 Well, thank you everybody for joining us today. I think we'll get started. It's great to see so many people attending these webinars. We have over 120 registrants, so that's a really impressive level of interest in our topic of the day. Today it's all about groundwater traces and we're lucky to have Frederick Cosmay from Geosyntec consultants to present to us on this topic and I'm sure it will be of interest to many of you. Before we get started, I'll just run through the outline of the day and a few administrative things. So I'm speaking to you now. My name is Richard Campbell. I'm the managing director of HydroTerror. Our presenter today is Frederick Cosmay and he's a principal from Geosyntec consultants. We really appreciate you presenting here today, Fred. And Churi is a field technician with HydroTerror and he's going to be handling the Q&A at the end of the session today. Before we get started, if you have a question and we do love your questions, that's a big part of why we are here today. Please use the Q&A button that's at the top of the screen. That would be excellent. Just put all your comments in there, not in the chat, but in the Q&A and we will endeavour to answer those questions at the end of this webinar. A little summary of reasons why we like to provide these webinars. HydroTerror really believes that knowledge sharing is very important and we like to facilitate it. So today I think it's a great learning experience opportunity from a real specialist in the area of hydrogeology. We also like to facilitate education and I think this is a topic that probably needs more training than we have out there. I know there's a few hydrogeology courses, but not many that would cover the use of traces. So it's one of those topics where education is lagging a bit behind industry need. And finally, we like to take a leadership position in the industry as we develop our marketplace for environmental monitoring. Today's webinar. So Fred's going to cover several things in this presentation today. Firstly, the differences between applied and environmental traces. Secondly, the key principles for applied tracer tests, their applications, future developments of these tests, monitoring technologies utilized and the availability of traces in Australia. Now, within HydroTerror, we obviously have a range of equipment for monitoring and we also do organise from time to time those traces that are used in these tracer tests. So when you're looking to conduct a tracer test, feel free to give us a call and we'll do our best to help you out at that side of things. But I suppose we should introduce the speaker of the day. So what do we know about Frederick Cosmay? Well, Fred started his career as an agricultural engineer training in Brussels. Well, he did his training and then he thought, no, agricultural engineering is not quite for me. So he went on and did geological engineering as well with a major in hydrogeology. Fred then embraced the world of consulting, leaving university in 1999 and really has had a career focused on contaminant hydrogeology since then. I was lucky enough to work with Fred in Golder Associates about 15 years ago, where we were both in the hydrogeology group. And it's a real pleasure to have Fred here to present to you today. Fred's also been heavily involved in the industry working, well, volunteering his time for ALGA. And he was the involved with the founding of the groundwater, fate and transport group within ALGA. He's passionate about nature and his wife is passionate about making cheese. So he spends a lot of time building their local cheese facility up in their company. So without further ado, I will pass over to Fred for our topic of the day, applied groundwater tracing. Another type of aquifer test. Hello, I hope you can hear me or if I haven't received any signal from Hydrotera, that means it's working, which is great. So thank you very much for attending the webinar today and thanks Richard for this lovely introduction. So today I'm going to talk about applied groundwater tracing and hopefully give you a bit of a sense for the possibilities in terms of aquifer tests. Let's see whether technology delivers. It does. So we're going to start with an introduction. And where I will essentially give you a bit of a difference between what I call applied tracers and environmental tracers. Then the bulk of the presentation today is focused on really what I love doing, which is applied tracers. But you can equally achieve similar outcomes using environmental tracers. And there are some pretty amazing specialists in Australia who can do that sort of stuff. So I'm going to concentrate on the applied tracer, just give you some ideas about how to do that with sort of monitoring devices you need or to think about a tracer test. We're going to go through then three main applications and such that you can see some real life example and how to get some really interesting information and useful and practical when you do a tracer test. So there is possibly a bit of a confusion in the industry, but there are two types of tracers. There is the applied tracers, which is essentially what I've done as long as I've been graduated as a hydrogeologist. And these are voluntarily introduced in groundwater. Something that is great about that is we know the quantity and because we know the quantity, it's more controlled. So some example of that you probably may have heard about bromide because it's a relatively conventional applied tracer. And you can also use fluorescent dye, like fluorescent, which is also a very common applied tracer. And then you have the environmental tracers, they are already present in groundwater. And like one of my friends at CSRO says, they are freely available in nature. Unfortunately, there is an