GROUNDWATER
hydrosphere = includes water in and on Earth’s crust
1. 97% contained in oceans
2. 90% of freshwater is in form of polar ice caps and
glaciers
3. ultimate source of all water on land is the oceans
4. infiltration = process where water enters the ground
and becomes
groundwater
groundwater = underground water that fill
almost all pores in rock and sediment
1. pores = spaces between fragments of
weathered rock and sediments
2. supplies about 1/5 of freshwater needs
3. groundwater system = area that has
connecting pores
ZONES OF
1. zone of saturation = layer of ground where all the
pores are filled with water
a. gravitational water = water that trickles down
due to gravity
b. capillary water = water drawn upward from
water table
2. water table = upper surface of zone of saturation
a. depth varies depending on local conditions
b. topography will follow topography of land above it
c. dependent on precipitation so will vary with
seasonal and other
weather conditions
d. rise during wet season,
drops during dry seasons
3. zone of aeration = lies between water table and
earth’s surface
a. uppermost region = holds soil water
- forms film around grains of topsoil
b. middle region = normally remains dry except during
rainfall, mostly air
c. capillary fringe = bottom region
1) water drawn up from zone of saturation
2) capillary action = attraction of water molecules
to other materials
ROCK PROPERTIES THAT AFFECT MOVEMENT & STORAGE
1. flows downhill in direction of slope of water table due
to gravity
a. rate depends on: permeability of materials
and gradient of water table
b. flow velocities through permeable materials is
always higher than those through impermeable
materials
2. porosity = percentage of open spaces in a given
volume of rock or sediment
a. determines the amount of water a rock can hold
b. can be fractures, cavities, or pores
c. influenced by:
1) sorting = amount of uniformity in size of particles in
sediment or rock
a) well sorted has particles all about same size
b) poorly sorted has particles of many sizes mixed
together
2) way particles are packed together
a) packed loosely then has many open spaces →
high porosity
b) tightly packed → few open
spaces → low porosity
3. permeability = how freely water passes through open
spaces in rock or sediment
a. affected by size and sorting of particles that make
up a rock or sediment
b. most permeable rocks are those made up of coarse
particles
Ex: sandstone
c. impermeable = rock or sediment through which
water cannot move
Ex: clay
4. aquifer = layer of permeable rock that has connecting
pores and transmits water freely
a. large amounts of water can flow through
b. contains porous layers of sediments such as sand
and gravel, sandstone, and limestone
c. aquicludes = impermeable layer that provides a
barrier to groundwater flow
TOPOGRAPHY AND WATER TABLE
1. water table is found at different depths below
ground surface
2. depth depends on
a. topography of land
b. permeability of rock
c. amount of rainfall
3. prolonged rainfall → water table rises
4. drought periods → water
table drops and flattens
5. perched water table = secondary water table
formed by a layer of impermeable rock above
the main water table
a. rock layer prevents water from seeping down into
the zone of saturation
b. water collects on top creating a second water
table
6. most areas only have one water table
EROSION & DEPOSITION
1. usually slightly acidic and will attack and dissolve
carbonate rocks such as limestone
2. cave = natural underground opening with connection
to Earth’s surface
3. caverns = large cave often containing many smaller,
connecting chambers
a. chemical weathering enlarges a number of
connected cracks and cavities
b. common in areas with
extensive limestone deposits
c. water is slightly acidic
[carbonic acid]
4. sinkholes = circular depression caused when roof of
cavern collapses
a. can extend below water table
b. usually occurs during dry periods
5 karst topography = region where the effects of
chemical weathering due to groundwater are
clearly visible
a. may include closely spaced sinkholes, caverns, and
streams that disappear
b. can appear in arid regions
c. sinking stream = surface streams
that drains into a
cave system
6. hard water = contains relatively large amounts of
dissolved minerals
a. usually ions of calcium, magnesium, and iron
b. common in limestone areas
c. unacceptable for many common uses
1) soap will not produce suds
2) has metallic taste
3) household appliances or fixtures may have build
up of minerals
d. soft water = contains few dissolved minerals
7. speleotherms = all mineral deposits formed in caves by
