Name: EPS 50 - Lab 10: Groundwater Flow and Glaciers Part 1: Groundwater Flow Part 2: Darcy s Law Part 3: Glacial Deposits and Flow -Chapter 17, p. 478-492: Hydrology of Groundwater -Chapter 17, p. 485-486: Darcy s Law -Chapter 21, p. 587-606: Glacial Flow and Landforms Introduction: Water is an important resource that is essential to life. The oceans and seas contain most of Earth s water (96%), but this water contains salt or high concentrations of other dissolved materials. So where can humans populations get their water? Glaciers and polar ice represent the highest percentage of freshwater, but they are not easily accessible. The most common source of freshwater is located beneath the surface as groundwater. Some of the rain and snow that falls on the land runs off into streams (runoff), some evaporates into air, and some is absorbed by plants. The rest of it sinks into the ground through infiltration (a process by which water enters rock or soil through cracks or small pores between particles), and is called groundwater. Groundwater is a vital resource that must be carefully managed. In this lab, we will look at some of the basic principles that govern the flow of groundwater. Objective: First, you will encounter an everyday groundwater flow scenario in which you are tasked with locating the source of groundwater pollution by inferring subsurface water flow. We then dig deeper to understand how water flows through porous media via Darcy s Law, with a hands-on exercise. Finally, the third part of this lab familiarizes you with ice flow in glaciers and the types of landforms that glaciers can create. Answers: All answers should be your own, but we encourage you to discuss and check your answers with 2-3 other students. This lab will be graded out of 100 points. -------------------------------------------------------------------------------------------------------------- Part 1: Groundwater Flow (29 pts) Groundwater pollution is becoming a critical issue as populations increase and the demand for water goes up. Scenario: The Smiths just bought a home in a nice suburban town. A few months ago, they started noticing a strange smell when they took showers, and that the drinking water had a foul taste to it. A week before, the local TV station ran a report on leakage from storage tanks at gas stations, and the Smiths suspected that this might be the cause of their problem. They hired a local environmental consulting firm, which has put you, as an all-star EPS 50 student, in charge. The following figure is a map of the Smith s neighborhood, showing the location of their home and two local gas stations the Smiths suspect to be the cause of their problem. You have surveyed the p. 1
neighborhood, and measured the amount of semi-volatile compounds in the soil around the Smith s home (marked by the dots on the map). These chemicals are released into the ground when corroded gas tanks leak and are indicators of soil and groundwater contamination. Concentrations greater than 50 parts per million (ppm) are considered dangerous. Useful information: 1 ml = 1 cm 3 nd = no detection Figure 1. 1.) Make a contour map of the soil contamination using 20 ppm intervals in Figure 1. Use red for values above the danger threshold, a second color for probable future threat (between 30-50 ppm), and a third color for possible future threat (10-30 ppm). (Optional: use the semi-transparent version of this figure on the last page of the lab, if you think it will improve readability.) (14 pts) p. 2
2.) Does either gas station have a leakage problem? Explain. (5 pts) 3.) In which direction does the local groundwater flow? How do you know? (5 pts) 4.) Which homes will be the next to feel the effects of the gasoline leakage? (color in those areas on the map and be sure to add a key to the map)(5 pts) Part 2: Darcy s Law (37 pts) Darcy s law is an empirical equation that describes the flow of a fluid through a porous medium. It was formulated by Henry Darcy in the 19 th century based on observations of the flow of water through sand beds. Darcy s law is widely used in the earth sciences, especially by hydrologists, who study the movement, distribution, and quality of water on Earth and other planets. In this section, we are going to conduct a simple experiment to verify Darcy s law, and to estimate the permeability of a geological material. Darcy s law can be written as: p. 3