unknown quantity of those tracers and therefore it's less control. But an example of that, classically, you've got the major ions, contaminants are great tracers in isotopes. So one of the things you need to ask yourself the question, which is really important in hydrogeology, too, is at what scale do you need to work? Do you want to do an assess a localised zone? Because you've got some de-napple or some napple somewhere. And you want to try to understand how the local zone works. You may want to walk at the side of a plume. Maybe you want to go bigger in a big site. Or you want to walk with a catchment. Obviously, when you introduce voluntarily a tracer, it's groundwater travel relatively slowly. So often you limit it to the scale that you can work on, which is typically more the local zone or the plume zone or the site. You rarely use applied tracers at the catchment scale. But that being said, I've done that in quifters that were pretty permeable, like cast. And then you can truly use that at the catchment scale and it can be great fun too. But always when you design a tracer test, think about the scale. Think about the anticipated velocity of groundwater. Because that's what is going to determine your tracer test. Other considerations, when you do a tracer test, obviously at the end of the day, there is a cost to an answer that you are trying to a question that you're trying to answer. And that question is a price and especially any sensor in particular. There are obviously side constraints that you need to think about. The build environment, some of the existing wells, etc. The aquifer conditions, of course, that determine the hydrodynamic of the aquifer. Detection limits are a pretty important component because it's really affecting your ability to detect a tracer. Whether you want some laboratory or field analysis, some sampling methods, you may want, I mean, you would want to look at the background concentrations, even with some of the fluorescence dye, some organic matter, certain contaminants can fluoresce and can interfere with your tracer test. It's always good to have a strong quality assurance, quality control protocol, and some idea of the spatial and temporal distribution of whatever you're trying to understand. And so, as someone says often to me, which I'm repeating here, it's important to begin with the end in mind and ultimately come up with a hypothesis to design your data collection. A lot of things that we do as practitioners is just trying to come up with a hypothesis and we test that hypothesis and hopefully you will understand why it's important further in the presentation that it's almost a discipline that you need to acquire when you do tracer tests in particular. So, applied tracers, so we're going to go through some key principles and how to basically do some tracer tests. Then we'll go and talk about three case studies. The first one is really what got me into tracer tests and it's called protection zone. Another one about groundwater recharge, which is a really nice story. Then we'll talk a little bit about effective porosity using an example very close to all part of the world in the western suburbs of Melbourne, then some conclusion and future development. So, what's the basic idea? Well, essentially you dissolve an own quantity of tracer in water and you introduce the solution into an aquifer via typically an injection well. But you don't have to limit yourself to that. You can do that into a sinkhole, that's pretty fun. A subsurface vault, a pond, a dam, ultimately anything that can get you to the system. You can also do that through the unsaturated zone, but it will possibly slow down and complicate your tracer tests so you may want to steer away from that. And then what you do is you monitor the changes in tracer concentration to obtain breakthrough curves, which is the little nice graph that you have here on the left hand side. With on the one hand the concentration in tracer with the time that you, the time since injection that you monitor in a particular portion of the system. In practice, it seems easy, but tracer tests methodology can be quite sophisticated. And you will see that some of the results can be highly dependent upon the adopted methodology. And sometimes, and maybe it's something you need to really think about, sometimes it seems too easy. And I think part of the reason, some of the tracer techniques, I think in Australia, have lost some of the interest, which is as early as the 70s and 80s, was essentially having probably the notion that it was too easy. You chuck a tracer somewhere and you hope for the best. And nothing happened. You don't find a tracer. It disappears and you don't necessarily achieve what you want to achieve, which is not really your outcome that you want to reach when you do a tracer test. You want to actually prove your hypothesis and you want to verify something. So the three main types of tracers for your information. The one that is probably more conventional and older is our salts. Analysis of salts is pretty conventional, but it has a higher detection limit. Think about 10 to 100 microgram per liter. Background is high, especially in some of our aquifers in Southeast Australia, being quite saline. And you can need quite a bit of salt to do a tracer test in the order of a few kilos sometimes, which can bring some issues about the toxicity due to the excess that you need to bring. What I love are the fluorescent dyes here in the middle. Because they have a very low detection limit, it can be as low as 0.001 microgram per liter. Yeah, sure. You need to address some background and interferences. Something I really want to stress on and one of the examples will support that. They are in a cruise, right? There are some publications that support