3.1 Whether known that dewatering lowers the local water table
60 There is a dispute between the parties as to whether below ground dewatering necessarily results in the lowering of the local water table, and whether this formed part of the common general knowledge as at the earliest priority date. Unless otherwise indicated, all further references to dewatering in these reasons is to below ground dewatering.
61 Allied Pumps submits that the level of a borehole prior to removing any ground water is more or less the level of the local water table and that, as water is removed, that level is lowered, and that this is the case irrespective of the purpose for removing the water. It submits that the water in the borehole is then replenished, at least in part, by the surrounding water table. Allied Pumps relied on the evidence of Mr Baarslag and Prof. Holmes.
62 Mr Baarslag was asked to identify the information that he knew and regarded to be well known and generally accepted by dewatering engineers by 16 August 2016. In response, he gave this evidence in his first affidavit:
Dewatering has many different meanings depending on the context in which it is used. Generally speaking, "dewatering" refers to removing water, and potentially other fluids, from solids. This can involve removing ground water to temporarily lower the ground water table or removing surface water out of the working area.
For example, in mining applications, water is commonly extracted from underground aquifers to allow for material to be excavated from areas that would otherwise be submersed in water. In civil applications, water is commonly extracted from underground reservoirs to allow for piping installations to occur in a dry environment that would otherwise be submersed in water. In construction applications, water is commonly extracted from underground reservoirs to allow for building works to take place in a dry environment that would otherwise be submersed in water. In oil and gas applications, water is commonly extracted from underground aquifers during the extraction of oil and gas from underground reservoirs. In each case, the ground water is lowered.
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In mining projects, it was common to artificially lower the ground water table. Drawing down the ground water level, by extracting water via pump, allows for minerals to be extracted when relatively dry. Both diesel and electrical pumps are used for dewatering applications. When a diesel pump is used, it is located on the surface. When an electric pump is used, it is typically submersed in fluid. This is referred to as an electric submersible pump. For mining dewatering applications, it is most common to use an electric submersible pump.
As part of a dewatering drilling operation, a bore hole (also referred to as a well) is drilled into the earth's subsurface. The bore hole fills with water as a result of underground aquifers. In order to remove water from the bore hole and to reduce the underground water level around the bore hole, it is common to locate an Electric Submersible Pump (Pump) into the bore hole. This is an example of "deep well artificial lift" (i.e. artificially pumping fluid from a deep well).
In deep well artificial lift applications, extracting water from below the ground causes a "cone of influence" on the underground aquifer around the well. This is shown in Figure [1]. The height and width of the cone of influence depends on many factors...
63 The "cone of influence" appears in Figure 1 above (depicted by the curved lines), being the figure which was extracted from Mr Baarslag's first affidavit.
64 Mr Baarslag expanded upon his affidavit evidence in the concurrent evidence session:
MR BAARSLAG: It is my view that, when you're pulling water out of a borehole, you're dewatering. In my opinion, there is no soil that doesn't have any hydraulic resistance. Therefore, there will always be a cone of influence of some description.
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MR BAARSLAG: So it draws the water table down. Whether that's a big cone or a small cone, it will draw it down somewhat and Mr Quick is right. It depends on the permeability, on how fast it gets, I guess, back to the previous level of where it was before you start[ed] pumping, but as soon as you start pumping, it will draw down.
MR BANNON: And those considerations in relation to permeability, do they apply equally to a dewatering exercise for a mining operation?
MR BAARSLAG: Yes. Yes. There - there is - there is no difference between drawing water out of a - a bore for the purpose of dewatering or for the purpose of water supply in terms of what it does in the ground.
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MR BAARSLAG: For instance, in Mount Tamborine, Coca Cola is pulling water out of the aquifer for the supply and - and to make fizzy drinks. Mount Tamborine doesn't have town water, and most people either rely on tank water that comes in trucks, or they have a bore. Coca Cola is not intending to lower the water table, but they are because they [dry] all these other people's bores out because theirs is not as deep, and they simply take too much, and it's a big dispute there, right there, at the moment, so that's - it's an unintended consequence.
65 Prof. Holmes gave this evidence during the same session:
PROF HOLMES: It seems to me, from just general engineering principles, if you need to get water out, you have to lower the surrounding water table from the borehole because, otherwise, you won't get inflow because if the borehole water level is at the level of the ground table, there's no water flow. You actually have to have a lowering of the localised water table around the borehole to let the water from the wider area flow in to where you want it to go. Now, whether it's a minimal lowering or a significant lowering, it's still lowering because, otherwise, you don't get the differential pressure that will get you the flow, so the two are interrelated. If you take water out of a borehole, you - just to get a replenishment of the water, you must have a lowering in and around the hole to let the water flow in.
Now, Mr Quick says that might be minimal. It might be. If the water table is huge, it might be substantial. If the water table is not so huge - you just have to read documentaries about people draining aquifers to realise that, within Australia, with limited water, there's constraints on how much water you can take out of a borehole for the use of taking water out so that you don't lower the water table too much - suggest that, by definition, taking water out of a hole, for any purpose, is lowering the water table. If your intent is to lower it for the purposes of lowering it, or your intent is to take water, it's the same engineering process. It's the same result.
66 UON submits that the proposition that dewatering necessarily results in the lowering of the local water table is not agreed to be factually correct, and therefore disputes that it formed part of the common general knowledge. It says that that is because whether the local water table is lowered by dewatering will depend in any given case on factors including the permeability of surrounding rock, and the ability of ground water to flow into the reservoir to replace the fluid that is extracted.
