Chapter 12: Groundwater and Wetlands
1.
Meet Your Drinking Water
2.
Holes in Earth Materials
3.
Groundwater Systems
4.
A Case Study: The High Plains
Aquifer
5.
Groundwater Quality
6.
Introduction to Wetlands
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Meet Your Drinking Water Self Reflection
Survey
Answer the following questions as a means
of uncovering what you already know about
groundwater and wetlands:
1. Which of the following have you experienced or
observed?
a. An underground cave
b. A spring
c. A wetland (or marsh or swamp)
The Good Earth/Chapter 12: Groundwater and Wetlands
Meet Your Drinking Water Self Reflection
Survey
Answer the following questions as a means
of uncovering what you already know about
groundwater and wetlands:
2. How often do you drink bottled water?
When at home, are you more likely to drink
bottled water or water from the tap? Why
do you make that choice?
The Good Earth/Chapter 12: Groundwater and Wetlands
Meet Your Drinking Water Self Reflection
Survey
Answer the following questions as a means
of uncovering what you already know about
groundwater and wetlands:
3. List all the things you use water for in and
around your home. In addition, what other
ways is water used in your community?
The Good Earth/Chapter 12: Groundwater and Wetlands
Meet Your Drinking Water
Which is
better to
drink?
Whether it is
from a bottle
or the tap,
our drinking
water
comes from
the same
place and
undergoes
similar
processing
and
monitoring
to make it
safe.
The Good Earth/Chapter 12: Groundwater and Wetlands
Meet Your Drinking Water
• The consumption of bottled water in the U.S. is
growing fast, faster than any other beverage.
• Tap water is just as good, and costs 1,000 times less
than bottled water.
• About ¼ of all bottled water is simply bottled tap water.
• Purified water = tap water that has undergone
additional treatment prior to bottling
Where does our drinking water come from?
Streams and lakes (on the Earth’s surface)
Groundwater (water in rocks or unconsolidated materials
below the Earth’s surface)
The Good Earth/Chapter 12: Groundwater and Wetlands
Meet Your Drinking Water
• Water supplies are most likely to be contaminated by human actions
• e.g. chemical leaks from storage tanks
• 53,000 community water systems in the U.S.
• Few become polluted, but this pollution can cause health risks
• Cleanups can be tricky, especially for underground sources
The Good Earth/Chapter 12: Groundwater and Wetlands
Meet Your Drinking Water
dry
cleaning
trucking
• Woburn, Mass – a
chemicals
case of groundwater
pollution with extreme
consequences
plastics
tannery
− Several potential
sources of pollution
− Children diagnosed with
leukemia after their
mothers drank water
from two polluted wells
while they were
pregnant
The Good Earth/Chapter 12: Groundwater and Wetlands
Meet Your Drinking Water
The families accused companies of illegally dumping chemicals
Geologists studied the interactions between the local rock and water
system in Woburn to try to determine how these factors influenced the
flow of chemicals to the wells:
• distance of each company from the wells
• properties of the chemicals themselves and how they influenced flow
• influence of local geology on flow
Jury found that chemicals from W.R. Grace could have contaminated
the wells. They settled for $8 million dollars
Surrounding landowners coughed up ~$70 million for clean up
National Priorities List – over 1500 sites in the U.S. where contamination
is likely by companies that are out of business or unknown
About ¼ of the U.S. population lives within 4 miles of an NPL site
The Good Earth/Chapter 12: Groundwater and Wetlands
Go back to the Table of Contents
Go to the next section: Holes in Earth
Materials
The Good Earth/Chapter 12: Groundwater and Wetlands
Holes in Earth Materials
There’s more water underground than in lakes and streams on
Earth’s surface (about 70% more!)
Most groundwater is in billions of tiny spaces between mineral
grains or in narrow cracks.
The amount of groundwater at any location depends on the
porosity and permeability of materials beneath the surface.
Porosity = the proportion
of a material that is made
up of spaces.
(e.g. if ½ the total volume
of a rock is pore space,
the porosity is 50%)
Depends on size and
arrangement of the grains
(better sorted – higher
porosity).
The Good Earth/Chapter 12: Groundwater and Wetlands
Holes in Earth Materials
As material grains compacted or cemented, porosity decreases.
The Good Earth/Chapter 12: Groundwater and Wetlands
Holes in Earth Materials
Do you think porosity is higher in unconsolidated material or in its
rock equivalent?
