Defining Cleanup Success for Groundwater Remediation

Hello and welcome, everyone. My name is Dane Menke. I’m 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.

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In today’s presentation, we’ll focus on defining cleanup success for groundwater remediation. With that, I’d like to introduce our presenters for today.

We are pleased to have with us Dr. John Wilson, Principal Scientist at Scissortail Environmental Solutions. Prior to working with Scissortail, Dr. Wilson served at the U.S. Environmental Protection Agency from 1979 to 2014 as a technical expert in biotransformation processes of organic compounds and groundwater in the subsurface environment. He’s the author of 61 journal articles and 14 books or book chapters on the topic of environmental science and groundwater remediation, as well as numerous government reports and conference proceedings. He holds a patent for biodegradation of halogenated aliphatic hydrocarbons and is the recipient numerous honors and awards for his contributions to the field of environmental remediation.

We’re also pleased to have with us today Todd Herrington, Global PetroFix Product Manager for Regenesis. Mr. Herrington collaborates with sales, operations, and R &D departments at Regenesis in order to provide environmental practitioners with a complete solution to quickly and effectively reduce petroleum hydrocarbon contaminants using PetroFix remediation fluid. Mr. Herrington has over 20 years of environmental remediation experience and has been with Regenesis since 2004.

All right, that concludes our introduction, so now I will hand things over to Dr. Wilson to get us started.

Today I want to talk with you about the issue of how to tell when we’re done with the cleanup. US EPA’s risk management paradigm addresses this question from the point of view of hazard and exposure. The states that implement the UST program though have put most of their attention on cleanups to destroy the hazard and there hasn’t been as much emphasis on evaluating exposure.

The result of that is we as a research community and a cleanup community are managing the contaminants instead of managing the aquifers as water supply. That puts us in a little bit of a We have one class of aquifers where groundwater moves readily through sands and gravels. Once a spill occurs, there’s a lot of contamination that can move quickly to a water supply well.

The risk is high. That’s the bad news.

The good news is our technologies for cleaning these sites up actually are effective. We can deal with this kind of spill. However, we have a large number of spills into clays and silts. The good news is these plumes don’t move very far. They rarely impact the monitoring well, but the bad news is they’re very difficult to clean up to the drinking water standard. These clay overburden sites are very common. There’s a good number of UST spills that fit this category. Many of our major cities are built on the floodplains of major rivers.

What I’m going to talk with you about today is approaches to characterize this particular category of science to see when we’ve done enough cleanup to justify calling it a success. A lot of my ideas are borrowed from work that’s published by Murray Einerson and Doug McKay, and I direct your attention to this paper. This is definitely worth your time to dig out of the library and spend a few hours with.

So let’s understand first how contamination behaves in these two layered systems where The NAPL is confined to a silt or clay. It’s actually lying above the transmissive material that comprises the effective portion of the water supply aquifer.

Spend a little time with this. The well on the left is a well that’s screened exclusively in the silts and clay overburden across the NAPL. Groundwater produced from the well on the left is highly contaminated. The well in the middle is one that’s sort of a representative well that’s very common at our UST sites. It’s screened across the NAPL and collects water from both the silt and clay and the aquifer underneath. It’s not nearly as contaminated, but the contamination is high. Then the well to the right is one that’s far downgradient. You can see that even though the wells that are screened across the NAPL show screaming high concentrations of contaminants of concern, these wells often show marginal contamination fairly close to the drinking water standard.

And the point I’m trying to make with my cartoon is that that highly contaminated water that’s produced by wells that are screened across the light, non-aqueous phase liquids, are not representative of the concentrations that are actually moving away from the source toward potential water supply well in the aquifer per se.

I’d like to walk through two case studies that illustrate that particular perspective. In the case studies, we measured the vertical distribution of total petroleum hydrocarbon using core samples. We also measured the vertical distribution of contaminants to the groundwater with conventional push tools. Then we did something that unfortunately is not very common in the underground storage tank market. We measured the vertical distribution of hydraulic conductivity, actually using the same push tools. Some years ago, Jung Cho and I published a paper on a little technique that I had developed that allows you to use a geoprobe tool to estimate the hydraulic conductivity of the material around the screen.

