Groundwater Depletion

Groundwater Water that moves downward into Earth’s surface due to gravity. Water stored underground in pore spaces of rock layers. Water in soil or rock that supplies springs and wells.

Permeable and Impermeable Layers permeable material allows water to pass through (sponge, bread, sandstone) impermeable materials do not allow water to pass through; also called aquitards or aquicludes Examples of this type of material include: clayshale bedrockgranite

Permeability Permeability – ability of rock to allow water to pass through Depends on the extent to which pores are connected to each other and the size of the pores - Examples:sand, gravel - permeable silt - less permeable clay and shale - impermeable

Permeability: allows water to pass through

Porosity The amount of water that soil or rock can hold depends on its porosity. Porosity is the % of a material’s volume that is pore space.

Porosity Porosity = Volume of Pores x 100 Total Volume High PorosityLow Porosity

Sometimes a material is porous but it won’t let water pass through. Cork is an example. If it let liquid through, it would leak out of the bottles! Pumice is pitted with holes but can float because water can’t get into it. In both cork and pumice, the pores are not connected to each other. Porous but not permeable …

Main Types of Porosity in Rocks In rocks that hold groundwater, the water fills the spaces between sand grains or in rock crevices and in limestone openings.

Particle Shape Rounded particles create more porosity while angular particles have less porosity. rounder = more porous

Particle Sorting Well sorted (same size) particles have greater porosity while poorly sorted (mixed size) particles have less porosity. uniform size = more porous

Aquifers a geologic formation (rock layer) that stores and/or transports water An unconfined aquifer has a permeable layer above A confined aquifer has impermeable layers both above and below it and may be under pressure.

The water table is the top of the water surface in the aquifer. Wells are used to get the water.

GROUNDWATER

Water table The level of the water table can be affected by different factors. These can include:  Amount of rainfall  Amount of time between rains  Season  Slope of the ground  Climate  Human impact

The saturated zone is the area beneath the water table where ALL pore spaces are filled with water. There is NO air in this zone.

Both air and water exist in the pore spaces of the unsaturated zone above the water table.

Recharge areas are surface areas where water seeps in and flows down to refill the aquifer. An aquifer’s recharge area may be far away.

Contamination of aquifers occurs from the surface. Since groundwater moves slowly, contamination continues for many, many years.