 lecture 30 of ground water hydrology. So, in this lecture the topics to be covered radiation logging method. So, within this radiation logging method natural gamma logging followed by gamma, gamma logging followed by neutron logging then we will move on to temperature logging, temperature logging method followed by Kaliper logging method followed by fluid conductivity logging method followed by fluid velocity logging method and then lastly miscellaneous logging methods. So, these are the topics which are proposed in this lecture and first we will start with the radiation logging. So, in this radiation logging, so within this we will start with the natural gamma logging and in this, so this is based on the principle of principle is the emittance of natural gamma rays by all rock soil formations. So, that is the principle on which this logging is based on and here, so this radiation originates from unstable isotopes of potassium, uranium and thorium and so the natural gamma activity, gamma ray activity clay is much higher, much higher than sands and carbonate rocks. So, the application of this natural gamma logging applications, one major application is lithology identification and of course, there are other this one also the identification of other fine grained formations like clay, shale, etcetera. So, these are the application and in this a typical natural gamma ray log will have say depth along the vertical axis and then the radio activity along the horizontal axis and here, so in this case, so this will constitute something like this and here, so this is 0, 0 and this corresponds to, so in the geological log, so maybe this corresponds to sand again. So, here it is sand and gravel and this is till, so here this is clay, then sandy clay, then again here this is sand and gravel and then again this is till and again say this could be gravel. So, like this, so we can identify the formation of the rock using this natural gamma logging. Next we will go to that is gamma, gamma logging, so here gamma ray radiation originating from or say coming out from a source probe and recorded after it is bat scatter, bat scatter is the gamma, gamma log and so the source probe consists of cobalt 60, cesium 137, so this is generally, so these isotopes of cobalt and cesium, so this is shielded from sodium iodide detector built inside into the probe. So, this again the applications of this, so one is lithology identification, then estimation of bulk density and porosity of formations. So, if this porosity is denoted as alpha, then this alpha can be written as gamma g minus gamma b, I am sorry rho g minus rho b divided by rho g minus rho f. So, here this rho g is the grain density and rho b is the bulk density, so this bulk density, so this is measured from a calibrated log and then this rho f, so this is the fluid density. So, if, so these three parameters are known, so then we can estimate the porosity of formation using this gamma ray logging and one last application of the third application of gamma ray logging is in location of casing, collars, grouts and zones of hole enlargement. So, using this gamma ray, gamma gamma radiation, so these casing, collars, grouts and hole enlargement zones can be located. So, next we will go to the another that is the last variety of this radiation logging, so that is neutron logging. In this case, so this is a neutron source and detector in a single probe which produces a record of hydrogen content of a borehole. So, here, so this hydrogen content, so this H content is proportional to interstitial water and therefore, this neutron log measures soil moisture above water table and porosity below water table. So, these two can be measured. So, here what happens is, see the mechanism is, neutrons have same mass as hydrogen and no charge, no electrical charge, they are neutral. So, when neutrons collide with this hydrogen, so there will be energy loss and neutrons are slowed and slowing down of neutrons. So, here this neutron probes use, which are currently available, beryllium combined with, so this is beryllium combined with radium 226, plutonium, so this is plutonium 239 or americium, so this is 241. So, these isotopes and this case, so obviously, so the application, major application is soil moisture estimation, then followed by porosity estimation. So, obviously, this small moisture estimation we have seen, so this is above water table and porosity estimation, this is below water table and here, so this for porosity estimation, large holes are used, large diameter holes are holes and larger probes are required and so here, there is on a typical neutron log. So, here this is the depth in meters below the ground level and this is the moisture content in percentage. So, this is neutron log of a shallow well in an unconsolidated alluvium, so this is taken from the US geological survey and here, so based on this, we can say, if the moisture content is more, so then we can say, it indicates a clay, this one and here, it indicates unsaturated zone, so here, this is sand and sandy silt, again for a small depth, it is clay, then followed by, so this is sand, so like this, using the neutron log, we can estimate the soil moisture and also, we can estimate the porosity. Next, we will go to caliper logging, so this caliper logging, it is the log of the bore hole diameter with its depth, so this is the and here, so obviously, so this is taken as the average bore hole diameter, because at a particular location, there can be the bore hole may have varying diameters, it may not be perfect circle and in this case, so the applications are of this caliper logging or lithology identification and next is the stratigraphic correlation, so they can also be used for location of fractures and other openings in rocks, so let us consider a typical caliper log, so this case, so this is the average hole diameter in centimeter along this one and here, there is depth, so this is the depth in meters and in this case, so it may show something like this, so here, this represents a