_Lab 6_ Groundwater and Glaciers (Emma Born).docx

100 points total Name: Emma Born Lab Section: EPS 50: Fall 2022 LAB 6: GROUNDWATER AND GLACIERS Due one week from today at the start of your lab section Introduction Saline water in the oceans and seas comprises the great majority of Earth’s water (96%). Freshwater resources, however, provide people with the water they need every day to live. Glaciers and polar ice hold the highest percentage of freshwater on Earth, but these are not easily accessible to most of the population. Water sitting on the surface is easy to visualize, such as rain that falls on the land and runs off into streams and rivers. But there is also plenty of water beneath our feet -- in fact, of the freshwater on Earth, much more is stored in the ground than is available in rivers and lakes (mostly within a half-mile of the surface). This water that infiltrates into the ground is called groundwater . Groundwater is a vital resource, and so it is important for society to both understand and manage.

Part 1: Groundwater Flow Scenario: The Smiths just bought a new house a few months ago. But recently, they started noticing a strange smell when they took showers and that the drinking water had a foul taste to it. The local TV station ran a report yesterday 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, an all-star EPS 50 student, in charge. The figure below is a map of the Smith’s new problem. You have surveyed the neighborhood, and measured the amount (ppm) of semi-volatile compounds in the soil around the Smith’s home (marked with dots). These compounds are released into the ground when corroded gas tanks leak and indicate groundwater contamination. Concentrations of these compounds over 50 parts per million (ppm) are considered dangerous. Figure 1. The distribution and concentration (ppm) of semi-volatile compounds in the ground around the Smiths neighborhood. nd = no detection. 2

1) Make a contour map of groundwater contamination in the area by drawing contour lines for 10 ppm, 30 ppm, and 50 ppm. Use different pencil colors for “above the danger threshold” (>50 ppm), “probable future threat” (30-50 ppm), and “possible future threat” (10-30 ppm). (10 pts) 2) Does either gas station have a leakage problem? Explain your reasoning. (5 pts) I would argue that both gas stations have a leakage problem because they both fall within the ‘above danger threshold’ 3) What additional problem(s) does your contour map reveal? (3 pts) The contour map also reveals a potential other source of leakage southwest of both gas stations 4) In which direction does the local groundwater flow? How do you know? (4 pts) From the Map, it is clear that groundwater flows in the NW direction. This is apparent because of the shape of the contour lines with respect to the gas stations (i.e. the source of contamination). The contour lines point in the NW direction and indicate that as compounds are released into the ground, they flow outward in the NW direction primarily. 3

Part 2: Darcy’s Law Darcy’s law is an empirical equation that describes the flow of a fluid through a porous medium. This law was formulated by Henry Darcy in the 19 th century based on experiments on the flow of water through beds of sand, and is widely used in Earth science (especially hydrology). In this section, we are going to conduct a simple experiment to verify Darcy’s law and estimate permeability (k) , the ability of a porous material to allow fluids to pass through it. Darcy’s law can be described as: where Q is the total discharge (m 3 /s), A is the cross-sectional area of flow (m 2 ), µ is the viscosity of the fluid (Pa ᐧ s), P a -P b (ΔP) is the fluid pressure change from A to B (Pa), and L is the distance the fluid travels (m). Figure 2. Schematic of Darcy’s law. 4

distribution of sediment grain sizes present). Order the samples of poorly-sorted (A), moderately-sorted (B, C), and well-sorted (D) sediments from lower to higher permeability. (4 pts) A B C D lower k higher k _A____ _B____ _C____ __D___ Next, we are going to test Darcy’s law with a device similar to Figure 2 and use it to measure the permeability of fine and coarse sand. You are going to measure the discharge (Q) and the pressure change (ΔP) from one end to the other. The pressure can be calculated from the height of the water column (h) using ΔP = ρgh where ρ is the density of room-temperature water (kg/m 3 ) and g is the gravitational acceleration constant (m/s 2 ). *Make sure to record your measured heights, grain sizes, and cross-sectional areas in terms of meters (m). 8) Record your measurements and calculated quantities from your Darcy’s law experiments in the table below. (26 pts) Observation Container A (coarse sand) Container B (fine sand) Grain size (m) 4*10 -3 m 10 -3 m A (m 2 ) 5.31 * 10 -4 m 2 5.31 * 10 -4 m 2 h (m) h sand = 5.5 cm = 0.055 m h water = 5.45 cm = 0.0545 m h sand = 5.15 cm = 0.0515 m h water = 5.56 cm = 0.0556 m 6

