Dane: Hello, everyone. My name is Dane Menke. I am the digital marketing manager at Regenesis and Land Science. Before we get started, I have just a few administrative items to cover. Since we’re trying to keep our time under an hour, today’s presentation will be conducted with the audience audio settings on mute. This will minimize unwanted background noise from the large number of participants joining us today. If you have a question, we encourage you to ask it using the question feature located on the webinar panel. We’ll collect your questions and do our best to answer them at the end of the presentation. If we do not address your question, we’ll make an effort to follow up with you after the webinar. We are recording this webinar, and a link to the recording will be emailed to you once it is available. In order to continue to sponsor events that are of value and worthy of your time, we will be sending out a brief survey following the webinar to get your feedback.

Today’s presentation will focus on effective methods for enhancing permeable reactive barriers using colloidal sulfidated zero-valent iron and activated carbon. With that, I’d like to introduce our presenters for today. We are pleased to have with us Dr. John Freim, the director of material science at Regenesis. Dr. Freim is well-known throughout the environmental industry for his work in developing breakthrough institute chemical reduction technologies, successfully employed throughout the environmental remediation industry. Dr. Freim has over 30 years experience in materials processing and 15 years in the environmental remediation industry, and led the establishment of the first Regenesis state-of-the-art colloidal product manufacturing facility. In his role at Regenesis, Dr. Freim is responsible for the manufacture of colloidal materials, including PlumeStop, liquid-activated carbon, and S-MicroZVI.

We’re also pleased to have with us today Ryan Moore, senior technical manager, and PFAS program manager at Regenesis. Ryan has 20 years of experience as an environmental project manager and laboratory account executive relating to multi-media contamination sites throughout the U.S. His experience is focused on site investigations of soil and groundwater contamination, corrective action evaluations, operation and maintenance of remediation systems, large soil removal remedial projects, and institute groundwater and soil treatment.

We’re also pleased to have with us today Andrew Kavanagh, remediation services project manager at Regenesis. Andrew has over five years experience as an environmental geologist and project manager related to soil, sediment, and groundwater contamination throughout the U.S. while working under various regulatory agencies. His experience includes the development of work plans to investigate soil and groundwater contamination for commercial and industrial properties and evaluation, selection, and implementation of remedial design methods. All right. That concludes our introductions. So, now, I will hand things over to Dr. John Freim to get us started.

Dr. Freim: All right. Thank you for the introduction, Dane. So, on this presentation, I’m going to be talking about the use of colloidal materials for in situ work remediation. And to get started, I’d like to give you a little background on what colloidal materials are. So, for our purposes with carbon and iron, we’re going to define these as solid particles suspended in a liquid, and in more particular, they’re small, solid particles in a liquid. So, with the colloid, really, there are two things that are needed. You have to have small particles, which are useful because they’re resistant to settling in a liquid due to viscous drag. On top of that, you generally need a dispersing aid to prevent agglomeration and maintain the colloidal stability.

If you don’t have a dispersion or dispersing aid, generally, these small particles won’t stay in suspension. They’ll agglomerate and settle out. And you can see in this little video here, this is two vials of PlumeStop. The one on the left has stabilizing agents. The one on the right we intentionally de-stabilized this using some chemistry tar parking agent. And you can see we’ve actually forced the material to agglomerate. The particles are big, they’re unstable, and they’ll fall out of suspension. So, what’s really important to realize here is that you need two things for a colloidal suspension. You need small particles, and you need to engineer them, so they don’t agglomerate and act like larger particles.

So, what are the benefits for using colloidal materials in in-situ remediation? Well, I think the largest benefit is that the particle size is smaller than the interconnected porosity. And because of that, the particles could actually fit within the sand grains of the soil particles intergranularly. And you get a nice, uniform distribution of the amendments on the subsurface. We just showed a video on the left of PlumeStop and the carbon passing through by gravity. The particles are so small and so well-dispersed, they’ll actually pass through a column of medium sand. On the right, there’s actually GAC, or granular-activated carbon, which is about 1,000 microns. And you can see, the particles are so large that they agglomerate and clog at the very top of the column. A similar thing with the colloidal iron on the right. That’s a sandbox. We inject a colloidal iron at low pressures, maybe 5 to 10 PSI. And you can see there’s a nice, beautiful front of the ZVI passing through the sand.

So, I’ll give you a little bit of introduction for those who aren’t familiar with our products. What is PlumeStop colloidal activated carbon? It’s a suspended carbon with a particle size of about 1 to 2 microns, on average. And as I was showing in the last slide, it’s much smaller than GAC, two to three orders of magnitude smaller than the carbon particle you can buy out of a bag. It’s about the size of a red blood cell. We use suspending polymers to promote the aqueous suspensions and transporting the surface. It’s got a really large surface area, as all carbons do, which means that it has extremely fast sorption. The kinetic sorption is almost instantaneous.

On a similar fashion, what’s colloidal ZVI? Well, our colloidal ZVI product is S-MircoZVI, which is, kind of, an acronym for sulfidated MicroZVI. And what’s unique about this is that we’ve engineered this to have a core-shell microstructure. So, we take zero-valent iron particles, and we chemically deposit a reduced iron sulfide surface onto the surface of these particles. It’s depicted in this picture on the right showing the iron and the metal and the iron sulfide on the surface. This is not actually a new technology. It was first reported back in the ’90s. And for some reason, it never was commercialized until a few years ago. And what’s really beneficial about this, it provides extremely rapid kinetics when it comes into contact with TCE and many other common groundwater contaminants.

