Answers to Lab Questions Once again, I have to remind you I am not an expert in this field! These are the best answers I know but you are welcome to revise or add to these as you see appropriate. Let me know about any changes or corrections and I will make updates. Part I. 1. You should measure close to 6 volts, if the battery is reasonably fresh. 2. You will see that each battery has a slightly different voltage; everyone should get different answers for this. In the five batteries that I had on hand, the results ranges from 6.46 to 6.13 volts. 3. Switching the meter probes should give you the same voltage, but negative. 4. Changing the scales should not change your measured voltage, but for example you will change from 6, 6.1, 6.14; at the millivolt scales you will probably be offscale and only a "1" will appear on the display. 5. Your body will act as a non-conducting material compared to the battery (although as the voltage increases this will no longer be the case), and you will probably measure something like 0.2 volts. By the way, these low voltages are not at all dangerous, you will not even notice anything when you put yourself in the circuit. Don't try this on a car battery or an electrical outlet though! Part II 1. You should measure less than full voltage. Depending on the size of your basin and the exact position of your probe, you should measure somewhere around 5 or 4 volts. 2. No - the flowpaths are essentially infinite in number. 3. Since there is an electrical potential field throughout the basin, this tells you that electrical flow is also occurring throughout the basin. So there are also electrical pathways throughout. 4. You can imagine that the water will spread out on the ground, and at a molecular scale will flow in a vast number of different pathways down the slope. The water which travels in the most efficient path will reach the bottom first; the same is true for electrical flow. In groundwater systems contamination from a leaking landfill for example will reach surrounding wells at different times, information which can be used to help determine where the leak is. 5. The other pathways can be drawn in any number of places; I've draw some examples in Figure 1c. Part IV. 1. If the region around the hole displays the lowest voltage in the basin, all drawn flowlines must converge upon it. 2. Impermeable means that the materials act as barriers to flow. In your electrical circuit, the equipotential lines stop at the system boundaries. Likewise, groundwater equipotential lines will also stop at the boundaries. In both systems, impermeable objects will affect the equipotential fields and the flowpaths in a number of ways - they may produce a shift in the equipotential lines, or a redirection of flow. One way to think of it is placing a large rock in the middle of a small stream. The stream still flows, but the water must now change direction to get around the rock. The channel is now narrower than before, and the water will flow faster in the narrower channel (you have the same amount of water to move, but less space to put it through, so it must increase its flowspeed). The same effect takes place in groundwater systems, and electrical systems. 3. Both methods have there own unique advantages. Well sampling can tell you if something unusual is in the well (such as mercury, lead, or solvents) which can be traced back to a landfill or dump. However, to pinpoint the source of the contamination, you need to drill and test many wells. Even if you determine the landfill as the source, you cannot tell precisely where in the landfill is leaking. With the electrical method, it doesn't tell you where the leaking material will travel, but it does pinpoint the source of the leak in the landfill. 4. If the landfill is empty, the system is much like our model: they simply fill up the basin with water and search for leaks. However, if the landfill is in use you may have a wide range of both conducting and nonconducting material within it. These will pose problems for the analysts to determine the equipotential field, and to identify small changes in the field which indicate areas of leaking. One advantage they have is using more powerful and sensitive equipment. 5. In the model you can see for yourself what will happen if the ground outside the landfill is not saturated. The system will not make a good connection and you will not get a completed circuit. In the field uses of this technique, they typically perform the test after a heavy rainfall or will pump water to saturate the ground. 6. Just as the material in the landfill can affect the electrical and water flow, the material outside will affect flow. Some minerals are metal-rich which can complicate the circuit. The type of material will also have varying porosity (ability to transmit water through open spaces) which strongly affects flow. 7. Man made structures, such as buildings, will produce non-continuous (sharp) changes in surface elevation lines. Likewise, a conducting object in a landfill can produce sharp changes in the electrical potential fields.