GEOL107: Chapter 11 Groundwater

Ground water

Water that lies beneath the ground surface, filling pores in sediments and sedimentary rocks and fractures in other rock types

What percentage of the hydrosphere does groundwater represent?

0.6%

Porosity

the percentage of rock or sediment that consists of voids

Porosity

measure of a rock's ability to hold water

Permeability

the capacity of a rock to transmit fluid through pores and fractures

Permeability

the interconnectedness of the pores within a rock

What are some examples of porous and permeable rocks?

Sandstones and conglomerates

What are some examples of porous and impermeable rocks?

Granites, schists, and unfractured limestones

Water table

Subsurface zone in which all rock openings are filled with water is the phreatic, or saturated zone

Where is the water table located?

the top of the saturated zone

What is the area above the water table called?

unsaturated zone/vadose zone

What is a perched water table?

an accumulation of groundwater that is above the water table in the unsaturated zone

Movement of ground water through pores and fractures is relatively _____ ( ____ to ____/day) compared to flow of water in surface streams

Slow, cms, meters

What does the flow velocity of groundwater depend on?

The slope of the water table and the permeability of the material

Aquifier

body of saturated rock or sediment through which water can move easily

What types of rocks commonly make up aquifers?

Sandstone, conglomerate, well-jointed limestone, sand, gravel, and highly fractured volcanic rock

Aquitard

rock/sediment that retards (repels) ground water flow due to low porosity and/or permeability

What types of rocks commonly make up aquitards?

Shale, clay, and unfractured crystalline rocks

Unconfined aquifer

aquifer in which there is no impermeable layer restricting the upper surface of the zone of saturation

Confined aquifer

an aquifer surrounded by a layer of impermeable rock or clay that impedes water flow

Well

a deep hole dug or drilled into the ground to obtain water from an aquifer

The water table can be lowered by pumping, a process known as _____ .

drawdown

Water may rise to a level above the top of a confined aquifer, producing a(n) _____ .

artesian well

Spring

a place where water flows naturally from a rock or sediment onto the ground surface

Examples of contamination in the water table

Pharmaceuticals
Pesticides/herbicides
Fertilizers
Feed lots
Mercury and gold mining
Landfill pollutants
Heavy metals
Bacteria, viruses and parasites from sewage
Industrial chemicals (PCBs, TCE)
Acid mine drainage
Radioactive waste
Oil and gasoline

If ground water is withdrawn more rapidly than it is recharged, what happens to the water table?

The water table will drop.

When the water table drops, what happens to the ground level?

The surface of the ground drops as buoyancy from ground water is removed, allowing rock or sediment to compact and sink.

Subsidence can crack foundations, roads and pipelines.

Caves

naturally-formed underground chambers

How are caves formed?

Acidic ground water dissolves limestone along joints and bedding planes

Caves near the surface may collapse, producing _____ .

Sinkholes

Rolling hills, disappearing streams, and sinkholes are common in areas with _____ .

Karst topography

karst topography

an area that has a land surface or topography with numerous depressions called sinkholes

Hot springs

springs in which the water is warmer than human body temperature

How are hot springs formed?

Ground water is heated by nearby magma bodies or circulation to unusually deep (and warm) levels within the crust

Hot water is less dense than cool water, and thus rises back to the surface on its own

Geysers

hot springs that periodically erupt hot water and steam

Geothermal energy

Energy derived from the heat in the interior of the earth

How is geothermal energy produced?

using natural steam or superheated water

Gaining streams

streams that gain water from the inflow of groundwater through the saturated zone

Losing streams

lose water to the saturated zone