Is That Your PFAS? Using Forensics to Identify Sources

My name is Dane Menke. I am the digital marketing manager here at Regenesis and Land Science. Before we get started, I have just a few administrative items to cover. Since we’re trying to keep this 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 the webinar or audio quality degrades, please try refreshing your browser. If that does not fix the issue, please disconnect and repeat the original login steps to rejoin the webcast. 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 don’t address your question within the time permitting, 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 discuss using forensics to identify PFAS sources. With that, I’d like to introduce our presenters for today. We are pleased to have with us Elizabeth Denley, PFAS Initiative Leader and Chemistry Director at TRC. As a Project QA chemist at TRC, Elizabeth Denley is responsible for providing quality assurance oversight in support of environmental investigation, including remediation programs, ambient air monitoring, and human health and ecological risk assessments. She’s currently serving on the Interstate Technology and Regulatory Council or ITRC PFAS team, is a co-leader on the PFAS Naming Convention sub-team, and won the 2017 ITRC Industry Affiliates Award for contributions to this team. She currently works on many different types of PFAS investigations with a specific focus on chemistry, sampling procedures, data interpretation, forensics, QAQC, and analytical methodologies.

We’re also pleased to have with us today Maureen Dooley, Vice President Industrial Sector at Regenesis. Maureen has over 25 years of experience in many aspects of the remediation industry, including project management, research and development, senior technical oversight, remedial design, and laboratory management. Her prior experience includes work to evaluate the biodegradation of a wide range of chemical constituents that include chlorinated solvents, petroleum hydrocarbons, explosives, aromatic hydrocarbons, and pesticides. In her current role at Regenesis, she provides technical leadership for complex soil and groundwater remediation projects, including PFAS groundwater contamination treatment throughout North America, as well as remediation design, strategy, and business development in the northeastern U.S. and eastern Canada. All right, that concludes our introduction, so now I will hand things off to Elizabeth Stanley to get us started.

Thank you. So I just want to say thank you to Regina Smith for allowing me to present today. And today I’m going to spend most of my time on technical aspects of PFAS forensics and some tools available to help you with source identification. I don’t really have enough time to share everything I’d like to, but I’m going to give you a snapshot or a few different tools or concepts that you need to think about in your forensics evaluations. Okay, so we know PFAS are complicated. There’s challenges with how PFAS cycles for the environment, the basis of toxicology and the regulations are all over the place. We still don’t have a final multi-lab validated standard EPA analytical methodology yet for non-drinking water matrices. And we do have limited options for treatment of PFAS. And the public perception was really driving a lot of the action that we are seeing.

But one of the major challenges of PFAS is that it’s costing a lot of money to investigate and clean up, and who is ultimately going to pay for this? Is it going to be the municipalities, the manufacturers of PFAS, the users of PFAS? And I won’t really discuss that specifically today, but in this determination of who will pay, forensics may come into play, and that will be the focus of my talk today. So understanding the potential sources of PFAS out there is important for our forensics evaluations and site characterizations. There’s many different industries or products where PFAS are used. And this information will be useful when you’re considering what types of sites might have PFAS contamination or from where the contamination might originate. And it will be an important part of your forensics analysis. So forensics is not just about chemistry, but also about looking into operational history, potential nearby sites or sources that may be affecting your site.

So PFAS are just about everywhere, so we need to use some of the specific source information when we’re trying to differentiate PFAS at our sites. And this table is really just a very brief summary, and it’s an example, but something you could use to start your analysis. Okay, so let’s begin discussing some of the technical concepts in PFAS forensics. So to start, TRC has developed and effectively used a PFAS forensics tool for source identification and differentiation. And the larger pie chart that you see on the screen here contains select PFAS analytes. So in my presentation today, we’re going to be using these compounds as the focus of discussion. So, you can see about half the pie chart on the left-hand side here covers what we call the perfluoro carboxylic acids, PFCAs, in a blue shade, so compounds like PFOA, PFNA. About half the pie chart on the right side covers the perfluoro sulfonic acids in the yellow, oranges, and reds, so compounds like PFOS, perfluoro butane sulfonic acid. And there’s also a couple of precursors, so I included telomers, 5-3-fluorotelomer carboxylic acid, 6 ,2-fluorotelomer sulfonate in these darker colors.

