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GROUNDWATERwww.google.com

en.wikipedia.org

Thompson Higher Education 2007; Monroe, Wicander, and Hazlett, Physical Geology

TCNJ PHY120 2013 GCHERMAN

GROUNDWATER is one of the most important geological resources for humans


• Worldwide 50% of

people obtain their

water from the

ground.

•70 times more

abundant in the

subsurface than in

surface reservoirs.

• Moves so slowly it is stored in the earth and remains available even in dry periods.

• In some places it flows from humid environments to dry ones, making water available.

• It serves as an underground reservoir of water that eventually runs into streams and

lakes.


Groundwater and Porosity and Permeability

•Groundwater and Porosity and Permeability

• The Water Table

• Water Wells

• Borehole Geophysics

• Groundwater Movement

• Recharge and Discharge areas, Springs and Artesian Systems

• Groundwater Erosion and Deposition

• Modifications of the Groundwater System And Their Effects

• Hydrothermal Activity

Groundwater is that water which occupies pore spaces and other cavities within

subsurface rocks and unconsolidated materials.


• Groundwater by volume is only about 1% of the of the hydrologic cycle but

constitutes approximately 22% of the world's fresh water supply.


Porosity is the

percentage

volume of

rock,

sediment or

soil which

consists of

pore space


• Soil is about half pore space, much

of which is filled with water.

•The rest is stored in unconsolidated

sediments, or cracks and joints in

rocks.

Porosity


Porosity


• Transmissibility is the ease

with which water moves through

rock

• A rock can have abundant

pore space but if these spaces

are not connected, groundwater

can not move through it.

•The pore spaces have to be big

enough and interconnected to

move water.

Permeability refers to the transmissibility of fluids through rock, sediment, or

soil.Connected pores gives rock permeability

Affected by:

• number of available conduits

• size of the conduits

• straightness of the conduits

TCNJ PHY120 2013 GCHERMANTCNJ PHY120 2013 GCHERMAN

Groundwater Movement mostly occurs by the work of gravity (water

flows down hill) but generally occurs very slowly (cm to meters/day)


Groundwater Zones

and the

Water Table

• The saturation

zone has all pore

spaces occupied

by water.

• The aeration zone

contains both air and

water in the pore

spaces of rock, soil or

sediment.

• The water table

surface separates

the aeration zone

from the

saturated zone.


The Water Table is an important concept called a potential surface and can not

be seen directly.

• Water Table mimics surface topography.

• Water table coincides with level of water in wells.

• Water table is important in explaining the flow of springs and streams,

and water levels in lakes.


Water Table Maps

• When the depth to the water table

is measured in wells at multiple

points in the same aquifer, the

elevations can be contoured to show

the groundwater flow direction

• The groundwater flow direction is always normal to the potential-surface contours


Water Table Fluctuates by Season


Water Table and Streams

• When the water table is

higher in elevation than a

stream, ground water flows

into the steam—called gaining

stream (usually in humid

climates).

• When water table is below a

stream it is called losing

stream and supplies water to

the ground (usually in desert

climates).


Aquifers, Aquitards, Aquicludes, and Confining Units

• An aquifer is an underground

layer of water-bearing permeable

rock or unconsolidated materials

(gravel, sand, or silt) from which

groundwater can be extracted

using a water well.

• The study of water flow in

aquifers and the characterization

of aquifers is called hydrogeology.

• An aquitard is low permeability material

along an aquifer that retards the flow of

groundwater.

• An aquiclude is a solid, impermeable area underlying or overlying an aquifer.

• When an aquiclude overlies an aquifer under confined pressure, the srtat are called

a confining unit overlying a confined aquifer.


Water Wells are devices similar to drinking straws that help people to

remove water from the zone of saturation.

• Once a well is pumping, a conical depression forms in the water table called a cone of depression.

• Wells must be below the

water table because during

pumping the water table is

lowered in elevation

(this is called drawdown).


A Perched Water Tableis when an aquitard blocks the downward

movement of water, and two water table

levels can form with the upper being a

perched water table.

• They can form springs on hillsides and in

road cuts.


Springs occur where

an aquifer and water

table intersect the

ground surface


Groundwater moves

slowly through aquifers,

from areas of high pressure

to areas of lower pressure

such as streams, lakes, and

swamps.

• When groundwater in an

aquifer is confined by aquicludes

and is under hydrostatic

pressure as the result of an

elevation difference between

the zone of recharge and lower

portions of the aquifer, an

artesian system exists.

