 Hello everyone, welcome to NPTEL course on groundwater hydrology and management. This is week eight, lecture three. In this week, there are different types of wells, how they are constructed and the different types and uses of wells. What we'll be doing today is that we look into the more deep aquifer wells. In the initial other classes, we looked at wells that are most commonly used in India, in terms of dug wells, where manual labor is needed. And then we looked at the drive wells, where you have to hit on the top of a drive point, which goes in and accesses the water. In today's lecture, we will look on more about the driving plus water jet methods. And more importantly, we will look at the drilling methods, where a borehole is drilled into the ground by the use of heavy machinery. So before that, I hope you had access to the PDF book that I shared in the last lectures. Most of the notes are from that also. However, the other books I use have already been given in the syllabus. In the drive point, and also while you are making the wells, there's a lot of debris which forms. I showed an image last time where there is a lot of rocks, sand, soil that can be inside the well. You'll have to constantly pull it out. And some people use pulling method and some people if it is big enough, they go in and take it through trolleys and stuff. But JCPs come and then the big bulldozers, excavators, they come and take the soil out. But what do you do when the well is so small? And the particles are very minute, which means it doesn't accumulate that fast. But however, if it accumulates, it just stops the drilling process. The drill bits break or the drill bits go into the screens of the well and the well doesn't work. Getting a well inside is different. But if the well is fully clogged, then it's a waste. I'll show you an example. You have a drive point where you have hit the well hard and it has gone in. On the top, you have a point. So when you hit and it goes in, it's fine. And then here you have all the screen, the well is screened till that end. What happens is if this is clogged, which is with all these debris and stuff is clogging, then water cannot flow in. You are wasting the well. And this debris has to be taken out often so that your well is working properly. So let's see how this works. In this method, you have a well dug. It is dug by using a drill, a small motor which is being pushed. And then you also have a mechanism to push water in. You flush water and then you pull out the debris. So as I show you, the water is under pressure in the tube. While the water is under pressure, it comes and as it hits the nozzle, the water comes out in a very subtle manner. So for example, I will draw it. Water is here. All this area is water and water comes out through the tube with the debris because water comes out of the nozzle with high pressure. So all we need to do is to make sure we understand that we have water. We keep on drilling. But if the debris is not coming out, that means there's no water. So you keep on drilling. But by the time you keep on drilling, the soil particles, the rocks here can collapse into the well. So to prevent that, what we do is we use this water jet method to push water into the well, inject water into the well, and take out the debris. So the debris comes out. And your settling point is here where you are settling pit or point where the water with the debris comes and all the sand silt and all the rock materials lay down. Then you take the water out, which is again siphoned back into. So it's like a cyclic work where you have the water taken, pushed into the system, and then it comes back out and then goes back into the same pond or pit where you take water and push it again. So it's not a full volume of water that you have to give to this pump. You can keep on pushing water, the same water that can be used as long as you filter it or take out the debris for which we are doing this work. So this method is kind of expensive, but it is needed in some locations, mostly in locations with a lot of debris. And as I showed you in the geohydrology map, a location which has a lot of rocks, hard rocks, there this method is very, very useful. You will have to constantly pour water to take out the debris. Pressure is water can aid in drilling also. It's not only to remove the debris, but also the water along with the spinning drill can help in breaking the particles faster. So think there is a drill which is spinning. So if there is water also hitting hard, water and the drill aid together. So they mix well together and they break the drills. Please Google some videos on that. You'll be seeing it. We cannot use those materials on NPTEL because of copyright issues. That's why I cannot put them here for your reference. But if you just Google type it in YouTube or any other video channel, you can find this pressurized water drilling which can be of help. Also in bringing sediments up, as I said, all of the debris can also be brought up. So two things can be achieved by just sending a pressurized water. All you have to do is have the pump. The pump would take the water and then there's a motor which pushes the water at a very high pressure and this can also go. And this length can be adjusted using a pulley system. Fraction is with higher instrumentation. So this is the same concept they use in fracturing which is deep, deep in the bedrock or near the bedrock region where gases are kept or they are captured. The gases are captured or locked into the rocks because of the rock formation. Sometimes there is degassing and the gas doesn't come out and these are hydrocarbons or gases that can be used for fuel. And to break those kind of rocks, people use fracturing