Dane: Hello and welcome everyone. My name is Dane Menke. I am the digital marketing manager here at Regenesis and Land Science. Before we start with the webinar today, I have just a couple of administrative items to cover.
Since we’re trying to limit our time to under an hour, today’s presentation will be conducted with 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 will 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 webinar will focus on PlumeStop liquid activated carbon with a technology overview on in situ Containment of Perfluorinated Chemicals. To give us insight into this topic, we are pleased to have with us today Regenesis manager of research and development Doctor Kristen Thoreson. Doctor Thoreson is the lean inventor of PlumeStop liquid activated carbon. She heads the chemical research and product development program at Regenesis. Her team is focused on developing advanced technologies for the treatment of recalcitrant compounds in mixed environmental media.
All right, that concludes our introduction so now I will hand things over to Kristen to get us started.Click Here To Read Full Transcript
Kristen: Great. Thanks for the introduction, Dane and thanks to everyone who’s joined us today. I’m happy to have this opportunity to talk to you about our most recent technology, PlumeStop and how it relates to the in situ Containment of PFAS contamination. So where I’d like to start today is really with a brief background on the contaminants we’ll be talking about today, PFAS and I don’t intend for this to be an in depth background. Going to many resources about that that give some really nice overviews of the background including one that I’ll have a reference to in a couple of slides by Dickenson and Higgins but I would like to just point out some of the background as it relates to this technology.
So what are we talking about today? Per and Polyfluorinated Alkyl substances that has the acronym PFAS and this really represents a really wide, complex mixture of fluorinated compounds. I believe there’s over a thousand different compounds that fall under this classification at this point. And the two that have got the most attention today are PFOS and PFOA so acid. These two compounds both have a chain lined of eight carbons and are two of the most commonly detected at sites where these PFAS compounds are found. That has to do with their direct use but also they are sometimes terminal products for some of the precursors. And they’re the two that we have focused on for this presentation as well.
Now, these types of compounds have been used widely in many different consumer products and that’s really because they have some quite interesting properties. For example, they’re water resistant which makes them useful in things like rain jackets. They’re grease resistant which has been useful in nonstick pans. And also, do not terminally degrade or combust which has made them useful on things like firefighting foams which is the picture shown in the middle on the bottom which is a hangar that had these firefighting foams released. And they’ve also been used in things like food containers because of their grease resistant properties.
And the reason why we’re talking about them and concerned is because there are many probably links to human health issues associated with these compounds and as you may imagine, when they’ve been used in this many variety of consumer products, they have ended up across the environment in many different places. The groundwater, surface water, soil, in the air. And that really brings us to the difficulties of these types of compounds. Specifically, we’ll be talking about when they’re located in the groundwater. So I’ve taken some information that I saw at a presentation at Patel in 2015 by David Woodward where he described some of the characteristics of these plumes in ground water and some of the highlights that really stuck out to me at that were the fact that these are the prime example of a large dilute plum. In many cases, they’re over a mile in length. In the picture I have shown up there, it’s multiple miles in length and in fact, there are times when they can’t even find the front of the plum. And the majority of those plums often times, at least three quarters are very low concentrations, typically less than 10 parts per billion. So we’re talking about very low level contamination which can often be difficult to treat across a very wide area. And because of those health issues, the EPA back in May 2016 set a revised health advisory limit for the combined concentration of PFOA and PFAS, 70 parts per trillion or .07 parts per billion. So we’re talking about starting with low concentrations and needing to get to even lower concentrations which is really…can be quite difficult to do with many technologies.
And at this point, the tools that we have in our toolbox that have been useful for other types of contaminants that we’re used to seeing have really not worked so far and that has to do with the fact that these compounds are extremely recalcitrant. Those carbon forming bonds that you saw in the compounds on the previous slide are very strong and they’re hard to break down and so these, when they get into the environment, will persist.
So when we think about remediation and treatment options, again, most of what we already know or what we tend to fall back now have just not been effective. So for example, there’s just no known bacteria currently that are capable of complete biodegradation. Many of the oxidation that we typically use has also not been effective at typical usage rates that we use in the environment. And there’s a nice summary in this web report by Dickenson and Higgins that really goes over all of this. And so there’s a lot going on in this chart. On the left hand side, there’s a number of different PFAS compounds including PFOA and PFAS bolded there and along the top there are a number of different treatment options and basically, if it’s in red, that has…means that those types of treatment options have not been effective to date whereas if they’re in green, those have been fairly successful in removing these from the groundwater. So you see Nano filtration and reverse osmosis are quite effective. However, they also tend to be quite expensive.
