Earth: Portrait of a Planet, 3 rd edition, by Stephen MarshakChapter 19: A Hidden Reserve:...

Earth: Portrait of a Planet, 3rd edition, by Stephen Marshak Chapter 19: A Hidden Reserve: Groundwater

Chapter 19A Hidden Reserve: Groundwater

©2008 W. W. Norton & Company, Inc.

Portrait of a PlanetThird Edition

earthearth

LECTURE OUTLINE

A Hidden Reserve: GroundwaterA Hidden Reserve: Groundwater

Prepared by

Ronald Parker Earlham College Department of Geosciences

Richmond, Indiana

Prepared by

Ronald Parker Earlham College Department of Geosciences

Richmond, Indiana


GroundwaterGroundwater Significant amounts of water reside underground. It is…Significant amounts of water reside underground. It is…

A major component of the hydrologic cycle.A major component of the hydrologic cycle. A major source of water for a thirsty world. A major source of water for a thirsty world. Largely hidden from view.Largely hidden from view.

Thus, groundwater is poorly understood by many people.Thus, groundwater is poorly understood by many people.It is a precious resource that is susceptible to contamination.It is a precious resource that is susceptible to contamination.


GroundwaterGroundwater Groundwater is an important resource. Groundwater is an important resource.

Drinking water for people and livestock.Drinking water for people and livestock. Irrigation.Irrigation. Industry.Industry.

It has been used It has been used

for millennia.for millennia.


The Hydrologic CycleThe Hydrologic Cycle Groundwater is a component of the hydrologic cycle.Groundwater is a component of the hydrologic cycle. Hydrologic cycle processes.Hydrologic cycle processes.

Evaporation.Evaporation. Transpiration.Transpiration. Precipitation.Precipitation. Infiltration.Infiltration. Runoff.Runoff.


The Underground ReservoirThe Underground Reservoir Some precipitation enters the subsurface via infiltration.Some precipitation enters the subsurface via infiltration. Soil properties and vegetation govern infiltration rate. Soil properties and vegetation govern infiltration rate. Infiltrated water adds to soil moisture and groundwater.Infiltrated water adds to soil moisture and groundwater.

Soil moisture wets the soil.Soil moisture wets the soil. Some is wicked up by roots, some is evaporated.Some is wicked up by roots, some is evaporated.


The Underground ReservoirThe Underground Reservoir Some infiltrated water percolates to a deeper level.Some infiltrated water percolates to a deeper level. It is added to water that fills subsurface void spaces.It is added to water that fills subsurface void spaces. This is groundwater.This is groundwater.


PorosityPorosity Groundwater resides in subsurface pore spaces. Groundwater resides in subsurface pore spaces. Pores are open spaces within any sediment or rock.Pores are open spaces within any sediment or rock. The total volume of open space is termed porosity.The total volume of open space is termed porosity. Geologic materials exhibit a wide range of porosities.Geologic materials exhibit a wide range of porosities.


PorosityPorosity Two categories of porosity: primary and secondary.Two categories of porosity: primary and secondary.

Primary porosity – Originally formed with the material.Primary porosity – Originally formed with the material.Voids in sediment.Voids in sediment.Vesicles in basalt.Vesicles in basalt.Open reef framework.Open reef framework.

Primary porosity may decrease.Primary porosity may decrease.With burial compaction.With burial compaction.With cementation.With cementation.

Crystalline rocks have Crystalline rocks have

very little primary porosity.very little primary porosity.


PorosityPorosity Two categories of porosity.Two categories of porosity.

Secondary porosity – Secondary porosity – Developed after rock Developed after rock formation.formation.Fracturing.Fracturing.Faulting.Faulting.Dissolution.Dissolution.


PermeabilityPermeability The ease of water flow due to pore interconnectedness.The ease of water flow due to pore interconnectedness. High-permeability material allows water to flow readily.High-permeability material allows water to flow readily. Water flows slowly through low-permeability material.Water flows slowly through low-permeability material. Many large and straight flow paths enhance permeability.Many large and straight flow paths enhance permeability.


Aquifers and AquitardsAquifers and Aquitards Aquifer – Sediment or rock that transmits water easily. Aquifer – Sediment or rock that transmits water easily. Aquitard – Sediment or rock that hinders water flow.Aquitard – Sediment or rock that hinders water flow. Aquifers and aquitards are commonly interlayered.Aquifers and aquitards are commonly interlayered.