So, we’ve done a lot of work testing the S-MicroZVI to quantify its rate kinetics. And this here is a plot that’s done in a bottle study in the laboratories at San Clemente, at the Regenesis laboratory. And this is a first-order rate kinetics plot. So, we’ve dosed a bottle with 150 micromolars of TCE. We added 4 grams per liter of S-MicroZVI. You take the concentrations versus time. And you have this nice exponential decay, which is indicative of first-order kinetics. And you notice that it goes away pretty quickly. The half-life on this is about three days. So, initially, we had 150 micromolar. Three days later, we had about 75 micromolar. And in about 16 days, it was all gone. And this is important because when you’re using iron in a barrier, you want something that reacts fast. And we’ll talk about this as we move along in the presentation.

You can compare this to bare ZVI. This is ZVI that’s not sulfidated. So, what we did is take iron of the same particle size and did not sulfidate it, did this exact same test. And you notice that this test took over 90 days to have maybe a 20% reduction in the concentration of TCE. So, bare ZVI is reactive, but it’s much, much slower kinetics than sulfidated iron. And in a barrier, kinetics are important. And we’ll talk about that as the talk progresses.

It’s also important to talk about the reactivity with daughter products such as with cis-DCE. Not every site is pure TCE or PCE. You also have some daughter products that are partially degraded. And we’ve done studies with this, as well. And we see that although cis-DCE does degrade with MicroZVI, the kinetics are slower. And if you run the numbers, they’re about 140th of that with TCE. So, it does degrade, but it’s slower. And that’s something we need to take into consideration when we do our designs.

Another thing that’s really beneficial about S-MicroZVI and ZVI, in general, is the reaction pathway that occurs when you encounter the PCE and TCE. So, there’s generally two different ways it can degrade. The most prevalent is this one on the bottom here. It’s called beta-elimination where the PCE and TCE are degraded directly to FA through these chlorinated settlings. This generally accounts for about 90% of the degradation. The top pathway with the single arrow is something you might be more familiar with. It’s more analogous to a biodegradation pathway where you have the degradation through daughter products. And this is an abiotic pathway. It just doesn’t happen as often as the bottom one. Probably about 10% of your parents are degraded with this method. So, that’s an introduction of our materials.

Let’s talk about what a permeable reactive barrier is, and how we can use these materials to enhance the performance of a PRB. So, this is your typical 30,000-foot view of a site where a PRB is applied. Up on the upper left where it’s red is where the source area is inside a building. And down towards the right, there’s a fishing lake, which is our receptor. So, our goal would be to prevent the groundwater that’s invecting from the up-gradient source from reaching the fishing lake. And to do that, we apply a permeable reactive barrier, that’s a series of injection wells, the groundwater invects naturally towards this barrier, passes through it. It’s cleaned up within the barrier. And if we do it right, we’re gonna prevent the transmission of contaminants through to the down-gradient of the receptor.

So, what we have here is an animation, which, kinda, depicts how PlumeStop and S-MicroZVI work when injected into the ground at a PRB. So, the center section here is that transmissive zone, which would be sand or silty sand. And on the top and the bottom, there are less permeable zones, which could be a clay. So, when we inject the S-MicroZVI and the PlumeStop through injection wells in the PRB, we’re gonna be pushing it through the transmissive zone. The particles are colloidal, and they’re suspended. So, they pass through quite nicely. And then, they’re gonna actually adsorb to the surfaces of the soil particles. Then, as our contaminants are passed through this zone, they’re gonna adsorb to the surface of the PlumeStop particles and react away with the S-MicroZVI. We’re also gonna get some back diffusion from the immobile porosity or the clay.

Here is SEM showing what this looks like at the microscale. This is a clean sand particle where it’s silica sand. The particles look like they’re about 50 to 100 microns. And that’s after we deposited PlumeStop. So, before we had a nice, clean sand surface. And afterwards, we can see there’s a rough exterior on the surface. Those are actually activated carbon particles, which have sorbed through the surface of the sand particles. And that’s gonna be our treatment mechanism. And we would pass our contaminated groundwater through the zone.

So, how long will a PRB last? Well, it depends a lot on the environment which you’re gonna encounter. There’s a lot of variables. And the important ones are, first of all, how much contaminants that we pass…passing through the barrier. So, that is dependent on the groundwater flow, the velocity. It’s also dependent on the concentrations of your contaminant within the groundwater. So, a faster-moving system will generally last slower than a slow-moving system. And something that’s more contaminated will generally last not as long as something that has fewer contaminants.

So, common situations are PFOA and PFOS. These are very, very hydrophobic contaminants. They sorb extremely well to carbon, kinda, like PCE. They really don’t want to be in water. And at typical concentrations which are PPT or PPB, you can have a barrier last decades, 50, 60 years without any break-through. So, that’s, kinda, the extreme example on one end. Probably the intermediate examples would be chlorinated solvents at low concentrations such as a PCE barrier’s gonna last, you know, on the order of a few years, 10 years. BTEX is very similar. On the other end of the spectrum, a very hydrophilic substance such as 1,4-dioxane just does not adsorb to carbon very well at all. So, if you have a situation with fast-moving water with 1,4-dioxane, you’re gonna have negligible performance.