that. And you will see in one of the examples, the context where it's used and hopefully it will make you a little more comfortable. And then you've got some of the nano-tracers. You even have bacteria and viruses. That happens. The analysis is a little more unconventional. It's really specific and it requires some risk assessments. So I wouldn't, you know, it's not for your information that you know that it's there, but it's not really the mainstream of tracer test. So how did you... So here are some of the great detection limits, typical of some of the fluorescent tracer tests. Here at the top you've got fluorescein. That's the reason why it's pretty popular. It's because it's got one of the lowest detection limits, 0.002. Then you've got sulforodamine, 0.06, somiozine, tinnopole. I like amino acid because that one is transparent. And so you don't see that and there's some advantages associated with that. Then a few other ones. Way to do a tracer test, but don't necessarily constrain yourself to very sophisticated monitoring. You can obviously detect that just visually, which, you know, in certain circumstances would be good enough. You have some fluoroscope, but then you can really get into the lower detection limit by using field fluorometer, which we will see what that can offer through a tracer test. You can use a spectrophotometer in your laboratory. And if you really need to achieve low detection limits, you've got active charcoal where you really literally filter your water and then you get the charcoal, which is really a granular activated carbon tested. So one of my favorite tool, the Gatshit, which is the high precision fluorometer. As you can see, it looks like a data logger. And it's designed to be placed inside groundwater monitoring wells. It's equipped with a data logger and a telemetry system. And it tests tracer specific sensors that provide the possibility to test up to three different dyes at the same time and conduct multiple tracer tests. So that's not necessarily very new. The first types of these fluorometer are dating nearly 20 years ago. They start to be more and more, I mean, multiple providers. This is just an example. They are orders. We can always talk about that if you have some interest. There are some of those in Australia, which can be rented. And so that obviously cuts down on the time you need to sample overnight because the tracer does that and the cost to do the lab testing. So here is the first example of tracer test, which is essentially where I've got into tracer test. You've probably heard from my accent that I wasn't born in Australia. And something important is that many European countries rely heavily on groundwater for their pot table water supply. Some areas are densely populated and there is a need to define protection zones inside which activities are regulated or prohibited. And it's got to a point where when there is an accident that occurs there is also a need to predict contaminant migration and support logistics of intervention. So in most EU countries, protection zones are typically defined using fluorescent dye tracers because they have this ability to quantify the effective porosity. Some of the hydrows amongst you might recognize this equation where groundwater velocity is the product between the hydraulic conductivity, the hydraulic gradient divided by the effective porosity. Really wanted to focus on the fact that these fluorescent dyes are used in zones where people are drinking the water from that aquifer. So if there was really some issue about toxicity, I would have thought the European would have known about that but there is more literature that demonstrate that it's not a problem then so why not using them? This is a tracer tested. I had some involvement quite early in my career. This image show an alluvial aquifer as you can see. It's pretty much gravel and relatively homogeneous. The layer here at that particular site, which was a groundwater extraction station for potable water, was about seven meters thick, some pretty high transmissivity somewhere between 10 to the minus four and 10 to the minus one square meter per second. Pretty high especially. And something important is the average storage coefficient by doing a range of long-term pump test was around 0.1. If you remember there is a rule of thumb that for unconfined aquifer you assume that the storage coefficient is essentially the drainable porosity of the aquifer and therefore it's equivalent to the effective porosity. And that's so you try to calculate your own water velocity and you try to define your protection zone around that. What was interesting here is we did a number of tests at that site with different tracers at increasing distances from the pumping well. We injected tracers and then essentially the exercise is almost like a pumping test. You've got a breakthrough curve and you try to fit that with a software and there are different softwares and you try to calibrate your breakthrough curve against some form of model with different parameters, which helps you to derive in this case the effective porosity that is then based to define how far you need to go to protect the zone around the water supply well. What you can see already here is remember the specific yield was around 0.1 and so 10% and here you've got an effective porosity that is lower and that is nearly sometimes a factor of 2 lower than that, which means because it's inversely proportional to the velocity, it means that in those cases if you use the specific yield to do your prediction you're going to underestimate the velocity to travel time to the way. So it's pretty important to try to get that right. So why essentially this is sort of repeating what I've said, but why is that the case and why do we have a lower effective