 Thank you everybody for joining us today for our latest in our Hydrotera webinar series. Today we have Gavin Mudd back again for those of you who are lucky enough to see his previous presentation on Mindsight Rehabilitation that was very popular with the audience and many many questions. So Gavin's back again with a wealth of knowledge to share has spent a career really looking at mine acid mine drainage and mine site rehabilitation. So today we're looking at a series of case studies from Gavin as well as a little bit of theory about acid mine drainage and certainly really appreciate Gavin's support of these webinar series and it's an honor to be able to share his knowledge out to the broader world which is a big part of what these presentations are all about. So before we get into it just a few administrative things. So I'm Richard Campbell I'm the Managing Director of Hydrotera and we're responsible for running this webinar series and Gavin Mudd or Professor Gavin Mudd I believe it is. So Associate Professor I should say at RMIT is the presenter today and Gavin has got a wealth of presentations related to the topic of today. In the background we actually have Michelle and Marcio is helping out Michelle today with keeping the webinar running. So thanks very much to Marcio and Michelle as well. If you have a question and we love questions use the Q&A button at the top of your screen and type into that. At the end of that I will read through those questions and then Gavin and myself will attempt to reply to those and if we don't get enough time we will come back to you in an email but certainly love getting questions and it's a great opportunity to share knowledge. All right so what's this webinar program all about? We see Hydrotera is having a pretty unique opportunity because of our market reach to help facilitate change by joining you know the wisdom of people like Gavin with our market and certainly seems to be very popular with people so it's it's great to be able to help do that. So Gavin's going to talk to us about mine rehabilitation and acid and metallophilus drainage. There'll be various case studies Captains Flat in New South Wales, Rum Jungle in the Northern Territory, Red Bank in the Northern Territory and Neath Greta in New South Wales. He's got some fantastic photos coming up and he also wants to share some ideas he has for monitoring of acid mine drainage in particular on rehabilitated sites. All right so I think we'll cut to the chase because there's a fair bit to get through. As I said we're hoping to help enable change and facilitate change through sharing of knowledge and also how technology can be applied to take things forward. More on that so just for those of you who didn't see Gavin's previous presentation a little bit on Gavin he was one of the first ever environmental engineers to graduate from RMIT back in 1995 having started his career through a PhD on coal ash impacts in the Latrobe Valley. He's pursued a very successful academic career at the University of Queensland, Monash University and then moving back to RMIT. Gavin has been at the forefront of environmental issues in mining for 25 years with his research recognised as the most authoritative around the world. Collaborations include the US Geological Survey, Columbia University, Yale University as well as participating in research in Europe. He has a huge number of publications. He has worked very closely with communities across Australia including the Indigenous communities especially with respect to uranium mining and is very well known for having a strong and independent view which is why he is such a fantastic presenter. So without further ado I think we'll hand over to you Gavin. No worries thank you again Richard and it's a pleasure to be here today. Hopefully my voice holds up I'm on the tail end of a rotten head coal. I just thought I'd reuse this slide from my previous talk earlier in the year which talks about mine rehabilitation and I think one of the things that's changed is really this sense of scale and I think that's one of the things that I think we're finally starting to get our heads around is that since we've developed environmental requirements and management in mining largely since we introduced environmental law I guess in the 1970s and mines have actually I think outpaced our approach like that and so our mines are getting much bigger at a faster rate than really I suppose what our environmental management and things are as well. So we really need to rethink and I suppose supersize our approach to environmental monitoring and other things as well but the other thing that I guess is perhaps more subtle is that although we are there are requirements for mine rehabilitation and so on it's still not something we've actually done a lot of because most mines are actually still operating and there's very few that have actually been rehabilitated and then monitored for 10 years or more and the reason why I make that distinction is because we know the problems such as acid and metalliferous drainage sometimes they may not emerge for 10 years or more right and so that we need to make sure we're constantly thinking about the nature of the the risks that are present and how we're monitoring for them and so on and the reason why that's important is because a lot of communities that I've visited and collaborated with or worked for they know these stories they know their local patch and that's certainly what drives a lot of community concern. Now it can also be that and especially in the digital age of course the stories and the information and photos and I've certainly been a part of this story as well I guess those photos tell a thousand words and so there's a lot of stories and so people can learn about these types of issues in the same way that we've learned about the tailings dam failures at Mount Polly in Canada which was just before the Samarko failure in Brazil and then of course the Grumadinho failure a couple of years ago okay so so really we need to think about not only just you know like how many mines we're doing but the fact that the scale is so much bigger okay next thanks Richard okay so just a quick reminder of the basics of how AMD works and there's lots of variations on the theme and so on but um largely the initial stages of AMD so yes please Richard next just the animations right we know that the initial stage is a largely geochemical and once you get to certainly acidic pH you know say pH 4.5 microorganisms will take over and then the rates can increase you know thousands and thousands of fold but effectively all we're doing is taking some form of iron sulfide such as pyrite or puritite or marcosite we're exposing that to water and oxygen in the surface environment and then what we're producing is say gotite our iron oxy hydroxides our sulfuric acid and a lot of heat right and so certainly when I've been around the place and I've been to sites in in Europe and elsewhere where you can look at the water and it's very very clear so that's a good indication that that's quite acidic from the you know so a lot of particles aggregate together and then you get clear water or that rustic sort of color you get so this is the database I guess I've been working on now and this is basically putting dots on the map for every mine around Australia that's you know mostly over the last 50 years but also a whole bunch before then and so what I've been building I guess is the database that then allows us to start to look at you know can we reprocess tailings to get critical metals out so the metals we need increasingly more of for renewable energy for batteries and other technologies so that's important how much waste rock right if we compare modern mines over the last 30 to 50 years there's sometimes a hundred fold more waste rock than we used to mine and so on so that scale is completely different all right the other thing of course is so the extent of rehab and so by going through you know basically assessing each dot on this map we can start to build up a database of rehab so so today I want to talk about just a small number of sites sites I know you know quite well and have visited so if we look at these we just remove all the rest of the dots and just look at the first one which is our captain's flat so and that's just down near near camber of course the other one as the old star trek line goes everything I learned I learned from rum jungle and so when I first started looking at thanks Richard when I first started looking at a lot of these sorts of issues and especially during my phd and looking at you know mining conferences