 Well, thank you everyone for joining us here today at Hydratera for another one of our webinar series. I really appreciate so many people attending. We're very excited about the attendance levels we've been getting. Today, we have a topic, groundwater level and pressure monitoring systems. This is an area where Hydratera does a lot of work. We provide a lot of instrumentation and we do a lot of installations and services. Today, we're joined by Steve Cody, who will be co-presenting with myself. Steve's recently joined Hydratera as our principal instrumentation technology person. Probably used the wrong word there. Steve comes with a wealth of experience. I will formally introduce him shortly. Today's session is all about groundwater level monitoring. A little bit about Steve. Steve started his career as an instrumentation technician working on things like atomic absorption spectrometers. Then he joined a company which was called MinData, which was a leader in this day in the surface water monitoring technology space. And really went from strength to strength there in terms of environmental monitoring experience from there. He's travelled the world. He's done weather station installations in India. He's done a lot of work in the mining sector. He worked a lot with what was coffee at the time. And now Tetra Tech in terms of in their monitoring group, which specialised in doing a lot of work in geotechnical and environmental monitoring systems installations. We're very excited to have Steve joining the Hydratera team. We're even more excited to have him helping on this webinar today. Thanks very much, Steve, for joining us. Thank you. Before we charge into the webinar, a few things that we need to talk about. So there's a Q&A button at the top of your screen. We love getting your questions. And also a big thank you to those who actually sent through questions prior to this webinar. That's a first for us. So we'll have to do our best to leave some time to address those questions too. But it was great to see those questions come through. So you just click on that Q&A button and type your questions in there. That would be great. Thank you. Why does Hydratera do these webinars? Well, we're quite passionate about sharing knowledge. And look, we do accumulate a huge amount of knowledge from our various supplies, technology people from around the world. And we do see our role as facilitating knowledge in the various technologies and how they can be applied. Secondly, we like to, we are quite passionate about training and educating the industry. And thirdly, it allows us to communicate to your changes in technology and take a leadership role in this sector. All right. So into the nub of it all. So today, I will be talking to you about continuous groundwater level monitoring, determining your monitoring requirements. Also be talking to you about some QAQC around that monitoring side of things and also a bit about how to report your groundwater level data. Then Steve Cody will be talking to you about all things technology. So he'll be providing you with a bit of a guide to selecting groundwater level monitoring technology and telemetry options. Finally, we will finish up with Q&A. So without further ado, I will charge in. So in terms of the essential components of your groundwater level monitoring program, often people ring us up and they leap straight to, I need a level logger or that sort of thing. But often when you dig a bit, you realise they haven't really mapped out all their considerations before they've rung us up and it does influence what you should use. But it's really important that you do think through a variety of things. So some of them I've listed down here today. So what parameters to be measured? Sometimes people ring up and they think they want level and by the end of the conversation, they are also wanting temperature and conductivity, for example. So it's good to think about that. You need to think about how many locations. So sometimes people want to monitor 40 wells, but they've only got a budget for 20. So it's important to think a bit about what are the critical wells before we go too far because you're better off to have good data from less wells sometimes rather than trying to spread your money too thin. When? So the frequency of measurement is very important. Frequency influences a whole lot of technology selection issues for us. In particular around battery and whether you have data loggers down holes and things like that. So it's important to have thought through how rapidly you really need to measure. And that obviously depends on the application. I'll talk a little bit more about that shortly. Then we get to the how and this is where we need to try and first select the method. What do I mean by method? A method will be something like using pressure transducers as distinct from using say a bubbler or using a sonic technology. So we need to just settle on a method. And that's a fair bit involved in choosing a method. Once we've settled on the method, we can really start looking at the technology types and ultimately select an equipment model. And within any sort of subcategory of that, Hydrotera often has 20 or 30 or more models to choose from. So there's another whole level of selection that follows from that. Best practice means you have your SOPs and your technical work instructions and your measurement methods and your data reporting all mapped out, aligned with those technologies that you've chosen. It's an incredible amount of rigor to reach that level, but that is what best practice looks like. So these are all things to consider when you're starting to plan your groundwater monitoring. Now, there's some really good guidance out there which doesn't cost you anything and that the Bureau of Meteorology did put this stuff together. So I do my best to promote it because I think it's a great resource. So there's this national industry guideline for hydrometric monitoring. And in there they have lovely figures like the one we've got here on the right, which they also have a lot of guidance about information that you should be collecting as part of your groundwater monitoring systems when you're setting them up, for example. But some terminology here and some things here are really important in the context of before you choose your instruments. Good to remember that groundwater level is a relative level and therefore at some point you need to be tying that level to a datum. So surveying is something that sometimes people forget to do when they're associated with their monitoring sites. It's very important to have survey data to allow you to plot up your relative levels. Natural surface elevation is also handy. A lot of people like to report in depth below ground surface so you need to know your length of stand pipe that's sticking up above ground surface. So depth to ground