GROUNDWATER

Sources of fresh water on Earth

GROUNDWATER

GROUNDWATER

• Basic information

• Definition and explanation

• water below Earth’s surface occurring in open spaces including fractures, joints, faults or other spaces between rock particles

• amount of groundwater is strongly influenced by magnitude of infiltration which is affected by other paths taken by precipitation in hydrologic cycle

GROUNDWATERwater in pores between sediments

water in fractures, faults, cracks

water in larger openings like vugs or caves

GROUNDWATER• Kinds of groundwater

• connate--entrapped brackish water

• juvenile--water originating directly from a magma

• meteoric--fresh circulating water which is the type commonly referred to as “groundwater”

• Qualities of rock materials in respect to contained groundwater

• porosity

• is a measure of water capacity of a rock material

• high porosity= contains a lot of water

GROUNDWATERhigh porosity --well sorted

low porosity--- poorly sorted

high porosity-- small platy sediments—well sorted

most sandstones most conglomerates—filling of openings

mudstones and shales

low porosity—igneous and metamorphic rocks

GROUNDWATER• permeability

• a measure of the ability of water to be transmitted by a substance

• is proportional to the degree of interconnected voids between particles

• larger open spaces in a rock will favor a higher degree of interconnection between openings

• moving water is filtered and stays pure• some rocks have high porosity but low

permeability which would yield low quality groundwater (shales, claystones, pumice)

GROUNDWATERhigh permeability—most sandy materials--sandstones

high permeability—well connected cracks

low permeability—mudstones-shales low permeability--pumice

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• specific yield

• the percent water obtained from a substance

• specific retention

• the percent water retained by a substance after water extraction

• an example of a non rock substance displaying specific yield and retention would be a sponge in which after squeezing out all water there still remains some water

GROUNDWATER• aquifer and aquiclude (aquitard)

• aquifer is a (high) permeable substance

• aquiclude is a (low) permeable substance

• Unconfined and confined groundwater

• Definitions

• unconfined

• groundwater in an aquifer with a lower barrier to movement caused by the presence of an aquiclude below, but not an upper barrier allowing water to fluctuate over distances upwards

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Unconfined water

free to move up, but not down

aquitard--aquiclude

confined groundwater in an aquifer with a lower and upper barrier for movementthere is an aquiclude located immediately above and below the aquifer

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aquitard--aquiclude confined water

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• Unconfined groundwater

• zone of saturation

• area of open space in rocks filled with water

• area with highest concentration of water

Groundwater zones

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Zone of Saturation

GROUNDWATER• water table

• is the upper level of the zone of saturation

• water table for unconfined groundwater can fluctuate up and down over relatively large levels

• zone of aeration (vadose zone)

• area above water table unsaturated with water and openings filled primarily with air

• small amounts of water present by retention and capillary action

• capillary action is greatest in the capillary fringe area

Groundwater zones

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Vadose or Aeration zone

Capillary Fringe Area

Water Table

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vadose (aeration) zone--unsaturated zone of saturation

water table

GROUNDWATER• changing levels of water table

• lowering (discharge) of water table takes place if the following usage is greater than replenishment to zone of saturation

• continued pumping of groundwater• plant usage• leaking of water at the Earth’s surface into

streams and lakes• rising (recharge) of water table

• rate of replenishment (primarily by infiltration) is greater than rate of depletion

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• a spring is a natural surface emission of groundwater--streams can form this way and many streams in the Ozarks are spring-fed--a hot spring is about 10-15 degrees F warmer than local annual mean air temperature because of an association of water with subsurface igneous intrusion

Mammoth Hot Springs in Yellowstone National Park

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Hot spring distribution in the USA

Old Faithful Geyser in Yellowstone National Park

A geyser is a hot spring which ejects steam and water at the surface with great force and in some cases at a consistent interval(see example below)

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• interrelationship of groundwater and streams

• in some cases streams can directly supply groundwater and vice versa

• an effluent (gaining) stream is supplied by groundwater and abundant in humid climates— a type of spring

GROUNDWATER• an influent (losing) stream supplies

water to the zone of saturation and is characteristic for arid climates— not a spring

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a spring forming a river or lake a spring gushing out from cracks

More Kinds of Springs

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springs from limestone aquifers

springs from faults or fractures etc.

spring from water forced up encountering a less or non permeable rock

A spring related to a perched water table

(this arises when there is groundwater in the zone of aeration above the main or regional water table)

GROUNDWATER• pumping of groundwater

• heavy pumping can cause a cone of depression of the water from drawdown and may leave many shallower wells dry at the surface

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• Confined groundwater

• artesian water can be a special type of spring

• flowage of subsurface water in a confined aquifer causes a pressure surface level which defines the level to which water can naturally rise

• if a surface opening is connected to the aquifer and is below the pressure surface, water can flow naturally at surface, otherwise it must be pumped

Confined artesian water

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• Groundwater effects in carbonate rocks

• Subsurface solution and precipitation effects

• chemical mechanism

• carbonate rock is dissolved by acids forming caves or caverns

• cave precipitates (speleothems) can form when the groundwater rich in dissolved limestone material becomes less acid

GROUNDWATERMost caves form below the water table, these formed above the water table

GROUNDWATER• some famous caves and speleothems

• famous caves are : Mammoth Cave , Kentucky; Shenandoah Caverns, Virginia; Carlsbad Caverns, New Mexico; Onondaga and Merimac Caverns, Missouri

• Missouri has more mapped caves than any other state and is called the “Cave State”

• the main speleothems are:1)stalactites which grow from the cave roof; 2)stalagmites which grow from the cave floor;3)columns which result from stalactites and stalagmites merging

Speleothems

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GROUNDWATER more speleothems

GROUNDWATER• Surface features

• Karst topography is a pitted looking Earth surface resulting from subsurface solution action and include sinkholes and solution valleys--enormous sinkholes are an example of mass wasting

Large sinkhole in Florida

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• Groundwater and stream pollution problems

• as mentioned before there is a strong interrelationship between streams and groundwater and if one is polluted or tainted the effects can be transferred to the other

GROUNDWATER• Saltwater encroachment and pollution of

groundwater

• pumping effects or mixing of groundwater and saltwater near ocean areas can cause undesirable effects or pumping too much water can cause the rising of salt water

GROUNDWATER• Septic tank leaks

• Sequiota Springs in Springfield is a good example of this

Another example of septic tank leakage

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• Landfills and industry

• landfills

• have evolved from “dumps” to a “state of the art” way to contain our wastes

• layers of clay and plastic liners at the bottom of the fill have recently been used to help contain leach ate

• landfills have been constructed on top of impermeable layers of rock like shale to help contain leach ate

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• industry

• guilty of dumping pollutants into streams and groundwater and adding by-product gases to the atmosphere resulting in acid rain

• waste water treatment facilities have also emitted elevated levels of phosphates and other toxic metals into streams--high concentrations of algae thrive on phosphates

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• Storm water runoff

• results from urbanization can cause a decrease of natural infiltration of precipitation in the subsurface causing greater runoff and flooding

• flooding can cause pollution