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Pore-Solution Sampling

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We have been discussing about geomaterial characterization and we have talked aboutphysical characterization, morphological characterization, geotechnical characterization, mineralogicalcharacterization and some part of chemical characterization which I have been talkingabout.And the whole emphasis is to give you an idea about that why these type of characterizationschemes are important in contemporary practice of geotechnical engineering and environmentalgeomechanics and what is the state of the art on the subject.So, in continuation with that what I have been discussing in the previous lecture Iwill be touching upon chemical characterization in details today.The obvious reason is that the chemistry of the material is becoming very, very importantto understand what is the state of the material, including the human body?Most of the assessment of the status of the human body or the geomaterials is being donebased on this chemical examination.So, under the head of chemical characterization, we will be discussing quite in details aboutthe pore solution sampling, which in my opinion is identical to the blood sampling, whichI have been telling you since several lectures there is an analogy between the way the medicalpractitioners, they diagnose the human body based on the fluids which can be retrievedfrom the body.Similarly, we can do the diagnosis of the materials by retrieving the pore solutionsfrom this.This is a very contemporary thought in professional practices of these days where the intentionis to treat the system and when I say a system, this is the geomaterial system based on theearly diagnosis and the application of the chemical characterization is best definedby the corrosion potential of the soils.In today's world, this subject has become very, very important as I cited last timealso all the buried structures in the soils have to be in contact with the severity ofthe soil and hence the corrosion of the buried structures because of the aggressive soilimport environment is becoming very important.And hence I will spend some time in describing what is the corrosion potential of the materialsand based on this the classification scheme has been developed.We will also be talking about this option the sorption-desorption mechanisms, whichis the easy way to quantify how geometrical contaminant interaction occurs.And this is a very contemporary thought, where any type of interaction with the materialof any contaminant in gaseous phase or the liquid phase can be quantified by studyingthe sorption-desorption mechanisms.Then, of course, we will move on to thermal characterization followed by electrical characterization,and this would be followed by the magnetic characterization and that would be a verycomprehensive discussion on environmental geomechanics.So, to begin with, when we talk about the pore solution sampling, as I said, the analogyis same as the blood sample or for that matter, any fluid which is from the body and thisis a prerequisite for soil water contaminant interaction studies and this is where thefocus is, in today's world, most of the industrial activities are polluting the geosystems orgeomaterials.So, and most of these issues are becoming, you know, legal issues.The warnings are being sent, notices are being sent, and if under no compliance even theclosures are being offered are being sent to the industries.I hope you understand these words are quite big and they are extremely difficult situationfor an industrial setup to handle.Basically, pore solution sampling helps in predicting the transport and fate of contaminantsin the soil mass, or even the rocks also.Why have not toured it because it is easy to study things in the soil because of therelative less denseness of the matrix or the porosity that higher as compared to the rocks.So, when we talk about the transport of contaminants in the geomaterials or the porous media thesecond question comes, what is the fate of the contaminant, how long it is going to survivein the porous media or it might multiply also depending upon the situations which you mightbe observing that prevail in the geosystems?So, contaminant transport and determination of fate of contaminants is also becoming verycontemporary, most of the time nuclear industry, thermal industry, thermal power industry,pharmaceuticals any type of manufacturing which you take would require, you know thetechnical guidance in terms of these steps, which would form the environmental impactanalysis also.So, we have discussed sometime back about the containment system and the barrier systems.So, the best would have been if I would have contained the things by designing good barriersin the soil mass, so that the contaminant does not spread into the entire geomaterialor the porous media.So, this is their pore solutions can help you in understanding whether the containmentand the barrier systems which have been designed or installed or functioning alright or not.So, this topic as I said is more of you know practical ideas and execution oriented.And if you check on the net a lot of activities are being done under the realm of pore solutionsampling and contaminant transport.This exercise will also help us in determining what are the safe limits of the disposal