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Groundwater

Groundwater contamination

Groundwater chemistry

Karst

Caves

Monroe & Wicander p. 330-335

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Groundwater Contamination

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Groundwater Contamination

Contaminated groundwater moves away fromsource of contamination in a contaminant plume

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Groundwater Contamination

Can map contaminant

plume Trace plume back to

source ofcontamination

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Groundwater Remediation

Dilution is one option

Removal is anotheroption

Removal typically byinjection and pumping

Sometimes removalby biological agents

(bioremediation) All of this is

EXPENSIVE!

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Groundwater Chemistry

Recall that dissolvedcarbon dioxide inwater creates a weak

acid carbonic acid Groundwater contains

mostly dissolvedsulfates and

bicarbonates of Ca,Mg, Na, K and Fe

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Groundwater Chemistry

Amount (andcomposition) of dissolvedmaterial in water dependson rocks the water flows

through

Hard water contains lotsof dissolve material

Soft water contains little

dissolved material

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Groundwater as a Geologic Agent

Creates distinctlandscapes in regionssusceptible to

chemical weathering Karst landscapes

created bydissolution-

precipitation reactions

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Karst

Dissolution

Limestones,dolostones and

marbles react mostreadily

Weathering results innear total removal ofcarbonate rock overtime

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Karst

Cementation

Groundwatereventually becomes

saturated with certainions (e.g. Ca, Mg, Si)

These materialsbecome precipitated

as cements betweenmineral grainselsewhere

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Karst

Replacement

Less commonprocess where water

dissolves matteralready present and ,at the same time,deposits from solutionan equal volume of adifferent substance

(e.g. petrified wood)

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Karst

Caves

Come in all sizes

Interconnected cavechambers andsystems called

caverns Form cave networks

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Cave Networks

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Cave Formation

Dissolution along joints or bedding planes nearwater table

Enlargement of passage(s) along most favorable

water flow route

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Evolution of Cave Systems

Rates of formation depend on acidity ofgroundwater, and water flow rates

~ 10,000 years to develop a continuous passage

~ 1,000,000 years to develop a cave system

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Caves

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Cave Deposits

Caves containprecipitates calleddripstones

Accumulations ofdripstone are calledspeleothems

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Cave Deposits

Stalactites are like carbonate icicles

Stalagmites project upward from cave floors

These two features may join to form columns

Also get soda straws, curtains

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Cave Deposits

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Spelunkers

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Sinkholes

Large dissolutioncavities open to thesurface

Some form as resultof cave roof collapse

Many result fromlowering of watertables

Can be a big problem!

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Karst Landscapes

Evolve over time bydissolution oflimestone landscapes

Some characteristicfeatures include:sinkholes, naturalbridges, disappearing

streams, blind valleys

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Karst Landscapes

Cone Karst

Tower Karst