and the journals and so on from jungle in the late 90s was promoted as a successful case study and so I was always interested is like well how successful and that's only been 10 years since the rehab was done so I guess that's one thing I've always been interested in is like well what was done how successful was it and so on and we'll we'll come back to that story and other sites I've been to is Red Bank which I still feel is probably one of the most polluting sites I've ever been to and it's much much smaller than both captain's flat and rum jungle and many other modern mines and yet the impact is rather extreme as we'll see and then some small scale sites around Neath Greta which are just a I think a good interesting community story around how the community approaches these types of things as well so next thank you so let's talk about captain's flat and it's in some ways it's a name that's long forgotten it's an old mine mainly had its two phases in the late 1800s which was pretty small only a couple hundred thousand tons of ore but there was water pollution left over so when the ACT was actually carved out of New South Wales there were specific causes put into the legislation making sure the New South Wales protected the the Malonglo River and it didn't impact on Lake Berligriffin for example the Malonglo River that flows through captain's flat goes down and then around to the west and through Canberra and the Lake Berligriffin is of course a dam on the Malonglo River so when we look at the more modern era there was a sort of a modest scale mine that was operated at captain's flat and it processed you know roughly you know I suppose a quarter of a million tons per year and lead zinc and copper and associated gold and silver all right and so it was pretty modest only you know about just over four and a quarter million tons of ore processed in total something like about 1.2 million tons of waste rock about 1.5 million tons of concentrates were exported leaving about 2.7 million tons of tailings there were some sort of small tailings dam collapses in the early years of the modern mine at captain's flat that certainly got attention but the the bigger problem was really this long-term constant discharge of acid and mine drainage into the Malonglo River and that was both from the tailings dam's accidents but also the direct discharge of liquid waste from the process plant or the mill as well as all the other mine drainage points being in the in the hilt there were some drainage pipes drilled from to drain the underground mines so the mine could keep operating and get rid of the groundwater so to speak and that was causing very significant impacts on the Malonglo River and what was known is that especially by the time you get to the late 60s there were some studies that were done by scholars at the Australian National University that showed you were getting zinc all the way down into Lake Burley Griffin and so it started to become this really contentious site about well what is the extent of water pollution associated with mining and so eventually of course in the in the mid 70s there was some new research done or some studies done and there was rehabilitation work done to stabilise the the race rock dumps and the tailings dams and there's been minor works done at times ever since and so it is one of these sites where we actually have various assessments done ever since so it's one of those few that we actually have more than 10 years of monitoring maybe not continuous and and so on but we at least have a sense of actually there so let's go to some photos next Richard so that six years ago my wife was going to a conference for as part of her PhD work in Canberra so so as you do we we took a little field trip down to Captain's Flats about an hour's drive so the top panorama photo so you can see from where the old process plant is there and you can see some of the old infrastructure but if you look down to the left you can see the the water supply dam that's actually supplies the water for the town of Captain's Flats and then you can see some of the southern dumps there as well so if you look on this you can see these sort of dumps on the ridge there now they were covered with soil covers at place during the 1970s but we can see these areas of bare soil and I'm not quite sure whether that's just you know a bit of random and a lack of growth there or whether there's capillary action that's causing a lack of growth I'm not sure so that's sort of looking towards this way down here so if we go and then you walk along the sort of road that hang on Richard yep thank you if we walk along the road there we can see you've got the the toe drain at the bottom of one of those tailings dam cells and you can see the acid mine drainage that's still emanating out from that and so you know certainly on the top and there's other panorama photo here you can certainly see that the it looks stable from an erosion point of view there is grass there there's certainly some cattle that you could see in the distance as well but so it certainly seems physically stable but we've still got this tail I guess of acid mine drainage now this photo in the middle here is quite important that's basically looking so you're on the road here and looking towards this sort of northern dumps here and what we can see down here we can see that the pipe this is one of these discharge pipes in the old underground mine sort of complex and so on and again evidence of acid mine drainage and again another one at the back here so these sort of two monitoring points here the or discharge points here we can see here in this photo but certainly when you look at the Molonglo River it certainly doesn't look to be you know heavily impacted anymore but I guess there's now going to be this long tail of a low level of acid mine drainage for a long time until basically all the pyrite's consumed thanks Richard now let's jump to the next case study and again I say sort of somewhat cheekily but certainly you know true is that a lot of what I've learned has been from rum jungle how you know why did the problem develop how was it rehabilitated and why has it failed all right and if we think about rum jungle it's used to be a very famous name in Australia it was a basically our first major uranium mine that supplied uranium for the nuclear weapons programs of the early Cold War era all right and so then about a two-thirds of the production was then also stockpiled in Sydney at the nuclear complex at what we now call Anstow so that's its history so it's actually a military project it wasn't actually a normal mining company that operated a mine for profit it was a mine purely for a military purpose so the leftover sort of waste I guess from that era is just over a million tons of uranium tailings and about two-thirds of a million tons of copper tailings or heat bleach pile material and about 17.5 million tons of waste rock now by the time the mine closed it was infamous and I really do mean infamous as a severe sight of acid mine drainage so let's have a look at that next Richard so we can see them the basic mine layout on the left here so we can see the main pit here it's what used to be called White's Pit after Jack White the prospect of the name or the found the original uranium minerals but the Canarycon and Waiwai people prefer that to be called main pit I guess they certainly have their reasons not to call it White's but I mean of course I see the Dyson's open cut here and the intermediate open cut which was basically for the copper heat bleach project all right so we can see the large waste rock dumps associated with each of those and certainly the other heat bleach pile in the middle here over on the side on the northern end up here is the old tailings dam area so that's where tailings used to be discharged to a floodplain one of the things that I guess is always curious is that the acid liquors from the process plant which is discharged onto that flood plain and there were times it's well documented that the liquor would just vanish into the ground and we now know of course that's related to the dolomite and IE solution channel so if you put acid onto an alkaline rock like that you will eat away the alkaline rock of course and create solution channels and so those solution channels look like they were going to basically gobbling up that liquid waste right so we can see some photos from before the rehabilitation works clearly not a healthy-looking environment thanks Richard now one of the reasons why I guess from jungle did attract so much attention is not only just because it was a severe