1122 Lab 4 - (Questions)

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Name: Simone A. Lattimore TA: Morgan Kerpics Lab 4 - Groundwater GEOL 1122 Before answering the questions for each section, make sure you have watched the video(s). After you have completed this worksheet, save it and upload it to the assignment folder for Lab 4 in iCollege. Please use your own words to answer the questions, and include as much detail as possible . Lab Objectives At the end of this lab, students should be able to:  Explain what groundwater is (and isn’t)  Understand the magnitude/scale of groundwater as a global hydrologic reservoir  Explain the basics of aquifers and name associated terminology  Explain the difference between porosity and permeability  Explain and name basic relationships between groundwater and surface water (i.e., gaining versus losing stream)  Understand land subsidence and its causes (recharge versus withdrawal)  Explain how to determine direction of groundwater flow and what controls flow velocity Part 1: Introduction To answer these questions, first watch the “Lab 4, Part 1: Introduction” video on iCollege. Please answer the questions in your own words. 1) H ypothesize a factor that you think will affect the rate (i.e., speed) by which precipitation infiltrates to recharge groundwater and explain how this factor will affect it (e.g. will it make recharge faster or slower) ( 4 pts) The rate at which precipitation infiltrates to recharge groundwater depends on soil type. Sandy soils with high porosity allow rapid infiltration, while clayey soils with low porosity slow it down. 2) Explain whether or not you would expect an aquifer to be composed of clay. (4 pts) An aquifer is unlikely to be composed primarily of clay. Clay has low permeability due to its fine particle size and tendency to retain water. Aquifers require higher permeability materials like sand or gravel to allow efficient groundwater flow. 3) Please use the internet to research whether or not karst terrain is found in the Atlanta area. Also include an explanation as to why or why not this terrain is present. ( Important : please include links to all websites used for this question) (4 pts) Research Result: Karst terrain is indeed found in the Atlanta area. Explanation: The region’s geology includes limestone and other soluble rocks, which are susceptible to dissolution by groundwater. This process creates features like sinkholes, caves, and underground rivers. The Piedmont region around Atlanta contains karst features Link to website:  https://www.usgs.gov/media/images/karst-map-conterminous-united-states-2020

 https://link.springer.com/article/10.1007/s13146-019-00525-z 4) You are a geoscientist measuring discharge at different points along a stream. You measure discharge as 3 m/s at one point in a stream, and then measure discharge as 4 m/s at a point 10 meters downstream with no tributaries between these points. Explain your reasoning as to whether this is evidence of a gaining stream or losing stream. (2 pts) Since the discharge increases downstream, this sort of demonstrates a gaining stream. A gaining stream receives water from groundwater through the streambed. Because of that, the increased discharge indicates groundwater contribution as the stream flows downstream Part 2: Porosity and Permeability Watch the linked YouTube video “Porosity and Permeability” in its entirety to answer these questions in your own words . 5) According to the video, what percentage of total US freshwater is supplied by groundwater, and what are the two main uses given for this water? (4 pts) 25% 6) Define the term “infiltration,” and explain its role in the context of the hydrologic cycle. Is infiltration considered a reservoir or a flux? (Hint: review the PowerPoint from the surface water lab) (4 pts) Definition: Infiltration refers to the process by which water from precipitation or surface runoff enters the soil and moves downward into the subsurface. Role in Hydrologic Cycle: Infiltration is a crucial part of the hydrologic cycle. It replenishes groundwater, contributes to streamflow, and helps maintain soil moisture. It is a flux that transfers water from the surface to the subsurface 7) As explained in the video, a common misconception is that groundwater is water found in underground rivers or lakes (this is in fact relatively uncommon). Explain where groundwater is actually commonly found. (4 pts) Groundwater is commonly found within rocks and sediments. It saturates pores or cracks in soils and rocks rather than forming underground rivers or lakes. Springs, seeps, swamps, and lakes also indicate groundwater presence. 8) Define porosity in your own words. (2 pts) Definition: Porosity refers to the volume of void spaces within a material, such as soil or rock, relative to its total volume. It displays the capacity of the material to hold water 9) If gravel is placed in a 400 ml (milliliter) container, filling it to the top, and 160 ml of water is added to completely fill the container, what is the porosity of the material? Give your answer in both decimal and percent forms and show/explain your work. (4 pts) Given: Container volume = 400 ml, Water added = 160 ml Porosity = (Volume of void spaces / Total volume) = (160 ml / 400 ml) = 0.4 or 40% 10) What is the common range in porosity for unconsolidated (i.e., not lithified) gravels and sands near earth’s surface? What is the percentage of shallow groundwater systems in the US that contain sand and gravel deposits? (2 pts)

