GROUNDWATERwww.google.com
en.wikipedia.org
Thompson Higher Education 2007; Monroe, Wicander, and Hazlett, Physical Geology
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GROUNDWATER is one of the most important geological resources for humans
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• Worldwide 50% of
people obtain their
water from the
ground.
•70 times more
abundant in the
subsurface than in
surface reservoirs.
• Moves so slowly it is stored in the earth and remains available even in dry periods.
• In some places it flows from humid environments to dry ones, making water available.
• It serves as an underground reservoir of water that eventually runs into streams and
lakes.
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Groundwater and Porosity and Permeability
•Groundwater and Porosity and Permeability
• The Water Table
• Water Wells
• Borehole Geophysics
• Groundwater Movement
• Recharge and Discharge areas, Springs and Artesian Systems
• Groundwater Erosion and Deposition
• Modifications of the Groundwater System And Their Effects
• Hydrothermal Activity
Groundwater is that water which occupies pore spaces and other cavities within
subsurface rocks and unconsolidated materials.
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• Groundwater by volume is only about 1% of the of the hydrologic cycle but
constitutes approximately 22% of the world's fresh water supply.
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Porosity is the
percentage
volume of
rock,
sediment or
soil which
consists of
pore space
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• Soil is about half pore space, much
of which is filled with water.
•The rest is stored in unconsolidated
sediments, or cracks and joints in
rocks.
Porosity
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Porosity
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• Transmissibility is the ease
with which water moves through
rock
• A rock can have abundant
pore space but if these spaces
are not connected, groundwater
can not move through it.
•The pore spaces have to be big
enough and interconnected to
move water.
Permeability refers to the transmissibility of fluids through rock, sediment, or
soil.Connected pores gives rock permeability
Affected by:
• number of available conduits
• size of the conduits
• straightness of the conduits
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Groundwater Movement mostly occurs by the work of gravity (water
flows down hill) but generally occurs very slowly (cm to meters/day)
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Groundwater Zones
and the
Water Table
• The saturation
zone has all pore
spaces occupied
by water.
• The aeration zone
contains both air and
water in the pore
spaces of rock, soil or
sediment.
• The water table
surface separates
the aeration zone
from the
saturated zone.
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The Water Table is an important concept called a potential surface and can not
be seen directly.
• Water Table mimics surface topography.
• Water table coincides with level of water in wells.
• Water table is important in explaining the flow of springs and streams,
and water levels in lakes.
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Water Table Maps
• When the depth to the water table
is measured in wells at multiple
points in the same aquifer, the
elevations can be contoured to show
the groundwater flow direction
• The groundwater flow direction is always normal to the potential-surface contours
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Water Table Fluctuates by Season
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Water Table and Streams
• When the water table is
higher in elevation than a
stream, ground water flows
into the steam—called gaining
stream (usually in humid
climates).
• When water table is below a
stream it is called losing
stream and supplies water to
the ground (usually in desert
climates).
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Aquifers, Aquitards, Aquicludes, and Confining Units
• An aquifer is an underground
layer of water-bearing permeable
rock or unconsolidated materials
(gravel, sand, or silt) from which
groundwater can be extracted
using a water well.
• The study of water flow in
aquifers and the characterization
of aquifers is called hydrogeology.
• An aquitard is low permeability material
along an aquifer that retards the flow of
groundwater.
• An aquiclude is a solid, impermeable area underlying or overlying an aquifer.
• When an aquiclude overlies an aquifer under confined pressure, the srtat are called
a confining unit overlying a confined aquifer.
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Water Wells are devices similar to drinking straws that help people to
remove water from the zone of saturation.
• Once a well is pumping, a conical depression forms in the water table called a cone of depression.
• Wells must be below the
water table because during
pumping the water table is
lowered in elevation
(this is called drawdown).
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A Perched Water Tableis when an aquitard blocks the downward
movement of water, and two water table
levels can form with the upper being a
perched water table.
• They can form springs on hillsides and in
road cuts.
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Springs occur where
an aquifer and water
table intersect the
ground surface
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Groundwater moves
slowly through aquifers,
from areas of high pressure
to areas of lower pressure
such as streams, lakes, and
swamps.
• When groundwater in an
aquifer is confined by aquicludes
and is under hydrostatic
pressure as the result of an
elevation difference between
the zone of recharge and lower
portions of the aquifer, an
artesian system exists.