water from reference point. Most common form of reporting is meters below top of casing. And that's from the top of your casing, or some people do it from the edge of their monument. But what's really important when you set your site up is that you have actually marked where you're taking those measurements from. Otherwise some people might assume it's from top of casing and some from top of monument. All of these things we've seen before. So there's some of the things to make sure you have in place to make best use of your data when you collect it. You also need to know what your well construction records are because your screen depth is obviously the key determinant on where your water level is going to be rising up to. I'm going to skip over that one. Monitoring frequencies. So I found this interesting report on the internet from the USGS about some considerations in terms of groundwater monitoring frequency. And when we're looking at monitoring of natural systems like catchments and that sort of thing, there's a few variables to take into account. So if you're dealing with a shallow aquifer, you've got a higher frequency of movement to get from a rainfall again to get a fairly reasonably rapid recharge of an aquifer that's in a water table aquifer, for example. So you might want to be picking up those variants in water level. So in which case that will start to determine the frequency of measurement you want to pick up. I've done projects where we've measured at like three minute interval because we're looking at strange diurnal fluctuations that occur in the water table, for example. So it's important to think about the processes you're trying to identify on the side. Groundwater flow and recharge rate. If you're trying to determine your recharge rates, you're looking at a relationship between the timing of a rainfall event and the response in the groundwater. So you need to be monitoring at a higher frequency to pick that up. Obviously, if it's rapidly recharging, we need to monitor more closely. Just got to move. Can't actually see a nice slide. There we go. Aquifer development, if you're looking at a pumping test and you've got rapid drawdown in response to that pumping test, you obviously need to be measuring at a really high frequency. Often people get into a bit of strife here where they might set a linear, a fixed interval, fixed frequency of measurement on their level loggers, for example. But realistically drawdown follows more of a logarithmic sort of pattern. So you really want to be measuring very quickly at the first part. So setting your level loggers up at a really high frequency. And some of the loggers, like so on, has a logarithmic function where you can pick that to select that. So you're getting a much higher reading frequency at the early stage of the drawdown that's induced by your pumping. Finally, climatic conditions. Obviously some parts of the world, it never rains. And there's not a lot of point in having a really rapid measurement frequency. Daily is more than enough in quite a lot of areas. For example, if you need to think about other areas, obviously very different. And if you're near streams and looking at groundwater surface water interaction, you need to make sure you're setting a frequency that's going to allow you to pick up not only stream level, but also groundwater level fluctuation in response to those changes. So you need a fairly high frequency in those sorts of situations. Hope that all makes sense. I might skip over this because I'm conscious that Steve's got quite a lot to present on. I think I've covered most of that in what I just said. I did want to talk about frequency of monitoring in the context of industrial facilities. I've just been talking about natural system like a catchment. But industrial facilities have a whole other set of things describing what frequency you set your groundwater level monitoring data at or lead shape level for that matter too. The first one is always have a look at your compliance monitoring requirements. So you have these approved monitoring plans, which are really what your facility needs to comply with. And so they often specify a frequency in them. And that frequency has to be complied with. So always check that when you're planning on what sort of technology to get because you might get a shock that your battery runs out if you're trying to measure something at a higher frequency than it can cope with, for example. So the sorts of compliance levels that come up around landfills, for example, which is what this example is, we're installing a lot of automated groundwater monitoring level systems for measuring lead shape depth on liners as a compliance criteria of not more than 30 millimetres on top of your liner. So it's important to make sure we can monitor that lead shape doesn't tend to move that rapidly except in response to pumping. And it's important to know that the pumping side of things is working. The second one that comes up quite a bit is more for monitoring of surface water, so lead shape level in your lead shape ponds. So there's typically a regulated freeboard amount. What's freeboard? It's the amount of wall left before it overflows, right? So you want to have a reasonable buffer there, otherwise we'll have lead shape flowing out. So we call that freeboard. And you can set up pressure transducers and other devices to measure the levels of those ponds. But the other one to think about, which is really important, is operational monitoring. So this typically requires a much higher frequency of monitoring than compliance monitoring. And that's because there's machines that turn on and off and respond to it. So automated pumps, for example, on groundwater dewatering, lead shape sumps, all of those sorts of things, and lead shape pond pumps, et cetera. Really important that you understand the responsiveness you need out of your monitoring system. Like for some systems, you might set up and say, I only need to send data out on a 15-minute basis. But if it's connected to a pump, we actually want something very direct, right? And so often we use a different sort of comms connected to these sensors than we would for, say, compliance monitoring, because you actually want a direct connection through. So it might be hooking straight into a SCADA system, or it might be going via radio and then continuously transmitting comms to allow for a very rapid switching on and off. So when you're thinking about why you're monitoring, you start to think about the frequency that you need to measure at. So I just wanted to go on about that a bit today. I hope that makes sense. One last thing is with the new EPA Act in, well, not quite so in you anymore, in Victoria, there's a real linkage between operational and compliance. It's emerging because you need to be sort of operating to your most efficient, right? I can't