1. Chapter 14 - Groundwater
Ms. Martel

2. 14.1 Water in the Ground
Although some rain and precipitation becomes runoff, water also enters the ground where it is stored as groundwater.
Factors that affect the amount of water that seeps into the ground are:
Type of rock or soil on which the water falls.
Climate, topography, vegetation, and land use.

3. Porosity
The amount of water that soil or rock can hold depends upon the amount of space, or pore space, between the grains of the material.
Porosity is the percent of a material’s volume that is pore space.
Factors that affect porosity are:
Particle shape. Rounded particles have more pore space. Flat materials or angular, have less pore space.
Sorting. Materials that are made up of particles that are the same size are well sorted. They are more porous.
Materials that are poorly sorted, ie. Are made up of a mixture of materials fill the porous spaces, reducing the porosity.

5. Permeability
Permeability is the rate at which water or other liquids pass through the pore spaces of a rock.
Typically, permeability increases with grain size because large grained materials have larger pore spaces.
A material that water cannot pass through is called impermeable.
Some of the water that passes through a sediment or rock sticks to particles, forming a film of water.
This film is called capillary water.
Measuring Porosity Mini-Lab

7. The Water Table
When rain falls, it enters the pores in the soil, the water will then continue downward until it reaches impermeable material.
As more rain falls, the part of the ground where all pore spaces are filled is called the zone of saturation.
The upper surface of this zone is called the zone of saturation.
The zone just above the zone of saturation, is called the zone of aeration, because air can enter this region.

8. In between these two zones is the capillary fringe.
The interaction between the water and the soil is called capillary action.
The water table’s distance from the surface depends upon many factors:
Rainfall, amount of time that passes between rains, the season, the slope of the ground surface, the thickness of soil, and the climate.
The water table is important in several ways:
Seepage of water from the water from the water table, keeps the streams flowing between rains and maintains the water levels of swamps and lakes.
It also supplies drinking water to springs and human made wells.

10. Ordinary Wells and Springs
Humans can reach groundwater that does not reach the surface by digging or driving wells into the ground. This is called an ordinary well.
On a hillside where the water table meets the surface, ground water may flow out as a spring.

11. Artesian Formations
Permeable layers of rock and sediment that store and carry groundwater in enough quantity to supply wells are called aquifers.
An artesian formation is when an aquifer dips underground between impermeable rock layers.
Great quantities of water may enter the aquifers of artesian formations. This can create a lot of pressure.
Artesian formations may be broken by cracks in the cap rock called fissures.
Artesian springs rise through these cracks and sometimes form a desert oasis.

13. Hot Springs, Geysers, and Fumaroles
Ground water can become heated if its is at a great depth.
Subsurface temperatures increase with depth, water from deep artesian wells or springs may be much warmer than normal.
In many recent regions of recent volcanic activity, igneous rocks near the surface are hot enough to boil water.
Sometimes volcanic gases make hot groundwater acidic.

14. A geyser is a hot spring that intermittently shoots columns of hot water and steam into the air.
It consists of long, vertical irregularly shaped tube that may extend hundreds of meters into the ground.
Because it is so far down into the Earth, water is heated by surrounding igneous rock etc.
This creates pressure, eventually the heat will rise to the top and steam is finally able to be released.

15. Where fairly recent volcanic eruptions have occurred, groundwater is released as steam, along with other gases, from fissures in the ground called fumaroles.
There are fumarole fields in Iceland and Japan.

16. 14.2 Conserving Groundwater
About 50% of drinking water comes from ground water, humans must conserve and protect ground water supplies.

17. Water Budgets
A water budget describes the income and spending of water for a region.
In a water budget, the income is rain or snow.
The spending includes water lost by use, by runoff, and by evapotranspiration.
If it rains during a time when the plants need little moisture, the extra moisture soaks in the soil, where it is stored between the grains of soil.
This is a time of soil recharge.
If the rain continues so that the soil becomes saturated the surplus water raises the water table or becomes part of a stream runoff.

18. If the need for moisture is greater than the rainfall, the plants can draw water from the soil water supply.
This is a time of soil water usage.
If the need for moisture continues to be greater than the rainfall, all of the water available in the soil may be used up.
When the water storage is gone, a water deficit occurs.

19. Groundwater Conservation
In many regions, humans are using groundwater faster than natural processes can replenish supplies.
In addition, pollution threatens groundwater supplies.

20. Overuse of Ground Water
When ground water supplies are depleted, the water table drops, thus lowering the water level in wells and springs.
This can cause them to go dry.
In coastal regions, this can cause the groundwater levels to fall below sea level, causing salt water to contaminate drinking water. This renders them unusable.
Subsidence occurs when the drop in groundwater causes the group levels to drop.
This compromises foundations of houses buildings, and underground pipes.

22. Groundwater Pollution
Groundwater is recharged by rain seeping down through the soil.
Any pollution agent in the soil becomes part of the groundwater.
This includes oil from roads, nitrated from fertilizers, pesticides from plants, farm wastes, sewage from septic tanks etc.
Hazardous wastes are poisonous by products of some industrial processes.
Toxic chemicals from accidental spills, careless disposal, or rotting underground storage containers pollute the sol around them, and the groundwater its in contact with.

23. For years, toxic wastes were dumped with little care, and their locations were never recorded.
In some cases houses were built on these sites.
When the toxic waste was later discovered, families had to be moved.
As yet, no simple or inexpensive way to purify polluted groundwater is known.
The best measure we have available to us is prevention of pollution in the first place.

24. 14.3 Groundwater and Geology
Minerals in Groundwater
When water evaporates to become water vapor, it leaves impurities behind.
As groundwater passes through the lower soil layers or bedrock, it dissolves minerals.
Much of this dissolved mineral matter remains in the groundwater.
When ground water contains large amounts of ions from dissolved minerals, it is called hard water.
Calcium ions are the most commonly found ions in hard water.

25. The ions of hard water interfere with the use of water.
In hot water pipes, groundwater containing dissolved minerals leaves behind deposits called boiler scale.
Artesian water is usually harder than ordinary groundwater. It usually is able to dissolve more minerals because of the heat.
By contrast, ordinary groundwater is almost always harder than river water.

26. Mineral Deposits by Groundwater
When groundwater that contains dissolved mineral cools or evaporates, mineral deposits are left behind.
Hot groundwater often leaves deposits of minerals in bedrock cracks and fissures.
Such mineral veins may contain quartz, calcite, gold, and silver.
Petrified wood is formed when minerals dissolved in groundwater replace the decaying wood of buried trees.
Perhaps the most important groundwater deposit is the cement that binds together sand grains and pebbles to form sedimentary rocks.

27. Mineral Springs
A spring with a high concentration of mineral matter is called a mineral spring. The high mineral content of the water may be due to any of the factors below:
Water passes through rock containing easily-dissolved minerals.
Water contains large quantities of gases, such as CO2 and hydrogen sulfide, that form acids when mixed with water.
Water dissolves minerals more easily because its very hot.

28. Caverns
Limestone is a common bedrock t hat dissolves more easily than some other types of rock.
Limestone is dissolved by the carbonic acid found in groundwater.
Frequently, limestone formations are split by fissures that run down from the surface and by cracks that run horizontally between the beds.
After thousands of years, the cracks between beds become so large that they form networks of underground tunnels.
These tunnels are called caverns, or caves.