GROUNDWATER Chapter 14

Objectives

Explain how porosity and permeability affect the storage and movement of groundwater

Describe the water table and features associated with it

Explain how artesian formations affect groundwater

Distinguish among hot springs, geysers, and fumaroles

14.1 Water in the Ground

Groundwater When it rains some of

that water seeps into the ground and is stored there.

Several factors affect how much water seeps into the ground Type of rock or soil Climate Topography Vegetation Land use

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: the percent of a materials volume that is pore space

Porosity

Particle shape Rounded particles

have a lot of pore space

Flat or angular particles have less pore space

Porosity Sorting

Pore space is greatest in materials made up of particles that are all the same size

Mixed materials have less pore space because smaller particles fill the space between larger particles

Permeability

The rate at which water or other liquids pass through the pore spaces of a rock Water passes easily through

materials with large pore spaces

Impermeable: a material that water cannot pass through. ex. fine grained clays and

shale

A material can be highly porous but not at all permeable Ex: Pumice has many

pores, but the pores are not connected so water cannot pass through

Nonporous rocks like granite can become permeable if cracks develop in the rock which allow water to pass through

Zone of Saturation When rain falls, it seeps into the ground until it

reaches an impermeable material Water will begin to fill in the pore spaces above the

impermeable material As more rain falls the water level rises higher and

higher forming a “zone of saturation”

The Water Table The upper zone of saturation is

called the water table

Zone of Aeration

Located between the water table and the surface

A section that has air within the pore spaces

Capillary Action

Capillary Fringe Where the zone

of saturation and the zone of aeration meet

Water rises slightly because the water molecules are attracted to the soil particles (capillary action)

The Water Table

The water tables distance from the surface can change depending on: Amount of rainfall/Climate Time between rains Slope of the ground Thickness of soil

The Water Table

Climate Humid climates: water table is near the

surface in places such as swamps, lakes and rivers

Desert regions: water table may be hundreds of meters below ground

Wells and SpringsAquifer: Permeable layers of rock and sediment that

store and carry ground water in enough quantity to supply wells

Ordinary well: When humans dig

down to the surface of the water table Must be deep enough to

provide water even during dry seasons when the water table may drop

Wells and Springs Springs are formed where the water table

meets the surface Can be the result of a perched aquifer in which

water accumulates on top of an impermeable layer that lies above the water table

Artesian Formations When an aquifer dips underground and is

sandwiched between two layers of impermeable rocks

Gravity moves the water downward and creates pressure

When a well is drilled the pressure causes the water to rise up

Hot Springs

When water comes up quickly through cracks from great depths below the surface

Groundwater may also become hot due to volcanic activity

GeysersA hot spring that intermittently shoots columns of hotwater and steam into the air

Formed from a tube that may extend hundreds of meters below the surface

The water becomes so hot that it expands and releases pressure through steam, pushing water out of the top

14.2 Conserving Groundwater

Objectives

List the factors that affect a water budget

Describe the results of overuse of groundwater

Explain how groundwater becomes polluted

Conserving Groundwater

50% of drinking water in the United States comes from groundwater

Therefore, we must conserve and protect groundwater supplies

Water Budgets

Describe the income and spending of water for

a region. Income = rain or snow Spending = water lost by runoff and

evapotranspiration

Water Budget

Recharge: When extra

moisture that is not needed by plants soak into soil. Leads to a

moisture surplus

Water Budget

Surplus: Occurs when rainfall is greater than

the need for moisture and the soil water storage is filled Water tables rises or water becomes part

of stream runoff

Water Budget

Usage: If the need for moisture > the

rainfall, the plants can draw water from the soil water supply If the need for moisture continues to be

greater than the rainfall, all of the water available in the soil may be used up

Water Budget

Deficit: Occurs when the need for moisture is

greater than the rainfall and the soil water storage is gone.

Groundwater Conservation

In many regions groundwater is being used faster than it can be replenished

Pollution threatens groundwater supplies

Groundwater Pollution

Oil washed from roads Nitrates from soil fertilizers Pesticides Farm Wastes Sewage from septic tanks Controversial drilling techniques such as

fracking and other oil and gas extraction techniques Fracking http://www.cbsnews.com/video/watch/?id=70

54210n

Overuse of Groundwater

When groundwater supplies are depleted, the water table drops Can cause many wells and springs to go

dry

14.3 Groundwater and Geology

Katchner Cavers, AZ

Objectives

Explain how minerals become present in groundwater

Describe how groundwater deposits minerals

List three factors that can cause a spring to have a high mineral content

Describe the role that groundwater plays in the creation of caverns and karst topography

Groundwater and Geology By eroding and depositing rock minerals

groundwater forms many distinctive geologic formations

Mineral in Groundwater

When water evaporates it leaves behind impurities, therefore rainwater contains almost no dissolved mineral

Objective 1 - As groundwater seeps into soil and rock, it dissolves minerals that stay in the water.

Objective 3 - Type of rocks, distance groundwater travels underground, and the water’s temperature all effect the amount of minerals dissolved.

Minerals in Groundwater

When groundwater contains large amounts of ions from dissolved minerals it is called hard water.

Calcium, magnesium, and iron ions found in hard water react with soap to form scum instead of suds.

Hard water can also leave deposits in pipes.

Mineral Deposits by Groundwater

Geyser waters dissolve silica and deposit it on the surface. Creating a geyserite.

Petrified wood is formed when minerals dissolved in groundwater replace the decaying wood cells of buried trees.

Groundwater deposit also create the cement that holds sedimentary rocks together.

Mineral Springs Springs with a high

concentration of mineral matter is called a mineral spring

Some of these spring areas have become health resorts (Hot Springs AK, Pagosa Springs, CO)

In desert regions alkali mineral springs may be poisonous.

Springs can also leave behind deposits. Calcite deposits are called travertine.

Tonto Natural Bridge, AZ

It is believed to be the largest natural travertine bridge in the world. The bridge stands 183 feet high over a 400-foot long tunnel that measures 150 feet at its widest point

Caverns Limestone is a common

bedrock that dissolves easily

When rainwater containing carbonic acid seeps into the ground limestone dissolves and forms caves.

Caves fill with water and slowly dissolves more limestone to create underground tunnels called caverns

Caverns When ground water drips

from the roof of a limestone cave it slowly deposits calcite, creating stalactites

Underneath the stalactites where the water drips to the ground it forms stalagmites.

Sometimes stalactites and stalagmites meet to form columns.

Karst Topography In some regions,

rainwater enters the ground through sinkholes.

Sinkholes are formed because carbon dioxide in the water has dissolved some of the rock beneath the surface.

Some sinkholes are shallow while others are deep enough to form ponds or lakes