Aquifers and AquitardsAquifers and Aquitards Unconfined – An aquifer that intersects the surface.Unconfined – An aquifer that intersects the surface.

In contact with the atmosphere.In contact with the atmosphere. Easily contaminated.Easily contaminated.

Confined – An aquifer beneath an aquitard.Confined – An aquifer beneath an aquitard. Isolated from the surface.Isolated from the surface. Less susceptible to pollution.Less susceptible to pollution.


Aquifers and AquitardsAquifers and Aquitards Example: Mahomet aquifer.Example: Mahomet aquifer.

Permeable sands in linear glacial meltwater channels.Permeable sands in linear glacial meltwater channels. Channels carved into underlying bedrock.Channels carved into underlying bedrock. Water-bearing sands supply prodigious volumes of water.Water-bearing sands supply prodigious volumes of water.


Aquifers and AquitardsAquifers and Aquitards Example: Dakota sandstone aquifer.Example: Dakota sandstone aquifer.

Cretaceous fluvial sandstones interlayered with shales. Cretaceous fluvial sandstones interlayered with shales. Deformation of the Black Hills uplifted the western end. Deformation of the Black Hills uplifted the western end. Recharge in the Black Hills fills a gigantic aquifer system.Recharge in the Black Hills fills a gigantic aquifer system.


Aquifers and AquitardsAquifers and Aquitards Example: Phoenix aquifer. Example: Phoenix aquifer.

Basin and Range faulting created basins next to uplifts.Basin and Range faulting created basins next to uplifts. Coarse basin sediments are recharged along the uplifts. Coarse basin sediments are recharged along the uplifts. Basins store large volumes of water used by cities.Basins store large volumes of water used by cities.


The Water TableThe Water Table The water table is a subsurface boundary.The water table is a subsurface boundary.

Above the water table, pores are mostly filled with air.Above the water table, pores are mostly filled with air.This is called the vadose (or unsaturated) zone.This is called the vadose (or unsaturated) zone.

Below the water table, pores are filled with water.Below the water table, pores are filled with water.This is called the phreatic (or saturated) zone.This is called the phreatic (or saturated) zone.

The capillary fringe separates the two zones.The capillary fringe separates the two zones.Formed of moisture wicked upward above the water table. Formed of moisture wicked upward above the water table.


The Water TableThe Water Table The depth to the water table is variable.The depth to the water table is variable.

In humid settings, the water table is closer to the surface.In humid settings, the water table is closer to the surface. In arid settings, it may be 10s to 100s of meters down.In arid settings, it may be 10s to 100s of meters down.

Perennial surface water exposes the water table.Perennial surface water exposes the water table. Streams.Streams. Lakes and ponds.Lakes and ponds. Wetlands. Wetlands.


The Water TableThe Water Table The water table is the top of the zone of saturation.The water table is the top of the zone of saturation. Water table position changes with rainfall. Water table position changes with rainfall.

During seasonally rainy periods, the water table rises.During seasonally rainy periods, the water table rises. During prolonged droughts, the water table falls. During prolonged droughts, the water table falls.

Ponds dry up if the water table falls below the bottom. Ponds dry up if the water table falls below the bottom.


Water Table TopographyWater Table Topography The water table is not flat; it is a sloping surface.The water table is not flat; it is a sloping surface. The water table is a subdued replica of the topography.The water table is a subdued replica of the topography.

The water table is high where the land is high. The water table is high where the land is high. The water table is low where the land is low.The water table is low where the land is low.

Water flows from higher elevations to lower elevations.Water flows from higher elevations to lower elevations. Topography is useful for estimating groundwater flow. Topography is useful for estimating groundwater flow.


Perched Water TablesPerched Water Tables Discontinuous aquitards may exist in the subsurface.Discontinuous aquitards may exist in the subsurface. These arrest downward infiltration to the water table. These arrest downward infiltration to the water table. These aquitards form perched water tables.These aquitards form perched water tables.

Overlie unsaturated material.Overlie unsaturated material. Represent a “false” water table.Represent a “false” water table. More easily dewatered.More easily dewatered.


Groundwater FlowGroundwater Flow Groundwater flows slowly under the influence of gravity. Groundwater flows slowly under the influence of gravity. Flow in the unsaturated zone is straight downward.Flow in the unsaturated zone is straight downward. In the saturated zone, flow is more complicated. In the saturated zone, flow is more complicated.

Governed by gravity and pressure.Governed by gravity and pressure.