techniques to break the rock and expose the or release the gas which is being caught by a suction pump into tanks. There also fracturing is done by using water. So now we come to the most abundant type of well in India which is the tube wells and most importantly the tube wells which are at a deep aquifer level. These go at least a couple of meters down if not hundreds. It is 300 feet below the ground and what happens is there is no way you can dig that kind of wells. You need to have a meter machine that can push an auger into it. An auger is kind of a drilling device or you have to have a truck. For example here you can see a truck where it is lifting the rotator or the drill bit up and down based on the depth which is needed. Here also there is water which comes out. So when you see a video of a bore hole being made, you will see that water is gushing out from the bottom of the well and that happens because pressurized water is sent. It's called hydraulics like a lot of water which is being pushed in and the pressure aids in breaking the rock and also bringing the sediments up. So here you could see the water is pushing and the sediments come out. But most importantly what you see here is the drilling system for rotary method wherein mostly it is used in the hard rock aquifers or deep aquifers which consist most of your or contributes to the most of the aquifers system in India. Initially these trucks were very expensive to get one to your location. So they would charge one lakh because the truck is big and it has to go through different paths to come to your location and then you drill it. You could see these trucks standing in the highway because anyone can call. They don't go home for some days, they just wait for a call and then they go and do the bowl works especially during the Arabi season. They also ask to deepen the well sometimes. So it is not only for making new wells but also to deepen or flush out another well. It is as I said in most parts of India and it is the most expensive method of the methods. The volume of water may be much lesser compared to a dug well. However, these wells are preferred because of the small size. Think about it, you have a piece of land. You have a piece of land and to make a dug well you have to contribute 10% of the land or say 5% of the land. However, for a bore drilling system you can just have a small point comparatively on a land and that one well location can cater as much as water as your dug well and in some cases depending on the depth, depending on the water connectivity, it can be more or less in terms of if the confined aquifer is small. So what you see here is that it is more expensive and could be done with casing or without deepening on the region. Normally casing cannot go to such depths. Think about the expenses for tubes to put that deep. You have to put metres of the metres of well tubes. So this one is what I am talking about casing. So mostly it is done without the casing but it depends on the region. The region requires that the casing is put so that they prevent the sediments from collapsing in. You have to put. Normally what happens is you have casing only to a particular depth and then after that it is nothing. You just drill and then it takes it out and then you have your well ready. So you have to understand that even though it is an expensive method, the other accessories will also add to the cost thereby making it unsustainable for farmers and now you know why there is a lot of farm loans that farmers take for these wells, especially from loan sharks where they take too much of interest and the farmer doesn't get enough profit so they end up in debt. What you saw in the drive point, in the drive point what we saw is there is a coupling of wells. So you have a drive and then you couple it to another length and you can keep on adding the length based on the depth you want to go for the well. So the same way here you can add depth by coupling at regular intervals the pipe which actually drills. You just take it out but when you start it, for example, the drill which goes in is just this depth and then you add another coupling to it. Another coupling. And so that's how 3, 4, 5 tubes would be kept. Always just 10, 15 tubes that are kept. It's like a steel pipe which is connected to the drill and then it goes in and rotates. So this is the part which rotates. It rotates and then the whole body of the drill rotates. What I'm trying to say is the drill body is not one length. It can be increased by a coupling and that is how easy it is comparatively to drill deeper depths. So with this ease, what do people do? What do farmers do? Farmers have gone deeper to aquifers without the need. What am I saying here is for example, you are getting water at this level. For example, you're getting water at this level. Still, the farmer says, oh, you're here. All I have to pay is just extra diesel for putting it much lower. So they just go deeper and deeper and deeper. Bringing the log, this whole truck and the machine to that place is the expensive part. Running it is not expensive. So what they do normally is they just bring the guy and ask when the water hits. As soon as they know when the water hits, they do some calculations and say, do you want this depth or do you want to go much deeper? They just have to pay some extra and the farmer goes deeper. I've seen a lot of people who complained that the water was good, but I was so jealous that I went down much deeper so that I'll have more groundwater, but then I opened the confined aquifer and it was so salty that all the water became salty. So think about if this was a non-permeable rock and this is where I said you should have stopped with the drill if