And these are examples of the many precursor compounds that can break down and be transformed into the terminal perfluoro carboxylic acids and perfluoro sulfonic acids. So throughout most of my slides, the color code will remain the same for these constituents. So I know this is not really easy to see, but this slide gives you a very big picture summary of some of the different signatures that we may see that can reflect different sources. So at the top of this slide, you can see a lot of the red, orange. These are the perfluoro sulfonic acid. So the red is PFOS. The yellow is perfluorohexanesulfonic acid. And you look at these signatures and it’s probably most likely from an aqueous film forming foam source, AFFF, the firefighting foam. And towards the bottom, you see maybe a plastic source with more of the blue perfluoro carboxylic acid, specifically PFOA.

But this slide also gives you the big picture summary of some of the different signatures that we can see, which can reflect different fate and transport scenarios also. So these types of chemical signatures can be used to identify various characteristics and not just of sources, but also characteristics of different fate and transport scenarios. So we may see the breakdown of certain PFAS precursor compounds like those fluorotelomers further downstream in a plume. And we can show a plume becoming more enriched in something else because of the breakdown of those precursors. There could also very well be a change in signatures due to co-mingling of more than one source, causing differences in pie charts along the length of a plume. So it’s critical to understand all potential sources along a PFAS plume. So the chemical signatures are a really good starting point in providing information on different sources and different fate and transport scenarios.

But they are just a starting point. Because with PFAS, as we know, there’s a lot going on. So I’m not going to really spend a lot of time on this slide today, but I presented it here because we’re just, you know, we’re beginning to understand more and more when there are certain PFAS chemicals that are more indicative of a particular product or industry. And some of that is highlighted here as examples for your reference. I want to spend a little bit of time today on AFFF, the firefighting foam, and show you some examples of how these signatures can be helpful because as most of us know, AFFF is one of the major sources of PFAS contamination. And more often or not, you’re going to be dealing with AFFF on a PFAS site.

So let me just start with a general overview. And in general, there’s three categories of AFFF. So first, there’s the legacy first-generation AFFF. And most of these were PFOS-based foams sold under the brand name 3M Lightwater. And although sales of this type of foam ended in 2002, many locations may still contain this in their inventory. So these foams will typically contain PFOS, perfluoro hexane sulfonic acid, and possibly even PFOA. Second, we have the legacy second-generation AFFF, and these were sold from about the 1970s to 2016, and these foams are fluorotelomer-based, and these foams contain long-chain fluorotelomers, most likely 8 ,2-fluorotelomer sulfonate mixed with 6 ,2-fluorotelomer sulfonate, but it is the longer-chain 8 ,2-fluorotelomer sulfonate that we’re concerned about because this fluorotelomer can break down to PFOA.

And third is the modern fluorotelomer AFFF. So most foam manufacturers have now transitioned to the use of only short-chain fluorotelomers, so the 6 ,2-fluorotellomer sulfonate. So these foams do not contain or break down in the environment to PFOS or PFOA. Now, these foams may contain trace quantities of PFOA as a byproduct of the manufacturing process, but PFOA is not an ingredient of these foams. So, due to the production methods, the variability in AFFF formulations through the years, AFFF can really contain complex mixtures of PFAS. But understanding just some of the basics can help us start to differentiate these different types of AFFF. And this will be important for your forensics analysis.

So here is a simplistic look at the different AFFF signatures. So the first one here is the first generation legacy, the PFOS-based AFFF. Again, also contains a good percentage of perfluoro hexane sulfonic acid, the C6. And actually, it’s important to note that different lots of AFFF produced by 3M had different ratios of PFOS to perfluoro hexane sulfonic acid. The second one here is a second generation AFFF. And this one has equal amounts of the 6 ,2 and 8 ,2 fluorotelomer sulfonate. It’s also a little PFOA here, which was likely from the breakdown of the 8 ,2 fluorotelomer sulfonate. And the last one is the modern fluorotelomer 8FFF, so the one most foam manufacturers has switched over to, with the major component being 6 ,2 fluorotelomer sulfonate. So again, this is just a very simple view of the different 8FFF signatures.

