Groundwater Notes - Earth's Environment

Earth’s EnvironmentEarth’s Environment

Lecture Outline : GroundwaterLecture Outline : Groundwater

Where is the water on Earth?Where is the water on Earth?

Look at the next slide’s diagram. In it Look at the next slide’s diagram. In it you’ll see that most of the water on Earth you’ll see that most of the water on Earth is salt water. Out of the fresh water, most is salt water. Out of the fresh water, most is frozen. Groundwater makes up the is frozen. Groundwater makes up the largest portion of fresh, liquid water on largest portion of fresh, liquid water on Earth.Earth.

Where is groundwater and how Where is groundwater and how does it get there?does it get there?

The Water Cycle shows us how water The Water Cycle shows us how water moves from phase to phase (gas, liquid moves from phase to phase (gas, liquid and solid) and from place to place on and solid) and from place to place on Earth.Earth.

Water that infiltrates into the earth Water that infiltrates into the earth becomes groundwater.becomes groundwater.

Where do you find Where do you find groundwater?groundwater?

Groundwater can be found in between Groundwater can be found in between individual pieces of sediment in a layer of individual pieces of sediment in a layer of unconsolidated material (not solid rock, unconsolidated material (not solid rock, but layers of sand, gravel, silt, etc.)but layers of sand, gravel, silt, etc.)

Groundwater can also be found in the Groundwater can also be found in the spaces that exist within solid rock.spaces that exist within solid rock.– Either pore spaces between individual grainsEither pore spaces between individual grains– Or in cracks that exist in solid rockOr in cracks that exist in solid rock

Intergranular = pore spaces in solid rock Intergranular = pore spaces in solid rock or unconsolidated materialor unconsolidated material

Fractured bedrock = cracks in solid rockFractured bedrock = cracks in solid rock

Solution enhanced = cracks that have Solution enhanced = cracks that have been enlarged by groundwater dissolving been enlarged by groundwater dissolving rock rock

Types of AquifersTypes of Aquifers

An aquifer is a layer of sediment or rock An aquifer is a layer of sediment or rock capable of holding and transmitting capable of holding and transmitting significant quantities of water.significant quantities of water.

Aquifers that have an impermeable layer Aquifers that have an impermeable layer above and below them are called above and below them are called “confined aquifers”“confined aquifers”

What’s an impermeable layer? A layer of What’s an impermeable layer? A layer of rock or sediment that doesn’t allow water rock or sediment that doesn’t allow water to flow through easily.to flow through easily.

Unconfined aquiferUnconfined aquifer

Also called a “Water Table” aquifer, this Also called a “Water Table” aquifer, this type does not have an impermeable layer type does not have an impermeable layer above the aquifer.above the aquifer.

See the next slide for a diagram showing See the next slide for a diagram showing two confined aquifers and one unconfined two confined aquifers and one unconfined aquifer.aquifer.

The Confining beds are also called The Confining beds are also called aquitards. They retard, or slow, the flow of aquitards. They retard, or slow, the flow of

water.water.

Other termsOther terms

The water table is the top of the saturated The water table is the top of the saturated zone.zone.

The saturated zone is the layer in the The saturated zone is the layer in the aquifer where every pore space or every aquifer where every pore space or every crack is completely filled with watercrack is completely filled with water

The unsaturated zone exists above the The unsaturated zone exists above the saturated zone, and may have moisture, saturated zone, and may have moisture, but the pore spaces or cracks also contain but the pore spaces or cracks also contain air.air.

Vadose zone and zone of aeration are Vadose zone and zone of aeration are other words for the unsaturated zone. other words for the unsaturated zone.

Water from the saturated zone can move Water from the saturated zone can move upward through capillary action into the upward through capillary action into the unsaturated zone.unsaturated zone.

Water table divides the two zones. The Water table divides the two zones. The position of the water table will vary. More position of the water table will vary. More

recharge raises the water table. recharge raises the water table.

Source of water – UnconfinedSource of water – UnconfinedIn an unconfined aquifer, water will seep into In an unconfined aquifer, water will seep into the ground directly above the aquifer. This is the ground directly above the aquifer. This is the recharge area.the recharge area.

Source of water - ConfinedSource of water - Confined

In a confined aquifer, the overlying aquitard In a confined aquifer, the overlying aquitard prevents water from the surface from prevents water from the surface from seeping into the aquifer.seeping into the aquifer.

Recharge, therefore, often comes from far Recharge, therefore, often comes from far away, in a place where the aquifer meets up away, in a place where the aquifer meets up with the surface.with the surface.

See the illustration on the next page.See the illustration on the next page.

GROUNDWATER RECHARGEGROUNDWATER RECHARGE

Groundwater entering the Groundwater entering the ground = RECHARGEground = RECHARGE

Recharge comes from direct precipitationRecharge comes from direct precipitation

Or snow meltOr snow melt

Or, in certain situations, it can come from Or, in certain situations, it can come from a streama stream

PrecipitationPrecipitation

Streams as a source of groundwater Streams as a source of groundwater recharge recharge (mostly in dry climates)(mostly in dry climates)

In locations where the In locations where the water table is below the water table is below the bottom of the stream, bottom of the stream, water from the stream water from the stream can run into the ground can run into the ground and feed the and feed the groundwater.groundwater.

This is called a losing This is called a losing stream or an influent stream or an influent stream.stream.

Induced recharge into wells Induced recharge into wells from streamsfrom streams

There are some situations where, even in There are some situations where, even in humid climates, water from streams ends up humid climates, water from streams ends up in wells. This occurs when a pumping well is in wells. This occurs when a pumping well is located in an aquifer near a river. Water located in an aquifer near a river. Water from the river is pulled into the pumping well. from the river is pulled into the pumping well. These tend to be very productive wells – These tend to be very productive wells – there’s a constant source of water. However, there’s a constant source of water. However, it is river water, albeit, filtered through the it is river water, albeit, filtered through the ground, but there can be quality issues.ground, but there can be quality issues.

Streams feeding groundwater through “Induced Recharge”Streams feeding groundwater through “Induced Recharge”

GROUNDWATER DISCHARGEGROUNDWATER DISCHARGE

Groundwater DischargeGroundwater Discharge

Groundwater can be discharged from the Groundwater can be discharged from the aquifer either through a aquifer either through a – Pumping wellPumping well– Or a streamOr a stream

Pumping wells lower the groundwater Pumping wells lower the groundwater through “drawdown”through “drawdown”

Drawdown often forms a cone-shaped Drawdown often forms a cone-shaped depression around the well, called a “cone depression around the well, called a “cone of depression.”of depression.”

Groundwater is also discharged Groundwater is also discharged into surface streams, wetlands into surface streams, wetlands and lakes (in humid climates).and lakes (in humid climates).