case of acid mine drainage but a lot of people in the 1970s were asking the question well if rum jungle as a uranium project causes this much damage we don't want the ranger uranium project but now though there's some technical differences there rum rum jungle is largely a base metal ore body that happens to have a bit of uranium in it whereas the ranger uranium deposit is a is a uranium deposit um and so it doesn't have the sort of anywhere near the degree of sulfides and it's also got a lot more alkaline rock in there that can buffer against that so there are some key differences there but certainly there's been sulfides form inside the tailings at ranger which is another issue but what that meant was is that in order to create confidence in the ranger uranium project the Australian government um especially after sort of studies uh investigated rum jungle um that were done by the Atomic Energy Commission and also CRA the I suppose the company that had operated rum jungle under contract had basically said well yeah we can rehabilitate and we can develop an approach there that should reduce the metal loads and achieve a good ecological recovery and so that was funded largely to hopefully demonstrate some confidence that we can achieve rehabilitation so the basic works that were done is the flood plain tailings were dug up and consolidated into the old Dyson spit and so that was then filled the remaining void was filled with waste rock and then soil covers put over the top the waste rock dumps themselves also had soil covers put on and and again when I was you know looking at the literature in the in the late 90s it was widely promoted and certainly uh last week I put together a conversation piece on rum jungle because it's just been funded again for another round of rehabilitation but certainly in the late 90s it's uh it was promoted a successful we've done the job it's worked and uh I think it certainly wants some engineering work excellence awards and things like that as well but by about that same time though um some of the other work which has now come to light was showing that actually the covers are failing uh and that there's two reasons for that and you know the first one in some ways we didn't have a sophisticated engineering understanding of unsaturated flow and how to design covers for problems such as acid mine drainage and from a theoretical point of view if we go back to our geochemical reaction we take sulfide iron sulfide add water add oxygen and then we get you know the rest is history so to speak so from an engineering point of view if we can isolate water keep it dry or we can isolate oxygen or both um then largely we can politely reduce and hopefully prevent acid mine drainage and the sulfide oxidation process from proceeding and so in some ways the the flawed engineering we now know that we should have built much much more sophisticated covers and thicker covers and so we in some ways that's forgivable we didn't really understand the nature of how to design covers to deal with and make sure that we've got covers that stay saturated and therefore prevent oxygen diffusion getting into the underlying waste rock the other one though I think is not forgivable and the covers were supposed to be uh 1.5 meters in total and in many places they were built um to 1 meter or 1.2 meters and they used the wrong types of soils so they use soils that were more reactive our high shrink swell capacity and so in the wet dry tropics up there of course in the dry season the clays dry out and you get shrinkage cracks opening up so the first rains coming in the wet season you get a huge amount of infiltration of water so not only does that allow oxygen to enter the waste rock dump um you also get a huge influx of water so you're maximizing the potential for acid mine drainage so and I think that certainly that shouldn't have been allowed to happen all right and so I think there's really there's two sides to that the one you could say yeah well it was a bit the design sure we we got that wrong but that's understandable but um it wasn't built properly and that's certainly uh yeah that's not understandable so about a decade ago the cornwealth government the Australian government started funding more studies to say well obviously we need to do something else we need to do another round of rehabilitation and so those showed that yes there's extensive AMD has come back again and this time a lot of the work that has been done and especially in conjunction with uh groups like the the canarican and the wario traditional owners um this time we're going to do pitback fill and the basic theory and this is something that certainly I've advocated um at sites like rum jungle and uh and elsewhere uh by doing pitback fill you've got plenty of water in terms of groundwater uh but the uh I suppose the solubility of oxygen in water is considerably less so instead of having say 20 21 percent or you know 200 000 odd parts million of oxygen in air we're now going down to say eight or 10 parts per million or milligrams per liter of oxygen in water and so that pitback fill uh although it's not an absolutely perfect solution it's certainly um I would argue orders of magnitude lower our long-term environmental risk and so we really reduce the role or the potential for AMD all right and so now they're looking at I've just gone through an environmental impact assessment process uh and uh about last week or the week before I think it was there was no now the funding committed to in the federal budget for an 11 years project at rum jungle thanks Richard so this is what a rehabilitated mind is is not supposed to look like so you can see here the photos from 2004 it's sort of the first time I got to visit rum jungle um and again in 2007 so you can see some more groundwater balls there this is the the finish river there and uh it's certainly not supposed to look like salts and uh and full of colors like this and so these colors are your ions that you get from the sulfite oxidation the greens can be associated with copper or sometimes other chemistry all right but the thing that's important with this uh top middle photo it's one you can see the yellow uh and I suppose tainting of the leaves in that tree there so it's obviously really struggling um but also you can notice the flow that's coming out of that waste rock dump so clearly there's significant water inside that waste rock dump that's coming out but the other important thing is that the salt which is basically I suppose our acid mine drainage so the the acidity dissolves up salts as well as heavy metals and so on and this would be several milligrams per liter uranium here right and so when you're looking at that it's coming from up the side of the waste rock dump and so it's not just coming out at the very base of the waste rock dump in a tow drainage or you know see between deception system it's coming up from the sides and there's certainly other photos I've got which show it stretching up even higher up the side of that waste rock dump and so what that shows you is that in order to do that you must have a very saturated waste rock dump that's got a lot of water sitting behind it and so that water is basically saturating the side wall there and causing that seepage so it shows you that you're getting so much water in through that cover that the uh it's basically uh yeah it's been a significant failure I guess and so hopefully um I know we're all hopeful I guess that the the new round of rehabilitation now will finally address that and by pick back fill for the most of the waste rock uh a lot of it um will substantially reduce this problem into the future thank you Richard now red bank as I mentioned I think it's uh you know it's a really small site literally two and a half million tons of waste rock but it was only operated for a couple of years as a modern mine it was pretty small and boutique even for a stay uh Bill Masterson was a a human I guess that had lived in a cave nearby with some Aboriginal women um and he basically used to mine a bit and take it down to Mount Isa every now and then and get to get some money I guess but um and so in the 90s it was developed as a modern mine but only lasted two years before it went bankrupt and there was no bond and I think that was uh it's an interesting case study because the law said there was supposed to be a bond and I'm not saying it was supposed to be even a hundred percent of the rehabilitation cost but there wasn't even any bond whatsoever let alone whether that bond would have covered the the actual works required now eventually of course a new company