Municipal water systems commonly have well
water pumped to elevated holding tanks
where gravity maintains pressure to the
recipients
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Groundwater Flow Rates are dependant upon the
permeability of the material and the
hydraulic gradient
• Flow rates are typically
10-100 cm/day, or 40-400 m/yr
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Karst
Topography is characterized by
sinkholes, solution
valleys, and
disappearing
streams, and
results from
groundwater
weathering and
erosion.
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Caves form
when groundwater
weathers and
erodes soluble rock
such as limestone
in the zone of
saturation.
cave
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Karst
Topography
Of the Irish
Barren Uplands
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Karst Topography
• As groundwater
percolates through the
zone of aeration and
flows through the
saturated zone, it
dissolves the
carbonate rocks and
gradually forms a
sytem of passageways.
•Horizontal
passageways carry
water to streams and
allows the local base
level to drop, creating
cave and cavern
systems.
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Cave Deposits
Buchan Cave, Victoria, Australia
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Cave Deposits
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Aquifer Systems consists of aquifers and aquitards.
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Aquifers and
Confining Units
of New Jersey
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The Great Artesian Basin
in Australia is arguably the largest
groundwater aquifer in the world
(over 1.7 million km²).
• It plays a large part in water supplies
for Queensland and remote parts of
South Australia.
Queensland
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• When withdrawal from wells exceeds
the rate of recharge, dry wells, loss of
hydrostatic pressure, saltwater
encroachment and ground subsidence
may result.
• Aquifer depletion is a problem in some
areas, and is especially critical in northern
Africa.
Groundwater Depletion and Ground Subsidence
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• New methods of groundwater
management such as artificial
recharge and injection of surface
waters during seasonal wet periods
has extended the life of many
freshwater aquifers, especially in the
United States.
• But there are other places like the
arid southwest USA where 10s of
meters of land subsidence is directly
related to groundwater depletion.
Groundwater Depletion and Ground Subsidence
9 m
in 52
years
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The Ogallala Aquifer of the central United States is one of the world's
great aquifers, but in places it is being rapidly depleted by
growing municipal use, and continuing agricultural use.
• This huge aquifer, which underlies portions of eight
states, contains primarily ‘fossil’ water from the time of
the last glaciation (10-85 Ka).
• Annual recharge, in the more arid parts of the aquifer, is
estimated to total only about 10 percent of annual
withdrawals.
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Saltwater Incursion
• Freshwater is less dense than saltwater
and will form a lens floating atop the salty
groundwater
•If excessive pumping occurs, a cone of
depression develops in the fresh
groundwater, which may result in
saltwater contamination of the well.
•Pumping water back into the fresh
groundwater system through recharge
wells can help lower the
freshwater-saltwater interface and
reduce saltwater incursion.
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The Edwards Aquifer in central
Texas is a carbonate aquifer has historically been
providing high quality water for nearly 2 million
people, and even today, is full because of
tremendous recharge from a number of area
streams, rivers and lakes.
• The primary risk to this resource is human
development over the recharge areas.
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Dollars and Ground-water Quality
•The Environmental Protection Agency
estimates that communities in the United
States need $12.1 billion in funding
immediately to protect the nation's drinking
water supplies and to meet minimum
health-based standards.
•The agency also estimates that
$138.4 billion will be needed
over the next 20 years to
upgrade or replace the water
infrastructure (2007).
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Dollars and Ground-water Quality
•The agency
also estimates
that $138.4
billion will be
needed over
the next 20
years to
upgrade or
replace the
water
infrastructure.
$263
billion
gap
(2013)
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Groundwater Pollution
• Groundwater contamination can be
natural or anthropogenic (man-derived)
• Contamination from anthropogenic
and animal sewage, landfills, and toxic
waste is becoming a serious problem.
• High-density
housing with
water wells and
septic very bad.
Arsenic in Groundwater can be either natural or anthropogenic
red
black
gray
red
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Arsenic in Groundwater
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Septic Systems have a life expectancy
of about 20 years, but regular maintenance and
best management practices can extend the life.
• Minimize the amount of solid material, water, and
chemicals like solvents, paint, etc., that goes in.
• Pump solids from the tank regularly (minimum
evry 4 years)
• Keep leach field free of rooted plants
• Divert surface water away from the field
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A common saying:
“The solution to
pollution is
dilution”
Groundwater Pollution commonly occurs as plumes that show
concentration gradients having constituents concentrations decreasing away from the
source area.