So I wanted to show you this. This is a catch basin sample. It’s from a Teflon-coated fiberglass manufacturer. And it has an obvious signature. It’s very distinct from the AFFF signatures that we just looked at. And it’s just, again, an example of the uniqueness of signatures in the manufacturing industry versus AFFF. So this signature is from an article showing 5 ,3-fluorotillomer carboxylic acid. It’s dominant in landfill leachate. And the article says it’s coming from carpeting. So it’s a very unique signature. 5-3-florotelamer carboxylic acid, though, may have different sources. So this one article does say that it could be coming from the carpeting. There’s other articles out there that say it can be a breakdown of one of the fluorotelomer alcohols. And sources to landfills can be a mixture of different ingredients to begin with. So it is complicated. And I do warn people that it can be easy to be misled by the presence of 5 ,3-fluorotelamercarboxylic acid. But again, you can see a very different signature here than the AFFF signatures.

OK, so now we’re going to add a different dimension to the forensics interpretations. So generating pie charts based on a regular PFAS analysis of individual PFAS compounds is step one. But then we need to look at how some of the very unique PFAS and transport concepts can also play a role in the forensics interpretations. So I want to spend time today on a few of the unique concepts, but there are more as well. So first, let’s look at PFAS transformation. So there are thousands of precursor PFAS compounds that we do not measure in a standard PFAS analysis, but these precursor PFAS compounds can transform or break down into the more persistent PFAS chemicals that we do analyze for, like PFOA and PFOS and others. So the signatures of surface water or groundwater from a release containing precursor PFAS, and some examples are here, like the 6-2 or 8-2 fluorotelomer sulfonate, the signatures may instead show a higher prevalence of the 6-2 or 8-2 fluorotelomer sulfonate transformation products.

So the precursor PFAS, like the 8 ,2 and 6 ,2 fluorotelomer sulfonate, like we just talked about in the AFFF, they will degrade into more soluble and more mobile compounds, and again, into the more persistent compounds, like PFOA, perfluoro butanoic acid, and others. So you can see the rules of thumb here on the right for the transformation of these fluorotelomer sulfonates. So if you detected PFOA associated with an AFFF release, it’s probably most likely from the use of the longer chain fluorotelomer-based foam, that second-generation foam, the A2 fluorotelomer sulfonate. So one tool that we have is called a top assay analysis. So the top assay takes our sample, and it does a very strong oxidation of it to break down any of those precursor compounds. The top assay will not break down the persistent compounds like PFOA and PFOS. It will only break down the precursors.

So in essence, the top assay accelerates the natural rate of transformation. It could be a more realistic estimate of potential environmental liability than the typical PFAS analysis, especially if a fluorocalamer-based AFFF was released or was the residual source. So you can see the pie chart here with the results. So this is the original sample before the oxidation. So if you look at the top of the slide here, after the top assay oxidation, you The sample was again, it was analyzed again for the regular list of PFAS, and after the oxidation, the total PFAS concentration increased by over an order of magnitude, about a million nanograms per liter. Now if we look at the bottom part of the slide, you can see the 6 ,2-fluorotellomer sulfonate, which is again a precursor PFAS, was oxidized because it reduced in concentration. It went from 40 ,000 nanograms per liter to 1 ,000 nanograms per liter. While many of the perfluoro carboxylic acids, so the light blue and the white here on the pie chart, increased in concentration.

So we’re seeing here a dramatic increase in concentrations for the C4, C5, and C7 perfluoro carboxylic acids. These are the same compounds that are shown as transformation products in our rules of thumb box here for 6 ,2-fluorotalamyl sulfonate. So we can use top assay to help us determine the ultimate source of the AFFF because of these PFAS transformation properties. It’s very important to think about PFAS transformation during your forensics analysis. So what are some specific examples of how top assay results can help us understand PFAS transformations of AFFF in a forensics investigation? So there’s a few tips here that could be used in conjunction with other information. So again, you need to look at the rules of thumb first for the transformation of the 6 ,2 and 8 ,2 flora telomere sulfonate, AFFF. And then you want to look at some ratios of the breakdown products. And also, you want to look at which breakdown products are or are not present, and you can start to figure out the AFFF source. So I’m not going to read these, but they can be helpful when you’re looking at scenarios where the potential for more than one AFFF source exists, something that’s been very helpful for us at airport sites.

