Prepared by Mark R' Noll

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Prepared by Mark R. Noll SUNY College at Brockport
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Groundwater

• Groundwater is an open, dynamic system
• Gravity is primary driving force
• Pulls water down
• Water enters the system at the ground surface
  through recharge
• Leaves the system through discharge

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Porosity

• Percent of the total volume that is open space
• Affected by the size and shape of particles
• Increased by fracturing or dissolution
• Decreased by compaction and cementation
• Well sorted sediments have higher porosity than
  poorly sorted sediments

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Permeability

• How easily fluid may pass through a rock
• A measure of how well the pores are connected,
  and how straight a path a fluid follows
• Permeability is a property of the rock
• Hydraulic conductivity is the ability of water to
  flow through a rock
• Other liquids such as oil flow through rock
• Density and viscosity influence flow rate

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The Water Table

• Water is found at some depth everywhere beneath
  the Earths surface
• The water table defines the boundary below which
  all pore spaces are filled with water
• The volume of pore spaces decreases as you go
  deeper into the crust
• Usable water is restricted to a few hundred
  meters below the surface

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The Water Table

• Forms the boundary between the Saturated Zone and
  the Unsaturated Zone
• The unsaturated zone is also referred to as the
  vadose zone or zone of aeration
• The Capillary Fringe is a thin layer in the
  unsaturated zone just above the water table
  surface

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Fig. 13.2. The water table
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Aquifers

• Aquifer
• A layer or zone in the subsurface capable of
  producing water to a well (in usable quantity)
• Aquitard
• Aquiclude
• Confining Unit
• A layer or zone in the subsurface that does not
  easily allow water to pass through it

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Aquifers

• Unconfined Aquifer
• An aquifer that has highly permeable material
  extending from ground surface downward to an
  aquitard at its base
• Recharge is from seepage, lateral flow of
  groundwater, or upward leakage through the
  aquitard
• Also called a water table aquifer

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Aquifers

• Perched Aquifer
• A layer of saturated soil found in the
  unsaturated zone
• Underlain by an aquitard of limited aerial extent
• Recharge is only from seepage
• Water flows to the edge and continues down

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Aquifers

• Confined Aquifer
• Aquitards form confining units top and bottom
• Recharge occurs in an area some distance away or
  by leakage through the aquitard
• The water level (potentiometric surface) may be
  above the top of the aquifer
• Artesian aquifers have a potentiometric surface
  above ground surface

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Fig. 13.9. An unconfined aquifer system
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Groundwater Flow

• Groundwater flows due to the force of gravity
• Hydraulic gradient defines the water table slope
• Hydraulic head is the elevation of the water
  table at a given point
• The water table surface usually mimics the ground
  surface contours

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Groundwater Flow

• Flow is from high to low hydraulic head
• Gravity creates water pressure
• Pressure forces water to flow downward to the
  water table
• Water continues to flow downward and outward
• Flow is along curved path

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Fig. 13.3 Groundwater Movement
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Discharge

• Groundwater and surface water are intimately
  linked
• Discharge occurs to lakes, streams and wetlands
• Maintains flow in streams during dry periods
• Artificial discharge is the result of wells

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Natural Discharge

• Springs include any natural flow of water from
  the ground surface
• Intersection of water table-ground surface
• Springs are caused by
• Aquitards intersecting the ground surface
• Faults cutting through an artesian aquifer
• Fractures in volcanic rock
• Road cuts

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Fig. 13.6a. Spring developing where
aquitards intersect the surface
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Wells

• Before Pumping
• Water table is nearly horizontal
• During Pumping
• Water table is depressed as water is withdrawn
  from the aquifer
• Forms cone of depression

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Wells

• Cone of Depression
• Depression of the groundwater forms an inverted
  cone in 3-D
• The cone of depression will continue to grow
  outward until
• Pumping is stopped
• The volume of recharge the volume of water
  discharged from the well

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Fig. 13.8. Pumping well creates cone of
depression
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Thermal Springs Geysers

• Geysers and hot springs require
• Hot rock bodies to heat groundwater
• Fractures system to transmit water
• Large supply of groundwater
• Geysers such as Old Faithful are the results of
  this process

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Thermal Springs Geysers

• Hot water contains thermal energy and dissolved
  ions
• Geothermal energy taps heat source
• Many mineral deposits are produced by hot water
  interacting with cooling igneous intrusions

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Groundwater Erosion

• Groundwater chemically weathers erodes the
  bedrock through dissolution
• Subsurface dissolution forms
• Caves
• Sinkholes
• Karst topography

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Karst Topography

• Karst topography is found in areas that have
  carbonate, sulfate, or salt beds at or near the
  ground surface
• Characterized by
• Solution valleys
• Disappearing streams
• Sinkholes

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Fig. 13.17. Evolution of Karst Topography
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Groundwater Deposits

• Minerals may precipitate from dissolved ions in
  groundwater
• CO2 in water dissipates into air
• pH of water changes
• CaCO3 is precipitated
• Other soluble minerals may occur
• Gypsum

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Groundwater Resources

• Groundwater is the largest reserve of fresh water
• Much larger than surface water resources
• Used for drinking water, irrigation industrial
  uses
• Excessive use may alter the groundwater system

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Groundwater Chemistry

• Groundwater may contain abundant dissolved ions
• Dependent on
• The type of rock in the aquifer
• The groundwater velocity
• The time the water has been underground

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Groundwater Chemistry

• The major ions present in groundwater are
• Bicarbonate ( HCO3-1), Sulfate (SO4-2),
  Chloride (Cl-1)
• Calcium (Ca), Magnesium (Mg), Sodium (Na),
• The pH of groundwater ranges form mildly acidic
  (5.5) to mildly alkaline (8)
• Human activity may alter the natural system

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Groundwater Pollution

• Types of groundwater pollution include
• Septic tank drainage
• Agricultural chemicals
• Industrial chemicals
• Petroleum products
• Landfills

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Saltwater Encroachment

• Salt water has a higher density than fresh water
  due to the dissolved salts
• Salt water intrusion occurs when groundwater
  resources in coastal areas are overused
• The salt water intrusion is not easy to reverse

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Fig. 13.27. Water resources in coastal areas
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Over-Pumping

• Lowers the water table
• Wetland areas may lose source of discharge
• Impacts ecology of area
• Results in compaction and subsidence of
  unconsolidated sediments

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Fig. 13.28. Changes in the Everglades due
to lowering of the water table
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End of Chapter 13