 When we talk about the contamination of soils particularly two components that is the chloride and sulphide become very very important to be detected in the soils. Why any guess? Why people should be talking about chloride and sulphide contents? The reasons are very simple because if you have soils which are having lot of chloride and sulphide what will happen? As a geotechnical engineer where I will face problems. Foundation could get corroded. Very good. Excellent. So the moment you do anything related with the concrete or cement and if the soils are very aggressive having lot of chloride or sulphide content or sulphate content they are going to attack the foundations and there are several cases of foundation failure which have induced because of these two culprits. So what is normally done is that you take the soils and dissolve them in water normally we maintain 2 is to 1 liquid solid ratio that means you take the weight of the soil and two times the weight of the soil is in the liquid form is added and this is stirred for several hours on a hot plate and so that all the chemical species get leached out and once the leaching process is over you measure filter the supernatant or the liquid and then measure the chloride and sulphide concentrations. There are ion exchange kits which are available in the market. These kits are similar to the ones which are used for checking your urine samples. So this chemistry is same either it is biochemistry or the chemistry of the soil we normally call the soil chemistry. This is sort of a titration which you are doing and knowing the number of drops of the ion exchange resin which you put in the solution you can compute what is the concentration of the contaminants. So changing the color of the solution is a good identification of what type of chemicals and what is their concentration which is available in the system. This is where actually soil salinity sensors are also being used they have been found to be very very useful and you know there are lot of soils which are saline in the all over the world and never cone country and because of the salinity you cannot even use them for agriculture purpose alright. So suppose if I am creating underground facility storage of hydrocarbons and the first question is what is the level of contamination of the soils because very soon you will realize that if soils are heavily contaminated even if you create a very thick concrete wall as a containment or for the underground tanks the chances are that all these chemical species will diffuse into the precious material which you are storing underground including the hydrocarbons and the water alright because even concrete is porous. So through pores the diffusion process may occur and the entire utility items which you have stored might get contaminated. Any sort of a concentration gradient ultimately would cause the diffusive contaminant transport the way you are dealing with the advective transport delta H upon L is I and the hydraulic gradient occurs and the seepage takes place the same way when concentration gradient develops these chemical species will migrate and become a part of the hydrocarbons and the water which you are storing alright we will discuss in details this thing. So soil salinity is an indication of the contamination level of the soils the need of the hour is all these saline soils or heavily you know sea water intruded impregnated soils can they be converted can they be rejuvenated there is a big problem I hope and the entire country is facing the coastal area as well as the locations like you know catch area deserts where you will realize lot of impregnation of the salt water is taking place in the geomaterials of the soil and then this becomes a big question that how to construct the infrastructure how to lay the foundations of the infrastructure. This is the technique which was developed by one of my PhD scholars during his PhD thesis Dr. Sridip you have met him all of you the professor at IIT Guwahati he did a wonderful work to develop lot of new innovative things in this context and what we have done is we have used a new equipment not now 2003-4 when he was working it was a post time in the country somebody had used this WP-4 equipment what we call it as a dew point and potentiometer dew point I think you understand what is dew point this is the moisture or the water vapors getting condensed on a surface so that is the dew point. And then potentiometer is an equipment which would measure what is the volume of the fumes or the vapors which are getting condensed on a surface WP-4 is the name of the equipment which is supplied by the company WP-4 is normally used for developing suction versus moisture content characteristics of the geomaterials. Now this is a point from where the initiation of unsaturated soils starts fine so those of you are interested in learning how to characterize the soils for their unsaturated state you have to go through the enormous amount of work which our research group has done starting from Sneha Kurian to you know Kanan Iyer I think Sneha Jayant, Anumant Rao, Ravi Ranjan Rakesh, Sridheep and so many people who have used this equipment and Vikas Thakur. So these are the guys you should read their papers and try to see how these equipments have been utilized and how the guidelines have been developed for establishing the basic characteristic curve for the soils which is known as soil water characteristic curve. So when we talk about the soil suction there are two components which everybody talks about one is the metric suction which is because of the metrics of the soil sometimes we call this as a metrics also and the second one is the osmotic suction which is because of the presence of the salts in the soils. And nowadays I am working on a third component of the soil suction and you guess what that would be. So if you analyze this closely you will find that the soil metrics represent the physical state of the material alright state of compaction gamma D is very important and what about this osmotic suction this represents the chemical state of the material. So what is remaining very good. So we have started now talking about the bio suction and two of my M-tech students they worked in this context Asha and Meenu if you see their paper they have tried to work on and they have established that these type of suction are very important and they cannot be ignored in the geomaterials. So for the time