Okay, so now let’s discuss another unique PFAS fate and transport concept that can also play a role in forensics interpretations. So here the issue is chemical sorption of specific PFAS to organic materials or solids. So it’s really important to understand for forensics because the sorption property can have a significant effect on the chemical signatures produced, And it can also significantly affect the concentrations of PFAS in a sample. So the longer chain PFAS compounds, so C8 and higher, and especially the perfluoro sulfonic acids, so compounds like PFOS, can have higher absorption to solids. So how can this affect forensics? So let’s look at the pie charts here. This is an example of groundwater that was sampled from a temporary well compared to same groundwater sampled from a two-inch well that was properly developed. You can see the turbid water has a much different composition than the clearer water with higher concentrations of the six carbon perfluoro sulfonic acid and the eight carbon PFOA.

And again, we know the longer chain PFAS and even more so for the perfluoro sulfonic acids adhere more to the solids. So depending on how that water was sampled, you know, either a temporary well or permanent well, and how much particulates were actually present, it could affect your forensics interpretation and ultimately determination of liability. So sometimes we submit wastewater samples, surface water samples, groundwater samples to labs, and these samples may be turbid or they may contain elevated levels of particulates. And when our samples are turbid or they have elevated levels of particulates, as I said, it could affect your forensics interpretation And it will be dependent on what the lab did with the sample. So the point here is something many people are not aware, which there’s a major inconsistency in the lab community on the handling of these aqueous samples with particulates for PFAS analysis.

There is no consistent method. And again, these particulates can significantly affect PFAS concentrations, and not only the concentrations, but also the PFAS signatures that we create. So the resulting concentrations of PFAS and the resulting fingerprint of PFAS is going to vary depending on how the lab handled the sample. So some of the potential differences from lab to lab are listed here for your reference, but it’s very important to one, you know, work with the lab ahead of time to figure out what you want based on your project objective, and two, if you’re receiving data that’s already been generated, please, you know, understand what the lab did and if particulates were an issue because this could affect your forensics interpretation.

So question the data that you are receiving. This is just a really good slide. I like to show just illustrating the persistence of PFAS. It’s from the Cape Fear River, from the Camorra site. The samples are upgrading of the site. And you can see the consistency of the signature. The scale is 10 miles. If you look at the pie chart here at mile four towards the top, you have 126 nanograms per liter, 20 miles downstream, you see pretty much the same signature, very, very similar concentrations. So there’s hardly any dilution or sorption, nothing much has changed, it’s actually kind of amazing. This is also good evidence that there’s not much absorption to soil going on here. Towards the bottom you see maybe a little contribution from a downstream source, but the mass of that possible contribution is really not substantial, and the overall fingerprint doesn’t really change. It’s actually fairly insignificant compared to what was in the So as we know, the standard PFAS analyte list continues to change.

Obviously, the more information we have on the composition, the better. The commercial labs right now, they can analyze for up to about 70, 75 different PFAS chemicals. But one of the problems is that the largest data set we currently have is from UCMR3, and that only includes six of the perfluoroalkyl acids. Now, in the next few years, with UCMR5 happening, we’re going to have a much larger data set that will include 29 different PFAS. But the comparison of signatures requires careful consideration of the analyte lists. So this slide shows the same exact data set, but the evaluation looks really different based on the analyte selected. So if you look on the left, if we had just analyzed for PFOA and PFAS, you know, you It’s a Teflon manufacturer. You’re seeing a lot of PFOA. But if you look at the same two pie charts for the same two samples, but looking at more analytes, you see something else completely different going on here. The signatures are very different. So make sure you understand the limitations of your signatures based on the analytes that your lab has reported.

