Ground water/ Hydrogeology Learning Objectives

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Ground water/ Hydrogeology Learning Objectives

• Ground water is a noun groundwater is an
  adjective
• Understand how soil properties affect hydraulic
  conductivity
• Understand the difference between pressure head,
  elevation
• head, velocity head and total head
• Understand Darcys Law
• Be able to describe the differences among
  unconfined, perched,
• confined and artesian aquifers
• Be able to define relevant groundwater terms
  including but not limited to water table,
  capillary fringe, vadose zone, storativity, and
  transmissivity
• Understand the spatial and temporal properties of
  aquifers and
• ground water
• Understand the effects of human activities on
  groundwater
• resources

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Ground water factoids

• Scientists estimate groundwater accounts for
  more than 95 of       all fresh water available
  for use.
• Approximately 50 of Americans obtain all or
  part of their       drinking water from
  groundwater.
• Nearly 95 of rural residents rely on
  groundwater for their       drinking supply.
• About half of irrigated cropland uses
  groundwater.
• Approximately one third of industrial water
  needs are fulfilled by       using groundwater.
• About 40 of river flow nationwide (on
  average) depends on       groundwater.

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Hydrologic Cycle
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Zones of Subsurface Water

• Zone of Aeration
• pores filled with both air and water
• Water held against gravity by surface tension
• Soil water/ soil moisture

• Zone of Saturation
• pores filled only with water
• Water drained through soil under influence of
  gravity.
• Ground Water

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Essential components of groundwater
The rate of infiltration is a function of soil
type, rock type, antecedent water, and time.
The vadose zone includes all the material between
the Earths surface and the zone of saturation.
The upper boundary of the zone of saturation is
called the water table. The capillary fringe is a
layer of variable thickness that directly
overlies the water table. Water is drawn up into
this layer by capillary action.
S. Hughes, 2003
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How does the geology affect the existence of
ground water?

• What is an aquifer?
• A permeable, water-containing unit.
• - Water enters from recharge.
• - Temporarily stored.
• - Leaves by flow to streams (baseflow)
• or springs, or to wells
• - Has sufficient water to be usable

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What is an unconfined aquifer?

• They are not sealed off at any point.
• Recharge can occur anywhere.
• Water at water table under atmospheric pressure.
• Must pump to remove water

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Unconfined Aquifer
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What is a confined (or artesian) aquifer?

• Sealed off
• Transmits water down from recharge area
• Water confined in aquifer unless
• drilled.
• - Water under hydrostatic
• pressure.
• - Water rises well may flow.

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Artesian well spouts water above land surface in
South Dakota, early 1900s. Heavy use of this
aquifer has reduced water pressure so much that
spouts do not occur today
Betsy Conklin for Dr. Isiorho
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Unconfined and Perched Aquifers
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How is this possible?
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Ground Water and Surface Water

• These are almost always connected
• If a stream contributes water to the aquifer its
  called a losing stream
• If a stream receives water from the aquifer its
  called a gaining stream
• Same stream can be both at different places or at
  different times

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Perennial Stream (effluent) (from Keller, 2000,
Figure 10.5a)

• Humid climate
• Flows all year -- fed by groundwater base flow
  (1)
• Discharges groundwater

S. Hughes, 2003
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Ephemeral Stream (influent) (from Keller, 2000,
Figure 10.5b)

• Semiarid or arid climate
• Flows only during wet periods (flashy runoff)
• Recharges groundwater

S. Hughes, 2003
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• Groundwater flow patterns are controlled by
  several factors
• Elevation and location of recharge and discharge
  areas.
• Heterogeneity of geologic material
• Thickness of material
• Current or historic land use practices

• Presence of streams, lakes, or springs can also
  greatly influence groundwater patterns.

(Fetter 2001)
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How does ground water move?

• Porosity by volume of an earth material that
  is pore space.
• Primary porosity depends upon
• - shape of grains
• - arrangement of grains
• - size distribution
• - compaction/cementn

• Permeability ability of an earth material to
  transmit water
• Depends upon
• - porosity
• - degree and size of interconnecting pores
  between larger pores

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What are some typical values of porosity and
permeability?

