Managing water in mines
Wherever you drill a hole, water from natural underground sources wants to flood in. And if you don’t keep an eye on this, it could impact on the water source for those living in the area; either depleting it or contaminating the drinking water with dangerous material or toxins from the mines. This is a situation that water consultant, Johannes Wagner, works to avoid...
Johannes - Well in this particular mine we're putting into the environment an average of 70 megalitres, that's a million litres per day, but we pump almost 100 or 110 megalitres per day.
Chris - Why the difference?
Johannes - The rest is being used in the plants. So we use our underground water also for processing, for mining, and for doing the gold, as our main transporter and the surplus water we keep clean and that’s suitable for disposal into the environment.
Chris - It's no mean feat to pump that mass of water up to 3 kilometres to the surface?
Johannes - Well, that’s actually a major part of our costings. So what we do is we have very big pump stations, obviously at the lowest points. At certain places we also do underground treatment, put the water into settlers, separate out the slush and the mud. The mud goes to the plant because there's also gold in there and then the rest we pump out through these huge pumps all the time, so it's a continuous process.
Chris - So where does all this water come from?
Johannes - Well the sources of water is mainly rainfall recharge, but also leaks in the system. You know, for example, the local municipality has got a 60% water loss, so their leaking pipes is actually also going down the mines. And then we have old sinkholes where, if there's a lot of rain, the stormwater runs directly into the mine workings that we've got to pump. So in the wet season we actually pump a lot more water than in a dry season.
Chris - So when you say 'leaking' pipes, are we talking freshwater or are we talking wastewater - sewage?
Johannes - We're talking both. The infrastructure is quite old of the municipalities and the course of the soils are moving in these dolomitic areas and that causes breaks in the pipes, and then because of that it leaks.
Chris - So you're pumping someone else's sewage out of your mine?
Johannes - We are. In fact, quite an amount. We estimate that almost 20 megalitres per day, 20 million litres per day at one mine of municipal water and wastewater we're pumping, which is not our water.
Chris - Is that not potentially a health risk for your miners?
Johannes - We have analysed this up to this point and so far we haven't detected anything. What we think is happening is because it goes through the wetted zone, the dolomitic areas act as a sand filtration system, so we pick up little bits of nitrates, you know nutrients but not really bacteria on anything. We do sample and monitor the situation though.
Chris - So what about when you don't want to work here anymore? Once this is worked out, you don't want to leave all these tunnels here and you can't presumably just let them flood because there will be consequences, wouldn't there? Have you got some kind of managed retreat strategy?
Johannes - Absolutely. Because a lot of people think we will create another acid mine drainage disaster, we did extensive planning and modelling and testing and we have a plan to close this mine in such a way that when it's done it will be almost as normal. In other words, the salt pollution will stop and it will return to the normal clean water situation.
Chris - So what is an acid mine tailings disaster that you mentioned, what is one of those?
Johannes - Well, what is happening on the centre of the Johannesburg area is, because of pyrites in the rock still left, and water and air and bacteria causes acid forming. The geological structures in that area is very much different from here. We don't expect, if we close the mines properly, any of that to happen here.
Chris - So what is the strategy? How will you do it?
Johannes - At closure, we will basically install plugs in the shafts, in the lower lying shaft areas, then carefully flood the mine in a controlled fashion with basically pressure relief valves because you don't want to create a pressure cooker by filling it up.
Chris - Oh, I see. Because the rock is so hot here, if you just let the water go in and seal the shaft off you going to have a high pressure buildup behind your plug?
Johannes - Just simply, if you fill up a tank you will have air on the top, and the air pressure will build up as you fill it up, so you've got to relieve the pressure because what we want to be doing is we don't want plug flow. We can fill up the mine and there's no water running through the mine, we won't have any pollution. So the whole thing is we fill up the mine up to the hot rock lavas, we plug it with concrete in a controlled fashion and then we let the normal recharge through to restore the situation, and that's basically the plan.