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Chapter 14Groundwater
Noteworthy Information
Factors that affect the amount of groundwater that seeps into the ground:
• type of rock or soil
• climate (dry climates, water evaporates)
• topography (mountainous regions water runs
off the rocky slopes)
• vegetation (slows flow and removes water)
• land use (pavement does not allow water to
enter the ground)
Factors that affect porosity of rock:
• particle shape (round vs. angular)
• sorting (well-sorted vs. poorly-sorted)
Factors that affect permeability of rock:
• particle size (small vs. large)
• sorting (well-sorted v.s poorly-sorted)
Distribution of Groundwater
Vadose
Phreatic
• A rock can have a number of pores that are not
connected to each other. (Pumice, Scoria)
Zone of Aeration
Water Table
Zone of Saturation
Impermeable Layer
Factors that determine the water tables
distance from the surface:
• amount of rainfall
• time between rains
• season
• slope of the ground
• thickness of soil
• climate
• human activity
What is an ordinary well?
• a well drilled into the permanent water table
What is a perched water table?
• water that collects on an impermeable layer
above the water table
Springs may result from a perched water table
Rollie’s Well
• The best aquifers are made of:
uncemented sands and gravels, sandstones
• Magma or cooling pluton is the heat source for geysers, fumaroles, and hot springs 100 F+ (strong sulfur smell)
• Geothermal gradient is the heat source for most Eastern U.S. warm springs (mild sulfur smell)
GeyserEruptionSequence
Deep Circulation of Groundwater
geothermal gradient10 C/km or 1.5 F/100ft
Warm Spring
What percentage of the drinking water in the United States comes from groundwater?
• 50 %
What problems have humans created for the groundwater supply?
• Using the groundwater faster than it can be replenished by nature.
• Polluting the groundwater supply
Problems that develop due to the over use of groundwater.
• The water table drops
• Saltwater intrusions
• Subsidence
How does groundwater become polluted?
• Pollution is carried by water seeping through the soil.
Formation of a cone of depression in the water table
Discharge exceeds recharge
Saltwater contamination due to excessive well pumping
Wildwood Crest
List a few examples of groundwater pollutants.
• Oil from roads
• Nitrates from soil fertilizers
• Pesticides applied to plants
• Farm wastes
• Sewage from septic tanks
Well design requires knowledge of local geology
What is the difference between hard water and soft water?
• Hard water contains large amounts of dissolved ions from minerals.
• Soft water contains very few ions from minerals.
Why is artesian water generally harder than ordinary groundwater?
• Artesian water travels farther and may be warmer than ordinary water, so it can dissolve more mineral matter.
Artesian Well Model
Hydraulic head and urban water supplies
Just like an artesian, saves money
List some states that have Karst Topography?
• Alabama, Florida, Tennessee, Indiana, Virginia,
Pennsylvania, Georgia, Missouri, South Dakota
and Wyoming.
What is Karst Topography?