re getting that continual release of hydrogen for a five-year period. So, often we can chew through that. But the addition of S-MicroZVI can greatly increase the rate of degradation on your site, minimizing daughter products.

Its delivery is very simple. This is being pumped into a 3DMe mix. So, there’s no need for…there’s no compressed gas and specialist mixing techniques. This is just add water and inject. So, in terms of the results, so this is from area one. This is the grid treatment. This is very much still in progress, but it’s always good to show one that’s super recent. And you can see that the S-MicroZVI did a great job at removing the TCE. Here we’re starting… In June, we saw the peak amount of DCE in that process. That has then dropped, but we’re seeing quite good levels of ethene being produced, which indicates that full dechlorination is occurring. The September results, which I actually received about two weeks ago, looking fantastic. And I think we’re starting to look at the drop of DCE. We’re then going into vinyl chloride. But again, more ethene is being produced. So, excellent results. If you look at this in relative proportions of chlorinated ethenes and ethanes based on the geometric mean of molar concentration, so, a big thank you to Richard Bewley for passing these on to me, it just illustrates, you know, this is what we were starting with in January in this area, we then move through to June, July, and then eventually September where ethene and ethane are dominant there.

Similar story in area two. So, we’ve not seen this massive reduction…well, the complete reduction in TCE that we saw in area one. So, if you remember area two was the permeable reactive barrier configuration. Still some very good results, though. We’re starting to see the vinyl chloride peak come through in September and we’re seeing increase in ethene production. Again, drawing back onto these, you can see as this is progressing, DCE is dominant but ethene and ethane is increasing. I’ve got the September one. The reason for this is that we have essentially installed a permeable reactive barrier, in-situ permeable reactive barrier upgradient of the targeted monitoring wells. So, this is just an illustration of what’s going on. You’ve got contaminated water advecting into the barrier, comparatively cleaner water coming out of it. That wave of cleaner water is gonna take a while to reach that monitoring well. So, there is gonna be a bit of a delay. One of the problems that you will have is back diffusion. And in this case, it’s from primary porosity into the fractures. So, the fractures you can see are the kind of moving red color there and then the blue would be your primary porosity of rock matrix. So, as that back diffusion continues, as that concentration gradient becomes greater, you’ll start to see cleaner water advecting away from the barrier. You still got contaminated water upgradient. And it’s gonna take a while for that to fully be realized in that downgradient well, but once it is, you’ll start to see full cleanup. So, with these permeable reactive barriers, it’s really important to have that conversation upfront, you know, not only with our clients, but also with the regulator and the liability holder so that they understand that, “Okay. In some areas you may see a slam dunk and you’re seeing great progress. In other areas, it might take a little bit of time because of this problem of untreated contamination downgradient of that PRB.” But it’s fairly easily explained.

Finally, then I’m aware that we’re running over time a little bit, chromium VI. So, this is a site that we did with BRD Environmental. It was a former sawmill where there was extensive chrome VI contamination, up to 15 milligrams per liter on the site. Here, we had weathered and fractured limestone. We installed a series of pre…we installed a series of wells, one in a grid configuration at the source, and then a second as a permeable reactive barrier downgradient of that source area. Here we co-injected 3DMe, so, the technology that I introduced to you before with MRC. So, MRC is a benign organosulfur compound and it’s used with 3DMe to alter the valency of chromium VI, dropping it down to chromium III, precipitating it out as a stable sulfide so it’s no longer mobile in the groundwater. So, we’re not getting rid of the chromium. It’s a metal. We’re not alchemists. We can just drop that valency to essentially make it immobile. In terms of the results here, I think these are sort of…speaks for itself. This is 2014 we did this then. So, injected the product in 2014. Two years of monitoring there afterwards, it shows that concentrations were dropped down to non-detect within two months, and pretty much stayed that way for quite an extensive monitoring period across that site. And that was in a fractured limestone bedrock.

So, in conclusion, this is a matrix that I have adapted from the ITRC. This is where they are recommending that you can use different technologies. So, you can see here you’ve got long-lived oxidants, which is broadly what RegenOx is. You’ve got long-lived reductants, which is what S-MicroZVI is. And then you have controlled-release substrates, which 3DMe and ORC would fall into that category as well. And that broadly shows that you can use these sorts of reagents across various geologies. [inaudible 01:02:11] the ITRC, coal looks like it gives us some issue. So, these are kind of sites that perhaps I can’t help you with. We could do maybe with ORC and 3DMe. Where you can use permeable reactive barriers, roughly where that says yes, again, we could look at exploring the use of something like PlumeStop to do that. So, I come across mainly sedimentary rocks, carbonates, and clastics. In Scandinavia, we mostly come across intrusive, so granites and other crystalline bedrocks. So, these technologies can absolutely work on these sites. And again, this is a third-party assessment, not necessarily of our technologies, but of long-lived oxidants, long-lived reductants and controlled-release substrates.

