11: Groundwater

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11 Groundwater

• Water resources
• Geologic Agent

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Hydrogeology Defined
Water
Earth

• Earth materials
• Rock
• Sediment (Soil)
• Fluids (Water)
• Geologic processes
• Form,
• Transform and
• Distribute (redistribute) Earth materials
• ? Water is a primary agent of many (all?)
  geologic processes

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Hydrogeology Defined Water Earth
Interactions
??

• Interactions go both ways
• Geology?Groundwater
• Geology controls flow and availability of
  groundwater because
• Groundwater flows through the pore spaces and/or
  fractures
• Groundwater ? geologic processes.

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Hydrogeology Defined Water??Earth Interactions

• Geology controls groundwater flow
• Permeable pathways are controlled by
  distributions of geological materials.
• E.g., Artesian (confined) aquifer

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Hydrogeology Defined Water??Earth Interactions

• Geology controls groundwater flow
• Permeable pathways are controlled by
  distributions of geological materials.
• Groundwater availability is controlled by
  geology.

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Hydrogeology Defined Water??Earth Interactions

• Geology controls groundwater flow
• Permeable pathways are controlled by
  distributions of geological materials.
• Groundwater availability is controlled by
  geology.
• Subsurface contaminant
• transport in is controlled
• by geology.

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Hydrogeology Defined Water??Earth Interactions
Groundwater controls geologic processes

• Igneous Rocks Groundwater controls water content
  of magmas.
• Metamorphic Rocks Metasomatism (change in
  composition) is controlled by superheated pore
  fluids.
• Volcanism Geysers are an example of volcanic
  activity interacting with groundwater.

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Hydrogeology Defined Water??Earth Interactions

• Groundwater controls geologic processes
• Landforms Valley development and karst
  topography are examples of groundwater
  geomorphology.
• Landslides Groundwater controls slope failure.
• Earthquakes Fluids control fracturing, fault
  movement, lubrication and pressures.

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Hydrogeology Subdisciplines

• Water resource evaluation
• What controls how much groundwater is stored and
  can be safely extracted?
• What controls where groundwater comes from and
  where it flows?
• What controls natural water quality natural
  interactions with geological materials control
  the chemistry of groundwater?
• How can we protect groundwater recharge areas and
  groundwater reservoirs from contamination and
  depletion?

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Hydrogeology Subdisciplines

• Contaminant Hydrogeology
• Anthropogenic effects degradation of water
  quality due to human influences (contamination)
• How fast are dissolved contaminants carried by
  groundwater?
• Transport pathways of contaminants Where are
  sources of contamination impacting the
  groundwater, where are the going and what are the
  destinations?
• Remediation (clean-up) of contaminants dissolved
  in the groundwater.

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Darcys Law Answers the fundamental questions of
hydrogeology.

• What controls
• How much groundwater flows?
• How fast groundwater flows?
• Where groundwater flows?

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Darcys Law

• Henry Darcys Experiment (Dijon, France 1856)

Darcy investigated ground water flow under
controlled conditions
A
Q Volumetric flow rate L3/T
A Cross Sectional Area (Perp. to flow)
Dx
Q
K The proportionality constant is added to form
the following equation
K units L/T
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Calculating Velocity with Darcys Law

• Q Vw/t
• Q volumetric flow rate in m3/sec
• Vw Is the volume of water passing through area
  a during
• t the period of measurement (or unit time).
• Q Vw/t HWD/t av
• a the area available to flow
• D the distance traveled during t
• v Average linear velocity
• In a porous medium a An
• A cross sectional area (perpendicular to flow)
• n porous For media of porosity
• Q Anv
• v Q/(nA)q/n

v
Vw
a
H
w
D
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Darcys Law (cont.)