ofcontaminants what should be the quantity and what should be the concentration of the contaminantswhich should be discharged.So, in other words for solution sampling also helps you in deriving the guidelines whichshould be adopted by the industries for disposal of contaminants in the general you are awareof leaching and attenuation characteristics of soils.So, leaching is a phenomena where the heavy metals or several species which might contaminatethe environment, come out of the waste matrix and then they transport into the porous mediaor geomaterials.Attenuation is the reverse process attenuation is something which is the capacity of theporous media to not allow migration of contaminants to occur.So, this is a sort of an inherent property of the geomaterial by which the geomaterialwould not let the contaminants migrate from one place to another place.So, it could be also termed as retardation capacity, retardation characteristics of porousmedia that means, the porous media is so active chemically that image in a species of chemicalswhich is passing through the porous media and get sorbed onto the porous media itself,it will discuss these things around.So, as it environmental geotechnical engineer where the jobs are where the challenges are,these are the topics in which industry requires your support and help.So, you design a barrier system which is attenuating the contaminants that would be a statementof the contaminants are leaching out of investment is that is known, but how can I stop thisprocess?That is very good, but if I cannot stop this process, what type of porous media I can createthrough which contaminant transport would not occur so easily.Or the third definition could be, I would like to create a porous media which wouldattenuate contaminant transport, alright.So, these are the three different types of issues which you might be coming across.Then, of course, everybody is concerned about the natural resources like groundwater.And we do not want our groundwater sources to get contaminated because of the industrialactivities.But unfortunately, this is what is happening.So, pore solution sampling is also going to help you in taking proper measures so thatthe groundwater reservoirs or the resources do not get contaminated.In today's world of electronics and sensors, it is very easy to monitor and protect theunderground facilities by installing sensors that discussing subsequently, there is anotherinteresting area where some of us are working.And we supplement our knowledge to the individual scientist who do not have much, you know,practice of dealing with the porous media.So, one of the challenges which environmental geomechanics professionals are facing is howto predict the loss of nutrition from the root zone because of over irrigation Alright.So, over irrigation leads to loss of nutrition also.So, all the nutrition which are present in the soil might get detached and this systemmight be equivalent to leaching of nutrition from the porous media.So, this type of a situation has to be avoided.Another situation which people might talk about is the microbial activity and this movementand the soils.So, where are the locations where the colonies of the microbial activity that are harpingor surviving in the soil must that can also be detected by pore solution sampling, thetechnical term given to this type of activity and the studies related to microbial detectionin soils could be under you know, flushing of bacteria.So, this is a topic on which a lot of research is being done beyond contaminant transport.Now, researchers are interested in finding out how microbial activity gets flushed outfrom the soils.So, it might be having both aspects you would like to stop the microbial flushing for maintainingthe good health of the soil.At the same time when the activity becomes very high, you like to flush it out of thesoil mass to maintain the balance.So, it depends upon how engineering is being done by a certain professional, I hope youcan realize that the application of these concepts could be several and tremendous.Then of course, the pore solution sampling is done for validation of the numerical modelingcourse, which have been developed by people and which are available in the market.So, there was a time when people were doing mathematical modeling for all the phenomenain geomechanics.And then later on some good sense prevailed to researchers, and they started questioningthat how good or bad these numerical modeling, you know, algorithms are, or the softwaresare.So, there is a big group of people which is working on the validity of the software itself.And that is the reason sometimes I always say you have to use software as very carefullybecause the knowledge is limited which has gone into development of the software's andwhat is happening in the world is at least few 10s of years ahead of the information.So there is a mismatch of the timescales itself in the mathematical models and questions."Professor - student conversation starts" Yes, native bacteria are the microbes thatare always there in the soil.And like whenever we are dealing with it, is it safe to assume that like in the giventime span, they would not be having any effect on the soil structure itself, where we areconstructing or if they are native, only native microbes for a given timescale of 30-40 years?So it is a good question