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Soil Contaminants and Corrosion Potential

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We have been talking about the material characterization and particularly the chemical characterizationand this is where I will cite one example a case study which was done by us few dayfew years back followed by the corrosion potential which is very important topic in today’sworld and a lot of industries, we have been piping and the underground or buried structuresare installed require studies to be conducted in this context.Of course, after this I will be switching over to the sorption-desorption and followedby thermal electrical and magnetic characterization.So, to begin with the case study normally, when you come across these type of situations,the questions you have to ask yourself, are what are the types of contaminants that youare going to deal with?Because depending upon the contaminants type, you will be having a strategy in your mind,or you be involving a strategy, which would help you in understanding what is the extentof contamination of geomaterials and how to remediate that.In other words the first question which comes to mind is whether these contaminants areorganic in nature or they are inorganic in nature.And this question is asked, because of the obvious reasons that the detection tools orthe equipment which you are going to use or the strategy which are going to follow willdepend upon the basic nature of the contaminants.So, we have discussed about different techniques in the previous lecture.And what we can reiterate is that normally CHNS analyzer is required this is the carbonhydrogen, nitrogen and sulfur analyzer is required this an equipment which helps youin finding all the CHNS components of the geomaterials.And then what type of alterations these components are going through or the elements are goingthrough in the process of getting contamination of soils that can be detected and quantified.FT-IR is the Fourier transform infrared spectroscopy.This I have talked about in the previous lecture and followed by GC-MS that is gas chromatographywith mass spectroscopy and of course, ICP-AES and AAS so, these are tools which are normallyused.So, just to show you how the.Results would look like; these are typical results, which convey from the FT-IR analysiswhich you get what is the extent of contamination of the soils.So, S1 to S11 are different codes of the soils depending upon either the time or the locationfrom where the samples have been withdrawn and on y axis we have percentage transmittanceand on the x axis we have the wavelength.I hope you understand from the basic background of chemistry, that wavelength is associatedwith the bonding between the two elements.So, what you are observing here is a typical pattern which shows what type of bonding andthe nature of the bonding is available in the soil mass or the geomaterials.So, for that matter here I have written it as I say silica oxygen stretching.And here the silica oxygen is in the bending.So, this is a sort of a bond and if you remember our preliminary discussion, the whole trickis about how to break these bonds so that the soils can be decontaminated.So, FT-IR happens to be a good tool where we can at least qualitatively, we can identifythe presence of foreign elements particularly contaminants in geomaterials.The second analysis is the results of the GC-MS, which I am showing here.So, as I said, this is the gas chromatograph mass spectroscopy.Depending upon the retention time, I can identify the compound and we can quantify by usingthe MS component associated with GC-MS.What is the extent of intensity.Intensity can be correlated with the percentage of these compounds which are present in thesystem.So, there is a big list of compounds that you can identify based upon their in the printin the geomaterials, these type of analysis are all part of forensic examination of thegeomaterials nowadays.And then comes once you have identified what is that you know, qualitative contaminationpresent in the system or quantitative contamination present the system you can plan the remediationtechniques.So, some of the remediation techniques which I am going to list over here are number oneis the air purging, I can twice the air inside the soil mass this is what I was talking aboutin the previous lecture also, where the compressed air or the compressed oxygen is pumped intothe geomaterials to oxidize the contamination which are present.And this could be a very good solution for the soils which are oil contaminated or hydrocarboncontaminated, where you can break the bond between the soils mass or the geomaterialand the hydrocarbons by purging the air.The second one is electro remediation, slightly complicated technique where with the helpof electric field, you can decontaminate the soils electro kinetic processes one of theprocesses another process could be electro osmosis.So, these are two processes which people have tried in the past.Of course, these methods have their limitations and strengths, which you should study by goingthrough the papers, which are available in the literature.And sometimes these techniques become very difficult to you know employ on the site becauseof the cost of the paraphernalia or maybe like electro remediation method is the biggestquestion would be, if you are passing a huge amount of current or the voltage is mightbe unsafe for the people who are working over there.There is another interesting technique by which you can do the remediation of geomaterialwhich is bioremediation and this is the upcoming area where a lot of research is being done.And I would suggest all of you to go through the literature, particularly on Google a lotof papers which are available on these techniques, their utilization, how to employ them whatare the limited And what are the strengths and so on and where we are as a nation areinternationally another method which can be tried I think some of you talked about thisphytoremediation.So this is also a very interesting technique of decontamination of the soil.Now, one thing you should realize over here is that it is a chicken egg story where thesoil gets contaminated first or the groundwater gets contaminated first this has to be decided,because many a times it so