OK, so I wanted to present a case study today. And in this case study, we were tasked with a forensics evaluation of data generated from a landfill. and we’re looking at groundwater and residential potable water samples. So 11 groundwater samples with concentrations greater than 100 parts per trillion total PFAS were selected for this evaluation. And I like to point out that sometimes it can become more challenging to do forensics on lower concentrations. So we selected 100 parts per trillion as our cut off for this evaluation and it was determined to be a good concentration for this site relative to total PFAS concentrations in other wells. The samples were analyzed for a list of 23 PFAS.

And there were a few different objectives. So first, we wanted to differentiate onsite landfill sources versus offsite sources of PFAS. So when you’re doing forensics, it’s important to understand that the patterns observed in groundwater, they could be representative of an old source or they could be due to fate and transport properties of PFAS like we have just discussed. And you have to understand that even when the patterns of contamination between wells appear similar, it may not be conclusive to the source of PFAS, because there could be something else going on related to freight and transport causing signatures to change. So our second objective was to determine if there was information on potential sources, so whether the source was a landfill mixture, an AFFF source, septic system, or something else. And our third objective was to identify hot spots or concentrated sources of PFAS within the landfill.

And then finally, we were trying to identify whether or not we needed to gather additional information or maybe needed to install additional monitoring wells or sample existing wells in order to verify sources that are determined not to be associated with the landfill. So this pie chart revealed three different trends of PFAS contamination, and this is a busy slide. But I want to point out the three trends. So PFAS trend one, shaded blue. So this trend includes the sample closest to the landfill source at the edge of the landfill. And it extends to two wells downgrading of the landfill to the north. PFAS trend two, which is shaded green, includes wells south of the landfill and some side gradient and downgrading at wells. And PFAS trend three, shaded orange, includes two wells northwest of the landfill. So there was three different patterns of contamination that we identified as trend one, two, and three.

And within each of these trends, we also identified some hot spots. So just so you can clearly see the different patterns of each trend, you can see the perfluoro hexane sulfonic acid and PFOS start to increase on trend two, and trend three had the highest PFOS. So besides pie charts, we also looked at some diagnostic ratios. So first we looked at the perfluoro carboxylic acids, their relative abundance to total PFAS. And you can see here what are some example of perfluoro carboxylic acids. And these values should remain consistent within a PFAS plume that’s associated with one source. Then we looked at the perfluoro sulfonic acids relative abundance to total PFAS. And these values also should remain consistent within a PFAS plume that’s associated with one source.

Now, values here greater than 0.5 may be a potential indication of a legacy AFFF source, so the one that’s produced prior to 2002. We also looked at the perfluoro carboxylic acid to perfluoro sulfonic acid ratio. So if the plume’s associated with a unique source, these values should increase with the groundwater sample’s distance from the source. Because remember that perfluoro carboxylic acids with similar fluorine chain lengths are more mobile than the perfluoro sulfonic acids. So as this gets further away from the source, this value should increase. Related to PFOA to PFOS ratio, here values less than one, so when you have more PFOS than PFOA, may be an indication of a potential legacy atrial blephsorus. Also, low PFOA to PFOS ratios could also be associated with septic leach fields. So we use the pie charts and we use the diagnostic ratios to help in our evaluation.

So let’s look at trend one again. So you can see the pattern from the well here that was located on the edge of the landfill towards the center of the landfill. And the signature down gradient of the north corner of the landfill is almost identical to the signature of the well on the edge of the landfill. So this well here on the edge of the landfill likely represents the landfill source and these downgradient wells likely represent the signature downgradient of this well. So the mixing of landfill leachate and groundwater is creating this consistent signature, which confirms that the plume from the landfill is moving offsite. Now as expected with this trend, the perfluoro carboxylic acid to perfluoro sulfonic acid ratio increases with distance downgrading it from the landfill. And PFAS signatures like this that are rich in the perfluoro carboxylic acid, so the blue shades here on the pie chart, especially the shorter chain perfluoro carboxylic acids are an indication of a landfill source.