the action of water
a. stalactites = cone shaped calcite deposit
suspended from the ceiling of a cavern
b. stalagmites = cone shaped calcite deposit built up
from the cavern floor
c. column = formed when a stalactite and stalagmite
grow together
d. referred to as dripstone formations because these
are formed from dripping water
e. composed of travertine
8. veins = areas of igneous rock where hot groundwater
collects metallic ions in solution and then deposits
them in metallic ores
9. natural bridge = arch of rock
a. uncollapsed rock between pairs of sinkholes
b. can form when surface river enters a crack in rock
formation, runs underground, then re-emerges
GROUNDWATER SYSTEMS: SPRINGS
1. ordinary springs = natural flow of groundwater to the
earth’s surface
a. commonly found in rugged terrain and hillsides
b. ground surface drops below water table, usually do
not flow continuously
c. emerge on sides of valleys, edges of perched water
tables, along faults
d. those that form where there is a perched water table
may flow continuously
e. in areas where an aquifer and an aquiclude come in
contact
f. karst spring = area where an entire river emerges
from the ground
2. artesian spring = natural flow of water to
earth’s surface from an artesian formation
a. form when cracks naturally occur in cap
rock
b. water under pressure flows to surface
c. also called fissure springs
3. hot springs = hot groundwater that rises to surface
before cooling
a. water heated when comes into contact with
magma or passes through areas where there has
been recent volcanic activity
b. temperature must be at least 37oC
c. contains large concentrations of minerals
4. geysers = hot springs that erupt periodically
a. shoots up water and steam
b. narrow vent leads to surface and connects with one
or more underground chambers
c. eruptions:
1) from surface pools shooting sheets of water and
steam
2) from small surface vents sending narrow columns
of water and steam high into air
d. geyserite = deposit of silicate mineral that forms
5. travertine = form of calcite that is deposited in
terraces around the mouth of hot springs
a. usually white but turns gray as it weathers
b. can also be red, brown, or yellow
6. mud pots = weathered rock around hot spring that
mixes with hot water to form liquid clay that
bubbles at surface
a. rock surrounding hot spring is chemically
weathered by volcanic gases
b. also called paint pots = clay can be colored by
minerals and organic materials
WELLS:
1. ordinary well = hole dug below water table
a. must go down into zone of saturation below water
table
b. if not deep enough it will dry up when water drops
below water table
c. pump brings water to surface
1) cone of depression = lowered area of water table
produced by pumping water from well
2) can drop to bottom of well causing it to dry
3) could also cause surrounding well in area to go dry
d. drawdown = difference between original water-table
level and water level in pumped well
e. recharge = water from precipitation and runoff is
added back to zone of saturation
2. artesian well = hole dug through cap rock of artesian
formation through which water flows freely
a. no pumping is necessary
b. artesian formation = sloping layer of permeable rock
sandwiched between two aquicludes and
exposed at surface
c. cap rock = top layer of impermeable rock
d. aquifer → permeable rock layer
e. water in lower part is under pressure from weight of
water above
THREATS TO WATER SUPPLY
1. overuse = supplies can be depleted is water is
pumped out at a rate greater than recharge rate
a. supply will decrease
b. water table will drop
2. subsidence = sinking of land due to excessive
withdrawal of water
3. pollution
a. most easily polluted are water-table unconfined
aquifers
b. if recharge area of confined aquifer becomes
polluted these aquifers will also be polluted
c. most common sources are sewage, industrial waste,
landfills, and agricultural chemicals
d. chemicals are dissolved and transported as ions so
they cannot be filtered out in sediments
e. at coastal areas contamination of water by salt
water; if water table drops below sea level this
allows salt water to enter
f. natural pollution source is
radioactive radon gas
PROTECTING
1. all major pollution sources need to be identified and
eliminated
2. pollution plumes already in ground can be monitored;
move slowly
a. time to find alternate water supply
b. stop by building impermeable underground barriers
3. polluted groundwater can be pumped to surface for
chemical treatment
4. conserve by:
a. regulating use
b. monitoring level of local water table
c. discourage excessive pumping when water table is
low