 So, as I said lysimeter is a pore solution collection device and there are two varieties of this zero tension lysimeter which is collecting the pore solutions from the saturated soils. One of the ways could be you saturate the soil sample and then squeeze or do a consolidation test alright. So, one good example to the question which you are asking or the answer to the question which you are asking would be, I will saturate the soil sample and I will compress it in a regular consolidometer ring and I will make arrangements so that the rather than you know keeping the water inside the ring I will allow the pore solutions to come out. So, I can dissipate the pore pressure and the pore solution which comes out would be nothing but the pore solution from the saturated soils this is a simple device which you can device alright. But you have to be careful about the chemical activities and its reaction with the tubings and the odometer material which you are using and you have to be very careful otherwise the chances are that you will be contaminating the pore solution externally. So, most of these studies require clean rooms you know where you have to maintain utmost cleanliness and you have to eliminate the chances of external contamination of the sample and these type of labs do not look like conventional geotechnical engineering laboratories. So, they are clinical laboratories where you do clinical examination and where these type of studies are becoming more important right now is when somebody hires you to you know to help the industry or the organization to fight a legal case because these type of cases are becoming very very routine nowadays allegations or violation of the environmental norms where you could be under say we are threat including the imprisonment I hope you are aware of this type of norms which are prevailing under the environmental acts of the republics and the countries. So, this is a simple model I hope this explains to you what the lysimeters would look like you know there is a control volume which has to be created this control volume could be of stainless steel this could be aluminum this could be perspex or inside the ground this could be the soil mass itself and there what we normally do is we excavate this mass soil and we fill up this space with the pervious fill and the pervious fill could be the sands or it could be the gravels or it could be the mixture of both of geotextile depending upon what type of precision you require and then at the bottom of this there is a drain which is taken out and once I do artificial rainfall alright. So, this could be done in the field also this could be done in the laboratory also you can do artificial rainfall you can sprinkle water sometimes you can waterlog this whole sample by flooding it and then as and when percolation takes place this soil which you have re-compacted become saturated and the percolation occurs all the pore solution gets accumulated into the pervious fields and then you can drain it out from here to a collection bottle and this collection bottle is similar to the one which normally nurses use for the storing of blood sample we call them as vials they also call them vials alright. So, analogy is simple I am sure you must have realized that though it appears to be a very simple device but this can answer a lot of questions which we ask first of all we can study what this soil is doing over there you know we can also find out the hydraulic conductivity. So, there are papers which have been published by my ex students you should refer to where we have determined the unsaturated hydraulic conductivity of soils Sneha, Kurian and Hanman Trau and all these papers you should be going through to realize that how the lysimeters can be utilized to obtain unsaturated hydraulic conductivity fine and here I can do some more experiments if this water which I am using for artificial rainfall I can contaminate it with some chemical species and then I can see what type of percolation is taking place and what type of percolants are getting deposited in the you know pervious fields. So, this is what is going to tell me how much is the sorption capacity of the soil under in situ conditions what is the attenuation properties of the geomaterials and hence I can use lysimeters for characterizing the soil mass also alright. So, this is one of the ways of taking out the pore solution this is part clear of course this process is very time consuming. So, what I can do I can make a small miniature setup and I can install it in the centrifuge and I can accelerate the seepage process by n square time is it not. So, this type of tricks people are doing to take out the pore solutions this another interesting example of how the field lysimeter looks like. So, in this case you take out the sample in the undisturbed from the field and you can place it over here alright and then you know we cover it with the gravels on all the sites and what happens this is the percolating water which is passing through this and then some mechanism by which we have connected the gravels to the outside environment in the form of wells and from here I can put a electrically operated pump which will pump out the pore solutions which can be collected in the leachate. So, this there are different designs of the lysimeters the whole idea is that you create a system which is having high permeability and packet on the top of the on the below the soil mass. However, as you are aware the limitations of the falling head test or the constant head test are that there could be percolation from the contact between the surfaces of the geomaterials which you have used and the lysimeter itself. So, this is not a very good way of studying the lysometric behavior of the geomaterials and of course, fines may get washed out. So, when we talk about the collides and the contaminant mobility that has to be studied into this. Similarly, another problem is that organic matters might react with the with the water and that might also get altered because of prolonged interaction with the water. Then you will find this type of zero tension lysimeters also in the literature do not draw them these are all available on the net you can see them and as I said these are all pre-historic nowadays such lysimeters are not being used. I will show you a very state of the art lysimeters and you will be surprised to know that the cost of the lysimeters run in few crores, tens of crores. So, Germans are the best in the world in designing the lysimeters. So, sometimes when you get time please visit