porosity that is below the specific yield because you think well the contaminants should travel through the whole drainable porosity. That's actually not the case because the contamination will follow the path of these resistance and so it will really follow the highways the more effective portion of the aquifer and therefore the specific yield is more about parameter than something that you can use to do some prediction and some of you hopefully have done some numerical modeling and have realized that maybe there is some improvement to bring when you do numerical model to possibly reassess the effective porosity for some of the calculation and fate and transport. That's obviously an aquifer, it's a porous aquifer, this is even more pronounced in fractured rock. For example, effective porosities as low as 0.03% have been measured in limestone, so think about that when you do a tracer test, think about that when you do a fate and transport modeling and you assume a 30% effective porosity. I'd be happy to try do with you that it can be as low as 10% if not less even in porous medium. That case study is some tracer testing on saturated zone and the little picture here is actually a vanyard in champagne, so that's where you cultivate the grapes for champagne. But what is fun about limestone, which we see in some way not very different to other media like basalt in Victoria, it's a dual porosity medium, so you've got fracture and matrix. That is used pretty extensively also in the EU, especially in the UK, not with the EU to exactly for a potable supply. And a key factor of that is vulnerability because especially the migration of nitrogen and pesticides resulting from agricultural activities through the unsaturated zone. So at the time there was a need to better predict the recharge mechanism and integrate that into the vulnerability element. So when that was the job that I did to support a PhD student at the time, but a PhD student now is a professor of hydrogeology who is still a really good friend of mine. And we had that really great site where we had a number of monitoring well screened in different parts of the unsaturated zone and then we had a groundwater extraction well which was pumping groundwater. And so we did two tests using one piece of meter that injecting the tracer in a monitoring well that had a distance of a vertical distance of 10 meter between the monitoring well in the unsaturated zone and the pumping well. But we did two tests. The first test, making a round with my arrow, the first test involved salt and the mass injected was around 100 kilo. That was mixed in a volume of 300 liter. But what we did here we put, essentially we put the hose down into the monitoring well and that represented about a shaser, about 300 liter per hour. That led to this breakthrough curve where essentially the tracer arrived in the pumping well through the unsaturated zone. We started to get the first arrival after five hours and we had the peak after 11 hours. So we're pretty happy. Pretty quick response. And then the second part of the PhD thesis started where the second test involved the lower mass 10 kilo. The volume injected was a lot lower, 30 liter. And in this case, we didn't put any shaser. So it just naturally migrated through the unsaturated zone without some support. And what was interesting for the exact same test setting, but different injection circumstances, we only started to get information and detection on the breakthrough curve after about one year. And essentially, it took nearly three years to get to the peak. And by that time, our PhD student had to finish his master thesis. So he was quite happy that he was there, but it took quite a long time. So why is that the case? Well, essentially, in the first case, when we put a hose down the monitoring well, we literally saturated the unsaturated zone. But it's like we had an intensive rain which used the active fractures to quickly migrate the tracer across the unsaturated zone. The second case was more the one representative of a natural recharge where the water went first through the matrix blocks. And the fractures were not really driving the transport of the tracer. And so that was a really interesting experience because usually you think about recharge, people think, okay, well, it takes about a meter for the recharge front to move. And it's actually not the case. Depending on the pattern, the groundwater contamination can migrate a lot quicker and have some very different impact to the aquifer and the groundwater table. And I'm sure we will discover that more and more at the moment because that's exactly what's happening with PFAS because PFAS can also, you know, it gets released in smaller quantities. And I'm sure that it follows some of the rainfall pattern with some of the extra complication that PFAS likes to stick at the top of the saturated zone. But that's another story. This is a test that we did in the fractured basalt in the western suburb of Melbourne. I wanted to acknowledge my former colleagues from Golder, now WSB, in supporting this test. And they're actually an NCT who have that that furometer. And so if you're interested, I'm sure they can give you some contact and they can help you doing that. But what we wanted to do is demonstrate that we can do some of these tests in Australia. What that was was a regularly conversion test in fractured basalt. So pretty similar to the same, the first experiment where we had extraction wells and we injected the tracer in a monitoring well within the zone of influence from that extraction well. That was in the context of a hydraulic containment system. We injected only 27 grams of fluorescein, so not a lot of quantity, which proves that if you would have had to do that with salt, we would