Well, welcome everybody to Hydrotera's latest webinar in our webinar series. Today our topic is all about passive soil vapor measurement and how we can use that data. We've had a fair bit of help putting this presentation together and I'm really appreciative of that help. In this particular instance we've got Dr Brent Davey who's co-presenting today. He's a principal environmental consultant for Fife and a bit more on him later. But I've also had a lot of support from Gary Hurst who's technical director from of land quality and remediation with SLR consulting. And Gary's been very helpful in putting some slides together in this presentation. But I will be presenting his slides. We've also had some support from Beacon Environmental, one of our suppliers who's also provided content today. So a real team effort pulling together this presentation for yourselves today. Fantastic turnout for this one. We've got over 250 odd registrants for this. So obviously soil vapor is of interest to the industry and great to have you all here today. Right, so before we get started just a few things. So we love your questions and Brent and myself will do our best to answer those questions at the end. If you have a question please use the Q&A button at the top of your screen and write your question in there. And at the end I will read them out and we will then do our best to answer them. So a little bit about our speakers. You probably most of you would probably know me by now after all these webinars. I'm the managing director of HydroTerror. I have worked quite a lot in the area of soil vapor around contaminated sites assessment management. Gary Hurst the technical director land quality and remediation with SLR consulting. He's done a lot of work with soil vapor particularly utilizing one of the technologies beacon which HydroTerror is a distributor for. But he's utilized that a lot with mapping groundwater contaminant plumes and there's some good information in this presentation about that. But then our special guest Dr Brent Davie principal and Borromell consultant with five is someone I've been working with on and off over the last 30 years and it's great to have you here Brent. So Brent is my co-presenter today. Brent's been working in the field for about 40 years. Originally he studied as a micro biologist and did his PhD in that area. He's quite passionate about how there is micro breakdown toxic compounds and has a wealth of experience with assessing such breakdown pathways and their metabolites. He has worked in the sort of laboratory field working with the Australian government analytical laboratories. So he's got a unique blend of expertise really. So there's the laboratory side. There's the microbial side and there's the contaminated sites side of things. He's got a lot of hands on experience dealing with these soil vapor sampling devices and monitoring and really brings a lot of hands on experience with where things can go wrong and how to use these things and when. So welcome to you Brent. And without further ado, I think we will hand over to yourself about now. Okay. It's helpful in all of this if we perhaps go back to the beginning. Well, maybe not that far back, but at least ask ourselves, you know, where have we come from? What did we used to do? And for most people studying, you know, air contamination, it began with air pumps, where you got used to be the standard asbestos air pump which just drew air through a filter. You could add an absorbent cartridge and that's what you see in the little image on the on the left of your screen. That thing looks a bit like a cigarette station. The device is actually an absorbent cartridge through which the air in the room is being drawn by this pump. And they work by pumping away and they're meant to be pumping away at a constant rate. And you leave them go for as long as you can to get the greater sensitivity you can. And then the cartridge gets it off to the lab and analyzed and they work out what the concentration in the area is the difficulty with the pumps is that while they were quite noisy. They tended to be to blend into the background and people didn't realize they were there. And so very often your results were compromised by for other reasons than what you're likely to think. For example, in this image, there's a tin of thinners immediately in the shelf immediately below the machine and while it was closed, we have no idea the extent to which it might have impacted the result. So there are a few issues. In the next slide, the same technology could be applied to in ground wells, multi levels and that sort of stuff. But as you'll see in that little image on the left, the whole issue is getting rather complicated. Each pump is pumping its own. Well, if you like to a different depth, but because we've got or needed to use different absorbance for different target chemicals in the soil gas. So let's start having these Christmas trees of tubing, which introduces all sorts of difficulties and takes a long while to set up. And the technology started to be limited by how many of these pumps you had available. But one of the other major limitations of the old pumping systems were that they ran out of puff. They were lucky to get 10 hours out of them, which meant that you often had to set them late in the afternoon and then go away and come back in the morning and collect them again to get your greatest sensitivity. Next slide. The other way that you looked at soil gas. In this case, the interface between soil gas, which is the gas between particles of soil in the soil matrix and soil vapor, which is what comes out. Trans crosses the surface and becomes enters the air is to use flux boxes and you can do it yourself. But these were homemade and still relied on the asbestos punch and still relied on had limitations as to time and time. The beauty of these sorts of designs is you can actually run concurrent controls for what's in the atmosphere. But nevertheless, they were fiddly time consuming and you had to do lots of tests to make sure that there wasn't leaks and that