Porosity is greater in unconsolidated materials:
-Sand, gravel are more porous than sandstone, conglomerate
-Specific yield – the groundwater that can drain from a rock or
sediment
-Specific yield = porosity – specific retention
-Specific retention = water on the surface of grains that will not
flow through the material (i.e. stuck on grain surfaces)
-The specific yield of fine-grained materials is low, even though
their porosity can be high
The Good Earth/Chapter 12: Groundwater and Wetlands
Holes in Earth Materials
Permeability = the capacity of
water to flow through earth
materials.
Water can flow readily through
materials with well connected
pore space or many fractures.
Connections between pore
spaces are wider in coarsegrained material (gravels) than
fine-grained material (sand).
Q: Why do you think
groundwater flows more
slowly than water on the
Earth’s surface?
High permeability does not always
go hand in hand with high
porosity.
A: More opportunities for friction to slow it
down as it pushes through spaces between
millions of tiny grains.
The Good Earth/Chapter 12: Groundwater and Wetlands
Holes in Earth Materials Checkpoint
12.2
Imagine that you have three identical containers (A,B,C).
A is filled with flour, B is filled with uncooked rice, and C
is filled with coffee beans. Predict what would happen if
you were to pour water into each container. How would
they rank in terms of permeability (from highest to
lowest)?
A)
B)
C)
The Good Earth/Chapter 12: Groundwater and Wetlands
Checkpoint 12.3
A large volume of liquid waste was dumped on the ground at Otis Air
Base, Massachusetts. Both the base and the city are located over the
same deposit of sand and gravel. Examine the following diagram and
predict the approximate length of time before the waste would begin to
show up in the drinking water wells of the city of Falmouth assuming a
flow rate of 0.5 meters per day.
a)
b)
c)
d)
10 months
8 years
16 years
40 years
The Good Earth/Chapter 12: Groundwater and Wetlands
Go back to the Table of Contents
Go to the next section: Groundwater Systems
The Good Earth/Chapter 12: Groundwater and Wetlands
Groundwater Systems
Groundwater is stored
in bodies of rock
and/or sediment called
aquifers, which are
composed of sufficient
saturated permeable
material to yield
significant quantities of
water.
The Good Earth/Chapter 12: Groundwater and Wetlands
Aquifers can form in a
variety of geologic settings
Aquifers can be
composed of
sands, gravels,
sandstone with
good porosity
and permeability,
and fractured
rocks.
The Good Earth/Chapter 12: Groundwater and Wetlands
Groundwater Systems
Aquifer Quality
-High porosity and permeability
-Most productive aquifers are found in unconsolidated earth materials (80% of all
groundwater withdrawn in U.S. comes from sand and gravel aquifers)
-Aquitards – low-permeability materials such as clay, shale, or unfractured igneous
or metamorphic rock, that act as a barrier to water flow
Open water Aquifer.
The Good Earth/Chapter 12: Groundwater Wetlands
Groundwater Systems
In general, the water table follows the shape of the
land surface
The top of the saturated zone is the water table, and it is highest under
hills and lowest in valleys. Water flows down the slope of the water table
(hydraulic gradient). When the water table intersects the land surface a
stream, lake, or spring will occur.
The Good Earth/Chapter 12: Groundwater and Wetlands
Groundwater Systems
Confined (Artesian) Aquifer – enclosed above
and below by impermeable materials. Water
can only enter the well through the exposed
rock layer (recharge zone).
The Good Earth/Chapter 12: Groundwater and Wetlands
Groundwater Systems Checkpoint 12.5
The following cross section simplifies the groundwater sources in a county
in a midwestern state. Which location would have the potential for the best
groundwater production?
a) Location A
b) Location B
c) Location C
d) Location D
The Good Earth/Chapter 12: Groundwater and Wetlands
Groundwater Systems Checkpoint 12.5
Liquid hazardous waste is
disposed of by pumping it
down injection wells. On
the following diagram,
which well location would
be most suitable for use
as an injection well?
a) Well A
b) Well B
c) Well C
The Good Earth/Chapter 12: Groundwater and Wetlands
Groundwater Systems
Inflow (recharge) vs. Outflow (discharge)
Especially important issue is southwestern states
Recharge can occur through infiltration of rainwater or streams
Losing streams – flow over ground in dry areas and lose water into the
groundwater supply
Recharge can also occur from stored groundwater, present from a wetter
time in the past (e.g. water that precipitated into the ground when the last
ice sheets melted; this is non-renewable water)
Gaining streams – gain water from an area with a high water table (this is
a form of discharge, not recharge, of groundwater)
The Good Earth/Chapter 12: Groundwater and Wetlands
Groundwater Systems
Confined Aquifers
Recharge occurs through eroded rocks at higher elevation than where water
is withdrawn.
