Transcript 3rd Guided Notes about Groundwater

rd
3
Guided Notes about
Groundwater
Section 10.3
1.
In most cases, groundwater
emerges wherever the water table
intersects the Earth’s surface. Such
intersections commonly occur in
areas that have sloping surface
topography.
2.
Groundwater tends to discharge at
Earth’s surface where an aquifer and
an aquiclude come in contact.
These natural discharges of
groundwater are called springs.
3.
In regions of near-horizontal
sedimentary rocks, springs often
emerge on the sides of valleys at
the same elevation, at the bases of
aquifers.
4.
Springs may also emerge at the
edges of perched water tables,
which are zones of saturation that
overly an aquiclude, which separates
it from the main water table.
5.
The temperature of groundwater is
generally the average annual
temperature of the region in which it
is located.
6.
Compared to air temperatures,
groundwater is colder in the
summer and warmer in the winter.
7. Hot springs have temperatures higher
than that of the human body. Most of
these are located in the Western United
States, in areas where the subsurface is
still quite hot from recent igneous activity.
Underground water is hot because
temperatures in Earth’s crust increase with
depth by 25ºC for every kilometer.
8.
Geysers are explosive hot springs
that erupt at regular intervals.
9.
Wells are holes dug or drilled deep
into the ground to reach
groundwater. A well must tap into
an aquifer. The simplest wells are
those that are dug or drilled below
the water table, into the zone of
saturation.
10. Overpumping
of the well lowers the
water level in it and produces a
cone of depression in the water
table. The difference between the
original water table level and the
level in a pumped well is called the
drawdown.
11. Recharge
is water from precipitation
and runoff that is added back to the
zone of saturation.
12. Water table aquifers are unconfined and
unprotected, and thus, easily polluted.
More reliable and less easily polluted
water supplies can be found in deeper
aquifers, called confined aquifers, which
are generally sandwiched between
aquicludes. The aquicludes form barriers
that prevent pollutants from reaching such
aquifers.
13. Because
the area of recharge is
usually at a higher elevation than
the rest of the aquifer, a confined
aquifer contains water under
pressure. The aquifer is called an
artesian aquifer.
14. When the rate of recharge is high
enough, the pressurized water in a
well drilled into a confined aquifer
may spurt above the land surface in
the form of a fountain called an
artesian well.
15. Agriculture=
41%
Electric Power Plants= 38%
Domestic Use= 10%
Industry= 11%
16. Ground
subsidence, the sinking of
land, is a problem caused by the
excessive withdrawl of groundwater.
17. The most common sources of
groundwater pollution are sewage,
industrial waste, landfills, and agricultural
chemicals. These pollutants enter the
ground above the water table, but they
are eventually flushed downward by
infiltrating precipitation and become mixed
with the groundwater. Most sewage enter
the groundwater from faulty septic tanks.
18. Salt
pollution is a threat to
groundwater supplies in many
coastal areas. The overpumping of
wells can cause the underlying salt
water to rise into wells and
contaminate the freshwater aquifer.