Groundwater FlowGroundwater Flow Hydraulic head, potential energy driving flow, is due to…Hydraulic head, potential energy driving flow, is due to…

Elevation above sea level.Elevation above sea level. Pressure exerted by weight of overlying water.Pressure exerted by weight of overlying water.

In the illustration below, the hydraulic head at pIn the illustration below, the hydraulic head at p11 > p > p22.. They have the same elevation.They have the same elevation. The weight of water over pThe weight of water over p11 is greater than that over p is greater than that over p22..

A piezometer is used to measure hydraulic head.A piezometer is used to measure hydraulic head. An open-ended pipe.An open-ended pipe. Installed below the water table.Installed below the water table. Water level is the hydraulic head.Water level is the hydraulic head.


Groundwater FlowGroundwater Flow Flow is determined by measuring hydraulic head. Flow is determined by measuring hydraulic head.

Flow Flow alwaysalways moves from high to low hydraulic head. moves from high to low hydraulic head. Thus water table highs flow to water table lows.Thus water table highs flow to water table lows.

Flow paths, however, are not straight lines. Flow paths, however, are not straight lines. Flow follows a curved, concave-up path.Flow follows a curved, concave-up path. Water can flow upwards moving to lower hydraulic head.Water can flow upwards moving to lower hydraulic head.

Upward flowUpward flow


Groundwater FlowGroundwater Flow Groundwater infiltrates through recharge areas.Groundwater infiltrates through recharge areas.

Flow is directed downward.Flow is directed downward. Commonly found in topographic uplands.Commonly found in topographic uplands.

Groundwater exits the subsurface from discharge areas.Groundwater exits the subsurface from discharge areas. Flow is directed upward.Flow is directed upward. Usually observed in topographic lows.Usually observed in topographic lows.


Groundwater FlowGroundwater Flow Groundwater flow occurs on a variety of scales.Groundwater flow occurs on a variety of scales.

Local – Shallow flow over short times and distances.Local – Shallow flow over short times and distances. Intermediate – Flow of moderate depth, time, and distance.Intermediate – Flow of moderate depth, time, and distance. Regional – Deep, long-distance, long-duration flow.Regional – Deep, long-distance, long-duration flow.


Groundwater Flow RatesGroundwater Flow Rates Groundwater movement is slow relative to surface water.Groundwater movement is slow relative to surface water.

It must percolate through pore openings.It must percolate through pore openings. Flow is further slowed by friction and electrostatic forces.Flow is further slowed by friction and electrostatic forces.

Typical rates of flow.Typical rates of flow. Ocean currentsOcean currents 3 km / hour 3 km / hour Steep river channel Steep river channel 30 km / hour30 km / hour Groundwater Groundwater 0.00002 km / hour 0.00002 km / hour


Groundwater Flow RatesGroundwater Flow Rates Groundwater flow rate is governed by several factors.Groundwater flow rate is governed by several factors.

Permeability of the porous material.Permeability of the porous material.High permeability increases the rate of groundwater flow.High permeability increases the rate of groundwater flow.Low permeability decreases it.Low permeability decreases it.

The hydraulic gradient – Spatial change in hydraulic head.The hydraulic gradient – Spatial change in hydraulic head.The head change over a The head change over a

horizontal distance, and... horizontal distance, and... The driving force for The driving force for

groundwater flow.groundwater flow. Steeper – Faster flow.Steeper – Faster flow. Less steep – Slower. Less steep – Slower.


Groundwater FlowGroundwater Flow Darcy’s Law – An equation that predicts the volume of Darcy’s Law – An equation that predicts the volume of

water passing through an area of an aquifer in a given water passing through an area of an aquifer in a given time.time.

Q = K Q = K (h(h11- h- h22/j) /j) AAwhere, where,

Q = Discharge volume (Q = Discharge volume (mm33/day/day).).

K = Hydraulic conductivity (K = Hydraulic conductivity (m/daym/day).).

hh11- h- h22/j = Hydraulic gradient (/j = Hydraulic gradient (m/m or dimensionlessm/m or dimensionless).).

A = Cross-sectional area perpendicular to flow (A = Cross-sectional area perpendicular to flow (mm22).).

May be paraphrased…“Discharge volume is proportional May be paraphrased…“Discharge volume is proportional to the hydraulic gradient times the permeability.”to the hydraulic gradient times the permeability.” Hydraulic conductivity is material permeability for water.Hydraulic conductivity is material permeability for water.


