• Water underground is not in underground lakes and rivers but stored in pore and fractures

Source of groundwater is infiltration of rain or surface water http://jnuenvis.nic.in/subject/freshwater/groundwater.htm

• Is the top of the zone of saturation where the water pressure is equal to atmospheric.
– Because of this equal pressure if a hole Is dug water will flow freely into that hole up to the top of the water table.
– water at the water table will flow freely into a well up to the height of the water table.
http://www.educaid.org.uk/gal_well.htm

Below the water table all pore spaces are filled with water
:
Saturated
Zone
© 2005 Pearson Prentice Hall

• Above the water table, water in the unsaturated zone is under negative pressure (less than atmospheric)
• Water in this zone will not flow freely into a well.
• This zone can contain air

Unsaturated
Zone
Above the water table water does not fill
Saturated
Zone

Soil-water
Zone
Water Table
© 2005 Pearson Prentice Hall
Unsaturated
Zone
Saturated
Zone

Water table changes seasonally and daily
Dry Period
Wet Period

Level of water in lakes and rivers is often the level of the surrounding water table

1207
Unconfined aquifer
Water table
Confined aquifer
Potentiometric surface

Confined aquifer –
Recharge only at the limited outcrop area
Unconfined aquifer – recharge everywhere the aquifer occurs

Gravity controls groundwater flow.
• Groundwater flows from high head to low head.

• Hole drilled and lined with PVC or stainless steel pipe.
• Bottom 1 to 2 feet of the pipe is slotted for the water to flow in.

• The level that water rises in a well.
• In an unconfined aquifer it is the elevation of the water table .

Elevations of the
Water Table
(head) at each well
Map of Water
Table Surface – from contours of water level elevation (head)
© 2005 Pearson Prentice Hall

Direction of groundwater flow is perpendicular to the head
(groundwater elevation) contours
© 2005 Pearson Prentice Hall

• Average linear groundwater velocity v x
= K (dh/dl) q

• Average linear groundwater velocity v x
= K (dh/dl) q
K
= hydraulic conductivity q
= porosity dh/dl = hydraulic gradient- change in head with distance. Calculated from the hydrologic map.

The greater the hydraulic gradient (dh/dl) the faster the groundwater velocity.
Fast
Slow

Confining layers

How long does it take a contaminant to travel.
• Travel time T = v x v x
L
= average linear velocity (previous slide)
L
= distance of flow path

• Nearly 50% of the population of the US uses groundwater for its drinking water supply.
• 30 % of stream flow in the US is derived from groundwater discharging to the stream.
• Many aquifers are being mined
– (that is withdrawal is greater than natural recharge)
• Reduced rainfall from global warming is predicted to increase the need for groundwater.

Groundwater
Pollution http://www.cee.vt.edu/ewr/environmental/teach/gwprimer/amd/amd2.html
• Any degradation of water quality as measured by biological, chemical or physical criteria
• with respect to health or ecology
– A pollutant is any substance in which an identifiable excess is known to be harmful to a desirable living organisms.

Examples of Groundwater pollutants

LNAPL ( Light Non-Aqueous Phase Liquid)
• Non-aqueous phase is organic liquid instead of water.
– Common LNAPL – gasoline
• LNAPL floats on water at the top of the water table
– Smears across the zone of water table fluctuation.
http://oceanworld.tamu.edu/resources/environment-ook/groundwaterremediation.html

LUST (Leaky Underground Storage Tanks) usually LNAPL – gasoline or other fuel

DNAPL ( Dense Non-Aqueous Phase Liquid)
• Sinks in water to the bottom of the aquifer
• Common DNAPL is dry-cleaning solvents http://oceanworld.tamu.edu/resources/environment-ook/groundwaterremediation.html

• Landfills are lined with clay or plastic.
• A network of drains collects the leachate and pumps it to the surface for treatment.
• Monitor wells installed around the landfill to monitor groundwater quality and to detect leakage.
• Old landfills are serious pollution problem http://oceanworld.tamu.edu/resources/environmentbook/groundwatercontamination.html

