 Namaste and welcome back to the video course on watershed management. In module number 7 on management of water quality, today in lecture number 28, we will discuss about groundwater pollution problems and transport processes. So, some of the important topics covered today include groundwater pollution sources, pollution control, groundwater pollution remediation, transport processes in surface and groundwater. Remember the key words for today's lecture, groundwater pollution, control, remediation and transport processes. So, as we discussed earlier, so when we deal with the water management say within a watershed, we have to deal with the surface water and the groundwater. So, it is not only the quantity of water what is to be made available to the flora and fauna or to the people within the watershed, we have to see the quality of the water. So, as we discussed in the previous lecture, the water quality is a major issue, surface water quality as well as groundwater quality are major issues which we have to deal nowadays. So, due to various reasons the quality of groundwater or surface water deteriorated very much. So, in today's lecture we will see the problems related to the groundwater quality. In the last lecture we have discussed about the surface water quality issues. So, when we deal with watershed management, so groundwater is a major component of the as far as water source is concerned, groundwater is a part of the hydrological processes which we have already considered. So, with respect to the infiltration and then the water is joining to the water table or the aquifer systems and then that will be interacting within the systems. So, that way whatever is happening within the surface, if any pollution source is there within the surface of the planet or within the surface of the watershed, then that will be also affected to the not only to the surface water, but to the groundwater also. So, that way when we deal with the watershed management, the groundwater quality is also a major issue. So, groundwater assessment we have to do with respect to quantity and then also we have to do the monitoring of the water quality. So, this as we discussed in the previous lecture, the water is concerned, we have to see how much pollution is there within the water or whether any water quality meets certain standards for various purposes like a drinking purpose, irrigation purpose or domestic purposes. So, like that we have to see whether the available water quality is safe for the proposed use. So, that way depending upon the use of water, say the physical, chemical, chemical and microbiological analysis of what we have to do. So, as we discussed in the last lecture also, so physical analysis, chemical analysis and microbiological analysis to see that the water quality standards are met. So, as far as groundwater is concerned, say very similar to the surface water since both the surface water and groundwater are interacting within the hydrology processes. So, some of the pollutants source include toxicity like micro pollutants and other industry pollutants, then pathogenic pollutions, then salinity problems. So, like that these are some of the common issues as far as groundwater quality is concerned. So, now let us look into the detailed aspects of groundwater, say related quality related problems. So, the problems with groundwater as we discussed in earlier lecture also, say some locations of the planet of the earth, say people are using too much groundwater, so that we overdraft is some of the issue, so that the water table is going down. And then say the issues related to mining, say especially say when the mining operation lot of wastewater is produced and that is say polluting the aquifer systems or the groundwater systems. Then subsidence, then like water logging problems, say wherever the water table is rises to say beyond certain level, then water logging and its related problems related to agriculture and other areas and then coastal aquifers problems like sea water introduction. So, the salt water mixes with the pure groundwater and then that is say the groundwater become useless or we cannot utilize for the purpose which we are looking for. So, that way groundwater pollution has become a major concern in the last few decades throughout the world. So, that way say nowadays the hydrologists or groundwater hydrologists we are always thinking say how we can preserve or conserve the existing groundwater source which is always the annual basis it is recharged due to rainfall and other sources. So, we have to conserve and preserve so that the water quality standards are met for either for drinking or any other purposes which we are looking for. So, say the last few decades due to the industrialization and various other human made problems the groundwater source has been say assaulted in different ways and then the quality of the groundwater in many locations have gone down. So, the groundwater quality is very much deteriorated due to rapid industrialization and human mismanagement. So, we can call this as human mismanagement it is not happening due to the natural causes mainly, but due to the human interventions within the system and then it is not appropriately done. So, that are the that are some of the major reasons as far as the deterioration of the groundwater is concerned. So, when we deal with the groundwater say as we discussed earlier also the manoeuvres of groundwater systems is concerned we have to deal with the quantity of the groundwater and the quality of the groundwater. So, as far as quantity is concerned the total volume that may be withdrawn annually from the aquifer. So, we have to see that there is a balance between what is recharged and what is withdrawn from the aquifer systems. So, that the groundwater table will not say go down drastically and then the location of pumping and artificial recharge rates and their rates. So, say if you consider an aquifer systems say depending upon the recharge rates how much we can pump out of the aquifer systems or if you are going for recharging say how much we have to recharge with respect to the available water. So, all these things we have to say deal effectively for groundwater management. So, we have to take certain decisions as far as the groundwater quantity is concerned and also groundwater quality is concerned. So, as I mentioned even if the sufficient quantity is available the quality of the groundwater is not good then we cannot use for the purpose which is which it is meant for. So, we have to take decisions related to groundwater quality. So, groundwater contamination as I mentioned can be due to various sources like hazardous