• Porosity
• clay 45-55
• sand 30-40
• sandstone 10-20
• shale 1-2
• limestone 1-10 (or larger)
• Permeability varies over several orders of
  magnitude. Expressed as a rate, e.g. ft/day

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Darcys Law

• formulated by Henry Darcy based on the results of
  1855 and 1856 experiments
• stating that the flow rate of water through
  porous materials is proportional to the hydraulic
  head drop and the distance (hydraulic gradient )
• The law holds only in laminar flows

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laminar flow

• smooth, viscosity dominated flow. the direction
  of motion at any point remaining constant as if
  the fluid were moving in a series of layers
  sliding over one another without mixing
• Reynold's number for groundwater
• Re d V ? / µ
• where d grain diameter, (usually d30),
• V velocity
• ? density of water
• µ viscosity of water
• Laminar flow Normally Re lt 1 Never gt 10

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Bernoulli's equation

• describes the behavior of a fluid moving along a
  streamline
• v2 z p
• 2g ?g
• Velocity Head Elevation Head Pressure Head
• In ground water v is so small that can ignore

Datum
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Darcys velocity v k i
p1
i ?h / L ?h (p1 z1) - (p2 z2) ?h is
the change in hydraulic gradient between point 1
and point 2
p2
z1
z2
Datum
L
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Darcys Law

• V k i
• V Flow Velocity
• k Hydraulic Conductivity
• (The rate at which a soil allows water to move
  through it )
• i Hydraulic Gradient i h / L
• (Change in hydraulic head per unit of horizontal
  distance )

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Darcys Law

• Q V A
• k i A Darcys Law
• A Cross-sectional area of the Soil
• k saturated hydraulic conductivity
• i the change in hydraulic gradient
• divided by the distance over which the
• gradient changed

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Hydraulic Conductivity, k

• Soil grain size
• Structure of the soil matrix
• pore size distribution
• pore shape
• porosity
• Type of soil fluid
• fluid density
• fluid viscosity
• Saturation

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How to get k (lab)

• Constant-head conductivity test
• Q K i A (remember Q VA and V Ki)
• i ?h / L so Q K (?h / L) A
• K Q (L / A?h)
• Q Discharge
• A Cross-sectional area

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How to get k (field)

• Pumping methods / Tracking methods
• Auger-hole method
• Saturated soil materials near the ground surface
  in the presence of a shallow water table.
• pumping the water out of an auger-hole extending
  below the water table and then measuring the rate
  of the rise of the water in the hole
• Tracking with dyes, chemicals, radiation, or
  electrical conductivity

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(Ward and Trimble 2004)

• Elevation head is the position of a particle
  relative to some standard measurement plane, sea
  level, etc.
• Pressure head is the height of a column of fluid
  that will produce a given pressure.

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(Ward and Trimble 2004)

• Groundwater contours at streams form a V, they
  point upstream when they cross a gaining stream
  and pointing downstream when they cross a losing
  stream.
• When a stream has a greater level than the water
  in a aquifer the water in the stream recharges
  the groundwater. This is common in the western
  U.S. where stream begin high in the mountains and
  flow in alluvial fans formed at the base.

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Monitoring Wells and Piezometers
Water levels within wetlands and adjacent to
streams involves investigating shallow
groundwater regimes.
Monitoring wells have perforation extending from
just below the ground surface to the bottom of
the pipe. Piezometers are perforated only at
the bottom of the pipe.
(WRP TN HY-IA-3.1)
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(WRP TN HY-IA-3.1)

• Monitoring Well Water levels in pipe is the
  result of intergraded water pressure along the
  entire length of pipe.
• Piezometer Water level inside the pipe is the
  result from water pressure over a narrow zone of
  the pipe.

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Instrument Selection

• Monitoring Wells
• Determining timing, duration, and frequency of
  the water table
• Collected data from various wells used to
  construct groundwater contour maps or
  potentiometric surface maps
• Piezometers
• Determining recharge or discharge
• Determining ground water flow direction
• Determine if perching layers are present

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Ground water management issues

• Vegetation removal can decrease interception and
  ET losses
• Leads to increase soil moisture- higher water
  tables
• Ground water extraction exceeding recharge
• Leads to higher pumping costs
• Land subsidence
• Sea water intrusion if coastal

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Ground water management issues

• Urbanization can decrease recharge opportunity
• Decrease soil storage, decrease low flows
• Ground water contamination
• Improper dumping of contaminants
• Difficult to clean up

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Well drawdown
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Problems associated with extreme groundwater
withdrawal

• Dry Wells cone of depression already seen
• Saltwater contamination near coast
• Groundwater withdrawal causes saltwater to be
  drawn into coastal wells, contaminating supply
• Contamination of Wells with sewage
• Formation of Collapse Sinkholes

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Saltwater contamination due to excessive well
pumping
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Sinkholes in Urban Settings
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• What happens when a new well here is heavily
  pumped?