Germany and see how lysimeters have been installed for different projects alright. So, this is something interesting worth seeing. You check it on net and you will find that there are some German companies who are selling lysimeters. So, you just type the word lysimeters and German companies and you can see is unimaginable. There will be a big hall like this inside people sit and observe what is happening in the fields or in the on the project on the project site. So, this appears to be a very complicated type of a system what has been done is that you have to install a sand layer and then there is a sloping bottom. So, that whatever percolation takes place from the undisturbed soil core passes through the sand gets collected over here and there is a air inlet which has been provided and there is a outlet which has been provided. So, these type of systems are very complicated to design under fuel condition, but yes these are these were designed and used some once upon a time. There is a simple example of what collection basin lysimeters are. Since we are like adding water the sample will no longer be undisturbed. Undisturbed or unsaturated. No, you are not altering the density you know, gamma D remains constant why gamma D should change. Gamma D then plus we would not be getting the exact concentration of the contaminants that are present right. So, one thing is when we are like adding external water, external water or contaminant let us say. Yeah, in that case the sample is getting disturbed right how in the form of concentration of the contaminants, how much will be the static pressure even for 1 meter water column on the soil sample which is exerting. But we are adding water. How would you add? Falling head test. So, did you ever take the effect of 1 meter height of the water which is standing in the tube? So, falling head test also you have done on a compacted sample. So, once you have done the compaction you have already created a state of the material corresponding to a density and the void ratio. Now, this density and the void ratio cannot be altered by 1 meter water column unless you apply very high pressures on this alright. So, your question is correct as long as the percolant is not pressurized I do not speculate any changes in the soil samples and the logic is this because I have already compacted it fine. The lysimeter when we are leaching through leaching we are obtaining the pore solution then the concentrations will be altered only the constituent like we will be getting. So, basically your question is about how to maintain the concentration of the contaminant. In your consolidation also you talk about different types of stresses, different combination of stresses, different types of draining conditions, one side closed, one side draining, one side partially draining, another side partially closed. So many conditions I can create is it not are you getting this point? So, I can create a C naught condition which could be variable with time also which could remain constant with time also clear by maintaining very high concentration of the fluid. So, delta C is going to be extremely low I can do all sorts of technical manipulations yes. Sir, can we check the chemical attenuation potential of the contaminant and soil by this chemical attenuation potential. Yes. Yeah, of course, so sometime after today's lecture when we will be discussing about sorption desorption techniques we will be using a quantified term there R, retardation coefficient and that R is basically attenuation coefficient of the material. By this method. By this method yes, yes, yes, exactly that is the whole fun see now you are into the thick of it and now you are talking about the philosophy and then later on comes the quantification of a process, we will do everything yes. So, this is a collection based in lysimeter normally this is designed for checking the vulnerability of the clay liners which are used in the landfills, vulnerability against what? Number 1 is percolation of water, number 2 against percolation of contaminants. Third, what else it could be? Temperatures, you see we have discussed so much that the liners which we are placing at the bottom of the landfills might get exposed to high temperature gradients, why? Because of the chemical reactions which are going on inside the landfills, so these are the barriers which might also act as a thermal barrier under any circumstances sorry under no circumstances the clay liner should crack either because of chemical reactivity or because of physical damages when you are laying and compacting or because of swelling, shrinking or because of chemical reactivity or because of extremely high temperatures and so on fine. So, here what we do is we put a clay liner on the top of a granular backfill and we place a perforated pipe at the bottom and why this is known as collection based in because you are creating a V sort of a system, so the percolants will get collected at the bottom most point which is triangular and from here which is perforated pipe system you can suck out all the leaches. These type of mechanisms or systems are normally prevailing and provided in landfills, so when you see the landfill design this type of clay liners are designed, okay. Now what I can do is I can expose this whole thing to the range, artificial range, let the water percolate through it and then I can find out what is the permeability of the clay liner under you know in situ conditions and what type of contaminants are going to pass through it as a function of time, all that manipulation can be done. So as and when the pore solution comes, those are the properties corresponding to time, so leachate characteristics after filtration would depend on the time of interaction also. Fluids with different viscosity will travel at different rates, so fluids with different viscosity will travel different, excellent, yes. So if we are going to create artificial range, is there a chance that the water we supply is going to be collected before the contaminants, yeah you are right, so yes there could be a chance, it has to be mathematically modeled, so imagine if this was a confinement, if this was kept in a confinement whole thing and if I allow rain water to get accumulated over here, so are you trying to say that the concentration is slowly building up, that is what your concern is? It is not about the concentration, even before the contaminants start to flow. Okay, let us say this boundary, alright. Is water capable to come even faster than the contaminants? No, but contaminants are in