happens that the soil becomes contaminated first, and thenbecause of the leaching of these unwanted contaminants or species, the groundwater tablebecomes contaminated.However, the reverse process is also possible, because non water table is a part of the geomaterialsystem.And in case there is a flux of contaminants which is present in this in the groundwateror the pore solution.The chances are that the geomaterials will be contaminated.So, when we do remediation techniques, both the aspects are kept in mind that is the contaminationof the soil as well as the groundwater or vice versa.The only thing would be taking out a sample of the groundwater will be easy.And this can be directly analyzed by using ICP-MS or GC-MS.However, when you are dealing with the soil phase of contamination, or the solid phaseof the contamination, then you have to extract the solution and that solution has to be analyzedby using different techniques.I will start now, a discussion on corrosion potential of soils and as I said, some prefaceI have given you in the previous lecture, why this subject is becoming more importantin the realm of geotechnical engineering.Most of the foundations and underground structures are exposed to the environment, particularlysubsurface and this is where the chances of contamination of the porous media are veryvery high and once you have contamination which is present in the soil or the groundwater.It may so happen that the underground structures might be under threat as far as their safetyor their structural health is concerned, why these studies are becoming very importantfor geotechnical engineers, because metal corrosion has become very important thingin undisturbed sites.Particularly when we compact the soils when we talk about the soils which are under In-situconditions and we insert a lot of elements like foundations or sheet piles of the pipesin the ground.And you did like to see what really happens to the cover of these elements in the formof the concrete or it could be a metal and the reinforcement which is lying inside.As I said, the buried pipelines and the backfilled soils have to be characterized properly whenyou are using them for different industrial applications.So, industry is facing two problems number one is how to convey liquids underground becauseoverhead conveyance is extremely hazardous and difficult.And second thing is that if I have to lay the pipelines, I have to backfill the soilto compact it is it not?So, from where this type of soils will come, which are supposed to the best soils are thegeomaterials, which would be safe for the health of the buried systems.So, I hope you can realize that this is directly coming into the realm of geotechnical engineeringand here the pretext is that soils change their chemical and physical nature over aperiod of time and depending upon the climate.So, these issues have been ignored earlier.And when I say climate and time, I hope the connotation you can understand is, this isbecause of the bacterial activity.So, the bacteria which harps in the soils gets activated or may become super criticalor may become dormant depending upon the environmental conditions.So, these are the situations which are bothering geotechnical engineers, when we talk aboutthe pipelines, you know, this is the pitting sort of a of a system and this is the corrosion.So, excessive pitting might leads to the corrosion of the metals.I have come across some of the cases where there was a litigation going on between theclient and the contractor where, you know, big pipelines were installed.And I hope you understand that the pipelines are extremely expensive utility items.And it so happened that by the time the pipelines was charged, charged in the sense when theywere opened for fluid flow, people realized that the conveyance of the liquid was 0.So, when we when they open the walls, they realize that nothing came out from that particularpipeline, and then the litigation started and then the inquiry started and what we realizeis that the entire pipeline was eaten up by the soil.And this is one of the piece of the pipeline which I collected and I brought to the laboratoryto do further analysis of what went wrong.So, these issues are becoming very, trivial and very critical in the in the contemporarysociety.I hope this connotation is clear when you have disturbed soils, the densities are goingto be different as compared to the density state of the undisturbed material.And hence the air permeability and water permeability and the form the rains is going to be different.And once you have ingress of fluids in the buried systems, this could be problematicbecause wherever oxygen is present, the tendency of the oxygen would be to oxidize the things.So, this is the answer to your question.So, permeability gets affected strength gets affected, durability gets affected and atthe micro level if you really analyze this issue, hope you will realize that the questionto be considered is that how microbial activity will grow in less compacted soil or more compactedsoil and this is where we talk about the concept of aerobic and anaerobic bacterial activity.So, compacted soil acts as a barrier for the air to communicate with or the environmentto communicate with the buried structure.I hope these logics will help you in understanding why this subject is becoming important.Yes, please "Professor - student conversation starts" In the past, we have used wooden pilesfor this purpose.Now it possible to use so you are talking about the monuments where the wooden pileshas been used.And I am sure that you must have realized that it was made sure by the engineers ofthat era "Professor - student conversation ends" that these wooden piles will not getoxidized, they do not get exposed to air.That means most of the time the system remains under submerged condition.So if you go to our most of the monuments where you have boudies we call them in Hindiand Urdu.I do not know what do you call them in your language.The there are several structures, monuments were 2 3 stories remain always submerged inwater.So, when you cut off supply of oxygen, the system would not get oxidized.And wood is a classic example of this wood under wet form, which is pretreated is alwaysmuch more durable than concrete.So this is the answer to your question.