industrial waste, leachate from landfills, agricultural activities such as the use of fertilizers and pesticides. So, as we discussed in the last lecture these kinds of pollutions can be either point source pollutions or the non-point source pollutions. So, point source is directly what is coming from just like an say from underground tanks if a leakage place and that is going to the aquifer systems or the groundwater is affected that is point source. But non-point source like say agriculture sources say like nutrients or herbicides or pesticides these kinds of pollutions are non-point source of pollutions. So, we have to deal the groundwater systems effectively. So, we have to that way we have to say that groundwater systems to be managed effectively as far as quantity and quality are concerned. So, management means making decisions to achieve goals without violating specified constraints. So, this say when we are looking say for example, from a given aquifer if you want to pump about 1000 meter cube per day. So, we have to see that the objective is to meet that 1000 meter cube per day, but we have to see that certain constraints say like the groundwater level should not fall below certain specified limits or say the quality of the groundwater should be good enough with respect to whether for the standards say for the drinking water or the agriculture purposes. So, that should be met. So, we have to see that specified constraints are made. So, good management requires information on the response of the managed systems to the proposed activities. So, here that means the aquifer systems or groundwater systems. So, if you are pumping this much water what happens or if the quality so if a contamination is going through the system the groundwater system how it is spreading and what will be the effects. So, this information enables decision maker to compare alternatives and ensure that constraints are not violated. So, say for example, if there is a pollutant source to the aquifer systems. So, and then if pumping the water is pumped for drinking purpose or water supply purpose from that aquifer system then how say whether there is will be an interaction. So, how we can manage this so the polluted pollution source or the plume. So, the decision maker has to take a decision by considering various options like groundwater modeling or groundwater pollution polluting modeling or contaminant transport modeling. So, any planning of mitigation or control measures once contamination has been detected requires the prediction of the path and the fate of the contaminants in response to the planned activities. So, like say if say if you are if you are going for say the control measures. So, we have to see that say the how much portion of the groundwater system is affected or how where the plume is moving and how what rate it is moving and whether that will reach the pumping well which we are say say we are pumping the water for water supply or other purposes. So, all these issues we have to see. So, any monitoring or observation network must be based on the anticipated behavior of the system. So, we can through groundwater modeling we can identify the anticipated behavior of the system. So, then if you are having a monitoring or observation network. So, through that we can identify what is the best way we can manage the groundwater systems as far as the groundwater pollution is concerned. So, now say whatever we are discussing is related to groundwater system management with respect to quantity or quality. So, now let us go into the details of groundwater pollution sources and then pollution control and the remediation aspects. So, groundwater pollution problems so as I mentioned say when we are dealing with the water source in a watershed. So, we have to see that not only that sufficient quantity of water is available, but quality is also good enough. So, use the water is useful only if quality is safe. So, that is very important aspect. So, quality is indicated by say as we discussed in the previous lecture the various indicators like dissolved or suspended solutes or the whether the water is basic or acidic say like a pH indicator or say the biological quality so like that. So, then say when we discuss say on a watershed basis or a river basis or aquifer basis we have to see what are the important sources of pollution. So, and then we have to see what are the important forms of pollutions whether it is the form is dissolved salts or domestic or industrial base or whether heat pollution or radioactive materials, pesticides, manures etc. So, what is the source of pollution and what kind of pollution is there, what is the form of pollution and then how the pollutants or the contamination is moving within the aquifer system. So, pollutant transport or solute transport say generally takes place with the flowing water. So, in the aquifer system the groundwater is moving from one location to another location according to the hydraulic gradients and other parameters. So, we have to see that how the solute is transported. So, various processes as we discussed earlier also processes like a convection, hydrogen and dispersions all these controls the groundwater pollutant movement or the contamination movement within the aquifer systems. So, groundwater pollution issues when we discuss about the various issues related to groundwater pollution we have to see some of the important things like pollution sources, then pollutant movement or contaminant movement then how we can control the movement of the plume or contamination and then how we can protect the groundwater systems and then wherever it is polluted how we can say remediate it. So, that we can retrieve back the to the even though it is not to the original system original quality, but to certain extent we can remediate it. So, what kind of remediation are possible. So, all these issues we have to consider. So, groundwater pollution issues include source identification then we have to identify where the contamination is moving or movement of the contaminant then control and protection and then pollution remediation. So, these are some of the important issues which we have to consider when we deal with the groundwater pollution. So, now let us look into the important sources of pollution. So, groundwater contamination sources. So, here some of the important contaminant sources I have listed like natural contamination, agricultural contamination, industrial contamination, underground storage tanks, land application and mining, septic tanks, waste disposal injection wells, landfills etc. So, if this is the water should or the area which we are considering. So, there can