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Methods of Assessing Soil Contamination

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Previous lecture we have been discussing about the chemical characterization the pore solutionsampling and how these pore solutions can be utilized for characterizing the geomaterials.Today I will be discussing one more technique of you know what is defined as soil washing.And this also is a technique to create pore solution by wash the sample with adequateamount of water and I can create pore solution and I can characterize the geomaterial.I will continue with discussion on corrosion potential of soils today and maybe sorptiondesorption will come later.This will be followed by thermal electrical and magnetic characterization.There is an interesting technique of characterizing science based on their chemical characteristics.Particularly if you want to assess what is the level of contamination of the soils, soilsmay get contaminated because of anthropogenic activities.The one of the interesting techniques to find out the definition of soils it is washing.It may so happened that soils may get contaminated because of several natural phenomena or anthropogenicprocesses.I think anthropogenic processes all of you understand this could be the influence ofthe industrial activities which are going on vigorously everywhere in the world.And the natural processes could be I am sure you must have heard about the oozing out ofarsenic in certain part in the country particularly in the eastern part of the country, wherethe arsenic comes out of the ground and contaminates the water, and this is an environmental effecton the soils, and soils leach out arsenic.So what I am trying to say is that the soil contamination could occur both naturally aswell as anthropogenically.And if you want to establish what is the level of contamination of soils.These techniques which I am going to talk about today would be very very useful.We have been working on the concept of soil pollution index.This is the quantification of how much the polluted the soil is, and why I am tryingto quantify the soil pollution or soil contamination is because of the simple fact that as a geotechnicalengineer, environmental geotechnologist, I will like to decontaminate the soils later.And when you decontaminate the soils, this process is quite time consuming as well ascost intensive.So, in today's world, everything is cost oriented, time oriented and you cannot use qualitativeterms just to define the soil is contaminated.The question which industries ask you is, what is the level of contamination?And how much time and effort it would take to decontaminate the soil.So, with this pretext, I will start my discussion on how would you assess the level of contaminationof geomaterials or the soils there are two techniques which are normally used and thesetechniques.Direct techniques are the direct methods and indirect methods and then a big series ofdirect methods which are available in the literature people have been working in thisarea.The first one is pore solution extraction.Which I was discussing in the previous lecture, you can take out a sample of geomaterial,it could be concrete, it could be soils it could be rocks, and you can place it in apressure membrane extractor, which I showed you last time, you can apply a certain amountof pressure through the compressed air.And in the process, the pore solution comes out and this pore solution can be analyzedby using atomic absorption is spectrophotometer, which I showed you when we are discussingabout the chemical characterization or this can be analyzed by using ICP-MS inductivelycoupled plasma mass spectroscopy.So, depends upon what is the level of accuracy you want, AAS is less accurate.It is normally use up to PPM levels parts per million of the concentration or the contaminantsICP-MS is used for, you know, PPB or PPT levels parts per billion or parts per trillion levels.And then people are using gas chromatography also particularly to identify the level ofcontamination which is a form of organic volatile substance, a gas chromatograph has becomenecessary equipment in modern day geotechnical engineering laboratories, because you wouldlike to ascertain the level of contamination of the soil before you start doing conventionaltest including the specific gravity liquid limit or particle size distribution.Then we have different types of ion selective electrodes in the market, which are very usefulto find out what is the level of contamination of the geomaterials.There are different types of probes and sensors which are nowadays being used and developed.And this is where geotechnical engineers like me would like to collaborate with people fromnano sciences, nano electronics metallurgy departments, physics professionals, chemicalengineers, biotechnology is microbiologists and so on.Because these are the guys who give inputs to a designer who could design a sensor fora specific purpose.So, gas sensing is the state of the art right now, liquid sensing is state of the art rightnow solid form of contaminants in the soil is also a very, very state of the art thingin the present scenario.So, all the phases of the matter can be detected by using the sensors.There is another series of tests which falls under the category of indirect methods.And this is where we have done a lot of work in our field by utilizing the impedance spectroscopyby employing an impedance analyzer.So, those of you who have some interest in electrical engineering, electronics engineering,you might have come across this equipment which is impedance analyzer or impedance spectrometer.So, what we do is we check the response of the material in a very wide range of frequencyof current AC, alright.So, we will talk about the discussion between what type of current should be utilized DCor AC.What are the advantages and disadvantages?And this is sort of a third eye for me, I hope you understand what the meaning of thirdeye is something which is not visible but you can look into a matter and you can realizewhat is happening.So, in any closed control volume if I want to see what is happening inside without openingup the system to the atmosphere, I would like to see what is happening inside the material.What is cooking up inside, we are using these concepts for even detection of the hydrateswhich gets formed in the sediments where Bhini is working on and in fact and Ganaraj whois trying to work on the