remember the exact words I used, but essentially that's what it means. And that means that really it's about us getting better and better at the operational side of things. What would that mean in terms of a landfill lead shape scenario, minimizing the time that you had lead shape pondered on your liner, for example. So optimizing your pumping frequency, for example. All right. So quality assurance around groundwater data. In my experience, people are pretty good at buying pressure transducers from Hydrotera. And thank you very much for doing that. Obviously, I appreciate it. But often they sort of aren't so strong on the QAQC around making sure they can keep track of what those numbers really mean when they download them. So a couple of things that I really came to communicate across today. So when you do get continuous monitoring data, she should be spot checking it regularly against a manual data. And that's manual data dipped with a tape. Okay. So we'll always have a check measurement. That allows us to keep an eye on things like what we call sensor drift, where the sensor might be slowly but surely measuring incorrectly. Well, sometimes sensor drift is actually not caused by the sensor at all. Sometimes it's what it's hanging from can be stretching. So you can get these errors that come in. So really important to have regular manual dip measurements. And there's some guidance in this national industry document that I've got a picture of there from the Bureau of Matrology around the frequency of check measurements. Okay. Also always refer to the manufacturer's manuals. The other big thing I've been seeing is that people will deploy a sensor and assume it's going to work forever. You know, it's, they might deploy, come back in 12 months, download the data. And it may not be everything they wanted, you know, they, you can get all sorts of things that clog up the holes in pressure transducers and that sort of thing. So it's good to be keeping an eye on the data on a pretty frequent basis. So the manuals that the various suppliers have are often really, really good, really comprehensive. And in there they will have recommended maintenance regimes a lot of the time. If they don't feel free to give us a call. Make sure you keep those spot check measurement records and sometimes the software of the loggers allow you to actually type that in there. So you've got a record there. Sometimes in tele-limited systems there's a spot to put a manual spot measurement as well. It's really important to keep those records. Next one is non-vented pressure sensors. So quite often people ring up and they want to buy a pressure transducer and I say, I'd like a non-vented one things. And then we start the discussion about, well, you'll need a baro logger for that, for barometric compensation. And I'll say, oh, do I really need that? Well, the answer is yes, you really do need that. And you need to do that for reasons that Steve's going to talk to about how they actually work. So make sure you always do your barometric compensation when you're using your non-vented pressure transducers. The one exception to that rule is if you're doing, say, a slug test on a site and that slug test might be over in about two hours, you're unlikely to get much barometric variation during that period. So you can sometimes get away with doing a slug test without bothering with your barometric pressure compensation. Last thing is, so with your barometric pressure compensation, sometimes people will use weather stations, for example, which can be quite a long way away from the site. You can get quite big variance, you know? So I think general rules of thumb is like about a 15 kilometre radius around your monitoring well site is probably okay. All right. So in terms of manual measurements, as I said, make spot checks to validate the data you're getting. Sometimes you'll do your download and you'll actually adjust those levels all up to match your manual reading as required. It's also good to validate the total depth of the well that you're monitoring from. You can do that by using something like a tagline, which has got markings on the tape. Some people do use the water level meters to do that, but the trouble with that is you can get over the pressure rating of the sensor and destroy that. So best to use a tagline when you're wanting to measure the full depth of the well. That's not the depth of the water, but the depth to the bottom of the hole. I found this interesting. So this is in this document. Just the errors that you should sort of cite when you're using manual readings, right? So what's the likely error from using a water level meter tape? Well, it looks like it's plus or minus one centimetre for a length of tape that's less than 60 metres. Looks like it's three centimetres for depths around 150 metres. And then it looks like it's up to 15 centimetres for a tape that you're dropping down about 500 metres. So these are quite big movements, right? Something to keep in the back of your mind when you're trying to correlate data logger data with your dip measurements. If there's an error of a centimetre, you might say that's okay. Now, Steve, I think I've left you enough time over to you. Yep. Far away. Can you hear me okay? Or good? Yep. All right. So I'm going to talk about some of the sensor technologies. I'm not trying to turn people into an expert, but I just want to try and give a taste of what to think about when you're selecting your instruments. And every choice you make, there are advantages and disadvantages. So let's go for the next slide, please, Richard. So I'm going to talk about mostly vibrating wire, four to 20 milliamps sensors, smart sensors. I want to touch on communications protocols and sometimes on to, or somewhat on to multi-parameter sensors. Some of those pressure transducers, vented and unvented, vibrating wire, bubblers and sonic level sensors. Next slide, please. So if you've worked on site, you've probably seen this kind of risk matrix thing to look after your health and safety. You still have to make the same considerations when you're selecting a sensor and logging combination. And there are risks and factors affecting your choices. Next slide. So just things to think about here, listed potential seasonal influences on water level range, water quality and temperature impacts on the equipment, the logistics of the installation or construction details and acceptable measurement uncertainty. So all of those things, you have to go through your head before you decide what you want. Next slide. So some of the risks that your face is the environmental effects on the quality of the readings. If you've got pH or something like that, try to measure water quality and you've got bacterial growth in the water, you're going to have to pull those sensors out at intervals and clean them. There's always a risk that