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.

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And today’s presentation will focus on “The Use of Geophysics for Optimizing Environmental Site Characterization and Remediation.” With that, I’d like to introduce our presenters for today.

We are pleased to have with us John Mundell, President and Chief Technology Officer at Mundell & Associates, an earth science, environmental, and water resources consulting firm based in Indianapolis.

He is a professional engineer and professional geologist with 40 years of diversified consulting experience in environmental, geotechnical, and water resource engineering.

John has been involved in the investigation and remediation of industrial sites and contaminated plumes throughout the United States, South America, and Europe. He specializes in the active capture or in situ treatment of very large and long plumes that threaten natural resources and drinking water supplies.

We’re also pleased to have with us today Ryan Brumbaugh, Senior Project Geophysicist at Mundell & Associates. Ryan has over 12 years of professional experience, managing and implementing engineering, environmental, and geoscience projects. During this period, he has acquired expertise in subsurface characterization, site assessment, non-destructive testing techniques, and project management.

He has applied geophysical techniques to large and small construction projects, engineering studies, pavement evaluations, environmental assessment and remediation, water resource evaluations, karst, delineation, and geological investigations. All right. That concludes our introduction. So, now I’ll hand things over to John Mundell to get us started.

John: Thank you, everyone. Well, I think we’ve got a good group here today. We’ll be talking about the application of geophysics for environmental site characterization and remediation.

And, if I can get the slides going here, our objective for the webinar is to introduce the use of geophysical survey methods to enhance standard environmental site characterization practices and to improve the design remedial alternatives for complex site and geologic conditions.

So, we’re gonna tell you a little bit quickly…very quickly about who we are, why geophysics. We’ll give you an overview of geophysical survey methods, and then we’ll hope to spend a good chunk of time on practical applications and then be able to address questions you might have.

So, very briefly, our firm has been involved quite a bit in the mixture of geophysics applied to various geologic, geochemical, and geophysical applications. Excuse me, environmental engineering water resources applications. And we’ve been doing this for a long time on projects. So we’re kind of a firm that specializes and this apply to a number of different areas. And we’ll talk today specifically about environmental.

So why geophysics? Well, as everyone knows who’s involved in environmental consulting, there’s a lot of work you do during phase one and phase two-site characterizations where you really try to reconstruct the site development history. You look for various features at sites like tanks, berry drums [SP], fill materials that can hold chemicals and active sources. You look for preferential pathways caused by piping systems and utilities.

Primarily, one thing you’re trying to develop is this idea of a conceptual site model where you want to refine both the surface conditions and exposure conditions and the complex geology. That’s really one of the things that geophysics brings to bear in this whole package, really trying to do a better job at characterizing the subsurface when you’re dealing with complex situations that a simple soil boring and or monitoring program can address.

So, this involves many times industrial contamination projects, ones that have multiple source areas, contaminant types, where you’re trying to really define and delineate the extent severity and type of contamination, and also migration pathway analysis where you’re trying to really look at where things are going once they’ve been released. And again, geophysics is really one of those tools you can use to try to understand the complexity of some of the things you might encounter that cause preferential pathways of movement for many of the chemicals.

So, part of the use of geophysics really is helping to identify those subsurface granular materials in aquifer systems, mapping those so you can understand perhaps the potential direction of the transport of chemicals, mapping fault systems, fracture systems, karst development that also provide those pathways, and then trying to use that information to place wells for monitoring in a kind of an optimal situation where perhaps placing recovery wells to do that…to do the remediation. And then also in using it to enhance design for in situ treatment where you may be injecting various materials into the ground and you want to get those materials at key places to actually achieve remediation. And in some cases, you can use geophysics actually monitor the progress or remediation over time.

So, a little bit of remediation one on one just to remind everybody, you know, to be effective, it’s always good to know where the source of your soil and your groundwater plume impacts are, where they’ve come from, where are those chemical source areas on a site, where the chemicals have gone and how significant they are. You know, if you don’t know these accurately, it is highly likely that you’re gonna fail when you try to develop a cleanup alternative and an approach for a site.

And as people on this call probably realized, we’ve had hundreds and hundreds of failures of people not understanding these things and have caused either things never to being cleaned up or have increased the cost of cleanups significantly. So, this slide’s a little bit about geologic complexity. Every state that we deal with or every country has its various geologic complexities. We’re coming to you from Indiana today, and so it’s just a reminder. You know, a lot of our complexities are dealt with in the glacial terrain that exists or in the bedrock that we encounter in the southern part of the state, oftentimes karst features or fractured faulted bedrock.

Every state has this kind of complexity that can cause a site to really make us pull our hair out sometimes. And this is a reminder. In Midwestern part, I always look at this as kind of the melting off of the front of a glacier, how aquifer systems and pathways are not always predictable by widely spaced borings and that could be…you know, we can have braided stream kind of development that has caused very complex subsurface conditions.