And then if you look next to that, you see granular activated carbon and ANI exchange that has good success over many of the different compounds. However, they sometimes drop off with the shorter chain.
And so based on this, it brings up the question, “Well, what is being done currently?” And so right now, the currently accepted method of how we can treat these is to use a pump and treat system where we pump the water through granular activated carbon bed and that has been quite successful to date at cleaning up the groundwater. And so it brings up the next question and this is really what we’re trying to focus on in this presentation is if we can use granular activated carbon ex situ, can we be using activated carbon in situ as well and that’s where we’re heading here today.
And before I jump in to too many more details, I would just like to preface this idea that when we’re talking about using activated carbon Ex situ versus in situ, we are looking at some different types of parameters. Really looking at different types of flux rates that are going through those. So in a pump and treat system, you’re obviously under pumping conditions which means you have high flow rates, high mass flux rates and a general shorter residence time in those beds whereas if we can use in situ, use activated carbon in situ, then we’re looking at even a natural flow rate of groundwater and an overall lower mass flux rate and a longer residence time or interaction with that activated carbon.
So I just wanted to point that out at this point and then we’ll go from there. So a few years ago, we set out to develop a new in situ technology and when we were in that development stage, in R&D stage which again is where I come from so it’s the part that I enjoy but also can be the challenge is we really wanted to develop something that had some…a few key functions. Namely, the ability to distribute in the subsurface to make sure that we can get contact with contaminants and also really not have to require too many injection points or have a need for fraking. And also something that can absorb quickly and accelerate biodegradation. Of course, this assumes that there is a biodegradation pathway available which there is currently not for PFAS so I’m not going to go into that part of it at all today.
And what we came up with was PlumeStop liquid activated carbon. So you see in the picture it really looks like blank ink and it is based on colloidal activated carbon meaning activated carbon on the size of one to two microns and then there’s some additional additives, some polymers and some other additives that allow it to distribute in the subsurface. And since it is based on activated carbon, the contaminants that we can treat with this and what we have been treating since its launch a few years ago was primarily chlorinated solvents like your PCTC as well as petroleum hydrocarbons but really anything that has an affinity for activated carbon is a place where PlumeStop can be used. So that includes PFAS since we didn’t know that currently granular activated carbon is already being used to clean these up in the pump and treat systems.
So the outline for the remainder of the talk is what I’d like to go through is the ability of PlumeStop to distribute in the subsurface and this is really a key part because if we cannot get PlumeStop into the subsurface and have it distribute, it’s not going to be successful. So I’d like to show some examples of how we get this into the ground and what we expect of it and then we’ll move into more specific…the absorption of PFAS, how long may we expect it to last and then finally we’ll end up with some in situ containment strategies where we believe PlumeStop could be used in some of these large plumes.
So a good place to start when we’re talking about the distribution is this simple column test that we ran in our lab. And so these are soil columns that are mostly sandy but they’re not clean sand so they do have silt and clay within them and they’re operated completely by gravity feed. So at the bottom, you can’t see it, but there’s a little stop at the bottom that can be opened allowing it to drain. And for this demonstration, we have liquid activated carbon on the left and a commodity powdered activated powder on the right and in both cases, they have the same total amount of carbon as a slurry which will be applied to the column and then flushed with a few poor volumes of clean water afterwards. So I’ll show you this time lapse of what this looks like. You can see that the liquid activated carbon is able to readily distribute through the column as opposed to the powder activated carbon which gets essentially filtered out within the top half or one inch or so of the column.
And again, this was flushed with clean water at the end so I’d also like to make sure to point out that you can see a staining of the soil after these columns have been flushed in the liquid activated carbon and that is really important because the formation of PlumeStop allows it to distribute within the subsurface but we obviously do not want it to distribute forever because then you just have a PlumeStop which wouldn’t actually help us at all. So there is an affinity between PlumeStop and the soil surface which allows it to actually deposit. We’ve called it paining the subsurface with activated carbon and that is that staining that you see.
So if you take a closer look at what that actually looks like on the molecular level here, these are some scanning electron microscopy images. On the left is a clean sand and on the right is the sand that has PlumeStop deposited on it. And so you can see there that that scale’s about 50 microns and so we’re looking at those particles of PlumeStop deposited onto the sand in that picture on the right.