• Seawater
– 35,000 mg/L NaCL
• Drinking water
– <250 mg/L NaCL

Salt water intrusion at Long Island New
York

http://www.cee.vt.edu/ewr/environmental/teach/gwprimer/roadsalt/roadsalt.html

• Used in areas lacking sewage treatment plants for household waste
• 30% of households in U.S. use septic tanks.
• Must remove bacteria, organic compounds and
From Thurston County (Washington State) Public Health & Social Services Department web page on Inspecting Your Septic Tank .

• Sewage flows to underground septic tank where solids drop to the bottom and bacteria breaks it down.
• The liquid leaks into the drain field and seeps into the soil zone where it is purified by bacterial activity in the soil.
From Thurston County (Washington State) Public Health & Social Services Department web page on Inspecting Your Septic Tank .

• Failure of septic system can occur because of
– Poor soil drainage
– Times of high water table
• Sewage will poor onto surface and into shallow soil zone if system fails.
– Can infiltrate into the groundwater and contaminate the aquifer
• Contaminants released
– Nutrients (nitrates/phosphates), metals, synthetic organic compounds, virus and bacteria.

• Many methods – these are just a few
• Sediment removal and treatment
• Pump and treat
• Vapor extraction
• Enhanced Bioremediation

• Old preferred remediation method, now seldom used.
• It is slow, taking decades to centuries to remove contamination and often fails to remove all contamination
– Some contaminants stick to soil and rock (they are adsorbed) and they cannot easily be removed (desorbed).
– Non-Aqueous Phase Liquids NAPLs cannot be removed.
• It is very costly.
From Environment Protection Agency

• Used to remove volatile organic compounds http://www.p2pays.org/ref/14/0_initiatives/init/winter98/success.htm

Enhanced Bioremediation
Bacteria living in the aquifer degrade toxic contaminants into less toxic compounds.
• Growth of the natural bacteria is stimulated by injecting nutrients and/or carbon compounds needed by the bacteria into the aquifer.
• The bacteria break down contaminants such as trichloroethylene TCE into non-toxic compounds such as carbon dioxide http://www.erc.montana.edu/MultiCellStrat/01-Waiting_UMB/BioremedSchem.htm

• English Rule (Absolute Ownership)
– Water can be pumped at will by landowner independent of effect on other users of the aquifer
• American Rule (Reasonable Use) – applied in areas were water supplies are limited
– Applied in much of the western U.S.
– Limits water use to what is reasonable and beneficial (hard to determine)
– Argue over what is beneficial use
• Is supplying water to a river more important than to crops?
– Safe yield calculated and used to regulate aquifers.

Texas groundwater law
“Law of the biggest pump”
• Based on the English rule - a landowner has a right to take for use or sale all the water that he can capture from below his land
– Once pumped, groundwater may be used or sold as private property
• Creation of groundwater conservation districts is the only way to limit use.

(Texas Groundwater Use
,

Well head protection of aquifer recharge zones http://www.geopanorama.rncan.gc.ca/h2o/okanagan/groundwater_e.php

Federal regulations protecting groundwater quality

• The Comprehensive Environmental
Response, Compensation, and Liability
Act (CERCLA), 1980, commonly known as
Superfund ,
• This law created a tax on the chemical and petroleum industries to be used to clean up releases of hazardous substances that may endanger public health or the environment.

Superfund National Priorities List
Sites http://www.nationalatlas.gov/natlas/Natlasstart.asp

RCRA
• Resource Conservation and Recovery Act.
• It controls all solid waste disposal and encourages recycling and alternative energy sources.

New
American Recovery and
Reinvestment Act of 2009
• $600 million to EPA to clean up land contaminated by hazardous wastes.
• Part of Federal stimulus funding program to create jobs.