ΔP (Pa) 1000[kg/m 3 ]*9.81[m/s 2 ]*0.0545 [m] = 534.645 [kg/(m*s 2 )] 1000[kg/m 3 ]*9.81[m/s 2 ]*0.0556[ m] = 545.436 [kg/(m*s 2 )] Total volume of water V 1 (after 20 s) (m 3 ) 3.8e-5 m 3 5e-6m 3 V 2 (after 40 s) (m 3 ) 4e-5 m 3 6e-6m 3 V 3 (after 60 s) (m 3 ) 4e-5 m 3 8e-6m 3 V 4 (after 80 s) (m 3 ) 4e-5 m 3 9e-6m 3 Discharge Q 1 (m 3 /s) 1.9e-6 m 3 /s 2.5e-7 Q 2 (m 3 /s) 2e-6 m 3 /s 3e-7 Q 3 (m 3 /s) 2e-6 m 3 /s 4e-7 Q 4 (m 3 /s) 2e-6 m 3 /s 4.5e-7 AVERAGE DISCHARGE Q avg (m 3 /s) 1.975e-6 3.5e-7 9) In this experiment we try to keep the water height (h) roughly constant. What quantities would be affected during the experiment if the water height were allowed to change? Explain. (4 pts) Height must be kept constant throughout the experiment (for both coarse and fine sand) to ensure a consistent measurement for change in pressure in both the variables. If there is variability in the height, the pressure goes from being a constant value to a variable value. If the derivation for change in pressure is constant (meaning the height is constant for each experiment), then we will receive an accurate measurement for discharge. In sum, if water height were to change, the change in pressure would vary 7

Permeability Pervious Semi-Pervious Impervious 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 Well sorted gravel Well sorted sand or sand & gravel Very fine sand & silt 11) Above is a table for the permeability of various unconsolidated sediment sizes. Indicate whether your coarse and fine sands are pervious, semi-pervious, or impervious. Describe two sources of experimental error that could affect your estimations of permeability. (6 pts) Coarse sand: ______Pervious_____________________ Fine sand: __________Semi-Pervious_________________ Sources of error: the height of the porous medium (i.e. the grain level) wasn’t constant for both coarse sand and fine sand. Similarly, the height of the initial water level above the sand, h, was not constant (though close enough) for both the coarse sand and the fine sand. Both of these inconsistencies have an effect on the permeability constant k. The height, h, being variable makes the change in pressure variable while the length of the porous medium L similarly affects the permeability constant. Part 3: Glacial Deposits and Glacial Flow Earth’s last major glaciation (growing ice sheets) occurred during the end of the Pleistocene epoch, and in North America this period of glacial advance is called the Wisconsin 9

Glaciation. The Wisconsin Glaciation reached its peak between 21,000 and 18,000 years ago. But since then, the massive ice sheets that once covered all of Canada and much of the northeastern United States have dramatically retreated (when glacial ice melts faster than it can accumulate). During this period, glaciation was not limited to North America. In fact, geologists have found evidence of extensive continental ice sheets covering Northern Europe and Asia, and the Antarctic ice sheet once reached the southern tips of South America and Africa. Glaciers , huge masses of ice that move slowly over land, have the power to dramatically alter the land surface by leveling peaks, carving out valleys, and transporting rocks and sediments over hundreds of miles. These landscape features are still evident today and allow us to reconstruct where these massive ice sheets existed and how they traveled. The following exercises will investigate a few prominent glacial features associated with the erosion, transportation, and deposition of material. 10

12) Figure 4 is a topographic map of a glaciated section of New York. Use this map to produce three topographic profiles along the long axes of the drumlins. For each profile, make sure to label each end (e.g. A-A’) as well as your horizontal (mi) and vertical (ft) axes. (12 pts) A to A’ _______________ B to B’ ______________________________ C to C’ ________________ 13) Given your understanding of how drumlins form and their characteristic morphology, which compass direction was the ice sheet flowing when these were formed? Explain your reasoning. (4 pts) Given the shape of the drumlins, it is clear that the glacier was flowing from North/Northwest to South/Southeast, 160 degrees. We know this because of the shape of the drumlins: as a glacier hits a hill or a mass it overcomes the mass and deposits sediment periodically as it flows over the mass. This leaves a drumlin that has a steeper slope on the side that the glacier came from (in this case North) and a shallower slope on the side of the drumlin that the glacier flowed (in this case South) 12

*BONUS* This map shows a prominent landscape feature associated with deglaciation. What is the name of this feature and how does it form? (+3 pts) This looks like it would be an end moraine that formed at a glacier margin. This landscape feature indicates the margin of the glacier (i.e. where the glacier stopped moving before it recesses, meaning that it melted) 14