sort of stuff. So what was wrong with the old gear? It's sensitivity was limited to how long you could pump. Basically, the calculation was how much air did you pull through the absorbent. And based on the concentration that the laboratory recovered from that absorbent, you can then work out what the concentration in air probably was. However, you had to assume that the pump pumped constantly. And that's a real issue in the sense that if they weren't new and generally we hired these things that they've been used a million times before. Even if they were calibrated, they didn't necessarily keep pumping constantly. So you were dealing with uncertainties as to the volume, but how you dealt with. If you're looking for low levels, you had to try and pump as long as possible, which meant that you needed probably two days on site as a minimum. And the gas train, you know, the sampling train had all sorts of issues as well. You often needed to put a vapor water vapor trap in other pre filters. So there were lots of branches and tea pieces and lots of other stuff. And I can remember some of my field guys working on this would take a whole morning to set up one particular array at one sample location. And as we'll get to that was one of the reasons I think that this new technology has been developed. And the other thing is that the pumps are quite noisy. And in a household setting or something like that, they can be very obtrusive, but maybe not intrusive obtrusive enough. One of the aims in indoor sampling is that you sample the place as it is where people don't realize in a sense that the sampling is happening. So that you can get a fair estimate of just what's going on in the space. But what you don't want to have happen is people opening tens of thinners or starting painting with turbs based paint. What are you doing with measuring? It's happened. So what's turned up? I guess the first of these historically were similar canisters. And I'll talk about all of these things shortly. One idea, just a big 10 basically quite sophisticated, of course, in which you into which you were able to introduce your sample. Close it off. It's done. It's very remarkably effective in practice, but I'll talk some more about them. I think beacon were actually next. They develop their passive soil gas samples. And because of Gary's great experience and expertise with these and the fact that Richard's the local Australian agent for them. I thought I won't spend much time just to say that they really do have an important place in this and we're one of the first and the simplest. And then the University of Waterloo in Canada has been doing lots of work in these sorts of advanced sampling technologies and they develop this very simple device called the Waterloo membrane sampler. It's really just like a standard gas soil. It's got a TPH trials, which has got a crimp seal with a membrane at the top. In this case, the membrane is water-resistant. So dimethylsilane or siloxane membrane, which doesn't let water through virtually anything else. And inside the vial is an absorbent, usually even just granulated carbon activated charcoal. And you can leave it in place for quite a long time. And I'll talk about that some more. And then finally, there's in the recent years, there's been this device called the radio, which I'll talk about. Okay, Richard, next one, please. So summa canisters, a lot of you will probably have met these things. They're quite sophisticated canisters as it happens, partly because they need to be reused. They're sufficiently expensive to do that. And therefore they need to be cleaned. And given that we are talking parts per trillion type analysis, they've got to be very clean. So these are very well made stainless steel spheres. They're coated with a silicone coating inside so that as far as possible, nothing sticks to them. And then they're fitted with a tap system, which includes a vacuum gauge.  And what you then do is hook it up to your site, as in the picture on the right there, hook it up to a gas bore in the ground or even just open it to the air and turn the tap open and suck in a volume of air. The trick is that you have to keep a residual vacuum in these things so that the lab can work out exactly how much air has been sucked in. So if you were to leave these canisters just open, so that they were inter-collaborated with atmosphere, the lab actually wouldn't be able to use, work out what the concentration in air was, because it actually makes working out the volume of air inhaled by these things, very difficult. And as I say, they're conceptually very simple, but they're often fraught in practice. There's lots of valves, the gauges are notoriously slow reacting. So you've got to watch them like a hawk and really, as I say, you can't leave them unattended. So they were an intermediate step, but they were a hell of a lot easier than using the old pumped systems. And like the pumped systems, they're not quite totally passive, but they're a good step in that direction. Next one, Richard, please. So get to beacon samplers. And because they're Richard's terrain, I'll get him to talk about them in greater details, but I'll skip over this, except to say that they are really quite easy to install, a little bit fiddly. But with practice, they're really good. The main thing you need to be aware of, and it's not necessarily a disadvantage, but you need to be aware of this currently I think only one lab in the states, sorry, one lab on the planet, and that's in the states, which does the analysis. It's because it's a very special absorbent matrix. But the results are really exceptional and remarkably reliable so it's worth doing. I'll leave that to Richard to talk you through the details of beacons. Next one, please. This is the radio allies. These, I think, one of the big advances of recent times. There are limitations but the one advantage is that they're available for most of the analytical laboratories in this country. And they are very good for hydrocarbons and other volatiles in there. And because that you can get two