So, in using geophysics, I wanna talk just very briefly about two challenges, the geologic complexity which we have. And the geologic complexity can really cause groundwater movement to occur in directions we don’t expect based on classic soil boring and or monitor oil-based exploration programs.

And we often get surprised, and it’s because we try to create models based on a very simple, very limited subsurface information. And because of this subsurface data density limits, it can also affect the accuracy of the conceptual site models that we are trying to develop in order to predict and assess groundwater movement and groundwater contaminant plume progression.

The second challenge we had…well, you can step back a little bit. One of the key things here related this geologic complexity is the amount of data we can gather. On the upper right, you can see kind of a…what I would call classic random soil boring approach where you’re trying to assess the picture of what is actually occurring at a site, and you’re limited to a few data points to really kind of piece together what’s happening. Now, if the site is uniform and is very predictable, a few borings are satisfactory.

However, if it’s very complex, like the lower-right picture, which is what we’re trying to actually see, that’s our conceptual site model, it’s the Mona Lisa, our site is a complex picture, then what you see here as we go through different approaches to gathering data where you might do perimeter, the borings or data collection, even geophysical data collection in certain key areas or parallel lines but more low-density spacing kind of a crisscross over the area you’re interested, or as you see increased amount of density of data collection all the way over to the lower right, whereas you begin to fill in data, you begin to really create the picture you’re looking for. So, this is all about data density.

Soil borings only produced generally low density and do not create the kind of pictures we’re looking for in the subsurface, whereas geophysical data density as the advantage now, we can collect lots of data in a short amount of time that help us make judgments.

The second challenge we’re dealing with is industrial complexity, just the historical sequence of events that have caused the site to be what it is. And that could be anything from how the chemicals and wastes were managed over time, different times, utilities, and foundations were put into an industrial site. All of those things create very complex and random site migration pathways, and they result in just a lot of confusion that takes a lot of sampling to understand, or perhaps with the use of geophysics, we can understand it even better.

And this is an example that were…you know, we have an industrial site let’s say that we have 400 by 300-foot area, where we have a history of possible environmental impacts, and we’re looking for things. We’re looking for buried stuff. And let’s say we’re looking for 25 foot by 45 foot buried waste area within this. And in the classical sense, let’s say we gave someone a lot of soil borings to complete and use a random kind of approach to that.

You can see this picture has 150 random soil borings, and we’re looking for that one little source area because, at the surface, it’s not apparent that we’re going to find that because there’s nothing visible we can see. Have we hit it? Do you think? Okay. This is great. We certainly could have hit it with that many chances. And we find out, “Oh, no, there’s the size. We missed it.” That’s the size of the source area we missed, darn. But we also missed these 11 locations and these 9 locations and these 13 locations. So, we’re playing a numbers game here.

Geophysics really comes to bear by increasing the data density and being able to look for the presence or absence of certain features. In this case, we could have used the fairly coarse geophysical data grid, and we would have found all of those targets that I showed that we had missed just from this.

So the idea of both data density and also using density defined things is something. Geophysical data collection and the approach we use can really aid in doing that. So, we’re gonna switch over now to Ryan to talk a little bit more about what is geophysics and also the methods that are used.

Ryan: Thanks, John. Yeah. I’ll jump into the particulars of the methods. So, applied geophysics, you know, ultimately, what are we doing? What is geophysics? We’re looking at the response that is created from the various materials that are in the ground.

We’re using techniques to look at indirect…take indirect measurements of what’s down in the ground based on the physical properties of the materials that are there without direct sampling. It has benefits, especially in cases where you have sensitive contamination where you would wanna limit moving things around or even accessing a site that could be dangerous. Geophysics oftentimes offers a way to collect information in a non-intrusive way.

So surface geophysics, I guess, kind of what I’m saying here, looking at the natural earth or the induced property. So, the earth has a magnetic field. We can measure the magnetic field. We can also induce a magnetic field manually and look at how it adjusts and how the subsurface conditions react to those induced fields.

So that’s the basis of where most of these tools are used, commonly applied techniques here, so the potential field methods, which include gravity and magnetics. So, these are naturally occurring fields that are throughout the world but have slight variations based on the variations in the materials on the earth. So we can passively just monitor those signals and identify anomalous locations based on the naturally occurring potential fields.

We can also transmit a method…transmit a signal and see how it is affected. So seismic ground-penetrating radar, in one sense, even the electrical methods are these where you’re injecting some sort of energy, whether it’s electricity or a sound wave, into the ground, and then you’re reading the response of the ground in response to that signal. And then electromagnetic methods, which there’s a variety of different electromagnetic techniques that…you’re basically using radio waves to affect and change a signal without direct connection to the ground.