• Other useful forms of Darcys Law

• Used for calculating Volumes of groundwater
  flowing during period of time

• Volumetric Flow Rate

• Volumetric Flux
• (a.k.a. Darcy Flux or
• Specific discharge)

• Used for calculating Q given A

Q

A

• Ave. Linear
• Velocity

• Used for calculating average velocity of
  groundwater transport
• (e.g., contaminant
• transport

Q
q


A.n
n

• Assumptions Laminar, saturated flow

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Darcys Law Application

• Settling Pond Example

• A company has installed two settling ponds to
• Settle suspended solids from effluent
• Filter water before it discharges to stream
• Damp flow surges

• Questions to be addressed
• How much flow can Pond 1 receive without
  overflowing? ?Q?
• How long will water (contamination) take to reach
  Pond 2 on average??v?
• How much contaminant mass will enter Pond 2 (per
  unit time)? ?M?

This is a hypothetical example based on a
composite of a few real cases
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Application (cont.)
Water flows between ponds through the saturated
fine sand barrier driven by the head difference
Pond 1
Pond 2
W 1510 ft
Outfall
Overflow
Elev. 658.74 ft
Elev. 652.23 ft
Dx 186
Sand
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Application (cont.)

• Develop your mathematical representation
• (i.e., convert your conceptual model into a
  mathematical model)
• Formulate reasonable assumptions
• Saturated flow (constant hydraulic conductivity)
• Laminar flow (a fundamental Darcys Law
  assumption)
• Parallel flow (so you can use 1-D Darcys law)
• Formulate a mathematical representation of your
  conceptual model that
• Meets the assumptions and
• Addresses the objectives

M Q C
Q?
v?
M?
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Application (cont.)

• Collect data to complete your Conceptual Model
  and to Set up your Mathematical Model
• The model determines the data to be collected
• Cross sectional area (A w b)
• w length perpendicular to flow
• b thickness of the permeable unit
• Hydraulic gradient (Dh/Dx)
• Dh difference in water level in ponds
• Dx flow path length, width of barrier
• Hydraulic Parameters
• K hydraulic tests and/or laboratory tests
• n estimated from grainsize and/or laboratory
  tests
• Sensitivity analysis
• Which parameters influence the results most
  strongly?
• Which parameter uncertainty lead to the most
  uncertainty in the results?

Q?
v?
M Q C
M?
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Ground Water Zones

• Degree of saturation defines different soil water
  zones

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Soil and Groundwater Zones
Unsaturated Zone
Water in pendular saturation
Caplillary Fringe Water is pulled above the
water table by capilary suction
Water Table where fluid pressure is equal to
atmospheric pressure
Saturated Zone Where all pores are
completely filled with water. Phreatic Zone
Saturated zone below the water table
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• Ground water and the Water cycle
• Infiltration
• Infiltration capacity
• Overland flow
• Ground water recharge
• GW flow
• GW discharge

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Bedrock Hydrogeology

• Hydraulic Conductivity of bedrock is controlled by

• Size of fracture openings
• Spacing of fractures
• Interconnectedness of fractures

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Porosity and Permeability

• Porosity Percent of volume that is void space.
• Sediment Determined by how tightly packed and
  how clean (silt and clay), (usually between 20
  and 40)
• Rock Determined by size and number of fractures
  (most often very low, lt5)

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5
1
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Porosity and Permeability

• Permeability Ease with which water will flow
  through a porous material
• Sediment Proportional to sediment size
• Gravel?Excellent
• Sand?Good
• Silt?Moderate
• Clay?Poor
• Rock Proportional to fracture size and number.
  Can be good to excellent

Excellent
Poor
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Porosity and Permeability

• Permeability is not proportional to porosity.