different types of absorbent, by the way, the way these come you get this little blue triangular mounting plate, which you don't need to use necessarily. There are other things that blue bit at the bottom you can get separately and it just seals off the diffuser. The orange and blue or yellow and blue device is the diffusing cartridge itself. And inside that fits that brown. That's the actual absorbent which fits inside the diffuser. And you once you retrieve the sample, you just pop it in that little tube up there and they provide these barcodes remembering that these absorbents are so sensitive that if you were to use a texture or something like that or even a standard adhesive label, it'll pick up components of the ink and the label and that sort of stuff. So these barcode labels are quite important part of the system. Now, while most of the Australian labs will provide you with just the two types 130 and 145. It's worth remembering that the same technology is available for measuring lots of other things. If you need to and very good at it. The other fundamental thing about beacons about radio loaves and waterloaves is that rather than depending on the volume of air. They depend on equilibrium factors so that they can give you the same answer like what is your concentration in your air, but it's based on a calibration of the devices that has been done by the manufacturers and various other people. So that you don't need to know what your volume is. So these are great for sticking in holes in indoor spaces and those sorts of things where you don't necessarily have a pump running you don't necessarily know what the volume is. But by their very nature, they tell you what the equilibrium concentration of your particular target compound is. The beauty about radio loaves is that they can be like so many of these other devices is that they can be left in situ for either very short times or days to weeks. And particularly radio loa which has been developed for just this purpose they can be used for anything from workplace monitoring for a few hours to weeks to get you a really sensitive determination. The main difficulty with the radio loa system is that the diffusion shield in particular is potentially susceptible to fouling by soil or water. And so these are best though you can use them for in-ground sampling but you need to be aware of this risk. But they're best in above ground work in indoor air or even just outdoor they work very well. Next one please Richie. I guess the technology of choice is either for measuring in-ground are either beacons or the Waterloo membrane samples. And this is just a quick rundown of their design. The key component is this PDMS membrane which allows soil gas, soil vapour, all those components into the vial but doesn't allow water and doesn't get blocked by water. That's the important thing. And then the absorbent sort of picks it up and the lab will take this whole thing and elute the whatever's been absorbed on the soil. So they're very useful in that sense. And that's as simple as it comes to install the things. You can even just hang them in any aspects if necessary but they're very easy to use in soil bores, those sorts of things. Next one please Richie. Waterloo again is offered by most of the labs. There are two different types sizes. But they've also got these thick membrane and low uptake versions which are good for, you know, you leave them in place and come back a month later. And they can still, the laboratory's result can still be interpreted in terms of what the concentration of your particular target analyte is in the soil vapour or the soil gas rubber. And this is particularly important if you're looking for breakdown products of things like chlorinated ethanes, you know, PCETCE. Or even metabolites of other components, hydrocarbons and so on. Because they may not be present at the sort of concentrations of your standard contaminants. But you want to be able to pick them up. So again, the waterloo's are particularly good for these in-ground applications. So I think Richard's now going to take over and look at the, give you some more details on the beacons. Thanks very much, Brent. I did add one slide in here. You might want to comment on this one too, Brent, just to one the spot. So it seemed to me you were talking about canisters and sorbents. And I guess this slide frame to summarise when you might use what you just talked about. That's, I mean, this is particularly useful. Yeah, the virtue of canisters is that they're good for the more volatile, you know, methane, propane, those sorts of things. And the short chain compounds that are very volatile. What canisters can't handle are the things that are frankly not volatile or the labs call semi-volatile. And as this diagram shows, the limits about C10. So PAHs, those sorts of things are simply not something you can pick up in canisters. But the beauty about the different sorbents that are available is that you can cover the whole range up to really quite large molecules using one or another of the sorbents. You can certainly will. Radiolos can water lose perhaps less so because you are looking at the, you're strictly looking at the most volatiles in the system. If you look at that, this diagram, the second run down the VAC slash SVACs, the standard TO-17, it's fair to say that beacons, radiolos and water lose can handle that range. I'd suggest that if you are concerned about the heavy hydrocarbons, beacons are probably superior. They can all manage the TO-15 range and so can canisters, but not quite as well. It depends on the molecular weight. Well done, Brent. That was a very good comment from the slide that I snuck in for you. All right, so now I'm going to talk a little bit about the importance of the conceptual site models for these surveys. It's one thing to take a measurement. It's another thing to actually sort of be able to put it in context and make sure we know why we're measuring where. So some of these slides were put together by Gary and thank you very much to Gary from SLR. I really appreciate