Groundwater

Water Cycle

Fill in Your Water Cycle

After Precipitation:

• Runoff: It can form rivers, flow downhill over the land surface back to the sea

• It can be used by plants and animals.• It can be stored in ponds, lakes or glaciers.• Infiltration (percolate): it can soak into the

ground and become part of the groundwater system.

Groundwater

• Water found in the cracks, crevices and pore spaces in the material of the Earth.

Porosity

• Porosity: the space between solid particles of soil or rock that can be filled with water, air, gas or oil.

• Porosity is affected by: Sorting, Packing, and Grain Shape.

Well sorted, irregular, loosely packed sediments have greatest porosity (i.e. Gravel).

Permeability

• Permeability: The ability of a rock or sediment to allow fluids to pass through its open pore spaces.

• The larger and better sorted the particles are, the more permeable the rock or sediment tends to be.

• Large gravel has best permeability (best aquifer)

• Sandstone also has good permeability (good aquifer)

• Clay has very bad permeability. The flat, fine grains make it impermeable

• Impermeable: Water cannot flow through this type of sediment.

Check for Understanding

• Which rock type would have the best porosity and permeability?

A. Loose, well sorted gravelB. Compacted, well sorted

sandstoneC. ClayD. Loose, poorly sorted gravel

Answer: A. Loose, well sorted gravel

Rock types and porosity: In general, well sorted = good porosity and very permeable.

Groundwater in Virginia

• What type of rock would hold groundwater in the Valley and Ridge Province?

• Answer: Limestone (in caves/caverns)• What type of rock would hold groundwater in the Blue Ridge

Province?• Answer: Granite (in the cracks)• What type of rock would hold groundwater in the Coastal Plain

Province?• Answer: In sand and sandstone and gravel

Groundwater Zones:

• Belt of Soil Moisture: Water collected directly by rain and used by plants

• Zone of Aeration: pore spaces are filled with air

• Zone of Saturation: pore spaces are filled with water

• Water Table: boundary between zones of aeration and saturation

• Capillary fringe: small amounts of water just above the water table held by capillary action

• Capillary action is caused by the attraction of water molecules to other materials.

Aquifers• A layer of soil or rock that can hold ground water• Confined layer (Impermeable Layer/Aquiclude): water cannot pass

through• Aquitard: layer of rock that makes it difficult for water to move.• Recharge: where water enters the groundwater system

Artesian Aquifer

• Artesian aquifer: An artesian aquifer is a confined aquifer containing groundwater that will flow upwards through a well without the need for pumping. Porous stone is confined between impermeable rocks or clay. This keeps the pressure high, so when the water finds an outlet, it overcomes gravity and goes up instead of down.

• Spring: A place where groundwater flows naturally from the ground. An intersection between the ground surface and the water table.

Cone of Depression

• Forms when more water is discharged (drawn out) from a well faster than the recharge rate. Can dry up other nearby wells.

Saltwater Intrusion and the Chesapeake Bay

• Because of density differences. Salt water is more dense and sits below freshwater.

• But pumping of all the freshwater allows saltwater to migrate upwards.

• Seasonal changes in rainfall also have an effect.

Geysers

• Geysers are formed over areas of volcanic activity such as Yellowstone National Park where magma is close to the surface.

• The magma heats the groundwater and due to pressure, forces the water upward.

• Old Faithful, is a Geyser.