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Table 11.1
5
1
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The Water Table

• Water table the surface separating the vadose
  zone from the saturated zone.
• Measured using water level in well

Fig. 11.1
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Ground-Water Flow

• Precipitation
• Infiltration
• Ground-water recharge
• Ground-water flow
• Ground-water discharge to
• Springs
• Streams and
• Wells

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Ground-Water Flow

• Velocity is proportional to
• Permeability
• Slope of the water table
• Inversely Proportional to
• porosity

Fast (e.g., cm per day)
Slow (e.g., mm per day)
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Natural Water Table Fluctuations

• Infiltration
• Recharges ground water
• Raises water table
• Provides water to springs, streams and wells
• Reduction of infiltration causes water table to
  drop

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Natural Water Table Fluctuations

• Reduction of infiltration causes water table to
  drop
• Wells go dry
• Springs go dry
• Discharge of rivers drops
• Artificial causes
• Pavement
• Drainage

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Effects of Pumping Wells

• Pumping wells
• Accelerates flow near well
• May reverse ground-water flow
• Causes water table drawdown
• Forms a cone of depression

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Effects of Pumping Wells
Gaining Stream

• Pumping wells
• Accelerate flow
• Reverse flow
• Cause water table drawdown
• Form cones of depression

Water Table Drawdown
Low well
Dry Spring
Cone of Depression
Gaining Stream
Low well
Low river
Pumping well
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Effects of Pumping Wells
Dry well

• Continued water-table drawdown
• May dry up springs and wells
• May reverse flow of rivers (and may contaminate
  aquifer)
• May dry up rivers and wetlands

Losing Stream
Dry well
Dry well
Dry river
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Ground-Water/ Surface-Water Interactions

• Gaining streams
• Humid regions
• Wet season
• Loosing streams
• Humid regions, smaller streams, dry season
• Arid regions
• Dry stream bed

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Confined Aquifers
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Confined Aquifers
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Ground-Water Contamination

• Dissolved contamination travels with ground water
  flow

• Contamination can be transported to water supply
  aquifers down flow
• Pumping will draw contamination into water supply

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Ground-Water Contamination

• Leaking Gasoline
• Floats on water table
• Dissolves in ground water
• Transported by ground water
• Contaminates shallow aquifers

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Ground-Water Contamination

• Dense solvents
• E.g., dry cleaning fluid (TCE)
• Sinks past water table
• Flows down the slope of an impermeable layer
• Contaminates deeper portions of aquifers

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Ground-Water Contamination

• Effects of pumping
• Accelerates ground water flow toward well
• Captures contamination within cone of depression
• May reverse ground water flow
• Can draw contamination up hill
• Will cause saltwater intrusion

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Ground Water Action

• Ground water chemically weathers bedrock
• E.g., slightly acidic ground water dissolves
  limestone
• Caves are formed
• Permeability is increased
• Caves drain
• Speleothems form

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Ground Water Action

• Karst Topography
• Caves
• Sink holes
• Karst valleys

• Disappearing streams
• Giant springs

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Ohio Groundwater Law

• 1843 Acton v. Blundell English Rule
• The landowner can pump groundwater at any rate
  even if an adjoining property owner were harmed.

• 1861 Frazier v. Brown English Rule in Ohio
• Groundwater is
• occult and concealed
• and legislation of its use is
• practically impossible.

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Wisconsin Groundwater Law

• 1903 Huber v. Merkel
• English Rule in Wisconsin
• A property owner can pump unlimited amounts of
  groundwater,
• even with malicious harm to a neighbor.

• 1974 Wisconsin v. Michels Pipeline Constructors
  Inc.
• English Rule Overturned
•  
• Landowners no longer have an absolute right to
  use with impunity all water that can be pumped
  from the subsoil underneath.

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English Rule Overturned in Ohio

• 1984 Cline v. American Aggregates
•  English Rule overturned in Ohio
•  
• Justice Holmes Scientific knowledge in the
  field of hydrology has advanced in the past
  decade so it
•  
• can establish the cause and effect relationship
  of the tapping of underground water to the
  existing water level.

• Today Lingering effects of English Rule
• It is very difficult to prove cause and effect to
  be defensible in court.

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