that. Some of them have also come from Beacon. So what are the things we need to think about when we're looking at this passive sampling approach? The first thing is that not all volatiles are the same. What does that mean? Well, it means that some volatiles are less volatile and others, and therefore tend to partition more to the soil matrix and less to the soil vapours. So if you're measuring for these things, those which are more volatile, you're obviously going to pick up more than those that are semi-volatile. So we talk about Henry's Law constant, which is a way of effectively talking about the relative volatility of such things and how they partition. And there's plenty of good references around which can give you a list of compounds and those constants. Some compounds are difficult to detect in soil. So sometimes they're only present in very low concentrations. So what Brent was talking about with the sensitivity of some of these samples and the associated lab analysis becomes really important. You can have a high degree of variability in the solubility of these compounds. And I think it used to be called an optional water partition coefficient. I think that's what that refers to there, which is the ability of a contaminant to partition into water from the soil. So these things all affect what we actually see when we collect a sample. Also, I suspect most of you know, like we have our light non-aqueous phase liquids and our dense non-aqueous phase liquids. This affects where you might find them and where they might accumulate. So depending on where we deploy, we may or may not see more or less of those. That becomes really important when you're trying to just quantify what the scale of remediation is because you might just come across a pocket of it because you've chosen to put a sample in a certain area. Compositions of Naples may affect solubility. Well, it's quite a complicated one, but basically Naples or various compounds can get together and that can affect their relative solubility. So a compound on its own versus how it might behave as a mixture can change. Emissions of volatile organic compounds and semi-volatile organic compounds may be highly variable in a spatial sense. They do tend to accumulate in certain areas and why that happens relates to a few things that I think Gary refers to below. So vertical and soil texture variances may result in vapour sources accumulating in some areas or being hidden in low permeability soils. Okay, so it's funny when you do your, some of you may have done hand auguring and PID measurements. You get your sandy soils that tends to, the vapour whooshes out of those sandy soils pretty quickly, whereas for your clay soils, you sometimes have to physically break open those soils to actually get a meaningful rating. So, you know, a lot of you have probably seen in a hands-on sense exactly that happening, but it does affect how vapours are distributed in the subsurface. So traditional vapour sampling may still be required, but it doesn't mean your source extent and intensity has been fully developed. So I suppose what Gary might be referring to as traditional layer might be some of the stream mechanist stuff that Brent was showing you earlier. Next slide. Well, maybe before we do, so just looking at these schematics on the right-hand side. It's all about that partitioning piece, okay? So a contaminant or a compound can be attached to a soil particle in part and reach some kind of equilibrium with the pool space between it. If it's been there long enough, you tend to do get that equilibrium. What does that equilibrium look like? It depends on the soil, like the organic content of those soil beds, for example, and that depends on the nature of the compounds themselves. Next slide. So what is a conceptual site model? Well, it's really, that schematic on this slide is a pretty good example of a really well done one. Often they're not graphically so magnificent. But in there we need to look at what are the contaminants of concern? Right, so what are we actually looking for? And we get that from our site history. What is the source and the mechanism of release? So that might be an underground storage tank. It might be an adjacent property and those contaminants are flowing down along the groundwater. It might be the vapours are actually moving along underground services. That's a common one, right? And that can lead to a really large spread of contaminants. So what are the primary and secondary transport mechanisms? What's really driving the movement of those vapours is what we try to work out as part of our conceptual model. In the end, these passive samplers do help us a lot to determine what the lateral and vertical extent of the contamination is. It also provides us with some indication of where those vapours are actually going in terms of what receptors are potentially being exposed to by those vapours. Brent, can you see that? Thanks. Yes. Okay, I've lost a couple of minutes, so I might charge on a little bit. A few things we need to know, okay, to really get this meaningful is what was the activity event and timing associated with the release of the contamination? That is not always easy to find out. We need to try and define our source areas. We need to understand our lithology. So that's the type of soil and geology beneath the site. We want to define the lateral and vertical extent of the impact, and we want to have a go at analyzing the risk, which means we need to know what those concentrations are and what those receptors are. What makes it hard, okay, is that these things tend to be variable, right? And they vary with time, and they're not clearly distributed. It's not a uniform world under there. So we use various high resolution tools to help us to characterize our thought. There's some examples on the left of some downhole imagery. I think it's using the MIFT technology, the MIHPT technology, which provides further information down through the profile to help inform such things. One of the techniques is passive soil vapour, so getting our high resolution