Geo 110 Unit 3

aquitard

an impermeable layer (clay rock)

aquifer

rock or sediment unit with high permeability and porosity (coarse sediments, sand, sandstone, and gravel)

Perched water table

aquifer with an aquitard underneath located above the water table

Artesian well system

characterized by free flowing water to surface

due to confined aquifer causing high water pressure

folded or curved rock in u shape

City water systems

Artificially high water table created by water tower

What is the best place to build a water tower

best to build a water tower on high ridge to increase pressure

Springs

natural outflow of groundwater onto surface where water table intersects surface

can be perched or not

Hot spring

Spring where water is 6-9 degrees C warmer than annual air temperature

occur in two scenarios

What two scenarios do hot springs occur

1.) 95% heated by hot magma or igneous rock beneath surface (yellowstone)

2.) Transported through folded rock and geothermal gradient (springs east of Rockies)

Geothermal gradient

natural rate at which earth heats up with depth

Geyser

Intermittent hot springs that erupt

1.) Large caverns underground heat water

2.) Water heats but doesn’t boil due to pressure

3.) heated water rises near surface, pressure is reduced and underneath water boils

4.) Eruption, then repeat

What mineral do hotsprings and geysers carry up to the surface

calcite

Cone of depression

Draw down in water table in shape of cone directly around high pumping well

Changes the hydraulic gradient causing water to flow towards draw down

Can change water table height and dry out other wells

Environmental problems associated with ground water

Most stem from treatment of ground water as a non-renewable source where water is withdrawn at a higher rate than refilled naturally

two effects: land subsidence, environmental impacts (saltwater intrusion, and septic and chemical plume movement

ex. High planes aquifer (Nebraska, Kansas, Oklahoma, and Texas), and San Joaquin Valley (California)

Land subsidence

sinking of land due to water withdrawal

Creates sinkholes and other collapsed earth features

Salt water intrusion

in areas by the ocean the salt water will be below the fresh water ground water

well near that boundary that overdraws can cause salt water to intrude into fresh water table

Septic and chemical plume movement

heavily pumped well can cause hydraulic gradient to shift toward pumping well can cause contaminated water to flow toward wells

Best aquifer?

stores a lot of ground water (high porosity) but also cleans it by increasing the time it takes to pass through ground, increasing the removal of contaminants (low permeability)