Groundwater FlowGroundwater Flow Geologic conditions vary in the subsurface.Geologic conditions vary in the subsurface. Darcy’s law predicts flow increase with an increase in…Darcy’s law predicts flow increase with an increase in…

Hydraulic conductivity, orHydraulic conductivity, or Hydraulic gradient. Hydraulic gradient.


Tapping GroundwaterTapping Groundwater Human use requires that groundwater be captured.Human use requires that groundwater be captured.

Wells – Holes excavated or drilled to obtain water.Wells – Holes excavated or drilled to obtain water. Springs – Natural groundwater outlets.Springs – Natural groundwater outlets.

There are many types of wells and springs.There are many types of wells and springs.


Tapping GroundwaterTapping Groundwater Wells are holes drilled or dug into the saturated zone.Wells are holes drilled or dug into the saturated zone.

Water is recovered by lifting or pumping.Water is recovered by lifting or pumping. Water flows from the aquifer into the well.Water flows from the aquifer into the well. Drawdown occurs if removal exceeds flow to the well. Drawdown occurs if removal exceeds flow to the well.


Tapping GroundwaterTapping Groundwater With drawdown, the water table near the well drops.With drawdown, the water table near the well drops. Water table decline forms a cone of depression.Water table decline forms a cone of depression.

A downward-pointed cone-shaped surface.A downward-pointed cone-shaped surface. Steepest near the well; flattens with distance.Steepest near the well; flattens with distance. The cone may expand outward with continued pumping.The cone may expand outward with continued pumping.


Tapping GroundwaterTapping Groundwater Drawdown from multiple wells in an area is additive.Drawdown from multiple wells in an area is additive. Cones of depression often interfere.Cones of depression often interfere.

A small well creates a small cone.A small well creates a small cone. A large well creates a large cone. A large well creates a large cone. One may dewater the other.One may dewater the other.

Competing uses often conflict.Competing uses often conflict.


Tapping GroundwaterTapping Groundwater Artesian wells tap confined, tilted aquifers.Artesian wells tap confined, tilted aquifers.

Upland recharge pressurizes the aquifer.Upland recharge pressurizes the aquifer. Water rises in artesian wells to the potentiometric surface.Water rises in artesian wells to the potentiometric surface.

Analogue of the water table for a confined aquifer.Analogue of the water table for a confined aquifer.Determined by hydraulic head elevation in recharge area.Determined by hydraulic head elevation in recharge area.

A well casing below this surface will flow without pumping.A well casing below this surface will flow without pumping.


Tapping GroundwaterTapping Groundwater Water distribution systems mimic artesian aquifers.Water distribution systems mimic artesian aquifers.

Water is pumped to an elevated storage tank.Water is pumped to an elevated storage tank. This elevation creates an artificial potentiometric surface. This elevation creates an artificial potentiometric surface. Pressure drives water through the Pressure drives water through the

distribution system. distribution system.


Tapping GroundwaterTapping Groundwater Springs are locations of natural groundwater discharge.Springs are locations of natural groundwater discharge.

Springs are marked by…Springs are marked by…Hydrophilic vegetation.Hydrophilic vegetation.Perennial wetlands.Perennial wetlands.Saturated soils.Saturated soils.Nonfreezing ground.Nonfreezing ground.Streamflow.Streamflow.


Tapping GroundwaterTapping Groundwater Springs are locations of natural groundwater discharge.Springs are locations of natural groundwater discharge. Springs are important resources for humans.Springs are important resources for humans.

Yield fresh, clear, clean water.Yield fresh, clear, clean water. No need for drilling.No need for drilling. Spring flow is often steady.Spring flow is often steady.

Springs form in many ways.Springs form in many ways.


Tapping GroundwaterTapping Groundwater Springs result from varied geologic features.Springs result from varied geologic features.

Where the water table intersects the land surface.Where the water table intersects the land surface. At the contact between high- and low-permeability layers. At the contact between high- and low-permeability layers.



Where water-bearing fractures intersect the surface.Where water-bearing fractures intersect the surface. Where a fault juxtaposes permeability contrasts.Where a fault juxtaposes permeability contrasts.



Leakage of a confined aquifer along a joint or fracture.Leakage of a confined aquifer along a joint or fracture. Exposure of a perching layer at the surface.Exposure of a perching layer at the surface.


