 Now, let us discuss with the about pore solution sampling. I intend to spend enough time today regarding this particular sub topic, because later on you will realize that this is a very good technique to understand what type of interaction has occurred between soils and contaminants. So, the logic which comes to my mind is that the pore solution sampling is identical to blood sampling of a patient. So, modern day what is happening in our medicine? This is what pathological examination is all about, is it not? And then based on blood sampling, you diagnose the disease and then recommend some medication, observation and all those things which we have already discussed. So, this is a prerequisite for soil water contaminant interaction studies. You must appreciate one point that there are two perceptions of defining soil contaminant interaction. One is whatever is retained in the pore solution and whatever is retained on the soil grains, is this clear? When soil is interacting with contaminant, certain fraction will remain in the liquid phase in the pore solution. Now, these fellows could not get adhere to the soil grain because of whatever, clear? And the second category is whatever gets adhere to the grains of the soil mass. So, these are two perceptions based on which you can further study soil water contaminant interaction. So, the simplest form is if you take out the pore solution, analyze what is the concentration of cations present in it and you can say the soil is contaminated to this extent. The second perspective we will be talking when we will be discussing sorption, capacitive of soil mass. That means, what amount of concentration of cations gets sobbed onto the material. So, this I will be studying in sorption, desorption studies or I will be discussing that. This is quite clear. The best application of this type of studies is to predict transport or fate of contaminants in the soil mass. Do you agree with the word that fate of contaminants? Normally you go to an astrologer to say what is my fate is it not what is stored in my future. So, why do people use the word fate of contaminants? Any guess? Good. Good. The latitude is almost good. That is correct. Transport is a easy phenomena. Whatever you pour on the soil mass, it simply gets percolated out and as if nothing has happened to the system, you would have been lucky if this type of situation prevails in most of the cases. But truly speaking, soil is active, contaminants are hyperactive. So, this type of situation will not occur so easily. Now, this is where you start talking about what happens to the contaminant when they get trapped in the matrix of the porous system. So, when you use the word what happens, this is nothing but the fate. So, they may decay there, they may multiply there, they may degenerate there, they may do something more wonderful. Now, this is what people are trying to understand that what ultimately happens to contaminants when they interact with soil mass. So, this becomes a very interesting phenomena to study and to capture. Similarly, if you are let us say setting up a power plant or industry or nuclear power station, the first question is that how far I should draw a boundary so that no population should be within this limits. How would it mean this? There has to be some mathematical modeling, there has to be some in situ observations to be conducted so that you can define that yes up to 25 kilometers from this point onwards, there should not be any populace because this is a danger zone. Now, this is where actually people talk about prediction of transport of contaminants. So, these are two very interesting sites of the coin I would say, where most of the time people try to understand either the transport mechanism or they try to understand what happens to the contaminant and the porous system because of this interaction. So, it is a very wide topic, very very wide topic. So, here you can create four type of situations passive soil, passive contaminants, active soil, active contaminants and the combination ok. So, this is what our friend, see universe is trying to do, is he here? I cannot see him. So, universe you agree with this? This is what you are trying to work on. It is a pure philosophy, he is trying to conceptualize and conceive this idea and then show in numerical terms that yes this type of interaction can be captured. Not photographically, but mathematically. Another good application is that it should be a very good methodology to design suitable containment and barrier systems, whether your barriers and containment are working properly or not. So, you think of a situation that below every containment or a barrier system, if you can take a dose of the leachates or whatever is coming out and if you analyze it and if you see that the concentrations are alarming, that means, your barrier system has already failed. Just like your blood sugar going very high, what doctor does? Immediately cautions you do not do this, do not consume sweets and so on. Immediately you have to take some actions to stop this type of transport out of the leachate facilities or the landfills. So, this is where actually safe disposal limits come in the picture. The basic question which I had in my mind when I was when I started my studies on this topic is that how this disposal limits are quantified, how these guidelines are prepared, is it not? So, basically it is based on observation or based on experience. So, all the guidelines are based on experience or the observations in terms of quantity and concentration of the leachates which are coming out of the system. Now, incidentally this can also help you in determining the leaching properties and attenuation properties of the soils. So, leaching is nothing, but if you add fresh water to the soil mass, whatever free ions may come out of this is leaching. So, this is leaching out of the elements from the soil matrix. Normally this type of thing will happen when soils are heavily contaminated alright, then only leaching will take place. So, the second thing which you are talking