So when we talk about the ability for PlumeStop to distribute, we get many questions regarding how does it distribute in low permeability zones, how can it deal with contamination in clays and injection radius of influence which are all very good questions. I think the answer to these, it’s important to take a step back and think about where are we trying to get PlumeStop within aquifer in order to be able to fully address all the contamination. So if we look at this illustration of an aquifer flux stone, you can see that like in most sites, there’s some heterogeneity. So there’s going to be some higher permeability zones which I like to think of as freeways. This is where the water’s moving and then there’s also lower permeability zones. I think of them more like parking lots where the water is not moving through as much.
So now, when we talk about contaminants transporting through the aquifer, how are we getting these one, two, three, four mile plumes. They’re obviously taking the freeways. They are moving through those higher permeability zones.
And the way that you get contaminants into the lower permeability zones is through forward diffusion as they’re traveling in those higher permeability zones. So there’s going to be forward diffusion where the contaminants move into the clays and that acts as residual storage over the long term.
Now, we know what we go out and apply PlumeStop to places where it’s going to be the easiest and the most…where we’re going to get best distribution is in those higher permeability zones. We apply PlumeStop most often with direct push or through injection wells under low pressure to avoid fraking and so we’re going to really coat those high permeability zones with PlumeStop and as you saw in the pictures before, we leave that coating, that painting of PlumeStop there which allows us to address the high…the contaminants are present in those high permeability zones but then also, it’s set up nicely to catch any kind of back diffusion that’s going to happen as the contaminants move out of the low perm zones and back into the high perm zones by having that PlumeStop permanently adhere there.
And so really, when we think about the distance and radius progressed, it’s going to depend on the volume and it’s going to depend on those high permeability zones as to exactly how far we get and we do a lot of upfront work prior to doing the injections really trying to identify those zones and to understand where we’re injecting the PlumeStop so we could have a good feel for where and how far that PlumeStop is going to go. I’ll touch on this briefly in another couple of slides as well just to get a little bit more into how far PlumeStop does travel.
So here’s a soil core that was taken at a PlumeStop site after PlumeStop was applied and so you can get this kind of feel very nicely. You see the low perm zone where it looks like a fairly tight clay and you don’t see PlumeStop there. However, there’s a higher permeability zone. It looks like it’s probably a little more sandy and that’s where the PlumeStop is applied.
So this gives you an idea of the field and I’d like to take a moment to go into this just a little bit farther by looking at a laboratory study that we’ve been doing over the past year. This is actually a collaboration with Tom at Colorado State University and Kevin Sailor at Smith where we use these laboratory tanks to really simulate back diffusion and to simulate these high and low permeability zones. So you can see in that picture there’s a tank that has all these stripes and those different stripes are alternating layers of low and high permeability soils and it’s operated in upward flow and the objectives for the study for us…we were looking at TCE and the transport, back diffusion and all that which doesn’t apply to this talk. However, it does allow us to give an example of how PlumeStop travels through a situation like this. So in this study, we applied PlumeStop with about one to one and a half poor volumes and then followed with clean volume flushing. And so the results of that you can see in this picture is very good distribution of PlumeStop through those high permeable zones but also some penetration into low permeable zones which we were quite pleased with because it’s obviously always nice to get some contact in those low perm zones where there is contaminant stored. Here’s another picture when we were dismantling these tanks. You can really get a feel that there’s fairly uniform distribution across both the high and low perm zones and the picture on the left shows that coloration does go all the way through. It’s not just on the surface like a glass effect. It does go all the way into those low perm zones where it had contact.
So if we relate it back to our first illustration, you really get a nice feel for these where we’re trying to put PlumeStop and we actually do see a little extra penetration into low K zones but we’re really trying to target those high K zones because that’s where we’re going to stop the contaminant flux and also be able to capture any back diffusion.
So one final point on the ability of PlumeStop to distribute. As I mentioned earlier, we wanted to make sure that we’re not going to see any type of plugging or self-clogging if we keep putting PlumeStop into these zones to see really how far can we expect it to go. So we set up a 16-foot column in our warehouse and filled it with fine to medium sound, operated in up flow so you can see a little pump on the bottom so it pumps water and then eventually PlumeStop up through this column and in the end we put about five and a half pore volumes of PlumeStop through and then flushed it with nine more pore volumes of clear water. And all this was done at low pressures and the highlight of this is just to demonstrate that we saw a nice distribution at the foot of the column so you can see the four-foot mark, you have a nice front coming up and then as it approached the end of the column and we did see it completely go through the entire column and we have some coming out. So that actually suggests that it went 16 feet but if it had been a longer column, it would’ve been able to transport even farther in this case. So in these high perm zones we do expect to have excellent transport of PlumeStop to be able to put our injection points a little bit farther apart and still get good distribution.