Tapping GroundwaterTapping Groundwater Oases in the Sahara develop Oases in the Sahara develop

from spring flow.from spring flow. Water from recharge areas flows Water from recharge areas flows

to oasis discharge points.to oasis discharge points. These locations have been These locations have been

culturally important for millenia.culturally important for millenia.


Hot Springs and GeysersHot Springs and Geysers Hot springs are groundwater discharges of hot water. Hot springs are groundwater discharges of hot water.

Temperatures range from 30Temperatures range from 30oo to 104 to 104ooC. C. The waters are usually rich in dissolved minerals.The waters are usually rich in dissolved minerals.

They develop in two settings.They develop in two settings. Where deep groundwater surfaces along faults.Where deep groundwater surfaces along faults. In geothermal regions.In geothermal regions.


Hot Springs and GeysersHot Springs and Geysers Where deep groundwater surfaces along faults.Where deep groundwater surfaces along faults.

Deep groundwater is warm.Deep groundwater is warm. The source of heat is the geothermal gradient.The source of heat is the geothermal gradient.

In geothermal regions.In geothermal regions. High geothermal High geothermal

gradients linked togradients linked to

shallow magma.shallow magma. Circulation returnsCirculation returns

heated groundwater heated groundwater

to the surface.to the surface.


Hot Springs and GeysersHot Springs and Geysers Distinctive geological features.Distinctive geological features.

Hot springs turn volcanic ash into a viscous slurry. Hot springs turn volcanic ash into a viscous slurry. Boiling springs create bubbling mudpots. Boiling springs create bubbling mudpots.



Hot springs lose dissolved minerals upon cooling. Hot springs lose dissolved minerals upon cooling. These minerals crystallize as deposits of travertine.These minerals crystallize as deposits of travertine.



Geothermal springs may produce brightly colored pools.Geothermal springs may produce brightly colored pools. Colors are due to bacterial metabolism of sulfur minerals. Colors are due to bacterial metabolism of sulfur minerals.


Hot Springs and GeysersHot Springs and Geysers Boiling water and steam erupts cyclically from geysers.Boiling water and steam erupts cyclically from geysers.

Water is heated to the boiling point in a vertical spring. Water is heated to the boiling point in a vertical spring. Pressure exerted by the water column prevents boiling.Pressure exerted by the water column prevents boiling. Pressure drops as bubbles form and all the water boils.Pressure drops as bubbles form and all the water boils. The cycle repeats after the emptied chamber is refilled. The cycle repeats after the emptied chamber is refilled.


Hot Springs and GeysersHot Springs and Geysers Hot springs are prized as health resorts and spas. Hot springs are prized as health resorts and spas.

Yellowstone National Park, Wyoming.Yellowstone National Park, Wyoming. Hot Springs, Arkansas.Hot Springs, Arkansas. Salton Sea, California.Salton Sea, California. Rotorua, New Zealand.Rotorua, New Zealand. Iceland.Iceland.


Groundwater ProblemsGroundwater Problems Groundwater is an important natural resource.Groundwater is an important natural resource.

It accounts for 95% of all the fresh water on Earth.It accounts for 95% of all the fresh water on Earth. It supplies a substantial portion of drinking water needs.It supplies a substantial portion of drinking water needs. Groundwater is threatened by…Groundwater is threatened by…

Mismangement.Mismangement.Overuse.Overuse.Pollution.Pollution.


Groundwater DepletionGroundwater Depletion Severe water table decline can alter surface water flow.Severe water table decline can alter surface water flow.

By capturing flow, wells may dewater streams and lakes.By capturing flow, wells may dewater streams and lakes. Especially problematic in Especially problematic in

arid and semi-arid regions.arid and semi-arid regions.San Pedro River,San Pedro River,

SE Arizona. SE Arizona.


Groundwater DepletionGroundwater Depletion Cones of depression are capable of reversing flow.Cones of depression are capable of reversing flow. An expanding cone may capture pollutants.An expanding cone may capture pollutants.


Groundwater DepletionGroundwater Depletion Beneath coastal land, fresh water “floats” on salt water.Beneath coastal land, fresh water “floats” on salt water. Pumping causes the fresh/salt boundary to rise.Pumping causes the fresh/salt boundary to rise. Eventually, salt water may enter the pumping well. Eventually, salt water may enter the pumping well. Salt water intrusion renders the water unpotable. Salt water intrusion renders the water unpotable.


Groundwater DepletionGroundwater Depletion Lowering the water table by diverting surface water.Lowering the water table by diverting surface water.

