Lab Groundwater
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School
Bowling Green State University *
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Course
1200
Subject
Geography
Date
Dec 6, 2023
Type
Pages
9
Uploaded by ConstableCrownGrouse11
Spring 2023
Groundwater
Purpose
The purpose of this lab is to 1) measure the properties that determine the quantity of groundwater
that can be stored in various sediments, 2) the rate at which groundwater can be transmitted
through these various sediments, and 3) to analyze the flow of groundwater using water well
data.
Introduction
Groundwater
is water stored below Earth’s surface in porous, permeable rock units and
sediments also known as
aquifers
. Understanding how the porosity and permeability of different
aquifers influence the flow of groundwater is key in developing groundwater as a resource and
protecting it from pollution. Groundwater comprises the largest portion of freshwater on land. It
provides drinking water to a significant percent of the public as well as water for irrigation and
industrial purposes.
Porosity
In sedimentary materials, water occupies small open spaces between the mineral grains, called
voids or
pore spaces
, as shown below. Petroleum and natural gas can also occupy pore spaces in
sedimentary rocks at greater depths. In crystalline rock (igneous and metamorphic), almost all
the pores consist of fractures.
The percentage of the bulk volume of rock or sediment that consists of open pore spaces is called
its
porosity
. The higher the porosity of the material, the greater is the amount of ground water,
oil, or gas that can accumulate in it.
= Pore space
= Sediment
Spring 2023
Lab Activity One
To illustrate the potential amount of storage of groundwater, you will determine the porosity of
three types of sediment: medium gravel, coarse sand, and a mix of fine gravel and coarse sand.
First you will make some predictions about the porosity of the different types of sediment by
answering the following questions:
Question #1: Think about the properties of sediment (size, sorting, and shape) and what influence
these properties might have in determining the porosity of the sediment. From the
properties listed in the table below, which properties do you think will have the
greatest
porosity? [1 point per column]
Size
Sorting
Shape
Coarse/large
Poorly-sorted
Angular
Mixed (coarse and
fine)
Moderately- sorted
Angular with some rounded
edges
Fine/small
Well-sorted
Rounded
Why? [2 points]
Question #2: Which properties do you think will have the lowest porosity? [1 point per column]
Size
Sorting
Shape
Coarse
Poorly-sorted
Angular
Mixed (coarse and
fine)
Moderately- sorted
Angular with some rounded
edges
Fine
Well-sorted
Rounded
Why? [2 points]
Now you will actually calculate porosity to test your predictions by following the procedure
below:
1.
Fill a large beaker with 200 mL of dry sediment.
2.
Fill a graduated cylinder with water.
3.
Slowly add water from the small beaker to the large beaker of sediment until the all of the
pore space in the sediment is filled (i.e., when there is a shallow film of water above the
sediment).
Spring 2023
4.
Determine the amount of water removed from the graduated cylinder, which now fills the
pore spaces. Record this value in the table below as the volume of pore space (V
p
).
5.
Calculate the porosity with the following equation and record your results in the table
below[1 point per column]:
N
V
V
p
t
=
100%
where N = porosity, V
p
= volume of pore space, V
t
= volume of sediment
Porosity Experiment Data
V
p
(mL)
V
t
(mL)
N(%)
Medium Gravel
200
Coarse Sand
200
Mixed Sediment
200
Question #3: a. Did the porosities you calculated confirm or contradict your predictions? [1
point]
b. If the porosities you calculated contradict your predictions, in what way were
your results different from what you predicted? [2 points]
Question #4: How would you explain your results? Explain the cause of differences in porosity
in the three different types of sediments. [3 points]
Permeability
The
permeability
of sedimentary material refers to its ability to transmit water or other fluids.
The higher the permeability, the more easily water is transmitted through the material.
Unfortunately, materials with high permeability more easily transmit pollutants into the
groundwater as well as freshwater. Permeability depends on two properties: 1) the size of the
pore spaces, and 2) how they are interconnected.
Permeability is one of the factors that control the velocity at which water can pass through
sediment and thus the quantity of water which can be transmitted in a given unit of time, or
discharge
. The relationship of these factors to the flow of unconfined groundwater through
sediment is known as
Darcy's Law:
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Spring 2023
K = hydraulic conductivity (a measure of permeability, or the ease with
which water is transmitted)
Q = discharge (or volume/time)
A = cross-sectional area of the material
Δ
h/l = hydraulic gradient
Lab Activity Two
To illustrate the ease with which water flows through different types of sediment, you will
calculate the permeability of three types of sediment: medium gravel, coarse sand, and a mix of
fine gravel and coarse sand.
Again, first you will make some predictions about the permeability of the different types of
sediment by answering the following questions:
Question #1: Think about the porosity of these sediments as well as how the properties of
sediment (size, sorting, and shape) may influence the connectivity of the pore spaces.
Which properties do you think will have the highest permeability? [1 point per
column]
Size
Sorting
Shape
Coarse
Poorly-sorted
Angular
Mixed (coarse and
fine)
Moderately- sorted
Angular with some rounded
edges
Fine
Well-sorted
Rounded
Why? [2 points]
Question #2: Which type of sediment(s) do you think will have the lowest permeability? [1 point
per column]
Size
Sorting
Shape
Coarse
Poorly-sorted
Angular
Mixed (coarse and
fine)
Moderately- sorted
Angular with some rounded
edges
Fine
Well-sorted
Rounded
Why? [2 points]
Spring 2023
Next you will actually calculate permeability to test your predictions by following the procedure
below:
1.