the instrument itself will fail or the calibration will drift. And if you've got something permanently fixed and grounded down a borehole, it's really difficult to pull it out and fix that up. You've got to also consider potential damage. If you've ever put a logging station in the middle of the bush with a lovely shiny solar panel on it, you often find the solar panels go missing. If you've got cable on the ground or in the air and the copper twos like some of the PVC cables, they will have a go at it and some of its animals like that will have a go at your cables. I've seen quite a few that get chewed out over a period of time. And then there's nature. I've done boreholes where the bushfires have gone through and the base state or the logger has been destroyed. Also, grounded cables, if you've got any ground movement, the cable just gets torn into pieces and that's the end of it. So all of those things will affect your decisions that you make. Next slide, please. So next one again. So pressure transducers. Basically, they generate an electrical signal that's proportioned to the pressure they're measuring. And if you look at those two diagrams there, the vented one is measuring the difference between the face of the transducer and the atmospheric pressure at the back. And if it's unvented, you're measuring a vacuum. The pressure, an absolute pressure on the front reference to the vacuum behind it. Atmospheric generally are low level, used in low level applications where they would be affected by air pressure. Once you start grounding stuff down boreholes that are greater than 200 metres, there's not much effect from air pressure. Okay, let's push on. Thank you, Richard. There's some examples of absolute and vented. Maybe I'll just talk to that. Yeah, maybe if you want to say something about that. So for those of you who are not aware, so an absolute pressure transducer doesn't have a vent line on it. This picture just shows two different deployments. The one on the left is where you've got a non-vented pressure transducer just hanging by a cable, just a bit of stainless steel cable. And then hanging up near the top of the well is what we call a barilogger, which is used for measuring the barometric pressure. And you download both of those to do a compensation or if they're hooked up to telemetry, you can do it automatically. The one on the right, you'll see at the top of the well cap there, there's a little vent there. And there's a vent line that runs all the way from that pressure transducer all the way up to the surface. And what Steve was talking about on the previous slide, this left-hand one is a vented scenario where that bottom arrow where you've got atmospheric pressure is actually the atmospheric pressure that's coming from that little vent at the top of the well on the right-hand side. So the air pressure is coming down there and it's pushing against the pressure, against the diaphragm that sits within this pressure transducer. So the difference here is between these two and I'm going to labour this a little bit because it's important to understand is the one on the right-hand side is automatically compensated for atmospheric pressure variations or barometric pressure variations because the air that's coming down that tube or the pressure that's coming down that tube is doing the compensation for you. The one on the left, the absolute pressure transducer is measuring effectively atmospheric pressure plus the head that's sitting above it. So you need to adjust for that so you measure your barometric pressure here and you can subtract that from the reading that's being taken with the absolute pressure transducer. So just to finish off on that. So the one on the left is how the vented one works. So where that arrow's stopping coming up from the bottom on that left-hand one, it's pushing against the diaphragm that flexes. It flexes in relation to the pressure being applied to it. The more it flexes, the more the electric current or resistance changes. So what these clever little devices do is they convert that flex, which is in response to the pressure to an electric signal that we can then record. So the one on the right, it doesn't have atmospheric pressure coming in behind it. It's just responding to all the pressure that's coming from outside. So if you look at that little picture to the right of that with the black, that's the nosecane off a so-called sliverlogger. There's a little hole there. That hole is where the water flows in and the lines above it are where the diaphragm is located. So it's flexing in response to the water that flows in through those little holes. So I hope that helps. Let me know if it doesn't make any sense. Back to you, Steve. Because the one thing to remember here is you've got the vented tube running all the way down into this pressure transducer. It doesn't like moisture in there. So most vented systems will have a moisture-absorbing thing up. A desiccant. Most will have a desiccant chamber that the air passes through to try and keep the moisture out once you get a puddle of moisture running down there and sitting on the back of the transducer. That's usually the end for it. So anyway, let's push on from there. I think we covered those. So differences between the absolute, you don't actually need a cable. If you've got a barrologger built into the back of the transducer and you can actually sit it down in the dark by itself running on its own battery for a long period of time and just pull it out to download it occasionally. There are advantages and disadvantages listed there for both of those transducer types. And there are all things you need to consider when you're selecting your system. Let's go. Next one, please. This is a diagram here of when we deploy absolute pressure transducers. These are ones without the cable. They need to be on a cable that doesn't stretch when Richard touched before on drift and degradation of your readings. Sometimes that's the cable stretches. There are borehole transducers that you can get that have a Kevlar strip. And the Kevlar doesn't allow the cable to stretch. But if you see the absolute ones there, they're just hanging in the hole. There's a barrologger up the top to log the barometric pressure and the submerged ones actually doing the work of monitoring the water level above the transducer. If you look at the one on the right-hand side, it's a similar thing. But you've got a direct read cable. So you've actually got an electrical connection to the surface. Yep. But basically you're using two loggers instead of trying to get the atmospheric pressure on the back of your submerged sensor. Let's go on. Next page, please. Similar sort of thing. You're talking about the cap on the well and trying to establish a reference point, claiming the cables to make sure they don't move. I thought they were a bit about... And