Today’s webinar will discuss estimating PFAS mass discharge in the Vado zone at Ellsworth Air Force Base. With that, I’d like to introduce our presenters for today.

We are pleased to have with us Dr. Grant Carey, president of Pore Water Solutions. Dr.

Carey has more than 30 years of experience, specializing in PFAS fate and transport, site characterization and remediation, DNAPL delineation, groundwater modeling, environmental forensics, and mining water management.

He is currently involved with seven SERTEP and ESTCP projects for the U.S.

Department of Defense with a focus on PFAS remediation, and most recently, the development of PFAS e-learning modules.

We’re also pleased to have with us today Dr. Paul Erickson, Vice President of Research and Development at Regenesis.

Dr. Erickson oversees the commercialization of new environmental solutions to address complex remediation challenges.

In his time with Regenesis, he has led the development of a number of remediation products and technologies, including Petrifix, AquaFix, SourceStop, and Flux Tracer.

He is an author on over 20 peer-reviewed scientific publications, mainly in the area of environmental chemistry.

All right, that concludes our introduction.

So now I will hand things over to Dr. Grant Carey to get us started.

Thanks Dane.

Hello everyone.

I just wanted to say thanks very much for attending today.

I really appreciate your time.

And we do have a lot to cover today with the presentation.

So if anyone wants a copy of the slides after we’re done, please send me an email gcarry.poorwater.com and I’d be happy to send the presentation to you.

So as Dave mentioned, I’ve been really fortunate to have been involved in a number of SIRT-IP and ESCP projects, mainly around colloidal activated carbon barriers like Plumestop, for example.

But today’s presentation is actually pretty different. We’re not focusing on the technology itself.

What we’re going to talk about are how we can use betasome mass discharge calculations to assess do we need to do a lot of remediation, say in the VADO zone to remediate soil, or do we want to focus more on remediation below the water table?

There is a project we’re actually very excited about with Poor Water Solutions.

It’s a new ESTCP project, but we’re actually developing four PFAS eLearning modules.

And you can see from the interface here, it’s got a simple menu on the left so you can review the module and come back anytime, go specifically to a section if you need a quick refresher.

It’s got a lot of volume controls.

these are fully narrated, we’ve got some animation effects to keep it interesting, exercises throughout the way, reference documents available to you.

So there’s a lot here and the modules, we’ve actually got two available.

We’re looking for reviewers, if anyone’s interested, send me an email.

The first one, instructed by myself, is an introduction to PFAS with some discussion of visualization methods.

The second one is all about conceptual site models at or FFF impacted sites by Dave Adamson and Chuck Newell at GSI Environmental.

Then the third one I’m working on now should be done pretty soon.

It’s everything you want to know about CAC barriers like plume stop, for example.

And specifically the lessons we’ve learned through a number of SIRDP and the SDCP projects with DOW.

And then the final module will be available later this fall by doctors Chuck Newell and Dave Adamson on PFAS monitored and enhanced retention processes for managing sites.

And one quick announcement, we’re also quite excited at Poor Water Solutions with a new teaming arrangement with NSafe.

We’re merging our combined expertise, experience, and proprietary tools for visualization and modeling, so we can offer enhanced and more innovative services to all of our clients.

So we’re quite excited about that and stay tuned for more news.

Okay, so let’s dive in.

I’m sure a lot of you have heard the term AFFF.

This is the aqueous film forming foam that’s been used to put out fires for many decades now since the late 60s, early 70s.

And the thing about AFFF, obviously up until recently, they’re looking for non-fluorinated AFFF products now, but until recently they have had high PFAS concentrations.

And with AFFF, they dilute the raw product with a lot of water, usually 94 to 97% water before they apply the foam.

So, when they were doing this in the old days with online burn pits, it was mainly water getting into the subsurface with high concentrations of PFAS, and that water would kind of get flushed down with periodic use during a fire training.

So these AFFF products had military uses and also a number of non-military uses as well.

So today we’re going to talk specifically about Ellsworth Air Force Base and conditions at the former fire training area.

And a picture’s worth a thousand words.

So thankfully Rita Krebs, who’s the remedial program manager at Ellsworth Air Force Base, provided this air photo to give you a snapshot of what this online burn pit looked like in 1985.

The area is called OU1, the former fire training area.

And at this site, they started using PFAS-containing AFFF in the early 1970s.

And they stopped using AFFF, they stopped doing fire training here in 1990, when they switched over and installed a new fully lined burn pit in another location.

So during fire training activities from early 70s to 1990, they would be basically using this AFFF mixed with water, which caused periodic flushing in the VADO zone.