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Flow direction can change
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Groundwater Overdraft

• Overpumping will have two effects
• 1. Changes the groundwater flow direction.
• 2. Lowers the water table, making it necessary to
  dig a deeper well.
• This is a leading factor in desertification in
  some areas.
• Original land users and land owners often spend
  lots of money to drill new, deeper wells.
• Streams become permanently dry.

S. Hughes, 2003
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Groundwater Overdraft

• Almost half the U.S. population uses groundwater
  as a primary source for drinking water.
• Groundwater accounts for 20 of all water
  withdrawn for consumption.
• In many locations groundwater withdrawal exceeds
  natural recharge rates. This is known as
  overdraft.
• In such areas, the water table is drawn down
  "permanently" therefore, groundwater is
  considered a nonrenewable resource.
• The Ogallala aquifer underlies Midwestern
  states, including Texas, Oklahoma, and New
  Mexico, while California, Arizona and Nevada use
  the Colorado River as their primary water source.
  All show serious groundwater overdraft.

S. Hughes, 2003
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Groundwater Overdraft in the Conterminous U.S.
(from Keller, 2000, Figure 10.13a)
S. Hughes, 2003
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where current ground moisture is significantly
lower than the long-term average,
http//www.circleofblue.org/waternews
/wp-content/uploads/2011/12/GRACE_GWS.png
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Groundwater Overdraft

• Water-level changes in the Texas--Oklahoma-High
  Plains area.
• The Ogallala aquifer -- composed of
  water-bearing sands and gravel that underlie
  about 400,000 km2.
• Water is being used for irrigation at a rate up
  to 20 times more than natural recharge by
  infiltration.
• Water level (water table) in many parts has
  declined and the resource eventually may be used
  up.

(from Keller, 2000, Figure 10.13b)
S. Hughes, 2003
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Pollution of Ground Water

• pesticides, herbicides, fertilizers chemicals
  that are applied to agricultural crops that can
  find their way into ground water when rain or
  irrigation water leaches the poisons downward
  into the soil
• rain can also leach pollutants from city dumps
  into ground-water supplies
• Heavy metals such as mercury, lead, chromium,
  copper, and cadmium, together with household
  chemicals and poisons, can all be concentrated in
  ground-water supplies beneath dumps

www.geology.iupui.edu/Academics/.../G110-10-Ground
_Water.ppt
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Pollution of Ground Water

• liquid and solid wastes from septic tanks, sewage
  plants, and animal feedlots and slaughterhouses
  may contain bacteria, viruses, and parasites that
  can contaminate ground water
• acid mine drainage from coal and metal mines can
  contaminate both surface and ground water
• radioactive waste can cause the pollution of
  ground water due to the shallow burial of
  low-level solid and liquid radioactive wastes
  from the nuclear power industry

www.geology.iupui.edu/Academics/.../G110-10-Ground
_Water.ppt
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Pollution of Ground Water (cont.)

• pumping wells can cause or aggravate ground-water
  pollution

Water table steepens near a dump, increasing the
velocity of ground-water flow and drawing
pollutants into a well
Water-table slope is reversed by pumping,
changing direction of the ground-water flow, and
polluting the well
www.geology.iupui.edu/Academics/.../G110-10-Ground
_Water.ppt
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Balancing Withdrawal and Recharge

• a local supply of groundwater will last
  indefinitely if it is withdrawn for use at a rate
  equal to or less than the rate of recharge to the
  aquifer
• if ground water is withdrawn faster than it is
  being recharged, however, the supply is being
  reduced and will one day be gone

www.geology.iupui.edu/Academics/.../G110-10-Ground
_Water.ppt
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Balancing Withdrawal and Recharge

• heavy use of ground water can result in
• a regional water table dropping
• deepening of a well which means more electricity
  is needed to pump the water to the surface
• the ground surface settling because the water no
  longer supports the rock and sediment

