Hello and welcome everyone. My name is Dane Menke. I am the digital marketing manager here at Regenesis and LandScience. 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 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 analytical tools to promote CVOC and PFAS plume stability. With that, I’d like to introduce our presenters for today.

We’re pleased to have with us Matt Burns, VP and Technical Director of Earth and Environment Practice for WSP. Matt Burns is a chemical and microbial process expert with a focus on in-situ remediation. He is a frequent author and lecturer on innovative investigation and remediation techniques to address metals, petroleum hydrocarbons, chlorinated VOCs, and emerging contaminants such as PFAS. He is a co-author on the PFAS Experts Symposium Statements on Regulatory Policy, Toxicology, Transport, Fate, and Remediation for PFAS Contamination Issues. We’re also pleased to have with us today Joe Ricker, Senior Technical Principal at WSP. For more than 27 years, Joe Ricker has helped clients optimize a wide range of remediation solutions associated with past and present environmental liabilities under various regulatory programs in the U.S. and globally. He is the lead developer of environmental data evaluation techniques known as Groundwater Plume Analytics Services. He also authored the Ricker Method Plume Stability Analysis in 2008, and has subsequently developed or co-developed additional patented plume analytics tools known as Remediation System Benefit Analysis, or RSBA, Spatial Change Indicator, and Well-Sufficiency Analysis.

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. 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. All right, that concludes our introduction. So now I will hand things over to Joe Ricker to get us started.

Okay, great. Thank you, Dan. I appreciate the intro there. So I’m gonna take the first part of this and talk about plume analytics and how they apply to natural attenuation. So I’m gonna jump into this here. So we use the term analytics, the idea of being that we’re taking complex data and distilling it in a way that we can communicate insights. So that’s really what the idea of groundwater plume analytics is. And so as Dane mentioned, there are several tools that we use in our line of work. But the primary one that I’m only going to discuss today is going to be the Ricker method plume stability analysis and how it applies to natural attenuation. So as we all know, with MNA, natural attenuation, we really want to show stability from a standpoint of that first line of evidence, you know, is a groundwater plume stable or shrinking? And so the Ricker method was designed to do that. So with the Ricker method, it’s more of a control volume approach, looking at a plume as a whole, stepping away from a well-by-well trend analysis and looking at a plume in metrics such as area, average concentration, mass, and center of mass. And so using those tools to understand behavior of a plume can go a long way towards demonstrating natural attenuation.

So I will show two different project examples, one for petroleum hydrocarbons and then one for chlorinated solvents and the nuances with chlorinated data with parent-daughter sequences, things of that nature. So I’ll talk about those momentarily. So the Ricker method was published. This is in the public domain. A lot of people use it. It’s freely available. But what you’ll see is everything, you know, coming out of the Ricker method analysis for two sites. So rather than explaining it, I’ll show it to you. The Ricker method starts off with an isopleth map. You can see that here. So this site that we’re looking at is a bulk terminal site. It’s in California. And different colored wells are because there are two different terminals with one co-mingled plume here. So as I said, the Ricker method looks at these metrics. On the bottom, you see area, average concentration, and mass, or mass indicator. The yellow cross in the middle is the center of mass. So we do this for every single event where there’s data available. So notice the date here is 1994.

And so we’re going to look at this for every event. So when I put this in motion, you can see it’s really an empirical analysis of existing data. So you can see the behavior over time. You notice several wells come in. These black wells come in eventually. This is actually a third site. So it’s really one large comical plume. You can see the center of mass I was tracking through time. you’ll notice a lot of the gray wells come in. These are all different remediation wells. And so there are four different remediation systems that were installed over time at this particular site. And then, you can see where it was in 2019 when this analysis ended. So I just showed you pretty much 25 years of remediation in 30 seconds. And that’s the idea of the Ricker method is to let you see the plume behavior and then using the data, these metrics on the bottom, using those to demonstrate stability or demonstrate, you know, that we can move to M &A or some other remedy away from these active systems, and I’ll talk more about that in a second.

So what we do is we can then trend these metrics and more of an objective analysis. So on the top you’ll see the area data plotted, and you can see there was an expansion in 2001 and then remediation at this site started in 2003, and from that period of time we trend the data, and you can see over here we’re using Mankindle and Regression, just two trend tests is all those are. And then you can see decreasing trend is the outcome with very high statistical confidence. Same thing with the average concentration in the middle, very strong decreasing trend. Same thing on the mass indicator on the bottom. You can see it was pretty stable for several years. Once remediation started, it took it down to this point, and then several of those systems were turned off and the natural attenuation took over at that point.

So this is again high-level what the rigor method does it’s looking at plume data to demonstrate the behavior of the plume So the next thing we can look at is the center of mass behavior so for the center of mass we post all the centers of mass on a single graphic and at this site groundwater flow is to The West and you can see that ground the centers of mass here that the darker colors are the earlier data The lighter colors are the more recent data and you can just track it visually here. The general migration of the center of mass is pretty strongly to the east now at this site groundwater flow is to the west So this is a very strong up gradient shift in the center of mass again and another measure or evaluation Of stability this chart on the right is just tracking the vector movement So if you can imagine center of mass at one location at the next event, it’s at a new location Connect those two with an arrow Mathematically, that’s a vector which is just, you know, quantity having direction and magnitude. So that’s it.