apologies, Steve, because I didn't give you much time to look at these slides. It was a big rush team for this one. But this connection at the top here is used when you've got an artesian well and you're wanting to measure heads in artesian wells. It's not always easy. So you can get fittings that allow you to connect your pressure transducer at the top of the well and get readings of your pressure head in real time. So that's a neat little fitting that you can get for that sort of thing. Next slide. Okay. So I'm going to talk now about some of the piezo styles in particular. And firstly, I'll start with vibrating wire. So if you want to move to the next slide, that photo there is a deployment in a tailings dam. And you can just see up the middle of that photo two very long cables running away. This is one of the big advantages of vibrating wire. It works by measuring the resonant frequency of a taut wire stretched between the body of the sensor and the diaphragm. It's a bit like a guitar string and a pickup. The measurement is a frequency. It's usually unaffected by long cable runs and cable resistance, which can be a problem with other signal types. And they're stable over long periods. So this is what I would use in grouted boreholes because you can't dig them out once they're in. But you need something that's going to last a long time. One of the drawbacks is that you need a logger with a specialized interface to actually pluck the wire and measure the return frequency. All right. Let's go. Next one. So this is a simplification of it. So you basically, they talk about a sweep frequency where somewhere around the hurts that the thing resonates at, you send a pulse down to the thing and it causes the wire to start vibrating and then you use that pickup to actually read back the output signal. And it's that frequency is what changes with the... In this example with those posts in the example of a pressure sensor, it's the difference between the back of the sensor and the diaphragm at the front. It changes the tension and when you change the tension, that resonant frequency changes. Okay. Next one. So we're all familiar with vibrating wire. There's a good example of one in real life. Now you've noticed on the guitar neck there, it changes the frequency by changing the length of the wire and the pickups there just below the bottom most fret. That's what turns it into an electrical signal that comes through the amplifiers. All right. Let's next slide, please. So these are some examples of installing vibrating wire piezos in deep hole, fully grounded bore holes. In installation A, we want to distinguish maybe with confined aquifers and things like that. We want to be sure that the pressure we're measuring is the pressure in that aquifer. The piezometer is down there at the end of the cable. It's generally surrounded by sand to make sure that we don't get any fines migrating into the diaphragm and causing some kind of mechanical obstruction that will change our reading. And installation B, you'll see the only difference between A and B is that in installation A, there's a small sand section between the bentonite grout. So bentonite makes the grout, makes the cement permeable, and so it will transmit water pressure through the cement. Typically with a piezometer, because the mechanical tolerances determine the resonant frequencies, you do have to do zero readings at depth. So there's a little bit more administrative stuff in measuring the piezometer in its raw state and before it goes underwater. And again, that's part of the QAQC process of making sure that you capture those readings before you commit. Because once you cement it in, once you ground it in, that's it, you don't get that back. All right. Next, please. Another step on. So gas bubble systems is another way of measuring. The way a gas bubble works in principle is you put a piece of tubing down the pipe and you have a little pump up at the top. You pump like a bike pump, you pump the air in, and when the pressure at the end of the pipe equals the pressure of the water head on it, the bubbles will equalise. So when you put more pressure on, you blow bubbles out the end of your pipe and when you stop it and the bubbles stop, then the pressure in your line is the pressure at the tip of that plastic tubing. These are limited to, I'm not sure what's the pressure, 200 metres or something, isn't it, Richard? It's getting really difficult to pump the pressure. You can run quite a long tube. It's limited by the head of water that can be above the orifice. So where you've got, you know, large fluctuations in your standing water level, a bubbler won't be very good for you, but where you're dealing with things like streams or leachate sumps, those bubbles are good for you. It actually comes down to, I think it's that sort of range of atmospheric pressure. So it's maybe up to eight metres or something like that and you can run these in terms of submergence, but I'd need to double-check that. Just that, well, I've got the floor. So that picture on the right there is a bubbler that we connected up to leachate sump. So the sump on the right there's got a sealed top, because it's also got gas accumulating in it, and it's got pneumatic pumps in there. But you see the tube that comes out of the white box mounted on the pole is your bubbler tube, and it's a very thick walled tube with a very narrow orifice in there. And the reason for that is they don't want it to flex in response to when you pressurise the air that's going down that tube. So that tube's actually strapped to the pump line that's down in the sump, and it's just attached by tape that's been wrapped around it, it's wrapped into that tube. And in the white box there, there's a little compressor that comes on and it blows that compressed air down that Steve was talking about. This one's all solar powered, so it can operate at a reasonable frequency. It's driving a compressor, so you can't measure at a really rapid frequency, but it's okay, I think we have that set up on like one measurement every 30 minutes on that system. So Bubblers are a great way for monitoring lead shade sumps and that sort of thing, and also stream water levels actually. Back to you Steve. So one of the big advantages of Bubblers is that the tubing is relatively cheap, and I've seen installations in streams where they get scoured out by flood waters and it's easy enough to just put another piece of piping pick. Oops, no he's coming up, sorry about that. And again, the big advantage of that is that the electronics is nowhere near the fluid. So you can make it quite a bit safer from nasty things happening. All right, let's go. Next one. Okay, next slide. So we're talking about, we'll be talking about vibrating wire and other types of sensors. The primary measuring technology may be the flexing of a diaphragm, but you've