being I will restrict my discussion on metric suction and the osmotic suction because this is the first time you are getting initiated into these type of discussions. So you can always build upon once you have the basics. So soil water characteristic curve is mostly utilized by the guys who are into the field of agriculture engineering or water resources. So if you talk to your colleagues who are doing modeling of reservoirs, irrigation modeling, irrigation scheduling you know soil nutritional analysis and all they would be very eager to know SWCC. This is also known as soil water retention curve SWRC but being a geotechnical engineer we like to use the term SWCC rather than SWRC but the connotation is same either soil water retention or soil water characteristic curve. So this essentially is a relationship between the moisture content which could be either gravimetric or this could be volumetric also it depends upon what techniques you are using. So if you are taking out a sample from the field which is undisturbed you can bring it cut in small pieces and use WP4 or pressure membrane extractor to obtain the suction. So psi corresponds to the total suction and W corresponds to the moisture content. This could be theta also theta is the volumetric moisture content. So I can plot a relationship between moisture content and suction. So the way you read this graph is lesser the moisture content alright okay what happens to the suction value extremely high and the more the moisture content the soil the suction value is less that is true because saturated soils will not show you negative suction or negative pressures. So this characteristic which you are seeing the red colour is sort of a fundamental behaviour of the soil and if you are very eager to learn this subject please refer to the papers by Vikas Thakur and Sridhi where we have talked intensively about measurement of ultra high suction in the soil and interpretation of SWCC and how to develop SWCC and how to use this SWCC followed by the work of Dr. Hanumanth Rao who has used SWCC to derive unsaturated hydraulic conductivity of the soils. So many times you ask this question what is the state of the development of the subject I hope now you are getting the answer you remember some time back you are asking these things it is not the first time this is being discussed this has been under our radar since several years and we have done a lot of work and I can probably say that we were the pioneers in working in these areas when nobody thought of these issues in geotechnical engineering as back as 2002, 2003 if at early 2000 okay. So as far as the interpretation is concerned what I have shown is that the initial portion of this curve is almost flat and then I have shown a point over air as a air entry value. Now air entry value is the value of the suction beyond which the water only sorry at this point only the air will enter the pores not before this. So the way the cycle valves work you know you have the valves there and then you pump in air air cannot come out this is sort of a reverse process we are sucking out the water from the soil but we are making sure that the air does not enter the voids what is the meaning of this I still assume soils to be saturated clear. So as long as the soils remain saturated the moisture content is very high but the suction is extremely low. So this air entry value can be a sort of an inflection point you know how to obtain the inflection point you extend this straight line portion and then you extend this straight line portion wherever they cut this becomes the air entry value and air entry value is a unique signature of the soil which has something to do with the type of the soil the gamma d the particle sizes and of course the method of measurement and then verbal condition. So nowadays the philosophy is like this that if I know the SWCC I need not to do any other experiment long back I had talked about the speculative modeling application of artificial intelligence in geomechanics where I had talked about different type of softwares which are used for speculative modeling. So if I know one of the parameters or if I know the SWCC curve I can speculate all other properties. So air entry value would be of great help to people like us who are into designing the barrier systems designing the disposal repositories for the nuclear waste why because soil is under continuous threat of elevated temperatures and the moisture migration is taking place from the soil. So I would like to study you know because of this thermal influence how the moisture gets changed in the sample and how the properties are changing over period of time. So these are the applications and the implications of this study. The second term which you are observing here is WR which would be very useful for the guys who are into agricultural sciences because WR corresponds to the residual moisture content fine. So residual moisture content corresponds to the wilting point correct. So people like you who can devise their automatic sprinkling systems if you have SWCC and if this SWCC is fed in the software what you can do is you can link this whole thing with a actuator and that actuator will actuate the irrigation system. So I can do precise irrigation the moment moisture drops below WR the suction values are going to be extremely high I can measure the suction in situ by using different type of sensors and I can put an algorithm in such a manner that the moment moisture content and the suction drops below a certain value I get a trigger and that trigger induces the irrigation. This could be a technique for disposal of the toxic waste also where what would you like to do if because of the inherent heat of the of the disposed waste the tendency of the geomaterial is to crack what I would like to do I might like to have to do you know artificial saturation also keep the system saturated are you realizing this. So this is what the state of affairs is here you have to do complete engineering of the system which are extremely life I hope you are getting an idea about where the applications would be you are asking sometime that air entry value is the point beyond which the moisture will drop but air will not enter into this is also known as the bubbling point clear. So this is the point beyond which the moisture loss is taking place but you are stopping air to enter and that is used for different applications you are not allowing system