We can plot those vector movements and you can see a lot of scatter, which actually is a picture of stability. If a plume was, say, growing, you might expect a lot of those vectors to line up in the same quadrant indicating it’s always going in the same direction. We don’t see that here. It’s actually very stable. What it is, it’s a lot of random back and forth movement with a net migration to the east. So again, a very strong picture of stability for this particular plume. So one thing I want to also highlight here, exact same plume I just showed you, but I’m going to overlay where those four remediation systems were installed at this particular site. And you can see wells get added inside this particular window.

So I’m going to focus on this dual-phase extraction system here. Wells get added, a second set of wells gets added up here, and then it’s going to continue for some period of time. And you’ll notice here in a few seconds, right there in 2011, several dual phase extraction wells were installed in that window. Let’s say I want to understand behavior just inside that particular window. It doesn’t have to be active remediation even. It could be an in situ remedy. It could be maybe you’re injecting ORC or PersulfOx or RegenOx or some type of in situ remedy in just a small portion of your plume and you want to evaluate behavior just inside that small portion. Well, we can do that here. If I click on this window, I can dive in and look at the behavior just inside that window. You can see in the early data, there were no wells in there, a first expansion, a second expansion, and then a very strong decrease through time.

Kind of zoom in on that. You can see during that dual phase extraction operation, system was turned off, natural attenuation took over, there’s no rebound. Being able to show this, even in a small portion of the plume, can be very strong. So, coming back to this, you can look at any one of these windows, as you might expect, they should look different. So, this one had SVE and O2 injection. Click on that. Just, I want to highlight here that it looks different. Parts of a plume look different. Things happen. Some wells go up, some go down. And, by the way, that’s the importance of looking at a plume as a whole in a control volume. You know, you might have decreasing trends in one well, maybe it’s degrading to another compound that’s increasing in another well. It’s very difficult on a well-by-well basis to sort that out, but in a control volume, plume wide, you really get a sense of the overall behavior of contaminants.

So again, I’ll click on these just very quickly. You can see different parts of the plume, different remedial strategies, different behavior, but all leading to you can evaluate progress inside those different windows or plume as a whole. So that’s everything I want to show you for that particular site. What I want to do is focus the remainder part of my time here on M &A for chlorinated solvent sites. So to do that, I’m gonna show a case study from the Chemdine Superfund site in Hamilton, Ohio. So for this site, very large site, it had chloroethanes, chloroethene’s, chlorobenzenes, chloromethanes, petroleum, just a very big mix, a big recycling facility, lots of just little drums. You guys are the old classic Superfund site has been pumping for 28 years. It was turned off in 2015 and transitioned to M &A. And I wanna walk through the nuances of doing that. It was a very cumbersome process almost.

So what I’m showing you, just early data, this is the site on the bottom. You can see a very large plume. It extends into the neighborhood. This is the Miami River out here. The plume goes out in there. These red wells are all extraction wells. They all come in in 1987, have been pumping for many, many, many years. And I’m showing you again, you know, 28 years of data in about 30 seconds. It’ll get to the end. I’ve stopped it at June of 2015. That’s when the system was turned off we did a pilot test to see if M &A was working. So I’m going to pause here real quick and take a kind of go left here to talk about with chlorinated data where you have parent compounds that degrade to daughter compounds, you know, it’s important to look at those data on a molar basis. I just want to just do a quick molar primer here why we do that and I know most folks on this call understand this. It is nice to have this as an understanding.

So in a theoretical sense, when you have, I’m going to use chloroethenes. So PCE, the dark red, it degrades, it creates trichloroethene, right? We’ve all seen this. And when it degrades, the total mass concentration decreases right away. Same exact data on a molar basis. Nothing happens here. It’s all, it’s flat. And that’s because, you know, when one molecule of PCE degrades, it creates one molecule of TCE. The number of molecules doesn’t change, right? It’s just converting from one to another until eventually that last daughter compound degrades to benign end products. And so we want to be on this part of the curve. So going to dive into that a little bit more. We’ve all seen this decay sequence. PCE degrades to TCE, which degrades to DCE. Actually, any one of three isomers of DCE, but predominantly cis-1, 2-DCE, which degrades to vinyl chloride.

We’ve all seen this graphic. I like to picture it with hamburgers. I’m just a very graphical, visual person. It’s easy for me to understand things. I like to picture PCE as a four-patty hamburger, kind of that Sasquatch burger. It’s heavy. It’s got four patties on it. And let’s say, you know, to follow the analogy here, you know, to get to a TCE burger, if I take one patty away, replace it with a slightly with a lettuce leaf, you know, it’s kind of synonymous here, right? So it’s lighter, but the number is the same. And let’s say that same thing converts to a DCE burger. This is two patties and same thing down to a quarter pounder would be like a vinyl chloride. And you can see, you know, the number of burgers is the same, but the weights are different. And that’s what I want to visualize here. So you can imagine I’ve got a tray of hamburgers, you know, one in one hand is the four patty Sasquatch burgers. I got 10 of them.