probably have to use maybe 10, 15 kilos, something like that. And we recovered that in the extraction well located at a distance of 17 meter away. The extraction rate was 1.6 litre a second. We had some contaminants that had fluorescein properties. So we had to accommodate for that in our approach and the design of the tracer. Here is the lovely breakthrough curve. We had the first arrival after six hours. The peak concentration arrival was in 40 hours. And we money-taught the tracer for about 16 days. So when you think about cost, we produced that with some data loggers. It's actually pretty cost-effective. It's just, it's two weeks of a data logger. A few grams of fluorescein. And what we were able to demonstrate in this case, we found that the effective fracture porosity of the basalt was around 1.3 percent, which proves that yes, in fracture drops, we can have some pretty low effective porosities. And that is probably some, that also means that there is a matrix porosity in basalt that is there definitely. And that plays a role as a storage zone for the contamination. But also think about if you do, you want to do some bioremediation or some relay on injection to try to get an idea of how much amendment you need in the ground, you're going to need a good estimate of the fractured porosity. And this is one of the best way to do that. So we went through the three examples. Hopefully you have realized by now that it's actually another toolbox to test aquifers. It's pretty versatile. There is nearly an infinite number of approaches. As I said, there is this importance of developing a hypothesis to be tested. I've honestly showed some traces that went wrong, but a lot of the ones that didn't is because the conceptual site model wasn't necessarily robust. And the tracer were in a different direction to what it was supposed to be. So if you do a tracer test, make sure you are happy with your tracer, your CSM, or be open to what we call the tracer truth. And then designing an applied tracer test is really about refining these hypotheses and bringing all these considerations about the design, especially in the injection approach, the tracer choice, the tracer monitoring, and the QHUC. I would just want to finish off, and that will give us plenty of time for the question, with some future development about tracers. One that I am particularly fond of is called resazarin. Resazarin is a fluorescent dye tracer that changes its fluorescent properties according to the redox potential. So when it gets in oxidizing condition, it has certain properties. When it gets in reducing condition, it changes to other properties, and you can really differentiate these conditions using that sort of tracer. It's been used to assess groundwater-surface water interaction. In particular, you've got to realize that the layer where there is interaction between groundwater and surface water is actually a zone that is highly reactive with lots of bacteria. And therefore, you've got often a gradient of strong redox, different redox condition, and it's been used to try to map that out. But I can see how that could be used to help other applications when you think about bioremediation or natural attenuation, and you want to quantify a little more some of that within your aquifer. That's it. So I think I will hand over to Richard and Nisteam, and I'll be more than happy to answer any questions. Well, thanks Fred for that excellent presentation. I think there's a lot of great information, and I'm sure the audience really appreciated what you had to say there today. From my perspective, there's a few things that I would like to mention in terms of key takeaways from today. Now, often as hydrogeologists, we create these conceptual models of sites. But in the end, sometimes we just need to really have a definitive answer of whether or not there is actually a flow path where we think there's one. We make a lot of assumptions as hydrogeologists and tracertests are one of the few truly definitive ways of determining whether or not there is actually a flow path there. So I think it's a great way to determine that. Second thing is be brave. A lot of people get a bit scared off with tracertests. I find injecting dyes into the ground and things like that. But be brave because they are worth doing and they are a very robust way of determining some things about groundwater flow paths. Finally, they're actually pretty cost-effective. So you think about all the other things we do in terms of characterising groundwater, like numerical modeling, that sort of things. I mean, they're a very practical way to determine quite a lot. So give them a go, I say. So without further ado, I'm sure you've got plenty of questions. Churi's going to run you through those questions with Fred and hopefully we can answer those questions for you today. If we can't, we will take them on notice and do our best to get back to you as quickly as possible. Without further ado, over to you, Churi. All right. Thank you very much, Richard. And thank you very much, Fred. That was very interesting. And there's a couple of questions here. There's a few comments in the chat from Claire, from Gareth, and Stephen, Mike. They're all saying thank you very much. Excellent presentation. They learned a lot. There is a question here from Mike asking, are all of the active tracer tests required to have an EPA approval? Well, I think that that's a really good idea. I'm just not sure the start of the conversation needs to be with the EPA. My understanding is the water authorities, if actually your authority to protect their groundwater resources associated with the ball construction license and that sort of stuff. So they would be the one I would tend to reach out first, depending on the circumstances, of course, and