Loading
Notes
Study Reminders
Support
Text Version

Lysimetric Studies and Laboratory Sampling

Set your study reminders

We will email you at these times to remind you to study.
  • Monday

    -

    7am

    +

    Tuesday

    -

    7am

    +

    Wednesday

    -

    7am

    +

    Thursday

    -

    7am

    +

    Friday

    -

    7am

    +

    Saturday

    -

    7am

    +

    Sunday

    -

    7am

    +

Video 1: Importance of Lysimetric Studies
So, in nutshell what is the basic philosophy of lysimeter is truly speaking there are twostrata.One is the lower compartment which is the leachate collection system and upper compartmentwhich is filled with the material sensors and moisture extraction systems like cups.And what I can do it, I can find out the how the system is going to behave when I talkabout let us say encapsulated nuclear waste because disposal of the nuclear waste hasbeen a big issue and the country wants to become a muscular country in terms of youknow.Today’s social political situation so, radioactivity and dealing with it has become very important.This is the attenuation property of soils has become very important.So, what I can do is I can take the atomic waste or highly toxic waste encase it in aunit this is what is known as encapsulation.So, I can freeze the entire material contamination into the matrix of cement or sometimes glass.Those of you who are interested read more about how this is done.So, glass is the best source of encapsulation of toxic waste.Why because glass is amorphous.Do you remember XRD patterns.So, there we were looking for the glassy here which is more reactive.So glass will not let anything come out of it.Now, when I am talking about this, you should also Google about the salt domes salt domeswhich nature provides salt domes.So, which nature provides and these are the best places to dump the atomic waste comingout of your reactors.Why?Again the same thing, salt is the most reactive phase, which will not let any species of contaminantsgo out of it and hence it acts as a best possible barrier system naturally provided.So, coming back to this story, I can take toxic waste atomic waste biowaste encapsulatedin a matrix of concrete, cement paste different type of resins and I can solidify it.Now, the question is before I dump it somewhere, I have to prove that nothing from this unitis going to leach out.So, this was a project which I dealt with for India.And a very educating work.And this type of modeling we did real life situation.And what I did is after embedding it somewhere here in the upper layer, I induced artificialbrains and live the system for certain duration and whatever leachates come, you can analyze.And you can show that the encapsulation which has been done is perfectly all right, nothingwill go out.Everybody is happy.Are you realizing the importance of this simple experiment, which was done, I am getting afeel of this, minus this, everybody would have been asking what will be the effect ofthis material on errant and then they are not let you install atomic establishments.And if nothing of the sort happens, then what will happen?You will always remain in 17th century.Deprived of electricity and power and weapons and whatnot, radiotherapy and medicines, somany applications.So are you realizing the whole cycle, where the science and technology gives answers tothe questions which would safeguard the society against the concepts are clear.So, I can design here how much is being retained by the soil, attenuation property or thisoption studies and everything, I can do a beautiful modeling to even see what is theeffect of temperatures, ambient temperatures after disposal.What are the temperatures in the ground, whether thermal cracking of the soil is taking placeor not because these are the thermal stresses, chemical stresses, radiation stresses allput together beautiful example of coupled phenomena and we use this concepts to findout you know the validity of the models which are being used.Okay.So until now we have been talking about the you know saturated systems of the soils.Zero tension lysimeter.And now I would like to show you how the ancient Lysimeters look like primarily they are usedfor unsaturated soils where you do not allow ingress of water happening in the soil mass.So, this is how these systems look like these are the last tubes of PVC tubes which arespecially designed for these are typically PVC tubes or the glass tubes of differentlengths.At the end there is a specialized ceramic cup which is attached and this is also knownas thimble thimble.So, these are the systems which have a specific air entry values.In medical sciences they use these type of things quite a lot.Most of the research in the environmental geomechanics is being replicated after seeingthe human body and how it functions so, these systems which are normally used in medicalsciences are now being used in geomechanics.So, in this tube, there are tube pipes which are inserted the philosophy is like this thatonce I inserted into the soil mass which is unsaturated, leave it for some time applysuction.So, when you apply suction, the water from the unsaturated soils gets sucked and thesuction should be so modulated that the pore solution comes and sits inside the tube.And once this happens, you can have another pipe which is connected to the sampling bottlevail and you can keep some sample that you have collected by applying some vacuum suction.So, this is how the tension lysimeter works.I will show you how it looks like and how it is calibrated and other things.What is the importance of the lysimetric studies this was a project which I did for AtomicEnergy Regulatory Board of India and BARC.So, as I said the lysimeters are basically the devices which create a control volumeof soil for studying various contaminant transport mechanisms under in-site conditions.There are 2 types of this field and laboratory studies in field studies unfortunately notmuch control on the boundary conditions all right and they are very expensive and veryvery time consuming.Though we did some of the field studies and laboratory studies also cannot simulate thein-situ stresses because once you retrieved the sample you know the in-situ stresses cannotbe simulated.Another problem is you cannot simulate the real matrix of the soil or the file structurewhich was line in which was in the real life situation.Another issue that special variability cannot be taken into account because the sample sizesare very small in the laboratory studies.So, under these circumstances, the lysimetric studies can be utilized as a intermittentapproach and I can simulate in-situ conditions also by controlling the boundary conditions.So, you may say that this is a sort of a one type of a solution which I get by doing lysimetricstudies.So, this is the case which I was talking about what type of instrumentation has been doneat a place where the atomic waste is dumped in India.So, what you are seeing over here is a stainless steel ring of 1.2 meter diameter and thiswas about two meter long.This ring was not two meter long this was also 1.25 meter length you can see from here.So, this was inserted into the ground by pressing it from the top the way the piling is done.So, inside the soil mass becomes a control volume and it does not get influenced by theoutside surroundings.Now, as far as the instrumentation is concerned, what you are observing is that there are twocubes T1 and T2.So, these are the PVC tubes which were installed after the sample was created.These are known as TDR cubes, time domain reflectometry tubes, and what you are observinghere is a TDR probe.This is what is known as time domain reflectometry probe and this is used for profiling the moisturecontent from top to bottom of the zone of interest and the type of volumetric moisturewhich you obtain from here.Remember this is a volumetric moisture to get from the TDR probes can be utilized toprofile the variation of groundwater regime in the sample, this is the groundwater.So fluctuation of water table can also be captured when you use arterial.So if you blow from top to bottom, and you could try to create a moisture profile, thesetype of groups are very useful.Why to because we wanted to see the spatial variation within a small group and they wereinstalled at different radial distances at different depths.So, this is a typical tension lysimeter on it.And what I have shown here is a thimble which is made up of a specialized ceramic cup whichhas a peculiar air entry value.So, this is the setup which has been created.Now what is normally done is we remove the top 100 mm of the soil and replace it withsand.And this sand is utilized as the source of contamination which is going to migrate throughthe soil.By using these type of setups we could study the cesium cobalt and tritium these are theratio mixture which we use to study their interaction with the soils.Why these radio isotopes were used because these radio isotopes are present in the sludgewhich comes out of the atomic reactors.So this is what actually you wanted to study.So, choice is yours you can use different combination of the radio nucleus.This is how the suction samplers look like.We train them in a CBR mold to see whether they are working all night or not.And then when you apply suction you know pore solution gets collected.