In addition, seeing the presence of PFOA at concentrations greater than PFOS, which is in red here, with the absence of flora telomeres indicates this is probably unlikely an AFFF source. So that’s trend one likely emanating from the landfill. So now let’s look at trend two. So there are these two wells right here south of the landfill. And concentrations at these two wells are lower by an order of magnitude than the concentrations at the side gradient wells. So, because of this, the origin of this plume is probably upgradient to the north of these two wells, which are south of the landfill. So before we talk about the potential source of Trenchu, let’s look at some ratios. So again, as expected, the perfluoro carboxylic acid to perfluoro sulfonic acid ratio increases with distance downgradient from the well couplet, which was again south of the landfill and closest to the source.

So, potential sources of this plume include the scale house septic system in the southern part of the landfall footprint, so just north of this well couplet. So, former scale house areas were generally not well-lined and many of them accumulated liquid waste for recycling or offsite disposal. And the liquid waste storage areas could be a source of PFAS from potentially high concentration PFAS solutions, including AFFF concentrate, alkaline cleaning fluids, and carpet treatment chemicals. So this was one area where we are recommending some future work to confirm the source. I think we may need to install a shallow well to determine if this PFOS richer groundwater is associated with the landfill or another source such as the scale house area.

OK, so now let’s look at trend three. So the pattern observed here was not a landfill source. In most landfill groundwater, PFOS is a minor constituent since PFOS and other perfluoro sulfonic acids would adsorb to the municipal solid waste in the soils more than PFOA and other perfluoro carbic silica acids. So if you remember from the slides about sorption, the perfluoro sulfonic acids have a higher tendency to bind to soil than the perfluoro carbic silica acids and the perfluoro carbic silica acids are leaching away from the soil or municipal solid waste quicker than those perfluoro sulfonic acids. So when higher concentrations of PFOS are detected there’s a higher likelihood of a different source. It could be maybe a liquid source such as the use of AFFF, it could be a chemical poured into a septic system, could even be a composting facility. And potential PFAS sources to septic systems include both perfluoro carboxylic acids and perfluoro sulfonic acids that could be found in carpets, carpet cleaning solutions, wash water from cleaning, water-resistant or stain-resistant clothing, and alkaline cleaning agents.

Okay, so in the case of these wells, again, they were located northwest of the landfill, there’s likely another up-gradient source because the PFOS-rich down-gradient groundwater results are generally not associated with landfills. So here we need to do some research on potential up-gradient sources and maybe install a new well depending on what we find. So in all of these evaluations that I’ve shown you, we have to remember also that when there’s low organic composition in the source matrix and in the groundwater, the PFAS composition of a groundwater plume will generally reflect the PFAS source composition. So that’s when there’s a low organic composition. In addition, when there’s a low organic composition, the longer chain PFAS may also be identified from these sources as those longer chain compounds are more mobile in matrices with lower organic compound, lower organic content. Under organic rich site matrix conditions, like a land film, those perfluoro sulfonic acid compounds may be selectively filtered out at a higher rate than the perfluoro carboxylic acids, resulting in more of a perfluoro carboxylic acid rich groundwater plume.

So my final slide, my takeaway messages for today, in the interest of time, I’m not going to read the slide, but I think the major takeaway message is that PFAS forensics involves not only chemical signatures, but a really good understanding of the unique fate and transport properties of PFAS. And it’s really important to also make sure you understand what analyte list you’re going to be including in your forensics evaluation. And with that, I’m now going to turn it over to Maureen Dooley of Regenesis.

Well, thank you, Elizabeth. That was a really interesting and enlightening presentation that speaks to the complexity of the class of compounds and how important understanding the sources and the fate and transport of PFAS in the subsurface. And, you know, some of the points that you’ve made in your conclusion, I think are really important. And they’re really important as it relates to even thinking about what the next phases are in remediation. And, you know, it’s the composition of the PFAS, you know, you know, what do you have, you know, what are, you know, and also the complexity of the hydrogeological conditions and how important is to understand that. So what I’m hoping to do in the next few minutes is to elaborate a little bit on data needs, how it relates to remediation, specifically in situ remediation.