In the other hand, I’ve got a tray of quarter pounders. The number of burgers is the same, right? But the weight is a whole lot different. And it’s the same thing with chlorinated site data. Let’s say I’ve got a site that’s all PCE, right? And over time, it all degrades to vinyl chloride. Well, at the end of the day, it’s a lot lighter. My total concentration goes from 10 milligrams per liter to 3.8 milligrams per liter. So the total concentration is a lot lower, but the number is the same. The number of molecules, all the PCE molecules converted to vinyl chloride molecules. So all I’ve done at this point is taken a lot of bad stuff and converted it to a lot of really bad stuff. There’s been nothing really happened, just converted to something else. So to follow this a little bit further, let’s say we’ve got a site that’s 400 burgers, all And just to follow my logic here, let’s say 25% of the site stays as PCE. Let’s say 25% degrades to TCE. Let’s say 25% degrades all the way to cis-1 ,2-DCE, and 25% degrades all the way to vinyl chloride.

At the end of the day, if we start and look at our molar, or sorry, our mass concentration in the beginning, I’m at 66 micrograms per liter. Maybe five, 10 years later, I’m at 45 micrograms per liter. My total VOC concentration goes down. Yay, that’s great, right? Well, not necessarily. The molar concentration is the same. You see, why it’s important, we want to be past that. We want our molar concentration to go down to truly unequivocally show that. So what I just showed you is kind of like this. My mass concentration is lower, molar concentration is the same. Where we want to be is out here, showing that decreasing molar data. And that’s when we can unequivocally say that I have truly attenuation or degradation. So just kind of a quick side note there.

Coming back to the site, I just showed you the total chloroethanes. Here’s the data for the site, total chloroethanes. You can see back when pumping started in 1987. Typical pump and treat, right? It goes down very quickly and goes asymptotic for many, many years. Kind of zoom in on that, and we have this, which I can’t believe the number of sites that are still like this, you know, 10 years of nothing, just asymptotic nothingness. We eventually did this, shut the system off, and I’m gonna talk more about the post shutdown data here momentarily, but the idea is turning the system off and then letting natural attenuation take over for a chlorinated site, it’s a little different. So what we’re gonna do is go through now the individual compounds. So PCE, I’m gonna show you the plume map data from June 2015 forward.

So our pilot test ran from 2015 to 2018. I’ve got data through 2020. So just to give you a sense of what’s going on. So when I plot the data, this is the Ricker method analysis, right? So I’ve got the area on the top, average concentration, and mass on the bottom. We waited six months to start trending because as typical with pump and treat sites, when you turn that off, you have a lot of that redistribution of the mass. And a lot of times it goes up, you get the classic rebound. And so we’re gonna start our trends from a later point, and you can see trending all the way through. I’m gonna highlight our pilot test period. Even during the pilot test, PCE is a really strong decrease. So it is clearly decreasing under a natural setting, right? So we can assume that a lot of that degradation is most likely creating TCE as it degrades.

So let’s see how the TCE plume is behaving next. So just, I’m gonna go through these pretty quick. Here’s the TCE plume data. Now we’re back to just regular, it’s one constituent, so we’re micrograms per liter and pounds. Looking at the behavior for TCE, again, looking at the behavior on the mass down here during the pilot test, TCE also, pretty strong decrease in the TCE plume data. And so now we know the TCE could also degrade to CIS-1-2-DCE, so again, just kind of following the sequence here, I’m gonna plot the CIS-1-2-DCE data. Note we’re taking it down to five parts per billion on the boundary. Just to get an apples to apples, I’m looking for behavior here. I’ve highlighted where the MCL is for CIS-1-2-DCE. But again, looking at the behavior for the CIS data, moving into the trends.

Now look at this. During the pilot test, it seemed pretty flat. Actually, it was slightly increasing. So this is where some of the experts from the regulatory side were like, hey, I wonder if we have some stall going on. Do we have stalling at daughter compounds? And so I’m gonna address that, show you that it’s not stall. So in fact, we go past this and look at vinyl chloride. Same thing, do we have any vinyl chloride degradation or attenuation? Play it to the end. come to the data during our pilot test, notice during the pilot test, it was actually increasing. So we have a pretty good increase of vinyl chloride. So again, are we stalling out at our daughter compounds here, which is a very important aspect of demonstrating natural attenuation. We want, or even any type of Isco remedy, right? Any type of in situ remedy, we wanna show that we’re not stalled out. We wanna, we’re having full attenuation all the way through to our benign end products.

And so to evaluate that, we’re gonna dive in a little bit deeper. We don’t always do this, but it’s nice to kind of dive into the data here. Um, here are the predominant compounds. I’m going to focus on this part of the plan, which is the 98% of the masses right here. That’s just five wells. So look at MW 15, clearly the highest concentration. Well, these data are all presented on the same scale. So you can see the scale of MW 15 compared to these other compounds. When I look at MW 15, I’ll click on this and kind of zoom in on it. You can see at shutdown, not a lot of change post shutdown. PCE goes up a little bit, but then it’s decreasing pretty substantially in that well. And look at the CIS-1 ,2-DCE data. It’s only slightly increasing over that period. I’ve also added molar fractions on the bottom within that well. And so when we have degrading compounds, we expect to see the fraction of parents go down as the fraction of daughters goes up.

This is just supplemental, nice to see. Notice the pattern here, PCE fraction is going down. So is the TCE fraction. And the fraction of DC is going up, so is the fraction of the vinyl chloride. So we probably have some pretty good degradation going on here. So I’m going to jump over to SC7 and look at this. Turn the system off, lots of rebound, mostly PCE. It comes up, but then it also immediately starts to decrease. The cyst DC only slightly decreases and a much more muted signature on the bottom. So what I’ll do now is look at these three downgradient wells that would be, you know, if something was happening, it would show up in these downgrading wells because groundwater flow is to the top of the page and to the right, kind of out in this areas where the groundwater flow is going.