Channelization has diverted Everglades surface flow.Channelization has diverted Everglades surface flow. This has led to drying of large parts of the Everglades.This has led to drying of large parts of the Everglades. Lack of freshwater flow has resulted in salt-water intrusion.Lack of freshwater flow has resulted in salt-water intrusion.


Groundwater DepletionGroundwater Depletion Water in pore space acts to hold grains apart.Water in pore space acts to hold grains apart. When ground water is removed…When ground water is removed…

Sediment grains compress, pores collapse.Sediment grains compress, pores collapse. The land surface cracks and sinks.The land surface cracks and sinks.

Subsidence is mostly irreversible.Subsidence is mostly irreversible.


Groundwater DepletionGroundwater Depletion Dramatic examples of subsidence are well-known. Dramatic examples of subsidence are well-known.

The Leaning Tower of Pisa, Italy.The Leaning Tower of Pisa, Italy. Venice, Italy.Venice, Italy. The San Joaquin Valley, California.The San Joaquin Valley, California.


Groundwater DepletionGroundwater Depletion Proactive measures can prevent withdrawal subsidence.Proactive measures can prevent withdrawal subsidence.

Structures are designed to recharge surface water.Structures are designed to recharge surface water. Recharge basins return water to the groundwater system.Recharge basins return water to the groundwater system. This serves to reduce the effects of excess withdrawal.This serves to reduce the effects of excess withdrawal.


Groundwater ChemistryGroundwater Chemistry Groundwater reacts as it flows through an aquifer.Groundwater reacts as it flows through an aquifer. Reactions are like chemical weathering. Reactions are like chemical weathering.

Dissolution/precipitation.Dissolution/precipitation. Oxidation/reduction.Oxidation/reduction. Hydrolysis.Hydrolysis. Hydration.Hydration.

Dissolved ion concentrations depend on T, P, and pH.Dissolved ion concentrations depend on T, P, and pH.


Groundwater ChemistryGroundwater Chemistry Ion concentrations generally increase with time.Ion concentrations generally increase with time.

Longer residence times result in more dissolved material.Longer residence times result in more dissolved material. Deep regional flow systems are typified by brines.Deep regional flow systems are typified by brines.

Minerals may crystallize out of groundwater. Minerals may crystallize out of groundwater. This is a mechanism that leads to sediment cementation.This is a mechanism that leads to sediment cementation. Common cements are calcite, quartz, and iron oxides.Common cements are calcite, quartz, and iron oxides.


Groundwater QualityGroundwater Quality Groundwater is often of high quality.Groundwater is often of high quality.

The filtering effect of porous media removes particulates.The filtering effect of porous media removes particulates. Clay minerals can absorb certain dissolved ions.Clay minerals can absorb certain dissolved ions.

Natural groundwater may contain unwanted substances.Natural groundwater may contain unwanted substances. Hardness.Hardness. Dissolved iron, manganese, and hydrogen sulfide gas.Dissolved iron, manganese, and hydrogen sulfide gas. Dissolved arsenic.Dissolved arsenic.


Groundwater QualityGroundwater Quality Hardness – Dissolution of carbonates adds CaHardness – Dissolution of carbonates adds Ca2+2+ and Mg and Mg2+2+. .

In excess, these cations…In excess, these cations… Reduce the effectiveness of soap.Reduce the effectiveness of soap. Mineralize in plumbing to create flow-clogging scale.Mineralize in plumbing to create flow-clogging scale.

Hardness is mitigated by ion exchange (water softening).Hardness is mitigated by ion exchange (water softening).


Groundwater QualityGroundwater Quality Iron and manganese – Derived from rock weathering.Iron and manganese – Derived from rock weathering.

These cations occur in reducing (OThese cations occur in reducing (O22-poor) groundwater.-poor) groundwater.

Cause taste/odor problems and stain plumbing and laundry.Cause taste/odor problems and stain plumbing and laundry.

Hydrogen sulfide (HHydrogen sulfide (H22S) – Rotten-egg gas.S) – Rotten-egg gas.

Contribute to taste and odor problems.Contribute to taste and odor problems.Commonly associated with high Fe and Mn.Commonly associated with high Fe and Mn.


Groundwater QualityGroundwater Quality Natural processes may render groundwater unpotable.Natural processes may render groundwater unpotable.

Arsenic – Naturally occurring poison.Arsenic – Naturally occurring poison.Derived from weathering of…Derived from weathering of…

Pyrite-bearing sediments and metamorphic equivalents.Pyrite-bearing sediments and metamorphic equivalents. Silica-rich volcanic ash deposits.Silica-rich volcanic ash deposits.