So, those are all great qualitatively. But can we actually quantitatively model the PRB performance? And the answer is yes. We’ve been blessed to have a model that’s been put together by Dr. Jeremy Birnstingl in the Bath, England office of Regenesis. And we can use this to quantify the behavior of the contaminants passing through the barrier. So, what do we need to make this model work? We’re gonna have inputs that are indicative of the situation. We’re gonna need the groundwater flow, the concentrations of the contaminants. There’s other groundwater species that might affect the barrier. We’ll talk about that later. How much material we’re putting in the ground, how much carbon, how much iron, bioremediation amendments, and the geometry. And that model is powerful enough to be able to handle all of these inputs and predict how they’re gonna affect the performance. The outputs are gonna give us the concentrations both within the barrier and down-gradient. It’s also gonna let us know how our amendments, particularly ZVI, are consumed during the process.

So, with that, I’m gonna start with a model of activated carbon alone. This is a barrier where we’re only sorption. We’re gonna have some assumptions here where it’s 10-foot wide. It’s a fairly rapid groundwater velocity of 250 feet per year. We’re gonna put 5 grams per liter activated carbon within the porosity. Start off with a technical concentration of TCE of 1,000 ppb. We’re gonna assume no degradation. So, this situation is sorption only. So, this is the output plot. I’d like to spend a little bit of time to explain what we’re seeing here. So, the X-axis is distance in feet from the start of the groundwater flow. So, we have groundwater that’s moving from left to right. And it’s encountering a barrier. And the barrier here is the [inaudible 00:17:23] rectangle. And that indicates where we’ve applied our activated carbon. You can see here the barrier is from 10 to 20 feet. It’s 10-foot wide. And as I’ve said earlier, we put 5 grams per liter of PlumeStop within effective porosity. The orange line is the TCE concentration. So, as I said earlier, this is happening left to right. We have 1,000 ppb TCE encountering the barrier. And then, on the right side, it shows what’s…all the down-gradient after the material has been cleaned.

Now, you notice that this is time-zero here. A couple key points here. One is that everything within the barrier we’re sending forwards instantaneously. So, all the contaminants that were originally in between 10 and 20 feet here have been removed from the aqueous space, and they’re sorbed to the carbon. You also see some down-gradient contaminants. And the reason why you see that is that they were there initially. They have not yet passed through the barrier at time-zero. They’re gonna naturally invect down-gradient and go away. So, don’t misunderstand this as that the barrier’s not working. This is just a time-zero assumption.

So, let’s look at what happens in one year. The barrier’s performing great. I think the key thing you need to take out of here is that down-gradient, there’s no aqueous space concentrations of TCE. The other thing you do notice is that there’s, kind of, a break in the barrier maybe at about 11 or 12 feet. And then, we can explain this is that the barrier is, kind of, filling up from left to right or up-gradient to down-gradient. In the first 2 feet of the barrier, the carbon’s saturated with TCE, can’t sorb it anymore, and relying on the down-gradient parts of the barrier to do the work.

So, as we click forward with two years, the profile is very similar. It’s just that the amount of carbon that’s been fully saturated with TCE is now about the first 4 or 5 feet. Three years, the barrier is advancing. It’s still performing well. There’s nothing coming out through the down-gradient side. Four years, we’re getting pretty close to filling it up. It’s still performing, but the carbon’s, kinda, getting very close to reaching its saturation point. And at five years, we’re seeing a break-through. So, what’s happened here is that the carbon within this barrier is fully saturated with TCE. It can’t adsorb any more. And then, because of that, we’re gonna get a break-through, or we’re gonna see concentrations down-gradient that are similar to what’s coming in. So five years, not bad by itself, but it would be nice if we could make these things last longer and have a better-performing barrier.

So, we’re gonna do the same simulation but with S-MicroZVI alone. The last series of slides I’ve showed you was sorption. This is gonna be reaction only. We’re gonna assume that there’s no sorption on the S-MicroZVI. All that we’re seeing is degradation. So, the barrier geometry is about the same. We’re using 5 frames per liter S-MicroZVI instead of PlumeStop, 10,000 ppb TCE influent. And then, here, we’re gonna go back to the earlier slides where we talked about the rate kinetics. We’re gonna use these to model the degradation within the barrier. So, we have empirically-determined rate constants. We’re gonna assume 90% goes to ethene, 10% goes to cis. No biodegradation within the barrier, and no competing electron acceptors.

So, this is one year in a S-MicroZVI barrier alone. And you can see here performance is quite different. One thing that’s notably different is that actually, you have some things passing through down-gradient into the down-gradient water. The green line is Fe, which is fine. It’s nontoxic. That’s what we actually want to see come out of the barrier. You can see that the TCE is the orange line, which is fully contained within the barrier. So, what this means is that the kinetics with TCE are fast enough to keep up. All of the reactions aren’t instantaneous. It’s fast enough to prevent the material from breaking through. It’s all degraded by the time it reaches to the back of the barrier. But one problem you see here is the red line, which is cis-DCE. So, as I noted earlier, cis-DCE has slower kinetics with iron than TCE does. And because of that, there’s not enough residence time in the barrier for it to degrade before it moves down-gradient. So, an iron barrier alone, the bottom line is that it works really well with the parent compounds but not quite so well with the daughters just because the kinetics are slower.

