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Learning Objectives (LO)
Lecture 24: Ground Water Read: Chapter 18 Homework due Tuesday Nov. 24
What we’ll learn today:!1. 1. Processes by which the water table gains and loses water!2. 2. Types of aquifers!3. 3. Human activities that contaminate groundwater!
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Most of Earth’s liquid freshwater is stored underground
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Total Water Fresh Water Oceans 96.6% Ice 1.7% 69.6% Groundwater 1.7% 30.1% (more than half is salty) Rivers & Lakes 0.007% 0.27%
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Groundwater is a major source of water for human activities
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Groundwater is found where the crust is porous (empty space in a rock)
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The Water Table = top of the saturated zone where water fills spaces in soil
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Wetlands form where the water table meets the surface
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Groundwater Lakes occur where the water table meets the surface
Walden Pond (Massachusetts) is a
freshwater lake (it has no stream
outlets)
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• Mostly soil infiltration but also stream flow
River flowing into ground (FL)
Groundwater is fed by snowmelt and rainfall in recharge areas
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Groundwater is lost to seepage and springs
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Base Flow: Streams can either feed or remove groundwater (depends on water table height)
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Base Flow into the ocean removes groundwater in Hawaii
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Groundwater flows in response to gravity and hydraulic pressure
Velocity of flow ranges from m/day to cm/century Depends on pressure gradient (slope of water table) Depends on permeability of the rocks
High Pressure
Low Pressure
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Porosity: amount of empty space in a rock
Permeability: ability of a rock to transmit groundwater (requires connected porosity)
High Porosity
Low Porosity
Low Permeability (not connected)
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Groundwater is stored in rock units called aquifers made of: porous media fractured rock
Aquifers
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An aquifer is an underground formation of saturated crust
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Aquifers on the Mainland
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Aquifers: Confined and Unconfined
Groundwater moves in response to hydraulic pressure
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Artesian Springs flow by
themselves due to pressure in a confined aquifer
(no pumping)
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Aquifers in Hawaii
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Aquifers on Oahu
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Groundwater that contains high levels of
dissolved minerals
Na, Fe, Ca, Mg, K, Cl, HCO3, SO4
Hard Water
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Groundwater is vulnerable to several sources of pollution
~70% of gasoline tanks are leaky!
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Moving pollutants toward wells & streams: Sewage Oil, gas, and chemicals Pesticides Landfill contaminants Road salt
Contaminant Plumes
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Saltwater Intrusion
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Air Sparging
Recirculation Wells Bioremediation
Permeable Reactive Barrier
Groundwater Remediation Treatments neutralize
Decompose organic compounds
Bubble-mixed water
Injecting O2 to mobilize contaminants
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Carbonic acid in groundwater can dissolve CaCO3 (limestone):
Solution cavity Karst Topography Sinkholes Caves
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“Big Room” in Carlsbad Cavern (NM)
Mammoth Cave (KY) is 540 km long
flowstone stalagmites
stalactites straws
drapery column
Speleothems are formed by dripping groundwater
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Hydrothermal Activity results from heated groundwater
Geyser: Eruption of hot groundwater
Fumarole: Eruption of volcanic gasses & water vapor
Hot Spring: Hot groundwater rises and flows
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• result from heating of water in a chamber into steam • steam rises & pushes colder water upward
Geysers
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Action Items for Tuesday, November 24:
1. Read Chapter 18 2. Homework #20
What you should know from today:!
1. 1. Processes by which the water table gains and loses water!2. 2. Types of aquifers!3. 3. Human activities that contaminate groundwater!