And then this AFFF stopping used in 1990.

So current conditions, we do have a PFAS plume in groundwater below the water table.

And in today’s seminar, we’re gonna look at evaluating I mean, how much mass is actually moving downward from the Vado zone below that little burn pit into the water table versus how much mass of PFAS, they say the horse has already left the barn.

How much massive PFAS sustaining the groundwater plume is already below that water table today.

So there was a really interesting study done by Hunter Anderson and Talon in 2022.

This documents the lysimeters that they installed at this former fire training area.

They had 12 lysimeter locations with nested shallow and deep lysimeter screens installed.

They monitored or sampled for poor water over four events.

And you can see the predominant PFAS that they found on the right.

Those are the predominant PFAS we also see in groundwater below the water table.

The interesting thing about this study is they estimated how much PFAS mass is actually in the VEDO zone as of 2022, versus how much mass is actually moving downward in grams per year to the water table.

And I’m just looking at PFOS, P-F-O-S as an example, we can see that there’s 130 ,000 grams of PFOS in soil below the Vedosome, below that former source area, and only 10 grams per year is actually going down to the water table.

That’s 0.01% of the mass remaining.

So this shows for all these PFOS constituents, there’s only a very small amount of PFAS relative to the mass and soil that’s actually discharging downward from the vadose zone to the underlying water table.

And this is 30 years after AFFF use had actually ceased at the site.

So a year later I was actually working with Hunter Anderson and a group of others on a paper where we were taking the source conditions at Ellsworth and evaluating hypothetical plume stop barriers.

Can they work with the source concentrations that were actually measured in groundwater below the water table at the Ellsworth Air Force Base.

And you can see in this two dimensional grid where you see these vertical lines with really small grid spacing.

That’s where we were looking at alternative locations for a plume stop barrier to see what would work.

And the one thing about the site is that we did some ballpark estimates and found leaving the source area below the water table, PFOA mass discharge was about 270 gram per year.

And we know from the previous paper by Hunter Anderson and his group, 17 grand per year PFOA was moving downward from the vadose zone to the water table.

So that shows that almost all that mass discharge leaving the source area, sustaining the damp gradient plume was coming from secondary sources below the water table.

Probably from back diffusion, there’s abundant silt and clay below the water table.

So we’re probably seeing the effects of back diffusion, maybe slow desorption.

And that’s what’s really sustaining the groundwater plumes at the site based on those numbers.

So just to make the point, we’ve got two types of mass discharge.

We’re gonna talk about soil to groundwater mass discharge.

That’s really the mass leaving the VEDA zone going to the underlying water table.

And then you’ve got the horizontal groundwater mass discharge, what’s leaving the source area and what’s the relative ratio of what’s coming from the VEDA zone versus what’s leaving the source area below the water table.

There’s a classic paper by Chuck Newell and others at GSI and Hunter Anderson, where they actually focused on these mass discharge calculations and the importance of estimating the recharge rate.

And there’s some key statements they had in that paper that I think really show how we can use these mass discharge numbers to decide on what remedial actions are needed at a site.

So for example, in this paper, Chuck and the team said that if the mass discharge from the VADO zone is low, relative to what’s leaving the source area below the water table in groundwater, then high intensity, high cost remediation of the unsaturated zone is likely counterproductive.

But the corollary, which happens at some sites, is when the mass discharge from the VEDA zone is large, it’s a large proportion of the mass discharge and groundwater leave in the source area, then remediation to manage risk from the unsaturated zone may be warranted.

So, this actually gives us something like a framework where we can evaluate, do we want to focus remedial action on, say, shallow soil in the vadose zone, or do we want to look more at remedial actions, at least in the interim, to manage the plume and groundwater?

And looking at mass discharge gives us a decision-making criteria that we can use to make those decisions.

So, how do we calculate mass discharge in the vadose zone?

It’s actually a pretty simple calculation.

It’s taking a look at the individual PFAS species and their concentrations in poor water, because it’s the poor water in the VEDA zone that’s moving down to the water table.

So we want those poor water concentrations, and we multiply those by the net recharge rate, which might be centimeters per year, inches per year.

And then we multiply by the area, say the area of the source zone, for example.

And then we have to do some unit conversions, but what we get is a mass discharge number typically reported in grams per year.

There was an interesting paper by Jack Costanza et al.

in 2025, really a group from EPA and it’s kind of a, it’s a review of suction lysimeters and pore water sampling and how remedial decision making should be done.