It turns out that the rate of production of water into the well proportional to the hydraulic conductivity. And so all we do is we would set a tube at a certain distance below the water table and we’d pump it until we had both air and bubbles and the rate of production of water at that distance is directly proportional to the hydraulic conductivity. So we use that tool and that approach to evaluate two spills. This is probably the most famous in California, maybe the most famous one in the world. This is the one in Portland.

The red dot is a sampling point that is about one year’s worth of groundwater flow travel time from the leading edge of the NAPL towards the most contaminated location at the site.

So what is plotted here is the vertical extent of total petroleum hydrocarbon as determined in analysis of the core sample. And then the vertical extent of hydraulic connectivity determined with that technique that I mentioned using the GEARPRO push tools. So each of those little vertical reaches is the vertical screen interval of the tool. We measure K and we push it down that length again, measure it again, push it down that length again. You see that sort of stair-step figure that represents hydraulic connectivity in this particular sampling location.

We use the push tools also to produce water for measuring BTEX compounds and then also the electronic sectors that control the behavior and distribution of the BTEX compounds in the aquifer. So you can see that in the first sample of the aquifer between 10 and 12 feet, there’s no sulfate in the water. We have the very highest concentrations of benzene. We go down another 18 inches, we’re starting to see some sulfate, and there’s much less benzene. We go down another 18 inches, and we’re back to sort of the background levels of sulfate in this particular aquifer, and the benzene more or less disappears.

So the benzene, instead of being uniformly distributed through the aquifer, it’s a little skin, or a skin right underneath the own napalm that’s producing the source of contamination. So we went down to the toe of the L-NAPL object and did the same thing. So again, this is the vertical distribution of TPH as analyzed in core samples and hydraulic conductivity. Down at the toe of the aquifer, you notice there’s sort of a deep attractor down about 18 feet, very highly conductive layer that would tend to pull the groundwater down deeper into the aquifer.

This is the vertical extent of benzene and sulfate, but we see the same pattern. The benzene is confined to the interval around the water table, it contains the L-NAPL. Where we have benzene there’s little or no sulfate, and where we have sulfate there’s little or no benzene.

So we took that concept of how the electron acceptors like sulfate, nitrogen, and oxygen or distributed in an aquifer and the relationship between the source of the contaminant and the vertical distribution of the contaminant and did another case study.

I was invited to go into a site where the cleanup was finished, at least the site owner and the contractor claimed it was, and the region wanted to know it, but they truly were finished with it. This particular site, it was owned by a power utility, an electrical utility that used at the service, these big line trucks. And they had a dry well underneath the garage where they just disposed of oil and gasoline and radiator fluid and whatever. When Ricker came in and they put on the monitoring wells, they discovered a plume of contamination. And they chose to clean it up using aerobic in situ bioremediation. So what they did is they installed two galleries pictured there as lines at the bottom of the well. So these are just trenches full of gravel where they injected groundwater amended with nutrients, phosphate, and hydrogen peroxide to supply oxygen. And then that was chased across the site with a recharge gallery below it.

And so we have a movement of oxygen and phosphate amended groundwater moving across the spill. You can see the work pit. There’s a well that was actually in the work pit or the contamination occurred, then the water was collected in a recovery well at the very top of the diagram and then recirculated back through the groundwater recharge gallery and the nutrient gallery.

So these are data on the distribution of concentrations of betex compounds in five wells that extend from the leading edge of the flow of remedial groundwater, that’s in W1, And then as we go up, MW2 is in the work pit, where the highest concentrations were. MW8 and MW2 is, and MW3 are further down the flow path, and then RW1 is the recovered well that recirculates the water.