1925
Subsidence of the land surface caused by the
extraction of ground water, near Mendota, San
Joaquin Valley, CA. Signs on the pole indicate
the positions of the land surface in 1925, 1955,
and 1977. The land sank 30 feet in 52 years.
1955
www.geology.iupui.edu/Academics/.../G110-10-Ground
_Water.ppt
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Ground Water in Space and Time
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Groundwater Hydrograph

• Seasonal water level fluctuations reflect
  variations in precipitation, evaporation, and
  transpiration.
• Periods of rising water levels indicate recharge

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Thurston County
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Mean
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Balancing Withdrawaland Recharge

• to avoid the problems of falling water tables,
  subsidence, and compaction, many towns use
  artificial recharge to increase recharge natural
  floodwaters or treated industrial or domestic
  wastewaters are stored in infiltration ponds in
  the surface to increase the rate of water
  percolation into the ground

www.geology.iupui.edu/Academics/.../G110-10-Ground
_Water.ppt
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Ground water chemistry

• One of the most important natural changes in
  groundwater chemistry occurs in the soil. Soils
  contain high concentrations of carbon dioxide
  which dissolves in the groundwater, creating a
  weak acid capable of dissolving many silicate
  minerals

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Ground Water vs Surface Water Quality

• GW quality, temperature and other parameters are
  less variable over the course of time than SW
• Range of groundwater parameters encountered is
  much larger than for surface water, e.g., total
  dissolved solids can range from 25 mg/L in some
  places in the Canadian Shield to 300 000 mg/L in
  some deep saline waters in the Interior Plains.
• At any given location, groundwater tends to be
  harder and more saline than surface water.
• It is also generally the case that groundwater
  becomes more saline with increasing depth, but
  again, there are many exceptions.

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Ground water and geology

• Ground water is also important quite apart from
  its value as a resource or its close connection
  with surface water supplies.
• Ignoring the effect of ground water on slope
  stability can be both costly and dangerous.
• The fluid pressures exerted by ground water, for
  example, play an important role in the occurrence
  of earthquakes.
• Geologists also know that the movement of water
  through underground geologic formations controls
  the migration and the accumulation of petroleum
  and the formation of some ore deposits.

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Ground water as energy source

• Ground water may be used as a source of heat.
  Ground source heat pumps are receiving increased
  attention as energy efficient commercial and
  residential heating/cooling systems. Although
  initial costs are higher than air source
  systems  due to the additional costs of the
  underground installations  the much greater
  energy efficiency of ground source systems makes
  them increasingly attractive.
• Research into the use of geothermal water has
  been carried out in a number of institutions
  across Canada. The City of Moose Jaw has
  developed a geothermal heating system for a
  public swimming pool and recreational facility.
  Carleton University in Ottawa already uses
  groundwater to heat and cool its buildings. The
  Health Centre complex in Sussex, New Brunswick
  has been utilizing an aquifer for thermal energy
  storage since 1995.

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Hydraulic fracking

• 2 million to 4 million gallons of water per well,
  as well as a variety of chemicalssome of them
  toxicto reduce friction, prevent corrosion, and
  kill bacteria in the well.
• 2 million to 4 million gallons of water, as well
  as a variety of chemicalssome of them toxicto
  reduce friction, prevent corrosion, and kill
  bacteria in the well.
• After tapping the well, fracking chemicals are
  pumped out along with any naturally occurring
  water. This flow-back water is often
  temporarily stored in open-air pits that, while
  lined, can leak or overflow during heavy rains.

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GAS WELL

• Shale gas deposits are far deeper than freshwater
  aquifers, reducing the potential for groundwater
  contamination from fracking chemicals, there have
  been incidents of aboveground chemical spills and
  gas leaks into well water
• One NAS study in PA and NY found higher
  concentrations of methane in water wells within 1
  km of gas wells.
• No evidence of fracking fluids
• Few studies, much contention
• Uses large amounts of water to inject chemicals

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Washington urls

• http//dnr.metrokc.gov/wlr/wq/groundwater.htm
  King County Groundwater
• http//www.ecy.wa.gov/programs/eap/groundwater/res
  ources.html WA DOE- GW assessment
• http//apps.ecy.wa.gov/welllog/
• WA DOE- well logs