EPA Maximum Contaminant Limit (MCL) is 10 ug/L (ppb).EPA Maximum Contaminant Limit (MCL) is 10 ug/L (ppb).


Groundwater ContaminationGroundwater Contamination Human activities add pollutants to groundwater flow.Human activities add pollutants to groundwater flow.

Dissolved and pure organic and inorganic compounds.Dissolved and pure organic and inorganic compounds. Dissolved metals.Dissolved metals. Pathogenic microbes.Pathogenic microbes.

Groundwater transports pollutants away from a source.Groundwater transports pollutants away from a source.


Groundwater ContaminationGroundwater Contamination There are many sources of groundwater contamination.There are many sources of groundwater contamination. Pollution is often not recognized until damage occurs.Pollution is often not recognized until damage occurs. Groundwater cleanup is slow, expensive, and limited. Groundwater cleanup is slow, expensive, and limited.


Groundwater ContaminationGroundwater Contamination Sanitary wastes.Sanitary wastes.

Failing septic systems.Failing septic systems. Animal feedlot runoff.Animal feedlot runoff.


Groundwater ContaminationGroundwater Contamination Agricultural wastes.Agricultural wastes.

Fertilizers.Fertilizers. Pesticides.Pesticides.


Groundwater ContaminationGroundwater Contamination Toxic chemicals.Toxic chemicals.

Industrial wastes.Industrial wastes. Paints and thinners.Paints and thinners. Degreasers and solvents.Degreasers and solvents.


Sources of ContaminationSources of Contamination Toxic chemicals.Toxic chemicals.

Petroleum storage.Petroleum storage.Underground storage tanks (USTs).Underground storage tanks (USTs).Gas stations.Gas stations.Petroleum terminals.Petroleum terminals.



Landfill leachate.Landfill leachate.



Mining wastesMining wastesMine overburden and spoil.Mine overburden and spoil.Mill processing tailings.Mill processing tailings.


Groundwater ContaminationGroundwater Contamination Two broad categories of contaminant introduction.Two broad categories of contaminant introduction.

Point source – A contaminant plume emanates from 1 spot. Point source – A contaminant plume emanates from 1 spot. Concentrations are highest near the source.Concentrations are highest near the source.Concentrations decrease with distance away.Concentrations decrease with distance away.

Nonpoint source – Pollution introduced over a broad area.Nonpoint source – Pollution introduced over a broad area.Concentrations diffused across a region.Concentrations diffused across a region.More difficult to identify and address.More difficult to identify and address.


Groundwater ContaminationGroundwater Contamination Groundwater contaminant plumes change over time.Groundwater contaminant plumes change over time.

They grow in length with groundwater flow.They grow in length with groundwater flow. They grow in width by diffusion and dispersion. They grow in width by diffusion and dispersion. Large plumes pollute large areas and affect many people.Large plumes pollute large areas and affect many people.


Groundwater ContaminationGroundwater Contamination Contaminant characterization is needed for cleanup.Contaminant characterization is needed for cleanup.

Monitoring wells are installed to assess flow behavior.Monitoring wells are installed to assess flow behavior. Chemical testing quantifies the amount of contaminants.Chemical testing quantifies the amount of contaminants.

Remedial strategies are designed to reduce health risks.Remedial strategies are designed to reduce health risks.


Groundwater ContaminationGroundwater Contamination Contaminant remediation is expensive.Contaminant remediation is expensive. Most remedial strategies include removing the source.Most remedial strategies include removing the source.

Pump and treat.Pump and treat. Volatilize and vaporize.Volatilize and vaporize. Steam clean.Steam clean.

Bioremediation utilizes bacteria to clean groundwater.Bioremediation utilizes bacteria to clean groundwater.


Groundwater ContaminationGroundwater Contamination Contamination is best prevented by managing landuses.Contamination is best prevented by managing landuses.

Landfills are now constructed with clay and plastic liners.Landfills are now constructed with clay and plastic liners. Underground storage tanks are now double-lined.Underground storage tanks are now double-lined. Best-management practices (BMPs) reduce contamination.Best-management practices (BMPs) reduce contamination.

Land-use management is especially important in Land-use management is especially important in wellhead protection areas (WHPAs). wellhead protection areas (WHPAs).


