AquifersAquifers

Is a body of highly permeable rock or Is a body of highly permeable rock or regolith lying in the zone of saturation.regolith lying in the zone of saturation.

Unconfined and Confined AquifersUnconfined and Confined Aquifers

• Unconfined aquifer – An aquifer having an upper surface that coincides with the water table and direct contact with the atmosphere.

• Confined aquifer – Bounded by aquicludes.

Artesian SystemsArtesian Systems

• Artesian well – If the top of the well is lower in altitude than the recharge area, the water will flow out of the well without pumping.

• A freely flowing spring supplied by an artesian aquifer is an artesian spring.

Mining GroundwaterMining Groundwater

• The volume of stored water is steadily diminishing because withdrawal exceeds natural discharge.

• Groundwater can also be a nonrenewable resource.

Land SubsidenceLand Subsidence

• The water pressure in the pores of an aquifer helps support the weight of the overlying rocks or sediments.

• Pressure is reduced when groundwater is withdrawn.• Land surface subsides as a result of this.• Pisa’s famous Leaning Tower leans because of

subsidence.• The tower was built on unstable sediments and began to

tilt when construction began.• The tilting increased when water was withdrawn from

deep aquifers.• Groundwater withdrawal is strictly controlled.

Water QualityWater Quality

• Much of the world’s water is unfit for human consumption.

• Many compounds are dissolved in water.• The composition of groundwater varies from

place to place according to the kind of rock in which the water occurs.

• Hard water for example has calcium and sodium bicarbonates.

• Soft water is just the opposite, it is found where volcanic rocks and sandstone are common.

GroundwaterGroundwater

• Water flowing through sulfur-rich rocks may contain hydrogen sulfide, which smells like rotten eggs.

• Common sources of water pollution is sewage.• Septic tanks, sewers, and barnyards

contaminate groundwater.• If contaminated water passes through a rock

with large pores, it can travel long distances and remain polluted.

Pollution by Sewage: GroundwaterPollution by Sewage: Groundwater

• If contaminated water percolates through sand, it can become purified within short distances.

• Sand is an excellent cleansing agent:– It filters out bacteria.– Oxidizes bacteria.– Places bacteria in contact with other organisms that

consume them.

Purification plants treat water supplies through sand.

Contamination by SeawaterContamination by Seawater

• Fresh groundwater is separated by seawater by a thin transition zone of brackish water.

• If freshwater is pumped from an aquifer then saltwater may move landward toward permeable strata.

• Once intrusion occurs it is difficult to reverse.

Toxic WastesToxic Wastes

• When rain water seeps through landfills, harmful chemicals reach into groundwater reservoirs.

• These are unfit for human consumption and are toxic to animals as well as plants.

• Pesticides and herbicides are sprayed over fields and gardens, some of their chemicals have been linked to cancer.

• DDT depleted the bald eagle population.

Underground Storage of WasteUnderground Storage of Waste

• Radioactive waste:1. Enclosing rocks should have few fractures and low

permeability.

2. The enclosing rock should have no present or future economic mineral potential.

3. Local groundwater should flow away.

4. Only very long paths of groundwater allowed.

5. Low rainfall.

6. Zone of aeration thick.

7. Rate of erosion low.

8. Earthquakes low.

9. Future climate change unlikely to affect groundwater.

Aquifers QuizAquifers Quiz

1. T/F An aquifer is a body of highly permeable rock lying above the zone of saturation.

2. Give two examples of good aquifers.3. An aquifer bounded by aquicludes is called a ______________ .4. The word artesian comes from a French town, Artois. What did the

Romans call this city?5. T/F When groundwater withdrawal exceeds recharge, the water table

rises.6. Give one example of how groundwater can be artificially recharged.7. T/F The water pressure in the pores of an aquifer help support the height

of the overlying rocks or sediments. 8. List three compounds usually found in groundwater.9. Give two compounds found in hard water.10. What two rocks are usually common where soft water is found?11. What mineral smells like rotten eggs?12. Give two reasons why sand is such a good cleansing agent.

DissolutionDissolution

• Dissolution – When minerals and rock materials pass directly into solution.

• Carbonate rocks are the most readily attacked by dissolution.

• Limestone, dolostone, and marble are the most common carbonates.

Chemical Cementation and ReplacementChemical Cementation and Replacement

• Calcite, quartz, and iron compounds are the chief cementing substances.

• Replacement – Is the process by which a fluid dissolves matter already present and at the same time deposits from solutions an equal volume of a different substance.

• Petrified wood is a common example.

Karst TopographyKarst Topography

• Karst Topography – Caves and sinkholes are so numerous that they form a peculiar topography characterized by small basins and a disrupted drainage pattern.

• Names after the Karst region in Yugoslavia.• It is most typical of carbonate landscapes, but it

can develop in areas underlain by dolomite, gypsum, and salt.

Karst TopographyKarst Topography

• It is best developed in moist temperature to tropical regions underlain by thick and widespread soluble rocks.

• The most common is the sinkhole karst, a landscape dotted with sinkholes of various size and shape.

• Cone karst and tower karst occur in thick, well jointed limestone that separates into isolated blocks as it weathers.

Tower KarstTower Karst

• Consists of isolated tower-like limestone hills separated by expanses of alluvium.

• These depressions can slowly fill and form a flat alluvial surface.

• One of the most famous lies in eastern China.• Pavement karst – Broad areas of bare limestone

in which joints and bedding planes have been etched and widened by dissolution, creating a distinctive land surface.

• Found in high-altitude regions.