Click on this SC6 and look at this. It was all DCE. Turn the system off and boom, whole lot of PCE comes in. And look at this. That’s a huge increasing trend of CIS 1-2-DC. It almost looks like a perfect conversion. Look at the bottom, the molar fractions. PCE is going down, DCE is going up strongly. This looks like a lot of mass came in and it’s now converting over and so I’m going to hit these pretty quick Look at se3 The only thing this is down gradient PCE doesn’t really change in that well. We have this huge influx of DC. This is why it’s important This is a well by well basis. I’d be like, oh my gosh that well is increasing one fact It’s probably DCE that’s being generated somewhere upgrading it right and it’s showing up here Lots of DCE increase and we see the same picture on this MW 31 PCE doesn’t really change, DCE goes up, really strong picture of that.

So the question is, you know, is it DCE stall? You know, we’re generating a bunch of DCE out there. And to do this, what I want to do is I’m going to take another side trip here to do another analogy because, again, I like my visual, I like to do this because it applies perfectly, I think, to chlorinated data. So for this example, this analogy, we’re going to use a classic tanks example, mass balance on a control volume is all this is. You know, don’t get too excited. It’s pretty straightforward stuff. These are two fundamental equations that would apply to doing a mass balance on any control volume, very fundamental things. So to illustrate this, let’s say I’ve got a tank that has two gallons of water in it, real easy, okay? This is easy math, start value, there’s two gallons in it.

Let’s say over time, I add or I bring in 10 gallons to it. So my total is now 12, okay? Follow my logic here. sometime later I walk away and I come back and all of a sudden it’s down to five you know can I solve for the output how much left the tank well we can know intuitively right that um you know it started with ten I added two it ended at five so it’s twelve minus five it’s got to be seven intuitively I can see that it’s seven but can I get to that same answer using these equations so using those equations my accumulation is my final value minus my start value I ended at five, I started at two, my accumulation is three. So what my output was my input minus my accumulation. So 10 minus three is seven. I could do the same answer. I can apply this guys to PCE degradation.

Same, now it’s a system of tanks. Remember one molecule of PCE when it degrades, it shows up as one molecule of TCE. When one molecule of TCE degrades, it shows up as a DCE molecule. If I can tie these all together and get a sense of, what’s really going on, it’ll go a long ways towards demonstrating natural attenuation of these chlorinated sites. And so I’m going to go a little closer to reality here. We’re going to end with the chemdine here momentarily, but again, theoretically, I’ve got a site. Let’s say it’s PCE. We do the Ricker method analysis or a plume-wide control volume analysis. I can calculate the mass of the plume. So my initial plume mass, say in this example, is 20 moles. That’s the total mass of that plume. Come back five years later, the volume or the mass is 10. So the mass, the total plume mass went down, right? Pretty easy to see. That’s my start value, final value. Use those same equations I just presented.

What’s my accumulation over that period? Well, it’s final minus start. 10 minus 20 is negative 10. So my accumulation is negative 10. So what’s my output? I’m going to use now, instead output I’m going to use the term here D to represent decay. So really in our world decay and attenuation for this example are synonymous. You know, what’s the attenuation rate? What’s the decay rate? What’s leaving this box? So my decay again is input minus accumulation. I’m going to assume zero input here. My accumulation is negative 10, so 0 minus negative 10 is 10. So it’s easy enough. I lost 10 moles. Well guess what? That 10 moles shows up as 10 moles of TCE, right? That’s the input to TCE. Follow through the logic here. Final minus start, I have my 24, I started at 32. So my accumulation here is negative eight. Follow the same equations, 10 minus negative eight here. I have a net decay of 18. So through PCE and TCE degradation, I have a net decay of 18 moles per year.

What that means is I am generating 18 moles per year of DCE. So let’s look at the accumulation of DCE again final minus start, but look at this that plume went up it increased It went up by 10 moles My accumulation is final minus start 50 minus 40 is 10. So this one this one, you know accumulated by 10 However, sometimes I don’t think we account for this we’re generating 18 So the net decay is 18 minus 10 is 8. So even though it’s accumulating it’s not stalled It still has a net decay of eight in order for this to be stall this output would have to be zero or negative Okay, so just by mass balance that tells us that so now just to carry this to the end here eight moles per year Of vinyl chloride. This one’s also increasing Only by one so but eight minus one is a seven. I have a net decay of seven throughout this whole series So let’s jump back now to the chemdine site. I’ve got the total chloroethene’s plume now I’ve already shown you the four individuals, PCE down to vinyl chloride, and so we let this one play out, and now we’re going to go to the mass data for this plume.

So I’m showing it to you slightly different. The yellow goldenrod background is the total moles of the plume, and I’m showing you the individual plume makeup. So the PCE is dark red, the TCE plume, these are all the contributors to that plume. So I’m going to walk through that little analogy I just did. I’m going to walk through those to come up with the net attenuation rates for the site. So first thing we want to do is get the accumulation rate. So the red is the PCE, and we just do a regression on that, again, from December 2015 all the way through June of 2018. That’s our pilot test period. You can see instead of a final value minus a start value, we get to that rate by putting a regression line on those data. And I have an attenuation rate. This is a true attenuation rate of minus 4.6 moles per year. That’s also my accumulation rate. So I’m gonna just populate this table down here, drop in minus 4.63 moles per year. So my attenuation rate, remember, if I assume zero to start, zero minus a negative 4.63, I have a net decay of PCE of 4.63 moles per year. That’s my attenuation rate or my decay rate.