So this looked almost like a gasoline spill when they started to clean it up. And after several years of work, they got it down to the concentrations in the right-hand column. Now, these are data for benzene, which is a risk driver, and unfortunately MWA didn’t reach the MCL for benzene. So based on the definition, the site wasn’t clean and could still impose a threat to groundwater quality in this aquifer as a water supply aquifer. So I was invited to see if it was clean.

The approach that we took was to install a series of – we didn’t install wells. But we used push technology to take core samples and transect on the downgradient side of the flushing of the mended water, since the black dots are locations where we took core samples. And then the triangle is the most contaminated location where we did a vertical evaluation of concentrations of contaminants in the groundwater underneath the L-NAPL object. So this is what the L-NAPL object looked like, that’s the red figure. And it was still there. There was plenty of L-NAPL after they’d done their cleanup.

And so at the most contaminated location, we went through and we did the thing with taking water samples, and so this figure shows the vertical extent of TPH as seen from analysis of core samples, and then each of those dots is the upper limit and the lower limit of screen on the push tool, and then the blue figure is the distribution of hydraulic conductivity.

And so this fits a little pattern that I’ve been showing you, that the TPH was in a silt and sand layer, and that the effective part of the aquifer, such as it is, in this case it’s only about two feet thick, maybe a little bit more than that, is underneath the L-NAPL. So these are data that compare the measured hydraulic conductivity and concentrations of MTBE, benzene, and BTEX.

And it’s no surprise that the appreciable concentrations are in that first water sample at 18 to 20 feet, and you’ll notice that the hydraulic conductivity in that interval is actually quite low compared to the deeper material in the true part of the aquifer. So, I used a concept that is well represented and well explained in a recent paper by Murray Einerson. Now Murray’s paper actually looks at a two-dimensional view and a transect of groundwater moving away from the source.

I’m going to reduce his concepts to a one-dimensional view and do some calculations using Murray’s approach and see if we can understand the importance of that high concentration in the shallowest zone. So they’re in red. The hydraulic conductivity was 0.39 feet per day.

So what I did is I took an average of the hydraulic conductivity across that entire interval including the transmissive aquifer and a little bit of the less transmissive material below it And I calculated the fraction of the hydraulic conductivity that was represented by the particular depth interval. That’s simply the measured hydraulic conductivity divided by the average and then divided by the number of samples. In this case there were six layers, so I divided by six. And so I get a way of weighting the benzene concentration by the proportion of flow that would move through that particular depth interval. So that’s the column on the extreme right. Those are weighted, the measured benzene concentration multiplied by the fraction of the hydraulic conductivity that’s represented by that interval.

And then I took an average of the weighted concentrations, which would represent the concentration that would actually be delivered to a water supply well downgradient. And in fact, that weighted average concentration is much less than the MCL. And so this is the approach that I offer to you, where you can use some calculations if you bother to measure hydraulic conductivity to understand the contribution that a particular concentration of contamination at a particular depth interval would make to the entire flow in an aquifer that would go to a monitoring well.

If you compare the measured benzene concentration of 11.3 to the weighted concentration of 0.0 You can see that that 11.3 micrograms per liter that was above the MCL represented one part of 10 ,000 of the water that would actually be getting to a monitoring well.

And wait, there’s even more good news on this because this particular aquifer had measurable concentrations of nitrate and typically sulfate, electronic receptors that are incapable of destroying B-text contamination through fermentation reactions.

So I went back and I looked at the original data, and if you’ll notice that RW1, that pumped well, the recovery well they installed for their remedy, actually is a pretty good surrogate for a water supply well, it’s green across the whole interval and it was pumped. And that was never contaminated, even at the very beginning, before they started the remedy, the concentrations of VTECs never exceeded the MCL for benzene.

So what could have been happening there, I surmise that the sulfate dissolved oxygen nitrate in the true part of the aquifer was diffusing up into the silts and clays, allowing the bacteria to degrade the BTEX compounds before they ever found their way into the aquifer, and that’s why they never showed up in the recovered well.