to become unsaturated clear but of course water is draining out. So this is a sort of a equilibrium which is existing at the interface of the contractile surface. I was thinking like sir at the shrinkage limit at the shrinkage limit what happens is the air enters no slightly below shrinkage no never at shrinkage limit also your sample is saturated clear and you take all at most care that the air should never enter remember if you have done haste and if you have fried your sample it is not a correct estimation of shrinkage limit sample should never crack number one if sample has cracked so after taking out the pad we should really use a lens to see whether the sample has cracked the air has entered into it or not. If air has entered discard the sample it should never be used. So by concept the shrinkage limit is the one below which still the soil is fully saturated or at this point the soil remains saturated and air has not entered into it that means the cracks are not formed agreed so let us not complicate the things. Use this air entry value sir. I told you air entry value is the one if you look at this graph you know the moisture remains constant so this is the point where the tendency of the air is just to enter into the system and because of this what is happening is the moment you increase sorry there will be a decrease in the moisture content and decrease in the moisture content is still holding from air to enter into the system clear. And then after that what is going to happen is if you apply pressure on the soil sample lot of water will come out. So that is why we call this as the initiation of entry of the air into the soil sample ok. Type on Google air entry value and bubbling point of the membranes and then see the videos it is ok. So working of the WP4 it is a equipment which is commercially available this appears to be a sort of a chamber where you have a dryer in which you can mount the sample over here in a small cup and there is a block chamber inside. So if you look into it this works on the principle of relative humidity that means if I take a sample which is saturated and if I leave it below beneath the fan what will happen the moisture will evaporate. And these moisture in the form of the evaporation if they get condensed on a mirror ok that mirror I can use some infrared technique to measure what is the volume of the moisture which has got condensed over there. So this is the calibration which is done in the form electronics to measure what is the relative humidity of the sample and this relative humidity can be converted into the suction value directly. This is this technique is also known as chilled mirror technology, chilled mirror technology so read about it which gives you the total suction. So the point here to be noticed is that most of these WP4 type of instruments they work in the range of 0 to 80 MPa but of course the new ones in the market go up to 350 MPa also of the suction value remember these are the negative pressures but what we have proven is that these equipments cannot be utilized for the range of 0 to 1500 kPa for that the pressure membrane extractor works better. So in short pressure membrane extractor and the WP4 result should be utilized together to get this WCC. More about this please read from the papers which I have referred to particularly the papers which have been written by Vikas Thakur alright. Now the pretext what we take from here is that if I take the soils in their native state which might be contaminated and if I establish the WCC and if I wash the soil sample several times by using water or different chemicals and if I keep on measuring the air suction values there will be a difference and that is what the contamination is. Now you may ask a question that you know in real life we cannot do this because there will be millions of tons or the millions of metric cube of the soil which might be contaminated. So how would you draw a parallel between the laboratory exercise and the field exercise? So the answers could be like you know I am using this technique first of all to establish what is the level of contamination whether the soils are contaminated or not. Nowadays I can create a small prototype sort of a thing in the lab to show if this is the volume of the material and if this is the level of contamination how much washing is required to get rid of all the chemicals which are adhering to it and then this becomes say this can be scaled up in the real life. So these type of challenges are still lying ahead of us we have to overcome them. Many studies have been done but when you have to take them to the field at a bigger scale you have to be very judicious in applying them. Does this answer your question that what is the significance and how the practical applications of these techniques have been made? If you look at this it is not the matter of time what is more interesting is I have to come up to the tail of the graph. So for few soils we have seen that this take months all these experiments are basically they test your nerves patients particularly when you are working on the organic materials it is very difficult to ooze out moisture from them even after drying and if you are drying them the chances are that they may catch fire or they may distort the volumetric deformations could be there so it becomes very tricky to work on it. But I hope you can understand that these are the questions which are being answered which will become tomorrow's guidelines and tomorrow's code of conduct. So this is the case study which I wanted to share with you. Incidentally you only talked about the case studies today and then this is the case study which I am talking about most of the coastal regions particularly the ports are very much concerned about the quality of the soil and all this comes under the green initiative of government of India. So most of the ports have to comply with the green ports status I hope you understand what is the meaning of the green port that means first of all this is a zero waste discharge nothing goes out of the port area either in the gaseous form liquid form or the solid form but if you do the audit of most of the ports you will realize because the cargo handling the soil is becoming contaminated imagine chemicals which are being brought in urea particularly different type of acids petroleum hydrocarbon items of day to day life and so on. So they get spilled over when you stack them and this is