We’ll click through two years, and it’s about the same. You notice we have bronze there. And that’s not because the iron is fully sorbed with the contaminant as with the carbon. That’s because the iron’s actually reacted away. It’s consumable, and it goes away. We assume the iron is consumed front to back. Five years looks about the same. Seven years, we’re right about where the TCE’s gonna break through. So, the performance is good. But we’re limited somewhat by the kinetics of the slower-reacting daughter products.

So, there’s synergistic behavior between S-MicroZVI and PlumeStop. As you’ll see, the shortfalls or the shortcomings with one will actually be overcome by the advantages with the other. So, what we’re gonna do here is put a barrier with both of them in, PlumeStop and the S-MicroZVI, the same conditions as before with the S-MicroZVI barrier, but we’re gonna add 5 grams per liter of carbon to the porosity as well. So, time-zero looks the same as it does with carbon. But at one year, it looks markedly different. You can still see that there’s ethane that’s broken through. And it’s past that down-gradient, which is great. That’s what we want to see.

But you notice that there’s no cis-DCE that’s passed through the barrier. And the reason why this is happening is that what the carbon does is it actually retards the progress of the contaminant through the barrier. It sorbs it, slows down the flow within the barrier. And because the flow is slower, it gives the iron more time to react with the slower degrading cis product. So, there’s cis still at, like, the first 5 feet of the barrier, but none of it’s gonna break through in the back. And you also notice that the PCE’s degrading much faster in the front of the barrier as well. That’s because its progress is also slower through the barrier. Three years, it’s basically the same. Everything’s moved a little farther to the front of the barrier. Five years, it looks about the same. It looks like, you know, we’re about halfway done with what we have with our iron in the barrier. And seven years, it’s still performing.

So, if you compare this to what we had before, S-MicroZVI, if I ran the model to see actually when we’re gonna have a break-through of cis, it was at 33 days. So, S-MicroZVI’s super reactive with TCE. But the fact that there’s a little bit of cis present from our reaction pathway means that it’s gonna fail earlier. Now, we can get around this by adding more iron or more carbon or biodegradation. As for this purpose, it shows you the weakness of an iron-alone barrier. For the situation of PlumeStop alone, I ran the model. TCE’s gonna break through at 635 days. But when you combine them, you get almost 4,000 days of performance. So, the enhancement is about six times compared to PlumeStop alone. So, they’re not linearly additives. They, actually, are synergistic and help each other to perform much better than each material alone. And there’s basically, you know, two reasons. The PlumeStop slows the flux of the barrier. And that gives the iron more time to react. I explained that earlier in the last couple slides. So, that’s how the PlumeStop helps the iron.

But the iron also helps the PlumeStop because as the water passes through the barrier, the DVI degrades the contaminants that are sorbed to the carbon, prevents them from being saturated, and provides more room or more saturation capacity for the freshwater that’s gonna come into the barrier. So, they’re truly synergistic. The benefits of one are used to overcome the shortfalls of the other. So practical considerations, then, of PRB. What I showed you were, kind of, simple hypotheticals. But in the real world, things are more complicated. So, there’s other situations that we need to take into consideration. One of them are competing electron acceptors in the groundwater for iron. These are primarily DO, dissolved oxygen, and nitrate. And these will consume iron. Iron will react with nitrate and DO and consume it. So, this is gonna decrease the performance. But our model allows us to input these and take these into consideration. And, in general, this is gonna shorten the lifetime of the barrier.

Concurrent biodegradation, this, generally, happens. Most environments aren’t sterile. So, if we have either native microbes such as sulfate reducers or dehalococcoides it, generally, increased the performance. So, you’re gonna have a combination of abiotic and biotic degradation with the barrier. And this one really helps when you have the slower-reacting species such as cis and vinyl. Also, there are sometimes competing hydrophobic species in the groundwater. Humic acid, for example, is often present. And this can sorb to the carbon and reduce its capacity.

All three of these could be modeled. As I said earlier, I mean, every situation is unique. So, we do not have a one-size-fit-all standard for barriers, and every one’s designed differently. So, how do we optimize the barrier performance? I think one of the key things is done, and we’ll talk about this in the second half of the talk with Andy and Ryan, is that you want to do a design verification with passive flux meters. This is really important because it will identify high contaminant flux zones within your ground. Within the same injection point, the same monitoring well, you can have transmissive zones and non-transmissive zones that are gonna behave very differently. And if you can identify these, you can place your amendments in the right locations and maximize performance.

Obviously, we can adjust the quantities of amendments that are applied. You can add more PlumeStop. You can add less PlumeStop. It’s not a fixed ratio. You can go carbon-rich. You can go iron-rich. It just depends on the situation. You can also add bio-amendments such as HRC. We can add dehalococcoides, BDI microbes to enhance performance. We can also adjust barrier configurations. So, instead of having a single 10-foot barrier, we could have multiple barriers. We can have a series of three barriers. You can also have different formulations or different concentrations of amendments in each barrier.

