Chapter 11 – WATER UNDER THE GROUND

Freshwater Underground• Ground water

– Subsurface water contained in pore spaces in regolith & bedrock

Freshwater Underground• Zone of aeration

– Mix of air & water

• Zone of saturation– Saturated with

water• Water table

– Top of saturated zone

• How groundwater moves– Porosity

• % of total volume of rock body or regolith made of open spaces (pores)

– Permeability• Measure of how easily a solid

allows fluids to pass through it

Freshwater Underground

• How groundwater moves– Hydraulic gradient

• Change in elevation divided by distance• Used to

determine rate of groundwater flow

Freshwater Underground

• How groundwater moves (continued)– Percolation

• Groundwater seeps downward

– Recharge• Replenishment of

groundwater– Discharge

• Subsurface water leaves saturated zone

• Becomes surface water– Spring

• Occurs where water table intersects land surface

Freshwater Underground

• How groundwater moves (continued)– Other methods of discharge

• Hot springs• Geysers

Freshwater Underground

• Where groundwater is stored– Aquifer

• Rock body or regolith that is water saturated, porous, & permeable

– Aquiclude• Layer of

impermeable rock

Freshwater Underground

• Where groundwater is stored– Aquifer

• Unconfined• Confined• Potentiometric

surface– Artesian well

Freshwater Underground

• Groundwater depletion– Cone of depression

• Cone-shaped dip in water table due to pumping

– Groundwater mining• Rates of groundwater withdrawal

continuously exceed rate of recharge

Freshwater Underground

• Groundwater depletion (continued)– Land subsidence

• Compaction– Salt water intrusion

Freshwater Underground

• Groundwater contamination– Contamination

Freshwater Underground

• Dealing with groundwater issues– Enhanced recharge– Conservation– Other sources

• Desalination (i.e. distillation; reverse osmosis; electrolysis)

• Icebergs

Freshwater Underground

• Natural methods– Filtration– Decomposition– Bacterial action

• Human methods– Exterior treatments– Dilution– Chemical

treatments

Freshwater Underground

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Groundwater in the U.S.

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• Groundwater Mining– Recharge rate vs. consumption rate

• Ogallala Aquifer: largest aquifer in U.S. – 225,000 sq miles– Found in 8 states– 30,000 years of

water accumulation

Groundwater in the U.S.

Ogallala Aquifer

Groundwater in Nebraska

Groundwater in Nebraska

What areas seem best suited for groundwater withdrawal?

Why do you think these areas are not utilized?Answer: The Nebraska Sandhills However, Crops do not grow well in sand, so the area is primarily used for ranching.

Groundwater in Nebraska

• When groundwater dissolves rock– Carbon dioxide + water =

carbonic acid• Adds acid to water in atmosphere

& underground

– Calcite + carbonic acid = dissolution

• Calcite dissolves

Freshwater Underground

• Factors of dissolution– Rock composition– Extent of rock fracturing,

jointing, & bedding– Acidity of water– Climate

Freshwater Underground

• When groundwater dissolves rock– Karst topography– Sinkholes– Disappearing streams

Freshwater Underground

• When groundwater dissolves rock– Cave

• Underground open space• Cavern = system of connected

caves • Stalactites• Stalagmites• Columns (pillars)

Freshwater Underground