Revised 8 / 06 (Monroe 6th ed.)

GROUNDWATER - Chapter 16




Origin of Groundwater

Occurrence and Movement of Groundwater



Water Table

Vadose Zone

Groundwater and Stream Flow

Aquifers and wells

Groundwater Contamination

Sukalot: a group activity

...and the Gods wept: the Love Canal

Prospecting for Groundwater

Geological Role of Groundwater




Give a general description of what groundwater is

DEFINE: aquifer, aquiclude

DEFINE: confined vs. unconfined aquifers

DIGRESS: Floodplain aquifers vs. bedrock aquifers

Groundwater has always held a special and mystical place in man's thoughts

Early workers had trouble figuring out where groundwater came from

Aristotle (384 - 322 B.C.)

Groundwater precipitated out of caverns in the earth

Because of "the cold which it encounters there"

Rainfall insufficient to account for rivers and springs

Seneca (3 B.C. - 65 A.D.)

Rainfall penetrates "only a few feet into the earth"

Perrault and Mariott - mid-17th century Frenchmen

Demonstrated the relationship between rainfall and spring flow

Groundwater and wells have been the basis of life forever

Wells have always been important to the development of an area

Walled cities needed a good INTERNAL source of water to withstand sieges

Michener's "The Source" (Psalm of the Hoopoe Bird)

Historic and recent urbanization have resulted in increased development of groundwater resources

Kanats - Underground water systems used in Persia (Iran)

Rome - did lead poisoning from water pipes cause the Empire to fall?

Wells - some were quite deep

Orvieto, Italy - 200' deep

Had 2 spiral staircases used by donkeys to bring water to the surface

Some Chinese wells were >4900' deep! - How did they dig these?

Water availability still represents the ultimate demographic control

However, several developments have allowed increased agriculture and urbanization in areas which are fundamentally arid

The ability to economically retrieve deep groundwater

As opposed to near-surface "floodplain" water

The ability to move it long distances

This is a fundamentally poor practice in the long term

And will probably result in severe social, economical and political unrest in the N-T-D-Future


Origin of Groundwater

Nearly all comes from surface precipitation which percolates into the ground

Also from connate waters - those included with the original rock

Both marine sediments and intrusives

Global groundwater supply is estimated at 8.5 million cubic kilometers

Estimates of the water budget in the U.S. indicates that:

Precipitation averages 30" per year

Evapotranspiration returns 21" to the atmosphere

Runoff returns 9" to the sea

So, where does groundwater come from?

Obviously, major groundwater systems develop very slowly

And, they are in a very delicate balance relative to use vs. recharge

DEFINE: Recharge area - where water is added to the aquifer

In many areas, groundwater can be considered a non-renewable resource

This is especially true of deep aquifers

Also arid environments (Example: So. California, Phoenix-Tucson)


Occurrence and Movement of Groundwater

Several factors relate to the occurrence and movement of groundwater


The percentage of the total volume of rock which is occupied by void space

Factors which determine porosity (Monroe; Fig. 16-1, pg. 499)

Commonly tied to the type of rock which contains the water (Monroe; Table 16-1, pg. 499)

Sedimentary rocks

Degree of sorting - probably most important

Packing arrangement

The porosity of the individual clasts

Amount of cement already filling up the void spaces

Grain size does not directly affect porosity

Some shales can actually have up to 90% open space!

However, extremely fine-grain rocks usually make poor aquifers

Due to surface tension which holds the water in the rock

Igneous and metamorphic rocks

Generally very dense crystalline rocks

Porosity usually controlled by fractures and faults

Lithology and surface weathering become very important here

DIGRESS TO: Chemical weathering and Bowen's Reaction Series

Granite vs. Gabbro vs. Schist


The measure of a rocks capability to transmit liquid through it's pore spaces

Generally a very slow process!

Book says average is "a few centimeters per day"

This is obviously only an average, and can fluctuate greatly

The size of the pore spaces is more important than the amount of void space!

As I said above, extremely fine-grain rocks usually make poor aquifers

Due to surface tension which holds the water in the rock

Porosity alone is useless as far as aquifers are concerned

Without interconnected pore spaces, the water (or oil, or gas) won't flow

DIGRESS TO: Wetsuits, thermos bottles, and thermopane windows

Water Table

The upper surface of the groundwater (Monroe; Fig. 16-2, pg. 500)

The level of water in adjacent wells

All openings in the rock below are saturated with water

But the water table doesn't extend down into the ground forever

Increased pressure reduces the pore spaces in the rock

Not necessarily completely level

Roughly parallels the ground surface (Monroe; Fig. 16-3, pg. 501)

Rises with the hills & sinks with the valleys

Intersects the surface in springs, streams and lakes

Vadose Zone

Above the water table

Completely dry to partially wet (but not saturated!)