Common range: 15-40% The percentage of shallow groundwater systems: 80% 11) Define permeability in your own words. Then, explain how permeability is different from porosity as precisely as possible. What example did the video give of a material with high porosity but low permeability? (4 pts) Definition: Permeability is the property of a porous material that determines its ability to allow fluids to flow through it. Difference from Porosity: While porosity relates to void spaces within a material, permeability specifically refers to how easily fluids can flow through that material. A material can have high porosity but low permeability if the pores are not well connected. The video example of high porosity but low permeability was clay Part 3: What is an Aquifer? Watch the linked YouTube video “What is an Aquifer?” in its entirety to answer these questions in your own words. 12) Please define the terms “aquifer” and “confining unit” in your own words, using as much detail as possible. (4 pts) Definition: An aquifer is a geologic formation that can store and transmit water. It contains interconnected pores or fractures that allow water to flow through it. Aquifers serve as natural reservoirs for groundwater. Definition: A confining unit is a geologic layer that restricts the flow of water. It has low permeability, preventing significant water movement. Confining units separate aquifers and limit vertical water flow 13) How does water from precipitation enter into a confined aquifer? How is this different from the recharge process in an unconfined aquifer? Additionally, list and explain all the processes given in the video by which groundwater levels in an aquifer can be increased or decreased. (4 pts) In a confined aquifer, water enters primarily through recharge from distant areas. Precipitation infiltrates the ground, travels through permeable layers, and eventually reaches the confined aquifer. This process differs from an unconfined aquifer, where water directly infiltrates from local precipitation. Groundwater levels in an aquifer can change due to processes like pumping, recharge, discharge, and seasonal variations. 14) Name and briefly discuss all of the different types of typical US aquifer geologies discussed in the video (e.g., sand & gravel, etc.). In doing so, compare and contrast their characteristics in terms of relative porosity and permeability, as well as where in the US these are generally found. (4 pts)  Sand & Gravel. Most common unconfined aquifer and provide about 80% of US groundwater. Is open to precipitation  Sandstone: These are highly porous and permeable, found in regions like the Midwest and coastal areas.  Limestone Aquifers: Formed from limestone rock, they occur in states like Florida, Missouri, Ohio. They have high porosity due to dissolution of the rock by water. They can be confined or unconfined.

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 Igneous & Metamorphic: no natural porosity or permeability, fractured, found in the US North West like Oregon, Washington, and other nearby states. They are not good aquifers. Part 4: Where is the Water Table? Watch the “Where is the Water Table?” video in its entirety to answer these questions in your own words . 15) What type of rocks contain the groundwater measured in this video? Why is this not typical, and what is the reason these rocks are able contain groundwater? (Hint: review the previous video to recall why these types of rocks are not commonly associated with groundwater) (4 pts) The groundwater measured in the video is contained within igneous and metamorphic rocks, which is atypical. These rocks are usually not associated with groundwater because they are less porous and have low permeability. However, fractures and faults within these rocks allow water to accumulate. 16) Name the instrument used to measure the monitoring wells in this video, and give a brief description of how it works. (2 pts) Piezometer. It consists of a pipe inserted into the ground, allowing direct measurement of water levels. When water rises in the piezometer, it reflects the water table elevation. 17) Two monitoring wells are located close together. You record the elevation (in meters above sea level) of the top of the PVC pipe for each well. Then, you measure the distance from the top of the PVC pipe to the water level surface at each well in meters. Results are recorded below: Well Name Elevation of top of PVC (m) Distance to Water Level Surface (m) Well A 150 2.1 Well B 152 3.5 Use these results to calculate the elevation of groundwater above sea level for both wells in meters (with work and units shown). Then, state whether groundwater is moving from Well A to Well B or from Well B to Well A. Please fully explain your work and reasoning. (4 pts) For Well A: Elevation = 150 m (top of PVC) - 2.1 m (distance to water level) = 147.9 m For Well B: Elevation = 152 m (top of PVC) - 3.5 m (distance to water level) = 148.5 m Groundwater is moving from Well A to Well B because Well B has a higher elevation.

1122 Lab 4 - (Questions)

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