So what they found is that pore water samples, if they’re going to be used to make remedial decisions only based on pore water samples alone, then you really have to prove that the pore water samples are representative.

and then they also recommend using a multiple lines of evidence approach for evaluating site cleanup levels.

And that would be based on pore water samples, soil samples, groundwater transects and leaching tests. And I actually agree with the first three.

The Vadozone transport processes for PFAS are quite complicated. The more data we have to make sure we have a robust CSM, the better.

The only thing with these leaching tests like SPLP, we’ve published a two-part series.

I’m today with mass discharge at Ellsworth Air Force Base.

The second part, I don’t have time to talk about today, but we did look at SPLP leaching test results.

And what we found is they were not representative of poor water concentrations.

So based on the second paper, we shouldn’t be using SPLP results to estimate PFAS mass discharge from the vadose zone to the water table.

But that’s a presentation for another day.

So the first paper, this is really all about taking the pore water samples that Hunter Anderson and his team from WSP had collected as part of a data gaps investigation, and we actually combined that with another set of lysimeters installed by Arcadis and BEM systems as part of the remedial investigation.

So two sets of lysimeters, we combined those results and we really wanted to look at all the lines of evidence and ask ourselves the question, are these pore water data reliable for estimating mouse discharge?

So, this cross-section, one thing we did is we put a lot of data on cross-sections to better understand transport through the Vados Zone, and you can see this is one lysimeter.

We’ve got a shallow pore water concentration of about 80 ,000 microgram per litre, let’s just call it total PFAS, and we’ve got a little over 500 microgram per litre, just about seven or eight feet below that.

So that’s a decline in concentration vertically of more than two orders of magnitude between the shallow and deep lysimeters.

And if you go and look at that Jenga Stanza paper, they questioned, you know, does that make sense?

Because the releases at this source area stopped in 1990.

I think there was surprise that we had this much attenuation between shallow and deep lysimeters, which raised the question, is the deep lysimeter really representative of poor water and can it be used for mass discharge estimates?

So one thing we did, which I highly recommend at any site you’re working on, if you’re doing Vadosome characterization, is look at the soil sample results.

Also, let’s just call it total PFAS.

You can see samples right from just below the ground surface, concentration of 100 ,000 microgram per kilogram total PFAS.

And you can see just down 10 feet or so, that concentration declined by two orders of magnitude, down to about 1600 microgram per kilogram.

And that’s the same level of attenuation we observed in the pore water.

So that’s telling us, okay, the soil samples actually corroborate the attenuation we observed in the pore water between shallow and deep. So that’s a line of evidence.

Those deeper pore water samples are representative of the attenuation occurring at the site.

And just to let you know, we did use the deeper lysimeter. That was the deepest lysimeter we had.

It was still about 10 feet above the water table, but that’s the pore water concentration set that we took to estimate mass discharge.

And you can see below that there’s continued attenuation or decline in PFAS in the soil sample results, but for the mass discharge estimates we didn’t take that further decline below the lysimeter into account.

So let’s talk about some basic veto zone concepts because it is for some people this may be new, so I wanted to talk about some of the nuances that make characterization of veto zones for PFAS more complicated than what we do below the water table.

So real quick refresher, I’m sure everyone’s familiar with this.

Obviously we have a water table, we have saturated zone with groundwater flowing typically horizontally below the water table, we have a capillary fringe that’s mainly saturated with water, maybe a little bit of trapped air, and above the capillary fringe it’s unsaturated where we’ve got both air and poor water in the pore spaces.

So the unsaturated zone plus the capillary fringe, that’s what we call the vadose zone.

Now with the vadose zone, what’s interesting is we have these, let’s say we’ve got a fairly low water saturation, we’ve got a lot of air in the pore spaces.

So in that case, we’ve got these brown sand grains that have these pendular rings of water that coat those sand grains.

Water’s the wetting fluid, it wants to coat the solid surfaces, air is non-wetting, it wants to be in the middle of the pore spaces.

And if you look between the air and the water, that’s what we call the air-water interface.

And that interface is really important because that’s where we get a lot of PFAS adsorption in the VEDO zone that increases retardation, especially for longer chain PFAS.

So, and I say for long chain PFAS, let’s just look at the molecular structure, because it’s so critical to adsorption to many different types of surfaces.

So simple PFA molecules break it down to the simplest form.

They have a tail and they have a head.

PFAS is a long chain sulfonate.

It’s got eight carbon atoms in its tail.

And then going down this list, we’ve got go from longer chain to shorter chain.

Now those tails with the carbon and fluorine atoms, those are hydrophobic.

Those tails do not want to be in water.