be like if farms are there then non-point source of pollutions and then if septic tank or the landfills. So, it will be seeped with respect to rainfall the contamination will be seeping down and then that will be joining the surface water or to the to the groundwater. So, that way various sources of pollution are possible. So, we have to identify what are the important sources of pollution and then we have to deal with the corresponding source say to control the pollution and then for the mediation. So, now let us look into various aspects of this groundwater pollution sources. So, as I mentioned the important source of pollutions already we have discussed. So, first one is the domestic waste. So, domestic waste can be like household waste, septic tanks, liquid fraction from septic tank pollutes groundwater then inefficient design increases pollution. So, like say especially household waste especially the sewage water coming from the house say so that you can say most of the time it will be directed drain to the either to the surface water or the say the drainage systems. So, that can mix say that can penetrate down or infiltrate down to the aquifer system. So, that way domestic waste can be a source and then say where septic tanks are there that can be the leakage related to septic tanks. So, that can create that can be source of pollution. Then agriculture pollution as we discussed in the previous lecture also. So, like artificial manure or fertilizers, pesticides, herbicides, then nitrate pollution, then uterification, health problems. So, say in drinking water long term problems like say the nitrates and all those kinds of pollutants are long term source of pollution. Then pesticides, insecticides, herbicides, fungicides all these things beneficial to farming causes serious threat to the to the surface water and the groundwater. So, once it is the surface water is polluted that will be interacting with the groundwater systems and then that will become a source of pollution. So, generally agriculture pollution is concerned it can be non-bond source of pollution. Then especially in urban areas say as far as the solid waste is concerned say most of the say cities or towns uses say landfills. So, the these solid waste will be collected in trucks and then deposited in landfills. So, if the landfills are not scientifically done and then proper measures are not taken then say this say from the landfill a liquid called leachate which is produced due to when this rainwater mixes with the the contaminant source within the landfill. So, that can penetrate down to the aquifer systems or the groundwater systems and then that can be a source of pollution. So, the third one is leachates from landfills. So, it is one of the commonly used cheapest solution as far as solid waste is concerned and then it can be same for domestic related or commercial zero industrial. So, this polluted liquids called leachates is a major source of pollution as far as the the the groundwater system is concerned. Then the next major source is industrial pollution. So, industrial sources like petrochemical industries, pharmaceutical industries. So, all these produces complex organic waste like non-accus waste liquids, it can be dense or light, then spills or leaks from tanks, pipelines. So, all these causes say these pollutant sources either directly coming in say on the soil surface that can penetrate down or infiltrate down to the aquifer systems and then it can be source of pollution to the groundwater systems. Or wherever surface groundwater pollution is there when surface and groundwater interaction takes place that become a source of groundwater pollution. Say for example, in Germany it is identified that it is about 240,000 non-accus waste liquid contaminated sites identified at various industrial sites. Say for example, Germany is concerned. So, that way this industrial pollution is a major source of pollution. Then say the contaminated land and urban pollution. So, effect of industrial pollution like waste disposed in land around urban areas. So, example mining and foundry waste, tar, oils, phenols etc. So, these all say are sources of pollution as far as the subsurface water or groundwater. Say for example, in United Kingdom it is identified that about 500 square kilometer of land is polluted that means its soil is polluted. So, in about 50,000 sites. So, this say whenever say the water with respect to rainfall, the runoff and then this water mixes with say interact with these sites then the condemnations will be say formed as a plume and that will be moving through the subsurface over the subsurface water and that will be becoming a source of pollution as far as the ground water is concerned. And then mining and seawater intrusion pollution. So, water draining from mines like the nature of this water will be acids, sulphates. So, lot of pollution will be there acidic or sulphates pollution, iron pollution, cyanates etc. So, this will be in solution. So, pollution these pollutes surface and groundwater and that become a source of pollution as far as ground water is concerned. And so, abandoned mines are a major threat say as far as the ground water is concerned. Then as I mentioned seawater intrusion say excessive pumping in coastal aquifers. So, that way the seawater intrude to the coastal aquifers and then that mixes with the groundwater in the coastal regions and that become a source of pollution. So, we have to look so that the overdraft of ground water should not be allowed in coastal areas, coastal aquifers. So, proper management measures should be adopted. Then dissolved salts and minerals like arsenic contamination say in Bengal basins. So, this arsenic contamination it is actually caused due to overdrafting of the ground water. Due to that say certain minerals or certain salts within the soil say ditch and that become a source of pollution. So, dissolved salts and minerals are also another source of pollution. So, now let us look say into what is the mechanism that is happening say as far as groundwater contamination is concerned. So, we have seen various sources of pollution. So, say for example, as shown in this figure. So, if the landfill is there and leachate is there. So, with respect to the movement of the groundwater. So, this condom and plume is moving. So, the changes in chemical concentration occurs in groundwater system by four distinct processes mainly the advective transport. So, that means the when the groundwater is moving with respect to the movement of the groundwater and the condoms like dissolved chemicals are moving with the groundwater flow. Then hydrodynamic dispersion. So, mechanical