So now I’d like to move into PlumeStop with PFAS and specifically PFAS absorption and how long we might expect it to last. So any time we’re going to try and identify the dose response for PlumeStop with the contaminant that we’re interested in, we’ll go into a lab and measure the isotherm which is really a partitioning equilibrium between how much of the contaminant ends up on the activated carbon and how much is left in the solution. And so we’ve done that for PFOA and PFAS and some of the other PFAS and unless you’re really used to looking at isotherms, these are a little bit hard to understand as to what this means. Are these good, are these bad? And so it brings up the question of it. Is there another way we can interpret these isotherms? And so a direction we’ve been working and continue to work on is the idea of integrating PlumeStop with fate and transport models and the idea here would be to use those isotherm parameters that we measure in the lab and incorporate them into models in order to allow us to predict the longevity of PlumeStop and also to optimize the doze to meet desired longevity of what your site might be requiring. And so we have been collaborating with professor Arturo Keller at UC Santa Barbara to do just that, to kick this idea off. And so in this case, we incorporated PlumeStop into the biomodel in order to look at this. And so I think the best way to go through this is to look at an example. So in one simulated plume scenario we look at a 50 parts per billion PFOA plume which is really the source on this…on that diagram. And that will have moving at about a 120 feet per a year and we’ll look at the model over the course of about eight years. And then in the second scenario, we’ll be able to add in a PlumeStop treatment, basically add in a PlumeStop barrier and see how that changes the transport of this plume. So in this scenario, we’ll look at a 25 foot PlumeStop barrier at a very typical field dose and then we’ll be monitoring the down-gradient concentration again over those eight years looking for how long we can keep the concentrations bellow those health advisory limits that the EPA recently set.
And again, a key part here is…we’re assuming only sorption. As I mentioned before, there’s really not many options at all for independent degradation so when we’re talking about using PlumeStop, we are talking about containing the plume. We’re not talking about destroying it. So this is a sorption only process.
So if we look at the results of this model output…so the first scenarios when you just have the natural flow of the plume, again, over those eight years. So you can see that after that timeframe, the plume will have extended at least a 1,000 feet at concentrations above the EPA health advisory limit.
Whereas, when we put in the PlumeStop barrier, we’re not able to contain that plume over those eight years without having any concentrations above the 70 parts per trillion eluting from the barrier over that time frame. So there we start to see the classic example of plume contained by installing a PlumeStop barrier.
Now, of course, this is one scenario and there are going to be many factors that will impact that longevity. So we’re really talking about mass flux and how much flux is going to come through that barrier. So we need to look or think about seepage velocity. So as you can imagine, if that plume was moving much faster, the breakthrough time would be shorter. We wouldn’t have seen the eight-year time frame. We might see something less but at the same time, if it was moving a little bit slower than that, we’d expect to have longer containment. Similarly, the contaminant concentration is going to play a large role so again, if it’s at a higher concentration, that will break through more quickly than if it is at a lower concentration.
It’s also very important to know and understand whether the contaminants are present. There is competition for these sites on activated carbon and so that’s something we do a lot to take into consideration. So if there are other…if it’s…in many cases, it’s not going to surely be a single component plume so we’re going to have to take into account anything else that’s there and then think about how those are going to compete and that’s going to influence the longevity of these barriers. I mean, also not even as contaminants but anything else that could possibly compete for those activated carbon sites like dissolved organic matter.
And then, of course, the PlumeStop dose. So that’s something that we can play with to try and get more or less a longer timeframe by increasing the PlumeStop dose as necessary. So another way to really describe all of this and perhaps a more familiar term is really thinking about a retardation factor. In essence, that’s really what we’re doing here. We are engineering aquifer retardation factor by being able to paint the subsurface with activated carbon. Activated carbon has much higher absorption capacity than any kind of natural FOC so we’re really bumping that up to something that’s going to really…so much higher retardation factor than what we typically observe.
So taking a step back just thinking about what exactly that retardation factor means. It’s how fast the contaminant is moving relative to groundwater. So when you have an RF of one, you have no retardation so the contaminant’s moving at the same rate as groundwater. If it’s two, it’s moving at half the rate and if it’s a 10, it’s moving at one tenth the rate of the groundwater. So some of the typical retardation factors that might be observed for VOCs and also for PFOS and PFOA are somewhere in the range of one to 20. Again, with normal FOC type values that you would encounter in the subsurface.