data. What does it look like? So this is some examples of beacon sampling. So really what this sort of technology gives you is the ability to put lots of samples in the ground at a much lower cost than using a traditional drill rig, for example. And you leave them there, and you can get some really nice spatial resolution of what those vapours are there. So that's a really powerful tool. And given the nature of the absorbance and the laboratory at the other end, you can really get some interesting speciation data, right? So what do I mean by that? What's actually there? You can have a much broader suite of contaminants analyzed for than you would typically be requesting from your laboratory. So they're a fantastic screening tool when you're looking at those metabolites and things that Brent is so passionate about as those compounds break down. It helps to provide some of that information. But you can see that picture on the right. So that's a pretty high density of sampling locations. And one of the services beacon does provide is they provide back their reports with that sort of data plotted out against your site maps. So it does make life a bit easier for you. Things to keep in mind, right? So these vapours are tricky. They like to vary depending on the time of year. They vary depending on whether you've had a rainfall event. There's all sorts of things that get in the way of vapour being a constant. And we certainly have a lot of technologies for looking at that temporal variability. But it does mean that needs to be thought about when you're thinking about how long to deploy your samplers for. Okay. So if you put them in for a day and pull them out, well, you may not get everything that you would if you leave them in for a couple of weeks. So typically people do leave these sorts of samplers in for longer rather than shorter periods. This schematic just shows an example of how TCE is varying with barometric pressure over a period of time. So once again, vapour concentrations can vary in both the subsurface and indoor air environments due to what we call barometric pumping. Soil moisture is another one, which I've seen a lot of impacts from that. Building ventilations are classic. Okay. So buildings either have a pressurized involvement or they can have a vacuum. Right. So it all gets down to how they ventilate it. And I've certainly worked on projects where the biggest sort of cause of movement of vapours into a structure was the fact that there was a differential in pressure between outside the building and inside the building. And that can be a problem. So there's a few examples of why this can get a little tricky, but it's also a good reason why to use these sort of passive sampling approaches. Let's keep an eye on time. So this one, I really like this slide because we often think, oh, let's characterise our soil. We've done our job. You know, we've contoured it. But I'm not sure how many of you would have been around when we had the Cranburn sort of landfill gas disaster where they had to evacuate a whole lot of homes out there and I triggered a whole lot of new legislation. But what was interesting there that that landfill gas was moving along a whole lot of these structures that wasn't just moving through the soil. In fact, it was quite well bound up in the soil, but it was shooting along a whole bunch of services and things. And those services, of course, are connected up to houses. So they become a really nice conduit for getting vapours up into houses. So a lot of these sort of vapour studies need to consider both subsurface and your indoor air quality, right? So it's good to do both. You understand the source better, but you're also keeping an eye on the receptor because you could do a lot of work and miss the fact that there was vapours coming back into a house through some of its services. I hope that makes sense to everyone. Okay, I think I can skip over that. So a little bit on beacon. How do these things really work? They are very simple as Brent mentioned. So they're small discrete absorbent tubes, which contain a solid sorbent in an inert container. Now that inert container, it's about five centimetres long and you hang it down inside a tube, which you put in the ground by you drill a hole.  The vapor moves through that little cap and interacts with the sorbents that are inside there. When you've finished the period of time that you wanted to deploy it there, you come along, you remove that, package it up and we ship it off to the US where those contaminants are extracted from those absorbents at a very specialised laboratory. It is an incredibly easy thing to deploy very, very quick. The nature of the absorbent means you can sample for a really high range of semi-volatile and volatile compounds. That's probably the real secret source here is that being able to get that very big range and also the sensitivity of the analysis that they do back in the US. They're suitable for indoor and outdoor assessment applications. They provide reliable time-average vapor mass data which can be used to inform on further site characterisation and positioning of vapor bores. So that last comment's worth just mulling over for a moment. These sorts of things are very useful tools. They guide us to then do further works to further characterise. They're a really good part of an assessment process but they're by no means the only part of it. You will need to collect other soil data to get your sort of mass concentration sort of things. This side is fantastic for characterising what contaminants you potentially have there and what contaminants are in the vapor phase. So on the right there, just charging through, you can see a picture of one of these jars. That's what it looks like and you can see the wire around the outside of that. So you want to revel that wire and you use that to hang the vial. It sort of hangs from a bit of foil that you stuff in the top of your soil tube. I think we might skip over that one. How well established is this technology in Australia? Well, very well. It's been around for a