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How are co-contaminants accounted for in these models? And this person is talking specifically about hydrocarbons and other PFOS. And what effect would you expect them to have on the assumed life of PlumeStop remedies?

That’s an excellent question. So there’s a couple things I wanted…I’d like to say about that because I was expecting that question. I’ve had the same. First, there’s actually some really good papers out there that look at mixtures of PFOS compounds even with dissolved organic matter that’s come with groundwater samples collected where they’ve done sorption isotherms, not for liquid…well, actually, REGENESIS is doing testing with PFOS compounds and other mixtures today. There are some sites where you really might have a complex mixture and you might need to actually have someone like REGENESIS, and they offer this as a service, do sorption isotherms or testing to see how the liquid activated carbon performs with a site-specific mixture. So if you have fairly low concentrations of co-contaminants, the nice thing about liquid activated carbon, because they’re small particles, they have a very high surface area relative to, say, granular activated carbon. So because they have so many sorption sites, if you have low concentrations of all the co-contaminants, you’re probably not gonna see much effect.

And I’ve seen a paper, there’s a good paper by Hansen et al., they looked at lower concentration PFOS mixtures with DOC, dissolved organic carbon at the 1 to 3 milligram per liter range, and they actually, with particle activated carbon, which probably has low sorption potential than liquid activated carbon because particle size makes a difference, they saw similar types of sorption properties. So lower concentrations, I wouldn’t be too concerned about it. If you do have high concentrations and a mixture a fairly complex mixture then I suggest doing site-specific testing. And that’s similar to doing batch testing. Like, if you’re gonna do microcosms in the lab or other bench scale-type testing, I think with PlumeStop and complicated mixtures, you might wanna do site-specific sorption isotherms to really make sure you’ve got the right parameters when you’re modeling this.

Please discuss the model parameter assumptions used to determine the retardation coefficients. Also, discuss the process used to calculate the expected desorption rates.

So first of all, the sorption and desorption, whether it’s Freundlich or Langmuir or linear isotherms, in this model, that’s an equilibrium process. So when you have a Freundlich isotherm, it’s more complicated than the linear isotherm. Linear isotherm…I don’t have the equation on a slide, in hindsight I should have had that, but it’s basically the sorb concentration is gonna be your KOC times your FOC times your water concentration, and your retardation coefficient would not change. Retardation is just 1 plus density divided by porosity times KD [SP], very simple. It ever changes.

But when it’s a Freundlich isotherm, it does change. There is an equation that we use. I’m not gonna verbally say it. I don’t think I have a slide that shows it, but it’s a widely used…basically, the retardation coefficient it’s equal to the slope of the sorption isotherm. And that’s really how it’s determined, or it’s related to this slope. So if there’s a simple equation, parameters would include the KF, which is your…really your sorption capacity. When you’re at unity concentration, there’s an exponent term in there, and there’s the water concentration. So as water concentration changes, with a Freundlich isotherm, your retardation coefficient changes as well. So in the reactive transport model, initially before a PlumeStop, there’s a switch that says, “There’s no Freundlich sorption it’s just linear isotherms, linear retardation coefficients.”

In the model, when PlumeStop is turned on, the model knows, “Okay, I’m in a grid cell where PlumeStop is present.” It’s got a certain…one of the parameters in the retardation coefficient as well is the fraction of liquid activated carbon per mass of soil similar to FOC. So the model will basically calculate the retardation coefficient based on the water concentration at each individual time step and each individual grid cell, and it’ll do the rest of the calculations accordingly.

How was the extent of the PlumeStop confirmed in the case study?

Oh, good question. So Rick’s gonna talk more about this, but from talking to Rick, he used 10-foot spacing, 3-meter spacing for the injection wells. And what he found to confirm it, because I asked the same question, so that is a good one, he actually saw monitoring wells that were more than 10 feet away from the injection wells. They were actually measuring looking for PlumeStop. The nice thing about PlumeStop is when you first inject it is a black color liquid. It’s just basically aqueous water with black carbon in it, but you can clearly see when you have PlumeStop in a monitoring well at least after the initial injection. Over time, those particles will attach to the soil and you won’t see it in groundwater over weeks or maybe a month or two. I’ll let Rick talk more about that. But he clearly showed that there were monitoring wells more than 10 feet away from the injection wells breakthrough of PlumeStop, so he knows that he’s at least got the equivalent of a 3-meter radius of influence. So that’s what I use.

So basically I developed a PlumeStop zone, I traced where he had the injection wells. And these were very…they were offset a little bit from each other in terms of transects, but he had a lot of wells and I just traced around them with 1.5-meter radius outside of each injection well.

Hi, Grant, just to add onto this. My understanding is they also collected soil borings as well to confirm. And so they were able to use, you know, both the visual from the groundwater, but there was confirmation where they looked at soil borings and could find the dark color. And so these are some of the standard methods that are used to make sure that we’re getting the distribution of the PlumeStop during an application.

Video Transcription

Dane: Hello and welcome, everyone. 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 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 focus on visualization and modeling tools for evaluating remediation performance. With that, I’d like to introduce our presenters for today. We are pleased to have with us Dr. Grant Carey, President of Porewater Solutions. Dr. Carey is an expert in mathematical modeling, NAPL characterization, and environmental forensics, with a focus on both litigation and regulatory projects across the United States and Canada. Dr. Carey has a Ph.D. in environmental engineering and has developed industry-leading modeling and visualization software. Dr. Carey is also an adjunct professor in the Department of Civil Engineering at the University of Toronto, where he is collaborating on research related to back-diffusion and long-term strategies for remediating complex sites. He has published or delivered more than 90 technical papers and short courses and was previously a trainer for several ITRC web seminars.

We’re also pleased to have with us today Maureen Dooley, Director of Strategic Projects at REGENESIS. Maureen has more than 25 years of experience in the remediation industry. In her current role at REGENESIS, she provides technical leadership for complex soil and groundwater remediation projects throughout North America, as well as remediation design, strategy and business development in the Northeastern United States and Eastern Canada. All right, that concludes our introduction. So now I’ll hand things over to Maureen to get us started.