Municipal water systems commonly have well

water pumped to elevated holding tanks

where gravity maintains pressure to the

recipients


Groundwater Flow Rates are dependant upon the

permeability of the material and the

hydraulic gradient

• Flow rates are typically

10-100 cm/day, or 40-400 m/yr


Karst

Topography is characterized by

sinkholes, solution

valleys, and

disappearing

streams, and

results from

groundwater

weathering and

erosion.


Caves form

when groundwater

weathers and

erodes soluble rock

such as limestone

in the zone of

saturation.

cave


Karst

Topography

Of the Irish

Barren Uplands


Karst Topography

• As groundwater

percolates through the

zone of aeration and

flows through the

saturated zone, it

dissolves the

carbonate rocks and

gradually forms a

sytem of passageways.

•Horizontal

passageways carry

water to streams and

allows the local base

level to drop, creating

cave and cavern

systems.


Cave Deposits

Buchan Cave, Victoria, Australia


Cave Deposits


Aquifer Systems consists of aquifers and aquitards.


Aquifers and

Confining Units

of New Jersey


The Great Artesian Basin

in Australia is arguably the largest

groundwater aquifer in the world

(over 1.7 million km²).

• It plays a large part in water supplies

for Queensland and remote parts of

South Australia.

Queensland


• When withdrawal from wells exceeds

the rate of recharge, dry wells, loss of

hydrostatic pressure, saltwater

encroachment and ground subsidence

may result.

• Aquifer depletion is a problem in some

areas, and is especially critical in northern

Africa.

Groundwater Depletion and Ground Subsidence


• New methods of groundwater

management such as artificial

recharge and injection of surface

waters during seasonal wet periods

has extended the life of many

freshwater aquifers, especially in the

United States.

• But there are other places like the

arid southwest USA where 10s of

meters of land subsidence is directly

related to groundwater depletion.

Groundwater Depletion and Ground Subsidence

9 m

in 52

years


The Ogallala Aquifer of the central United States is one of the world's

great aquifers, but in places it is being rapidly depleted by

growing municipal use, and continuing agricultural use.

• This huge aquifer, which underlies portions of eight

states, contains primarily ‘fossil’ water from the time of

the last glaciation (10-85 Ka).

• Annual recharge, in the more arid parts of the aquifer, is

estimated to total only about 10 percent of annual

withdrawals.


Saltwater Incursion

• Freshwater is less dense than saltwater

and will form a lens floating atop the salty

groundwater

•If excessive pumping occurs, a cone of

depression develops in the fresh

groundwater, which may result in

saltwater contamination of the well.

•Pumping water back into the fresh

groundwater system through recharge

wells can help lower the

freshwater-saltwater interface and

reduce saltwater incursion.


The Edwards Aquifer in central

Texas is a carbonate aquifer has historically been

providing high quality water for nearly 2 million

people, and even today, is full because of

tremendous recharge from a number of area

streams, rivers and lakes.

• The primary risk to this resource is human

development over the recharge areas.


Dollars and Ground-water Quality

•The Environmental Protection Agency

estimates that communities in the United

States need $12.1 billion in funding

immediately to protect the nation's drinking

water supplies and to meet minimum

health-based standards.

•The agency also estimates that

$138.4 billion will be needed

over the next 20 years to

upgrade or replace the water

infrastructure (2007).


Dollars and Ground-water Quality

•The agency

also estimates

that $138.4

billion will be

needed over

the next 20

years to

upgrade or

replace the

water

infrastructure.

$263

billion

gap

(2013)


Groundwater Pollution

• Groundwater contamination can be

natural or anthropogenic (man-derived)

• Contamination from anthropogenic

and animal sewage, landfills, and toxic

waste is becoming a serious problem.

• High-density

housing with

water wells and

septic very bad.

Arsenic in Groundwater can be either natural or anthropogenic

red

black

gray

red


Arsenic in Groundwater


Septic Systems have a life expectancy

of about 20 years, but regular maintenance and

best management practices can extend the life.

• Minimize the amount of solid material, water, and

chemicals like solvents, paint, etc., that goes in.

• Pump solids from the tank regularly (minimum

evry 4 years)

• Keep leach field free of rooted plants

• Divert surface water away from the field


A common saying:

“The solution to

pollution is

dilution”

Groundwater Pollution commonly occurs as plumes that show

concentration gradients having constituents concentrations decreasing away from the

source area.