So these attenuation processes are consuming the contamination as fast as it leaves the source zone in the silts and clays. They’re not going to move away from the spill, and in fact, a receptor downgrading is protected. And so I really think what we need to do is evaluate whether in fact the distribution of contamination and the benefit of the natural processes are protecting the aquifer as a source of drinking water. If it is, it’s not necessary to clean up all the contamination, all the monitoring wells to the drinking water standard.

You only need to clean up your site to the point where the drinking water, the groundwater that leaves the spill meets the drinking water standards. To do that, you need information on the vertical distribution of hydraulic conductivity.

How do you get that information? Well, one way is, as a more conventional approach in this paper by Cho et al., I’ve written a fair number of papers that have received several hundred citations in the literature. I don’t think anybody ever read this paper, and nobody uses this approach with me. But GeoProbe Systems, my friend Wes McCall put together a little system that allowed you to do a conventional, traditional slug test on the temporary push tools. So you can use conventional groundwater practice, do a slug test on a push tool, and get the number that I got using a very standard approach.

Another thing you can do, they’ve developed a very neat technique called electrical conductivity testing that allows you to recognize and distinguish the silts and clays from the sands and gravels and these electrodes can be mounted on push tools and introduced into the earth to do vertical profiling, and the way it works, silts and clays have a lot of exchange capacity, the ions have exchange capacity associated with the surfaces, and so the electrical conductivity of silts and clays are higher than the electrical conductivity of sands and gravels, and so the contrast between the two can be used to index whether The probe at that instant is in a silty clay or in a sand and gravel.

And GeoProbe has actually adapted that and extended it. They also have come up with what they call a hydraulic profiling tool. What this thing does is it pushes water out into the aquifer as the tool penetrates and the resistance to flow is an indication of the local hydraulic conductivity. So the red line there is the pressure that develops in the tool as it tries to push water out into the formation. You can see in the first 10 feet of this case, those pressures are high. That’s because it was penetrating salts and clays.

And then below about 12 feet, then the pressure above the pressure that’s the natural weight of the groundwater in the atmosphere is minimal. And that’s associated with sands and gravels. That’s the red line, and you’ll see that that’s also confirmed by the blue line, which is the estimate of electrical conductivity. So these tools together can allow you to resolve intervals where water’s moving from intervals where water’s not moving, from the clay and silt overburden and the effective part of the aquifer.

This is something I pulled off of GeoProbe’s web page. They can actually take that difference in the pressure and estimate K in feet per day. That’s the right-hand column. If you’ll compare that, the blue stuff, high values of K on the right-hand side, you’ll notice that corresponds to a minimum of electrical conductivity in the column on the left-hand side. So the two tools, the two measures together really give you a very quick way of figuring out where you are in terms of vertical extent of the effective part of the aquifer.

I had this tool on one of my sites. They can produce this information at a particular location in less than an hour. That includes setup and cleanup. And they’re not the only ones that do it, to be fair. There’s other approaches that are very efficacious. The Waterloo Profiler now upgraded to the advanced profile system produces similar information using a very effective system. So there are people in the marketplace that can give you the numbers that I used in the calculation I showed you. And so what I would like people to start thinking about is installing monitoring systems that monitor the aquifer.

The conventional screens at UST spills, the well on the left and the well in the center, the real purpose for that is to try to find Ellen apples so they know where the spill is to clean it up. They’re really designed to map the spill. They’re not designed to evaluate the threat to water supply. And I think that we’re making a mistake using the wells that are designed for one purpose for the other purpose of evaluating the threat to water supply. I think we need to install special wells that are screened across just the interval that’s going to act as the aquifer downgrading the source of contamination.

So it’s going to be more than just throwing in wells and taking water samples and sending it off to the chemistry. You’re going to have to invest in the geophysical site characterization and understand your geology, and then install monitoring wells that are truly downgrading of the NAPL. And I recommend that you check the OVM data on the well construction logs to make sure that in fact they are downgrading the well NAPL.

And then interpret concentration data on wells that are a faithful representation of the behavior of the aquifer as a way of evaluating whether in fact you’ve achieved cleanup and now ready to transition to either M &A or other passive approaches.