became the owner and that was just simply called red bank copper and they were certainly trying to develop it and they wanted to develop it as a way to try and say well let's get this AMD under control right because it was becoming a really sort of infamous site like um like rum jungle but but again if we think about the numbers it's uh almost an order of magnitude lower in its mine way so two and a half million tons versus say uh you know rum jungle which is around about 20 all right and so a friend of mine Charles Roche who's uh with the Mineral Policy Institute um he visited the site in 2010 based on some um when he visited the community at MacArthur River he said oh I think it's I think it's bad I can't really judge but and so we were lucky enough to be able to plan a trip to visit red bank in 2011 part of our mining legacies project I guess and so um the photos that we're able to take of the the pollution there I think were were really instrumental in actually helping to get some change in the Northern Territory Russell Ball who was a senior um I suppose a bureaucrat within the department there in the Northern Territory was able to get what he called the mining legacy fund up and running which is simply like the super fund in the U.S. it's a 1% levy on operating mines in the Northern Territory and that way the Northern Territory government has the funds to deal with a lot of legacy mines and at that stage of course red bank was not declared a legacy mine it was only a few years later when it was really obvious that uh the company red bank copper was never going to be able to find the funding to develop red bank and the NT government basically called it in and um cancelled the lease and so now red bank is actually declared an abandoned mine all right but I think that was one of the nice things that came from that is that 1% levy and so I think Russell Ball deserves a lot of credit for that because he overcame his minister his department and the industry to implement what is good public policy so if you look at the photos here this is some photos and these are um from um Mike Fawcett um in terms of the aerial works and Mike Fawcett used to run the mining legacy program within the department up there in the Northern Territory and so once they've called red banking you have to work out how to fix it and how to remediate it so we can see here the the aerial image so you can see the small pit there the sandy creek pit uh and you can see where they've done the small sort of experimental like heap leech pile in the middle there the old tailings dam um like the old process plant so and the Savannah Way is the main road there and you can see Henry Hans Creek just on the left there it's sort of some interesting colors but the photos on the right also give a sense of I suppose what you're actually seeing in the creek uh next thanks Richard so these are some of our photos that we had so we can see here one of one of the things that I think is just absolutely remarkable about red bank is you've got this uh waste rock dump you're getting seepage into the water table and with the the pit being a sink for groundwater of course the groundwater is basically streaming in through the side walls of the uh the pit there at sandy creek and some I've never seen that anywhere else nowhere near to that extent you might see you know some individual seeps and so on but never sheeting right through the whole wall of the open cut that's uh rather remarkable now when they did the environmental impact statement for the potential redevelopment of red bank in uh 2009 um we can see Henry Hans Creek there on the on the photos on the bottom um that's about 400 milligrams per liter each of aluminium and copper in the creek already all right so it's quite um not quite industrial gray but not far from it either all right and so um thanks Richard just a little next animation but um so that's about ph3 uh that we're dealing with there and so um and we'll see I think the the work that's been done they'll probably have to backfill the pit and so on at red bank but another side I visited um not long after red bank was the community in the hunter valley the lower hunter um and there were some community members that have noticed that these old mines and I know really many old underground mines in the the lower hunter there um not far away from uh mateland and underneath gratter area that once you had the groundwater rebound so the underground mines close you get the groundwater rebound and this odd colored water was starting to emanate out and so which of course we recognize as acid mine drainage and so one of the local community members um had started uh saying well what's happening these are all long abandoned mines the companies no longer exist um government not doing anything about it so um so he said about we can see on the sort of photo on the right here the top right that he said about basically building a live dosing plant you know just a small little activity you can see the little generators there and pumps and so on um and he said about trying to sit there treat the water himself and so um and I think the the thing that's really sad about this is that rather than government going well actually there's a problem here we didn't recognize um and clearly communities that concerned about it because it does impact on the on the values for recreation and other things downstream let alone the ecological values uh they actually just said right right well we'll find you instead so we'll find the community member um and threaten them with legal action if they don't stop so I think that to me is the wrong approach we really need to be saying well actually community have got obviously a vested interest in protecting their own local patch and I think that's something that's uh something that really should be celebrated and you can see on the sort of bottom middle photo down here um that that's the sort of leftover so he was forced unfortunately to to stop his live dosing and treatment of that acid drainage and trying to help at least remediate the problem um and we can see the sort of leftover of that there now right so I think whenever we hear stories that communities are concerned about mining or opposed to mining one of the things I've learned is there's often good reason so and whether it's stories like this where local members have actually local community members have seen the sort of the legacies that can be left um you know all sorts of other reasons but I think you know to me I've always sort of tried to think through and engage well what's the science what's the issues there all right and so it's uh and often there is there is there is a reason there is stories there is a a basis there as to where that community concern comes from thanks Richard I thought I'd add in a bit of a bonus site because it's something at least to give a hopefully a bit of an international flavor and if we look at the with Water's Rancher that's the the gold area of around Johannesburg uh it's probably mined and processed something of the order of seven billion tons of ore over the last 130 odd years and certainly um just under a third of the world's gold has come from South Africa alone but the legacy is of course that several billion tons of ore is now several billion tons of tailings and that gold also has low levels of uranium in it and a lot of the mines have long since closed down so in the west round area west of Johannesburg those mines largely closed in the 1950s and so as you proc ground water rebound you've now got this groundwater carrying acid mine drainage up into the surface environment and you've got these old tailings dams there and you can see there's even trees growing on the side but hopefully you can also see the the amount of fine dust that's being blown away from those tailings dams and you have communities living right next door you've got communities like Soweto you've got the other neighborhoods and you know suburbs of Johannesburg as well all right and so you've got millions and millions of people living in a context where you've got this free flowing acid mine drainage and I really do mean down streets and streams of the suburban areas around the west round and so on um and that's also impacting on people so the photo at the top right here is a retirement village that was built literally next door to the photo of this tailings dam and it was lasted about two years before it was shut down because of course all the dust problems is not the sort of thing you want for a retirement village so um so again so in some ways I think the the scale problems I think you