GROUNDWATER

FRESHWATER IS ONE OF EARTH’S MOST ABUNDANT

AND IMPORTANT RENEWABLE RESOURCES.

CHAPTER 10: GROUNDWATER

Vocabulary Terms: Turn in today

Aquiclude, aquifer, geyser, hot spring, infiltration, permeability, spring, water table, zone of saturation, zone of aeration, CAVE, KARST TOPOGRAPHY, SINKHOLE, STLACTITE, STALAGMITE, ARTESIAN WELL, DRAWDOWN, RECHARGE, WELL

TAKE HOME TEST WORD BANK

• Artificial selection (use twice)• Mutation• Symbiosis• Invasive• Niche (use twice)• herbivory

CHAPTER 10: GROUNDWATER1. Describe how groundwater storage and underground

movement relate to the water cycle2. Illustrate an aquifer and a aquiclude3. Relate the components of aquifers with the presence of

springs4. Explain how groundwater dissolves and deposits rocks and

minerals5. Illustrate how caves form6. Describe the features of karst topography shape the

landscape7. Explain how groundwater is withdrawn from aquifers by

wells8. Describe the major problems that threaten groundwater

supplies

THE HYDROLOGIC CYCLE

The circulation of Earth's water supply Processes involved in the cycle1. Precipitation2. Evaporation3. Infiltration4. Runoff5. Transpiration

THE HYDROLOGIC CYCLE

SOURCES OF EARTH’S WATER

PRECIPITATION AND GROUNDWATER

• The Evaporation of seawater introduces water into the atmosphere in the form of water vapor and clouds.

• Precipitation brings moisture from the atmosphere back to Earth’s surface.

• Infiltration: the process by which precipitation that falls on land surfaces enters the ground and becomes ground water.

GROUNDWATER STORAGE

• Subsurface materials have porosities ranging from 2 or 3 percent to more than 50 percent.

Well sorted sedimentsHigh porosity

Poorly sorted sedimentsLow porosity

•Porosity is the percentage of pore space in a material.

ZONE OF SATURATION

• The zone of saturation is the depth below Earth’s surface at which groundwater completely fills ALL the pores of a material.

• The water table is the upper boundary of the zone of saturation.

• The Zone of aeration: the area above the water table, materials are moist but the pores contain mostly air

Zone of Aeration

GROUNDWATER MOVEMENT

•Permeability is the ability of a material to let water pass through it. •Materials with large, connected pores have high permeabilities. •Sand and gravel have high permeabilities.

•Fine-grained materials typically have low permeabilities because their pores are so tiny. •silt, clay, and shale, are said to be impermeable.

•Water moves faster (velocity) through permeable materials.

GROUNDWATER MOVEMENT

PERMEABILITY

High permeability Low permeability

GROUNDWATER MOVEMENT

•Aquifers are underwater permeable layers where most groundwater flow takes place.•Aquicludes are impermeable layers that block the flow of groundwater.•Clay and shale layers are examples of aquicludes

WELLS

• Wells are holes dug or drilled deep into the ground to reach a reservoir of groundwater.• The simplest wells are those that are dug or drilled below

the water table.

WELLS

• Overpumping of the well lowers the water level in it and produces a cone of depression in the water table around the well.

WELLS

• Drawdown: the difference between the original water-table level and the water level in the pumped well.

• Recharge: the process in which water from precipitation and runoff is added back to the zone of saturation.

CONFINED AQUIFERS•Water-table aquifers are unconfined and unprotected, and thus, they are 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.

CONFINED AQUIFERSArtesian Wells

– Because the area of recharge is usually at a higher elevation than the rest of an aquifer, a confined aquifer contains water under pressure.

– The aquifer is called an artesian aquifer.

– Artesian well: a well drilled into a confined aquifer from which water spurts above the land surface in the form of a fountain.

GROUNDWATER EROSION AND DEPOSITION

•Most groundwater contains some acid, usually carbonic acid. •As a result, groundwater is usually slightly acidic and attacks carbonate rocks, especially limestone.

• Limestone consists mostly of calcium carbonate (CaCO3), which dissolves readily in any kind of acid.

•Cave: a natural underground opening with a connection to Earth’s surface. •Practically all caves are formed when groundwater dissolves limestone.•Most caves develop in the zone of saturation just below the water table.

KARST TOPOGRAPHY

KARST TOPOGRAPHY• Characteristic surface features formed by

the dissolution of limestone include:• Sinkhole: a depression in the ground caused by the collapse of a cave or by the direct dissolution of bedrock by acidic rain or moist soil. • Sinking stream: forms when surface water drains into a cave, flows underground and leaves a dry valley above• Karst topography: describes limestone regions that have sinkholes, sinks, and sinking streams

Florida Sinkhole-karst

HARD WATER

• Water that contains high concentrations of calcium, magnesium, or iron is called hard water.

• Hard water is common in limestone areas where the groundwater is nearly saturated with calcium carbonate.

NATURAL DEPOSITS

• Dripstone formations:• Stalactites: cone-shaped or cylindrical structures that hang from a cave’s ceiling like icicles.• Stalagmites: mound-shaped dripstone deposits that form as water drops splash to the floor of a cave.• Travertine: the type of limestone that composes dripstone formations.

Stalactite Stalagmite

NATURAL DEPOSITS

THREATS TO OUR WATER SUPPLY

• Overuse:•If groundwater is pumped out at a rate greater than the recharge rate, the groundwater supply will inevitably decrease, and the water table will drop

THREATS TO OUR WATER SUPPLY

• Subsidence:•Ground subsidence, or the sinking of land, is a problem caused by the excessive withdrawal of groundwater•Water pressure helps carry the weight of the material overlying an aquifer. •What happens if there is nothing to support this weight?

Pollution in Groundwater

• Confined aquifers, though somewhat protected from local pollution, become contaminated when their recharge areas are polluted.

• The most common sources of groundwater pollution are sewage, industrial waste, landfills, and agricultural chemicals.

GROUNDWATER POLLUTION

CHEMICALS

• Chemicals dissolved or transported with groundwater are in the form of ions and molecules, and thus, they cannot be filtered out in fine-grained sediments.

• Chemicals generally move downslope as a mass of contaminants that spreads through the environment. (pollution plume)

SALT

• In many coastal areas, the contamination of freshwater by salt water is the major problem.

• The overpumping of wells can cause the underlying salt water to rise into the wells and contaminate the freshwater aquifer.

PROTECTING OUR WATER SUPPLY

• Pollution plumes that are already in the ground can be monitored through observation wells.

• Pollution plumes may be stopped by building impermeable underground barriers.

– Polluted groundwater can be pumped out for chemical treatment on the surface.