1 Name: Water Movement (adapted from Wards) LAB BACKGROUND: While some precipitation falls to the earth and runs off into streams and river, another portion seeps slowly through the soil into the upper layers of the earth s crust. This underground water, or groundwater, fills the empty spaces or pores between rock and solid particles. Subsurface rock and sediments units through which large volumes of water can flow and be stored are called aquifers. How water travels through these aquifers is determined by a number of factors. Porosity is the percentage in a given volume of open pore space in a given volume of rock or sediment, and determines the total amount of water a material will hold. The larger the volume of pore spaces, the higher its porosity, and the more water it can hold. Porosity is largely influences by factors of particle size, shape, assortment, and compaction. Another factor affecting ground water movement is permeability. Permeability refers to the ability of a rock or sediment to transmit water freely. The rate at which a material transmit water depends not only on its total porosity, but also on the size of the passageways between its openings. To be considered permeable, the open spaces in a rock must be connected. The size and sorting of the particles composing the rock or sediments will affect it permeability. Generally, materials of larger particle size which are well-sorted will be more permeable. PART I Materials 4 plastic tubes 1 package plastic beads, 4mm 1 package plastic beads, 7mm 1 package mixed beads 1 package of mixed sand 1 graduated cylinder, 100 ml Water Procedure In this exercise, you will be asked to determine the porosity of four different samples, and then compare what effect particle size and sorting have on overall porosity. 1. Fill one of the plastic tubes with water. Pour the water into an empty graduated cylinder and record the volume on Data Table I. This represents the total volume of the tube. EMPTY the tube. 2. Fill one of the tubes with the 4mm beads. Place your thumb over the top of the tube, tap it gently up and down on the table to settle and compact the beads. Add more beads till the tube is filled and level at the top. 3. Fill the graduated cylinder to 100mL of water.
2 4. Pour the water from the graduated cylinder into the plastic tube until the water level just reaches the top of tube. 5. Subtract the total water left from 100 and record on Data Table I (this equals your volume of pore space. 6. CAREFULLY drain the water, pour the beads into the plastic container to dry. 7. Repeat steps 2-6 with the 7mm beads, mixed beads, and mixed sand. Part II Materials 3 plastic pots 1 plastic tray/catch pan 1 graduated cylinder 3 pieces of cloth 3 plastic drain supports 1 sample each of coarse, medium and fine sand Water Stopwatch Procedure In this second part of your investigation, you ll observe the permeability of three different sands and compare the drainage rates for each sample. Follow directions closely in constructing your permeability models. 1. Place a piece of cloth in each of the plastic pots 2. Fill each pot to the level where the inside rime flares out (about ¾ from the top) with one of the sands provided. Check to make sure the cloth is still covering the bottom holes, and that no sand is leaking out. 3. Place the pot containing the coarse sand into the plastic tray and balance it on top of the small plastic drain support provided. The support should be positioned under the center of the pots so that it does not block any of the drain holes. 4. Fill the graduated cylinder to 100 ml. Have the timer ready!!! Pour the 100ml of water (yes all of it) into the pot of coarse sand. Time and record in Data Table II how long it takes for the water to drain through the pot. 5. When the water has completed draining, collect the water now settled in the plastic tray, and carefully pour it back into the empty graduated cylinder. Record the amount of water drained through the pot in Data Table II. Calculate the percentage of water retained by the sand in the put by subtracting the amount of water drained into the tray from the original 100mL added. Divided this difference by the original 100ml to find the decimal amount and then multiply by 100 for the percentage. 6. Now Calculate the rate of drainage for the sand by dividing the amount of water drained into each tray by the amount of time it took the water to drain 7. Repeat steps 3-6 with the other two sands. Proceed to Question
3 Questions: Part I 1. What is the total volume of the plastic tube? 2. Do each of the bead size represent well sorted or poorly sorted particles? 3. What is the total volume of the larger (7mm) beads, including the pore space 4. How much water was required to fill the tube of larger (7mm) beads? 5. What is the volume of the pore space between the large beads? 6. What is the porosity of the large beads? (state your answer as a percent) 7. What is the volume of the pore space between the smaller (4mm) plastic beads? 8. What is the porosity of the small beads ( state your answer as a percent) 9. How do the porosities of the larger and small beads compare? 10. Does your data suggest there is a relationship between particle size and porosity? EXPLAIN 11. Does the mixed sample of the small and large beads represent well sorted or poorly sorted particles? 12. What is the porosity of the mixed beads sample? ( state your answer as a percent)
4 13. Did mixing the bead size have any effect on the porosity? Explain your answer. 14. How does the shape and character of the mixed sand sample differ from the beads used in the investigation? 15. Is the mixed sand well sorted or poorly sorted? 16. What is the porosity of the mixed sand? (stat your answer as a percent) 17. How does the porosity of the mixed sand compare to the mixed bead sample? EXPLAIN your answer 18. What effect would adding finer particles have on the overall porosity of the mixed sand? EXPLAIN Part II 19. Which sand had the highest drainage rate (drained most quickly)? 20. Which sand retained the most amount of water? 21. Which sand retained the least amount of water? 22. If we consider that high drainage rate and low water retention rate are characteristics of high permeability, which of the sample was most permeable? 23. Which of the samples were least permeable? 24. What factors do you think affected the permeability of these samples?
5 25. What does your data suggest about grain size and permeability? EXPLAIN 26. What do you think might happen to the permeability of these samples if we mixed finer clay particles with the sand? EXPLAIN 27. Is it possible for a rock to have high porosity but low permeability? EXPLAIN Answer questions using the following word bank. (Note one word is used twice) Word Bank: Porosity Capillarity Permeability 28. Water is drawn upwards from the water table into the soil above by the process of (28). 29. What type of water movement increases as soil particle size decreases? (29). 30. What type of water movement increases as soil particle size increases? (30). 31. You have equal amounts of sand and clay both are completely saturated. There is an equal amount of water in both, which means that both samples have the same (31). 32. State the relationship between porosity and particle size (direct/indirect) 33. State the relationship between permeability and particle size (direct/indirect) 34. State the relationship between capillarity and particle size (direct/indirect)