then bring EPA along. In some ways, but I think things have changed in terms of there has been a change in guidelines for the injection of remediation chemical. You could somehow look at that in a similar way. And what that means is EPA is not really involved in an approval process. They want to make sure that you comply with the guidelines. Depending on the stakeholders and auditors, you may want to get them involved in the support and then just make sure you have the authority across that. But I have a discussion with EPA. We went to present that there was a strong interest in doing these sorts of tests. And so there is enough literature to demonstrate that they are in your course. I hope that answers that question. And there's also a kind of follow along on that question. There's another one from Yelaine. Yelaine, sorry about the pronunciation of your name. She also says, thank you very much for this presentation. And they're also wondering what is your experience with regulatory approval in Australia for these tracers? I know you just covered that briefly. But is there anything more specific you can add to that? Look, I think at the end of today, it varies. But I think the main point of start is it's also a matter of discussing with the relevant stakeholders and then identify who these stakeholders are. And then because in some circumstances they may not necessarily need to have regulatory approval. And it's just making sure we're doing the right thing. Right. But I've done some tracer tests in South Australia. For that particular site, we didn't necessarily need to go to the regulator. But we presented the tracer test afterwards and then we're pretty happy to have that as a pretty strong line of evidence. So look, I would be saying, yes, let's make sure that everyone is on board. Let's make sure that we have the right approvals. But let's also be conscious that the risk is also limited. And what is the benefit that you get out of a tracer test versus leaving some contamination there with a very poor knowledge about how it impacts some receptors? And I think perhaps, I mean, that's a debate and that depends on what the other questions are. But I think we need to, in our industry, we also need, in some ways, we are a bit like doctors of human nature and we need to perform surgery. And when you do something like that, well, there are consequences in what you're doing. But it's still about trying to do the right thing. And does the surgeon always need to get approval from his regulator to perform surgery? I think it depends on some of the cases. But I think we also practitioner us and we need to, it's really about doing the right thing and making sure the stakeholders are on board. All righty. A couple of technical questions here. Is a typical injection bore a 50 mil bore usually? Yeah, Luca, I think that that seems about right. You can do that with smaller balls. I think the big question is how it's not so much about the typical injection bore. To me, it's about how do you want to deliver the tracer? And there are two ways. Either you have a very short, lived pulse that you want to deliver, which is what we did in the third example. Or do you want to deliver a relatively constant flow of tracer? And then think about that in terms of what you're trying to achieve. When you do the more classical one is just a pulse. For that, at the end of the day, it's really about mixing the tracer with the right volume. You really think about the well volume. And you try to have a shazer that is enough to make sure that it's pushing the well volume out of the aquifer. That's really more important. Then obviously, there is some consideration around connectivity with the bore. But hopefully, if you're a good hydrogeologist, you have well developed your well. You've even done that with a baler. You've done that possibly with a bit of a lift such that you are sure that it's actually going in the formation. All right. Another question. With the various case studies that you talked about, do you think that any of these would have also benefited from using environmental tracer methods in combination with the applied tracers? Yes. More data is always fun. Let me think about each of them. I'm just not sure with the first case and the second case whether you want to have some precision about the effective porosity. Because in the first case, it's really about defining your protection zone, so your transfer time. And in the third case, it's really about the effective porosity. And therefore, potentially if it's remediation, the quantity of amendment you want to inject. And precision means not to have too many in the equation. And having a known quantity makes a big difference. In the context of the third one, I think there would have been some merit in doing that. And I think it's been done elsewhere. And then look, I mean, it's also a question of cost. And how much you want to do that? What I often find is environmental tracer can become quite expensive when you start to think about isotopes. If you rely on salts and major iron, that's obviously cheap. But the price per sample can become relatively quickly cost prohibitive. So it's possible, but it depends on how much it comes back to the big question at the start. What is the price of the answer that you're trying to provide? Alrighty, thank you. And more specific questions. What is the brand model of the fluorometer that you showed in your presentation? That's a really good question. Well, I'm not sure. On the top of my head, I know the brand. Maybe you may want to reach out to be after the call, so the details are shared. But there are several brands. And there are more and more. There is one that I I'm watching on LinkedIn. It's a Belgian firm from the French-speaking part of Belgium. He's