So, these methods play out in basically the three categories there. And I’m gonna go through just briefly each of these example methods and to show a brief example of what some of the data sets would look like that would be expected, metal detection, electromagnetic conductivity, resistivity, you can see the list here, seismic microgravity. I would say this is not an exhaustive list as well. These are just a lot of the most common methods that are used for environmental site characterization.

So the EM61 is a system that’s been around for a long time. It’s a time-domain system. It generates electromagnetic pulse and then listens to the echo from the ground. The timing and the amplitude of that response is an indicator of metal that’s present in the ground.

You can cover a lot of ground very quickly. It’s a very good tool for identifying tanks and piping at sites, and as you can see much better picture of where the utility lines could be going across the site as well as identifying maybe historic reinforcements that may not be obvious from the ground surface or even foundation remanence.

The electromagnetic conductivity meters also come in a variety of flavors. They’re all basically doing the same thing. There’s a transmitter and a receiver pair that are offset horizontally, and the transmitter sends out a radio signal. The receiver receives it. And instead of using a time domain, you’re looking at the frequency domain. It’s analyzing the phase shift that happens in that wave as it transmits to the ground.

The spacing of the antenna and the frequency that’s used to determine the depth of investigation and the resolution of what you’re looking at. So, there’s variations on this and even multi-frequency or multi-depth systems that have multiple antennas used in conjunction with one another to allow a variety of different uses.

So this is an Em34. It’s a traditional deep conductivity meter. This is imagery that gives you information down to the tens of meters when used correctly. In this case, the hot colors are the conductive areas that would indicate that a conductive plume is migrating through a bedrock zone.

This is a slightly shallower zone. It’s maybe 20 feet deep, and we’re looking at historic fill. So, zones that have been disturbed will be different than the native material that has not been disturbed. So, it enables a very quickly…you cover a lot of area, and then you can isolate areas that you need to do more additional investigations with more detail density scanning.

And then the EM38 is more traditionally…more of an archaeology type tool. Its depth of investigation is limited to about five feet, but it can also give you a lot of indications of shallow utility corridors and pathways that are oftentimes result of, you know, when we put in sewer lines and trenching that can become significant transport control mechanisms at a site whenever you have migration across them.

Another example here. The cold colors are the…low conductivity indicate granular material that’s potentially fill, you know, material. And then the hotter materials indicate a higher clay content. So, depending on what you’re looking for, the interpretations maybe, you know, used for different things, whether you’re looking for fill, as that was a waste that you need to characterize or whether you’re looking for areas that are prone to subsidence where you have a high clay content that you might need to deal with.

Electrical resistivity is a more direct method where you’re actually injecting current in the ground. It utilizes a computer-controlled system that has set of cables and electrodes that are connected together. And you get a lot more detailed imagery, but it’s a little bit more labor-intensive to collect, and so you’re spacings are limited for how much data you can cover in the same amount of time.

The way that it works, you have a pair that inject current, a pair of electrodes that inject the current and then you have another pair of electrodes that read the voltage. And from the current and the voltage, you can calculate the resistivity with Ohm’s law. So, you do that a whole bunch of different times, and you end up with a profile and an interpreted resistivity that then can be interpreted from a geology standpoint. So, the top is the raw data and the bottom is the interpreted geology model based on the resistivity values.

Seismic is probably one that people are familiar with. You have a vibration sensor in the ground, and you hit the ground, and the energy source transmits through. You keep track of the timing with a seismograph. This is example of a traditional seismic refraction where the energy is traveling along the interface boundary between faster rock below and the shallower, oftentimes the unconsolidated materials at the surface. You can also use surface wave techniques to supplement conditions that a seismic refraction would not be advantageous to use.

So this is an example of the results that you could potentially achieve where you have a low area of bedrock that would be a point of accumulation. And by utilizing multiple lines across the site, you can develop a map and trace a potential flow pathway in an area of accumulation in this context.

As I mentioned, surface waves are just another mode of seismic. There are multiple modes of seismic data acquisition and processing. The surface wave and shear wave models are advantageous oftentimes in urban settings because they handle noisy environments to a much greater extent than the refraction does. In many cases, they’re actually utilizing that vibration and noise as the source for the processing. There’s options for seismic as well to identify variations in bedrock and possible flow pathways, which are oftentimes the key controlling factor.

Microgravity, cross the gravity of world of…they’re variations that are related to the volume of mass between the surface and the center of the earth. By taking very sensitive measurements of that gravity, you can identify zones where there’s a deficiency of mass. And this is an example. The bottom right is actually a seismic refraction profile that identifies a low-velocity zone right in this area. So, the bedrock is fractured or missing. And there’s a corresponding drop in the gravity response across this zone. And so by utilizing a grid or a line of microgravity, you can identify zones where there’s a mass deficiency that would indicate mines or voids at a site. It is able to image much deeper than some of the other systems.