becoming a big work for environmental geotechnologies to establish that the soils there are uncontaminated and in case they are contaminated you have to clean it up. There are many instances where the fire has to taken place at this place of storages of these consignments which are known as containers they have exploded also and this type of accidents happen in the factories and once they meet this fate you have to clean up the entire area. So if you characterize the soils of the marine nature which are in the course of Bombay these are the properties of the soils. You have specific gravity, particle size distribution, liquid limit, classification is typical MH type soil this chemical properties come from the XRF analysis XA fluorescence and then if you look at the chloride and sulphide content these are extremely high and the cation exchange capacity is also high. So chloride content tells you that the soils are impregnated heavily with this marine seawater and then you have to do something to create the facilities over there. So what we did is we took this as a initiation point for studies and we started washing them to nullify the contamination level. So what you will observe here is that we have given number of washings to the soil sample LS is the liquid to solid ratio the process sample you take certain amount of soil and add 2 times the water so this becomes L by S equal to 2 measure the chloride content and sulphide content and keep on increasing the volume of the water to wash the soil sample or you can literally wash it also. So then L by S becomes 4 times 6 times 8 times 10 times and then keep measuring these things until you get something which is within the permissible limits. So this is one of the techniques which we worked on and what we have shown here is that if you measure the electrical conductivity of the supernatant and number of washing what you will observe is that as the number of washing increases the conductivity of the pore solution decreases. So remember we were talking about the pore solution and its application to establish whether the soils are contaminated or uncontaminated. So in literal words what you have to do is you have to bring down these salinity from this point to this point if you want to make this soil usable for different applications clear. So electrical conductivity data has to be manipulated in terms of the time and money. So these type of relationships have to be developed. And then if you measure the SWCC of the contaminated and washed soils so what you will realize is that these are the peculiar SWCC curves for the contaminated soils and uncontaminated soils or the washed soils. And what you will realize is for a given moisture content there is so much suction different. Now this is the osmotic suction. So what I am trying to convey here is that soil water characteristic curve itself happens to be a interesting way to establish the level of contamination of the soils. Sir this washing process is done in large scale. So that is what I told you sometime back that before you launch something in the market what do you do? The thing is that wash water it is like we are contaminating something. Oh yes. You have read our mind correct. So that cell is going to be a secondary source of contaminant you are right. But see as a technologist what you have to do you have to keep on trying different options you cannot say that I cannot do it. It is like we are just transferring the pollutants from one source to. That is right. So from your own mistakes you learn is it not. So somebody must have washed soils in the beginning and then someone else must have asked this question that what you are going to do with this slurry. Third person would have asked how would you dry it up now this soil. Fourth person would have asked how would you reconstitute the samples from the slurry state to this state. This is how the S&T grows develops when you have to ask lot of questions. So your questions are valid. Now coming back to your point the question would be any not to do the washing. Cleaning is you know a connotation there could be another interesting way of getting rid of the contaminants by making this a stand mark as a batch is a benchmark and saying if I do any treatment clear and if my results that superimpose on this graph on the left hand side or right hand side I know that this is the 100% drying or the cleaning process clear. And where do I stand if I adopt any other technique and quantify my efforts that what type of decontamination of soils I have achieved by other methods. Now this is what exactly Ghan Raju is doing. So suppose if I give you a heap of mountain like the mountain which you have in the IIT campus on which you climb and see the moulin this is the size of the mountains of the red mud or let us say industrial byproduct which is lying here and there. Now somebody asked me a question can you neutralize this whole mud so that I can use it for some purpose are you getting this point this is where this type of study becomes very useful. So what I will do is I will inject some gases I will inject some chemicals I will inject water and I will do all sorts of logistics to take out the effluents so that they do not pollute the world geoenvironment and after doing all this if I take out a sample and do this test and superimpose it over here I know that complete washing was this and I am somewhere here it shows that yes I have decontaminated soils. This answer is better than saying nothing can be done at least I have lower down the extent of contamination of the soils because these are the solutions which have to be given to the industry and the governance. So imagine if I remove all this chloride and sulphide with pH equal to 30 I am sure you cannot walk on this material with your rubber shoes why it is all alkalinity and God forbid if you slip over there and if you touch the material you are gone absolutely so it is very dangerous to work on this type of deposits and go to Australia I mean there are the soils which might be having sulphate contents and acidity of the soil could be of the order of 2.5 to again you cannot access these places forget about taking out sample with the help of a drill bit itself will get dissolved in no time. So these are the challenges which people are facing and trying to overcome so this must be giving you an idea about the complexities associated so the people who ask the question where the solutions.