GROUNDWATER

hydrosphere = includes water in and on Earth’s crust1. 97% contained in oceans2. 90% of freshwater is in form of polar ice caps and glaciers3. ultimate source of all water on land is the oceans4. 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 needs3. groundwater system = area that has

connecting pores

ZONES OF1. 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 table2. 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 precipi-

tation 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 sizeb) 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 moveEx: 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 TABLE1. water table is found at different depths below

ground surface2. depth depends on a. topography of land b. permeability of rock c. amount of rainfall3. prolonged rainfall → water table rises4. 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 & DEPOSITION1. usually slightly acidic and will attack and dissolve

carbonate rocks such as limestone2. cave = natural underground opening with

connection to Earth’s surface3. 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 periods5 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: SPRINGS1. 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 SUPPLY1. 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 drop2. 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

eliminated2. pollution plumes already in ground can be

monitored; move slowly a. time to find alternate water supply b. stop by building impermeable underground

barriers3. polluted groundwater can be pumped to surface for

chemical treatment4. conserve by: a. regulating use b. monitoring level of local water table c. discourage excessive pumping when water table

is low