In New Jersey, parties that are determined to be responible for groundwater contamination

are required to delineate the ‘horizontal and vertical limits’ of pollution plume, usually by

drilling test, observation, and monitoring wells.


• In the future, naturally

occurring bacteria may provide

solutions for many

groundwater pollution

problems.

• Bacteria have been shown to

convert uranium in

contaminated waters to a

highly insoluble form.

• Some microbes living in

oxygen-free sediments can

break down derivatives of

hydrofluorocarbons, which are

among the compounds under

Bacteria and Groundwater Pollution

consideration to replace ozone-destroying chlorofluorocarbons (CFCs).

• And, microbes which degrade toxic carcinogenic aromatic hydrocarbons like

benzene and toluene can be boosted to work in anaerobic conditions commonly

found in heavily polluted aquifers.

EOS, July 19,1994.


• Geysers and hot springs develop where groundwater is heated by hot subsurface

rocks or the geothermal gradient.

• Geysers are hot springs which periodically eject hot water and steam.

Hydrothermal Systems


Hot Springs Deposits,

Yellowstone, National Park,

Wyoming, USA


• Hydrothermal systems are considered primary targets

in the search for fossil evidence of early life forms.

• These environments are favorable for the generation

of organic compounds necessary for life.

Hydrothermal Systems and Early Biological Evolution

• They may also have provided sanctuaries for

heat-loving microorganisms during catastrophic earth

events.

• High rates of mineralization would favor preservation.

GSA Today, July, 2000.

• Some scientists believe that hydrothermal vents were the cradle of life, that may have began well

before 3.2 billion years ago.

• They argue that the mix of high heat and cold seawater in the vent environment led to the

formation of the first organic compounds, and that the formation of pyrite in ancient vents from

sulfur and iron could have produced energy to force organic compounds to combine, leading

eventually to the creation of life.

• In this context it has been proposed that metal sulfides of black smokers (one type of deep sea

vent) could act as catalysts in the first step toward building organic molecules.

• Using electron ionization mass spectroscopy, they found few differences when they compared

organic compounds from current vents with biologically diverse vents fossilized in 3.2-billion-year-

old greenstone from South Africa.


Old Faithful,

Yellowstone

The Geysers, Sonoma County, California

Geothermal Systems ~ 120 mi North of San

Francisco is piped directly to

electricity-generating turbines to produce

electricity for regional distribution

Geysers

Old Faithful is a cone geyser located in Wyoming, in

Yellowstone National Park, USA. N, it was the first

geyser in the park to receive a name. It is also

considered to be the most predictable geographical

feature on Earth erupting almost every 91 minutes.


• Geothermal energy It provides

a relatively clean source of

energy for heat and electricity.

• In New Jersey, a study of the

geophysical parameters needed

to design geothermal systems

shows that the efficiency of

geothermal systems in this region

increases as geological materials

become more consolidated and

hardened into rock.

• Substrate in southern New

Jersey consists of sand, silt, clay,

and gravel, which are less

efficient at storing and diffusing

heat than are the igneous,

metamorphic, and compacted

sedimentary rocks of higher

latitudes.

Geothermal Energy is formed from the steam and hot

water which resides in Earth's crust.

Dowsing, Divining, Water-Witching, and Doodlebugging

• Dowsing is the GOD-given talent of

finding subsurface features of interest

without using scientific instruments.

• Employed in attempts to locate ground

water, buried metals or ores, gemstones,

oil, gravesites, and many other objects and

materials, as well as ‘Earth currents’.

• ‘Dowsing’ or ‘water-witching’ for

water

• ‘Doodlebugging’ for oil

•There is no accepted scientific

rationale behind divining, and

there is no scientific evidence that

it is effective.

Fractured

Bedrock

Hydrogeology

A. Upward cross flows occur in wells

that penetrate deep aquifers with

strata dipping in the same direction

as topographic grade over long

distances.

B. Downward cross flows occur

where strata dip in a direction

opposite to long topographic

grades.

C. Wells that penetrate strata

intersecting both recharge areas on

hilltops and hill slopes and

discharge areas in valleys can have

both upward and downward cross

flows.

In general, cross flows can be expected to coincide with the direction of leakage in thick sequences of poorly conductive strata that

confine bed-parallel water-bearing units.

Profile diagrams illustrating the relationship between topographic grade and

direction of cross flows in wells under natural (nonpumping) conditions.

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