Another thing that we can do that’s, kind of, unique is we can actually vary the placement of the amendments within the barrier. For example, it was shown that if you put the iron at the beginning of the barrier and the carbon at the back of the barrier, in some situations, it will work better than it does when you have everything put together. So, thank you for your time. We’re gonna segue to the next part of the talk here. And I’ll stick around at the end if you have any questions.

Ryan: All right. Thank you, John, for that. This is Ryan Moore. I’m the Great Lakes district manager, senior technical manager with Regenesis. And then, I’m also the PFAS program manager for the company. So, today, we’re gonna, kinda, transition here and talk about a case study here in the Midwest where we used this same combination that John’s been talking about with PlumeStop and S-MicroZVI. Like I said, the practice is located in the Midwest, kinda, the upper Midwest region. We’re, kinda, working along a right-of-way in between properties and, kind of, upgrading of a residence house, a residential property. Some of the uniqueness of this site was that there was some significant variation in the seepage velocity. And Andrew will talk about that in our DVT component of it. But just to, kinda, give a reference here, the shallow interval consisted mostly of a silty sand. And it had seepage velocity that had, you know, some ranges but, you know, no more than about 170 feet per year.

As you got deeper in the aquifer though, it did change more to a sand to, kind of, a sandy gravel aquifer. So, pretty large gravel pieces within that aquifer. At that transition, too, the transitivity of the aquifer increased significantly. And we had calculations up to 660 feet per year. Primarily, cis was the main compound of concern. But there was PCE, TCE, and vinyl chloride in the mix at pretty significant levels, you know, over 50,000 parts per billion. The primary driver for mediation at this site was vapor intrusion. Again, this is a pretty elongated plume coming from a chemical manufacturing facility. And the plume’s been around for a long time. And it was found that these chlorinate solvents were migrating through this, kind of, neighborhood and neighboring properties under these houses. Like I said, this is a combined approach where we were using some PlumeStop, S-MicroZVI. We did also utilize HRC, and then some bacteria that was harvested from the project site, as well.

This is, kind of, just a quick map of the overlay of what we were planning on doing. You can, kinda, see the groundwater flowing from the northwest to the southeast fashion. The, kinda, arc or, like, L-shape, I guess, of the PRB was just to maximize placement of the reagents to protect the house that you see in the bottom right-hand corner. For this test that we were doing here, it consisted of 18 injection points. We had some planned monitoring points where there were some existing monitor walls that were put in within the PRB location. And then, there were some pre-existing monitoring wells that were about 20, 25 feet down-gradient. You can also see there’s, kind of, a star, red star there too. You know, we had planned confirmation cores both pre and post-application. And then, I’m gonna transition and let Andrew, kinda, really talk about what we did from a design verification testing and, kind of, going about how that helped us in the field to make adjustments. So, Andrew, do you wanna, kinda, talk a little bit about your design verification and what you guys were doing there in the field?

Andrew: Yeah, absolutely. Thank you, Ryan. I’d like to start with a quote that can likely be attributed to every environmental or remediation designer. And that quote is, “It’s dark down there.” The phrase always stuck with me because its meaning is two-fold. In the literal sense, it is, in fact, dark underground. And in a figurative sense, most of the data points collected from the site investigation are only a snapshot of a much bigger picture. So, at Regenesis, we use a pre-application process called design verification testing or DVT to illuminate the subsurface with respect to modeling assumptions. It’s a process where we can confirm design assumptions, fill in data gaps, and validate reagent placement. A model is really only as good as the quality of data that is input. So, if you input bad data, you’re gonna get bad data out. As part of our DVT step, the services division worked with the client to go to this site to identify and confirm grain fabric, lithology changes, and associated porosity variations, as well as fine content within the target treatment zone using soil cores pre-application. During the application, we used piezometers and took additional soil cores to further verify the design. I’ll detail that in the coming slides.

Additionally, passive flux meters were installed to better understand contaminant movement and quantitatively define the velocity within those zones. Most groundwater velocity assessments are a function of an estimated porosity, a measured gradient, a generalized conductivity pump test, and our soil tests. These assessments tend to have a wide margin of error, or they’re too generalized to show high-resolution data within the aquifer. We want to take a little bit more of a surgical approach. And passive flux meters have shown us that most sites have 90% of contaminant mass moving through about 10% of the aquifer. Even if the initial velocity tests are accurate, they don’t empirically measure contaminant flux, which is a critical component of modeling treatment.

So, this is a core taken during the DVT where we identified a sharp contact in both grain size and consolidation between 23 and 24 feet. This was a really good visual indicator for us of a strong transport zone. And we can take that observation a step further. Within this context, gravel shifts from about half a centimeter to a centimeter gravels, and beneath that much larger 1 to 4-centimeter gravels. And the result, we can expect an increase in Reynolds number and more turbulent, higher velocity groundwater flow. So, we made sure to capture that zone in our passive flux meter deployment and kept a close eye on it during the application.

These are the passive flux meter results. On the left, we’re showing DVT1 covering the 15 to 20-foot interval. On the right, we’re showing SPMW4, which is covering the 20 to 25-foot interval. Now, both of these wells were within the proposed barrier alignment. Taking a look at DVT1, we see that about 150 milligrams of cis are moving through this zone. And the Darcy velocity is around 5 centimeters a day, which translates to roughly 60 feet per year. A conservative estimate for seepage velocity, given the geology here in that interval, is around 170 feet per year, which is pretty pedestrian and nothing too wild.