So now when we talk about using PlumeStop, again, at the same kind of dose that were used in that model scenario previously, we’re not talking about changing the retardation factor, for example, PFOA by orders of magnitude and again, that depends on what the concentration on that PFOA or plume is and it’s slightly improved case what PFOS has a little bit more stronger affinity for activated carbon.
As we saw earlier in many cases, these plumes are on the lower concentration range so we’re talking about change in retardation factor by three, four magnitudes and more when we’re able to apply PlumeStop in the subsurface.
So finally, I’d like to end with a couple of ideas of where PlumeStop can be used on these large plumes, some containment strategies. So I’ll take you through a few illustrations of this. The first one is really the model that we already looked at. It matches using a single barrier to cut off the plume to…with the idea there to contain the plume and limit its expansion. This comes in handy if you’re trying to keep the plume from moving onto a neighboring property or protecting a sensitive receptor like a river or something bad as it’s shown in the picture.
And the idea here is if you know the total mass it’s upgrading to that you could essentially dose that barrier appropriately in order to contain that plume so that now it’s on…contained completely within that barrier rather than across that entire zone.
A similar strategy is now just using a sequence of barriers. So this has that possibility of addressing the larger area of the plume and again, it allows you to potentially contain that plume in multiple short area soaked barriers rather than having it across that entire site at this point.
And the third strategy, it’s a unique idea. It’s more of an emergency response or preemptive type controls that if there’s a place where there might be a spill or even with a spill just happened, you can potentially use PlumeStop here to contain it so it doesn’t even develop a plume. From this case you can see here’s your spill and as it would now typically start to move down and create a plume, it’s now contained in that barrier that you put up around it.
And in the fourth strategy here, we’re thinking about localized receptor protection. So again, these plumes are usually quite large. So it maybe not be feasible to use this in our wide area of the plume. However, if there’s a certain neighborhood or a well or something like that, you can actually do just the opposite of we just described. You can actually surround whatever that is you’re trying to protect and essentially, you’re making a filter. This would allow you to put PlumeStop around there so if you’re extracting the water out of that well, you have an interim procedure to help clean up that well and prevent those contaminants from getting in that receptor.
And again, as I mentioned, these plumes are usually quite large so that you can start to pick off little portions or certain areas that really need to be addressed immediately rather than thinking about the entire thing by using something like PlumeStop.
So just to review the technology benefits where PlumeStop can help manage PFAS plumes is that we really have the ability to turn the subsurface into an activated carbon filter and this comes into play because it’s injectable and you can put in wide centers and at depth and as we went through it, it really allows you to engineer the retardation factor and that all has to do with this ability to inject activated carbon in injectable form of activated carbon.
And as what this gives you at the end of the day is a passive plume control and containment. So by putting in a passive barrier, it leads to perhaps an avoidance or even a decrease in some of the ex situ pump and treat systems and the expenses associated with that.
But really, a key part of it is it prevents expansion of the problem without interrupting the groundwater flow. So keeping it to a small problem for now like putting up fences around it.
And then the final point I’d like to end with is that when we use PlumeStop with…for other contaminants, we often pair it with some kind of destruction technology like enhanced dechlorination by adding an electron donor and so obviously there’s a lot of people working hard right now to try and come up with some destructive technologies for these PFAS compounds and so there’s certainly potential to contain these plumes within a PlumeStop barrier and then go back down the road when a destructive technology is developed and pair it with that and go and be able to clean up those barriers over time.
And so with that, I’d like to close and hopefully we have some time for some questions.
Dane: Yeah, definitely. Thank you, Kristen. That does conclude the formal section of our presentation. At this point, we’d like to shift into the question and answer portion of the webcast. Before we do this, just a few reminders. First, 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, after the webinar, you will receive a link to the recording as soon as it is available.
All right. So let’s circle back to the questions. If we are unable to answer your questions, we will follow-up with you after the webinar. All right, so Kristen, the first question here is given that PlumeStop was developed to disperse in the aquifer, what’s to stop it from remobilizing over time and increasing concentrations seen in production wells? Has this been tested to see if there are any soil types that it does not adhere to?