Ground-penetrating radar is one that I think probably a lot of people are familiar with these days. It’s a great tool to use when it works, but it’s limited when you have conductive material at the surface. The energy just gets absorbed into the ground, and you don’t get a response back. You know, countrywide, anything that’s dark brown or purple is basically GPR is useless. And so you have to understand the limitations of the system whenever…and that’s the case with all of these methods, understanding limitations.

So, a radar example here. There’s a slab with reinforcement at the top and then three tanks below. So, when it works, it’s really nice, and you can very confidently locate things when you have a strong signal. And then lastly, borehole logging that can be used as a supplemental, you know, camera views on the left side to inspect casings and wells that are in place, but also some of the traditional wireline logging that allows for characterization of the geology and the different zones and lithology changes that are occurring. It can be very helpful, especially when paired with a surface geophysics to steer those.

This is some of the more modern acoustic televiewer and optical televiewer imagery where you actually see the rock characteristics. And on the left, you’ll notice, there’s a little black streak, and that’s actually free product running out of a little tiny hole, a little bug, and accumulating on the surface of the water. Those are tools that you can work in a dry hole as well as in a wet well. And that example on the right side is an acoustic televiewer. So, I’m gonna pass it back over to John and let him talk about some practical applications.

John: Thanks, Ryan. Let’s continue with some of those related to some of the environmental site assessment work that needs to be done oftentimes. So let’s go through some examples, finding tanks, pipes, utilities, site, history, characterization with fills and drums.

This is an example of a site that’s…oops, let’s go back, where we’re able to map both the location of foundations, remnant foundations, as well as finding underground storage tanks. You can see this was EM61, channel difference map that kind of indicated where those locations were. Over here are GPR profile lines that also identified lines four and line zero, the location of an underground storage tank.

We’ve got a site here, again, just looking at both finding tanks and also looking at reinforcements. Over here, on the right side, you can see the ground-penetrating radar profile can pick that up as well as, again, finding possible USTs, reflection of possible UST’s down here a long line two where we’re going over this kind of reinforcement. We’re able to actually go over known USTs. So you’re confident that you can find USTs even under some reinforcements if you use the right kind of antenna frequencies.

This is the mapping of a former manufactured gas plant site. You can pick up a lot of features in those kind of assessments. It’s just gas holders and various utilities that act as preferential pathways. This kind of a map really gives you an idea of where to look. So this may help guide a lot of your soil boring and monitorial placement.

This is a simple drum search with an EM61 search. And you can see that we have large anomalies from this resulting from the readings, and it turns out that those same kind of results were mapped exactly over the top of drums that were found at a particular site. In this case, there were 4,000 drums. So, if you can’t find 4,000 drums, you’re not a very good geophysicist.

This is a case where we use two technologies, both 2D, electrical resistivity profile that looks a lot like geologic cross-section where we encountered…resistivities were high, and we knew that we had lots of coarse sand and gravel. But we also identified two waste burial areas across this particular cross-section, which is down here. This is EM31 map that, again, showed high resistivity in coarse sand and gravels and this waste materials buried there. This helped in this particular site because we actually knew about this, and there was gonna be a large excavation. So, we’re able to manage the waste ahead of time and knew that we were going to encounter this instead of having a delay caused by an unknown condition.

This is an example of a site where three different kinds of techniques were used to map the site, EM61, ground-penetrating radar, a grid that creates kind of a slice map at fixed depth to kind of see the reflections, certain depth below the ground surface, and then a terrain conductivity map. You can see that some techniques pick up certain things, like over here, we had two anomalies that…several anomalies were picked up by the EM61, whereas the GPR picked up a shallow trench and an unknown utility. And the GEM-2 looked deeper actually. We’re able to pick up another area of concern that kind of needed some investigation. So, using combination of techniques really helps, you know, finding the historical development of the site. I’ll pass it back to Ryan.

Ryan: Thanks, John. For my last history here, we’re gonna focus a little bit more on particular site and give a little bit bigger…more complete scope of what it looks like for multiple methods to come to bear on a site that’s challenging that we’re trying to identify preferential pathways. And this is an area where there was karst.

So this site, multiple locations, multiple properties had previous work done in drilling, and it became clear, “Wow, this is really a challenging site. We’re not sure how to characterize what’s happening where.” We did a limited survey with terrain connectivity, try to isolate some of the shallow anomalies that were there and really locate historic foundations that may have been at the site, as well as utilities that could be preferential pathways.

With any of these sites, we have to be aware of the things that are at the site and take into account. So in this case, there were vehicles and things that were on-site that would actually cause anomalies that we have to be careful not to give credit to in the data set if it’s caused by something that’s causing an interference pattern in the data set.