67 By his second affidavit, Mr Quick gave evidence that, when oil is lifted from an oil reservoir, it will not necessarily lower the level of the surrounding ground water and that, whether it does will depend on factors including the permeability of the surrounding rock, and the ability of ground water to flow into the reservoir to replace fluid that is extracted.
68 During the hearing, Mr Quick applied the same reasoning to a dewatering operation on a mine. His evidence was somewhat confusing and illogical, and culminated in a claim that he was qualified to comment on the issue because he had been dux of earth science at high school:
MR BANNON: No, and so that - well, you would agree that, if your only purpose is to use a bore for water supply, you want that bore to be replenished from the water table as you pour water out, don't you?
MR QUICK: Yes, that's true.
MR BANNON: And it's your intention that it be - when you use it for a water supply only, it's your intention that it be replenished from the water table.
MR QUICK: Yes.
MR BANNON: And reducing - replenishing it from the water table reduces the level of the local water table, doesn't it?
MR QUICK: Generally, it will. That's right. It depends on the permeability and the supply of where that aquifer is being fed from.
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MR BANNON: Well, do you understand, in mining applications - and I've heard your answer previously is through experience, but nevertheless, do you understand that, in mining applications, if you are dewatering in anticipation of digging, it's a continuing continuous process? The pumps run all the time. Did you understand that?
MR QUICK: Yes, so dewatering is a different application from water supply. In dewatering, you're deliberately attempting to lower the water table, which means you need enough withdrawal capacity to affect that water table. So you have to have enough bores to do it and big enough pumps to do it to substantially affect that water table and bring it down so that it's clear of underground shafts or open cut pits or whatever you're trying to remove the water - lower the water table to protect so that you don't get ingress of water into those workings. So that's a different purpose. If you're intending on simply supplying water, then the last thing you want to do is drain your aquifer. So you don't want to lower the water table. It's a different objection.
MR BANNON: But do you understand that, in a mining application, when you are using bores for a dewatering purpose, the pumps run all the time because, if they don't, the water table just goes back up again? Did you understand that?
MR QUICK: Yes, that's true.
MR BANNON: So in a mining application, a dewatering purpose, the lowering of the water table is a temporary thing, isn't it?
MR QUICK: While the pumps run, yes.
MR BANNON: Yes.
MR QUICK: That's - yes, it is a temporary thing. If the dewatering pumps were to stop for some reason, for any period of time, then the water table will seep back up.
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MR BANNON: But what I'm suggesting to you is you read the claims. You satisfy the claims if you've got one pump down one borehole which has the relevant elements. Correct? Right. So understanding that, the impact of one pump in one borehole for a dewatering purpose of lowering the water table, firstly, is only effective while the pump is running, while you're pulling water out. You agree?
MR QUICK: Yes, that's right. I agree on that.
MR BANNON: And it's a lowering, a temporary lowering of the water table in the immediate vicinity of that individual borehole.
MR QUICK: That's right. Yes.
MR BANNON: Right. Now, tell me, if you can, the difference between that circumstance and pumping water out of a well for water supply in terms of the impact on the immediately surrounding water table. Can you tell me that?
MR QUICK: Yes. The difference between a supply and a dewatering application is supply is trying not to deplete the well because, eventually, you're going to run out of supply. So you would locate that where you have plenty of water flowing into the - from the aquifer into the well and you would draw it off at a rate that's less than the inflow rate. Otherwise, you're going to suck air. So it's a different objective and you would locate it in a different place.
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MR BANNON: With your background, your experience, you're not in a position to actually dispute the proposition, are you, that, no matter where you put this borehole, if you're pulling water out, it will, necessarily, lower, to some degree, the water table. You're not qualified to resist that proposition, are you?
MR QUICK: I'm not a qualified hydrologist, but I'm a well-experienced engineer. I've had - worked on many different sites around this country and overseas, and several of those sites that I've worked on have had bore fields and dewatering systems that I've had to review, and, yes, I'm qualified enough to speak on - - -
MR BANNON: Sorry. When you say you've had to review the dewatering system, I thought you said your involvement was just in electrical componentry and that sort of thing. Are you wanting to expand on that?
MR QUICK: No. I'm not claiming to be a hydrologist or a - - -
MR BANNON: Right.
MR QUICK: Although I'm familiar with the sciences and geology. I was dux of earth science in high school. I am quite familiar with how these things work, and you do need some appreciation of the mechanics and the hydraulics in doing any kind of electrical and instrument-control design and software and - and functional arrangements. So yes, I would say I'm qualified to comment.
69 I find that dewatering necessarily results in the lowering of the local water table, and that this formed part of the common general knowledge as at the earliest priority date. If water finds its way into a borehole or well from the local water table (whether quickly or slowly, depending on the permeability of the walls of the borehole and other factors) and then that water is removed by the artificial lift system, the physical dislocation of the water from the water table into the borehole and then out of the borehole must necessarily result in a reduction of water in the local water table (and therefore a lowering of that water table), however temporary or insignificant the reduction in the level might be. That is because the water from the water table will enter the borehole and replace the water which has been removed by the artificial lift system.
70 In making this finding, I rely upon and accept the evidence of Mr Baarslag and Prof. Holmes, whose evidence I prefer over that of Mr Quick for the reasons explained above and because, as already observed, I found Mr Quick's evidence on this issue to be confusing and illogical, and occasionally self-contradictory. For example, he appeared to conflate what could or would be done to avoid diminishing the water table substantially in a water supply situation with the physical consequences of dewatering on the water table irrespective of the purpose of the removal of the water.