hydraulic or molecular and ionic diffusion. So, various intermixing within the pores takes place and then say the diffusion dispersion all this process take place. So, hydrodynamic dispersion is another important mechanism of the pollutant movement or plume movement. Then fluid sources like a water of one composition is introduced into and mixed with water of different composition. So, say if you are keeping the say some kinds of oils or other kinds of chemicals in a tank in the underground. So, that may mix say if they do to any leakage that can mix. So, fluid sources also can be say that you say under certain pressures this will be moving through the aquifer system. So, water of one composition is introduced into and mixed with a water of different composition. So, all the polluted water from the surface water that can be also another sources source as far as the groundwater is concerned. So, that is fluid sources. Then reactions. Some amount of a particularly sold chemical specious may be added or removed from groundwater as a result of chemical biological and physical reactions in the water or between the water and the solid aquifer materials. So, whatever the contamination is there within the aquifer systems. So, that can change its phase due to various reactions between the chemicals say like say the radioactive polluted materials. So, after sometime say the material become another phase or multi phase liquids movement. So, that may interact and then say various kinds of say chemicals can interact and due to reactions. So, say the change the nature of the contamination itself can change. So, that way as far as groundwater contamination mechanisms are concerned important mechanisms are advective transport hydrodynamic dispersion fluid sources and reactions. So, related to this transport process we will be discussing later in details in this lecture itself. So, now say what we discussed is we have seen the groundwater pollution sources and then what is the mechanism of this plume movement or contamination spreading. So, now how we can protect the groundwater or how we can control the pollution. So, let us look briefly into various pollution control measures. So, once aquifers are contaminated it is very difficult to restore it is very expensive process. So, it is always sensible to prevent the pollution. So, vulnerability of pollution depends on aquifer nature like the hydraulic conductivity, what kind of soil is there and what type of contamination is there. So, there are many parameters depending upon which the vulnerability may be serious or mild vulnerability. So, frostpure and unsaturated thickness and all these things. So, we can prepare vulnerability maps showing possibility of aquifer contamination. Say for example, if there is an industry or if there is a source of pollution is identified. So, then for that particular aquifer systems or particular area particular watershed we can prepare vulnerability maps. So, say within these many days say this is the area which may be polluted or due to if these kinds of leakage takes place these are the possibilities. So, like that we can have vulnerability maps. Actually in many countries like United States of America and European countries like Germany, Netherlands, United Kingdom these countries have prepared such kinds of vulnerability maps since in many of these countries groundwater is one of the important source of water supply. So, that way to protect this groundwater. So, they have prepared the groundwater vulnerability maps. So, from these maps we can identify whether this particular aquifer system is vulnerable and then what kind of measures can be taken to protect the groundwater as a resource. So, then say we have seen that various source of contamination is there. So, if we can control the source itself through various strategies then we can reduce the scope of groundwater pollution. So, let us look into some aspects of the source of control strategies. So, to minimize or prevent pollution before a contamination. So, this is the main aim of the source control strategies. So, volume of waste is reduced or threat due to waste is reduced. So, whatever the either solid waste or liquid waste we can reduce it. So, that the vulnerability is reduced. So, this is mostly applicable in new sites say, but in all the sites we can reduce the abatements the spending can be reduced. So, the source control strategies depends upon say the hydrogeological parameters of the sites. Then how much area is rendered the situation and what kind of contaminant plume or type of waste. So, depending upon that we can adopt typical type of source control strategies say like to minimize the pollution or to protect the systems. So, some of the advantages of the source control strategies include say it reduce the threats to the groundwater pollution accelerates time for stabilization of waste disposal. Some other disadvantages include increased capital and maintenance costs since we have to spend money to control the source. So, that will not be further spreading to the aquifer systems or to the groundwater system. And then also we have to go for monitoring of the whether say once it is say the source is controlled whether any possibility of further leakage or further movement or the contamination. So, we have to monitor the system with the skilled operators. So, these are some of the disadvantages. Then another model which is tested in many of the European countries and in US include the source protection zones. So, here in the slides say you can see that say if this is the total catchments of the aquifer systems where from where the groundwater is pumped for various purposes. So, actually we can have protections of individual groundwater sources say like if particular valley is there or boreholes or springs. So, we can go for protection measures. So, we can define the protection zones say like as I mentioned what is done in United Kingdom, USA, Germany etcetera around the sources. So, if this is the pumping wells. So, we can have generally three types of protection zones. The first zone is this is the first zone say generally in this country is say for example, 50 days of travel time of the water say 1 particle water to reach this well 50 days. So, that we can delineate this zone and then absolutely no kinds of say any kind of pollutant or industrial activities or any activities not allowed in the zones. So, that the water pumped from this area is protected. So, that is zone 1. Then zone 2 is actually the area where 400 days of travel time for the water particles. So, there only the various activities are allowed on a controlled way. So, that there is no scope for