At the same site, we collected radar and resistivity profiles. And there’s a great correlation here between this excavation and this gravel that shows up in the resistivity and then also a very good indication of what you’d expect in these karst conditions where you have angulatory bedrock conditions and potentially highly weathered clay field or even water-filled voids below the initial bedrock surface.

So, several of those profile lines that we did with both radar…and the radar being a great tool to help characterize where there’s utilities and to account for any interference patterns and also identifying these potential vertical flow pathways through the initial bedrock surface.

By combining multiple profiles, then we’re able to do, you know, a map view from the resistivity data and identify zones where there may be weaknesses in the rock and try to connect some of these flow pathways in map view. And you can look at…this is a different site, but it’s an example of using multiple elevations and how you can quantify the areas that are weathered and flow zones at various different depths and how they may not be the same zones, all the red areas in this.

Basically, the red and purple areas are zones where the rock is missing and potentially, you know, high probability of material transport through those areas at various depths. Back to our original site. We generated a top rock map and located…these are some zones that we think you should put new wells in. And then those new wells came into play. And we see the streaks in this are indicating free product seeping into the well. So, this was a very successful use of both surface geophysics as well as borehole geophysics that then was used to further the remediation at this site.

Additional, this is sort of a single-shot, one-off slide that shows multiple resistivity profiles identifying flow pathways as well as using borehole geophysics to characterize the different depths where there may be bedding plane interfaces that would interface to help characterize an injection event and better know how to place the injections. Similarly, here, identifying these flow pathways that these breaks in the rock that come through these…hot colors indicate low competency of rock and potential flow pathways. For our last case history, I’m gonna pass it over to John, and he’ll take questions at the end.

John: Thanks, Ryan. This is a case…industrial site that it operated for many years on this piece of property. And it was known that there was a large release. There were already wells that were placed along city blocks, trying to map if there was a plume coming from the site. We used a little bit of hydrogeology to figure out from where the site was, where the plume could have gone. It’s over a very large area, going all the way toward a large water…a body of water over here.

So we used geophysics to really try to map where the plume was because the plume disappeared with the previous consultant. They lost track of it. They didn’t know where it was going. And so this was the area we targeted, and through that targeting, we performed 2D resistivity profile lines throughout the urban area along right-of-ways, as you can see here, and several in the source area to understand where the chemicals were coming from. This is kind of the…just kind of a typical roadway of what we were putting the resistivity profile lines along.

This is a typical one of which we encountered where we had limited amount of sand and gravel that had a silt and clay layer above it and a silty clay layer below it. Along this profile line, it was fairly continuous, but there were areas that had high resistivity and perhaps greater potential for preferential flow along those. This allowed us once we did these lines to create a map of where we believe the plume was, and we put in additional wells, and lo and behold, we were able to find a plume from beyond this point where the plume went. And we mapped it, and we also did a couple things, put in additional monitoring wells, but also helped us to design a system of permeable reactive barriers and a source removal on treatment program for remediation.

And the bottom line is where we put these permeable reactive barriers, this approach has worked, dramatically reducing the intensity and size of the plume and were into the last year too where we’re trying to get the levels to be able to use an environmentally restrictive ordinance on the water use.

So, in closing remarks, we just wanted to say there are numerous geophysical techniques that are available on any project. They really increase the confidence in putting together the history of a site and improving a conceptual site model. And the use of complementary techniques always allows for better overall characterization. No dependency on just one particular technique is good. And these really allow remediation to proceed effectively.

In many cases, with the use of this data, sites that have sit around for a decade or even more than a decade have been able to be cleaned up in a few years after the improved characterization has occurred. So with that, I would like to go ahead and possibly take questions and see what we have from the listeners.

Dane: All right. Thank you very much, John. As John said, that does conclude the formal section of our presentation. So at this point, we’d like to shift into the question and answer portion of the webcast.

Before we do this, quickly, just a couple of 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 us know how we did. Also, after the webinar, you will receive a link to the recording as soon as it’s available.

All right. So, let’s go ahead and circle back to the questions. Let’s see. The first question here, John, is, “Are there any geophysical methods that are effective for steep slopes and/or wooded areas?”

John: It’s a very good question. Obviously, a lot of these geophysical techniques are used under many different kinds of site-specific conditions. For example, 2D Resistivity that we’ve talked about here today can be used along a steep slope as long as you can walk up the slope and are able to put the electrodes in the ground and have them seat properly.

In non-environmental cases, we’ve used 2D Resistivity to actually map landslides and use those for engineering projects because those are often caused by excessive water problems and drainage issues.