Kristen: Okay. That’s a good question. So as we saw in that flow column that we looked at early on and we saw that painting of the aquifer…so that has to do with all those additives that are present within the formulation and as the PlumeStop adheres, that is a permanent picture and over time, the other additives will wash away or degrade which means that the mechanism for any movement of PlumeStop is now going to be removed over time. And so there really is no possible way for those particles to remobilize at that time without any kind of…basically their car has been taken away from them at that point. Then they will agglomerate and not to be able to move any further.
So we don’t see that kind of mobilization. And it is important to know that the amount and the extent of what we have PlumeStop deposit is going to depend on the soil type. And so we know that the more clay and silt that’s present, the more PlumeStop will adhere to it as opposed to a clean sand. So that’s something that we’ve taken into account and it’s important for us to know as far as understanding how far we expect it to go. So there is not any soil type that it will not adhere to. It’s just a matter of how much adhere.
Dane: All right. Great, thank you. So next question here is is it possible to reach the low levels required by regulatory cleanup levels?
Kristen: Yeah, so that’s an important question, obviously. We need to make sure that’s possible. I think we have evidence because granular activated carbon is already used ex situ and the good news about activated carbon is that it actually works a little bit better at lower concentrations. The way that isotherms work is that they actually improve at lower concentrations. That’s where they get better which is in opposition to most technologies. Usually, it will lose efficiency at lower concentration. So this is a good part about activated carbon but in the end, yes. We can reach those regulatory cleanup levels with PlumeStop as well.
Dane: All right. Thank you. So the next question here is can there be reinjection after the PlumeStop is spent?
Kristen: Yeah, so that’s an important one when we’re thinking about PFAS since we don’t have a destructor pathway right now and so we’re talking only about sorption which means that there was likely a time point where the capacity will be filled up and at that point, there is no issue at all with going back and reinjecting more PlumeStop either into the same wells or same general area through direct push where it had been applied previously. We will see an additional coating go in that same area. We might see a little bit more transport slightly down-gradient but in general end up applying an additional layer of PlumeStop in that same area. And we also have some means of…that we’re working on right now to really control where the PlumeStop is going so we can try and make sure we get a nice, thick dose where we need it if there happens to be a soil type where we don’t see it as much deposition as we’d like. We do have a means for increasing that as necessary.
Dane: Okay. Next question here is what analyses should be run to determine if PlumeStop is going to work including soil and or groundwater chemistry?
Kristen: Okay, that’s always a good question, one we’re thinking about in situ technologies and I think there’s two parts…actually, question and one is first just getting PlumeStop into the ground. Is there anything that we look for? And we will tend to analyze for total dissolve solids and oncentrations because that can affect how far we expect it to go. However, the good news is that most concentrations you encounter in aquifers are really not going to have any impact there but it’s something we will check prior to injection to make sure we’re not going to run into anything that might limit its transport. But generally, PlumeStop can be used in wide range in redux, DOORP types. It’s really robust in that nature. The second part, I think, I alluded to a little bit is really understanding everything that’s present in that aquifer which means knowing all the contaminants or anything that might have TOC, anything that might have a potential to absorb the carbon because we can preferentially only absorb the contaminants we’re interested in. So we need to really know the full picture at every site so that we know how to design for it and make sure we get enough PlumeStop and to capture the contaminants we are interested in. so even if there are contaminants that maybe aren’t the one we’re looking for, we need to know about those as well to get the proper dose installed.
Dane: All right, great. Okay, the next question here is what about the shorter chain linked PFASs? Granular activated carbon is known to be largely ineffective for shorter chain lengths.
Kristen: Yeah, so that is…when you have to think about granular activated carbon, it is going to have a stronger affinity for those longer chain link PFAS compounds like PFOA and PFAS but there certainly are shorter chain link present as well and the affinity does drop off and so what has been observed with granular activated carbon is and I would point back to one of the earlier slides that I talked about is that when we’re putting in PlumeStop in the ground and we’re using the natural flow rates, that total flux it’s going through is going to be whatever that natural flow rate is and so if we know all these isotherms, we know how they’re going to interact, it’s something we can design for. It may require multiple barriers in that case to get everything including those shorter chains which have less affinity but the trends are the same as far as what has been observed with other activated carbons.
Dane: All right. Thanks very much, Kristen. That will be the end of our chat questions. If we did not get to your question, someone will be following up with you. If you need immediate assistance with a remediation solution from Regenesis, please visit regenesis.com to find your local technical representative and they will be happy to speak with you.
Thanks again to our presenter Doctor Kristen Thoreson and thanks to everyone who could join us. Have a great day.