know sometimes we uh we talk about our issues in Australia but I think it's uh sobering sometimes when you think of the scale of problems overseas as well all right so these are not small issues to deal with okay next one thanks Richard so out of all of that I think we're on uh in good time but to me acid mine drainage is still one of the biggest problems we've got with mine rehabilitation there's you know a whole bunch of other aspects we need to think about with mine rehabilitation but but certainly AMD I think is one of the biggest ones and certainly we've come a huge long way we've you know from sites like rum jungle like captain's flat we've now taught ourselves that yes we can get very serious impacts on our product ecosystems on communities um and we need to be really careful in how we go about engineering our um rehabilitation approaches to sites that um have acid mine drainage risks so with sites like rum jungle we've learned that the very simple you know two layer cover systems are not enough they don't work all right so really we have to go to much more complex multi-layered systems like four five or six layers and so some of these uh learnings I guess are what will be applied to sites like uh um macaque the river and certainly macaque the river has issues just in terms of operations and managing its acid mine drainage and salt boat oxidation as well as spontaneous combustion there as well but um all right so captain's flat the simpler um covers seem to be effective it for the most part like it's certainly not allowing a massive amount of acid mine drainage but there is a slow tail that's going to be there for a long time all right um thanks I'll get to that question so um what we know um that's not you know waste rock dumps not the only source we can see open cut mines as we've seen a red bank the underground mines both at uh Neath Gratter but also in the the big waters range in South Africa and so on and we know you know from sites you know whether it's in Australia or all of the literature internationally that amd can last anywhere from decades to centuries or even millennial in places and we know that from places like the southern part of Spain all right so um so therefore we need to be monitoring we need to be actually looking at this long term there are other sites that I that we know about such as a Gijinbang near tomorrow where the site has been relinquished and there's no mining lease anymore so effectively that means the New South Wales government is liable for rehabilitation um you know issues there but you've now got an acidic pit water there all right and so um now that mine closed you know 25 years ago but you know again how much are we really monitoring and how public is all that evidence and so I think one of the the ideas that I think I certainly I think we need to be pushing for a lot more is that we really do establish you know much much more sophisticated approach to environmental monitoring and assessment of our rehabilitation with respect to acid mine drainage and that's something that I think you know the the sites I've talked through today are not the only ones there are certainly other sites around Australia we could talk about um such as Bracungo in South Australia and and many others all right but I think what we need to make sure of is that when we're thinking about mining and rehabilitation and especially with respect to acid mine drainage we really understand the value of that investment in monitoring and and making sure we use that data to assess the success of rehabilitation or otherwise because if we're if we're not successful then like Rumchungo we still have a liability we still have a need to come back and spend more money again in the future uh to keep dealing with the problem so I think there's uh as much as there's a great problem there that also means there's a great opportunity so um but leave it there thanks to Richard and the Hydro Terror team and I'm happy to open up for questions cheers. Well Gavin thanks very much for that uh certainly kind of sobering particularly that South African experience there with um what's obviously a massive liability sitting there causing a lot of environmental impact we've have three questions at the moment keep those questions coming um I think that's a good that's probably that's a good one thanks Dean um that map and the data associated with is uh well hopefully be sent off for publication uh in the very near future so uh once that's done um uh certainly it will become public and uh hopefully we're um uh be able to use it going forward for all sorts of work especially in uh collaboration with Geoscience Australia and and others as well so but yeah that's a good question there thanks Dean. Next question from Ian Rutherford um thanks so much Gavin you have shown us some serious examples are these extreme or typical of the thousands of abandoned mines on your map? Yeah thanks Ian I think that's a really good question and I think in some ways yes these are extreme examples certainly the ones like Rumjungle are the extreme from from yesteryear but in other ways part of the problem is we don't necessarily really understand like um we haven't done a great assessment and I often make the distinction between yesteryear mining which was much smaller so yesteryear mines were 10 000 tons a year uh of tailings or all processed or maybe 50 000 tons for a bigger mine and so on and so the scale was a lot less and they were typically all underground so they didn't have large race rock dumps um or things like that and so um so a lot of the yesteryear mines I think probably don't have the degree of acid mine drainage risk except certain sites but the problem is I think with um a lot of our modern mines over the last 50 years is the scale is so much bigger we're mining a lot more raw bodies that are that do contain sulphides and so we uh we haven't done an assessment of actually well how many of them have an acid mine drainage risk how big is that acid mine drainage risk all right if we think of some other examples out there from the literature sites some of the iron ore mines excuse me some of the iron ore mines in apulba for example are mining billions and billions of tons of waste rock for their billions of tons of iron ore now 10 to 15 percent of their waste rock is uh highly sulphidic and reactive it's um sort of a black sort of a periodic shale like material and so part of the reason they identified that is because the explosives were going off early when though as they're mining from the mountains and moving down deeper below the water table they're mining from the oxide or weathered zone in the surface down below the the um into the sort of the fresh rock and so that was where there was um unweathered sulphides and so and of course if your explosives are going off early that's obviously a huge uh occupational health and safety risk and so the investigations into that highlighted the fact that they've got very significant acid mine drainage risks associated with that material and so that's 10 to 15 percent of um you know some mines in the pulver that are billions of tons of waste rock which actually dwarfs rum jungle like um so um and then you've got other sites like matt lile and matt morgan and so on but certainly the map that i've got and that's sort of one of the future assessments i want to be able to do is to actually start to put a risk assessment around every site for acid mine drainage so we can actually work out well what is typical what is extreme uh how successful are we and where aren't we successful and why and so on and basically do the much more comprehensive assessment that really no one's done yet and i think there's certainly stories out there we know for different sites but we've never done that sort of systematic assessment like that so that's certainly uh on the card but that's that's for down the track thanks for that gavin that's um certainly sobering to think of uh how many sites there are it's uh it's great that you've pulled that together um our next question is from rajiv barvaraju i hope i got that pronunciation right what role could selective removal technologies like acid resistant membranes or absorbers slash resins play here this would add a resource recovery benefit to strengthen the case yeah it's a really good question and i think that's something a lot of people um excuse me have certainly been looking at because if you've got the the high concentration of metals the the exact concentrations and and and uh i suppose the range of metals that would be present will vary enormously both even like you know between different