the liquid form, so they are dissolved in the water itself, water is the carrier, oh yeah, so your point is correct, so these contaminants are dissolved in water and that solution is percolating through it or it could be reverse way. If I want to see what is the level of contamination of this clay liner, I will be washing it through with the more purest form of the water, clear? And then let me see what gets percolated, so this is sort of a washing experiment, pre-contamination, desorption experiment and then I would like to study how much the soil would like to retain into it, clear? An agricultural scientist will be very happy to do this type of experiment in a lysimeter, why? Because he is going to grow a crop and he wants to see even if the extreme flooding occurs, what are the chances that this soil will retain nutrition into it even after let us say one year of flooding of the entire system, see I have changed the context of the problem now, but yes this is what agricultural scientist would like to study. So this is where you require very high attenuation capacity of the soils also, clear? So very high sorption rates is good, very high desorption rate could also be good for something else, for another situation, is this what you are asking? So the thing was I was assuming the contaminants to be in a fluid form and water and the contaminants are going to be having different viscosity. Contaminants are mostly heavy metals mostly because you are interested in knowing how heavy metals would leach and cause what type of havoc to the porous media, clear? So either you can take the leaches which are coming out of landfills and you can pour them over here and you can simulate a condition, what type of clay liners should be designed, at what porosity, made up of what soil, made up how much depth, thickness all these things. So it depends upon what you want to do, so I can use pure water, I can use contaminated water, this is what is known as artificially created contaminants. So if you understand that these are the heavy metals for which you want to see the response of the clay liner, I will use that particular species of the contaminant in the water, dissolve it, make a solution and let it pass through it. Or I can create a competitive, you know, contaminant migration also. So I will have different species of contaminants in the solution form, multi-contaminant system I may create and then I would like to see which contaminant is coming faster. So and which has higher sorption capacity on the soils, so all these things can be done. There is a bigger picture of the whole studies. Sir, what is the efficiency of collection of this porous liner? What is the efficiency? How can we make sure that the entire porous solution is getting collected? How the entire porous solution is getting? Collected. Collected where in this, you know this is a sloping area, is it not? So nothing would stand as it is somewhere here or the whole idea of making a sloping ground is that whatever is percolating will come and get collected over here. Okay, whatever is percolating is collected but how can we make sure that entire thing is getting percolated? I need not to wait for that because most of the time, you know how the sampling is done. You may do sampling with respect to time or with respect to spatial distances, alright. So I will do maybe 10 times sampling for 10 days or 20 days or 30 days or 1 year and that is it. I mean I need not to wait for the entire system to get dried up or whatever. Write down this question and when I am discussing the breakthrough curve, please ask me this question again. I think you will get a better picture. So yes. Sir, like any preferential drainage paths are there in K-Rainer and it will affect the contaminant collection. Yeah, you are right. So that always remains there. So that is the biggest limitation of creating these type of systems where the interface comes that is a known devil. When I was studying about the MSW landfills liners in which the codal provision is like you have a 1.5 meter clay liner. So is it like 1.5 meter is set like for a particular leachate depth. So they have given consideration like to a leachate depth for a typical landfill or is it just a casual number. You see again as I said these are the thoughts which are under scanner. So if a person like me is a consultant, I cannot afford 1 meter you know storage space in a landfill for creating a liner system. Second question is in today's world I do not have so much of the clays from where I am going to bring them when they are strict you know warnings and what do you call as strictures that you should not excavate soil from anywhere. So all this is the neo concept where I would like to decrease the size of the clay liner from 1 meter to 2 centimeter alright, CCLs. So first of all the concepts are required and second is alteration of the concepts to make your ideas more contemporary. So in all my consulting projects right now I am going for you know what is the thickness of the liners which I use 3 mm I cannot lose 1 meter space of storage multiplied by the whole area of the landfill. How much volume? This would be 1 year or 2 year of storage of the entire bombasticity. It is not 12,000 tons per day what you are talking about 8,000 which has come down to now 6,000 per day in Bombay. So are you realizing the concepts and what can be done by using these simple experiments you know big, big questions can be answered. So suppose somebody asked you a question that create a thermal barrier for my building. I can use the same concept what I have to do rather than percolating the water what I will be doing I will be exposing this surface to a thermal gradient and then I will measure temperatures over here to tell you whether the whole thermal barrier is intact or not. So I guided 2 PI the thesis is based on this concept where we have designed thermal barriers for defense. These are the applications of the modern day science and technology. This type of systems are also used for finding out the efficiency of the clay liners you know how much they are leaking, how much they are cracking and to determine their hydraulic conductivity which I have already discussed whether they are properly functioning or not. So I can put a electronic sensor also at the bottom of the clay liner. So the moment a certain species of contaminant comes I can detect it and this can produce a sound or light or you know some sort of an alarm and I know that the liner has failed. So these type of techniques are being used in contemporary world.