Water is under pressure. Water can flow without pumping until water table
equals elevation where water is withdrawn.
The Good Earth/Chapter 12: Groundwater and Wetlands
Groundwater Systems
Groundwater can reach the surface at springs and wetlands. Springs
form where (a) fractures or (b) cave systems intersect the land surface.
(c) Wetlands may form where several small springs distribute water over
a region underlain by a low-permeability material such as clay or shale.
The Good Earth/Chapter 12: Groundwater and Wetlands
Groundwater Systems
Look at
these graphs
– which one
do you think
is a gaining
stream?
Why?
The Good Earth/Chapter 12: Groundwater and Wetlands
Groundwater Systems
How does groundwater interact with oceans?
In coastal regions, fresh water is found floating above a denser layer of
saltwater. Saltwater infiltrates the ground just like fresh water. Where the
freshwater layer meets the coast it flows into the ocean.
In coastal cities, freshwater can be extracted from the freshwater layer, but
if it is extracted faster than it is replenished, saltwater can flow into wells.
The Good Earth/Chapter 12: Groundwater and Wetlands
Groundwater Systems
Consequences of Human Actions
• Rapid population
growth = greater need for
groundwater
Goundwater overdraft - the
supply cannot replenish as
fast as we extract it for
human use
• Decline in water table
The water table
surrounding a well can
decline if water is pumped
out too fast. The surface of
the depleted water table
forms a cone of depression
around the well.
Trying to pump groundwater is like sucking up a
spilled drink from a table. No matter how big a
straw you use, most of the drink stays on the table
top.
The Good Earth/Chapter 12: Groundwater and Wetlands
Groundwater Systems Checkpoint 12.9
Two wells (A and B) are drilled in rocks that
have the same porosity, but the rocks
around well A have a higher permeability
than those around well B. Suppose both
wells are pumped at the same rate. Which
statement is true?
a) Well A will have a larger cone of depression.
b) Well B will have a larger cone of depression.
c) The cone of depression will be the same for both
wells.
The Good Earth/Chapter 12: Groundwater and Wetlands
Groundwater Systems
Consequences of Human Actions
• When groundwater is rapidly removed from unconsolidated material,
the grains may compact as the empty pore spaces close
Subsidence – A drop in the ground surface in response to a decrease in volume of
the underlying sediment
Subsidence due to groundwater
withdrawal has occurred in some of the
world’s largest cities. It is responsible for
the lean in the leaning tower of Pisa.
The Good Earth/Chapter 12: Groundwater and Wetlands
Go back to the Table of Contents
Go to the next section: A Case Study: The
High Plains Aquifer
The Good Earth/Chapter 12: Groundwater and Wetlands
A Case Study: The High Plains
Aquifer
About 2/3 of all fresh U.S.
groundwater pumped from aquifers
is used for irrigation, much of which
occurs in the Great Plains (Texas,
Oklahoma, Kansas, Nebraska, and
their neighbors).
Was originally dubbed “The Great
American Desert” – unfit for cultivation.
Irrigation for the Great plains is mainly
taken from the High Plains aquifer
-Sand and gravel with some underlying
sandstone
-Open aquifer – partially recharged by
rain and snowmelt
-Water table is typically less than 100
meters below the surface
Today, the High Plains aquifer
produces more water than
any other groundwater source
in the nation!
The Good Earth/Chapter 12: Groundwater and Wetlands
A Case Study: The High Plains Aquifer
More than 170,000 wells draw water from the aquifer.
The largest area of irrigation-sustained cropland in the world!
There is no contemporary source for water the recharge the whole aquifer.
Most of the water in the aquifer entered it during the last glacial maximum
(wetter climate).