Also called the Zone of Aeration

Water moves downward through this zone to the water table

Basically consists of 3 separate zones

Zone of soil moisture

Portion most familiar to us - it's at the top

Responds to local moisture conditions and precipitation

Where the roots live

Therefore, this water is mostly trapped, and lost by evapotranspiration

Intermediate Zone

Below the zone of soil moisture - usually dry

Water percolates through the Intermediate Zone to the water table

The capillary fringe

Extends a short distance above the water table

Thread-like extensions of water which migrate upward by capillary action

Like colored water up a celery stalk


Groundwater and Stream Flow

Groundwater and surface water are part of the same system

Effluent stream (Monroe; Fig. 16-3, pg. 501)

Derives its water from the water table

Common to temperate climates

Associated with relatively stable water tables

Directly reflects the water table

Streams flow when the water table intersects the surface

Dry when the water table drops

EXAMPLE: Deer Creek bridge

Influent stream

Adds water to the groundwater supply

Common in arid regions

The water is usually from more humid areas upstream which are destined to flow down into a desert

EXAMPLE: the Colorado River and the Nile

Associated with fluctuating water tables


Aquifers and wells

Aquifer: a sub-surface layer of rock which, because of its porosity and permeability, will hold and transmit water

Must satisfy both requirements or it's not an aquifer

Book says "yield to a well," but not necessarily

Aquifers also supply springs and rivers

Aquiclude - can't hold or can't transmit water (fails one or both)

Two basic types of aquifers

Unconfined aquifer

Water level stands at the water table

The water level will drop as a result of pumping

A "Cone of Depression" will form around the well (Monroe; Fig. 16-5, pg. 503)

How long the cone stays there is proportional to the rate which water can move through the aquifer to locally recharge an individual well

Can affect nearby wells

Over-pumping of several adjacent wells can cause the cones to intersect

Can result in a regional lowering of the water table

Confined aquifer (Monroe; Fig. 16-6, pg. 504)

A permeable horizon between two impermeable rock layers

REVIEW: Recharge area - where water is added to the aquifer

Can result in artesian wells

Free flowing wells associated with confined aquifers

Artesian-pressure surface

The level to which water will rise in a confined aquifer

Basically, water "seeks its own level"

However, friction within the aquifer interferes with this

The artesian-pressure surface will decline in relative altitude away from the recharge area

Flowing vs. non-flowing artesian wells

Depends on whether the pressure surface intersects the surface or not

Too many wells into an artesian system can reduce the pressure

Change flowing wells to non-flowing wells

Water wells

Drilled or dug to tap water from aquifers

Over-pumping can be a real problem in areas of slow recharge

Almost like mining - non-renewable resource in many (most?) areas

Southwest - relate the problems in Tucson (Dave Christopherson)

Southern California - relate some of the water haggles

Mono Lake a good example

Now California wants to divert water from up here

I say give them the water, even if it means some additional dams

That's better than them all moving up here

Remember-water is the ultimate demographic control, and population centers will adjust to reflect availability

Coastal areas - encroachment of sea water is a special problem

EXAMPLE: Fountain Valley, California (Monroe; Fig. 16-14, pg. 514)

Land subsidence due to Over-pumping

(Monroe; Figs. 16-15 to 16-18, pgs. 515 to 516)

Due to compaction of the sediments after the water is removed

Also results from over-production of oil and/or gas

EXAMPLE: Gulf Coast island

This can lead to a permanent reduction in porosity due to compaction

Springs (Monroe; Fig. 16-4, pg. 502)

Places where water flows or seeps onto the surface

Occur where the water table intersects the current erosional level of the ground

Actually, effluent streams are just springs with a lot of water!