In New Jersey, parties that are determined to be responible for groundwater contamination
are required to delineate the ‘horizontal and vertical limits’ of pollution plume, usually by
drilling test, observation, and monitoring wells.
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• In the future, naturally
occurring bacteria may provide
solutions for many
groundwater pollution
problems.
• Bacteria have been shown to
convert uranium in
contaminated waters to a
highly insoluble form.
• Some microbes living in
oxygen-free sediments can
break down derivatives of
hydrofluorocarbons, which are
among the compounds under
Bacteria and Groundwater Pollution
consideration to replace ozone-destroying chlorofluorocarbons (CFCs).
• And, microbes which degrade toxic carcinogenic aromatic hydrocarbons like
benzene and toluene can be boosted to work in anaerobic conditions commonly
found in heavily polluted aquifers.
EOS, July 19,1994.
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• Geysers and hot springs develop where groundwater is heated by hot subsurface
rocks or the geothermal gradient.
• Geysers are hot springs which periodically eject hot water and steam.
Hydrothermal Systems
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Hot Springs Deposits,
Yellowstone, National Park,
Wyoming, USA
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• Hydrothermal systems are considered primary targets
in the search for fossil evidence of early life forms.
• These environments are favorable for the generation
of organic compounds necessary for life.
Hydrothermal Systems and Early Biological Evolution
• They may also have provided sanctuaries for
heat-loving microorganisms during catastrophic earth
events.
• High rates of mineralization would favor preservation.
GSA Today, July, 2000.
• Some scientists believe that hydrothermal vents were the cradle of life, that may have began well
before 3.2 billion years ago.
• They argue that the mix of high heat and cold seawater in the vent environment led to the
formation of the first organic compounds, and that the formation of pyrite in ancient vents from
sulfur and iron could have produced energy to force organic compounds to combine, leading
eventually to the creation of life.
• In this context it has been proposed that metal sulfides of black smokers (one type of deep sea
vent) could act as catalysts in the first step toward building organic molecules.
• Using electron ionization mass spectroscopy, they found few differences when they compared
organic compounds from current vents with biologically diverse vents fossilized in 3.2-billion-year-
old greenstone from South Africa.
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Old Faithful,
Yellowstone
The Geysers, Sonoma County, California
Geothermal Systems ~ 120 mi North of San
Francisco is piped directly to
electricity-generating turbines to produce
electricity for regional distribution
Geysers
Old Faithful is a cone geyser located in Wyoming, in
Yellowstone National Park, USA. N, it was the first
geyser in the park to receive a name. It is also
considered to be the most predictable geographical
feature on Earth erupting almost every 91 minutes.
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• Geothermal energy It provides
a relatively clean source of
energy for heat and electricity.
• In New Jersey, a study of the
geophysical parameters needed
to design geothermal systems
shows that the efficiency of
geothermal systems in this region
increases as geological materials
become more consolidated and
hardened into rock.
• Substrate in southern New
Jersey consists of sand, silt, clay,
and gravel, which are less
efficient at storing and diffusing
heat than are the igneous,
metamorphic, and compacted
sedimentary rocks of higher
latitudes.
Geothermal Energy is formed from the steam and hot
water which resides in Earth's crust.
Dowsing, Divining, Water-Witching, and Doodlebugging
• Dowsing is the GOD-given talent of
finding subsurface features of interest
without using scientific instruments.
• Employed in attempts to locate ground
water, buried metals or ores, gemstones,
oil, gravesites, and many other objects and
materials, as well as ‘Earth currents’.
• ‘Dowsing’ or ‘water-witching’ for
water
• ‘Doodlebugging’ for oil
•There is no accepted scientific
rationale behind divining, and
there is no scientific evidence that
it is effective.
Fractured
Bedrock
Hydrogeology
A. Upward cross flows occur in wells
that penetrate deep aquifers with
strata dipping in the same direction
as topographic grade over long
distances.
B. Downward cross flows occur
where strata dip in a direction
opposite to long topographic
grades.
C. Wells that penetrate strata
intersecting both recharge areas on
hilltops and hill slopes and
discharge areas in valleys can have
both upward and downward cross
flows.
In general, cross flows can be expected to coincide with the direction of leakage in thick sequences of poorly conductive strata that
confine bed-parallel water-bearing units.
Profile diagrams illustrating the relationship between topographic grade and
direction of cross flows in wells under natural (nonpumping) conditions.