So, what that means is I’m generating 4.6 moles per year of TCE, right? So, let’s go to the TCE data and let’s see what the rate on that one is. Well, it’s also decreasing as an accumulation of minus 2.81 moles per year. I’ll populate the table here with it. And so, to come up with the net TCE attenuation rate, I take the input, 4.63, minus the accumulation rate, I get a net decay of 7.44. So again for Chemdine through TCE, I have an attenuation rate of 7.4 moles per year. So in reality, what that means is I am generating 7.4 moles per year of DCE. So let’s look at the DCE data. Look at the accumulation rate of DCE. Like I said, it’s positive, it’s growing, it’s accumulating, and it has a positive accumulation rate. And again, some of the concerns was we’re stalled at DCE because we’re accumulating at 0.7 moles per year. But what was not accounted for, my goodness, we’re creating 7.4 moles per year is coming in. We’re only seeing 0.7. So the net difference, right, the input is 7.4 minus the 0.7. Our net attenuation rate is actually 6.7 moles per year. really strong. That’s a pretty strong statement to say that my DCE is actually decaying at 7 moles per year.

You know, it’s not growing, it’s decaying. In fact, so we go to look at the vinyl chloride data, it is also positive. It has an accumulation rate of 0.75 moles per year, but we’re generating 6.7 moles per year of vinyl chloride. Walk through the math here, our net decay through vinyl chloride is 5.98 moles per year. And so in fact, add these up, it should match the net decay of the total VOCs plume. This mass balance, it should match this and they do. So, we don’t have stall here, we actually have a pretty strong decay. The entire plume is 45 moles. Through three years, we’re at minus six moles per year. That’s a pretty stout attenuation rate. On a molar basis, absolute decreasing, absolute evidence that this plume is not only stable, it is decreasing, degrading quite readily under natural conditions. So again, accumulation doesn’t necessarily mean stall. Gotta keep that point out for these chlorinated sites where we have, or for that matter, any parent-daughter sequence site.

And so one last slide here just, or next to last, pretty high level. I’m showing you the data five years prior to shut down, you know, the data five years post-shutdown, Two key observations, total mass is decreasing, total molar mass is decreasing. That’s that first line of evidence of natural attenuation. We want to show that the plume mass is decreasing very strongly here. And then for chlorinated data, we have the fraction of PCE parent compounds going down, the fraction of TCE is going down, the fraction of DC is going up, the fraction of vinyl chloride is going up. This is a textbook reductive dichlorination signature, very strong analysis showing that we have degradation of chloroethanes. By the way, at this site, we did the same thing for chloroethanes and demonstrated very similar outcomes. Just don’t have time to show it here.

So at the end of the day, key takeaways, there was strong empirical evidence of reductive dichlorination to show that natural attenuation will work and was working, in fact, at this site. Another key takeaway here is although we observed accumulation of daughter compounds, there was still very significant net attenuation. This led to an eventual permanent shutdown of that system, very costly as you can all imagine, and then an eventual, you know, finally a year after that, approval of both US EPA and Ohio EPA of the M &A remedy. Just a quick picture here, 1984, lots of drums, same building in the background. Last year we abandoned 151 monitoring wells at the site, complete removal. There’s only 16 wells remaining at the site. Just a great way to demonstrate, show that natural attenuation can be done and you can do it using existing data. So what I’m going to do is I’m going to transition now to Matt Burns who will take some of the principles of natural attenuation, you know, whole plume analysis and how some of those principles might apply to, say, even a PFAS site. So I’m going to turn it over to you, Matt.

Thank you. Hey, thanks, Joe. My name’s Matt Burns. I’m a technical director of the US Environment Practice. And I’m also an engineer by training. And I specialize in biogeochemistry and engineering of subsurface conditions to clean up sites. So following up on Joe’s plume analytic presentation, I thought you would all be interested in probably all thinking does this apply to PFAS? So it’s probably a good idea to take a few minutes and address that question. So over the past several years I’ve been working with a group of PFAS experts organized by the Remediation Journal. We now have several articles in print. Hopefully you’re aware of these articles. They’re phenomenal. The latest article I co-authored was on available in situ remediation techniques. It came out in January. You can see the list on the article cover. The names listed in the far left are a subset of the article co-authors that contributed to a recent webinar on the EPA low health advisories that were just issued and their impacts on available in situ technologies. Basically the impact on our January article.

As you would imagine, we did address M &A. So I’d like to give you a quick rundown on the available technologies for in situ dealing with PFAS and impacts of the health advisories, including M &A of course. But please recognize that I’ve modified some of the content to better represent my own personal opinions. So I’ll take all the negative heat you might see or think of as I run through this, but anything positive please know that I’m sharing all credit with my co-authors. Let’s start by framing the EPA’s recent actions with lifetime drinking water health advisories. On the right-hand side, I’ve plotted the old health advisories for PFOS and PFOA, you know, 70 parts per trillion. It’s the second red dot down from the top. The 2022 updated interim of PFOS and PFOA health advisories are plotted at the of the scale. That is 20 and 4 parts per quadrillion, respectively. You know, initially, I tried to plot these on a linear scale to be more dramatic, but it wouldn’t fit in the screen. So definitely note it’s a logarithmic scale. The other 2022 health advisers the EPA issues were for Gen X, dynamo acids, at 10 parts per trillion and two parts per billion for PFBS.