You can use almost any of these as long as you can carry the equipment. There comes a point where they’re very dangerous. I think we showed you a ground-penetrating radar unit that basically rolls. Well, you can get those that also are carried sometimes, but again, it comes down to just what you can walk safely with.

Dane: All right. Thank you very much, John. So the next question here is, “In trying to locate areas of historical excavation and fill, what methods are most applicable for a site that has multiple utilities, active tanks, and other metal interferences?”

John: Oh, that’s a good question. I think really the combination of EM techniques and ground-penetrating radar, we’ve had a lot of success with because either heavy metal detection like EM61 or other EM methods really helps locate those metallic utilities. They help locate tanks.

And then the ground-penetrating radar, if you have clay at a site, you may not penetrate. But notice the many trenches with utilities are filled with gravel and granular materials. And those are easily imaged with the ground-penetrating radar. So, both that and tank pits that are filled with granule material show up very well with good data density with GPR. So, I would say that combination is probably the best that we could offer.

Dane: Okay, great. So, let’s see here. I’m getting several more questions streaming in here. The next one is, “In the urban example, did you detect the chlorinated solvents or just the permeable zones?”

John: That’s a good question. And oftentimes people ask that. Can you find low PPB of chlorinated solvents? And you can’t really. Twenty years ago, we had some geophysical shysters that would go around claiming that and hopefully were drummed out of the business very quickly.

As far as chlorinated solvents go, sometimes, if they’re so intense, they may affect the conductivity. But in these cases, we’re really looking for pathways. We’re really trying to understand the geology. And we found that if you understand the geology, you have a pretty good idea of where the migratory pathways for those kinds of chemicals go.

You know, in chlorinated solvents cases, they can sink. They can sit down on top of the low bottom of a low spot in a bedrock, in permeable bedrock or clay layer. In the case of petroleum, they can still find those low spots and those higher permeable highly weathered areas.

So, really, the only thing I would say is this. When you’re thinking about petroleum hydrocarbons, occasionally, you can pick up halos of bioactivity going on that changes the conductivity of the groundwater because you’ve got a lot more dissolved solids in the water. You might be able to pick up zones of heavily impacted petroleum and impure product. But as far as tracking chlorinated solvents plumes, you’re looking at the geology mainly.

Dane: Okay, great. So, next question here is, “What would you recommend from munitions sites?”

John: Well, I’d recommend not to step on any first of all. A lot of people use flyover kind of surveys where you’re looking at, you know, electromagnetic kind of reflections with different specialized equipment that are carried by planes or drones. That’s a whole specialty area of people who deal with those kinds of areas. And you have to do them very carefully. We’ve been in sites where we knew that that was a situation and we had to really steer clear because you have to do it very safely. But usually, those are kind of done annually at least in our experience.

Dane: All right. Okay. So this next question is very simple and direct. It just costs with three question marks.

John: Well, if you have a million dollars, you can do one of these per day. No, I’m kidding. Really, if you look at…you know, of course, they go from very low and simple lesson one day, GPR go and check and find a trench under $1,000 to, you know, spending on 150-acre site over multiple years, a $100,000 on geophysics.

But if you want a ballpark really and you’re looking at like a multiple…kind of a multiple approach characterization of a site, we’re looking maybe in a range of like 7,000 to $10,000 per day. That includes everything, you know, including the report. You know, you’ve got a site where you take three days to do it. You may be between 20 and $30,000. So, a lot of what we showed you were…and we have many more case histories. But several laws we showed you maybe were on the order of two to three, four days. So, they ranged probably somewhere between 15,000 and $25,000.

But what happened was…that sounds like a lot obviously, but when you get into drilling and [inaudible 00:45:01] bedrock and understanding what’s going on and having failures, it’s actually these kinds of expenditures during site characterization really has helped save a lot of money and have helped direct-injection programs like the people like Regenesis and others have where you have to know where you want to inject and what’s depth you want to inject. And in those cases, they’ve saved money where you inject where you should and you don’t try to inject where you shouldn’t. I think they pay for themselves when they’re done correctly.

Dane: Okay. So we are still getting a lot of questions here. The next one is, “What are the depth limitations of a GEM-2 survey? Does your firm have your own e-logging tools?”

John: Well, GEM-2 survey, and we’ve used GEM-2 equipment in the past. We don’t currently use it because, you know, I say the various operational things you encounter when you use equipment for a long period of time. You know, we believe that, you know, you’re typically looking in the maybe 20 foot to 30-foot range maximum with something like that. You get a lot more signal-to-noise ratios and certain kind of conditions with that kind of equipment.

The EM kind of equivalent kind of techniques we showed you, each has a particular zone where you’re looking at top 5 feet for some instruments, 10 to 20 feet for other instruments, the EM34 where you actually can space out the receiver and the source. You know, you make it up to 40 meters with something like that. Sometimes that’s a very methodical slow approach where you might choose to use like 2D ERI, which can get you maybe, I don’t know, upwards of 250 feet if you’ve got the right spacing. So, it varies.