So, in conclusion, the in-situ remediation of fractured bedrock using fractured bedrock aquifers, using injectable substrates, it’s not new. It’s been tried and tested many times. There’s hundreds of case studies out there showing its possible use. But subsurface characterization is expensive, but will yield massive project savings. Your focus needs to be on fracture geometry and interconnectivity so that we know exactly where to target our remediation efforts. But ultimately, there needs to be the exception of…there needs to be…you need to accept that there will be known unknowns and that you should plan accordingly, be that in contingency, and it’s a contingency sum that may be drawn on. Maybe it’s in additional investigation or negotiated regulatory closeout. When you are choosing reagents, it goes back to these cornerstones, ensure that they are easy to apply, appropriately reactive and persistent, and crucially must distribute well, and stick around in these high-flow fracture zones. And reach out to remediation specialists. I mean, the key thing, not only with fractured bedrock sites, but really our whole industry, is to try and get as many different people in the room as possible, different expertise, and often you’ll come up with the best solution. If you want more information, we have well over 200 case studies on our site. Just stick in Bedrock, hit Search and you will find a wealth of information. Many of them are on that I’ve talked about…well, all of them that I talked about are on there in far more detail. But we’ve also, you know, enough content here where you can search by industry, products, country, etc. We’re trying to make it as transparent and easy for you as possible. So, that’s everything.

Amanda: That’s great.

Jack: Thanks. Yeah. Thank you for your time.

Amanda: Thank you, Jack.

Jack: Yeah.

Amanda: That was a lot crammed in, in an hour. I am aware we’re over time, but I’ve looked at some of the questions that have come in and they’re quite interesting. So, I was gonna try and see if we can answer at least a couple.

Jack: Okay.

Amanda: But before we do that, just very quickly, after the webinar, you’ll receive a follow-up email with a link to a short survey. If you’re familiar with our webinars, you’ll know about this already, but we really appreciate your feedback. So, please take a minute to let us know how we did. And in the survey, there’s also a space to request certificates of attendance, which may contribute to continuing your Continuing Professional Development, CPD. So, if you’d like that, please fill it in by clicking the link in the follow-up email. And also just to remind you again, that after this webinar you will receive a link to the recording as soon as we can make that available if you have missed any of the last hour. Right. So, I’ll have a look at the questions. First one. Any issues with different rock types? For example, is it easier to remediate crystalline bedrock versus sedimentary?

Jack: Yes. I’d say it probably is if the characterization has been done well. With some crystalline bedrock, you are unlikely to have that problem with back diffusion. That’s gonna be fairly impermeable. You may wanna be reaching for, maybe not enhanced bio, but certainly ISCR and ISCR technology. So, yes, it’s certainly…certainly doable.

Amanda: Okay. Great. Here is another question. Have you had any experience with tracer testing in bedrock? Would it help in refining a remediation design?

Jack: It certainly would, particularly, if you’re thinking of recirculation. Something that I would encourage, though, is the reagents themselves often can act as a tracer. So, instead of using a… I’ll modify that answer. The use of tracers is a good idea if you’re near a sensitive receptor and you’re worrying about something entering a surface water body, for example. If that isn’t so much of a…if that isn’t so much of an issue, then it could be that you can use one of the reagents as a tracer because using something like 3DMe, for example, you will start to see changes in redox, you will start to see changes in pH with, say, something like PetroCleanze or RegenOx. So, there would be geochemical indicators that would indicate if you’ve successfully distributed that product. But it certainly can add some value and it’s something that we could discuss on a site by site basis.

Amanda: Okay. Great. Thank you. Right. This is another one. I noticed all the case study you showed were of dual-porosity sedimentary rocks. Why is that?

Jack: That is because… Well, a lot of them were in the U.K. And that is because here in the U.K., chalk, in particular, is often sort of a highly protected aquifer, principal aquifer, so, there is a…very much a need to remediate and preserve the groundwater quality there. We’ve certainly done sites with crystalline bedrock. It is slightly more rare often because they’re just…it’s been decided that there isn’t a risk. It may not be…it may not be a important groundwater resource, for example. But there’s certainly ones out there that we could have covered.

Amanda: Okay. Great. Well, I’ll just…I’ll just have one more final one. This has just come in. It says here, “We have a site with a crystalline bedrock where there is clear evidence on MNA at 15 to 20 meter but no indication at 7 to 10 meter. Any idea what would be the likely cause?”

Jack: It’s maybe different fracture networks. You might have… That’s a really hard question. It might be that…without seeing the site, it would sound to me like perhaps you have something that is diving taking nutrients from weathered bedrock and maybe even some organics from the surface and maybe pulling them down that is enabling that MNA to occur. Yeah. Sorry, Amanda. Did they say what the contaminant was?

Amanda: No, they didn’t. No, sorry.

Jack: No. So, it will depend on the contaminant. I mean, my contact details are all out there. So, if you wanna send me some information on that site, please do. You’ve got a QR code there as well. We’ve all got used to those during COVID or certainly have here in the U.K. So, if you wanna connect with me and ask me any questions directly, please do.

Amanda: Okay, great. Well, I think we’ll leave it here then. Thank you very much, Jack, for your presentation. If your question didn’t get answered, and I see there’s still questions coming in, so just to say, don’t worry, we will follow up with you via email within the next few days. So, thank you all for joining us. And enjoy the rest of your day. Bye.

Jack: Thank you.