 of this lecture 23 on groundwater hydrology and here in this lecture we will complete the from miscellaneous sources which we have started in the previous lecture. So, that we will be completing that we will be continuing with and completing then followed by attenuation of this groundwater pollution and underground distribution groundwater pollutants. So, these are the topics which will be covering in this lecture and moving on to this groundwater pollution miscellaneous sources. So, we will be in the previous class in the previous class in the previous lecture we discussed about the various causes such as urbanization the miscellaneous causes of groundwater pollution such as urbanization, surface spills and surface discharges, stockpiles and septic tanks cesspools. So, today we will go to that is roadway de-icing followed by saline water intrusion this is just listed here. So, we will be discussed in detail it will be discussed in detail in another module another separate module we are just listing here. So, it will be followed by two more the causes miscellaneous causes that is interchange through wells followed by surface water. So, these are the four remaining causes under the miscellaneous sources we will be discussing today. Now, coming to this roadway de-icing. So, this is very essential in winters especially in areas in locations experiencing snowfall snowfall and other solid forms of precipitation. So, in this so to remove the ice certain de-icing agents are spread on the road roadways and this one. So, the so certain salts are spread on the roadways. So, as to remove the ice from the roads and this the salt application salts used for de-icing the application ranges from this 2 to say 11 metric tons per I am sorry this is a British ton which almost is same as the metric ton. So, that is a per single lane or say per lane per kilometer in the winter season. So, therefore, so what this does is so the the main salts are NaCl sodium chloride and followed by CaCl2 and this one. So, so these salts they will percolate into the ground water and then they will increase the salinity as well as the chloride and sodium and calcium content. So, that is it is very important to consider this in the that is abatement or reduction of the pollutants. So, next that is saline water in intrusion. So, that will be discussed separately in a module in a new module. Then now we will go to the interchange through wells. So, here so this wells offer vertical connection highly permeable vertical connections among various aquifers. So, in this so therefore, what happens is so through these wells so the pollutants enter from one aquifer to another aquifer through the through these wells. Now, let us discuss two separate cases as given by this one that is the so the so ground water pollution through wells. The first case is when the case one when ground water table is above the piezometric surface. So, again so for both is and case two say when the ground water table is below the piezometric surface and for both these cases they are taken from the same source that is at all from 1976. Now, let us consider this case one. So, here so this is the ground surface and this is a well in this case. So, this is the water table whereas the piezometric surface that is below the water table. So, this is the piezometric surface and let us indicate this as P s. So, in this case so this is a confined aquifer and in between there is a clay layer and then let us consider just one confined aquifer and one unconfined aquifer. So, here what happens is so because the piezometric surface is below the water table. So, there will be flow into the well. So, this is the ground water flow and along with this the pollutants also are flowing. So, this is the unconfined aquifer and here it is the confined aquifer and this is the impervious strata and in such case what happens is this along with ground water. So, the pollutants will move that is downward in a downward direction and then so they get distributed to this lower confined aquifers. So, this is case one when the ground water table is above the piezometric surface. Now, let us also consider this case two when this ground water table is below the piezometric surface. So, this is the ground level and then in this case the water table I am sorry the piezometric surface is above. So, this is the piezometric surface which is indicated by the abbreviation PS and then so there is a water table which is below the piezometric surface and there is a let us consider one. So, this is a clay layer and then so this is the unconfined aquifer this is the confined aquifer. So, in this case because the piezometric surface is above the water table. So, in this case there will be flow from the well into the aquifers and in this case because the piezometric surface is above. So, the pollutants move from that is the in an upward direction and so this pollutants get distributed in the upper aquifers. So, like this so the wells so they result in this they cause pollution through that is when in two cases the first one is when the ground water table is above the piezometric surface and the second case is when the ground water table is below the piezometric surface. Now let us come to the last cause of among the miscellaneous sources that is a surface water. So, in this surface water so this the polluted surface water bodies polluted water bodies become sources of this ground water pollution. So, in this case let us say there is a so this is the ground surface and then so there is a well with a strainer here. So, this is the ground surface and here so there is a polluted surface water body. So, this is a polluted water body and in this case and so this is a pumping well and through this so this is the water level in the pumping well and here so below this so this is the pumping water level. So, this is the pumping level and suppose the original so this is the original water table. So, in this case from below the this pumping level this so the the ground water enters the from the polluted water body obviously. So, therefore, the pollutants they will enter the well and then so they will cause the they will cause the ground water pollution. So, these are some of the causes of the miscellaneous sources of ground water pollution. Now, we will move on to this attenuation of a attenuation so that is reduction of ground water pollution. So, this reduction so this whenever there is a polluted ground water we need to take all appropriate measures so that we can reduce this reduce or attenuate this ground water pollution and there are various mechanisms are there and so these mechanisms so they are firstly it is the filtration then the second one is the sorption the third one the third mechanism is the chemical processes the next mechanism is the microbial or microbiological decomposition and last but not the least it is the dilution. So, these are the mechanisms which will reduce the ground water pollution. Now, let us discuss these mechanisms one by one so firstly we will consider this filtration. So, this filtration so it removes the suspended materials or suspended pollutants hence reduces this ground water pollution. So, in this case so it can remove particulates of Fe iron or manganese and precipitates formed by chemical reactions. So, this filtration basically there will be a filter substance filter layer and that filter layer will remove the surface pollutants or the suspended pollutants and that is very important in case of the surface polluted surface water infiltrating into the ground water and then causing pollution. So, that this filtration will take care of that so in this filtration so the polluted surface water infiltration is impeded. So, now let