you had good water, but some people what they do, they just go further down and go to this aquifer underneath which is salty water. Now when you drill this, this water because of pressure will come up and mix with the unconfined or the other confined aquifer thereby making the all the water salty. I'll do it again just for your clarity. So this was the initial point where the good water was there and it was separated by another water using a non-permeable layer or aquitard, aquilude we call that and then there is another aquitard, aquilude and then there is water. So water is present both in this region and this region. So if you know that the water is good and it is enough by the depth of the thickness of the water level, you should have stopped, but what normally people, some farmers do is they keep on drilling and expose this water. Once you expose this water because there is no casing, you see there is no casing, then this water would rise and mix into this water. There is no casing and this water would come down. So there is a mix of water and this water which is more salty, naturally it is more salty as you go down the profile. Now it makes all the water salty. There is no cleaning of this aquifer anymore. You have depleted it, you have made the connections between the aquifers and now it is full of salt. You need to do something to reduce the salt. All you can do is take the water up, purify it and then use it for agriculture drinking, which is not very profitable to the farmers. That is why you see in cities you have a lot of ROs which are taking this salt and then removing the salt, filtering it out and then giving you drinking water. Let's move on. So this system is of good use in the Indian network, at least to get the wells done, but how deep you should go should be very calculated. Okay, so we have seen the three types. We have seen the dug well, the drive well and the drilling method. Now there is also something called a combination which is called the dug come bore well. So which means you dig first, you make the first well which is a dug well until here you do a dug well and then after that, after that you go down into the dug well and then you drive your second well. So initially you would stop here in the normal scenario for dug well, you would stop here. But then once this water level has gone down, once this water is not enough, what farmers do is inside the well, they'll get inside the well and then start drilling another well. Okay, here you cannot bring your JCP or your truck into it. So this has to be mostly a drive point well which we saw in today's example also. So then you dig deeper so that you come to this hard rock aquifer or this aquifer which is going to give water. So now when you make this connection, when you make this pipe through the pipe connection through your well driving point, then this water would go up and mix with the dug well both ways. So if this goes down in the bottom, the high water can come down or if the water here is more, initially it is more, so you can go up. And also depending on the pressure difference. And also you can put your pump head here where you want to pump from if it can be here or here based on the water level. So here's where how you could convert a dug well into a bore well. So always bore is for deep aquifers. It is much, much deeper and the width is smaller. Whereas dug well is, it is the shallow aquifer and it is much bigger. Okay. So here you have a ground surface GS and then you have the well lining on the both sides. Then you have a dug well which has water table but then it is very small so you need extra water and you made this connection. So this is also done and it is not as bad as your deep deep bore wells. However caution has to be here because you're also connecting a shallow aquifer and a deep aquifer for water. And the deep aquifer may not be as good as your shallow aquifer in terms of salt levels. Okay. So we've talked about salt levels. We've talked about the methods that are used for taking the debris out, etc. What is important is also the casing part. The casing is the side of the well that you make so that the debris doesn't fall in. So the debris is major, major impact of causing factor for your groundwater wells and the performance of the well. So it is important to make sure that the casing and the screening are understood. So the casing is what is put on the sides of your walls of the well so that your debris doesn't move. So this rock and other things don't move. However, you want the water to move. So there's small spaces where water can move or water can move from down up. The other part is your screening. As I said, the screen is where actual water can move into the well. Okay. So these are arranged in particular fashion like a matrix and then nodes are placed. It has a particular geometry, not random geometry so that maximum water comes. If you don't do this well, for example, I have a land and I just dig a well, water just comes in. What happens is all the sediments also come in and in due course of time, you'll have a lot of sediments here rather than water. More importantly, your pump is on the top, but the suction opening is down. This is a suction opening where water moves in. If there is debris, this whole pipe gets clogged and water doesn't move. You have to change the pipe. Sometimes you have a nozzle or the mouth of the tube where the water goes. That is clogged because of these sediments and rocks. More importantly, these can also go into your machinery and impact your pump depending on the pump style. There are pumps which don't get affected at all, but there are many pumps which get affected. Okay. So for all this, there is a need to reduce the debris