groundwater pollution to the over the to that area. And then the last one is the zone 3 where entire catchment itself we can say wherever especially the water is used for drinking or for the water supply purpose. Then say we can declare that in this zone say certain kinds of activities certain pollutant causing industries can be stopped. So, as I mentioned we can have three zones and then we can have within this protection zones pollution activities prohibited or restricted say zone 1, zone 2 or zone 3 as discussed. As far as the contamination is concerned. So, we can go for stabilization or solidification strategies. So, in this same pollution control strategies we can isolate the waste material in a solid matrix before land filling say for example. So, the stabilization solidification strategies are very effectively used in many countries. Then these kinds of say methodologies are popular for hazardous and radioactive waste disposal say especially radioactive waste. So, we can isolate and then put it in a congate vault and then put it in a very deep say rocky area underground. So, that there is no scope for any kind of pollution. And then also we can chemically fix the waste in a solid matrix. So, if the say particular type of contamination is say if it is possible to say mix with certain other chemicals. So, that that material become inert. So, that there is no source of pollution. So, that process called chemically fix the waste in a solid matrix. Then important stabilization of solidification processes include like cement adding, addition of lying or pozzolanic materials, embedding waste in thermoplastic materials like bitumen or paraffin etcetera. Then addition of organic polyester encapsulation in inert coating, glass formation of waste with silica etcetera. So, there are a number of techniques say for stabilization or solidification. So, depending upon the contamination material or pollutant source, we can go for specified stabilization or solidification strategies. And then that way we can control the pollutant source. So, that the groundwater can be protected. Then another commonly used technique is called hydraulic control. So, here say as shown in the slides. So, we are manipulating the subsurface hydraulic gradient through pumping or recharge. Say for example, if this is the the contaminant plume and here if there are certain wells pumping the water for water supply then say we restrict this the movement of this contaminant plume towards the pumping well through say certain pumping or recharge at various locations. So, that is that process called hydraulic control or through well systems. So, this is actually plume management. So, we control the movement of water phase and then hence plume. So, the plume movement is controlled. So, generally three common classes of well systems are used like withdrawal through shallow systems, deep systems and then injection of water. So, we can either through pumping of the water or injection. So, that appropriate hydraulic gradient is generated within the aquifer system. So, that this contaminant plume movement is restricted. It should it will not go to the to the nearby area of the of the of the pumping well, but its movement will be restricted. So, here actually this is one of the most assured system and but the there should be good understanding of the the systems through round water simulation and aquifer characterization. So, the demerit is high operation and maintenance. So, since we have to either pump water or recharge and then continuous monitoring is required. So, this methodology is called hydraulic control also called well systems. Then some other techniques like surface water control, capping and liners. So, these are also used in many countries for the ground water protection or ground water pollution control. So, surface water control like capping and liners used in conjunction each other. So, what we do say the surface water where which is polluted we can control its movement and then we can give certain capping or lining so that so this contaminant water is not moving to the aquifer systems. And then another one is surface water control where we can construct certain diversion beams or drainage ditches etcetera so that the polluted water is not mixing to the aquifer systems. So, this minimizes the amount of water flowing into a site reducing the amount of infiltration. Then say we can have go for capping so that the area is capped so that further contamination is not taking place or the plume movement is restricted. Then we can also go for impermeable liners so which inhibits downward flow of low quality leachate or pollutant by adsorption process. So, we can have certain impermeable liners using clay or other materials so that that will not say the contaminant plume or contaminant source will not reach the pure water source or the aquifer systems. So, all these are used as preventive measures so that we can control the polluted movement and then we can protect the aquifer systems or the groundwater systems. So, again further say some of the other techniques used is like a sheet piling, then grouting and slurry walls. So, here this sheet piling involves driving lengths of steel or concrete or timber that connects together a thin impermeable barrier of two flow. So, this is effective and economic and piles can be reused. So, we can control the movement of the pollutants. Then grouting means injecting a liquid slurry or emulsion under pressure into soil. So, this occupy available pores so injected fluids solidify so that the permeate reduces and materials used are say generally used materials are cement asphalt clay. So, this reduce water and contaminant movement so that the plume will be stopped at particular locations. Then another technique is so called use of slurry walls. So, slurry walls are used to encapsulate an area to either prevent groundwater pollution or contaminate water. So, digging a trench around the area and then backfilling with impermeable material. So, this prevent the movement of plumes. So, like that say like as we discussed this is a surface water control and capping on liners. So, this can be using sheet piling grouting slurry walls etcetera. So, now say whatever discussing groundwater pollution sources then the mechanism movement of the pollutant and then how we can protect the groundwater systems or how we can control the pollutant movement. So, now once the groundwater system of the aquifer is polluted then what we can do. So, that process is called groundwater pollution remediation. So, we are trying to remediate or we remove the contamination from the aquifer systems or from the groundwater system. But