Now, taking a look at the graph on the right, which represents the deeper interval, 20 to 25 feet, we have around 5,000 milligrams of cis moving through this interval, a Darcy velocity around 11 centimeters a day. And that translates to about 140 feet per year. An estimate for seepage velocity using a 20% effective porosity would be over 660 feet per year. This is extremely powerful. Contaminant flux in the deeper zone is almost 35 times higher. And we’ve quantitatively identified a large amount of mass moving at a high rate through a smaller section of the aquifer. What this does is it enables us to selectively target and place reagent only in the zones that are needed at the doses that are required. This removes a lot of guesswork from our model. Now, we have good data going in. So, we want to get out in the field.

Our approach to in situ injections in the services division and at Regenesis is dynamic remediation. This means we’re constantly evaluating, adapting, and overcoming. Our design verification does not stop once we stop the injection. When we go in the field, we trust the model but we continue to verify it. What sets the RRS group apart is our ability to adapt efficiently and intelligently. Before we mobilize to a site, our field teams have a sound understanding of the hydraulic properties of the aquifer through remedial design and what the drivers of it are. They have a thorough comprehension of the reagents being applied, their chemistry, their distribution properties within the subsurface, and the aquifer response to them, both physically and geochemically.

Our field teams communicate in real-time with our design team. Pressure and flow responses, as well as observations, are documented in our injection logs that are viewable in real-time to the technical team and the Regenesis project personnel. This allows us to make adjustments with little to no downtime. And we put technically-savvy professionals in the field for injections. Things in the field don’t always go as planned. And the best way that I can capture the caliber of our personnel is by saying that RRS crews don’t make phone calls to identify the problem. They call in to identify the solutions. They call to explain the pros and cons of each. And then, they make informed adjustments in the client’s best interest.

During our initial site walk at the site here in the Midwest, we measured our barrier geometry, marked out our injection points. and the RRS team made the observation that the topography within the barrier wasn’t quite flat. And as a result, we adjusted the treatment interval in 6 of the 18 borings. We did this by measuring the elevation change from benchmark locations such as wells and DVT borings. And then adjusted the drilling depth to accommodate for topographic highs to ensure that the remedial solution would be delivered to the same vertical zones throughout the barrier. This observation was absolutely critical, considering what we learned about the mass transport in the bottom of the treatment interval from 20 to 25 feet. Without this attention to detail and understanding of why these details are paramount, we may have failed to adequately cover 30% of the mass flux zones within the barrier.

The verification testing and placement validation continues throughout the application. During the injection application, we confirmed lateral distribution of PlumeStop and S-MicroZVI using piezometers and monitoring wells, both visually and geochemically. When the injection crew influences a well or a piezometer with remedial solution, they take a sample and perform an in-field concentration test to correlate and check that that concentration matches what our models are predicting. Because the monitoring wells are typically screened over a 5 to 10-foot interval, we take soil bores to confirm we have adequate vertical distribution. And once we have worked out any adjustments and we have all positive indicators that our model and design is field-verified, we start to ramp up production. However, we continually check all monitoring points for placement validation throughout the entire application. This process ensures the client’s investment isn’t squandered with poor placement, inadequate application methods, or lack of detail.

So, this is an image sent from the field team of a soil core taken in between two adjacent injection points within the barrier. And it’s an excellent visual confirmation that we have reagent distribution within the designed ROI or radius of influx. I think we hear a lot in in situ remediation that it’s a contact sport when it comes to activating carbon and ZVI. And I think it’s pretty safe to say that we have contact here. This is thorough and consistent saturation and effective pore volume [inaudible 00:42:26]. So, really quick, I want to recap the layout of the barrier and just draw attention to the monitoring wells here before we show performance data. Just down-gradient to the barrier, we have SPMW4 and DVT1 that are situated, you know, right within the barrier just a few feet down-gradient. And then further down-gradient, about 20 to 25 feet, we have PZ17-39 and PZ20-34. And, again, groundwater flow direction is to the southeast. I’m gonna turn it back over to Ryan and John to elaborate on the performance.

Ryan: Yeah, thank you, Andrew. You know, kinda, like you’re looking at the graphs, kinda, speak for themselves, within the barrier, we had greater than 99% reduction very quickly within the first couple sampling events. Just to describe the graphs that you are seeing, on the right-hand side of that is the actual DCE concentrations. As we were saying, it was primary DCE build-up in this location when we were doing the application, so the scale’s a little different. And then, on the left side are the rest of the concentrations, the rest of the constituents. Very quickly, this is about what we expected in terms of dose-response, maybe a little bit quicker. And this is even more evident when we look at the down-gradient, again, 25 feet or so down-gradient. Total concentration, there’s 65% removal. But if you look at it, it continues to go down in both the shallow and deeper intervals. John, I know you, kinda, looked at this data and had some thoughts related to the modeling. I know we don’t have the models on here. But do you want to say anything about that real quick?

Dr. Freim: Yeah. Thanks, Ryan. So, I ran this situation through our model. And the results correlate quite well. One thing that’s important to understand here is that we did have a pretty substantial biological component to this remediation program where we injected HRC up-gradient. And that’s primarily to address the cis. And when you look at the model, the concentrations, they are falling, generally, as predicted as they would by the model. As we stated earlier, it’s really important to realize that there’s a substantially different flux in the upper zone as there is compared to the lower zone. And there’s also substantially different concentrations. And this is reflected in the model. And it’s behaving as expected. And we assume that in a few more months, we’ll see close to zero concentration of all contaminants at these modern wells.