long time and it has been utilised a lot on various case studies and audit sites in Australia. This is a CRC report which covers the use of passive samplers and I would strongly recommend that you obtain a copy of that document. It's produced here by the CRC care and it provides a lot of technical guidance on this. Is there anything there? So one important point there is they offer excellent contaminant source mass distribution for low diffusion zones, e.g. in high moisture or low permeability areas. They're also very useful where advection is likely to be limited or can be averaged for the purposes of screening. So those last two points there, they can inform on the location of more quantitative investigations, making inform on the need to conduct further remedial investigations to refine remediation decision process is a really valid one. Often people leap to remediation without enough site characterisation and spend a lot of money which isn't that effective. So these provide that high resolution data to allow us to do a better job. I'll skip over a few of these. I want to get to a couple of case studies. Just before I do, so this just shows you what it's like on site. There's a toolbox there that's full of samplers. Each one of those little vials is the sampling vial. We provide a drill that's used to core the soil and then you put these aluminium tubes into the hole that you've created and then you load those samplers in. It's very little you need to carry around with you to be able to undertake one of these sorts of surveys. So it's a really efficient process over that. Just a couple of case studies. So many things to Gary Hearst. These are actually case studies that he has worked on. So this is a gasworks site in Australia with coal tar. So dense non-aquif phase liquid contaminants and they were trying to delineate better the presence of those Dean Apples. The site was under audit. It had shallow alluvium with an aquatard bedrock at six metres below ground level and groundwater was intersected at four and a half metres below. The dense non-aquif phase liquid impacts in soil and shallow groundwater included benzene and naphthalene considered key volatile organic compounds. So they in this instance they used 40 passive samplers installed some targeted some grid across unsealed areas. So that's worth pondering. Isn't it? Where do you put your samples? Do you spread them out on a grid or do you inform your locations with a site history and better knowledge of where the contaminants are likely to come from? I think you do a bit of both. So when they delineated these source zones, they found some unexpected finds. Okay. They discovered there were some new waste disposal areas. So if you think about it from a remediation point of view, there were areas that they identified using this that they didn't know about at the start of the process. It informed the need for vapor balls at hotspot locations. Okay. So they found some hotspot locations in that data that's contoured on the right. They observed good correlation between the passive samplers, so the beacon samplers, VOC concentrations, when they compared it with the semi-canister samples. Okay. So those two technologies that both covered by Brent, they were getting similar results out of these. So where there were variations noted was where the strata was more permeable. Presumably where strata is more permeable, the semi-canister's got a broader area that it's potentially dragging those vapours from than the passive sampler. But perhaps Brent can chat about that at the end of this. What did they manage to conclude out of this study that the majority of Dean Apple Mass was in groundwater rather than in the unsaturated zone? I don't know if that's necessarily a good news story. Testaments I knew where it was. Second case study. This was an aviation facility in Australia once again also under audit. Consisted of a shallow estuarine sand. Three shallow groundwater, three metres below ground level with an aquatide and six metres below ground level. Chlorinated hydrocarbon impacts, so TCE and TCA and the great degradation products of DCE and vinyl chloride. Some extended dissolved phase plumes were identified, but source areas were not well delineated, only suspected. Due to the limited access, 100 passive samplers were installed across several source areas, all in hard stand operational and access working areas. So sometimes with those sorts of areas, we use vapor pins which allow you to have a sort of stainless steel cover that sits over the holes that you've drilled through. And that creates an area that you can go back to again and again if you want to put more passive samples in over a period of time. So just keep in mind that in some areas, particularly hard stand areas, you don't really want to be leaving a whole lot of holes open across those areas. And that's where you do use things like vapor pins. So out of that study that they did, source zones were identified and the position of vapor boxes were fixed. Firmed up the scope of further high resolution site characterisation to inform the scale of remediation, very important. And it reduced the scale of remediation required, so they ended up saving their client a lot of money. Last case study, Australian case study, that is, some formal textile manufacturer. It was once again an audit site. It had a localised spill of dry cleaning solvent, PCE, over a long period of time. The lateral extent of the source zone was unknown. There were low permeability clays up to 30 metres thick with lenses of cow creek causing perching of PCE pools, creating hotspot vapor sources. Sounds like quite a complicated conceptual model. No impacts to groundwater were that they're aware of. 60 passive samplers were installed, effectively delineated the extent and identified two main spill zones and an external waste area. You can see the configuration on the right. Passive sampler mass deviated significantly from the soil concentration mappings. This is expected given the difficulties in reporting PCE concentrations due to high volatility. So there's a bit of an error creeping into one of those two methods right there. So it's interesting when you get two different sorts of approach to measuring such things. Informed on the use of membrane interface probe and EC mapping of soil texturing to delineate vertical and lateral PCE mass distribution. In other words, what they're saying there was we had a little bit of a look at the MIB data earlier in this presentation. They really needed to bring a lot of things together to get a good feel for where this contamination was. A 3D visualization of the DNAPL source zone was then created. Now I'm going to stop there because we want a bit of time for some questions. And I can see we've got eight in the chat and one in the Q&A.  