this is a quite a very complex process and it is also very expensive. So, once a groundwater is polluted the question is how to restore or improve to acceptable standard. So, whether it is very depending upon the use whether for irrigation or any other purpose how we can get to the acceptable standard. So, for this say we have to study the system thoroughly. So, first we have to determine the distribution of pollution. Then we have to design a remediation strategy. So, as I mentioned once an aquifer is polluted to make into the actual original level is impossible task, but of course we can do certain measures. So, that say the contamination say can be reduced or to certain level with the aquifer systems or the groundwater can be remediated. So, in this all this process the first step is same we have to stop first once a contamination is identified or contaminant plume is identified. First step is we have to contain that pollution or containment of the plume and then second one is say we have to go for remediation. So, containment is also very important as far as the plume movement we have to contain otherwise again it will spread through the aquifer system. So, first step is containment second one is the remediation. So, generally for groundwater pollution remediation is concerned two types of technologies or techniques are used. First one is called on-site techniques and second one is called in situ techniques. So, on-site techniques means generally we will be pumping out the polluted water from the aquifer systems and then we can treat it and then either we can put it back to the aquifer systems or we can use it or we can spill to the nearby surface water sources like lakes or rivers. Then second one is so called in situ techniques. So, here actually we are not pumping out the polluted water we are doing say we are adding some say materials like for bioremediation or say airs purging or various techniques where in situ there itself we have say where the hot spot or the condemnation is there itself we are trying to remedy it. So, that is that technique is called in situ techniques. So, as I mentioned here as say on-site techniques say we generally we pump the polluted water treat and recharge back to the aquifer systems. So, one of the most commonly used method is pump and treat. So, there we pump the polluted water and treat it and then either use it or put it back. Then in situ techniques directly remediate the contaminated water in the aquifer itself. So, in situ technologies say actually it is we say we do not know the actual the total groundwater system or subsurface system. So, that way it is quite complex process. So, this in situ technologies are still under development. So, it requires say complete site characterization, but it is a very complex process and expensive. So, many technologies are under development as far as in situ technologies concerned. So, we will have an overview of some of the important techniques used either on-site which is so called pump and treat and some of the in situ technologies we will have a brief review in this lecture. So, as I mentioned one of the most commonly used treatment technology is on-site technique pump and treat. So, here what we do the contaminant plume wherever it is there in the hot spot we through bore holes or through wells we pump this polluted water out of the aquifer systems. And then we treat outside depending upon the contamination and then we can either pump it recharge back to the aquifer system or we can use it or we can spill it to the nearby sources surface water sources. So, the contaminant ground water is captured, pumped, treated and re-infiltrated back. So, for effective installation accurately we have to determine the location of the plume. So, this plume location is very important. So, accordingly only we can design a pump and treat system. Then we have to determine the hydrogeological parameters of the aquifer like hydraulic conductivity, porosity, then chemical properties of the plume. Then design we have to design the capture systems. So, say by pumping itself then installation of extraction and infiltration well. So, if you are going to infiltrate back to the aquifer systems we have to also design the infiltration wells. So, this pump and treat as we discussed earlier this is also a plume management or we can also use to contain the plume at certain locations. So, as we discussed earlier. So, some of the advantages of this pump and treat on-site technique include it is simple to operate and design is simple. But some of the limitations this need long time say depending upon the area and depending upon the contamination it may requires many years to remediate an aquifer system. And then there is possibility of design failure. So, the wells are not located properly or the pumping rate is not proper. Then the pump and treat may not become successful. Then it is very expensive. And then say for example, volatile organic contaminants this pump and treat may not be so effective. So, these are some of the limitations as far as the pump and treat is concerned. So, now let us look into some of the commonly used in situ technologies. So, first one is so called bio remediation. So, bio remediation what we will be depending upon the contamination depending upon the plume we can identify certain microbial bacteria. So, this bacteria can be the activities of this bacteria can be enhanced within the aquifer system itself. So, that the contamination is consumed by the bacteria and then it will be converted into harmless products. So, microbial processes used to degrade or transform the contaminants to less toxic or non-toxic forms mitigating or eliminating the contamination. So, as far as microbial processor concerned it can be either aerobic conditions where sufficient oxygen is available. So, sufficient oxygen presents microorganisms convert organic contaminants into carbon dioxide and water. So, this depends upon the microbial cell mass within the system. So, we can inject oxygen so that the aerobic activities aerobic conditions will be improved. And another one is anaerobic condition where the say it is the say the microbial process are enhanced without say oxygen. So, nutrients such as sulphates, nitrate are provided and contaminants are converted to methane and other compounds. So, this is what is done in anaerobic conditions. So, this bio remediation can be either aerobic conditions or anaerobic conditions. So, say bio remediation say generally used for organic compounds or organic contamination. So, some of the important parameters say we have to identify whether the contamination or the plume which we consider whether it is