about is the attenuation characteristics of the soils. So, attenuation characteristics of the soil what it indicates is that whatever contaminants you are pouring on the soil sample they remain captured in the soil mass attenuation alright, stopping property of the soils. Now, these type of studies will also be very significant and useful when you talk about intrusion of pollutants in the groundwater resources. What is the dose of the contaminants which is migrating into the freshwater supply? So, some of you or maybe some other researchers they are trying to understand the ingress of salt water in the freshwater supply. So, the best thing is you sample a pore solution and then see what type of chloride ions are present in the freshwater supply and whether you require some containment of the barrier system to stop this type of process. Prediction of the loss of the nutrients from the root zone. So, you can think of devising some instruments or maybe electronics or Q-tree where the moment nutrients leach out from the root zones there should be a sort of a alarm system. Now, this type of alarm system is also placed below the landfill liners. So, the moment concentration of the leachate increases there is a alarm and then you get enough time to correct this. Detection of the microbial activity in the soil. What type of microbial degeneration are taking place in the soil mass? This can also be checked. Microbial activity will normally decompose the soil mass and once the decomposition takes place there could be some elements which may leach out of the soil matrix. So, this is how the microbial activities can also be studied in the soil with the help of pore solution sampling techniques and the best thing you can do is you can validate the solid transport models particularly mathematical models. The biggest question is the type of mathematical models which are being used by the professionals whether they are accurate or not clear. Now, this is where the question is how to select the parameters which are going to be in the mathematical models. So, for getting this mathematical model parameters you have to conduct some field instrumentation or laboratory instrumentation. Then whatever results you are getting from the mathematical models you can always check by observations in situ observations. So, this is a very hot topic for research you know in the 21st century and then if your models are not matching with the field observations the critical commentary what is why it is so happening and in what way the mathematical model should be refined or in what way the detection technique should be refined you know then this becomes a two sided problem. So, one side you try to modify mathematical models and the parameter estimation. So, this becomes a very challenging task. Let us discuss a bit about sampling techniques. The first category of sampling techniques is in situ or the field and the second broad category is laboratory alright. So, in in situ techniques normally we go for lysimeters. I have discussed this in previous lecture I had shown you one or two slides today I will be discussing in details how lysimeters are designed, how they are installed and ultimately what is the basic idea of doing lysimeter studies that means to collect the pore solution and the moment you have collected the pore solution you know what is the extent of contamination and what is the extent of soil contaminant interaction which has already gone through. So, when we talk about lysimeters there are two categories of lysimeters one is zero tension lysimeter another one is tension lysimeters. In your perception what is meant by zero tension lysimeter and tension lysimeter and what is the difference between the two yes please Sneha, Sangita why is the word tension being used there Ravi some guess at least you are very close very good please think again and answer you are very close that something is applied to collect the pore solution that is right. Now what is that you are going to apply very good. So, suction that means depending upon the state of the soil there could be either free drainage which happens mostly in saturated soil mass or if the soil happens to be unsaturated there you have to apply suction to collect the samples. So, you are quite close very good Binnell and Jan when you talk about in C2 instrumentation sometimes soil salinity sensors are also used. So, these sensors basically tell you how salinity soil masses is it not. So, again your electrical conductivity will be different for soils which have more salts in them. So, if you do a if you perform it as let us say in runoff catch where you have mostly brackish water where the electrical conductivities will be very very high as compared to normal water. So, this is where you can easily find out that soil solution has more of chloride ions or salts and hence the conductivities are very high alright. Sometimes absorption techniques are also used I will cover these techniques bit in details in today's lecture. As far as laboratory is concerned we normally talk about centrifugation technique to drain out water from the soil mass. And then most common technique is pressure membrane extractor PME you apply some pressure squeeze out water from the soil mass whatever pore solution gets collected analyze it by ICP, ICP MS or by atomic absorption spectrophotometer it is ok. So, broadly we have two categories when this field another one is laboratory. So, let us start with the in C2 studies basically lysimeters are designed for in C2 studies. Agricultural scientists were the first to use lysimeters, but slowly and slowly we have encouraged upon their expertise. And hopefully you will understand that why we have entered into this field we means geotechnical engineers. The basic objective of these studies is to simulate disposal facility in a control volume. What is the disposal facility? Disposal facility is nothing, but a repository where the waste is being dumped alright. So, the basic intention is to find out guidelines what should be the proper dose which should not be crossed