So they tend to want to absorb the surfaces like soil organic matter, activated carbon like plume stop and air-water interfaces as well.

So the longer the tail, the more hydrophobic it is, the more it wants to adsorb to these different types of surfaces.

And the more they tend to bioaccumulate, that’s where longer chain species of PFAS tend to be the ones that are regulated most often.

So in the VEDO zone, when you collect a soil sample, there’s actually three compartments where PFAS mass is stored.

So we’ve got sand grains with coatings of natural organic matter that are going to have PFAS adsorbed to them, so that’s one compartment.

We’ve got adsorbed PFAS mass, and then we’ve got PFAS dissolved in the pore water.

And right now we’re looking at a conceptual picture of PFOS in soil where most of the PFOS is going to be adsorbed to that air-water interface.

That’s that blue line.

So you can see PFAS molecules, the heads are hydrophilic, they want to be in the water, and the tails are hydrophobic.

That’s why they stick out of the water into the air.

This is actually how the PFAS adsorb to the air-water interface in situ.

So for PFOS, most of the mass in the soil sample, if it’s a low water saturation, will be adsorbed to the air-water interface in situ.

So when you get a soil sample, you’re getting total PFAS concentrations across all three of those compartments.

And if you’re So, we’ve all seen this retardation calculation for PFAS below the water table. Pretty simple.

Kd, the retardation coefficient as well, are based really on the fraction of organic carbon.

In the VADO zone, there’s an extra term, the one in blue.

That represents absorption of PFAS to the air-water interface.

Longer chain PFEAs, the ones that are regulated, tend to absorb fairly strongly to that air-water interface. And shorter chain compounds, not as much.

It’s similar to how they absorb with carbon and soil or activated carbon or any kind of absorbent like that.

So one thing that’s important with made also characterization, it’s really critical to know this.

When you take a soil sample, you send it to a commercial lab for chemical analysis like PFAS or VOCs or hydrocarbons, the labs typically do a gravimetric moisture content measurement.

So they measure what’s the mass of water per mass of soil, gram per gram in that soil sample.

They need that to actually report the concentrations as a dry weight in their analytical reports.

So if you’ve collected soil samples and sent them to a commercial lab you probably have reports that have the gravimetric moisture content.

And using the equation shown on this slide we can easily calculate the water saturation where soil samples were collected and if you’re doing VEDO soap characterization that is critical critical data.

Sometimes people, we install moisture content probes, but anywhere we collect a soil sample, we get these free measurements by the lab.

So really important to know that and to mine your old lab reports for that data if you’re characterizing VADO cells for PFAS transport. Okay, so let’s look at Ellsworth Air Force Base.

I’m going to walk through the lines of evidence we look for to demonstrate that the pore water samples are representative and reproducible so we can use them for mass discharge estimates.

So I really wanna thank my co-authors here, Rita Krebs from the Air Force Civil Engineers Center.

Rita’s the remedial program manager at Ellsworth Air Force Base.

And I really wanna thank Rita because not only did she make all the great data sets that she has at Ellsworth available to us, she’s allowing me to be here so I can actually present to you what we learned, which is helping everybody to learn more about these VEDA zones.

so thanks very much Rita for that.

And then we’ve also got Dave Adamson from GSI Environmental, Kevin Mumford from Queen’s University, Bo Guo from the University of Arizona, and then from Poor Water Solutions we have Mia, Gabe, Kira, Sabrina, and Maya who’ve all helped with these writing of these two papers that we’ve done.

So in this presentation I’m going to walk through the multiple lines of evidence to evaluate our poor water samples representative and can we use for mass discharge estimation.

So one thing we looked at was how reproducible or what was the variability of pore water concentrations between sampling events.

There’s always going to be some variability.

If it’s a lot of variability, then it just means we have to look more closely to see are they truly representative. We also looked at vertical attenuation.

I showed the example of how we confirmed with soil data that the pore water sample attenuation between shallow and deep was actually representative? That was an important question that we answered.

Then we looked at geology data, we looked for evidence, you know, are there, is there layering that would cause lateral migration of PFAS that might explain some of the higher PFAS concentrations south of the former burn pit.

We also spent a fair bit of time looking at a regional study by Driscoll et al, USGS, looking at what the net recharge rate was to the water table.

That’s a key part of this mass charge calculation.

So one thing with poor water samples, typically I would recommend at least four events, maybe five, and one thing we would need to do is we need to kind of compare data for the different PFAS species between each of the events to look for if there’s extreme variability more than we expect, then we want to look at that.