Both of these final health advisories. The PFOA and the PFOS are revised interim advisories or revised interim advisories. The green dot is there for comparison, five parts per billion. The MCL for TCE and benzene is five parts per billion. My first and most important take related to the new health advisories is don’t get too worked up about how low these are. They are not enforceable. Picograms per liter is not measurable, nor is it likely achievable with current technologies. I take the health advisories to indicate a downward pressure on all enforceable criteria that the EPA plans on developing across multiple programs. Basically, lower health advisories are likely to lead to lower enforceable criteria. The EPA is scheduled to lease proposed MCLs for PFOA and PFOAs by the end of the year. Best guesses of what these will be is probably the single parts per trillion levels, consistent with the detection limits for EPA drinking water analytical methods and the revised RSLs for tap water that were released in May.

You know, this enforceable standard assumption, you know, in that single part per trillion range, single, like, you know, in the, you know, between one and 10 somewhere, probably a four-ish, five-ish for PFOA, you know, it frames the balance of the discussion, you know, for specific remediation technologies. You know, I’m not going to discuss the specific remediation technologies and even pretend that you can get down to health advisory levels. Before diving into each of the technology categories, there are some general considerations that lower enforceable criteria will have across all remediation technologies. First, the plumes are going to get larger, and so will the cleanup costs. A couple larger plumes with lack of cost-effective treatment options, and it gets a bit ugly, confusing.

Something has to give. Because of this quandary, the 2019 PFAS Experts Symposium article called for a paradigm shift towards receptor protection rather than broad-scale groundwater aquifer restoration. As a result of the likely lower enforceable criteria, more detailed conceptual models will be needed. The number and complexity of sources, flow paths, receptors that were not significant previously under previously considered enforceable criteria, based on that 70 parts per trillion-ish level, they might now be significant. Background concentrations, forensics, become more financially actionable investigation drivers. Unfortunately, detailed and extended investigations may become a tactic to avoid implementing current and inefficient, costly groundwater restoration remediation activities in anticipation that better options might be available in the future, or maybe even a paradigm shift that they mentioned a couple seconds ago will be available in the shift in the future.

Addressing source areas might also be de-emphasized. What I mean by this is that efficient source area mediation typically involves addressing only areas where contaminants are present at concentrations greater than the natural assimilative capacity of the aquifer. With low criteria and no degradation, natural assimilative capacity is greatly limited. The question will be asked is, you know, how much impact could a PFAS source treatment area really have on achieving compliance over a typical planning horizon of say 20 to 30 years? In most cases, probably very little. With discounting, benefits that won’t be realized until the distant future aren’t economically viable. You know, spend at the plume boundary along the receptor flow paths are likely to return better value. Of course, this is a generality.

Site-specific drivers may necessitate source treatment, or perhaps the definition of sources will be narrowed for PFAS to those that lead to potentially complete exposure pathways. Before I shift to the specific technologies, I should point out that none of the in situ technologies that I’ll be discussing are destructive. At best, the contaminants are held in place, but subject to future mobilization. But with proper planning, the risk of mobilization can be mitigated. But lower enforceable standards may mean that leachate coming from a soil treatment or bleed coming from an in situ treatment may be significant, perhaps even causing increased performance monitoring to figure that out. So let’s get into some of these technologies. So in situ, stabilization and solidification is a developing technology, but widely available. Published stabilization data are very limited, but promising.

Most studies were run with analytical limits appropriate for higher compliance criteria, which is unfortunate. So the performance to likely enforcement standards is probably possible, but it hasn’t been verified by the suite of publications that are in literature right now. Data does show that solidification with Portland cement only is less effective than stabilization technologies. So with lower enforceable criteria, we’re probably likely to see a decline in solidification projects. I touched on the potential for deprioritizing source zone treatments a couple slides ago, But if reducing mass flux is a site-specific priority, then stabilization remains a very viable approach, albeit with re-evaluation of dosing and mixing and even potentially putting an impermeable cap on to respond to the lower limits. So hydrocolloidal activated carbon is the default technology to address PFAS-affected groundwater.

At least 20 applications have been specifically for PFAS. And hundreds of applications have been made with this technology to address other organic contaminants. And Maureen Dooley is going to touch on these, or at least a specific example of a PFAS plume stop application and case study in about two minutes. So there are several peer-reviewed studies available for this technology going back at least six years. Functionally concerns are there. You know, they haven’t been fully answered. You know, things like competitive absorption, desorption, long-term lifespan, you know, how stable is it going to be as it ages. They’re actively being studied by a bunch of different researchers. You look for a publication from Jeremy Birnstingl on competitive exclusion very soon. There are also some laboratory and to alternatives of additional types of amendments, such as ion exchange and biochar. These amendments may or may not provide some advantages of addressing low compliance criteria, but they’re far from being vetted.