Where Q is the total discharge (units in m 3 /s); A is the cross-sectional area of flow (m 2 ); µ is the viscosity of the fluid (Pa*s); Pa-Pb is the fluid pressure change from a to b (Pa); L is the distance the fluid travels (m)., Figure 2. 6.) Solve for the units of permeability, k, which is not described above. Show your work. (Hint: compare the units on the left and right hand sides of Darcy s law) (4 pts) Next, we are going to test Darcy s law and use it to measure the permeability of different materials. The device we are going to use is similar to Figure 2, but we are only going to test fine and coarse grain sand sizes. You are going to measure the discharge(q) and the pressure change (Pb-Pa) from one end to the other. The pressure can be converted from the height difference using ΔP = ρ g (h2 h1) Again, you need to be careful to keep all of the units in MKS (meters, kilograms, seconds). ρ= density; g=acceleration due to gravity. 7.) There are four materials in Figure 3. The grain size decreases from left to right (labeled a-d in the figure). Which materials do you think will transmit water best? Rank the four p. 4
materials in decreasing order of permeability and explain your prediction. (4 pts) (a) (b) (c) (d) Figure 3. 8.) Record your measurements below: (13 pts) Observation Container A (Coarse) Container B (Fine) Grain size (m) A (m 2 ) ΔH (m) ΔP (Pa) p. 5
Volume (m 3 ) of Water (20 s) Volume (m 3 ) of Water (40 s) Volume (m 3 ) of Water (60 s) Volume (m 3 ) of Water (80 s) Q1 (m 3 /s) Q2 (m 3 /s) Q3 (m 3 /s) Q4 (m 3 /s) Qavg 9.) In this experiment we try to keep the water level at the same height, so ΔH is a constant. What will happen if we don t keep the water level at the same height? Explain what quantities will change and what will not. Can you still obtain a reasonable permeability with this new condition? (6 pts) 10.) The viscosity of water at room temperature (~20 C) is 8.9*10-4 Pa*s. Use this number to estimate the permeability of the two materials (show work). (6 pts) Coarse Sand p. 6
Fine Sand 11.) Below is a table for the permeability of unconsolidated gravel, sand, and clay. Do your measured values fall within the range of the expected values? Why or why not? (4 pts) Permeability Pervious Semi-Pervious Impervious Unconsolidated sand & gravel Well Sorted Gravel Well Sorted Sand or Sand & Gravel Very Fine Sand, Silt, Loess, Loam k (m 2 ) 10-7 10-8 10-9 10-10 10-11 10-12 10-13 10-14 10-15 10-16 10-17 10-18 10-19 Part 3: Glacial Deposits and Glacial Flow (34 pts) The last major glaciation occurred during the end of the Pleistocene epoch, and in North America this glacial advance is called the Wisconsin Glaciation. The Wisconsin Glaciation reached its maximum between 21,000 and 18,000 years ago. Since then, the massive ice sheets that covered all of Canada and much of the northeastern United States in over 2 km of ice have receded and disappeared. During this period, glaciation was not just limited to North America. In fact, geologists have found evidence of extensive continental ice sheets covering Northern Europe and Asia, and the p. 7
Antarctic ice sheet expanded to the southern tips of South America and Africa. Glaciers have the power to dramatically alter the land, by leveling peaks, carving out valleys, and transporting materials hundreds of miles. These features are still evident today and allow the astute observer to reconstruct where these massive ice sheets existed. The following exercises will investigate a few prominent glacial features associated with the erosion, transportation, and deposition of material. 12.) Figure 4 below (page 9) is a topographic map of a glaciated section of New York. The scale bar indicates 1 mile. 10 foot contours, heavy lines every 50 feet. Use the map to produce three topographic profiles along the long axes of the drumlins. Label your three profiles with the notation A-A, B-B, and C-C respectively. Illustrate your selected profile traces on the topographic map. Be sure to identify the Scale you are using and what units it is in. (15 pts) p. 8
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Figure 4. 13.) Given your understanding of how drumlins form, what direction was the ice sheet flowing when these were formed? Explain your logic. Be sure to answer with compass coordinates (Azimuthal or Quadrant), left/right up/down is not a sufficient answer. (3 pts) *hint-pages 598-606 of your textbook discuss glacial landforms. 14.) How does the formative process and morphology of drumlins differ from the formative process and morphology of roches moutonnées? To answer this question, either describe in words or sketch how these two glacial features are similar and how they differ. If the profiles you constructed for the drumlins in this exercise were roches moutonnées, what direction would ice flow have been? (8 pts) p. 10
15.) The image below (Figure 5) has a prominent feature associated with glaciation. What is this feature? (2 pts) Figure 5. 16.) Explain how this feature is formed, and what materials it is typically composed of. Are these materials most likely sorted or unsorted? Provide your reasoning. (6 pts) p. 11
Optional semi-transparent version for making color contour map for Question 1: Figure 6. p. 12