The water saturation will change over time depending on when it rains compared to when you go to do sampling, and as water saturation changes, poor water concentrations will change.

So we expect some variability, but more extreme variability has to be looked at more closely.

So we can see the blue data series with the blue fill, that’s the first quarter, that’s the first sampling event.

And we can see for this particular lysimeter, that actually has, it’s about an order of magnitude lower in concentration for all or most of these PFAS species compared to the other three events that were done later.

and that’s actually fairly typical of pore water sampling with lysimeters.

Sometimes when you install the lysimeters you’re injecting water that can actually cause dilution so if you sample soon after the lysimeters are installed you might get dilution of PFAS in the pore water and we can see with this particular lysimeter example the first event Q1 is quite a bit lower in concentration than the other three and the other three are pretty close together which is good that’s what we want to see.

So then looking at this, we can see for all, but PFAS sometimes actually isn’t that different between Q1 and the other three events, but the other species, certainly Q1 is quite a bit lower than the other three events.

The other three events tend to be pretty close together in concentrations.

So that tells us, okay, we’re going to, we ignored the first event in case it’s not representative and we just average the pore water concentrations from the last three events to get average water concentration to use in the mass discharge estimates.

And then radial diagrams are also useful when you have shallow and deep lysimeters.

You’ve got, in this case, seven PFAS of interest that are predominantly in poor water.

It’s a lot of data, especially when you’re looking at multiple lysimeters across the former fire trading area.

So we use radial diagrams to map how things change spatially.

And just looking at this one lysimeter location, this is the legend, and the black dotted line, that’s just the site maximum that we use sometimes as a reference series on these diagrams.

The shallow lysimeter concentrations are the orange fill data series and the sort of greenish blue smaller data series, those are the deep lysimeter pore water concentrations.

Now the axis is set up so that the axes for the longer chain compounds are on the left of the radial diagram.

Sulfonates on the top, carboxylates in the precursor on the bottom.

As you go for sulfonates, as you move from left to right, chain length gets smaller with these axes.

And same with the carboxylates on the bottom, as you move from left to right, chain length gets smaller.

And you can see on the left side, the shallow concentrations are about three orders of magnitude higher than the deep concentrations.

And that means that there’s a big decline in PFAS concentrations, long-chain PFAS concentrations, between the shallow and deep asymmeters.

And as you go from left to right, the difference between the shallow and deep gets smaller.

And on the right side, we only have about one order of magnitude difference.

And that’s exactly what we expect to see when air-water interface adsorption is a key factor causing this vertical attenuation or vertical decline in PFAS concentrations.

It’s showing that the long chains are more attenuated than the short chains.

Now when we put it on a map, you can see lysimeter 107, that’s the same as the legend that we just looked at.

Now if you look at lysimeter 104 and 106, those are near the former brim pit, high concentrations in pore water, and we actually see something a little different.

If you compare the orange and the blue-green data series, the long and the short chain compounds at those two locations have similar decreases between shallow and deep.

So we don’t see the difference in attenuation between long chain and short chain at 104 or at 106.

And that’s telling us, okay, that’s probably not air-water interface adsorption driving the attenuation at those two locations.

That’s probably more related to limited vertical flow.

And we know that lysimeter 104, the deep lysimeter screen, Sorry, the shallow screen is actually in a clay.

So maybe the clay is limiting water infiltration through it.

And so it’s more a limited water flow driving the attenuation at those two locations.

So that’s the kind of thing we can start to see in these data when we use radial diagrams to overlay the shallow and deep concentrations.

And then another thing we looked at was water saturation.

We wanted to know, do we have much water flow actually going from the shallow part of the zone down to the water table.

We know that there’s limited precipitation, 16 inches per year, that evapotranspiration is over 90 percent of total precipitation at the site.

And what we’re seeing is when I look at this number 15 percent, that’s a low water saturation for a sand.

And now if we expand the cross-section and now we’re looking at multiple locations around this depth, 13 to 15 feet below ground surface we have low water saturations at most of these locations and that’s telling us we actually looks like we have fairly low water flow through the deeper part of the VEDO set and that’s consistent with the USGS regional estimate of a net recharge rate of 1.5 centimeter per year. It’s pretty low flow moving down to the water table.

So this is the kind of cross section where we’re looking at geology, soil concentrations, poor water concentrations, water saturation from the moisture content results.

We’ve actually got a blue dash line where there appears to be a semi-continuous clay layer.

There’s some soil borings we used to develop that, not shown in the section because there was no PFAS data on those other borings.

And we’re showing the water tables.

So all this data combined is a really powerful one figure we can look at to understand what’s happening in the VEDO cells.

