GEO Lab4
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Apr 3, 2024
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Name: Ali Butt
TA: Carley Wilshire
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)
Soil texture is one element that could have an impact on how quickly precipitation seeps in to replenish groundwater. Coarse-textured soils, because of their bigger pore spaces, like sandy soils, permit water to permeate more quickly, causing groundwater recharge to occur more quickly. Fine-textured soils, such as clay soils, on the other hand, have smaller pore spaces, which make water enter more slowly and consequently slow down groundwater recharging.
2)
Explain whether or not you would expect an aquifer to be composed of clay.
(4 pts)
Because clay has a poor permeability and a restricted capacity to store and convey groundwater, clay aquifers are less common. Although clay can be an aquitard, confining layer, or component of the aquifer, aquifers are usually composed of materials with higher permeability, including sand, gravel, or fractured rock. Because of its compact form and
tiny pore spaces, clay is less suited to serve as the main material in an aquifer. As a result, although clay could exist in an aquifer, it usually does not dominate.
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)
In general, the Atlanta region is not home to any karst terrain. The majority of the crystalline rocks that make up Atlanta's geology are gneiss, schist, and granite. These materials do not allow for the development of karst features like sinkholes, caverns, or subterranean drainage systems. Although karst features are not common in the near region of Atlanta, they can be found in various portions of northern Georgia, especially in places containing limestone and dolomite formations. Thus, karst terrain is not commonly linked with the Atlanta area.
https://education.nationalgeographic.org/resource/karst/
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)
The stream appears to be acquiring water, based on the rise in discharge downstream, which occurs over a span of 10 meters without any tributaries in between 3 m/s to 4 m/s. A gaining stream experiences an increase in discharge downstream as water from groundwater sources is fed to the stream channel. Given the rise in discharge, the groundwater is entering the stream channel and influencing the total flow. As a result, the stream reported rise in discharge points to the possibility that it is gaining water from groundwater sources.
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)
80 % of total US freshwater is supplied by groundwater. The two main uses for ground water are:
Drinking water: (Potable Water)
Groundwater is an essential source of drinking water. It is frequently drawn from wells and aquifers and treated to fulfil drinking water regulations.
Irrigation & Agriculture:
Water for crops and cattle is obtained through the widespread irrigation of agricultural land using groundwater, especially in areas where surface water supplies are scarce.
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)
Infiltration: The process through which water from the ground surface seeps into the soil or
rock layers is called infiltration.
Within hydrologic cycle, it is essential for recharging aquifers by allowing infiltrated water to flow downward. Since infiltration involves the transfer of water from one component surface water to another groundwater without being held as a reservoir, it is referred to as a flux in the hydrologic cycle.
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)
Aquifers are the porous permeable rocks that contain groundwater. These aquifers are made
of materials that have the ability to store and transfer water, including sand, gravel, or broken rock. Although rivers and lakes can be found in some geological settings, their prevalence is far lower than that of groundwater. Because of this, the majority of the freshwater resources on Earth are found in aquifers, where groundwater is found.
8)
Define porosity in your own words. (2 pts)
Porosity is the measure of the pores or void spaces found in a materials, such as rock, silt, or soil. It is given as a percentage and shows the amount of empty space relative to the material's overall volume.
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)
Porosity = 160/400 = 0.4 * 100 = 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)
For unconsolidated gravels and sands close to the surface of the Earth, porosity usually ranges from 20% to 40%. It is estimated that between 60% and 70% of US shallow groundwater systems have sand and gravel deposits. Because of their high porosity and permeability, sand and gravel deposits are frequently linked to shallow aquifers in many
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parts of the US, making them significant sources of groundwater for a variety of uses, including agricultural, and drinking water supply.
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)
The ability of a substance, like soil, sediment, or rock, to allow the passage of liquids, such gas, oil, or water, via its pore spaces is referred to as permeability.
Fluid flow is quantified by permeability, which is the capacity of a substance to transfer fluids through its pore spaces. On the other hand, porosity quantifies the amount of space in
a substance, its ability to hold liquids. Permeability is the degree to which fluids can pass through the vacant spaces that porosity shows are available for storing fluids.
Clay, Shell and Granite have high porosity and low permeability.
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)
Aquifer: A naturally occurring reservoir for the storage and distribution of water. It is a geological feature or rock layer that transfers and holds groundwater.
Confining Unit: A confining unit, sometimes referred to as an aquitard or an aquiclude, is a
low permeability feature that is usually positioned between aquifers to prevent water flow between them.
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)
Rainfall water infiltrates a confined aquifer directly by way of recharge zones when the confining layer is either nonexistent or ineffective. In contrast, recharge in an unconfined aquifer happens when precipitation refills groundwater levels by penetrating the aquifer straight from the surface without being hindered by confining layers.
Ground water in an aquifer can increased or decreased by Seasonal precipitation, changes in groundwater consumption
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)
Sands and gravel: Common geologies found in aquifers that have high porosity and permeability, which allow for extensive groundwater circulation and storage. Ohio and North Dakota.
Sandstones: Because of their well-connected, porous pore spaces that allow groundwater to
flow through them, sandstones are significant aquifers. western states and the Appalachian region of the Midwest.
Carbonates: (Limestone) Carbonate aquifer geologies in the United States that allow for substantial groundwater storage and conveyance because of their high porosity and permeability as a result of dissolution processes. Missouri, Ohio and Florida.
Fractured igneous and metamorphic rocks: These aquifers, which are less porous and permeable than carbonates, are sporadically found in the United States. They rely on faults and fractures to flow groundwater, which supplies confined groundwater supplies. Areas like in the Appalachians.
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) Metamorphic Rocks. As they are unable to store groundwater due to lower porosity.
16) Name the instrument used to measure the monitoring wells in this video, and give a brief description of how it works. (2 pts)
The device is called water level meter, a measuring tape connected to a probe that, upon contact with water, emits a beeping sound. Using this, we determine the length.
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 of groundwater = 150 m + 2.1 m = 152.1 meters above sea level
For Well B:
Elevation of groundwater = 152 m + 3.5 m = 155.5 meters above sea level
Based on the elevations calculated:
Elevation for Well A is 152.1 meters.
Elevation for Well B is 155.5 meters.
Groundwater is moving from high elevation, Well B to low elevation, Well A.
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