a really young guy. He's in his 30s and invented a pretty nice type of fluorometer that is even better than the one I've showed. He's not selling them. He's renting them. But he's got a service associated with that. So yeah, sorry for not answering that question right away. But in some ways, I think it's also important to me. It's part of the design. It's good to be aware of the different monitoring devices in the pros and cons, because that can also affect your cup. So Perchance, was it a, hold on a minute. Let's see. Mike mentioned specifically an Abalia FL24. I think that might be that. Yes. Well spotted, Mike. But there are some changes in ownership for that one. And it may not necessarily be, may no longer be available through that particular supplier. So it's also rapidly evolving Abalia. A couple more questions here. One question is, missed the injection rate for the Golder example, that the breakthrough is quite quick. Do you recall the injection rate there? There wasn't really an injection rate. So that was a, it's called DRAC, which is a near instantaneous injection. So pretty much it was based on the volume of, within the well, and how to displace that volume. That was it. Nothing really fancy. How useful are tracer tests for determining whether groundwater is discharging to a surface water body? It's from Steven. That's a really good question, Steven. Thanks for asking that one. Look, they are useful, but it can be also, you know, you need to have a pretty good idea of what your discharge zone or discharge point is. And that takes a lot of work in itself. And so it's possible. I've done that, but there is a lot of upfront work in understanding the CSM. That was an example where also, I'm also very mindful not to ask to, you know, a number of cases that I have, they ultimately belong to cuts. But so, but one example that that I've done to try to help with that was not, was there is actually a tracer technique that you can use that we've used to assess the behavior. No, sorry. I want to be too. So, yeah, so essentially it's possible, but you need to have a pretty clear idea about where the discharge point is. Or you have different hypotheses and then you may want to use a number of a fluorometer at those locations. That being said, if you're in that situation, you would want to use some of the cheap major irons and TDS and whatnot approaches beforehand. And then the tracer test becomes the ultimate verification of the hypothesis that you have developed with multiple lines of evidence. That's probably a better way to look at that. Now, no, the other thing I wanted to say is often in Australia, because all of our CDs are along the coast, the aquifers are tidally influenced, which makes things a little more complicated. But a technique that we've used to help bringing more lines of evidence is and using tracers is there is a technique that consists of treat feeding a well with a tracer. And that tracer is going to be diluted by the through flow through the well screen. And so if you're able to measure the concentration of the tracer within the well that is being drip fed, it's a direct measurement of the groundwater velocity. And that varies as the title changes. And then depending on how close it is from the discharge point, it can have a specific response. And we've done that on a transit to try to better understand where the discharge point was. And it just in this case, the discharge point was a little was not at the end of the transit. It was somewhere in the middle, because there was a particular feature that that acted as a preferential pathway. So that was a long answer, but I hope it generally answers your question. And I'd be more than happy to discuss that with you for lunch at some point. All right, and then we've got one final question from Giuseppe says, Hi, Fred, what would be the ideal ground coverage, i.e. plant spacing per square meter, ideal to improve water retention or increase field capacity in a state like Victoria with approximately 500 millimeters of rain per year? I'm not sure I understand the whole question. So can you repeat that? So if you have 500 millimeter of rain per year, what would be the ideal ground coverage of plants, I would assume, to improve water retention or increase field capacity? Oh, look, I think, I mean, I think at the end of the day, I'm not sure whether you would want to engineer groundwater recharge naturally, you can do that. But if you rely on a natural coverage, I think to me, it's to try to rely on a diverse vegetative cover, because ultimately plants helps improving the retention, but also cleaning the water before it gets to groundwater. It's a very interesting question because it almost begs the question, can we engineer a mother nature? And I'd be saying, well, no, mother nature is probably a better environmental engineer than us. And so I would more rely on observing that particular location, try to assess what would be the best cover naturally with some experiment and try to enhance what happens naturally, based on these experiments, rather than coming with a rule of thumb and hoping that we would make the world better, because that's a little bit, I think we are preempting a bit too much overall on this planet if we do that. All right. Well, I think that should conclude this wonderful presentation. Very informative. Thank you again, Fred. I enjoyed that a lot. And I hope everybody else that attended enjoyed that too. And everybody who asked questions, thank you very much. And hopefully you got some good answers. So once again, thank you very much, Fred. And thank you everybody for attending. Have a good weekend. Thank you. And don't hesitate to reach out if you've got more questions. I love to talk about, I love to talk and I love to talk about races.