Video 2: TDR Studies and Pressure Membrane Extractor
Just to show you how the activities are done in the field.This is how the whole system has been created the two SS tubes are fitted for suction samplersare fitted these are the cubes which are connected to the suction samplers.Now, you can see that we are giving you know, this is the strontium crimson red color istypical color of the strontium radionuclide and then we leave this whole thing for rainfallsto come.This experiment which was very expensive was done during the flash floods off.You can see here the externals going completely from 15 June and 2 July and then came theflash floods off what is this July 2005 these glass tubes are broken and they got flooded,but we got good data there is none which we did and analysis.Area studies are normally done to establish the variation of soil moisture in the entiredomain and particularly, this is the groundwater variation which causes this type of profilethis could be because of the percolation due to the rains also.And this takes care of the evapotranspiration because on this accident if you remember thesoil sample is exposed to the environment.So, evapotranspiration, percolation, fluctuation of groundwater table everything is taken careof.So, this is a very comprehensive setup which has been done if you want to read this outcomeof the study you should refer to this work which we published in geotechnical and geologicalengineering application of in-situ lysimetric studies for determining soil hydraulic conductivityunder field conditions.This is how established the movement of cesium and cobalt is in an active form and we didthe modeling for 500 days, the whole purpose was to design the repositories where the wasteis being dumped and how the whole system behaves, you know, how much is getting sorbed ontothe soil mass at a given depth.So, these type of studies become very useful when you design the repositories where thewaste is being dumped.Now, this is the another instrument which was fabricated by one of my master studentDr. Vikas Thakur now he is a professor at NTNU Norway.So, this is the system which was created.Now, what you are seeing observing here is that this is the control volume where I cankeep the sample and this is connected to a pressure retention unit and pressure retentionin this connected to a compressor.So, with the help of the compressor the pressure is built up in the tension unit and this pressureof air can be used to pressurize the sample in the pressure membrane extractor.So, rather than using the water in the cell, the sample which is kept here is being pressurizedwith the compressed air and why it has been done answering your question.Now you are seeing a situation where the fluid is compressed and just percolating throughthe sample.So it displaces the core solution which gets connected into the boil which is kept overhere.So if you look at the shoulder view of the pressure membrane extractor, this is how itlooks like.It is a chamber where the bottom portion is connected to a drain.And on the drain we keep a percolating material, mostly a geotextile on the top of this wekeep a cellulose acetate membrane.Cellulose acetate membranes are used for a lot of treatment of the human body, particularlythe filtrations of different type of fluids.Membrane technology is a big subject in chemical engineering, so, to create a membrane whichwill function at a certain pressure for certain types of contaminants or ions, good exampleof membrane technologies is the ROs which you are using or the water filters that youare using.So, when the air is inlet, what happens, this air pressure acts on the samples of the soilswhich are kept in small these are the rings.So, they are open from both top and bottom.And what we do is we keep the filter paper on the top of the filter paper we keep thering and we pore the soil slurries in the rings and we place them over here.So, when you apply air pressure, the pore solution comes out and that is collected inthe bottles.So, this is a pressure membrane extractor.This was done by our cells, but now in the market, you will find that commercially availablepressure membrane extractor are available.These are primarily used by the guys who are working in unsaturated soil mechanics or theguys who are working in a biomedical engineering or agricultural scientists, those who arevery much interested in uptake capacity of the soils and plants and those who are workingin the field of nutrition, ingress and loss from the soils.So, these type of equipment can be utilized quite easily.