mines but also over time as well now processing of those solutions you can recover those metals now in some places there's there's sites i know of where uh that acid mine drainage is actually used to recover copper so the the acid drainage is basically allowed to proceed uh and then the solutions are captured at the bottom of the waste rock uh piles to uh capture and then process for copper and that happens at mines in america i know cases in kazakhstan and elsewhere um so there's certainly opportunities for that and that i think that might be uh a way to help fund the rehabilitation or the remediation of some of these sites as well um or at least cover the cost of treatment so um certainly there's various technologies out there um solvent extraction and others that can be used and membranes um and you know ion exchange processes so they're certainly well worth looking at and sometimes they might even be economic so definitely thanks for that one gavin that's that's interesting i didn't know that there were sites where you could economically extract that i suppose it's no different to heap leech and it's hotly more uncontrolled fashion um put the americans called dump leech i guess yeah uh next question comes from aamon lay lie most of the treatments shown relate to covering up to reduce the flow rate and dilute slash redirect flow i suppose this means increasing the duration for monitoring is there any thought to chemical treatment to reverse some of the chemical reaction in addition yeah that's actually uh a lot of the approach that i guess we're focused on in australia have been very much the engineering approach which is um covers and isolation all right and so um now there are other approaches out there like more recently those had some interactions with the um jim goose sec on uh in america where he started using bactericides uh back 25 years ago in america at certain sites especially small coal sites and things like that and um regulators at the time and and this is something we're following up on but regulators at the time said oh that's a one-off treatment um you're basically you're putting a band-aid on you're not actually treating the oxidation process all right so now he's come back 25 years later and looked at some of these sites and they're um they're still working there still hasn't been any uh emergence of amd again at those sites so um he's certainly looking at that so i think that's something that i think i you know my comment was oh it's a one-off treatment it's not going to work long term but um he said well actually yeah there's evidence it does so now whether it's bactericides whether there's other chemical treatments there's things like uh you know orksol is one of the commercial products out there like taking red mud from an aluminum refinery because of the alkalinity in that that can be used to basically neutralize the acidity and once you can if you can maintain a neutral pH then you don't have the the uh preferred chemical environment for bacteria to thrive and really drive the whole oxidation process so i think there's a lot of these sort of technologies and the different treatment approaches you need to understand your site like uh now Carrington i think it's called up in the northeast corner of New South Wales has had that that type of approach used um so i think sometimes they can be very useful and certainly a man Carrington the um the papers suggest that's worked really well um but again that was at the time then the long after mining was done so i'd be interested to follow up again 10 20 years later and see whether it's still the case and that that's i think where we get the great evidence longer term so so there's a whole range of both chemical as well as um i suppose bacterial you know bactericide or biological processes that can possibly be used as well and they may still be used in conjunction with a lot of the normal physical engineering approaches as well but a lot of that is always comes back to understanding your site and uh making sure that whatever design and approach you use is relevant for that site hopefully works well for that site so Gavin why aren't they being adopted more at the moment is it because the uh that there's no money left to do that or uh is it just technology needs to be further developed uh i think it's probably a multitude of factors i think Richard i think part of it is our um you know like just just admitting my own professional bias in some ways i you know there's some treatments i expected wouldn't work and yet there is some evidence to suggest that it can right so i think it's certainly that there's also um the fact that once the the mines have gone bankrupt the companies have gone bankrupt they no longer exist that is not you know um and if there's no bond like red bank um you know government's got to find the money from somewhere else which is why i think the NT policy is a good one and i think that's sort of policy now whether it stays at 1% if you rolled it out nationally or he said let's put a 0.1% nationally or something i think if we had a sort of you know treasure chest of a war chest so to speak um to fund a lot of the cleanup of all these old mines including modern mines that have failed in terms of gone bankrupt or things like that or where we've got our assessments wrong um as well as old mines from yesteryear um i think we'd be able to do with a lot of community concern much better all right so i think there's yeah and sometimes regulators i think um they're coming from the same sort of professional concepts as we do so so sometimes i think we you know i suppose i've learned that it's always good to keep a really open mind and and think about your site think about what works what the climate is what the criteria you're trying to achieve are you know in some ways like rum jungle we've now incorporated cultural criteria into rehabilitation they're still sacred sites on the rum jungle site so that they need to be protected um all right so i think there's all of those things we need to that's what i suppose keep in mind yeah that's a complicated situation uh we've got a lot of questions mounting up so we're gonna keep moving on um dan evans hi gavin great talk can you comment on new south wales legacy mines approach of focusing on minimizing off boundary impacts through risk prioritization and limited remedial works given the lack of funding slash insurance bonds for their sites yeah it's that's a really difficult one because it cuts the heart i guess if our governments approach this historically and i think there are certainly sites where that can work when you can and a lot of it is like well there's no people here so therefore the impacts don't matter right and i think that's problematic problematic because it means that we're not worrying about what the environmental impacts are and a lot of sites uh especially the old yesteryear sites are are small right in comparison to say sites such as katie or north parks the new south rails and uh and and coal mines you know modern coal mines as opposed to old coal mines etc right so i think there's that that scale difference there which means that when you're doing a risk assessment of these old mines you automatically mean because they're small and because they're not necessarily right next to someone's home uh the risk comes out as pretty minimal right and i think that that downgrades and basically ignores a lot of the environmental impacts that are going on but also and i think you know hopefully as i've been able to show if we can't rehabilitate now the smaller sites like one jungle or others i think it's quite legitimate for community members to say well if we can't fix the old sites how confident are we that our rehabilitation approaches are going to work for our big mega sites so i think there's so in that sort of sense when you're looking at the risk assessment framework sometimes it's failing to link the sort of the bigger picture that we really need to demonstrate a good success on our older sites and our smaller sites to make sure we have the confidence to deal with our bigger sites because if we get it wrong on the big sites we're not just dealing with you know five or ten or 20 million tons of race rock we're dealing with billions of tons that that coal mines and iron ore mines and no and elsewhere so some good demonstration sites is sort of what you're advocating for there i think um absolutely and exactly what that means in terms of a you know a new approach i guess that's something um yeah the northern territory system i think is probably a better way to go like we have you have a better