So we’ve talked about the absorption to the air-water interface, especially for long chain PFAS, that really can limit vertical migration.

We also talked about the limitation of water flow vertically.

So there was this excellent paper by Ilka Wallace, who’s from Flinders University in Australia, and she looked at a similar semi-arid site that’s actually in Australia, but similar precipitation, similar high level of evapotranspiration.

And what they found with PFAS is that there was what Dave Adamson and Chuck Newell call a zero-flux plane.

Above that plane, if you look at the image on the right, we’ve got upward water flow because there’s so much evapotranspiration in the top one to two meters that actually creates an upward flow direction.

And then below that zero flux plane, we’ve got a downward flow direction with more limited net recharge.

And that might be a reason why we have such high PFAS concentrations in the top meter or two in the veto zone, but below that, everything attenuates pretty quickly.

So we might have a similar process, and this is the kind of thing that modeling would be helpful to actually confirm.

And then one thing I wanted to point out, so we’re talking more now about net recharge, which is what the vertical water infiltration that goes down to the water table.

That’s less at Ellsworth Air Force Base, probably a lot less than the water actually moving through the ground surface.

Because of the evapotranspiration, the water that does come in through the ground surface, a lot of that water never makes it to the water table.

It’s lost through evaporation and transpiration processes.

And that’s why we have such a limited net recharge rate to the water table.

So when estimating mass discharge, we’ve got different pore water concentrations.

So we’ve actually set up these Tyson polygons in the source area.

And Hunter Anderson had actually done this with their 12 lysimeter locations, using just the deep lysimeters to estimate mass discharge.

What we did because we had the extra RI lysimeter dataset that Arcadis had done, and BEM systems as well.

So we use the combined data set on the right to see, well, if we have more lysimeters near the burn pit, does that make much difference in the mass discharge that’s estimated?

And if it doesn’t, then that shows, okay, we’ve probably got enough lysimeters around the burn pit. So looking at the mass discharge numbers, this is what we estimated.

This is in that first paper, which is available online now, it’s published.

And you can see we’ve fairly low mass discharge for most of these species, a bit more for PFHXS and PFHXA.

And now when we add the groundwater mass discharge, we can see in all cases, except for maybe PFHPA, which is actually lower concentration than most of the other species, we can see the vadosome contributions are small relative to what’s already below the water table in terms of back diffusion and probably desorption from sand in the aquifer.

So, in this case, the mass discharged from the VEDO zone is just a small part of what’s actually leaving the source area below the water table.

So, in terms of conclusions, we talked about how the first pore water sampling event had low results, both for the data gaps investigation set and the RRI set as well.

And that’s typical of a lot of sites that we’ve seen. And that’s probably because of the dilution during lysimeter installation.

That we also show with multiple lines of evidence that poor water results were representative and reproducible and can be used for mass discharge estimation.

So we did the mass discharge estimates, we ignored the attenuation in soil PFAS below the lysimeter, between the lysimeter and the water table. So we’re a bit conservative there.

And what we found is there are substantial secondary sources, probably back diffusion from the abundant silt and clays below the water table.

And that’s the scenario where we say the horse has left the barn, PFAS got down below the water table a long time ago, and that’s really driving and sustaining the groundwater plume today.

So even if extensive veto zone remediation was done, that probably wouldn’t have a significant effect on the groundwater plumes.

So in terms of recommendations, I’d certainly recommend during the simulator installation, there is an approach you can take to use a tracer to check for this dilution effect.

And maybe we need to start using more of a lag between when the lysimeters are installed and the first monitoring event to make sure that that first event is more usable than it has been at other sites.

And then in terms of looking at data, I certainly agree with EPA and Jenkins-Stanza, multiple lines of evidence are really needed for evaluating PFAS in the veto zone, soil samples, poor water samples, groundwater transects, cross-sections like the ones we saw and that all helps us get a better understanding of that more complicated data set.

And then I really encourage use of soil samples, multiple depths in the VEDO zone.

If you wanna see if there’s much PFAS attenuation, soil samples are a cheap, pretty reliable way of actually allowing us to visualize that.

And make sure you’re getting this moisture content data from lab analytical reports, super helpful for understanding water saturations and how they change vertically and laterally at a site.

And then I find visualization is a key with these cross sections, radio diagrams, sometimes stacked bar maps.

So it all helps us get a better understanding.

And then if you want to do modeling to estimate mass discharge or to estimate site-specific screening levels for soil, you can use PFAS Leach.

It’s a new model developed by Boko and Marc Brousseau as part of CERNEP and the SECP projects.