otherwise the ground water the soil will become contaminated and there will be an impact on environment directly. So, what you are doing is you are trying to simulate disposal facilities in a control volume. How waste should be disposed on the soil or in the soil in the best possible manner. So, that it does not hamper the atmosphere sorry environment. Now, when you are doing this hope you will agree with the fact that moisture movement is the biggest culprit. Because the waste will come in contact with water and then along with the water the species of the contaminants will get leached out and they will migrate into the soil mass contaminating the environment. And then second issue is the concentration of the contaminants. What is the concentration which is getting leached out? Now, this is where environmental geotechnical technology has to play a very important role. Suppose if I tell you that your disposal facility happens to be located in the heart of the city. So, you do not want to take any chances that there should not be any movement of moisture from the system and there should not be any concentration of contaminant moving out of the facility clear. So, this is where the geotechnics of landfills, liners, geotextiles, liners, systems, GCL and all this comes into the picture. So, this is where geotechnical engineering takes over what has been done by agricultural scientists. Their primary aim was what should be the dose of the pesticides or the fertilizers which should be used so that excessive leaching does not takes place into the geoenvironment. So, the obvious answer is if you want to do in-situ studies the best thing is you create a lysimeter. One more thing I want to tell you at this stage is the lysimeter can also be replicated in the laboratory at a miniature level. Of course, it will have it is own limitations, but yes you can take the same soil from the in-situ. You can remold it to the same conditions and you can do a study at a smaller level of volume level. So, what is the lysimeter? Lysimeter is a device which collects and senses percolating water through soil mass and it helps in determining the concentration of water soluble contaminants. The meaning of the word lysi is nothing but whatever secretes out or whatever moves out and meter is nothing but the one which is going to check this or measure it. So, it is a device which collects and senses percolating water through the soil mass and helps in determining the concentration of water soluble contaminants. There is a limitation whatever is soluble in water will only come out and what is not whatever soluble will not come out. And the basic idea of doing this study is that I want a solution in the time space domain. A good example of where which I should cite over here is when you solve consolidation equation, you solve this equation for pore water pressure as a function of x and t. So, at a given depth after a given time what is the pore pressure which is still remaining in the sample. The same thing I can modify I can replace you by the concentration and my question is if there is a facility where the waste is being disposed what is the concentration at a certain distance at a given time. And this concentration has to be less than the permissible limit of the concentration. Then your facility can work very well and everybody is going to be happy with you. This can be a reverse problem also at a given time what is the concentration at a given distance what is the concentration. I hope you can understand this point whatever pore solution is coming out yes take see this is the facility and something is leaching out of this. I want to find out at a given time at a distance of x what is the concentration C t and this concentration should be much less than the permissible limit. I have several ways of doing this either I can check the concentration at this point itself by using a lysimeter. I can do a bore lock over here take sample of the soil make their solution again test what is the concentration that is one of the ways is a destructive method. I can devise another technique by using a probe I can find out what is the concentration at this point at this point at this point at this point and so on. So, I will be having a concentration profile like this agreed. So, this will be for a given time I can do it in a domain of distance at a given distance how the concentration is changing. So, that also I can find out. So, that becomes a reverse problem it changes according to a scale. That is right correct there could be a special variation of the concentration that is right. So, again you have to normalize these special concentration variation and then you have to come up with a representative number most probably. So, you have whatever variation is because this is going to happen in plan in the whole domain. So, this is the plan I can find out concentrations all over and then I can go for some normalization and averaging of the values. So, the basic idea is I should get some concentration which is representative at a given distance even if I know the concentration at this point I can use some mathematical models to check what is the concentration at this point. So, this becomes a very good mathematical modeling problem. Now, again the question is for doing this type of mathematical modeling how you are going to generate the input parameters and that is the challenge this is what most of the hydro geologists are doing. So, they go for different bore logging they collect the water sample soil course and they generate from both the perceptions what is the concentration of ions present in the water as well as in the soil samples. This becomes a holistic modeling exercise is this ok any other point which confirm my. So, ultimately what we are doing right now is we are trying to understand a phenomena we are understanding the physics of the phenomena then slowly and slowly all this physics part will take help from the mathematics to do the modeling. So, that answer to a real life situation can be obtained that is the philosophy is clear.