“Fossil” water being used up faster than it is recharged
Water table is dropping over much of the aquifer
The Good Earth/Chapter 12: Groundwater and Wetlands
A Case Study: The High Plains Aquifer
The groundwater overdraft has caused a drop in the water table of
up to 70 meters. Left panel shows thickness of saturated zone,
center panel shows rises/drops in water table, and right panel
shows variations in annual precipitation. Approximately 11% of the
total groundwater supply has been extracted.
The Good Earth/Chapter 12: Groundwater and Wetlands
A Case Study: The High Plains Aquifer
Checkpoint 12.13
Which is the best explanation for the changes in water level
in the High Plains aquifer? Explain why you chose your
answer.
a) The distribution of present-day rainfall on land above the
aquifer
b) Differences in thickness of the rocks that make up the
aquifer
c) The number of water wells that have been drilled into the
aquifer
d) The type of crops supplied by irrigation from the aquifer
The Good Earth/Chapter 12: Groundwater and Wetlands
A Case Study: The High Plains Aquifer
Checkpoint 12.14
Sketch your prediction of the approximate shape of the High Plains aquifer
below some of the Great Plains states. Use the templates here and what you
know about the character of the aquifer. Indicate the depth below the surface
along the side of each diagram.
The Good Earth/Chapter 12: Groundwater and Wetlands
A Case Study: The High Plains Aquifer
Checkpoint 12.16
Much of the agriculture in the middle United States
relies on water from the High Plains aquifer. What
are the long-term implications if we continue to use
large volumes of groundwater for irrigation faster
than it can be replenished?
The Good Earth/Chapter 12: Groundwater and Wetlands
Go back to the Table of Contents
Go to the next section: Groundwater Quality
The Good Earth/Chapter 12: Groundwater and Wetlands
Groundwater Quality
Although natural groundwater is not pure, in the U.S. it
typically contains few chemicals in sufficient quantities
to cause harm.
Under certain conditions harmful elements (arsenic,
mercury) can contaminate drinking water.
In Bangladesh – widespread groundwater
contamination by arsenic – may end up being the worst
mass poisoning in history.
-Most densely populated nation in the world
-One of the poorest nations in the world
-People used to drink surface water contaminated with
pollutants until wells were drilled in late 1970’s
The Good Earth/Chapter 12: Groundwater and Wetlands
Groundwater Quality
High concentrations of arsenic in
the water – discovered after
wells were already in use.
On map – darkest greens are
highest proportion of wells
contaminated by arsenic.
Worst affected wells are south of
the confluence of the Ganges
and Brahmaputra rivers.
These two rivers are sourced
from the Himalayan foothills –
the rocks there contain
unusually high natural
concentrations of arsenic.
~Half the population of
Bangladesh (60 million people)
may be exposed to arsenic
levels above the WHO standard.
The Good Earth/Chapter 12: Groundwater and Wetlands
Groundwater Quality
In the U.S. the standard
for arsenic in drinking
water is 10 ppb (parts per
billion, or 0.05 milligrams
per liter, as set by WHO).
In Bangladesh, the
standard is 50 ppb.
Some wells in
Bangladesh have levels
as high as 2,000 ppb.
Arsenic levels tend to be
higher in western states
that have more igneous
and metamorphic rocks.
The Good Earth/Chapter 12: Groundwater and Wetlands
Groundwater Quality
Nature can cause contamination of groundwater, but mostly
it is due to human activities.
Sources of human and natural contamination can be from
point sources and nonpoint sources.
A point source can be specifically identified and located –
e.g. a leaking gasoline storage tank.
A point source, once identified, can be shut down.
Nonpoint sources occur over a wide area.
Examples of human contaminants in groundwater: Benzene, nitrates,
pesticides, fertilizers, microbes from untreated human and animal
waste.
The Good Earth/Chapter 12: Groundwater and Wetlands
Groundwater Quality
Potential sources of groundwater pollution in the U.S.
The Good Earth/Chapter 12: Groundwater and Wetlands
Groundwater Quality Checkpoint 12.17
Did the natural arsenic contamination of groundwater
in Bangladesh originate from a point source or
nonpoint source? Explain the reasoning behind your
answer.
a. Point source
b. Nonpoint source
The Good Earth/Chapter 12: Groundwater and Wetlands
Groundwater Quality Checkpoint 12.19
Use the Venn diagram provided
here to compare and contrast
groundwater pollution from human
actions (e.g., Woburn) and natural
sources (e.g., Bangladesh). Place
features unique to either group in
the larger areas of the left and right
circles. Note features that they
share in the overlap area in the
center of the image.