biodegradable and then what is the phase of the distribution. Then we have to identify the soil type, then the properties of the aquifer. So, all these things are very important as far as the bio remediation. But this bio remediation is one of the cheapest techniques available as far as groundwater pollution remediation is concerned. Only difficulty is that we have to identify for the given contamination of the plume. We have to identify what kind of microbial bacteria can be used to say for the remediation and then how to enhance its activities within the aquifer systems. So, this is so called bio remediation. Then some other techniques like in-situ flushing say for example, here what we do we inject a solution into a zone of contaminated soil or groundwater. So, down gradient we extract the polluted water and then this water is treated and then it can be reinjected. So, this is the technique of in-situ flushing. So, flushing solution can be simply water or we can introduce certain chemicals within the water so called surfactants or co-solvents. So, this may speed up the movement of the contamination to the pumping well. So, the co-solvents of surfactants can be also added within the systems. So, in-situ flushing enhances the conventional pump and treat say for example, so that can be combined with the pump and treat. And so, this the success of the in-situ flushing depends upon the site. So, like hydrogeology, contaminant nature and then the aquifer thickness, aquifer materials etc. So, the efficiency depends upon the solubility and mobility of the plume. Some of the advantages include acceleration, inside cleanup, broad range of contaminants can be dealt with the in-situ flushing. Limitation below possibility of say further spreading when we are putting the water or the surfactants then there is a possibility that the condemnation can further spread to the aquifer systems. So, these are some of the limitations as far as in-situ flushing is concerned. Then another commonly used methodology is called air sparging. So, here what we do we inject air or oxygen under pressure into saturated zone to volatilize the groundwater contaminants and to promote biodegradation in saturated or unsaturated soil by increasing subsurface concentration. So, generally this air sparging can be used for volatile organic contaminants. The volatilized vapor migrates through the vadozone or the unsaturated zone and these are collected by the vacuum pumps. So, sometimes this air sparging is also called bio sparging since when we introduce the air, the bio remediation process also will be enhanced within the systems. And then this air sparging can be used to remediate volatil or semi-volatile contaminants like petroleum products, B-tex, medicine toluene and that kind of pollutants, then chlorinated solvents etcetera. So, say this is a very say effective in areas where more pervious areas homogeneous soils and large saturated thickness the air sparging is more effective. So, some of the advantages of the systems include a law maintenance in situ remediation, minimum disturbance to the sites. So, since this process once it is set it will keep on going for long time without much interference and remediation can be achieved in a reasonable time. Some of the limitations include not efficient for pollutants which form complexes with soil or not efficient in low permeable areas. So, mainly air sparging we can use for volatile organic contaminants. Then another commonly used in situ technique developed in Germany is called groundwater circulation wells. So, this is an in situ technique for volatile organic contaminants amenable to air stripping. So, here what we do say if this is the hot spot of the contamination plume and this is the aquifer systems. So, here there will be a pumping well and through say here we create an artificial flow field that flushes and transform the contaminants from aqueous phase to gaseous phase. So, here we strip with air and then there will be hydraulic gradient will be generated and then these are the path line shown and here say the water is again taken back here and then it will be circulated. So, that is why it is called a groundwater circulation well. So, typical groundwater circulation system consists of single well or with two hydraulically separated or skinned sections are shown in this figure. So, pumping in the lower followed by air stripping and in reinfiltration the upper screen creates this recirculation pattern in aquifer systems. So, this is the typical pattern. So, pumping mechanism controls the circulation processes and then exchange of large pore volumes. So, continuous flushing, dissolution, diffusion and desorption takes place. So, this creates a complex 3D flow field and the efficiency depends upon radius of influence of the well. So, this is the radius of influence of the well and then well screen length, number of screens etcetera. So, some of the advantages include less investment and operating cost, no extraction, no lowering of groundwater levels, some of the limitations it is not suitable in thin aquifer systems and not efficient in low permeable regions. And this methodology was used mainly for volatile organic contaminants. So, whatever we are discussing, we are discussing about the how to remediate once the groundwater is contaminated, to remediate the groundwater contamination or how to remediate an aquifer systems. So, now say let us see some of the important transport processes taking place within aquifer or within a surface water. So, this transport processes what we are discussing is common to surface water as well as the groundwater systems. So, the processes involved in transport of chemicals from say for example, watersheds say this process are very complex and the process can be either physical, chemical and biological. So, the physical some of the important physical processes can be like convection, suspension and deposition, dispersion, diffusion, say tillage etcetera what is happening within the watershed. Then chemical process can be like a sorption, ion exchange, crystallization, hydrolysis, oxidation reduction, photochemical reactions etcetera. And then the third one is the biological or biochemical processes. So, these are some of the important processes of happening say as far as the movement of the contamination within a surface water or the the groundwater. So, let us look into some of the important details of this transport processes. So, as I mentioned convection say it is the transporting fluids carries the transporting fluids carries the constituents like either dissolved or suspended contamination. So, the water is the principal carrier. So, since the