chapter 16 groundwater

Porosity

a % measure of the amount of empty space (pore or void space) between sedimentary grains or within cracks and fractures of rocks.

Permeability

 is the ability for liquids & gas to pass through connected pores.

Aquifers

a body of porous rock or sediment saturated with groundwater.

Unconfined aquifers

a groundwater reservoir where the water table, the upper surface of the saturated zone, is at atmospheric pressure and directly connected to the land surface.

Confined aquifers

an aquifer below the land surface that is saturated with water.

Aeration

mixture of dry, soil, water wet soil particles, rock, and air.

Capillary fringe

transition zone between aeration and saturation. 

Saturation

soil or rock where the pores are full of water and no air; like a sponge full of water

How springs form

When groundwater, under pressure from an aquifer, emerges at the Earth’s surface through natural opening.

How groundwater flows in general

From areas of high hydraulic head, often following the slope of the water table

Caves

• Slightly acidic groundwater flows along a crack or fracture in soluble bedrock and eventually enlarges it. 

• Caves form if the dissolved portion is large enough that a human can enter it 

• Usually found in limestone but also in marble, gypsum, & rarely halite. 

• What types of rocks occur in caves

Stalactites

A mineral formation that hangs from the ceiling of a cave, hot spring, or other structures like a bridge or mine

Stalagmites

An upward-growing mound of mineral deposits that have precipitated from water dripping onto the floor of a cave

Cone of depression

A circular area surrounding a well where groundwater levels are reduced from pumping

Salt water intrusion

The denser salt water will flow under the less dense fresh water and will eventually mix forming unpleasant tasting water

Threats to groundwater

Groundwater contamination and depletion pose significant threats to groundwater resources, according to geology. These threats are primarily caused by human activities, but also by natural geologic processes.