Can be caused by many different situations


Groundwater Contamination

Aquifers can become contaminated easily and in many ways

Axiom: the closer to the surface, the easier to contaminate

Many in the more developed areas have already been polluted beyond rational use

There are lots of ways an aquifer can become contaminated

Unfortunately, many aquifers were contaminated in the past without an understanding of, or regard for, the long-term consequences

Direct pumping of pollutants underground

"Out of sight, out of mind"

Sanitary landfills in recharge areas (Monroe; Fig. 16-19, pg. 517)

Percolation of water through the dump and into an aquifer

Not-so-sanitary landfills

Hazardous waste dumps

Poor underground mining practices

Relate the problems in the Tri-State lead/zinc district

Nuclear waste disposal

Possibly the most significant long-term problem

Relate the current findings at Hanford

The radioactive waste is reaching the Columbia much sooner than expected

The Columbia River basalt may be more permeable than originally thought

Search on for a "permanent" storage facility

Yucca Mountain, Nevada

In areas of poor recharge, restricted permeability, etc., contaminants can persist far longer than we have!

What to do! A group activity...


Sukalot, a city of 37,003 on the plains of eastern Colorado, gets its municipal water from several producing wells drilled into the Fullawata Sandstone. Local medical personnel (and mothers) report increases in stillbirths, as well as increased birth defects and genetic disorders, and demand a study to determine the cause. Recent testing indicates alarming amounts of chemical pesticide contamination (300X greater than EPA maximums), as well as significant increases in toxic metals, possibly related to gold and copper mining in the Rockies. We are at a public hearing to examine the problem, and determine a solution.

The cast:

Water Quality Control Board representative - reports the contamination problems

Medical representative - relates medical findings

EPA representative - your basic bureaucrat demanding a fix (at any cost)

City Engineer - the voice of reality concerning what can and cannot be done

The Mayor - worried about his city (and re-election in 5 months)

City legal council - worried about his city's liability (and the mayor's re-election)

Mayor's Public Relations Dog - worried about his mayor's image (and re-election)

Farmer's representative - supports use of pesticides

Miner's representative - supports mining (past, present, and future)

Pissed off citizens, some with deformed kids, etc.


Assign roles to students. Break for 30 minutes so everyone can consider their position and "get into the part." Begin meeting and fully explore the situation.


Click here for an additional activity related to contamination at the Love Canal


Prospecting for Groundwater

Groundwater is a minable resource

Also, in many cases, a non-renewable resource

Permanent lowering of the water table in many developed areas indicates that normal amounts of rainfall are not sufficient to replenish the aquifers

Demand for groundwater is steadily increasing

Especially in the developing countries - "many of which are in arid regions"

Why are the developing countries in arid regions?

They're currently undeveloped because they don't have any water

Methods used to located groundwater vary

Water witching (dowsing)

Has anybody here ever used one?

More "scientific" methods

Geologic mapping

Geophysical surveys

Basically trying to define favorable units and/or structures


Geological Role of Groundwater

Important to the formation of many sedimentary rocks

As a cementing agent

Transports natural cementing agents into unconsolidated sediments

ie. calcite, silica, and iron oxide

Precipitates out into the void spaces and binds individual grains together

Often results in a loss of porosity and permeability

Geysers (Monroe; Fig. 16-22, pg. 520)

Percolating groundwater is heated by a near-surface magma source

Increased pressure keeps the water at the bottom from boiling

Continued heating raises temperature of water closer to surface

Some of the water escapes

Reduces the pressure at depth

The hot water flashes to steam and the geyser erupts

Mineral deposits commonly surround the geysers

These are leached from subsurface rocks which the super-heated water passes through

2 kinds of hot-water deposits occur

Siliceous sinter - composed of silica

Travertine - composed of calcium carbonate (Monroe; Fig. 16-24, pg. 522)

Hot Springs

More wide spread than geysers (Monroe; Fig. 16-20 and 21, pgs. 519 and 520)

Like geysers, they obtain their heat from buried magma

Or they can be Juvenile Water (recently freed by cooling magma)

Geothermal energy

Often these areas can be tapped as a source of geothermal energy

Make electricity

Limestone areas - (starts on Monroe; page 505)

Underground caverns

Stalactites, Stalagmites, Columns

Karst topography (Monroe; Fig. 16-7, pg. 505)

Surface features common to areas underlain by limestone

Several major karst areas in the U.S.

Distinctive features include: (Monroe; Fig. 16-9, pg. 507)

A lack of surface drainages

Water sinks into underground caverns and waterways

Re-appears farther away

Often as a river emerging from a giant spring

Large surface depressions

Can be kilometers across

Probably caused by subsurface solution cavities

Sinkholes (Monroe; Fig. 16-8, pg. 506)

Smaller depressions

Definitely the result of solution of the underlying limestone

Some extend down into caverns

Can act as natural wells if they intersect the water table

Sinkholes still forming in many karst areas



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