And I think what I really want people to think about is, what’s the information you need for remediation design? Can this be incorporated as part of site characterization activities when data are being collected and to gain an understanding of the PFAS fate and transport. So this next slide, I know this is a little bold, but what if we could bring you a PFAS groundwater remediation solution that is proven much lower cost than pump and treat and guaranteed up to 30 years? Now, I bring this up. This is a very complicated class of compounds and we have limited remedial options. And I think an ideal situation would be one where we can use in-situ remediation to be able to mitigate these problems in a cost-effective manner. And so I think, you know, the place to start with this is, you know, really what is our objective?

You know, when we’re looking at in-situ remediation, we want to eliminate risk. So risk is the combination of hazard and exposure. If we are able to reduce exposure, we’re going to reduce risk. Now, what we’ll talk about is colloidal activated carbon. And we know that can, PFAS compounds can sorb to that. And Elizabeth mentioned that in some of her investigations and how when you have additional organic matter, certain classes of PFAS compounds will tend to get bound up in it. So, if you’re able to engineer a system where you can bind this up, change some of the mobility characteristics and reduce exposure, you know, this can be a feasible option, you know, for a risk management scenario And this approach is also really consistent when you think about natural attenuation. So, what I want to refer to is a paper that Dr. Newell published recently on monitored natural attenuation, and he lays out some processes for doing site investigation and considering natural attenuation as a program for PFAS-impacted groundwater.

But, you know, just stepping back for a second, you know, what is natural attenuation? And going back to what EPA defines this is, this is an approach that relies on natural attenuation processes to achieve site-specific remedial objectives with a timeframe that’s reasonable. And there are a number of natural processes that include the reduction of mass, toxicity, mobility, volume, or concentration of contamination. So, the processes that are typically associated with natural attenuation, the first one is transformation. Now, with PFAS, what’s interesting about this is, as Elizabeth discussed, with precursors, you can observe a lot of transformation, but that transformation may end up as PFAS or a compound like that. And so for natural attenuation and looking to reduce toxicity, degradation processes are not really something that’s available unfortunately now. This is something that we would look at for chlorinated solvents or petroleum hydrocarbons.

A second process is reduction of contaminant concentrations. Quite often this is achieved if you have source mitigation. So if you have source mitigation, and then there is less contaminant getting into groundwater. And so that’s not really what we’re talking about here. So what I want to refer to is the reduction of contaminant mobility and bioavailability. So this is getting into enhanced sorption. If you have organic material, which we see in the natural conditions, you may have some segment of the PFAS constituents tending to sorb. What we’re looking at is the application of colloidal activated carbon to enhance sorption and also change mobility and the transport properties of PFAS through groundwater and reducing mobility and reducing exposure.

So just getting back to what is plume stop, it’s a form of activated carbon. and we mill this down to one to two microns. It is then suspended in a polymer, and that allows us to inject it into the saturated subsurface with low pressure and get this widespread distribution. We’ve been involved with the colloidal carbon and Plum Stop for many, many years. Commercial applications began in 2015, and actually our first application of Plum Stop to address PFAS contamination occurred in 2016. And over this time period, we certainly have gained a lot more understanding of how to use colloidal carbon and how best to apply it in the subsurface.

Just briefly, sites that we’ve been working on. We have projects across, really in the US and across the world. We probably have over 26, 28 field applications to date. The types of sites that we’re working on predominantly have been industrial manufacturing, airports, but we also have applications in DOD facilities, other bulk storage, and superfund sites. So what’s the process that takes place? So you have groundwater plume, contamination is moving through. We will apply the colloidal carbon. It will take about 30 days to establish this barrier, and then some of these individual PFAS compounds will become sorbed to the colloidal carbon, so we’re in essence creating this Brita filter. I’m not going to get into tons and tons of detail based on time.

At the end of the presentation, I do have a link to a video that gets into a lot more detail about almost the fate of the individual PFAS compounds within this barrier and then helps to explain why we are able to maintain and sustain the longevity and the longevity of the barrier that may lead into decades of treatment in our ability to keep groundwater concentrations and PFAS concentrations below target levels for an extended period of time. So the mode of action here is adsorption. So as groundwater moves through the PFAS compounds are sorbed, what we’re in essence doing is we’re changing the FOC of the subsurface. And if we think of this in terms of retardation factors, PFAS will have a retardation factor naturally in a range of individual compounds of three to 20, meaning that we’ll travel anywhere from three to 20 times slower than groundwater flow rates.