Great model, easy to use, it helps a lot with parameter estimation.

So I encourage you to use that as well.

All right, so I’m going to leave it there and I’m going to pass it on now to Paul Erickson to talk about his presentation.

Thanks Grant and thank you everyone for tuning in again today.

So what I’d like to do now is move into a little bit more on the management side of PFAS impacted site.

Grant did a great job setting up the situation in terms of PFAS mass distribution that’s often seen or plausible on a lot of these sites.

And what I’ll do is spend some time talking about how these different areas that are present on a site can be managed using in-situ methods and what’s required in each of those situations.

And so starting first down at the plume, I’ll work my way up towards the source, but oftentimes we’ve got these larger areas impacted with PFAS and oftentimes more dilute concentrations, you know, that’s indicative of a plume.

So, in those areas, we’re going to treat them different than the higher concentrations you find directly beneath an impacted vadose zone.

And then, obviously, third, impacted soils will be managed yet again in a different way.

And so, here at Regenesis, we have different options depending on those areas that are being worked in.

Again, starting with the plume, we’ve got plume stop treatment, which I really won’t addressed today, you know, but this is something that we’ve been now deploying now for upwards of 10 years.

And more recently, we’ve done work in source zones using product line called SourceStop.

And so a couple different forms I’ll talk about today.

And what I’d like to do is really highlight the amendment offerings that we have in each of these different regions of a source area, explain when and where they’re best deployed.

And then what I’d finish up with is a quick case study that demonstrates some of the principles that Grant talked about using lysimeters.

In this case, though, we’re going to talk about how we can use lysimeters and demonstrate them as a remedial assessment tool. How is performance look?

That’s something we can also use lysimeters for and we’ve done in the past. So a bit about SourceStop.

We’ve got two different forms that make up this product family, a liquid and a solid form.

I’ll focus really on the solid form of the product today.

Both of them are meant for source zone treatments through PFAS immobilization or stabilization, so reducing the leachability on our soils, or in the case of groundwater, reducing what’s already there, the migration of what’s already there by more of an injection style.

But really the goal is the same, is we’re using a known and proven sorbent, activated carbon, getting it into forms that are best applied in these different either soils or aquifers to achieve this immobilization objective.

And so both of the products, both the liquid and the solid form, employ some amount of colloidal activated carbon, which you get enhanced rates of adsorption using smaller particle carbon.

So, VEDO sown soils treatment using source-stop-solid, really the idea here is that you’re mixing in the amendments to the soil to get this leachability reduction.

And so, anytime you’re on site working with an amendment, you know, you need a couple of things to happen.

One is you’ve got to be able to mix it, and so we formulated this product, source-stop-solid, so that it’s got both handling and mixing benefits over other absorbents on the market.

So principally here you’ve got low dust and then the low need for moisture, which I’ll touch on in a second, and it distributes quite nicely into soils.

And really the objective again is well-mixed soils are what you need in order to get that reduction in leachability for your PFAS in situ.

And so the product itself, Source Stop Solid, it’s an engineered composite microaggregate, it’s a combination of both the colloidal carbon that Regenesis uses and several other products and then some powdered activated carbon as well.

And again this is an amendment that gets mixed in directly into soils in the the unsaturated zone primarily.

And so again the objective is good dispersion, good mixing and so that’s what you need in order to get a good contact and immobilization of the PFAS that are on these soils that you plan on leaving in place in this because you can leave your soils in place in some cases so long as you can demonstrate that the contaminant mass that’s there has been rendered immobile, you know, and we’re going to look at a couple of different ways that that folks use to to demonstrate that and show effectiveness in the treatment.

So one of the the key handling benefits of Soar Stop Solid over other amendments is this ability for it to wet quite nicely.

And so if you look at a lot of other powdered sorbents that are used in in situ stabilization and immobilization they’re quite hydrophobic by design they don’t mix very well into soils and so one of the design principles of SoarStop was that we wanted something that was easy to mix in had nice wettability and that’s what you see here in this demonstration here is that you know whether you can use soil moisture that’s native or you need to add a little bit more moisture depending on the workability of the soils that’s really what the water is for that you at is to work the soils, it’s not so critical that you need water on mixing jobs in order to get good distribution because the product’s been engineered for that property on its own.

And so another big attribute, handling attribute for the product, SoarStop Solid, is that it’s got a much less dustier handleability over other powdered sorbents.

And so, you know, this can be a real hazard that you either have to use dust suppression equipment onsite or just be very careful of the wind direction when you’re using most amendments.