funding basis on which to um to remediate all these old sites okay next question Keith Osborne Gavin can you please comment on how successful passive water treatment processes both abiotic e.g limestone drains and biotic such as constructed wetlands have been yeah i remember during my phd we used to have limestone drains at the um at the loying power station there and depending on you know a bunch of factors but certainly the coating of go-toitich would get from precipitation would cover the limestone and then you'd get very little contact between the the acidic water and then the actual limestone and so the you'd have to constantly come and either you know scrape off the go-toit or um or crush up the limestone so you're basically creating contact again so limestone drains can work but they require a lot of active maintenance and um and careful attention um biotic wetlands can certainly work and there are examples out there in the literature um but again i mean i think they're putting band-aids on the problem and so i think whether they're they may still be an appropriate approach the example i'm probably one of the best examples of um of not so much uh abiotic um you know wetland but uh just a treatment plant was actually at the old golden cost mine in new zealand where um they've got a fully automated water treatment plant that treats the uh the the modest amount of acid mine drainage that comes out of the waste rock dumps there and the old underground mining uh and so that that's you know directed into this water treatment plant and treated so that they meet the water quality criteria downstream so uh there are certain examples out there that you can find of of all of these types of things saying that they can work um but i guess you have to balance up uh how much active maintenance or operations are required versus the criteria you're trying to look at and uh and so on and there's sites like equity silver in um in uh budge columbia in canada which will require hundreds of years of monitoring you know and stuff and so you can have these sorts of approaches where you have a treatment system there um but you're looking at a basically almost effectively perpetual um you know treatment uh process that you've got to manage okay good answer there gavin i think um one of the challenges is just the duration these systems need to run for um next question from andrew spark looks like andrew's chasing some assistance we might um send you an email andrew he is working with an abandoned open-cut mine that is full of water and looking for guidance to current treatment strategies do you want to just make a broad comment of you know what she's quick comments i mean i think a lot of it um comes down to also um excuse me um what criteria are you trying to achieve all right now i mean i've seen open cuts in the gold fields in western australia that are full of amd um and the normal expectation is are you in the desert there's not enough rain for the drive amd well there is a teutonic bore there's you know many other mines i've seen um so it so i think a lot of the sort of the various treatment strategies depend on well what are you treating for are you treating just to to remove the problem from the open cup are you treating so that the water could be reused for agriculture or for drinking water or some other purpose i think um and again depending i guess on what that purpose is will depend on what treatment strategies might work and so on but the other thing too i guess is uh um is it just to how much groundwater um surface water interaction is there between the water in the pit and the groundwater they're all the questions i guess i'd be thinking about um but yeah happy to take that offline and um talk about that further via email if you like andrew just before we move on gavin so were you involved at all with that there was in western australia they had a a program called something like the open pits irrigation program where they were looking at using these pits effectively as water supplies for those um remote areas were you involved with that no i wasn't involved with that i've certainly seen some of the literature on that but but again a lot of it comes down to understanding your water quality understanding what the use you're putting that water to um there's been a lot of work in the colibation for example in the old coal mines there where they've had very significant acid water in there build up in their old open cups there as well and so they've had to and again i think it's a combination of wetlands and understanding the catchment not just the mine as well so um yeah so there are examples out there but um but that that specific work was not something i was involved with no okay um next question from an anonymous attendee hi gavin with large sulphuric waste dumps do engineered covers just delay the inevitable amd effects ah that's kind of a trillion dollar question um um yes and no i i think in many ways our covers do delay the rates quite a lot now i suppose the question then becomes if you've delayed the rate down to let's just magically say it's 1000 times lower than it would be without the covers um yeah and yes i think is a previous question pointed to as well does that mean we just it's just increasing the duration of monitoring we need to worry about um and i suppose that's true to an extent as well but um but effectively managing i suppose the capacity of our environment to um absorb those effects or the risks that we have whether it be to communities or to the aquatic ecosystems and and so on so um so i think in some ways yes they kind of are but we're managing that process to make them sure that the environmental risks are vastly reduced compared to what they would be if there were no covers all right and i think it's also you know part of the reason why in looking at failures like rum jungle and thinking about that uh and other sites you know where um you know there's these great experts out there like ward wilson from canada and so on that was one of the great innovators in in developing the software like soil cover and so on to actually allow the design of soil covers for amd and um he's actually gone to the things like no no i actually have got he's gone away from soil covers now to look at in pit disposal because um whether it's erosion or or other or sometimes tree roots you can get ways that the the integrity of that engineered cover can be significantly impacted so i think um in some ways yes and certainly i argue that i think the best long-term approach is generally going to be pit backfill right um and whatever's left and we have to do with covers maybe but um but again you know there's real cost to that but i think we also need to understand not only the cost of doing that in terms of pit backfill but also the cost of having to maintain a site with the engineered covers uh effectively in perpetuity the macaque the river mine uh when it went through its last environmental assessment process precisely to work out how to manage all of its uh rather severe acid mine drainage problems and associated with its waste rock and so on uh it's now put a 1000 year time frame on rehabilitation the first time in australia i think that's ever been done and that's largely due to concerns around how long um how long term this sort of amd risk is there uh and so on i mean i think really the only other site that would even come closer or more stringent that would be the range of uranium mine where solids from tailings are not allowed to cause impacts for 10 000 years all right so i think there's a it's a big question that one but certainly part of my thinking on that is to say well yeah that's really why i do prefer pit backfill because i think at least you've removed the oxygen from the equation and so um although sometimes you can still get arctic mobilized in the geochemical conditions inside a pit um the overall risks i think are vastly lower than what they would be above ground but it's uh it's difficult and a lot of that will be site-specific as well in terms of the various risks and issues involved so i could just ask a question gavin the uh have you ever seen the case where i guess the environment just adapts to these acid mine range discharges and you know do you think given uh it's going to be almost uh what would appear that you know these a thousand years is a long time what do you think the environment itself may adapt and you'd get a different blend of species and perhaps that's um funny you should ask that richard because there is actually evidence for that and um and there's actually evidence even it's size like one