got to get that signal back up the wire back to where it's going to be useful to you. Vibrating wire is good because it's a frequency which is unaffected by cable lengths. Another one to consider is 4 to 20 milliamps. So our little piece of electronics that's down in our sensor will take the output and turn it into a signal that's either somewhere between 4 and 20 milliamps output current. There are several variations on this. 4 to 20 milliamps is mostly used in industrial applications and 2 wires is all you need for low power pressure sensors and you may have 3 wire versions which are things like flow meters that need more than 4 milliamps to operate. So you provide a third wire that gives it enough power. As I say, they're generally unaffected by cable resistance but it's important that you make sure that your little box of electronics down the bottom of the hole has got enough voltage to actually operate properly and you don't get voltage drops through the cable so you have to increase the voltage at the logger end to make sure that the sensor end gets good enough voltage to happily operate and do the 4 to 20 milliamp side of it. It's a pretty easy technology to measure. You basically pump your current through a resistor and measure the voltage. And like I say, it's common in industrial applications. It's certainly simpler to read than 4 to 20 milliamps, simpler to read than vibrating wire because it's just a voltage. The other way we transmit signals is with digital sensors and these are ones where the electronics is down the hole. It reads the data, it processes the data, it does calibration and it sends a number. The STI-12 which is a 1200 board, low data rate protocol for a lot of sensors that are in use or Modbus which is a faster type of thing used for mostly industrial type gear. And as I said, the sensor contains that does all the processing and it's a digital communication. I haven't seen anything in this vein from Ethernet type stuff. We talk about communications hardware protocols like Canbus and so on. They're all in that vein of these digital sensors. So let's push on. Next slide please. Keep going, keep going. Did you want to talk about the telemetry, Richard? Sure. So in terms of what you need to consider when you're thinking about what to purchase and what to configure, there's sort of three options that I've put there in front of you. So one is what I call bare sensors and these are sensors that don't necessarily have like a data logger down the hole, for example. They tend to have minimal electronics down the hole just enough to get us our measurement and you have the data logger and the power supply and everything at the surface along with your telemetry unit. So we use that sort of configuration up in the Surat base and where we're monitoring deep groundwater where the temperature of the groundwater is quite high and the deployments are quite deep and it has proven very reliable because you've got the minimum amount of electronics really in contact with those ground waters. The second one there is the smart sensors and that is so you can have two sorts of combinations of smart sensors. So you can have smart sensors without a data logger. Now these are the ones that still referred to like where you've got a comms coming out as a number and SDI-12 is a very common way, a common communication protocol for those numbers to be coming out as is Modbus. So SDI-12 was actually invented by the USGS and for that reason I think it became entrenched as the more common comms used for a lot of the sort of catchment environmental monitoring side of things whereas Modbus came more from an industrial background. But both of them are produced out of these digital devices and it's a number that's going up the cable from those devices as distinct from a voltage. So sometimes you'll have a smart sensor without a data logger down the hole and that can be pretty useful. In fact you can have a smart sensor without a data logger or power supply down the hole but you can have a number coming up the cable. So sometimes that makes a lot of sense to do as well. So three choices there really when you're looking at how to integrate. If you think about it from a money point of view and a complexity side of things a lot of the time you do have a telemetry unit at the surface and there's one on the right for example. Telemetry systems often have a data logger in them anyway so why would you have a data logger down the hole as well? Well the answer to that is if you want some redundancy. So if you're worried about the telemetry going down at least you know you've got that data on your data logger down the hole. But what I've found over time is the keeping these systems as simple as possible actually works best. So with these really long-term deployments I quite like the idea of bare sensors with no data logger and telemetry at the surface just from experience. But a lot of people like the idea of a data logger down a hole that means you can start monitoring without telemetry and when you get further funding you can accommodate telemetry. The other reason that you might choose to go that way is you might be monitoring for a couple of years and then you can remove those data loggers and use them somewhere else. So they've got more flexibility in how they're used if they've got a data logger internally. So there's a few things to consider right. And then in terms of the types of telemetry that you have we've done a previous webinar on telemetry which you might want to look at on our website. But you do have many options and really depending on your choice there will determine to some degree what sensors you choose. And some telemetry units can't take inputs from some sensors or sometimes they need to be configured. So quite often people will purchase a sensor from us and then come back and say, I would like to hook this into our telemetry and we have to pay a fair bit of extra money sometimes to get that particular telemetry system configured to take the inputs from a particular sensor. So it's always good to have a chat about these things and that's why Hydrotera exists. So how to choose a particular model of equipment? There's a lot in this. So I just thought I'd list a few of these down. We've covered quite a lot of it here. So the first thing I'd say is when you think you know what you've got, you're probably just getting started. So on the right-hand side there you've got an example of a spec sheet from a science level logger. There's a lot of information there. And every sensor that we sell has a whole lot of data sheets and manuals and what you need to try and do is look at these things and say, well, what does this really mean to me in terms of my project? So an interesting one here on the spec on the right-hand side is battery life. 10 years based on one reading per minute. It's quite impressive, right, isn't