neutralization of heavily polluted soils by different techniques,even Jasmine is working this area by air purging by acid purging or by different types of reactivegases when they are purged into the system.So, impedance spectroscopy, as I said is becoming a non-destructive technique to establish themechanisms which occur in the porous media.And I will give you some exposure of how this is being used.Incidentally, material scientists have used impedance spectroscopy to defining the facechange in the material, particularly for the allies.And this concept can be extended in the geomechanics.If I want to see what is the state of the material like soils?When they are exposed to super critical temperatures, particularly in the frozen zones, and at veryelevated temperatures, there is a wide range of activities that you can do.The second one is the electrical resistivity method, where you can find out the electricalresistivity of the geomaterial has to relate to the porosity of the medium.And I am sure you will realize that porosity is a term which is very, very important togeotechnical engineers, because all the mechanical properties and engineering properties of thegeomaterial will depend upon the porosity and the shear strength, the compressibilitythe consolidation the you know, the volumetric deformation, swelling, shrinking, whateverso, everything can be related as a function of the porosity and electrical resistivitygives you a good methodology to measure the porosity and the alterations in the porositieswhich are happening inside the system because of physical, chemical, electrical, mechanical,biological mechanisms.There are some electromagnetic methods which are being used in the contemporary societyof the world.These are known as TDR and FDR probes very state of the art things, which we have usedfor finding out the in-situ moisture content and the soils and the MSW and the landfillsthese type of studies have been done by my ex-students, Agnes and Dr. Patel and now,we are extending these studies through Arif and others.So, as the name reflects TDR and FDR are time and frequency domain reflectometry and theseare the techniques which are used for determining the in-situ density and in-situ moisture contentvolumetric not that the gravimetric.So, gone are days when people used to bring the samples to the laboratory to determinethe moisture content as simple as you know, you can understand that why this has beenwritten off this technique because chances are that you are disturbing the sample.Number 2, it is very difficult to preserve the moistures in the sample for a pretty longtime productions on the problem really wants to measure in-situ, then the application ofdielectric constant is being done for finding out the fundamental behavior of the geomaterialand level of contamination also, and this is where ground penetrating radars have beenused by people.So, this is the state of the art on the subject.What I suggest is to follow this discussion, you should go through the papers which arewritten by my students.And most of this matrix has already been covered in our laboratory.So, there is nothing new that become a routine exercise.So, this is just to tell you that already, these techniques have been mastered, and theyhave been shown to be working alright in the field as well as in the laboratory.However, the caution that both these techniques or the methodologies have their limitations.First of all, these are the expensive instrumentation and very cumbersome methodologies though theyappear to be very simple, even in the direct methods, the preparation of the sample isquite cumbersome, very expensive.And indirect methods, the gadgets which are used themselves are very expensive.So, intensive and rigorous sample preparation has to be done, which is time consuming, andthere is a complicated process which is involved related to the calibration and analysis ofthe results.And for both the techniques will require skilled and trained manpower or the personals.So, these are the limitations, but this is the future of the subject, because most ofthe consulting houses and the business houses they are looking for experts who can givethem quick answers or who can give them the solutions as far as the monitoring of a processis concerned, can we use all these methods for any kind of soil or any particular divisionis there?I knew somebody who asked this question and that turned out to be you.So, very difficult question to answer.And particularly if you read the papers, which are written by Social Lakshmi, these techniquesare not universal.So, now, you are going into the intricacies of these techniques.And I think these techniques have to be evolved in such a manner that people should know theirlimitations and you know, their shortcomings but there is no harm in trying all the techniquestogether and then putting on a scale and seeing them how do they compare with each other.So, a quick answer to your question is if you have organic soils chances are that indirectmethods will not work.Why?Because impedance measurement is mostly dielectric based and dielectric constant of organic matteris difficult to define.Another issue is that the organic matter will keep decaying.So, all these parameters will depend upon the exposure conditions and the time whenyou are measuring these properties, which itself is a question mark will come to this,but do I read a lot there is journal known as sensors.And if you follow the IEEE journals on sensors, this is the modern day geotechnical engineersare eyeing their publications because of a simple reason that electronics and geotechnicalengineering you know, they are quite hand in gloves.And unless we work together we can solve these issues.Remember, the soils which are contaminated that are not the right place for humans toaccess are you getting this point, so suppose if I tell you an example with a pH of thesoil is 12 or 13.The first question is how would we access the site?How would you take all the samples?There could be a situation where the soils are emitting fumes.So, you have to take a lot of the cautions I hope you can imagine anyone when you areaccessing these type of sites, lot of precautions have to be taken so that you face less healthhazards.And the sampling becomes another issue.Are you getting a point?So, it is a very big theme of discussion.Anything else?But I am sure you will realize that this is where the challenges and this is what peoplelike we should be taking up.