Ryan: Yeah. And we only have a few data points right now but the site is being continued monitoring. And there’s some additional work planned that has occurred and is going to occur. So, we’ll continue to share that over time as the data comes in. So, I’ll, kinda, let Andrew finish us off here on some key takeaways.

Andrew: Yeah, absolutely. Thanks, guys. So, you know, successful remediation projects are all about balance and, specifically, upsetting the balance and tipping the scale back in your favor. Installing a permeable reactive barrier is like putting up a fence. And so, the first part of that is selecting the right hardware for the job. And for this job, it was a combination of PlumeStop and Micro-ZVI with an additional biocomponent. The next step is picking the right tools to install your materials. We’ve all heard the phrase, “Measure twice, cut once.” Well, the way that we over at Regenesis approach in situ remediation is we measure twice and cut once, and then we keep measuring. That’s how our design verification test and dynamic remediation approaches function. Lastly, hire professional help. Hire someone who’s going to pay attention to detail. Hire somebody who is going to give you cut sheets and mockups, layouts and models. Hire someone who builds fences for a living. Don’t ask the cashier at the hardware store to come help you on the weekend.

When installing a PRB, solid coverage is key, and you don’t want any holes in your barrier. You don’t want any holes in your design. And if there are gaps, you want a team that can identify them and fill them effectively. Why would we demand accurate and precise performance during the investigation from the sampling labs, field staff, mapping software, measuring tools, and spend a bunch of money on chemical, and then skimp out on the installers? That would be like spending millions developing and building a Formula One race car over five years and then, on race day, giving the keys to a kid in the crowd who just got his learner’s. At Regenesis, we align our team top to bottom with the client’s objectives. We gain satisfaction not by lining our pockets and then moving onto the next site, but by helping our clients achieve their goals. With that, I’d like to open it up for questions.

Dane: All right. Thank you very much, Andrew. And that concludes our presentation for the day. So, at this point, we’d like to shift into the Q&A portion of the webcast. First, just a couple of quick reminders. You will receive a follow-up email with a brief survey. We really appreciate your feedback, so please take a minute to let us know how we did. Also, you will receive a link to the recording of this webinar as soon as it is available. All right. So, let’s go back to the questions. We do have a lot of questions. If we don’t get to your question, someone is going to make an effort to follow up with you. All right. So, we are getting a number of questions here regarding injection pressures. We have regarding, Dr. Freim, your presentation. John, it says, “You showed a vial with agglomerated and settled PlumeStop. So, would you be able to inject this at the same pressure as dispersed PlumeStop? And would the ZVI suspensions also settle if de-stabilized?” And then, just another question regarding, “What are the typical injection pressures with PlumeStop and S-MicroZVI?” So, John and Andrew, do you guys both want to weigh in on that?

Dr. Freim: Yeah, I’ll start. Thanks for the question. So, agglomerated colloidal suspensions are typically, I would say, 100 to 1,000 microns in diameter is the size of the agglomerates. And this is typically much larger than the interconnected soil porosity. So, they will not inject. It will be just like injecting a packed material or a powdered carbon. You’re gonna have absolutely zero advantage compared to the colloidal material. Iron is exactly the same way. If you put a small particle size iron into your mix tank, it’s gonna agglomerate through natural forces such as the Van der Waals attractive forces. But also, you can magnetize small particle size iron. It’s not dispersed. You’re gonna have big clumps. You’re not gonna be able to inject it into the ground. The injection pressure is typically for a colloidal material, 20, 30 PSI, depending on the lithology. For an agglomerating material, you’re gonna have to frack the ground, which could be hundreds of PSI.

Andrew: Yeah. So, I’d like to touch on the injection pressures here. The PlumeStop and S-MicroZVI, they’re designed to be injected under low pressure. And part of that is, you know, we want to stay within the failure envelope of whatever media we’re pumping into. And they work by coating the soils. They don’t rely on fluid velocity for distribution since they’re colloidal. They’re not a thick slurry that’s got to be fracked into the subsurface. And by using low pressure, you know, one, you eliminate a lot of health and safety concerns that you have with high-pressure, high-velocity injections. And this also…low pressure yields better control over the reagent and its distribution. When you fracture a fluid into the subsurface, you know, excluding planimetric units like shales or units that have a known and mapped fracture networks, it’s, kinda, like trying to steer a rocket with no wings.

Furthermore, the sheer stress is highest in tangential vectors. So, the solution is either gonna want to go up or down, and preferentially, up, since there’s less initial resistance in the vadose zone. So, this is true for all phreatic zone injections. But it’s really exacerbated with high-pressure, high-velocity injections. If you’re pumping it in at 30 gallons a minute and you start to see daylighting, well, within 30 seconds, you’ve potentially lost 15 gallons of your investment.

Dane: All right. Thanks, Andrew. So, Ryan and Andrew, you guys both mentioned design verification testing or DVT. So, we have a few questions about that. So, one is, “What do you think are the most important pre-application testing steps that can be done for the site?” And then, also, we have another question. “Can the design verification testing be done in the same mobilization as the injection work? And what if I have a limited budget and a not-that-well-developed CSM?” You guys both want to weigh in on those?