us come to the second mechanism of attenuation or reduction of this ground water pollution that is the sorption and within this sorption. So, basically so here that is there are two types of sorption are there the first one is the adsorption and the second one is the absorption. So, here in this adsorption it is the so this adsorption is the accumulation of material so in this case the pollutant at water solid interface. So, that is adsorption and this absorption is the intermixing of pollutant solute molecules that is known as absorption. So, in this absorption process so the pollutants the sorptive materials clays metallic oxides and hydroxide and hydroxides so that is hydroxides then this organic matter. So, they are used to facilitate the process of sorption or the induce the mechanism of sorption. So, here except chloride because chloride is mostly soluble. So, most of the materials are most of the pollutants sorbed that means either adsorbed or absorbed under favorable conditions and of course, this one the nitrate and sulphate soft lesser degree. So, in this case so using this sorptive materials that is clays metallic oxides hydroxides as well as organic matter. So, most of the materials most of the pollutants they are made to undergo either adsorption or absorption and thereby so it is removed. So, this is the second mechanism of attenuation or reduction of this ground water pollution. So, now, we will go to the third mechanism that is the chemical processes pollution attenuation. So, in this the precipitation or say formation of precipitates in ground water occurs when ions are in sufficient quantity. So, this important ions involved so the important ions involved in precipitation reactions are this precipitates their calcium Ca plus 2 mg plus 2 then the bicarbonate sulphate and of course, the trace elements involved are trace elements with precipitation potential arsenic ion. So, ions of arsenic cadmium barium copper cyanide so fluoride Fe ferrous comma ferric lead then mercury molybdenum zinc and radium. So, the ions of these metals as well as the these compounds so these radicals so they also have the potential for precipitation. So, in this case wherever see whenever there is a minimum moisture near free surface near the surface so this precipitation takes place. So, this is the chemical process so which is a mainly precipitation and in the zone above water table this oxidation is the important chemical process for pollution attenuation. So, here in this case this complex organic compounds so they undergo oxidation that is a step wise oxidation and eventually they are they get themselves converted to CO 2 and H 2 O the carbon dioxide and water along with numerous inorganic ions. So, this is a step wise oxidation process and here so this additionally oxidation so this is additionally oxidation and reduction occurs along with other chemical processes results in formation of precipitates comma deposits of insoluble trace metals and gases. So, thereby this for radioactive pollutants so this radioactive decay is the important mode of pollution attenuation as we all know half life period means the particular radioactive material it will decay and thereby its volume will be reduced to half. So, now let us go to the other that is a mechanism of attenuation of pollution that is microbial or say microbiological decomposition. So, here basically so this is the it is the ultimate destruction pollutants due to microorganisms. So, here this bacteria comma viruses say they tend to move slower through porous media than in water. So, this pathogens are largely removed by passage through say 1 meter of soil containing substantial amount of clay and silt. So, basically when this clay and silt so they are fine textured soil. So, when they are present and so when this bacteria or and virus they are made to pass through them so then obviously so they are retained there and thereby the pollution is reduced. And we will now come to the last one that is the dilution and we all know that the pollutants and there is a very famous say that pollution the solution is dilution that is a solution to pollution is dilution. So, in this case the pollutants which are flowing pollutants flowing in ground water get diluted in concentration by hydrodynamic dispersion. So, here longitudinal and lateral spreading of pollutants takes place thereby reducing the concentration level of pollutants. So, this is also very important mechanism of attenuation of pollution. So, now we will go to the last one of the last topic to be covered in this lecture that is the underground distribution of pollution. So, here suppose there is a waste site and let us say this is the waste site. And then this is the direction of ground water flow direction. Then what happens is and of course let us say here there is a river. So, this is a river. So, in this case so the concentration so this is a b this is c. So, this is d so this is e. So, here so this is taken from the source. So, this figure is taken from the source Legrand 1965. So, here the concentration a is greater than b which is greater than c which is greater than d which is greater than e. So, whenever there is a waste site and in the vicinity of that. So, there is a stream or a river and then there is a this general ground water direction ground water flow direction. Then obviously, so the concentration decreases as we move away from the waste towards the river. So, but still even this decrease concentration itself is many times quite significant to cause this the distribution of the underground distribution of the pollutant as well as eventually the pollution of the water in the river of the stream. So, similarly there have been other this one. Suppose there is a land fill. So, this is a land fill and in this case so the concentration profiles which emanate from this land fill. So, they gradually decrease as we move away from the land fill in this case. So, this is taken from. So, this figure is taken from. So, this is the pollutant plume from a land fill. So, this is taken from a study by Cole in 1975 and in this case. So, this is the general ground water flow direction then in that direction. So, the pollutant plume will. So, this is the ground water pollutant plume. Similarly, say here when there is another say suppose this is the waste site and this is a former boundary and then so this is the latter or say present boundary and in this case. So, this is the ground water flow direction. So, this is the enlarging plume and for all this the source is the same study by Legrand in 1965 and then. So, for a reducing plume if it is an enlarging plume then the area of this pollutant plume increases. On the other hand if it is a reducing plume in this case say suppose this is the waste site then the if the former boundary is one and the present boundary. So, this is the present boundary or latter say that is the present boundary. So, the present boundary will become shorter whereas, the former boundary is larger. So, this is the case of a reducing plume and then so there can also be so also this nearly stable like that. So, there can be nearly stable plume in which the former boundary as well as the present boundary is more or less the same. So, this in case of nearly stable plume so the former and the present boundary are almost same. So, this is the source and of course, a shrunken plume in that case what happens is. So, it is basically largely reducing plume wherein the present boundary of the plume is drastically reduced. So, this is the regarding the ground water pollution that is the underground distribution of this ground water pollution. And in the next lecture we will move on to the ground water quality analysis. Thank you.