Each permeability apparatus has been filled with 15 cm of sediment.
2.
Slowly
add enough water to the tube to saturate the sediment. Once the sediment it
saturated continue to add enough water until you reach the 15 cm mark above the
sediment.
3.
Release the clamp at the bottom of the apparatus and use a stopwatch to measure the time
it takes, in seconds, for the water surface to drop 15 cm. (i.e., stop the stopwatch when
the water level reaches the top of the sediment). Record the time in the table on the
following page.
4.
Repeat the experiment three times and then average the times together. Record your
results in the table.
5.
Darcy
’s Law can be simplified to the following equation since discharge = area x time
and hydraulic gradient = 1 (for a vertical tube):
K = hydraulic conductivity, or permeability
V = volume
A = cross-sectional area
T = time it takes for the water to pass through the sediment
Note: The diameter of the tube is 3.4 cm (radius = 1.7 cm), thus the cross sectional
area (A =
π
r
2
) is 9 cm
2
. The volume is equivalent to the height of the water multiplied by the
area (15 cm x 9 cm), or 135 cm
3
.
Calculate the average time (sec) for each sediment type and record your answers in the table
below. [1 point per box]
Permeability Experiment Data
Trial 1 Time
(sec)
Trial 2 Time
(sec)
Trial 3 Time
(sec)
Average
Time (sec)
Medium Gravel
Coarse Sand
Mixed
Sediment
Spring 2023
Calculate the permeability (K) for each sediment type using the equation above and
record your answers in the table below. [1 point per box]
Permeability Calculation Data
Volume (cm
3
)
Area (cm
2
)
Average Time (s)
Permeability (K)
(cm/s)
Medium
Gravel
135
9
Coarse Sand
135
9
Mixed
Sediment
135
9
Question #3: a. Did the permeabilities you calculated confirm or contradict your predictions? [1
point]
b. If the permeabilities you calculated contradict your predictions, in what way
were your results different from what you predicted? [2 points]
Question #4: How would you explain your results? Explain the cause of differences in
permeability in the three different types of sediments. [3 points]
Lab Activity Three
In this activity you will analyze the flow of groundwater from well data. Below is a contour map
of Gillette, Wyoming. Note, these contours show the groundwater table elevation relative to sea
level, not land elevation as in the earlier topographic maps Lab 6 activity.
This map of groundwater elevations can be used to determine the direction of ground water flow.
The orientation and relative spacing between contour lines gives some idea as to the shape of the
water table using the same principles we established for topographic maps.
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Spring 2023
Instructions on how to proceed with this act
ivity can be found in the video titled “Groundwater
lab Gillette, WY Map Instructions Video” found in the Lab 11 (Groundwater) Additional
Resources/Materials Canvas shell.
Using the map below or the separate .jpg version found in the found in the Lab 11 (Groundwater)
Additional Resources/Materials Canvas shell, & following the instructions outlined, indicate the
groundwater flow directions and answer the following questions.
Question #1: At the points marked (X), draw arrows approximately one cm in length to show the
direction of groundwater flow. [0.5 point each]
Note: Flow lines are always perpendicular (at 90°) to equipotential (contour) lines
of the groundwater, and point in the direction from higher to lower values.
Question #2: Draw a dashed line along the groundwater divide. [1 point]
Note: Groundwater divides typically occur where water levels are highest and
groundwater flows in opposite directions on either side of the divide.
Question #3: a. What is the general direction of ground water flow north of the city of Gillette?
[1 point]
b. What is the general direction of groundwater flow 2 miles SW of the city of Gillette?
[1 point]
Question #4: A water well is to be located at point W, south of the city of Gillette. The elevation
of the ground surface is 6500 feet.
How deep must you drill to hit water? [1 point]
Question #5: A landfill is to be located within a 5-mile radius of the city of Gillette. Locate a site
so that any possible leakage will flow away from the city of Gillette and the water well W.
Label
your site with “L”.
[1 point]
Question #6: a. If a waste-water injection well were planned at point A, would the waste-water
flow toward the water well W? [1 point]
Spring 2023
b. Would the waste water flow toward the city of Gillette? [1 point]
Question #7: City Council decides to put in a new waste-water injection well one mile outside the
city limits. You are asked to locate the injection well. Where would you put it and why? Label the
location of your well on the map with “WI”.
[2 points]
Question #8: A coal mine is to be located at M. The elevation of the ground surface is 5000 feet and
the mine will be 200 feet deep. Will pumping be needed to keep the mine dry? Why or why not? [2
points]
Checklist Before Leaving
Answered questions and completed all activities on pages 2-7.
Completed porosity and permeability tables.
Gillette groundwater map with flow lines, groundwater divide, and landfill and waste water
injection well labels.
Staple the entire lab together and turn it in with your name on the front page.
Spring 2023
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
N
4600
Groundwater elevation contour in feet above sea level
Water well
M
W
A
4350
4400
4450
4400
4350
4300
4400
4450
4500
4600
4600
4550
4550
4650
4650
4700
4650
4600
4500
0
0
1
2
3
4
5
1
2
3
4
5
kilometers
miles
4550
4550
Gillette
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