Colloidal activated carbon is potentially viable across a wide range of applications. Exposure pathway disruption, source area mass flux, groundwater to surface water mass flux, and mass discharge zones, and even wider applications are technically feasible, but probably not economically viable. To address uncertainties related to lower enforceable criteria, such as competitive absorption, bleed-through, more conservative and more costly protocols might be needed, such as defining mass flux zones with more accuracy and precision, higher amendment dosing, and more robust delivery protocols to increase distribution efficiency may also be needed. Combining with the M &A or even enhanced M &A is another potential way to hedge direct treatment as well. So we’ve made it to the slide of interest. Ultimately, the M &A is gonna be used to address PFAS. The increasing size and number of plumes a commensurate with the lower enforceable standards. So we’re gonna get a lot more plumes and a lot bigger as the standard decreases, it’ll cast a wider net. Available treatment alternatives and economics are gonna necessitate that M &A as at least a component of remedial action plans is gonna have to happen.

This is in line with the paradigm shift towards receptor protection rather than broad-scale groundwater aquifer restoration that I mentioned earlier. Also, previous classes of contaminants that were also once thought to be recalcitrant, by the way, using those as examples, M &A applications increased as fate and transport science matured. So fate and transport science for PFAS right now is very immature. But, you know, there might be some solutions here, and this is where we’ll get into plume analytics and plume stability. You know, M &A protocols are widely accepted for many contaminants, you know, including where non-destructive pathways provide attenuation, right? So think about inorganics and radionuclides. Natural attenuation for those is widely accepted. Dispersion, dilution, and sorption do attenuate, you know, inorganics and radionuclides, and they also attenuate PFAS. As tools are needed to evaluate, and the tools that are needed to evaluate M &A, at least on a plume stability basis, the primary line of evidence, are now available, as Joe just showed you. The plume analytics are a great way of getting started down the M &A pathway.

We have a couple of sites where we’re evaluating PFAS data using plume analytics right now. We hope to be able to present that information shortly. And significant research on PFAS, fate, and transport is also ongoing. This was going to allow a science-based, multiple lines of evidence approach to evaluating PFAS M &A, similar to evaluation of M &A for other contaminants. Chuck Mules co-authored a paper recently. Check that one out. It’s on some natural attenuation pathways. And he defines a little bit of his thoughts on it and maybe how to quantify. And there’s also an ESTCP project that David Adamson is working on. He’s a PI. So that should be coming out hopefully shortly. And provide some together, those two should provide a little bit more clarity on those secondary and tertiary lines of evidence for PFAS M &A. But until fate and transport science is better understood, there’s going to be a fundamental lack of information to assess longevity of M &A.

The black box plume stability assessment is retrospective. This gap in knowledge may be addressable on interim basis. Just going with that primary line, is it stable or isn’t it? And you can address that with additional performance monitoring, and maybe a little bit more than what’s typically applied to other M &A sites. Further, pathway consideration, better CSMs, as we’ve discussed, will be fundamental to M &A, especially as robust CSM information on appropriate M &A performance monitoring in Sentinel Well locations. So if you’re not looking in the right place, You might not see if you’re getting the correct amount of performance. So with that, I’ll just leave this up here I’m not going to read it to you. These are kind of the net takeaways and Maureen will join now and present a case study with PFAS treatment using PlumeStop.

Well, thank you, Joe and Matt. I really appreciate the in-depth discussion of M &A and the tools and Joe, honestly I am trying to think of sites that I can apply your methodology to. I really, really appreciate the visualization that you used. And also the complexity with some of these chlorinated solvent sites. I think you described that really, really quite well. And with that, I concur completely on your assessment of the impact of the health advisories and this paradigm shift. I mean, the idea of extracting every molecule of PFAS compounds out of the ground to put them who knows where, I really think that moving forward, we really are looking at risk management and that’s really, honestly, the only feasible way to address this issue moving forward. So, what I want to do briefly is I want to talk about tools that, I want to stay on the topic of tools. This is what has been a part of this seminar and this webinar. And I want to talk about the tools that we use at Regenesis to assess carbon sorption and how we can use that to enhance contaminant reduction.

With, you know, our ability to try to look at being predictable and to then have the confidence that we can meet site objectives. So as Matt has talked about that natural attenuation and M &A is something that we have been using for a very long period of time, and Joe was showing how that was used in a chlorinated solvent site, and definitely there’s the applicability to PFAS compounds with focus on reduction of contaminant mobility and bioavailability. And when you’re doing these assessments, what you’re looking at are the natural conditions. And if natural conditions are not sufficient, you can add reagents to change conditions, which may be to enhance degradation of compounds like chlorinated solvents, or to change contaminant mobility and bioavailability. And all of that factors in to creating a scenario where you can have reduced exposure, manager risk as part of an M &A scenario.

Matt had mentioned or referred to a paper by Dr. Newell on monitored natural attenuation. In this paper talks about some of the guidance and information you may want to collect if that’s a consideration for your particular site. So one thing that was mentioned was colloidal activated carbon, or as we refer to as plume stop, as a reagent that may be used to enhance sorption, and specifically for PFAS, but it’s used in chlorinated solvent sites. And so plume stop itself is an activated carbon particle that’s been mined, you know, that’s been milled down to one to two microns suspended that allows us to inject this, you know, under low pressures to get widespread distribution and in essence create this Brita filter underground.