water is moving in surface water in a river or in an aquifer systems. So, when the water is moving the contamination is taken with that. So, that is the process of convection. Then suspension and deposition means the process by which solid particles moved into and returned from water. So, it can be rainfall and overland flow. So, these are some of the major factors as far as suspension and deposition is concerned. So, the materials held in suspension depends on the turbulence of flow. Turbulence say when the turbulence is reduced the particle settles. Say for example, when rainfall takes place the overland flow keep on say the level can keep on increasing and depending upon the velocity the turbulence can be generated and the suspension and say when the velocity comes down the turbulence reduced. So, the particle settles or deposition takes place. Then another important transport process is so called dispersion. So, this is the result of irregular or unequal transport either in surface water or groundwater. So, these and other disturbance in streams in canals or the rivers. And in porous medias concerned the pathways since the soil matrix is packed in such a way that there is a sensual movement within the soil matrix. So, that can be a reason of the dispersion. So, some constituents move ahead or lag behind. Then another one is diffusion process, transport process. So, net movement of constituting in response to concentration difference or gradient. So, this is the process of called diffusion. Then in watersheds say tillage say affects the chemical transport indirectly by modifying the water and sediment movement. So, tillage means the soil surface is the pattern is changed by tilling. So, that can affect the movement. So, these are some of the physical processes which can take place as far as the transport is concerned either in surface water or groundwater. Now, chemical process are concerned say for first one is sorption. So, this means the movement of a constituent between the solid and the solution phases. So, sorption can be either adsorption. So, this occurs when chemical leaves the solution and adheres to some solid and it can be desorption that means the reverse process. So, at equilibrium a balance between desorption or adsorption can take place. So, this is one of the important chemical process. Then ion exchanges so the exchange of an ion in a solution for an ion of similar charge on the surface of an oppositely charged solid. So, this is so called ion exchange. Then the transport process can crystallization. So, when it occurs when concentration of a chemical in solution exceeds its solubility. So, then automatic crystallization starts so that the concentration reduces. Then another important chemical process can be hydrolysis. So, this reaction of a chemical with water to form different compounds. So, this is the process called hydrolysis. So, this is also a transport mechanism the chemical transport. Then oxidation and reduction so reactions occurs when one chemical loses an electron and is oxidized while another gains the electron and is reduced. So, these are some of the important chemical transport processes which can take place either in surface water or in the ground water. Then some of the important process like biochemical processes or biological processes. In biochemical processes enzymes that various micro organism contains can act rate reaction rates organic chemicals can be transformed into other chemicals bio oxidation reduction hydrolysis and other reactions occurring in the micro organisms. So, similarly various the biological processes like activities of bacteria or viruses can also change the the the transport phenomena what is happening within the surface water or ground water. So, as we discussed as far as the water is concerned either surface or ground water some of the chemical constituents can be sediments salts nutrients pesticides oxygen demanding materials heavy metals micro organisms water temperature etcetera. So, these details we have seen in the last lecture. So, now based upon this say what we discussed the last two lectures now in the next lecture we will be discussing the water quality analysis and water quality modeling. So, with with respect to this transport process which we discussed in this lecture. So, now some of the important references used for today's lecture include say some of the website from say central pollution control board water resource ministry ground water board and some of the test books like a free sanitary ground water and then guidelines for water quality management. Then some one tutorial questions for today critically study the ground water pollution problems in India study various sources and courses. So, you can get the details from this CPCB or water resource ministry website study the various measures that can be adopted to reduce the ground water pollution in India. Then some self evaluation questions illustrate the ground water quality issues on watershed scale. What are the important sources of ground water pollution? What are the different source control strategies for ground water pollution? Describe the onsite ground water pollution remediation. Describe the in situ ground water circulation wells systems for ground water pollution remediation. So, these questions you can easily answer by going through the today's lecture. Then few assignment questions like describe the ground water management systems for quantity and quality. Then discuss the various measures of ground water protection and pollution control. What are the important techniques for ground water pollution remediation? Describe the in situ ground water pollution remediation. What are the various transport processes involved in pollutant movement in surface water and ground water? So, all these questions you can answer by going through today's lecture. And finally, one unsolved problem. So, in your area in your watershed critically study the possible ground water pollution problems. Identify the possible costs of ground water pollution such as point source or non-point sources, agriculture sources or industrial sources. Then study how this pollution problem can be controlled or what kind of remediation activities can be adopted wherever pollution problems are there. What we discussed today include the ground water pollution sources, then pollution control and then remediation. And we also discussed about the transport processes taking place either in surface water or ground water. So, in the next lecture we will be discussing about the water quality modeling say how we can model either the pollutant movement in surface water or ground water. Thank you.