And again, ground-penetrating radar can be stopped at a few feet with a lot of clay at a site, all the way down to, you know, tens of feet in really nice coarse beach deposits. And let’s see. I think…what was it?

Dane: That’s good enough for that one? Okay. Okay. Yes. So, let’s see here. The next question is, “How well does the resistivity testing work in an area with dense utilities?”

John: Not so good sometimes. And that’s a really good question because you may go and mobilized a site and have scoped out 2D Resistivity, and you get to the site, and you find along corridors of right-of-ways where we get access. You may have key utility lines you’re facing. What we normally try to do is incorporate an alternative technique, which is often seismic to kind of go along. And since we own our own equipment, we’ll bring that oftentimes along, or we scope it in. And if we find one line has a lot of electrical interference, we’ll do a seismic line to at least try to get a good detail, the top of bedrock.

What we’ve also found sometimes is that you can interpret sometimes electrical interference on the 2D ERI lines where they’ll give you perhaps geometric shapes, but the absolute value of the resistivities will be off because of the electrical influence. So, they’re still useful in some cases because of the shapes of the geology and other things, but the absolute values might be off. So, you’re right. I mean, that’s a good question. You can really have limited success with those if you don’t watch it.

Dane: All right. So, we still have several more questions here. The next question is, “How would you approach a large site that has little prior information and has a limited assessment budget?”

John: Well, you always start with…you know, we always look at those as doing desktop studies. If someone asked us to take a quick look at something, we may be able to do a desktop study for a couple thousand dollars and pull up all the geology we know to understand where we think things could be. We could also look at a number of historical aerial photos that might give us some credence until, you know, what we could expect.

You know, if it’s a large site, we may pick a technique like an EM or GPR where we’ll drag those instruments behind the gator [SP] or something and really cover acres and acres of land in a few days. That’s one of the most cost-effective ways of getting, you know, something done for a lower price. You know, for some clients, lower means under $1,000, and for others, it means under 50,000.

Using Global Positioning Systems now and towing equipment using in some cases drones can really cut cost. The thing about geophysics. Over my career when I was doing this many decades ago, getting the survey set up and collecting data was a big deal. And so we couldn’t collect very intense data at that time. And over the last 10 to 20 years with the Global Positioning Systems and newer equipment, we can collect a lot of data over acres and acres of land in a few days.

Dane: All right. So, let’s see here. The next question is, “For areas with buried treated wood pilings and/or concrete debris, would ERI or electromagnetism be better?” And this person says, “A shallow groundwater table has interfered with the GPR surveys previously.”

John: Oh, wow, we had a nice case history all ready to go today, and we took it out that has exactly those things, but we had a limited amount of time. But I would say, in a specific case I know where we had buried wood debris and…what else did you say? I think you said…

Dane: It was, yeah, buried wood pilings and concrete debris.

John: Yeah. Buried wood pilings, concrete debris, we used EM61 and EM31 or equivalent EM mapping technique. And those show up. Wood shows up very well oftentimes as higher conductivity zones. The concrete debris shows up at high resistivity or low conductivity zones, and so using those kinds of two surface instruments, and then after you do that, doing a line or two of 2D ERI across the anomalies.

I would love to show you what we had here, but we took it out of our presentation. But doing the 2D line right over those anomalies can show you the depth of those and also, you know, the character and maybe estimate of volume. So, we’ve had a lot of success with those kinds of techniques.

Dane: All right here. So the next question is, “Is the current EM…for example, EM31 or EM61. Is the current EM technology a lot less sensitive to cultural interferences?”

John: I wouldn’t say they’re less sensitive. I would say there’s ways of correcting for them. For example, the EM61, you know, we have coil settings where you listen to the…you send a signal to the ground and then you listen. In that case, you have coils at different depths above the ground, and you can basically filter some of the cultural noise that you may get with very near surface metallic debris that is not significant. You can filter out and actually see deeper.

So, yeah, everything is affected by cultural noise, and the EM techniques can do that. For example, we didn’t talk about how…what a pain in the rear end is, is to change parking lots filled with cars or to move dumpsters or things you need to get out of the way so you can look beneath the ground. So you always will be faced with those kinds of things when using EM approaches, but some have filtering techniques to really help you understand, are you seeing near-surface small stuff? Are you seeing buried materials deeper? The metallic materials are more significant.

You can also pick up. Obviously, like we showed, you can see oftentimes. Sometimes you can see through, not with EM. You can see through the reinforcing with some GPR antennas, higher range antennas like 1,000 antennas. Yeah. So anyway, I think the good thing about Ryan’s pointing this out to me was the modern instrumentation. You may have a better signal-to-noise ratios than what we have in the past because of the technologies. So, it’s improved…it’s improved.