SoarStop solid, as you can see in this video, really has this almost like a much heavier feel that doesn’t dust up and transport with the wind, which can be a real handling benefit on site.

So now what I’ll do is walk through a mini case study for some of the pilot testing that we did with source stop back now three years ago.

And so this was an area that we were piloting on.

It was a former fire training area, quite high PFAS in a fill soil.

So this site was actually treated for hydrocarbons and received an NFA a number of years ago, but as many sites of late have had, they had to open it back up when the possibility of PFAS was demonstrated.

And so that was the case here.

And, again, this is the smaller pilot.

PFOS dominated in these soils, but you’ll see there was a lot of other substituents that were present as well.

And in this particular case, we used about a 4% mix of our amendment here, our source stop.

And what I’ll focus on for the performance monitoring is in these black dots you see here where we place lysimeters both within the treated area after we were finished and the same time outside of the treated area here in a control plot so that we could get an idea of what the pore water concentrations, PFAS concentrations, were either in a location that we hadn’t treated with source stop solid or within the treatment area itself.

And so day of, you know, for the actual treatment for the pilot project, you know, the goal is, of course, always to get good even distribution.

So with this material, we were able to do typical either bucket mixing or you can see here in the background of this one photo using a cutting tool to mix in our source stop into the soils directly.

So this is quite effective.

You get this nice even distribution of our amendment into the soil that you’re targeting.

And then as I mentioned, the lysimeters are a convenient tool that we can use to monitor with repeatable from, You can go back to the same location and it’s not required that you take soil samples, but rather you’re gonna put these devices in the ground as Grant talked about as well.

And you can take your soil pore water samples and you can come back and do this.

And it’s a much less invasive way to demonstrate or understand what’s the migration of water that’s passing through these areas, either treated or untreated on its way to the groundwater.

What’s the PFAS component in those pore waters?

and have we eliminated the risk of leaching from our areas which are causing posing a risk to our groundwater?

And so this is a diagram of what the area looked like, both the control and the treated area.

And to give you a better sense of what these devices look like, we’ve got a picture of them here as we were preparing to put them into the treated area and control areas after the work.

And so these were lyseminers made by soil moisture.

And you can see they’ve got this little ceramic cone the bottom.

That’s really where the pore water gets pulled in after you put a vacuum on the devices, which you can see the pump here that you use with these types of lysimeters.

And here’s another photo showing them going into the control area.

You know, we in this case use a direct push method to get them down because we were going at five and about ten feet below ground surface for these lysimeters.

If they’re at the surface, you know, you’re sampling really much shallower vadose zone, then you may not need these tubing type apparatuses, tubing type lysimeters, but instead you can keep them quite shallow and the tops of the lysimeters can stick up.

In some cases that that’s a route that you go when you’re using this type of pore water samplers.

And so the data, so I’m showing you here data from 6, 12, and 24 months in both the untreated and the treated areas of the site.

And so you can see that the, in each case, you know, these are from the shallow area, so I’m not showing the deep.

The data were roughly the same, but in this case you can see that the leachability reduction in those soils that were treated was substantial, and that’s reflected in the pore water concentrations that we get with this within those lysimeters.

So in the the samples that were outside in the control area, we still have substantial levels of pore water in our in our VADO zone and that’s what we’re doing when we do our treatment is we’re immobilizing the PFAS in those soils and that’s then dropping the leachable fraction of PFAS and then that has the effect of lowering the pore water concentration within those soils and so you know this is good evidence that treated areas once you’ve immobilized or mixed in the sorbent into these PFAS impacted areas you can drastically reduce how much PFAS will leach out of them.

And then that becomes protective of groundwater that’s residing beneath these soils.

And so, you know, asymmeters are great for being able to go back and sample repeatedly.

They’re fantastic for modeling purposes, as Grant mentioned.

You know, and they do correlate with the SPLP results, so the synthetic leaching procedure results that’s more commonly used where, you know, One takes a soil sample, you submit it to a lab for demonstration of leachability on the soils.

Pour water is an equally impactful way to get monitoring data on these sites.

And again, you can use lysimeters, not only for site assessment and site characterization, but also for performance monitoring.

Okay, and to wrap things up, here’s a figure kind of showing the number of sites that we’ve got across the US and really the world.

We’ve now done over 80 remediation projects using either SoarStop or PlumeStop to treat PFAS specifically, and also a growing number of sites that are in the review phase, the design and review phase, nearing 300.

So if you’ve got a site that you’re interested in learning a little bit more about how we might be able to work together, get in touch with us, we’d love to talk to you.