If you tell people to put it in the Q&A, they will put it in the chat. I've noticed this over time. But before we move to that, just a couple of takeaways on what we've presented so far. I'll have chips with mine. I beg your pardon? I'll have chips with mine. Sorry, Reggie. Good. So soil vapour technology has been used for many years. Brent's been working with it for all of those years. Choose monitoring technologies to match the medium and the application. Okay. So in other words, Brent went through different sorts of ways to collect this data, different devices. They all have their place. Okay. And it's important to get some advice on which one to use when. Ensure the analytical suite that you're getting from the analysis of these passive samples is sufficiently comprehensive to cover the range of volatile contaminants that may be present, including your degradation products. Okay. So sometimes a compound that starts off, you know, TCE is a good example. It will degrade to another one. It's just as bad. But if you're only analyzing for TCE, you're going to miss out on the full story. So that's why we need a broad range of compound analysis. Soil vapour data should not be used on its own. It requires soil matrix mass data as well. And I'd argue also requires some groundwater data if you're dealing with shallow systems. Development of a conceptual site model is not optional. It's essential. Okay. And the more information you have to inform that often means that there's less remediation required. Okay. So you ultimately end up saving your clients a lot of money. Now over to Q&A Brent. I will read out the questions. I'll start with the Q&A button. This question from Keith Osborne. Given the variability of direct soil vapour measurement, is it better to use predictive soil vapour concentrations modelled from groundwater concentrations for what's HHRI? Health hazard risk assessment, is it? Human health. Human health. No. I would argue that the modelling is always, because it's dependent on assumptions about how things behave in soil systems and because soil is so complicated and complex, your model is no better than trying to get some actual measurements of soil gas. It's, in fact, trying to get that latter measurement better will give you the best bang for your buck. Modelling is fraught with all sorts of difficulties and can often lead you up the creek. Remembering also that most modelling tends to be very conservative, but notwithstanding the variation you can see sometimes in your actual monitoring work, if you can really think about what you are actually measuring in situ, you can often get some very good in situ data that is the most useful thing to inform what's going on. Couldn't agree more. In terms of how we can access these webinars, we will send you a link. It's available on our website. If you go to the About Us section on our website, we have a list of all the webinars, and you can click on those and access them there. So just go to the About Us section in Hydrotera. Now I'll shift to the chats. Ooh, lots of questions here. Richard, please share your screen. I've covered that one already. All presentations, can you use the passive data for quantitative human health risk assessment when to not use the information for risk assessment? That is very similar to the one that was in the Q&A. I think the important point about all of these passive samplers is that they actually give very reliable quantitative data. It's not just presence or absence, but that's how I guess these devices began. But the point I made earlier on about equilibrium concentrations is quite important in this case because what you're getting is these devices are calibrated in their development to tell you that if the laboratory gets a particular concentration out of the device, that is within a standard deviation or so of a particular concentration in the vapor phase of the air. So you can use these devices for human health risk assessment. They are actually often more reliable than putting in soil gas pours for a variety of reasons. But you do need to understand what is going on with your particular device. I noticed there was a question very recently. What's the saturation point of your device? That depends on the device and the absorbent you're using. But because it's a... I ended with depend on the analyte you're after, but because it's a key question, the manufacturers of all of these devices provide tables that say, yeah, you can't leave your passive sampler or whatever brand in contact with vapor above this concentration for longer than however long. But provided you are within that range, the result is meaningful and will correlate to the actual conditions in the ground. So how long you leave it there is a big part of it, isn't it, Brent? Yeah, you need to know what you're looking for. You need to get some idea of what the concentration might be. And in many ways, these devices are much easier to do that with than sinking bores and hoping. So the exploratory side of things is often worth doing with these devices as well. But yes, you do need to get some idea of how... what the concentrations that you're going to be hunting for.  