1. Can occur anywhere there are people
2. Can occur anywhere
3. May not be obvious to those using the
system
4. Affected by local geology
5. Occurred in relatively recent past
6. May have been occurring for millions of
years
7. If contaminated, may cause illness or
death
8. Typically associated with a point source
9. Typically associated with a non-point
source
10. Can be mitigated by using clean water
11. Once identified, pollution source often
can be cleaned up
12. Once identified, pollution source often
cannot be cleaned up
The Good Earth/Chapter 12: Groundwater and Wetlands
Go back to the Table of Contents
Go to the next section: Introduction to
Wetlands
The Good Earth/Chapter 12: Groundwater and Wetlands
Introduction to Wetlands
Ramsar Convention: A treaty intended to preserve and protect more
than 321 acres of wetlands around the world (12 sites in the U.S.)
To be a wetland an area must be saturated with water and have
poorly drained soils and specific types of plants.
Two types: coastal and freshwater
The Good Earth/Chapter 12: Groundwater and Wetlands
Introduction to Wetlands
Wetlands must meet the following criteria:
Hydrologic conditions – water present on land surface, or soils in
root zone must be saturated during growing season or longer.
Hydrophytic vegetation – specific plants that are water-tolerant and
grow under wet conditions (e.g. cattails, wild rice, willows, sawgrass)
must be present
Hydric soils – poorly drained soils that exhibit anaerobic conditions
during growing season
The Good Earth/Chapter 12: Groundwater and Wetlands
Introduction to Wetlands
In lower 48, largest wetland areas are in Texas, Florida, Minnesota.
Outside of Alaska, wetlands have declined by ~55% since 1600’s in the
U.S.
~10% or less of original wetlands remain in California, Ohio, and Iowa.
Losses are due to draining to support agriculture, or draining and infilling
for urbanization and development.
Why should we care?
Wetlands perform many positive functions in the
environment such as improving water quality in rivers by
filtering out sediments and contaminants, providing breeding
grounds for fish and shellfish which supports commercial
fishing, providing ecological habitats for migrating birds,
modifying the effects of flooding by slowing runoff, and
providing recreation for humans.
The Good Earth/Chapter 12: Groundwater and Wetlands
Introduction to Wetlands
The Florida Everglades (the “river of grass”) experienced a loss of
wetlands due to population growth and urbanization.
Development in the early 1900’s had four goals – “dike it, dam it, divert it,
drain it.” Lost 50% of original wetlands destroying fish and wildlife habitats.
Wetlands were replaced by agricultural sugarcane, and expansion of
coastal cities further stressed the ecosystem.
The Good Earth/Chapter 12: Groundwater and Wetlands
Introduction to Wetlands
Checkpoint 12.22
After a series of summer thunderstorms, Cathy’s
lawn is covered with a shallow pond of water up to 15
centimeters (6 inches) deep in places. The water
remains for nearly 10 days. Does the water in
Cathy’s backyard make it a wetland? Explain your
answer.
The Good Earth/Chapter 12: Groundwater and Wetlands
Introduction to Wetlands Checkpoint
12.23
Use the Venn diagram below to
compare and contrast wetlands
and groundwater systems.
Write features unique to either
groups in the list and put their
corresponding numbers in the
large areas of the circles. Write
features found in both in the
list and put those numbers in
the intersection of the circles.
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
11.
12.
13.
14.
15.
Source for drinking water
Used for recreation
Part of hydrologic cycle
Involve the slow flow of water
Contain vegetation
Contain poorly drained soils
May be freshwater or saltwater
Below ground
Above ground
Affected by agricultural practices
May be polluted due to human actions
May reduce the effects of flooding
Less today than in the past due to
human actions
Example: Florida Everglades
Example: High Plains aquifer
The Good Earth/Chapter 12: Groundwater and Wetlands
Groundwater and Wetlands Concept
Map
Complete the concept
map to evaluate your
understanding of the
interactions between
the earth system,
groundwater and
wetlands.
Label as many
interactions as you
can using information
from this chapter.
The Good Earth/Chapter 12: Groundwater and Wetlands
The End
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The Good Earth/Chapter 12: Groundwater and Wetlands