it? But sometimes what people do is that, and I've seen this happen, I'll have something hooked up to a telemetry system and they've adjusted the reading rate remotely and they've forgotten to reset it and so they put it down to a frequency of maybe every 10 seconds or whatever they're doing and before they know it, they've sucked the battery dry on their sensors. So it's really important to make a careful decision about do you want to have an internal battery powered pressure transducer or do you want to have power at the surface? If it's going for a long time, you might think, maybe I don't need to power down the hole. So a lot of things to think about, really the purpose of this slide is to just make that clear. There are a lot of things to think about and often people rush in to purchasing. HydroTera has a wide range of suppliers and we have, honestly, we've probably got 70 different models of level measurement devices. So we'd just like to talk a pre with you to work out what's the best option. So on the left, the sorts of things we would be considering is do you want to have absolute or gauged? The big one to think about there is will this area flood? Okay, so one time we sold a big bunch of sensors to DELP and they had a large flood event about three months later and about 20% of those which were all vented once fully submerged, the desiccant couldn't take them anymore and those sensors were ruined because water can stand about into the electronics. So where there's flooding, don't use your vents. It's not a good idea or you need to mount them well up a pole. Some people disagree with me about vents. I'd like to save you first. There's a bit more accuracy around a vent, so you've got to talk it around. You've got to decide if you want a bare sensor or if you want a data logging sensor. You want to decide if it's going to be telemetered or not. It's good to decide all of this at the same time because then we can really configure up good outcomes for you. Very important to decide your submergence range. If you put like a sensitive one, like you can see in the bottom right hand box here, we've got a range here. M5, it means it's calibrated for five metres of flex. What does that really mean? Well, an M5 has a thinner diaphragm than an M200. It's just made thinner. It's made thinner so it's more sensitive. What happens to an M5 when you put it down and submerge it 200 metres? What do you think happens there? It obviously fails and the sensor dies. That's not what you want to do. You want to think pretty carefully about the range you want. The other thing to consider is the accuracy you need. There's no point sticking an M200 in a hole where you're looking at five sensitive fluctuations because it'll be too thick to give you the sensitivity you're looking for. So important to think about that. Finally, because we need to get to a few questions. Operating temperature range is really important. In here, you will see up the top right hand on that spec, temperature compensation range, 0 to 50 degrees Celsius. So that means that'll be fine in that range. Minus 10 to plus 50 degrees C. But once you start getting outside that, you're going to start getting errors. So you need to be careful with temperature. Really, we're doing some weapons and geothermal spring stuff at the moment. It's between 43 and 50 degrees C. So that's one way you do want to keep an eye on that. That's an example. Well, same gas monitoring. You also get pretty high temperatures because you're actually your inlet coming from 800 metres down or something like that. It's a long way down. Finally, just a little bit about our website. We've invested a huge amount of effort and money into building a real resource here. You can come in under the groundwater heading there and you'll see these various subheadings, level, level and conductivity. There's a whole range of different sensors in there and data log instances and telemetry systems, that sort of thing. You can do a bit of your initial searching in there or feel free to call us up about that. Now, I'm going to skip over the reporting, except to say the Bureau of Matrology puts together some really good explanatory notes of the sort of information you should be reporting when you collect groundwater data. Now, this guidance is really for the water authorities and their contractors, but it does highlight what you really need to collect to be doing this properly. Okay? Or the information you need to be able to access. So I'd say to you, let's not try and digest all of that here right now, but it's the sort of things that the Bureau puts into our systems when we configure our systems. You can access this recording to look at these slides on our website. So feel free to log in and get that information. So just in summary, when you're planning, think about the parameters you need to measure. Think about how many locations. It's very important to think about the frequency you want. Then start thinking about the technology, and that's really where HydroTerror's got a team of instrument technicians and electronic engineers to help. And then think about the quality assurance processes you need in place to make sure that those systems are truly measuring what they're reporting back to you. There are several methods you've heard Steve talking about today. They're actually more than the ones we've covered today, but they're the common ones used for groundwater. VWPs, very important role they play, particularly in mine sites on tailing stamps and that sort of thing, and also in geotechnical investigations. More standard pressure transducers and smart pressure transducers are used a lot for more groundwater resource monitoring and monitoring of open water bodies. There are many suppliers, and you need to choose carefully, and HydroTerror's here to help with that. Now over to some questions. So well done, guys. I've called these the early bird questions. Thanks very much for sending these through, so I'm going to start with these. So John Hayes, vented versus unvented. Any preference? What works in bores greater than 200 metres deep? Steve, do you want to have a go at that one? Yeah, basically, in deep holes, unvented is better because it's sealed, essentially. You can't stuff it up by getting condensation in the part tube. So yeah, when you say bores, I'm thinking fully grouted, but if you're not fully grouted, you might have to do the math and figure out how much different atmospheric pressure makes to your readings. Okay, yeah, I think that'll do. All right. Next question from Matthew Von Snarks. Dealing with high iron content water monitoring, inexpensive near real-time remote monitoring solutions. I certainly know that iron in, so where we find high iron, well, in quite a few ground water places around the shore, but up around the Murray River on the assault interception