So thank you for your attention today. Okay thank you very much John.

Now we will go to Todd Herrington of Regenesis. Thank you. Thank you John for that talk.

It was great sitting here next to you and just learning from you and you know really good stuff that you had there.

Today I want to transition into some slides that about a new product that we have called PetroFix which is a remediation technology designed to treat petroleum fuel spills and soil and groundwater.

I think it segues well into some concepts that John presented today and I’d like to get into a few of those and then we’ll get into some Q &A.

Just real quick as I started in the industry many years ago I started with consulting that we studied natural attenuation so back then John was actually at the EPA we spent a lot of time with John it was just a lot of fun to do that so I would say today it’s it’s great to be here with him again today you know working on remediation. One of the things that resonates with me when John’s talk is obviously a great site characterization is going to be really needed to do effective remediation, but one of the concepts also is really trying to control flux and trying to control bioremediation.

The concept of contamination being bound in, say, clay overburden sites, Ellen Apple that you know, goes from that or is in high K zones, you know, we as remediation practitioners and sites that I look all day long, you know, how do we control that?

How do we minimize that?

And I think one of the questions, you know, it’s kind of transitioned from this talk into PetroFix is that what if we could in these high K zones where contaminant flux from El Napo or Clayover Burden is moving quickly and there is risk to downgrading?

Well, there is risk to offsite migration. Now, what can we do? What if we could make that high K zone act like clay or act like a tight formation? That’s actually something that we’re able to do with PetroFix, this new product. So I want to get into that a little bit.

PetroFix actually was released last year at the UST Tanks Conference. It’s only been out for a couple months. We haven’t spent a lot of time discussing it, so that’s one of the exciting things is to go over this today.

What is it, what is the mode of action, and what’s special? First of all, it is an activated carbon-based remedial fluid. It is a carbon that’s milled down to one to two micrometers in size, and it’s an activated carbon. That picture shows really what it does look like diluted when you put it in the aquifer, and it goes in easily with low pressure. Once it does go in, it does literally coat the soil and provides a layer on that soil for contaminants to sorb to.

So once plume stop goes in, it does set, it is positionally stable after say a few days, you know, close to after the injection and contaminants will sorb to that and you get that immediate removal of dissolved phase contamination out of groundwater. What we also do is, once they’re absorbed in place, is we do provide beneficial electron acceptors typically in the form of sulfate and nitrate that give a great blend that stimulates anaerobic bioremediation and permanent destruction in situ and on the petrifix, which actually also creates a regenerative effect freeing absorption sites for this material.

It comes in 55-gallon drums, it’s really easy to apply, it shifts as a liquid. Some of the electron acceptors are mixed actually in the drums, but we also provide a separate mix in a bucket of an electron acceptor blend that’s added just before injection. It’s very safe to use, easy to handle, no special equipment really required. Just to be able to do, have pumps that are able to handle low to moderate pressures and high volumes.

It is safe to use around existing infrastructure. Once we get into this, I’m starting to get a lot of calls and inquiries. And there’s probably three main areas that we see most likely applications for you more common. One would be excavations. When you remove those tanks, when you’re digging out that contamination and getting into the smear zone, do you want to put the clean backfill in or can you put something in there to sort of mop up any residual contamination?

This is a common approach in the industry and it’s something that PetroFix would work really, really well for. Probably the biggest area we see this being used, and most common designs that we’re seeing is a grid approach, and that is attacking the source areas through direct push injection with GeoPro. We also believe that the use of this material, say in a barrier formation along a property boundary or a road where you need to minimize contaminant migration is also certainly within the realm of being able to use this material.

There are other carbon-based injectates on the market or CBI’s. Some of you might be sitting there thinking, or aware of those, or have used carbon before. I wanted to make some important distinctions with what you’re able to use with PetroFix. There’s probably three different categories carbon on the market most commonly versus granular activated carbon that’s typically in the 400 to 1000 micron diameter size looks like sand typically if you hold it in your hand and that is the top left picture when trying to get into this ground it does take high pressure it is larger than the pore throat size of more soils and does result in aquifer fracturing to get it in Similarly, powdered activated carbon is much smaller, it is 5250 microns in diameter and when put in a liquid it’s a bit easier to apply but still the diameter of that material is larger than a typical pore space size of soil.

