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11: Groundwater. Water resources Geologic Agent. Hydrogeology Defined. Water. Earth. Earth materials Rock Sediment (Soil) Fluids (Water) Geologic processes Form , Transform and Distribute (redistribute) Earth materials

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11 groundwater
11: Groundwater
  • Water resources
  • Geologic Agent
hydrogeology defined
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

hydrogeology defined water earth
Hydrogeology DefinedWater 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.
hydrogeology defined water earth interactions

Shale

Sandstone

Shale

Hydrogeology DefinedWaterEarth Interactions

Geology controls groundwater flow

  • Permeable pathways are controlled by distributions of geological materials.
    • E.g., Artesian (confined) aquifer
hydrogeology defined water earth interactions5
Hydrogeology DefinedWaterEarth Interactions

Geology controls groundwater flow

  • Permeable pathways are controlled by distributions of geological materials.
  • Groundwater availability is controlled by geology.
hydrogeology defined water earth interactions6
Hydrogeology DefinedWater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.

hydrogeology defined water earth interactions7
Hydrogeology DefinedWater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.
hydrogeology defined water earth interactions8
Hydrogeology DefinedWater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.
hydrogeology subdisciplines
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?
hydrogeology subdisciplines10
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.
darcy s law answers the fundamental questions of hydrogeology

Potentiometric

Surface

Darcy’s Law Answers the fundamental questions of hydrogeology.
  • What controls:
    • How much groundwater flows?
    • How fast groundwater flows?
    • Where groundwater flows?
darcy s law

Darcy’s Law

Henry Darcy’s Experiment (Dijon, France 1856)

h1

h2

Dh

: Hydraulic Gradient

h

Slope = Dh/Dx

~ dh/dx

h1

Dh

h2

Dx

x

x1

x2

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:

Kunits [L/T]

calculating velocity with darcy s law
Calculating Velocity with Darcy’s 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 = H∙W∙D/t = a∙v
    • a: the area available to flow
    • D: the distance traveled during t
    • v : Average linear velocity
  • In a porous medium: a = A∙n
    • A: cross sectional area (perpendicular to flow)
    • n: porous For media of porosity
  • Q = A∙n∙v
  • v = Q/(n∙A)=q/n

v

Vw

a

H

w

D

darcy s law cont
Darcy’s Law (cont.)
  • Other useful forms of Darcy’s 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

darcy s law application

Pond 2

Pond 1

658

652

N

0

5000 ft

Darcy’s 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

application cont

Q? v? M?

Dh=6.51 ft

K

W

b=8.56 ft

Contaminated

Pond

Dx =186 ft

b

Clay

Dx

Not to scale

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

application cont17
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 Darcy’s Law assumption)
      • Parallel flow (so you can use 1-D Darcy’s law)
    • Formulate a mathematical representation of your conceptual model that:
      • Meets the assumptions and
      • Addresses the objectives

Q?

v?

M?

M = Q C

application cont18
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?

ground water zones
Ground Water Zones
  • Degree of saturation defines different soil water zones
soil and groundwater zones
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

slide21
Ground water and the Water cycle
    • Infiltration
    • Infiltration capacity
    • Overland flow
    • Ground water recharge
    • GW flow
    • GW discharge
bedrock hydrogeology
Hydraulic Conductivity of bedrock is controlled by

Size of fracture openings

Spacing of fractures

Interconnectedness of fractures

Bedrock Hydrogeology
porosity and permeability
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, <5%)

30%

5%

1%

porosity and permeability24
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

porosity and permeability25
Porosity and Permeability
  • Permeability is notproportional to porosity.

30%

Table 11.1

5%

1%

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

Fig. 11.1

ground water flow
Ground-Water Flow
  • Precipitation
  • Infiltration
  • Ground-water recharge
  • Ground-water flow
  • Ground-water discharge to
    • Springs
    • Streams and
    • Wells
ground water flow28
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)

natural water table fluctuations
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
natural water table fluctuations30
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
effects of pumping wells
Effects of Pumping Wells
  • Pumping wells
    • Accelerates flow near well
    • May reverse ground-water flow
    • Causes water table drawdown
    • Forms a cone of depression
effects of pumping wells32
Effects of Pumping Wells
  • Pumping wells
    • Accelerate flow
    • Reverse flow
    • Cause water table drawdown
    • Form cones of depression

Gaining

Stream

Water Table

Drawdown

Low well

Dry Spring

Cone of

Depression

Gaining

Stream

Low well

Low river

Pumping well

effects of pumping wells33
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

ground water surface water interactions
Ground-Water/ Surface-Water Interactions
  • Gaining streams
    • Humid regions
    • Wet season
  • Loosing streams
    • Humid regions, smaller streams, dry season
    • Arid regions
  • Dry stream bed
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

Ground-Water Contamination
ground water contamination38
Ground-Water Contamination
  • Leaking Gasoline
    • Floats on water table
    • Dissolves in ground water
    • Transported by ground water
    • Contaminates shallow aquifers
ground water contamination39
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
ground water contamination40
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
ground water action
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
ground water action42
Karst Topography

Caves

Sink holes

Karst valleys

Disappearing streams

Giant springs

Ground Water Action
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. BrownEnglish Rule in Ohio

Groundwater is

“…occult and concealed…”

and legislation of its use is

“…practically impossible.”

Ohio Groundwater Law
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. MichelsPipelineConstructors 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.”

Wisconsin Groundwater Law
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.

English Rule Overturned in Ohio