Chapter I7

Underground Water

Global distribution of water

• Oceans 97.2%

• Glaciers 2.15%

• Groundwater 0.61%

• Lakes 0.01%

• Atmosphere 0.001%

• Rivers 0.0001%

The Distribution of Water on EarthThe Distribution of Water on Earth

The water cycleThe water cycle

• The continuous movement of water on, The continuous movement of water on, above and below the earth’s surface is above and below the earth’s surface is called the water cycle OR hydrologic called the water cycle OR hydrologic cycle.cycle.

The water cycleThe water cycle

• Processes:Processes:

– EvaporationEvaporation

– TranspirationTranspiration

– PrecipitationPrecipitation

Dry Period:Dry Period:

Streams bring in Streams bring in small amounts of small amounts of

water…water…

and carry away and carry away small amounts.small amounts.

DamDam

Wetlands

Wet Period:Wet Period:

Streams bring in Streams bring in large amounts of large amounts of

water…water…

which is stored…which is stored…

and slowly released and slowly released during dry periods.during dry periods.

DamDam

Wetlands

Average U.S. Annual PrecipitationAverage U.S. Annual Precipitation

WaterWater

• Atmospheric water: vaporsAtmospheric water: vapors

• Surface water: rivers. Lakes, Surface water: rivers. Lakes, oceansoceans

• Subsurface water: groundwaterSubsurface water: groundwater

Distribution of underground Distribution of underground waterwater

• 2 zones2 zones– Unsaturated zone: vadose Unsaturated zone: vadose zonezone

– Saturated zoneSaturated zone– Separated by Water TableSeparated by Water Table

Underground materials

•Underground materials may either contain water or they may be dry.

•In order to contain water, they have to be porous and permeable.

Underground materials

•Porosity: is a measure of the material ability to hold water.

•Permeability: capacity of a material to transmit water.

PorosityPorosity varies withvaries with % Cement% Cement

SortingSorting

FracturingFracturing

MORE POROUSMORE POROUS LESS POROUSLESS POROUS

NoncementedNoncementedSandSand

CementedCementedSandstoneSandstone

Porosity Porosity Varies with %Varies with % Cement Cement

MORE POROUS LESS POROUS

Well SortedWell SortedSandSand

Poorly SortedPoorly SortedSandSand

Porosity Porosity Varies withVaries with Sorting Sorting

MORE POROUS LESS POROUS

Fractured ShaleFractured Shale Unfractured ShaleUnfractured Shale

Porosity Porosity Varies withVaries with Fracturing Fracturing

Porosity and Permeability of Porosity and Permeability of Different Aquifer TypesDifferent Aquifer Types

Type of AquiferType of Aquifer PorosityPorosity PermeabilityPermeability

GravelGravel Very HighVery High Very HighVery HighCoarse- to fine sandCoarse- to fine sand HighHigh HighHighFine-grained sand & siltFine-grained sand & silt ModerateModerate Mod - LowMod - LowSandstone, mod. cementedSandstone, mod. cemented Mod - LowMod - Low LowLowFractured ShaleFractured Shale LowLow LowLowMetamorphic RocksMetamorphic Rocks LowLow Very LowVery LowUnfractured ShaleUnfractured Shale Very LowVery Low Very LowVery Low

AquifersAquifers

• Any geologic material which Any geologic material which can yield water in significant can yield water in significant amounts.amounts.

• Aquifers must be porous and Aquifers must be porous and permeable.permeable.

• Any geologic material which Any geologic material which cannot hold and transmit cannot hold and transmit water is called Aquiclude.water is called Aquiclude.

Types of aquifers

•2 types–Unconfined aquifer–Confined aquifer

•Unconfined aquifer: no confining layer on top of the saturated zone

Unsaturated Zone:Unsaturated Zone:Pores include both air and water

Saturated Zone:Saturated Zone:Pores filled with water

Groundwater Table

Unconfined AquiferUnconfined Aquifer

•Confined aquifer: the saturated zone is capped by a confining layer.

•Good aquifers include;–Unconsolidated deposits–Sandstone–Conglomerate–Jointed limestone

•Good aquicludes are;–Shales–Granite–Marble

Springs

•A spring forms where underground water flows naturally onto the land surface.

•A spring occurs when water table intersects the land surface.

Groundwater erosion and deposition

•Depending on the chemical environment, water erodes the material over which it moves.

•Later on the eroded material is deposited at another location.

Groundwater erosion and deposition

•Erosional features:–Caves–Sinkholes–Karst topography

• Caves: underground Caves: underground chambers large enough for chambers large enough for humans to enter into it.humans to enter into it.

– Speleothems: calcite Speleothems: calcite deposits formed by dripping deposits formed by dripping water from cave ceiling.water from cave ceiling.

Two types of speleothems:Two types of speleothems:

•Stalactites: pendants of Stalactites: pendants of calcite hanging from roof calcite hanging from roof ceiling ceiling

•Stalagmites: cone-shaped Stalagmites: cone-shaped bodies of calcite formed on bodies of calcite formed on cave floor.cave floor.

Mammoth Cave, KYMammoth Cave, KY

•Sinkholes: depressions formed by the collapse of a cave roof.

•Karst topography: an area underlain by numerous caves and sinkholes.

Subsurface Features of a Karst LandscapeSubsurface Features of a Karst Landscape

Dishman Lane collapse, Bowling Green Ky.Dishman Lane collapse, Bowling Green Ky.

Feb. 2002Feb. 2002

Depositional features

•Petrified wood•Geodes•Concretions

•Petrified wood: organic material is replaced by silica.

•Geodes: partly filled bodies of silica having crystals of quartz or calcite.

•Concretions: calcite or silica carried by groundwater can replace original material such as shells, bones or twigs.

High-temperature underground water

•Hot springs: water temp. is higher than 37º C.–Water gains heat from hot igneous bodies

–Water may also be heated through deep circulation.

• Geysers: type of hot spring that periodically erupts hot water (100º C) and steam.

• Eruption may be regular as in Old Faithful geyser….79 mins. 45-105 mins

• Irregular eruptions are common. Ranging from days to weeks.

Hydrothermal Systems Hydrothermal Systems Water enters the ground Water enters the ground by infiltrationby infiltration

Heated water Heated water begins to rise begins to rise

Hot Springs:Hot Springs: form when form when heated groundwater heated groundwater reaches the surface reaches the surface

Geysers:Geysers: form where a form where a complicated plumbing complicated plumbing system allows steam system allows steam

pressure to be built up, pressure to be built up, causing intermittent causing intermittent

eruptions eruptions

•Hot water deposits: calcite deposited in the form of travertine.

Geothermal energy

• Electric power can be generated from the hot water and steam from a hot spring.

• San Francisco Geysers field. 2000 MW. Mostly used for room heating.

Water Contamination

•Water is considered contaminated when it is harmful to human use.

•Sources of water contamination:–Agricultural activities–Human wastes–Industrial effluents

•Agricultural Activities

–Herbisides–Pesticides–Fertilizers–Animal wastes–Slaughter houses

•Human wastes

–Household garbage–Septic tanks–City landfills

• Industrial wastes:

–Heavy metals from industries

–Mine wastes–Radioactive wastes

Remediation

•Natural remediation•Site selection

–Yucca Mountains, Nevada•Sealing landfills:

–Geosynthetics, geotextiles–Clay blankets