that was going into the pumping by putting a screen worm. The screen also prevents or slows down the recharge of water. So it is not a win-win situation. Some of the water is also lost because you have to get water to move through these small holes, which is slow. So there are two types. You have the bore well, which is going into a deep aquifer. And then you have the large hand dug well, which is in the smaller aquifer. Just for this image, you can see both in the same depth, but mostly this will be way, way below the opening and other things. The circumference, the size of the well is also of much importance in the dug well and the bore. So this is what I said. Let's take this is the land and this is the land for this two wells. Okay. So now you have compromised on this land for growing crops because you cannot grow crops here. Whereas in the second, this is the first and the second, the first is run using your dug well. However, as I said, you have a crop only this area, you are losing a very small fraction of the area when compared to land with just dug well. Sorry, with just bore well. You can see that the land loss is much less compared to this, like maybe four times, five times the width of bore well, you could say. More importantly, it is needed because most of these lands, the small farmlands are already small. And you don't have space to lose more land for water, right? Maintenance, all these things. This is more maintenance. You have to cover it. You have to make sure nothing falls into it. It's too big. People get to wash things in it or bait, etc. thereby polluting the water, whereas here it's just closed. Nothing can pollute and other things. You just close the top cement or something and whenever you have to change the nose of the tube or the pump, then you take it out. So let's get into the specifics of this. Casing. The casing prevents debris from falling into the well. It increases stability of the well because slowly when these particles move, suppose your particles are moving slowly, one by one, it is moving. Then at one point, there will be a landslide kind of an effect where all these soil moves into the well. It is called collapse of the well. The well collapse can happen. But in this case, since you are preventing the movement, you are making strong boundaries. So there is no even a small amount of soil movement. So that is where the stability is kept. Now why would these move the soil? It depends on the water movement and also the disturbances which occur on the side. It's not an earthquake, but soil does move when, because your well is there, water is moving. So there is a movement of soil also. Allows to choose the aquifer. This is another interesting part which I showed in the previous example. This casing, the casing allows you to choose the water. For example, this is first water, second water or first aquifer, second aquifer. You don't want the first aquifer. Maybe there is an industry which is polluting water in it. You don't want the first aquifer. So what do you do? You case the top layer and only open the well, the bottom layer where a good water comes in, the deeper good water. And it can become expensive as how much depth you go in this profile. Now let's look at screening. Screening also allows you to get into the specific depth of water access. The screening depth is determined well drilling. So where you put the screen is also very determinant of the water available. For example, some people would put, even though this whole water is the same water, they would put the screen here just to make sure that the top water comes in from the aquifer. I don't want to put it down because if the water table falls down, then all the sand, silt, clay or the sediments will also come in. So you can pick and choose the specific depth of water access, even within an aquifer. Then determine when drilling because while you drill, while this debris comes out, I showed in your previous slide also, the debris will come out as and when you put pressurized water or you can take the sample at every depth. So when you analyze the sample, you understand that some rocks are not good, which means the water will also be not good. Too salty, too much with micro nutrients or ores, you don't want that. So you have to wait till you replace it or you go to a different depth. Can aid in separating salty water also, same like casing, your screening can also aid in reducing the salt content, the minerals that go into the well because it has a filter on a very small hose. Okay, so I think we have covered most of the different types of wells, where the wells are to be placed and the type also covers the access to the aquifers, what type of aquifers there are, how much money you have also depends on how you spend and what type of well you can get. Okay, so a dug well is much cheaper compared to a bore well in terms of the machinery, but the overall cost and time, if you want time, then the borehole is very, very cheap because you just call the guy, he'll come in a day before the morning he'll start and by afternoon you have the water ready, you have the well ready, you'll go, whereas a dug well takes long, long time. So if that aspect, it is expensive, dug wells, you can look at some studies which have done the comparative analysis of these two wells, but more importantly, the friendly nature to the aquifer is better in the dug well compared to the bore well. With this, I would stop here on the third lecture. In the fourth lecture, we would look at the wells have been established now. How do you take water out? It is through the pumps. We look at different pumps, why they use, how they use, and what are the alternatives. I will see you in the next class. Thank you.