After the application of the colloidal carbon, your retardation factors may increase to something as large as 10 ,000, which means the travel or transport is 10 ,000 times slower than natural groundwater flow rates. That means we are able to sequester these compounds for an extended period of time. How does this look when you’re scoping out something at full scale? Example if you have, say, an airport site, you have fire training area, and you need to cut off a plume before it migrates to some sensitive receptors, you can inject the material and create this barrier. But this is a nice conceptual picture, looks really pretty, it’s a cartoon. What is the data that we really need and we really need to understand?

We need to understand groundwater flow, we need to understand flux, we need to understand contaminant concentrations. And I think really interesting point and an important point that Elizabeth brought up with a top analysis, if things are transforming, if some of these precursors are transforming, You know, what’s our maximum load of PFAS going to be? And I think that’s important information to understand. And also very critically, what is the distribution? We may look at a well screen and this 10, 20 foot thickness, but there’s a lot of heterogeneity and a lot of flux and microflux zones, and the better understanding we have of these components, I think the better design we can provide. So what are our considerations? You know, one, what are the types of PFAS components present? You know, what are our targets? You know, what are the regulatory standards, longer chain versus shorter chain? What’s our groundwater flux?

That’s really, really important. Contaminant concentrations, both target and non-target compounds. And are we able to apply this material to get the distribution that’s required? In the picture to the right, we can see a soil boring, this black color is the colloidal carbon. We really need this consistent distribution through the subsurface to be able to create this barrier and not have any holes and get that net when we’re looking to achieve standards that are in the part per trillion. So we have a process that we will go through where we want to conduct some design verification testing. We also look at flux in using passive flux meters. Taking that data, we’re going to put together a design. That design will also incorporate us running models, looking at competitive absorption, back to fusion. And we will often want to do some sort of injection verification. Can we get the ROIs that we need? And then based on that, we can put together a full design and allow to provide estimates on what the longevity of a barrier is.

So this design verification, we’re looking at subsurface investigation specific to the application. And this is really not anything that’s out of the ordinary. We’re looking at detailed, you know, boring logs. We want to understand flow rates. Maybe it’s a, you know, an injection test that takes a day or two, you know, the incorporation of passive flux meters, but also high resolution sensing tools. So these are a lot of tools that are used in these initial investigations. And I think thinking forward, you know, are we getting the information we need for remediation? Because if we’re looking for just plume characterization, it may not include what we need for remediation design. Our flux tracer tool is our passive flux meter. I’m not going to spend a lot of time. You can go to our website on this.

But basically, this is a pre-assembled device that you can place in an existing well, put it there for two weeks, retrieve it. This is something that consultants, you guys do this yourselves. You send this device back to us and we can do analysis to look at, you know, in one foot sections, you know, what the flow, you know, what it calculating Darcy flux, mass flux in groundwater, which is extremely useful in our designs. You know, ultimately, we want to have this data available so we can get results that show rapid reduction, sustained treatment, you know, have a program that doesn’t require O &M, no waste generated, sustainable and low cost. This figure shows the results from our first test, our first application of Plum Stop for PFAS that was in Ontario and we’re at six years right now and we’ve still been able to maintain the targets.

The other important thing I want to bring out a lot of things people talk about longevity and with Regenesis, if we go through this process of evaluating a site, running a DVT, doing the flux tracers, going through this commissioning phase and confirming feasibility, we are going to warranty our barriers for a standard 10 years and up to 30 years. So we have confidence that we have a good understanding of the capability of the colloidal carbon. And if, you know, we have, you know, we look at the site details, this is certainly something that is going to be standard for us in moving forward with some of these PlumeStop PFAS applications. So really, in summary, over Regenesis, we have a suite of remediation technologies. The colloidal carbon is something that, you know, can be used and is being used to address and reduce the risk of PFAS and groundwater. Data collection data is really, really important and our design verification is an important stage for us to really understand your site to develop these cost-effective strategies. So with that, again, I want to thank Elizabeth for a really, really great presentation.