schemes, for some reason there was a huge amount of iron when the pumps are operating, and particularly you get the buildup of this bacterial iron, sort of, it's like a jelly, actually, that builds up. That would block the holes in most of the pressure transducers, so that would make it difficult. The bubbler poses a potential option depending on your water level fluctuations you're looking at. They're probably my two thoughts, Steve. Did you have some thoughts on that one? No. It's a short answer. I'm joking. So welcome back to all of these questions with an email, by the way. I've got some ideas for remote low-cost monitoring there. In terms of... Did you want to say something? I was just going to say that high iron content is more the environment you're putting your sensor, not the way you measure it. So like anything else, like fines or bacterial or other contaminations, you have to choose sensors that will deal with that situation. In the Solon's manual, there's some guidance there about using balloons. You can fill a balloon up, partially fill it with distilled water, and use its high wire at the top of it and lower it down, and it creates a protected zone so it's still getting the pressure. It's protecting the sensor, which does seem to work quite well, but you need to go and change that water because in the end it does equilibrate and you can end up with the water quality that's on the outside being the same as on the inside of that balloon in a preparative time. So that's another approach I've seen there. Next one's a good question. Chantal Millis, how do you manage process conflicting telemetry data collected and raw logger data when both return different level data? I was going to say, this whole business of collecting data can be a bit of a religious war at times. I'm in favour of collecting raw data and post-processing it. But if you're talking about where you put some calibration parameters into your logger or into your transducer and you can't recover the raw data, so if something starts to go wrong and you start to get weird readings you start to say, did I get my datum wrong? Did I get my scaling factors wrong? Did I, who knows? And that's why I tend to prefer to just keep the raw data, the raw logger data and do all your calculations post-processing. So I suppose there's two parts to that answer. I think there's, when you have this sort of divergence of readings it does require a fair bit of analysis to work out those potential sources of error. And there are several. Need to just work through them, I guess one by one really. In terms of the next question, Liz Carey. These presentations are always great. Thanks Liz, like that one. Always interested in landfill lead shape monitoring considerations. So in the landfill side of things, the main ones we use are the bubblers and the smart pressure transducers. That's typically what we've been utilizing and we have done quite a few also where we might have used a bare sensor for more of the operational monitoring connected up to telemetry and connected in for immediate pump control. So the pressure transducers are something that we use a lot of in the landfill space, that's for sure. Next question was from Tanya Asprey. New light non-aquarius phase liquid detection in a well. You're sort of chasing the holy grail there. I have seen a automated hydrocarbon monitoring system which I'm trying to remember its name. It's global and it lowers down a solid inch of the well and it detects when it hits products and when it hits water and then it retracts it and it therefore is telling you because it's measuring from the top how far it's deployed. It continues the depth to napple and it continues the base of the napple because it's got a sensor that measures the water beneath the napple. So I'll send you through the name of that device. I haven't dealt with that for quite some time but I'm not sure if there's any. We have just sold a real-time hydrocarbon sensor up to Ampol actually for one of their refinery sites that was more for a surface water application. Not sure if that would be helpful for you in terms of delineating napple itself. But yeah, there are hydrocarbon sensors probably more than you realize and some of them are available on fairly standard multi-parameter sensors but they typically are not speciated down to the level of BTECs for example. It's more a total content of oil content. Now, we have... I'm just going to try and have a little bit of a chat. Just give me a second. Q&A, one more question from Travis. Groundwater monitoring is new to me. So sorry if this is obvious. Bubblers seem like an old school but reliable system but least vulnerable to external factors due to the minimal electronics involved. Is this the case? Well, they're not really old school. I reckon they're about the same age as all the pressure transducers. They have their place and I think it is where you think that signal transducers into that water is going to lead to a failure of that sensor either due to temperature or due to bioclogging. And sometimes with things like leachate in particular that's a problem. They're also very sensitive. So they are actually very good for surface water monitoring where you're looking at those fluctuations and like Steve said, it's cheaper to replace tubing than replace a deployed transducer if you get a big flood of in through. So they have a few real advantages and they are the preferred means of quite a few of the sort of water authorities out there who are measuring stream flow. They're less utilized in groundwater because they've got their limitations on the fluctuation that they can handle. But they are, we've found them very useful in the context of monitoring leachate. They do tend to cost a bit more than a straight pressure, well they do cost more than a straight pressure transducer because you're also paying for the compressor side of things. Yeah, you're paying for the plumbing. And what you need to remember is sometimes the pressure that you have to generate at the head of the tubing where the logger is quite high. And so you have to have this change over solenoid arrangement so that you can pressurize your pipe and then measure the back pressure. And it's a risk with the plumbing that if you over, you could over pressure your measuring sensor which is like, it's a level sensor just like any other except that it's built in up the top of the pipe not down the bottom of the hole. And so if you have any sort of mechanical failure or problem with the plumbing then it can be quite fatal to the device. Okay, so I think that concludes today's webinar. We've gone a bit over time today but thank you very much everyone for attending. We've still got a lot of people online so I think that's a credit to you Steve, well done. And many thanks everyone for turning up today. It's been great to have you all here. Thank you.