This chart that just came up is textbook values derived for the average pore diameter for soils, medium sand, fine sand, and silt. What’s interesting with PetroFix, and we think it’s going to give you a lot of options, is that it’s milled down to one to two microns in size, which means that when injected as a liquid it can go and does go into soils down to silt, what has a pore throat diameter of three to eight micrometers.

And that’s why you’re able to use much lower pressures, high volumes, we think you’re going to experience much better delivery of this material of the CBI’s out there. When it goes into the ground, when you inject PetroFix, it looks like you’re spray painting the soil. It really does. You’re able to coat the high K zones from floor to ceiling, so to speak is one way to site. One interesting point I want to point out and related to what John said in his presentation is the importance of that interface, that L-MAPL interface very often between say clay overburden or low K parts of the aquifer that are going in to say sand. That often is the most severe location.

You have the highest contaminant concentrations, you have the highest levels of back you have the highest flux rates and how do you deal with that?

When you put PetroFix in, it does coat the soil. It actually will coat that interval, that interface, and does a great job of helping stop and prevent any sort of flux or back diffusion coming through there. So this is a picture that I just showed on the right of an actual soil core taken from a PetroFix application that’s performing really well. What you’ll notice there is that where we put and the PetroFix, you just get a nice even distribution of the liquid activated carbon across that interval. So I think it really helps, it will help you be successful in trying to get the product where you need to get and get the results that you need to get.

So let me move on. I meant to say it a little bit earlier, but we’re really excited about one feature of this technology, and that is that this is the first time that we’ve done an online design assistant and calculator for you. This is something that we want you to be able to play with and access, and so we have a website called PetroFix.com, and if you go there, there’s gonna be a lot of helpful resources, such as an online design assistant, there’ll be application guidance, there are technical resources and technical bulletins, including a great YouTube video or training videos on YouTube that’s less than about 10 minutes long that shows you how to use the software.

Once you set up an online account, you can play around whenever you want, as much as you want, for your site to come up with what you need, you know, the dosing concentrations and volumes that you have. It does walk you through. You put in, say, depth of groundwater, vertical injection interval, soil type, contaminant concentrations. It will guide you, it will let you know if you’re out of bounds with certain things, you’ll get certain indicators or flags.

But eventually, when your design is complete, you’ll get your output, you’ll get an application summary. In fact, you’ll be able to download this information as a PDF, which is really useful because you can send this off to a drilling firm, a direct push operator, that can give you a bid and you can turn key this technology yourself. And so it’s really, really great. We’re really excited about this and just giving you control, allowing you access to do this when you need and be able to get, quite frankly, generate estimates in less than 30 minutes or sooner.

So with that, just keeping it short and sweet and just giving an overview, I’d be happy to take any questions as we come up either today or offline, or if you need any other information or any sort of kind of help or training, office we have to set it up for you. But with that I’ll just transition over to Q &A period if that’s okay. Okay great thank you very much Todd.

That concludes the formal section of our presentation and at this point we’d like to shift into the question and answer portion of the webcast. Before we do this just a couple of quick reminders. First you will receive a follow-up email with a brief survey. We really appreciate your feedback so please take a minute to let know how we did. And also after the webinar, you’re going to receive a link to the recording as soon as it is available. All right, so let’s circle back to the questions.

If we do not address your question, we’ll make an effort to follow up with you after the webinar. Okay, great. Well, thank you very much.

If you would like more information about environmental consulting services from Scissortail Environmental solutions, please visit scissortailenv.com.

And if you’d like more information about PetraPix, please visit petrapix.com.

Thanks again very much to Dr.

John Wilson and to Todd Herrington, and thanks to everyone who could join us.

Have a great day.