So, you know, when we get started with this, you know, this mode of You know, particularly if we were looking at compounds like, say, chlorinated solvents, is we would apply the plume stop, and so the contaminant is going to sorb onto the sites, onto the plume stop particles that coat the sand, and in the picture on the left, that just shows the sand particle, and if you look at the scale, it’s about 50 microns. So this great surface area that’s created by the application of this colloidal carbon, it’s really fantastic for microbial colonization. So if you have a degradable contaminant, microbes are gonna colonize and degrade any of those sorbed contaminant or in that micro environment with the colloidal carbon. And that also allows you to clear off sites and recycle them so there’s additional sorption sites that are available for additional contaminant. And in this picture, you see the colloidal carbon coding the sand particle, and please note the 10 micron scale.

So looking forward, can we model upfront PRB performance, you know, using something like a colloidal carbon? And the answer is yes. And I want to spend just a couple of minutes on how we use this tool in a predictive way for how, you know, when we’re considering sites for Plum Stop application. And this is a model that was developed by Dr. Birnstingl. And as Matt mentioned, there’s some papers that will be coming out. And just very briefly, PLU Stop is a tool for engineering the KD in the subsurface. We’re changing the FOC. And what happens as a result of that is you’re going to change the equilibrium such that you have a reduction in dissolved phase. So if you have something that wants to absorb into this carbon, you have this equilibrium change such that so you’ll end up with a reduction in your contaminant concentration and it’ll be sorbed to the surface of the colloidal carbon. And you also are changing transport of these compounds because the retardation factor has changed. So by adjusting this factor, it’s also lends itself well to modeling.

And so what we’ll do with the plume stop is we’ll use this internal model to look at plume stop that we have very specific isotherm parameters that are input into the model to allow us to predict longevity of the plume stop dose, but also optimize the system to get a dose to meet the desired longevity. Now, just in full disclosure, I’m not getting into the weeds in this model because that certainly is way above my pay grade. But if anyone has questions and wants to get in depth, I can get you in touch with the people that work with us day in and day out and know the ins and outs of this. So just really honestly contact me directly, but ultimately what we have in our model just showing it in big picture is this is for a long-term prediction model.

We’re going to look at competitive sorption and degradation if applicable. So those sites where you have VOCs and PFAS, you can look at what the predicted performance of this barrier will be over the long-term, and we’re also looking at very specific site conditions, mass flux, thickness, barrier, and time factor. But let’s just look at some pictures and examples of where this has been used. So the first site, I just wanna talk about a combined technology for a PRB where we co-applied our colloidal activated carbon and also our colloidal sulfidated zero valent iron. For this particular example, we were looking at TCE and DCE. We had 200 foot per day groundwater velocity, and we had some assumptions where in this model, we assumed no biodegradation at all. So just sorption.

And what’s critical for this site, this is the property that needed to be remediated within a two-year timeframe. So you have a pretty extensive plume and the green lines represent the barriers that are the colloidal carbon and the colloidal sulfidated ZVI. and they’re about 60 feet apart. And so the model that was used, we used our predictive plume force model. And what you see on the left is concentration and then distance in feet on the X axis. And so here are the individual barriers, roughly 60 feet apart. And this is at the onset of the application. This is the prediction after a half of year is clean water is starting to move through this barrier. and then after one year and then after a year and a half. So this is the time it takes for the clean water to come through and we start to see this reduction. So what did we see in real time?

So in real time, these are the results from a series of different barriers where the wells are roughly 15 feet down gradient. And you see a very rapid reduction due to the application of the colloidal carbon of all of the compounds which include PCE, TCE, CIS, and vinyl, and the generation of ethane, which is a result of the abiotic destruction from the SMZVI. So Joe, in this case, we saw the final degradation product, so that allows us to know and understand that we were getting complete destruction of the chlorinated solvents. And what is the role of the colloidal carbon? And this is another opportunity where we use this model to see what the impact of including colloidal carbon versus not, where on the left we see the application, the predicted results of a berry with plume stop, electron donor and ZVI, versus just electron donor and ZVI.

And here you see the generation of the different biodegradation products, and I think Joe went into a lot of great detail on how that works and the impact in looking at M &A. Here by including the colloidal carbon, a lot of that activity is happening in that zone, that micro zone of sorbed contaminants. So we really don’t see that in the groundwater or in the aqueous phase. And then finally, we also use this model to look at the potential and feasibility of using plume stop to address PFAS compounds. And this is an example of a site, the Grayling site, that we’ve presented in the past, but just showing some of the model. What’s the predictability? We have our plume stop barrier, in essence, on the other end. Everything is coming out at non-detect. And looking at the multiple scenarios, we were able to demonstrate that we would have treatment for up to 75 years. Other sites, this is a site that we have really the most data on. And these are the types of results that we can get where we’re almost six, almost seven years out where we’ve been to non-detect. And this site has also gone through modeling to look at what the potential is through third party. And that also corresponded with the type of information we generated where you can see decades of treatment.

So really with that, why these tools are important, and I’d say on both sides, on the predictive side and also the types of type of information that both Joe and Matt were presenting, is that when you’re moving forward into a project, and particularly for us, if we’re looking at PFAS, it’s important for us to really understand the feasibility and the predictability because Regenesis will offer a warranty on PFAS PRBs. So if we have a site that we go through an evaluation and it meets the criteria, we will provide a lump sum price, payment will only be due if performance criteria are met, and we have a standard 10-year warranty. And using tools like this, allow us to be able to offer this type of warranty. And also the predictability of using a colloidal carbon allows us to do that as well. So with that, I’m happy to close and take any questions.