jungle and i remember in the um the uh mid-2000s i think there was a study that came out of from some research at anstow basically demonstrating that fish were becoming more tolerant to copper all right and so they looked at the studies and looked at over time and the same species and so on and they're able to show that yeah they're getting fish there in the finnish river are getting more tolerant to copper and there's similar research i've seen in uh places like the tinto region of spain which of course is where the very name where your tinto comes from um and so yes that does happen um now whether that's a healthy thing for an ecosystem whether that's something we would want uh that's an entirely different question but yes you know nature does adapt and there's issues there but uh i would sort of push that you know if you're getting that amount of exposure of metals into things like fish uh and then especially if you've got you know hunter gatherer processes like people going fishing and um and stuff they're downstream on the uh the flood plain downstream from um jungle for example uh that's something i would need to be carefully assessed so it's um so yeah it's there's certainly evidence for it but it's something that i think there's a lot more questions around that need to be answered as well not just the the fact that therefore happens and it's automatically a good thing i think it raises just as many questions i think there's a probably answers absolutely no just thought i'd ask uh next question uh elissa flatly thanks gavin are you finding that amd increasing with the increase in diversion of river channels for mining practices and these associated changes in surface hydrology um um that's hard to answer actually it's probably not often i'll say that but that's um because a lot of that um certainly in my experience a lot of the amd is typically coming from overburden dumps it's coming from tailings dams um or from old mines like underground mines or open cuts etc so um i'd qualify that because i'm not 100 certain that um i know certainly the acid mine drainage problems that um you know various coal winds up in the bow and basin which is where there's been a lot of river diversions um there's certainly acid sulfate soil issues to manage in some of the letro valley mines as well so um so but whether the fact that you're getting more river diversions is causing that i don't know i don't know whether that's the direct link i'd probably say that the amd is increasing probably more i think the greater causal factor is really the just the sheer scale of um uh wastewater and overburden um and the scale of modern mineways compared to just uh river diversions but certainly in some cases river diversions are um are associated with either either an amd problem or an ass problem like an acid sulfate soil problem so hopefully that helps anyway Alyssa i think you did very well answering a question that you thought you're going to find difficult to answer now we've got uh we're pretty much out of time it's 133 but i am going to give a couple of bonus questions uh one to our good friend Giuseppe Greco from uh melbourne zoo do you have or had cases experienced where plants have been used to absorb or control heavy metals in the soil like species such as arundo donax for the common reed yeah thanks Giuseppe it's an area of research that i suppose is getting a lot more attention lately like there's some um some folks up at um at uh uq for example that are looking at certain species that absorb nickel and they're getting you know percent levels of nickel inside the sap so now um you know the hyper accumulator you know species there's there's some known for arsenic for um for copper and nickel and uh and selenium you know um you know custer of course was tricked by the uh the shoe in america the shoe indians to um get his cattle his horses sorry to eat a certain type of grass that was known by the local shoe to be poisonous because of its uh high concentrations of selenium so i think some of this stuff is out there we know about it um i i think i don't think it's been too many cases where it's been actively used overall as a treatment methodology um certainly you know fracid mind drainage but it certainly can be used as part of a contaminated site remediation approach it's um and i think the potential for that's probably going to get a lot better in the future as we as we certainly understand the the potential of hyper accumulators to extract out you know particular metals and so that that's certainly a potentially quite a good approach all right um i think we'll give it three more questions um i'll try and be quick it's a great credit to uh that we continue to get so many questions coming through so great effort um next questions from another anonymous attendee great presentation have you come across any innovative techniques for acid mind drainage affected high walls if complete backfilling is impractical um i suppose the quick answer that is no um high walls uh not an error i've done a lot of working in coal um but uh yeah when you've got context like that that does get very difficult so um i think best way to do that is send me an email and i'm happy to follow up on that um through email sounds good um given that question's anonymous please make sure you do send that email through um next question from rimky van dam what are the challenges with and opportunities for monitoring acid mind drainage in groundwater surely what is seen in the creeks is only the tip of the iceberg yes absolutely i know it's a point i forgot to make so thanks rimky when you do the mass balance at rum jungle in the late 90s one of the things they realized is that when you look at the flow in the finished river times concentration gives you a kilograms or tons of metals and you look at the same calculation from the waste rock dumps you can only account for two thirds of the metal load in the finished river from waste rock dumps so roughly the the expectation therefore was that one third is coming from groundwater and so the studies that were done um throughout the 2010s um all right they looked at that and what they're showing is incredible compartmentalization now some people coming from a groundwater background don't like that term um so let's just say incredible heterogeneity all right and you could get bores that were sometimes you know 100 meters apart that one was fresh so less than 500 milligrams per liter tds and arguably natural groundwater with no um the basic neutral pH and low metals and so on um and yet 100 meters away you've got seawater quality with acidity and uh you know metals through the roof um all right so i think um a lot of that will come down to the hydrogeology of your specific site but again it comes back to understanding uh how your site works so with red bank for example we know that groundwater is a critically important pathway for a transport of amd i mean the fact we can see it coming um through the pit walls is is pretty stark but the other point i um i forgot to make with red bank as well is when you go along the savanna way and the savanna way actually drives across handra hands creek um the the water is polluted upstream in handra hands creek right so if you've got the drainage line that comes out on the southern side of red bank and that drainage line goes straight down into handra hands creek upstream of that and upstream of the savanna way road uh the creek is polluted and the only way you explain that is that because the mine and the the waste rock dumps and everything else were on a ridge and so a lot of the groundwater is therefore going north um upstream into the mine and polluting handra hands creek upstream so certainly groundwater can be very critical and and again the extent of that will be highly variable depending on your site but it's a it's a great point and it's something i think we often underestimate right well unfortunately i think that's probably where we're going to have to leave it um we will email out answers to these other outstanding questions um but many thanks for everyone attending today i think it's um amazing how many people are still on and obviously very interested in your question response so many many things gavin that was great and i'm sure we'll have you back again indeed happy to help and uh look forward to it but for the folks that i didn't get a chance to answer the questions please email me and and ritchett and uh davin dot market r m a t dot e d u a u and uh happy to follow up but we'll go from there thank you thank you very much everybody and have a good day indeed cheers catch you around