Groundwater ExcessGroundwater Excess Rising water tables.Rising water tables.

Excess groundwater may initiate slope failures.Excess groundwater may initiate slope failures.Groundwater adds weight to the material. Groundwater adds weight to the material. Increase in pore pressure decreases material strength.Increase in pore pressure decreases material strength.

Basement flooding.Basement flooding.


CavesCaves Caves develop when groundwater dissolves limestone.Caves develop when groundwater dissolves limestone. Groundwater is weakly acidic.Groundwater is weakly acidic.

COCO2 2 reacts with water to form carbonic acid. reacts with water to form carbonic acid.

HH22O + COO + CO22 = H = H22COCO33

COCO22 is added to rainwater as it falls through air. is added to rainwater as it falls through air.

COCO22 is also added to water infiltrating soil organic matter. is also added to water infiltrating soil organic matter.


CavesCaves Cave networks develop when proper conditions exist.Cave networks develop when proper conditions exist.

Limestone bedrock.Limestone bedrock. Abundant fresh water.Abundant fresh water.

Caves grow as joints are enhanced by solution.Caves grow as joints are enhanced by solution. Cave geometry reflects Cave geometry reflects

the joint pattern.the joint pattern. Stratal changes Stratal changes

influence dissolution.influence dissolution.


Caves and KarstCaves and Karst Speleothems are formed from precipitation of dripstone.Speleothems are formed from precipitation of dripstone.

Develop when groundwater entering a cave degasses CODevelop when groundwater entering a cave degasses CO22..

CaCOCaCO33 is precipitated from this water on interior surfaces. is precipitated from this water on interior surfaces.

Over time, CaCOOver time, CaCO33 coatings grow into spectacular forms. coatings grow into spectacular forms.

Stalactites – Hang down.Stalactites – Hang down.Stalagmites – Point up.Stalagmites – Point up.Columns.Columns.


Caves and KarstCaves and Karst Limestone dissolution creates unique karst landscapes.Limestone dissolution creates unique karst landscapes. Karst landforms bear evidence of dissolution.Karst landforms bear evidence of dissolution.

Disappearing streams.Disappearing streams. Natural bridges.Natural bridges. Caves.Caves. Speleothems.Speleothems. Sinkholes.Sinkholes. Springs.Springs.

Karst creates irregular terrain.Karst creates irregular terrain.


Karst LandformsKarst Landforms Karst landforms develop in a series of stages.Karst landforms develop in a series of stages.

Establishment of the water table in limestone.Establishment of the water table in limestone.Requires draining the seawater that formed the limestone.Requires draining the seawater that formed the limestone.Exposure above sea level in a humid region.Exposure above sea level in a humid region.

Development of a cave network via dissolution.Development of a cave network via dissolution.Dissolution maximized near the water table.Dissolution maximized near the water table.



The water table drops in response to stream incision. The water table drops in response to stream incision. This initiates a new layer of cave formation.This initiates a new layer of cave formation. Groundwater moving down through the first cave…Groundwater moving down through the first cave…

Degasses CODegasses CO22..

Precipitates dripstone and flowstone speleothems.Precipitates dripstone and flowstone speleothems.



Continued dissolution results in eventual roof collapse.Continued dissolution results in eventual roof collapse. This process creates sinkholes and troughs.This process creates sinkholes and troughs. Remnant limestone forms ridges, hills, and natural bridges.Remnant limestone forms ridges, hills, and natural bridges.


Karst LandformsKarst Landforms Sinkholes result from roof collapse. Sinkholes result from roof collapse. Sinkholes decorate large regions of karst landscapes. Sinkholes decorate large regions of karst landscapes.


Karst LandformsKarst Landforms Tower karst is prominent in China and Thailand.Tower karst is prominent in China and Thailand. Natural bridges are formed when collapse is incomplete.Natural bridges are formed when collapse is incomplete. Disappearing streams fall into underground caves, only Disappearing streams fall into underground caves, only

to emerge as a spring many kilometers away. to emerge as a spring many kilometers away.


Cave LifeCave Life A highly specialized ecosystem has developed in caves.A highly specialized ecosystem has developed in caves.

Bacteria metabolizing sulfur minerals.Bacteria metabolizing sulfur minerals. Bats.Bats. Fish.Fish.

Caves and Karst Caves and Karst LandscapesLandscapes


Chapter 19A Hidden Reserve: Groundwater

©2008 W. W. Norton & Company, Inc.

Portrait of a PlanetThird Edition

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