Ryan: Yeah, thanks, Dane. You know, I feel that a lot of the most important steps that the clients can take either through our RRS group or on their own is to really identify those transition zones within the aquifer and to try to, you know, better identify where is that contaminant really fluxing through? Here in the Midwest where I’m located, you get a lot of, like, clay sites with sands and silt seams. And so, having a good understanding of that and seeing, you know, what’s really fluxing through that zone, that’s gonna, kinda, make or break your PRB. So, we can do really good coverage across 95% of the PRB. But if we’ve missed one zone where, you know, a significant amount of mass is fluxing through, it’s gonna present itself as a failure for the total PRB. So, you know, the [inaudible 00:52:46] flux meters or there’s other high-risk characterization tools like HPT, MIPS [SP], LIF, those tools are all very helpful to make sure we identify those zones and to get a better handle on that before you’re out in the field. You know, Andy, do you wanna, kinda, talk a little bit about what you can do when you’re out there?

Andrew: Yeah.

Ryan: You know, some of these tools you really need to do beforehand. But there are some things you can do when you’re out there getting ready to inject.

Andrew: Yeah. So, you know, some of the DVT components, there’s a time factor there with some of the analysis. A lot of what we can do in the field for DVT, you know, can be done within the same mobilization, which, you know, lends itself back to just our efficiency with communication and analytics and, you know, a continual DVT as the injection is happening. We’re constantly refining the application. So, you know, we can do a lot of things in the same mobilization as the injection work and, you know, save the client money in the long run.

Dane: Okay. All right. Thank you, guys. So, here’s another question. This one is for John. And it is, “What will happen if you use your stabilization polymers with powdered carbon or powdered ZVI?”

Dr. Freim: All right. Thanks for the question. And the answer is they would still not behave very well at all. The problem is that powdered carbon is gonna have a particle size of tens of microns to hundreds of microns. Even if you stabilize it, the particle size is gonna be large enough or it’s not gonna behave with the colloidal material. Exactly the same thing with a powdered iron. Iron is harder to suspend because it’s denser. The gravity acts upon it more aggressively, and it sinks faster. So, even if you put, say, a 10-micron ZVI particle with a polymer coating on it, it’s still not gonna behave colloidally because it’s gonna settle with the gravity. So, those things are basically too big. You have to have both small particles and a suspended material. One or the other is not enough. You have to have both.

Dane: Okay. Thank you, John. So, here’s another question. This one’s for Ryan. And it is, “What type of baseline groundwater analysis should be completed?”

Ryan: Yeah, that’s a good question. You know, typically for these types of projects, we want to get a lot of the same tests that you would do for, like, maybe M&A. So, a lot of the geochemical parameters, DO, nitrates, sulfates, you know, ORP, etc. You also may want to look at TOC, at any potential non-target compounds. So, you know, this was a coordinated solvent site that we talked about. However, there is some petroleum hydrocarbons at this project, you know, in other areas. So, maybe we need to look at TPH or benzine or something else that might be fluxing through the zone. So, you know, you definitely want to do the baseline analysis enough in advance to have a good handle of what’s the potential demand on both the S-MicroZVI and the PlumeStop. But yeah, nothing too crazy in terms of the analytical that you need. Sometimes, you might look at also what your microbial counts are before you get out there just to see if you need to inoculate. But pretty typical tests would be required. So, yeah, a good question.

Dane: All right. Thanks, Ryan. So, here’s another question for Andrew. And it is, “Do you have to use a specific in…” I’m sorry, “Do you have to use a specific injection tool with PlumeStop and S-MicroZVI?”

Andrew: Yeah, a good question. No, you don’t. We come prepared with every tool in the toolbox. So, that could be top-down, bottom-up, 5-foot fixed open screen, 4-foot bottom-up retractable screen, extendable tip. The way we look at that is, you know, what is gonna be the best tool to use for the site geology and product placement? So, our methodology isn’t tied to a specific injection tool since our approach is dynamic, meaning that, you know, our initial assessments lean toward a top-down, 4-foot screen. But our placement validation as we’re working through it on the site is less than optimal, we can really easily pivot to a different tooling and approach until we’ve optimized performance with no negligible effects or no negative effects. And, no, we’re not tied to any specific injection tool. So, a good question.

Dane: All right. Thank you, Andrew. So, here’s another question, and it is for John. And it’s, “The remediation approach that you talked about, does this approach work with source-area treatment?”

Dr. Freim: All right. Thanks for the question. And the answer is yes, you know, using carbon and iron together works great in the barrier and it also works great in the source area. I generally define a source as a slow-moving zone. One caveat might be if you had DNAPL or a non-dissolved base of contaminants, it’s gonna make it a little more challenging because these reactions occur in the aqueous phase. But if that is the case, there are some tools in our toolbox that we can also use to address DNAPL sites as well.

Dane: All right. Thank you very much, John. So, that is going to be the end of our chat questions. If we did not get to your question, someone will make an effort to follow up with you. If you’d like to learn more about remediation solutions from Regenesis, please visit regenesis.com. Thanks very much, again, to our presenters, Dr. John Freim, Ryan Moore, and Andrew Kavanagh. And thanks to everyone who could join us. Have a great day.