A lot of times, if they’re not affected 10 feet away…if you stay 10 feet away from something, for example, they may not be affected, whereas before maybe you would have been affected by more noise. That’s the beauty of using multiple techniques because you’re gonna find that some of the EM techniques, you can’t see anything in a certain area of the site and another one you might or ground-penetrating radar, you might pick up something. And that’s when you also pull in. You know, if you’ve got your instruments there outside seismic, again, you’re trying to find anything from top or rock to buried utilities line that sometimes shows up as strange blips in the data.

Dane: All right. Okay. So we still have several more questions. I’m not sure if we’re gonna be able to get to all of the questions. But if we do run out of time before we get to your question, we’ll definitely make an effort to follow up with you after the webinar. So this next question is, “How effective is the 2D Resistivity and/or seismic refraction in a CA6 and CA1 material overlying clay till?” This person is saying they’re most concerned with tagging the top of a clay and water table, and the deepest excavated area was approximately 30 feet below ground surface.

John: You were asking on that. What were you asking? Which techniques were you asking on that?

Dane: The 2D Resistivity and/or the seismic refraction.

John: And the deepest excavation was what?

Dane: Thirty feet below ground surface.

John: Yeah. I think what comes to mind is whether in those techniques, different techniques for the seismic, you have to have a strong enough contrast in density to kind of pick up on those contrasts of those materials. In the same way, for resistivity, the same thing happens as far as resistivity goes. You need to have a strong enough contrast.

When you have very closely spaced electrodes in 2D ERI, you can pick up a lot of very subtle near-surface things as long as your data density is great enough. And so we’ve been able to find differences in material that are very subtle in the top 10, 20 feet with a good spacing of 2D ERI. I like that and where I’m looking at different materials.

With seismic, when you get that shallow of material changes, you may get into difficulties in interpreting the data because it is shallow, and if you don’t have a strong enough…if you don’t have a strong enough contrast in material density and philosophy, for example, you may not see that. In that case, I would pick 2D ERI, in that case, to try to look at that.

The other thing, we use an instrument like a CMB Explorer where it looks at EM at different depths. Sometimes, looking at different depths below the surface, you can pick up patterns, and you can also see material contrasts in the soils that could be picked up by something looking at, not just a single depth like an EM31, but…you know, it depends on what kind of orientation you have for your instrument. But looking at multiple depths can also help you interpret that.

Dane: Okay. All right. So, next question here is, “Is it possible to monitor in situ cleanup methods using geophysics, for example, in situ chemical oxidation?”

John: Oh, it’s absolutely yes. We’ve looked at a few opportunities to try to do that. The beauty of that is once you set up a profile line like a 2D ERI profile line, you can just time that as an injection goes on, for example, to just take readings at different times. So, there’s both published literature on a few cases where people have done that. And we’ve gone back to a couple sites on a different time and redone a line or two at a different time. And sometimes you get may be subtle changes in that case, not so much in injections as much as oh, there’s a lot of rainfall or different time of year where you can get changes over time.

So, definitely, this is an opportunity for the future. We’d love to support anybody who is thinking about doing that because we have very clear idea of how we might go about doing that and really getting good data on the radius of influence of the ejection and overtime where the various injected materials are dispersed.

Dane: All right. So we have time for maybe one more question, and that is, “What geophysical methods would be most effective to identify historic narrow stream channels at various depths below a site?”

John: Okay. That’s cool. It depends on, you know, how big they are and how thick they are. For example…I’ll give you something we’ve done in the past. We used an EM31 one time to map drain tiles, shallow drain tiles in a field that were filled with sand and gravel. There’s certain processing you have to do to do that.

Once we process that data…in fact, I took that slide out too today. We were able to map those shallow. Those trenches were only two foot by three foot deep. But if you have good enough data density, you could actually find shallow filled tiles.

Now, if you’re talking about a shallow stream or a stream that kind of cuts through, I think with the right data density…let’s say we’re looking in the upper 30 feet or something like that. I think you could collect enough EM data to really…and maybe GPR data if there’s not too much clay overlying the sand and gravel.

But definitely, EM data would pick up on lower conductivity materials. Yeah. I think it’s possible. We’d have to get in the details there, but I wouldn’t say no at this point.

Dane: All right. Well, thank you very much, John. That is going to be the end of our chat questions. If we did not get to your question, someone will make an effort to follow up with you. If you’d like to get more information about consulting services from Mundell & Associates, please visit mundellassociates.com.

If you’d like to learn more about remediation solutions from REGENESIS, please visit regenesis.com. Thanks again to John Mundell and Ryan Brumbaugh, and thanks to everyone who could join us. Have a great day.