So there's a few questions sort of around this theme or comments as one from Matt Taylor here. You know, the temporal variation aspect is a hard one to grasp. How long do you recommend vapour sampling needs to occur to get good temporal data? What's your view on that, Brent? Okay, I mean, that was a great slide that showed, you know, these temporal peaks. But the question is, in terms of risk to people, do they matter? You know, if I was in that space breathing, what determines the actual hazard to me? Is it the peak level? Is it some sort of average or what? And I would argue that a device that measures over a longer period continuously would perhaps give you a more useful answer in that regard than trying to, you know, get a measurement every 10 minutes or whatever in your system. I mean, the only way you could actually get those, those sort of curves, if you don't have the resources that the Americans seem to have, would be to hitch up a gas chromatograph or something to pump the air straight out of the room into the chromatograph. And that's not going to happen. So, yeah, I think the something that takes a longer period and gives you an average figure over that is probably more useful for health risk assessment than the kind of instantaneous reading that Beacons were talking about. So, in terms of instantaneous reading, so what do you mean by that? Like the end of the day, you're deployed over a certain period of time and it reaches an equilibrium over that time. Yeah, I guess the concept of instantaneous is not correct in using a, you know, passive sample, like the Beacons or the Waterloo or Radiolo. But that, in a sense, highlights one of the difficulties of things like some mechanists that even though they do take some time to breathe in, if you like, they're still taking a snapshot of pretty much the moment you open the tap. Thanks for those artifacts there, Brent.  And if you happen to pick a time when you're at the peak or in the trough, it's going to give you a different result. And so, again, it may be more sensible to look at something that takes an average. I think that the difficulty with something like Summers is that the instantaneous reading is actually not as meaningful as the average. And you ask yourself the question, why are we doing this? What do we need to know the concentration in air for, for example? It's usually about the health risk. Is it safe to be in this space? You know, can I live in this room, this house or whatever with this vapour happening? And I'd argue that it's really the average concentration that people are facing. And that the sorts of technologies we've talked about are probably pretty good for that purpose. Okay, it's always the tricky question to answer, isn't it? Yeah. I guess when you've got the Sumer canister and you turn up on site on a day and it happens to be one of those days where we've just seen that temporal graph showing highs and lows. If you turn up and it's low, you're going to be getting a snapshot in low conditions, right? And that could affect how you tie that into your modelling. The other thing that's important with a Sumer is, as you pointed out, that if you attach it to a ground, to a gas bore, for example, it may actually draw air from a much bigger volume underground than your passive detectors will sample. And that needs to be borne in mind, too. I mean, think about how these things work.  Because as soon as you open it and that vacuum starts drawing air out of your target space, that's what it's doing. And so you need to consider what the volume, the effect volume, if you like, that the Sumer canister is. And similarly for your passive devices. But I think the data that Beacon had produced and a number of others, Waterloose in particular, show that those passive devices are particularly good for measuring what's actually in the soil around the device itself. So they're much more targeted than, say, a Sumer canister sucking out of a gas bore in the ground. Yeah, that makes sense. So Bettina Zimmerman has asked what was used to monitor those variations in TCE.  I'm not sure that slide was provided to me by Beacon. So I'll have a look and come back to you on that one. It would be fair to say that virtually all the suppliers have got absorbents that will reliably measure TCE, well, the chlorinated ethanes, because they're so important. So yeah, I don't know the answer to that one, but they all can. And I noticed there was a question for someone about vinyl chloride. And I have to admit that I very rarely see vinyl chloride in my samples, but that's because it's not there rather than whether or not the absorbent picks it up. I just haven't worked on sites with a lot of TCE problems. Someone else may be able to comment on that. So I'm not sure which case study we're referring to now. I'd have to have a look back. We're running out of time, consistency of that. Just a quick one here from Dalwitz. What is the saturation limit for the passive sampler for subsurface sampling? Again, that's one of these bits of data that the manufacturers can tell you, because it is, in a sense, dependent on the particular matrix you're using for your absorbent. And Beacon will have figures. The Waterloo's will have figures, and so will Radiella. And in the Radiella case, it depends on which particular absorbent you use. We can provide those numbers to you. As can most of the labs for the Waterloo's and the Radiella's. Now, last one from Matt Taylor to everyone. I agree. Thanks for the response, Brent. These grab samples evade by representing one moment in time is hard to justify as being representative of the overall risk. And vinyl chloride oxidises so rapidly, it tends to not. Stick around. Thanks for those comments, Matt. Well, thanks very much, everybody, for joining us today. It's been really enjoyable having Brent on board, and many, many thanks to you, Brent, for providing your wisdom. Thanks also to Gary Hurst for those case studies. Really appreciate that, Gary, and hopefully next time we can get you here in person. Great. And let's call it a day. Thanks, Richard. Thanks for the opportunity. It's always good to be talking with you. Right, Brent. See you later. Cheers. See you later. Bye, everybody. Thank you.