what you are asking there, what is the impact of the native bacteriaon the on the porous media, is it?This is the general question.And I think from day one, I have been highlighting that the chances are that either these bacteriawould upgrade the system or they will degrade the system.So upgradation means there could be some cementation which might occur because of the microbialchemical process which might prevail in this porous media."Professor - student conversation ends"A good example of this would be precipitation alright because bacteria has a tendency tochange the pH of the pore solutions also inside the geomaterials.And there are metals which would not be in the soluble form corresponding to a searchand certain pH vlaues.So, if these type of things happen, the pores are going to get clogged because of the precipitationsof the salts.How are the another scenario could be that this bacteria might up the porous media itselfand hence might induce a lot of secondary or tertiary porosity in the system that’sthe voids.What I was thinking was there with this one for not Sofia, as long as its formation likenow suddenly if we are assuming that it might eat up or like is it unsafe assumption likemillions of years, your assumption is your thinking processes good.Only change you have to make nothing in processes that you are talking about the situation whichis prevailing before the soil came in contact with the contaminants.And the chances are when the soil and the bacteria come in contact with the externalagencies like contaminants, the growth might get aggravated, because many times these contaminantswould act like a nutrition to the bacteria.Right.What you are thinking is correct.So the native bacteria would have been living there or, you know, colonizing over theresince several years that is fine.But then the ingres of contaminants might change their characteristics.So you have to think of this situation.So this creates a very different context altogether, I am sure you must have realized.So let us move on to the details of the sampling techniques.Broadly, these are defined or classified in two groups.One is the In-situ which is the field.Another one is a laboratory which is the ex-situ techniques.Under In-situ field conditions or you know when we have to take the samples from thesites lysimeters are used lysimeters are the setups which were used for measuring the dischargeor percolation.So word Lysimeter corresponds to seepage or percolation.So lysimeters is a system which measures percolation in the soil mass.So, these lysimeters could be designed both in the laboratory as well as in the in-situcondition and I will show you some examples of what I did for Atomic Energy RegulatoryBoard of India.This was a unique experiment, which we did.Sometime back I will share this with you and I will show you how this whole thing was conducted.So these lysimeters could be either zero tension Lysimeter tension corresponds to suction.That means the Lysimeter.When they are used for saturated soils would not exhibit any suction and hence they areknown as the zero tension lysimeters.However there could be tension lysimeters also the soils are unsaturated or partiallysaturated.So, the challenge would be to take out the pore solution from the size which are notfully saturated alright and this is where tension lysimeters are utilized.There are some soil salinity sensors also which are used for sampling of the pore solution.And there are some absorption techniques also which have been used since long but they havebecome outdated in the sense because they are not very contemporary.However, as far as laboratory sampling techniques are concerned centrifugation is the simplestthing you take the sample in a in a glass tube or in a control volume and centrifugeit at a very high speed.So, when I say centrifugation is not at 50 G or 100 G to 200 G is going to be millionsof G values.So, the RPMs would be of the order of you know 1 lakh RPM, 5 lakh rpm and so on.So, these are the ultra-centrifuges which are used for taking all the solutions fromthe soil mass.And this is an interesting technique which has been used by us also and a lot of peopleare using to drain out the pore solution from the samples, particularly in-situ sampleswhich are brought to the lab and then you can fit them in a setup and you can spin themin ultracentrifuge to expel the pore solution.There is another interesting device which is being used in the market by people andit is known as pressure membrane extractor PME.I will discuss about this, how the pressure membrane extractor works and how the poresolution sampling can be done.Apart from this I can use some fluid displacement methods also by putting a fluid of certaindensity which is higher than the density of the pore solution in the soil mass and thenby you know density separation techniques, I can force the lighter fluid to come out,but these are very tricky methods.Sir, in laboratory, what we do for saturated and unsaturated soils.Lysimeters can be designed in the laboratory environment also.So, it is only a matter of the dimensions.So, my field lysimeter would be running in few meters and laboratory lysimeters couldbe as small as centimeters.Fine.The mechanism and the concept remains and we will talk about this and tension sensorscan also be utilized to derive the pore fuids.I will talk about this.