GROUNDWATER
GROUNDWATER
Sources of fresh water on Earth
GROUNDWATER
• Basic information
• Definition and explanation
• water below Earth’s surface occurring in open
spaces including fractures, joints, faults or
other spaces between rock particles
• amount of groundwater is strongly influenced
by magnitude of infiltration which is affected
by other paths taken by precipitation in
hydrologic cycle
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water in pores between
sediments
water in fractures, faults, cracks
water in larger
openings like vugs
or caves
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• Kinds of groundwater
• connate--entrapped brackish water
• juvenile--water originating directly from a
magma
• meteoric--fresh circulating water which is the
type commonly referred to as “groundwater”
• Qualities of rock materials in respect to
contained groundwater
• porosity
• is a measure of water capacity of a rock
material
• high porosity= contains a lot of water
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high porosity
--well sorted
low porosity--poorly sorted
high porosity-- small platy
sediments—well sorted
mudstones
and shales
most sandstones most conglomerates—
filling of openings
low porosity—igneous and
metamorphic rocks
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• permeability
• a measure of the ability of water to be
transmitted by a substance
• is proportional to the degree of
interconnected voids between particles
• larger open spaces in a rock will favor
a higher degree of interconnection
between openings
• moving water is filtered and stays pure
• some rocks have high porosity but low
permeability which would yield low quality
groundwater (shales, claystones, pumice)
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high permeability—most
sandy materials--sandstones
low permeability—mudstonesshales
high permeability—well
connected cracks
low permeability--pumice
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• specific yield
• the percent water obtained from a
substance
• specific retention
• the percent water retained by a substance
after water extraction
• an example of a non rock substance
displaying specific yield and retention
would be a sponge in which after squeezing
out all water there still remains some water
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• aquifer and aquiclude (aquitard)
• aquifer is a (high) permeable substance
• aquiclude is a (low) permeable substance
• Unconfined and confined groundwater
• Definitions
• unconfined
• groundwater in an aquifer with a lower
barrier to movement caused by the
presence of an aquiclude below, but not an
upper barrier allowing water to fluctuate
over distances upwards
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Unconfined
water
aquitard--aquiclude
free to move up,
but not down
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confined
groundwater in an aquifer with a
lower and upper barrier for
movement
there is an aquiclude located
immediately above and below the
aquifer
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aquitard--aquiclude
confined water
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• Unconfined groundwater
• zone of saturation
• area of open space in rocks filled with
water
• area with highest concentration of water
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Groundwater zones
Zone of
Saturation
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• water table
• is the upper level of the zone of saturation
• water table for unconfined groundwater
can fluctuate up and down over relatively
large levels
• zone of aeration (vadose zone)
• area above water table unsaturated with
water and openings filled primarily with air
• small amounts of water present by
retention and capillary action
• capillary action is greatest in the capillary
fringe area
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Groundwater zones
Vadose or
Aeration
zone
Capillary
Fringe Area
Water Table
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vadose (aeration)
zone--unsaturated
water table
zone of saturation
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• changing levels of water table
• lowering (discharge) of water table takes
place if the following usage is greater than
replenishment to zone of saturation
• continued pumping of groundwater
• plant usage
• leaking of water at the Earth’s surface
into streams and lakes
• rising (recharge) of water table
• rate of replenishment (primarily by
infiltration) is greater than rate of
depletion
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• a spring is a natural surface emission of
groundwater--streams can form this way
and many streams in the Ozarks are
spring-fed--a hot spring is about 10-15
degrees F warmer than local annual
mean air temperature because of an
association of water with subsurface
igneous intrusion
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Mammoth Hot Springs in
Yellowstone National Park
Hot spring distribution in the USA
A geyser is a hot spring which ejects steam
and water at the surface with great force
and in some cases at a consistent interval
(see example below)
Old Faithful Geyser in Yellowstone National Park
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• interrelationship of groundwater and streams
• in some cases streams can directly supply
groundwater and vice versa
• an effluent (gaining) stream is supplied
by groundwater and abundant in humid
climates— a type of spring
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• an influent (losing) stream supplies
water to the zone of saturation and is
characteristic for arid climates— not a
spring
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More Kinds of Springs
a spring forming a river or lake
a spring gushing out
from cracks
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springs from
limestone aquifers
springs from faults
or fractures etc.
spring from water
forced up
encountering a less
or non permeable
rock
A spring related to a perched water table
(this arises when there is groundwater in the zone of
aeration above the main or regional water table)
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• pumping of groundwater
• heavy pumping can cause a cone of
depression of the water from drawdown
and may leave many shallower wells dry at
the surface
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• Confined groundwater
• artesian water can be a special type of spring
• flowage of subsurface water in a confined
aquifer causes a pressure surface level
which defines the level to which water can
naturally rise
• if a surface opening is connected to the
aquifer and is below the pressure surface,
water can flow naturally at surface,
otherwise it must be pumped
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Confined artesian water
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• Groundwater effects in carbonate rocks
• Subsurface solution and precipitation effects
• chemical mechanism
• carbonate rock is dissolved by acids
forming caves or caverns
• cave precipitates (speleothems) can form
when the groundwater rich in dissolved
limestone material becomes less acid
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Most caves form below the water table,
these formed above the water table
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• some famous caves and speleothems
• famous caves are : Mammoth Cave ,
Kentucky; Shenandoah Caverns, Virginia;
Carlsbad Caverns, New Mexico; Onondaga
and Merimac Caverns, Missouri
• Missouri has more mapped caves than any
other state and is called the “Cave State”
• the main speleothems are:1)stalactites
which grow from the cave roof;
2)stalagmites which grow from the cave
floor;3)columns which result from
stalactites and stalagmites merging
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Speleothems
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more speleothems
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• Surface features
• Karst topography is a pitted looking Earth
surface resulting from subsurface solution
action and include sinkholes and solution
valleys--enormous sinkholes are an example
of mass wasting
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Large sinkhole in Florida
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• Groundwater and stream pollution problems
• as mentioned before there is a strong
interrelationship between streams and
groundwater and if one is polluted or
tainted the effects can be transferred to the
other
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• Saltwater encroachment and pollution of
groundwater
• pumping effects or mixing of groundwater
and saltwater near ocean areas can cause
undesirable effects or pumping too much
water can cause the rising of salt water
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• Septic tank leaks
• Sequiota Springs in Springfield is a good
example of this
Another example of septic tank
leakage
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• Landfills and industry
• landfills
• have evolved from “dumps” to a “state of
the art” way to contain our wastes
• layers of clay and plastic liners at the
bottom of the fill have recently been
used to help contain leach ate
• landfills have been constructed on top of
impermeable layers of rock like shale to
help contain leach ate
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• industry
• guilty of dumping pollutants into streams
and groundwater and adding by-product
gases to the atmosphere resulting in acid
rain
• waste water treatment facilities have also
emitted elevated levels of phosphates and
other toxic metals into streams--high
concentrations of algae thrive on
phosphates
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• Storm water runoff
• results from urbanization can cause a
decrease of natural infiltration of precipitation
in the subsurface causing greater runoff and
flooding
• flooding can cause pollution