casing, this represents crevices, this represents soft water and sand and again, so this represents caving shells, again crevices and this represents liner and so on. So, in this case, so this is a caliper log and in this case, so the typical, so this is the caliper and then, so this caliper, so this goes on, so this is a typical caliper and here, you can show, so this is the bore hole with different rock formations, so this is a caliper, so this is a caliper logging, so next we will go on to this fluid conductivity logging, so this is a continuous log of electrical conductivity of fluid in a bore hole, so this is a fluid conductivity, so the probe is, the probe measures the alternating current voltage drop across two closely spaced electrodes, it is governed by electrical resistivity between the electrodes and we know that the fluid resistivity, so this, if we abbreviate the electrical resistivity as E r, so this fluid electrical resistivity, which is measured in ohm meter, so this is the reciprocal of, that is the fluid conductivity and this conductivity is measured in, so this is the micro seamance per centimeter, so this is a micro seamance per centimeter, so this electrical resistivity is the reciprocal of this one and the applications, so the applications are, one is the location of saline water zone, two is extrapolation, this fluid electrical, the conductivity log can be used for extrapolation of water sample data and in this case, say for example, a typical fluid conductivity log, it will have, so this is the depth in meters and then the specific conductance in micro seamance per centimeter, in this case, so suppose this fluid electrical, fluid conductivity log, so it has a shape something like this, so this indicates, so here obviously, so this is a, so this is fresh water overlying a saline water, so obviously, saline water is a good conductor of electricity, so its specific conductivity is much higher, so of the order of say something like 40,000 whereas, so the fresh water has very negligible as fun, may be even less than 1000 or around 1000 micro seamance per centimeter, so next we will go to the fluid velocity logging, so in this fluid velocity logging, so it consists of or measurement within a borehole, so its applications to reveal strata contributing water to a well, to estimate the hydraulic differences, so estimate differences in hydraulic parameters of various aquifers intersected by a well and thirdly, to estimate casing leakages, in the casing pipes, in this case say suppose, so this is a well and it has, so there is, so this is a well screen, so this is a well screen, this is also a well screen, here say suppose there is a, so this is a pump, in this case the fluid, so the fluid velocity logging, it will be something like this, I am sorry it starts at the pump level, so it is, this is the upper aquifer and here this is again and so on, so basically, so this is a typical, so this indicates upper aquifer, so this indicates lower confined aquifer and so this is the velocity, so this is the depth, so this is regarding the fluid velocity logging and with this, so these three applications that is the strata revelation, then estimation of differences in hydraulic parameters and then the casing leakages can be estimated. So next we will go to the last item of this module that is on miscellaneous methods of logging, so in this, there are this TV or say television logging, there is acoustic logging and the third one is the casing logging, so these are the three important techniques which are grouped under the miscellaneous logging and here, so this is, now let us come to this TV logging, so this is in this a TV camera, television camera is a very convenient tool, so this TV camera lowered in a well, so it is a wide angle camera, so this is typically less than say 7 centimeter in diameter and when it is lowered inside a well, so it provides visual inspection of a borehole, so the applications, so the applications are, one is location of changes, geological strata changes, so inspection of well casing condition, then the third one is checking for debris in wells, location of sand entrance zones, so there is also what is called a photologue, so this photologue, so it is basically photographs taken in a well that is within a well at close time intervals, so this is regarding the TV logging, next we will go to what is called the acoustic logging and this is also known as sonic logging, so in this, so it measures sound velocity through rock surroundings, rock surrounding an uncased fluid filled hole and so therefore, if porosity is greater, is higher, the closer is the measured sound velocity to that of fluid, so the applications of this acoustic logging, estimation of depth and thickness of porous zones, second is the estimation of porosity, third is identification of fractured zones and next application is the determination of bonding of cement between casing and formation, between the casing and the formation, so these are some of the applications of acoustic logging and lastly we will go to this casing logging, so this casing logging, so here a casing collar locator is used for locating collars, perforations and screens in casings and so it consists of magnets wrapped in a wire coil, so this fluctuations, voltage fluctuations caused by mass metal, a mass metal cutting magnetic lines of force, magnetic flux lines are recorded, so there are other subsurface methods, which include the pumping test, the ground water level measurements, water quality measurements, so all this have been already discussed, most of this have been discussed in the previous lectures and few might be discussed in the next lectures, so basically this subsurface investigation of ground water, it is the more complete and it provides, it is almost complete information as compared to the surface information, as compared to the surface investigation, so that needs to be properly complies utilized to arrive at the ground water, to arrive at a holistic investigation of the ground water, thank you.